玉米品种对根际微生物利用光合碳的影响

Effects of Maize Variety on Rhizospheric Microbe Utilizing Photosynthetic Carbon

通过温室盆栽试验,以玉米品种郑单958(ZD)和陕单8806(SD)为对象,采用磷脂脂肪酸(PLFA)联合^(13)CO_2标记技术对不同品种玉米光合同化碳在玉米—根际土壤系统的分配特征以及利用新光合同化碳的微生物群落进行了定量研究。结果表明:ZD的生物量及其植株和根际土壤的^(13)C含量均显著高于相应的SD处理,说明玉米品种能够显著影响光合同化碳的分配。根际土壤中部分PLFA-C百分比和PLFA-^(13)C百分比在两品种间显著不同,且ZD种植土壤中表征细菌(包括革兰氏阳性菌(G^+)和革兰氏阴性菌(G^-))和真菌的PLFA-C及PLFA-^(13)C含量均显著高于种植SD土壤。ZD土壤中表征G^+、G^-、真菌和放线菌的PLFA-^(13)C含量分别占总PLFA-^(13)C的2.4%、33%、35%和0.3%,而上述参数在SD土壤中的值分别为5.9%、55%、11%和1.1%。ZD处理较SD处理提高了真菌/细菌比值,降低了环丙脂肪酸/前体比值。本研究表明根际微生物对光合同化碳的利用受玉米品种的显著影响,G^-和真菌是利用光合同化碳的主要群落。

[Objective]Photosynthesis of terrestrial vegetation is the major force driving carbon cycling between the soil and the atmosphere.Photosynthetic carbon is a primary source of carbon in the soil and affects significantly biomass and composition of the microbial community in the rhizosphere in the form of rhizodeposit.Therefore,if plants different in variety may have different effect on distribution of photosynthetic carbon,rhizospheric microbe may also vary in community composition and microbial utilization of photosynthetic carbon as affected by plant variety.In order to understand and predict carbon cycling in the plant-soil system,a large volume of research work has been done on how to quantify transportation and distribution of photosynthetic carbon in the system.However,so far little is known about effects of plants different in variety on transportation and distribution of photosynthetic carbon in the plantsoil system and on rhizospheric microbe utilizing photosynthetic carbon.The study on input,distribution and microbial utilization of photosynthetic carbon in the plant-soil system is essential to understanding soil carbon sequestration process and soil biochemical processes.[Method]To that end,a pot experiment was carried out using the PLFA and ^13CO_2 labeling technique to quantatively study partitioning of photosynthetic carbon and utilization of newly photosynthesizedby carbon by rhizospheric microbe in two maize-rhizospheric soil systems different in maize variety,Zhengdan 958（ZD） and Shandan 8806（SD）.The distribution of newly photosynthesized carbon to soil microbe was estimated by analyzing the ^13C profile of microbial phosphlipid fatty acids（PLFA）.This experiment had two groups：one labeled for 7 days with ^13CO_2（98 atom%^13C）and the other labeled with ～（12）CO_2 in natural abundance.Based on the difference between the two groups in abundance of ^13C,the distribution of photosynthetic ^13C in the maize-rhizospheric soil systems was calculated.[Result]Results show that Treatment ZD was 20%and 24%higher than Treatment SD in biomass of shoot and root,respectively,and 260%and 159%higher in ^13C content in the shoot and root,respectively.In comparison with Treatment SD,Treatment ZD significantly increased ^13C in the shoot and lowered ^13C in the root.In addition,Treatment ZD significantly increased organic carbon content,δ^13C value and ^13C content in the rhizosphere soil,but decreased ^13C percentage in the rhizosphere soil,as compared with Treatment SD.These findings indicate that the distribution of photosynthetic carbon in the maize-rhizospheric soil system was influenced by maize varieties.Treatment ZD was significantly higher than Treatment SD in δ^13C value of 11 types of PLFA among the total of 14.Significant difference in distribution of individual PLFA- C percentage was observed between Treatments ZD and SD,indicating that the microbial communities in the two treatments differed in composition.Besides,Treatment ZD was much higher than Treatment SD in 18：2w6,9c PLFA-^13C percentage and much lower in a15：0,18：1w7c and cy19：0 PLFA- ^13C percentage.Treatment DZ was89%,65%,61%,629%,and 127%higher than Treatment SD in content of gram-positive bacteria,gramnegative bacteria,fungi and total PLFA- C,respectively,but was 6.4,3.4,5.2,26.2 and 8.6 times higher in ^13C content in the above-listed microbes,respectively.In Treatment ZD,the PLFA- ^13C content in grampositive bacteria,gram-negative bacteria,fungi and actinomycetes accounted for 33%,35%,2.4%,and0.3%,respectively,of the total PLFA- ^13C,respectively,while in Treatment SD it accounted for 55%,11%,5.9%,and 1.1%,respectively.Treatment ZD was significantly higher than Treatment SD in ratio of fungi to bacteria in PLFA- C and PLFA- ^13C,but much lower in ratio of cyclopropane PLFA to their precursor in PLFA- C and PLFA- ^13C.However,the two treatments did not differ much in ratio of gram-positive bacteria to gram-negative bacteria in PLFA- C and PLFA- ^13C.[Conclusion]In conclusion,this study demonstrates that maize varieties significantly affect the biomass and photosynthetic carbon distribution in the maizerhizospheric soil systems,and consequently composition of the microbial community in the rhizosphere and microbial utilization of photosynthetic carbon,and that gram-negative bacteria and fungi communities may be the principal microbial communities that utilize newly photosynthesized carbon in the rhizosphere.