The interplay of labile organic carbon, enzyme activities and microbial communities of two forest soils across seasons

Abstract

Soil labile organic carbon (LOC) responds rapidly to environmental changes and plays an important role in carbon cycle. In this study, the seasonal fluctuations in LOC, the activities of carbon-cycle related enzymes, and the bacterial and fungal communities were analyzed for soils collected from two forests, namely Betula albosinensis (Ba) and Picea asperata Mast. (Pa), in the Qinling Mountains of China. Results revealed that the seasonal average contents of microbial biomass carbon (MBC), easily oxidized organic carbon (EOC), and dissolved organic carbon (DOC) of Pa forest soil were 13.5%, 30.0% and 15.7% less than those in Ba soil. The seasonal average enzyme activities of β-1,4-glucosidase (βG), and β-1,4-xylosidase (βX) of Ba forest soils were 30.0% and 32.3% higher than those of Pa soil while the enzyme activity of cellobiohydrolase (CBH) was 19.7% lower. Furthermore, the relative abundance of Acidobacteria was significantly higher in summer than in winter, whereas the relative abundance of Bacteroidetes was higher in winter. Regarding the fungal communities, the relative abundance of Basidiomycota was lowest in winter, whereas Ascomycota predominated in the same season. In addition, the soil LOC was significantly positively correlated with the CBH, βG and βX activities. Changes in LOC were significantly correlated with Acidobacteria, Bacteroidetes and Basidiomycota. We conclude that the seasonal fluctuations in forest soil LOC fractions relied on carbon cycle-associated enzymatic activities and microorganisms, which in turn were affected by climatic conditions.

The dominant microorganisms vary with aggregates sizes in promoting soil carbon accumulation under straw application

“…Additionally, soil enzymes, produced by soil microorganisms, are reported to regulate the overall processing of SOC through degrading different molecules [13] or depolymerizing macromolecular substrates [14]. Some enzymes (e.g., β-Glucosidase and β-Xylosidase activities) show a strong relationship with SOC content and are generally reported to be good indicators of soil biological change [15,16]. It is remarkable that, even if the complexity of SOC-related mechanisms is widely recognized, most studies focused on a single factor, with fewer focused on multiple factors regulating SOC.…”

“…As the basic unit of soil, aggregate plays a key role in C cycling [17]. Containing more than 90% of sequestered SOC, aggregate can be divided into macro-(>0.25 mm) and micro-(<0.25 mm) aggregates [15,16]. Previous studies have shown that macroaggregate (>0.25 mm) contains more SOC content than micro-aggregate (0.053-0.25 mm), the same as labile SOC [18].…”

“…Previous studies have shown that macroaggregate (>0.25 mm) contains more SOC content than micro-aggregate (0.053-0.25 mm), the same as labile SOC [18]. As the basic element in soil structure, aggregate provides spatially heterogeneous microenvironments for soil microorganisms [15,16]. Large variance in environmental conditions in different sizes of aggregate, including water potential, oxygen concentration, and resource availability [19], could result in diverse biomass and community diversity for microorganisms [20][21][22] and affect their functions related to C turnover [23].…”

“…The distributions of microbial biomass and enzyme activity in aggregate fractions were reported to be primarily governed by the aggregate sizes [25], due to different availability of organic substances [26]. Furthermore, fungi were found to contribute to the C turnover more greatly and rapidly in macro-aggregates than in micro-aggregates [15,16]. There is extensive evidence that aggregate sizes affect microbial community composition and enzyme activity.…”

“…As the microhabitats for microorganisms, the aggregates are greatly changed in their physical conditions under fertilization [32]. For example, soil moisture within aggregate was directly altered by fertilizer application, which plays a key role in the survival of soil microorganisms [15,16]. The application of manure increased the microbial biomass in the form of phospholipid fatty acids (PLFA) in macro-aggregates, e.g., bacterial, fungal, and AM fungal biomass, while not significantly affecting biomass in micro-aggregates.…”