Root trait controls on rhizosphere priming effects during early-stage litter decomposition in anoxic peat

Abstract

Litter represents the transitional stage between plant biomass and soil organic carbon, with its transformation influenced by overlying vegetation. Plant regulation of litter decomposition through priming effects in wetlands represents an important knowledge gap, as roots influence rhizosphere processes differently than in upland soils by releasing both exudates and oxygen into the otherwise water-saturated, oxygen-depleted soil matrix. To investigate the role of plants in rhizosphere priming in anoxic wetlands, two sedge species with contrasting belowground traits (rhizomatous vs. tussock-forming) were grown on uniformly carbon-13-labeled litter in waterlogged peat in a greenhouse microcosm experiment. Litter-derived respiration affected by sedge roots was quantified using a two-end-member mixing model. Rhizosphere enzyme activities were mapped using zymography, while oxygen and carbon dioxide (CO₂) dynamics were visualized using planar optode imaging. Litterbag mass loss was determined gravimetrically. Cumulative litter-derived CO₂ respiration was 87% higher under rhizomatous Eriophorum angustifolium and 106% higher under tussock-forming E. vaginatum than in the unplanted treatment, whereas litter mass loss was only 10 and 19% higher in the planted treatments, respectively. Initial positive priming effects of > + 200% declined to negative priming of < − 20% within 3 months in both planted treatments. In both species, β-glucosidase activity was elevated around mature roots, while acid phosphatase activity was elevated across the entire root system compared with background levels. Our study provides experimental evidence that sedges enhance early-stage litter decomposition in anoxic peat regardless of their belowground morphological traits, likely through root oxygen loss and stimulation of rhizosphere enzyme activity.