|Abstract: ||The Supramontes region and Gennargentu massif are two of the most interesting territories of Central Eastern Northern Sardinia. Riparian vegetation among
mountainous waterways of these territories are mainly constituted by Alnus glutinosa with other associated taxa such as Taxus baccata, Ilex aquifolium and Rhamnus
persicifolia. Rare and threatened Sardinian endemic species such as Ribes multiflorum subsp. sandalioticum, Aquilegia barbaricina, Rhamnus persicifolia and Paeonia corsica
grow under and close to the canopy of such riparian woods.
Temperature is considered one of the major environmental factor governing seed germination in moist soil and, also is responsible for changes in dormancy states of
seeds. Seed dormancy prevents germination in a specified period of time, under any combination of environmental factors that otherwise favour germination and it is
mediated, at least in part, by the plant hormones abscisic acid and gibberellins. Dormancy can be broken by some environmental stimuli, such as a cold and/or warm
stratification and gibberellic acid (GA) treatment. As dormancy is present throughout the higher plants in all major climatic regions, adaptation has resulted in divergent
responses to the environment. Through this adaptation, germination is timed to avoid
unfavourable weather for subsequent plant establishment and reproductive growth. In non-dormant seeds, the germination response to accumulated temperature could be
modelled by a thermal time (θ) approach; in this model, seeds accumulate units of thermal time (°Cd) to germinate for a percentile g of the population. When seeds are
subjected to temperatures (T) above a base temperature for germination (Tb), germination rate increases linearly with temperature to an optimum temperature (To),
above which germination rate starts to decrease. In the sub-optimal range (To – Tb), germination occurs in the time tg, when the thermal time accumulated has reached the
critical value (θg) for a percentile g of the population, and can be described as θg = (T –Tb)tg.
In this work, the class of dormancy and thermal requirements for seed dormancy release and germination were investigate and/or confirmed for R. persicifolia, A.
barbaricina, P. corsica and R. multiflorum subsp. sandalioticum; a thermal-time model, based on a soil heat sum approach, was developed in order to characterize its Thermal niche for germination and predict its seed germination phenology in the field.R. persicifolia showed physiological dormancy (PD), while the other three
species highlighted morphophysiological dormancy (MPD); in particular, epicotyls MPD was found in P. corsica and confirmed in R. multiflorum subsp. sandalioticum.
Thermal thresholds (Tb and θ50) requirements of seed germination were identified for all these species; in addition, the thermal thresholds for embryo growth was detected for A. barbaricina. The soil heat sum model developed in this work may have applicability to
predictions of in situ regeneration of other species growing on Mediterranean mountain waterways. This work could confirmed that the studied species, belonging to different families placed in different phylogenetic clades, could have experienced a convergent evolution on their seed morphology and type of seed dormancy, as a response to similar environmental and climatic conditions due by the same habitat and ecosystem.|