Abstract
Impact of soil water regimes on physiological responses and water use efficiency (WUE) for Vigna unguiculata L. Walp. (cowpea) inoculated with rhizobia still remains implicit. Therefore, the goal of the current study was to examine the leaf gas exchange, abscisic acid (ABA) and hydraulic signaling, WUE and carbon and oxygen isotopic compositions (δ13C and δ18O) of cowpea under different soil water levels. The treatments included soil water regimes at three levels (90%, 70%, and 50% of soil water holding capacity (SWHC)) and two inoculation forms (inoculated and non-inoculated with rhizobia). The results showed that across the inoculation treatments, reduced soil water regimes depressed both stomatal conductance (gs) and photosynthesis (An) of the leaves, nonetheless, the decrease of gs was more pronounced compared with the reduction in An. Consequently, the intrinsic water use efficiency (WUEi) was improved in the treatments under decreased soil water conditions. Plant WUE was also improved when soil water contents decreased as exemplified by the increased leaf δ13C and δ18O, indicating the enhanced plant WUE was mainly attributed to the decrease of gs. Significant interactions between soil water regimes and rhizobia treatments for root water potential (RWP), leaf water potential (LWP), and gs were found due to the different responses of rhizobia to varied soil water regimes. Inoculation could improve plant water status and gs under 70% and 90% SWHC compared to 50% SWHC with negative effect from rhizobia. A moderate soil water regime is suggested for cowpea production in terms of high WUE with a minor biomass reduction.
Highlights
Water deficit represents the most important restriction for biomass production in many tropical areas of developing countries [1]
The results showed that gs was impaired more significantly than the An by the partial in gs was primarily responsible for the increase of water use efficiency (WUEi) in the treatments with medium and low closure of stomata under deficit soil water conditions
The results showed that under the treatments with 70% and 90% soil water holding capacity (SWHC), rhizobia inoculation increased root water potential (RWP), Leaf water potential (LWP), and gs, under treatment with 50% SWHC, inoculation with rhizobia showed a negative effect on plant water status and stomatal opening
Summary
Water deficit represents the most important restriction for biomass production in many tropical areas of developing countries [1]. Walp.) is a vital food legume that has been cultivated successfully in tropical and sub-tropical regions where water is scarce [2,3]. It is a major source of dietary protein for humans as well as for animal feeding [4], and it can grow under limited water and high temperatures in low fertility soils. It has the capacity to fix nitrogen which improves soil fertility It is considered as one of the important crops under future climate change scenarios where an increase in temperature and reduction in rainfall has been predicted in these regions [5]. A better understanding of cowpea’s responses to water stress is essential for improving yield and quality under future climate scenarios
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