Reduced Soil Respiration Research Articles

Turning Up the Heat: More Persistent Precipitation Regimes Weaken the Micro-Climate Buffering Capacity of Forage Grasses During a Hot Summer.

Developing climate-proof forage grasslands does not only require developing plant communities that are soil drought resistant, but also adept at buffering elevated atmospheric temperatures to minimize heat stress for plant and soil. Previous studies indicate that the emerging trend towards rainfall regimes with longer dry and wet spells negatively affects forage grass performance (i.e., greater physiological plant stress and yield loss) in Western Europe. We conducted a 120-day open-air experiment testing whether a hot summer (+3°C for the first 60 days) exacerbates the negative effects of increased persistence in precipitation regimes (PR) (3 vs. 30 days consecutive wet/dry) on the performance of four distinct forage varieties (Dactylis glomerata, Festuca arundinacea, Lolium perenne (tetraploid) and Lolium perenne (diploid)) across two soils differing in management history (permanent vs. temporary grasslands). Our results indicate that climate warming indeed worsens negative effects of more persistent PR on forage grass productivity and physiological plant stress by inducing more extreme soil drought and elevated micro-climatic temperatures, but permanent grassland soils with elevated organic carbon can buffer yields. Moreover, higher yielding varieties are more proficient at buffering soil surface and canopy temperatures and maintaining plant greenness and stomatal opening under water shortage and elevated temperatures (Dactylis and Festuca) were impacted less than those which could not (both Lolium cultivars). These results indicate that not only differences in resource-extraction traits but also the ability of a species to buffer its surrounding microclimatic conditions shapes its response to future climate change. Given the indirect positive effects such temperature-buffering traits may have on soil functioning (e.g., reduced soil respiration during heat waves limiting carbon loss), we argue that managers should also incorporate such traits when developing climate-proof forage grasslands.

Vegetation and Precipitation Patterns Define Annual Dynamics of CO2 Efflux from Soil and Its Components

Respiration of soil heterotrophs—mainly of bacteria and fungi—is a substantial part of carbon balance in terrestrial ecosystems, which tie up organic matter decomposition with the rise of atmospheric CO2 concentration. Deep understanding and prediction of seasonal and interannual variation of heterotrophic and autotrophic components of CO2 efflux from soil is limited by the lack of long-term, full-year measurements. To better understand the impact of current climate changes on CO2 emissions from soils in the mixed forest and mowed grassland, we measured CO2 efflux every week for 2 years. Heterotrophic (SOM-derived + leaf litter) and root-associated (root with rhizosphere microorganisms) components were partitioned by the root exclusion method. The total CO2 efflux from soil was averaged 500 g C m−2 yr−1 in the forest and 650 g C m−2 yr−1 in the grassland, with shares of the no-growing cold season (Nov–Mar) of 22% and 14%, respectively. The heterotrophic component of CO2 efflux from the soil averaged 62% in the forest and 28% in the grassland, and it was generally stable across seasons. The redistribution of the annual precipitation amounts as well as their deficit (droughts) reduced soil respiration by 33–81% and heterotrophic respiration by 24–57% during dry periods. This effect was more pronounced in the grassland (with an average decline of 56% compared to 39% in the forest), which is related to lower soil moisture content in the grassland topsoil during dry periods.

