Soil Enzyme Activities Research Articles

Soil bacterial community structure and co‐occurrence networks in response to the succession of secondary forests in subtropical regions

AbstractA large amount of secondary successional vegetation (subtropical evergreen broadleaved forests) has formed after the extensive deforestation and cultivation of coniferous forests in Wuyi Mountain, Southeast China. However, we lack a detailed understanding of the dynamic changes in microbial community structure and its co‐occurrence network during succession. The features that are responsible for alterations in the soil bacterial community remain poorly defined. Therefore, we compared the soil physicochemical properties, enzyme activities, and bacterial diversity among three different forests (a coniferous forest [CF], early stage of succession; a mixed conifer‐broadleaf forest [CBMF], middle stage of succession; an evergreen broadleaf forest [EBF]; late stage of succession). Results indicated that the contents of soil organic carbon and microbial biomass carbon (MBC) in CBMF were higher compared with those in CF. The alpha diversity indices were the highest in CBMF. Functional annotation of prokaryotic taxa predicted the relative abundances of chemoheterotrophy and aerobic chemoheterotrophy were lower in CF than in the other two forests. Bacterial network topology was affected by forest succession, with CBMF having more complex bacterial networks. Mantel's test indicated the soil nitrate nitrogen content (P = 0.03) was the most important property that shaped the bacterial community composition, bacterial diversity was influenced by soil pH (P = 0.026), and the contents of available phosphorus (P = 0.04) and MBC (P = 0.022) during the succession process. In conclusion, the succession of secondary forests promoted soil nutrient accumulation and improved bacterial diversity and network complexity.

The effect of white grub (Maladera Verticalis) larvae feeding on rhizosphere microbial characterization of aerobic rice (Oryza sativa L.) in Puer City, Yunnan Province, China

BackgroundRhizosphere microorganisms are vital in plants’ growth and development and these beneficial microbes are recruited to the root-zone soil when experiencing various environmental stresses. However, the effect of white grub (Maladera verticalis) larvae feeding on the structure and function of rhizosphere microbial communities of aerobic rice (Oryza sativa L.) is unclear.ResultsIn this study, we compared physicochemical properties, enzyme activities, and microbial communities using 18 samples under healthy and M. verticalis larvae-feeding aerobic rice rhizosphere soils at the Yunnan of China. 16 S rRNA and ITS amplicons were sequenced using Illumina high throughput sequencing. M. verticalis larvae feeding on aerobic rice can influence rhizosphere soil physicochemical properties and enzyme activities, which also change rhizosphere microbial communities. The healthy and M. verticalis larvae-feeding aerobic rice rhizosphere soil microorganisms had distinct genus signatures, such as possible_genus_04 and Knoellia genera in healthy aerobic rice rhizosphere soils and norank_f__SC − I−84 and norank_f__Roseiflexaceae genera in M. verticalis larvae-feeding aerobic rice rhizosphere soils. The pathway of the metabolism of terpenoids and polyketides and carbohydrate metabolism in rhizosphere bacteria were significantly decreased after M. verticalis larvae feeding. Fungal parasite–wood saprotroph and fungal parasites were significantly decreased after M. verticalis larvae feeding, and plant pathogen–wood saprotroph and animal pathogen–undefined saprotroph were increased after larvae feeding. Additionally, the relative abundance of Bradyrhizobium and Talaromyces genera gradually increased with the elevation of the larvae density. Bacterial and fungal communities significantly correlated with soil physicochemical properties and enzyme activities, respectively.ConclusionsBased on the results we provide new insight for understanding the adaptation of aerobic rice to M. verticalis larvae feeding via regulating the rhizosphere environment, which would allow us to facilitate translation to more effective measures.

Effects of Land-Use Type and Salinity on Soil Carbon Mineralization in Coastal Areas of Northern Jiangsu Province

