荒漠草原植物群落结构及其稳定性对增水和增氮的响应

通过在荒漠草原开展增水和增氮野外控制试验，研究增水和增氮对荒漠草原植物群落结构、物种多样性及群落稳定性的影响。结果表明：（1）增水和增氮处理显著影响了荒漠草原植物群落结构和地上生物量，而对植物群落稳定性影响不显著（P>0.05）。增水处理显著增加了豆科和禾本科植物地上生物量（101.3%和57.9%）（P<0.05）；增水+增氮处理显著增加了植物群落盖度（43.2%）和地上生物量（112.4%）及不同功能群（禾本科和杂类草）植物盖度（75.5%和47.3%）和地上生物量（139.3%和85.7%）（P<0.05）。与增氮处理相比，增水+增氮处理显著增加了植物群落和不同功能群（禾本科和杂类草）植物高度、盖度和地上生物量（P<0.05）。（2）增水、增氮和增水+增氮处理均显著降低了植物群落Pielou指数（11.7%、8.7%和10.2%）（P<0.05）。（3）增水和增水+增氮处理提高了荒漠草原植物群落稳定性，而增氮处理降低了荒漠草原植物群落稳定性。增水处理荒漠草原植物群落稳定性效应大于增水+增氮处理。研究表明，荒漠草原植物群落结构受到氮沉降和降水增加的共同影响。增加降水对荒漠草原植物群落稳定性的积极效应可能会抵消部分氮沉降的消极影响，荒漠草原植物群落地上生物量及群落稳定性可能有所增加。

Response of plant community structure and its stability to water and nitrogen addition in desert grassland

Desert grassland is predicted to be responsive to global climate change, such as increased atmospheric nitrogen deposition and precipitation. The structure, function and stability of plant community in desert grassland are often directly and indirectly affected by increased nitrogen deposition and precipitation. However, the response mechanism of plant community structure and stability in desert grassland to increase nitrogen deposition and precipitation are still not clear. We conducted the field experiments with water and nitrogen addition in desert grassland of Ningxia, China. We assessed the effects of increased atmospheric nitrogen deposition and precipitation on the plant community structure, species diversity and the plant community stability. The field experiment was conducted with four treatments, including control (CK), water addition (W), nitrogen addition (N), and water addition+nitrogen addition (W+N). We found that: (1) the plant community structure and aboveground biomass were effected significantly by water and nitrogen addition in desert grassland, but the plant community stability were not changed significantly(P>0.05). The plant aboveground biomass of Leguminosae and Gramineae were increased significantly by water addition (101.3% and 57.9%)(P<0.05). The coverage and aboveground biomass of plant community were significantly increased by 43.2% and 112.4% under water and nitrogen addition together, respectively. Water and nitrogen addition together also significantly increased the coverage (75.5% and 47.3%) and aboveground biomass (139.3% and 85.7%) of Leguminosae and Gramineae(P<0.05). Compared with nitrogen addition, water and nitrogen addition together significantly increased the height, coverage, aboveground biomass of plant community and different functional groups (Leguminosae and Gramineae)(P<0.05). (2) The Pielou index of plant community was decreased significantly by water addition, nitrogen addition, water and nitrogen addition together (11.7%, 8.7% and 10.2%)(P<0.05). (3) Plant community stability was improved by water addition, water and nitrogen addition together in desert grassland, while reduced by nitrogen addition. The effect of plant community stability by water addition was better than that of water and nitrogen addition together. The results indicated that the plant community structure would be affected by nitrogen deposition and precipitation increment in desert grassland. The positive effects of the increased precipitation on plant community stability in desert grassland may potentially offset negative effects of nitrogen deposition. Increased precipitation might lead to the increase of plant community aboveground biomass and plant community stability in desert grassland.