Physiological and morphological differences in the heterophylly of Sabina vulgaris Ant. in the semi-arid environment of Mu Us Desert, Inner Mongolia, China

Sabina vulgaris is a heterophyllus tree with two leaf forms: needle leaves and scale leaves. Most seedlings establish under a tree canopy and have only needle leaves, whereas mature individuals grow in the open and have both leaf forms. To clarify the functional traits of both leaf types, we studied the leaf mass per area (LMA), nitrogen content, stable carbon isotope composition, and photosynthetic traits of the two leaf forms. Scale leaves had a larger LMA, higher leaf area-based photosynthetic rate, higher water-use efficiency, and stronger tolerance of photoinhibition compared to needle leaves. Conversely, needle leaves had a lower light compensation point and higher leaf mass-based photosynthetic rate than scale leaves. With their low light compensation point and dark respiration rate, needle leaves appeared to be more effective at maximizing photosynthetic production under light-limited conditions in the inner crown or dark seedling stage. In contrast, scale leaves appeared to be more efficient at the canopy surface due to their higher area-based photosynthetic rate, tolerance to photoinhibition, and higher water-use efficiency. These different leaf functional traits of scale and needle leaves indicate functions similar to those of sun and shade leaves, respectively, in other tree species.