雪被斑块对川西亚高山森林6种凋落叶冬季腐殖化的影响

Effects of snowpack on early foliar litter humification during winter in a subalpine forest of western Sichuan

亚高山森林凋落叶腐殖化是联系植物与土壤碳库和养分库的重要通道,在冬季可能受到雪被斑块的影响。该文采用凋落物网袋法,于2012年11月–2013年4月研究了川西亚高山森林不同厚度雪被斑块(厚雪被、中雪被、薄雪被和无雪被)下优势树种岷江冷杉(Abies faxoniana)、方枝柏(Sabina saltuaria)、四川红杉(Larix mastersiana)、红桦(Betula albo-sinensis)、康定柳(Salix paraplesia)和高山杜鹃(Rhododendron lapponicum)凋落叶在不同雪被关键期(雪被形成期、雪被覆盖期和雪被融化期)的腐殖化特征。结果表明:亚高山森林冬季不同厚度雪被斑块下6种凋落叶均保持一定程度的腐殖化,其中红桦凋落叶腐殖化度最大,达4.45%–5.67%;岷江冷杉、高山杜鹃、康定柳、四川红杉和方枝柏凋落叶腐殖化度分别为1.91%–2.15%、1.14%–2.03%、1.06%–1.97%、0.01%–1.25%和0.39%–1.21%。凋落叶腐殖质在雪被形成期、融化期和整个冬季累积,且累积量随雪被厚度减小而增加,但在雪被覆盖期降解,且降解量随雪被厚度减小而增大。相关分析结果表明,亚高山森林凋落叶前期腐殖化主要受凋落叶质量影响,且与氮和酸不溶性组分呈极显著正相关,而与碳、磷、水溶性和有机溶性组分呈极显著负相关。表明冬季变暖情景下雪被厚度的减小可能促进亚高山森林凋落叶腐殖化,但凋落叶腐殖化在不同雪被关键期受雪被斑块和凋落叶质量的调控。

Aims Foliar litter humification is an important ecological process relating to soil carbon and nutrient budget in subalpine forest ecosystems, and the process of foliar litter humification can be affected by various snowpacks with different thicknesses in winter. However, little is known on the effects of snowpack on foliar litter humification. The objective of this study is to explore the effects of snowpack on early foliar litter humification during the first winter in subalpine forest. Methods A field litterbag experiment was conducted in a subalpine forest in southwestern China from November 2012 to April 2013. Air-dried foliar litter of fir （Abies faxoniana）, cypress （Sabina saltuaria）, larch （Larix mastersiana）, birch （Betula albo-sinensis）, willow （Salix paraplesia）, and azalea （Rhododendron lapponicum） were incubated under snowpacks with varying thicknesses （deep snowpack, medium snowpack, thin snowpack, and no snowpack） due to variations in the canopy openness. Net accumulation of humus carbon, humification de- grees, and humification rates were measured at snow formation, snow cover, and snow melt stage as foliar litter humification proceeded. Important findings Significant humification was observed in the six foliar litter types during the first winter regardless of the condition of snowpacks. The highest humification degree was observed in birch foliar litter （4.45%-5.67%）, and the humification degrees were 1.91%-2.15%, 1.14%-2.03%, 1.06%-1.97%, 0.01%o- 1.25%, and 0.39%-1.21%, respectively, for fir, azalea, willow, larch, and cypress foliar litter under varying snowpacks. The net accumulation of humus carbon of all foliar litters increased at the snow formation, snow melt stage, and the whole winter, which exhibited an increasing tendency with the decrease of snow cover thickness. In contrast, net accumulation of humus carbon showed a declining trend at the snow cover stage, and significantly increased with the decrease of snow cover thickness. In addition, correlation analysis results indicated that the humification degree was positively correlated with total nitrogen and acid-insoluble residues and negatively related to the organic carbon, total phosphorus, and water- and organic-soluble components. These results clearly suggest that foliar litter humification in subalpine forest can be enhanced by reduced snow cover in a scenario of climate warming, although the humification degree is controlled by snowpack and litter qualities at different stages of snow cover in winter.