不同施氮量和分施比例对棉花幼苗生长和水分利用效率的影响及其根源ABA调控效应

Regulation of root-sourced ABA to growth and water use efficiency of cotton seedlings and their response to different nitrogen levels and distribution ratios

研究了分根交替供水(APRI)条件下不同施氮量(高氮HN 200kg/hm^2、中氮MN 120kg/hm^2和低氮LN 80kg/hm^2)和分区氮肥施用比例(1:3,2:2和0:4)处理下,经历干旱胁迫后棉花幼苗(品种:汴棉5号)株高、茎粗、根冠生物量、气体交换参数、水分利用效率(WUE)、总根长和根系表面积以及根源脱落酸(ABA)含量的变化。以期进一步明确根源ABA对棉花幼苗生长和WUE调控的生理生态效应。结果表明:施氮量和氮肥分施显著增强了干旱条件下根源ABA对棉花幼苗生长和WUE的调控作用,但根源ABA对氮利用效率无显著影响。高氮处理下棉花幼苗生长受到干旱的影响最小,具有最好的生长状态和最大的根源ABA含量,但其WUE最低;而低氮处理下的棉花幼苗生长最弱但具有最大的WUE。无论施氮量为何,0:4施氮比例棉花幼苗在干旱条件下生长最弱,1:3施氮比例幼苗则生长最好,且具有最大的WUE和根源ABA含量、根系总长度和表面积;2:2和1:3施氮比例的棉花幼苗在根冠生长和叶面积上未表现出明显的差异;0:4和1:3施肥比例的棉花幼苗在气孔导度、蒸腾速率、WUE和根源ABA含量上差异不明显。因此,施用氮肥以及适当施肥比例能够诱导根源ABA产生更强的信号作用,调控棉花幼苗减少水分消耗、维持更好的根系形态(根长和表面积以及细根比例的维持和增长)和光合能力来维系干旱条件下植株更好的生长和更高的WUE,尤其1:3施肥比例下。虽然干旱条件下低氮耦合1:3施氮比例具有最大的WUE,但中氮耦合1:3施氮处理可以在得到最高生物量的同时得到较高的WUE,同时做到高产、省水和节约氮肥。

Different nitrogen levels（ high nitrogen,HN 200 kg/hm^2; medium nitrogen,MN 120 kg/hm^2; and low nitrogen,LN 80 kg/hm^2） and nitrogen distribution ratios（ 1：3,2：2,and 0：4） were applied to cotton seedlings（ variety：B）. These cotton seedlings were then cultured using alternative partial root-zone irrigation（ APRI） and subjected to a 15-day-drought stress. Plant height, stem width, root and shoot biomass, gas exchange parameters（ including net photosynthetic rate [Pn],stomatal conductance [Gs],transpiration rate [Tr],and intercellular concentration of carbon dioxide [Ci ]）,leaf area,water use efficiency（ WUE）,total root length,root surface area,nitrogen use efficiency（ NUE）,and root-sourced（ root tissue and root xylem sap） ABA concentrations of cotton seedlings were determined. The aim of this experiment was to clarify the available regulation of root-sourced ABA to cotton seedling growth and WUE. Theresults showed that nitrogen application with a suitable distribution ratio improved the regulation of root-sourced ABA to growth and WUE of cotton seedlings under drought stress,although NUE was not significantly related to root-sourced ABA.The HN-treated cotton seedlings showed the highest growth and biomass and had the largest root-sourced ABA concentrations and NUE but the smallest WUE. The LN-treated cotton seedlings showed the least growth and the lowest biomass,but had the highest WUE. Irrespective of nitrogen levels,the 0：4-distributed cotton seedlings were the weakest,but the 1：3-distributed were the strongest with the highest NUE,WUE,and root-sourced ABA concentration. There were no obvious differences of growth,root and shoot morphology,and leaf area between 1：3-distributed and 2：2-distributed cotton seedlings.The Pn of cotton seedlings was not affected by different nitrogen distribution ratios,and Ci was not influenced by different nitrogen levels or distribution ratios. The differences of gas exchange parameters, WUE, and root-sourced ABA concentration between 0：4-distributed and 1：3-distributed cotton seedlings were not significant. Therefore,less water consumption（ less stomatal conductance and transpiration rate） and enhanced root morphology（ larger total root length,root surface area,and higher fine root proportion） were stimulated by root-sourced ABA directly or indirectly to maintain better growth and higher WUE of cotton seedlings under drought stress,especially in the 1：3-distribution ratio of nitrogen.Although the 1：3-distributed cotton seedlings with LN had the highest WUE,those with MN had greater NUE,biomass,WUE. This treatment combination could realize higher production,less water consumption,and nitrogen application simultaneously.