Effects of Prescribed Burns on Soil Respiration in Semi-Arid Grasslands

Carbon fluxes are valuable indicators of soil and ecosystem health, particularly in the context of climate change, where reducing carbon emissions from anthropogenic activities, such as forest fires, is a global priority. This study aimed to evaluate the impact of prescribed burns on soil respiration in semi-arid grasslands. Two treatments were applied: a prescribed burn on a 12.29 ha paddock of an introduced grass (Eragostis curvula) with 11.6 t ha−1 of available fuel, and a simulation of three fire intensities, over 28 circular plots (80 cm in diameter) of natural grasslands (Bouteloua gracilis). Fire intensities were simulated by burning with butane gas inside an iron barrel, which represented three amounts of fuel biomass and an unburned treatment. Soil respiration was measured with a soil respiration chamber over two months, with readings collected in the morning and afternoon. Moreover, CO2 emissions by combustion and productivity after fire treatment were quantified. The prescribed burns significantly reduced soil respiration: all fire intensities resulted in a decrease in soil respiration when compared with the unburned area. Changes in albedo increased the soil temperature; however, there was no relationship between changes in temperature and soil respiration; in contrast, precipitation highly stimulated it. These findings suggest that fire, under certain conditions, may not lead to more CO2 being emitted into the atmosphere by stimulating soil respiration, whereas aboveground biomass was reduced by 60%. However, considering the effects of fire in the long-term on changes in nutrient deposition, aboveground and belowground biomass, and soil properties is crucial to effectively quantify its impact on the global carbon cycle.

Response of soil biochemical properties and ecosystem function to microplastics pollution

Microplastics (MPs)-induced changes in soil nutrient cycling and microbial activity may pose a potential risk to soil ecosystem. Although some studies have explored these topics, there is still a large space for exploration and a relative lack of research on the mechanism by which soil health and its functions are affected by these changes. Thus, this study investigated the effects of polyethylene (PE) MPs with two particle sizes (13 μm and 130 μm) at five concentrations (0%, 1%, 3%, 6% and 10%, w/w) on soil biochemical properties and ecosystem function. The findings revealed that the exposure to 13 μm MPs significantly reduced soil respiration (Res) rate, β-glucosidase (Glu) and catalase (CAT) activity, which accompanied with enhanced urease activity and decreased soil pH, available phosphorus (AP), dissolved reactive phosphorus (DRP), dissolved organic carbon (DOC) and available potassium (AK) content in most cases. However, 130 μm MPs exerted negligible influence on the DOC and DRP content, Glu and CAT activity. High concentrations of 130 μm MPs significantly reduced soil pH, total dissolved nitrogen (TDN), AP and AK content, but significantly increased soil Res rate. Overall, soil ecosystem function was significantly reduced by the addition of MPs. The Res rate, soil AP and DRP content and Glu activity were the most important predictors of soil ecosystem function. We found that the risk posed by MPs to soil ecosystem function was dose-dependent and size-dependent. These findings underscore that MPs can alter soil functions related to soil nutrient cycling and provide further insights into MPs behavior in agroecosystems.

No-Tillage Treatment with Total Green Manure Mulching Reduces Soil Respiration by Regulating Soil Water Content Affecting Heterotrophic Respiration

Green manure is widely applied in agricultural production due to its beneficial soil modification and fertilization effects. However, the mechanisms underlying the effects of green manure return methods on soil respiration (Rs) and its components remain unclear. This study aimed to investigate the effects of green manure return methods on Rs in maize fields by quantifying Rs levels. A field experiment was conducted from 2021 to 2023 in the inland river oasis irrigation area of Gansu, with five treatment conditions: tillage with a full quantity of green manure incorporated into the soil (TG), no tillage with a full quantity of green manure mulched on the soil surface (NTG), tillage with roots incorporated into the soil and above-ground green manure removed (T), no tillage with above-ground manure removed (NT), and conventional tillage and leisure (CT). The results showed that, compared with CT, the NTG treatment increased the maize grain yield while reducing the soil heterotrophic respiration rate (Rh) by 8.5–9.8% and Rs by 6.7–8.7%, but did not significantly affect the soil autotrophic respiration rate (Ra), and decreased the carbon emission efficiency (CEE) by 20.8–25.6%. The increase in the soil water content (SWC) significantly reduced Rh during all growth periods, which was the primary factor in the reduction of Rs. Additionally, the net ecosystem productivity carbon sequestration (NEP-C) of the farmland ecosystem was positive under this system, indicating that the soil acts as a carbon “sink”. Therefore, a no-tillage treatment with a full quantity of green manure mulched on the soil surface can be used as a reasonable green manure return method to reduce carbon emissions from farmland in arid oasis irrigation regions.

