Characterization of Microbial Carbon Metabolism in Karst Soils from Citrus Orchards and Analysis of Its Environmental Drivers

Karst regions (KRs) have created significant karst carbon sinks globally through the carbon cycling process involving &ldquo:water-carbon dioxide-carbonate rock-biota&rdquo:. Soil organic carbon (SOC) represents a crucial component of these carbon sinks. Microorganisms play a vital role in the soil carbon cycle, influencing the formation and preservation of SOC. Therefore, investigating the carbon metabolism of soil microorganisms in KRs is essential for clarifying the unique biogeochemical cycling mechanisms within these regions. In this paper, soils from karst regions (KRs), mixed regions (MRs) and non-karst regions (NKRs) were collected from citrus orchards in Mao Village, Karst Experimental Field, Guilin City, Guangxi Zhuang Autonomous Region, China. The ability to use different carbon sources was analyzed by Biolog-Eco microtiter plate technique: the number of microorganisms was detected by the plate colony counting method, and the microbial biomass was determined by the chloroform fumigation method. The results showed that the soil bacterial number (5.69 &plusmn: 0.39 &times: 106 CFU/g), microbial biomass carbon (MBC) (608.24 &plusmn: 63.80 mg/kg), microbial quotient (SMQ) (3.45 &plusmn: 0.18%), and Shannon&rsquo:s index (H&prime:) (3.28 &plusmn: 0.05) of the KR were significantly higher than those of the NKR. The pH showed a significant positive correlation (p &lt: 0.05) with the bacterial number and H&prime: (p &lt: 0.05): SOC showed a highly significant positive correlation with bacterial number (p &lt: 0.01), and a significant positive correlation with MBC, H&prime:, and average well change development (AWCD) (p &lt: 0.05). Total nitrogen (TN) showed a significant positive correlation with MBC (p &lt: 0.05): available potassium (AK) showed a significant positive correlation with bacterial number and MBC (p &lt: 0.05). Exchangeable calcium (Ca2+) demonstrated significant positive correlations with bacterial number, MBC, and H&prime: (p &lt: 0.05). The above results indicate that soil bacterial number, carbon metabolic ability and diversity were highest in the KR. pH, SOC and exchangeable Ca2+ were the main influencing factors for the differentiation of soil microbial carbon metabolic diversity between the KR and NKR.