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_nwas linearly correlated with SLW until mid-August, when P_nbegan to decline. During September the relationship between SLW and P_nwas a quadratic. Leaf R_dand SLW were linearly correlated throughout the season. Leaf P_nand R_dwere 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_nis probably limited to the first half of the season, because of increased variation after mid-August.Former Graduate Research Assistant (presently Assistant Professor, Department of Horticulture and Forestry, Rutgers University, Cook College, New Brunswick, NJ 08903, USA) and Associate Professor, respectively.