Altered Volatile Emissions and Incomplete Photosynthetic Recovery after Heatwave-Associated Drought and Rewetting in the Woolly Feather-Moss Tomentypnum nitens

Abstract Mosses dominate ground cover in many ecosystems and are central to carbon and nutrient cycling, water regulation, and surface energy balance. Their poikilohydric physiology, without stomatal control or vascular transport, couples metabolism closely to moisture. While climate extremes affecting moisture become more frequent, how drought and rewetting affect volatile organic compound (VOC) emissions from mosses remains poorly understood. This study examined how a heatwave-associated drought and subsequent rewetting affected VOC emission rates and blend compositions in the moss Tomentypnum nitens. Subarctic heath mesocosms containing T. nitens were maintained in climate chambers during a pre drought period and exposed sequentially to a three-week heatwave-associated drought, and one week rewetting treatment. Moss shoots detached from mesocosms were enclosed in a gas-exchange cuvette to measure VOC emissions analyzed by GC-MS, net photosynthesis and evaporation rates. Tissue water content was also determined. Drought strongly reduced water content and evaporation and shifted net photosynthesis from positive to negative values. Total VOC emissions declined by 90% in response to drought and recovered after rewetting (p = 0.06). Drought also shifted the VOC blend toward hydrocarbon dominance (nearly 80% of total). After rewetting, the blend contained a greater proportion of oxygenated VOCs and a smaller proportion of sesquiterpenes than before drought. The legacy effects of drought on VOC blend may influence both the ecological roles of moss VOCs and their contribution to biosphere-atmosphere interactions.