Climate warming is anticipated to make high latitude ecosystems stronger C sinks through increasing plant production. This effect might, however, be dampened by insect herbivores whose damage to plants at their background, non-outbreak densities may more than double under climate warming. Here, using an open-air warming experiment among Subarctic birch forest field layer vegetation, supplemented with birch plantlets, we show that a 2.3°C air and 1.2°C soil temperature increase can advance the growing season by 1-4 days, enhance soil N availability, leaf chlorophyll concentrations and plant growth up to 400%, 160% and 50% respectively, and lead up to 122% greater ecosystem CO 2 uptake potential. However, comparable positive effects are also found when insect herbivory is reduced, and the effect of warming on C sink potential is intensified under reduced herbivory. Our results confirm the expected warming-induced increase in high latitude plant growth and CO 2 uptake, but also reveal that herbivorous insects may significantly dampen the strengthening of the CO 2 sink under climate warming.

Ecosystem processes, such as plant litter decomposition, are known to be partly genetically determined, but the magnitude of genetic variation within local populations is still poorly known. We used micropropagated field-grown saplings of 19 Betula pendula genotypes, representing genetic variation in a natural birch population, to examine (1) whether genotype can explain variation in leaf litter decomposition within a local plant population, and (2) whether genotypic variation in litter decomposition is associated with genotypic variation in other plant attributes. We found that a local B. pendula population can have substantial genotypic variation in leaf litter mass loss at the early stages of the decomposition process and that this variation can be associated with genotypic variation in herbivore resistance and leaf concentrations of soluble proteins and total nitrogen (N). Our results are among the first to show that fundamental ecosystem processes can be significantly affected by truly intraspecific genetic variation of a plant species.

No abstract