Warming increases plant-available nutrients in the SPRUCE bog
Abstract
Warming is expected to increase the release of carbon from highly-organic peatland soils, potentially leading to a positive feedback to future warming. The relative balance of peat accumulation will depend in part on whether vegetation growth is increased in response to warming and increased nutrient availability, or whether this response is limited by increased drying in the warmed treatments.
We quantified the effects of a range of ecosystem warming (from +0 to +9°C), as well as elevated [CO2], on plant-available nutrients in the SPRUCE (Spruce and Peatland Responses Under Changing Environments) experiment in an ombrotrophic bog in northern Minnesota, USA over a period of 5 years. We used ion-exchange resin capsules to monitor monthly changes in plant-available nutrients (i.e., NH4-N, NO3-N, and PO43-) throughout the peat profile and across hummock-hollow microtopography. NH4-N was by far the most available N source, with NO3-N making up a negligible fraction; PO43- availability was intermediate. Warming—combined with a longer frost-free period—tripled the availability of NH4+ and PO43- in the warmest treatment plots. Furthermore, increases in PO43- availability with warming were greater than increases in NH4+, especially in deeper peat. However, the increase in nutrients was much greater below the rooting zone. There is thus far no effect of elevated [CO2] on nutrient availability. Interestingly, the same warming response was not apparent in the subset of porewater nutrients collected and measured at bi-weekly intervals at a comparable depth increment in the hollows. While porewater total organic carbon concentrations were increased by warming, indicating increased mineralization of organic matter, there was no difference in porewater NH4+, NO3-, or PO43- concentrations across the warmed plots. Taken together, these lines of evidence indicate that warming has increased the mineralization of peat, leading to increased nutrient availability. In turn, increased nutrient uptake by the vegetation has depleted the availability of nutrients in the rooting zone and in porewater. The additional nutrients taken up by the plant community are detectable in increased N and P concentrations in Sphagnum mosses; however, this may be luxury uptake, as evidence indicates that moss production has declined with warming.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B12B..02I
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0470 Nutrients and nutrient cycling;
- BIOGEOSCIENCES;
- 1622 Earth system modeling;
- GLOBAL CHANGE