Ecology. 2014 Jul;95(7):1861-75. doi: 10.1890/13-2221.1.
Climate warming in arctic tundra may shift dominant vegetation from graminoids to deciduous shrubs, whose functional traits could, in turn, alter biotic and abiotic controls over biogeochemical cycling of carbon (C) and nitrogen (N). We investigated whether shrub-induced changes in microclimate have stronger effects on litter decomposition and nutrient release than changes in litter quality and quantity. In arctic tundra near Toolik Lake, Alaska, USA, we incubated a common substrate in a snow-addition experiment to test whether snow accumulation around arctic deciduous shrubs altered the environment enough to increase litter decomposition rates. We compared the influence of litter quality on the rate of litter and N loss by decomposing litter from four different plant functional types in a common site. We used aboveground net primary production values and estimated decay constant (k) values from our decomposition experiments to calculate community-weighted mass loss for each site. Snow addition had no effect on decomposition of the common substrate, and the site with the highest abundance of shrubs had the lowest decomposition rates. Species varied in their decomposition rates, with species from the same functional type not always following similar patterns. Community-weighted mass loss was 1.5 times greater in the high shrub site, and only slightly decreased when adjusted for soil environment, suggesting that litter quality and quantity are the primary drivers of community decomposition. Our findings suggest that on a short time scale, the changes in soil environment associated with snow trapping by shrubs are unlikely to influence litter nutrient turnover enough to drive positive snow-shrub feedbacks. The mechanisms driving shrub expansion are more likely to do with shrub-litter feedbacks, where the higher growth rates and N uptake by shrubs allows them to produce more leaves, resulting in a larger litter N pool and faster internal cycling of nutrients.
北极苔原气候变暖可能会使优势植被从禾本科植物转变为落叶灌木,其功能特征反过来又会改变生物和非生物对碳(C)和氮(N)生物地球化学循环的控制。我们研究了灌木引起的微气候变化对凋落物分解和养分释放的影响是否大于凋落物质量和数量的变化。在美国阿拉斯加图利湖附近的北极苔原,我们进行了一项雪地添加实验,以测试北极落叶灌木周围的积雪积累是否足以改变环境,从而提高凋落物分解率。我们比较了四种不同植物功能类型的凋落物在同一地点对凋落物和 N 损失速率的影响。我们使用地上净初级生产力值和从分解实验中估计的衰减常数(k)值来计算每个地点的群落加权质量损失。雪地添加对常见基质的分解没有影响,而灌木丰度最高的地点分解率最低。不同物种的分解速率不同,来自同一功能类型的物种并不总是遵循相似的模式。高灌木地点的群落加权质量损失增加了 1.5 倍,而在调整土壤环境后仅略有下降,这表明凋落物质量和数量是群落分解的主要驱动因素。我们的研究结果表明,在短时间尺度上,与灌木捕获积雪相关的土壤环境变化不太可能影响凋落物养分周转,从而无法驱动正的雪-灌木反馈。驱动灌木扩张的机制更可能与灌木-凋落物反馈有关,其中灌木较高的生长速率和 N 吸收能力使它们能够产生更多的叶子,从而形成更大的凋落物 N 库和更快的养分内部循环。