Effects of nitrogen limitation on water relations of jack pine (Pinus banksiana Lamb.) seedlings

The water relations of shoots of young jack pine (Pinus banksiana Lamb.) seedlings were examined 6 and 15 weeks after the initiation of four different dynamic nitrogen (N) treatments using a pressure‐volume analysis. The N treatments produced a wide range of needle N concentrations from 12 to 32 mg g−1 dry mass and a 10‐fold difference in total dry mass at 15 weeks. Osmotic potential at full turgor did not change over the range of needle N concentrations observed. Osmotic potential at turgor‐loss point, however, declined as N concentrations decreased, indicating an increased ability of N‐deficient jack pine plants to maintain turgor. The increase could be attributed largely to an increase in cell wall elasticity, suggesting that elasticity changes may be a common, significant adaptation of plants to environmental stresses. Dry mass per unit saturated water almost doubled as needle N level dropped from 32 to 12 mg g−1 and was inversely correlated to the bulk modulus of elasticity. This suggests that cell wall elasticity is determined more by the nature of its cross‐linking matrix than by the total amount of cell wall material present. Developmental change was evident in the response of some water relation variables to N limitation.