Abstract:

This aim of this study was to determine the optimal nitrogen application rate for high-efficiency cultivation of switchgrass （Panicum virgatum） with good yields and quality in saline-alkali soil in Yinbei， Ningxia. Switchgrass was grown with different levels of nitrogen and its photosynthetic characteristics and drought resistance were analyzed. The P. virgatum cultivar ‘Cave-in-Rock’ was used as the experimental material， and four levels of nitrogen were applied in the field experiment， as follows： no added nitrogen （0 kg·ha^-1， N₀）， low nitrogen （60 kg·ha^-1， N₆₀）， medium nitrogen （120 kg·ha^-1， N₁₂₀） and high nitrogen （240 kg·ha^-1， N₂₄₀）. The photosynthetic characteristics， contents of osmotic compounds， and activities of antioxidant enzymes in leaves of switchgrass at different growth stages were determined， and the drought resistance of switchgrass was evaluated by the multivariate membership function method. The results showed that with increase in nitrogen application levels， the relative chlorophyll content （SPAD value）， net photosynthetic rate （P_n）， stomatal conductance （G_s）， and intercellular CO₂ concentration （C_i） in switchgrass initially increased and then decreased， with peak values in the medium nitrogen （N₁₂₀） treatment. Compared with the leaves of plants in the N₀ treatment， those in the N₆₀， N₁₂₀， and N₂₄₀ treatments showed increases of 4.73%， 18.71%， and 8.86%， respectively， in the SPAD value； increases of 5.55%， 17.02%， and 12.41%， respectively， in the P_n value； increases of 7.87%， 56.18%， and 39.33%， respectively， in G_s； and increases of 7.86%， 30.71%， and 13.81%， respectively， in C_i. The maximum transpiration rate was in the N₂₄₀ treatment， and the leaf water-use efficiency gradually decreased with increasing nitrogen application levels. The results of the membership function analysis showed that the maximum average value of drought resistance indexes was in the N₁₂₀ treatment. Therefore， application of nitrogen at an appropriate level （120 kg·ha^-1） can improve the photosynthesis and drought resistance of switchgrass growing in saline-alkali soil.

Key words: saline-alkali land, switchgrass, nitrogen application, photosynthetic characteristics, drought resistance, membership function method