Differences in photochemistry and response to heat stress between silver fir (Abies alba Mill.) provenances

The acclimation of silver fir to the conditions of the plantation sites has greater influence on PSII thermostability and performance than does on local adaptation. Forest ecosystems are frequently exposed to heat stress, which adversely affects their growth, performance, and ultimately survival. The knowledge of physiological responses to heat can help mitigate the effects of climate change by facilitating the choosing of suitable reproductive material for future reforestation programs. However, the intraspecific variation of adaptive traits, including the response to heat, has not been well documented. Therefore, we attempted to determine how PSII photochemistry of different silver fir (Abies alba Mill.) provenances varies in responses to heat stress and to reveal if intraspecific variation in PSII performance and thermostability is more affected by the climate of provenance origin or the plantation site. We tested 17 fir provenances sampled at two contrasting international provenance trial sites: Hertnik in Slovakia (390 m a.s.l.) and Kaprun in Austria (1100 m a.s.l.). Short-term heat stress was simulated for seven temperatures ranging from 20 to 51 A degrees C using a water bath. The PSII thermotolerance was assessed via parameters of chlorophyll a fluorescence derived from the OKJIP transient. We observed several climatic variables of the provenances that significantly affected the photochemistry performance and thermostability of PSII, reflecting an additive hereditary basis. Almost all measured parameters varied significantly between trial plots and showed significant trial-by-provenance interactions pointing to acclimation triggered by the different conditions at the trial plots. Overall, the performance of PSII under non-stressing conditions and after heat treatment was better for provenances growing at the warmer trial site at Hertnik.