Decomposition of black pine (Pinus nigra J. F. Arnold) deadwood and its impact on forest soil components

Deadwood decomposition is a complex and dynamic process with large implications for biogeochemical cycling of carbon (C) and nitrogen (N) in forest soil and litter. Moreover, it affects functional and structural diversity of fungal and bacterial communities in these components. Mesocosms with deadwood blocks at progressive decay classes were set in a black pine forest and incubated for 28 months in the field with the aim to assess the impact of deadwood decomposition on i) CO2, CH4 and N2O fluxes; ii) C and N pools and allocation among deadwood, litter and soil; iii) the fungal and bacterial structural diversity and activity. CO2, CH4 and N2O fluxes from deadwood were monitored throughout the field incubation; deadwood biomass loss and decay rate for each decay class were calculated. The stock of C and N, enzyme activities, fungal and bacterial communities in deadwood, litter fractions (fresh, fragmented and humified) and soil at two depths were measured. Emissions of CO2 and CH4 increased over the deadwood decomposition advancement and the decay reached the maximum rates in the last decomposition classes. N2O fluxes were low and showed either production (prevalent in the first year) or consumption. Independent of the decay class, 20% of C stored in deadwood was lost as CO2 in the atmosphere, whereas 32% was transferred to the fragmented and humified litter fractions in the last decay class. A corresponding increase of cellulose and hemicellulose degrading enzymes was found in deadwood, also favored by substrates accessibility through fragmentation and successional changes in fungal and bacterial communities. Deadwood, litter fractions and soil components were clearly distinguished in terms of chemical and microbiological properties and activities. Fragmented and humified litter fractions were the only components responsive to the advanced stage of deadwood decomposition, being directly affected by the physical redistribution of fragmented organic matter. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Deadwood decomposition plays a significant role in the biogeochemical cycling of carbon and nitrogen in forest soil and litter, impacting the diversity and activity of fungal and bacterial communities. During the decomposition process, CO2 and CH4 emissions increase, while N2O fluxes remain low. A portion of the carbon stored in deadwood is lost as CO2 to the atmosphere, with some transferred to fragmented and humified litter fractions.