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The effects of climate change on plants are particularly pronounced in the Arctic region. Warming relaxes the temperature and nutrients boundaries that limit tundra plant growth. Increased resource availability under future climate conditions may induce a shift from a conservative economic strategy to an acquisitive one. Following the leaf economics spectrum that hypothesizes a strategy gradient between survival, plant size and costs for the photosynthetic leaf area, light absorption of tundra plants may increase. We investigated climate change effects on light absorptance and the relationship between light absorptance (fraction of absorbed photosynthetically active radiation, FAPAR) and structural and nutritional leaf traits, performing a soil warming and surface soil fertilization experiment on two deciduous tundra shrub species. Our results show that fertilization and warming combined increase light absorptance in Arctic shrubs and that FAPAR is correlated with leaf nutrients but not with structural leaf traits. This indicates an economic strategy shift of shrubs from conservative to acquisitive induced by warming and fertilization combined. We found species‐specific differences: FAPAR was influenced by warming alone in Betula nana but not in Salix pulchra, and FAPAR was correlated with leaf phosphorus in B. nana but not in S. pulchra. We attribute this to water limitation of B. nana that generally grows in drier areas within the study site compared to S. pulchra. We conclude that FAPAR is a measure that opens up more possibilities to estimate nutritional leaf traits and nutrient cycles, plant economic strategies, and ecological feedbacks of the tundra ecosystem on broader scales. Plain Language Summary: The effects of climate change on plants are very strong in the Arctic. Tundra plants are usually limited by temperature and nutrients. Tundra plants usually have an energy saving strategy, with long lifespan and small leaves. A warmer environment with more nutrients may shift their strategy to faster growth, larger leaves, and more light absorption. We examined climate change effects on the light absorptance of two tundra shrubs. In order to do this, we made an experiment in which we warmed and fertilized the soil. We furthermore studied the relationship between light absorptance and plant traits. Our results show that fertilization and warming combined increase light absorptance in Arctic shrubs. Furthermore, we could show that light absorptance is strongly related to the concentration of nutrients in the leaves. We also found differences in light absorptance between the two shrub species. We believe that these differences are due to Betula nana growing in drier areas with less water compared to Salix pulchra. We think that light absorptance is a good measure for predicting changes in nutrient cycles and plant strategies in the tundra ecosystem. Key Points: Fertilization and warming combined increase light absorptance in two deciduous Arctic shrub species. This indicates an economic strategy shiftLight absorptance is correlated with leaf nutrients but not with structural leaf traits in Arctic shrubsThere are species‐specific differences between the shrub species in regard to light absorptance [ABSTRACT FROM AUTHOR]

Despite the importance of high-latitude surface energy budgets (SEBs) for land-climate interactions in the rapidly changing Arctic, uncertainties in their prediction persist. Here, we harmonize SEB observations across a network of vegetated and glaciated sites at circumpolar scale (1994-2021). Our variance-partitioning analysis identifies vegetation type as an important predictor for SEB-components during Arctic summer (June-August), compared to other SEB-drivers including climate, latitude and permafrost characteristics. Differences among vegetation types can be of similar magnitude as between vegetation and glacier surfaces and are especially high for summer sensible and latent heat fluxes. The timing of SEB-flux summer-regimes (when daily mean values exceed 0 Wm -2 ) relative to snow-free and -onset dates varies substantially depending on vegetation type, implying vegetation controls on snow-cover and SEB-flux seasonality. Our results indicate complex shifts in surface energy fluxes with land-cover transitions and a lengthening summer season, and highlight the potential for improving future Earth system models via a refined representation of Arctic vegetation types., (© 2022. The Author(s).)