Coupled Biogeochemical Cycles and Feedback Governing Planetary Boundaries

The planetary boundaries framework identifies nine key Earth system processes that regulate the stability, resilience, and functioning of life support of our planet. However, these boundaries do not operate independently. The functioning, resilience, and stability of the planet emerge from complex interactions and feedbacks among coupled biogeochemical cycles, operating across spatial and temporal scales. Crossing individual planetary boundaries increases the risk of triggering non-linear responses, cascading effects, and potentially irreversible changes in Earth system dynamics.
Growing evidence suggests that several planetary boundaries may already have been transgressed, largely as a consequence of human-driven perturbations of biogeochemical cycles. Alterations in nutrient, carbon, redox-sensitive element, and trace metal cycles modify ecosystem functioning and weaken the capacity of natural systems to buffer anthropogenic pressures. Understanding how coupled biogeochemical processes generate feedbacks, thresholds, and emergent behavior is therefore essential for linking planetary boundary research with actionable environmental management and governance.
This Research Topic aims to advance a process-based and integrative understanding of coupled biogeochemical cycles and the feedback mechanisms through which they regulate Earth system stability and planetary boundaries. While individual elemental cycles such as nitrogen (N) and phosphorus (P) are well established within the planetary boundaries framework, increasing attention is needed on their interactions with other cycles, including carbon (C), silicon (Si), sulfur (S), iron (Fe), and redox-sensitive elements.
For example, the N–P–Si system illustrates how human perturbations of element cycles can propagate through coupled land–water–ocean feedbacks. Industrial N fixation, altered P fluxes, land-use change, damming, and intensive agriculture modify dissolved silica transport from terrestrial to aquatic systems, affecting diatom productivity, C sequestration efficiency, and coastal ecosystem structure. Such examples highlight how multi-element coupling, biological mediation, and human pressures jointly shape feedbacks across ecosystems and scales, rather than acting through isolated pathways.
The objective of this Research Topic is to foster contributions that explicitly address biogeochemical couplings, feedback mechanisms, non-linear responses, and thresholds, linking process-level understanding with regional to global implications for planetary boundaries. We particularly encourage studies that integrate empirical data, conceptual frameworks, and modeling approaches to bridge ecosystem-scale processes with Earth system dynamics.