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

最大的生物碳库之一是森林树木的木材。一旦树木死亡，含有木材的碳就会被微生物和昆虫等生物体消耗。这种碳可以作为二氧化碳或甲烷气体排放到大气中。此外，只有一些微生物可以分解木质素，这是木材的关键组成部分。当他们无法做到这一点时，剩余的木质素就会被锁在土壤中。热带地区的树木中储存着大量的碳，但人们对这些碳的最终去向知之甚少。微生物和白蚁都消耗热带木材，但哪一种起作用会改变碳释放的速度和形式。通常情况下，微生物需要大量的水分才能在木材上茁壮成长，但白蚁可能需要更少的水分，因为它们可以躲在巢土丘中，如果太干燥，它们可以储存水分。科学家们一直在试图模拟环境变化下的全球碳循环，但他们尚未将微生物和昆虫对木材的腐蚀纳入研究。这项研究的研究人员预测，这些生物对全球碳循环产生巨大影响。这项实地试验工作将跨越澳大利亚昆士兰州降雨量不同的生态系统，从潮湿的雨林到干燥的稀树草原。在这些不同的地点，研究人员将比较白蚁与微生物消耗木材的速度以及在潮湿和干燥季节释放的气体。研究结果将被纳入计算机模型，以确定白蚁和微生物如何影响区域到全球范围的碳循环。这些信息将反馈给科学界，以便更好地预测全球碳循环。这个项目是美国科学家之间的国际合作，英国该项目得到了美国国家科学基金会国际科学与工程办公室的部分支持。此外，研讨会将汇集项目科学家与林业利益相关者，以制定潜在的战略，防止木材中的碳腐烂，减少自然碳排放。该项目还将支持对青年科学家的教育和培训。本项目将解决三个问题：Q1。是什么控制了粗木屑的碳周转率？周转率将通过测量白蚁和微生物活动来确定，这取决于气候和木结构。潮湿的条件下，应增加营业额，但白蚁应增加营业额相对更多的干燥条件下，由于他们的水资源保护策略。密度大、木质度高的木材应该腐烂得更慢。Q2.是什么控制着从粗木屑中释放出的碳的命运？碳命运（二氧化碳，甲烷，土壤有机残留物）将取决于木材腐烂的阶段和白蚁和微生物群落的组成。腐烂的后期阶段，产甲烷古菌的丰度或活性增加（或细菌嗜甲烷性降低）以及白蚁物种的变化应导致更大的甲烷/二氧化碳比率。更大的有机残留物的形成，预计发生时，碳损失是通过白蚁。Q3.在环境变化下，木材周转机制如何影响生态系统水平的碳通量？到目前为止，粗木屑在地球系统模型中的参数化程度很低（例如，假定粗木碎片仅通过物理破碎而腐烂）。第一季度和第二季度的现场数据将用于驱动环境变化下木材周转和气体排放的新预测模型。为了测试Q1，并确定相对木材相关的微生物和白蚁腐烂率，以应对降水量的变化，松树块已知吸引白蚁将被放置在六个网站。块将封闭在细网或没有孔，以限制白蚁进入。在四年的雨季和旱季结束时，将收获这些石块。为了确定木结构对腐烂的影响，将在雨林和萨凡纳地点放置10个物种/地点的复制日志。甘蔗将在雨季和旱季结束时收获。对于原木/块，将测量初始和最终质量、密度和化学成分。为了测试Q2，将收集木材子样品和木材中的白蚁，以确定白蚁群落、微生物群落和腐烂基因组成以及有机残留物的形成。将对采伐的原木/块测量二氧化碳和甲烷。由于一些白蚁生活在土墩巢中，因此将建立实验土丘，并在为期一年的实验中测量土丘中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woodCLM，这是一个来自社区土地模型的生态系统模型。将比较修改后的模型和原始模型的结果。使用woodCLM，木材动态和气体排放将模拟未来的环境情景下的网站。 该项目将包括在研究生和博士后一级的培训，是与英国科学家进行的国际合作努力的一部分，由联合王国自然环境研究理事会资助。

One of the largest biological reservoirs of carbon is in the wood of forest trees. Once trees die, wood-containing carbon is consumed by organisms such as microbes and insects. Such carbon can be emitted into the atmosphere as carbon dioxide or methane gas. Additionally, only some microbes can break down lignin, a critical building block of wood. When they are unable to do so, remaining lignin gets locked in soil. The tropics have vast stores of carbon in trees but little is known about where that carbon ends up. Both microbes and termites consume tropical wood, but which one does the job alters how fast and in what form carbon is released. Typically, microbes need lots of moisture to thrive on wood, but termites may require less since they can hide in their nest mounds and store water if it becomes too dry. Scientists have been trying to model global carbon cycling under environmental change, but they have yet to include the decay of wood by microbes and insects in their studies. The researchers on this study predict that these organisms have an enormous impact on global carbon cycling. The experimental field work will cut across ecosystems with varying rainfall in Queensland, Australia, from wet rainforest to dry savanna. At these different sites, the researchers will compare how fast termites versus microbes consume the wood and what gases are released during wet and dry seasons. The results will be incorporated into computer models to determine how termites and microbes affect carbon cycling at regional to global scales. Such information will be fed back to the scientific community to make better predictions about the global carbon cycle. This project is an international collaboration between scientists in the U.S., the U.K. and Australia, and is