| Soil salinization in arid and semi-arid areas is one of the most important environmental problems restricting the sustainable development of global agriculture.The saline and alkaline land in ningxia Yellow River Irrigation area accounts for about 1/3 of the cultivated area,Soil salinization is also the main obstacle to agricultural development in ningxia Yellow River irrigation area.Therefore,to accelerate the improvement of saline-alkali land is a basic and long-term task to enhance the sustainable development of agriculture and improve the comprehensive production capacity of agriculture.lt is reported that planting salt-tolerant herbage is the most ecologically and economically beneficial measure in salt-alkali land improvement.Echinochloa frumentacea is an annual grass called barnygrass and belongs to salt-tolerant herbage,which can be planted and harvested on severely saline alkali wasteland.However,due to the unclear mechanism of salt-alkali tolerance,the unclear adaptive planting range,and lack of sufficient scientific evidence on the effect of salt-alkali land improvement,this has not only caused great difficulties to the production practice,but even restricted the application and development of Echinochloa Frumentacea in salt-alkali land improvement.Root system is the first part of halophyte to experience soil salt-alkali stress,and also the growth and development regulatory center with the strongest regulation ability.Therefore,this study systematically revealed the response mechanism of Echinochloa frumentacea root system to saline-alkali stress from the aspects of root morphological structure characteristics and physiological and biochemical characteristics through laboratory and field experiments,the effect of improving saline-alkali land by Echinochloa frumentacea was comprehensively evaluated.On this basis,the suitable planting range,planting mode and fertilizer requirement characteristics of Echinochloa frumentacea seed in saline-alkali land were determined.It’s not only provides reference basis for the cultivation and extension of Echinochloa frumentacea and the improvement and utilization of saline alkali land resources,but also has great significance for improving the ecological environment,ensure the red line of cultivated land and driving the development of planting and animal husbandry.The specific conclusions are as follows:1.It is one of the important strategies of salt tolerance to maintain high capacity of sodium limit in root system of Echinochloa frumentacea seed.In other words,under saline-alkali stress,the root system of Echinochloa frumentacea seed kept a high K+/Na+ ratio by intercepting Na+.However,its sodium limiting ability was limited to a certain extent.When NaCl and Na2SO4 stress concentrations ≤120mmol·L-1,its sodium limiting ability increased with the increase of stress concentration.Moreover,salt stress in this range promoted the longitudinal elongation of roots,inhibited the lateral growth of roots,and increased the root volume,total absorption area and active absorption area.However,when the stress concentration≥ 180mmol·L-1,its sodium limiting ability decreased with the increase of stress concentration,and the morphological indexes of root were also inhibited.Under Na2CO3 and NaHCO3 stress,its sodium limiting ability decreased with the increase of stress concentration,and all indexes of root morphology also showed a gradually decreasing trend.When Na2CO3 stress concentration ≥45mmol·L-1,NaHCO3stress concentration≥60mmol·L-1,roots lost vitality,and then lost the sodium limiting ability.2.The root proline,soluble sugar,SOD,POD and CAT of Echinochloa frumentacea seed play a role in the physiological mechanism of salt-alkali tolerance under low concentration salt-alkali stress,but under high concentration salt-alkali stress,proline is the main factor to cope with high concentration salt stress.When NaCl,Na2SO4 stress concentration≥240mmol·L-1,Na2CO3 stress concentration≥60mmol·L-1,NaHCO3 stress concentration≥45mmol·L-1,SOD,POD and CAT contents in root system began to decrease.However,the content of proline increased sharply at different concentrations.At the same time,under the mixed salt treatment,the proline content of roots of Echinochloa frumentacea seed increased sharply with the increase of stress intensity,which was 30%～162%higher than that of the control.3.The root system of Echinochloa frumentacea seed has unique morphological and structural characteristics that can adapt to salt-alkali stress,and its penetration and expansion ability is very strong,which makes the root system have higher ability to absorb salt and promote the downward leaching of salt.Its root system can penetrate into the soil about 40cm,and its absorption of Na+and SO42increased with the increase of total root length,active absorption area and root activity.The amount of Soil leaching Na+,Cl-and SO42-increased with the increase of total root length,average root diameter and root volume.The total absorption of ions,leaching of salt ions and K+/Na+ratio in roots of Echinochloa frumentacea seeds planted in saline soil were significantly higher than those in alkaline soil.The absorption and leaching amount of salt ions and K+/Na+ratio of The seeds of Echinochloa frumentacea were affected by their own root characteristics and the type of saline land.In addition,the strong accumulation characteristics of Na+and SO42-in roots of Echinochloa frumentacea seed can be used to improve the sulfate soil,and the strong leaching capacity of Cl-can be used to dechlorinate the chlorinated saline-alkali land to reduce the toxic effect of Cl-on plants.4.The formation of aerenchyma of Echinochloa frumentacea root system is the characteristic expression