River Ecosystems Laboratory, Alpine and Polar Environmental Research Center, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
Systems Ecology Research Group, Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg.
Glob Chang Biol. 2022 Jun;28(12):3846-3859. doi: 10.1111/gcb.16169. Epub 2022 Apr 1.
The shrinking of glaciers is among the most iconic consequences of climate change. Despite this, the downstream consequences for ecosystem processes and related microbiome structure and function remain poorly understood. Here, using a space-for-time substitution approach across 101 glacier-fed streams (GFSs) from six major regions worldwide, we investigated how glacier shrinkage is likely to impact the organic matter (OM) decomposition rates of benthic biofilms. To do this, we measured the activities of five common extracellular enzymes and estimated decomposition rates by using enzyme allocation equations based on stoichiometry. We found decomposition rates to average 0.0129 (% d ), and that decreases in glacier influence (estimated by percent glacier catchment coverage, turbidity, and a glacier index) accelerates decomposition rates. To explore mechanisms behind these relationships, we further compared decomposition rates with biofilm and stream water characteristics. We found that chlorophyll-a, temperature, and stream water N:P together explained 61% of the variability in decomposition. Algal biomass, which is also increasing with glacier shrinkage, showed a particularly strong relationship with decomposition, likely indicating their importance in contributing labile organic compounds to these carbon-poor habitats. We also found high relative abundances of chytrid fungi in GFS sediments, which putatively parasitize these algae, promoting decomposition through a fungal shunt. Exploring the biofilm microbiome, we then sought to identify bacterial phylogenetic clades significantly associated with decomposition, and found numerous positively (e.g., Saprospiraceae) and negatively (e.g., Nitrospira) related clades. Lastly, using metagenomics, we found evidence of different bacterial classes possessing different proportions of EEA-encoding genes, potentially informing some of the microbial associations with decomposition rates. Our results, therefore, present new mechanistic insights into OM decomposition in GFSs by demonstrating that an algal-based "green food web" is likely to increase in importance in the future and will promote important biogeochemical shifts in these streams as glaciers vanish.
冰川退缩是气候变化最具标志性的后果之一。尽管如此，生态系统过程及其相关微生物组结构和功能的下游后果仍知之甚少。在这里，我们使用跨全球六个主要地区的 101 个冰川补给溪流（GFS）的空间替代时间的方法，研究了冰川退缩如何影响底栖生物膜的有机物质（OM）分解率。为此，我们测量了五种常见胞外酶的活性，并使用基于化学计量学的酶分配方程来估计分解率。我们发现分解率平均为 0.0129（% d），冰川影响（通过冰川流域覆盖率、浊度和冰川指数来估计）的降低会加速分解率。为了探索这些关系背后的机制，我们进一步将分解率与生物膜和溪流特性进行了比较。我们发现叶绿素-a、温度和溪流水中的 N:P 共同解释了分解率变化的 61%。与冰川退缩一起增加的藻类生物量与分解率显示出特别强的关系，这可能表明它们在为这些贫碳生境提供易分解的有机化合物方面的重要性。我们还发现 GFS 沉积物中有大量的壶菌真菌，它们可能会寄生这些藻类，通过真菌分流促进分解。在探索生物膜微生物组时，我们试图确定与分解率显著相关的细菌系统发育群，发现了许多与分解率正相关（例如，Saprospiraceae）和负相关（例如，Nitrospira）的群。最后，我们使用宏基因组学发现了具有不同比例 EEA 编码基因的不同细菌类别的证据，这可能为某些与分解率相关的微生物关联提供了信息。因此，我们的研究结果通过证明基于藻类的“绿色食物网”在未来可能变得更加重要，并将促进这些溪流中重要的生物地球化学变化，从而为 GFS 中的 OM 分解提供了新的机制见解，随着冰川的消失。
