Elevated atmospheric CO₂ affects decomposition of Festuca vivipara (L.) Sm. litter and roots in experiments simulating environmental change in two contrasting arctic ecosystems

Abstract

Mass loss, together with nitrogen and carbon loss, from above‐ground material and roots of Festuca vivipara were followed for 13 months in a high Arctic polar semi‐desert and a low Arctic tree‐line dwarf shrub heath. Festuca vivipara for the study was obtained from plants cultivated at two different CO2 concentrations (350 and 500 μL L–1) in controlled environment chambers in the UK. Each of the four resource types (shoots or roots from plants grown in elevated or ambient CO2 concentrations) was subsequently placed in an experiment simulating aspects of environmental change in each Arctic ecosystem. Air, litter and soil temperatures were increased using open‐topped polythene tents at both sites, and a 58% increase in summer precipitation was simulated at the high Arctic site. Mass loss was greatest at the low Arctic site, and from the shoot material, rather than the roots. Shoots grown under an elevated CO2 concentration decomposed more slowly at the high Arctic site, and more quickly at the low Arctic one, than shoots grown at ambient CO2. After 13 months, greater amounts of C and N remained in above‐ground litter from plants grown under elevated, rather than ambient, CO2 at the polar semi‐desert site, although lower amounts of C remained in elevated CO2 litter at the low Arctic ecosystem. In the high Arctic, roots grown in the 500 μL L–1 CO2 concentration decomposed significantly more slowly than below‐ground material derived from the ambient CO2 chambers. Elevated CO2 concentrations significantly increased the inital C:N ratio, % soluble carbohydrates and α‐cellulose content, and significantly decreased the inital N content, of the above‐ground material compared to that derived from the ambient treatment. Initially, the C:N ratio and percentage N were similar in both sets of roots derived from the two different CO2 treatments, but soluble carbohydrate and α‐cellulose concentrations were higher, and percentage lignin lower, in the elevated CO2 treatments.The tent treatments significantly retarded shoot decomposition in both ecosystems, probably because of lower litter bag moisture contents, although the additional precipitation treatment had no effect on mass loss from the above‐ground material. The results suggest that neither additional summer precipitation (up to 58%), nor soil temperature increase of 1 °C, which may occur by the end of the next century as an effect of a predicted 4 °C rise in air temperature, had an appreciable effect on root decomposition in the short term in a high Arctic soil. However, at the low Arctic site, greater root decomposition, and a lower pool of root N remaining, were observed where soil temperature was increased by 2 °C in response to a 4 °C rise in air temperature. These results suggest that decomposition below‐ground in this ecosystem would increase as an effect of predicted climate change. These data also show that there is a difference in the initial results of decomposition processes between the two Arctic ecosystems in response to simulated environmental change.

Soil and Plant CO2Emission in Response to Variations in Soil Moisture and Temperature and to Amendment with Nitrogen, Phosphorus, and Carbon in Northern Scandinavia

“…This estimate corresponds with the difference in air and soil temperature shown in this study and in field experiments at different sites with similar climatic regime and soils (e.g. Havstrom et al, 1993;Callaghan and Jonasson, 1995;Chapin et al, 1995;Robinson et al, 1997). Assumptions of changed precipitation and moisture regime in future arctic areas are much more uncertain and variable (Rowntree, 1997).…”

“…However, at the same time as soil moisture levels close to, or below, 200% apparently exerts a stronger control on the soil CO 2 emission than changes in temperature, increased temperature probably increases respiration of aboveground plant tissue, and possibly CO 2 emission from surface litter. In a previous study, root litter decomposition at 0 to 5 ern depth was enhanced by a 2°C soil warming at a nearby heath (Robinson et al, 1997).…”

Optimum liquid density in separation of the physically uncomplexed organic matter in Arctic soils

“…Soils from Churchill and Daring Lake had generally higher OAC:AroC and OAC:AC ratios than soils from Truelove, indicating that subarctic (Churchill) and low arctic (Daring Lake) surface soils store relatively more labile SOM than the high arctic soils (Truelove). Similar to Robinson et al (1997), these results suggest that subarctic and low arctic SOM is likely more sensitive to climate change than SOM from the High Arctic. Furthermore, the results suggest that organic surface soils from the Arctic are likely more sensitive to climate change than mineral surface soils.…”

“…However, only few studies have attempted to elucidate differences among distinct arctic sites (ecosystems). Increasing in situ temperature by 2 ЊC increased SOM decomposition in the subarctic (Abisko, Sweden) but had no significant impact on SOM in the High Arctic (Ny-AaNlesund, Svalbard) (Robinson et al, 1997). Therefore, the latter study suggested that SOM qualities, rather than soil temperature, might initially drive SOM decomposition in the Arctic.…”

Soil microbial and nutrient dynamics in a wet Arctic sedge meadow in late winter and early spring

“…As described by Schmidt and Lipson (2004), plant and microbial growth during summer often deplete soils of available nitrogen. Decomposition of plant litter in the fall and early winter results in a release of available N and C substrates in soil (Robinson et al, 1997), which supports microbial growth during the cold season. The fungal/bacterial ratio is apparently high in winter but in summer the ratio decreases, at least in alpine sites (Lipson et al, 2002;Schadt et al, 2003).…”