Fungal community dynamics and driving factors during agricultural waste composting.

This study was conducted to identify the driving factors behind fungal community dynamics during agricultural waste composting. Fungal community abundance and structure were determined by quantitative PCR and denaturing gradient gel electrophoresis analysis combined with DNA sequencing. The effects of physico-chemical parameters on fungal community abundance and structure were evaluated by least significant difference tests and redundancy analysis. The results showed that Cladosporium bruhnei, Hanseniaspora uvarum, Scytalidium thermophilum, Tilletiopsis penniseti, and Coprinopsis altramentaria were prominent during the composting process. The greatest variation in the distribution of fungal community structure was statistically explained by pile temperature and total organic carbon (TOC) (P < 0.05). A significant amount of the variation (74.6 %) was explained by these two parameters alone. Fungal community abundance was found to be significantly related to pH, while pH was significantly influenced by pile temperature and nitrate levels (P < 0.05), and these parameters were found to be the most likely to influence or be influenced by the fungal community during composting.

Variation in antibiosis ability, against potato pathogens, of bacterial communities recovered from the endo- and exoroots of potato crops produced under conventional versus minimum tillage systems.

The culturable component of bacterial communities found in the endoroot and associated exoroot (root zone soil) was examined in potatoes (Solanum tuberosum L.) grown under either conventional or minimum tillage systems. Bacterial species--abundance relationships were determined and in vitro antibiosis ability investigated to discover whether tillage practice or bacteria source (endo- or exoroot) influenced bacterial community structure and functional versatility. Antibiosis abilities against Phytophthora erythroseptica Pethyb. (causal agent of pink rot of potatoes), Streptomyces scabies (Thaxt.) Waksm. and Henrici) (causal agent of potato common scab), and Fusarium oxysporum Schlecht. Emend. Snyder and Hansen (causal agent of fusarium potato wilt) were selected as indicators of functional versatility. Bacterial community species richness and diversity indices were significantly greater (P = 0.001) in the exoroot than in the endoroot. While both endo- and exoroot communities possessed antibiosis ability against the phytopathogens tested, a significantly greater proportion (P = 0.0001) of the endoroot population demonstrated antibiosis ability than its exoroot counterpart against P. erythroseptica and F. oxysporum. Tillage regime had no significant influence on species-abundance relationships in the endo- or exoroot but did influence the relative antibiosis ability of bacteria in in vitro challenges against S. scabies, where bacteria sourced from minimum tillage systems were more likely to have antibiosis ability (P = 0.0151). We postulate that the difference in the frequency of isolates with antibiosis ability among endoroot versus exoroot populations points to the adaptation of endophytic bacterial communities that favour plant host defence against pathogens that attack the host systemically.