Effects of Traffic Stress on the Physiological Characteristics of Agrostis stolonifera

Chengdong JI,Ping CHEN,Yunyun ZHOU

1.Hunan Golf and Tourism College,Changde 415900,China;2.Changsha Hawaii Grass Industry Co.,Ltd.,Changsha 410200,China;3.Zhongkai University of Agriculture and Engineering,Guangzhou 510225,China

Golf is a glamorous sport.It has been developed rapidly in China,and has been in favor of high-income earners.As the soul of golf course,green turf is a class of turf which has the highest requirements by quality[1].The green-turf grass usually has following properties:dwarfness,cutting resistance,strong tillering ability,uniform texture and strong diseases and pest resistance[2].Agrostis stoloniferaL.is a kind of cool-season grass,and it has been widely used as a planting for green turf of golf course due to its cutting resistance,cold resistance,drought resistance,strong regeneration ability and strong lateral spreading capacity of stolons[3].

Atpresent,the domestic researches on green-turf grass mainly focus on its resistance to high or low temperature,soil matrix,drought,flood and other adverse environmental conditions,and the researches on effects of traffic stress on green-turf grass mainly focus on the changes in appearance or single physiological indexes of grass[4-6].In fact,the effects of trampling on turf are multifaceted,including the effects on growth of shoot and roots and a series of physiological changesin metabolism.Especially under high temperature and humidity,there are rare reports on the effects of traffic stress on physiological and biochemical indices ofAgrostis stoloniferaL.Therefore,in this study,total 3 creeping bentgrass varieties(lines)were used as tested materials,and referring to the average daily ac commodation of a single standard 18-hole golf club in Guangdong in summer,the tested materials were trampled by testers in golf-specific shoes.The effects of traffic stress on physiological characteristics ofAgrostis stoloniferaL.in summer were investigated in order to provide important theoretical basis for the selection and cultivation of new green-turf grass varieties resistant to trampling and a scientific basis for the conservation and management of green turf in the same climate zone.

Materials and Methods

Overview on test site

The test was carried out in the green demonstration(113°20′E,23°10′N)of the Department of Grassland of Zhongkai University of Agriculture and Engineering.The test site was located in Haizhu District,Guangzhou City,Guangdong Province.It is a typical subtropical monsoon climate zone with annual average temperature of 21.4-21.9℃,average temperature of 28.0-28.7℃in the hottest months(July to August),absolute highest temperature of 38.7℃,average temperature of 12.4-13.5℃in the coldest month (January),absolute lowest temperature of-2.6℃,frost-free period of 320-345 d,average annual rainfall of 1 623.6-1 899.8 mm (which is mainly concentrated in the flood season from April to September)and average annual sunshine of 1 820-1 960 h.The top 20-cm soil layer has pH value of 5.9,ammonia nitrogen of 14.40 mg/kg and available phosphorus and potassium of 12.84 mg/kg and 9.51 mg/kg.

Materials

The tested materials included three creeping bentgrass varieties,Yuexuan 1,New Strain No.2 and Penncross.The Penncross seeds were introduced from America,and Penncross was treated as the control in this study.Yuexuan 1 and New Strain No.2 were all new varieties(lines)bred based on Penncross.Yuexuan 1 obtained the approval from the National Forage Variety Approval Committee in December,2012 with registration number of 288.

Test design

Referring to the average daily accommodation of a single standard 18-hole golf club in summer,the test treatments were designed.The green turf with grass height of 6 mm was trampled by testers with golf-specific shoes.A total of 4 treatments were designed,including TreatmentA (no trampling),Treatment B (mild trampling,100 steps/(m3·d)),Treatment C(moderate trampling,300 steps/(m3·d))and Treatment D (severe trampling,500 steps/(m3·d)).For each treatment,the trampling was all completed in morning and afternoon(half for each).The 6-conseccusive-d trampling,along with 1-d interval,was treated as one treatment cycle.In case of moderate or heavy rain,the treatments were not carried out.After 4 treatment cycles,the samples were collected and their physiologicalindexes were determined.

Indexes determination and methods

The leaf relative water content was determined with gravimetric method[7];the relative plasma membrane permeability was determined with electric conductivity method[8];the peroxidase activity was determined with guaiacol method[9];the SOD activity was determined with photochemical reduction method[9];the catalase activity was determined with ultraviolet absorption method[10];the proline content was determined with sulfosalicylic acid extraction method[9];the MDA content was determined referring to the method described by Zhanget al[11].

