极端降水事件对科尔沁沙地一年生植被的影响

在科尔沁沙地奈曼旗,大于10 mm的降雨属极端降雨。根据当地多年平均降雨量,设置雨量×降雨次数的双因素模拟试验(T₁,共288 mm、分18次;T₂,共288 mm、分9次;T₃,共576 mm、分36次;T₄共576 mm、分18次;CK,接收当年的自然降雨),考察极端降雨对科尔沁沙地一年生植被的密度、多样性指数、生物量及根冠比的影响。结果表明:(1)在萌发期,植株密度在各处理下均维持在2 000株·m^-2;而在生长发育后期,T₃、T₄维持在400株·m^-2,而T_I、T₂维持在1 600株·m^-2,CK下为1 200株·m^-2,说明降雨总量决定了能完成生活史的沙地一年生植被的数量。(2)T₁、T₂、T₃3种极端降雨模式均显著提高沙地一年生植被的生物多样性指数,说明科尔沁沙地一年生植被的生物多样性不是由年降雨量单一因素决定的,而是由每次降雨量与降雨次数的分布共同决定的。(3)T₃、T₄显著降低了沙地一年生植被的水分利用效率。

Effect of Extreme Precipitation Event on Annuals in the Horqin Sandy Land

Precipitation records of Naiman Meteorological station in recent 40 years depict a rain fall pattern of low intensity and high frequency. Rainfall events ≥10 mm accounted only for 10% of total rainfall frequency, 10-25 mm of rainfall accounts for 7% of total, 25-50 mm of rainfall accounts for 2% of total.Rainfall more than 10 mm is an extreme precipitation in the region according to the method of the probability density function. The total rain of the experiment were 2 levels which were mean value of natural rainfall and doubling the value while the treatments were16 mm and 32 mm each time. The number of plants, biodiversity index, biomass and root-shoot ratio of annuals were studied to explore the response of annuals to the extreme precipitation event under simulated rainfall in the Horqin Sandy Land. There were five treatments which is T_I、T₂、T₃、T₄ (T₁, total 288 mm and 18 times;T₂,total 288 mm and 9 times;T₃,total 576 mm and 36 times;T₄,total 576 mm and 18 times,and CK,received natural rainfall in 2011). The results shows that the plant density was about 2 000·m^-2 with no significant difference among the five treatments during the germination period.T₂ and T₂ were at about 400·m^-2 while T_I and T₂ were at about 1 600·m^-2 which were a little larger than CK (1 200·m^-2) in the late stage of annuals growth,which showed that total rainfall determine the number of annuals which be able to finish its growth cycle. T₁, T₂ and T₃increased the biodiversity index of annuls significantly,which illustrated that the biodiversity index of the annuals doesn't simply be determined by the total rainfall, but the distribution of rain quantity each time and rainfall frequency. The T₂ and T₂ reduced the water use efficiency significantly which due to the water infiltration depth is greater than the range of root, and annuals couldn't make full use of the rain under the extreme rainfall pattern. In other words, the extreme rainfall pattern doesn't benefit the amount of dry matter of annuals in the Horqin Sandy Land.