摘要:以黄土丘陵区退耕草地群落典型优势种白羊草、长芒草和达乌里胡枝子为研究对象，测定不同氮磷（主区N：0，50，100 kg N hm^-2 a^-1；副区P：0，40，80 kg P₂O₅ hm^-2 a^-1）添加处理下叶片光合气体交换参数、叶绿素荧光参数、叶片氮磷含量、光合氮利用效率（PNUE）和光合磷利用效率（PPUE），探究不同优势种光合生理特征对外源氮磷添加的响应特征与物种差异。结果表明：单独氮添加下，3个优势种的净光合速率（P_n）、蒸腾速率、水分利用效率（WUE_i）、气孔限制值（Ls）和光系统Ⅱ（PSⅡ）活性高于或显著高于未施肥处理，白羊草和达乌里胡枝子的PNUE和PPUE以及长芒草的PPUE显著增加。单独磷添加下，仅达乌里胡枝子的P_n、WUE_i、Ls和PNUE相比未施肥处理显著增加。氮磷共同添加下，50 kg N hm^-2 a^-1处理下，施磷后达乌里胡枝子的P_n以及三个优势种的PNUE显著增加，白羊草的PPUE显著降低；100 kg N hm^-2 a^-1处理下，施磷后达乌里胡枝子的P_n和PNUE均显著增加，白羊草PPUE和长芒草的PNUE的仅在40 kg P₂O₅ hm^-2 a^-1处理下显著增加。3个优势种的P_n均与PSⅡ最大光化学效率和叶片氮含量呈显著正相关关系，长芒草和达乌里胡枝子的P_n与PSⅡ潜在活性和叶片磷含量呈显著正相关关系。总体表明，氮磷对黄土丘陵区退耕草地优势种光合生理具有一定的交互作用，物种属性和施肥水平影响其光合生理特征响应程度。



Abstract:In order to clarify the photosynthetics characteristics and difference in response to nitrogen and phosphorus additions, three dominant species (Bothriochloa ischaemum, Stipa bungeana and Lespedeza davurica) of farm-withdrawn grassland communities in the loess hilly-gully region were selected. A split-plot experiment including three N (0, 50, and 100 kg N hm^-2 a^-1) and three P (0, 40, and 80 kg P₂O₅ hm^-2 a^-1) treatments was conducted to investigate the effect of N and P addition on net photosynthetic rate, transpiration rate, water use efficiency, stomatal limitation, initial fluorescence, photosystem Ⅱ maximal efficiency, photosystem Ⅱ potential activity, leaf N content, leaf P content, photosynthetic nitrogen use efficiency and photosynthetic phosphorus use efficiency of the three dominant species. Results showed that net photosynthetic rate, transpiration rate, water use efficiency, stomatal limitation, photosystem Ⅱ maximal efficiency and photosystem Ⅱ potential activity under 50 and 100 kg N hm^-2 a^-1 treatments were significantly higher than those under no N addition treatment of three dominant species. Nitrogen addition significantly increased photosynthetic nitrogen use efficiency and photosynthetic phosphorus use efficiency of B. ischaemum and L. davurica. The photosynthetic phosphorus use efficiency of S. bungeana. net photosynthetic rate, water use efficiency, stomatal limitation and photosynthetic phosphorus use efficiency under 40 kg P₂O₅ hm^-2 a^-1 and 80 kg P₂O₅ hm^-2 a^-1treatments were significantly higher than those of L. davurica under no P addition treatment. Under 50 kg N hm^-2 a^-1treatment, compared with no P application, net photosynthetic rate of L. davurica and photosynthetic nitrogen use efficiency of the three dominant species increased significantly, and photosynthetic phosphorus use efficiency of B. ischaemum decreased significantly at 40 kg P₂O₅ hm^-2 a^-1 and 80 kg P₂O₅ hm^-2 a^-1 treatments; while under 100 kg N hm^-2 a^-1treatment, compared with no P application, net photosynthetic rate and photosynthetic nitrogen use efficiency of L. davurica increased significantly, photosynthetic phosphorus use efficiency of B. ischaemum and photosynthetic nitrogen use efficiency of S. bungeana only increased significantly at 40 kg P₂O₅ hm^-2 a^-1 treatments. There were positive relationships between net photosynthetic rate with photosystem Ⅱ maximal photochemical efficiency and leaf N contents of the three dominant species, and positive relationships between net photosynthetic rate with photosystem Ⅱ potential activity and leaf P contents of S. bungeana and L. davurica were also found. In summary, N and P exhibited interaction effects on the photosynthetic of dominant species of farm-withdrawn grasslands in the loess hilly-gully region. The species traits and fertilization levels greatly affected plant photosynthetic characteristics response extent. 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.





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