METABOLIC SWITCH. “Clearly, when photosynthesis is reduced cell energy requirements must be met through metabolic pathways such as glycolysis or oxidative phosphorylation. Accordingly, photosynthetic rates and capacities of adult needles are temperature- and/or photoperiod-dependent, peaking in the summer.”
http://jxb.oxfordjournals.org/content/66/11/3113.full