Responses in Ecosystem Carbon Balance

Increased gross C fixation was found early in the growing season in tussock tundra after 3.5 years of warming, but the net ecosystem production still was negative because of a higher growing season respiratory C loss (Hobbie and Chapin, 1998). Also, measurements in the Swedish treeline heath after seven years of treatment showed a mid-season C loss in warmed plots relative to 

Overall, the results from eco.system experiments, which have been conducted across a broad variety of ecosystem types in the Arctic, have shown both large similarities and dissimilarities. Within all manipulated ecosystem types, it appears that N or P addition has led to the greatest response, followed by a lower and much more variable response to warming, while water addition generally has led to small responses. Most responses, regardless of type of treatment, have occurred through the direct or indirect effect of the treatment on the N (or P) cycle (Shaver et al, 1992), which also feeds back to the ecosystem carbon balance in a variety of ways (McKane et al, 1997). 

In spite of large soil stores of organic matter and plant nutrients, net primary production within almost all arctic ecosystem types is limited by low availability of plant-available nutrients, particularly N, and of P in wet ecosystem types. This is due to slow microbial mineralization rates associated with low temperature and often combined with extreme wet or dry conditions in several ecosystem types. Furthermore, soil microorganisms immobilize nutrients and may even act as competitors with the plants for nutrients during the growing season, when the nutrient demand by both microbes and plants is high. Recent research has, however, shown that plants can partially circumvent possible competition 

This contribution is based largely on research supported by the US National Science Foundation, the Danish and Swedish Research Councils, and the Swedish Environmental Protection Board. 

Abuzinadah, R. A., and Read, D. J. (1988). Amino acids as nitrogen sources for ectomycorrhizal fungi. Utilization of individual amino acids. Trans. Br. MycoL Sac. 91,473-479. 

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