Vascular plants affect properties and decomposition of moss-dominated peat, particularly at elevated temperatures

Abstract

Abstract. Peatlands, storing significant amounts of carbon, are extremely vulnerable to climate change. The effects of climate change are projected to lead to a vegetation shift from Sphagnum mosses to sedges and shrubs. Impacts on the present moss-dominated peat remain largely unknown. In this study, we used a multiproxy approach to investigate the influence of contrasting vascular plant types (sedges, shrubs) on peat chemistry and decomposition. Peat cores of 20 cm depth and plant material (Sphagnum spp., Calluna vulgaris and Eriophorum vaginatum) from two ombrotrophic peatlands in the Italian Alps with a mean annual temperature difference of 1.4 ∘C were analyzed. Peat cores were taken under adjacent shrub and sedge plants growing at the same height above the water table. We used carbon, nitrogen and their stable isotopes to assess general patterns in the degree of decomposition across sampling locations and depths. In addition, analytical pyrolysis was applied to disentangle effects of vascular plants (sedge, shrub) on chemical properties and decomposition of the moss-dominated peat. Pyrolysis data confirmed that Sphagnum moss dominated the present peat irrespective of depth. Nevertheless, vascular plants contributed to peat properties as revealed by, e.g., pyrolysis products of lignin. The degree of peat decomposition increased with depth as shown by, e.g., decreasing amounts of the pyrolysis product of sphagnum acid and increasing δ13C with depth. Multiple parameters also revealed a higher degree of decomposition of Sphagnum-dominated peat collected under sedges than under shrubs, particularly at the high temperature site. Surprisingly, temperature effects on peat decomposition were less pronounced than those of sedges. Our results imply that vascular plants affect the decomposition of the existing peat formed by Sphagnum, particularly at elevated temperature. These results suggest that changes in plant functional types may have a stronger impact on the soil carbon feedback in a warmer world than hitherto assumed.

Latitude, Elevation, and Mean Annual Temperature Predict Peat Organic Matter Chemistry at a Global Scale

“…Peat stability and decomposition rates are influenced by a combination of many factors, including water table depth, electron acceptor availability (Blodau, 2011;Heimann et al, 2009), and microbial community (Bragazza et al, 2016;Hodgkins et al, 2015;LaRowe & Van Cappellen, 2011;Norby et al, 2019), but also by the source vegetation and associated organic matter quality (Wang et al, 2021;Zeh et al, 2020). After accounting for dominant peat-forming surface vegetation in our analyses, latitude and elevation had by far the strongest relationships with carbohydrates and aromatics (Table S3 in Supporting Information S1).…”

“…One key factor affecting peat chemistry is the chemical characteristics of the organic matter inputs (Zeh et al, 2020). Peatlands vary in vegetation composition, and the dominant factors affecting plant community composition include latitude, mean annual temperature (MAT), elevation, and hydrology, especially groundwater versus rainwater inputs.…”

Controls on autotrophic and heterotrophic respiration in an ombrotrophic bog

“…While the remnants of roots in the clipped plots may partially explain why the respiration values were sometimes higher in these plots than in the shrub only or sedge only plots, we cannot ignore that this phenomenon occurred mostly when it was hotter and drier. Zeh et al (2020) for example, found a higher degree of decomposition of peat under sedges than under shrubs, particularly when temperatures were higher. It may also be possible that the vascular plants in these conditions are inhibiting the respiration of the microbes below (Robroek et al, 2016), with the mosses providing a priming effect to respiration (what may be called plant-mediated HR).…”

Linear Disturbances Shift Boreal Peatland Plant Communities Toward Earlier Peak Greenness

“…Rcc has been successfully used to monitor vegetation senescence (Liu et al, 2020) and investigate plant stress after water table drawdown (Peichl et al, 2015). The difference in reflectance in the red spectrum could also allow for separation among common peatland plant functional groups, namely vascular versus nonvascular plants that have different impacts on ecosystem function (e.g., rates of nutrient cycling, carbon storage; Zeh et al, 2020).…”