• Journal of Resources and Ecology
  • Vol. 11, Issue 3, 322 (2020)
Guangyu ZHANG1、2、3, Jiangwei WANG1、2、3, Haorui ZHANG1、2、3, Gang FU1、2, and Zhenxi SHEN1、2、*
Author Affiliations
  • 1Lhasa Plateau Ecosystem Research Station, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
  • 2Engineering and Technology Research Center for Prataculture on the Xizang Plateau, Lhasa 850000, China
  • 3University of Chinese Academy of Sciences, Beijing 100049, China
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    DOI: 10.5814/j.issn.1674-764X.2020.03.010 Cite this Article
    Guangyu ZHANG, Jiangwei WANG, Haorui ZHANG, Gang FU, Zhenxi SHEN. Comparative Study of the Impact of Drought Stress on P.centrasiaticum at the Seedling Stage in Tibet[J]. Journal of Resources and Ecology, 2020, 11(3): 322 Copy Citation Text show less

    Abstract

    Nearly half of the land in Tibet is arid or semi-arid. Due to its special topographical, geomorphic and climatic conditions, the natural conditions are harsh, the ecosystem is fragile, and the carrying capacity is very limited (Sun et al., 2012; Zhang et al., 2015). Global climate change and the impact of human activities have further aggravated the situation in recent years, and grassland degradation has become one of the most serious ecological problems facing Tibet (Liu et al., 2012; Fu et al., 2018). In order to relieve the pressure of natural grassland and protect the ecological environment in Tibet, the vigorous promotion of human-made grassland has become a key measure (Gao et al., 2014; Duan et al., 2019). Pennisetum centrasiaticum Tzvel is a perennial forage of Pennisetum in Gramineae. P.centrasiaticum is widely distributed in arid and semi-arid areas of Tibet. Its rhizome system is developed and has strong resistance to adversity. It has genes to resist disease, insects, cold and drought that wheat crops lack. The biomass and nutritional quality of P.centrasiaticum are high at jointing stage (Li, 1983; Gao, 2008). PEG-6000 can simulate drought stress by regulating the osmotic pressure of solutions to limit water entering seeds, so the use of PEG-6000 offers a fast and reliable method to simulate a drought environment for the purpose of screening drought-resistant varieties (Hegarty, 1977; Van den et al, 2006). At present, there are few studies of P.centrasiaticum in Tibet. There is no data about the use of PEG-6000 to simulate a drought environment to screen out the P.centrasiaticum from different areas. The meteorological data from 1971 to 2014 showed that drought conditions in Tibet have worsened over the years, and this may cause devastating, long-term damage to the agriculture, economy and ecosystem of Tibet (Li et al., 2019). Seedling stage is the key stage of forage growth, and is sensitive to water response. Therefore, identifying varieties with strong drought resistance at seedling stage can be of significant value as a guide for production. Drought resistant forage types are key to the development of animal husbandry in Tibet (Cui et al., 2015).

    1 Introduction

    Nearly half of the land in Tibet is arid or semi-arid. Due to its special topographical, geomorphic and climatic conditions, the natural conditions are harsh, the ecosystem is fragile, and the carrying capacity is very limited (Sun et al., 2012; Zhang et al., 2015). Global climate change and the impact of human activities have further aggravated the situation in recent years, and grassland degradation has become one of the most serious ecological problems facing Tibet (Liu et al., 2012; Fu et al., 2018). In order to relieve the pressure of natural grassland and protect the ecological environment in Tibet, the vigorous promotion of human-made grassland has become a key measure (Gao et al., 2014; Duan et al., 2019). Pennisetum centrasiaticum Tzvel is a perennial forage of Pennisetum in Gramineae. P.centrasiaticum is widely distributed in arid and semi-arid areas of Tibet. Its rhizome system is developed and has strong resistance to adversity. It has genes to resist disease, insects, cold and drought that wheat crops lack. The biomass and nutritional quality of P.centrasiaticum are high at jointing stage (Li, 1983; Gao, 2008). PEG-6000 can simulate drought stress by regulating the osmotic pressure of solutions to limit water entering seeds, so the use of PEG-6000 offers a fast and reliable method to simulate a drought environment for the purpose of screening drought-resistant varieties (Hegarty, 1977; Van den et al, 2006). At present, there are few studies of P.centrasiaticum in Tibet. There is no data about the use of PEG-6000 to simulate a drought environment to screen out the P.centrasiaticum from different areas. The meteorological data from 1971 to 2014 showed that drought conditions in Tibet have worsened over the years, and this may cause devastating, long-term damage to the agriculture, economy and ecosystem of Tibet (Li et al., 2019). Seedling stage is the key stage of forage growth, and is sensitive to water response. Therefore, identifying varieties with strong drought resistance at seedling stage can be of significant value as a guide for production. Drought resistant forage types are key to the development of animal husbandry in Tibet (Cui et al., 2015).

