Effects Of Management Practices On Soil Microorganisms Funtion Stotichiometry Characteristics Of Pinus Tabulaeformis Plantations In Loess Plateau

Vegetation construction was the key measure of regional soil erosion control and ecological environment improvement,and artificial afforestation was an important measure of vegetation construction on the loess plateau.Pinus tabulaeformis had become the main tree species for afforestation in the project of returning farmland to forest on the loess plateau because of its functions of soil and water conservation,water conservation and soil improvement.Since the 1990s,different management practices have been taken to manage and protect the Pinus tabulaeformis plantation in Yichuan county.This study focused on Pinus tabulaeformis plantation as the research object under different management practices,through the methods of field experiment and indoor analysis,to study the changes of soil water-soluble carbon（WSOC）,water-soluble nitrogen component content,oxidizable organic carbon fractions,soil organic carbon（SOC）stability,and soil microbial characteristics.This study analyzed the effects of different management practices on soil microbial community structure and metabolic function diversity as well as soil microbial characteristics on the stability of SOC,explored the interactions and changes of soil microbial and soil enzyme stoichiometric characteristics,and clarified the impact of different management practices on the soil microbial stoichiometric homeostasis.These have important reference value for providing scientific basis for the sustainable management and vegetation restoration of the loess plateau.The main results are as follows:（1）Management practices affected WSOC content and soil water-soluble nitrogen component content,especially natural shrub regeneration（SL）and planting Pinus tabulaeformis young forest（SPL）had a significant impact on the WSOC content of 0-20 cm soil layer and soil water-soluble nitrogen component content.The WSOC of SL in the 0-20 cm layer was highest,while the WSN,soil ammonium nitrogen（NH₄⁺-N）and water-soluble organic nitrogen（WSON）of SPL were highest in the 0-20 cm layer.The content of WSOC,water-soluble total nitrogen（WSN）and soil nitrate nitrogen（NO₃^--N）showed similar results,which in the 0-20 cm layer were higher than 20-40 cm layer.Three-dimensional fluorescence spectrum analysis showed that the main component of soil DOM was humus.Among them,the soil DOM humus content of SPL was relatively high,and its main source was litter decomposition.（2）The contents of MBC,MBN and MBP were higher in the 0-20 cm layer than in the 20-40 cm laye.The comparison results of microbial biomass under different management practices showed that MBC,MBN and MBP of SL were highest,followed by MBC and MBP of SPL.Total phospholipid fatty acids（PLFAs）,Gram-negative bacteria PLFAs,Gram-positive bacteria PLFAs,and fungal PLFAs changed similarly:the content in the 0-20 cm layer were higher than in the 20-40 cm layer.AWCD of the six carbon sources in the carbon source utilization efficiency of the microbial community were consistent,reaching the highest at 240 h.The comparison results of different management practices showed that SL had the highest BR,SIR and four PLFAs,followed by SPL.Among them,microorganisms of SL had the highest utilization efficiency of carbohydrates,carboxylic acids and amino acids,while microorganisms of cleared grassland（GL）had the highest utilization efficiency of polymers,phenolic compounds and amine compounds.The results of richness index(H_PLFA,H_BIOLOG)and evenness index(E_PLFA,E_BIOLOG)showed that the diversity of microbial community structure and the diversity of microbial community function remained basically unchanged.（3）The content of the fourth component（C4）and soil carbon pool index（CPI）of SL were significantly higher than other management practices,while the content of the first component（C1）of oxidizable organic carbon was the lowest.Path analysis showed that MBC directly affected CPI and lability index（LI）,while MBC had a greater indirect effect on CPI through H_BIOLOG and E_BIOLOG.（4）The activities ofβ-1,4-glucosidase（BG）,β-1,4-N-acetylglucosaminidase（NAG）and alkaline phosphatase（AP）were higher in the 0-20 cm layer than the20-40 cm layer.The activities of BG,NAG,AP and soil enzyme stoichiometric ratio of BG:NAG of SL in the 0-20 cm layer were higher than other management practices.Regression analysis showed that the stoichiometric ratio of soil carbon:nitrogen（soil C:N）and MBC:MBN in the 0-20 cm layer and 20-40 cm layer was weakly plastic and weakly homeostatic,respectively.And the stoichiometric ratio of soil carbon:phosphorus（soil C:P）and MBC:MBP in the 0-20 cm layer and the20-40 cm layer showed weakly homeostatic and homeostatic,respectively.