Sep 2023, Volume 5 Issue 3

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    Yaoyao Tong, Jina Ding, Mouliang Xiao, Muhammad Shahbaz, Zhenke Zhu, Ming Chen, Yakov Kuzyakov, Yangwu Deng, Jianping Chen, Tida Ge

    ● Microplastics (MPs) increased activities of N and P hydrolases in paddy soil.

    ● MP amount increased nutrient acquisition ratio and total enzyme activity.

    ● MPs lead to soil nutrient decreased through microbial action.

    ● MPs impact nutrient availability and agricultural ecosystem functions.

    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.

    Zhengxin Xu, Can Hu, Xufeng Wang, Long Wang, Jianfei Xing, Xiaowei He, Zaibin Wang, Pengfei Zhao

    ● Occurrence of microplastics was widespread in long-term mulched farmland soils.

    ● Abundance exhibited obvious differences in different film mulching durations.

    ● Plastic film residue was the important source of farmland soil microplastics.

    ● This study offers useful data on microplastic pollution in long-term mulched areas.

    Soil contamination from film debris following the prolonged application of mulching film has emerged as a worldwide concern. However, the extent that mulching films contribute to soil microplastics, and the spatial distribution of soil contamination from film debris remain unclear. In this study, the cotton field in Xinjiang (China), which underwent film mulching for a prolonged period of 5−30 years, was selected as the research location. A total of 360 soil samples were collected, aiming to study the spatial distribution characteristics of mulching film debris pollution. The samples were extracted using the density flotation method combined with stereomicroscopic; the source, composition, abundance, and distribution characteristics of soil MPs were identified by the scanning electron microscopic, and Fourier transform infrared spectroscopic analyses. In soil mulched for a 30 year period, the abundance of microplastics across the studied soil depth (0−60 cm) was 78.51±2.57 n/(100 g). The μ-FTIR analyses revealed that the composition of the microplastics matched that of polyethylene materials. Therefore, plastic mulching could be inferred as a major contributor to microplastic pollution in agricultural lands. Overall, it is necessary to study the distribution characteristics of plastic film remaining for further study of plastic pollution in farmland soils.

    Erika Valente de Medeiros, Érica de Oliveira Silva, Gustavo Pereira Duda, Mario Andrade Lira Junior, Uemeson José dos Santos, Claude Hammecker, Diogo Paes da Costa, Fabio Fernando Araujo, Arthur Prudêncio de Araujo Pereira, Lucas William Mendes, Ademir Sergio Ferreira Araujo

    ● The enzymatic stoichiometry varied between land-use in both soil depth.

    ● The values of C- and N-acquiring enzymes were higher at 0−5 cm depth.

    ● Soils under different land-use types in the Brazilian semiarid are P-limited.

    This study hypothesized that different land-use affect the microbial enzymatic stoichiometry and C-, N-, and P-acquisition in Brazilian semiarid soils. Thus, the enzymes β-glucosidase (C-acquiring enzyme), urease (N-acquiring enzyme), and acid phosphatase (P-acquiring enzyme) were assessed in soil samples collected at 0−5 and 5−10 cm depth from a tropical dry forest, a protected area with Angico, a protected area with Ipê, scrub area, and an agricultural area with maize. The values of C-, N-, and P-acquiring enzymes were used to calculate the enzymatic C:N, C:P, and N:P ratios. The values of C:P and N:P ratios were higher at 0−5 cm depth, while no significant variation, between soil depth, was observed for C:N ratio. The values of C- and N-acquiring enzymes were higher at 0−5 cm in tropical dry forest areas and Angico forest, respectively. In all land use types, the values of vectors L and A were higher than 1° and 45°, respectively. This study showed that both land-use and soil depth influence the enzymatic stoichiometry, showing higher values of C- and N-acquiring enzymes in native and protected forests at soil surface.

    Haixin Zhang, Yimei Huang, Shaoshan An, Quanchao Zeng, Baorong Wang, Xuejuan Bai, Qian Huang

    ● Decay stages and meteorological factors affect leaf litter’s microbial community.

    ● Bacteria and fungi were mainly affected by OC, TN, pH, and water content of leaf litter.

    ● Bacterial (6.6) and fungal (3.6) Shannon indexes were the largest after 125 days.

    ● Microbial diversity and decay stage directly regulated the litter mass-loss rate.

