Soil tillage or herbicide applications are commonly used in agriculture for weed control. These measures may also represent a disturbance for soil microbial communities and their functions. However, the generality of response patterns of microbial communities and functions to disturbance have rarely been studied at large geographical scales. We investigated how a soil disturbance gradient (low, intermediate, high), realized by either tillage or herbicide application, affects diversity and composition of soil bacterial and fungal communities as well as soil functions in vineyards across five European countries. Microbial alpha-diversity metrics responded to soil disturbance sporadically, but inconsistently across countries. Increasing soil disturbance changed soil microbial community composition at the European level. However, the effects of soil disturbance on the variation of microbial communities were smaller compared to the effects of location and soil covariates. Microbial respiration was consistently impaired by soil disturbance, while effects on decomposition of organic substrates were inconsistent and showed positive and negative responses depending on the respective country. Therefore, we conclude that it is difficult to extrapolate results from one locality to others because microbial communities and environmental conditions vary strongly over larger geographical scales.

In each country, soil samples were taken at least one season after experimental plot preparation (2016 and/or 2017) and at minimum 6 weeks after tillage/herbicide application around the time of grapevine flowering. Eight subsamples were taken in the two central inter-rows of each plot to a depth of 10 cm approximately 30 – 50 cm apart from each other and were pooled afterwards into one mixed sample, summing up to a total of 405 soil samples. The number comprises n= 54 samples for Austria 2016, France 2017, Romania 2017, Germany 2016 and Germany 2017, but n = 77 for Switzerland 2016 and n = 58 for Switzerland 2017. Thus, we included samples for bacteria and fungi for each country for at least one season (2016 for Austria, 2017 for France and Romania) or two seasons for Switzerland and Germany. DNA extraction from each soil sample was either performed directly after soil sampling or samples were stored frozen at -20° C until extraction. DNA was extracted from 0.25 g of mixed soil sample per inter-row by using the DNeasyPowerSoil Kit® following the manufacturer’s protocol (QIAGEN N.V., Venlo, Netherlands).

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