Jun 2023, Volume 5 Issue 2

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    Qing Qu, Hongwei Xu, Guobin Liu, Sha Xue

    ● The PSF of three species is positive in response to different soil origin.

    ● The PSF of early-species is negative in response to plant growth period.

    ● The PSF of mid- and late-species is negative in early- species soil over time.

    ● The PSF of mid- and late-species is neutral in mid- species soil over time.

    ● The PSF of mid- and late-species is positive in late-species soil over time.

    Secondary succession is the process by which a community develops into a climax community over time. However, knowledge on the mechanisms, relating to soil legacy effects (soil chemistry and enzyme activity) and plant–soil feedback (PSF), driving community succession remains limited. In this work, we examined the PSF associated with three succession stage species through a 2-year greenhouse experiment. Setaria viridis, Stipa bungeana, and Bothriochloa ischemum were selected to represent dominant and representative early-, mid-, and late-successional stage species, respectively, of semiarid grasslands on the Loess Plateau. In response to the different soil origin, the shoot biomass of early-, mid-, and late-species were all higher when grown in their own soil than in other species’ soils, which indicated that the PSF of three species were positive. Over two growth periods, the early-species experienced a negative PSF, but the mid- and late-species experienced negative, neutral and positive PSF in the soil of early-, mid- and late-species, respectively. Our study demonstrates that soil legacy effects and PSF have a significant impact on community succession processes.

    Xiao Liu, Xia Xu, Tian Ma, Shiwei Zhou, Xiaoli Bi, Hongbo He, Xudong Zhang, Weihuan Li

    ● SOC stocks and MCP capacity and efficacy decreased under medium and heavy pollution.

    ● The decrease in MCP capacity was tightly related to the decline in SOC storage.

    ● The lower MCP efficacy implied worse SOC stability under the heavier level.

    Heavy metal pollution can lead to a great loss of soil organic carbon (SOC). However, the microbial mechanisms that link heavy metal pollution to SOC remain poorly understood. Here, we investigated five apple-orchard soils at different distances from a Pb-Zn smelter. After assessing the heavy metal pollution level based on Grade II of the national soil environmental quality standard (China), we found SOC stocks and microbial carbon pump (MCP) capacity (i.e., microbial residue carbon) under medium and heavy pollution levels were significantly lower than those under safe, cordon and light pollution levels. The structural equation model showed causality in the SOC variations linked to pollution level through MCP capacity, which could contribute 77.8% of the variance in SOC storage. This verified MCP capacity can serve as a key parameter for evaluation of SOC storage under heavy metal pollution. Soil MCP efficacy, i.e., the proportion of microbial residue carbon to SOC, also decreased under medium and heavy pollution. This suggested that, with a heavier pollution level, there was a higher rate of reduction of microbial residue carbon in soil than the rate of reduction of SOC. As MCP efficacy can be a useful assessment of SOC stability, the significantly positive relationship between MCP efficacy and clay content in correlation analysis implied that lower MCP efficacy was correlated with SOC stability under the heavier pollution level. Our study provides valuable insights to identify the mechanisms of microbially mediated C transformation processes that are influenced by heavy metal pollution in agroecosystems.

    Luhua Yang, Renhua Sun, Jungai Li, Limei Zhai, Huiling Cui, Bingqian Fan, Hongyuan Wang, Hongbin Liu

    ● Fertilization had stronger impact on the root microbiome than on the soil microbiome.

    ● Organic-inorganic fertilization led to higher microbial network stability than exclusive mineral or organic fertilization.

    ● The variances of the soil and root microbiome were attributed to the soil organic matter and the total nitrogen respectively.