Data analysis

The data was processed using Excel,and the variance analysis was performed using SPSS 11.5.

Results and Analysis

Effect of different traffic stress on leaf relative water content

As shown in Table 1,with the increase of trampling intensity,the leaf relative water contents in the three creeping bentgrass varieties were all trended to be decreased.Under different trampling intensities,the leaf relative water content was all highest in Yuexuan 1.The results of variance analysis showed that the leaf relative water content all differed significantly among different trampling intensities and creeping bentgrass varieties (P＜0.05).

Effect of different traffic stress on relative plasma membrane permeability

Drought,extreme temperatures,heavy metal ions,salt and air pollution all can cause damage to cell membrane,leading to increased membrane permeability in plants cells[12].Table 2 showed that with the increase of trampling intensity,the relative plasma membrane permeabilities of the tested turfgrass varieties were all increased significantly.Under different trampling intensities,the leaf relative plasma membrane permeability was all highest in Penncross,and under the highest trampling intensity,the leaf relative plasma membrane permeabilityin Penncross reached 23.48%,which was 1.34 and 1.66 times higher than those in New Strain No.2 and Yuexuan 1,respectively.The effect of traffic stress on leaf relative plasma membrane permeability of Yuexuan 1 was relatively small.The variance analysis showed that the leaf relative plasma membrane permeabilityalldiffered significantly among different trampling intensities and creeping bentgrass varieties(P＜0.01).

Effect of different traffic stress on peroxidase activity

As shown in Table 3,the peroxidase activity of Yuexuan 1 was all highest under different stress treatment,while of Penncross was lowest.With the increase of trampling intensity,the peroxidase activity was reduced rapidly.The decrement of leaf peroxidase activity of Penncross was largest,followed by that of New Strain No.2,and the decrement of leaf peroxidase activity of Yuexuan 1 was smallest.Under the 3 traffic stresses,the decrements of leaf peroxidase activities of Penncross,New Strain No.2 and Yuexuan 1 were 39.85%,23.63%and 7.51%,respectively.The variance analysis showed that the peroxidase activity all differed significantly among different trampling stresses and creeping bentgrass varieties(P＜0.01).Under the mild traffic stress,Yuexuan 1 and New Strain No.2 all showed higher tolerance,and their peroxidase activities were increased,which might be due to the physiological response of protection enzyme system to traffic stress.With the continuous increase of trampling intensity,the peroxidase activities of Yuexuan 1 and New Strain No.2 were all decreased gradually,but their decrements were all smaller than that of Penncross.

Table 1 Effect of traffic stress on leaf relative water content of Agrostis stolonifera %

Table 2 Effect of traffic stress on leaf relative plasma membrane permeability of Agrostis stolonifera %

Table 3 Effect of traffic stress on leaf peroxidase activity of Agrostis stolonifera U/(g·min)

Table 4 Effect of traffic stress on leaf SOD activity of Agrostis stolonifera U/(g·min)

Effect of different traffic stress on SOD activity

As shown in Table 4,under the mild traffic stress,the leaf SOD activities of the tested turfgrass varieties were all increased,and the increments of Yuexuan 1,New Strain No.2 and Penncross were 3.57%,2.36%and 0.43%,respectively;under the moderate stress,the leaf SOD activities of Penncross and New Strain No.2 were trended to be decreased,but the leaf SOD activity of Yuexuan 1 was increased continuously;under the severe stress,the leaf SOD activities of the 3 turfgrass varieties were all reduced rapidly,and the decrement of Penncross was largest.Under the same traffic stress,the leaf SOD activity of Yuexuan 1 was all higher than those of New Strain No.2 and Penncross.The variance analysis showed that there were significant differences in leaf SOD activity among different trampling intensities and turfgrass varieties(P＜0.05).

Effect of different traffic stress on catalase activity

Table 5 showed that with the increase of trampling intensity,the leaf catalase activities of New Strain No.2 and Penncross were reduced continuously,but the leaf catalase activity of Yuexuan 1 was increased first and then decreased;under thesevere stress,the leaf catalase activities of the 3 turfgrass varieties were reduced by 17.10%,48.58%and 58.12%,respectively compared with that of control;the leaf catalase activity of Yuexuan 1 was all highest under different trampling treatments.The results of variance analysis showed that there were significant differences in leaf catalase activity among different trampling intensities(P＜0.05)and turfgrass varieties(P＜0.01).

