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

最大的生物碳储存库之一是在森林树木的木材中。一旦树木死亡，含有木材的碳就会被微生物和昆虫等生物消耗掉。这样的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，木质素是木材的关键组成部分。当它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了大量的碳，但人们对这些碳的最终去向知之甚少。微生物和白蚁都会消耗热带木材，但哪一种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头上茁壮成长，但白蚁可能需要较少的水分，因为它们可以隐藏在巢穴中，如果变得太干燥，就会储存水分。科学家们一直试图在环境变化的情况下模拟全球碳循环，但他们的研究尚未包括微生物和昆虫对木材的腐烂。参与这项研究的研究人员预测，这些生物对全球碳循环有着巨大的影响。试验田工作将跨越澳大利亚昆士兰从湿润的雨林到干燥的稀树草原的不同降雨量的生态系统。在这些不同的地点，研究人员将比较白蚁和微生物消耗木材的速度，以及在雨季和旱季释放的气体。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内的碳循环。这些信息将反馈给科学界，以便对全球碳循环做出更好的预测。该项目是美国、英国和澳大利亚科学家之间的国际合作，并得到了NSF国际科学与工程办公室的部分支持。此外，研讨会将把项目科学家与林业利益攸关方聚集在一起，制定防止木材中碳的腐烂和减少自然碳排放的潜在战略。该项目还将支持初级科学家的教育和培训。本项目将解决三个问题：第一季度。是什么控制着粗木屑碳周转的速度？周转率将通过测量白蚁和微生物的活动来确定，这取决于气候和木材结构。潮湿的条件应该会增加周转量，但由于白蚁的节水策略，在干燥的条件下，白蚁应该会相对更多地增加周转率。密度高、木质化程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来的碳的命运？碳的命运(二氧化碳、甲烷、土壤有机残留物)将取决于木材腐烂的阶段以及白蚁和微生物群落的组成。腐烂的后期、产甲烷古菌丰度或活性的增加(或细菌甲烷化作用的减弱)以及白蚁种类的变化应该会导致更大的甲烷/二氧化碳比率。当碳通过白蚁流失时，预计会形成更多的有机残留物。第三季度。在环境变化下，木材周转的机制是如何影响生态系统水平的碳通量的？到目前为止，粗木屑在地球系统模型中的参数化很差(例如，粗木屑被假定仅通过物理碎裂而腐烂)。第一季度和第二季度的现场数据将被用来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并确定与木材相关的微生物和白蚁对降水变化的相对衰减率，将在六个地点放置已知的吸引白蚁的松树块。大厦将被封闭在有或没有洞的细网中，以限制白蚁的进入。这些地块将在雨季和旱季结束时收获，为期四年。为了确定木材结构对腐烂的影响，将在雨林和稀树草原放置10个物种/地点的重复原木。原木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，将收集木材亚样和木材中的白蚁，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。将对收获的原木/块进行二氧化碳和甲烷的测量。由于一些白蚁生活在土丘巢穴中，将建立实验丘，并在为期一年的实验中测量二氧化碳和甲烷的通量。为了测试第三季度，现场数据将被纳入WoodCLM，这是一个从社区土地模型派生的生态系统模型。修改后的模型和原始模型的结果将进行比较。使用Wood CLM，将在这些地点未来的环境情景下模拟木材动力学和气体排放。该项目将包括研究生和博士后水平的培训，是由英国自然环境研究理事会(NERC)资助的与英国科学家的国际合作努力的一部分。

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).