    P.centrasiaticum from 12 sites in Tibet were selected as the experimental materials for this paper. Physiological indexes were measured at seedling stage, and the drought resistance of the P.centrasiaticum from the 12 sites was evaluated using the membership function method. The main objectives of this study were to identify P.centrasiaticum with strong drought resistance ability in the seedling stage, to provide raw materials and a material basis for the development of local grassland animal husbandry, to alleviate the contradiction between grass and livestock, and to protect the deteriorating natural grassland ecological environment in Tibet.

    2 Materials and methods

    2.1 Plant materials

    The study materials used in this study were P.centrasiaticum seeds taken from 12 sites in Tibet in 2017 (Table 1).

    Source of seedlingsGeographical coordinatesElevation (m)Compact form
    Linzhi93° 94′ N, 29° 79′ E3117LZS
    Linzhou91° 08′ N, 29° 88′ E3889LZX
    Xietongmen88° 21′ N, 29° 42′ E3891XTM
    Sog93° 79′ N, 31° 83′ E3940SX
    Longzi92° 32′ N, 28° 42′ E3948LZ
    Namling89° 08′ N, 29° 64′ E3949NML
    Purang81° 16′ N, 30° 34′ E4061PL
    Dingjie87° 77′ N, 28° 37′ E4163DJ
    Gyirong85° 32′ N, 28° 89′ E4198JL
    Sa’gya87° 90′ N, 29° 00′ E4233SJ
    Damxung91° 05′ N, 30° 51′ E4333DX
    Tingri87° 04′ N, 28° 47′ E4413DR

    Table 1.

    Locations where P.centrasiaticum seedlings were collected in 12 sites in Tibet

    2.2 Experiment design

    Seedling cultivation: According to the germination rate test, the P.centrasiaticum seeds from the 12 sites were sown in seedling trays on May 24, 2018. After sowing, the seedling tray was placed in a 25 °C incubator for cultivation, with 14 hours of level 5 light and 10 hours of darkness per day. An appropriate amount of water was sprayed every day into the seedling trays to ensure normal growth of the P.centrasiaticum seeds. When the seedlings had grown to a stage with three to four leaves, seedlings at the same growth level were selected for stress treatment. Seedlings with consistent growth were transferred to PEG-6000 solutions with different water potentials (0, -0.7, -1.4, -2.1 and -2.8 MPa) that has 4 replicates for each water potentials. The quantity was weighed and hydrated every day to maintain the water potential. Samples were taken after 5 days of drought stress. The seedling samples obtained were quick-frozen at -80 ℃ for assessment.

    2.3 Index measurement and methods

    The formula for calculation of PEG-6000 for different water potentials (Michel and Kaufmann, 1973) is as follows:

    ΨS = - (1.18 × 10-2) × C - (1.18 × 10-4) × C2+ (2.67 × 10-4) × C × T + (8.39 × 10-7) × C2 × T

    where ΨS represents the solution of water potential (MPa); C is the concentration of the PEG-6000 solution (g kg-1); T is the temperature (℃).

    The methods used for determination of physiological indexes: The content of malondialdehyde was determined by a kit method. The content of proline was determined by Ninhydrin colorimetry. The content of total chlorophyll, chlorophyll a, chlorophyll b and carotenoid were determined by Colorimetry (Li, 2000).

