Photoprotection in heteromorphic leaves of savin juniper (Juniperus sabina L.)

Savin juniper has green, photosynthetic branchlets with scale and/or needle leaves and these heteromorphic forms may contribute differentially to its success in open, arid environments. To test differences in photoprotection between fully sun-exposed scale-holding branchlets (SHB) and needle-holding branchlets (NHB), we measured gas exchange, chlorophyll (Chl) fluorescence, and pigment concentrations. NHB had higher net photosynthetic rate, stomatal conductance, and intrinsic water-use efficiency. In contrast, SHB had higher nonphotochemical quenching. Chl a, Chl b, and antheraxanthin concentrations were higher in NHB. SHB had higher zeaxanthin, lutein, and carotenoids (Car), and higher Chl a/b, Car/Chl, and α-carotene/β-carotene ratios. The results indicate greater engagement of xanthophyll-based thermal dissipation in SHB. Branchlet types acclimate to strong light using different strategies; SHB by investing in photoprotective mechanisms, and NHB by having a high photosynthetic capacity. Heterophylly may allow savin juniper to be more functionally flexible under variable environmental conditions.