Clemson University TigerPrints All Theses Theses 5-2011 FINE ROOT RESPONSES TO SOIL DECOMPACTION AND AMENDMENT IN RED MAPLE (ACER RUBRUM) John Mcintyre Clemson University, john_mcintyre@ncsu.edu Follow this nd dditionl works t: https://tigerprints.clemson.edu/ll_theses Prt of the Forest Sciences Commons Recommended Cittion Mcintyre, John, "FINE ROOT RESPONSES TO SOIL DECOMPACTION AND AMENDMENT IN RED MAPLE (ACER RUBRUM)" (2011). All Theses. 1107. https://tigerprints.clemson.edu/ll_theses/1107 This Thesis is brought to you for free nd open ccess by the Theses t TigerPrints. It hs been ccepted for inclusion in All Theses by n uthorized dministrtor of TigerPrints. For more informtion, plese contct kokeefe@clemson.edu.
FINE ROOT RESPONSES TO SOIL DECOMPACTION AND AMENDMENT IN RED MAPLE (ACER RUBRUM) A Thesis Presented to the Grdute School of Clemson University In Prtil Fulfillment of the Requirements for the Degree Mster of Science Plnt nd Environmentl Science by John R. McIntyre My 2011 Accepted by: Dr. Christin E. Wells, Committee Chir Dr. Dougls G. Bienlenberg Dr. Ptrick D. Gerrd
ABSTRACT A combintion tretment (AFM), designed to decompct nd mend urbn soils, nd its individul components (ir tillge, fertilizer, nd mulch) were tested to determine their effects on fine root morphology. The site ws n urbn re locted in Anderson, SC nd included 50 red mples (Acer rubrum) growing in compcted, nutrient poor soils. Tretments were instlled in November 2005, nd dt ws collected through summer 2008. Dt collection included minirhizotron imges, soil moisture redings, soil temperture redings, nd pre-dwn lef wter potentils. The AFM tretment hd the lowest root production, root stnding crop, nd medin root lifespn. The AFM tretment hd the highest rte of root turnover. Medin root lifespn for the AFM tretment ws 248 dys, followed by the mulch-only tretment which hd medin root lifespn of 434 dys. Medin root lifespn for ll other tretments exceeded 800 dys. The mulched plots (AFM nd mulch-only) hd significntly higher soil wter content nd folir lef wter potentils during periods of summer drought. Overll, the AFM tretment produced nd mintined the fewest number of roots, hd the highest rte of root turnover, but provided the most improvements to previously mesured soil prmeters s well s overll tree ppernce nd performnce. ii
TABLE OF CONTENTS TITLE PAGE... i ABSTRACT... ii LIST OF TABLES... v LIST OF FIGURES... vi CHAPTER I. INTRODUCTION... 1 Soil Compction... 1 Urbn Soils... 2 Soil Decompction... 6 Previous Experiments... 9 Anderson Site Minirhizotron Experiment...11 Pge II. MATERIALS AND METHODS...21 Site Chrcteriztion...21 Tretment Instlltion...22 Minirhizotron Instlltion...24 Wter nd Temperture Mesurements...25 Sttisticl Anlysis...26 III. RESULTS...28 Cumultive Root Production nd Mortlity...28 Sesonl Trends in Production nd Mortlity...28 Fine Root Longevity...29 IV. DISCUSSION...38 Root Production...38 Stnding Crop nd Mortlity...41 Sesonl Ptterns...42 Survivl Anlysis...43 iii
LITERATURE CITED...47 Pge iv
LIST OF TABLES Tble Pge 1.1 Soil ph nd nutrient concentrtions beneth red mple trees t four urbn sites in the estern United Sttes in spring 2007. Within site nd column, mens following by different letters re significntly different (SAS PROC GLIMMIX, Fisher s LSD, α = 0.05)...19 1.2 Soil ph nd nutrient concentrtions beneth red mple trees t four urbn sites in estern United Sttes in spring 2008. Within site nd column, mens following by different letters re significntly different (SAS PROC GLIMMIX, Fisher s LSD, α = 0.05)...20 3.1 Type III tests of fixed effects on fine root production...36 3.2 Type III tests of fixed effects on fine root mortlity...36 3.3 Type III tests of fixed effects on fine root stnding crop...36 3.4 Cox proportionl hzrds regression nlysis of the effects of tretments, root dimeter nd root depth on the risk of root mortlity from Feb. 21, 2006 to July 16, 2008...37 v
LIST OF FIGURES Figure Pge 1.1 Soil strength mesured with Clegg impct hmmer t individul sites in the spring of 2006, 2007 nd 2008. Within site nd yer, tretment mens with different letters re significntly different (Fisher s LSD P <0.05; N = 10 for ech br)...12 1.2 Percent soil orgnic mtter t individul sites in spring 2007 nd 2008. Within site nd yer, tretment mens with different letters re significntly different (Fisher s LSD P <0.05; N = 10 for ech br)...13 1.3 Chnge in trunk dimeter (DBH) during the 2007 growing seson (N = 10 per tretment group). Error brs represent one stndrd error of the men. Within site, tretment mens with different letters re significntly different (Fisher s multiple comprisons procedure, α = 0.05)...14 1.4 Exmples of tree condition rtings. The tree on the left received condition rting of 4, while the tree on the right received condition rting of 10...15 1.5 Visul condition rtings in fll 2007. Dt re pooled cross ll sites (N = 40 for ech tretment). Error brs represent one stndrd error of the men. Tretment mens depicted with different letters re significntly different (Fisher s multiple comprisons procedure, α = 0.05)...16 1.6 Pre-dwn lef wter potentil nd volumetric soil wter content for the 2006 nd 2007 sesons in Anderson, SC (soil moisture: N = 2 for mulch nd N = 3 for no mulch; wter potentil: N = 10 per tretment). Asterisk denotes significnt difference in tretment mens t α = 0.05 using Fisher s multiple comprisons procedure...17 vi
1.7 Root length density over time. Dt hve been pooled cross sites (N = 40 per tretment). Error brs represent one stndrd error of the men. Tretment mens depicted with different letters re significntly different using Fisher s multiple comprisons procedure (α = 0.10)...18 2.1 Three groups of declining red mples (Acer rubrum) locted in the Anderson Sports nd Entertinment Center, Anderson, SC tht were used in the current experiment...27 3.1 Averge stnding root crop (m/tube), totl root length production (m/tube) nd totl root length mortlity (m/tube) mesured from minirhizotrons over the intervl from Feb. 21, 2006 to July 16, 2008. Within pnel, tretment mens with different letters re significntly different (SAS PROC GLM, Fisher s LSD, α = 0.05)...31 3.2 New root length production (m/tube) on minirhizotrons from Feb. 21, 2006 to July 16, 2008. Dtes on which one or more tretments were significntly different from control re indicted by the presence of tretment bbrevitions bove the relevnt dt points. Plus nd minus signs indicte the direction of the difference (SAS PROC MIXED, Fisher s LSD, α = 0.1)...32 3.3 Root length mortlity (m/tube) on minirhizotrons from Feb. 21, 2006 to July 16, 2008. Dtes on which one or more tretments were significntly different from control re indicted by the presence of tretment bbrevitions bove the relevnt dt points. Plus nd minus signs indicte the direction of the difference (SAS PROC MIXED, Fisher s LSD, α = 0.1)...33 Pge vii
