高山森林凋落叶腐殖化过程中胡敏酸(Humic acid, HA)、富里酸(Fulvic acid, FA)等腐殖物质的累积是土壤形成和碳吸存的重要途径，并可能受到冬季不同厚度雪被斑块的影响，但一直缺乏必要关注。本文采用凋落物网袋法，于2012/2013年冬季研究了川西高山森林天然形成的不同厚度雪被斑块(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)腐殖化过程中胡敏酸和富里酸累积特征。结果表明：经过一个冬季，6种凋落叶胡敏酸碳和富里酸碳含量在各雪被关键期均表现出随雪被厚度减少而增加的趋势，而净累积量表现出在雪被形成期和融化期随雪被厚度减少而增加、在雪被覆盖期随雪被厚度减少而减少的趋势，且均受到凋落叶初始酸不溶性组分含量的影响。同时，不同雪被斑块下6种凋落叶胡敏酸碳均累积且净累积量为四川红杉>康定柳>岷江冷杉>高山杜鹃>红桦>方枝柏，而除红桦外的其他5种凋落叶富里酸碳均出现不同程度的降解且降解量为四川红杉>高山杜鹃>康定柳>方枝柏>岷江冷杉>红桦。这些结果清晰地表明，未来气候变暖情景下冬季雪被的减少可能促进高山森林凋落叶腐殖质累积，但在雪被覆盖不同时期受到雪被斑块特征和凋落叶基质质量的调控。
Accumulation of humic substances, such as humic acid and fulvic acid, during humification of foliar litters is one of the main pathways of soil formation and carbon sequestration in alpine forest ecosystems, where low temperature and frequent geological activities often limit soil formation. Snow cover, a typical meteorological characteristic during winter in alpine forests, may play an important role in foliar litter humification thanks to its insulation effect during the snow covering stage and its leaching effect during the snow cover melting stage. What’s more, the ongoing climate change is altering the pattern of snow cover, which could also have some essential effects on litter humification. However, the results so far available are still not clear which limits the understanding of foliar litter humification and its response to changes in winter snow regime in cold biomes. Therefore, to explore effects of snowpacks different in depth on accumulation of humic acid and fulvic acid during the early foliar litter humification stage, a field litterbag experiment was conducted in an alpine forest in Southwest China in the winter of 2012/2013. Air-dried foliar litters of six local species dominant in the region, namely, fir ( Abies faxoniana), cypress (Sabina saltuaria), larch (Larix mastersiana), birch (Betula albo-sinensis), willow ( Salix paraplesia) and azalea (Rhododendron lapponicum) were incubated under snowpacks different in depth (deep snowpack, moderate snowpack, thin snowpack and no snowpack), naturally formed at the forest gap center, canopy gap, extended gap and under the closed canopy, respectively. Thereafter, concentrations of humic acid carbon and fulvic acid carbon were measured, and for calculation of net accumulations at three critical stages, i.e. snow cover forming stage, snow covering stage and snow cover melting stage, in the first winter of the incubation as foliar litter humification proceeded. Results clearly showed that the concentrations of humic acid and fulvic acid carbons both displayed a rising tendency with the snow cover decreasing in depth during the three critical stages, and the net accumulations of the two humic substances also exhibited a similar trend at the snow cover forming and melting stages, but a reverse trend at the snow covering stage. However, net accumulation of the two humic substances was affected by the initial concentration of acid-insoluble residues in the foliar litters. In terms of net accumulation of humic acid carbon in the foliar litters incubated under snowpacks of any depth, the six different species of foliar litters followed an order of larch > willow > fir > azalea > birch > cypress. The net accumulation of humic acid carbon in the foliar litters of cypress, larch and willow significantly increased with the snowpacks decreasing in depth, but the net accumulation of humic acid carbon in the foliar litters of fir, birch and azalea were lower under thin and no snowpack than under deep and moderate snowpacks. However, fulvic acid carbon in the foliar litters except for that of birch was observed degrading to a varying extent, showing an order of larch > azalea > willow > cypress > fir > birch. Humic acid carbon accumulated in all foliar litters but fulvic acid carbon decomposed under snowpacks at the snow cover forming stage, and net accumulations of both humic acid and fulvic acid carbons in the foliar litter of fir, cypress, birch and azalea significantly increased with the snowpacks decreasing in depth. Humic acid and fulvic acid carbons in the foliar litters except for that of cypress decomposed at the snow covering stage, and net accumulation of fulvic acid carbon in the foliar litters except for that of willow significantly decreased with the snowpacks decreasing in depth. Most of the humic acid and fulvic acid carbons in foliar litters accumulated at the snow cover melting stage, and the net accumulation of humic acid carbon in the foliar litters of cypress, larch and willow and fulvic acid carbon in the foliar litters of fir, cypress, birch and azalea significantly increased with the snowpacks decreasing in depth. Meanwhile, the humic acid carbon to fulvic acid carbon ratios showed a significantly decreasing trend with the snowpacks decreasing in depth at the snow cover forming and melting stages, but increased at the snow covering stage, whereas the ratios in the foliar litters except for that of birch were lower than 1, suggesting that the formation of fulvic acid was faster than humic acid at the early foliar litter humification stage. In addition, canonical correspondence analysis showed that net accumulations of humic acid carbon and fulvic acid carbon were positively related to concentrations of nitrogen and acid-insoluble residues, but negatively related to concentrations of carbon, phosphorus and soluble components. These findings suggest that the early humification of foliar litter in alpine forests is promoted by reduced snow cover in the scenario of climate warming, but it is controlled by litter qualities and snowpacks at different stages through the winter.
倪祥银,杨万勤,徐李亚,何 洁,李 晗,吴福忠.雪被斑块对高山森林凋落叶腐殖化过程中胡敏酸和富里酸累积的影响[J].土壤学报,2014,51(5):1138-1152. DOI:10.11766/trxb201401020006 Ni Xiangyin, Yang Wanqin, Xu Liya, He Jie, Li Han, Wu Fuzhong. Effects of winter snowpack on accumulation of humic acid and fulvic acid during humification of foliar litters in an alpine forest[J]. Acta Pedologica Sinica,2014,51(5):1138-1152.复制