Root traits governed by biological and environmental factors Louise Comas
Breeding for root traits: a new frontier Critical functions Functional traits still poorly understood Dynamic Don Tremain, Tree with roots Getty Collection High C costs
Talk outline Plant strategies belowground: root trait evolution Effects of plant management and environment on root dynamics & functioning (UC Davis walnut research & breeding program) (USDA corn & sunflower water deficit research )
Evolved plant strategies below ground What can we learn from natural selection? Root system structure Coarse roots (structural support, plumbing) Fine roots (physiologically active, ephemeral) (3 rd ) 2 nd 1 st order
Root morphology Seedling traits 300 (a) SRL (m g -1 ) 250 200 150 100 50 SRL Fast > Slow (P<0.05) Mature tree traits SRL (mg -1 ) 0.00 0 AN AS QR QA PV TC Aceraceae Fagaceae Pinaceae 140.0 BL 120.0 FG CO 100.0 AN 80.0 QR QA 60.0 CG AS Fast-growing seedlings faster root proliferation more soil eplored 40.0 PV 20.0 0.0 PS Fast Fast Slow Comas et al. 2002; Comas & Eissenstat 2004
SRL = m g -1 Consistency Inde = 0.44 - Unordered linear parsimony - Square-root reconstruction - Tree based on APGII 2003 Comas & Eissenstat 2009
Phylogenetic pattern 0.13-0.40 0.40-0.68 0.68-0.96 0.96-1.24 1.24-1.51 1.51-1.79 1.79-2.07 2.07-2.35 2.35-2.62 2.62-2.90 2.90-3.18 Paleozoic Mesozoic Cenozoic Carboniferous Permian Triassic Jurassic Cretaceous Paleo-gene Cenozoic Neogene 300 200 100 0 MY Comas et al 2012 IJPS
Evolution in root diameter 1.4 Paleozoic Mesozoic Cen. Diameter (mm) 1.2 1.0 0.8 0.6 0.4 0.2 R 2 = 0.83 P < 0.05 Lower [CO2] Greater stom. density High leaf vein density Thinner roots = less corte for less impedance to water movement? 0.0 0 100 200 300 400 Distance from each node to root of the tree (MY) Comas et al 2012 IJPS
Trade-offs between morphology & RLD Root length density (cm/cm 3 ) 6 4 2 R 2 = 0.69 P < 0.05 20 40 60 80 100 SRL (m/g) Comas et al 2012 IJPS, data from Withington et al 2006
Conclusions Within close relatives, longer SRL and thinner roots allow fast-growing species to eploit soil pockets more quickly (with higher costs but faster returns on these costs) Root morphology more hard-wired than physiology Evidence suggests that angiosperms evolved thinner roots with longer SRL, potentially to increase water uptake & transport, and out compete plants in upland habitats
Effects of plant management and environment on root dynamics & functioni NE US vineyards Juice grape production Lake Erie region, NY Soil: Chenango gravelly loam Training: high-wire bilateral cordon Minimal pruning to reduce costs and raise crop yield Vitis labruscana Bailey cv Concord Issues with alternatebearing vines
Questions Balanced growth theory - does irrigation compensate for root growth? Irrigated vs non-irrigated? Competing sinks - do roots compete with fruit for plant carbon? Minimal vs heavy pruning? Timing?
Conventional wisdom in grape Roots compete with fruit for plant carbon Root growth is bimodal - major root flush in spring with a smaller root flush in fall Mullins MG, Bouquet A. Williams LE. 1992. Biology of the Grapevine.
