Effect of repeated pruning cycles on growth and physiology of maple trees

Transcription

1 Effect of repeated pruning cycles on growth and physiology of maple trees A. Fini 1, M. Faoro 2, G. Amoroso 2, R. Piatti 2, P. Frangi 2, F. Ferrini 1 1 Università di Firenze Department of Plant, Soil and Environmental Science; Viale delle Idee, 30, Sesto Fiorentino (Firenze) 2 Fondazione Minoprio - MiRT; viale Raimondi, 54, 22070, Vertemate con Minoprio (Como)

2 Pruning can be one of the best things an arborist can do for a tree and one of the worst things an arborist can do to a tree (Shigo, 1989). The effects of different pruning methods on tree health and physiology has received little attention and deserve further research (Clark and Matheny, 2010)

3 Pruning cuts Topping/heading: cuts are done in the middle of the internode Removal: branches were cut at their insertion with the stem, having care not to damage branch collar removal Reduction: branches were cut back to a lateral with sufficient size to become a new leader (modified from Gilman, hort.ufl.edu)

4 Materials and methods Plant material and treatments In spring 2005, 28 uniform cm (4-5 in.) circumference maples were planted in an experimental plot at the Fondazione Minoprio (Vertemate con Minoprio, Como, Italy; N, 9 04 E). Trees were allowed to establish and grow undisturbed for 3 years. In February 2008, plants were pruned in order to reduce crown size by 1/3 according to the following treatments: Topping (T, 7 plants) Removal cut (RM, 7 plants) Reduction cut (RD, 7 plants) Control (C, 7 plants)

5 Plant material and treatments and in February 2010 they were pruned again with the same treatments as in Pruning (1 st cycle) Measurements Measurements 2005 Planting 2010 Pruning (2 nd cycle)

6 BEFORE PRUNING IMMEDIATELY AFTER PRUNING ONE YEAR AFTER PRUNING lateral REDUCTION laterals leader leader TOPPING leader REMOVAL lateral

7 Materials and methods Measurements Length and diameter of the whole branch, of the leader shoot and of lateral shoots developed after pruning within 20 cm from cut were measured in Feb. 2008, Dec. 2008, Dec and Dec on all pruned branches. Stem diameter was measured on all trees at 1,3 m in Feb. 2008, Dec. 2008, Dec and Dec The number of suckers developed/released after pruning was counted every year Wound healing was measured in Dec. 2008, Dec. 2009, and Dec using the Woundwood Coefficient (Schwarze, 2008) b h r

8 The stress required to cause the failing of the attachment between the primary branch and the new leader shoot (or lateral shoot in control) was measured 2 years after pruning using the methods proposed by Kane et al. (2008). Materials and methods Measurements Kane et al., 2008, AUF

9 Materials and methods Measurements In July 2008 and 2009, ten leaves per tree (70 per treatment), were scanned with A-3 scanner to determine average leaf area. Leaf Mass per Area (LMA) was then calculated as the ration between dry weight and leaf area LMA = leaf mass (g) / leaf area (m 2 ) Leaf greenness index, which has been related to chlorophyll and nitrogen content (Percival et al., 2008), was calculated using a SPAD-meter (Minolta)

10 Significance of LMA (Bussotti, 2008, Global Change Biol.; Poorter et al., 2009, New Phytol.; Fini, 2011, PhD Thesis) Leaf mass per area is leaf dry mass per unit surface area LMA is an important indicator of plant strategies LMA is determined by leaf thickness and leaf density LMA usually increases from herbaceous, to woody deciduous and to woody evergreen species Within a species, LMA can be affected by environmental conditions and cultural practices Leaves with high LMA have high metabolic cost, are build to persist and are better able to tolerate stress than those with lower LMA Leaves with low LMA have low metabolic cost, low stress tolerance and are often shed or die in response to stress

11 Significance of LMA (Bussotti, 2008, Global Change Biol.; Poorter et al., 2009, New Phytol.; Fini, 2011, PhD Thesis)

12 Materials and methods Measurements Carbon assimilation (A, mol m -2 s -1 ), transpiration (E, mmol m -2 s -1 ), stomatal conductance (gs, mmol m -2 s -1 ), and Water Use Efficiency (WUE) were measured 3 times in the first year after pruning (2008) and twice in the second (2009) using an infrared gas analyzer (CIRAS 2, PP-System). Stomatal limitations to photosynthesis were calculated from A/Ci curves as described by previous works (Lawlor, 2002, Ann Bot; Long and Bernacchi, 2003, J. Exp. Bot) Apparent rate of carboxylation (V cmax, mol m -2 s -1 ) and apparant contribution of the electron transport to ribulose regeneration (J max, mol m -2 s -1 ) were measured from A/Ci curves in 2010)

13 Significance of stomatal vs. mesophyll limitation to A Photosynthesis requires that atmosferic CO 2 enters the leaf through the stomata and, then, diffuse in the mesophyll to the sites of carboxylation. When stomata close in response to environmental stresses, CO 2 in the chloroplast may become limiting and carbon assimilation decreases (STOMATAL LIMITATION)

14 Also, mesophyll-related factors may limit photosynthesis (changes in g m, V cmax, J max e TPU also occur Rubisco impairment or down-regulation Impairment of Ribulose regeneration

15 Significance of stomatal vs. mesophyll limitation to A How to calculate stomatal limitation: Long and Bernacchi, 2003, J. Exp. Bot.and mesophyll factors:

16 The experimental design was a complete randomized with one tree per replicate and 7 replicates. 6 pruning cuts per tree were done. Data were analyzed with GLM (SPSS 12.00) and when sample size was unbalanced Tukey-Kramer test was used.

