Seasonal Changes in Respiration, Photosynthesis, and Translocation of the 14C Labelled Products of Photosynthesis in Young Pinus strobus L. Plants

Abstract

Three-year-old Pinus strobus plants, grown under conditions of either high or low light intensities, were brought from the nursery to the laboratory every three to four weeks from the middle of April 1961 until January 1962. Translocation, measured as the amount of 14C recovered from the roots at the end of seven hours of illumination following exposure of the shoot to 14CO2, was found to be high in the spring, dropping to negligible amounts during June and July, increasing again in the autumn and declining after October. Seasonal variation in root respiration was found to parallel that of translocation. Rates of apparent photosynthesis were low during the spring, rising to a maximum during September, and then declining over the winter. The respiration, photosynthesis, and translocation of the low-light grown plants followed a similar pattern to those grown in high-light, except that in general rates were of a lower order. In the high-light grown plants more than 90 per cent of the absorbed carbon was present in the ethanol-soluble form, of which sugars formed at least 90 per cent. This was even more pronounced in the case of low-light grown plants. The main sugar was always sucrose. The raffinose content was found to decrease during the warmer months. The new needles, during their period of maximum growth, fixed carbon dioxide photosynthetically at a rate comparable to that of the old needles. The new stems also possessed a relatively high carbon dioxide fixing ability. Shoot growth, as measured by the increase in length of the new leader stem and new needles, showed the typical patterns for pine species.