| Quercus equifolioides shrub in the subalpine area of western Sichuan is one of the main vegetation types in the region,which plays an important role in the carbon nitrogen cycle and water conservation of the regional terrestrial forest ecosystem There is still a lack of clear understanding of the impact mechanism of microbial biomass and extracellular enzyme activity related to carbon,nitrogen,and phosphorus cycling,as well as their stoichiometric ratios,which limits the assessment of carbon,nitrogen,and phosphorus storage potential in shrub soils.In early August 2022,this study measured and calculated the carbon,nitrogen,and phosphorus storage,microbial biomass,soil enzyme activity,and ecological stoichiometry of Quercus equifolioides shrub at three altitude gradients（2551 m for low altitude,3091 m for medium altitude,and 3549 m for high altitude）in the concentrated distribution area of Quercus equifolioides shrub within the Wolong National Nature Reserve after trenched treatment（TR）for 12 years（surface 0-15 cm,sub layer 15-30cm）.The aim is to:（1）analyze the impact of root removal on soil carbon,nitrogen,and phosphorus storage,microbial biomass,enzyme activity,and ecological stoichiometry;（2）Exploring the altitude gradient variation characteristics of soil carbon,nitrogen,and phosphorus storage,microbial biomass,enzyme activity,and ecological stoichiometry;（3）Reveal the main influencing factors of soil carbon,nitrogen,and phosphorus storage,microbial biomass,and soil enzyme activity.The results of this study,on the one hand,provide basic data for the estimation of soil carbon and nitrogen reserves and the implementation of carbon neutrality in the study area;On the other hand,it can also provide scientific basis for the carbon Nitrogen balance and its fixation effect of the forest ecosystem of alpine hardwood evergreen broad-leaved forest in western Sichuan,and also provide basis for the protection and utilization of hardwood evergreen broad-leaved forest resources.The research results are as follows:（1）Trenched treatment（TR）had a significant impact on the soil carbon,nitrogen and phosphorus storage of Quercus aquifolioides shrub（P<0.05）,which showed that the soil carbon storage at 2551 m,3091 m and 3549 m decreased by 55.59%,50.94%and 40.52%respectively compared with that without root cutting（CK）;The nitrogen and phosphorus reserves decreased by 43.85%,39.72%,43.39%,and 48.14%,41.70%,and 31.61%,respectively.In addition,the surface soil carbon,nitrogen and phosphorus reserves of TR were significantly higher than those of the sub layer（P<0.05）,and the soil carbon storage and nitrogen reserves showed a significant change trend of first rising and then falling with the elevation gradient（P<0.05）,which showed that the low altitude was significantly lower than the middle and high altitude;Phosphorus reserves showed an opposite trend of change（P>0.05）.In terms of ecological stoichiometry,trenched treatment（TR）had a significant impact on the soil C:N:P of Quercus aquifolioides shrub（P<0.05）.The results showed that C:N and C:P at 2551 m,3091 m,and 3549 m decreased by 4.79%,8.68%,56.92%,and16.89%,6.33%,and 11.48%compared to non root cutting（CK）,while N:P increased by0.94%,5.39%,and 60.14%,respectively.In addition,TR soil C:N showed no significant difference between different altitude gradients（P>0.05）,while C:P showed a trend of first significant increase and then decrease with altitude（P<0.05）,and N:P showed a trend of first decreasing and then increasing with altitude（P<0.05）.Redundancy analysis（RDA）shows that SOC,TC,and TN are the main influencing factors.（2）Trenched treatment（TR）had a significant impact on soil microbial biomass,carbon,nitrogen,and phosphorus（P<0.05）in the Quercus aquifolioides shrub,which showed that the soil microbial biomass,carbon,nitrogen,and phosphorus in the shrubland at 2551 m,3091 m,and 3549 m decreased by 21.78%,29.22%,40.33%,and 26.26%,17.26%,38.28%,and 23.12%,42.10%,and 51.3%,respectively.In addition,the soil microbial biomass,carbon,nitrogen,and phosphorus content in the surface layer were significantly higher than those in the sub layer soil（P<0.05）,and MBP showed a significant downward trend with increasing altitude gradients（P<0.05）.MBC and MBN showed a significant upward trend first and then downward trend（P<0.05）;In terms of ecological stoichiometry,trenched treatment（TR）had a significant impact on the MBC:MBN:MBP of Quercus aquifolioides shrub（P<0.05）.The results showed that MBC:MBP increased by 16.94%,9.35%,28.72%,and 34.83%respectively in the shrub soil at 3091 m and 3549 m after root removal,while MBN∶MBP increased by 35.39%and 18.92%,respectively.At an altitude of 2551 m,MBC:MBN and MBC:MBP decreased by 30.42%and 6.37%in the surface layer,and increased by 16.67%and 43.68%in the sub layer.MBN:MBP increased by 4.79%and12.28%in different soil layers,respectively.MBC:MBN in different soil layers showed a trend of first decreasing and then increasing with the elevation gradient（P>0.05）,while surface MBC:MBP and MBN:MBP in different soil layers showed a significant trend of first increasing and then decreasing with the elevation gradient（P<0.05）.The change trend of sub layer MBC:MBP was positively correlated with the elevation gradient.Redundancy analysis（RDA）shows that TN,TP,and SOC are the main influencing factors.