Effect of Paulownia and Buckwheat Intercropping on Soil Microbial Biodiversity, Dehydrogenase Activity, and Glomalin-Related Soil Protein

Intercropping of trees and classical crops has been proposed as a practice to help adapt to climate change and protect soil against erosion. However, the effects of intercropping on soil biology are not sufficiently quantified. Therefore, the aim of this study was to evaluate microbiological changes in the soil resulting from the intercropping of Paulownia and buckwheat. A field experiment, involving an intercropping and control no-tree variant, was conducted from 2019 to 2022 with a plot size of 30 m2. Buckwheat rhizosphere soil samples were collected twice in both 2021 and 2022 in order to evaluate the effects of intercropping on a range of parameters describing soil microbiome status: abundance of microorganisms, bacterial and fungal community structure (using Illumina MiSeq sequencing), dehydrogenases (DHA) activity, and total glomalin-related soil proteins (T-GRSP). In addition, the colonisation of buckwheat roots by fungi, yield, and biometric traits of the plant were determined. Next-generation sequencing showed that Actinobacteria, Proteobacteria, and Acidobacteria were dominant in the microbiome of every variant of the experiment, regardless of the crop. In contrast, the mycobiome was dominated by fungi classified as Ascomycota and Mortierellomycota. This observation corresponded to an increase in buckwheat yield in intercropped plots. Biometric traits, namely buckwheat yield and total kernel weight per plant, showed higher values when buckwheat was intercropped with Paulownia compared to the control. DHA activity was stimulated by intercropping at the first sampling date, whereas glomalin concentration and abundance of microorganisms were not dependent on the cropping systems tested. This study shows that tree-based intercropping (TBI) systems promote a more diverse soil microbial community and function than conventional agriculture. Our results also suggest that TBI positively impacts buckwheat biometric traits, supporting its implementation in rural landscapes. The yield under intercropping cultivation amounted to 0.65 t ha−1, while in control sites it was 0.53 t ha−1. The total abundance of bacteria under intercropping cultivation was higher compared to monoculture in 2021 at the first term of sampling (4.3 × 104) and in 2022 in the second term of soil sampling (4.6 × 104).