中国温带和亚热带8个树种叶和吸收根协同分解

A coordinated decomposition between leaf litter and absorptive roots across eight temperate and subtropical tree species in China

叶和细根(<2mm)是森林生态系统的分解主体,二者是否协同分解,将极大影响所属植物在生态系统碳(C)循环中的物种效应。已有研究显示,叶和细根的分解关系具有极大的不确定性,认为很大程度上归因于细根内部具有高度的异质性,导致叶和细根在功能上不相似。为此,使用末梢1级根和细根根枝作为研究对象,它们在功能上同叶类似,称为吸收根。通过分解包法,分别在黑龙江帽儿山和广东鹤山,研究了2个阔叶树种和2个针叶树种(共8个树种)的叶和吸收根持续2a多的分解。结果发现,分解速率k(a^(-1),负指数模型)在8个树种整体分析时具有正相关关系(P<0.05),在相同气候带或植物生活型水平上是否相关,受叶的分解环境及吸收根类型的影响;N剩余量整体上并不相关,亚热带树种的叶和细根根枝的N剩余量在分解1a后高度显著正相关,温带树种的叶和1级根的N剩余量在分解2a后显著高度正相关。本研究中,根-叶分解过程是否受控于相同或相关的凋落物性质是决定根-叶分解是否相关的重要原因,其中分解速率与酸溶组分正相关、与酸不溶组分负相关。比较已有研究,总结发现,根-叶分解关系受物种影响较大,暗示气候变化导致物种组成的改变将极大影响地上-地下关系,也因此影响生态系统C循环。

Leaves and fine roots （ 〈 2mm） account for the majority of annual litter production in forests. Whether their decomposition is coordinated would largely influence species effects on terrestrial ecosystem C cycling. Currently, the relationship between leaf and root decomposition is still highly uncertain, which may be caused by the ambiguous and arbitrary definition of fine roots. Within fine roots, only the distal root tips （R1） or root branches （R1-3） are functionally comparable to leaves as resource acquisition organs （absorptive roots）. Here, we investigated decomposition of leaf litter and absorptive roots using litter bags for two years across eight temperate and subtropical tree species in China. Results showed that decay rates k （a^-1, negative exponential model） were positively correlated between leaf litter and absorptive roots when all eight temperate and subtropical trees were examined in combination, but when tree species were separated by climate zones or growth forms, the correlation was influenced by the soil depth at which leaf litter decomposition occurred, and the type of absorptive roots. N remaining in the leaf and root was not correlated when all eight trees were examined in combination. However, N remaining in the leaf and root was highly and positively correlated between leaf and R1-3 among subtropical trees after one year of decomposition, and between leaf and R1 among temperate trees after two years of decomposition. Here, the correlation between the decomposition of leaf and root was mainly influenced by whether both leaf and root decomposition were controlled by the same or related litter chemistry. In this study, all litter decay rates were positively related to acid soluble C fractions, but negatively related to acid insoluble C fractions. Summarizing results from our study and other studies, we found that the relationship between leaf and root decomposition was largely affected by species. Therefore, species composition dynamics due to climate change would largely affect above-and below-ground relationships and thus ecosystem C cycling.