季节性雪被对高山森林凋落物分解的影响

Effect of seasonal snow cover on litter decomposition in alpine forest

季节性雪被可能对高山森林凋落物分解产生重要影响,但一直没有深入的研究。该文采用凋落物分解袋法,于2010–2012年雪被覆盖下几个关键时期(冻结初期、深冻期和融化期)以及生长季节,研究了川西高山森林代表性树种岷江冷杉(Abies faxoniana)、红桦(Betula albosinensis)、四川红杉(Larix mastersiana)和方枝柏(Sabina saltuaria)凋落叶在不同厚度冬季雪被下的分解动态。经过两年的分解,不同雪被覆盖下岷江冷杉凋落物分解率为33.98%–39.55%,红桦为46.49%–48.22%,四川红杉为42.30%–44.93%,方枝柏为40.34%–43.84%。相对于无雪被覆盖环境,厚型雪被覆盖均小幅提高了4种凋落物两年的失重率(1.57%–5.57%)。3个针叶树种(岷江冷杉、四川红杉和方枝柏)Olson凋落物分解系数k均以厚型雪被覆盖最大,薄型雪被覆盖最小,而阔叶树种红桦分解系数k则表现为无雪被>薄型雪被>较厚型雪被>厚型雪被>中型雪被。尽管在第二年生长季中雪被对红桦凋落物分解的促进作用不明显,但雪被覆盖明显促进了两年各个关键时期岷江冷杉、四川红杉和方枝柏凋落物的分解。第一年雪被期凋落物分解对当年分解总量的贡献达42.5%–65.5%,季节性雪被变化明显改变了凋落物冬季分解格局,对深冻期凋落物分解过程影响尤为显著。综上所述,当前气候变化情景下冬季雪被的减少可能减缓该区森林凋落物分解过程,但相对于易分解的阔叶凋落物,针叶凋落物的响应特征可能更为强烈。

Aim Seasonal snow cover may play an important role in litter decomposition in subalpine forest, but little information has been available on the effects of different snow depths on litter mass loss. Therefore, our objective was to characterize the rate of mass loss during litter decomposition under different snow cover conditions. Methods A field litterbag experiment was conducted in an alpine fir forest of western Sichuan, China from October 2010 to October 2012. Samples of air-dried leaf litter of fir （Abiesfaxoniana）, larch （Larix mastersiana）, cypress （Sabina saltuaria） and birch （Betula albosinensi） were placed in nylon litterbags （20 cm - 20 cm, 10 g per bag）, and the edges were sealed. Mass loss rates were investigated at different critical stages （onset of freezing period, deep freezing period, thawing stage and growing season） during two years of decomposition. Important findings Two years of decomposition resulted in mass loss of 33.98%-39.55% for fir, 46.49%48.22% for birch, 42.30%-4.93% for larch and 40.34%43.84% for cypress. Compared with no snow cover, thick snow cover marginally increased mass loss by 1.73%-5.57%. The k values from the Olson decomposition constant for three coniferous litters （fir, larch and cypress） were highest under thick snow cover and lowest under no snow cover. However, the k value for birch, a broad-leaved species, showed the ranked order of no snow cover 〉 thin snow cover 〉 thicker snow cover 〉 thick snow cover 〉 medium snow cover. Although snow cover did not significantly promote decomposition of birch litter during growing season in the second year, snow cover significantly promoted decomposition of fir, larch and cypress litters at all investigated stages in two years. Additionally, mass loss during snow cover period in the first year accounted for 42.5%,65.5% of the entire first year decomposition, indicating that seasonal snow cover dramatically changed the decomposition of leaf litters in winter, especially at the deep frozen stage. In conclusion, litter decomposition in this alpine forest would be delayed by the decrease of winter snow cover predicted with climate change. Compared with broad-leaved litter, coniferous litter could display stronger responses to such changes of snow cover.