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Understanding of controls on primary production and net ecosystem production in the Arctic, and on variation in the responsiveness of different arctic ecosystems to climate change and disturbance, has advanced rapidly over the past two decades. The aim of this chapter is to review and summarize these more recent advances, starting in the mid-1970s. Considerable progress has been made in understanding the controls over primary production and its variation across the Arctic landscape. The greatest future need is to understand how long-term changes in primary production are linked to soil processes. One specific need is for new data on root biomass, root production, and the partitioning of belowground respiration into root and soil components. Basic measurements of net ecosystem production (NEP) are also lacking from many kinds of Arctic ecosystems, and information is needed to delineate more clearly the landscape patterns of NEP and its environmental correlations. Controls on soil organic matter accumulation and carbon–nutrient interactions in Arctic soils are another key to improving our understanding. Perspectives on the role of temperature in Arctic ecosystems have changed especially dramatically in the past three decades, from an early focus on adaptations to a low-temperature environment and direct effects of low temperature on individual plants and species. Great progress has been made in understanding indirect effects of temperature and interactions of temperature with other environmental variables in control of plant processes.

Publisher Summary This chapter discusses the constraints on the impact of atmospheric carbon dioxide and interactions between carbon and other living organisms. Carbon is, leaving oxygen aside, the quantitatively most important element in living organisms. An increasing availability of this element through an increasing atmospheric carbon dioxide concentration is therefore expected to have a direct impact on organisms. The constraints are basically of two kinds: the extent to which different components in an ecosystem can adjust the element ratios, ecosystem stoichiometry, that is, how flexible are plant and soil C:N ratios; and the extent to which an increasing availability of one element can change the availability of other elements, that is, if an increase in carbon dioxide concentration can increase the retention of nitrogen in the ecosystem. Stoichiometry places constraints on the amount of carbon stored in ecosystems. From the perspective of carbon-nitrogen interactions, there are three ways in which the amount of carbon in the ecosystem can change: Change the total amount of nitrogen in the ecosystem while maintaining C:N ratios; Change the C:N ratios of the ecosystem components; and change the distribution of nitrogen among ecosystem components.