, Volume 240, Issue 2, pp 343-352

Ecophysiological significance of chlorophyll loss and reduced photochemical efficiency under extreme aridity in Stipa tenacissima L.

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Stipa tenacissima L., a perennial tussock grass widely found in semi-arid environments of the Iberian Peninsula and North Africa, is subjected to multiple stresses during the extreme summer conditions of south-east Spain. We characterised the photoprotective mechanisms of S. tenacissima during the transition from spring to summer and autumn. S. tenacissima experienced a marked water deficit (Ψ{ pd} < -8.4 MPa) and the complete suppression of CO2 assimilation in August, associated with a 72% reduction of maximal photochemical efficiency of PSII (F{ v}/F{ m}). These reduced F { v}/F{ m} values were related to the pre-dawn maintenance of high levels of epoxidized forms of xanthophyll-cycle pigments (DPS{ pd}, ca. 42% higher than spring values), and with a 60% reduction in the concentration of total chlorophyll (Chl a+b). These changes were associated with a low capacity of dissipation of the excitation energy non-radiatively (measured as NPQ). Leaves showed a complete recovery of F { v}/F{ m} and xanthophyll and chlorophyll concentrations after the autumn rainfall, which reached levels similar to that of spring. This poikilohydric-type response of S. tenacissima to stress allows for a greater tolerance of water shortage, high temperature and high light intensity, which are typical in these semi-arid environments and accounts for its distinctive opportunistic growth.