Root Inputs in Podzol Soils: Effects on Nutrient Cycling and Connections between Soil Horizons

Ehrenfeld和Parmelee在温室微观世界研究中表明，在新泽西松林的沥青松林的营养贫乏的矿物土壤中，活根刺激根际效应与根的输入量成正比，但在有机森林地面上没有这种效应。由于这一发现对森林生态系统的养分循环具有重要意义，因此需要进行实地试验。研究人员建议在田间试验中测试他们的结果，在每个土壤层的地块上进行2年的分解，N矿化率，真菌和微动物丰度以及土壤渗滤液化学，其中引入了不同数量的活根和死根。然而，在未受干扰的森林中，有机土壤和矿质土壤是连续的，并且必须存在养分连接的途径。层间的联系包括真菌生长和转运、渗滤液和根系生长，这些可能影响相邻层的养分循环速率。从一个地面层转移到另一个地面层的养分量可能因根系和动物放牧而改变。因此，Ehrenfeld和Parmelee建议进行额外的实地和微观研究，以确定哪些途径在连接视界中最重要，哪些响应变量对连接的存在敏感，以及连接如何受到根输入的影响。他们将使用重建土壤剖面的微观模型来研究源自有机层的连接如何影响矿物土壤中的养分循环速率。他们将使用杀菌剂和去除渗滤液来确定真菌和渗滤液作为联系的相对重要性，并确定土壤动物如何影响这些联系的程度。将测量与现场试验相同的响应变量。在田间，他们将量化真菌在层间的生长速率和通过真菌在层间的氮（15N）通量。它们还将确定动物对渗滤液营养物质的影响。这项研究得到了机构的大力支持。调查人员都是高素质的科研工作者。

Ehrenfeld and Parmelee have shown in greenhouse microcosm studies that live roots stimulate a rhizosphere effect proportional to the amount of root input in the nutrient-poor mineral soil of the pitch pine forests in the New Jersey Pinelands but have no such effect in the organic forest floor. Because this finding has important implications for nutrient cycling in forest ecosystems, field experimentation is required. The investigators propose to test their results in a field experiment in which decomposition, N mineralization rate, fungal and microfaunal abundance and soil leachate chemistry are followed for 2 years in plots of each soil horizon, into which varying quantities of live and dead roots are introduced. In undisturbed forests, the organic and mineral soil horizons are contiguous, however, and pathways of nutrient connection must exist. Connections between horizons include fungal growth and translocation, leachate, and root growth, and these may influence nutrient cycling rates in an adjacent horizon. Amounts of nutrient transferred from one horizon to the other may be modified by roots and by faunal grazing. Therefore, Ehrenfeld and Parmelee proposed to conduct additional field and microcosm studies to identify which pathways are most important in linking horizons, which response variables are sensitive to the presence of connections, and how the connections are affected by root inputs. They will use microcosms with reconstructed soil profiles to investigate how connections originating in organic horizon influence nutrient cycling rates in mineral soil. They will use biocides and removal of leachate to determine relative importance of fungi and leachate as connections, and to determine how soil fauna affect the magnitude of these connections. The same response variables as in the field experiment will be measured. In the field they will quantify rate of fungal growth between horizons and flux of N (15N) between horizons through fungi. They will also determine the influence of fauna on the nutrient quality of leachate. The institutional support for this research is excellent. The investigators are highly qualified productive research scientists.