叶凋落物碳、氮和磷元素对模拟淋溶的响应

Response of litter carbon, nitrogen and phosphorus to simulated leaching

叶凋落物是陆地和水生生态系统有机质和营养元素的重要来源.虽然淋溶是凋落物碳和养分释放的重要途径,但不同物种对淋溶响应的差异性很少被量化.此外,不同元素的可溶性是否存在显著差异,凋落物的性状能否用于预测凋落物对淋溶的响应还不清楚.本研究选择15个亚热带森林常见树种的凋落物进行6 h的模拟淋溶实验,测定了淋溶后凋落物的质量损失、碳、氮和磷元素的溶出量.同时测定了11个凋落物性状,分析了这些性状与淋溶结果的关联性.结果发现,不同物种淋溶后的质量损失、碳、氮和磷溶出量均存在显著差异(P<0.001).碳、氮和磷的可溶性也存在显著差异(P<0.001),磷的平均溶出量为12.99%,显著高于碳(2.53%)和氮(2.97%),这表明淋溶是磷元素释放的重要途径.同时,这也导致淋溶后凋落物C:P和N:P值显著升高(P<0.001).凋落物性状与淋溶结果有显著关联性,最大持水力是影响碳溶出的最重要因子,而比叶面积是影响氮和磷溶出的最重要因子.本研究表明,短期的淋溶过程就可以导致较大比例的元素释放,这改变了凋落物的化学组成,进而可能会影响后续生物驱动的分解.但淋溶对不同元素的影响程度不同,因此不同元素不能同等对待.凋落物性状可以预测凋落物对淋溶的响应.

Leaf litter is the main input of organic carbon and nutrients to terrestrial and freshwater ecosystems. The decomposition of leaf litter is crucial to the regulation of ecosystem carbon and nutrient dynamics. Abiotic leaching, i.e., water extraction of soluble elements from litter, is an important mechanism for release of carbon and nutrients from litter, providing easily accessible energy and nutrient source for microbes. However, relatively few studies have quantified the response of different litter species to leaching. In addition, it remains largely unclear that whether different elements in litter differ in solubility and whether the response of elements to leaching can be predicted by initial litter traits. In order to fill these knowledge gaps, recently senesced leaf litter of 15 subtropical broad-leaved tree species were leached in de-ionized water over 6 h in lab. Litter mass loss, carbon, nitrogen and phosphorus release after leaching were quantified. In addition, for each litter species, we measured 11 litter traits, including leaf thickness and toughness, maximum and standardized water holding capacity, contents of carbon, nitrogen, phosphorus, lignin and cellulose, specific leaf area and leaf dry matter content, and tested the influence of these litter traits on elements release pattems. After leaching, there were significant variation in litter mass loss, carbon, nitrogen and phosphorus release among different litter species （P〈0.001）. Litter carbon, nitrogen and phosphorus elements showed significantly differential solubility （P〈0.001）. The average soluble fraction of phosphorus was 12.99%, significantly greater than that of carbon （2.53%） and nitrogen （2.97%）, suggesting that leaching is an important avenue for phosphorus release. The greater solubility of phosphorus also gave rise to significantly incresed C：P and N：P ratios in leached litter （P〈0.001）. The response of elements to leaching could be predicted by initial litter traits. The maximum water holding capacity of litter was the best predictor of carbon release, while the specific leaf area was the best predictor for both nitrogen and phosphorus release after leaching. We concluded that, despite the short duration of leaching, a considerable amount of nutrient release can occur, which influence litter chemistry and then probably affect subsequent microbial decomposition process. However, elements in litter have differential solubility so that different elements cannot be treated equally. Like microbe-mediated decomposition, trait-based approach can be used to predict the response of litter to leaching.