Climatic and edaphic influences of manganese and carbon interactions in plants and soils across biomes in the US

Manganese (Mn) is an essential micronutrient for plant growth and health and is thought to play a critical ecological role during litter decomposition. Plants acquire soluble Mn from the soil, accumulate it in foliage with negligible reabsorption during senescence, and return it to the soil in leaf litter. The positive linear relationship between foliar Mn and litter mass loss during decomposition reported by previous studies suggests that Mn may influence soil C storage, presumably through enhanced oxidation of lignin by fungal-produced Mn peroxidase. Yet, much of what we know on the relationship between Mn and soil C is restricted to a few biomes. To fill this gap in Mn-C research, we extracted biogeochemical data from plants and soils (from the megapits and distributed plots) from the National Ecological Observatory Network (NEON) database and examined relationships associated with interactions between Mn and C in across a wide range of biomes. We found that foliar Mn concentrations increased with decreasing soil pH, whereas Mn concentration in O horizons increased with pH, consistent with previous reports that soil pH is an important control on Mn solubility and plant uptake regardless of soil Mn concentrations. While C (and N) stocks (kg m^-2) in organic horizons decreased as Mn concentrations increased up to 2412 mg kg^-1, with differences in O horizons (Oa, Oe, and Oi) driving this pattern, stocks increased with Mn:Ca ratios. These results suggest that organic matter stocks in the O horizon is negatively associated with Mn concentration in NEON sites. In the O horizon, C stock decreased with increasing mean annual temperature (MAT), but we found no statistically significant relationship between Mn concentration and climatic variables (i.e., MAT and mean annual precipitation). The negative correlation between Mn concentration and C storage is in line with previous studies and is consistent across biomes. We will include results from experimental data to discuss mechanisms that could explain the observed patterns in surface soils.