The Carbon Budget of a Young Apple Tree1

Abstract

Photosynthesis and dark respiration of the above ground components of young orchard-grown apple trees (Malus domestica Borkh.) were measured by infrared gas analysis. Soil and root respiration were determined by CO2 absorption. Maximum net photosynthesis (Pn) of shoots was 2.0 g CO2 m–2 hr–1 and light saturation level was 500 Wm–2 (global solar radiation). Photosynthetic efficiencies of shoots were at a maximum (6%) at 100 Wm–2 was 2 to 3% at light saturation. Pn rates of stems and fruits were very low and even at high irradiance did not exceed the compensation point. Dark respiration (Rd) increased exponentially with temperature. Rd per unit weight was comparable for leaves and stems, less for roots and very little for fruits; per unit area the rates for leaves and fruit were small, while those for stems were large. Estimates of dry matter accumulation by growth analysis and by net CO2 uptake were remarkably similar, despite a gross simplifying assumption with regard to light interception by the leaves.

Carbon Balance Model of a Growing Apple Shoot: II. Simulated Effects of Light and Temperature on Long and Short Shoots

“…The environmental inputs were daily solar radiation values in langley per day, and maximum and minimum temperatures. The physiological parameters for the model were determined from a set of potted 'Jonamac' trees grown at Geneva, N.Y., and from the literature (1,2,11,14). An increase in the leaf area was modeled as a linear function of accumulated growing degree-days, with a base of 4°C (7).…”

“…These processes, in turn, are affected by various environmental inputs, the most important of which are light and temperature. Light has a significant effect on the photosynthesis rate within the normal range of growth conditions (1,14), but little or no direct effect on the respiration rate and growth rates, whereas temperature is relatively more important to respiration (2,11) and growth rates (6) than to photosynthesis rates (ignoring extreme temperatures) (14). Therefore, shoots growing under different climatic conditions would be expected to show differences in C import and export.…”

Carbon Flux in Apple Trees: The Effects of Temperature and Light Intensity on Photosynthetic Rates1

“…Proctor et al (10) developed a model descriptive of the carbon budget in a young apple tree. Refinement and extension o f this type o f m odel m ay provide a basis for defining the re lationship between net assimilation rate and productivity.…”

“…A sliding scale of fruit firmness and soluble solids has been utilized in some production areas for determination of early harvest of apples (2,10). Mattus (10) suggested 18.5 lb.…”

“…Previous work has supplied some insight into the effect of temp on Pn rates in apple trees (5,10,12) inadequacies have limited definitive work to temp between 15 and 30°C. Because temp may range from below 0° to over 38° during the growing season, the effect of temp from -1.6 to 44° on Pn in 'Golden Delicious' was determined.…”