Supported by Beijing Municipal Natural Science Foundation (6142005).

1 Introduction

Arbuscular mycorrhiza (AM)is a kind of common endotrophic mycorrhiza, which can form symbiosis with plant roots, promote the absorption of nutrients by plants and enhance the resistance of plants[1]. Extensive studies have conducted on the resistance, protecting against soil pollution, improving soil and improving fruit quality of AM, and it has broad application prospects. The big mycelial network of AM will increase the absorption area of plant roots and promote water absorption in CipressusduclouxianaandCatalpabungei under dry conditions, as well as preventing the loss of body water[2]. Wang Liping etal.[3]found that AM promoted the growth and root development of maize plants, and the increase of biomass showed an ideal remediation effect on petroleum-contaminated soil. Wu Jianxin etal.[4]found that AM promoted nutrients absorption by roots and improved the quality of strawberries. In this study, the effects of 5 kinds of AM fungi on the growth of Glycyrrhizauralensis Fisch. were investigated to screen out the fungi that could promote the growth of G. uralensis and adapt well to the environment, thereby proving reference for the production and large-area popularization in the future.

2 Materials and methods

2.1 Experimental materials The seeds of G. uralensis were purchased from Beijing Shizhen Chinese Herbal Medicine Technology Co., Ltd. The tested fungi (Acaulosporamellea, G. mosseae, G. versiforme, G. aggregatumandG. etunicatum) were purchased from Institute of Plant Nutrition and Resources of Beijing Academy of Agriculture and Forestry Sciences. The tested substrate was composed of peat, vermiculite and sand (1∶0.5∶1), which was sterilized under high pressure at 121℃ for 2 h and dried for use.

2.2 Experimental methods The experiment was conducted in the intelligent greenhouse in Green Technology Demonstration Garden of Beijing Vocational College of Agriculture in 2015. Before the sowing, the seeds of G. uralensis were soaked in 1% potassium permanganate solution for 30 min, rinsed with running water and soaked in clear water for 1 d. Subsequently, the seeds were rinsed with clear water and soaked in 1% potassium permanganate solution for 10 min. Then, the seeds were scattered evenly on a layer of sterilized wet gauze and covered with a layer of gauze for promoting germination. After the seeds germinated, sowing and inoculation were carried out synchronously.

贯彻全面从严治党的战略方针，必须认真完成好抓基层、打基础的工作，使每个农村基层党组织都成为坚强的战斗堡垒，这是党长期执政的客观要求。在公共权力体系内，农村基层党组织的权力并不大，但是在财政转移支付和资源大规模下乡的背景下，其在行政村范围内却掌握着资源分配的决定权，存在贪污腐败的机会，需加大对这种权力末梢的反腐力度。在农村基层，全面从严治党需要农村党组织与村委会职能分工，在协调配合进行乡村治理过程中相互制约。

Plastic pots with specifications of 25 cm (mouth diameter) ×20 cm (bottom diameter) × 40 cm (height) were selected for cultivation. They were first disinfected with 2% potassium permanganate solution for 10 min and then loaded with the substrate to a height of 35 cm. In each pot, 10 g of inoculant was placed. A total of 20 pots, with 5 plants per pot, were arranged for each treatment. On the basis of conventional management, appropriate irrigation was carried out, and Hoagland nutrient solution was poured once a month.

8月二铵市场收获关键词“稳健”。内销市场上，秋季市场销售流向已经基本确定，经销商催货回运为主。当前，企业9月份出口订单已经敲定，在出口和内销市场需求双向支撑下，二铵国内价格或有望在9月中旬前后调整，预计幅度50元/吨。

3 Results and analysis

3.1 Effects of AM on growth of glycyrrhiza plants

3.1.2 Effects of AM on main root length, fresh weight and dry weight of glycyrrhiza plants. As shown in Table 1, the main root lengths of glycyrrhiza plants in the fungi inoculation treatment groups were 6.54%, 21.18%, 13.24%, 19.94% and 35.20% higher than that in the control group. The results of variance analysis showed that the main root lengths in the G. etunicatum, G. mosseae and G. aggregatum treatment groups were significantly higher than those in the A. mellea and control groups (P<0.05). The fresh weight and dry weight of glycyrrhiza plants inoculated with G. etunicatum were significantly higher than those in the other groups (P<0.05).

