Phosphorus Nutrition and Water Relations of European Beech (Fagus sylvatica L.) Saplings Are Determined by Plant Origin

Climate change, specifically the increasing frequency and intensity of summer heat and drought, has severe influences on the performance of beech forests, including decline in growth, reduced nutrient turnover, enhanced mortality, and a shift in spatial distribution northwards and towards higher elevations. The present study aimed to characterize the physiological responses of Croatian beech saplings originating from 10 natural forest stands to experimentally applied water deprivation in a common-garden experiment. The aim was to evaluate the extent to which external factors such as climate, as well as nitrogen (N) and phosphorus (P) availability in the soil of the natural habitats, control the response of beech saplings to water deprivation. For this purpose, beech saplings from 10 forest stands that differed in terms of soil type, chemical soil properties, as well as climate were collected in winter, cultivated in an artificial soil substrate under controlled conditions for one year, and then subjected to 29 days of water deprivation. Responses to water deprivation were observed in the antioxidative system (total ascorbate, reduced ascorbate, oxidized ascorbate, and redox state) in leaves and fine roots. The latter allowed us to categorize saplings as adapted or sensitive to water deprivation. P over N availability in the soil rather than climatic conditions in the natural habitats controlled the response of beech saplings to the water-deprivation event. The categorization of saplings as adapted or sensitive to water deprivation was related to genetic parameters. The results of this multidisciplinary study (tree physiology, climate, and genetic data) are considered to be highly significant and beneficial for the adaptation of European beech forests to changing climatic conditions.