Abstract Soil amendments are known to improve soil health, but if and how they influence the soil microbiome over time is unclear. In this study, soil amendments were applied to young avocado trees and the rhizosphere and root microbial communities measured. Bacterial and fungal communities were hypothesised to change over time and to vary between soil amendment regimes: monthly mineral fertiliser, or a liquid nutrient fertiliser combined with a biostimulant applied monthly or quarterly. Communities were characterised by 16 S and ITS amplicon sequencing. Over 12 months, amendment regime explained less than 2% of bacterial and fungal community variation in either the rhizosphere or roots. Some rhizosphere taxa differed between amendments one month after the first amendment application, but these differences did not persist at later timepoints. Instead, pre-sampling climate, including mean air temperature and cumulative rainfall, and sampling timepoint, explained more rhizosphere community variation than amendment regime. In root samples, community composition differed between planting and the trial endpoint, with no significant effect of amendment observed at either timepoint. Therefore, microbial communities were more strongly influenced by climate variables than amendment regime, and detecting amendment effects may require longer trial durations, in more mature trees.
Zaman et al. (Mon,) studied this question.