3.4 Root stnding crop (m/tube) visible on minirhizotrons from Feb. 21, 2006 to July 16, 2008. Dtes on which one or more tretments were significntly different from control re indicted by the presence of tretment bbrevitions bove the relevnt dt points. Plus nd minus signs indicte the direction of the differenct (SAS PROC MIXED, Fisher s LSD, α = 0.1)...34 3.5 Survivorship curves for roots from five tretment groups. All roots produced between Feb. 21, 2006 nd July 16, 2008 were pooled nd given common strt dte. Survivl probbilities were generted using the bseline sttement of PROC PHREG in SAS. Medin lifespn is defined s the first time point t which the survivl probbility is less thn or equl to 50%...35 Pge viii
CHAPTER I: INTRODUCTION Soil Compction Soil compction is the destruction of soil ggregtes nd collpse of lrge ertion pores tht results from the trnsloction nd resorting of soil prticles (Coder 2000). When surfce pressure is pplied to soil, the bonds of ggregting gents tht hold soil prticles together re broken. The prticles subsequently become reoriented in configurtion tht hs higher mss per unit volume (Cssel 1983; Kozlowski 1999). Compction is often mesured in terms of bulk density, which is the dry weight of soil per unit volume (g/cm 3 ). While idel bulk densities vry by soil texture nd type, bulk density of 1.3 g/cm 3 or less is considered optiml for most soils (Russell 1973; Smiley 1990). Soils with bulk densities greter thn 1.3 g/cm 3 re considered to be compcted (Smiley et l. 1990), nd bulk densities of 1.4 to 1.65 g/cm 3 severely restrict root growth in most soil types (Alberty et l. 1984). Compction occurs on recent construction sites, ner rods, nd in res where foot, equipment or vehiculr trffic repetedly tke plce (Youngberg 1959; Foil nd Rlston 1967; Tylor 1974; Chipperini nd Donnelly 1978; Snds et l. 1979; Perry 1982; Wrgo 1983; Alberty et l. 1984; Pittenger nd Stmen 1990; Smiley et l. 1990; Crul 1992; Dy nd Bssuk 1994; Rndrup 1997; Jim 1998; Smiley 2001). As result, urbn soils frequently exhibit high bulk densities. Soils on the Ntionl Mll in Wshington D.C. hd bulk densities of 1.7 to 2.2 g/cm 3 (Ptterson 1977), nd 1
street-side soils in Syrcuse, NY hd bulk densities of 1.54 to 1.90 g/cm 3 (Crul nd Klein 1980). Bulk densities rnging from 1.38 to 1.84 g/cm 3 were reported for disturbed soils ner construction sites in Minnepolis/St. Pul, while the bulk densities of djcent undisturbed soils rnged from 0.90 to 1.18 g/cm 3 (Alberty et l. 1984). As soil becomes incresingly compcted, its bulk density eventully reches threshold known s the growth limiting bulk density (GLBD), bove which plnt roots cn no longer elongte through the soil. The pproximte bulk densities t which roots cnnot penetrte wet soil vry from 1.4-1.6 g/cm 3 for fine-textured soils to 1.75 g/cm 3 for corse-textured soils (Kozlowski 1999). For exmple, sunflower root growth ws hlted by bulk density of 1.75 g/cm 3 in sndy soil nd 1.63 g/cm 3 in cly soil (Dddow nd Wrrington 1983). Growth limiting bulk densities cn lso vry by species. Quercus robur nd Lrix sibiric roots cesed growing t bulk densities of 1.84 nd 1.89 g/cm 3, respectively, while Tili cordt nd Pice bies roots cesed growing t 1.55 nd 1.61 g/cm 3 (Kozlowski 1999). Urbn Soils Nturlly-occurring soils re formed through the interctions of prent mteril, climte, living orgnisms, lndscpe position, nd time (Broderson 2000). This nturl process of soil formtion yields well-structured soil, formed s result of physicl disintegrtion nd chemicl decomposition of the underlying bedrock or 2
sediments (Brdy 1984; Crul 1985). The ggregtion of snd, silt, nd cly prticles over time decreses bulk density nd cretes lrge pore spces between prticles nd ggregtes. This pore spce ids ertion, wter permebility, nd root penetrtion (Crul 1985). Nturl soil formtion hs been interrupted in most urbn soils, nd humn ctivities tend to destroy soil structure nd increse bulk density (Ptterson 1976; Crul nd Klein 1980; Crul 1985). Most urbn soils hve been intentionlly modified to mke them more structurlly sound nd desirble for the support of buildings nd rods. Mechnicl compction is n importnt prt of the construction process, serving to increse lod bering cpcity, prevent soil settlement nd frost dmge, improve stbility, reduce wter seepge, nd prevent soil settling (Multiquip 2009). Extreme sptil vribility is common in urbn soils, with chrcteristics chnging bruptly from one re to the next (Kys 1982; Crul 1985). The verticl vribility in urbn soils is commonly referred to s lithologic discontinuity (Crul nd Klein 1980; Crul 1985). It results from scrping wy the top lyers of soil nd then bckfilling with the scrped topsoil or soil from seprte site. In nturl soils, there re grdul but distinct verticl chnges in the soil profile, with orgnic-rich lyers ner the surfce nd minerl-rich lyers t depth. In urbn soils these shifts re more brupt, nd soil lyers cn chnge from orgnic to minerl in ny given order. 3
Urbn soils tend to exhibit hydrophobic crust, which rises from combintion of fctors. First, foot nd vehiculr trffic cler the soil surfce of vegettion nd compct the underlying soil. The lck of n orgnic litter lyer then exposes the soil surfce to the elements. The kinetic energy of rindrops impcting bre soil destroys ggregtes nd wshes fine prticles into the soil profile, filling smll pore spces nd leding to crust formtion (Hillel 1980; Crul 1985). As result of this surfce crust, wter infiltrtion nd gseous diffusion to the root zone re reduced. As soils become incresingly compcted, there is reduction in pore spce, prticulrly ir-filled pore spce. As result, soil ertion cn be significntly reduced. Gs diffusion cn no longer occur freely, nd oxygen levels fll below those required to sustin plnt growth nd soil orgnism ctivity (Tiz nd Zeiger 2010). In compcted soil profile, pores drin much more slowly, nd pore spce tht normlly contins oxygen is occupied by wter. Surfce coverings such s sphlt nd concrete further reduce the surfce re for oxygen diffusion. Compcted urbn soils re lso prone to drought stress. Wter is held in soil pores under surfce tension; if the pores re smll enough, surfce tension becomes so gret tht it prevents wter uptke by roots (Crul 1985). Soil compction increses the proportion of very smll dimeter soil pores nd therefore mkes it more difficult for tree roots to extrct wter from the soil (Crul 1985). 4
