Nitrogen and phosphorus cycling in an ombrotrophic peatland: a benchmark for assessing change.

Aims: Slow decomposition and isolation from groundwater mean that ombrotrophic peatlands store a large amount of soil carbon (C) but have low availability of nitrogen (N) and phosphorus (P). To better understand the role these limiting nutrients play in determining the C balance of peatland ecosystems, we compile comprehensive N and P budgets for a forested bog in northern Minnesota, USA. Methods: N and P within plants, soils, and water are quantified based on field measurements. The resulting empirical dataset are then compared to modern-day, site-level simulations from the peatland land surface version of the Energy Exascale Earth System Model (ELM-SPRUCE). Results: Our results reveal N is accumulating in the ecosystem at 0.2 ± 0.1 g N m-2 year-1 but annual P inputs to this ecosystem are balanced by losses. Biomass stoichiometry indicates that plant functional types differ in N versus P limitation, with trees exhibiting a stronger N limitation than ericaceous shrubs or Sphagnum moss. High biomass and productivity of Sphagnum results in the moss layer storing and cycling a large proportion of plant N and P. Comparing our empirically-derived nutrient budgets to ELM-SPRUCE shows the model captures N cycling within dominant plant functional types well. Conclusions: The nutrient budgets and stoichiometry presented serve as a baseline for quantifying the nutrient cycling response of peatland ecosystems to both observed and simulated climate change. Our analysis improves our understanding of N and P dynamics within nutrient-limited peatlands and represents a crucial step toward improving C-cycle projections into the twenty-first century.

Selective sorption of dissolved organic carbon compounds by temperate soils.

BACKGROUND: Physico-chemical sorption onto soil minerals is one of the major processes of dissolved organic carbon (OC) stabilization in deeper soils. The interaction of DOC on soil solids is related to the reactivity of soil minerals, the chemistry of sorbate functional groups, and the stability of sorbate to microbial degradation. This study was conducted to examine the sorption of diverse OC compounds (D-glucose, L-alanine, oxalic acid, salicylic acid, and sinapyl alcohol) on temperate climate soil orders (Mollisols, Ultisols and Alfisols). METHODOLOGY: Equilibrium batch experiments were conducted using 0-100 mg C L(-1) at a solid-solution ratio of 1∶60 for 48 hrs on natural soils and on soils sterilized by γ-irradiation. The maximum sorption capacity, Q(max) and binding coefficient, k were calculated by fitting to the Langmuir model. RESULTS: Ultisols appeared to sorb more glucose, alanine, and salicylic acid than did Alfisols or Mollisols and the isotherms followed a non-linear pattern (higher k). Sterile experiments revealed that glucose and alanine were both readily degraded and/or incorporated into microbial biomass because the observed Q(max) under sterile conditions decreased by 22-46% for glucose and 17-77% for alanine as compared to non-sterile conditions. Mollisols, in contrast, more readily reacted with oxalic acid (Q(max) of 886 mg kg(-1)) and sinapyl alcohol (Q(max) of 2031 mg kg(-1)), and no degradation was observed. The reactivity of Alfisols to DOC was intermediate to that of Ultisols and Mollisols, and degradation followed similar patterns as for Ultisols. CONCLUSION: This study demonstrated that three common temperate soil orders experienced differential sorption and degradation of simple OC compounds, indicating that sorbate chemistry plays a significant role in the sorptive stabilization of DOC.