Table 1 Effects of AM on the growth ofGlycyrrhizauralensis Fisch.

StrainnamePlantheightcmBasaldiametermmMainrootlengthcmFreshweight∥gAbovegroundUndergroundDryweight∥gAbovegroundUndergroundAm16．86±2．23c0．85±0．12c13．68±1．65b0．81±0．18d0．35±0．06d0．26±0．04d0．14±0．03cGm39．63±2．93a1．26±0．08a15．56±2．63a1．63±0．13c0．96±0．17bc0．57±0．06c0．43±0．11bGv36．17±3．35a1．15±0．06ab14．54±2．20a2．91±0．30b0．73±0．07c1．04±0．15b0．29±0．05bcGa39．40±2．18a1．19±0．10ab15．40±2．10a2．85±0．18b1．00±0．12b1．05±0．08b0．44±0．06bGe39．92±5．25a1．32±0．17a17．36±4．72a3．95±0．29a1．90±0．12a1．51±0．25a0．95±0．19aCK30．41±4．12b1．03±0．11bc12．84±2．30b1．31±0．15c0．36±0．06d0．42±0．05cd0．13±0．03c

Note: Different lowercase letters in the same column indicate significant differences at the 0.05 level. Am, Acaulosporamellea; Gm, G. mosseae; Gv, G. versiforme; Ga, G. aggregatum; Ge, G. etunicatum; CK, control. The same below.

3.1.1 Effects of AM on plant height and basal diameter of glycyrrhiza plants. As shown in Table 1, different AMs had different effects on the growth of G. uralensis. As the growth proceeded, the plant height of inoculated glycyrrhiza plants was increased significantly, 44.56%, 30.32%, 18.94%, 29.55% and 31.26% respectively higher than the control, and the plant height of glycyrrhiza plants inoculated with G. etunicatum was increased most greatly. The results of variance analysis showed that there were significant differences in plant height of G. uralensis between G. etunicatum, G. mosseae, G. aggregatum, G. versiforme and A. mellea, control groups (P<0.05). The basal diameters of glycyrrhiza plants inoculated with the 5 kinds of AM fungi were increased by 17.32%, 22.57%, 12.32%, 16.02% and 28.34% respectively compared with that in the control group, and the basal diameter of glycyrrhiza plants inoculated with G. etunicatum was increased most greatly. The basal diameters of glycyrrhiza plants inoculated with G. etunicatum and G. mosseae were significantly different from those of glycyrrhiza plants in the A. mellea and control groups (P<0.05). The plant height and basal diameter of glycyrrhiza plants inoculated with A. mellea showed negative growth, which might be related to the activity of the inoculated fungi, non-standard inoculation, sampling consistency and improper management or testing.

3.2 Effects of AM on activity of protective enzymes in glycyrrhiza plants

By studying the relationship between SPD activity and water stress in peanut[22]and Pinustabulaeformis[23], it was found that SOD activity decreased and the plant appeared unadapted to the outside world in the early stage of water stress; but with the increased intensity of water stress, the adaptability of plant increased, and its SOD activity increased. There were evident differences in SOD activity among different cultivars. Studies also showed that under moderate water stress, the activities of SOD, POD and CAT increased significantly; but with aggravation of water stress, the balance of active oxygen metabolism was destroyed, the lipid peroxidation aggravated, the SOD activity decreased[24], the POD and CAT activities continued to rise, and the main root length increased with the extension of water stress duration[25]. Ma etal.[26]found that under cold stress, the SOD activity increased in cold-tolerant varieties (lines) and decreased in cold-sensitive ones; and under high temperature stress, the SOD activity of all the varieties (lines) decreased. However, some scholars held the opposite view, that is, low temperature could increase the content of reactive oxygen species in plants, reduce the activity of SOD and enhance lipid peroxidation[27].Under salt stress, the POD and SOD activity increased first and then decreased with the increase of salt concentration.

