Study On The Difference Of Photosynthetic Carbon Allocation In Different Purple Soil-crop Systems And Its Relationship With Fertilizer Nitrogen Use Efficiency

The synthesis of photosynthetic carbon by plants through photosynthesis is the starting point of the soil-plant-microbial interaction process,and it is closely coupled with the nitrogen uptake and utilization of plants.Reasonable nitrogen application can promote plant growth,and increase the distribution of synthetic photosynthetic carbon to underground parts of plants.More photosynthetic carbon distribution to underground parts is beneficial to increase the number and activity of rhizosphere soil microorganisms,and enhance the availability of soil nitrogen.So,what are the differences in the allocation of photosynthetic carbon between crops in different soil-crop systems?What are the influencing factors?How do these differences affect soil-plant-microbial interaction processes,and thus lead to differences in fertilizer nitrogen uptake and use efficiency among different soil-crop systems?It’s not clear.Purple soil is one of the important tillage soils in Sichuan region.By studying the photosynthetic carbon allocation and differential mechanism of different purple soil-crop systems and the difference and mechanism of nitrogen use efficiency of crop fertilizer,and analyzing the relationship between photosynthetic carbon allocation and nitrogen absorption and utilization efficiency of crop fertilizer,it is expected to reveal the coupling relationship between carbon and nitrogen of different purple soil-crop systems and regulate the carbon and nitrogen conversion process of different purple soil-crop.To provide scientific basis for improving carbon and nitrogen utilization efficiency of crops in purple soil.In this study,we took the acid purple soil-rice/wheat system and calcareous purple soil-rice/wheat system in Sichuan province as the research objects,carried out the ¹⁵N isotope root box pot experiment,combined with the rhizosphere bag method and the ¹³C-CO₂ pulse labeling test,the tillering stage of rice,jointing stage and booting stage;Wheat:¹³C-CO₂ pulse labeling was carried out in different purple soil-crop systems at different growth stages,and differences in crop fertilizer nitrogen use efficiency and their relationships were studied,so as to clarify the photosynthetic carbon allocation and differential mechanism in different purple soil-crop systems.The mechanism of nitrogen use efficiency difference in crop fertilizer and its relationship with photosynthetic carbon allocation difference were revealed.The main research results are as follows:（1）Compared with different purple soil-wheat systems,different purple soil-rice systems had more significant differences in the distribution of photosynthetic ¹³C among soil-crop-microorganisms（P<0.05）.Due to the weak nitrogen retention ability of calcareous purple soil-rice system,31.49%-65.69%of photosynthetic ¹³C was allocated to rhizosphere/non-rhizosphere soil,and 1.31%-2.62%of photosynthetic ¹³C was used for microbial biomass amplification in rhizosphere/non-rhizosphere soil.The proportion of photosynthetic ¹³C in rhizosphere and non-rhizosphere soil microbial biomass was 2.20-2.77 times and 3.17-3.37 times of that in acid purple soil-rice system.（2）Compared with different purple soil-wheat systems,the fertilizer ¹⁵N utilization efficiency of different purple soil-rice systems was more affected by different p H of purple soil,and was significantly correlated with crop root length and NAG enzyme activity（P<0.05）.The utilization efficiency of fertilizer ¹⁵N in acid purple soil-rice system was26.79%-30.95%higher than that in callitic purple soil-rice system.The utilization efficiency of fertilizer ¹⁵N in acid purple soil-wheat system was 12.41%～13.13%higher than that in callitic purple soil-wheat system.（3）The difference of photosynthetic ¹³C allocation in different purple soil-rice systems was more closely related to fertilizer nitrogen use efficiency,and the photosynthetic ¹³C allocation in soil-plant-microorganisms was more correlated with the content of ¹⁵N in each part of fertilizer（P<0.05）.By regulating root morphology and rhizosphere soil environment,including soil p H,extracellular enzyme activity and root secretion of organic acids,crops can change the downward distribution of photosynthetic¹³C,thus affecting the utilization of soil carbon and nitrogen by microorganisms,and ultimately leading to the differences in the efficiency of carbon and nitrogen use in different purple soil-crop systems.