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.

微生物对死去的植物进行分解，从土壤中吸入大量二氧化碳到大气中。在不断变化的环境条件下，预测呼吸速率通常具有挑战性，可能是因为包括真菌在内的多种微生物群参与了这一过程。我们的研究目标是：(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沉降后分解的大规模估计中。具体来说，我们将检验腐生营养真菌物种对碳源的吸收速率不同的假设，因此“粗鲁者”迅速获得不稳定的化合物，而“竞争者”主要依赖于缓慢、持续地吸收顽固性化合物。如果这一假设得到支持，它将提出真菌物种之间资源分配的机制。我们还预计，在氮素利用率较高的情况下，竞争对手对分解的贡献将受到抑制，这种减少将在年轻的火痕中最为明显，因为那里有大量的顽固性基质，如木屑。为了实现这些目标，拟议的工作包括三种主要方法，将以阿拉斯加的北方森林为基础。首先，我们将在野外条件下对蘑菇进行双同位素标记，以检查可能影响真菌对底物使用分配的权衡。将放射性碳（14C）标记的顽固底物和13C标记的不稳定底物的混合物应用于土壤，并测量从已知真菌物种的蘑菇中呼出的二氧化碳的同位素特征的时间表。14C和13c标记的二氧化碳的释放将表明不同物种使用顽固性碳和不稳定碳的程度。13CO2呼吸的时间将表明不同物种开发新的不稳定碳源的速度。其次，我们将检查真菌的自然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顽固的化合物，那么竞争对手将比竞争对手拥有更老的C。第三，我们将真菌物种的功能作用信息与阿拉斯加沿火灾时间序列的自然和氮肥地区蘑菇丰度调查数据相结合，以估计真菌群落的变化对土壤中碳转化的影响。我们预计，添加氮将降低木质纤维素降解物分解森林火灾产生的木质碎片的能力。这项工作的智力价值包括对全球变化下微生物群落组成变化的大规模后果的检查，有可能提高我们预测生态系统对环境反应的能力。更广泛的影响包括现场标记技术的发展，利用加速器质谱测量14C的灵敏度，以尽量减少实验伪影。