缺钾对香蕉苗期地上部、根系生长及氮磷钾吸收的影响

【目的】明确香蕉苗缺钾的表型症状,探讨缺钾和恢复供钾对香蕉苗生长及氮磷钾营养平衡的影响,为香蕉苗营养诊断和平衡施肥提供依据。【方法】通过石英砂培养试验,以正常的完全营养液为对照,观察记录香蕉苗缺钾的表型症状及出现时间,对比研究缺钾和缺钾后恢复供钾条件下香蕉苗的地上部和根系的生物量、根系形态参数、氮磷钾吸收等变化。【结果】缺钾的表型症状为:老叶发黄,中部叶片主叶脉先呈现橙黄色,并逐渐向叶缘蔓延,然后部分叶片叶缘出现近椭圆形小枯斑,叶柄呈现浅红褐色,缺钾严重时,橙黄色叶片近叶脉处的叶肉发黑,进而干枯死亡,枯叶呈褐色,完全展开的新叶不挺立,上部叶片柔弱、下披。缺钾显著抑制香蕉苗生长,缺钾处理较正常处理的地上部和根系生物量降低了31%和39%,其根长、根表面积和根体积减少了30%、31%和34%,且细根减幅大于中根。缺钾同时改变了香蕉苗氮磷钾平衡,其地上部、根系和全株的氮含量分别增加了19%、21%和19%,磷含量分别增加了40%、12%和38%,钾含量分别降低了73%、56%和72%,氮、钾吸收量降低,根系的磷吸收量降低;缺钾处理的地上部、根系和全株的N/K、P/K显著升高,地上部和全株N/P显著降低,根系N/P显著升高。缺钾后恢复供钾,香蕉苗缺钾表型症状消失,但香蕉苗的生物量以及氮、磷、钾含量和吸收量不能同步恢复,香蕉苗生物量仍低于正常处理,各部位的氮含量、根系的磷、钾含量仍高于正常处理,地上部和全株的钾含量和吸收量也未增加至正常水平。供钾后地上部和全株的磷吸收量显著降低,且低于正常处理。【结论】缺钾对香蕉苗营养状况的影响显著大于对表型性状的影响,营养状况的恢复滞后于表型性状的恢复,香蕉苗施肥要针对其营养特性施用。

Effects of potassium deficiency on growth and N, P and K balance of banana shoots and roots

Objective To make clear morphological symptoms of potassium (K) deficiency in banana seedlings, discuss the effects of K deficiency and K resupply on growth and nitrogen (N), phosphorous (P), K balance of banana seedlings and provide a basis for nutrition diagnosis and blanced fertilization of banana seedlings.Method Through quartz sand culture experiment, complete nutrient solution cultivation was marked as the control treatment to observe morphological characteristics and appearance time of K-deficient symptoms. K deficiency and K deficiency-resupply treatments were conducted to study the changes of biomass, root morphological parameters and N, P, K uptake of banana seedlings.Result The K-deficient symptoms were old leaves chlorosis, successive orange-yellowing of main veins and margins of middle leaves, small oval spots in leaf margins and reddish brown petioles. When the seedlings were in severe K deficiency, mesophylls near the veins of orange-yellow leaves were blackening and dried to death, the dead leaves were brown, fully expanding new leaves were not erect, and the upper leaves were soft and drooping. K deficiency significantly inhibited the growth of banana seedlings. Compared with CK, the biomass of shoots and roots in K deficiency treatment decreased by 31% and 39% respectively, the length, surface area and volume of roots decreased by 30%, 31% and 34% respectively, and the decrease ranges of fine roots were more than that of middle roots. K deficiency also changed N, P, K balance of banana seedlings. Compared with CK, N contents of shoots, roots and whole plants in K-deficient treatment increased by 19%, 21% and 19% respectively, P contents increased by 40%, 12% and 38% respectively, K contents decreased by 73%, 56% and 72% respectively, N and K uptake decreased, P uptake of roots decreased, N/K and P/K ratios in shoots, roots and whole plants increased significantly, N/P ratio in shoots and whole plants decreased significantly, and N/P ratio in roots increased significantly. After resupplying K in K deficiency treatment, the K-deficient morphological symptoms of banana seedlings disappeared, but the biomass, N, P and K contents and uptakes of banana seedlings could not recover simultaneously. The biomass of banana seedlings was still lower than that of CK, and N contents of shoots, roots and whole plants and P, K contents of roots were higher than those of CK. K contents and uptakes of shoots and whole plants did not increase to normal levels. P uptakes of shoots and whole plants decreased significantly and was lower than that of CK.Conclusion The effects of K deficiency on nutrition status of banana seedlings are significantly greater than that of phenotypic characteristics, and the recovery of nutrition status lags behind phenotypic characters. Banana seedling fertilization should apply to its nutritional characteristics.