高寒矮嵩草草甸植物类群对模拟降水和施氮的响应

 研究了青藏高原高寒矮嵩草（Kobresia humilis）草甸植物类群对模拟夏季增减雨量、冬春增雪以及增施氮肥下的响应。结果表明：1999年模拟减少降雨20%～40%和增加雨量20%～40%下禾草类、杂类草和莎草类的综合优势比（SDR）和地上生物量变化均不显著。冬春增雪100%有利于禾草类夏季的生长，冬春增雪对植物类群的影响大于夏季雨量的增加。夏季增施氮150 kg·hm－2和增施氮300 kg·hm－2禾草类的盖度比、高度比、SDR和地上生物量明显增大，而杂类草的盖度比和高度比、SDR及地上生物量在施氮300 kg·hm－2下显著减低，在施氮150 kg·hm－2水平上禾草类的生物量的增加与杂类草生物量的降低存在相互补偿的作用机制。在水分资源不利的（如减少雨量）的干扰下，其敏感性表现为杂类草大于禾草类，莎草类最小。莎草类植物对各种处理下响应不敏感，也说明它对资源环境的波动有很强的适应性。缺水年（1999年）模拟增加雨量20%～40%的条件下，可缓解降水量减少的影响，相反模拟减少雨量20%～40%会增强干旱的影响程度。

RESPONSE OF PLANT GROUPS TO SIMULATED RAINFALL AND NITROGEN SUPPLY IN ALPINE KOBRESIA HUMILIS MEADOW

The response of different plant groups to simulated rainfall changes in summer, increased snow in winter and spring, and nitrogen fertilization application in late June were studied in an alpine Kobresia humilis meadow in Qingzang plateau. The results indicated that the response of summed dominated ratio (SDR) and above-ground biomass in different plant groups were not significantly different with 20%-40% rainfall reduction or 20%-40% increased rainfall in 1999. A 100% increase in snow in winter and spring was more favorable to the growth of plant groups than were other rainfall treatments. Both a single late June application of 150 N kg·hm-2 and 300 N kg·hm-2 in soil increased the coverage ratio, height ratio and SDR of grasses. The coverage ratio, height ratio and SDR were significantly decreased at the strong N application (300 N kg·hm-2). There were obvious compensatory effects between grasses and forbs at the application of 150 N kg·hm-2. The sensitivity of the three plant groups was quite different. Grasses were most, forbs were less and sedges were least sensitive to simulated rainfall and available N in the improved disturbing condition. Forbs were most, grasses were less, and sedges were least sensitive to simulated rainfall and available N in the undesirable disturbing condition. It seemed that sedges were most tolerant to fluctuation in environmental resources. Simulated rainfall increasing by 20%-40% could moderate the effect of lower precipitation in a water deficient year (1999), while rainfall decreased 20%-40% could intensify the effect of drought.