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The lifestyles of plants affect their approach to photosynthesis. The long-lived evergreen trees must cope with wide temporal variation in water and nutrient availability that herbaceous species largely avoid. Evergreen trees have thus evolved mechanisms to conserve water and nutrients, and to tolerate water and nutrient stress. However, some of these adaptations have a cost. For example, evergreen trees have lower rates of photosynthesis per unit nitrogen, which can be partly explained by the use of Rubisco for nitrogen storage and the higher internal resistance to CO₂ diffusion. The high internal resistance to diffusion of CO₂ in evergreen trees might be an unavoidable consequence of anatomical and biochemical traits associated with leaf longevity, nutrient conservation and/or drought tolerance.