Dynamic Distribution And Transformatin Of Photosynthetic Fixed Carbon In Crop-Soil System Under Plastic Film Mulching And Fertilization

Photosynthetically fixed carbon?C?is the beginning of C fixation in atmosphere-plant-soil system,and also is an important source of soil organic carbon?SOC?.Plastic film mulching and fertilizer application can increase crop yields,but it also seriously affects the fixation and transportation of photosynthetically fixed C in soil.Because of the limitations of previous experiments and testing techniques,new photosynthetically fixed C and organic C in the original soil can not be distinguished.Therefore,the mechanism of immobilization and transport of new photosynthetically fixed C in plant-soil system has not been known clearly.Based on the Long-term Experiment Station of Brown Earth in Shenyang Agricultural University,this research has been carried out by using the method of in-situ ¹³C–CO₂ pulse labeling during maize seedlings under no-mulching treatments?no fertilization,CK;nitrogen fertilizer,N4;organic manure,M4?and the corresponding plastic film mulching treatments?no fertilizer,FCK;nitrogen fertilizer,FN4;organic manure,FM4?.Maize shoots,roots,rhizosphere soil and bulk soil were collected at 1 hours,1 days,3 days,7 days and 30 days after labeling.The dynamic distribution of photosynthetic fixed C in plant,soil and microorganism have been determined,and the effectiveness of mulching and fertilization and the fixation mechanism of photosynthetic C have been discussed,which provided a theoretical basis for SOC turnover.The main results are as follows:?1?The application of organic manure and nitrogen fertilizer under mulching promoted the fixation of photosynthetic C in soil and improved the¹³C assimilation rate.The amount of net photosynthetically fixed¹³C was the highest in FN4 and FM4 treatments at the 1^sthour after labeling,with a ¹³C assimilation rate of 75.5%.The average of ¹³C assimilation rates was about 54.4%in the treatments of M4,FCK and CK.The lowest was in N4 treatment,with a¹³C assimilation rate of 31.2%.The average¹³C assimilation rate was 36.5%at the 30th day after labeling.?2?Application of organic manure and nitrogen fertilizer under no-mulching increased the distribution of photosynthetically fixed C in the underground parts?root,rhizosphere soil and bulk soil distribution?.The proportion of net photosynthetically fixed¹³C underground increased with days after labeling.The averages of 17.81%,20.12%and 16.24%of photosynthetically fixed C were distributed to root,rhizosphere soil and bulk soil,respectively,in the N4 and M4 treatments in the 30th day after labeling.Meanwhile,the proportion of photosynthetic C underground in N4 and M4 treatments was 19.84%and 24.22%higher than other treatments,respectively.?3?Soil dissolved organic C?DOC?and microbial biomass C?MBC?decreased with time after labelling.The content of DOC in soil under mulching at 1 hour or 1 day after labeling was significantly higher than that under no-mulching.At 3³0 days after labeling,the DOC content in bulk soil under mulching was about 17%lower than that under no-mulching.Under the same mulching or no-mulching condition,the content of MBC in rhizosphere soil was higher in organic manure treatment than that in no fertilization and nitrogen fertilizer treatments.?4?Plastic film mulch and fertilization enhaced the photosynthetically fixed C to form soil DOC.The contents of ¹³C-DOC in rhizosphere soil reached the first peak at the first day after labeling were 21.84,4.28,2.80 and 2.90?g kg^-1in FN4,FM4,FCK and M4 treatments,respectively.And the second peaks at the 30^thday after labeling were 13.44,5.91,4.74 and6.42?g kg^-1,respectively.No significant difference?P>0.05?in ¹³C-DOC contents of rhizosphere soil was found among days in CK treatment.?5?The interaction of film mulching and fertilization significantly effected the contents of¹³C in soil MBC.The content of¹³C-MBC in rhizosphere soil reached the highest at the 1hour or 1 day after labeling,then decreased with time,and fianlly decreased by 50%⁹3%compared with the highest value at the 30th day after labeling.FN4 treatment significantly increased?P<0.05?the ¹³C-MBC content of rhizosphere soil under mulching.Under no-mulching,the¹³C-MBC content in rhizosphere soil increased by 30%⁹9%in organic manure treatment?M4?compared with no fertilizer treatment?CK?,and increased by 45%¹50%compared with nitrogen fertilizer treatment?N4?.In conclusion,the photosynthetically fixed C is transformed underground rapidly,and their fixation and distribution are influenced by mulching and fertilization.The utilization of photosynthetically fixed C by microorganism needs to further study in the soil with long-term mulching and fertilization.