氮水添加对放牧背景下荒漠草原生产力的影响

Influence of nitrogen and water addition on the primary productivity of Stipa breviflora in a desert steppe under different grazing intensities

水分与氮素作为干旱和半干旱草原生产力的共同限制性因子在退化草原的生态快速修复过程中备受关注。以不同放牧强度背景下的短花针茅荒漠草原为研究对象,开展围封模拟放牧利用实验,同时添加氮素和水分。通过分析历史放牧强度与年份对生产力的影响,以及添加氮素和水分对不同功能群植物生物量的作用,探讨放牧强度对短花针茅草原生产力的内在作用机制,以及如何实现荒漠草原资源合理开发和可持续利用。研究结果显示,降雨量与放牧强度决定着短花针茅草原的植物群落结构。氮素和水分添加可分别提升11%—29%和12%—32%的群落地上生物量,且二者存在显著的交互作用。不同功能群植物的地上生物量对氮素与水分添加的响应存在差异,多年生丛生禾草对氮素和水分添加响应最敏感。氮素与水分添加可显著提高多年生丛生禾草的地上生物量,但与自然降水量相关。氮素添加对地上生物量的影响在正常降雨和稍旱年份作用显著,而水分添加在干旱年份作用显著。在正常降雨年份,以半灌木植物为优势种的轻度放牧背景以添加水分对提升生产力最宜,以多年生丛生禾草和半灌木为共优种的中度放牧背景和以多年生丛生禾草为优势种的重度放牧以同时添加水分和氮素对提升生产力最为宜;在干旱年份不同放牧强度背景下均以同时添加水分和氮素对提升生产力最为宜。我们的结果表明了养分与资源的改善有利于退化短花针茅草原的快速恢复和可持续生产。

Nitrogen and water as a co-limitation of primary productivity in steppe has attracted much attention in the rapid restoration of the degraded grassland. In this study, we take desert steppe of Stipa breviflora under different grazing intensities as study object, and simulation grazing, nitrogen addition, and water addition were carried out at the fenced site. By analyzing the effects of historical grazing intensity, year, nitrogen addition, and water addition on total aboveground biomass and plant biomass of different functional groups, we discovered the regulation mechanism of sustainable utilization of Stipa breviflora in a desert steppe under different grazing intensities. The results showed that rainfall and grazing intensity determined the structure of plant community in the desert steppe of Stipa breviflora. Nitrogen addition and water addition enhanced total aboveground biomass by 11%—29% and 12%—32%, respectively, with significantly interaction. The response of plant growth to nitrogen and water addition was different in different functional groups, and perennial bunch grasses were most sensitive to nitrogen and water addition. Nitrogen addition and water addition significantly increased aboveground biomass affecting the perennial bunch grasses, but associated with rainfall. The effect of nitrogen addition on aboveground biomass was significant in normal rainfall and lightly dry years, while water addition was significant in dry years. In normal rainfall years, water addition to increase productivity is most appropriate in the light grazing grassland which is with semi-shrubs as dominant species, while combined nitrogen and water addition to enhance productivity is most appropriate in the moderate grazing grassland which is with semi-shrubs and perennial bunch grasses as co-dominant species, and in the heavy grazing grassland which is with perennial bunch grasses as dominant species. In dry years, combined nitrogen and water addition to increase productivity is most appropriate in grassland under different grazing intensities. Our results show that the improvement of nutrients and resources is beneficial to the rapid recovery and sustainable production of the degraded Stipa breviflora steppe.