C4 photosynthesis and water stress

It is suggested that there is a limited capacity for photorespiration or the Mehler reaction to act as significant alternative electron sinks under water stress in C(4) photosynthesis. This may explain why C(4) photosynthesis is equally or even more sensitive to water stress than its C(3) counterpart in spite of the greater capacity and water use efficiency of the C(4) photosynthetic pathway.