Eperimental layout Block 1 Block 2 Block 4 Block 3 eperimental vines buffer vines root tubes 25-yr-old vines, treatments initiated in 1991 Completely randomized block design; 22 factorial eperimental unit = 5 vines plus 2 as buffer study duration = 4 years (1997-2000) roots observed with minirhizotrons
Minirhizotrons Record images: every 2 wks (active vines) 1 per month (dormant)
Root production Average total root production (mm cm -2 yr -1 ) 2.5 2.0 1.5 1.0 0.5 0.0 NI Irr NI Irr Dry years Wet years Comas et al. 2005 New Phytologist
Root distribution 0-20 1997 in dry years 21-40 41-60 61-80 Non-irrigated Irrigated (wet) 81-110 0-20 1998 21-40 41-60 * (dry) Depth (cm) 61-80 81-110 0-20 21-40 41-60 61-80 ** ** 1999 (dry) 81-110 0-20 2000 21-40 41-60 (wet) 61-80 81-110 Comas et al. 2005 New Phytologist 0.0 0.2 0.4 0.6 0.8 1.0 Mean fine root production (%)
Timing of root production 0.06 0.04 1997 Heav/NI Heav/Irr Min/NI Min/Irr 0.02 0.00 (wet) 0.06 1998 New roots (mm cm -2 ) 0.04 0.02 0.00 0.06 0.04 1999 (dry) (dry) 0.02 0.00 0.06 0.04 2000 (wet) 0.02 Comas et al. 2010 AJGWR 0.00 Mar Apr May Jun Jul Aug Sep Oct Nov
Root production rate Dry years Wet years Rate of root production (mm cm -2 d -1 ) 0.03 0.02 0.01 0.00 0.03 0.02 0.01 Heav/NI Heav/Irr Min/NI Min/Irr bl bl v v 1998 0.03 0.02 0.01 0.00 bl v 1997 1999 2000 bl v 0.00 Ear Bud dev dev Flwr Frt set dev Frt Frt dev dev Frt Frt ripe ripe Sht Sht dorm dorm Bud dev Flwr dev Frt dev Frt ripe Sht dorm Ear dev Frt set Frt dev Frt ripe Sht dorm Vine phenology Comas et al. 2005 New Phytologist
Root phenology & distribution Depth (cm) 0-20 21-40 41-60 61-80 Mean fine root production (mm cm-2 d-1) 2.5 2.0 1.5 1.0 0.5 0.0 1.5 1.0 0.5 0.0 1.5 1.0 0.5 0.0 1.5 1.0 0.5 0.0 1.5 Minimally pruned Heavily pruned 81-110 1.0 0.5 0.0 Apr May Jun Jul Aug Sep Oct Apr May Jun Jul Aug Sep Oct Comas et al. 2005 New Phytologist
Conclusions No evidence of C limitations on root growth Amount & timing of root growth is controlled by both plant and environment (canopy development & soil moisture)
Aging effects on root function Root boes Ephemeral fine roots 1mm
Root metabolism with age White roots (%) TTC reduction (A g -1 DW) 100 75 50 25 0 80 70 60 50 40 30 20 10 (a) (b) % white % dark Plot 1 Zero 0 0 1 2 3 4 5 6 7 8 9 Root age (weeks) Respiration TTC reduction 55 50 45 40 35 30 25 20 15 10 5 0 Respiration (nmol O 2 g -1 DW s -1 ) Comas et al. 2000 New Phytologist
Metabolic decline w/ pigmentation White Brown Black TTC reduction (A g -1 d.wt.) 140 120 100 80 60 40 20 0 1 mm White Brow n Black Control Root pigmentation 3902 4 8 Jul 97 1 Nov 97 0 30 Mar 98 Comas et al. 2000 New Phytologist
Root functioning with age Other work has shown nutrient uptake capacity declines quickly with root age (P in apple, Bouma et al 2001; N in grape, Volder et al 2005); What about water uptake? Young roots have high C costs but greatest nutrient acquisition capacity Apples vs oranges (Eissenstat 1999) Other environmental factors, especially temperature effects on root growth & function?
Implications & future directions Some broad generalizations may hold (fast growth, drought adapted = long SRL, thin diameters) Compleity in root functioning demands in-depth knowledge of the system breeders are breeding for What root traits do plants need to sustain yields under different types of drought? Different strategies for different species?
Acknowledgements Grape Research David Eissenstat, PSU Root evolution Alan Lakso, Cornell Kevin Mueller, Univ Minnesota Laurie Anderson, Ohio Wesleyan Lyla Taylor, Univ of Sheffield Rick Dunst, Cornell Vineyard Lab Peter Midford, NESCent Hilary Callahan, Barnard/Columbia David Beerling, Univ of Sheffield Funding sources USDA/CSREES Eastern & Western Viticulture Consortium NSF IOS NESCent
Standing root A. White roots B. Brown roots C. Total roots populations 1.6 1.4 1.2 1.0 0.8 1997 veraison Heav/NI Heav/Irr Min/NI Min/Irr bloom veraison harvest (wet) 0.6 0.4 0.2 0.0 1.6 1.4 1998 veraison veraison harvest 1.2 Roots present (mm cm -2 ) 1.0 0.8 0.6 0.4 0.2 0.0 1.6 1.4 1.2 1.0 0.8 1999 veraison bloom bloom veraison harvest (dry) (dry) 0.6 0.4 0.2 0.0 1.6 1.4 1.2 1.0 2000 veraison bloom veraison harvest 0.8 0.6 (wet) 0.4 0.2 0.0 Comas et al. 2005 New Phytologist Apr May Jun Jul Aug Sep Oct Nov Apr May Jun Jul Aug Sep Oct Nov Apr May Jun Jul Aug Sep Oct Nov