Microbial indicators as innovative methods to assess the performance of woody crops in soil organic carbon sequestration and natural resource valorisation

Abstract

Molecular techniques for studying soil microorganisms allow to quantify the presence of specific functional groups from the total soil DNA and thus to assess their dynamic in response to the land use. Using this approach, a study was carried out to assess the increase the soil organic carbon (C) of arable land in the central Po Valley with three woody species (white willow, black locust, hybrid poplar) in short rotation forestry. Being fungi the most involved microorganisms in the C-cycle and representing the larger part of microbial biomass in volume, total fungi e the two most widespread main fungal degraders in the upper soil layer (Ascomycetes and Basidiomycetes) were used as indicators of the effectiveness of land use in increasing soil organic C. An innovative molecular technique (SYBR® Green I dye on the QuantStudio™ 3D digital PCR system) which allows to overcome the critical issues associated with the relatively low concentration of fungal DNA compared to that of bacteria was used. Compared to the ploughed soil, total organic carbon (TOC), microbial biomass and enzyme activities increased significantly in the woody plantations. However, TOC increased to different degrees among the woody species. White willow and black locust showed a greater increase in soil TOC than arable (+30 and 20% respectively), followed by hybrid poplar with a smaller increase of +12%. The increases in soil TOC in the three plantations were not correlated with the total woody mass, assessed 15 years after abandonment. Total fungi and Ascomycetes were highly correlated with microbial biomass and TOC, while Basidiomycetes were not. Ascomycetes, which commonly prevail in agricultural soils, were still the most abundant even after a short rotation forest cycle of 15 years and can be taken as good indicator of C sequestration activities into the soil. Soil tillage strongly reduced the content of Basidiomycetes and short rotation forestry managed to increase it at least 4-5 times over a 15-year cycle of short rotation forestry, suggesting that it can act as a qualitative indicator of C sequestration. Since Basidiomycetes have different biological and morphological characteristics than Ascomycetes, combining them (i.e., as Ascomicetes:Basidiomycetes ratio) seems to be a good option for choosing the most suitable woody species for carbon accumulation in agricultural soils.

Keywords

• soil fungi
• ascomycetes
• basidiomycetes
• short rotation forestry
• hybrid populus (populus × canadensis)
• white willow (salix alba l.)
• black locust (robinia pseudoacacia l.)