积雪对祁连山亚高山草甸土壤呼吸速率的影响

草地作为陆地生态系统的重要组成部分,是分布最广的植被类型之一,全球草地面积约占陆地面积的1/4,土壤碳储量约占全球总碳储量的1/5,在气候变化和陆地生态系统的碳循环方面起着重要作用。我国各类天然草原面积近4亿hm~2,约占国土面积的41.7%,草地的总碳储量约占陆地生态系统总碳储量的16.7%,其中土壤层占93.1%,在碳储量中占有重要的地位。土壤呼吸是陆地生态系统碳循环的主要环节,其中草地土壤呼吸占陆地土壤呼吸量的5.6%,因此草地土壤碳库正成为草地生态系统研究的热点。祁连山草地资源丰富,亚高山草甸是祁连山自然保护区的基质景观。积雪作为冰冻圈的重要组成部分,对土壤温度和土壤水分具有调控作用,是影响土壤呼吸的重要因素,但是目前关于积雪对土壤呼吸的影响研究少见。研究区选择祁连山中部天涝池流域,利用LI-8100开路式土壤碳通量测定系统,探讨了土壤不同融化状态下积雪对祁连山亚高山草甸生态系统呼吸速率和土壤呼吸速率的影响,并分析了地表温度和土壤温度、地表空气相对湿度和土壤体积含水量对土壤呼吸的影响。结果表明:(1)雪覆盖降低了生态系统呼吸和土壤呼吸速率,但当日融化的积雪对次日生态系统呼吸有促进作用;(2)呼吸速率与土壤温度和地表温度呈显著指数关系(P0.01),与地表空气相对湿度呈线性相关关系。降雪后,全融土壤中呼吸速率与温度和地表空气相对湿度间的相关性好;(3)温度较高时,温度对呼吸速率的作用强;温度较低时,温度对呼吸速率的影响不大。

The effect of snow on soil respiration rate in subalpine meadows of the Qilian Mountains

As an important component of terrestrial ecosystems, grasslands are one of the most widespread vegetation types worldwide, covering nearly a quarter of the world''s land surface. The soil carbon reserves amount to one fifth of the global total; thus, grasslands play a significant role in climate change and the global carbon cycle. The area of different kinds of natural grasslands in China is approximately 400 million hm², accounting for approximately 41.7% of the land area. The total carbon reserves of grasslands account for approximately 16.7% of the total carbon reserves of the terrestrial ecosystems, of which the soil accounts for 93.1%; thus, soil carbon reserves occupy an important position in the global carbon reserves. Soil respiration is the main link in the carbon cycle of terrestrial ecosystems, in which grassland soil respiration accounts for 5.6% of terrestrial soil respiration. Therefore, scholars have paid attention to carbon storage of grassland ecosystems. The Qilian Mountains have abundant grassland resources. Subalpine meadows are the dominant ecosystem in the Qilian Mountains Nature Reserve. Snow, as a significant component of the cryosphere, is one of the most important factors that affects soil respiration because of its regulation and control of soil temperature and soil water content. At present, research on soil respiration in the subalpine meadows is lacking, and research regarding the effect of snow on soil respiration is also limited. The Tianlaochi catchment was selected as our study area. We observed respiration rate (R_s) under snow cover with three different soil melting states (soil non-frozen state, soil frozen state, soil melt and frozen state) in subalpine meadows of the Qilian Mountains through five snow events using a soil carbon flux automatic measurement system LI-8100 (LI-COR, USA). The effect of snow at different soil melting states on R_s was analyzed. The results showed that:(1) snow decreases R_s in the ecosystem and in bare soil, but it improves R_s in the ecosystem on the following day if snow is melted in one day; (2) The relation of R_s with temperature exhibits an exponential function (P < 0.01), which with the relative surface humidity expresses a linear function. During snow cover, the correlation between R_s and temperature in the non-frozen soil was the best. (3) The effect of temperature on respiration rate was strong when the temperature was high, whereas the effect was a weak when the temperature was low.