    Plant health and performance are highly dependent on the root microbiome. The impact of agricultural management on the soil microbiome has been studied extensively. However, a comprehensive understanding of how soil types and fertilization regimes affect both soil and root microbiome is still lacking, such as how fertilization regimes affect the root microbiomeʼs stability, and whether it follows the same patterns as the soil microbiome. In this study, we carried out a long-term experiment to see how different soil types, plant varieties, and fertilizer regimens affected the soil and root bacterial communities. Our results revealed higher stability of microbial networks under combined organic-inorganic fertilization than those relied solely on inorganic or organic fertilization. The root microbiome variation was predominantly caused by total nitrogen, while the soil microbiome variation was primarily caused by pH and soil organic matter. Bacteroidetes and Firmicutes were major drivers when the soil was amended with organic fertilizer, but Actinobacteria was found to be enriched in the soil when the soil was treated with inorganic fertilizer. Our findings demonstrate how the soil and root microbiome respond to diverse fertilizing regimes, and hence contribute to a better understanding of smart fertilizer as a strategy for sustainable agriculture.

    Panpan Jiao, Lei Yang, Xiaodong Nie, Zhongwu Li, Lin Liu, Peng Zheng

    ● The bacterial and fungal diversity decreased greater in 5%−36% DRW than 5%−25% DRW.

    ● Fungal network was complicated after 1-cycle DRW, but that for bacteria occurred until 4-cycle DRW.

    ● Stronger DRW treatment enhanced the pulse amplitude of respiration in soil.

    Altered drying-rewetting (DRW) procedures due to climate change may influence soil microbial properties and microbially-mediated carbon cycling in arid and semi-arid regions. However, the effects of DRW of different intensities on the microbial properties and respiration are not well understood. Thus, the responsive patterns of microbial communities and carbon mineralization in agriculture soil on the Chinese Loess Plateau to DRW treatments with different wetting intensities (5%−25% and 5%−36%) and frequency (1-cycle to 4-cycle) were investigated. Continuous moisture levels of 5%, 25% and 36% were used as control. Results revealed that the reduction of bacterial diversity and richness were greater for 5%−36% than 5%−25% treatment, while diversity of fungi was similar for different wetting intensities. Bacterial communities became clustered by wetting intensity rather than cycle number, however fungal community was unaffected by DRW. The complexity of bacterial co-occurrence network increased because of higher nodes, edges, average degree, diameter and average cluster coefficient after 4-cycles, and the interaction was more complex after 1-cycle for fungi. Rewetting caused a pulse-like increase of respiration rate, and the pulse amplitude was greater for DRW with high rewetting intensity and decreased with the increase of cycle number. The cumulative CO2 emission for DRW treatments was lower than that for the continuous moisture conditions. The net reduction of carbon release for 5%−36% treatment was 1.18 times higher than that for 5%−25% treatment. Our study provides experimental evidence of the positive potential of DRW processes for maintaining soil carbon stock in an agriculture system on the Loess Plateau.

    Anandkumar Jayapal, Tanushree Chaterjee, Biju Prava Sahariah

    ● Mine tailings (MTs) are complex waste materials produced by mining activities and containing toxic organics and inorganics, including heavy metals present in the mining area, with high potential for environmental degradation.

    ● Bioremediation is an efficient and cost-effective technique for management of MTs, considering the complexity and wide coverage area by the later.

    ● Fortified with functional accessories provided by various cellular and molecular aspects of the cells of microorganisms and plants, pollutants in MTs are treated by mechanisms of biosorption, biodegradation, bioaccumulation, bioleaching and biosorption.

    Mine tailings (MTs) are the materials dumped on a mining site after mineral extraction, containing scattered traces of residual minerals, dug-up soils, and a disturbed ecosystem. Abandoned and untreated MT can pose threats to the surrounding ecosystem due to the presence of various primary and secondary toxic components, such as organic substances [PAH (polycyclic aromatic hydrocarbons), phenolics] and inorganic materials (sulfur, cyanide), metals and metalloids. All these pollutants originate from nature, and there is a possibility to remedy the problems generated from them. Conventional physical-chemical and biological techniques are often considered for treating the polluted environment and are recognized as having great efficiency. Physicochemical processes, such as incineration, and soil washing with solvents, encounter limitations of cost-effectiveness associated with further environmental concerns. The advantages accompanying bioremediation, the alternative to physicochemical treatment, are its cost-effectiveness, its environmentally benign nature, and complete mineralization of pollutants, instead of the generation of secondary toxic intermediates as in the case of the physicochemical process, make it more attractive for dealing with MT. This manuscript emphasizes use of basic treatment techniques and bioremediation mechanisms for dealing with pollutants from MT that target the revival of nature by utilizing natural agents, plants (phytoremediation), bacteria, fungi, and algae.

