| The grasses of the genus Barnyardgrass have strong resistance to salinity and alkalinity,and are an important pioneer species in the improvement and utilization of saline-alkali land.The salt tolerance at the germination stage and seedling stage of plant seeds is the key period for breeding salt-tolerant varieties,understanding the salt-tolerance mechanism of Barnyardgrass at seed germination and seedling stages,establishing a salt-and-alkali tolerance index system,and comprehensively evaluating its saltalkali tolerance can provide a theoretical basis for the selection and breeding of salt-and-alkali tolerant pasture varieties in different types of saline-alkali land.Echinochloa frumentacea(Roxb.)Link,Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.and Echinochloa crusgalli(L.)Beauv.’Chaomu 1’ were used as experimental materials in this paper.The materials were tested in an artificial climate chamber using a salinity stress test with three salinity treatments:treatment A(neutral salt)NaCl:Na2SO4=1:1,treatment B(salt mix)NaCl:Na2SO4:NaHCO3=1:2:1 and treatment C(salt mix)NaCl:Na2SO4:NaHCO3:Na2CO3=1:1:1:1,at the seed germination stage,each treatment was set to CK、30 mmol·L-1,60 mmol·L-1,90 mmol·L-1,120 mmol·L-1,150 mmol·L-1,200 mmol·L-1,250 mmol·L-1,350 mmol·L-1,a total of 9 gradients,each treatment at the seedling stage was set at CK、30 mmol·L-1,90 mmol·L-1,150 mmol·L-1,250 mmol·L-1,350 mmol·L-1 for a total of 6 gradients.The germination characteristics of Echinochloa frumentacea(Roxb.)Link,Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’ and Echinochloa crusgalli(L.)Beauv ’Chaomu 1 ’ were measured and analyzed during the seed germination stage.The biological parameters,photosynthetic gas exchange parameters,chlorophyll fluorescence parameters,antioxidant protective enzymes,osmoregulatory substances,cell membrane permeability and malondialdehyde content of the three barnyard grasses were measured and analyzed at the seedling stage.The methods of principal component analysis and membership function were used to analyze the measurement indicators,in order to establish the salinity and alkali tolerance evaluation system of the three types of barnyardgrass under different types of salinity and alkali stress,and then to evaluate the salinity and alkali tolerance of the three barnyard grasses.By establishing the regression function of salt concentration,relative germination rate and relative plant height,the salttolerance thresholds at germination and seedling stages were calculated.The results showed that.1、During the seed germination period,different saline stresses had significant effects on the biological characteristics of Echinochloa frumentacea(Roxb.)Link,Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.and Echinochloa crusgalli(L.)Beauv.’Chaomu 1’ seeds(P<0.05).With the increase of alkaline salt proportion in saline stress treatment,the average germination time of three barnyard grasses showed a tendency to be prolonged,and all other indicators showed a decreasing trend.2、At the seedling stage,the SPAD values of Echinochloa frumentacea(Roxb.)Link and Echinochloa crusgalli(L.)Beauv.’Chaomu 1’ were not significantly different under the three salinity treatments,except for the highly significant differences in all growth and physiological indicators of the three barnyard grasses under the different salinity treatments(P<0.01).The plant height,stem thickness,above-ground biomass,below-ground biomass,net photosynthetic rate,stomatal conductance and potential PSII activity of the three barnyard grasses all tended to decrease with increasing proportions of alkaline salts in the salinity stress treatments.Intercellular CO2 concentration was higher under treatment A(neutral salt)than other treatments,initial fluorescence and soluble protein content were highest under treatment B(saline complex salt),while malondialdehyde content,cell membrane permeability,three antioxidant protective enzyme activities and proline content were highest under treatment C(saline complex salt).Under the same saline-alkali stress treatment with different gradients,the net photosynthetic rate(Pn),transpiration rate(Tr)and stomatal conductance(Gs)of Echinochloa frumentacea(Roxb.)Link,Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.and Echinochloa crusgalli(L.)Beauv.’Chaomu 1’ all decreased.The intercellular carbon dioxide(Ci)showed a downward trend in A treatment,and first decreased and then increased in B treatment and C treatment.Stomatal factor limitation was the main factor responsible for the decrease in leaf Pn in all gradients of treatment A and under low saline stress(≤ 90 mmol·L-1)in treatments B and C.Non-stomatal factor limitation became the main factor for the decrease in leaf Pn under high stresses in treatments B and C.In the neutral salt treatment,the proline content of Echinochloa frumentacea(Roxb.)Link,Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.and Echinochloa crusgalli(L.)Beauv.’Chaomu 1’ all increased gradually with the concentration;reduce.Under the low concentration