Role of phosphorus and nitrogen in photosynthetic and whole plant carbon gain and nutrient use efficiency in eastern white pine

In white pine (Pinus strobus) seedlings grown in five forest soils from New York State, net photosynthetic capacity (Amax)$\text{plant}^{-1}$was correlated with total foliar N$\text{plant}^{-1}$(r2= 0.57), but was more highly correlated with total foliar P$\text{plant}^{-1}$(r2= 0.82). There was no relationship (r2< 0.01) between Amax$[\text{g leaf}]^{-1}$and foliar N$[\text{g leaf}]^{-1}$for the pooled data set, but there was a significant (P < 0.001), but weak (r2= 0.20) positive relationship between Amax$[\text{g leaf}]^{-1}$and foliar P$[\text{g leaf}]^{-1}$across all soils. However, within two of the five soils leaf N concentration was a significant (P < 0.05) determinant of photosynthetic capacity. Due to differences in soil nutrient availabilities a large range in foliar P: N ratio (0.02-0.15) was observed, and the proportion of leaf P: N appeared to control Amax$[\text{g leaf N}]^{-1}$. Whole plant nitrogen (NUE) and phosphorus (PUE) use efficiencies were well correlated with whole plant P: N ratio. In addition, NUE was well correlated with Amax$[\text{g leaf N}]^{-1}$and PUE was well correlated with Amax$[\text{g leaf P}]^{-1}$. However, NUE was not well correlated with PUE, and Amax$[\text{g leaf N}]^{-1}$was not well correlated with Amax$[\text{g leaf P}]^{-1}$. These results indicated that P and/or N limitations were important components of photosynthetic nutrient relations in white pine grown in these five soils and suggest that both P and N and their proportions should be considered in analyses of photosynthesis-nutrient relations.