从调节源—库关系看环剥对荔枝幼树根梢生长与坐果的调控

荔枝常因幼树花而不实而颗粒无收.糯米糍品种4年生幼树盛花期主干环剥,并保持不愈合至采果.对照树全年根、梢各有3个生长期,环剥树采前无根、梢生长;对照树有4次生理落果峰,环剥树第2、3落果峰不明显,采前落果峰也很低.研究认为荔枝幼树根系的“库”力在竞争中占优势,根与梢的生长相克又相促,果实在竞争中处于劣势,环剥完全抑制了根与梢的生长,使果实在“库”力的竞争中得以转弱为强.

Regulation of Root and Shoot Growth and Fruit-dorp of Young Litchi Trees by Trunk Girdling in View of Source-Sink Relationships

Serious fruit-drop on young litchi trees,resulting usually in complete loss of fruits,canbe alleviated by girdling.An experiment has been conducted with 4-year-old‘Nuomici’litchitrees.Three trees were trunk-girdled at full bloom(April 26)and the girdles were renewedregularly until harvest.Another 3 trees were left untreated as control.The control treesshowed 3 root growth cycles(May;June/July and October)(Fig.C)and 3 flushes(June;Ju-ly/August and Sept./Oct.)(Fig.A).No root and shoot growth were observed on girdledtrees until the girdles healed up in July.There were 4 fruit-drop waves shown on controltrees,whereas on girdled trees,besides the lst wave of fruit-drop,being associated with thelack of fertilization,the other 3 waves were much less intensive(Fig.B).It is suggestedthat,the 2nd and 4th waves of fruit-drop were linked with the root growth peaks immediatelypreceding the drops,and the 3rd wave linked with the lst(summer)flush,which coincidedthe drop.Non-bearing young litchi trees are characterized by its vigorous root growth,onwhich the further top growth is based,hence,the sink strength of root system must bestronger than that of other organs,being at variance with bearing mature trees.The pat-terns of source-sink relationship was modified by girdling in favour of the fruits,whichchanged from weak to stronger in the competetion of assimilates and/or hormones with othersinks.