State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Beijing Normal University, Beijing, China.
PLoS One. 2012;7(7):e42042. doi: 10.1371/journal.pone.0042042. Epub 2012 Jul 26.
Macrophyte decomposition is important for carbon and nutrient cycling in lake ecosystems. Currently, little is known about how this process responds to detritus quality and water nutrient conditions in eutrophic shallow lakes in which incomplete decomposition of detritus accelerates the lake terrestrialization process. In this study, we investigated the effects of detritus quality and water nutrient concentrations on macrophyte decomposition in Lake Baiyangdian, China, by analyzing the decomposition of three major aquatic plants at three sites with different pollution intensities (low, medium, and high pollution sites). Detritus quality refers to detritus nutrient contents as well as C:N, C:P, and N:P mass ratios in this study. Effects of detritus mixtures were tested by combining pairs of representative macrophytes at ratios of 75:25, 50:50 and 25:75 (mass basis). The results indicate that the influence of species types on decomposition was stronger than that of site conditions. Correlation analysis showed that mass losses at the end of the experimental period were significantly controlled by initial detritus chemistry, especially by the initial phosphorus (P) content, carbon to nitrogen (C:N), and carbon to phosphorus (C:P) mass ratios in the detritus. The decomposition processes were also influenced by water chemistry. The NO(3)-N and NH(4)-N concentrations in the lake water retarded detritus mass loss at the low and high pollution sites, respectively. Net P mineralization in detritus was observed at all sites and detritus P release at the high pollution site was slower than at the other two sites. Nonadditive effects of mixtures tended to be species specific due to the different nutrient contents in each species. Results suggest that the nonadditive effects varied significantly among different sites, indicating that interactions between the detritus quality in species mixtures and site water chemistry may be another driver controlling decomposition in eutrophic shallow lakes.
水生植物残体分解对湖泊生态系统的碳和养分循环具有重要意义。目前，人们对富营养化浅水湖泊中这一过程如何响应碎屑质量和水体养分条件知之甚少，因为碎屑不完全分解会加速湖泊向陆地化方向发展。本研究以中国白洋淀为例，通过分析三种主要水生植物在低、中、高污染区三个不同污染强度地点的分解情况，研究了碎屑质量和水体养分浓度对水生植物残体分解的影响。本研究中的碎屑质量是指碎屑中的养分含量以及 C:N、C:P 和 N:P 质量比。通过将两种具有代表性的水生植物以 75:25、50:50 和 25:75（质量比）的比例混合，测试了碎屑混合物的影响。结果表明，物种类型对分解的影响大于地点条件。相关分析表明，实验结束时的质量损失主要受初始碎屑化学性质的控制，特别是碎屑初始磷（P）含量、碳氮（C:N）比和碳磷（C:P）质量比。分解过程还受到水化学的影响。湖水中的硝态氮（NO3-N）和氨氮（NH4-N）浓度分别延缓了低污染区和高污染区碎屑的质量损失。所有地点的碎屑均发生净磷矿化，高污染区碎屑磷释放速度慢于其他两个地点。由于每个物种的养分含量不同，混合物的非加性效应往往具有物种特异性。结果表明，由于不同地点碎屑质量和水体化学性质的相互作用，非加性效应存在显著差异，这可能是控制富营养化浅水湖泊分解的另一个驱动因素。