Consecutive annual mowing reduces soil respiration and increases the proportion of autotrophic component in a meadow steppe

BcakgroundSoil respiration (Rs), as the second largest CO2 emissions of terrestrial ecosystems, is sensitive to disturbance and consequent environmental changes. Mowing is strategically implemented as an management approach and has the potential to influence carbon cycling in meadow steppes. However, it remains unclear how and why Rs and its heterotrophic (Rh) and autotrophic (Ra) components respond to consecutive mowing and associated ecological consequences. Here, we conducted a field mowing experiment in a meadow steppe in 2018 and monitored Rs, Rh, and Ra from 2019 to 2022.ResultsWe observed a significant reduction in Rs by 4.8% across four years, primarily attributed to a decrease in Rh. This decline in Rs intensified over time, indicating an accumulative effect of mowing. In addition, mowing induced an generally increasing Ra/Rs ratio over the experimental years with a simultaneous increase in the ratio of belowground to aboveground biomass (BGB/AGB). Furthermore, structural equation modeling results revealed that the decline in Rs was largely ascribed to reduced microbial biomass carbon (MBC) under mowing, while the increased Ra/Rs was primarily explained by the enhanced BGB/AGB. Partial regression analysis suggested that the biotic factor of microbial biomass dominated changes in soil respiration induced by mowing rather than abiotic soil temperature.ConclusionsOur findings showed that consecutive mowing decreased Rs and raised Ra/Rs in meadow steppe by decreasing plant biomass and altering the proportion of biomass allocation. This observed decline in Rs would help to reduce CO2 concentration in atmosphere as well as alleviate global warming. However, considering the concurrent lower microbial biomass, the potential positive impacts of mowing on climate and ecosystem function should be reevaluated in future grassland management practices.

Influence of Biochar-Reinforced Hydrogel Composites on Growth and Biochemical Parameters of Bean Plants and Soil Microbial Activities under Different Moisture Conditions

Hydrogels have shown promise in improving soil quality and alleviating plant drought stress. This study investigated the effectiveness of four hydrogel composites composed of polyvinyl alcohol, sodium alginate, and pine or olive tree biochar in improving bean (Phaseolus vulgaris) plant growth and soil microbial activities. The experiment was conducted in natural soil, where biochar–hydrogel composites were applied at a concentration of 0.75% hydrogel per soil weight (w/w) for 35 days under two different moisture conditions: adequate moisture (70% of water holding capacity (WHC)) and drought stress (40% WHC). The results showed variation between hydrogel composites and, more importantly, between water regimes. Under water deficit conditions, biochar–hydrogel composites consistently caused a decrease in plant weight and in chlorophyll (CHL) CHLa/CHLb ratio. Furthermore, antioxidant enzyme activities and malondialdehyde and protein levels generally increased in contrast to the observations at 70% WHC. Regarding microbial activities, the composites reduced soil respiration (12–38%) while promoting phosphatase activity (42–65%) under both moisture regimes. Overall, the introduction of hydrogel composites did not show consistently positive effects on either plants or soil microorganisms. To thoroughly evaluate the efficacy of these hydrogels as soil amendments, further studies are needed, considering different soil types, plant species, and hydrogel application rates.

Tillage Depth Regulation and the Effect of Straw Return on Soil Respiration in Farmland

