Phenotypic plasticity
We aimed to assess phenotypic plasticity by determining the
response of V. alpina populations to short-term heat spells
mimicking heat-wave conditions. Despite the overall good
tolerance to the heat spells exhibited by V. alpina plants, we
did observe differences among populations in the level of phenotypic
plasticity towards the simulated heat wave. Such differences among
populations were principally due to different water acquisition
capabilities (Chaves et al. 2002) which results in different WUEs at a
given level of stomatal opening (Medrano et al. 2009). The significant
increase of net photosynthesis and WUE under heat spells showed
by SWE (Fig 4b) resulted in a simultaneous increase of biomass (Fig.
4a), consistent with the overall effects of climate warming on plants
(Wang et al., 2018; Song et al., 2019). Phenotypic plasticity can evolve
and can be selected to cope with variable environments (Ackerly et al
2000; Richards et al 2006), promoting population persistence through the
development of more adapted traits (Nicotra et al. 2010; Richardson et
al. 2017). However, we also found that such plastic response to warmer
growing conditions did not occur in the other populations of V.
alpina, whose biomass was lower and did not change between treatments.
This apparent lack of responses may occur in extreme environments, which
select so strongly for stress adaptations that populations evolve
decreased plasticity, maintaining traits better adapted to an extreme
environmental disturbance (Matesanz et al. 2010). Furthermore, low above
ground biomass is common under limited water availability, allowing
plant to better conserve water and reduces evapotranspiration (Basu et
al., 2016; White et al. 2023). This may explain why the populations
showing the lowest biomass (PRA), also showed the lowest mortality in
response to heat spells (Fig. 4g).