Effects of water stress and fertilization on leaf gas exchange and photosynthetic light-response curves of Bothriochloa ischaemum L.

Bothriochloa ischaemum L. is an important species in many temperate regions, but information about the interactive effects of water stress and fertilization on its photosynthetic characteristics was inadequate. A pot experiment was conducted to investigate the effects of three water 80% (HW), 40% (MW), and 20% (LW) of field capacity (FC)] and four fertilization regimes nitrogen (N), phosphorus (P), nitrogen with phosphorus (NP), and no fertilization] on leaf photosynthesis. Leaf gas exchange and photosynthetic light-response curves were measured at the flowering phase of B. ischaemum. Water stress decreased not only the leaf gas-exchange parameters, such as net photosynthetic rate (P _N), stomatal conductance (g _s), transpiration rate (E), and water-use efficiency (WUE) of B. ischaemum, but also downregulated P _N-photosynthetically active radiation (PAR) curve parameters, such as light-saturated net photosynthetic rate (P _Nmax), apparent quantum efficiency (AQE), and light compensation point (LCP). Fertilization (N, P, and NP) enhanced the daily mean P _N values and P _Nmax under the HW regime. Addition of N (either alone or with P) improved the photosynthetic capacity of B. ischaemum under the MW and LW regimes by increasing P _N, P _Nmax, and AQE and reducing dark respiration rate and LCP, but the addition of P alone did not significantly improve the photosynthetic performance. Decline in P _N under each fertilization regime occurred during the day and it was caused mainly by nonstomatal limitation. Our results indicated that water was the primary limiting factor for photosynthesis in B. ischaemum, and that appropriate levels of N fertilization improved its potential photosynthetic capacity under water-deficit conditions.