Straw return and tillage depth treatments are one of the most important agricultural management measures that affect farmland soil respiration, but the mechanism of their interaction affecting farmland soil respiration remains unclear. Therefore, 116 published research articles were used through Meta-analysis technology for dryland farmland ecosystems in China to explore the effects of straw return and tillage depth treatments and their interaction on farmland soil respiration and its regulatory factors, which will provide important data support and a theoretical basis for achieving "carbon neutrality" in farmland ecosystems. The results showed that no tillage reduced soil respiration by 8.3%, and the effects of shallow and deep tillage treatments on soil respiration were not significant, but the increase in soil respiration still showed a trend of deep tillage>shallow tillage>no tillage. However, both shallow and deep tillage had relatively small effects on soil respiration and soil organic carbon (SOC), whereas no tillage reduced soil respiration by 8.3% and increased SOC by 7.05%. Therefore, implementing no tillage measures is of great significance for soil carbon sequestration and emission reduction in farmland ecosystems. In addition, tillage depth significantly regulated the impact of straw return on soil respiration, and the increase in soil respiration showed a trend of deep tillage straw return>shallow tillage straw return>no tillage straw return, with an overall average increase of 14.51%. The increase in soil respiration under different tillage depth treatments after straw return was closely related to the change in soil bulk density, crop yield, SOC, soil temperature, and moisture, and the contribution to the increase in soil respiration showed a trend of soil bulk density>crop yield>soil organic carbon>soil moisture>soil temperature. However, SOC increased by 29.32%, 10.12%, and 23.94%, respectively, in the deep tillage straw return, shallow tillage straw return, and no tillage straw return treatments, whereas soil respiration increased by 29.32% and 18.92%, respectively, in the deep tillage straw return and shallow tillage straw return treatments, and it only increased by 1.2% in the no tillage straw return treatment. Therefore, no tillage straw return was also beneficial to soil carbon sequestration and emission reduction in farmland ecosystems. Thus, in the dryland farmland ecosystem of China, tillage depth treatments regulated the impact of straw return on soil respiration, which was mainly related to soil physical and chemical properties, especially being closely related to soil bulk density. Moreover, no tillage and no tillage straw return are important agricultural management measures that are conducive to soil carbon sequestration and emission reduction.

Addition of biochar decreased soil respiration in a permanent no-till cover crop system for organic soybean production

The increase in soil carbon sequestration under long-term no-till (NT) and cover crop management has been shown to form part of a sustainable agricultural management practice system. Along with the increase in soil organic carbon (SOC), soil respiration in this system was also enhanced by the increased soil temperature through the decomposition that causes carbon loss from the soil. To overcome this issue, biochar can be applied. However, the addition of biochar into this system is not well studied. Therefore, the aim of this study was to investigate the effect of this system on soil respiration. The experiment was conducted at the Center for International Field Agriculture Research & Education, Ibaraki University. Long-term tillage practices, such as NT and moldboard plowing (MP), cover crops such as rye (RY) and fallow (FA), and biochar application such as with biochar (WB) and no biochar (NB) were applied to a split–split plot in a randomized complete block design with four replications. The daily CO2 flux was measured every week at 9:00–11:00 a.m. The daily soil respiration was affected by tillage and cover crop with NT practice had significantly higher daily CO2 flux than that of MP (23.8%–107.4% and 38.0%–107.8%), while RY had higher flux than that of FA (11.9%–81.2% and 34.9%–65.4%) in 2020 and 2021 soybean growing season, respectively. Additionally, in the 2020 cover crop growing season RY also increased daily CO2 flux approximately 41.8%–88.2% compared to FA. Biochar addition significantly reduced soil respiration in soybean and cover crop seasons compared to NB by 24.0%–50.7% and by 25.9%–48.3%, respectively. This reduction in soil respiration by the biochar decreased annual CO2 emissions by 17.6% and 13.0% in 2020 and 2021. The values of these emissions ranged from 9.6 Mg ha−1 for MP FA WB to 18.9 Mg ha−1 for MP RY NB in 2020 and from 7.5 Mg ha−1 for MP FA WB to 13.7 Mg ha−1 for NT FA NB in 2021. This study highlights the crucial role of biochar in reducing soil respiration and enhancing SOC sequestration. The addition of biochar into this system was able to reduce soil respiration by regulating the soil temperature, soil moisture, and protect the SOC from decomposition. Biochar addition also increased the SOC and decreased the soil bulk density, which improves soil porosity. Therefore, these findings would be very useful to be included within the global scenario of soil organic matter management.

