During the decomposition process of soil organic carbon (SOC), microbial products such as microbial necromass and microbial metabolites may form an important stable carbon (C) pool, called ...microbially derived C, which has different decomposition patterns from plant-derived C. However, current Earth System Models do not simulate this microbially derived C pool separately. Here, we incorporated the microbial necromass pool to the first-order kinetic model and the Michaelis-Menten model, respectively, and validated model behaviors against previous observation data from the decomposition experiments of
C-labeled necromass. Our models showed better performance than existing models and the Michaelis-Menten model was better than the first-order kinetic model. Microbial necromass C was estimated to be 10-27% of total SOC in the study soils by our models and therefore should not be ignored. This study provides a novel modification to process-based models for better simulation of soil organic C under the context of global changes.
Altered freeze‐thaw cycle (FTC) patterns due to global climate change may affect nitrogen (N) cycling in terrestrial ecosystems. However, the general responses of soil N pools and fluxes to different ...FTC patterns are still poorly understood. Here, we compiled data of 1519 observations from 63 studies and conducted a meta‐analysis of the responses of 17 variables involved in terrestrial N pools and fluxes to FTC. Results showed that under FTC treatment, soil NH4+, NO3−, NO3− leaching, and N2O emission significantly increased by 18.5%, 18.3%, 66.9%, and 144.9%, respectively; and soil total N (TN) and microbial biomass N (MBN) significantly decreased by 26.2% and 4.7%, respectively; while net N mineralization or nitrification rates did not change. Temperate and cropland ecosystems with relatively high soil nutrient contents were more responsive to FTC than alpine and arctic tundra ecosystems with rapid microbial acclimation. Therefore, altered FTC patterns (such as increased duration of FTC, temperature of freeze, amplitude of freeze, and frequency of FTC) due to global climate warming would enhance the release of inorganic N and the losses of N via leaching and N2O emissions. Results of this meta‐analysis help better understand the responses of N cycling to FTC and the relationships between FTC patterns and N pools and N fluxes.
1. Freeze‐thaw cycle significantly increased inorganic N, NO3− leaching, and N2O emission, but significantly decreased soil total N and microbial biomass nitrogen. 2. Temperate and cropland ecosystems with relatively high soil nutrient contents were more responsive to FTC than alpine and arctic tundra ecosystems with rapid microbial acclimation. 3. Altered FTC patterns (such as increased duration of FTC, temperature of freeze, amplitude of freeze, and frequency of FTC) due to global climate warming would enhance the release of inorganic N and the losses of N via leaching and N2O emissions.
Microbes are widely distributed in soils and play a very important role in nutrient cycling and ecosystem services. To understand the biogeographic distribution of forest soil bacteria, we collected ...115 soil samples in typical forest ecosystems across eastern China to investigate their bacterial community compositions using Illumina MiSeq high throughput sequencing based on 16S rRNA. We obtained 4,667,656 sequences totally and more than 70% of these sequences were classified into five dominant groups, i.e., Actinobacteria, Acidobacteria, Alphaproteobacteria, Verrucomicrobia, and Planctomycetes (relative abundance >5%). The bacterial diversity showed a parabola shape along latitude and the maximum diversity appeared at latitudes between 33.50°N and 40°N, an area characterized by warm-temperate zones and moderate temperature, neutral soil pH and high substrate availability (soil C and N) from dominant deciduous broad-leaved forests. Pairwise dissimilarity matrix in bacterial community composition showed that bacterial community structure had regional similarity and the latitude of 30°N could be used as the dividing line between southern and northern forest soils. Soil properties and climate conditions (MAT and MAP) greatly accounted for the differences in the soil bacterial structure. Among all soil parameters determined, soil pH predominantly affected the diversity and composition of the bacterial community, and soil pH = 5 probably could be used as a threshold below which soil bacterial diversity might decline and soil bacterial community structure might change significantly. Moreover, soil exchangeable cations, especially Ca(2+) (ECa(2+)) and some other soil variables were also closely related to bacterial community structure. The selected environmental variables (21.11%) explained more of the bacterial community variation than geographic distance (15.88%), indicating that the edaphic properties and environmental factors played a more important role than geographic dispersal limitation in determining the bacterial community structure in Chinese forest soils.
In this work, a convenient and dual-signal readout optical sensing platform for the sensitively and selectively determination of beta-glucosidase (β-Glu) activity was reported using protein-inorganic ...hybrid nanoflowers BSA-Cu
3
(PO
4
)
2
·3H
2
O possessing peroxidase-mimicking activity. The nanoflowers (NFs) were facilely synthesized through a self-assembled synthesis strategy at room temperature. The as-prepared NFs could catalytically convert the colorless and non-fluorescent Amplex Red into colored and highly fluorescent resorufin in the presence of hydrogen peroxide via electron transfer process. β-Glu could hydrolyze cyanogenic glycoside, using amygdalin (Amy) as a model, into cyanide ions (CN
−
), which can subsequently efficiently suppress the catalytic activity of NFs, accompanied with the fluorescence decrease and the color fading. The concentration of CN
−
was controlled by β-Glu-triggered enzymatic reaction of Amy. Thus, a sensing system was established for fluorescent and visual determination of β-Glu activity. Under the optimum conditions, the present fluorescent and visual bimodal sensing platform exhibited good sensitivity for β-Glu activity assay with a detection limit of 0.33 U·L
−1
. The sensing platform was further applied to determinate β-Glu in real samples and satisfactory results were attained. Additionally, the optical sensing system can potentially be a promising candidate for β-Glu inhibitors screening.
