Effects of soil moisture deficits on the water relations of bambara groundnut (Vigna subterranea L. Verdc.)

Journal of Experimental Botany, Apr 1997

The components of leaf water potential (ψl) and relative water content (RWC) were measured for stands of bambara groundnut (Vigna subterranea) exposed to three soil moisture regimes in controlled-environment glasshouses at the Tropical Crops Research Unit, Sutton Bonington Campus. Treatments ranged from fully irrigated (wet) to no irrigation from 35 days after sowing (DAS) (dry). RWC values varied between 92–96% for the wet treatment, but declined from 93% to 83% in the dry treatment as the season progressed. ψl at midday decreased in both the wet and dry treatments, but the seasonal decline was more pronounced in the latter: seasonal minimum values were −1.19 and −2.08 MPa, respectively. Plants in the wet treatment maintained turgor (ψp) at about 0.5 MPa throughout the season, whereas values in the dry treatment approached zero towards the end of the season. There was a linear relationship between ψp and ψl9 with ψp approaching zero at a ψl of −2.0 MPa. Mean daily leaf conductance was consistently higher in the wet treatment (0.46–0.79 cm-1) than in the intermediate and dry treatments (0.13–0.48 cm s-1 Conductances in the intermediate and dry treatments were similar, and the lower evapotranspirational water losses in the latter were attributable to its consistently lower leaf area indices (L): L at final harvest was 3.3, 3.3 and 1.9 for the wet, intermediate and dry treatments. Bambara groundnut was apparently able to maintain turgor through a combination of osmotic adjustment, reductions in leaf area index and effective stomatal regulation of water loss.

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Effects of soil moisture deficits on the water relations of bambara groundnut (Vigna subterranea L. Verdc.)

Journal of Experimental Botany Effects of soil moisture deficits on the water relations of bambara groundnut (Vigna subterranea L. Verde.) S.T. Collinson 1 E.J. Clawson 1 S.N. Azam-Ali C.R. Black 0 0 Department of Physiology and Environmental Science, University of Nottingham , Sutton Bonington Campus, Nottingham LE12 5RD , UK 1 Department of Agriculture and Horticulture, University of Nottingham , Sutton Bonington Campus, Nottingham LE12 5RD , UK The components of leaf water potential (V,) and relative water content (RWC) were measured for stands of bambara groundnut (Vigna subterranea) exposed to three soil moisture regimes in controlled-environment glasshouses at the Tropical Crops Research Unit, Sutton Bonington Campus. Treatments ranged from fully irrigated (wet) to no irrigation from 35 days after sowing (DAS) (dry). RWC values varied between 92-96% for the wet treatment, but declined from 93% to 83% in the dry treatment as the season progressed. V, at midday decreased in both the wet and dry treatments, but the seasonal decline was more pronounced in the latter: seasonal minimum values were -1.19 and - 2 . 0 8 MPa, respectively. Plants in the wet treatment maintained turgor (Vp) at about 0.5 MPa throughout the season, whereas values in the dry treatment approached zero towards the end of the season. There was a linear relationship between Vp and ¥*j, with <PP approaching zero at a V, of -2.0 MPa. Mean daily leaf conductance was consistently higher in the wet treatment (0.46-0.79 cm s"1) than in the intermediate and dry treatments (0.13-0.48 cm s*1). Conductances in the intermediate and dry treatments were similar, and the lower evapotranspirational water losses in the latter were attributable to its consistently lower leaf area indices (/.): L at final harvest was 3.3, 3.3 and 1.9 for the wet, intermediate and dry treatments. Bambara groundnut was apparently able to maintain turgor through a combination of osmotic adjustment, reductions in leaf area index and effective stomatal regulation of water loss. Vigna subterranea; water relations; soil moisture Introduction Bambara groundnut (Vigna subterranea L. Verde.) is grown as a subsistence crop in semi-arid regions of Africa where the success of other legumes is uncertain because of poor soils, drought and disease (Vietmeyer, 1978; Haq, 1983). However, previous research on the crop has been limited, largely because its commercial value is restricted by a low lipid content (5-8%; Deshpande and Damodaran, 1990; Brough and Azam-Ali, 1992), even though it is an important source of protein at the subsistence level. Previous controlled environment experiments have shown that bambara groundnut is capable of producing a worthwhile yield under conditions where groundnut (Arachis hypogaea L.) may fail completely (Babekir, 1989). The mechanisms which enable bambara groundnut to produce at least some yield during severe drought are poorly understood, but may be linked with its relatively high root: shoot biomass ratio and small leaf area, which restricts transpirational loss of water (Collinson et al., 1996). Crops grown in drought-prone areas display varied responses to water stress which may be divided into three categories; escape, avoidance and tolerance (Turner, 1979). Drought escape is demonstrated by desert ephemerals and some short duration dryland crops which have a condensed growth cycle and reach maturity before drought occurs; their short life-cycle is often combined with developmental plasticity. Crop species displaying this type of adaptation are often photoperiod-sensitive so that flowering coincides with the average date of the end of the rainy season (Ludlow and Muchow, 1988). Drought-avoiding species, such as cowpea (Vigna unguiculata (L.) Walp.) and sorghum (Sorghum bicolor (L.) Moench), avoid water deficits by maximizing water uptake and minimizing water loss. This response is typified by the tropical legume, Siratro, which has deep roots to maximize water uptake, stomata which are sensitive to decreased leaf water potential and increased leaf-to-air vapour pressure deficit, and exhibits paraheliotropic leaf movements to reduce interception of incident solar radiation (Ludlow, 1989). Other species, such as groundnut, pigeonpea (Cajanus cajan (L.) Millspaugh) and cotton (Gossypium hirsutum), have developed mechanisms to survive drought through dehydration tolerance. In these species, osmotic adjustment often assists in turgor maintenance, hence allowing stomatal opening, photosynthesis and leaf expansion to be maintained over a wider range of soil moisture stress than in more susceptible species. Although bambara groundnut has clearly evolved mechanisms to withstand drought, the lack of quantitative evidence regarding the nature of its responses means that it has not yet been categorized into one of the three groups outlined above. Begemann (1988) examined 72 landraces of bambara groundnut grown under two water stress regimes in Ibadan, N (...truncated)


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S.T. Collinson, E.J. Clawson, S.N. Azam-Ali, C.R. Black. Effects of soil moisture deficits on the water relations of bambara groundnut (Vigna subterranea L. Verdc.), Journal of Experimental Botany, 1997, pp. 877-884, 48/4, DOI: 10.1093/jxb/48.4.877