Response of soil CO2 emissions and water-carbon use efficiency of winter wheat to different straw returning methods and irrigation scenarios.

The shortage of water resources and the increase of greenhouse gas emissions from soil seriously restrict the sustainable development of agriculture. Under the premise of ensuring a stable yield of winter wheat through a reasonable irrigation scenario, identifying a suitable straw returning method will have a positive effect on agricultural carbon sequestration and emission reduction in North China Plain. Straw burying (SR) and straw mulching (SM) were adopted based on traditional tillage under in the winter wheat growing season of 2020-2021 and 2021-2022. Three irrigation scenarios were used for each straw returning method: no irrigation (I0), irrigation 60 mm at jointing stage (I1), and irrigation of 60 mm each at the jointing and heading stages (I2). Soil moisture, soil respiration rate, cumulative soil CO2 emissions, yield, water use efficiency (WUE) and soil CO2 emission efficiency (CEE) were mainly studied. The results showed that, compared to SM, SR improved the utilization of soil water and enhanced soil carbon sequestration. SR reduced soil respiration rate and cumulative soil CO2 emissions in two winter wheat growing seasons, and increased yield by increasing spike numbers. In addition, with an increase in the amount of irrigation, soil CO2 emissions and yield increased. Under SR-I1 treatment, WUE and CEE were the highest. SR-I1 increases crop yields at the same time as reducing soil CO2 emissions. The combination of SR and irrigation 60 mm at jointing stage is a suitable straw returning irrigation scenario, which can improve water use and reduce soil CO2 emission in NCP. © 2023 Society of Chemical Industry.

Responses of Soil Respiration to the Interactive Effects of Warming and Drought in Alfalfa Grassland on the Loess Plateau

Elevated temperature and frequent drought events under global climate change may seriously affect soil respiration. However, the underlying mechanism of the effects of warming and drought on soil respiration is not fully understood in the context of the Loess Plateau. This study examined the response of soil respiration (Rs) to multiple factors, including warming (W), drought (P), and their interaction (WP), in the semi-arid grassland of the Loess Plateau in Northwest China. The research period was from May to November 2022, with an open-top heating box used for warming and a rain shelter used for drought. The results showed the following: (1) Rs ranged from 1.67 μmol m−2 s−1 to 4.77 μmol m−2 s−1, with an average of 3.36 ± 0.07 μmol m−2 s−1. The cumulative soil carbon flux ranged from 500.97 g C·m−2 to 566.97 g C·m−2, and the average cumulative soil respiration was 535.28 ± 35.44 g C·m−2. (2) Warming increased Rs by 5.04 ± 3.11%, but drought inhibited Rs by 3.40 ± 3.14%, and the interaction between warming and drought significantly reduced soil respiration by 11.27 ± 3.89%. (3) The content of particulate organic carbon (POC), dissolved organic carbon (DOC), soil organic carbon (SOC), and readily oxidized carbon (ROC) decreased with the increased soil depth. ROC after W and WP treatments was significantly higher than that of the control, and POC after P treatment was significantly higher than CK (p < 0.05). (4) The seasonal variation of soil respiration was positively correlated with soil temperature, soil water content, plant height, and leaf area index (p < 0.05), but the response rules differed during different regeneration periods. Soil water content; soil water content and leaf area index; and soil water content, soil temperature, and leaf area index were the factors that regulated the variation in soil respiration in the first, second, and third regeneration periods, respectively. These results clearly showed the limiting effect of drought stress on the coupling between temperature and soil respiration, especially in semi-arid regions. Collectively, the variations in soil respiration under warming, drought, and their interactions were further regulated by different biotic and abiotic factors. Considering future warming, when coupled with increased drought, our findings indicate the importance of considering the interactive effects of climate change on soil respiration and its components in arid and semi-arid regions over the next decade.