supported, in part, by the NSF Office of International Science and Engineering. Additionally, workshops will bring together project scientists with forestry stakeholders to develop potential strategies for preventing the decay of carbon in wood, and reducing natural carbon emissions. The project will also support education and training of junior scientists. Three questions will be addressed in this project: Q1. What controls rates of coarse wood debris carbon turnover? Turnover rates will be determined by measuring termite and microbe activity, which are dependent on climate and wood construction. Wetter conditions should increase turnover, but termites should increase turnover relatively more in dry conditions due to their water conservation strategies. Dense, highly lignified wood should decay more slowly. Q2. What controls fates of carbon liberated from coarse wood debris? Carbon fates (carbon dioxide, methane, soil organic residues) will depend on the stage of wood decay and the composition of termite and microbial communities. Later stages of decay, increased abundance or activity of methanogenic archaea, (or decreased bacterial methanotropy) and changes in termite species should result in greater methane/carbon dioxide ratios. Greater organic residue formation is predicted to occur when carbon loss is via termites. Q3. How do mechanisms of wood turnover scale up to affect ecosystem-level carbon fluxes under environmental change? To date, coarse wood debris is poorly parameterized in Earth system models (e.g., coarse wood debris is assumed to decay only via physical fragmentation). Field data from Q1 and Q2 will be used to drive new predictive models of wood turnover and gas emission under environmental change. To test Q1 and determine relative wood-associated microbe and termite decay rates in response to precipitation variation, blocks of pine known to attract termites will be placed at six sites. Blocks will be enclosed in fine-mesh with or without holes to limit termite access. Blocks will be harvested at the end of wet and dry seasons for four years. To determine the influence of wood construction on decay, replicate logs of ten species/site will be placed at rainforest and savannah sites. Logs will be harvested at the end of wet and dry seasons. For logs/blocks, initial and final mass, density and chemistry will be measured. To test Q2, wood subsamples and termites in wood will be collected to determine termite community, microbial community and decay gene composition, and organic residue formation. Carbon dioxide and methane will be measured for harvested logs/blocks. As some termites live in mound nests, experimental mounds will be established and carbon dioxide and methane fluxes will be measured in mounds in a one-year experiment. To test Q3, field data will be incorporated into woodCLM, an ecosystem model derived from the Community Land Model. Results from the modified and original models will be compared. Using woodCLM, wood dynamics and gas emissions will be simulated under future environmental scenarios at the sites. The project will include training at the graduate student and postdoctoral levels, and is part of an international collaborative effort with scientists in England funded by the United Kingdom's Natural Environment Research Council (NERC).