Land-use change from native forest to avocado orchards: Effects on soil nutrient transformation and microbial communities

Abstract

Land-use change is known to alter soil microbial communities and the processes they carry out. However, there is meager information about how conversion of natural forests to agricultural land for avocado production affects soil nutrient concentration and microbial activity and diversity. Total soil nutrients (C, N and P), microbial ecoenzymatic activity, and microbial diversity were studied in avocado orchards and contiguous forest fragments in Michoacán state, México. Within orchards, samples were taken from fertilized areas beneath avocado trees as well as from unfertilized areas. Results showed that (i) total phosphorus concentration was higher in avocado orchards compared to native forests soils; (ii) transformation of native forests to avocado orchards decreased the ecoenzymatic activity necessary for degradation of lignified compounds and phosphate monoesters; (iii) bacterial diversity was higher in avocado orchard soils compared to native forest soils while fungal diversity was higher in avocado unfertilized soils; (v) transformation of native forests to avocado orchards increased the evenness of bacterial and fungal communities; (vi) transformation of native forest to avocado orchards caused significant changes in the composition of soil microbial communities; however, this was clearer for fungal communities than for bacterial communities; (vii) abundance of ectomycorrhizal fungi and antagonists of plant pathogens decreased in avocado orchards while pathogenic and saprotrophic fungal guilds increased. Our results suggest that land use change from native forest to avocado orchards generates important changes in the dynamics of soil organic carbon and soil organic phosphorus in avocado orchard soils, probably due to the predominant conventional management model in the avocado belt. Furthermore, this type of land use change results in the increased abundance of important microbial groups identified as phytopathogens and the decrease of beneficial microbial groups. These changes should be taken into account to formulate forest and soil conservation polices and of more sustainable agricultural management models that consider soil microbial communities and their functions.