缙云山亚热带森林林下常见蕨类叶与细根分解碳氮磷释放动态

Patterns of carbon, nitrogen and phosphorus dynamics during decomposition of fern leaf and fine root in a subtropical forest

凋落物分解是森林碳和养分循环的关键环节.长期以来森林凋落物分解研究主要关注森林优势树种.虽然蕨类植物是亚热带森林林下层的重要组分,占林下层大量的生物量,但其凋落物分解过程很少被关注.本研究用缙云山亚热带常绿阔叶林林下12种常见的蕨类叶和细根进行分解实验,监测分解113, 198, 386和586 d后的碳氮磷释放动态.结果表明:蕨类叶与细根初始碳含量无显著差异,但叶的初始氮磷含量均显著高于细根.多数物种叶的碳氮磷释放速率显著快于细根,且叶的碳氮磷主要表现为简单的直接释放模式,而细根的碳氮磷释放则表现出直接释放、富集-释放、富集-释放-富集、始终富集等复杂模式.氮、磷残余率随碳残余率的变化格局分别受初始氮、磷含量的影响.叶与细根间碳氮磷残余率的相关性表现出不同的格局:碳残余率在分解113, 198和386 d后均为显著正相关,但586 d后关系不显著;而磷残余率除在113 d时关系不显著外在其他时间点均显著正相关;但氮残余率在整个分解过程均无显著关系.该结果表明地上地下分解速率是否存在显著相关性与元素类型及分解时间有关.本研究结果为进一步量化蕨类植物对森林生态系统碳和养分循环的重要性提供参考.

Litter decomposition is a major driver of carbon and nutrient cycles and has major implications for carbon sequestration and plant nutrient availability in terrestrial ecosystems.The vast majority of litter decomposition studies have focused on the tree component in forest ecosystems,while little attention has been paid to understory components.Ferns,one ancient and diverse group of vascular plants,comprise a significant part of most forest understory layer.However,empirical study regarding decomposition rate and carbon,nitrogen and phosphorus release patterns of fern leaves and fine roots remains rare.Therefore,it is difficult to predict the ecological consequences of fern community changes resulting from forest management practices or other environmental changes.In this study,we examined the patterns of mass loss and carbon,nitrogen,and phosphorus gain,retention or loss during the decomposition of leaves and fine roots(<2 mm)of 12 herbaceous fern species in a subtropical evergreen broad-leaved forest in Jinyun Mountain,Southwest China.We measured the initial carbon,nitrogen,and phosphorus concentrations of leaves and fine roots,and monitored the changes in carbon,nitrogen,and phosphorus after 113,198,386 and 586 day’decomposition in the field.We hypothesized that:(H1)fern leaves would decompose faster than fine roots;(H2)nitrogen and phosphorus release patterns would be affected by the initial tissue nitrogen and phosphorus concentrations;and(H3)carbon,nitrogen and phosphorus release patterns of leaves and fine roots would coordinate across different fern species.The results showed that:(1)Initial carbon concentration of fern leaves were similar to fine roots,while initial nitrogen and phosphorus concentrations of leaves were significantly higher than those of fine roots.Litter mass,carbon,nitrogen and phosphorus remains of fern leaves were generally significantly lower than those of fine roots,supporting our first hypothesis(H1).(2)Carbon,nitrogen and phosphorus of fern leaves and roots exhibited different loss patterns.Leaf carbon,nitrogen and phosphorus generally directly lost during the entire decomposition process.By contrast,carbon,nitrogen and phosphorus of fine roots showed more complicated patterns such as direct loss,gain-loss,gain-loss-gain and always gain.In support of our second hypothesis(H2),we found that nitrogen or phosphorus release patterns were influenced by the initial tissue nitrogen or phosphorus concentrations,respectively.(3)Carbon remains between leaves and fine roots were significantly correlated after 113,198 and 386 day’decomposition in the field,but not after 586 d.Phosphorus remains between leaves and fine roots were significantly correlated after 198,386 and 586 day’decomposition in the field,but not after 113 d.By contrast,there was no significant relationship of the nitrogen remains between leaves and fine roots during the entire decomposition process.Thus,our third hypothesis(H3)was only partly supported.This result suggests that the above-and below-ground covariation patterns depend on specific element and the duration of decomposition.Our study improves our understanding of how fern species influence the carbon and nutrient cycling in subtropical forest.