Net photosynthesis, water use efficiency, leaf water potential and leaf rolling as affected by water deficit in tropical upland rice

Abstract

Growth and production of tropical upland rice is often impeded by drought. Little is known on varietal response of CO2 assimilation to water deficit under tropical field conditions. A drought-susceptible semidwarf (IR20) and a drought-resistant traditional (Azucena) rice were grown in a dryland field experiment with sprinkler irrigation during the dry season in the Philippines. Differential irrigation was imposed for 11 days during vegetative growth using a line source sprinkler. Net photosynthesis, leaf conductance, transpiration, leaf rolling and leaf water potential were determined during the stress cycle at pre-noon and afternoon, with all measurements on the same leaf. No varietal differences in maximum photosynthetic rate and in the relationship between photosynthesis and leaf conductance were observed. In both rices, partial stomatal closure and nonstomatal inhibition reduced assimilation rates in the afternoon. Leaf water deficits restricted gas exchange through at least three apparently independent mechanisms: leaf rolling, reduced stomatal conductance and non-stomata1 inhibition which became evident only at severe degrees of stress. Stomata1 closure and leaf rolling were more sensitive to water deficit in Azucena which maintained higher leaf water potential throughout the stress cycle. Both stomatal closure and leaf rolling improved water use efficiency at moderate stress while nonstomatal inhibition of photosynthesis reduced water use efficiency.

Quantitative trait loci associated with stomatal conductance, leaf rolling and heading date mapped in upland rice (Oryza sativa)

“…In field drought trials, Dingkuhn et al (1989) showed that 'Azucena' started displaying leaf rolling symptoms at -0-5 MPa leaf water potential but in IR20 this was delayed until a leaf water potential of ~ 2-0 MPa. Similar results were previousl^^ obtained by Turner et al (1986a) who showed that 'Azucena' and 'IAC25' started rolling at -0-5 MPa whereas IR20 and IR36 started only at -1-5 MPa.…”

“…Dingkuhn et al (1989) found that associated with the trait despite the fact that the stomata of'IR20'close at more negative leaf water parents did not differ significantly and the heripotentials than stomata of 'Azucena'. Our data show tability was zero.…”

“…These traits were described by O' Toole & Cruz (1980) who found similar relationships between leaf water potential and both leaf rolling and stomatal closure in two diverse varieties. Dingkuhn et al (1989) demonstrated that leaf rolling and stomatal closure contribute to increased water use efficiency in water stressed rice. These authors and Turner et al (1986 a) showed that 'Azucena', a droughtresistant upland variety, rolls its leaves and shuts its stomata at less negative leaf water potentials than 'IR20', an improved lowland rice often used as a drought susceptible check.…”

Role of Canopy Coverage in Water Use Efficiency of Lowland Rice in Early Growth Period in Semi-Arid Region

“…Even though plant transpiration could affect the evaporation by altering the VPD inside the canopy, the effects were presumed to be small in this study because the pots were arranged sparsely enough and the experiments were conducted in the early growth period during which the pot was not fully covered by the canopy. Previous studies revealed the effects of stomatal conductance, leaf nitrogen and carbon content, and the ratio of intercellular to ambient CO 2 concentration (C i / C a ) on transpiration efficiency and P/T (Maruyama et al, 1985;Dingkuhn et al, 1989;Adachi et al, 1996) and also reported a negative correlation between P/T and carbon isotope discrimination (CID) (Dingkuhn et al, 1991;Kondo et al, 2004;Impa et al, 2005). However, CID showed a poor relationship with WUE, especially in the tillering period, and Zhao et al (2004) pointed out the possibility of breakdown of relationship between WUE and P/T to explain the poor relationship.…”

Water Use of Tree Lines: Importance of Leaf Area and Micrometeorology in Sub-Humid Kenya

“…Stomatal resistance may increase at increasing saturation deficits (Dye and Olbrich 1993;Cienciala et al 1994;Meinzer et al 1997), or at decreasing soil water availability (Jing and Ma 1990;Mc Murtrie and Landsberg 1992). Other plant responses to high atmospheric water demand or low soil water supply are leaf rolling (Dingkuhn et al 1989;Sobrado 1990) and leaf shedding (Hatton and Wu 1995), which reduces the leaf area.…”