Urbn soils typiclly lck n orgnic lyer of leves nd litter. These items re removed nd discrded s wstes, tking with them nitrogen, sulfur, phosphorous, nd other nutrients tht would otherwise hve returned to the soil (Crul 1985). Orgnic mtter decomposition improves soil structure nd wter-holding cpcity, but these benefits re not relized in urbn soils. Urbn soils, especilly those on sites of recent construction, often contin foreign mterils. It is not uncommon to find n ssortment of items such s brick, concrete, plstics, PVC, wood scrps, nd even metls when excvting urbn soils. Mny of these items re simply leftover scrps from the construction process tht hve been discrded nd covered with bckfill (Crul 1985). Every cubic centimeter of spce occupied by such mterils is cubic centimeter of lost pore spce. While the mterils my not be directly toxic, their brekdown cn relese gses nd byproducts tht re hrmful to plnts. They my lso impede root penetrtion. Urbn soils tend to hve higher ph thn nturl soils. Urbn soils in Syrcuse, New York nd Phildelphi, Pennsylvni were observed to hve verge ph vlues of 8.0 nd 7.6 respectively. In study conducted in Berlin, street side soils were observed to hve ph of 8.0, while nerby ntive forest soils hd ph of only 4.0 (Bockheim 1974; Crul nd Klein 1980). The optiml soil ph for plnt growth is pproximtely 5.5 to 6.5. When the soil ph drops below or exceeds this rnge, soil nutrient vilbility is reduced nd microbil processes of orgnic mtter decomposition nd 5
nitrogen fixtion re slowed (Bockheim 1974; Crul nd Klein 1980; Crul 1985). Soil Decompction Compction is serious problem for urbn nd lndscpe trees. It reduces root nd shoot growth, impedes tree estblishment, nd excerbtes both drought nd hypoxi stress (Ptterson 1977; Fite et l. 2011). One of the first methods pioneered in the erly 1900s for the llevition of soil compction ws the use of dynmite. Chrges were plced round n existing tree nd detonted, lifting the tree up severl feet (R.A. Brtlett, personl communiction; Smiley et l. 1990). While dynmite ws phsed out in the 1940s, mny new methods hve been proposed for the llevition of soil compction beneth estblished trees. These methods hve hd mixed results: some hve worked, but most hve not. Among the more prcticl nd well known techniques re tillge nd orgnic mtter incorportion, verticl nd rdil mulching, pneumtic decompction, nd soil mendment. Tilling nd orgnic mtter incorportion is one of the only techniques tht effectively reduces bulk density, llevites soil compction, nd improves soil fertility (Ptterson 1975; Ptterson 1977). This method involves mechniclly loosening the soil with tiller or similr device. Subsequent incorportion of orgnic mtter helps ensure tht the loosened soil profile stys open. Unfortuntely, conventionl tillge is only n option where there re no pre-existing trees, s it is inherently dmging to estblished root systems (Dy nd Bssuk 1994). 6
Verticl nd rdil mulching involve cutting holes or trenches into the soil of tree s root zone; these holes or trenches re then bckfilled with mterils such s mulch, perlite, vermiculite, or other orgnic mtter (Klisz 1994; Wtson 2002). Holes re typiclly rrnged in the form of concentric rings round the trunk (Pittenger nd Stmen 1990); trenches typiclly rdite outwrd from the trunk like the spokes of wheel (Klisz 1994; Dy nd Bssuk 1994; Dy nd Bssuk 1995; Wtson 2002). The dimeter nd size of the holes or trenches vries with the size of the tree, its loction, nd the re to be treted. Neither verticl nor rdil mulching hs been shown to reduce soil bulk density, nd their effects on tree growth hve been inconsistent. Klisz (1994) found tht roots did not effectively colonize verticl mulch chnnels nd tht trees did not seem to benefit from the procedure. Pittenger nd Stmen (1990) found no improvement in the growth of rdilly-mulched trees reltive to controls over the course of two-yer period. On the other hnd, Wtson nd collegues (1996, 2002) reported deeper rooting nd denser root growth in the mended fill soil of rdil trenches, s well s lrger growth rings following soil replcement in pits. A vriety of pneumtic injection devices hve been developed to physiclly frcture compcted urbn soils with high-pressure ir or nitrogen (Smiley et l. 1990). These include the Grow Gun (Grow Gun Corp., Arvd, CO), the Terrlift (R.E. Jrvis Co., Fyville, MA), nd the Terrvent (Pinncle Concepts Ltd., Cornwll, Englnd). Once 7
frctures hve been creted, they my be bckfilled with vriety of mterils including perlite, vermiculite, nd liquid fertilizers. Studies hve rrely shown significnt decreses in bulk density following tretment with the Terrlift or the Grow Gun (Smiley et l. 1990, Rolf 1994, Smiley 1994, Smiley 2001). These mchines pper to crete single sucer-shped frcture plne but do not lter the physicl properties of the bulk soil (Smiley et l. 1990). Soil mendments hve existed since the dwn of griculture nd re one of the few methods known to reduce soil bulk density nd improve plnt performnce (Dy nd Bssuk 1994; Ptterson 1977). Amendments cn be incorported into the soil profile or pplied to the surfce s mulch lyer. Soil mendments such s expnded slte nd sintered fly-sh hve been shown to llevite soil compction nd reduce bulk density for four yers fter incorportion (Ptterson 1977). Fredrich nd Hm (1982) found tht height nd dimeter growth of silver mples were significntly greter for mulched trees thn controls; mulched trees grew n verge of 0.66 m in height during one-yer period, while controls grew only 0.16 m. None of the soil decompction methods evluted to dte hs provided significnt, long-lsting chnges in soil physicl properties without dmging intct root systems. Recently, we hve begun to evlute combintion tretments tht incorporte multiple interventions designed to decompct nd mend urbn soils. Root Invigortion, ptented process developed by the Brtlett Tree Experts 8
