Linkages between soil organic carbon fractions and carbon-hydrolyzing enzyme activities across riparian zones in the Three Gorges of China

Abstract

The effect of flooding on soil enzyme activities and soil organic carbon (SOC) dynamics remains a widely debated topic. Here, we investigated spatial variations in C-hydrolyzing enzyme activities, soil C contents in different fractions [i.e. labile and recalcitrant carbon (LC and RC)] from 6 sites with four different elevations at two soil depths (0-10 cm and 10-30 cm) in riparian zones of the Three Gorges Reservoir, China. At region scales, the SOC, RC contents, and RC/SOC (RIC) generally showed decreasing tendency from the upstream to the downstream. The C-hydrolyzing enzyme activities were higher in the midstream compared to other sites, which did not correspond well with the changing trend of SOC content, but matched with the spatial variation in LC content. At ecosystem scales, the RC and RIC declined with decreased elevations, but the LC showed opposite trend. Whereas, the four C-hydrolyzing enzyme activities and the specific enzyme activities were corresponded well with the changing trend of Lc content. Soil c contents and enzyme activities were generally higher in top soil than deep soil across sites and elevation zones. These results reveal that the LC is the tightest factor in regulating C-hydrolyzing enzyme activities, whereas the soil C quality (i.e. RIC) and flooding collectively drive C-hydrolyzing enzyme activities possibly by affecting decomposition rates of SOC in the riparian zones. Anthropogenic activities such as large hydroelectric project can directly affect ecosystem processes and function by altering vegetation types, soil properties and hydrology 1,2 , and ultimately modify soil carbon (C) and nitrogen (N) cycling 3-5. Soil organic carbon (SOC), one of the largest and most susceptible C pools of the earth surface ecosystem, can act either as source or sink for C primarily counting on multiple factors including human activities 6-10. It is well known that the SOC pool is generally determined by the balance between litter C input and decomposition 7,11 , while the SOC decomposition process is predominantly catalyzed by a variety of extracellular enzymes 12-14. Particularly, these enzymes can hydrolyze substrates and catalyze important transformations involving in soil organic matter (SOM) synthesis 15,16. Although some studies have evaluated changes in soil C and N dynamics under large hydroelectric project 3,4,17 , how spatial variations in SOC dynamics link to C-hydrolyzing enzyme activities at region and/or ecosystem scales under large hydroelectric project remains largely unclear. The linkages between SOC and C-hydrolyzing enzyme activities can be influenced primarily by altering vegetation types under large hydroelectric projects 2,3,18,19. Most SOC exclusively originates from plant residues on site, and hence alterations in vegetation type are expected to change the quality and quantity of SOC, which in turn can affect C-hydrolyzing enzyme activities 20-23. For instance, previous studies have reported that soil hydrolytic enzyme activities are tightly related to SOC content 12,23,24 ,...

Altered activities of extracellular soil enzymes by the interacting global environmental changes

“…The activity of C‐hydrolysing soil enzymes can be influenced, eventually leading to higher levels of carbon sequestration, by targeted mineral fertilisation (Dong et al, 2022), soil amendment (Zaborowska et al, 2018), and alteration of the vegetation cover (Mackay et al, 2016; Zhang et al, 2020).…”

Spatial distribution characteristics and ecological assembly process of bacteria and aerobic anoxygenic photosynthesis bacteria in Three Gorges Reservoir

“…The statistical signi cance of water quality parameters and diversity index in different regions was measured by using the one-way analysis of variance (ANOVA) of Tukey's HSD test [30,31]. Unique and shared microbes in sediments from different regions were assessed by Venn analysis.…”

Macrofungi Cultivation in Shady Forest Areas Significantly Increases Microbiome Diversity, Abundance and Functional Capacity in Soil Furrows

“…We found that the activities of two hydrolases (glucosidase and cellobiosidase) were significantly boosted in the soil beneath the fungal bed as compared to the other areas, but the oxidase activity remained stable. The reasons for various responses might be the preferential use of labile C by microbes, for instance, after wine-cap mushroom cultivation in shady forest areas (with micro-spray irrigation system installment in the forest canopy), and soil microbes tending to use labile C components, and thus not increasing the input of oxidase for decomposing recalcitrant C in the forest soil beneath the cultivation beds [ 15 ], because this activity is concentrated in the cultivation beads themselves, where there is abundant organic matter. On the other hand, from an ecological point of view, in shady forest areas, cultivation of mushrooms showed a positive effect of the use of fungal beds, obtained as a subproduct from the same local forested areas, in forest soils, as it favors the stabilization of the soil recalcitrant C pool, which plays crucial roles in major soil functions and ecosystem services [ 17 ].…”

“…The process of macrofungi cultivation involves artificial management strategies including forest land topsoil tillage, fermentation of mixed forest by-products (used as mushroom-cultivating substrates), inoculation of the targeted hyphae into the substrates (termed as “fungal bed”), the construction of furrows adjacent to fungal beds (used as paths for mushroom collection), and micro-spray system installment in forest canopies [ 7 , 9 ]. The varied soil moisture regimes (induced by artificial spray) could influence deeper soil organic carbon (SOC) decomposition rates and stability by mediating soil enzyme activities [ 15 ]. In general, soil carbon (C) components are decomposed by different soil extracellular enzymes.…”