Department of Chemical Ecology and Ecosystem Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
Ecology. 2012 Apr;93(4):770-82. doi: 10.1890/11-0721.1.
Resource stoichiometry (C:N:P) is an important determinant of litter decomposition. However, the effect of elemental stoichiometry on the gross rates of microbial N and P cycling processes during litter decomposition is unknown. In a mesocosm experiment, beech (Fagus sylvatica L.) litter with natural differences in elemental stoichiometry (C:N:P) was incubated under constant environmental conditions. After three and six months, we measured various aspects of nitrogen and phosphorus cycling. We found that gross protein depolymerization, N mineralization (ammonification), and nitrification rates were negatively related to litter C:N. Rates of P mineralization were negatively correlated with litter C:P. The negative correlations with litter C:N were stronger for inorganic N cycling processes than for gross protein depolymerization, indicating that the effect of resource stoichiometry on intracellular processes was stronger than on processes catalyzed by extracellular enzymes. Consistent with this, extracellular protein depolymerization was mainly limited by substrate availability and less so by the amount of protease. Strong positive correlations between the interconnected N and P pools and the respective production and consumption processes pointed to feed-forward control of microbial litter N and P cycling. A negative relationship between litter C:N and phosphatase activity (and between litter C:P and protease activity) demonstrated that microbes tended to allocate carbon and nutrients in ample supply into the production of extracellular enzymes to mine for the nutrient that is more limiting. Overall, the study demonstrated a strong effect of litter stoichiometry (C:N:P) on gross processes of microbial N and P cycling in decomposing litter; mineralization of N and P were tightly coupled to assist in maintaining cellular homeostasis of litter microbial communities.
元素化学计量（C:N:P）是决定凋落物分解的重要因素。然而，元素化学计量对凋落物分解过程中微生物氮和磷循环过程的总速率的影响尚不清楚。在一项中观实验中，使用具有天然元素化学计量（C:N:P）差异的山毛榉（Fagus sylvatica L.）凋落物在恒定的环境条件下进行培养。在三个月和六个月后，我们测量了氮和磷循环的各个方面。我们发现，总蛋白解聚、氮矿化（氨化）和硝化速率与凋落物 C:N 呈负相关。磷矿化速率与凋落物 C:P 呈负相关。与凋落物 C:N 的负相关关系对于无机氮循环过程比总蛋白解聚更为强烈，这表明资源化学计量对细胞内过程的影响强于细胞外酶催化的过程。与此一致的是，细胞外蛋白解聚主要受基质可用性的限制，而受蛋白酶数量的限制较小。相互关联的氮和磷库与各自的产生和消耗过程之间的强烈正相关表明了微生物凋落物氮和磷循环的前馈控制。凋落物 C:N 与磷酸酶活性之间（以及凋落物 C:P 与蛋白酶活性之间）的负相关关系表明，微生物倾向于将丰富的碳和营养物质分配到细胞外酶的产生中，以获取更有限的养分。总的来说，该研究表明凋落物化学计量（C:N:P）对分解凋落物中微生物氮和磷循环的总过程有很强的影响；氮和磷的矿化与协助维持凋落物微生物群落的细胞内稳态紧密耦合。
