The Effects Of Carbon, Nitrogen And Phosphorus Addition And Acidification On Soil Respiration And Temperature Sensitivity Of Farmland In The Loess Plateau

The cultivated land area in the loess area accounts for more than 15%of the total cultivated land area in China.The poor rainfall resources in this area and it is one of the lowest areas of soil productivity and soil organic carbon storage in China.A large amount of nutrient addition and soil acidification can change the soil environment.These factors change soil microbial respiration and root respiration to change soil respiration rate and temperature sensitivity,thus affecting climate change and soil carbon balance.Although there are many studies on soil respiration in the loess region,it is still unclear how to change the CO2 emission and temperature sensitivity of soil under the condition of nutrient addition and acidification,and how to change the soil properties of the loess region.In this paper,there have 12 treatments,CK,N120,N240,P150,P300,C,5%acidification,10%acidification,NP,NC,CP,NCP.The soil respiration rate changes at 15 and 25? were compared and analysis the soil temperature sensitivity during the culture period.The changes of soil pH,total carbon total phosphorus,organic carbon,ammonium nitrate nitrogen and microbial biomass carbon,nitrogen and phosphorus were measured during the respiration.Correlation analysis and path analysis are conducted on soil respiration rate,Q10 and soil properties,and the main influencing factors were analyzed.The following are the main conclusions of this article.(1)The addition of carbon and nitrogen can increase soil respiration rate,in which carbon source can greatly increase soil respiration.Carbon and nitrogen sources,carbon and phosphorus source added after the soil respiration rate is higher than that of single carbon source adding soil,its peak were 2.1 mg·g-1·d-1,1.6 mg·g-1·d-1.The peak value of soil respiration added by carbon nitrogen and phosphorus source is 2.47 mg·g-1·d-1.This is because the addition of carbon source increase soluble carbon content in the soil,it can improve the soil microbial activity,so as to speed up microbial respiration,greatly promote the decomposition of carbon in the soil ability,eventually led to the increase of CO2 emissions.With the continuous degradation of carbon source,soil respiration rate is decreasing gradually.The addition of phosphorus has little effect on soil respiration.The rate of soil respiration increased significantly after acidification.(2)After the addition of carbon and nitrogen source,the soil Q10 value increased slightly.After a single nitrogen source,the soil temperature sensitivity is between 0.7?6.9,and the addition of single phosphorus source makes the soil Q10 value between 0.58?19.9,and a significant increase after breathing 19d.After the addition and acidification of carbon source,the Q10 value of the soil in the respiratory 19d was not significantly changed,and slightly increased after 19d.The mixture of carbon and nitrogen,carbon and phosphorus and nitrogen and phosphorus was more stable than that of single added soil.After the addition of carbon,nitrogen and phosphorus sources,the content of organic matter in the soil is increased and the quality of the substrate is enriched.The effective decomposition of the substrate is the main source of CO2 in the process of soil respiration.The rich soil substrate contributes to the process of soil respiration,thus greatly improving the sensitivity of soil respiration.(3)After the addition of carbon and nitrogen phosphorus source,the soil properties were changed around respiration.Adding nitrogen source,increase the content of total nitrogen and nitrate nitrogen in the soil,significantly increased the content of ammonium nitrogen in the soil,the ammonium nitrogen in the soil decreased greatly after respiration,while the nitrate nitrogen had a certain increase.This is because the nitrate nitrogen is not easy to be adsorbed by soil particles and soil colloids compared with ammonium nitrogen,so the promotion is slower.However,the process of microbial growth will consume ammonium nitrogen first and the nitrification process is faster,thus showing the increase of nitrate nitrogen content.The addition of phosphorus significantly increased the content of total phosphorus and available phosphorus in the soil.The content of total phosphorus and phosphorus significantly changed after respiration,and the content of total nitrogen,total carbon and organic carbon was slightly improved,and the content of available phosphorus and nitrate nitrogen decreased greatly,content of total carbon and organic carbon in soil decreased and the content of available phosphorus increased after respiration.The content of nitrate nitrogen has not changed much.This is because carbon sources increase the content of organic matter in the soil.They can immobilize the phosphorus in the soil,which reduces the content of available phosphorus,and the addition of glucose provides nutrients to the microorganisms in the soil,thus promoting the accumulation of nitrogen and the efficiency of soil fixation,which increases the total carbon content.After the addition of carbon source,the soil microbial biomass increased significantly,and the addition of nitrogen and phosphorus sources correspondingly increased the content of MBP and MBN.This is due to the addition of nitrogen and phosphorus to enhance the assimilation and fixation of microorganisms.The addition of carbon sources makes the decomposition of organic carbon source faster,the soil metabolism activity is strengthened,soil nutrients are raised,and soil nutrients are improved,ensure higher microbial biomass.Acidification reduced the pH of soil,increased the content of available phosphorus,decreased the total carbon content of soil after respiration,and increased the content of ammonium nitrogen and reduced the content of nitrate nitrogen in soil.This is due to the suitable pH value to promote the enrichment of available phosphorus in soil aggregates with different particle sizes,thus increasing the content of available phosphorus in the soil;the migration and transformation of nitrogen are influenced and regulated by the soil acidity and alkalinity,the decrease of the soil pH value,promotion the ammoniation process,thus improving the soil ammonium nitrogen content.Soil acidification reduced microbial biomass content,but MBP increased significantly after 5%acidification.(4)There is a correlation between the respiration rate and organic carbon in the soil with nitrogen and phosphorus added,which has a extremely significant correlation with MBC and MBP,the Q10 is related to the whole total carbon.The soil respiration rate is significantly related to the MBC after the carbon source,which is extremely significant correlation with the ammonium nitrogen and MBP,and the Q10 is significant relate to the soil total nitrogen and MBP.After soil acidification,soil pH is correlated with many soil properties.Soil Qio is significantly correlated with nitrate nitrogen content.After the addition of nitrogen and phosphorus,the pH had a negative effect on organic carbon,and the effect of available phosphorus was positive.Organic carbon had effect on nitrate nitrogen,respiration rate and total carbon.Both MBP and MBC had a positive effect on soil respiration rate,and total carbon had a negative effect on Q10.After the addition of carbon source,ammonium nitrogen has a positive effect on MBP and soil respiration rate,and MBP and MBC have positive effects on soil respiration rate,and total nitrogen has a negative effect on Q10.After soil acidification,pH had a positive effect on nitrate nitrogen and organic carbon.Nitrate nitrogen had positive effects on Q10 and MBC.