of neutral salt stress,the CAT activity of Echinochloa frumentacea(Roxb.)Link had a small increase;under the high concentration stress of C,the SOD activities of Echinochloa frumentacea(Roxb.)Link and Echinochloa crusgalli(L.)Beauv.’Chaomu 1’.Obviously,the POD activities of the three have a smaller variation range.3、During the seed germination period,the germination rate of Echinochloa frumentacea(Roxb.)Link,Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.and Echinochloa crusgalli(L.)Beauv.’Chaomu 1’,showed highly significant positive correlations(P<0.01)with germination potential and germination index under different types of saline stresses;germ length was highly significant with radicle length,germination rate,germination potential,germination index and vigour index(P<0.01).At the seedling stage,the plant height of Echinochloa frumentacea(Roxb.)Link,Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.and Echinochloa crusgalli(L.)Beauv.’Chaomu 1’ showed highly significant positive correlations(P<0.01)with stem thickness,biomass accumulation,SPAD value,net photosynthetic rate,stomatal conductance and transpiration rate under different types of saline stress,Plant height and proline content showed significant negative correlations with malondialdehyde content and cell membrane permeability under different types of saline stress.(P<0.01)Photosynthetic gas exchange parameter stomatal conductance was significantly positively correlated with initial fluorescence,maximum fluorescence,maximum photochemical quantum yield of PSII and potential activity of PSII(P<0.05),and highly significantly negatively correlated with intercellular CO2(P<0.01).4、According to the principal component analysis,it was found that the germination potential,germination rate,radicle length and germination index of seeds could be used as the identification indicators for the identification of the salinity and alkali tolerance of the three species of barnyard grass during the germination period;seedling height,stem thickness,above-ground and below-ground biomass,net photosynthetic rate,intercellular carbon dioxide,transpiration rate,maximum fluorescence,malondialdehyde content,superoxide dismutase activity,catalase activity,proline content and soluble protein content can be used as identification indicators to identify the salinity tolerance of the three plants at the seedling stage.According to the calculation result of membership function,in the seed germination stage,the order of the three kinds of barnyard grass under treatment A is as follows:Echinochloa frumentacea(Roxb.)Link>Echinochloa crusgalli(L.)Beauv.’Chaomu 1’>Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’;under treatment B:Echinochloa crusgalli(L.)Beauv.’Chaomu 1’>Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.>Echinochloa frumentacea(Roxb.)Link;under treatment C:Echinochloa crusgalli(L.)Beauv.’ Chaomu 1 ’>.Echinochloa frumentacea(Roxb.)Link>Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.At the seedling stage,the order of the three barnyard grasses is:Under A treatment:Echinochloa frumentacea(Roxb.)Link>Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.>Echinochloa crusgalli(L.)Beauv.’Chaomu 1’;under treatment B:Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.>Echinochloa crusgalli(L.)Beauv.’Chaomu 1’>Echinochloa frumentacea(Roxb.)Link.under treatment C:Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.>Echinochloa crusgalli(L.)Beauv.’Chaomu 1’>Echinochloa frumentacea(Roxb.)Link.During seed germination,in treatment A:the salt tolerance LC50 of Echinochloa frumentacea(Roxb.)Link,Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.and Echinochloo crusgalli(L.)Beauv.’Chaomu 1’ during germination were 266.01 mmol·L-1,242.73 mmol·L-1 and 289.53 mmol·L-1;In treatment B:the salt-tolerant LC50 of the three was 238.31 mmol·L-1,174.66 mmol·L-1 and 258.85 mmol·L-1;In treatment C:the salt-tolerant LC50 of the three was 158.53 mmol·L-1 136.99 mmol·L-1 and 179.70 mmol·L-1;At seedling stage,in treatment A:the salt-tolerance LC50 of Echinochloa frumentacea(Roxb.)Link,Echinochloa crusgalli(L.)Beauv.var.mitis(Pursh)Peterm ’Ningxia’.and Echinochloa crusgalli(L.)Beauv.’Chaomu 1’ were 495.33 mmol·L-1,387.09 mmol·L-1 and 503.56 mmol·L-1,respectively;In treatment B:the salt-tolerant LC50 of the three was 408.70 mmol·L-1,355.55 mmol·L-1 and 467.00 mmol·L-1;In treatment C:the salt-tolerant LC50 of the three was 345.36 mmol·L-1,329.91 mmol·L-1 and 393.60 mmol·L-1.To sum up,this study revealed the salinity and alkali tolerance mechanism of three types of barnyardgrass,screened out the salinity and alkali tolerance index system,and based on this,comprehensively evaluated and ranked the salinity and alkali tolerance of different barnyardgrass.The results of this study provide a theoretical basis for guiding the identification and cultivation of salinealkali-tolerant forage resources,development and utilization of saline-alkali land and ecological restoration in salinized areas. |
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