Reconciling plant and microbial ecological strategies to elucidate cover crop effects on soil carbon and nitrogen cycling

Plant economics, the way plants allocate and utilize resources, affect
multiple soil processes through interactions with root and associated
microbial communities. However, the interplay between plant economics and
microbial ecological strategies remains poorly understood, which is
crucial for integrated manipulation of plant- and microbe-mediated
functions in mitigating climate change and sustaining soil health. We used
a field experiment with 11 cover crop species grown monocultures in the
same base soil to test whether microbial ecological strategies are
associated with plant economic strategies and if their interactions are
linked to soil functions. A principal component analysis (PCA) was
performed on root and leaf traits to identify the loadings of cover crop
species on the plant trait space. Metagenomic analysis of rhizosphere
microbial communities was conducted to infer their ecological strategies
based on genetically encoded community-aggregated traits. We found a
synchronous relationship between the conservation gradient of plant
economic strategies and the trade-offs in microbial ecological strategies.
Conservative plant strategists, such as Lolium multiflorum,
Triticum turgidum, and Brassica juncea, fostered microbial communities
characterized by high growth yield potentials (Y-strategies). This
included increased microbial carbon fixation pathways, citrate cycle,
ribosome, and valine, leucine and isoleucine biosynthesis. As a result,
microbial metabolic efficiency improved, shown by higher microbial biomass
carbon content and a lower metabolic quotient (qCO2), led to enhanced soil
organic carbon accumulation. In comparison, acquisitive plants like
Astragalus sinicus, Vicia villosa, Trifolium incarnatum, and Medicago
sativa stimulated microbial resource-acquisition strategies
(A-strategies). This included enhanced bacterial chemotaxis, secretion
systems, biotin metabolism, and cell motility pathways, which in turn
increased soil exoenzyme activity and accelerated soil nitrogen
mineralization. Consequently, these species enhanced soil nitrogen
availability and had substantial feedbacks on subsequent main crop
productivity. Synthesis. This study demonstrates how plant economic
strategies influence the balance between different microbial ecological
strategies, specifically the trade-offs in Y- and A-strategies. These
interactions exert control over carbon and nitrogen dynamics in the soil
ecosystem. Our findings provide the insights for implementing nature-based
solutions to improve agroecosystem management practices.