Changes in Ecosystem Production, Soil Nutrient Availability and Microbial Biomass in a High Arctic Semi Desert During the Growing Season and the Freeze-in Period

Carbon dioxide fluxes in a high arctic semi desert at Zackenberg Research Station in Northeast Greenland were measured continuously from the 5th of July through 10th of October, covering both the growing season and the freeze–in period. To study the effects of anticipated increased summer precipitation due to climate change, water has been added weekly during the growing season to the field plots since 1996. Water addition was combined with phosphorus and nitrogen amendment in 1996, 1997 and 2007 in a fully factorial design to simulate the effects of increased nutrient availability due to expected future warming. CO₂ efflux was measured in situ in closed chambers as uptake through gross ecosystem production (GEP), release through ecosystem respiration (ER), and as net ecosystem production (NEP). Furthermore, soil respiration, nutrient availability and microbial C, N and P were measured at intervals throughout the experiment.

Preliminary results show that water addition has a significant, positive effect on ER during the growing season in complex interactions with nitrogen and phosphorus addition. Likewise, GEP increased with combined water and phosphorus addition. Water addition significantly increased fine root biomass as well as microbial biomass C and P, possibly due to greater root exudation from the increased below ground plant biomass. During the growing season an increase in microbial C/N-ratio was observed, indicating a shift in the microbial community composition.

Our results indicate that future increased mineralization and precipitation during summer will have a greater impact on GEP than ER as the increase in CO₂ uptake in plants exceeds the increase in ecosystem respiration in this high arctic semi desert. Hence, increased summer precipitation in widespread high arctic semi desert may lead to denser vegetation and faster nutrient organic matter turnover. Data collected during the freeze-in period are currently being analysed.