| The soil microbial community is not only an essential component of the ecosystem,but also an active participant of material cycle and energy flow in the ecosystem,which has an irreplaceable role in maintaining the stability and sustainability of ecosystems.However,the soil microbial community is one of the most sensitive organisms in the environment,and its structure and activity are controlled by various factors of biology and abiological environment and their interactions.Therefore,the soil microbial community structure and enzyme activity changes with the environmental factors Which is of great significance to understand the soil ecosystem processes dominated by environmental factors.The altitude gradients can cause significant changes in the biological and abiological factors such as climate,vegetation composition and soil properties in a short distance,and thus have a combined effect on the structure and activity of soil microbial community.As the most important water resources protection area in the upper reaches of the Yangtze River,the Minjiang River Basin played an important role for regulation of regional climate,conservation of biodiversity,conservation of water and indication of climate change.At the same time,the elevation gradient of the area is large and the vertical climatic belts are obvious.From the high altitude to the low altitude,the alpine desert,subalpine/alpine meadow,alpine forest,subalpine forest,ecotone of arid valley and mountain forest,arid valley shrub and evergreen broad-leaved forest.That provides a natural laboratory for studying the response of soil microbial community structure with climate change in smaller areas.In this study,seven typical vegetation of 442 m?3994 m in the Minjiang River Basin were used to study the soil microbial community structure,biomass and enzyme activity with altitude gradients and critical periods,and to provide a scientific basis for further revealing the process of soil ecosystems dominated by altitude gradients.The research shows:The content of PLFAs in soil microbial groups significantly increased with altitude gradients.The content of soil microbial total PLFAs and bacterial PLFAs in the soil organic layer show in the order Subalpine forest(E5)>Alpine meadow(E7)>Mid-subtropical forest(E1)>Alpine forest(E6)>Arid valley-forest ecotone(E4)>North subtropical forest(E2)>Arid valley(E3),show E7>E1>E6>E2>E4>E5>E3 in the soil mineral layer;soil fungi show E5>E4>E7>E3>E6>E1>E2 in soil organic layer.as E4>E7>E3>E6>E5>E2>E1 in the soil mineral layer.Gram-positive bacteria show the order E7>E5>E1>E6>E2>E4>E3 in the soil organic layer.as E7>E1>E6>E2>E4>E5>E3 in the soil mineral layer;soil Gram-negative bacteria manifested as E7>E5>E1>E6>E4>E2>E3,as E7>E6>E1>E2>E5>E3>E4 in the soil mineral layer.The change trend of ratio of soil microbial fungus to bacteria and ratio of Gram-positive bacteria to Gram-negative bacteria with altitude gradients is not uniform in the ever periods.The trend of soil microbial fungi/bacteria and gram-positive bacteria/negative bacteria in soil microbial community structure is not uniform at all times.Soil microbial fungi/bacteria in the soil organic layer as E3>E5>E4>E7>E6>E2>E1,as E4>E3>E5>E7>E6>E2 in the soil mineral layer;Gram-positive bacteria/negative bacteria in the soil organic layer show the order E3>E2>E6>E4>E5>E1>E7,as E5>E6>E3>E4>E2>E1>E7 in the soil mineral layer.There was a significant positive correlation between soil microbial total PLFAs content,soil bacteria and altitude gradients,soil moisture,soil organic carbon and soil total nitrogen,and negatively correlated with soil total phosphorus.Soil bacteria were also significantly correlated with soil freeze-thaw cycles.Soil fungus was significantly correlated with altirude gradients,soil water content,soil organic carbon and soil total nitrogen.The ratio of soil microbial fungus to bacteria was significantly correlated with soil temperature.Soil Gram-positive bacteria were significantly correlated with altitude gradients,soil moisture,freeze-thaw cycles,soil organic carbon and total nitrogen,and negatively correlated with soil temperature.Soil Gram-negative bacteria were significantly correlated with altitude gradients,soil moisture,soil organic carbon and total nitrogen.The ratio of Gram-positive bacteria to Gram-negative bacteria was significantly negatively correlated with soil moisture,temperature and organic carbon,and was significantly correlated with soil freeze-thaw cycles.The soil microbial biomass carbon and nitrogen significantly increased with altitude gradients.Altitude gradient and sampling time significantly affected soil microbial biomass carbon and nitrogen.Soil microbial biomass carbon and nitrogen were significantly correlated with altitude gradients,soil moisture,soil organic carbon and total nitrogen,and negatively correlated with soil total phosphorus.The ratio of soil microbial biomass carbon to soil microbial biomass nitrogen was significantly negatively correlated with altitude gradients and soil freeze-thaw cycles.The change of soil enzyme activity with altitude gradients is consistent with the trend of soil microbial biomass carbon and nitrogen,showing a trend of decreasing first and then decreasing,and then back again.Soil sucrase activity was significantly correlated with altitude gradients,soil moisture,freeze-thaw cycles,soil organic carbon and total nitrogen,and negatively correlated with soil temperature.Soil urease and acid phosphatase activity were significantly correlated with altitude gradients,soil moisture,soil organic carbon and total nitrogen,and negatively correlated with soil total phosphorus.In summary,with the increase of altitude,the content of PLFAs of soil microbial community,soil microbial biomass and soil enzyme activity decreased from mid-subtropical evergreen broad-leaved forest to arid valley,and then increased to the subalpine forest and then reduced to the alpine forest,and thereafter increased to the alpine meadow in the Minjiang River basin.This spatial pattern is caused by the main control facter is soil moisture,organic carbon,total nitrogen,temperature,total phosphorus.At the same time,the content of PLFAs of soil microbial community,microbial biomass and soil enzyme activity were significant at different seasons,and this significant difference was the result of seasonal interaction of soil water and heat conditions and nutrient contents.Therefore,the elevation gradient and seasonal variation not only directly affect soil microbial community,microbial biomass and soil enzyme activity,but also indirectly affect the soil microbes by changing environmental factors,hydrothermal conditions,vegetation composition and soil physical and chemical properties.That is theoretical basis to understand how is altitude gradient effect and environmental factors affect soil microbial community structure,biomass and enzyme activity,and for in-depth understanding of soil biochemical processes. |
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