Seasonal correlations of specific leaf weight to net photosynthesis and dark respiration of apple leaves.

Specific leaf weight (SLW), net photosynthesis (P n ), and dark respiration (R d ) of apple leaves were monitored for an entire growing season. Leaves were sampled from the canopy interior and periphery to provide a range of SLW. Leaf P n was linearly correlated with SLW until mid-August, when P n began to decline. During September the relationship between SLW and P n was a quadratic. Leaf R d and SLW were linearly correlated throughout the season. Leaf P n and R d were significantly correlated through most of the season, but the relationship was not always linear. Specific leaf weight appears to be a reliable index of the previous light environment of a leaf, but use to estimate P n is probably limited to the first half of the season, because of increased variation after mid-August.