（3）Trenched treatment（TR）had a significant impact on soil enzyme activity in the Quercus aquifolioides shrub（P<0.05）,with a decrease of 13.64%,13.54%,and 7.86%in NAG at 2551 m,3091 m,and 3549 m,respectively,βG decreased by 12.25%,10.41%,and7.94%,while AP decreased by 20.91%,0.37%,and 10.27%.However,LAP only showed significant differences in TR and CK at high altitudes（3549m）（P<0.05）,with a decrease of15.57%and 7.15%in surface and sub layer soils,respectively.In terms of ecological stoichiometry,trenched treatment（TR）had a significant impact on the ecological stoichiometry of soil enzyme activity in the Quercus aquifolioides shrub（P<0.05）.The results showed that C:Neea of the shrub soil at 2551 m,3091 m,and 3549 m increased by4.37%,0.92%,and 3.35%,respectively.N:Peea increased by 10.24%,4.29%,and decreased by 2.78%at high altitudes.C:Peea increased by 3.94%,5.68%,and decreased by 1.94%at high altitudes.Overall,The removal of roots has a relatively small impact on the ecological stoichiometry of soil enzymes.In addition,the enzyme activity of the surface soil was significantly higher than that of the sub layer soil（P<0.05）.With the increase of altitude,the enzyme activity of different soil layers in the Quercus aquifolioides shrub of Sichuan Yunnan alpine region（NAG,LAP,βG,AP）and enzyme chemical nitrogen phosphorus ratio（N:Peea）showed a trend of first increasing and then decreasing（P<0.05）,while enzyme chemical carbon nitrogen ratio（C:Neea）and carbon phosphorus ratio（C:Peea）were opposite.Redundancy analysis（RDA）showed that TN and available phosphorus were the main influencing factors,confirming that the soil in the high-altitude forest areas of western Sichuan is mainly limited by nitrogen.（4）Soil enzyme activities（AP,βG,NAG and LAP）in Quercus aquifolioides shrub communities were significantly correlated with nutrient content（SOC,TN,DOC,NO3--N,etc.）.TheβG,AP and LAP activities of top soil were significantly correlated with gravel content and soil density,while the LAP activity of subsoil was significantly correlated with Porosity and water holding capacity.Enzyme activity（NAG and AP）is closely related to the content of nutrients such as TN,SOC,TP,DOC and NO3--N.Otherwise,there is a significant correlation between soil microbial biomass carbon,nitrogen,phosphorus,and nutrient content,as well as p H value,in quercus aquifolioides shrub communities.SOC,TN,and TP are the main limiting factors for MBC,MBN,and MBP,respectively.There is a significant correlation between soil moisture,gravel content,and MBC.In addition,there is a significant correlation between capillary water capacity and MBP,while other physical indicators are all correlated,but the significance is not significant.In summary,removing the root system resulted in a long-term state of organic carbon and nitrogen deficiency in the study area.Compared to the control,the soil carbon,nitrogen and phosphorus storage,microbial biomass,and enzyme activity of Quercus aquifolioides shrub in the Sichuan Yunnan alpine region showed a decreasing trend.However,for its ecological stoichiometry,due to the lack of carbon and nitrogen nutrients,it showed an upward trend;The spatial gradient changes of soil carbon,nitrogen,phosphorus storage,microbial biomass,enzyme activity,and ecological stoichiometry of Quercus aquifolioides shrub in Sichuan Yunnan alpine areas vary with altitude gradient changes.The peak values of various indicators are mainly concentrated at mid altitude（3091m）;Soil bulk density is the main physical property factor that affects soil carbon,nitrogen,and phosphorus storage,microbial biomass,enzyme activity,and ecological stoichiometry.Soil TN,SOC,and TP are the main chemical property factors.Nitrogen shows the highest correlation coefficient with various soil nutrients in correlation analysis,indicating that nitrogen is the main limiting factors of the soil carbon,nitrogen,and phosphorus storage,microbial biomass carbon,nitrogen,and phosphorus,enzyme activity and its ecological stoichiometry. |
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