Effects of Exogenous Phenolic Acids on Allelopathy of Potted Soybean Seedlings

Long CHEN,Meiling ZHANG,Mingyue XIN,Jiandong LI

1.Panjin Meteorological Bureau,Panjin 124010,China;

2.Dawa Meteorological Bureau,Dawa 124200,China;

3.College of Agronomy,Shenyang Agricultural University,Shenyang 110866,China

Effects of Exogenous Phenolic Acids on Allelopathy of Potted Soybean Seedlings

Long CHEN1,Meiling ZHANG2,Mingyue XIN1,Jiandong LI3*

1.Panjin Meteorological Bureau,Panjin 124010,China;

2.Dawa Meteorological Bureau,Dawa 124200,China;

3.College of Agronomy,Shenyang Agricultural University,Shenyang 110866,China

In this study,several generally reported exogenous phenolic acids were selected as regents for potting experiments,aiming at revealing the effects of different concentrations of exogenous phenolic acids on the growth and development of soybean seedlings.The growth and development indicators of soybean seedlings treated with five different concentrations of exogenous phenolic acids,such as plant height,leaf area,root nodule number and root-shoot ratio,were determined and compared.According to the experimental results,three exogenous phenolic acids with different concentrations exhibited slight effects on plant height of potted soybean seedlings.The leaf area of potted soybean seedlings treated with 1.0 g/kg benzoic acid and cinnamic acid varied extremely significantly compared with the control.Root nodule number of potted soybean seedlings treated with 1.0 g/kg benzoic acid and vanillic acid increased remarkably,but 1.0 g/kg cinnamic acid had little effects on root nodule number.When the concentration of phenolic acids was 1.0 g/kg,three phenolic acids exhibited the maximum effects on root-shoot ratio of potted soybean seedlings.Overall,low concentrations of exogenous phenolic acids exhibited no significant effects on the growth and development of potted soybean seedlings;high concentrations of exogenous phenolic acids inhibited the growth and development of potted soybean shoots,increased root nodule number and improved root-shoot ratio.

Potted soybean;Exogenous phenolic acid;Growth and development; Effect

A llelopathy is a biological phenomenon by which plants produce biochemicals that promote or inhibit the growth,survival, and reproduction of other plants(or microorganisms)during the growth and development period[1].Rice[2]reported that plant allelopathy also involved beneficial impacts and self-allelopathy of different plants.In the late 1980s,as people noticed the drawbacks in controlling crop diseases using chemical substances and sought for biogenic pesticides,plant allelopa thy gradually drew the attention of ecologists around the world.At present,plant allelopathy has become one of the hot issues in agroecology and bioecology[3].

In recent years,numerous tests have demonstrated the close relationship between continuous cropping obstacle and allelochemicals in root exudates.A large amount of exogenous phenolic acids can be released by rice root excretion and straw decomposition,including p-hydroxybenzoic acid, coumaric acid,syringic acid,vanillic acid,amygdalic acid and ferulic acid. The accumulation of these exogenous phenolic acids in soil will reduce rice yield in next season[4].Liu et al.[5]found that p-tert-butylbenzoic acid isolated from rhizosphere soil could inhibit root growth of wheat and maize at high concentrations and promote that at low concentrations.Booker et al.[6]reported that treating cucumber seedlings with cinnamic acid could decrease leaf water potential and turgor

Currently,a large number of studies have been carried out on root exudates of soybean and soil extracts. Wanget al.[9]treated soybean seeds with decomposed liquids from soybean stubs under constant temperature and found that decomposed liquids from soybean stubs could significantly inhibit the germination of soybean seeds,decrease root activity of soybean seedlings,damage biofilm and reduce stress resistance. Duet al.[10]analyzed the allelopathy effects of aqueous extract and root exudates of soybean on soybean seedlings using tissue culture technique under sterile condition.Based on the principle of negative pressure, Wanget al.[11]detected a variety of exogenous phenolic acids in the directly extracted soil solutionin situ.Zheng[12]identified decomposed liquids from soybean stubs by HPLC and found that high concentrations of cinnamic acid,benzoic acid,vanillic acid and hydroxybenzoic acid strongly inhibited the germination rate and embryonic root growth of soybean seeds,and the inhibitory effect was weakened with the reduction of concentration.There was a negative correlation between the increasing phenolic content in soybean roots and soybean yield during continuous cropping.Investigating the effects of exogenous phenolic acids on the growth and development of soybean has a very important significance for analyzing the mechanism of allelopathy effects of phenolic acid on soybean and regulating the continuous cropping of soybean[13-14].

