No abstract

Stem photosynthesis has been suggested to play relevant roles to cope with different biotic and abiotic stress factors, including drought. In the present study, we performed measurements of stem hydraulic conductance and non-structural carbohydrate content in the evergreen Laurus nobilis L. and the deciduous Populusalba L., subjected to inhibition of stem photosynthesis and successive exposure to a drought-recovery cycle in order to check if stem photosynthesis may be involved in allowing hydraulic recovery after drought stress relief. Stem shading affected the growth of L. nobilis but not of P. alba saplings. By contrast, inhibition of stem photosynthesis was coupled to inhibition of hydraulic recovery following embolism build-up under drought in P. alba but not in L. nobilis. The two study species showed a different content and behavior of nonstructural carbohydrates (NSCs). The differences in NSCs’ trend and embolism reversal ability led to a significant relationship between starch content and the corresponding hydraulic conductance values in L. nobilis but not in P. alba. Our findings suggest that stem photosynthesis plays a key role in the maintenance of hydraulic functioning during drought especially in the deciduous species. This, in turn, may increase their vulnerability under current global climate change scenarios.

With the recent climate warming, tundra ecotones are facing a progressive acceleration of spring snowpack melting and extension of the growing season, with evident consequences to vegetation. Along with summer temperature, winter precipitation has been recently recognised as a crucial factor for tundra shrub growth and physiology. However, gaps of knowledge still exist on long-living plant responses to different snowpack duration, especially on how intra-specific and year-to-year variability together with multiple functional trait adjustments could influence the long-term responses. To fill this gap, we conducted a 3 years snow manipulation experiment above the Alpine treeline on the typical tundra species Juniperus communis, the conifer with the widest distributional range in the north emisphere. We tested shoot elongation, leaf area, stomatal density, leaf dry weight and leaf non-structural carbohydrate content of plants subjected to anticipated, natural and postponed snowpack duration. Anticipated snowpack melting enhanced new shoot elongation and increased stomatal density. However, plants under prolonged snow cover seemed to compensate for the shorter growing period, likely increasing carbon allocation to growth. In fact, these latter showed larger needles and low starch content at the beginning of the growing season. Variability between treatments slightly decreased over time, suggesting a progressive acclimation of juniper to new conditions. In the context of future warming scenarios, our results support the hypothesis of shrub biomass increase within the tundra biome. Yet, the picture is still far from being complete and further research should focus on transient and fading effects of changing conditions in the long term.