Compny (Stmford, CT), is one such tretment. The Root Invigortion tretment uses compressor nd specilized ir tool to chnnel high-pressure ir into the soil, loosening it in mnner similr to mechnicl tillge but with miniml root dmge. Orgnic mtter nd prescription fertilizer re then dded to the tretment re nd incorported into the soil using the ir tool under low pressure. The tretment re is then topped with 2-3 inch lyer of mulch pplied to the soil surfce. It is hypothesized tht the combintion of ir tillge, fertilizer nd mulch will improve urbn soil conditions to greter extent thn ny single tretment lone. Previous Experiments In recent study, we ssessed the effects of four soil remedition tretments (Root Invigortion nd its three individul components) t four urbn sites long the estern cost of the US (Fite et l. 2011). Tretments included Root Invigortion (herefter referred to s AFM), ir tillge only (A), fertilizer only (F), mulch only (M), nd n untreted control (C). The four test sites included public civic center complex in Anderson, SC; rodside plnting in Myrtle Bech, SC; golf course in Pittsburgh, PA; nd college cmpus in Boston, MA. Ech site hd 50 declining red mples (Acer rubrum) growing on poor qulity urbn soil. Dt were collected from 2006-2008 to ssess bove- nd below-ground tretment responses. Across ll sites, key results included the following: 9
1. Soil strength ( prmeter relted to bulk density) ws significntly reduced by the AFM tretment for up to three yers (Fig. 1). Soil strength ws trnsiently reduced by the A nd M tretments t some sites, but they recovered to pre-tretment levels within three yers. 2. Soil orgnic mtter content ws generlly incresed by the AFM nd M tretments. In Pittsburgh, orgnic mtter content ws decresed by the A tretment (Fig. 2). 3. The AFM tretment incresed levels of multiple soil nutrients t ll sites nd ws more effective thn the F tretment t most sites (Tbles 1 nd 2). 4. Trunk dimeter (DBH) ws incresed by the AFM tretment t two sites nd incresed by the A tretment t one site (Fig. 3). 5. AFM improved condition rtings (visul ssessments of tree helth nd vigor) cross ll sites (Fig. 5). Additionl mesurements tken only t the Anderson site indicted tht the AFM nd M tretments hd significnt impct on wter reltions: 1. Volumetric soil moisture content ws significntly higher under mulched tretments (AFM nd M) on three smpling dtes in 2006 nd seventeen smpling dtes in 2007 (Fig. 6). 2. Lef wter potentils were improved by the mulch tretments (AFM nd M) on three smpling dtes in 2007 (Fig. 6). 10
Anderson Site Minirhizotron Experiment Root growth dt from soil cores showed few differences in root length density mong tretments (Fig. 7), but coring is known to be n inccurte mesure of root production nd mortlity (Hendrick nd Pregitzer 1992). In the current work, we nlyzed root responses to tretments in more detil by instlling nd monitoring minirhizotrons beneth ll experimentl trees in Anderson, SC. Minirhizotrons (root observtion tubes) re used to nondestructively monitor root production nd disppernce in situ (Johnson et l. 2001). They consist of buried plstic tubes tht llow specilly-dpted cmer system to cpture imges of fine roots tht hve grown ginst the tube surfce (Johnson et l. 2001). Anlysis of the resulting imges llows for direct observtion of individul roots nd provides estimtes of root production nd turnover tht cnnot be obtined from trditionl core smpling methods (Hendrick nd Pregitzer 1992). We used minirhizotron dt from the Anderson site to evlute fine root responses to the AFM tretment nd its individul components. Root length, production rtes, mortlity rtes, depth distribution nd verge dimeter were ssessed on 38 smpling dtes, nd Cox proportionl hzrds regression technique ws used to nlyze the effects of the tretments on root longevity. 11
175 150 Anderson, SC 125 100 75 50 25 c b c b b b c b c bc 175 150 Boston, MA 125 Clegg Impct Vlue (Percent of Control) 100 75 50 25 175 150 b b b b Myrtle Bech, SC c c 125 100 75 bc b c b b b bc b b b 50 25 175 150 125 100 75 50 25 0 Pittsburgh, PA c b b b C AFM A F M C AFM A F M C AFM A F M 2006 2007 2008 Figure 1.1 Soil strength mesured with Clegg impct hmmer t individul sites in the spring of 2006, 2007 nd 2008. Within site nd yer, tretment mens with different letters re significntly different (Fisher s LSD P <0.05; N = 10 for ech br). 12
12 Anderson, SC 10 8 6 4 b b b c b bc bc 2 12 Boston, MA Soil Orgnic Mtter (%) 10 8 6 4 2 bc bc c 12 Myrtle Bech, SC 10 8 b bc c bc 6 4 2 b b b b 12 Pittsburgh, PA 10 8 6 4 2 0 b b b b b b c c C AFM A F M C AFM A F M 2007 2008 Figure 1.2 Percent soil orgnic mtter t individul sites in spring 2007 nd 2008. Within site nd yer, tretment mens with different letters re significntly different (Fisher s LSD P <0.05; N = 10 for ech br). 13
Figure 1.3 Chnge in trunk dimeter (DBH) during the 2007 growing seson (N = 10 per tretment group). Error brs represent one stndrd error of the men. Within site, tretment mens with different letters re significntly different (Fisher s multiple comprisons procedure, α = 0.05). 14
Figure 1.4 Exmples of tree condition rtings. The tree on the left received condition rting of 4, while the tree on the right received condition rting of 10. 15
Figure 1.5 Visul condition rtings in fll 2007. Dt re pooled cross ll sites (N = 40 for ech tretment). Error brs represent one stndrd error of the men. Tretment mens depicted with different letters re significntly different (Fisher s multiple comprisons procedure, α = 0.05). 16
Figure 1.6 Pre-dwn lef wter potentil nd volumetric soil wter content for the 2006 nd 2007 sesons in Anderson, SC (soil moisture: N = 2 for mulch nd N = 3 for no mulch; wter potentil: N = 10 per tretment). Asterisk denotes significnt difference in tretment mens t α = 0.05 using Fisher s multiple comprisons procedure. 17
F Figure 1.7 Root length density over time. Dt hve been pooled cross sites (N = 40 per tretment). Error brs represent one stndrd error of the men. Tretment mens depicted with different letters re significntly different using Fisher s multiple comprisons procedure (α = 0.10). 18
