Comparison of pretreatment,preservation and determination methods for foliar pH of plant samples

植物叶片pH值的测定及样品预处理和保存方法的比较研究

To compare current methods of pretreatment/determination for plant foliar pH,we proposed a method for longperiod sample preservation with little interference with the stability of foliar pH.Four hundred leaf samples from 20 species were collected and four methods of pH determination were used:refrigerated(stored at 4°C for 4 days),frozen(stored at−16°C for 4 days),oven-dried and fresh green-leaf pH(control).To explore the effects of different leaf:water mixing ratio on the pH determination results,we measured oven-dried green-leaf pH by leaf:water volume ratio of 1:8 and mass ratio of 1:10,and measured frozen senesced-leaf pH by mass ratio of 1:10 and 1:15.The standard major axis regression was used to analyze the relationship and the conversion equation between the measured pH with different methods.Foliar pH of refrigerated and frozen green leaves did not signifcantly differ from that of fresh green-leaf,but drying always overrated fresh green-leaf pH.During the feld sampling,cryopreservation with a portable refrigerator was an advisable choice to get a precise pH.For long-duration feld sampling,freezing was the optimal choice,and refrigeration is the best choice for the shorttime preservation.The different leaf:water mixing ratio signifcantly infuenced the measured foliar pH.High dilution reduced the proton concentration and increased the measured pH.Our fndings provide the conversion relationships between the existing pretreatment and measurement methods,and establish a connection among pH determined by different methods.Our study can facilitate foliar pH measurement,thus contributing to understanding of this interesting plant functional trait.

植物叶片pH值是叶片能量运转、新陈代谢、养分平衡等生理活动的重要调节因素。但目前尚缺乏一套合适的植物叶片样品的保存和测试方法,能同时满足叶片样品的长期保存和接近鲜叶片pH值测定的要求。本文通过探索植物叶样品的预处理和保存方式以及叶:水混合比例对叶片pH测定值的影响,提出一种能够长期保存植物叶片,同时对叶片pH值影响较小的测定方法,并且建立不同处理方法间的转换关系。本研究采集多种植物的叶片样品,并分别进行短期冷藏、冷冻和烘干处理保存,以刚采摘的新鲜绿色叶片作为对照,研究叶片样品不同保存方式对其pH值的影响。对烘干绿色叶片按叶片和水1:8的体积比和1:10的质量比分别进行pH值测定,对冷冻叶片:水按质量比为1:10和1:15的比例分别进行测定,分析不同加水比例对所测叶片样品pH值的影响。结果表明,短期冷藏和冷冻处理对植物叶片pH值的测量结果没有显著影响,但是烘干处理一般会使测定值偏高。因此,在长时间的野外采样工作中,通过便携式冷藏箱对植物样品进行冷冻保存,是保持叶片样品pH值稳定、即更接近新鲜叶pH测量值的较好的样品保存方式。对于长时间野外采样,冷冻预处理是植物叶样品保存的最佳选择;而冷藏预处理是短时间保存的最佳选择。不同的叶片:水比例对pH测量值存在显著影响:样品稀释比例越高,氢离子浓度越低,测量到的叶片pH值越大。因此,为了建立现有不同植物叶pH值测量方法之间的联系,本文为叶片样品的不同前处理和测量方式提供了转换关系。本研究结果将有助于植物叶片pH值的研究,从而提高对这一功能性状的认识。