雪被斑块对高山森林两种灌木凋落叶质量损失的影响

高山/亚高山森林灌木层植物凋落物的分解对于系统物质循环等过程具有重要意义,并可能受到冬季不同厚度雪被斑块下冻融格局的影响.该文采用凋落物分解袋法,研究了高山森林典型灌层植物华西箭竹(Fargesia nitida)和康定柳(Salix paraplesia)凋落物在沿林窗-林下形成的冬季雪被厚度梯度(厚型雪被斑块、较厚型雪被斑块、中型雪被斑块、薄型雪被斑块、无雪被斑块)上在第一年不同关键时期(冻结初期、冻结期、融化期、生长季节初期和生长季节后期)的质量损失特征.在整个冻融季节,华西箭竹和康定柳凋落叶的平均质量损失分别占全年的(48.78±2.35)％和(46.60±5.02)％.冻融季节雪被覆盖斑块下凋落叶的失重率表现出厚型雪被斑块大于薄型雪被斑块的趋势,而生长季节无雪被斑块的失重率明显较高.尽管如此,华西箭竹凋落物第一年分解表现出随冬季雪被厚度增加而增加的趋势,但康定柳凋落物第一年失重率以薄型雪被斑块最高,而无雪被斑块最低.同时,相关分析表明冻融季节凋落叶的失重率与平均温度和负积温呈极显著正相关,生长季节凋落叶的失重率与所调查的温度因子并无显著相关关系,但全年凋落物失重率与平均温度和正、负积温均显著相关.这些结果清晰地表明,未来冬季变暖情境下高山森林冬季雪被格局的改变将显著影响灌层植物凋落物分解,影响趋势随着物种的差异具有明显差异.

Effect of snow patches on leaf litter mass loss of two shrubs in an alpine forest

Aims Litter decomposition of understory species is one of the essential components in material cycling and other important processes in alpine/subalpine forest ecosystems. Natural snow patches with different snow depths in winter could play an important role in litter decomposition due to significantly different freeze-thaw characters, but little information has been available. Therefore, our objective was to understand the effects of snow patches on litter decomposition of dwarf bamboo (Fargesia nitida) and salix (Salix paraplesia), two representative understory shrubs in alpine forest.
Methods A field experiment using litterbags was conducted in an alpine forest in western Sichuan, China. Samples of air-dried leaf litter were placed in nylon litterbags, and the litterbags were placed on the forest floor along a snow depth gradient from forest gap to canopy cover. Five snow patches with different snow depths were selected: thickest snow cover patch (SP1), thicker snow cover patch (SP2), middle thick snow cover patch (SP3), thinner snow cover patch (SP4) and no snow cover patch (SP5). Mass loss was measured at five critical periods as decomposition proceeded (onset of soil freezing period, soil freezing period, soil thawing period, early growth period and later growth period) of the first year of decomposition.
Important findings Mass loss of dwarf bamboo and salix litters in the freeze-thaw season accounted for (48.78 ± 2.35)% and (46.60 ± 5.02)% of the first year of litter decomposition, respectively. Both litters displayed higher mass loss rate under the patches with snow cover compared with no snow patch in the freeze-thaw season, but showed higher mass loss rate under SP5 in the growth season. Over the first year of decomposition, although mass loss rate of bamboo litter increased with the increase of winter-snow depth, salix litter showed the highest value under SP4 and lowest value under SP5. In addition, correlation analysis indicated that mass loss rate in the freeze-thaw season was positively related to daily mean temperature and negative cumulative temperature, whereas mass loss rate in the growth season was not related to any investigated temperature factors. However,1-year mass loss rate was significantly related to daily mean temperature and negative/positive cumulative temperature. These results indicated that change of snow pattern would have significant effects on understory litter decomposition in the alpine forest in the scenario of warmer winters, but the effects could be various in different kinds of litter.