| The full operation of the Three Gorges Reservoir(TGR)on the Yangtze River,China,has formed a hydro-fluctuation belt with an annual water level change of 30 m spanning an area of 350 km~2.Such a change in water level has led to a direct decline of plant community within the hydro-fluctuation belt.Revegetation is an environmentally friendly measure in restoring ecological integrity of the hydro-fluctuation zone of the TGR,and is also crucial for maintaining sound riparian ecosystem functions and services.The study site(107°32?–108°14?E,30°03?–30°35?N)is located in the Ruxi River basin in Gonghe Village of Shibao Township,Zhong County,Chongqing municipality of China.To explore the indicative changes of soil fertility and quality upon revegetation in the hydro-fluctuation belt of the TGR of China,plots of different vegetation types at elevations between 145 m to 175 m above sea level in Zhong county of the TGR were sampled in June 2016(T1),September 2016(T2),June 2017(T3),and September 2017(T4),to study the contents of soil microbial biomass carbon(SMBC),soil microbial biomass nitrogen(SMBN)and soil microbial biomass phosphorus(SMBP).Results showed that:(1)The order of water content at the same altitude is grassland>forest>unplanted soil in the hydro-fluctuation belt of the TGR.There was no significant difference in soil water content of tree vegetation in four periods.Compared with the soil pH value of unplanted soil(6.89-7.56),the restoration of artificial arbor vegetation(6.22-6.84)caused soil pH to change from weak alkalinity to weak acidity,but the pH of all vegetation types increased slightly after water flooding,and the soil pH of low altitude is higher.During the period from June to September,the total soil nutrient content increased during the restoration of artificial vegetation,but the available soil nutrient content shows a decreasing trend.The soil physiochemical properties of each vegetation type were inconsistent after flooding,and in 2017,the soil nutrient content gradually increased as compared to 2016.Planting Cynodon dactylon at the altitude of145~155 m can improve soil nutrient content,and some of the indicators showed a significant difference.The vegetation restoration of Cynodon dactylon at elevations of155~165 m and Hemarthria altissima at 165~175 m can significantly increase the soil nutrient content and improve soil physiochemical properties.(2)The restoration of artificial vegetation can significantly improve soil microbial biomass in the hydro-fluctuation belt of the TGR,which is of great significance to the recovery of soil microbial resources.Under different vegetation types,the soil microbial biomass of Cynodon dactylon at all altitudes were relatively high,while the soil microbial biomass of Taxodium distichum at 165-175 m was relatively high.Soil microbial biomass has a higher turnover rate than the total nutrient in the soil,and it will have a significant difference when the vegetation recovery growth time is shorter.On the time scale,soil microbial biomass of all vegetation types showed a downward trend after T2-T3 flooding.During the growth period of T1-T2 and T3-T4,soil microbial biomass significantly increased.The overall performance of soil microbial biomass increased slightly in 2017 compared to the same period in 2016.(3)The soil microbial biomass carbon-nitrogen ratio of Taxodium distichum(7:1-9:1)fluctuated slightly in four periods,and the fungal(10:1)content was relatively abundant,with stable and strong carbon sequestration capacity.The ratio of SMBC/SOC and SMBN/TN in the same vegetation types showed a significant increase along with elevation.In terms of time,SMBC/SOC and SMBN/TN of each vegetation type decreased slightly after T2-T3 flooding,and increased slightly during T1-T2 and T3-T4 growth peorids.The overall performance was slightly increased.Artificial vegetation restoration can significantly increase the contribution of soil microbes to soil carbon,nitrogen and phosphorus pools,among which the highest contribution of Cynodon dactylon was at altitudes of 145 to 155 m and 155 to 165 m.As for 165 to 175m,the highest contribution of soil carbon and nitrogen pools was recorded by the Taxodium distichum,and the contribution of herbaceous vegetation to the soil phosphorus pool was the highest.In conclusion,vegetation restoration can make the soil more stable,can improve soil microbial biomass and play an important role in the soil carbon,nitrogen and phosphorus pool.It is suggested that ecological construction of vegetation restoration should be strengthened in the areas with serious soil erosion in the TGR,to improve the stability of the ecological system in the reservoir bank.At the same time,we should pay attention to the differences between elevations and vegetation types,and planting patterns should be comprehensively selected so as to achieve the best soil quality restoration effect.From the perspective of soil physiochemical properties and soil microbial biomass,Cynodon dactylon should be vegetated at altitudes of 145 to 155 m and 155 to 165 m,and Taxodium distichum and mixed herbaceous vegetation of Cynodon dactylon and Hemarthria altissima at 165~175 m can effectively improve soil quality. |
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