Growth and physiological responses of three warm-season legumes to water stress

Authors: BAATH, GURJINDER - Oklahoma State University; ROCATELI, ALEXANDRE - Oklahoma State University; KAKANI, VIJAYA - Oklahoma State University; SINGH, HARDEEP - Oklahoma State University; Northup, Brian; Gowda, Prasanna; KATTA, JHANSY - Oklahoma State University

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2020
Publication Date: 7/22/2020
Citation: Baath, G.S., Rocateli, A.C., Kakani, V.G., Singh, H., Northup, B.K., Gowda, P.H., Katta, J.R. 2020. Growth and physiological responses of three warm-season legumes to water stress. Scientific Reports. 10:12233. https://doi.org/10.1038/s41598-020-69209-2.
DOI: https://doi.org/10.1038/s41598-020-69209-2

Interpretive Summary: Forage production during summers in the Southern Great Plains (SGP) is affected by erratic amounts and timing of rainfall, which impacts the productivity and function of forages in the region. In response, there has been a continued exploration of annual warm-season legumes to identify species that are capable of producing useful amounts of high quality forage during the summer. Mothbean (from India), tepary bean (trom the U.S. desert Southwest) and guar (from India) are three grain-type legumes known for their drought tolerance, which are also capable of producing high quality forage. However, it is necessary to compare how these legumes perform across a range of different levels of available soil water, to select the most reliable option for the SGP. In this study, we compared the vegetative and physiological responses of mothbean, tepary bean and guar across four water levels (100%, 75%, 50%, and 25% of soil water holding capacity) in a greenhouse setting. We found tepary bean tolerated water stress better than guar or mothbean because it had systems that reduced the amounts of water transpired during photosynthesis, and improved water use efficiency (WUE). There was no evidence of limitations related to gas exchange through the stomata on leaf surfaces, and photosynthesis under water stress was mainly controlled by stomatal regulation in all three species. Although, the photosynthetic rate of tepary bean was lower than the other two species, it generated more biomass due to a greater capacity to retain carbon in leaf biomass within plants. Tepary bean also has a greater leaf-to-stem ratio and soil covering ability under different water levels than mothbean or guar, which would make this species a more reliable option for forage production in the SGP.

Technical Abstract: Prolonged drought periods are a major limitation to forage production by most available grasses and legumes during summers in the Southern Great Plains (SGP). Drought-tolerant annual legumes such as mothbean (Vigna acontifolia), tepary bean (Phaseolus acutifolius), and guar (Cyamopsis tetragonoloba) may serve as alternative summer forages, and add resilience to SGP agricultural systems. However, an understanding of the comparative response of these species to different water regimes is needed to identify the most reliable option. This greenhouse experiment was conducted to compare mothbean, tepary bean, and guar for their vegetative growth and physiological responses to four different water regimes: 100%, 75%, 50%, and 25% of field capacity (FC), applied from 27 to 77 days after planting (DAP). Tepary bean showed the lowest stomatal conductance (gs) and photosynthetic rate (A), but it maintained the highest instantaneous water use efficiency (WUE) among species under 50% and 25% FC treatments. The A inhibitions were found to be mainly caused by stomatal regulations in all three species under water deficit conditions. Despite maintaining higher A, growth rates of guar and mothbean were lower than tepary bean due to their limited leaf sink activity. At final harvest (77 DAP), the biomass yield generated by tepary bean was 38-60% and 41-56% higher than guar and mothbean, respectively, across water deficits. Tepary bean was identified as the most drought-tolerant and reliable option for SGP among the tested species, considering its higher biomass production, instantaneous WUE, leaf-to-stem ratio, and soil covering ability under a range of water regimes.