The impact of climatic variations on the reproductive success of Gentiana lutea L. in a Mediterranean mountain area.

Increases in temperature have been predicted and reported for the Mediterranean mountain ranges due to global warming and this phenomenon is expected to have profound consequences on biodiversity and ecosystem functioning. We hereby present the case of Gentiana lutea L. subsp. lutea, a rhizomatous long-lived plant living in Central-Southern Europe, which is at the edge of its ecological and distributional range in Sardinia. Concretely, we analysed the reproductive success experienced during three phenological cycles (2013/2014, 2014/2015 and 2015/2016) in four representative populations, with particular attention to the phenological cycle of 2014/2015, which has been recorded as one of the warmest periods of the last decades. The Smirnov-Grubbs test was used to evaluate differences in temperature and precipitation regimes among historical data and the analysed years, while the Kruskal-Wallis followed by the Wilcoxon test was used to measure differences between anthesis and reproductive performances among cycles and populations. In addition, generalised linear models were carried out to check relationships between climate variables and reproductive performance. Significant differences among climate variables and analysed cycles were highlighted, especially for maximum and mean temperatures. Such variations determined a non-flowering stage in two of the four analysed populations in 2014/2015 and significant differences of further five reproductive traits among cycles. These results confirmed that in current unstable climatic conditions, which are particularly evident in seasonal climates, reproductive success can be a sensitive and easily observable indicator of climatic anomalies. Considering the importance of this issue and the ease and cost-effectiveness of reproductive success monitoring, we argue that research in this sense can be a supporting tool for the enhancement of future crucial targets such as biodiversity conservation and the mitigation of global warming effects.

Seed Germination in Cistus ladanifer: Heat Shock, Physical Dormancy, Soil Temperatures and Significance to Natural Regeneration.

Seeds of Cistus ladanifer experience bursts of germination following fires. The effects of heat shock from 10 °C to 150 °C on seed germination were investigated by final germination plus the number of days required for germination to start and finish, and symmetry of cumulative germination. The occurrence of physical dormancy in C. ladanifer seeds was investigated by a variety of methods, including imbibition, scanning electron microscopy (SEM) and light microscopy, and use of dyes. The significance of responses of C. ladanifer seeds to fires was investigated essentially by abstracting existing literature and by using fire effects models and simulations. Parameters of germination were variously affected by heat treatments-positively in the range 80⁻100 °C, negatively above 130 °C. Non-dormancy was consistently found in about 30% of seeds but no evidence was obtained to support the existence of physical dormancy in the dormant fraction of C. ladanifer seeds. Two complementary processes seem to be in place in seeds response to fire. A direct fire-driven increase in germination of virtually all seeds in response to the appropriate heat load produced by fire or, in the absence of such heat loads, the germination of the non-dormant fraction provided that above-ground vegetation burns.

Plant water relations influence carbon gain in a grass occurring along sharp gradients of soil temperature.

• The effects of supraoptimal soil temperatures on plants are not well known, despite their importance with fluctuating temperatures in many habitats. The effects of warm soils on carbon gain and water relations were evaluated for Dichanthelium lanuginosum , a grass that can persist in soils sustained at > 45°C by geothermal heating. • Microclimate, root and shoot biomass, photosynthetic gas exchange, and soil/plant water relations were measured under different root-zone temperatures in the field and glasshouse. • Carbon gain at midsummer decreased markedly for plants in 35-50°C vs c. 30°C soils, due to foliar necrosis and stomatal constraints to photosynthesis. Daily rates of dehydration, estimated from changes in leaf water potential, were also 30% greater for plants in the warmer soils. Soil water, evapotranspiration, and ratios of root : shoot biomass and area could not explain greater plant dehydration in warmer soils. • Reduced uptake of soil water may therefore lead to water stress and stomatal limitations to photosynthesis in warm soils, and may thereby influence the local-scale distribution of D. lanuginosum along steep gradients of soil-temperature within geothermal basins.

Elevational patterns of Polylepis tree height (Rosaceae) in the high Andes of Peru: role of human impact and climatic conditions.

We studied tree height in stands of high-Andean Polylepis forests in two cordilleras near Cuzco (Peru) with respect to variations in human impact and climatic conditions, and compared air and soil temperatures between qualitatively defined dry and humid slopes. We studied 46 forest plots of 100 m(2) of five Polylepis species at 3560-4680 m. We measured diameter at breast height (dbh) and tree height in the stands (1229 trees in total), as well as air and soil temperatures in a subset of plots. The data was analyzed combining plots of given species from different sites at the same elevation (±100 m). There was no elevational decrease of mean maximum tree height across the entire data set. On humid slopes, tree height decreased continuously with elevation, whereas on dry slopes it peaked at middle elevations. With mean maximum tree heights of 9 m at 4530 m on the humid slopes and of 13 m at 4650 m on the dry slopes, we here document the tallest high-elevation forests found so far worldwide. These highest stands grow under cold mean growing season air temperatures (3.6 and 3.8°C on humid vs. dry slopes) and mean growing season soil temperatures (5.1 vs. 4.6°C). Mean annual air and soil temperature both decreased with elevation. Dry slopes had higher mean and maximum growing season air temperatures than humid slopes. Mean annual soil temperatures did not significantly differ and mean annual air temperatures only slightly differed between slopes. However, maximum air temperatures differed on average by 6.6 K between dry and humid slopes. This suggests that the differences in tree height between the two slopes are most likely due to differences in solar radiation as reflected by maximum air temperatures. Our study furthermore provides evidence that alpine Polylepis treelines grow under lower temperature conditions than global high-elevation treelines on average, suggesting that Polylepis species may have evolved special physiological adaptations to low temperatures.