Securing Soil Biodiversity: Impact of Soil Type and Land Use on Microbial Diversity and Functions

Abstract

Soil harbours abundant and diverse microbial communities, including bacteria and fungi, which are crucial for ecosystem functions and services such as nutrient cycling, climate mitigation, and human health. Human activities, particularly agricultural practices, significantly alter soil characteristics, the structure of soil microbial communities, and their functional traits. This thesis investigates the biodiversity of both abundant and rare bacterial communities across various soil types and land uses. This thesis reveals that abundant and rare bacterial communities, along with their functional traits, exhibited distinct responses to soil type and land use changes. Specifically, cropping enhanced the biodiversity of abundant bacterial communities in more fertile soils, but consistently diminished the diversity of rare communities across different soil types. Moreover, this thesis quantitatively assessed the capacity and condition of soil function as the habitat of biodiversity within the Soil Security Assessment Framework (SSAF), considering both abundant and rare bacterial communities. Heterogeneities were identified across 13 different soil types (pedogenons), where cropping improved the condition of abundant bacterial biodiversity but adversely affects rare communities. Additionally, this thesis investigated denitrification pathways in various flooded paddy soils at a national scale. Fungal denitrification emerged as the dominant contributor, followed by chemical denitrification in both basal and nitrogen-induced conditions. Overall, this thesis examined the impact of soil type and land use on microbial biodiversity and functional traits, highlighted the significance of both abundant and rare bacterial communities in soils, advocates for a quantitative approach to assess soil function as the habitat of biodiversity, and explores various denitrification pathways in soil nitrogen cycling and their contribution to atmospheric nitrous oxide production.