MOBILIZATION BY PINUS RESINOSA CONES AND SHOOTS OF C14‐PHOTOSYNTHATE FROM NEEDLES OF DIFFERENT AGES

Abstract

Current‐year, 1‐year‐old, 2‐year‐old, and 3‐year‐old needles of 25‐ to 30‐year‐old Pinus resinosa trees were separately exposed to C14O2 at various times during the growing season. Currently produced C14‐photosynthate was preferentially mobilized in the following order: second‐year cones > current needles > current internodes > first‐year conelets. A changing seasonal pattern was shown in sources of current photosynthate for growth of cones and shoots. One‐year‐old needles were the major source of current photosynthate for growth of both cones and shoot internodes. During June the 2‐ and 3‐year‐old needles contributed appreciable amounts of current photosynthate to both cones and developing shoots, but after late June their contribution was slight. The supply of carbohydrates to all tissues, except 2nd‐year cones, from the three age classes of old needles declined late in the season as tissues mobilized increasingly more carbohydrates from current‐year needles. Nevertheless, the bulk of the C14‐photosynthate produced by current‐year needles was retained by them. The preferential mobilization of carbohydrates by reproductive tissues over vegetative tissues is emphasized as is the importance of both reserve and currently produced carbohydrate for growth of various tissues.