| 1. |
- Li, Yuhong, et al.
(författare)
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Contrasting response of organic carbon mineralisation to iron oxide addition under conditions of low and high microbial biomass in anoxic paddy soil
- 2021
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Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 1432-0789 .- 0178-2762. ; 57:1, s. 117-129
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Tidskriftsartikel (refereegranskat)abstract
- In contrast to what is observed in aerobic uplands, microbial biomass and the presence of electron acceptors, such as iron oxides, play a crucial role in regulating soil organic C (SOC) mineralisation in paddy soils. However, the related underlying mechanisms are still poorly explored. We conducted an anaerobic incubation study to investigate changes in CO2 emissions from SOC and acetate (13C-labeleld) in response to iron oxide (ferrihydrite and goethite) addition in chloroform-fumigated and unfumigated paddy soils. The iron oxides, as electron acceptors, increased CO2 emissions from SOC with stronger impact under ferrihydrite than goethite addition. However, the acetate addition, as a preferable C source for reducing microbes, decreased SOC mineralisation and caused a negative priming effect. CO2 emission from both acetate and SOC was affected by microbial biomass change. In the acetate-treated soil, goethite in the fumigated soil (i.e. high microbial biomass) increased CO2 emissions from acetate, providing electron acceptors, and decreased CO2 emissions from SOC. Ferrihydrite accepted electrons and adsorbed acetate, resulting in a slight decline in CO2 emission from acetate. However, in the fumigated soil (i.e. low microbial biomass), both iron oxide additions reduced CO2 emissions from acetate and SOC and likely the dominant role of both iron oxides shifted from being electron acceptors to being adsorbents, thus limiting acetate accessibility to microorganisms. The results suggest that microbial biomass is a key driver in shifting the effects of iron oxides on organic C mineralisation in anaerobic paddy soils.
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| 2. |
- Li, Yuhong, et al.
(författare)
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Oxygen availability determines key regulators in soil organic carbon mineralisation in paddy soils
- 2021
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; , s. 108106-108106
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Tidskriftsartikel (refereegranskat)abstract
- Rice paddy agro-ecosystems play an important role in global carbon (C) sequestration. Because of flooding management, paddy soil experience periodical changes in oxygen availability, which may make soil organic carbon (SOC) mineralisation unique as compared to upland or other wetland ecosystems. However, at present, information about the relevant mechanisms involved in paddy SOC mineralisation is limited and unclear. We selected three paddy soils with variable iron (Fe) contents, which were either fumigated with chloroform (to reduce microbial biomass) or remained un-fumigated. Soils were incubated for 78 days in one of three treatments: alternating nonflooded–flooded (NF: moist for 0–30 days (oxygen-abundant) and flooded for 31–78 days (oxygen-limited)), continuously flooded (CF: oxygen-limited), and continuously anaerobically flooded (AF: oxygen-depleted). Fumigation reduced the microbial biomass C by more than 70%. Except for the nonflooded period in the NF treatment, the SOC mineralisation rate, at the late stage of each treatment, was significantly lower in the fumigated than in the un-fumigated soil. A multiple regressions showed that a reduction in dissolved organic C contents over time contributed to the cumulative SOC mineralisation only during the nonflooded period in the NF treatment. Furthermore, the labile C pool size was smaller in the AF treatment relative to the other treatments. These imply that dissolved substrates in oxygen-depleted paddy soil were of greater recalcitrance, most likely due to thermodynamic reasons. SOC mineralisation correlated with changes in the redox potential and the Fe2+ contents in the CF and AF treatments only. This indicates that under oxygen-limited and -depleted conditions, Fe played a significant role as an electron acceptor during SOC mineralisation. Correlation and linear regression analyses also suggest that Fe influenced dissolved organic C contents, and hydrolase and oxidative activities. Our findings show that SOC bioavailability is a rate-limiting factor for SOC mineralisation, but only under oxygen-abundant conditions. However, under oxygen-limited or -depleted conditions, microbial biomass, the recalcitrance of organic C compounds, and the availability of electron acceptors are key regulators in determining the intensity and rate of SOC mineralisation.
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| 3. |
- Liu, Yuhuai, et al.
(författare)
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Effects of root exudate stoichiometry on CO2 emission from paddy soil
- 2020
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Ingår i: European Journal of Soil Biology. - : Elsevier BV. - 1164-5563 .- 1778-3615. ; 101
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Tidskriftsartikel (refereegranskat)abstract
- Root exudates are a labile source of carbon (C) for microorganisms that can lead to increased CO2 emission. Root exudates can vary in C:N stoichiometric ratio and their impact on microbially driven soil organic matter (SOM) turnover in paddy soils still remains unclear. The objective was to explore the underlying mechanisms involved in SOM decomposition due to root exudate (artificial) addition with three different C:N ratios (10, 20, and 40) during 45 days incubation. Different root exudates C:N ratios were obtained by adding mineral N and exudate components (glucose, oxalic acid, and glutamate) to paddy soil. N-only addition decreased dissolved organic C to limit CO2 emissions, which is an indicative of C sequestration. Conversely, simulated C:N stoichiometric ratios of root exudates significantly increased both microbial activity and metabolism without altering the microbial biomass C:N ratio. However, soil available dissolved organic C to NH4+ ratio decreased by exudates addition. The stoichiometric ratio of key C and N compound degrading enzymes activities increased only with C:N = 10 and remained unchanged with exudates C:N = 20 and 40. The qCO2 values increased with decreasing N-containing compounds in root exudates (i.e. highest CO2 emission was observed under C:N = 40 exudates addition). The results suggest that increasing exudates C:N ratio intensify CO2 emission due to high microbial N demand. Overall result show that root exudates C:N ratio and soil available N co-regulate on CO2 emission, which was controlled by microbial and potential extracellular enzyme activities.
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| 4. |
- Tong, Yaoyao, et al.
(författare)
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Microplastics affect activity and spatial distribution of C, N, and P hydrolases in rice rhizosphere
- 2023
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Ingår i: Soil Ecology Letters. - : Springer Science and Business Media LLC. - 2662-2289 .- 2662-2297. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- Microplastics provide a new ecological niche for microorganisms, and the accumulation levels of microplastics (MPs) in terrestrial ecosystems are higher than those in marine ecosystems. Here, we applied the zymography to investigate how MPs — polyethylene [PE], and polyvinyl chloride [PVC]) at two levels (0.01% and 1% soil weight) impacted the spatial distribution of soil hydrolases, nutrient availability, and rice growth in paddy soil. MPs increased the above-ground biomass by 13.0%–15.5% and decreased the below-ground biomass by 8.0%–15.1%. Addition of 0.01% and 1% MPs reduced soil NH4+ content by 18.3%–63.2% and 52.2%–80.2%, respectively. The average activities of N- and P-hydrolases increased by 0.8%–4.8% and 1.9%–6.3% with addition of MPs, respectively. The nutrient uptake by rice plants and the enzyme activities in hotspots increased with MP content in soil. The accumulation of MPs in paddy soil could provide an ecological niche that facilitates microbial survival, alters the spatial distribution of soil hydrolases, and decreases nutrient availability. [Figure not available: see fulltext.].
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