New frontiers in forest carbon processes: novel methane dynamics, pyrogenic carbon, and restoration of highly impacted sites

森林在全球碳循环中发挥着核心作用。甲烷(CH4)占人为气候强迫的25%，森林既是CH4的重要来源，也是CH4的汇。最近的研究表明，通过树干和叶组织的甲烷排放具有重要意义，我们的实验室在受高度影响的森林土壤中发现了CH4排放的“热点”。最近的研究还表明，森林土壤中普遍存在但成片的火灾遗留热解碳(PYC)，它可以极大地促进树木的生长，并可能增强土壤CH4的氧化。目前对于将这些进程纳入全球模式或为森林管理提供信息所涉及的模式或机制方面的知识不足。我们提出了三个相互关联的项目来填补这些研究空白。(1)热解碳与森林组成、土壤温室气体通量的关系。从燃烧残留物中提取热解碳或作为生物炭添加到土壤中，可能会通过增加土壤养分和水分保持而极大地促进树木的生长，并由于增强土壤通气性而减少CH4排放。由于凋落物中单萜的抑制作用，针叶树下土壤CH4的氧化也可能减少；当地树木多样性对土壤温室气体通量的影响已被提出，但尚未在森林中进行检验。该项目将使用大型测绘的森林林中的测量数据，结合长期的生物炭添加和林分转换实验，来解决这些潜在的影响，测试PYC、被子植物丰度和当地树木多样性增加将增加当地土壤CH4氧化的假设。(2)治理森林和城市绿色基础设施中的甲烷排放热点。我们最近的研究表明，在温带森林的原木登陆处，高度退化的土壤是高土壤CH4外流的“热点”。该项目将使用观察性研究和实验来评估这种模式是否也存在于受管理的北方森林和城市绿色基础设施中，以更好地了解其中涉及的机制，并测试涉及生物炭添加、土壤接种和其他土壤处理的缓解方法。(3)新的甲烷动力学：冠层对甲烷的氧化。我们的初步测量表明，高地(排水良好)地点的树叶是一个重要的CH4汇；然而，关于物种或森林类型之间的变化机制或模式知之甚少。调查研究将检验这样一种假设，即叶片对CH4的吸收能力与“叶片经济”性状相关，甲烷营养菌对叶片的季节性定植导致可预测的季节模式和冠层CH4吸收，以及由于缺乏对甲烷的定植，城市环境下叶片对CH4的吸收减少。拟议的研究方案将有助于从根本上了解森林中的CH4动态和碳过程，还将直接开发适用于林业和城市绿色基础设施的减缓气候变化的新方法。

Forests play a central role in the global carbon cycle. Methane (CH4) accounts for >25% of anthropogenic climate forcing, with forests acting as both important CH4 sources and sinks. Recent studies suggest important fluxes through tree stems and foliar tissues, and our lab has discovered "hotspots" of CH4 efflux in highly impacted soils in managed forests. Recent studies also indicate pervasive but patchy fire-legacy pyrogenic carbon (PyC) in forest soils that can greatly increase tree growth and possibly enhance soil CH4 oxidation. There is currently insufficient knowledge on either patterns or mechanisms involved to integrate these processes into global models or to inform forest management. We propose three inter-related projects to address these research gaps. (1) RELATIONS BETWEEN PYC, FOREST COMPOSITION, AND SOIL GHG FLUX. PyC from fire residues or added to soils as biochar can potentially strongly enhance tree growth by increasing soil nutrient and water retention, and reduce CH4 emissions due to enhanced soil aeration. Soil CH4 oxidation may also be reduced beneath conifers due to inhibitory effects of monoterpenes leached from litter; effects of local tree diversity on soil GHG fluxes have been proposed but not examined in forests. This project will use measurements in a large, mapped forest stand, in conjunction with long-term biochar addition and stand conversion experiments, to address these potential effects, testing the hypotheses of that increased PyC, angiosperm abundance, and local tree diversity will increase local soil CH4 oxidation. (2) MITIGATION OF CH4 EMISSION HOTSPOTS IN MANAGED FOREST AND URBAN GREEN INFRASTRUCTURE. Our recent studies show that highly degraded soils at log landings in temperate forests are "hotspots" of high soil CH4 efflux. This project will use observational studies and experiments to assess whether this pattern also is found in managed boreal forests and urban green infrastructure, to better understand the mechanisms involved, and to test mitigation approaches involving biochar additions, soil inoculations, and other soil treatments. (3) NOVEL METHANE DYNAMICS: CH4 OXIDATION BY CANOPY FOLIAGE. Our preliminary measurements indicate that tree foliage on upland (well-drained) sites is an important CH4 sink; however, little is known concerning either mechanisms or patterns of variation among species or among forest types. Survey studies will test the hypothesis that foliar CH4 uptake capacity is correlated with "leaf economics" traits, that seasonal leaf colonization by methanotrophs results in predictable seasonal patterns and canopy stratification of CH4 uptake, and that foliar CH4 uptake is reduced in urban settings due to a lack of methanotroph colonization. The proposed research programme will contribute to fundamental understanding of CH4 dynamics and C processes in forests, and will also directly develop novel approaches to climate mitigation applicable in forestry and urban green infrastructure.