两个菠萝品种对不同形态氮素的获取策略

Nitrogen acquirement strategy of different nitrogen forms in two pineapple cultivars

氮是与菠萝产量关系密切的大量营养元素之一。本试验分别在4月和9月两个生长季节,选择了广东省徐闻县田间生长的‘巴厘’和‘台农17’两个菠萝品种不同年龄的植株为研究对象,测定了不同年龄植株的形态、生理和生长特征,并利用稳定性同位素15N示踪技术分析了菠萝对3种形态氮素[铵态氮、硝态氮和氨基酸态氮(甘氨酸)]的获取策略,以探讨菠萝吸收氮素的偏好。结果表明,在4月份果实收获期,与‘巴厘’相比,‘台农17’菠萝的产量(单个鲜果重)和根生物量较低,但其植株高度、单株生物量、叶片N、K含量和比叶面积无显著差异,叶片碳稳定性同位素(δ^(13)C)和P含量较高。在4月和9月,两菠萝品种间对不同形态的氮素吸收均有显著差异。总体而言,‘台农17’比‘巴厘’的氮吸收能力强(P<0.05)。‘台农17’菠萝较强的氮吸收能力和水分利用效率更有助于将其分配到地上以促进光合作用,从而维持其植株在较短生命周期内的生长。两菠萝品种都偏好吸收铵态氮(36.8%~64.6%),其次是甘氨酸(23.2%~47.1%),对硝态氮吸收速率最低(9.1%~31.5%)。处于营养生长阶段的菠萝植株(5~8个月)比果实收获时期的氮吸收速率高。随着年龄的增长,铵态氮贡献率逐渐增大,而甘氨酸贡献率逐渐降低。不同季节和年龄条件下,不同形态氮素的吸收速率与土壤氮含量和其他所测得植物性状的相关性不显著。总之,本研究首次证实田间菠萝的根系具有较强直接吸收利用有机氮的能力,菠萝的品种和生长阶段都是影响氮素获取策略的重要因素。

Pineapple[Ananas comosus(Linn.)Merr.]is China’s third largest tropical fruit,with the largest planting area in Xuwen County,Guangdong Province.As one of the most important macronutrients,nitrogen is closely related to pineapple yield.However,the uptake preferences for different nitrogen forms in field-grown pineapple plants remain unclear.In this study,the morphological,physiological,and growth traits of plants with different ages were measured in two field-grown pineapple cultivars(‘Tainong 17’and‘Bali’)with different growth periods in April and September,respectively,in Xuwen County.In addition,nitrogen acquisition strategies for three different forms of nitrogen(ammonium nitrogen,nitrate nitrogen,and glycine)in the pineapple roots were determined using the stable isotope 15N tracer technique.The results indicated that the growth period of the‘Tainong 17’pineapple(16 months)was shorter than that of‘Bali’(20 months).During the fruit harvest period in April,compared with the‘Bali’pineapple(796 g fresh fruit weight per plant),‘Tainong 17’pineapple plants had lower yield(532 g fresh fruit weight per plant),root biomass,and P content;but had similar plant height,plant biomass per plant,leaf N and K contents,and specific leaf area.As an indicator of longterm water-use efficiency,the δ^(13)C value ranging from-15.16‰to-13.28‰,was higher in the leaves of‘Tainong 17’pineapple than that in‘Bali’.Neither cultivar nor age greatly affected the leafδ^(13)C values.In April and September,there were significant differences in the different forms of nitrogen uptake between the two pineapple cultivars.The nitrogen uptake capacity of‘Tainong 17’pineapple was higher than that of‘Bali’.The high acquirement capacity of nitrogen and water use efficiency of‘Tainong 17’pineapple is attributed to promoting photosynthesis and thus maintaining plant growth in a relatively short life cycle.Both pineapple cultivars preferred to acquire ammonium nitrogen(36.8%–64.6%),followed by glycine(23.2%–47.1%),and the uptake rate of nitrate nitrogen was the lowest(9.1%–31.5%).The nitrogen uptake rate of pineapple plants in the vegetative growth stage(5–8-month-old)was higher than that of plants in the fruit-harvesting stage.However,with increasing plant age,the contribution rate of ammonium nitrogen increased,whereas that of glycine gradually decreased.Across different pineapple cultivars and plant ages,the rates of different forms of nitrogen uptake were not linearly correlated with the soil nitrogen content or measured plant traits.To the best of our knowledge,this is the first study to show that the roots of field-grown pineapple plants can directly absorb organic nitrogen from the soil.Cultivar and plant growth stages of pineapples are important factors that affect nitrogen acquisition strategies.However,the linear relationships between the absorption rates of different forms of nitrogen and soil nitrogen content or measured plant traits were very weak.These results contribute to nitrogen fertilizer management in pineapple plantations.