Photosynthesis and nutrient-use efficiency in response to N and P addition in three dominant grassland species on the semiarid Loess Plateau

Understanding the ecophysiological and nutrient-use strategies of dominant species is important for clarifying plant growth and an ecological process in their community under unbalanced N and P inputs. This study investigated effects of N and P addition [main plot: 0, 25, 50, and 100 kg(N) ha(-1) year(-1); subplot: 0, 20, 40, and 80 kg(P) ha(-1) year(-1)] on leaf N and P contents (LNCa and LPCa), photosynthetic capacity (P-Nmax) and photosynthetic N- and P-use efficiencies (PNUE and PPUE) in three species (Stipa bungeana, Bothriochloa ischaemum, and Lespedeza davurica) in a semiarid grassland in China. At the assessing time, N addition alone significantly increased LNCa and LNCa/LPCa ratio of Stipa bungeana (C-3 grass) only, while P-Nmax increased significantly in all three species. Under N addition, P addition caused significantly lower LNCa, but higher PNUE and PNmax in Bothriochloa ischaemum (C-4 grass) and Stipa bungeana. The LNCa, P-Nmax, and PNUE of Lespedeza davurica (C-3 legume) increased significantly after P addition regardless of N application. The LNCa/LPCa for optimum PNUE changed with species. The P-Nmax and PNUE of Bothriochloa ischaemum and Stipa bungeana had a peak when LNCa/LPCa attained similar to 11 and similar to 20. Lespedeza davurica tended to retain greater P-Nmax and PNUE at lower LNCa/LPCa. Our results indicated that the C3 grass was more sensitive to N and P addition than the C-4 grass and the C-3 legume in terms of leaf N and P contents and P-Nmax. Such interspecific variations of nutrient use in response to N and/or P addition are favorable for maintaining the diversity and the stability of the grassland community.