Artificial light at night (ALAN) causes shifts in soil communities and functions.

Artificial light at night (ALAN) is increasing worldwide, but its effects on the soil system have not yet been investigated. We tested the influence of experimental manipulation of ALAN on two taxa of soil communities (microorganisms and soil nematodes) and three aspects of soil functioning (soil basal respiration, soil microbial biomass and carbon use efficiency) over four and a half months in a highly controlled Ecotron facility. We show that during peak plant biomass, increasing ALAN reduced plant biomass and was also associated with decreased soil water content. This further reduced soil respiration under high ALAN at peak plant biomass, but microbial communities maintained stable biomass across different levels of ALAN and times, demonstrating higher microbial carbon use efficiency under high ALAN. While ALAN did not affect microbial community structure, the abundance of plant-feeding nematodes increased and there was homogenization of nematode communities under higher levels of ALAN, indicating that soil communities may be more vulnerable to additional disturbances at high ALAN. In summary, the effects of ALAN reach into the soil system by altering soil communities and ecosystem functions, and these effects are mediated by changes in plant productivity and soil water content at peak plant biomass. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Shading effect from trees reduces soil respiration in urban lawns

Shading effect from trees reduces soil respiration in urban lawns

Impacts of snow-farming on alpine soil and vegetation: A case study from the Swiss Alps

Snow-farming is one of the adaptive strategies used to face the snow deficit in ski resorts. We studied the impact of a shifting snow-farming technique on a pasture slope in Adelboden, Switzerland. Specifically, we compared plots covered by a compressed snow pile for 1.5, 2.5 or 3.5 years, which then recovered from the snow cover for three, two or one vegetation seasons, respectively, with control plots situated around the snow pile.In plots with >1.5 years of compressed snow pile, plant mortality was high, recovery of vegetation was very slow, and few plant species recolonized the bare surface. Soil biological activity decreased persistently under prolonged snow cover, as indicated by reduced soil respiration. The prolonged absence of fresh plant litter and root exudates led to carbon (C) limitation for soil microbial respiration, which resulted in a significant decrease in the ratio of total organic carbon to total nitrogen (TOC/TN) under the snow pile.Microbial C, nitrogen (N) and phosphorus (P) immobilization decreased, while dissolved N concentration increased with compressed snow cover. Longer snow cover and a subsequent shorter recovery period led to higher microbial C/P and N/P but lower microbial C/N. Nitrate and ammonium were released massively once the biological activity resumed after snow clearance and soil aeration.The soil microbial community composition persistently shifted towards oxygen-limited microbes with prolonged compressed snow cover. This shift reflected declines in the abundance of sensitive microorganisms, such as plant-associated symbionts, due to plant mortality or root die-off. In parallel, resistant taxa that benefit from environmental changes increased, including facultative anaerobic bacteria (Bacteroidota, Chloroflexota), obligate anaerobes (Euryarchaeota), and saprophytic plant degraders.We recommend keeping snow piles in the same spot year after year to minimize the area of the impacted soil surface and plan from the beginning soil and ecosystem restoration measures.

Long-term nitrogen addition reduced soil respiration contributed by decline in the understory plant cover but not species richness

Long-term nitrogen addition reduced soil respiration contributed by decline in the understory plant cover but not species richness

Research Progress on Effects of Biochar on Soil Environment and Crop Nutrient Absorption and Utilization

