Radiocarbon Experiments in Boreal Forests to Assess Roles of Fungal Species in Decomposition

北方森林放射性碳实验评估真菌物种在分解中的作用

• 批准号: 0433918
• 负责人: Kathleen Treseder
• 金额: $ 26.31万
• 依托单位: University of California-Irvine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-10-01 至 2008-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0433918&HistoricalAwards=false
• 关键词: Radiocarbon; Experiments; Boreal; Forests; Assess

Decomposition of dead plant material by microbes elicits a large flux of respired CO2 from soils to the atmosphere. Respiration rates are typically challenging to predict under changing environmental conditions, potentially because multiple microbial groups, including fungi, contribute to this process. The objectives of our study are (1) to examine the potential for fungal species to perform different roles in decomposition, and (2) to incorporate these differences in large scale estimates of decomposition following forest fires and N deposition. Specifically, we will examine the hypothesis that saprotrophic fungal species differ in uptake rates of carbon sources, so that "Ruderals" quickly acquire labile compounds, while "Competitives" primarily rely upon slow, constant uptake of recalcitrant compounds. If this hypothesis is supported, it would suggest a mechanism for resource partitioning among fungal species. We also expect that contributions to decomposition by Competitives will be inhibited under greater N availability, and this reduction will be most pronounced in young fire scars, where recalcitrant substrates are abundant as woody debris. To address these goals, the proposed work encompasses three major approaches that will be based in boreal forests of Alaska. First, we will perform dual-isotope labeling of mushrooms under field conditions to examine trade-offs that may influence partitioning of substrate use among fungi. A mix of radiocarbon (14C) labeled recalcitrant substrates and 13C labeled labile substrates will be applied to the soil, and a timeline of isotope signatures of CO2 respired from mushrooms of known fungal species will be measured. The release of 14C- versus 13C-labeled CO2 will indicate the extent to which different species use recalcitrant versus labile carbon. The timing of 13CO2 respiration will indicate the rate at which different species can exploit new labile C sources. Second, we will examine natural 14C signatures of fungi to estimate the ages of compounds decomposed by individual species. We expect that Competitives will possess older C than do Ruderals, if Competitives are specializing on more recalcitrant compounds. Third, we will combine information regarding functional roles of fungal species with data derived from surveys of mushroom abundance in natural and nitrogen-fertilized areas along a fire chronosequence in Alaska, in order to estimate effects of shifts in fungal communities on carbon transformations in the soil. We expect that nitrogen additions will reduce the ability of lignocellulose degraders to decompose woody debris generated by forest fires. The intellectual merit of the proposed work includes an examination of large-scale consequences of shifts in microbial community composition under global change, potentially improving our ability to predict ecosystem responses to the environment. The broader impacts include the development of field-labeling techniques that take advantage of the sensitivity of accelerator mass spectrometry measurements of 14C in order to minimize experimental artifacts.

微生物对死植物材料的分解引起了从土壤到大气的大量呼吸二氧化碳通量。在不断变化的环境条件下预测呼吸率通常具有挑战性，这可能是因为包括真菌在内的多个微生物群有助于这一过程。我们研究的目标是（1）研究真菌物种在分解中发挥不同作用的潜力，（2）将这些差异纳入森林火灾和n沉积后分解的大规模估计中。具体而言，我们将研究以下假设：腐烂的真菌物种在碳源的摄取速率上有所不同，因此“舵”迅速获得了不稳定的化合物，而“竞争者”主要依赖于缓慢，持续不断地摄取recalcitrant剂的化合物。如果支持该假设，它将提出一种用于真菌物种资源分配的机制。我们还期望在较大的n可用性下会抑制竞争对手分解的贡献，而这种减少在年轻的消防疤痕中最为明显，在年轻的消防疤痕中，顽固的底物像木质碎片一样丰富。为了解决这些目标，拟议的工作涵盖了将基于阿拉斯加北方森林的三种主要方法。首先，我们将在田间条件下对蘑菇进行双异位标记，以检查可能影响真菌中底物使用分配的权衡。将使用放射性碳（14C）标记的顽固底物和13C标记的不稳定底物的混合物，并将测量来自已知真菌物种蘑菇的CO2呼吸的同位素特征的时间表。 14C与13C标记的二氧化碳的释放将指示不同物种使用顽固的碳与不稳定碳的程度。 13CO2呼吸的时机将表明不同物种可以利用新的不稳定C来源的速率。其次，我们将检查真菌的天然14C特征，以估计单个物种分解的化合物的年龄。我们预计，如果竞争对手专门研究更多的顽固化合物，竞争者将拥有比Ruderals更古老的C。第三，我们将结合有关真菌物种的功能作用的信息，以及来自阿拉斯加的火焰序列的天然和氮气中的蘑菇丰度调查得出的数据，以估计真菌群落转移对土壤碳转化的转变的影响。我们预计，添加氮将降低木质纤维素降解器分解森林火灾产生的木质碎片的能力。拟议工作的智力优点包括检查全球变化下微生物群落构图转变的大规模后果，从而有可能提高我们预测生态系统对环境的反应的能力。更广泛的影响包括开发现场标记技术，这些技术利用了14C的加速器质谱测量的灵敏度，以最大程度地减少实验伪像。