2.3 Index measurement The plant height, basal diameter (the diameter of stem 5 cm above the ground) and protective enzyme activity of G. uralensis were measured at the seedling stage, rapid growth stage and turning point of growth from fast to slow, respectively. At the turning point, the main root length, aboveground fresh weight, underground fresh weight, aboveground dry weight and underground dry weight were measured. For the measurement of growth indexes, 5 in-situ points were arranged randomly for each treatment throughout the growth period. The activity of superoxide dismutase (SOD) was determined by nitroblue-tetrazolium (NBT) reduction method[5]; the activity of peroxidase (POD) was determined using guaiacol method[6]; and the activity of catalase (CAT) was determined with potassium permanganate titration method[6].

Fig.1 Effects of AM on SOD activity ofGlycyrrhizauralensis Fisch.

Table 2 Mean comparison and significance analysis of effect of AM on the protective enzyme activity ofGlycyrrhizauralensis Fisch.

AmGmGvGaGeCKSOD89．28±6．27ab80．99±4．96b75．57±20．46b86．26±7．63ab88．05±8．98ab110．26±7．66aPOD59．14±6．31a53．36±2．88ab56．69±3．29a48．44±2．17b47．50±5．46b58．06±1．87aCAT1．72±0．30b1．61±0．08b1．59±0．12b2．72±0．13a2．80±0．49a2．95±0．66a

Studies showed that the inoculation promoted the growth of plants, of which the plant height was increased more obviously, but the increase amplitude differed significantly among different strains[7-8]. Under the influence of stress, such as cold, drought and pollution[9], the increase in activity of nitrogenase in the rhizospheric environment[10]provided sufficient nutrients for the root system[11], thus promoting the growth of plants[12-14]. Within a certain intensity range of salt stress, AM fungi could expand the absorption area of nutrients, increase the dry weight of underground part of safflower, and regulate the mineral nutrients around the root system, thus improving the surrounding osmotic adjustment environment and promoting the growth[15].Wu Huifeng etal.[16]found that many fungi could form symbiotic relationship with Dendrobiumcandidum at seedling stage, increase their biomass and promote their growth. However, some studies have shown that the growth-promoting effect varies among different strains and different crops[17]. Liu Airong etal.[18]found that in the substrate with high nutritional level, the inoculation of AMF obviously promoted the growth of cucumber at the seedling stage. It suggests that different environments have some impact on AM’s promoting plant growth.

Fig.2 Effects of AM on POD activity ofGlycyrrhizauralensis Fisch.

3.2.3 Effects of AM on CAT activity of glycyrrhiza plants. At the former 2 stages, no significant differences were found in CAT activity among the treatment groups (P>0.05), about 0.24-3.50 times higher than that in the control group. At the last stage, the CAT activities in the treatment groups all increased obviously. On August 6, the CAT activities in the A. mellea, G. mosseae and G. versiforme treatment groups were higher than that in the control group. But on September 20, the CAT activities in the treatment groups were all lower than that in the control group (Fig.3). As shown in Table 2, there were significant differences in CAT activity between G. etunicatum, G. aggregatum and A. mellea, G. mosseae, G. versiforme treatment groups.

Fig.3 Effects of AM on CAT activity ofGlycyrrhizauralensis Fisch.

4 Conclusions and discussions

3.2.2 Effects of AM on POD activity of glycyrrhiza plants. In the early period, the POD activities in various treatment groups were all higher than that in the control group. After entering the rapid growth stage, the POD activities in the treatment groups all increased. On August 5, the POD activity in the control group reached the maximum. In the later period, the POD activities in the treatment groups declined compared with those on August 5. The decrease of POD activity in the G. versiforme treatment group was greatest, 61.80%. The POD activity in the control group was higher than those in the treatment groups (Fig.2). As shown in Table 2, there were significant differences in POD activity between A. mellea and G. aggregatum, G. etunicatum treatment groups (P<0.05).