    The calculation formula for the membership function method: The parameters of proline and chlorophyll content that correlated positively with drought resistance were expressed in the following formula (Yan et al., 2018):

    u(Xijk) = (Xijk-Xmin)/(Xmax-Xmin)

    The parameters of malondialdehyde content that correlated negatively with drought resistance were expressed in the following formula:

    u(Xijk) = 1 - (Xijk-Xmin)/(Xmax-Xmin)

    where u(Xijk) is the membership degree of k index in j water potential stage of i grass species, Xmin and Xmax represent the minimum and maximum values of the k comprehensive index; the average value of each index membership degree was used as the comprehensive evaluation standard of the drought resistance ability of germplasm.

    2.4 Statistical analysis

    Data were collected in Excel 2016, variance analysis was conducted using SPSS 19 software, the LSD method was used to carry out multiple comparisons of P.centrasiaticum in different areas under the same osmotic pressure were carried out by, and plots were completed with SigmaPlot 12.5. The membership function method was used to evaluate the drought resistance of P.centrasiaticum from the 12 sites.

    3 Results

    3.1 Differences of MDA among the sites

    For the control, the MDA content of seedlings from Linzhi was the highest, and the MDA content of seedlings from Tingri was the lowest (Fig. 1). MDA content decreased gradually as elevation increased. When the water potential was ‒0.7 MPa, the MDA content of seedlings from Namling and Longzi was low, and the MDA content of seedlings from Linzhi was the highest, which indicated that drought resistance of seedlings from Namling and Longzi was high, and that of seedlings from Linzhi was low. When the water potential was ‒1.4 MPa, the MDA of seedlings from Gyirong was the lowest, significantly lower than that of seedlings from other sites (P 【-逻*辑*与-】lt; 0.05); While, the MDA contents of seedlings from Xietongmen, Sog, Linzhou and Linzhi were higher, significantly higher than that of seedlings from other sites. When the water potential was -2.1 MPa, the MDA of seedlings from Gyirong, Damxung and Tingri were lower than that of other sites, and that of seedlings from Purang and Xietongmen were higher than that of other sites. When the water potential was -2.8 MPa, the MDA contents of seedlings from Linzhi and Xietongmen were higher, while the MDA contents of seedlings from Longzi, Dingjie and Tingri were lower. With the decrease of osmotic type, the MDA of P.centrasiaticum in the same site showed a tendency of increasing first, then decreasing and then increasing. As a whole, with the increase in drought stress, the MDA content generally increased.

    Figure 1.

    3.2 Differences of Pro in seedlings from different sites

    For the control, the Pro content of seedlings from Linzhi, Linzhou and Xietongmen was higher, significantly higher than that in other areas (P 【-逻*辑*与-】lt; 0.05) (Fig. 2), while the Pro content of seedlings from Damxung was the lowest. When the water potential was -0.7 MPa, the Pro content of seedlings from Xietongmen was the highest, and compared with the control, the Pro content of seedlings from Tingri increased the fastest. When the water potential was -1.4 MPa, the Pro content of seedlings from Linzhou and Xietongmen was significantly higher than that of seedlings from other areas (P 【-逻*辑*与-】lt; 0.05). The Pro content of seedlings from Namling, Gyirong and Sa’gya was relatively low. Compared with the control, the Pro content of seedlings from Damxung increased the fastest. When the water potential was -2.1 MPa, the Pro content of seedlings from Xietongmen was the highest; it was significantly higher than of seedlings from other areas (P 【-逻*辑*与-】lt; 0.05). Compared with the control, the Pro of content seedlings from Damxung increased the fastest, and the Pro content of seedlings from Purang and Tingri increased faster than others. When the water potential was -2.8 MPa, the Pro content of seedlings from Linzhou, Xietongmen, Namling, Dingjie, Gyirong and Tingri and Sa’gya continued to increase, among which the Pro content of seedlings from Longzi, Sa’gya and Tingri increased rapidly, while the content of seedlings from Linzhou and Xietongmen was the highest. Overall, as drought stress increased, the Pro content of seedlings generally increased first and then decreased.

    Figure 2.

