Experimental Analysis of Interactions Among Saprotrophic Fungi from A Phosphorous-Poor Desert Oasis in the Chihuahuan Desert

Fungal ecological interactions play a key role in structuring community assemblages. These associations may involve both antagonistic and synergistic relationships, which are commonly influenced by abiotic factors such as nutrient conditions. However, information for extreme, oligotrophic systems remain poor. Herein, interactions among key members of the aquatic transient fungal community (<i>Aspergillus niger</i>, <i>Cladosporium</i> sp., and <i>Coprinellus micaceus</i>) of a low-nutrient freshwater system in the Cuatro Ciénegas Basin, Mexico were studied. Pairwise interaction bioassays were explored <i>in vitro</i> under different nutrient conditions, including carbohydrates-rich, carbohydrates and amino peptides-rich, and low nutrients. Our results indicated that antagonistic patterns prevail among the studied taxa. However, nutrient-dependent changes were observed in <i>Cladosporium</i> sp. shifting to synergy under carbohydrates-rich conditions, suggesting changes in the fungal community composition as a result of nutrient enrichment. Remarkably, our findings contrast with previous work demonstrating mainly synergistic interactions between our tested fungal isolates and co-occurring autochthonous bacteria (<i>Aeromonas</i> spp. and <i>Vibrio</i> sp.) under low-nutrient conditions. This observation may indicate that bacteria and fungi exhibit distinct community-level responses, driven by nutrient conditions. This contributes to the knowledge of fungal community dynamics and interspecific interactions in an oligotrophic ecosystem, highlighting the relevance of nutrient-based shifts and antagonistic interactions in ecosystem dynamics.

真菌生态互作在群落构建过程中发挥关键作用。这类关联既包含拮抗（antagonistic）与协同（synergistic）两种关系，且通常受养分条件等非生物因子调控。然而，目前针对极端寡营养（oligotrophic）生态系统的相关研究仍较为匮乏。本研究以墨西哥夸特罗西亚内加斯盆地一处低养分淡水生态系统中的水生暂驻真菌群落关键类群——黑曲霉（*Aspergillus niger*）、枝孢霉属（*Cladosporium* sp.）和粪生鬼伞（*Coprinellus micaceus*）为研究对象，解析其种间互作关系。研究在体外（in vitro）条件下，于三种不同养分梯度中开展两两互作生物测定：高碳水化合物条件、高碳水化合物与氨基肽复合条件以及低养分条件。研究结果显示，受试真菌类群间普遍呈现拮抗互作模式。但枝孢霉属（*Cladosporium* sp.）的互作模式随养分条件发生显著改变：在高碳水化合物条件下其互作模式转为协同，这表明养分富集会改变真菌群落组成结构。值得注意的是，本研究结果与此前的研究结论存在显著差异：此前研究显示，在低养分条件下，本研究用到的真菌分离株与共存的土著细菌——气单胞菌属（*Aeromonas* spp.）和弧菌属（*Vibrio* sp.）——之间主要呈现协同互作。这一现象表明，细菌和真菌的群落级响应存在显著差异，且该差异由养分条件主导。本研究成果丰富了寡营养生态系统中真菌群落动态及种间互作的相关认知，同时凸显了养分驱动的互作模式转变与拮抗互作在生态系统动态中的重要性。