    Litter microorganisms play a crucial role in the biological decomposition in forest ecosystems; however, the coupling effect of meteorological and substrate changes on it during the different stages of leaf decomposition in situ remains unclear. Hence, according to meteorological factors dynamics, a one-year field litter of Quercus wutaishanica in situ decomposition experiment was designed for four decay stages in a warm temperate forest. Microbial community composition was characterized using Illumina sequencing of fungal ITS and bacterial 16S genes. Bacterial (6.6) and fungal (3.6) Shannon indexes were the largest after 125 days’ litter decomposition (October). The relative abundance of Acidobacteria after 342 days and Bacteroidetes after 125 days were 3 and 24 times higher than after 31 days, respectively. Some non-dominant species (bacteria: Firmicutes, Planctomycotes, and Verrucomicrobia; fungi: Chytridiomycota and Glomeromomycota) may be absent or present at different decomposition stages due to litter properties or meteorological factors. Chemoheterotrophy and aerobic-chemoheterotrophy were the dominant bacterial functional groups, and the dominant fungal functional groups were saprotrophs, pathotrophs, and symbiotrophs. Precipitation and relative humidity significantly affected bacteria. Temperature, sunlight intensity, and net radiation significantly affected fungi. Besides, among the relative contributions of changes in bacterial and fungal community structure, leaf litter properties alone explained the variation of 5.51% and 10.63%. Microbial diversity and decay stage directly affected the litter mass-loss rate, with meteorological factors (precipitation, relative humidity, air temperature, and sunlight intensity) being indirect. Our findings highlight the importance of microbial diversity for leaf litter decomposition and the influence of meteorological factors.

    George P. Stamou, Nikolaos Monokrousos, Anastasia Papapostolou, Effimia M. Papatheodorou

    ● We assess the recovery of microbial networks underneath crust to repeated rainfall.

    ● The network fragmentation after the second heavy rain was milder than at the first one.

    ● Cohesive networks were related to high enzyme activity involved in C, N, and P cycles.

    ● Loose networks were related to high Ca, K, Mg, NH4 and organic N.

    ● The network in dry-crusted soils collapsed after the second heavy rain.

    Biological soil crusts (BSCs) are an important multi-trophic component of arid ecosystems in the Mediterranean region. In a mesocosm experiment, the authors investigated how the network of interactions among the members of the soil microbial communities in four types of soil sample responded when soils were exposed to two simulated extreme rain events. The four types of soil samples were: covered by Cladonia rangiformis and previously hydrated (+BSC+H), covered by C. rangiformis and dried (+BSC-H), uncovered and hydrated (-BSC+H), uncovered and dried (-BSC-H). Network analysis was based on the co-occurrence patterns of microbes; microbes were assessed by the phospholipid fatty acids analysis. The authors further explored the relations between networks’ metrics and soil functions denoted by enzymatic activity and soil chemical variables. All networks exhibited Small world properties, moderate values of clustering coefficient and eigen centrality, indicating the lack of hub nodes. The networks in -BSC-H soils appeared coherent during the pre-rain phases and they became modular after rains, while those in +BSC-H soils kept their connectivity till the second rain but this then collapsed. The network metrics that were indicative of cohesive networks tended to be related to enzyme activity while those that characterized the loose networks were related to Ca, K, Mg, NH4+ and organic N. In all mesocosms except for +BSC-H, networks’ fragmentation after the second heavy rain was milder than after the first one, supporting the idea of community acclimatization. The response of microbial networks to heavy rains was characterized by the tendency to exhibit degradation-reconstruction phases. The network collapse in the crusted only mesocosms showed that the communities beneath crusts in arid areas were extremely vulnerable to recurring heavy rain events.

    Sana Khalid, Muhammad Shahid, Zeid A. ALOthman, Abdullah A. Al-Kahtani, Behzad Murtaza, Camille Dumat

    ● Soil processes affect metal chemical speciation and their biogeochemical activity.

    ● The current study predicted chemical speciation of eight metals in two soil layers.

    ● Divalent forms of metals predominated in both soil layers (79.9%).

    ● Chromium showed a chemical speciation that varied from that of the other metals (95.8% as CrOH+).

    ● Mean percentage ages of all metal ions were similar for all 15 field locations investigated.

