Short‐Term Weather Variability Alters Plant Carbon Balance in Arctic Tundra Species

ABSTRACT Increasing weather variability is an aspect of global change with poorly understood impacts on organisms and ecosystems. Model predictions have shown that weather variability can diminish physiological performance, but empirical corroboration remains limited. Here, we explore the effects of short‐term variation in temperature and light on plant physiological functioning and the resulting leaf carbon balance. Plant dark respiration ( R d ) and net CO 2 assimilation ( A ) both respond non‐linearly to environmental drivers such as temperature and light, which indicates that weather variability would impact average performance. Leveraging Jensen's inequality, which describes non‐linear averaging, we hypothesized that variable temperature would elevate R d relative to stable temperature, while variable light would reduce A compared to stable light, and that the responses would be stronger where the response functions are more curved. From the dry heath tundra nutrient enrichment plots at the Arctic Long‐Term Ecological site (Toolik Field Station), we measured the R d and A responses of three common Arctic plant species ( Betula nana, Chamaenerion angustifolium, Calamagrostis stricta ) to short‐term high‐frequency variation in temperature and light, respectively, at mean temperatures of 15°C and 25°C. As predicted by theory, temperature variability increased average R d and light variability decreased average A , but only at 15°C for R d and at 25°C for A , where the response functions were more curved. Moreover, experimental results yielded greater responses to variability than predicted by Jensen's inequality. For example, high light variability (600 to 1800 PAR) produced average A rates equivalent to constant low light at 600 PAR. Increases in R d and decreases in A under more variable conditions suggest diminished carbon sequestration in Arctic plants experiencing greater weather variability even without a shift in the mean. This investigation provides unique empirical evidence that weather variability can exert an overall negative impact on the carbon balance of Arctic plant communities.