Field confirmation of genetic variation in soybean transpiration response to vapor pressure deficit and photosynthetic compensation

Plants with limited transpiration rate (TR) under high vapor pressure deficit (VPD) offer the potential to conserve soil water and thus decrease the occurrence of soil water deficit. Genetic variability in TR response to VPD has been observed in the greenhouse for soybean (Glycine max (L.) Merr.) genotypes related to PI416937, but these differences have yet to be measured in the field. The objective of this study was to observe under field conditions leaf gas exchange properties of PI416937 in comparison to nine other genotypes to determine if it expressed limited TR at high VPD. Genotypic differences in stomatal conductance measurements (a proxy for TR) matched those obtained under controlled environment conditions. Genotypes varied from no stomatal response to VPD, to strong negative responses resulting in full stomata closure at ∼4 kPa. There was a greater proportional genetic variability in stomatal conductance in the field (75% at high VPD) than was observed in the greenhouse, but this variation was correlated with greenhouse TR. However, photosynthesis was considerably limited in genotypes that had a stomatal response to VPD. Although field differences in photosynthetic capacity among genotypes were not correlated with greenhouse measurements, there was sufficient genetic variation to allow the possibility of selection of high photosynthetic capacity to overcome about a 34% decrease in stomatal conductance. Thus, a targeted breeding program to combine the water conserving TR-VPD response with increased photosynthetic capacity has the potential to increase soybean yields in field water-deficit environments

Diurnal pattern of primary metabolites exudation in legume sheds light on the major influence of root NSC and AA status

International audienc

Comparison between gradient-dependent hydraulic conductivities of roots using the root pressure probe: the role of pressure propagations and implications for the relative roles of parallel radial pathways

The definitive version is available at www.blackwell-synergy.comHydrostatic pressure relaxations with the root pressure probe are commonly used for measuring the hydraulic conductivity (Lpr) of roots. We compared the Lpr of roots from species with different root hydraulic properties (Lupinus angustifolius L. ‘Merrit’, Lupinus luteus L. ‘Wodjil’, Triticum aestivum L. ‘Kulin’ and Zea mays L. ‘Pacific DK 477’) using pressure relaxations, a pressure clamp and osmotic gradients to induce water flow across the root. Only the pressure clamp measures water flow under steady-state conditions. Lpr determined by pressure relaxations was two- to threefold greater than Lpr from pressure clamps and was independent of the direction of water flow. Lpr (pressure clamp) was two- to fourfold higher than for Lpr (osmotic) for all species except Triticum aestivum where Lpr (pressure clamp) and Lpr (osmotic) were not significantly different. A novel technique was developed to measure the propagation of pressure through roots to investigate the cause of the differences in Lpr. Root segments were connected between two pressure probes so that when root pressure (Pr) was manipulated by one probe, the other probe recorded changes in Pr. Pressure relaxations did not induce the expected kinetics in pressure in the probe at the other end of the root when axial hydraulic conductance, and probe and root capacitances were accounted for. An electric circuit model of the root was constructed that included an additional capacitance in the root loaded by a series of resistances. This accounted for the double exponential kinetics for intact roots in pressure relaxation experiments as well as the reduced response observed with the double probe experiments. Although there were potential errors with all the techniques, we considered that the measurement of Lpr using the pressure clamp was the most unambiguous for small pressure changes, and provided that sufficient time was allowed for pressure propagation through the root. The differences in Lpr from different methods of measurement have implications for the models describing water transport through roots and the potential role of aquaporins.Helen Bramley, Neil C. Turner, David W. Turner and Stephen D. Tyerma