Many researches are concentrated on the reasons of continuous cropping obstacle in soybean,but little information is available about the effects of exogenous phenolic acids on the growth and development of soybean seedlings[15].Exogenous phenolic acids are the most important allelochemicals,including benzoic acid,cinnamic acid and vanillic acid which are generally reported.In this study,the effects of different concentrations of exogenous phenolic acids on allelopathy of potted soybean seedlings were analyzed,aiming at revealing the effects of phenolic acids on continuous cropping obstacle in potted soybean and providing scientific basis for the regulation of continuous cropping obstacle in soybean.

Materials and Methods

Materials

Soybean cultivar"Tiefeng No.29" was used as the experimental material.

Experimental design

On June 10,2010,the field trials were carried out in the proving ground of scientific research base of College of Agronomy,Shenyang Agricultural University.The potting soil was sandy loam,containing 1.8%organic matter, 0.109%total nitrogen,0.06%total phosphorus,81 mg/kg alkali-hydrolyzable nitrogen,18.6 mg/kg available phosphorus and 64 mg/kg available potassium,pH(water immersion)6.6. Three treatments were designed as follows:T1,benzoic acid treatment; T2,vanillic acid treatment;T3,cinnamic acid treatment.Five concentration gradients were set:0,0.01,0.1, 0.5,1.0 g/kg,respectively.Each concentration was repeated three times. Three pots were treated in each group and totally 39 pots were treated.Soybean seedlings potted in normal sandy soil were used as the control.To decrease the influence of adverse weather on growth of potted soybean, the experiment was conducted in a 3.5 m×14 m plastic greenhouse with steel frame.Potted soybean seedlings were watered regularly according to the evaporation capacity and actual water deficiency to maintain soil moisture.All the potted soybean seedlings were observed and managed regularly according to daily weather condition. Samples were collected since the 18th d after the germination of all seedlings. Three soybean seedlings in each pot were collected with three replications. All the indicators were determined immediately after sampling.

Determination methods

Determination of plant heightThe plant height of soybean seedlings was measured using a 150 cm plastic ruler.Determination of leaf areaThe leaf area of soybean was measured with hole-punching method.

Determination of root nodule numberThe collected soybean roots were was washed for manual counting in the laboratory.

Determination of root-shoot ratio

The collected fresh samples were dried in a drying oven at 105℃for 30 min to deactivate enzymes,dried to constant weight at 85℃,and cooled to room temperature before determination.

Data analysis

All the experimental data were analyzed using DPS(7.05)statistical software.

Results and Analysis

Effects of exogenous phenolic acids on plant height of potted soybean

As shown in Fig.1,compared with the control,the effects of three phenolic acids with different concentrations on plant height of potted soybean seedlings varied slightly.When the concentration of phenolic acids was lower than 0.1 g/kg,the effects of different phenolic acids on plant height of potted soybean seedlings demonstrated a descending order of cinnamic acid treatment＞benzoic acid treatment＞vanillic acid treatment.As the concentration of phenolic acids ranged from 0.1 to 1.0 g/kg,the inhibitory effects of different phenolic acids demonstrated a descending order of benzoic acid treatment＞cinnamic acid treatment＞vanillic acid treatment.Compared with the control,plant height of potted soybean seedlings treated with 1.0 g/kg cinnamic acid was significantly lower.