17 Wound size and healing (1 st cycle) Treatment Wound area 2/2008 (cm 2 ) Wound closure 12/2008 (%) Wound closure 12/2009 (%) Topping 2,5 b 0 c 1 c Removal 4,2 a 65 a 93 a Reduction 2,7 b 44 b 72 b Control P ** ** ** topping removal reduction

18 Wound size and healing (2 nd cycle) Treatment Wound area 2/2010 (cm 2 ) Wound closure 2/2011 (%) Topping 3.29 b 4 b Removal 7.11 a 17 a Reduction 4.11 b 19 a Control - - P ** ** Results confirmed that removal lead to larger wounds than the other treatment Wounds created with topping cuts heal slower than using other pruning methods One year after pruning, wound healing occurred at a similar rate in reduction and removal.

19 Frequency Treatment Effects at the whole-tree level Ø stem 2/2008 (cm) ΔØ stem 2/ /2008 (cm) ΔØ stem (cm) ΔØ stem (cm) Dieback in 2008 (%) Dieback in 2009 (%) Dieback in 2010 (%) Topping 6,0 1,1 b 1,0 0,90 b 9 a 26 a 26 a Removal 6,7 1,8 a 1,1 1,69 a 0 b 0 b 0 b Reduction 6,2 1,8 a 1,5 1,59 a 0 b 3 b 0 b Control 6,3 1,1 b 1,3 1,68 a 0 b 0 b 0 b P n.s. ** n.s. ** ** ** ** Suckers per plant >7 n. suckers topping removal reduction control

20 Effects at the branch level Treatment L/D branch 2/2008 L/D branch 12/2008 L/D branch 12/2009 L/D branch 2/2010 L/D branch 12/2010 Change in L/D 2010 Topping 24.2 c 58.5 b 75.8 b c c 155% a Removal 0.0 d 61.5 b 65.4 c Reduction 35.4 b 64.6 b 75.9 b b 64.4 b 12% b Control 63.7 a 81.5 a 85.9 a a a 1% b P ** ** ** ** ** ** Topping and reduction cut reduced branch length and slenderness if compared to control Despite a greater reduction in slenderness immediately after pruning, L/D of topped branches increased more than in other treatments in the growing seasons after pruning L/D was lower than 125 in all treatments: if branch union is stable, pruning is not likely to affect whole branch stability in the short-run

21 What about here? Gilman

22 Frequency Effects at the shoot level (1 st cycle) Watersprout developed within 20 cm from pruning cuts topping removal reduction control >4 n. watersprouts May lateral watersprouts become codominant? Diameter ratio 2008 Diameter ratio 2009 L/D leader 2008 L/D leader 2009 Topping 0,87 a 0,73 a 74,86 94,18 a Reduction 0,35 b 0,32 b 72,58 79,38 b Control 0,32 b 0,52 ab 75,57 89,91 a

23 Frequency Effects at the shoot level (2 nd cycle) Watersprout originated within 20 cm from pruning cuts topping removal reduction control >4 n. watersprouts The larger wounds caused in the 2 nd cycle resulted in higher watersprouts release. Still, development of watersprouts was higher in topped branches AGAIN. WHAT ABOUT CODOMINANCE? Diameter ratio 2011 L/D leader 2011 Topping 0.77 a a Reduction 0.29 c b Control 0.46 b a

24 σ (MPa) Effects at the shoot level It has been recently found that well attached branches can be considered safe when slenderness is lower than 125 (Dahle and Grabosky, 2010). However, if branch attachment is weak or if the branch presents signs of structural damage or dacay, failing can occur when slenderness is higher than 40 (Mattheck, 2007) b * a Breaking stress a b * It has long been known that a adventitious a shoots are less strongly attached to the parent branch, since they are attached at Topping the cambium level (Dahle Reduction et al., 2006). Control

25 Effects at the shoot level I m the boss How can I outcompete them? I m the boss No, I m the boss Yes, you are Yes, you are Treatment No, I m the boss Primary growth of shoots on pruned branched in 2008 (cm) Primary growth of shoots on pruned branched in 2010 (cm) Topping a a Removal c b Reduction b b Control d b P ** **

