Summer litter decomposition is moderated by scale-dependent microenvironmental variation in tundra ecosystems
Summer litter decomposition is moderated by scale-dependent microenvironmental variation in tundra ecosystems
复制标题
苔原生态系统中尺度相关的微环境变化调节了夏季凋落物的分解
作者：
Gallois E
苔原土壤是世界上最大的有机碳储存库之一，然而随着气候变暖，这些碳很容易加速分解。在冻土带生态系统中，凋落物分解的景观尺度控制知之甚少，这阻碍了我们对全球碳循环的理解。我们研究了地表气温、土壤湿度和永久冻土融化深度的热总和对凋落物质量损失和分解速率(k)的影响程度，以及空间阈值作为环境变量成为分解的可靠预测因子的程度，采用茶包指数协议，研究了加拿大育空地区齐奇塔鲁克-赫歇尔岛异质苔原景观。我们发现，在景观中较湿润的地区，绿茶凋落物质量损失更大，分解速率(k)更快，而在永久冻土活土层厚度较深、地表热总和较高的地区，这种情况较少。我们还发现，在湿润而非温暖的微点上，朝北的分解速率(k)相对于朝南的分解速率更高。空间异质性地下条件（土壤湿度和活动层深度）比热总和更能解释局部尺度（< 50 m2）分解指标的变化。令人惊讶的是，海拔和坡度对凋落物分解没有很强的控制作用。研究结果表明，冻土带凋落物分解的环境控制存在相当大的尺度依赖性，在< 50 m2尺度下，湿度的作用大于热总和。我们的研究结果强调了微环境控制对凋落物分解在快速变暖的冻土带生物群落碳循环估算中的重要性和复杂性。
Tundra soils are one of the world's largest organic carbon stores, yet this carbon is vulnerable to accelerated decomposition as climate warming progresses. The landscape‐scale controls of litter decomposition are poorly understood in tundra ecosystems, which hinders our understanding of the global carbon cycle. We examined the extent to which the thermal sum of surface air temperature, soil moisture and permafrost thaw depth influenced litter mass loss and decomposition rates (k), and at which spatial thresholds an environmental variable becomes a reliable predictor of decomposition, using the Tea Bag Index protocol across a heterogeneous tundra landscape on Qikiqtaruk–Herschel Island, Yukon, Canada. We found greater green tea litter mass loss and faster decomposition rates (k) in wetter areas within the landscape, and to a lesser extent in areas with deeper permafrost active layer thickness and higher surface thermal sums. We also found higher decomposition rates (k) on north‐facing relative to south‐facing aspects at microsites that were wetter rather than warmer. Spatially heterogeneous belowground conditions (soil moisture and active layer depth) explained variation in decomposition metrics at local scales (< 50 m2) better than thermal sum. Surprisingly, there was no strong control of elevation or slope on litter decomposition. Our results reveal that there is considerable scale dependency in the environmental controls of tundra litter decomposition, with moisture playing a greater role than the thermal sum at < 50 m2scales. Our findings highlight the importance and complexity of microenvironmental controls on litter decomposition in estimates of carbon cycling in a rapidly warming tundra biome.