Climate and pedogenesis exert divergent controls on dissolved organic matter during long-term ecosystem development

Abstract

Dissolved organic matter (DOM) plays a central role in terrestrial carbon and nutrient cycling, underpinning essential ecosystem functions. Despite its importance, the mechanisms affecting long-term DOM dynamics during ecosystem development remain elusive due to complex variation in pedogenesis-associated nutrient status and biological activities. Here, we investigated the concentrations, optical properties, and compositional attributes of soil DOM across two 2-million-year coastal dune chronosequences under contrasting climatic conditions in southwestern Australia. Using fluorescence excitation-emission matrix spectroscopy coupled with parallel factor analysis, we elucidated distinct effects of climate and pedogenesis on DOM properties. Cooler and wetter climates were associated with greater DOM humification and accumulation. During the progressive phase of ecosystem development, both chronosequences exhibited greater topsoil DOM concentrations and proportions within soil organic matter (SOM), accompanied by a greater abundance of microbial-derived protein-like substances, which enhance DOM availability to microbes. Conversely, the retrogressive phase was characterized by lower DOM concentrations and proportions within SOM, alongside a transition to plant-derived humic substances and greater humification, suggesting increased DOM stability in old soils. Our findings highlight the dual role of DOM in providing bioavailable nutrients during the progressive phase and promoting soil carbon and nutrient accumulation during the retrogressive phase. These insights contribute to our understanding of the changing role of DOM during long-term ecosystem development and future climatic conditions.