New frontiers in forest carbon processes: soil chars, methane emission hotspots, and high-resolution inventory

森林在全球温室气体动态中发挥着核心作用，是二氧化碳和甲烷的重要但对环境敏感的汇。本建议涉及将树木生物学与森林碳过程联系起来的新出现的研究问题，重点关注森林碳循环的两个重要和相互关联的组成部分，这些组成部分尚未得到很好的解决：土壤炭（天然炭和设计的“生物炭”）和树木对二氧化碳和甲烷土壤通量的影响，特别关注“甲烷排放热点”。******自然炭发生在大多数森林土壤中，并且越来越被认为在土壤养分和碳动态中起着关键作用，而土壤养分和碳动态已被灭火大大改变。焦炭的物理化学性质和动力学特征仍然很差，但可能因源树种、火灾强度和焦炭风化而有很大差异；自然炭与设计的“生物炭”的可比性几乎没有受到关注。建议的研究将：(1)量化温带、寒带和热带森林生态系统中自然炭的空间变异性，检验根据场地地形和水文可以预测炭的数量并影响生产力和群落组成的假设；(2)量化和实验阐明物种特异性树木对碳的反应机制；(3)研究添加木炭对森林生产力、生态系统过程和生物多样性的长期影响。******甲烷通量对于理解森林-气候反馈同样至关重要，但森林生态系统中甲烷动态的驱动因素仍然知之甚少。直到最近才有仪器能够对甲烷通量进行快速、准确的现场测量。建议的研究将：(1)量化土壤甲烷和二氧化碳外排与土壤变量和当地树木群落组成的空间变异性；(2)树木大小和树种对土壤甲烷和CO2外排的影响试验；(3)评估粗木屑和活树的甲烷排放；(4)研究与土壤炭化有关的土壤甲烷和二氧化碳流出率，验证炭化会因孔隙度增加而增加土壤氧化（从而增加甲烷净吸收量）的假设。拟议的研究将共同提供更好地管理森林以减缓气候变化所需的基础科学，特别侧重于涉及设计生物炭和增强森林甲烷汇的新方法

Forests play a central role in global greenhouse gas dynamics, constituting a critical but environmentally sensitive sink for both carbon dioxide and methane. The present proposal addresses emerging research problems that link tree biology to forest carbon processes, with a focus on two important and inter-related components of the forest carbon cycle that are poorly resolved: soil charcoals (both natural chars and designed "biochars") and effects of trees on soil fluxes of CO2 and methane, with particular attention to "methane emission hotspots". ******Natural chars occur in most forest soils, and are increasingly recognized as playing a critical role in soil nutrient and carbon dynamics that has been drastically modified by fire suppression. The physico-chemical properties and dynamics of chars remain poorly characterized, but likely vary greatly with source tree species, fire intensity, and char weathering; the comparability of natural chars to designed "biochars" has received almost no attention. The proposed studies will: (1) quantify spatial variability in natural chars in temperate, boreal, and tropical forest ecosystems, testing the hypothesis that char quantities are predictable from site topography and hydrology and influence both productivity and community composition; (2) quantify and experimentally elucidate mechanisms for species-specific tree responses to char; (3) examine long-term effects of char additions to forest productivity, ecosystem processes, and biodiversity.******Methane flux is similarly critical in understanding forest-climate feedbacks, but the drivers of methane dynamics in forest ecosystems remain poorly understood. Instrumentation has only recently become available to enable rapid, accurate field measurements of methane flux. The proposed studies will: (1) quantify spatial variability in soil methane and CO2 efflux in relation to soil variables and local tree community composition; (2) test for effects of tree size and species on soil methane and CO2 efflux; (3) assess methane emissions from coarse woody debris and live tree heartrot; (4) examine soil methane and CO2 efflux rates in relation to soil chars, testing the hypothesis that chars will increase soil oxygenation (and thus increase net methane uptake) due to increased porosity. Together the proposed studies will provide fundamental science needed to better manage forests for climate mitigation, specifically focusing on novel approaches involving designed biochars and enhancements for forest methane sinks.**