NSFDEB-NERC:Tropical deadwood carbon fluxes: Improving carbon models by incorporating termites and microbes

该项目的目标是测量热带枯木(粗木质碎屑；CWD)的周转率，并确定在当前和未来气候条件下决定CWD碳(C)命运的机制。木本植物是地上最大的陆地生物碳库，CWD生物量可能很大，但估计很少。我们关于失误的大部分知识来自温带系统，在那里CWD被认为是缓慢循环的。人们对热带CWD池和周转量知之甚少，尽管活树的生物量很大。由于气候(较暖的温度和有时较多的降水)、木材结构和损失路径(白蚁的作用增加)的差异，CWD很可能在热带系统中是动态的。该项目结合了澳大利亚热带地区的现场、分子和建模方法，那里的白蚁和真菌是木材周转的关键因素。从雨林到稀树草原的连续不断的林带，加上现有的长期数据和基础设施，使其成为一个理想的地点。是什么控制着CWD C的流动率？周转率将由白蚁和真菌活动决定，这取决于气候和木材结构。更温暖和更潮湿的条件应该会增加周转率，但白蚁应该在干燥条件下增加周转率，因为它们有节水策略。高度木质化的木材应该腐烂得更慢。Q2.是什么决定了CWD的C的命运？C的命运(二氧化碳、甲烷、有机残留物)将取决于白蚁和微生物群落的腐烂阶段和功能组成。腐烂的后期，产甲烷菌的增加，甲烷氧化菌的减少，以及白蚁种类的变化，应该会导致更多的CH4：CO2。当碳通过白蚁流失时，会产生更多的有机残留物。第三季度。在气候变化下，木材周转的机制是如何影响生态系统级C通量的？澳大利亚北部的气候变暖将增加木材的周转率，改变木材的命运。到目前为止，CWD在地球系统模型中的参数化很差(例如，CWD仅通过物理碎片衰减)。第一季度和第二季度的现场数据将被用来驱动气候变化下木材周转和温室气体(GHG)产生的新预测模型。为了测试Q1并确定相对腐生微生物和白蚁对降雨量变化的响应速度，一种已知能吸引白蚁的新型基质(辐射松树)将被放置在6个地点(降雨梯度实验)。这些白蚁块将被封闭在有或没有洞控制白蚁进入的细网中；块将在雨季和旱季结束时收获4年。为了确定木材结构对腐烂的影响，将在雨林和大草原地点放置10个类似封闭的树种/地点的重复原木(普通花园实验)。原木将在两个雨季和两个旱季结束时收获。对于测井/块，将测量初始和最终质量、密度和化学成分。当地气象站将提供气候数据。为了测试Q2，将收集木材样本和木材中的白蚁，以确定白蚁群落、微生物群落和功能基因组成，以及有机残留物的形成。将测量收获的原木/块的二氧化碳和甲烷。由于一些白蚁生活在土丘中，将建立实验丘(白蚁中微体实验)，并将在一年内每月测量土丘的二氧化碳和甲烷通量。为了测试第三季度，现场数据将被纳入到WoodCLM中，这是一个从社区土地模型衍生出来的生态系统模型。修改后的模型和原始模型的结果将进行比较。使用Wood CLM，将在未来气候情景下模拟木材动力学和温室气体排放

Objectives of this project are to measure rates of tropical deadwood (coarse woody debris;CWD) turnover and identify mechanisms that determine fates of CWD carbon (C) under currentand future climates. Woody plants are the largest aboveground terrestrial biotic C store,and CWD biomass is likely substantial but poorly estimated. Much of our knowledge of turnovercomes from temperate systems, where CWD is thought to be slow cycling. Less is known abouttropical CWD pools and turnover, despite large living tree biomass. Due to differences inclimate (warmer temperatures and sometimes greater precipitation), wood construction, andloss pathways (increasing role of termites), it is likely that CWD is dynamic in tropicalsystems. This project combines field, molecular, and modeling approaches in tropical Australia,where termites and fungi are key agents of wood turnover. A continuous belt of forest fromrainforest to savanna with existing long-term data and infrastructure makes it an ideal location.Three questions will be addressed: Q1. What controls rates of CWD C turnover? Turnover rateswill be determined by termite and fungal activity, which are dependent on climate and woodconstruction. Warmer and wetter conditions should increase turnover, but termites should increaseturnover relatively more in dry conditions as they have water conservation strategies. Densehighly lignified wood should decay more slowly. Q2. What controls fates of C from CWD? C fates(CO2, CH4, organic residues) will depend on stage of decay and functional composition of termiteand microbial communities. Later stages of decay, increased methanogens, decreased methanotrophsand changes in termite species should result in greater CH4:CO2. Greater organic residue formationwill occur when C loss is via termites. Q3. How do mechanisms of wood turnover scale up toaffect ecosystem-level C fluxes under climate change? Climate warming in Northern Australiawill increase turnover rates and alter C fates of wood. To date, CWD is poorly parameterizedin Earth system models (e.g., CWD decays only via physical fragmentation). Field data fromQ1 and Q2 will be used to drive new predictive models of wood turnover and greenhouse gas(GHG) production under climate change. To test Q1 and determine relative saprobic microbeand termite decay rates in response to precipitation variation, blocks of a novel substrate(Pinus radiata) known to attract termites will be placed at 6 sites (Rainfall gradient experiment).Blocks will be enclosed in fine-mesh with or without holes manipulating termite access; blockswill be harvested at end of wet and dry seasons for 4 years. To determine influence of woodconstruction on decay, replicate logs of 10 species/site similarly enclosed will be placedat rainforest and savannah sites (Common garden experiment). Logs will be harvested at endof 2 wet and 2 dry seasons. For logs/blocks, initial and final mass, density and chemistrywill be measured. Local weather stations will provide climate data. To test Q2, wood subsamplesand termites in wood will be collected to determine termite community, microbial communityand functional gene composition, and organic residue formation. CO2 and CH4 will be measuredfor harvested logs/blocks. As some termites live in mounds, experimental mounds (Termite mesocosmexperiment) will be established and mound diel CO2 and CH4 fluxes will be measured monthlyfor 1 yr. To test Q3, field data will be incorporated into woodCLM, an ecosystem model derivedfrom the Community Land Model. Results from the modified and original models will be compared.Using woodCLM, wood dynamics and GHG emissions will be simulated under future climate scenarios