Differential effects of N, P and K on photosynthesis and partitioning of N in Pinus pinaster needles

We investigated the response of one- year-old Pinus pinaster Ait. growing on a sandy, nutrient-poor soil to the factorial addition of N, P and K. We tested two hypotheses: ( 1) fertiliser application increases rates of light-saturated photosynthesis (A(max)) and leaf-level wateruse efficiency (WUE, as indicated by carbon isotope composition), and ( 2) greater concentrations of N and Rubisco explain fertiliser-promoted increases in Amax and WUE. Two years after fertiliser application, the height of P. pinaster was significantly greater in plots to which P was added (127 +/- 7 cm; mean +/- SE of three replicate plots) compared to those without added P (70 +/- 10 cm), but was unaffected by addition of N or K. The fraction of N present as Rubisco varied between 4 and 18% and was unrelated to N concentrations, but positively related to P and K concentrations. A(max) and delta C-13 did not vary significantly among treatments and were unrelated to concentrations of Rubisco, N, P or K. We conclude that fertiliser application two years previously has little effect on current A(max) and delta C-13 of P. pinaster, and thus the previously reported effects of fertiliser on gas exchange are likely ephemeral.