Relationships among Water Use Efficiency, Carbon Isotope Discrimination, and Specific Leaf Area in Maize

Abstract

Plant fractionates heavy carbon isotopes during photosynthesis, which usually occurs when CO2 diffuses to the car- boxylation site, and during carboxylation reaction. On account of CO2 fixation process is coupled with water transpiration during the photosynthesis, it is possible to apply stable carbon isotope to study crop water use efficiency (WUE). At present, stable car- bon isotope techniques have been widely studied and applied in C3 plants, however, the relative studies are less reported in C4 plants. In this way, a pot experiment was conducted from June 9 to September 25 in 2007 to study the variation of leaf area (LA), specific leaf area (SLA), water use efficiency (WUE), and carbon isotope discrimination (Δ13C) in maize (Zea mays L.) under different water deficit conditions. The objective was to understand the relationship among WUE, Δ13C, and SLA. Maize were subjected to four water treatments, i.e.: 75–100% (W1), 50–75% (W2), 30–50% (W3), and 0–30% (W4) of field water-holding capacity of the soil. The WUE, SLA, and Δ13C values were measured at seedling, jointing, booting, tasseling, filling, and mature stages. The dry matter accumulation at jointing was obviously affected by W2 and W3 treatments, and decreased significantly in W4 treatment after booting. WUE increased with water stress during all growth stages in W2 and W3 treatments, but decreased significantly in W4 treatment after booting. SLA reached maximal value at booting. Leaf Δ13C decreased in W1, W2, and W3 treatments from jointing to mature, whereas leaf Δ13C value was greater in W4 treatment than in W2 and W3 treatments. Stem Δ13C significantly and positively correlated and presented no significant difference with leaf Δ13C, which indicated that carbon isotope was not fractionated during photosynthate transport from leaves to stems. Maize Δ13C was negatively correlated with WUE; SLA and Δ13C presented positive correlation and both negatively correlated with WUE.