Ecophysiological responses of Opuntia to water stress under various semi–arid environments
Keywords:Drought, mycorrhizas, Opuntia, photosynthesis, plasticity.
In this review, information relating to the ecophysiological response of Opuntia robusta plants in wild populations and cultivated plants of O. ficus–indica under various environments is presented. The succulence of O. ficus–indica allowed plants to maintain photosynthetical activity for five months after rains had come to an end. The highest values of carbon gain were observed in the autumn and at the beginning of winter, coinciding with fresh temperatures and an increase in irradiance. The combined effect of photosynthetic plasticity, the association with mycorrhizal fungi and the avoidance and tolerance mechanisms such as the cessation in the formation of both new cladode and new roots allowed wild plants of O. robusta growing in a rocky environment to maintain carbon gain after being exposed to prolonged drought. The development of daughter cladodes on mother cladodes of O. ficus–indica during the dry spring season, lead to physiological drought which was noticeable not only in the reduction in photosynthesis and chlorophyll content but also in the relative water content. Daughter cladodes caused physiological stress on mother cladodes during the spring dry period even on well–watered plants and their effects were exacerbated by the decrease in irradiance.