PLANTING DENSITY EFFECTS ON ASSIMILATION AND PARTITIONING OF PHOTOSYNTHATES DURING GRAIN FILLING IN THE LATE-SOWN WHEAT

Leaf blades of the late-sown winter wheat produced the major portion, i.e., more than 60 %, of the total C-14-photosynthates at grain fillin g, but ear (rachis and glumes) only about 15 %, sheaths about 11 %, an d stem internodes about 11 %. The change of plant density in this expe riment had little influence on the (CO2)-C-14-photoassimilation of the ear (rachis and glumes), flag leaf lamina, sheaths and stem internode s, but markedly affected photosynthesis of the second, the third and l ower leaves. The photosynthetic rate [expressed as specific radioactiv ity s(-1) kg(-1)(d.m.)] and the amount of (CO2)-C-14 photosynthates de creased significantly in the second, the third and other lower leaves at a high plant density. Upon grain-filling of the late-sown wheat, th e grain was the major importer of photosynthates. Yet partitioning to the stem internodes depended on the plant density. Stem was the import er of photosynthates at a low plant density, but the exporter at a hig h plant density. In plants at a low plant density st fairly large prop ortion of photosynthates was distributed into the roots. The middle an d lower above-ground parts of the late-sown wheat at a high plant dens ity decreased or lost their function early. As a result, the plant sen esced earlier. However, the grain setting, filling and yielding were r estricted. An appropriately low plant density was suitable for prolong ing the function of the middle and lower organs, delaying the senescen ce of plant, increasing the source supply for grain filling, and impro ving the grain yield.