不同水氮条件下骆驼刺幼苗生长及氮效率变化特征

在荒漠生态系统氮沉降背景下，研究退化植被幼苗对水分和氮素变化的响应特征，对实现植被恢复和重建具有重要意义。在塔里木盆地南缘对骆驼刺（Alhagi sparsifolia）幼苗通过2年的水分（干旱、中水和湿润）和氮素（不施氮、低氮（51 mg/kg）、中氮（102 mg/kg）和高氮（306 mg/kg））添加试验，研究骆驼刺幼苗干物质累积、生物固氮和氮效率对水氮条件变化的响应。结果表明，骆驼刺幼苗不同器官的干物质累积和吸氮效率对水氮条件变化的响应因生长年份而异，但幼苗整株干物质累积和吸氮效率在2个生长年份的变化趋势却相似。在干旱条件下，骆驼刺幼苗的干物质量、吸氮效率和生物固氮量均在低氮处理下显著增加，之后随施氮量增加而降低。水氮交互可显著提高幼苗干物质累积、吸氮效率和生物固氮量，其中以中水中氮处理的效果最好。水氮添加有降低骆驼刺幼苗氮素利用效率（NUE）的趋势，但在干旱和中水条件下施氮可显著提高幼苗的生物固氮比例，然而生物固氮比例与NUE仅在第2个生长年份呈显著负相关。在2个生长年份，骆驼刺幼苗干物质量与吸氮效率和生物固氮量呈极显著正相关关系，但与NUE和生物固氮比例并无明显相关性。这表明骆驼刺幼苗主要是通过调节吸氮效率和生物固氮量来适应水氮条件变化，进而影响幼苗干物质累积。

Responses of plant growth and nitrogen efficiency of Alhagi sparsifolia seedlings to different water and nitrogen levels

The plant growth is generally co-limited by water and nitrogen (N) in desert ecosystems. Increasing global N deposition necessitates to evaluate the response of desert plant seedlings against variable N and water input levels. As it will affect the success of the degraded vegetation restoration and reconstruction. A two-year pot experiment was conducted to examine the effects of water addition (drought, moderate water level, and high water level), N addition (no N, low level with 51 mg/kg, moderate level with 102 mg/kg, and high level with 306 mg/kg) and their interaction on seedlings of Alhagi sparsifolia at the southern rim of the Tarim Basin. We analyzed the effects of water and N addition on the dry matter accumulation, biological N fixation, and N efficiency of A. sparsifolia seedlings. The results showed that the effects of water and N additions on dry matter accumulation and N absorption efficiency of different organs varied by years, but whole seedlings showed the similar trend in both years. Under drought treatment, low N addition significantly improved the dry mass, N absorption efficiency and biological N fixation amount of A. sparsifolia seedlings, but all these decreased with the increasing N rate. Interaction of water and N increased the dry mass, N absorption efficiency, and biological N fixation amount of A. sparsifolia seedlings. Among all the treatments, the moderate water and N (102 mg/kg) was the best combination to improve the dry matter accumulation, N absorption efficiency and biological N fixation amount. Water and N additions tended to reduce the N use efficiency (NUE). However, N addition significantly enhanced the biological N fixation ratio under drought and moderate water conditions. A significantly negative relationship occurred between the NUE and biological N fixation ratio only in the second year. The dry mass was significantly positively related with N absorption efficiency and biological N fixation amount, except NUE and biological N fixation ratio. It suggested that A. sparsifolia seedlings could adjust their N absorption efficiency and biological N fixation amount to adapt changing water and N additions, and it could further affect the dry matter accumulation of seedlings.