19 TABLE 1.1 Soil ph nd nutrient concentrtions beneth red mple trees t four urbn sites in the estern United Sttes in spring 2007. Within site nd column, mens following by different letters re significntly different (SAS PROC GLIMMIX, Fisher s LSD, α = 0.05). Site Tretment ph NO 3 P K C Mg Zn Mn Cu B (ppm) (kg/h) (kg/h) (t/h) (kg/h) (kg/h) (kg/h) (kg/h) (kg/h) C 6.1 bc 1.3 7.3 b 182.2 c 1.2 b 132.8 c 2.6 b 45.7 2.4 b 0.7 b AFM 6.7 1.2 22.4 306.4 1.9 b 355.5 6.8 60.0 4.9 1.3 b Anderson, SC A 6.2 bc 0.7 6.9 b 212.1 bc 1.3 b 141.5 bc 2.5 b 45.7 2.9 b 0.6 b F 6.0 c 1.0 9.2 b 204.1 b 1.2 b 171.6 bc 2.6 b 54.7 2.7 b 0.6 b M 6.5 b 1.2 5.0 b 233.3 bc 2.2 180.0 b 4.0 b 56.2 2.0 b 1.6 C 5.7 b 2.8 b 96.7 b 126.4 b 2.0 cd 206.5 c 10.0 bc 44.6 b 6.3 0.6 b AFM 6.6 3.3 b 268.0 167.1 5.6 364.7 25.6 66.1 3.2 b 1.0 Boston, MA A 5.8 b 4.2 100.7 b 121.7 b 1.9 d 188.6 c 7.8 c 36.8 b 6.2 0.4 c F 6.0 b 4.1 118.7 b 124.1 b 2.4 bc 215.3 bc 10.9 bc 44.9 b 6.3 0.6 b M 5.8 b 1.9 b 94.0 b 115.2 b 2.5 b 239.6 b 12.7 b 57.1 3.8 b 0.6 b C 7.2 b 1.9 61.8 b 83.2 5.2 101.8 b 3.6 b 15.8 b 0.7 b 0.6 AFM 6.4 b 0.9 53.2 b 103.4 6.8 205.0 5.3 b 31.8 0.8 b 0.7 Myrtle Bech, A 7.3 b 1.6 48.0 b 84.7 6.6 134.0 b 4.8 b 17.8 b 0.8 b 0.6 SC F 6.2 b 1.2 75.4 102.9 6.0 132.7 b 9.0 40.3 1.6 0.7 M 7.6 1.3 71.9 b 113.9 6.3 150.5 b 5.9 b 17.4 b 1.0 b 0.8 C 6.1 b 4.8 97.6 b 350.8 b 4.3 409.7 11.9 77.4 bc 1.8 b 1.2 bc AFM 5.9 b 2.0 c 134.8 383.9 b 5.2 406.3 11.9 111.2 b 2.0 b 1.7 b Pittsburgh, PA A 6.3 b 3.9 b 117.9 b 320.5 b 4.4 467.2 7.7 b 67.8 c 1.8 b 1.1 c F 4.8 c 2.0 c 88.7 b 243.9 c 4.8 281.1 b 10.5 b 168.9 6.2 0.6 d M 6.8 2.7 bc 107.5 b 400.0 5.7 502.2 8.0 b 80.9 bc 1.2 b 1.8
20 TABLE 1.2 Soil ph nd nutrient concentrtions beneth red mple trees t four urbn sites in the estern United Sttes in spring 2008. Within site nd column, mens following by different letters re significntly different (SAS PROC GLIMMIX, Fisher s LSD α = 0.05). Site Tretment ph P K C Mg Zn Mn Cu B (kg/h) (kg/h) (t/h) (kg/h) (kg/h) (kg/h) (kg/h) (kg/h) C 6.1 bc 12.3 b 220.3 b 1.2 b 146.5 c 3.8 b 51.0 2.4 b 0.7 b AFM 6.6 22.8 302.0 1.9 b 363.3 6.5 55.7 3.0 1.3 b Anderson, SC A 6.2 bc 12.8 b 220.5 b 1.3 b 150.6 c 3.5 b 47.2 2.6 b 0.7 b F 5.9 c 8.7 b 216.8 b 1.2 b 158.6 c 3.5 b 55.6 2.2 b 0.7 b M 6.3 b 7.7 b 233.1 b 2.6 204.7 b 4.0 b 61.6 1.6 b 1.8 C 5.5 b 157.0 b 169.1 1.7 bc 182.9 b 10.3 b 35.7 b 5.9 0.3 b AFM 6.3 316.7 192.8 4.4 297.7 22.4 51.2 3.9 0.7 Boston, MA A 5.5 b 182.9 b 199.7 1.6 c 169.3 b 11.2 b 30.5 b 4.9 0.3 b F 5.6 b 177.9 b 179.4 1.9 bc 187.3 b 11.2 b 35.2 b 5.9 0.3 b M 5.6 b 131.9 b 122.5 b 2.0 b 205.4 b 11.8 b 39.9 b 3.6 0.3 b C 7.0 b 55.2 74.3 4.8 91.7 b 2.8 b 10.9 b 2.0 0.6 AFM 6.5 b 33.7 b 86.2 6.0 173.9 4.1 b 28.8 0.4 0.7 Myrtle Bech, SC A 7.1 b 50.2 b 78.6 5.4 124.3 b 3.4 b 11.6 b 1.5 0.6 F 6.8 b 45.0 b 96.4 5.9 118.5 b 4.8 27.9 1.1 0.6 M 7.7 47.8 b 94.8 6.6 138.2 b 3.6 b 12.5 b 2.0 0.7 C 6.0 b 70.3 b 266.1 3.6 333.9 b 13.0 55.8 c 2.2 b 1.1 b AFM 5.7 b 112.1 275.7 4.5 323.1 bc 10.5 b 83.6 b 1.8 b 1.2 b Pittsburgh, PA A 6.2 b 110.7 257.5 3.6 398.5 b 6.5 c 42.6 c 1.7 b 1.0 b F 4.8 c 67.5 b 176.6 b 3.6 216.6 c 8.2 bc 94.2 3.7 0.4 c M 7.0 91.5 b 306.4 5.7 460.0 6.6 c 58.4 bc 0.9 b 1.6
CHAPTER II: MATERIALS AND METHODS Site Chrcteriztion The reserch site ws locted in Anderson, South Crolin t the Anderson Sports nd Entertinment Center (ASEC). The ASEC is public prk, thletic field, nd civic center complex tht is highly trfficked by locl residents. Three groups of pproximtely 10-yr-old red mples (Acer rubrum) were selected for use in this study, providing us with totl of 50 trees (Fig. 1). The first group of trees comprised 30 red mples locted directly in front of the civic center, with prking lot on one side nd sidewlk on the other. These trees hd n verge trunk dimeter of 12.7 cm t 1.4 m bove the soil line (DBH). The soil in this group ws sndy lom with 60% snd, 22% silt, nd 18% cly. At the time of tretment ppliction, the trees displyed thin chlorotic cnopies with little internode elongtion. The second group of trees included five recently-plnted red mples locted in n open field djcent to the mjor ccess rod for the ASEC. The trees hd thin chlorotic cnopies, moderte limb diebck, nd n verge dbh of 7.6 cm. The soil in this group ws sndy cly with 46% snd, 18% silt, nd 36% cly. The third group of trees included 15 red mples plnted ner sports field longside the mjor ccess rod for the ASEC. The trees hd reltively helthy cnopies with little to no chlorosis or diebck, nd n verge dbh of 10.2 cm. The soil in this group ws sndy cly lom with 58% snd, 18% silt, nd 24% cly. 21
Pre-tretment soil bulk densities were mesured by collecting 5.8 cm dimeter soil core from beneth ech tree pproximtely 0.75 m from the trunk. Cores were trimmed to 7.6 cm in length, nd lef litter nd orgnic mtter were removed from the tops. The cores were stored t 5 C in wx-lined pper bgs for less thn one week before processing. Cores were trnsferred to luminum trys, dried for seven dys to constnt weight t 65 C, nd weighed to clculte dry bulk density (g/cm 3 ). Pre-tretment soil bulk density cross the site verged 1.41 ± 0.02 g/cm 3, slightly lower thn the growth limiting bulk density for this soil type (1.6 g/cm 3 ; Dddow nd Wrrington 1983). Prior to the experiment, composite soil smples were collected from the upper 15 cm (6 in.) of soil beneth 8 trees t the site nd nlyzed by A&L Anlyticl Lbortory (Memphis, TN) to determine soil ph nd minerl nutrient concentrtions. Pretretment soil nutrient levels in prts per million (ppm) were: 12.3 ± 2.6 Phosphorus (P), 138.7 ± 14.4 Potssium (K), 112.7 ± 23 Mgnesium (Mg), 942.3 ± 274.3 Clcium (C), 13.6 ± 0.3 Sodium (N), 51.7 ± 3.7 Iron (Fe), 104.3 ± 39.8 Mngnese (Mn), 1.6 ± 0.3 Copper (Cu), 2.7 ± 1.2 Zinc (Zn). The pre-tretment percentge orgnic mtter of the soil ws 2.8 ± 0.9, nd the soil ph ws 5.7 ± 0.4. Tretment Instlltion Five tretments (Airspde tillge (A), fertilizer (F), mulch (M), Root Invigortion (AFM) nd control (C)) were pplied to ten replicte trees in 22