    Zhichao Xia, Yue He, Jiahui Xu, Zuodong Zhu, Helena Korpelainen, Chunyang Li

    ● Sexually dimorphic belowground responses to cope with drought.

    ● Females show more morphological plasticity in response to water deficiency.

    ● Males influence rhizosphere micro-organisms to compensate for resource acquisition.

    ● Microbial responses are associated with root trait adjustments to drought.

    How sex-related root traits and soil microbes and their interactions respond to drought remains unclear. Here, we investigated how fine root traits and the composition of rhizosphere microbial communities in Populus euphratica females and males respond to drought in concert in 17-year-old plantations. Females increased specific root length (SRL) in response to drought. However, males showed no changes in their roots but significant increases in arbuscular mycorrhizal hyphal biomass and population of Gram-negative bacteria in the rhizosphere. Also, fungal symbiotroph communities associated with root systems in males differed from those in females under drought. We further demonstrated that the Gram-positive to Gram-negative bacteria ratios positively correlated with the SRL, while fungi to bacteria ratios were negatively correlated. Meanwhile, the relative abundance of symbiotrophs was negatively correlated with the SRL, while saprotroph abundance was positively correlated. Nevertheless, the relative abundance of symbiotrophs was positively correlated with the root carbon content (RCC). These findings indicate that microbial responses to drought depend highly upon the sex of the plant and microbial group and are related to root trait adjustments to drought. This discovery also highlights the role of plant-microbial interactions in the ecosystems of P. euphratica forest plantations.

    Shuo Zhang, Ying-Ping Wang, Xi Fang, Jinlei Chen, Nannan Cao, Pingping Xu, Mengxiao Yu, Xin Xiong, Xiangping Tan, Qi Deng, Junhua Yan

    ● Soil C-, N-, P-acquiring enzymes changed significantly during vegetation restoration.

    ● Microbial metabolisms were co-limited by C and P during vegetation restoration.

    ● Microbial C limitation was significantly affected by microbial CUE under the influence of litter quality.

    ● Microbial P limitation was significantly affected by soil elements and their stoichiometry under the influence of AGB.

    Changes in litter quality (carbon:nitrogen, C:N) and above-ground biomass (AGB) following vegetation restoration significantly impact soil physicochemical properties, yet their effects on soil microbial metabolic limitations remain unclear. We measured litter quality, AGB, soil physicochemical properties, and extracellular enzyme activity (EEA) along a vegetation restoration gradient (7, 14, 49, 70 years, and nearly climax evergreen broadleaved forests) in southern China. We also evaluated soil microbial metabolic limitations by a vector analysis of the EEA. Results revealed the soil microbial metabolisms were co-limited by C and phosphorus (P). The microbial C limitation initially decreased (before 14 years) and then increased, while the microbial P limitation initially increased (before 49 years) and then decreased. Partial least squares path modeling (PLS-PM) showed that the microbial C limitation was mainly attributed to microbial C use efficiency induced by litter quality, suggesting that microorganisms may transfer cellular energy between microbial growth and C-acquiring enzyme production. The microbial P limitation was primarily correlated with AGB-driven change in soil elements and their stoichiometry, highlighting the importance of nutrient stoichiometry and balance in microbial metabolism. The shifts between microbial C and P limitations and the strong connections of plant–soil-microbe processes during vegetation restoration revealed here will provide us with helpful information for optimal management to achieve forest restoration success.

    Olexander Zhukov, Olga Kunakh, Nadiia Yorkina, Anna Tutova

    ● Soil penetration resistance increases as a result of park reconstruction.

    ● Soil compaction explains one-third of the variability in soil macrofauna.

    ● The abundance of the earthworm Aporrectodea rosea increases after reconstruction.

    ● The abundance of the earthworm A. calliginosa decreases after reconstruction.

