Plant-soil interactions and carbon dynamics in mountain ecosystems

Background/Question/Methods: There is currently much interest in the topic of ecosystem carbon (C) cycling and especially the ability of terrestrial ecosystems to sequester C in the face of global change. Mountain ecosystems, including peatlands and montane grasslands, are of particular interest because they represent a sizable stock of terrestrial C due to low rates of decomposition, and hence the accumulation of organic matter, under often nutrient poor, cold and waterlogged conditions. Much work has been done to improve our understanding of the drivers of C release from soils, but this has largley focused on abiotic drivers such as temperature and soil moisture.  In contrast, the influence of biotic factors on ecosystem C exchange, such as changes in vegetation composition and productivity, remain relatively unexplored. Here, we present findings from a series of experiments carried out in the British mountains to test how variations in plant community composition resulting from land use change influence soil microbes and C cycling. First, we present findings from a long-term field experiment and associated mesocosm study which were designed to test whether management to restore botanical diversity of upland meadows has additional benefits for soil C sequestration; and, second, we present findings from a  field experiment in an ombotrophic peatland in northern England where we used stable isotopes (13C), in combination with selective removal of dominant plant functional groups, to examine the effects of plant functional group identity on short-term plant-soil C fluxes.

Results/Conclusions: We found that long-term management to restore botanical diversity in an upland meadow had significant benefits for soil C sequestration, and that this was related largley to an increased cover of legumes. Associated mesocosm studies revealed that net ecosystem exchange and belowground C allocation to roots and mycorrhizal fungi increased with increasing plant species diversity, but, as above, these responses were driven largely by the presence of legumes in more species-rich grassland mesocosms. In peatland, differences in net ecosystem exchange were identified in areas where plant species composition had been altered by land use. We also found significant effects of removing different plant functional groups (i.e. dwarf-shrubs, graminoids, and bryophytes) on CO2 fluxes and tracer 13C uptake and turnover.  In particular, the removal of ericoid dwarf-shrubs increased rates of photosynthesis and respiration by >200% relative to the undisturbed control. We conclude that plant functional groups differentially influence the uptake and short term flux of C, suggesting that changes in plant functional composition have the potential to alter short term patterns of C exchange in mountain ecosystems.