November 2005. Tretments were ssigned in rndomized complete block design consisting of 10 replicte blocks, with ech tretment rndomly ssigned to one tree per block. Blocks were estblished bsed on tree loction within the three tree groups described bove. The soil surrounding ll trees ws treted with Roundup Pro herbicide (15.5 ml per 1 L Monsnto Compny, St. Louis, MO) to eliminte turf in 1.5 m (5 ft.) dimeter ring from the trunk pproximtely two months prior to tretment ppliction. Vegettion control ws mintined with Roundup Pro throughout the experiment. Trees receiving the A tretment were ir-tilled to depth of 15-20 cm (6-8 in.) in 1.5 m rdius round the trunk using the Airspde series 2000 (Concept Engineering Group, Veron, PA). Trees receiving the F tretment were fertilized with 375-470 g of Brtlett Boost Grnulr (24-7-7, 6% S, 1% C, 0.1% Fe, 0.05% Cu, 0.05% Zn); (F.A. Brtlett Tree Expert Co., Stmford, CT); 0-565 g Tiger 90 (0-0-0-90 S) (Tiger- Sul Products, Clgry, AB); 0-265 g Epsom Slt (100% MgSO 4 ); (Top Co Assocites, Skokie, IL); 0-1.4 kg Pelletized dolomitic lime (ASC Minerl Processing, Allerton, IL). These products were pplied to the soil surfce s grnulr product or drench within 1.5 m rdius of the trunk. Trees receiving the M tretment were mulched to depth of 5-7.5 cm in 1.5 m rdius round the trunk using 0.45m 3 of bgged, shredded hrdwood mulch. Controls received no mendment or tillge tretment, but were mintined with 1.5 m rdius vegettionfree zone (Fite, et l. 2011). 23
Trees receiving the AFM tretment received ir-tillge s in the A tretment. Tilled soils were then mended with 0.28 m 3 of bgged, composted cow mnure nd the prescription fertilizer mterils from the F tretment. Amendments were pplied in 1.5 m rdius, nd incorported into the loosened soil profile using the Airspde. Finlly, AFM trees were mulched s described for the M tretment. All trees lso received 106 L of irrigtion t the time of tretment ppliction. Minirhizotron Instlltion One cler butyrte observtion tube (minirhizotron) ws instlled beneth ech of the 50 study trees in November 2005. Minirhizotron tubes were 77 cm in length nd 5.5 cm in outer dimeter; they were instlled t 30 ngle from the verticl nd plced 0.75 m from the trunk. The bottoms of the tubes were seled with crylic plugs; tops were wrpped in blck electricl tpe, plugged with rubber stoppers, nd covered with tn luminum covers to exclude light nd moisture. Over the course of four yers, 11 tubes were dmged nd hd to be dropped from the study. A specilized cmer system nd lptop computer (BTC-2 Minirhizotron Video Microscope, Brtz Technology, Crpinteri, Cliforni) were used to cpture imges of roots tht hd grown ginst the minirhizotron tube surfces. Imges were collected pproximtely bi-weekly from the onset of ctive growth in the spring until the onset of dormncy in the fll. Imge collection begn on Februry 21, 2006, pproximtely three months fter tube instlltion, nd ended on July 16, 2008. 24
Imges were nlyzed using Rootfly Softwre (http://www.ces.clemson.edu/~stb/rootfly/, Clemson University, Clemson, SC). Dte of ppernce, dte of deth, dimeter, nd length were recorded for ech root. Roots were clssified ded when they disppered or becme blck nd shriveled. Roots which were live t the end of the study or which were lost due to tube dmge were treted s right-censored in subsequent survivl nlyses. Wter nd Temperture Mesurements Time domin reflectometry probes were plced horizontlly t 15.5 cm soil depth beneth one tree from ech tretment. Volumetric soil moisture content ws mesured weekly during the growing seson using the TRASE time domin reflectometry system I (Soilmoisture Equipment Corp., Snt Brbr, CA). Soil wter content dt from the mulched (M nd AFM) nd unmulched (A, F, nd C) tretments were combined for subsequent nlyses. One HOBO pendnt temp soil temperture logger (Onset Computer Corportion, Bourne, MA) ws instlled pproximtely 15.5 cm (6 in.) beneth the soil surfce ner ech group of experimentl trees. Soil temperture ws logged hourly over the course of the experiment nd verged dily cross ll loggers. 25
Sttisticl Anlyses All sttisticl nlyses were performed using SAS 9.1 (SAS Institute, Cry, NC, USA). The effect of tretment on totl root production, totl root mortlity, nd verge stnding root crop ws ssessed using nlysis of vrince nd SAS PROC GLM. Comprison of tretment mens ws performed using Fisher s LSD with α = 0.05. The effects of tretment nd dte on root production, mortlity nd stnding crop were nlyzed using repeted mesures nlysis of vrince nd SAS PROC MIXED. Tests of dependent vribles were conducted t the α = 0.1 significnce level to protect ginst type II errors in light of the mrked sptil vribility of minirhizotron dt. Where pproprite, comprison of tretment mens on individul dtes ws performed using Fisher s LSD with α = 0.1. Cox proportionl hzrds regression (SAS PROC PHREG) ws used to evlute the effects of tretments, root dimeter, nd root depth on the risk of root mortlity. Fine root survivorship curves were lso constructed using PROC PHREG. 26
Figure 2.1 Three groups of declining red mples (Acer rubrum) locted in the Anderson Sports nd Entertinment Center, Anderson, SC tht were used in the current experiment. 27
CHAPTER III: RESULTS Cumultive Root Production nd Mortlity Averged cross ll smpling dtes, AFM trees hd significntly lower fine root stnding crop (m root length visible per minirhizotron) thn control nd F trees (Fig.1). Control trees verged 23.5 ± 13.4 m/tube, while AFM trees verged 4.6 ± 1.0 m per tube, n 80% reduction. Totl (cumultive) root production followed similr pttern, with control trees verging 66.8 ± 36.2 m/tube nd AFM trees verging 21.5 ± 3.5 m/tube over the course of the experiment. The A, F nd M tretments did not differ from control in stnding crop or totl production, nd there were no differences in totl mortlity mong tretments. Sesonl Trends in Production nd Mortlity Overll, rtes of root production were highest in 2006, the first yer following tretment ppliction nd minirhizotron instlltion (Fig. 2). There were few cler sesonl trends in root production, lthough it ws interesting to note tht low level of root production ws still seen in lte utumn, winter nd erly spring when the trees were not in lef. AFM trees produced significntly less root length thn control trees on five smpling dtes in 2006: My 17, June 7, Aug 21, Oct 3, nd Dec 19 (P < 0.1, Fig. 2, Tble 1). A nd M trees produced less root length thn control trees on two nd three of these dtes, respectively. Fertilizer-only trees produced more root length thn control on 28
