Relating microbial community structure to functioning in forest soil organic carbon transformation and turnover

Abstract

Forest soils store vast amounts of terrestrial carbon, but we are still limited in mechanistic understanding on how soil organic carbon (SOC) stabilization or turnover is controlled by biotic and abiotic factors in forest ecosystems. We used phospholipid fatty acids (PLFAs) as biomarker to study soil microbial community structure and measured activities of five extracellular enzymes involved in the degradation of cellulose (i.e., β-1,4-glucosidase and cellobiohydrolase), chitin (i.e., β-1,4-N-acetylglucosaminidase), and lignin (i.e., phenol oxidase and peroxidase) as indicators of soil microbial functioning in carbon transformation or turnover across varying biotic and abiotic conditions in a typical temperate forest ecosystem in central China. Redundancy analysis (RDA) was performed to determine the interrelationship between individual PFLAs and biotic and abiotic site factors as well as the linkage between soil microbial structure and function. Path analysis was further conducted to examine the controls of site factors on soil microbial community structure and the regulatory pathway of changes in SOC relating to microbial community structure and function. We found that soil microbial community structure is strongly influenced by water, temperature, SOC, fine root mass, clay content, and C/N ratio in soils and that the relative abundance of Gram-negative bacteria, saprophytic fungi, and actinomycetes explained most of the variations in the specific activities of soil enzymes involved in SOC transformation or turnover. The abundance of soil bacterial communities is strongly linked with the extracellular enzymes involved in carbon transformation, whereas the abundance of saprophytic fungi is associated with activities of extracellular enzymes driving carbon oxidation. Findings in this study demonstrate the complex interactions and linkage among plant traits, microenvironment, and soil physiochemical properties in affecting SOC via microbial regulations.

Effects of temperature, soil substrate, and microbial community on carbon mineralization across three climatically contrasting forest sites

“…The strong effect of temperature on the rate of soil C mineralization does not rule out the importance of soil microbial community, as it is recognized that climate and environmental factors can mask the influence of decomposer community on decomposition, due to the fact that soil microorganisms may both adapt to and be affected by climate and environments (Canarini, Carrillo, Mariotte, Ingram, & Dijkstra, 2016; Keiser & Bradford, 2017). Moreover, the structure and functions of soil microbial communities are further constrained by soil physiochemical properties and SOM quality (Fabian, Zlatanovic, Mutz, & Premke, 2017; Sun et al., 2016; Xun et al., 2015; You et al., 2014, 2016). Growing evidences show that soil geochemistry and physical structure impose direct effects on SOM stability by creating physiochemical barriers preventing microorganisms to access carbon sources (Bardgett et al., 2008; Chenu & Plante, 2006; Delgado‐Baquerizo et al., 2015; Doetterl et al., 2015; Plante, Conant, Stewart, Paustian, & Six, 2006).…”

“…For example, the cool temperate forest soils with rich SOM and better development were closely associated with the total bacteria and gram‐negative bacteria group, similar to the findings of other studies (Balser & Firestone, 2005; Kramer & Gleixner, 2008; You et al., 2014). The subtropical soils, being more acidic, were strongly associated with actino‐bacteria—a metabolically versatile group of microorganisms that degrade lignin and cellulose (Rousk et al., 2010).…”

“…The subtropical soils, being more acidic, were strongly associated with actino‐bacteria—a metabolically versatile group of microorganisms that degrade lignin and cellulose (Rousk et al., 2010). Our previous studies well established that biotic and environmental factors control soil C transformation and turnover by shaping the soil microbial structure (Sun et al., 2016; You et al., 2014, 2016). …”

“…We measured the activities of four soil enzymes that are involved in degrading lignin (phenol oxidase, PO and peroxidase, PER), cellulose (β‐1,4‐glucosidase, BG), and chitin ( N ‐acetyl‐β‐glucosaminidase, NAG), respectively (You et al., 2014, 2016). PO and PER were measured using 1‐3,4‐dihydroxyphenyla‐lanine (L‐DOPA) as substrate (Li et al., 2010; Sinsabaugh et al., 1993).…”

“…Bacterial community ( B ) was considered to be comprised of PLFAs i14:0, 15:0, i15:0, a15:0, i16:0, 16:1w7c, 17:0, a17:0, cy17:0, 18:1w7c and cy19:0; gram‐positive bacteria ( PB ) of i14:0, i15:0, a15:0, i16:0, a17:0, i17:0; gram‐negative bacteria ( NB ) of 16:1w7c, cy17:0, 18:1w7c, cy19:0; actinomycete ( Act ) of 10Me16:0, 10Me17:0 and 10Me18:0; saprotrophic fungi ( Sap ) of 18:2w6,9c; and arbuscular mycorrhizal fungi ( F ) of 16:1w5c. Other PLFAs ( other ) such as 14:0, 16:0, 16:1 w9c, 17:1w8c, and 18:1w9c were also used for analysis of the microbial community (You et al., 2014, 2016). …”