Effects of phenolic acids on leaf area of potted soybean

As shown in Fig.2,when the concentration of phenolic acids was 0.01 g/kg,leaf area of potted soybean seedlings in cinnamic acid treatment was lower than that in the control with no significant differences;leaf area of potted soybean seedlings in benzoicacid treatment and vanillic acid treatment was higher than that in the control with no significant differences. When the concentration of phenolic acids was 0.1 g/kg,leaf area of potted soybean seedlings in cinnamic acid treatment was significantly lower than that in the control.When the concentration of phenolic acids was 0.5 g/kg, leaf area of potted soybean seedlings in benzoic acid treatment was significantly lower than that in the control; leaf area of potted soybean seedlings in vanillic acid treatment was lower than that in the control with no significant differences.When the concentration of phenolic acids was 1.0 g/kg, leaf area of potted soybean seedlings treated with three phenolic acids was lower than that in the control;specifically,leaf area of potted soybean seedlings in benzoic acid treatment and cinnamic acid treatment varied extremely significantly compared with the control.

Effects of exogenous phenolic acids on root nodule number of potted soybean

As shown in Fig.3,when the concentration of phenolic acids was 0.01 g/kg,root nodule number of potted soybean seedlings in cinnamic acid treatment and benzoic acid treatment was higher than that in the control, while root nodule number of potted soybean seedlings in vanillic acid treatment was significantly lower compared with the control.When the concentration of phenolic acids was 0.1 g/kg,root nodule number of potted soybean seedlings treated with three phenolic acids exhibited no significant differences compared with the control. When the concentration of phenolic acids was 0.5 g/kg,root nodule number of potted soybean seedlings in vanillic acid treatment was significantly lower than that in the control,while root nodule number of potted soybean seedlings in cinnamic acid treatment and benzoic acid treatment exhibited no significant differences compared with the control.When the concentration of phenolic acids was 1.0 g/kg, root nodule number of potted soybean seedlings in benzoic acid treatment was extremely significantly higher than that in the control,while root nodule number of potted soybean seedlings in vanillic acid treatment was significantly higher than that in the control.

Effects of exogenous phenolic acids on root-shoot ratio of potted soybean

As shown in Fig.4,root-shoot ratio of potted soybean seedlings treated with different concentrations of benzoic acid and vanillic acid showed an increasing trend.To be specific,rootshoot ratio of potted soybean seedlings increased in 1.0 g/kg cinnamic acid treatment and declined gradually in 0.01-0.5 g/kg cinnamic acid treatment.When the concentration of phenolic acids was 0.01 g/kg, root-shoot ratio of potted soybean seedlings in cinnamic acid treatment and vanillic acid treatment was higher than that in the control;root-shoot ratio of potted soybean seedlings treated with benzoic acid was remarkably higher than that in the control.When the concentration of phenolic acids was 0.1 g/kg,root-shoot ratio of potted soybean seedlings in benzoic acid treatment and vanillic acid treatment was significantly higher than that in the control;root-shoot ratio of potted soybean seedlings in cinnamic acid treatment was remarkably lower than that in the control.When the concentration of phenolic acids was 0.5 g/kg,rootshoot ratio of potted soybean seedlings in vanillic acid treatment was lower than that in the control;rootshoot ratio of potted soybean seedlings in cinnamic acid treatment was significantly lower than that in the control;root-shoot ratio of potted soy-bean seedlings treated with benzoic acid was higher than that in the control with no significant differences.When the concentration of phenolic acids was 1.0 g/kg,root-shoot ratio of potted soybean seedlings in three treatments was higher than that in the control; specifically,root-shoot ratio of potted soybean seedlings treated with benzoic acid was extremely significantly higher than that in the control,while root-shoot ratio of potted soybean seedlings in other two treatments exhibited no significant differences compared with the control.

Discussions

In general,low concentrations of benzoic acid and cinnamic acid exhibited no significant effects on the growth and development of potted soybean seedlings;high concentrations of benzoic acid and cinnamic acid inhibited the growth and development of potted soybean shoots,increased root nodule number and improved root-shoot ratio; low concentrations of vanillic acid promoted the growth of potted soybean shoots and inhibited the growth of potted soybean roots;high concentrations of vanillic acid inhibited the growth and development of potted soybean shoots,increased root nodule number and improved root-shoot ratio.

