Changes in soil fertility and microbial communities following cultivation of native grassland in Horqin Sandy Land, China:a 60-year chronosequence

Background Grassland conversion to cropland is a prevailing change of land use in traditionally nomadic areas,especially in the Mongolian Plateau. We investigated the effects of grassland conversion followed by continuous cultivation on soil properties and microbial community characteristics in Horqin Sandy Land, a typical agro-pastoral transition zone of Northern China. Soil samples were collected from the topsoil(upper 20 cm) across a 60-year cultivation chronosequence(5, 15, 25, 35 and 60 years) and unconverted native grassland. Soil physico-chemical properties were determined and high-throughput sequencing was used to assess microbial community diversity and composition.Results Grassland cultivation resulted in changes to soil properties in both the short and longer term. Initially, it significantly increased soil bulk density(BD), electrical conductivity(EC), soil total nitrogen(TN), available phosphorus(AP) and available potassium(AK) concentrations, while reducing soil water content(SWC) and soil organic carbon content(SOC). Over the next 35–55 years of continuous cultivation, the trend for most of these characteristics was of reversion towards values nearer to those of native grassland, except for SOC which remained highly depleted.Cultivation of grassland substantially altered soil microbial communities at phylum level but there was no significant difference in microbial α-diversity between native grassland and any cropland. However, soil bacterial and fungal community structures at phylum level in the croplands of all cultivation years were different from those in the native grasslands. Heatmaps further revealed that bacterial and fungal structures in cropland tended to become more similar to native grassland after 15 and 25 years of cultivation, respectively. Redundancy analysis indicated that SOC, EC and BD were primary determinants of microbial community composition and diversity.Conclusions These findings suggest that agricultural cultivation of grassland has considerable effects on soil fertility and microbial characteristics of Horqin Sandy Land. Intensive high-yield forage grass production is proposed as an alternative to avoid further native grassland reclamation, while meeting the grazing development needs in the ethnic minority settlements of eco-fragile regions.