The productivity of Pinus radiata D. Don plantations can be increased on many soils by N and P fertilization. Foliar analyses are usually taken as a guide for nutrient management, but there is little information about the relationship of foliar nutrient status to foliar physiology. This paper provides such information from N and P fertilization experiments. The concentrations and contents of N and P in the needles of P. radiata change because of accumulation during needle growth, retranslocation during shoot growth, and replenishment from current uptake during periods of little shoot growth. Up to 60% P and 50% N may be retranslocated in a single growing season from needles less than one year old. Three years after fertilizer application to a 10-year-old thinned P. radiata stand, net carbon assimilation rate per unit leaf area was in the order NP>P>N. There were positive associations between foliar P and assimilation at full sunlight, diffusive conductance and quantum yield. Foliar N was negatively associated with these variables. Higher concentrations of P and N were both accompanied by higher instantaneous water use efficiency by the foliage. Estimated trends in whole tree assimilation were similar to those in aboveground biomass accumulation. The interplay between the dynamic nature of nutrients in the foliage and their influence on the physiology of needles is discussed.

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Potted Eucalyptus globulus Labill. seedlings were grown in sand with added inorganic nutrients. Three treatments were applied: (1) inorganic nitrogen was added regulary (N2), (2) in a small initial quantity only (N1) and (3) after a period of N deficiency (N3); other nutrients were supplied regularly. Biomass increment, foliar nutrient concentrations and gas exchange of leaves were measured. Carbon assimilation, N uptake, growth, and leaf production and expansion were all greater at higher N. Partitioning of dry matter to roots and tops of seedlings was unaffected by treatment. Carbon assimilation and diffusive conductance were linearly related at saturating light and were positively associated with foliar N concentrations; intercellular CO2 partial pressures were constant at c. 246 μbar. The relationship between carbon assimilation and foliar N concentration was better when calculated per leaf weight than per leaf area. Dark respiration was positively associated with foliar N concentration. Following refertilisation of N-deficient seedlings, foliar N and carbon assimilation increased rapidly; about 20 days later N uptake declined and seedling biomass started to increase. Instantaneous transpiration efficiency [c. 5 mmol (CO2) mol-1 (H2O)] was not significantly affected by foliar N concentration or treatment. Instantaneous nitrogen use efficiency of leaves: (rate of carbon assimilation)/(leaf N content) was greater at higher N. In contrast to the literature, there was no simple relationship between nitrogen use efficiency of whole seedlings (biomass gain)/(nitrogen concentration) and seedling N. Instantaneous transpiration and nitrogen use efficiencies were generally high compared with values published for many woody plants. A simple model predicted that, with no environmental constraints, exposed mature leaves with high N (1.5 mmol g-1) assimilate 5.4 times more carbon than similar leaves with low N (0.5 mmol g-1). Night respiration of foliage is a greater proportion of daily carbon balance for leaves with low N. When environmental factors constrain carbon assimilation foliage with high N is most affected.

We used the heat-pulse velocity technique to estimate transpirational water use of trees in an experimental 16-year-old Pinus radiata D. Don plantation in South Australia during a 4-month period from November 1993 to March 1994 (spring-summer). Fertilization and other silvicultural treatments during the first 8 years of the plantation produced trees ranging in diameter at a height of 1.3 m from 0.251 to 0.436 m, with leaf areas ranging from 83 to 337 m(2). Daily water use was greater for large trees than for small trees, but transpiration per unit leaf area was nearly identical. Daily transpiration was highly correlated with available soil water in the upper 1 m of soil and weakly correlated with irradiance and air temperature. For the stand (0.4 ha), estimated rates of transpiration ranged from 6.8 to 1.4 mm day(-1) in wet and dry soil conditions, respectively. Total water use by the plantation during the 4-month study period was 346 mm. Water transpired by the trees was about three times that extracted from the upper 1 m of soil. Large trees extracted water from the same soil volume as small trees and did not exhibit a greater potential to extract water from deeper soil when the upper horizons become dry.