A perspective on leaf litter breakdown in streams
A perspective on leaf litter breakdown in streams
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DOI：
10.2307/3546505
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发表时间：
1999-05-01
期刊：
影响因子：
3.4
通讯作者：
Dobson, M
中科院分区：
文献类型：
--
作者：
Gessner, MO;Chauvet, E;Dobson, M
凋落叶分解是河流和其他水生环境中一个关键的生态系统水平过程，利用借鉴陆地系统的模型对其进行了概念化。我们认为，目前对淡水中这一过程的看法需要从概念上加以改进。具体来说，我们认为分解分三个不同的时间阶段（浸出、调节、破碎）进行的观点被过分强调了。浸出，即浸泡后24小时内可溶性叶片成分的大量流失，通常被认为是定义明确的第一阶段。然而，最近的证据表明，最初的溶质损失在很大程度上是实验叶片通常经受的非自然干燥过程的影响。新鲜凋落叶在浸泡时确实会失去溶质，但在整个分解过程中会逐渐失去溶质，而不是在湿润时立即失去溶质。第二个分解阶段是调节，描述了微生物定植对腐食动物叶片适口性的增强，因此最终针对一组生物（有助于凋落物降解），而不是解决分解过程本身。此外，条件作用暗示了食腐无脊椎动物的关键作用，并低估了微生物分解者已建立的直接降解活性。因此，如果浸出和调节通常不是描述淡水中凋落物分解过程部分的有用操作符，那么强调浸出、调节和破碎为三个连续阶段的传统概念就失去了很大的吸引力。因此，我们提出了一个新的概念模型，在这个模型中，凋落物分解的各个子过程的重合和相互作用得到了更强烈的认识。在这个模型中，我建议从凋落物分解的产物的角度来看待这个过程，作为对通常关注凋落物质量损失的观点的补充。考虑了六种主要的分解产物：细菌、真菌和碎纸机生物质；溶解有机物；细颗粒有机物；CO2、NH4+、PO43-等无机矿化产物。我们提出了一个方案，说明这些产品在整个击穿过程中的假设形成。然而，为了提高对过程的理解，在实验工作中应用所提出的概念框架是必要的。
Leaf litter breakdown, a critical ecosystem level process in streams and other aquatic environments, has been conceptualized using models borrowed from terrestrial systems. We argue that current views of the process in freshwaters need to be conceptually improved. Specifically, we think the idea that breakdown proceeds in three distinct temporal stages (leaching, conditioning, fragmentation) has been overemphasized. Leaching, the massive loss of soluble leaf components within 24 h after immersion, is generally considered to constitute a well-defined first stage. Recent evidence suggests, however, that the initial solute losses are largely an effect of the unnatural drying procedures to which experimental leaves are normally subjected. Fresh leaf litter does lose solutes when immersed, but gradually throughout the breakdown process rather than instantly upon wetting. Conditioning, the second breakdown stage, describes the enhancement of leaf palatability for detritivores by microbial colonization, and is thus ultimately targeted towards a group of organisms (which contribute to litter degradation) rather than addressing the breakdown process per se. Furthermore, conditioning implies a key role for detritivorous invertebrates and underrates the established direct degradative activity of microbial decomposers. If, thus, leaching and conditioning are not generally useful operators to describe portions of the litter breakdown process in freshwaters, the traditional concept, which emphasises leaching, conditioning and fragmentation as three sequential stages, loses much of its appeal. Consequently, we propose a nea conceptual model, in which the coincidence and interplay of various subprocesses of litter breakdown is more strongly recognized. In this model, me propose to view the process in terms of the products of litter breakdown-as a complement to the usual perspective which focuses on litter mass loss. Six primary breakdown products are considered: bacterial, fungal and shredder biomass; dissolved organic matter; fine-particulate organic matter; and inorganic mineralization products such as CO2, NH4+ and PO43-. We present a scheme illustrating the hypothesized formation of these products throughout breakdown. However, to improve understanding of the process, application of the proposed conceptual framework in experimental work is necessary.