Abstract
AbstractBackgroundNorthern peatlands have accumulated vast amounts of carbon (C) as peat. Warming temperatures may affect peatland C stores by increasing microbial decomposition of ancient peat through enhanced input of labile root exudates by expansion of vascular plants, thereby accelerating atmospheric warming.AimsWe set out to explore how much freshly assimilated C is allocated belowground by vascular plants, and if the above‐ to belowground allocation is affected by temperature and plant functional types.MethodsWe traced the C allocation pathways of two dominant plant functional types (i.e., sedges and shrubs) in two peatlands under different temperature regimes by combining selective plant removal in mixed sedge‐shrub vegetation and in situ 13C pulse‐labelling. Aboveground to belowground C allocation as well as the C turnover were assessed by quantifying 13C in plant leaves and soil respiration and by measuring δ13C in dissolved organic C. A depth‐resolved quantification of 13C in the peat soil gave additional insight into belowground C allocation patterns.ResultsTemperature did not affect the rate at which 13C was assimilated into shoots, but higher temperature decreased the fraction of assimilated C that was allocated belowground by vascular plants. Sedges assimilated CO2 faster into their shoot biomass (faster depletion in 13C in shoots) and allocated more of the assimilated 13C belowground than shrubs. Conversely, sedges retained this belowground allocated C better than shrubs, leading to lower 13C in soil respiration measured under sedges.ConclusionsClimate induced vascular plant expansion will increase input of fresh assimilates into the peat substantially, even though part of this effect will be offset by reduced above‐ to belowground allocation rates. If shrub density increases relative to sedges, fresh assimilates are more likely to be respired than translocated to roots where they could reach and, potentially mobilize, ancient C stored in deeper peat layers.
Highlights
Peatlands play an important role in the terrestrial carbon (C) cycle as they store one-third of the global soil C on only 3% of the land surface (Gorham, 1991; Turunen et al, 2002)
Following up on the experiment design by Zeh et al (2019), here we present the results of a selective clipping experiment with in situ 13C pulse-labelling to quantify the recently assimilated C of two plant functional types at two peatlands with contrasting temperatures
The majority of vascular plant biomass in peatlands is belowground (Wang, Heijmans, et al, 2016) and surface dissolved organic carbon (DOC) has been reported to be highly influenced by vegetation (Tfaily et al, 2018), we found no 13C in DOC
Summary
Peatlands play an important role in the terrestrial carbon (C) cycle as they store one-third of the global soil C on only 3% of the land surface (Gorham, 1991; Turunen et al, 2002). There is growing concern that climate-induced shift towards vascular plant dominated conditions will compromise the future C sink function of peatlands due to two main reasons: first, by reducing the rate of new peat formation as a result of increased decomposition rate of fresh litter (Zhang et al, 2019) and second by stimulating decomposition of existing peat. Warming temperatures may affect peatland C stores by increasing microbial decomposition of ancient peat through enhanced input of labile root exudates by expansion of vascular plants, thereby accelerating atmospheric warming. Conclusions: Climate induced vascular plant expansion will increase input of fresh assimilates into the peat substantially, even though part of this effect will be offset by reduced above- to belowground allocation rates. If shrub density increases relative to sedges, fresh assimilates are more likely to be respired than translocated to roots where they could reach and, potentially mobilize, ancient C stored in deeper peat layers
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