    3.3 Differences of chlorophyll in seedlings from different sites

    In the control, the chlorophyll content in P.centrasiaticum seedlings from Linzhou and Sog was the highest (Fig. 3), while the content in seedlings from Dingjie, Gyirong and Sa’gya was lower. When the water potential was -0.7 MPa, the chlorophyll content of seedlings from Sog was the highest, and it was significantly higher than that in other sites (P 【-逻*辑*与-】lt; 0.05). When the water potential was -1.4 MPa, the chlorophyll content of seedlings from Xietongmen was the highest, and it was significantly higher than that in other sites (P 【-逻*辑*与-】lt; 0.05). In addition, the chlorophyll content of seedlings from Sog was significantly higher than that in all sites except Xietongmen (P 【-逻*辑*与-】lt; 0.05). When the water potential was -2.1 MPa, the chlorophyll content of P.centrasiaticum seedlings from Purang was the highest, the content of seedlings from Linzhi and Damxung was also higher, and the content of seedlings from Namling was the lowest. When the water potential was -2.8 MPa, the chlorophyll content of P.centrasiaticum seedlings from Sog and Xietongmen was higher, while that of Linzhi was the lowest. As a whole, with the increase in drought stress, the chlorophyll content of seedlings generally increased firstly and then decreased.

    Figure 3.

    3.4 Comprehensive evaluation

    The results of the above indexes can only indicate the total physiological response of a single index under drought stress, and it is difficult to judge the drought resistance capacity of specific regions. Using the membership function analysis method, the membership function values of the 12 P.centrasiaticum materials were calculated by using the mean values of the three drought resistance indexes measured in this experiment under different water potentials (Table 2). Membership function values were used to calculate the averages, which ranked from high to low were: Xietongmen 【-逻*辑*与-】gt; Linzhou 【-逻*辑*与-】gt; Sog 【-逻*辑*与-】gt; Damxung 【-逻*辑*与-】gt; Tingri 【-逻*辑*与-】gt; Namling 【-逻*辑*与-】gt; Gyirong 【-逻*辑*与-】gt; Linzhi 【-逻*辑*与-】gt; Purang 【-逻*辑*与-】gt; Dingjie 【-逻*辑*与-】gt; Longzi 【-逻*辑*与-】gt; Sa’gya.

    SitesMDAProChlorophyllAverage membership function valueRanking
    Linzhi0.3410.7460.2320.4408
    Linzhou0.4600.7680.5150.5812
    Sog0.5050.3790.6620.5153
    Xietongmen0.3180.8340.6370.5961
    Longzi0.7140.3260.1650.40211
    Namling0.7370.3980.2070.4486
    Purang0.5150.4380.3660.4409
    Dingjie0.6470.3900.2630.43310
    Gyirong0.7290.2290.3720.4437
    Sa’gya0.6510.2960.1780.37512
    Damxung0.6800.4070.3020.4634
    Tingri0.7400.3400.2890.4565

    Table 2.

    Membership function values of drought resistance indexes and comprehensive drought resistance ranking of P.centrasiaticum from 12 sites

    4 Discussion

    4.1 Relationship between membrane lipid peroxidation and drought resistance

    Plant cell membranes play an important role in maintaining the stability of cells. Drought stress subjects plants to peroxidation and change in the content of MDA in the plants (Zhang et al., 1994; Jiang et al., 2001). With the decrease of water potential, the balance between the production and elimination of reactive oxygen species in P.centrasiaticum was destroyed, and this resulted in oxidative damage, membrane lipid peroxidation, and malondialdehyde production. Finally the growth and development of P.centrasiaticum were affected (Liu et al., 2009; Pan et al., 2014). The increase of plasma membrane permeability was positively correlated with the accumulation of MDA, while the accumulation of MDA was negatively correlated with growth (Wong et al., 1997). Many studies of the photosynthetic parameters and physiological indexes of plants have shown that the content of MDA can be used to effectively evaluate the drought resistance of plants (Wu et al., 2014; Wang et al., 2015). The higher the content, the more drought resistance a plant has, and the slower the increase, the stronger the drought resistance. In drought stress situations, the relative content of MDA in the leaves of herbaceous plants increases gradually as a result of the aggravation caused by drought stress (Ding et al., 2013; Zhang et al., 2018). The increase of MDA content in drought resistant plant is smaller (Zhou et al., 2009). As the time of drought stress lengthens and the degree of aggravation from drought stress increases, the content of MDA in Brassica napus seedlings increased (Xie et al., 2013). In this study, with the decrease of water potential, the balance between the production and elimination of reactive oxygen species in P.centrasiaticum was destroyed, which resulted in oxidative damage, membrane lipid peroxidation, malondialdehyde production. Finally the growth and development of P.centrasiaticum were affected. With the decrease of water potential, the MDA in seedlings from the 12 sites showed an overall upward trend, and this was consistent with the results of previous studies (Liu et al., 2009; Pan et al., 2014). Therefore, the content of MDA can be used as a physiological index to evaluate the drought resistance of P.centrasiaticum germplasm. The MDA content of P.centrasiaticum in Linzhi was higher under 5 osmotic patterns, which indicated that the drought resistance ability of these seedlings was weaker than those from other areas.

