Effects Of Phosphorus Addition On Different Soil Respiration Components In Chinese Fir Plantation And Its Mechanism

Soil respiration is the second largest carbon flux between the atmosphere and terrestrial ecosystem,its slight change will deeply increase or decrease the concentration of carbon dioxide in the atmosphere,thus having an deeply impact on global warming.Soil nutrients affect soil respiration by regulating microbial growth and metabolism.Clarifying the relationship between soil respiration and soil nutrients is very important to predict global terrestrial carbon cycle,which is a hot topic in the field of global change.Phosphorus is one of the key nutrient elements that limit the primary productivity of terrestrial ecosystem.However,subtropical forest soil is highly weathered,most of which is fixed by iron and aluminum oxides,and the content of available phosphorus in soil is low,which leads to the limitation of microbial activities in this region.At the same time,anthropogenic activities lead to phosphorus deposition and a large amount of phosphate fertilizer input,which changed the soil phosphorus nutrient status and then affect soil respiration.However,how will soil respiration and its components(autotrophic respiration,heterotrophic respiration and mycorrhizal induced respiration)respond to the change of phosphorus nutrient?What is the influence mechanism?There are still uncertainties.Therefore,two treatments,phosphorus addition and control,were set up on the sample plot of Cunninghamia lanceolata plantation.Soil respiration was divided into three components:soil heterotrophic respiration,root respiration and mycorrhizal induced respiration by compartment isolation technology,and the effects of phosphorus addition on different soil respiration components of subtropical Cunninghamia lanceolata plantation were explored.Combined with the changes of biological and abiotic factors such as soil physical and chemical properties,microbial community composition,enzyme activity and root attributes after phosphorus addition,the mechanism of phosphorus addition on different respiratory components of Cunninghamia lanceolata plantation was clarified.This study is helpful to deeply understand the mechanism of phosphorus regulating soil respiration and the changes of its component,and provides a theoretical basis for incorporating phosphorus into the earth system model,which has important practical significance for the forest management and management of Cunninghamia lanceolata plantations in China.The main results are as follows:(1)Phosphorus addition significantly changed soil physical and chemical properties,and soil p H,total phosphorus(TP)and available phosphorus(AP)increased significantly after phosphorus addition.It is clear that phosphorus addition increases soil phosphorus availability and may alleviate soil acidification caused by nitrogen deposition.After phosphorus addition,soil dissolved organic carbon(DOC)increased significantly,and the degradation and aromatization index of soil DOC increased significantly,which indicated that phosphorus addition would increase the risk of soil organic carbon leaching loss and increase the proportion of soil DOC stable carbon.The mineral nitrogen(NH₄⁺-N and NO₃^--N)and dissolved organic nitrogen(DON)in soil decreased significantly after phosphorus addition,which suggested that phosphorus addition would change the process of soil nitrogen transformation,reduce the leaching loss of nitrogen,and might lead to the change from phosphorus limitation to nitrogen limitation in Cunninghamia lanceolata plantation ecosystem.(2)Addition of phosphorus significantly increased soil microbial biomass carbon(MBC),microbial biomass nitrogen(MBN),microbial biomass phosphorus(MBP)and phospholipid fatty acids of different types of microorganisms,while decreased soil MBC/MBP and MBN/MBP.However,the ratio of Gram-positive bacteria to Gram-negative bacteria(GP:GN)and fungi to bacteria(F:B)did not significantly changed after addition of phosphorus.Correlation analysis showed that the contents of total phosphorus,available phosphorus and DOC in soil are the key factors acts on the soil microbial biomass,indicating that phosphorus may be one of the nutrient elements limiting soil microbial growth in Cunninghamia lanceolata plantation,and phosphorus addition promoted soil microbial growth by improving soil phosphorus availability and DOC content.(3)Phosphorus addition significantly reduced soil acid phosphatase activity,but had no significant effect on soil?-glucosaccharase(?G),?-N-acetyl glucosaccharase(NAG)and cellulose hydrolase(CBH)activities,but?G/ACP and NAG/ACP increased significantly,which indicated that microbial phosphorus nutrient demand decreased and soil organic phosphorus conversion rate decreased,while soil microbial demand for carbon substrate and nitrogen nutrient increased.(4)Phosphorus addition significantly increased the annual total respiration flux and heterotrophic respiration flux of Chinese fir plantation soil,while the annual cumulative fluxes of root respiration and mycorrhizal respiration increased after phosphorus addition,indicating that phosphorus addition will increase soil carbon dioxide emission and phosphorus may be one of the nutrient elements limiting soil microbial activity of Chinese fir plantation.The Q₁₀ of soil total respiration,heterotrophic respiration,root respiration and mycorrhizal respiration increased after phosphorus addition,and the Q₁₀of soil total respiration and heterotrophic respiration responded significantly to phosphorus addition,which indicated that phosphate fertilizer addition may increase the temperature sensitivity of soil respiration,and future climate warming may increase the decomposition rate of soil organic carbon with high phosphorus availability.The results of correlation analysis showed that soil heterotrophic respiration was positively correlated with abiotic factors such as DOC,NO₃^--N,AP and TP,and positively correlated with biological factors such as GN,?G,MBC and MBN/MBP.The results of redundancy analysis show that soil AP and DOC are the key factors to explain the change of soil respiration components,which suggests that the change of soil heterotrophic respiration after phosphorus addition is the result of the joint regulation of biological and abiotic factors,and that phosphorus addition mainly affects soil respiration by changing microbial biomass,community composition and carbon matrix availability.To sum up,short-term phosphorus addition can directly or indirectly affect soil microbial activity and improve soil respiration by changing soil phosphorus availability and DOC content,while short-term phosphorus addition has no significant effect on root respiration and mycorrhizal induced respiration.The results clarify the possible mechanism of phosphorus addition affecting soil respiration and its components by regulating soil biological factors and abiotic factors,and provide theoretical basis for improving the earth system model and subtropical forest operation and management.