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

Abstract

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 (PNmax) 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 (C3 grass) only, while PNmax increased significantly in all three species. Under N addition, P addition caused significantly lower LNCa, but higher PNUE and PNmax in Bothriochloa ischaemum (C4 grass) and Stipa bungeana. The LNCa, PNmax, and PNUE of Lespedeza davurica (C3 legume) increased significantly after P addition regardless of N application. The LNCa/LPCa for optimum PNUE changed with species. The PNmax and PNUE of Bothriochloa ischaemum and Stipa bungeana had a peak when LNCa/LPCa attained ~ 11 and ~ 20. Lespedeza davurica tended to retain greater PNmax and PNUE at lower LNCa/LPCa. Our results indicated that the C3 grass was more sensitive to N and P addition than the C4 grass and the C3 legume in terms of leaf N and P contents and PNmax. 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.