通过为期6年的野外人工控制实验,研究了刈割和施肥对青藏高原高寒草甸群落特征、生产力水平和多样性水平的影响,以期为天然草场的合理利用提供科学依据.结果显示,(1)刈割后群落的物种组成发生了变化,与对照相比,中度和重度刈割区矮嵩草的重要值分别增加了13.28%和27.89%,同时一些适口性差的毒杂草的重要值也相对增加.(2)中度和重度刈割后,禾本科重要值由48.65%分别降至36.63%和40.15%,豆科重要值由2.78%分别增至7.49%和7.53%,杂草重要值由38.78%分别增至46.61%和44.34%;而施肥后,禾本科重要值由35.85%增至47.78%,豆科和杂草的重要值分别由8.18%和46.32%降至3.68%和40.17%.(3)中度和重度刈割后群落高度由19.62 cm分别降至7.58 cm和5.88 cm,而盖度由62.78%分别增至77.96%和75.04%,密度由644 ind·0.25 m-2分别增至876 ind·0.25 m-2和924 ind·0.25 m-2,生产力由104.63 g·0.25 m-2分别增至117.62 g·0.25 m-2和123.72 g·0.25 m-2;施肥使群落的高度、盖度以及生产力分别由8.47 cm、65.56%和88.86 g·0.25 m-2增至13.58 cm、78.29%和141.79 g·0.25 m-2.(4)群落物种多样性在施肥后均显著降低,而在刈割后均显著增加,且丰富度指数和Simpson指数均在中度刈割后达最大值.(5)刈割使群落生产力与物种多样性表现出微弱正相关或不相关,而施肥使生产力与物种多样性表现出显著负相关或微弱负相关.刈割导致一些优良牧草的优势地位大大降低,同时也导致适口性差的杂草的优势地位升高;而施肥则有利于优势物种的生长,且在一定程度上抑制了杂草的生长.该结果支持中度干扰假说,并暗示物种多样性与生产力的关系可能是多变的,且这种关系取决于群落所受扰动因素的类型和强度.总之,在高寒草甸的管理过程中,放牧强度和营养添加应控制在合适的范围,以达到保护物种多样性和合理利用的双重目的.%To study the effects of clipping and fertilization on the community characteristics, productivity and species diversity of alpine meadows, we conducted a 6-year field experiment on the Qinghai-Tibet Plateau. The results showed that: (1) the species composition of the alpine meadow community had been changed by clipping treatments.The important value of Kobresia humilis was increased by 13.28% and 27.89% after moderate and heavy clipping treatments. The important value of toxic weeds with poor palatability was improved after clipping as well. (2) The importance value of grasses decreased from 48.65% to 36.63% and 40.15% after moderate and heavy clipping treatments, while the importance value of legumes increased from 2.78% to 7.49% and 7.53%, and the importance value of forbs increased from 38.78% to 46.61% and 44.34%, respectively. By contrast, fertilization increased the importance value of grasses from 35.85% to 47.78%, and decreased the importance value of legumes and forbs from 8.18% and 46.32% to 3.68% and 40.17%, respectively. (3) The coverage of community was increased from 62.78% to 77.96% and 75.04%, while the density increased from 644 ind·0.25 m-2to 876 ind·0.25 m-2and 924 ind·0.25 m-2, and the production increased from 104.63 g·0.25 m-2to 117.62 g·0.25 m-2and 123.72 g·0.25 m-2by moderate and heavy clipping treatments except for the total height reduced from 19.62 cm to 7.58 cm and 5.88 cm, respectively. Fertilization significantly increased the height, coverage and production of community from 8.47 cm, 65.56%, 88.86 g·0.25 m-2to 13.58 cm, 78.29%, 141.79 g·0.25 m-2, respectively. (4) Species diversity increased after clipping, moreover, the Richness index and Simpson index achieved the highest value when the clipping intensity was moderate. However, species diversity was decreased by fertilization. (5) The production of the study community showed weak positive correlation or no correlation with species diversity in clipping treatments, and showed weak and significant negative correlations with species diversity in fertilized treatments. These results suggest that clipping would decrease the dominance status of high quality forage, and increase that of the toxic weeds with poor palatability; however, fertilization can promote the growth of forage grass and suppress noxious weed. Additionally, the intermediate disturbance hypothesis proves to be valid in such an alpine meadow grazing system. It also indicates that the relationship between the aboveground net primary production and species diversity is context-dependent, depending on the types and intensity of disturbance. In sum, grazing and fertilization should be managed at a moderate level, so that we can preserve biodiversity when the alpine meadow is utilized for local stock farming.
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