农田土壤自养微生物碳同化潜力及其功能基因数量、关键酶活性分析

研究农田土壤自养微生物碳同化潜力,对全面认识农田生态系统碳吸收和碳储存有着重要意义.选取6种典型农田土壤,通过14C连续标记示踪技术结合密闭系统模拟培养,量化了土壤自养微生物碳同化潜力及其向土壤活性碳库组分转化,同时结合分子生物学技术及酶学分析方法,探讨了不同土壤自养微生物细菌固碳功能基因(cbbL)丰度及关键酶(RubisCO)活性.结果表明,土壤自养微生物具有可观的CO2同化潜力,在本实验条件下,全球每年表层(0~20 cm)土壤通过自养微生物的同化作用可固定的碳为0.57~7.3 Pg.供试土壤的14C土壤有机碳(14C-SOC)含量范围为10.63~133.81 mg·kg-1,而14C可溶性有机碳(14C-DOC)、14C微生物生物量碳(14C-MBC)含量范围分别为0.96~8.10 mg·kg-1、1.70~49.16 mg·kg-1.土壤可溶解性有机碳(DOC)、微生物量碳(MBC)和SOC的更新率分别为5.07%~14.3%、2.51%~13.12%和0.09%~0.64%.土壤细菌cbbL丰度范围为2.40×107~1.9×108copies·g-1,且RubisCO酶活性(CO2/soil)范围为34.06~71.86 nmol·(g·min)-1.相关分析表明,土壤14C-SOC与14C-MBC及RubisCO酶活性均呈极显著正相关关系(P<0.01).说明土壤对大气CO2的同化作用主要是由自养微生物参与的同化过程,且较高的RubisCO酶活性意味着较高的自养微生物CO2同化潜力.

Carbon Dioxide Assimilation Potential, Functional Gene Amount and RubisCO Activity of Autotrophic Microorganisms in Agricultural Soils

Carbon dioxide (CO₂) assimilation by autotrophic microorganisms plays a significant role in carbon sequestration in terrestrial ecosystems. Here, experiments were carried out to determine the contribution of autotrophic microorganisms to atmospheric CO₂ fixation in 6 representative agricultural soils. Soils were incubated continuously in an atmosphere of ¹⁴CO₂ and the distribution of labeled C into soil organic carbon (¹⁴C-SOC) was determined after 110 d. Meanwhile, the amounts of the cbbL genes were determined by Quantitative PCR and the RubisCO activity was measured in different soils. The results showed that substantial amounts of ¹⁴CO₂ were fixed into ¹⁴C-SOC (ranged 10.63-133.81 mg·kg^-1 after 110 d of continuous labeling, with an annual, global rate of about 0.57-7.3 Pg. The microbially fixed C was also incorporated into the active carbon poolthe dissolved organic C (¹⁴C-DOC) and in the microbial biomass C (¹⁴C-MBC)], and ranged from 0.96 to 8.10 mg·kg^-1 and 1.70 to 49.16 mg·kg^-1, respectively. The proportion of ¹⁴C-SOC in SOC was 0.09%-0.64%. The ¹⁴C-DOC/DOC and ¹⁴C-MBC/MBC were 5.07%-14.3% and 2.51%-13.12%, respectively. Thus, the distribution and transformation of microbially fixed C had a larger influence on the dynamics of DOC and MBC than on the total SOC dynamics. Moreover, the abundance of soil bacteria cbbL gene and RubisCO activity were in the range of 2.40×10⁷-1.9×10⁸ copies·g^-1 and 34.06-71.86 nmol·(g·min)^-1, respectively. The ¹⁴C-SOC content was significantly correlated with both the ¹⁴C-MBC content (P<0.01) and the RubisCO activity (P<0.01) in all tested soils. We concluded that autotrophic CO₂ assimilation by soil microbes is significant to the global C cycle.