Understanding how soil organic carbon (SOC) changes over time and depth in agricultural systems is critical for informing soil health stewardship and carbon monitoring in SOC-focused programs. Yet, knowledge is limited on how SOC trajectories vary across depth and among different fractions and soil health metrics—particulate organic carbon (POC), mineral-associated organic carbon (MAOC), permanganate oxidizable carbon (POXC), and mineralizable carbon (MINC). We analyzed archived soils from three long-term Midwest trials: two in Nebraska comparing residue removal and retention in continuous corn over 10 and 19 years, and one at the Great Lakes Bioenergy Research Center (GLBRC) comparing continuous corn and perennial switchgrass after 9 years. At the 19-year Nebraska experiment, increasing plant inputs through residue retention enhanced SOC, particularly in surface soils. At both Nebraska experiments, POXC more closely tracked total SOC than MAOC, POC, or MINC. At GLBRC, surface-level SOC losses occurred under corn, whereas switchgrass exhibited whole-profile SOC losses. Across sites, MAOC showed minimal change, MINC often declined, and POC responses were variable, while POXC was the most reliable indicator of SOC gains and losses. Extending sampling beyond surface soils revealed larger changes, highlighting that surface-focused measurements alone can misrepresent SOC dynamics. Overall, long-term monitoring across multiple SOC fractions and depths is essential for accurately assessing SOC change under different management practices. Our findings provide actionable insights for regenerative agroecosystems and highlight the potential use of POXC as a soil health metric for informing management decisions and SOC-focused programs.
Fabaceae is a large, diverse, and abundant plant family with origins in the tropics. Many species in this plant family can fix nitrogen through symbiotic relationships with bacteria living in root nodules. This has been a common lens through which biogeochemists seek to understand the distribution and role of this important plant family in tropical ecosystems. However, species in this family have many additional functional traits that distinguish them from co-occurring taxa. Here we discuss how considering a wider range of traits including wood, leaf, seed, and phenological traits can help us better understand the distributions of legumes over biogeographic and ecological gradients (latitudinal, continental, climatic and succession) and their ecosystem-level consequences.
As tropical peatlands in Southeast Asia are increasingly drained for agriculture, the net effect of this conversion on nitrous oxide (N2O) emissions remains unclear. We examined how this land-use change affects nitrogen (N) cycling by comparing two contrasting tropical peat ecosystems in Sarawak, Malaysia: a managed oil palm plantation and a pristine peat swamp forest. We measured soil N2O and dinitrogen (N2) emissions, and for microbial functional and structural community and diversity, we quantified the abundances of N cycle functional genes and conducted metagenomic sequencing of microbial communities from below-ground (peat soil and litter) and above-ground (canopy soil and tree leaves) ecosystem compartments. The oil palm plantation soil was a significant N2O emitter (65.48 ± 43.18 μg N m−2 h−1), whereas the peat swamp soil acted as a near-complete N2O sink (0.89 ± 1.18 μg N m−2 h−1). Soil microbial communities played a central role in N transformations, with the genus Roseiarcus being the strongest predictor of soil N2O emissions, and Paludisphaera most strongly linked to soil N2O sink capacity. Oil palm leaves harboured approximately 89
Wildfires release a spectrum of organic matter, from environmentally persistent black carbon to rapidly degradable anhydrosugars. Levoglucosan—a soluble, biolabile anhydrosugar formed from cellulose and hemicellulose combustion—was measured across five coastal California watersheds impacted by the 2020 CZU Lightning Complex Fires. Levoglucosan concentrations peaked during the earliest post-fire flows and declined over time, independent of stream discharge. This behavior contrasts with black carbon, which was discharge-driven and increased with time-since-fire due to delayed solubilization. These findings reveal that not all pyrogenic carbon (PyC) behaves alike: labile compounds can dominate early post-fire fluxes and are efficiently transported to coastal lagoons and nearshore zones, potentially enhancing microbial processing and organic matter remineralization in downstream systems. Ignoring these fast-cycling fractions risks underestimating wildfire impacts on aquatic carbon cycling and coastal ecosystem function. Expanding focus beyond recalcitrant PyC to include labile compounds is essential to capture the full impact of terrestrial fires on carbon dynamics across the land–ocean aquatic continuum.