26 Treatment Effects at the leaf level (1 st cycle) Leaf greenness index 08 (SPAD) Leaf greenness index 09 (SPAD) Average leaf area 2008 (cm 2 ) Average leaf area 2009 (cm 2 ) Leaf Mass per Area 2008 (mg/cm 2 ) Leaf Mass per Area 2009 (mg/cm 2 ) Topping 45.0 a a b Removal 39.0 c b a Reduction 42.9 b b a Control 40.2 c b a P ** n.s. ** n.s. * n.s. Topped branches developed larger, leaves with more chlorophyll, and with lower leaf mass per area in the growing season after pruning. Leaves with low LMA have a greater potential for fast growth but a short life span and high susceptibility to oxidative stress (Bussotti, 2008) Higher LMA are associated with higher capacity to tolerate stresses and enhanced nutrient conservation (Aerts and Chapin, 2000). Topping lead to the production of large leaves with high chlorophyll content, characterized by a high potential for growth but lower capacity to withstand stress because of lower LMA

27 Treatment Effects at the leaf level (2 nd cycle) Leaf greenness index 10 (SPAD) Leaf greenness index 11 (SPAD) Average leaf area 2010 (cm 2 ) Average leaf area 2011 (cm 2 ) Leaf Mass per Area 2010 (mg/cm 2 ) Leaf Mass per Area 2011 (mg/cm 2 ) Topping a a a a 8.35 c 6.85 b Removal c b b b 9.90 b 8.37 a Reduction b a b b a 8.58 a Control bc ab b c ab 8.44 a P ** ** * ** * ** As in the 1 st cycle, topping resulted in leaves with more chlorophyll in the first growing season after pruning. Average leaf area was higher in topped trees than in the other treatments both in the first and in the second growing season after pruning Higher leaf area may result in a less efficient dissipation of heat through convection and may result in higher leaf temperature Leaf mass per area was lower in topped trees than in the other treatments both in the first and in the second growing season after pruning

28 Treatment Effects at the leaf level V cmax May 2011 J max May 2011 V cmax Sept 2011 J max Sept 2011 Leaf T ( C) 2010 Leaf T ( C) 2011 Topping a a a a 27.7 a 29.2 a Removal 93.4 b b 93.0 b b 26.0 c 28.7 b Reduction ab b 98.0 b b 27.1 b 28.4 b Control 89.5 b b 96.0 b b 25.7 c 28.3 b P * ** ** ** ** ** Leaves of topped trees had higher apparent rate of carboxylation and apparent contribution of electron transport to ribulose regeneration if compared to the other treatments If considering the activity of enzymes related to photosynthesis, their activity was higher in topping than in the other treatments, and, without other limitations, this should lead to higher carbon assimilation. When significant differences were found, leaves in topped trees were about 1-2 C warmer than control

29 A ( mol m -2 s -1 ) A ( mol m -2 s -1 ) Effects at the leaf level A temporary increase Carbon in carbon assimilation assimilation in maple (1 st cycle) was found in the first n.s. n.s. ** n.s. months 14 after a pruning n.s. in topped trees. Thereafter, topping despite a 12 removal ab greater 10 investment in chlorophyll and photosynthetic reduction enzymes ab control 8 by topped b plants if compared to control, differences among 6 treatments 4 disappeared. 2 WHAT 0 DID LIMIT PHOTOSYNTHESIS IN TOPPED MAPLES? June 08 July 08 August 08 May 09 July a b Metabolic ** a n.s. b impairment? 6 (Rubisco breakdown, 4 2 impairment in RuBP 0 regeneration) Carbon assimilation in maple (2 nd cycle) n.s. 1-May-10 1-Jul-10 1-Sep May-11 5-Jul-11 n.s. Heat stress due to larger leaves? ** a a ab b topping removal Lack of CO 2 due reduction because stomatal control conductance is not infinite?

30 Effects at the leaf level Treatment Ls (%) May 2011 Lm (%) May 2011 Ls (%) Sept 2011 Lm (%) Sept 2011 Was A higher in Yes Yes No No topping? Topping 10 b -52 b 41 a -11 Removal 11 b -3 a 21 b 4 Reduction 10 b -17 a 22 b -2 Control 17 a - 18 b - P * * * n.s. CO 2 DIFFUSION THROUGH STOMATA WAS THE MAIN LIMITATION TO CARBON ASSIMILATION IN TOPPING!! In other words, it was useless to invest so much resources in chlorophyll and enzymes related to photosynthesis, because carbon assimilation became limited by CO 2 availability in the leaf

31 Stomatal vs. mesophyll limitations. It sounds confusing to me!!!! The powerful engine of a Ferrari is useless if speed limit (imposed by stomatal conductance) is at 50 mph!!!

32 Conclusions We provide here new evidence supporting old knowledge: Myth: topping will make trees easier to maintain (Tree owner s manual) FAKE: topped branches grew faster, more slender and codominance often occurred Myth: topping invigorates trees (Tree owner s manual) FAKE: topping altered tree physiology, providing a shift to a more pioneer behavior, but at expenses of stress tolerance. Moreover, topping increase plant investment to leaves, but that is useless because stomatal factors prevent the increase of photosynthesis when environmental conditions are sub-optimal

33 THANK YOU FOR YOUR ATTENTION This work has been done under a research project called Miglioramento delle tecniche produttive e della qualità del prodotto nel vivaismo ornamentale - TECPRO financed by Regione Lombardia