Moisture and Saprotroph Effects on Log Decomposition Processes

凋落木的分解是促进森林生态系统生物地球化学循环和生产力的一个重要过程。由于木质凋落物可占上述生物量的22%，因此它是植物吸收营养物质和释放到大气中的二氧化碳的重要来源。然而，影响原木分解、二氧化碳和养分释放速率的因素仍然知之甚少。腐殖菌定植模式和生物多样性受水分影响，在腐殖菌分解过程中起着重要作用。这些因素的重要性还没有经过实验评估。我们的目的是评价原木含水率和腐殖酸群落发育对原木分解和矿化速率的影响。我们将验证以下假设：(1)分解过程的初始速率由昆虫的渗透深度和腐烂与非腐烂真菌的建立决定；(2)分解速率是原木含水量的函数；(3)分解速率与腐殖菌群落多样性呈正相关。我们预计，从未定植的原木到被昆虫隧道穿透的原木，再到被腐烂和/或非腐烂真菌定植的昆虫隧道，分解和矿化率将逐渐增加。这些假设将通过比较道格拉斯冷杉原木中由于破碎、呼吸和淋滤而导致的木材密度和碳/营养损失的变化来验证，这些变化包括控制水分含量和控制初始腐殖菌定植（韧皮部蛀虫与边材蛀虫，非腐烂真菌与腐烂真菌）。在分解原木中腐殖酸的建立将表明生物多样性对这一生态系统过程的功能重要性。

Decomposition of woody litter is a major process contributing to biogeochemical cycling and productivity in forested ecosystems. Because woody litter can amount to 22% of above biomass, it represents a substantial source of nutrients for plant uptake and carbon dioxide for release to the atmosphere. However, factors affecting decomposition and rate of carbon dioxide and nutrient release from logs remain poorly known. Saprotroph colonization patterns and biodiversity, as affected by moisture content, have been ascribed and important role in the decomposition process. The importance of these factors has not been evaluated experimentally. Our objective is to evaluate the influence of log moisture content and Saprotroph community development on log decomposition and mineralization rates. We will test hypothesis that (1) initial rates of decomposition processes are determined by the depth of penetration by insects and establishment of decay vs. non-decay fungi, (2) decomposition rate is a function of moisture content of logs, and (3) decomposition rate is positively related to the diversity of the saprotroph community. We expect decomposition and mineralization rates to increase incrementally from uncolonized logs to logs penetrated by insect tunnels, to insect tunnels colonized by decay and/or non-decay fungi. These hypotheses will be tested by comparing changes in wood density and carbon/nutrient losses due to fragmentation, respiration, and leaching in Douglas-fir logs with manipulated moisture content and manipulated initial saprotroph colonization (phloem borers vs. sapwood borers, non-decay fungi vs. decay fungi). Manipulation of saprotroph establishment in decomposing logs will indicate the functional importance of biodiversity to this ecosystem process.