Chestnut green waste composting for sustainable forest management: Microbiota dynamics and impact on plant disease control

Making compost from chestnut lignocellulosic waste is a possible sustainable management strategy for forests that employs a high-quality renewable organic resource. Characterization of the microbiota involved in composting is essential to better understand the entire process as well as the properties of the final product. Therefore, this study investigated the microbial communities involved in the composting of chestnut residues obtained from tree cleaning and pruning. The culture-independent approach taken highlighted the fact that the microbiota varied only slightly during the process, with the exception of those of the starting substrate and mature compost. The statistical analysis indicated that most of the bacterial and fungal species in the chestnut compost persisted during composting. The dominant microbial population detected during the process belonged to genera known to degrade recalcitrant lignocellulosic materials. Specifically, we identified fungal genera, such as Penicillium, Fusarium, Cladosporium, Aspergillus and Mucor, and prokaryotic species affiliated with Bacilli, Actinobacteria, Flavobacteria and γ-Proteobacteria. The suppressive properties of compost supplements for the biocontrol of Sclerotinia minor and Rhizoctonia solani were also investigated. Compared to pure substrate, the addition of compost to the peat-based growth substrates resulted in a significant reduction of disease in tomato plants of up to 70 % or 51 % in the presence of Sclerotinia minor or Rhizoctonia solani, respectively. The obtained results were related to the presence of putative bio-control agents and plant growth-promoting rhizobacteria belonging to the genera Azotobacter, Pseudomonas, Stenotrophomonas, Bacillus, Flavobacterium, Streptomyces and Actinomyces in the chestnut compost. The composting of chestnut waste may represent a sustainable agricultural practice for disposing of lignocellulosic waste by transforming it into green waste compost that can be used to improve the fitness of agricultural plants.