Leaf-age effects on seasonal variability in photosynthetic parameters and its relationships with leaf mass per area and leaf nitrogen concentration within a Pinus densiflora crown

Abstract

In the temperate zone of Japan, Pinus densiflora Sieb, et Zucc. bears needles of up to three age classes in the upper crown and up to five age classes in the lower crown. To elucidate the effects of leaf age on photosynthetic parameters and its relationships with leaf mass per unit area (LMA) and leaf nitrogen (N1) concentration on an area (Na) and mass (Nm) basis, we measured seasonal variations in LMA, N1, light-saturated photosynthetic rate (Amax), stomatal conductance (gs), maximum rate of carboxylation (Vcmax) and maximum rate of electron transport (Jmax) in leaves of all age classes in the upper and lower crown. Leaf mass per unit area increased by 27% with increasing leaf age in the lower crown, but LMA did not depend on age in the upper crown. Leaf age had a significant effect on Nm but not on Na in both crown positions, indicating that decreases in Nm resulted from dilution. Photosynthetic parameters decreased significantly with leaf age in the lower crown (39% for Amax and 43% for Vcmax), but the effect of leaf age was not as great in the upper crown, although these parameters exhibited seasonal variation in both crown positions. Regression analysis indicated a close relationship between LMA and Na, regardless of age class or when each age class was pooled (r2 = 0.57-0.86). Relationships between LMA and Na and among A max, Vcmax and Jmax were weak or not significant when all age classes were examined by regression analysis. However, compared with older leaves, relationships among LMA, Na and A max were stronger in younger leaves. These results indicate that changes in LMA and N1 mainly reflect light acclimation during leaf development, but they are only slightly affected by irradiance in mature leaves. In conclusion, LMA and N1 are useful parameters for estimating photosynthetic capacity, but age-related effects need to be taken into account, especially in evergreen conifers. © 2008 Heron Publishing.