To demonstrate the responses of plant (Pakchoi) and soil to poly-γ-glutamic acid (γ-PGA) is essential to better understand the pathways of the promotional effect of γ-PGA on plant growth. In this ...study, the effects of γ-PGA on soil nutrient availability, plant nutrient uptake ability, plant metabolism and its distribution in a plant-soil system were tested using labeled γ-PGA synthesized from
C
-
N-L-glutamic acid (L-Glu). γ-PGA significantly improved plant uptake of nitrogen (N), phosphorus (P), and potassium (K) and hence increased plant biomass. γ-PGA greatly strengthened the plant nutrient uptake capacity through enhancing both root biomass and activity. γ-PGA affected carbon (C) and N metabolism in plant which was evidenced with increased soluble sugar contents and decreased nitrate and free amino acids contents. About 26.5% of the γ-PGA-N uptake during the first 24 h, after γ-PGA application, was in the form of intact organic molecular. At plant harvest, 29.7% and 59.4% of γ-PGA-
N was recovered in plant and soil, respectively, with a 5.64% of plant N nutrition being derived from γ-PGA-N. The improved plant nutrient uptake capacity and soil nutrient availability by γ-PGA may partly explain the promotional effect of γ-PGA, however, the underlying reason may be closely related to L-Glu.
•Chinese pine forest had higher winter soil CO2 flux than larch forest.•Snow depth and inorganic N did not explain the differences in winter CO2 flux.•Soil microbes explained the differences in ...winter CO2 flux between the two sites.•Litter layer was important to winter CO2 flux, especially when snow depth was <30 cm.
Larch and Chinese pine plantation forests are important carbon (C) sinks in the temperate regions, especially in China. However, their soil respiration in winter is still poorly studied. Here we explored the different microbial characteristics and winter soil respiration in larch and Chinese pine plantation forests in northeastern China, which has similar climate and basic soil characteristics. Results showed that both mean and cumulative winter soil CO2 fluxes were significantly higher in Chinese pine forest (0.45 µmol m−2 s−1 and 46.39 g C m−2, respectively) than in larch forest (0.25 µmol m−2 s−1 and 25.92 g C m−2, respectively). Snow depth and inorganic nitrogen (N) could not explain the differences in winter soil respiration between the two sites. Instead, Chinese pine forest had higher soil microbial biomass, fungi abundance, F/B (ratio of fungi to bacteria), and extracellular enzymatic activities (EEAs) than larch forest, which could lead to higher winter soil respiration in Chinese pine forest than in larch forest. Our findings indicated that the thermal insulation effect of litter cover was important to winter soil respiration, especially when the snow cover depth was less than 30 cm. Soil microbes played a more important role in soil respiration than soil nutrient status and should be carefully considered for better estimation of the C budget in different forest ecosystems. Although soil respiration was higher in Chinese pine forest, soil organic C content was also higher, suggesting its better C sequestration capacity than larch forest.
Nitrous oxide (N2O) is an important greenhouse gas and is involved in the destruction of ozone layer. However, the underlying mechanisms of the high soil N2O emission during the freeze-thaw (FT) ...period are still unclear. Here, we conducted a mesocosm study with high frequency in situ measurements to explore the responses of soil microbes to the FT cycles and their influences on soil N2O emission. We found the high N2O emission rate during the FT period was mainly due to the release of substrates, the maintenance of high enzyme activities at the freezing stage, and the fast recovery of microbial biomass nitrogen (MBN) and high microbial activities at the thawing stage. Physical isolation of previously produced N2O was an important mechanism for the higher N2O flux at the thawing stage. With increasing numbers of the FT cycles, MBN at the thawing stage remained stable and potential dehydrogenase activities at the thawing stage also remained stable after the first eight FT cycles and only declined during the last two cycles, suggesting the sustainability of the biological mechanisms. Our study suggests that although MBN declined, microbial enzymes could maintain high activities at a few degrees Celsius below zero in this temperate forest soil and produce high N2O fluxes even at the freezing stage, which were trapped under the ice layer and released at the thawing stage, resulting in high soil N2O emission during the FT period.
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•Soil N2O emission was high during the freeze-thaw (FT) period in the temperate forest.•Soil enzyme activities were maintained at high level at the freezing stages during the FT period.•Physical isolation of previously produced N2O at the freezing stage was an important mechanism for N2O emission.•The biological mechanism could sustain after several numbers of the FT cycles.
Background
The production and consumption of greenhouse gases (GHGs) in soils are largely regulated by biological processes. Increasing atmospheric CO
2
may alter these processes, thereby affecting ...GHG emissions and their feedbacks to climate.
