Changes of the photosynthetic behaviour in annual C<sub>3</sub> species at late successional stage under environmental drought conditions

Abstract

Differences in structural, physiological, and biochemical features between C3 and C4 species resulted in different wateruse efficiencies and different adaptations to climate. This paper aimed at investigating, at a late successional stage, the water-use efficiency of two forage species, Dichanthium ischaemum and Dasypyrum villosum, which exhibit different growth forms (perenial, annual) and photosynthetic mechanisms (C4 and C3, respectively). The annual C3 species Avena fatua, at an early successional stage, was included in our experiments to contrast its behaviour against D. villosum. The experiment was conducted during the growing season in low-elevation grasslands of North Greece. Midday leaf water potential, net photosynthetic rate, transpiration rate and stomatal conductance were measured. Instantaneous water-use efficiency (WUE) and intrinsic water-use efficiency (WUEi) were calculated in D. ischaemum, D. villosum, and A. fatua. The results suggest that, under natural rainfall conditions, the annual C3 grass species D. villosum exhibits a similar WUE with higher values of WUEi than the perennial C4 species D. ischaemum at late stage of succession on the low elevation Mediterranean grasslands. Moreover, A. fatua at an early successional stage, exhibited different photosynthetic behaviour than D. villosum at a late successional stage. These findings indicate that the annual C3 species D. villosum under drought and at a late successional stage seems to modify the WUE obtaining values similar to those of C4 species. The extent to which the ecophysiological characteristics of D. villosum are environmentally or intrinsically determined remains to be answered.