半干旱区沙质草地生态系统碳循环关键过程对水肥添加的响应

为探寻半干旱区草地生产力进一步恢复的主要限制因素，该文采用3因素2水平析因设计对草地进行水（0，80 mm）、氮（0，20 g/(msup]]2/sup]]·a)）、磷（P2O5）（0，10 g/(msup]]2/sup]]·a)）添加实验，研究了2004年地上净初级生产力（ANPP）与土壤呼吸的响应. 8种处理分别为添加水（W）、加氮肥（N）、加磷肥（P）、加水+氮肥（WN）、加水+磷肥（WP）、加氮肥+磷肥（NP）、加水+氮肥+磷肥（WNP）和对照（CK），每种处理6次重复，随机分配在48个4 m × 4 m的样方中. 研究结果表明:施氮肥不仅增加了ANPP，而且推迟了植物生长高峰期； 草地生产力明显受到氮素的制约，水分和磷素并不是该生态系统的主要限制性因子； 土壤呼吸7月份最高；干旱期添加水与不添加水处理的CO2排放速率差异显著； 添加水增加了土壤CO2的排放速率，但是施磷肥对土壤呼吸存在抑制效应. 建议对半干旱区沙质草地的管理应以施氮肥为主，辅以磷肥，不宜灌溉. 

Responses of key carbon cycling processes to the addition of water and fertilizers to sandy grassland in semi_arid region

In order to find out the main factors limiting further natural restoration of grassland productivity in the southeastern Keerqin Sandy Lands, the paper analyzed the effects of manipulation of water (80mm), nitrogen(N,2g/(msup]]2/sup]]5a)) and phosphorus (P2O5,10 g/(msup]]2/sup]]5a)) on the aboveground net primary productivity (ANPP) and soil respiration of sandy grassland in a fully factorial experiment. In total, there were eight treatments: water addition (W), nitrogen fertilizer addition (N), phosphorus fertilizer addition (P), water + nitrogen fertilizer addition (WN), water + phosphorus fertilizer addition (WP), nitrogen + phosphorus fertilizer addition (NP), water + nitrogen + phosphorus fertilizer addition (WNP) and control (CK). Each treatment was replicated six times and randomly assigned to 48 plots (4 m×4 m) which were separated by a 2 m buffer. Results showed that nitrogen fertilizer not only increased ANPP but also delayed the growth peak. It was found that only nitrogen limited further restoration of productivity and this ecosystem was not limited by water and phosphorus. Soil respiration was most active in July and the difference between adding water and non_adding water treatments was significant. Water addition increased soil CO2 efflux, whereas phosphorus addition restrained soil respiration. The results suggest that reasonable management of sandy grassland should include no irrigating, adequate applications of nitrogen fertilizers and phosphorus fertilizers in this semiarid region.