提高营养液镁浓度可缓解黄瓜幼苗亚低温胁迫

【目的】我国北方地区冬春季栽培黄瓜经常遭受亚低温 (15℃/8℃) 胁迫，用标准营养液育苗常会造成黄瓜植株矮小、叶片发黄等问题。研究调整营养液中镁和钾离子浓度，以便达到缓解亚低温对黄瓜幼苗伤害作用的目的。【方法】选用‘博耐 3000'黄瓜幼苗为试材，利用人工气候箱，以常温 (25℃/18℃) 下黄瓜山崎标准营养液配方 (K+ 6 mmol/L、Mg2+ 2 mmol/L) 为对照，在标准营养液其他元素保持不变的基础上，设置两个钾离子水平 (K+ 6、12 mmol/L)，4 个镁离子水平 (Mg2+ 2、4、6、8 mmol/L)，在亚低温 (15℃/8℃) 下栽培黄瓜幼苗，于处理后幼苗生长的 0、7、14、21 d 调查了不同镁钾水平营养液栽培的黄瓜幼苗的根系形态、干物质积累和分配以及对钾和镁元素吸收。【结果】1) 亚低温下适当增加营养液中的 Mg2+ 浓度，能显著提高黄瓜幼苗的壮苗指数，当营养液中 Mg2+ 和 K+ 均为 6 mmol/L 时，壮苗指数达到最大值 0.17；2) 镁和钾对根系形态影响不同，K+ 浓度与根长和根系总表面积成正相关，且主要影响直径范围为 0～0.5 mm 的根系，Mg2+ 与根系平均直径正相关且主要影响 > 1.0 mm 的根系；较高的 K/Mg 比例有利于黄瓜 0～0.5 mm 根系的生长，根系总长和总体积的增加，但显著抑制了 0.5～1.0 mm 和 > 1.0 mm 根系的生长。3) 亚低温下，茎叶中干物质量降低而根中升高，在 K1 (6 mmol/L) 水平时，随 Mg2+ 浓度升高，根和茎中干物质量升高，叶中干物质表现为先升高后下降，且营养液中高浓度的 Mg2+ 有利于干物质向叶中分配。4) 营养液中镁离子浓度小于 6 mmol/L 时，一定程度地提高 Mg2+ 浓度能促进对 K 的吸收，营养液中的 Mg2+ 和 K+ 在镁钾吸收上表现为协同作用，当 Mg2+ 大于 6 mmol/L 时，镁和钾表现为显著的拮抗作用；亚低温下，根茎叶的镁吸收量相比 CK 分别下降 25%、72% 和 58%，而营养液中 K+ 和 Mg2+ 均为 6 mmol/L 时，有利于缓解这一阻碍效果。【结论】冬春季黄瓜育苗时，山崎黄瓜配方营养液中的 Mg2+ 和 K+ 均为 6 mmol/L 而其他元素浓度保持不变时，黄瓜幼苗的壮苗指数、根系形态、干物质积累和钾镁元素综合效应表现较好，能有效地抵御亚低温对黄瓜幼苗的伤害。

Increasing magnesium level in hydroponic solution will relieve suboptimal temperature stress to cucumber seedlings

Objectives] In northern China,cucumber seedlings are often subjected to suboptimal temperature (15 ℃/8 ℃) stress during spring or winter season.Under such environment,the hydroponic cucumber seedlings using standard nutrient solution are weak and their leaves become yellow in color.A study was conducted aiming to relieve the adverse effects of suboptimal temperature stress by adjusting magnesium (Mg) and potassium (K) concentrations in the nutrient solution.Methods] Hydroponic experiment was conducted inside a climatic chamber with cucumber ‘Bo Nai 3000’ as materials.The day/night culture temperature was 25 ℃/18℃ for control and 15 ℃/8 ℃ for treatment.On the base of a standard Yamazaki cucumber nutrient solution in the control,two levels ofK+ (6 and 12 mmol/L) and four Mg2+ (2,4,6 and 8 mmol/L) were set for the treatments under suboptimal temperature.The root morphology,dry matter accumulation and distribution as well as K and Mg absorption in cucumber seedlings were investigated every 7 days since the cultivation,and 4 investigations were did in total.Results] 1) Appropriate increasing of the Mg2+ concentration in the culture solution significantly improved healthy seedling index under suboptimal temperature.When the Mg2+ and K+ concentrations were all 6 mmol/L,the seedling index reached the maximum value of 0.17.2) The effects of Mg2+ and K+ on root morphology were different.K+ concentration was positively correlated with the total root length and root surface area,the effect was mainly on roots of 0-0.5 mm in diameter;Mg2+ was positively correlated with the average diameter of the root system,the effect was mainly on roots of ＞1.0 mm in diameter;higher K/Mg ratio was beneficial to the increase of total length and volume of roots of 0-0.5 mm in diameter,but not for those of roots of 0.5-1.0 mm and ＞1.0 mm in diameter.3) Compared to normal temperature,the dry biomass of stems and leaves were decreased while the root dry biomass increased under suboptimal temperature.Under K+ concentration of 6 mmol/L,root and stem dry biomass were increased with enhanced Mg2+ concentration.The high Mg2+concentration of nutrient solution contributed to the distribution of dry matter to leaf.4) When Mg2+ was less than 6 mmol/L,interaction effect existed between Mg2+ and K+,while significant antagonism effect existed when Mg2+ was higher than 6 mmol/L.The absorptive amount of Mg under suboptimal temperature decreased by 25％,72％ and 58％ in root,stem and leaf respectively,compared to CK.Conclusions] Under suboptimal temperature,6 mmol/L Mg2+ and K+ in Yamasaki cucumber nutrient solution improved the seedling index of cucumber seedlings,root morphology and dry matter accumulation.It can effectively resist the adverse effects of suboptimal temperature on cucumber seedlings.