Soil microbes, resource availability and plant herbivory in Arctic coastal ecosystems

自然系统中碳(C)和氮(N)等基本营养物质的缺乏限制了微生物和植物的生长，从而间接影响了动物的生产力。这一点在寒冷的北极土壤中尤为明显，在潮湿的泥炭土壤中，土壤微生物分解进展缓慢，莎草是鹅的主要食物来源。然而，北极和高山土壤中微生物生物量的峰值出现在冬末，而不是在雪盖土壤的夏季。推动这些生物体生长的必要营养似乎是在冬季衰老的植物组织分解时释放出来的。耐寒微生物的积累在春季融化时急剧下降，同时土壤中可溶养分的库也减少了。植物生长的开始和夏季微生物群落的建立被认为部分依赖于这些水池和冬季微生物分解释放的营养物质。从一个微生物群落向另一个微生物群落过渡的控制以及所涉及的微生物类型知之甚少。这一建议是基于一系列田间扰动实验，旨在确定温度、养分可获得性和植物生长对冬春季边界不同微生物组活动的作用。这项研究的更广泛的意义是，北极鹅广泛以生长在这些沼泽中的莎草为食，这些饲料植物的营养供应的任何中断，与初春融化(气候变化)和植物开始生长之前融化水中营养物质的损失有关，都可能对所有营养水平的生产力产生不利影响。在一项相关的研究中，将研究莎草的模拟草食对夏季土壤微生物生长的潜在碳限制的影响。草食作用改变了植物凋落物的输入，也可能改变了根部的有机酸分泌，这些共同作用可能会改变土壤微生物的活动，其结果是土壤中生长所需的碳、氮和磷的有效性发生了变化。这些扰动和粪便输入可能会影响土壤养分动态，从而影响这些放牧系统中潜在的牧草质量和有效性。

The lack of essential nutrients, such as carbon (C), and nitrogen (N) in natural systems, limits the growth of microorganisms and plants, which indirectly affects animal productivity. This is especially evident in cold Arctic soils where soil microbial decomposition proceeds slowly in wet peaty soils in which sedges are a prime food source for geese. However, peak microbial biomass in Arctic and alpine soils is realized in late winter, not summer, in snow-covered soils. The essential nutrients to drive growth of these organisms appear to be released from the decomposition of senescent plant tissue over the winter. The build-up of cold-tolerant microorganisms declines sharply at spring thaw concurrent with declines of pools of soluble soil nutrients. The onset of plant growth and the establishment of a summer microbial community is thought to be partly dependent on these pools and nutrients released from the decomposition of the winter microbes. The controls on this transition from one microbial community to another and the type of microorganisms involved are poorly understood. This proposal is based on a series of field perturbation experiments designed to determine the roles of temperature, nutrient availability and plant growth on the activity of different groups of microorganisms at this winter-spring boundary. The wider significance of this study is that Arctic geese feed extensively on sedges growing in these marshes, and any disruption of the nutrient supply to these forage plants, associated with early incipient spring thaws (climate change) and the loss of nutrients in melt water before plant growth has started, could adversely affect the productivity of all trophic levels. In a related study, the effect of simulated herbivory of sedges on potential carbon limitation of soil microbial growth in summer will be examined. Herbivory changes plant litter input and possibly organic acid exudation from roots that together may alter soil microbial activity as a result of changes in the availability of soil carbon, nitrogen and phosphorus for growth. These perturbations and faecal inputs may be expected to affect soil nutrient dynamics and therefore the potential forage quality and availability in these grazed systems.