Effects of Water and Nitrogen on Eco-physiological Characteristics of Two Dominant Grassland Species on the Semiarid Loess Plateau

To investigate the eco-physiologcial traits in response to water and nitrogen supplying conditions of native species is of importance for understanding their eco-adaptation to the local environment, and also finding rational agronomy measures for using them in artificial grassland construction. In this study, using Bothriochloa ischaemum (C4 grass) and Lespedeza davurica (C3 legume) as research materials, a pot experiment was conducted to compare the leaf photosynthetic traits, leaf fluorescence parameter characteristics and leaf relative water content of the two dominant native species under three different soil moisture conditions (80%FC, 60%FC and 40%FC) and two nitrogen supplying (0 g N kg-1 and 0.025 g N kg-1) conditions when sown individually or in mixture. Results showed that as soil water content decreased from 80% FC (field capacity) to 40% FC, leaf net photosynthetic rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), and stomatal conductance (Gs) of monocultured plants showed an increasing trend, while the photosynthetic parameters of mixculture plants generally exhibited a decreasing trend. The Pn values of L. davurica were significantly higher than those of B. ishchaemum (P<0.05), and the maximum value was 12.50 mmol m-2 s-1. As soil water content decreased, the initial fluorescence values (Fo), maximum potential quantum yield of PSII (Fv/Fo), and maximum photochemical efficiency (Fv/Fm) values under no nitrogen treatment showed no significant change (P>0.05). Overall, the data indicated that when B. ischaemum and L. davurica were mixcultured, there existed a significant mutualistic effect under low soil water situation, indicating mixculture of B. ischaemum and L. davurica was beneficial for coping with drought in the semiarid region.