Linking fungal dynamics and functional genes to environmental factors

Sammanfattning

Decomposition is a key ecosystem function and one of the fundamental processes in freshwater ecosystems, driving nutrient cycling and energy flow within aquatic food webs. However, decomposition processes can be strongly influenced by nutrient enrichment coming from agriculture. Aquatic hyphomycetes (subgroup of aquatic fungi) are among the most important organisms driving decomposition in streams, making their response to environmental change a pivotal factor in overall ecosystem health. This study investigates whether fungal decomposition-related genes can help us understand how environmental conditions affect decomposition processes. A laboratory decomposition experiment was conducted using three species and a mixed species community grown in a mineral solution with three different N:P ratios and a carbon source of cellulose substrate for decomposition. Decomposition was assessed as cellulose mass loss, DNA abundance was quantified and qPCR was performed with primers for cellobiohydrolase (CBHI, a functional gene) to determine gene copy number. For all groups an increase in P (lower N:P ratio) resulted in an increase in mass loss (decomposition). DNA abundance was significantly positively correlated with decomposition for all the groups and increased P-levels generally resulted in higher DNA concentrations for most groups. In contrast, qPCR analysis revealed CBHI copy numbers did not differ significantly between nutrient treatments and showed no significant relationship with decomposition. The positive association between DNA abundance and decomposition within species groups indicates that molecular measurements have potential to be used as proxies for fungal activity. However, the absence of a predictable correlation between CBHI copy numbers and decomposition indicates that CBHI abundance alone cannot yet predict ecosystem functioning. Further research is needed to evaluate the applicability of aquatic fungal functional gene-based approaches for monitoring decomposition processes in freshwater ecosystems.