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Seasonal changes of whole root system conductance by a drought-tolerant grape root system Alsina, Maria Mar Smart, David R. Bauerle, Taryn de Herralde, Felicidad Biel, Carmen Stockert, Christine Negron, Claudia Savé, Robert Producció Vegetal Fructicultura Protecció Vegetal Sostenible 633 The role of root systems in drought tolerance is a subject of very limited information compared with above-ground responses. Adjustments to the ability of roots to supply water relative to shoot transpiration demand is proposed as a major means for woody perennial plants to tolerate drought, and is often expressed as changes in the ratios of leaf to root area (AL:AR). Seasonal root proliferation in a directed manner could increase the water supply function of roots independent of total root area (AR) and represents a mechanism whereby water supply to demand could be increased. To address this issue, seasonal root proliferation, stomatal conductance (gs) and whole root system hydraulic conductance (kr) were investigated for a drought-tolerant grape root system (Vitis berlandieri3V. rupestris cv. 1103P) and a non-drought-tolerant root system (Vitis riparia3V. rupestris cv. 101-14Mgt), upon which had been grafted the same drought-sensitive clone of Vitis vinifera cv. Merlot. Leaf water potentials (cL) for Merlot grafted onto the 1103P root system (–0.9160.02 MPa) were +0.15 MPa higher than Merlot on 101-14Mgt (–1.0660.03 MPa) during spring, but dropped by approximately –0.4 MPa from spring to autumn, and were significantly lower by –0.15 MPa (–1.4360.02 MPa) than for Merlot on 101-14Mgt (at –1.2860.02 MPa). Surprisingly, gs of Merlot on the droughttolerant root system (1103P) was less down-regulated and canopies maintained evaporative fluxes ranging from 35– 20 mmol vine21 s21 during the diurnal peak from spring to autumn, respectively, three times greater than those measured for Merlot on the drought-sensitive rootstock 101-14Mgt. The drought-tolerant root system grew more roots at depth during the warm summer dry period, and the whole root system conductance (kr) increased from 0.004 to 0.009 kg MPa21 s21 during that same time period. The changes in kr could not be explained by xylem anatomy or conductivity changes of individual root segments. Thus, the manner in which drought tolerance was conveyed to the drought-sensitive clone appeared to arise from deep root proliferation during the hottest and driest part of the season, rather than through changes in xylem structure, xylem density or stomatal regulation. This information can be useful to growers on a site-specific basis in selecting rootstocks for grape clonal material (scions) grafted to them. The authors gratefully acknowledge the expert assistance of Sam Metcalf and financial support from the Institut de Recerca i Tecnologia Agroalimenta `ries that allowed Maria del Mar Alsina to conduct this study. Further financial support was provided by the USDA Western Viticulture Consortium under agreement number 05-34360-15800 to DR Smart and the American Vineyard Foundation under agreement number V301 to DR Smart. info:eu-repo/semantics/publishedVersion 2010-09-17 info:eu-repo/semantics/article Alsina, María Mar, David R. Smart, Taryn L. Bauerle, Felicidad De Herralde, C. Biel, Christine M. Stockert, Claudia Negrón, and Robert Savé. 2010. “Seasonal Changes of Whole Root System Conductance by a Drought-tolerant Grape Root System.” Journal of Experimental Botany 62 (1): 99–109. doi:10.1093/jxb/erq247 0022-0957 http://hdl.handle.net/20.500.12327/2970 https://doi.org/10.1093/jxb/erq247 eng Journal of Experimental Botany Attribution-NonCommercial 4.0 International http://creativecommons.org/licenses/by-nc/4.0/ info:eu-repo/semantics/openAccess 11 Oxford University Press