Abstract
The assessment of microbial functional diversity is an important indicator of soil quality. Different methodological approaches are currently used; among them are enzyme activities (EA) and CLPP (community level physiological profile) techniques (e.g. MicroResp™, MR). The aims of the study were: i) to assess the efficacy of both methods in capturing differences among various land use categories when different levels of selected explanatory variables such as, total organic carbon (TOC) and pH are considered, and ii) to explore, through a quantile regression approach, the possible relationships between each of the two methods with land use category, TOC and pH. The Shannon diversity index (H’), calculated from EA and MR data, was chosen as a synthetic index deriving from the same mathematical model. The quantile regression model (QRM), the Kruskal-Wallis and Spearman rank correlation tests were performed.Enzyme activities and MicroResp were reliable ecological indicators to assess soil microbial functional diversity. No correlation was found between the diversity indexes, H’EA and H’MR; it was therefore supposed that the two methods may target complementary components of microbial functional diversity. Both methods were effective in capturing differences among various land use categories, in particular H’MR in soils with low TOC content (<1.5%). Moreover, the QRM approach allowed a more detailed analysis along the distribution of the diversity indexes (H’EA and H’MR) indicating that H’EA was more dependent on the selected variables.
Highlights
The links between ecosystem functioning and levels of soil biodiversity have been the focus of the recent scientific literature (DelgadoBaquerizo et al, 2016; Creamer et al, 2016b; Griffiths et al, 2016; Nannipieri et al, 2003)
While both of them failed to discriminate in alkaline soils, only MicroResp was completely effective along the whole total organic carbon (TOC) gradient, including low TOC values (< 1.5%)
In studies aimed to evaluate the effect of land use change on microbial functional diversity, the community level physiological profile (CLPP)-MicroResp approach can be suggested as soil microbial catabolic evenness among various land-uses is usually related to differences in organic C pools (Degens et al, 2000)
Summary
The links between ecosystem functioning and levels of soil biodiversity have been the focus of the recent scientific literature (DelgadoBaquerizo et al, 2016; Creamer et al, 2016b; Griffiths et al, 2016; Nannipieri et al, 2003). Adhikari and Hartemink (2016) claimed for new insights into soil microbial diversity and their role in soil functional variability. Since up to 80/90% of soil functions, from humification to mineralization, is microbially-mediated, the diversification of soil microrganisms in terms of structure and/ or activity is essential to maintain functioning of terrestrial ecosystems (Pereira Silva et al, 2013). Emmerling et al (2002) and Wellington et al (2003) report that if microbial genetic diversity assesses a latent diversity, which may not be expressed, functional diversity is related to the actual activities resulting from that potential so that “functional rather than taxonomic diversity may provide greater insight to microbial roles in ecosystems” (Zak et al, 1994) Microbial functional diversity is defined as “the sum of the ecological processes, and/or capacity to use different substrates developed by the organisms of a community” (Insam et al, 1989). Emmerling et al (2002) and Wellington et al (2003) report that if microbial genetic diversity assesses a latent diversity, which may not be expressed, functional diversity is related to the actual activities resulting from that potential so that “functional rather than taxonomic diversity may provide greater insight to microbial roles in ecosystems” (Zak et al, 1994)
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