Root architecture and functional traits of spring wheat cultivars with contrasting tolerance to water deficit
Studies about the functioning of roots under water-limited conditions are of great importance, considering that the root system determines access to the soil and has an essential role in plant water balance. Thus, a set of genotypes was evaluated in a glasshouse under different water regimes in tubes of 160 cm long and 16 cm diameter in three trials between 2015 and 2017. In the 2015 trial, 15 spring wheat genotypes differing in their tolerance to water deficit and yield performance were evaluated under well-watered (WW) regime. In the 2016 and 2017 trails, five genotypes with contrasting tolerances to water deficit were selected from the 2015 trial and were evaluated under WW and water-stressed (WS) regimes. Results in 2015 indicated that aerial biomass (AB) was not significantly different among the 15 genotypes, while the root biomass (RB) and root weight density (RWD) distribution in soil layers were significantly different. In 2016 and 2017, the RB of the 5 genotypes was not significantly different between the water regimes. However, the WS regime plants showed a sharp decrease in the water use (WU), compared with the WW regime plants. Furthermore, the WU showed significant correlations with RWD in the different soil layers, within both water regimes in 2016, and within the WS regime in 2017. The results of the 2016 and 2017 trials confirmed the idea that a larger root system is important to achieve high WU, but it is not necessarily an advantage for higher AB. In 2017 trial, the oxygen and hydrogen isotope composition of plant and soil water and the evaporative enrichment in the leaf were analysed. Significant differences were found in soil and stem water isotope composition between WW and WS regimes, but not in the leaves (except for leaf hydrogen stable isotope enrichment). Conversely, no significant genotype differences were detected in soil and stem water, but genotype effects were significant for leaf water isotopic composition. The results indicate that the tolerant genotype QUP2529 partly relies on a more effective water uptake, which would allow this genotype to keep higher transpiration rates under mild water stress.