Methods and aims
Here, we used an open top chamber (OTC) experiment to examine the effects of elevated CO
2
for ten years on soil GHG fluxes in a
Quercus mongolica
dominated system in northeastern China.
Results
Our results showed that elevated CO
2
increased soil CO
2
emissions, consistent with increased microbial biomass and the abundance of arbuscular mycorrhizal fungi and actinomycetes. Additionally, elevated CO
2
increased CH
4
uptake due to stimulated growth of methanotrophs. The seasonal mean soil N
2
O flux was not changed by elevated CO
2
, consistent with unchanged ammonia oxidizing bacteria, archaea and denitrifiers, which was probably due to large variations between the individual OTCs and with time. However, seasonal cumulative soil N
2
O emissions increased by 64.7% under elevated CO
2
. Our results also hinted that nitrification by ammonia oxidizing archaea was the major process of soil N
2
O emissions.
Conclusions
In our study elevated CO
2
increased soil GHG emissions and the cumulative global warming potential by 27.8%, causing an important positive feedback to climate change.
•Experimental removal or addition of 50% of the snow pack was conducted throughout the winter.•A rapid and transient response of microbes to temperature was found under snow manipulation.•Snow ...addition enhanced soil CO2 effluxes only when soil temperature significantly increased.•PLFA analysis confirmed transient changes in microbial communities by snow addition.•Cumulative soil CO2 effluxes were not affected by altered snow depth.
Global climate change is altering snow depth in winter, which could significantly affect soil respiration and microbial communities. However, belowground responses are still uncertain as they depend on the thermal effects on soils, the acclimation of soil microbial communities and ecosystem type. Here, we conducted a snow manipulation experiment including 50% removal of snowpack (mean snow depth after treatment was 3.1 ± 0.7 cm), ambient snow (mean snow depth was 6.3 ± 0.7 cm), and 50% increase of snowpack (mean snow depth after treatment was 9.6 ± 1.5 cm) to explore the effects of altered snow depth on winter soil respiration and microbial communities in a mid-latitude plantation forest with continental climate with dry winters. Winter soil CO2 effluxes varied from 0.09 to 0.84 µmol m−2 s−1 with a mean of 0.32 ± 0.07 µmol m−2 s−1. The cumulative soil CO2 effluxes from 11 December 2014 to 21 March 2015 were 27.3 ± 1.1, 26.5 ± 2.1, and 29.5 ± 1.3 g C m−2 under reduced, ambient and added snowpack, which corresponded to 5.7 ± 0.2%, 5.5 ± 0.3%, and 5.8 ± 0.1% of the annual soil CO2 effluxes, respectively. Our one-year observation results suggested that although snow reduction decreased soil temperature, microbial biomass carbon (MBC) and soil respiration did not change, suggesting microbial adaptation to cold conditions between −4 °C and −1 °C. In contrast, snow addition increased soil temperature, MBC, and soil respiration. Microbial community structure (F/B, ratio of fungi to bacteria) was also changed and soil enzymatic (β-glucosidase) activities increased under snow addition. However, these effects were short-lived and disappeared when soil temperature did not differ between the addition and control plots at the 14th day after treatment. These results indicated that the responses of soil microbial communities and respiratory activities to changing soil temperature were rapid and the response of soil respiration to snow addition was transient. Consequently, altered snow depth did not affect cumulative soil CO2 effluxes. Our study suggests that wintertime soil respiration rates are generally low and snow manipulation has minor effects on soil CO2 efflux, soil temperature (the determinant driver of wintertime soil CO2 efflux) and soil microbial biomass at our site.
Understanding the physiological adaptations of non-treeline trees to environmental stress is important to understand future shifts in species composition and distribution of current treeline ecotone. ...The aim of the present study was to elucidate the mechanisms of the formation of the upper elevation limit of non-treeline tree species, Picea jezoensis, and the carbon allocation strategies of the species on Changbai Mountain. We employed the 13C in situ pulse labeling technique to trace the distribution of photosynthetically assimilated carbon in Picea jezoensis at different elevational positions (tree species at its upper elevation limit (TSAUE, 1,700 m a.s.l.) under treeline ecotone; tree species at a lower elevation position (TSALE, 1,400 m a.s.l.). We analyzed 13C and the non-structural carbohydrate (NSC) concentrations in various tissues following labeling. Our findings revealed a significant shift in carbon allocation in TSAUE compared to TSALE. There was a pronounced increase in δ13C allocation to belowground components (roots, soil, soil respiration) in TSAUE compared to TSALE. Furthermore, the C flow rate within the plant-soil-atmosphere system was faster, and the C residence time in the plant was shorter in TSAUE. The trends indicate enhanced C sink activity in belowground tissues in TSAUE, with newly assimilated C being preferentially directed there, suggesting a more conservative C allocation strategy by P. jezoensis at higher elevations under harsher environments. Such a strategy, prioritizing C storage in roots, likely aids in withstanding winter cold stress at the expense of aboveground growth during the growing season, leading to reduced growth of TSAUE compared to TSALE. The results of the present study shed light on the adaptive mechanisms governing the upper elevation limits of non-treeline trees, and enhances our understanding of how non-treeline species might respond to ongoing climate change.
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