Aims Changes in precipitation pattern and increases in nitrogen deposition have been predicted in previous studies of global change, and these may significantly affect plant growth in terrestrial ecosystems and the availability of resources such as water and nutrients for plant use. Our objective was to determine photo-physiological responses and adaptation of licorice (Glycyrrhiza uralensis), a dominant legume species in the Kubuqi Desert, to different water and nutrient (N, P) supplies.
Methods Using a completely randomized design, we subjected second-year licorice seedlings to water treatment at four supplement levels (3/8, 1/2, 1, and 2 times mean annual precipitation of the study area) and four nutrient treatments (CK, N: 83mg N·kg-1 soil, P: 92 mg P·kg-1 soil, and NP: 83 mg N+92 mg P·kg-1 soil) in 2005. We also determined diurnal changes of photo-physiological characteristics and light response curves.
Important findings Water supply and nutrient addition significantly affected licorice physiological characteristics. Water stress decreased gas exchange characteristics, such as net photosynthesis rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr), and down-regulated several A-PAR relationship curve parameters, such as maximum net photosynthetic rate (Pmax) and apparent quantum efficiency (AQE). The major control of photosynthesis under severe water shortage (W1) varied between stomatal and non-stomatal limitation. Therefore, the second-year licorice seedlings performed a quick physiological response and corresponding regulation to water supply. Nutrient addition could increase Pn, especially under high-water supply, and phosphorus addition could also stimulate Pmax and light saturation point (LSP) and diminish light compensation point (LCP) under extremely low water supply. Shortage of water supply or nutrient addition combined with high water supply (W4) would decrease photosynthetic water use efficiency (PWUE). Our results suggest that water supply is the primary limiting factor and nutrient addition is secondary for licorice photosynthesis in this desert area.