    This study is based on a park in an industrial city in Ukraine. In 2019, a 2.8 ha area of the park was reconstructed. The park’s reconstruction aimed to create a comfortable environment for visitors and to improve the efficiency of ecosystem services, and thereby enhance the quality of life of citizens. The reconstruction of the park was found to cause changes in the physical properties of soils and the structure of the soil macrofauna community. The increases of soil compaction in the layers at depth 5–20 cm and the soil electrical conductivity were a consequence of technological operations during reconstruction. The park reconstruction activities can also explain 29% of the variation in the soil macrofauna community. Extracting the variation induced by the park reconstruction from the community variation induced by other causes was a major challenge. The specific changes in the community of soil macrofauna following the reconstruction of the park were revealed. The abundance of soil animal species A. rosea, A. trapezoides, H. affinis, H. rufipes, B. affinis was found to increase after the reconstruction. The earthworm A. trapezoides decreased in abundance due to the park reconstruction.

    Ji Chen, Irene Cordero, Daryl L. Moorhead, Jennifer K. Rowntree, Loraé T. Simpson, Richard D. Bardgett, Hayley Craig

    ● Reduced oxygen increased microbial metabolic quotient (qCO2).

    ● Reduced oxygen enhanced microbial specific C-, N- and P-acquiring enzyme activity.

    ● Reduced oxygen increased microbial C relative to N and P limitation.

    ● Reduced oxygen increased microbial N relative to P limitation.

    ● Specific enzyme activity was positively related to qCO2 under reduced oxygen.

    Mangroves are one of the most ecologically sensitive ecosystems to global climate change, which have cascading impacts on soil carbon (C), nitrogen (N) and phosphorus (P) cycling. Moreover, mangroves are experiencing increasing N and P loadings and reduced oxygen availability due to intensified climate change and human activities. However, both direct and interactive effects of these perturbations on microbially mediated soil C, N and P cycling are poorly understood. Here, we simultaneously investigated the effects of N and P loadings and reduced oxygen on microbial biomass, microbial respiration, and extracellular enzyme activities (EEAs) in mangrove soils. We calculated the microbial metabolic quotient (qCO2), which is regarded as a useful inverse metric of microbial C use efficiency (CUE). Our results show that reduced oxygen significantly increases both qCO2 and microbial specific EEAs (enzyme activity per unit of microbial biomass) for C-, N- and P-acquisition regardless of N or P loadings. Furthermore, we found that qCO2 positively correlated with microbial specific EEAs under reduced oxygen, whereas no clear relationship was detected under ambient oxygen. These results suggest that reduced oxygen increases microbial specific EEAs at the expense of increasing microbial respiration per unit biomass, indicating higher energy cost per unit enzyme production.

    Shuyu Hou, Jue Wang, Jun Dai, Mohammed Boussafir, Chi Zhang

    ● Earthworm remove PAHs from soil by bioaccumulation and stimulating microbial degradation.

    ● Biochar can adsorb PAHs and promote microbial degradation in soil.

    ● Earthworm improve the adsorption process of biochar by bioturbation.

    ● Biochar reduce the vermiaccumulation and improve the decomposition of PAHs by earthworm.

    Polycyclic aromatic hydrocarbons (PAHs) in soil pose a threat to the health of humans and other organisms due to their persistence. The remediation method of combined application of biochar and earthworms has received growing attention owing to its effectiveness in PAHs removal. However, the earthworm–biochar interaction and its influence on PAHs in soil has not been systematically reviewed. This review focuses on the effectiveness of combined application of earthworms and biochar in the remediation of PAHs-contaminated soils and the underlying mechanisms, including adsorption, bioaccumulation, and biodegradation. Earthworm–biochar interaction activates the functional microorganisms in soil and the PAHs-degrading microorganisms in earthworm guts, promoting PAHs biodegradation. This review provides a theoretical support for the combined application of biochar and earthworms in the remediation of PAHs-contaminated soils, points out the limitations of this remediation method, and finally shows the prospects for future research.

    Yong-Guan Zhu, Yi Yang, Ole G. Mouritsen