Contrasting Management Techniques and Soil Types Affect Network Connections between Soil Properties and the Tulip Microbiome

Abstract

Conventional agriculture relies on high inputs of chemical fertilisers and pesticides, leading to extensive soil damage. As a result, there has been a shift towards organic cultivation to ameliorate these negative effects. However, knowledge gaps remain concerning how different agricultural management regimes can alter soil properties, root-associated biota and relationships between them. We sampled soils and bulbs from clay and sand tulip fields with conventional, organic and hybrid (i.e., intermediate between conventional and organic) management regimes to determine effects on abiotic and biotic soil properties, tulip bulb microbiomes/biota and network connectivity between them. We found that soil abiotic properties were not driven by management. However, soil microbial community composition was determined by interactions between soil type and management. Specifically, conventional management created more heterogeneous and homogenous bacterial and fungal soil communities, respectively, across soil types, while organic and hybrid soil communities differed between soil types. A partial least squares path model revealed that across all fields, soil properties determined the composition of tulip bulb biota (i.e., microorganisms, nematodes), while management techniques did not play a significant role, neither directly nor indirectly. Network analyses revealed more modular (i.e., independent) nodes of association in fields with sandy soils. Specifically, management techniques (i.e., chemical usage, ploughing depth, diminished crop rotation) formed a cluster that was independent from most soil (abiotic and biotic) and bulb biotic properties, while clay field networks showed the opposite. Our results indicate that conventional agriculture can homogenise soil microbial communities, with potential impacts on soil function and buffering capacity to stress. Increased modularity between soil properties, management techniques and tulip bulb biota in sand fields could mean increased resistance to disturbance and abiotic and biotic stress as a result of higher functional redundancy. Interactions between agricultural management regime and soil type must be taken into consideration when determining long-term influences on crop microbiome/biota associations and the potential effects on soil health and productivity.