of saline-alkali tolerance and hypoxia avoidance,and is the internal factor of its good growth in low-lying or flooded conditions.The aerenchyma formation of roots of Echinochloa frumentacea was affected not only by salt concentration but also by soil pH.When the stress concentration was ≥180mmol·L-1,the dissolution of root parenchyma was blocked and the formation of aerated tissue was severely inhibited by pH,which was an adaptive mechanism of roots of Echinochloa frumentacea to saline-alkali conditions.5.Echinochloa frumentacea fruit has strong saline-alkali tolerance and is widely cultivated in saline-alkali land.According to unary linear regression analysis,the salt tolerance value of Echinochloa frumentacea seed was 46.64～110.57mmol·L-1,the salt tolerance threshold value was 129.04～219.57mmol·L-1,and the acid and alkali tolerance(pH)value was 8.18～8.45.The threshold value of acid and alkali resistance(pH)is between 8.77 and 9.20.Therefore,planting Echinochloa frumentacea seeds in the saline-alkali land of 8.18≤pH≤8.45 can not only improve the saline-alkali land,but also obtain high yield,and realize the perfect combination of production value and ecological value.The grain yield and grass yield of Echinochloa frumentacea seed planted in the saline-alkali land of 8.45≤pH≤9.20 would decrease,but it could be used as a halophyte to improve the saline-alkali land.6.The dominant bacterial community of salt-alkali tolerant in the rhizosphere of Echinochloa frumentacea is one of the important factors of improving saline alkali land.At phyla level,firmicutes were the dominant bacteria in the rhizosphere soil.The spores produced by firmicutes could resist dehydration and extreme environment.The secondary dominant flora was actinomycetes and acidobacteria ranked third.At the genus level,the absolute dominant bacterial community in the rhizosphere soil was Bacillus,which was more alkaline tolerant.The e secondary dominant flora was halophilic actinomycetes streptomonas and acidobacteria ranked third.The relative abundance of Bacillus and Halophilic actinomycetes was 22.60%and 7.10%higher than that of bare land,respectively.There was a significant positive correlation between Bacillus and soil pH and soil alkalinity.Halophilic actinomycete streptomonas was significantly positively correlated with soil total salt content and negatively correlated with soil pH.Acidobacteria were negatively correlated with soil pH and positively correlated with soil total salt content.7.In the first year of planting Echinochloa frumentacea in saline and alkaline land in Yinbei region of Ningxia,there was no significant difference between the improved effect of planting Echinochloa frumentacea and alfalfa barngrass,licorice,oat and salthorn,but after planting two years,the improved effect of planting Echinochloa frumentacea in saline and alkaline land was obviously better than alfalfa,barngrass,licorice,oat and salthorn.According to the evaluation results of the improvement effect of Echinochloa frumentacea seed on salinic-alkali land based on the membership function combined with factor analysis method,the reduction of salt content in 0-20cm soil layer of Echinochloa frumentaceai seed planted continuously for 2 years was 1.71%higher than that of alfalfa,the soil bulk density was 3.80%lower than that before planting,and the content of available phosphorus was 4.81%higher than that before planting.Organic matter,total nitrogen and alkali-hydrolyzable nitrogen in 0-20cm soil layer decreased in the first year,but increased in the second year,increasing by 8.97%,19.05%and 1.12%,respectively,compared with before planting.8.According to the results of field research,the saline-alkali land area of northern ningxia silver can be continuous cropping 2 years in Echinochloa frumentaceai of saline-alkali land gradually realize desalting,and low-toxin chemical planting alfalfa to improvement of saline-alkali land,also can be used in Echinochloa frumentaceai and other leguminous forage grass or crops field rotation,make saline-alkali land can be improved at the same time to effectively utilize the soil.In addition,if Echinochloa frumentaceai seeds are continuously cultivated in saline-alkali land for two years,sufficient base fertilizer(phosphate fertilizer and potassium fertilizer)should be applied in the first year,and sufficient potassium fertilizer should be applied in the jointing stage.Adequate basal fertilizer(phosphate fertilizer and potassium fertilizer)should be applied in the second year,and sufficient k should be applied at jointing,if for herbage harvesting no n should be applied,but if for grain harvesting sufficient n should be applied at booting.in summary,this study has defined the adaptive planting range of Echinochloa frumentaceai in saline alkali soil,preliminarily revealed the morphological characteristics,physiological characteristics and ion absorption characteristics of Echinochloa frumentacea root under saline alkali stress,and deeply analyzed the correlation between Echinochloa frumentacea root characteristics and salt spraying effect and salt absorption effect under saline soil and alkaline soil conditions,The changes of rhizosphere microbial community structure and the correlation between rhizosphere microbial community and environmental factors(pH,total salt and alkaline soil degree)were analyzed,and the improvement effect of Echinochloa frumentacea on saline alkali land in Yinbei area was comprehensively evaluated.The conclusion shows that the adaptive planting range of Echinochloa frumentacea root is relatively wide,and it is an ideal plant for biological improvement and utilization of saline alkali land. |
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