Soil microbial communities and their carbon assimilation are affected by soil properties and season but not by plants differing in their photosynthetic pathways (C3 vs. C4)

This study investigates the influence of C3 and C4 plants, soil texture and seasonal changes on the structure and assimilation of plant-derived C of soil microbial communities. In 2012 we collected soil samples in the growing and non-growing season from a vegetation change experiment cropping herbaceous C3 and C4 plants for 6 years on two soils differing in their texture. Phospholipid fatty acids and their compound-specific δ13C values were used to determine microbial community biomass and its composition and the assimilation of C from plants to soil microorganisms, respectively. While soil microbial biomass differed mainly between seasons, the microbial community composition was related to soil texture. The proportion of plant-derived C assimilated by soil microorganisms was best explained by soil texture, too. In contrast, differences in photosynthetic pathways of plants had no impact on microbial biomass or on microbial community composition but expectedly on the isotopic composition of the microbial markers. Our results demonstrated that vegetation, differing in C3 plants and C4 plants, has no effect on the soil microbial community and their proportion of assimilated C derived from plants, if plants are similar in their productivity and phenology. Thus, our study verifies that vegetation change experiments are beneficial in exploring the interactions of plant soil and microbes and how environmental properties, such as seasonality or soil type impact this interaction.