SOURCE-SINK MANIPULATION EFFECTS ON POSTANTHESIS PHOTOSYNTHESIS AND GRAIN SETTING ON SPIKE IN WINTER-WHEAT

Source-sink manipulation could regulate the net photosynthetic rate (P -N) Of winter wheat after anthesis, however, the direction and magnitu de of the regulation varied with time after anthesis. The P-N was sign ificantly increased by source reduction at the initial time of grain f illing, but sink reduction had little influence on the P-N, which sugg ested that the sink (spike) limitation did not occur at this time. Sou rce-sink relation markedly affected P-N during rapid grain filling. Th e P-N was increased by source reduction and decreased by sink reductio n significantly, which indicated that P-N Was closely associated with the change of source or sink size. The effect of source-sink manipulat ion on P-N had some relationship with the occurrence of plant senescen ce at the time of late grain filling. Source reduction accelerated the senescence and dropped the P-N, meanwhile, sink reduction delayed the senescence and promoted the P-N A direct relation between the effect of source-sink manipulation on P-N and stomatal limitation was not fou nd. Removing one quarter of leaves (RQ) had little influence on spike development after anthesis. In this case there was enough compensation in source production through photosynthesis. Removing one half of lea ves (RH) made grain mass per spike and mass of grains lowered, especia lly the grain mass in the top and base positions of spike declined mar kedly. The source supply was grain-limiting. Removing one quarter of s pikelets (RS) was beneficial to grain-setting in the remaining spikele ts, leading to the increase of grain mass. Thus promoting the source s upply of photosynthates after anthesis is of major importance for grai n to set and to develop.