Environmental gradients as ?natural labs? for elucidating the regeneration dynamics of three Nothofagus species under different climatic scenarios in Patagonia

CAGNACCI J; MARCHELLI P; BATLLA DIEGO; ESTRAVIS-BARCALA M; PASTORINO M; ARANA VERONICA; GONZÁLEZ-POLO M; MARTÍNEZ-MEIER A

Buenos Aires

Simposio; Fronteras en Biociencias 3; 2018

We work in Patagonian forests, the southernmost woody ecosystems of the world, in which three tree species have a clear altitudinal distribution. Nothofagus obliqua is frequent at 650-850 m above the sea level, N. nervosa at 900-1000 m and N. pumilio is distributed above 1000 m up to the treeline. Temperature is the environmental factor that shows the strongest association with altitude. In this ecosystem, by coupling mathematical models with ecological data, we previously demonstrated that seed responsiveness to temperature of the three Nothofagus species was linked to the thermal characteristics of their preferred ecological niche and that this trait contributed to germination dynamics across altitude. In their natural distribution range, there was overlap in the timing of germination of the species, which was restricted to early-spring. By contrast, outside their species distribution range, germination was temporally uncoupled with altitude (Arana et al., 2016 New Phytologist 209:507). Here, through a combination of physiological and ecological approaches we evaluated the effect of this germination dynamics across elevation on fitness, measured as seedling survival. For this purpose, we simulated germination pulses (from late winter to late spring) of the three species in the forest, inside and outside their distribution range during two consecutive years, sowing c.a. 4800 germinated seeds/spp/year. We measured the dynamics of emergence and seedling mortality every 30 days, during two years. Our results show that inside their natural ecological niche, germination dynamics influences species´ fitness. Moreover, we show that the previously described intra-specific phenotypic plasticity in germination dynamics across elevation adjusts temporal patterns of germination to the environment more favorable for seedling survival. We discuss our results in the context of the way in which seed traits in combination with natural gradients of temperature, influences species´ fitness across elevation.