    From soil contamination and risk assessment perspectives, it is imperative to understand the ecological processes occurring in soils. Certain soil processes greatly affect chemical speciation of potentially toxic metals (PTMs), and thus also influence their biogeochemical activity. The current study analyzed chemical speciation of eight PTMs (Cd, Cr, Fe, Cu, Mn, Ni, Zn, and Pb) in upper and lower soil layers for 15 agronomic fields of Vehari-Pakistan using Visual Minteq software. The divalent forms of most PTMs (PTM2+) generally predominated in both soil layers (79.9% overall occurrence). However, chromium revealed a different pattern of chemical speciation (95.8% as CrOH+) compared to other PTMs. The mean percentage of all the PTMs2+ was slightly higher for the lower soil layer (81.3%) than in the upper layer (78.4%), the trend being same for all the PTMs, except Cr. This higher PTMs2+ percentage in lower soil layers than upper layers was due to lower content of organic matter and other anions such as Cl and HCO3. The mean percentage ages of all the PTMs2+ was similar among all the 15 agronomic fields, which was confirmed by strong Pearson correlation values (R2 > 0.95). The PCA graph grouped all the agronomic fields and PTM2+ closely, except Cr2+ and Cu2+. This grouping confirmed the similar chemical speciation of PTMs, except Cu and Cr in studied fields.

    Michael O. Asare, Wazi Apoh, Jerry Owusu Afriyie, Jiřina Száková, Dinkayehu Alamnie Asrade

    ● Past human activities result in the formation of Anthrosols and the accumulation of nutrients.

    ● Enrichment in physicochemical properties relates to the intensity of settlement activities.

    ● The level of releasability contributes to the extended retention of nutrients in soils.

    ● Past settlement sites represent nutrient-rich Anthrosols suitable for arable fields.

    The fertility of human-altered soils, Anthrosols, developed from past settlement activities for crop production is scarcely studied. The study evaluated the fertility of Anthrosols developed from the 15th to mid-20th century AD settlement in Old Buipe, Savanna region, Ghana, to determine whether abandoned localities are suitable for arable fields. Human activities enhanced the physical attributes of the Anthrosols: brown to dark brown intergrain fine soil, 15%−35% organic matter, 15%−30% potsherd, and 5%−15% charred materials. The Anthrosols were slightly acidic to neutral reactions (\textcolor[RGB]32,147,147pH[H2O] 5.67−6.83, \textcolor[RGB]32,147,147pH[CaCl2] 5.83−6.95), high cation exchange capacity (CEC; 18.77−45.31me/100 g), electric conductivity (EC = 0.28−0.36 dS m−1), accumulation, and distribution of organic C, total N, P, Mn, Cu, Zn, K, and Fe, and available P, K, Ca, Mg, S, Mn, Fe, Cu, and Zn. Plant-available nutrients were comparatively higher than concentrations in non-anthropogenic soils. The level of releasability (bioavailable fractions of total concentrations) of P, K, Ca, Mn, Fe, Cu, and Zn partly compensates for low plant-available portions. Enrichment of chemical and physical properties of Anthrosols make them fertile for arable fields. The signatures of settlement activities are strong and can remain in soils for a long time, even under harsh environmental conditions.

    Ruibo Sun, Daozhong Wang, Zhibin Guo, Keke Hua, Xisheng Guo, Yan Chen, Binbin Liu, Haiyan Chu

    ● The abundance of N-cycling genes differently responded to NPK application.

    ● Chemical NPK application greatly altered the N-cycling microbial community structure.

    ● Soil acidification was the main driver for the variation in the N-cycling microbial community.

    ● Manure addition was beneficial for stabilizing the N-cycling microbial community.

    Straw and manure are widely applied to agricultural systems, and greatly shape soil N-cycling microflora. However, we still lack a comprehensive understanding of how these organic materials structure soil N-cycling microbial communities. In this study, metagenomic analysis was performed to investigate the compositional variation in N-cycling microbial communities in a 30-year long-term experiment under five fertilization regimes: no fertilization (Control), chemical fertilization only (NPK), and NPK with wheat straw (NPK + HS), pig manure (NPK + PM), and cow manure (NPK + CM). Long-term NPK application differentially changed N-cycling gene abundance and greatly altered N-cycling microbial community structure. NPK + HS resulted in a similar pattern to NPK in terms of gene abundance and community structure. However, NPK + PM and NPK + CM significantly increased most genes and resulted in a community similar to that of the Control. Further analysis revealed that serious soil acidification caused by long-term NPK fertilization was a major factor for the variation in N-cycling microbial communities. The addition of alkaline manure, rather than wheat straw, stabilized the N-cycling microbial community structure presumably by alleviating soil acidification. These results revealed the strong impact of soil acidification on microbial N-cycling communities and illustrated the possibility of resolving nitrogen-related environmental problems by manipulating pH in acidified agricultural soils.

    Humira Nesar, Shahid Afzal, Zarrin Imran, Wasim Ahmad

    ● Impact of marshy area reclamation by various vegetations on soil nematode community was investigated.

    ● Nematode abundance was lowered by reclamation mostly due to bacterivores.

    ● Reclamation effectively diminished the nematode metabolic footprint.

