Root biomass in the upper layer of the soil profile is related to the stomatal response of wheat as the soil dries

Abstract

Terminal drought is a common abiotic stress affecting wheat yield in Mediterranean-type environments. As terminal drought develops, top layers of the soil profile dry, exposing the upper part of the root system to soil water deficit while deeper roots can still access soil water. Since open stomata rapidly exhausts available soil water, reducing stomatal conductance to prolong availability of soil water during grain filling may improve wheat yields in water-limited environments. It was hypothesised that genotypes with more root biomass in the drying upper layer of the soil profile accumulate more abscisic acid in the leaf and initiate stomatal closure to regulate water use under terminal drought. The wheat cultivar Drysdale and the breeding line IGW-3262 were grown in pots horizontally split into two segments by a wax-coated layer that hydraulically isolated the top and bottom segments, but allowed roots to grow into the bottom segment. Terminal drought was induced from anthesis by withholding water from (i) the top segment only (DW) and (ii) the top and bottom segments (DD) while both segments in well-watered pots (WW) were maintained at 90% pot soil water capacity. Drysdale, initiated stomatal closure earlier than IGW-3262, possibly due to higher signal strength generated in its relatively larger proportion of roots in the drying top segment. The relationship between leaf ABA and stomatal conductance was strong in Drysdale but weak in IGW-3262. Analysis of ABA metabolites suggests possible differences in ABA metabolism between these two genotypes. A higher capability of deeper roots to extract available water is also important in reducing the gap between actual and potential yield.

Osmotic potential at full turgor: an easily measurable trait to help breeders select for drought tolerance in wheat

“…), but is known to close its stomata in response to soil drying while leaf water potential also declines (Saradadevi et al. , ), so carbon assimilation and hence, growth would be reduced, supporting the observation in this study. ‘Janz’ is a widely adapted cultivar, which may be related to its conservative behaviour as observed here in terms of shoot biomass under WW conditions.…”

“…All of the cultivars in this study, except 'Kukri', are considered drought tolerant (see references in Table 1) and were bred in different environments. For example, 'Drysdale' was developed for high transpiration efficiency through selection based on carbon isotope discrimination (Condon et al 2004), but is known to close its stomata in response to soil drying while leaf water potential also declines (Saradadevi et al 2014(Saradadevi et al , 2015, so carbon assimilation and hence, growth would be reduced, supporting the observation in this study. 'Janz' is a widely adapted cultivar, which may be related to its conservative behaviour as observed here in terms of shoot biomass under WW conditions.…”

Optimal Wheat Seeding Rate is Influenced by Cultivar‐Specific Topsoil and Subsoil Root Traits

“…The SEM provided evidence that the topsoil roots were critical factor influencing yield components (spike number, number of grains, thousand kernel weight), especially when crops did not suffer drought stress; however, excessive roots in the topsoil pose a risk to grain yield through strong competition for soil water during vegetative growth, leading to insufficient soil water after anthesis. In addition, more roots in the dry topsoil layers would increase abscisic acid (ABA) levels, which would decrease stomatal conductance and photosynthesis (Du et al, 2013; Saradadevi et al, 2016; Saradadevi et al, 2014), possibly influencing grain filling and reducing grain yield.…”

Canopy temperature of high‐nitrogen water‐stressed cotton

“…For example, bulk leaf tissue ABA of water‐stressed plants was at least 50% greater than xylem sap ABA. It has been suggested that xylem sap ABA has better control of stomatal conductance than bulk leaf tissue ABA (Saradadevi, Bramley, Palta, Edwards, & Siddique, 2016) because it is thought that the effect of ABA on stomatal conductance is driven by the accumulation of apoplastic ABA (Sirichandra, Wasilewska, Vlad, Valon, & Leung, 2009). However, we observed greater concentrations of ABA, ABA‐GE, and phaseic acid in bulk leaf tissue than in xylem sap.…”