Search for: All records

ABSTRACT Microbial necromass contributes significantly to both soil carbon (C) persistence and ecosystem nitrogen (N) availability, but quantitative estimates of C and N movement from necromass into soils and decomposer communities are lacking. Additionally, while melanin is known to slow fungal necromass decomposition, how it influences microbial C and N acquisition as well as elemental release into soils remains unclear. Here, we tracked decomposition of isotopically labeled low and high melanin fungal necromass and measured¹³C and¹⁵N accumulation in surrounding soils and microbial communities over 77 d in a temperate forest in Minnesota, USA. Mass loss was significantly higher from low melanin necromass, corresponding with greater¹³C and¹⁵N soil inputs. A taxonomically and functionally diverse array of bacteria and fungi was enriched in¹³C and/or¹⁵N at all sampling points, with enrichment being consistently higher on low melanin necromass and earlier in decomposition. Similar patterns of preferential C and N enrichment of many bacterial and fungal genera early in decomposition suggest that both microbial groups co-contribute to the rapid assimilation of resource-rich soil organic matter inputs. While overall richness of taxa enriched in C was higher than in N for both bacteria and fungi, there was a significant positive relationship between C and N in co-enriched taxa. Collectively, our results demonstrate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate but also necromass C and N release and that both elements are rapidly co-utilized by diverse bacterial and fungal decomposers in natural settings. IMPORTANCERecent studies indicate that microbial dead cells, particularly those of fungi, play an important role in long-term carbon persistence in soils. Despite this growing recognition, how the resources within dead fungal cells (also known as fungal necromass) move into decomposer communities and soils are poorly quantified, particularly in studies based in natural environments. In this study, we found that the contribution of fungal necromass to soil carbon and nitrogen availability was slowed by the amount of melanin present in fungal cell walls. Further, despite the overall rapid acquisition of carbon and nitrogen from necromass by a diverse range of both bacteria and fungi, melanization also slowed microbial uptake of both elements. Collectively, our results indicate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate, but also necromass carbon and nitrogen release into soil as well as microbial resource acquisition. 

Abstract Microbial necromass is increasingly recognized as an important fast‐cycling component of the long‐term carbon present in soils. To better understand how fungi and bacteria individually contribute to the decomposition of fungal necromass, three particle sizes (>500, 250–500, and <250 μm) ofHyaloscypha bicolornecromass were incubated in laboratory microcosms inoculated with individual strains of two fungi and two bacteria. Decomposition was assessed after 15 and 28 days via necromass loss, microbial respiration, and changes in necromass pH, water content, and chemistry. To examine how fungal–bacterial interactions impact microbial growth on necromass, single and paired cultures of bacteria and fungi were grown in microplates containing necromass‐infused media. Microbial growth was measured after 5 days through quantitative PCR. Regardless of particle size, necromass colonized by fungi had higher mass loss and respiration than both bacteria and uninoculated controls. Fungal colonization increased necromass pH, water content, and altered chemistry, while necromass colonized by bacteria remained mostly unaltered. Bacteria grew significantly more when co‐cultured with a fungus, while fungal growth was not significantly affected by bacteria. Collectively, our results suggest that fungi act as key early decomposers of fungal necromass and that bacteria may require the presence of fungi to actively participate in necromass decomposition. 

Purpose A better knowledge of how deadwood decomposes is critical for accurately characterizing carbon and nutrient cycling in forests. Fungi dominate this decomposition process, but we still have limited understanding of fungal community structuring that ultimately controls the fate of wood decomposition. This is particularly true in tropical ecosystems. To address this knowledge gap, our study capitalized on an extreme storm event that caused a large and synchronized input of deadwood to the forest floor. Methods Here we report data for the first year of wood decomposition of trees in a Puerto Rican dry forest for nine tree species that were snapped by Hurricane Maria in 2017. We measured wood properties and the associated fungal communities after 12 months of decomposition and compared them with initial wood properties and stem-inhabiting fungal communities to identify the best predictors of wood decomposition rates and chemical changes. Results Changes in wood chemistry were primarily explained by rapid xylan losses, the main hemicellulose component for the studied tree species. Fungal communities were dominated by saprotrophic and plant pathogenic fungi and showed moderate changes over time. The initial relative abundances and ratios of different fungal functional guilds were significant predictors of both xylan and glucan losses, with plant pathogenic fungi accelerating cellulose and hemicellulose decomposition rates compared to saprotrophs. Conclusion Our results confirm that fungi present at the time of treefall are strong drivers of wood decomposition and suggest that plant pathogenic fungi might act as efficient early decomposers of hemicellulose in dry tropical forests.