    ● Robust management strategies must be adapted for conservation and protection of marshy ecosystems.

    Marshy areas are ecologically important and sensitive areas which are under immense pressure, such as reclamation by various terrestrial vegetations. However, how these vegetation types disrupt the stability of nematode community is scarce. The present study determined how the soil nematode community responded to shifting environmental states by using nematode abundances, nematode indices and metabolic footprints as indicators. In this context, we selected three types of reclaimed vegetation around a marshy land (MR) in Dachigam National Park, Kashmir, which includes grassland (GL), forest (FR) and cropland (CL) to investigate the soil nematode community. Acrobeloides, Plectus, Eudorylaimus, and Aphelenchus proved more sensitive to reclamation effect. Results revealed decrease in total nematode and bacterivore abundance. Reclamation reduced diversity in CL, whereas no effect was observed in the GL and FR as compared to MR. Channel index indicated shift from fungal decomposition to bacterial decomposition pathway in GL. The nematode faunal profile depicted grassland (GL) as the most structured ecosystem compared to MR, FR, and CL. Our results suggest that vegetation type regulates the structure, function, and stability of the soil food web, which has significant implications for managing the vegetation cover in a sustainable manner in the Dachigam National Park.

    Shinichi Watanabe, Makoto Shibata, Yoshiko Kosugi, Lion Marryanna, Keitaro Fukushima, Arief Hartono, Shinya Funakawa

    ● Some O horizons showed higher nitrification rate than mineral horizons.

    ● Both total N and pH were positively correlated with nitrification rate in O horizon.

    ● Nutrient richness in litters supported active nitrification in O horizon.

    ● Nitrification rate in O horizon increased along with a pH threshold of 5.5–6.0.

    High nitrate leaching has been observed from the O horizons of some tropical forests; however, the drivers of high nitrate production (active nitrification) in these O horizons have not yet been identified. This study investigated the drivers of active nitrification in the O horizon of tropical forest soils by focusing on two of the most widely recognized controlling factors of nitrification, total N, and pH. We collected mineral and O horizons from eight tropical forests in Cameroon, Indonesia, and Malaysia and measured gross nitrification rates. Some O horizons showed significantly higher gross nitrification rates than mineral horizons, indicating that these O horizons have a high potential for nitrification. Gross nitrification rates in the O horizons were positively correlated with both total N and pH, and the chemical properties (e.g., total content of N, P, and base cations) were intercorrelated. These correlations suggested that the underlying driver of nitrification in the O horizon was nutrient richness in the litter. Results also indicated a threshold of gross nitrification rates around pH values of 5.5–6.0. We elucidate that active nitrification and subsequent high nitrate leaching from the O horizon could be driven by nutrient-rich litter, possibly derived from soil fertility and tree species.

    Fang-Jie Zhao
    Yuhuai Liu, Yingying Zhong, Can Hu, Mouliang Xiao, Fan Ding, Yongxiang Yu, Huaiying Yao, Zhenke Zhu, Jianping Chen, Tida Ge, Jina Ding

    ● Film mulching decreased soil organic C content in soil aggregates with 0.053–0.25 mm diameter.

    ● Fiber-shaped microplastics readily combined with the soil aggregates of 0.053–0.25 mm in diameter.

    ● Film- and granule-shaped microplastics were dominant in 0.25–2 mm soil aggregates.

    ● Natural and human activities changed the shape and size distribution of particle in soil.

    Microplastic distribution is non-homogeneous in agricultural soil following plastic film degradation. However, the distribution of microplastics by shape and particle size in different soil aggregates remains unknown. To elucidate the distribution of microplastic shapes and particle sizes in soil aggregates with increasing years of film mulching, four paired fields with film mulching (FM) and no mulching (NM) were examined at 1, 5, 10, and 20 years after continuous mulching. An increase in soil aggregates of 0.053–0.25 mm diameter was observed; however, soil organic carbon content decreased after long-term FM. Microplastics primarily combined with 0.053–2 mm soil aggregates. Specifically, long-term FM was associated with dominance of film- and fiber-shaped microplastics in soil aggregates of 0.25–2 mm and 0.053–0.25 mm diameter, respectively. Fiber- and granule-shaped microplastics of 0.25–1 mm diameter primarily combined with 0.053–0.25 and 0.25–2 mm soil aggregates, respectively. Film-shaped microplastics of diameter > 1 mm and diameter 0.05–0.25 mm primarily combined with 0.25–2 mm soil aggregates. Therefore, distribution of microplastics in soil aggregates can be used to monitor soil health and quality, greatly enhancing our understanding of the risk posed by microplastics to the environment.