    4.2 Relationship between osmoregulation substances and drought resistance

    Osmoregulation is an important physiological mechanism for plants to adapt to drought stress, and as a result, has become the most active research field in drought resistance physiology (Lutts et al., 1999; Singh et al., 1972). Many studies have shown that Pro is accumulated in plants under conditions of water loss, and that plants absorb water from the outside to resist drought stress, using substances such as Pro to make osmotic adjustments. The higher the content of Pro, the stronger a plant’s drought resistance ability (Munns et al., 1979; Abrams et al., 1990; Medrano et al., 2002; Ni et al., 2004). The relative content of soluble sugar and proline increased with the increase of drought stress and the extension of stress time, and the increased content was positively correlated with drought resistance (Xie et al., 2013). It was found that the relative value of Pro content could be used as a physiological index to evaluate the drought resistance ability of potatoes in the early stage of growth (Ding et al., 2013). Furthermore, osmoregulation substances are related to stomatal opening and closing. In order to avoid too much transpiration, plants need to close stomata to reduce transpiration, but plants also need to absorb carbon dioxide for photosynthesis, so stomatal opening and closing plays a key role in the balance between photosynthesis and transpiration, while osmoregulation matter can make plants maintain a moderate transpiration rate (Wright, 1969). In this study, Pro content first decreased and then increased with the decrease of water potential. This may have been because mild drought did not cause a rapid reaction of proline. Therefore, the content of Pro can be used as a physiological index to evaluate drought resistance of P.centrasiaticum germplasm.

    4.3 Relationship between photosynthetic physiology and drought resistance

    When a plant is under drought stress, the stomata on the leaves close, and the amount of carbon dioxide absorbed by the plant is reduced, resulting in a slowdown of photosynthesis. The decrease of chlorophyll content in plants with strong drought resistance was small, while the decrease in plants with weak drought resistance was large (Mou et al., 2016). The chlorophyll content of grass with strong drought resistance was higher than that of the grass with weak drought resistance. On the one hand, this is a result of the sharp decrease of water content caused by the weakening of chlorophyll biosynthesis; on the other hand, it is a result of the accumulation of active oxygen in plants caused by drought. The accumulation of oxygen free radicals directly or indirectly activate membrane lipid peroxidation, resulting in membrane permeability damage and accelerating chlorophyll decomposition. Under drought stress conditions, the contents of chlorophyll a, chlorophyll b and total chlorophyll, and the chlorophyll a/b ratio decreased compared with the control. This result was consistent with previous results (Zhang et al., 2003; Liao et al., 2018).

    5 Conclusions

    In summary, the balance between production and elimination of reactive oxygen species in P.centrasiaticum was destroyed, leading to membrane lipid peroxidation, the production of MDA, and the accelerated decomposition of chlorophyll. P.centrasiaticum absorbed water from the outside by secreting proline and other osmotic regulating substances to resist drought. The drought resistance of P.centrasiaticum was strong in Xietongmen, Linzhou and Sog.

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    Guangyu ZHANG, Jiangwei WANG, Haorui ZHANG, Gang FU, Zhenxi SHEN. Comparative Study of the Impact of Drought Stress on P.centrasiaticum at the Seedling Stage in Tibet[J]. Journal of Resources and Ecology, 2020, 11(3): 322
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