Tolerância a regimes térmicoscontrastantes em mudas de Myrsine coriacea provenientes de matrizes localizadas ao longo de um gradiente de altitude

Abstract

Species with a wide geographical distribution, such as Myrsine coriacea (Primulaceae), may include divergent ecophysiological changes, which may be a consequence of long-term adaptation to the specific conditions of each place of occurrence. We investigated the effects of contrasting thermal regimes on growth, photosynthetic performance and biochemical characteristics of M. coriacea plants, the results of matrices located along an altitude gradient in the Atlantic Forest. The hypothesis that there is a divergence of ecophysiological strategies for tolerance to contrasting thermal regimes between plants from populations located at low and high altitudes was tested. For this, the seedlings were produced after the collection of native seeds. Subsequently, as plants were grown in climate greenhouses (altitude: 120 m) under contrasting thermal regimes. The experiment was set up in a randomized design, in a 2 x 7 factorial scheme: two contrasting thermal regimes [Low atmospheric demand (BDA) and High atmospheric demand (ADA)]] and seven populations, located along an altitude gradient (639 a 1774 meters of altitude). The plants were grown for 120 days under contrasting conditions of air temperature (Tar) and vapor pressure deficit (DPV): BDA (Tar (mean) day/night: 28.2/21.2 °C and DPVmean day/night: 0.60/0.05 kPa) and ADA (Tar (mean) day/night: 30.2/25.3 °C and DPVmean day/night: 1.19/0.22 kPa). The results indicate greater biomass production in the BDA, greater photosynthetic capacity per unit of leaf area in the ADA, no variation in the concentration of photosynthetic pigments between the thermal regimes and different responses in the leaf nutrient concentration and isotopic carbon ratio 13 ( 13C), regardless of the origin altitude. Origin altitude explained most of the total variation in most of the characteristics analyzed. With the increase in the original altitude, mainly above 900 meters of altitude, the differences in growth characteristics between thermal regimes intensified, while, generally, no significant trend occurred in photosynthetic and biochemical characteristics. Plants from the population located at 1774 meters of altitude stood out with greater divergence in ecophysiological responses from other populations, with less biomass production and photosynthetic performance, and different biochemical responses. Probably, differential strategies to deal with contrasting thermal regimes may have led to the differentiation of ecotypes within the species under thermal variations in an altitudinal gradient, as in the population of 1774 meters of altitude. The results demonstrate that the ecophysiological performance of M. coriacea populations, located at altitudes below 900 meters, is more limited, which can be aggravated in a scenario of global changes. Adaptive strategies can facilitate survival in situ, but occurring at higher altitudes or latitudes (with lower temperatures) can contribute to survival in this scenario. The use of the species for forest majestic in places of low atmospheric demand (low temperatures), is recommended with seedlings from matrices located at higher altitudes (above 900 meters). In contrast, management in places with high atmospheric demand (high temperatures), seedlings from all altitudes sampled in this study can be used, with the exception of the population of 1774 meters of altitude.