Compared with the control,three exogenous phenolic acids with different concentrations exhibited no significant effects on plant height of potted soybean seedlings;moreover,0.5 g/kg vanillic acid exhibited remarkable effects on plant height of potted soybean seedlings compared with the control, which indicated that exogenous phenolic acids had slight effects on cell elongation growth of soybean stems. Different concentrations of benzoic acid and cinnamic acid strongly decreased leaf area of potted soybean seedlings;specifically,leaf area of potted soybean seedlings treated with 1.0 g/kg benzoic acid and cinnamic acid varied extremely significantly compared with the control,which demonstrated that exogenous phenolic acids might inhibit the growth and development of soybean seedlings by inhibiting leaf growth.In addition,1.0 g/kg benzoic acid and vanillic acid significantly increased root nodule number of potted soybean seedlings,but cinnamic acid treatment had little effects,which indicated that the inhibitory effects of exogenous phenolic acids on root nodule number of potted soybean seedlings were improved with the increase of phenolic acid concentration.The root-shoot ratio of potted soybean seedlings in three treatments showed an increasing trend,which reached the maximum when the concentration of phenolic acids was 1.0 g/kg;particularly,root-shoot ratio of potted soybean seedlings treated with 1.0 g/kg benzoic acid varied extremely significantly compared with the control, suggesting that exogenous phenolic acids exhibited higher inhibitory effects on the growth of potted soybean shoots than on roots.

In this study,potting experiments were conducted under simulated field environment using several allelochemicals generally reported in studies on continuous cropping obstacle in soybean,to investigate the concentration range and action mechanism of different phenolic acids based on the growth and development of potted soybean seedlings.The experimental reagents were solid crystal powder and the mixing process might be influenced by manual operation and uneven soil physicochemical properties, thus resulting in non-regular phenomena in some phenolic acid treatments. Furthermore,the effects of single exogenous phenolic acid on the growth and development indicators of soybean seedlings were preliminarily analyzed.However,the effects of various phenolic acid combinations on physiological,biochemical and photosynthetic indicators of soybean at seedling stage and other stages require further investigation.

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Responsible editor:Xiaohui FAN

Responsible proofreader:Xiaoyan WU

外源酚酸对盆栽大豆苗期生长发育影响研究

陈龙1,张美玲2,辛明月1,李建东3*
（1.盘锦市气象局，辽宁盘锦124010；2.大洼县气象局，辽宁大洼124200;3.沈阳农业大学农学院，辽宁沈阳110866）

以普遍报道的几种外源酚酸为试剂，通过盆栽实验，旨在探讨不同浓度外源酚酸对苗期大豆生长发育的影响。通过设置5种不同浓度外源酚酸的盆栽试验，测定不同浓度外源酚酸对盆栽大豆苗期生长发育指标影响。结果表明不同浓度3种外源酚酸对苗期大豆株高的影响总体较小。1.09 g/kg苯甲酸处理和肉桂处理的苗期大豆叶面积与对照差异达到极显著水平。1.09 g/kg苯甲酸处理和香草酸处理均显著增加了盆栽大豆根瘤数，肉桂酸影响较小。1.09 g/kg不同浓度3种酚酸对盆栽大豆根冠比影响最大。总体上，低浓度外源酚酸对盆栽大豆生长发育影响效果不显著；高浓度外源酚酸抑制了盆栽大豆地上部分生长发育，增加了盆栽大豆根瘤数和提高了盆栽大豆根冠比。

盆栽大豆；外源酚酸；生长发育；影响pressure,thus significantly reducing water absorption.Under the stress of allelochemicals,treating maize withCatharanthus roseusleaf extract could significantly decrease seed germination rate and remarkably inhibit the activity and leaf water potential at seedling stage[7].In addition,Zhanget al.[8]reported that root exudates ofPedicularis longifloravar.tubiformiswere toxic to highland barley,causing slow grow or death.

辽宁省高等学校创新团队科研资助项目（2009T088）。

陈龙（1982-），男，安徽阜阳人，助理工程师，硕士，研究方向为农业生态学，E-mail：1228ehenlong@163.com。*通讯作者，李建东（1964-），男，辽宁沈阳人，博士生导师，博士，主要从事植物化感和野生大豆遗传多样性研究，E-mail：sylijandong@126.com。

2015-02-14

修回日期 2015-05-10

Supported by the Scientific Research Fund for Innovative Research Team of Colleges and Universities in Liaoning Province(2009T088).

*Corresponding author.E-mail:sylijiangdong@126.com

Received:February 14,2015 Accepted:May 10,2015