Acclimation of subarctic vegetation to warming and increased cloudiness

Abstract

Subarctic ecosystems are exposed to elevated temperatures and increased cloudiness in a changing climate with potentially important effects on vegetation structure, composition, and ecosystem functioning. We investigated the individual and combined effects of warming and increased cloudiness on vegetation greenness and cover in mesocosms from two tundra and one palsa mire ecosystems kept under strict environmental control in climate chambers. We also investigated leaf anatomical and biochemical traits of four dominant vascular plant species (Empetrum hermaphroditum, Vaccinium myrtillus, Vaccinium vitis‐idaea, and Rubus chamaemorus). Vegetation greenness increased in response to warming in all sites and in response to increased cloudiness in the tundra sites but without associated increases in vegetation cover or biomass, except that E. hermaphroditum biomass increased under warming. The combined warming and increased cloudiness treatment had an additive effect on vegetation greenness in all sites. It also increased the cover of graminoids and forbs in one of the tundra sites. Warming increased leaf dry mass per area of V. myrtillus and R. chamaemorus, and glandular trichome density of V. myrtillus and decreased spongy intercellular space of E. hermaphroditum and V. vitis‐idaea. Increased cloudiness decreased leaf dry mass per area of V. myrtillus, palisade thickness of E. hermaphroditum, and stomata density of E. hermaphroditum and V. vitis‐idaea, and increased leaf area and epidermis thickness of V. myrtillus, leaf shape index and nitrogen of E. hermaphroditum, and palisade intercellular space of V. vitis‐idaea. The combined treatment caused thinner leaves and decreased leaf carbon for V. myrtillus, and increased leaf chlorophyll of E. hermaphroditum. We show that under future warmer increased cloudiness conditions in the Subarctic (as simulated in our experiment), vegetation composition and distribution will change, mostly dominated by graminoids and forbs. These changes will depend on the responses of leaf anatomical and biochemical traits and will likely impact carbon gain and primary productivity and abiotic and biotic stress tolerance.

Carbon and nitrogen-based gas fluxes in subarctic ecosystems under climate warming and increased cloudiness

“…Detailed results of vegetation and soil physiochemical properties have been presented by Ndah et al 49 Briey, all three study sites were acidic (pH 3.6-4.0). Mesocosms from the P site had higher organic layer depth on average (11 cm) than the T1 (7 cm) and T2 (4 cm) sites.…”

“…Mesocosm soil physiochemical properties, such as the soil organic layer depth, organic matter content, bulk density, NO 3 − , NO 2 − , and NH 4 + concentrations, pH, electrical conductivity, carbon and nitrogen content, total organic carbon content, gravimetric water content, and water holding capacity, were also analyzed at the end of the second growing season. Methods of vegetation surveys and analyses of soil physiochemical properties have been described in detail by Ndah et al 49…”

“…86 The positive relationship of isoprene emission with soil organic matter and negative relationship with gravimetric water content may be due to the inuence of these soil properties on isoprene emitting plant species such as the graminoids Carex vaginata and Deschampsia exuosa which were present especially in mesocosms from the tundra sites (T1 and T2). 49 Isoprene is also thought to be produced as a metabolite by soil microorganisms, 89 hence soil organic matter and gravimetric water content may inuence microbial metabolism and production or consumption of isoprene. 89,90 Warming and/or increased cloudiness may alter the pattern of resource allocation between above-and belowground biomass, thereby modifying BVOC emission responses.…”

“…The tundra sites were characterized by podsol soil formation while the palsa site was a peatland, with several meters of peat and with discontinuous permafrost underneath. Mesocosm collection, vegetation composition, and soil physiochemical properties at the sites have been described in detail by Ndah et al 49 Aer collection, mesocosms were weighed and transported to the laboratory and regularly sprayed with distilled water to avoid desiccation. Prior to the start of the rst and second growing seasons in 2020 and 2021, respectively, mesocosms were maintained at +4 °C in a well-ventilated dark room to achieve plant dormancy occurring in (sub)arctic winter under snow.…”

“…In the increased cloudiness treatments, PAR was decreased by 50% compared to the control and represented thick-cloud layer conditions (cloud optical depth of 30). The experimental setup and climate simulation have been described in detail by Ndah et al 49 Mesocosms were exposed to the summer climate treatments in the chambers during two consecutive years (2020 and 2021) and for a three-month period (June-August) each year, averaging the length of the main growing season in the subarctic. Mesocosms were rotated within chambers on a weekly interval and mesocosms and treatments rotation between chambers was done on bi-weekly intervals to minimize chamber effects.…”