Variation among Cowpea Genotypes in Sensitivity of Transpiration Rate and Symbiotic Nitrogen Fixation to Soil Drying

Abstract

Cowpea (Vigna unguiculata L. Walp.) is often considered a crop species appropriate for drier environments. However, little or no information exists on two key physiological traits for drought conditions: early decrease in transpiration rate in the soil drying cycle and sustained N fixation activity under low soil‐water conditions. In this study, the responses of these two traits to soil drying were compared among 10 genotypes. The fraction of transpirable soil water at which transpiration rate began to decline varied from 0.59 to 0.24. The genotypes with the higher thresholds for the transpiration decrease offer a conservative water use strategy during soil drying and, hence, may be especially appropriate for very dry areas. The fraction of transpirable soil water at which N fixation rate began to decline ranged from 0.33 in one line to another line in which there was no decline in N fixation rate. Five lines had especially low thresholds for the decline in N fixation rate, which would be highly desirable in arid areas. In fact, N fixation tolerance to drought in these five lines is superior to any responses observed in other grain legumes. There was no correlation between the thresholds for decline in transpiration and N fixation.

Expression of Drought‐Tolerant N2 Fixation in Heterogeneous Inbred Families derived from PI471938 and Hutcheson Soybean

“…Measurement of TR and N 2 fixation activity in response to soil drying was achieved by following the protocol established by Sall and Sinclair (1991) and recently described by Devi and Sinclair (2013) and Sinclair et al (2015). One or 2 d before the dry‐down experiment was to begin, acrylic lids were attached to the pots and sealed around the base of the plant stem.…”

Interactions between water and nitrogen in Australian cropping systems: physiological, agronomic, economic, breeding and modelling perspectives

“…Two lines were identified that outperformed commercial checks under water deficit, but trade-offs were apparent under high-yielding conditions. In a glasshouse experiment comparing the normalised acetylene reduction activity of 10 cowpea lines in response to soil drying, the fraction of transpirable soil water at which N 2 fixation rate began to decline was 0.33 in the most sensitive line, whereas in another line there was no decline in N 2 fixation rate (Sinclair et al 2015). Whereas the sensitivity to water deficit in legume N 2 fixation is recognised, intra-specific variation is significant and has putatively adaptive value.…”

Neglecting legumes has compromised human health and sustainable food production

“…However, nitrogen fixation is extremely tolerant to soil drying in cowpea 35 . The incorporation of improved drought tolerance and nitrogen fixation traits into elite lines of grain legumes is anticipated to generate better yielding cultivars that can be grown on marginal land.…”