Soil fertility and plant diversity enhance microbial performance in metal-polluted soils

Summary

This study examined the effects of soil physicochemical properties (including heavymetal pollution) and vegetation parameters on soil basal respiration, microbial biomass, and the activity and functional richness of culturable soil bacteria and fungi. In a zinc and lead mining area (S Poland), 49 sites were selected to represent all common plant communities and comprise the area's diverse soil types. Numerous variables describing habitat properties were reduced by PCA to 7 independent factors, mainly representing subsoil type (metal-rich mining waste vs. sand), soil fertility (exchangeable Ca,Mg and K, total C andN, organic C), plant species richness, phosphorus content, water-soluble heavy metals (Zn, Cd and Pb), clay content and plant functional diversity (based on graminoids, legumes and non-leguminous forbs). Multiple regression analysis including these factors explained much of the variation inmostmicrobial parameters; in the case of microbial respiration and biomass, itwas 86% and 71%, respectively. The activity of soil microbes was positively affectedmainly by soil fertility and, apparently, by the presence of mining waste in the subsoil. The mining waste contained vast amounts of trace metals (total Zn, Cd and Pb), but it promoted microbial performance due to its inherently high content ofmacronutrients (total Ca, Mg, K and C). Plant species richness had a relatively strong positive effect on allmicrobial parameters, except for the fungal component. In contrast, plant functional diversitywas practically negligible in its effect on microbes. Other explanatory variables had only a minor positive effect (clay content) or no significant influence (phosphorus content) on microbial communities. The main conclusion from this study is that high nutrient availability and plant species richness positively affected the soilmicrobes and that this apparently counteracted the toxic effects ofmetal contamination.