Coordination between water supply and demand at leaf and plant level helps to explain differential growth patterns in olive genotypes in response to mild water stress

Abstract

Hydraulic traits could help to anticipate the impacts of climate change and improve crop productivity. However, the mechanisms explaining their role on plant photosynthesis and thus, plant growth and yield, are just emerging. We conducted an experiment to recognize differences in growth patterns among different olive genotypes and to determine whether hydraulic traits may help to explain such differences through their effect on photosynthesis. We estimated the relative growth rate (RGR), its components, gas exchange, hydraulic traits and photosynthetic capacity parameters in different olive genotypes over a whole year under well-watered and water-stressed conditions. We observed a different response to water stress in the RGR of the genotypes which was best explained by the net CO2 assimilation rate (NAR). Further, net photosynthesis, closely related to NAR, was mainly determined by hydraulic traits, both at leaf and whole plant levels, mediated through their effect on stomatal conductance. We observed a decrease in the ratios of leaf area:sapwood area and leaf area:root area in water-stressed plants which was more remarkable in the olive genotype Olea europaea subsp. Guanchica (GUA8) whose RGR was less affected by water deficit. In addition, at leaf level, water-stressed plants of GUA8 presented a better photosynthetic capacity through a higher mesophyll conductance to CO2 and foliar N. We conclude that hydraulic allometry adjustments of whole plant and leaf physiological response were well coordinated, helping to buffer the water stress experienced by GUA8. That explained its higher RGR compared to the rest under water stress conditions