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Stomatal control and water use efficiency of soybean (Glycine max L. Merr.) during progressive soil drying

2004; Elsevier BV; Volume: 54; Issue: 1 Linguagem: Inglês

10.1016/j.envexpbot.2004.05.002

1873-7307

Fulai Liu, Mathias Neumann Andersen, Sven‐Erik Jacobsen, Christian R. Jensen,

Plant Stress Responses and Tolerance

The objectives of this study were to investigate the involvement of root and shoot factors in controlling leaf gas exchange of soybean (Glycine max L. Merr.) during progressive soil drying, and its implication in improving water use efficiency (WUE) at mild soil water deficits. Soybeans were grown in pots in a climate-controlled glasshouse. Shoot dry mass (DM), transpiration (E), stomatal conductance (gs), light-saturated photosynthetic rate (Amax), leaf water potential (Ψl), leaf osmotic potential (Ψπ), leaf turgor pressure (Ψpl), root water potential (Ψr), and xylem sap ABA concentration ([ABA]xylem) were followed in well-watered and drought-stressed plants. As soil dried, gs, E, Amax, Ψl, Ψπ, Ψpl, Ψr, [ABA]xylem, and DM of the drought-stressed plants started to diverge from the well-watered controls from 8, 8, 9, 9, 9, 11, 7, 7, and 14 days after imposition of stress (DAIS), respectively. During soil drying, [ABA]xylem increased linearly with decreasing Ψr. To minimize day-to-day variation, gs, Ψpl, [ABA]xylem, and WUE of the drought-stressed plants were expressed relative to the well-watered controls. It was found that the relative gs decreased linearly from 1.0 to about 0.40 with increasing relative [ABA]xylem; thereafter it decreased further to 0.10 and was linearly correlated with decreasing relative Ψpl, indicating that at mild soil water deficits gs was seemingly controlled by root-originated ABA; and Ψpl significantly affected gs only at severe soil water deficits. Relative WUE at single leaf level (WUEleaf) was around 1.0 for fraction of transpirable soil water (FTSW) > 0.60–0.65, thereafter it increased exponentially and reached a peak at FTSW = 0.25–0.30. As FTSW approached zero then relative WUEleaf declined linearly to less than 1.0. Similarly, relative WUE at whole plant level (WUEplant) increased exponentially as FTSW < 0.60 and reached a peak at FTSW ≈ 0.20, and then declined dramatically as the soil was further dried. The results indicate that WUE, at both single leaf and whole plant levels, was improved at mild soil water deficits.