As a by-product generated from the pyrolysis of biomass, biochar is extraordinary for improving the soil environment of agricultural fields, improving soil fertility, and promoting nutrient uptake and the utilization of crops. In recent years, breakthroughs in progress have been made regarding the fertility value of biochar and in investigations into the physicochemical properties of soil and into plant nutrient utilization. This review focuses on the physicochemical and biological properties of soil, on soil pollution remediation, on greenhouse gas emissions, and on the effects of biochar on the uptake and utilization of soil nutrients and plant nutrients, as well as on the preparation of biochar, and on biochar produced under different conditions. The results of the relevant studies show that the main characteristics of biochar depend on the biochemical properties and pyrolysis temperature of raw materials, which play an important role in nutrient transport and transformation in the soil. At low temperatures (≤400 ℃), the biochar prepared from manure and waste contains a large amount of nitrogen, which can be used as a nutrient source for plants. In addition, biochar enhances soil fertilizer retention by reducing soil nutrient loss, which in turn promotes nutrient uptake and utilization by crops. By controlling pyrolysis temperature and by optimizing biochar input, one can effectively reduce soil respiration, as well as reduce carbon emissions to achieve the goal of controlling carbon sources and increasing carbon sinks. Therefore, a long-term series of mapping studies on the effects of biochar application on agricultural ecosystems should be conducted, which in turn, it is hoped, will provide a theoretical reference for the physiological and ecological effects of biochar croplands.

Continuous cropping of cut chrysanthemum reduces rhizospheric soil bacterial community diversity and co-occurrence network complexity

Long-term continuous cropping causes a significant decline in the quality of cut chrysanthemum (Chrysanthemum morifolium Ramat.), but the microbial mechanism behind it remains unclear. Here, we examined the impacts of different numbers of years of continuous cropping on the bacterial communities and enzymatic activities in the rhizospheric soil of cut chrysanthemum. Our results showed that continuous cut chrysanthemum cropping for 6 years (Y6) or 12 years (Y12) significantly decreased (P < 0.05) the soil respiration rate and enzymatic activities of alkaline phosphatase and β-glucosidase compared to cropping for only 1-year (Y1). 12 years of continuous cropping resulted in significant decreases in soil bacterial numbers and α-diversity (e.g., Shannon index). Continuous cropping treatments shifted the bacterial community composition, lowering the relative abundances of the phyla Proteobacteria and Acidobacteria and increasing the relative abundances of Actinobacteria and Chloroflexi. Moreover, continuous cropping reduced the bacterial network complexity relative to noncontinuous cropping. Structural equation modeling (SEM) showed that long-term continuous cropping significantly decreased the soil bacterial count and community diversity mainly because of the limitation of soil organic carbon and total nitrogen, which in turn led to a reduction in soil respiration. Overall, our results demonstrated that continuous cut chrysanthemum cropping for 12 years had negative impacts on soil bacterial diversity, community complexity and soil biological activity.

Effect of nonbiodegradable microplastics on soil respiration and enzyme activity: A meta-analysis

Nonbiodegradable microplastics (MPs) are emerging contaminants in the environment and potentially threaten soil health. In recent years, the impact of MPs on soil ecology has attracted widespread attention, but the responses of soil respiration and enzyme activity to MPs exposure remain unclear. Here, a meta-analysis including 1980 observations was used to assess the effects of MPs on soil microbial activity. MPs exposure significantly (p < 0.05) increased soil respiration by 18.2 % but did not significantly (p > 0.05) affect soil enzyme activity; moreover, these effects varied with MP type, concentration, size, and exposure period. The amendment of polypropylene (PP) MP increased soil respiration and enzyme activity by 58.8 % and 10.2 %, respectively, whereas exposure to polyethylene terephthalate (PET), polyethylene (PE) and polystyrene (PS) MPs reduced soil enzyme activities by 13.0 %, 6.8 % and 5.0 %, respectively. The soil respiration was unaffected and increased when the MPs concentrations were below and above 5 %, respectively, whereas soil enzyme activity was stimulated and inhibited when the MPs concentrations were less and >10 %, respectively. The size of MPs only significantly (p < 0.05) affected the response of soil respiration to MPs, as small (<500 μm) and large (≥500 μm) sizes of MPs increased and reduced soil respiration by 53.4 % and 5.8 %, respectively. Short-term (≤30 days) exposure to MPs increased soil respiration by 50.2 %, whereas the presence of MPs inhibited soil enzyme activity by 3.3 % when the incubation period ranged from 30 to 100 days. In addition, MPs exposure significantly (p < 0.05) increased soil respiration by 77.9 % in alkaline soil (pH > 7.5) and by 41.6 % in the absence of plants. The amendment of MPs significantly (p < 0.05) increased and reduced soil enzyme activities in acidic and alkaline soils by 4.3 % and 5.5 %, respectively, and significantly (p < 0.05) improved soil enzyme activity by 4.5 % in the presence of plants. Specifically, MPs significantly (p < 0.05) increased the activities of acid phosphatase and fluorescein diacetate hydrolase by 8.3 % and 17.1 %, respectively, but did not significantly (p > 0.05) influence urease, β-glucosidase, and catalase activities. Overall, our results suggested that MPs have nonnegligible impacts on soil microbial activity, and it is urgently necessary to explore the long-term effects of MPs on soil ecology in the natural environment.

