Deciduous species must rely on stored reserves in stems and roots for the initiation of new season springtime growth. So perhaps evergreen species that can photosynthesize year-round rely more on leaf photosynthate to initiate springtime growth and store less in stems and roots. To test this hypothesis, Wyka et al. (2016) investigated whole-plant non-structural carbohydrate (NSC) and nitrogen levels among three species pairs consisting of an evergreen species and a related deciduous shrub.
Consistent with their hypothesis, the authors found that, while N pools did not differ with leaf habit, plant size-adjusted pools of NSCs in stems and roots were lower in evergreen than deciduous shrubs. They also found that foliage of all species contained more than half of the plant’s carbohydrate and N pools, suggesting that leaves are a major storage site regardless of leaf habit. Surprisingly, compared to their deciduous counterparts, longer-living foliage of evergreens did not have higher concentrations of defensive phenolic compounds, indicating that they may rely primarily on structural defenses for protection. This unique study highlights the importance of measuring organ biomass ratios (whole plant carbohydrate pool:plant size) rather than just the carbohydrate concentration when quantifying within-plant carbon partitioning.