three dtes: Sept 12, Oct 3 nd Dec 9. There were no differences in root production mong tretments in 2007 nd 2008, nd there were no significnt differences in root mortlity mong tretments on ny smpling dte (Fig. 3, Tble 2). Stnding crop ws defined s the mount of root length visible on given smpling dte. It grdully incresed for ll tretments in 2006 nd then remined t reltively constnt vlues throughout 2007 nd 2008. There ws significnt effect of tretment on stnding crop, nd this effect differed cross smpling dtes (Fig. 4, Tble 3). In 2006, AFM trees hd mrkedly lower stnding crops thn control trees, nd this difference continued through the summer of 2007. In June 2007, control tube with prticulrly high stnding crop ws lost to physicl dmge; its loss eliminted ny difference between control nd AFM stnding crops. Following this event, F trees hd significntly higher stnding crop thn control trees for the reminder of the experiment. Fine Root Longevity In ddition to producing fewer roots, AFM trees lso produced shorter-lived roots (Fig. 5, Tble 4). AFM roots hd medin lifespn of 248 dys, M roots hd medin lifespn of 434 dys, nd roots from the control, A nd F tretments hd medin lifespns of greter thn 800 dys. Both AFM nd M tretments were ssocited with significnt increses in the hzrd of root mortlity, while A nd F tretments hd no 29
effect on the hzrd. Controlling for other covrites, lrger dimeter roots nd roots t lower soil depths hd lower hzrd of mortlity. 30
100 Averge stnding crop 80 60 40 20 b b b 0 100 Totl root length production m root length per tube 80 60 40 20 b b b 0 100 Totl root length mortlity 80 60 40 20 0 C AFM A F M Tretment Figure 3.1 Averge stnding root crop (m/tube), totl root length production (m/tube) nd totl root length mortlity (m/tube) mesured from minirhizotrons over the intervl from Feb. 21, 2006 to July 16, 2008. Within pnel, tretment mens with different letters re significntly different (SAS PROC GLM, Fisher s LSD, α = 0.05). 31
18 16 Root Length Production (m/tube) 14 12 10 8 6 4 A - AFM - F - M - AFM - M - AFM - F+ AFM - F+ A - AFM - F+ M - 2 0 Feb Apr Jun Aug Oct Dec Dte 2006 Root Length Production (m/tube) 18 16 14 12 10 8 6 4 2 A AFM C F M 0 Jn Mr My Jul Sep Nov Jn Mr My Jul Dte 2007-2008 Figure 3.2 New root length production (m/tube) on minirhizotrons from Feb. 21, 2006 to July 16, 2008. Dtes on which one or more tretments were significntly different from control re indicted by the presence of tretment bbrevitions bove the relevnt dt points. Plus nd minus signs indicte the direction of the difference (SAS PROC MIXED, Fisher s LSD, α = 0.1). 32
Root Length Mortlity (m/tube) 18 16 14 12 10 8 6 4 A AFM C F M 2 0 Feb Apr Jun Aug Oct Dec Dte 2006 18 16 Root Length Mortlity (m/tube) 14 12 10 8 6 4 2 0 Jn Mr My Jul Sep Nov Jn Mr My Jul Dte 2007-2008 Figure 3.3 Root length mortlity (m/tube) on minirhizotrons from Feb. 21, 2006 to July 16, 2008. Dtes on which one or more tretments were significntly different from control re indicted by the presence of tretment bbrevitions bove the relevnt dt points. Plus nd minus signs indicte the direction of the difference (SAS PROC MIXED, Fisher s LSD, α = 0.1). 33
80 Root Length (m/tube) 60 40 20 A AFM C F M AFM- AFM- AFM- AFM- AFM- AFM- M- 0 Feb Apr Jun Aug Oct Dec Dte 2006 80 60 A- AFM- M- F+ Root Length (m/tube) 40 20 AFM- M- 0 Jn Mr My Jul Sep Nov Jn Mr My Jul Dte 2007-2008 Figure 3.4 Root stnding crop (m/tube) visible on minirhizotrons from Feb. 21, 2006 to July 16, 2008. Dtes on which one or more tretments were significntly different from control re indicted by the presence of tretment bbrevitions bove the relevnt dt points. Plus nd minus signs indicte the direction of the difference (SAS PROC MIXED, Fisher s LSD, α = 0.1). 34
100 75 Survivorship(%) 50 25 A AFM F M C 0 0 200 400 600 800 Dys fter First Appernce Figure 3.5 Survivorship curves for roots from five tretment groups. All roots produced between Feb. 21, 2006 nd July 16, 2008 were pooled nd given common strt dte. Survivl probbilities were generted using the bseline sttement of PROC PHREG in SAS. Medin lifespn is defined s the first time point t which the survivl probbility is less thn or equl to 50%. 35
TABLE 3.1 Type III tests of fixed effects on fine root production. Effect Numertor DF Denomintor DF F-Vlue Pr > F Tretment 4 29 1.59 0.2038 Dte 34 1229 7.81 <.0001 Tretment x Dte 136 1229 1.31 0.013 TABLE 3.2 Type III tests of fixed effects on fine root mortlity. Effect Numertor DF Denomintor DF F Vlue Pr > F Tretment 4 29 0.67 0.621 Dte 34 1216 6.74 <.0001 Tretment x Dte 136 1216 0.93 0.7074 TABLE 3.3 Type III tests of fixed effects on fine root stnding crop. Effect Numertor DF Denomintor DF F Vlue Pr > F Tretment 4 29 2.36 0.077 Dte 35 1247 16.59 <.0001 Tretment x Dte 140 1247 1.87 <.0001 36
TABLE 3.4 Cox proportionl hzrds regression nlysis of the effects of tretments, root dimeter nd root depth on the risk of root mortlity from Feb. 21, 2006 to July 16, 2008. Prmeter DF Prmeter Estimte Stndrd Error Chi- Squre Pr > Chi- Squre Hzrd Rtio A 1 0.26233 0.10465 6.2843 0.0122 1.3 AFM 1 0.86586 0.10195 72.1351 <.0001 2.377 F 1-0.04229 0.09278 0.2077 0.6486 0.959 M 1 0.74294 0.09951 55.7426 <.0001 2.102 Root dimeter 1-0.00878 0.00283 9.6461 0.0019 0.991 Depth 1-0.05612 0.00233 580.6932 <.0001 0.945 37
CHAPTER IV: DISCUSSION Root Production Decompction nd mendment of the root zone through ir-tillge, fertiliztion nd mulching (AFM) resulted in the production of fewer roots with shorter lifespns. While the ptented nme for the AFM tretment, Root Invigortion TM, implies tht this tretment promotes root growth, it ppers to do the opposite. While seemingly prdoxicl, this result is not unexpected. Numerous ecologicl nd gronomic studies hve reported tht root:shoot rtios re greter when belowground resources re in short supply (Dvidson 1969; Kummerow 1980; Shipley nd Mezine 2002; Skinner nd Coms 2010). Incresing the vilbility of wter, nutrients nd other soil resources cn likewise reduce lloction to root growth, s we observed in the current experiment. Previous dt collected t the Anderson, SC site indicte tht the AFM tretment hd beneficil effect on soil qulity nd tree wter sttus (Fite et l. 2011). The AFM tretment reduced soil strength, mesure of compction, by pproximtely 75%. It incresed levels of four soil nutrients (phosphorus, potssium, mgnesium nd zinc), rised the soil orgnic mtter content to 6%, nd significntly improved soil wter vilbility. In ddition, trees tht received the AFM tretment hd higher visul condition rtings nd significntly higher lef wter potentil during periods of drought. Nonetheless, the AFM trees produced fewer roots, prticulrly in the first seson following tretment ppliction. While root length production my seem dvntgeous due 38