Canada Goldenrod Invasion Regulates the Effects of Soil Moisture on Soil Respiration

Canada goldenrod (Solidago canadensis L.) is considered one of the most deleterious and invasive species worldwide, and invasion of riparian wetlands by S. canadensis can reduce vegetation diversity and alter soil nutrient cycling. However, little is known about how S. canadensis invasion affects soil carbon cycle processes, such as soil respiration, in a riparian wetland. This study was conducted to investigate the effects of different degrees of S. canadensis invasion on soil respiration under different moisture conditions. Soil respiration rate (heterotrophic and autotrophic respiration) was measured using a closed-chamber method. S. canadensis invasion considerably reduced soil respiration under all moisture conditions. The inhibition effect on autotrophic respiration was higher than that on heterotrophic respiration. The water level gradient affects the soil autotrophic respiration, thereby affecting the soil respiration rate. The changes in soil respiration may be related to the alteration in the effective substrate of the soil substrate induced by the invasion of S. canadensis. While the effects of S. canadensis invasion were regulated by the fluctuation in moisture conditions. Our results implied that S. canadensis invasion could reduce the soil respiration, which further potentially affect the carbon sequestration in the riparian wetlands. Thus, the present study provided a reference for predicting the dynamics of carbon cycling during S. canadensis invasion and constituted a scientific basis for the sustainable development and management of riparian wetlands invaded by alien plants.

Nutrient addition, fire and grass competition affects biological nitrogen fixation in Vachellia sieberiana, and associated soil respiration

Biological nitrogen fixation (BNF) by woody legumes is likely to vary due to factors such as nutrient availability, fire and grazing. BNF may also alter soil properties by increasing soil fertility, consequently affecting rates of soil respiration. Given the widespread increase in woody plant density in southern African savannas, we investigate the factors influencing BNF in a common encroaching woody legume, Vachellia sieberiana. We conducted a pot experiment using a matrix of grass and seedlings of V. sieberiana. We then assessed the effects of increased nutrient availability (nitrogen (N) and phosphorous (P)) through fertilizer addition, as well as simulated fire and grazing on the rate of BNF, the number and weight of root nodules, and soil respiration. We found a significant decrease in BNF with fertilizer addition, and increases in BNF after fire application. Soil respiration increased with fertilizer addition and decreased after fire application. Grazing had no independent effect on any of the response variables. However, decreased grass biomass, and therefore reduced competitive interactions between tree seedlings and grasses, resulted in increased BNF across all treatments. Furthermore, we found that larger woody seedlings achieved higher rates of BNF, with a positive correlation between the rate of BNF and both the number and weight of root nodules. We conclude that BNF in V. sieberiana is facultative and strongly influenced by grass competition, with differing responses to varying environmental factors. Fertilizer addition suppresses BNF because the presence of readily available N negates the costs of fixation. V. sieberiana seedlings compensated for N lost by fire application by increasing BNF. Soil respiration was found to increase with fertilizer addition, possibly due to higher carbon (C) inputs into the soil. Conversely, fire reduced soil respiration by removing biomass, and thus reduced C input into the soil.