Multidimensional stoichiometric mismatch explains differences in detritivore biomass across three forest types

The ecological stoichiometry theory provides a framework to understand organism fitness and population dynamics based on stoichiometric mismatch between organisms and their resources. Recent studies have revealed that different soil animals occupy distinct multidimensional stoichiometric niches (MSNs), which likely determine their specific stoichiometric mismatches and population responses facing resource changes. The goals of the present study are to examine how long-term forest plantations affect multidimensional elemental contents of litter and detritivores and the population size of detritivores that occupy distinct MSNs. We evaluated the contents of 10 elements of two detritivore taxa (lumbricid earthworms and julid millipedes) and their litter resources, quantified their MSNs and the multidimensional stoichiometric mismatches, and examined how such mismatch patterns influence the density and total biomass of detritivores across three forest types spanning from natural forests (oak forest) to plantations (pine and larch forests). Sixty-year pine plantations changed the multidimensional elemental contents of litter, but did not influence the elemental contents of the two detritivore taxa. Earthworms and millipedes exhibited distinct patterns of MSNs and stoichiometric mismatches, but they both experienced severer stoichiometric mismatches in pine plantations than in oak forests and larch plantations. Such stoichiometric mismatches led to lower density and biomass of both earthworms and millipedes in pine plantations. In other words, under conditions of low litter quality and severe stoichiometric mismatches in pine plantations, detritivores maintained their body elemental contents but decreased their population biomass. Our study illustrates the success in using the multidimensional stoichiometric framework to understand the impact of forest plantations on animal population dynamics, which may serve as a useful tool in addressing ecosystem responses to global environmental changes.生态化学计量理论为研究生态系统不同组分间的元素流动提供了基本框架，消费者-资源之间化学元素比的错配直接影响了有机体生长和种群动态。不同土壤动物类群存在化学计量生态位上的分化，这导致不同动物类群应对食物资源变化时会产生不同程度的元素错配。 本研究基于北京东灵山三种森林类型(天然辽东栎次生林和人工种植油松林和落叶松林)开展调查，测量了两种土壤动物分解者类群(正蚓科蚯蚓和马陆)及其生境中的凋落物的十种化学元素含量，量化了分解者和凋落物之间的化学计量错配程度，并评估了化学元素错配如何影响两种分解者的密度和生物量。 研究发现，六十年油松林种植显著改变了凋落物化学元素组成，但并未显著改变两种分解者的化学元素含量。在三种森林中，蚯蚓和马陆具有明显的化学计量生态位分化，从而展示不同的元素错配模式；但两种分解者在油松林中均受到更为严重的化学计量错配程度，这种错配导致两种分解者在油松林中密度和生物量更小。整体上，在具有较低凋落物质量的油松林中，分解者维持了体内元素含量但降低了种群生物量。 本研究展示了在多维度化学计量理论框架下探究人工林种植对土壤动物种群动态影响的可行性，该理论框架可作为一种有效的工具来探究生态系统如何响应全球环境变化。.