to the increse in surfce re for wter nd nutrient uptke (Eissenstt 1992), roots lso incur significnt construction nd mintennce costs (Hodge 2004). In fct, the crbon llocted to root mintennce my fr exceed tht llocted to root production, mking lrge numbers of long-lived roots n expensive investment (Eissenstt nd Yni 1997). Under AFM, improvements in soil tilth, wter reltions, orgnic mtter nd fertility occurred throughout the root zone. If 10 roots in this modified rooting environment could do the work of 100 roots growing in typicl urbn soil, why should the tree wste vluble energy nd stored resources putting out the extr 90 roots? A cost-benefit model of plnt resource lloction ws first explored in detil by Bloom et l. (1985). In their seminl pper, they dvnced the hypothesis tht, plnts continue to produce leves or roots until the mrginl revenue from this incresed production is equl to the mrginl cost. By this resoning, the plnt will cese to produce new root length when the cost of doing so exceeds ny dditionl nutrient or wter benefit. Lower rtes of root growth would therefore be expected under very high nutrient supply, when mss flow nd diffusionl flux re sufficient to bring resources to the existing root system, nd under very low supply, when dditionl root growth will not bring the plnt into contct with dditionl resources. Conditions of low-moderte or ptchy resource supply should fvor root growth becuse continued growth will llow the plnt to ccess new, unexplored resources. Experimentl evidence for reduced root production under very high belowground resource supply hs been shown in number of systems. Persson nd Ahlstrom (1990) showed 50% reduction in fine root growth of Norwy spruce nd Scots pine in response 39
to nitrogen fertiliztion. Qu et l. (2003) found less root growth in lrch seedlings fertilized with high-dose vs. low-dose fertilizer, lthough the high-dose trees hd greter shoot biomss. High rtes of irrigtion in the nursey were shown to reduce the root:shoot rtio of Acer pseudopltnus seedlings by 36% compred with trees receiving low rte of irrigtion. It is importnt to note tht these studies, like the AFM tretment, mnipulted ll or most of the tree root zone. Studies in which only ptches of soil re enriched in wter or nutrition generlly show enhnced root prolifertion in the ptches (Drew nd Sker 1975 nd 1978; Jckson nd Cldwell 1989; Pregitzer et l. 1993). On severl 2006 smpling dtes, F trees showed greter root production thn controls. This result is surprising, given tht the sme fertilizer mterils pplied in the context of the AFM progrm did not elicit greter root growth. A potentil explntion for this discrepncy lies in the differing response of roots to fertile ptches vs. highly fertile soil. The F tretment fertilizer ws pplied in bnd on the soil surfce, wheres the AFM fertilizer ws incorported throughout the root zone to depth of 6-8 inches using the ir tool. The F fertilizer ws therefore loclized to more discrete re, nd roots my hve proliferted upwrds to ccess it. The AFM fertilizer ws distributed throughout the root zone, nd its nutrients my therefore hve been more redily ccessible to the root system vi mss flow nd diffusion, reducing the need for new root growth. The extent to which llevition of soil compction directly contributed to reduced root production is unknown. To our knowledge, this is the first study to directly mesure the 40
impct of lrge-scle decompction on tree root growth. While the A tretment ws designed to mesure the effect of decompction without fertilizer nd mulch ddition, in prctice this tretment ws less successful in reducing compction thn the full AFM tretment. We hypothesize tht the ddition of orgnic mtter nd mulch in the AFM tretment helped to hold open the loosened soil structure. Without these dditions, soils in the A tretment recompcted more quickly. The A tretment produced less root length thn the control tretment, but this difference ws not significnt except on two individul smpling dtes. Stnding Crop nd Mortlity Tretment differences in fine root stnding crop reflected those in fine root production, with the AFM tretment hving lower stnding crop thn the control nd the F tretments. Interestingly, tretment differences were estblished in 2006 nd persisted with little chnge until the end of the experiment despite ongoing root production nd mortlity. This result my point to the existence of n optiml vlue for stnding crop tht chnges with soil chemicl nd physicl properties nd is mintined by djustments to rtes of production nd mortlity. If this is the cse, we would expect stnding crops from the tretment groups to converge s time psses nd the effects of the tretments re ttenuted. There were no tretment differences in totl root length mortlity, nor were there differences in root length mortlity on individul smpling dtes. If the mount of root 41
lost were simply proportionl to the mount of root produced, we would hve expected the C nd F trees to show greter root length mortlity. However, this ws not the cse. The mount of root lost ws similr in ll cses, despite the AFM trees hving 80% less stnding root length. This result reflects the greter hzrd of mortlity for AFM (nd M roots), discussed below. Sesonl Ptterns Sesonl ptterns in root production nd mortlity re difficult to discern from this dtset. The most obvious trend is tht root production ws fr greter for ll tretments in 2006 thn in 2007 nd 2008. This is likely due to root system disturbnce nd subsequent root regrowth following minirhizotron instlltion in 2005 (Joslin nd Wolfe 1999). Tretment responses were lso most pronounced during 2006, perhps becuse the tretments hd been recently pplied. Tretment differences my lso hve been mgnified by higher rtes of root production following minirhizotron instlltion. Previous work suggests tht some tree species show repetble sesonl peks in root production (Lyr nd Hoffmn 1967; Atkinson 1980; Glenn nd Welker 1993; Reid nd Bowden 1995). In the current study, production peks occurred in individul tretments on individul dtes, but there were no cler ptterns tht repeted from yer to yer. Interestingly, we did observe root production during the fll nd winter when the trees were not in lef. Reserch in northern forests nd orchrds suggests tht little root production occurs overwinter (Hendrick nd Pregitzer 1992; Wells nd Eissenstt 2001), 42