Effect of different traffic stress on proline content

Asa osmoticregulation substance,stressed can cause the accumulation of proline in plants,and the accumulation amount can reflect the resistance ability of plants to some extent[12].Table 6 showed that under the mild stress,the proline contents in the tested turfgrass varieties were increased rapidly,and the increment of proline content in Yuexuan 1 was 1.87 and 1.25 times higher than those in Penncross and New Strain No.2,respectively;under the moderate stress,the leaf proline contents in Yuexuan 1 and New Strain No.2 were increased continuously,while the leaf proline content in Penncross was started to be reduced;under the severe stress,the leaf proline contents in the tested varieties were all trended to be decreased,and the decrement of Yuexuan 1 was relatively slow.Under different trampling intensities,the leaf proline content in Yuexuan 1 was all highest,followed by those of New Strain No.2 and Penncross.The variance analysis showed that there were significant differences in leaf proline content among different trampling intensities(P＜0.01)and turfgrass varieties(P＜0.05).

Table 6 Effect of traffic stress on free proline content in leaves of Agrostis stolonifera μg/g

Table 7 Effect of traffic stress on MDA content in leaves of Agrostis stolonifera μmol/g

Effect of different traffic stress on MDA content

As shown in Table 7,with the increase of trampling intensity,the MDA contents in the tested turfgrass varieties were all trended to be increased.Under the mild stress,the increments were relatively slow;with the increase of trampling intensity,the leaf MDA contents in the varieties were all increased rapidly;underthe severe stress,the increments of leaf MDA contents in Yuexuan 1,New Strain No.2 and Penncross were 41.50%,56.76%and 77.68%,respectively.Under different trampling treatments,the leaf DMA content was all highest in Penncross,followed by New Strain No.2,and the leaf MDA content in Yuexuan 1 was lowest.It indicated that the tolerance of Yuexuan 1 was better to traffic stress,and the esterification degree of membrane lipids in Yuexuan 1 was relatively low.The results of variance analysis showed that the leaf MDA content all differed significantly among different trampling intensities and turfgrass varieties (P＜0.01).

Conclusions and Discussion

One of the functions of protection enzyme system is to scavenge free radicals[13].Catalase activity determines the scavenging efficiencyofH2O2.SOD,as a protection enzyme against active oxygen,can disproportionate O2-·to produce H2O2.Peroxidase can also scavenge free radicals through catalyzing the reaction between H2O2and phenols.The synergic effect between SOD and peroxidase can transform the O2-·and H2O2,which have the strongest harm,into harmless H2O and O2,and the synergic effect between peroxidase and catalase can effectively scavenge H2O2in plants,preventing the excessive accumulation of oxygen radicals in plants,thereby maintaining the metabolism balance of active oxygen and reducing the damage of free radicals to cells.In this study,in the treatment of mild trampling,the peroxidase and catalase activities in Yuexuan 1 were increased simultaneously,thereby assisting plants to tolerate traffic stress.However,under moderate stress,the peroxidase activity was increased,but the catalase activity was reduced,weakening the tolerance of plants to traffic stress.Some scholars have pointed out that the accumulation of proline in plants under stress will help improve the antioxidant capacity and adaptability of plants,and once the stress is relieved,the accumulated proline will directly participates in the metabolism of plants.However,the mechanism of proline accumulation in plants under traffic stress is still unclear.It is speculated that the proline accumulation in plants under traffic stress may be due to the water shortage caused by damaged cell membrane under traffic stress.In this study,the accumulation of high-content free proline endowed Yuexuan 1 higher resistance compared with New Strain No.2 and Penncross.

Under stress,chain reactions will occur among generated and accumulated O2-·,·OH and H2O2,leading to inactivation ofmacromolecules in bodies.The peroxidation of lipids on plasma membrane will eventually result in increased MDA accumulation and plasma membrane permeability[14].The results of this study showed that among all the treatments,the leaf MDA content in Yuexuan 1 was lowest,and the active oxygen radicalsscavenging antioxidant enzyme system(peroxidase,SOD,catalase)in Yuexuan 1 also showed higher activity compared with New Strain No.2 and Penncross,indicating that the trampling tolerance ofYuexuan 1 was highest,while of Penncross was lowest.

The leaf relative water contents,proline contents, relative plasma membrane permeabilities,protection enzyme activities and MDA contents in the three creeping bentgrass varieties all differed significantly among different trampling intensities(P＜0.05).Based on the performance of physiological traits,it could be concluded that Yuexuan 1 has good tolerance to trampling.

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