The significance of soil microalgae and cyanobacteria to assess pesticide stresses, in agricultural soils
Abstract
Standardized soil microbial indicators, used to assess the impacts of agricultural practices and/or contaminations, lack of sensitivity and genericity against pesticide stresses, especially for herbicides. Soil photosynthetic microorganisms, mainly represented by micro-algae (chlorophyceae, xanthophyceae and diatoms) and cyanobacteria, can growth in soil surface. So, they could be an original microbiological model for herbicides risk assessment in agricultural soils. Nevertheless, their structural and functional biodiversity and the environmental factors influencing their communities are still largely unknown. Then, to improve our understanding of these photosynthetic microorganisms, we need to 1) develop biochemical and molecular methods to characterize their activities and genetic diversity and 2) analyse their responses to herbicides in agricultural soils. Several methodologies commonly used for aquatic systems were adapted to soil. Cultural approaches are still helpful to isolate edaphic species for further ecotoxicological tests and barcoding approaches. Photosynthetic pigments can provide biomass (chlorophyll-a) or structural (pigment diversity) indicators. Several
genetic markers from aquatic studies were successfully applied on soils samples, but a current limit is the lack of databases of these specific genetic markers. Toxic effects on photosynthetic microbial biomass and
diversity have been evidenced at doses close to recommended field rates, throughout field and microcosm approaches. The comparison of the responses of photosynthetic microbial communities, between
different cropping systems (organic vs. conventional), highlighted a tolerance increase for some herbicides in conventional soils. Genetic diversity characterization of micro-algal and cyanobacterial communities in these cropping systems, provides further results to identify taxa relating to tolerance. Then, various genus of microalgae
and cyanobacteria have been identified for their high sensitivity to herbicides. Overall, micro-algal and cyanobacterial communities showed a higher sensitivity to herbicide in soils, compared to commonly studied bacterial and fungal community. These innovative investigations demonstrate the suitable issues of soil photosynthetic microorganisms as indicators reporting non-target impacts of herbicides on soil biodiversity and functioning. Prospects for monitoring remediation of polluted soils (heavy metals, HAP) should be considered
Domains
Life Sciences [q-bio]
Origin : Files produced by the author(s)