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首页> 外文学位 >Soil nitrogen cycling and ectomycorrhizal community composition following disturbance in Michigan jack pine forests.
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Soil nitrogen cycling and ectomycorrhizal community composition following disturbance in Michigan jack pine forests.

机译：密歇根杰克松林扰动后土壤氮循环和外生菌根群落组成。

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Disturbance events, such as wildfire or clearcutting, exert profound influence over the structure, composition and functioning of forest ecosystems. Since nitrogen (N) is generally considered the nutrient most limiting for plant growth in boreal and cold temperate forests, it is critical to understand how disturbances may alter soil N availability and how plants subsequently access that N. In this dissertation, I utilized the jack pine (Pinus banksiana) ecosystem of northern Michigan to ask three fundamental questions regarding the effects of disturbance: (1) do the initial recoveries of soil carbon (C) and N pools and dynamics differ following wildfire vs. clearcutting harvesting?; (2) how do available forms of organic and mineral soil N change over time following wildfire?; and, (3) how does community composition of ectomycorrhizal fungi on jack pine roots change following disturbance?;Clearcutting is replacing wildfire as the major disturbance in many forest types, but the implications for soil C and N cycling are little understood. In chapter 3, I compared the initial recovery of C and N pools and dynamics in clearcut, wildfire-burned stands, and intact jack pine stands. Amongst other findings, I observed higher potential nitrification in the clearcut vs. wildfire-burned stands, due to differences in microbial gross nitrate consumption rates. Since the production of nitrate can lead to leaching losses of N and base cations, this finding has potential implications for the recovery of these forests following clearcutting.;Secondly, studies of successional changes in soil N availability have almost exclusively focused on minerai N; yet, plants can take up forms of organic N, such as amino acids, at biologically important rates. In Chapter 4, I investigated changes in amino acid- and minerai N availability along a ten-site chronosequence of jack pine stands, varying in age from 4 to 60 y post-wildfire. Overall, my results suggest that heterotrophic consumption, not production via proteolysis, controls soil amino acid availability. Moreover, since I found that amino acid N exceeds mineral N in a time period where jack pine growth rates and N demand are highest, I speculate that amino acid N may be important to the N economy of these forests.;Lastly, symbioses between host plants and mycorrhizal fungi can enhance rates of amino acid uptake and allow plants to access complex organic N forms. In Chapter 5, I investigated changes in the belowground community composition of ectomycorrhizal fungi (EMF) using molecular methods along a six-site chronosequence of jack-pine dominated stands (5, 11, 19, 23, 47 and 56 y post-wildfire). Overall, the results of this chapter show that EMF community composition can shift dramatically within the first decades of forest stand development. This compositional shift was primarily driven by higher relative abundances of Rhizopogon and Thelephora taxa in sites age 5 and 11, and increases in Cortinarius in older stands. Since EMF taxa can vary in ability to access N for their plant host, this shift in community may have implications for jack pine nutrition over stand development.
机译：野火或砍伐等干扰事件对森林生态系统的结构，组成和功能产生了深远的影响。由于氮（N）通常被认为是寒带和寒温带森林中植物生长的最主要养分，因此了解干扰如何改变土壤氮素的有效性以及植物随后如何吸收氮素是至关重要的。密歇根州北部的松树（Pinus bankiana）生态系统问三个基本问题：扰动的影响：（1）野火与清除伐木后土壤碳（C）和氮库的初始回收率和动态变化是否不同？ （2）野火后，有机态和矿质氮的有效形态如何随时间变化？ （3）干扰后，千斤顶松树根上的外生菌根真菌的群落组成如何变化？；在许多森林类型中，以砍伐森林代替野火是主要的干扰，但是对土壤碳和氮循环的影响知之甚少。在第3章中，我比较了C和N池的初始恢复以及在明晰，野火燃烧的林分和完整的千斤顶松林中的动态变化。在其他发现中，由于微生物总硝酸盐消耗速率的差异，我观察到与野火燃烧的林分相比，在林分截割的林地中潜在的硝化作用更高。由于硝酸盐的产生会导致氮和碱阳离子的淋失，因此这一发现对砍伐后这些森林的恢复具有潜在的影响。第二，土壤氮素有效性的连续变化研究几乎完全集中在矿井氮上。但是，植物可以以生物学上重要的速率吸收有机氮的形式，例如氨基酸。在第4章中，我研究了野火后4到60 y年龄的千斤顶松树林沿十个位点的时间序列氨基酸和矿物质氮的利用率变化。总的来说，我的结果表明，异养消耗而不是通过蛋白水解生产，可控制土壤氨基酸的利用率。此外，由于我发现在顶生松生长速率和氮需求最高的时期内，氨基酸N超过矿物N，因此我推测氨基酸N可能对这些森林的N经济很重要；最后，寄主之间的共生关系植物和菌根真菌可以提高氨基酸吸收率，并使植物获得复杂的有机氮形式。在第5章中，我使用分子方法研究了以杰克松为主的林分（野火后5、11、19、23、47和56）的六个位点的时间顺序，研究了外生菌根真菌（EMF）地下群落组成的变化。 。总体而言，本章的结果表明，EMF社区组成在林分发展的头几十年内会发生巨大变化。这种成分的变化主要是由5和11岁时的根际植物和根瘤菌类的相对丰度较高，以及较老林分的Cortinarius含量增加所致。由于EMF分类单元在其植物寄主中获取N的能力可能会有所不同，因此群落的这种转变可能会影响林分发育过程中的杰克松营养。

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