1.4 培养基的配制 马铃薯葡萄糖琼脂培养基（PDA）：马铃薯100 g（去皮），葡萄糖粉10 g，琼脂条8.5g，去离子水加至500mL。

The growth, development, aging and death of plants are a kind of cycle of life and also a natural law. In this process, the protection system formed by the plant itself can resist the interference from the adverse environment in the proper range. Modern doctrine generally believes that the aging of plants is related to the increase in contents of reactive oxygen species and oxygen free radicals in plant body under stress. The reactive oxygen species included hydrogen peroxide, hydroxyl radical and superoxide anion. SOD, POD and CAT are three kinds of protective enzymes widely present in plants, and they can form a protective enzyme system and effectively play a synergistic role in the removal of reactive oxygen species. POD and CAT also have the function of eliminating hydrogen peroxide[19-21].

3.2.1 Effects of AM on SOD activity of glycyrrhiza plants. As shown in Fig.1, the activity of SOD in G. uralensis increased first and then decreased with the proceeding of growth. In the early stage of growth (June 11), the SOD activity in the G. aggregatum treatment group was higher than those in the other groups. As the growth accelerated, the external environment was constantly changed(e.g. the weather became hot after entering July), and the plants also faced the threat of drought, so their SOD activity showed a rapid upward trend. On August 5, the SOD activity in the control group was highest, 8.92%, 14.54%, 20.79%, 25.43% and 27.89% higher than those in the A. mellea, G. etunicatum, G. aggregatum, G. mosseae and G. versiforme treatment groups. In the later period, the drought stress was relieved, and the SOD activity in G. uralensis declined correspondingly. The decrease was obvious. On September 19, the SOD activity in glycyrrhiza plants inoculated with G. aggregatum was lowest. The results of variance analysis showed that there were significant differences in SOD activity between G. mosseae, G. versiforme treatments and the control groups (Table 2, P<0.05).

预制光缆敷设时应预留适当的余量，且需精确控制预留长度。若预留长度不够，则需退回厂家重新加工及发货，对工程工期造成延误；若预留长度过长，给柜内盘线困难，且影响舱内光缆敷设、整齐、美观。因此，如何有效控制预制光缆余长在工程实施时非常重要。

Kong Jing etal.[28]inoculated bacteria to alfalfa, and they found the activities of SOD, POD and CAT in the leaves of alfalfa decreased obviously with the aggravation of water stress. Hu Guixin etal.[29]found that under water stress, the POD activity in the stems of bacteria-inoculated tall fescue significantly declined and the CAT activity in the leaves increased compared with those of non-inoculated ones. The responses of mycorrhizal fungi to water stress were affected by the intensity of water stress and host plants, and the process was complicated[30]. After the inoculation with fungi, the root system of G. uralensis was bound to form mycorrhiza, a protection system could be formed to a certain extent, and the mycorrhizal fungi would probably reduce the content of oxygen free radicals in glycyrrhiza plants, thus alleviating the damage caused by adverse environmental conditions[31-32].

This study found that the plant height, basal diameter, man root length, aboveground fresh weight, underground fresh weight, aboveground dry weight and underground dry weight of AM fungi-inoculated glycyrrhiza plants were increased compared with those of non-inoculated ones, which was consistent with the finding of Zhang Zhongfeng etal.[33]. However, the effects of different fungus species on plant growth were significantly different. G. etunicatum, G. mosseae and G. aggregatum showed significant promoting effect on the growth of G. uralensis. With the growth of plants, the activities of SOD and POD increased first and then decreased, and the activity of CAT continued to increase. The activities of protective enzymes in the glycyrrhiza plants inoculated with G. etunicatum, G. mosseae and G. aggregatum were significantly lower than those in the other treatment groups, and these fungus species were superior to the others in resisting adverse environmental conditions. However in this study, the interval between every two consecutive times of irrigation was not long, and whether the high temperature or water stress influences the growth of plants still needs repetitive studies. In the future, the resistance and ecological adaptability of inoculated G. uralensis under different stresses and in different ecological conditions can be studied in depth.

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就在沈大高速公路建设之时，在南方却酝酿着另一种建设模式。出于经济发展的需要，处于改革前沿的广东，急需打通广州与深圳的交通大通道。但当时广东公路建设财政拨款一年只有600万元，还不够修半公里高速公路……