Sea level rise due to glacier melting caused by climate warming is a major global challenge, but the mechanism of the effect of salinity on soil carbon (C) mineralization in different land types is not clear. The pathways by which salinity indirectly affects soil carbon mineralization rates need to be investigated. Whether or not the response mode is consistent among different land-use types, as well as the intrinsic links and interactions between soil microbial resource limitation, environmental stress, microbial extracellular enzyme activity, and soil carbon mineralization, remain to be demonstrated. In this paper, three typical land-use types (wetland, forest, and agroforestry) were selected, and different salinity levels (0‰, 3‰, 6‰, and 32‰) were designed to conduct a 125-day laboratory incubation experiment to determine the soil CO2 release rate, soil physicochemical properties, and soil enzyme activities, and to correlate C mineralization with biotic and abiotic factors. A correlation analysis of soil physical and chemical properties, extracellular enzyme activities, and carbon mineralization rates was conducted to investigate their intrinsic linkages, and a multiple linear regression of C mineralization at different sites was performed to explore the variability of mineralization among different site types. Structural equation models were established in the pre- and post-incubation stages to study the pathways of soil C mineralization at different incubation times, and the mechanism of mineralization was further verified by enzyme stoichiometry. The results showed that, at the end of 125 days of incubation, the 32‰ salinity addition reduced the cumulative mineralization of forest and agroforestry types by 28.41% and 34.35%, respectively, compared to the 0‰ salinity addition. Soil C mineralization in the three different land-use types was highly correlated with the active C fractions of readily oxidizable C (ROC), dissolved organic C, and microbial biomass C (MBC) in the soil, with the standardized coefficients of multivariate linear regression reaching 0.67 for MBC in the wetland and −0.843 for ROC in the forest. Under long-term salinity additions, increased salinity would reduce the microbial respiratory quotient value by inhibiting β-glucosidase activity, thus indirectly affecting the rate of CO2 release. With added salinity, the mineralization of non-saline soil was more susceptible to the inhibitory effect of salinity, whereas the mineralization of salinized soil was more controlled by soil C pools.

Effects of short-term simulated acid rain and nitrogen deposition on soil nutrients and enzyme activities in Cunninghamia lanceolata plantation

Acid rain and nitrogen deposition are emerging as global scale environmental issues due to increasing industrial emissions and agricultural pollutants, which seriously impac t the sustainable development of global ecosystems. However, the specific effects both acid rain and nitrogen deposition interactions on forest soil ecosystems, particularly as relates to the soil nutrient content and enzyme activities, remain unclear. Therefore, we established a simulated sample plot of acid rain (SR, NR) and nitrogen deposition (N) and their interactions (SRN, NRN) in a subtropical Cunninghamia lanceolata (C. lanceolata) plantation in the Yangtze River Delta region of China to investigate the impacts of these factors via correlation analysis and structural equation model (SEM). The results showed that acid rain had a stronger effect on soil pH than nitrogen deposition in C. lanceolata plantation, while the simultaneous addition of acid rain and nitrogen deposition exacerbated soil acidification. Soil available potassium, ammonium nitrogen and nitrate nitrogen in C. lanceolata plantation responded more obviously to acid rain and nitrogen deposition, in which acid rain, nitrogen deposition and their interactions significantly reduced soil available potassium content, while acid rain and nitrogen deposition interactions significantly increased soil ammonium nitrogen and nitrate nitrogen content. Nitric acid rain, nitrogen deposition and their interactions significantly increased soil NAGase activity, but significantly decreased soil urease activity; the single-factor treatment of acid rain and nitrogen deposition significantly increased soil arylsulfatase activity, while the interaction of acid rain and nitrogen deposition significantly decreased soil arylsulfatase activity; in general, the interaction of acid rain and nitrogen deposition had a stronger effect on the soil ecosystem of the C. lanceolata plantation than that of single acid rain or nitrogen deposition, of which nitrogen deposition exacerbated the effects of acid rain on the soil ecosystem of C. lanceolata plantation mainly by changing the soil pH and the content of effective nutrients.

The role of afforestation with diverse woody species in enhancing and restructuring the soil microenvironment in polymetallic coal gangue dumps.

To elucidate the effects of long-term (20years) afforestation with different woody plant species on the soil microenvironment in coal gangue polymetallic contaminated areas. This study analyzed the soil physicochemical properties, soil enzyme activities, soil ionophore, bacterial community structure, soil metabolite, and their interaction relationships at different vertical depths. Urease, sucrase, and acid phosphatase activities in the shallow soil layers increased by 4.70-7.45, 3.83-7.64, and 3.27-4.85 times, respectively, after the restoration by the four arboreal plant species compared to the plant-free control soil. Additionally, it reduced the content of available elements in the soil and alleviated the toxicity stress for Cd, Ni, Co, Cr, As, Fe, Cu, U, and Pb. After the long-term restoration of arboreal plants, the richness and Shannon indices of soil bacteria significantly increased by 4.77-23.81% and 2.93-7.93%, respectively, broadening the bacterial ecological niche. The bacterial community structure shaped by different arboreal plants exhibited high similarity, but the community similarity decreased with increasing vertical depth. Soils Zn, U, Sr, S, P, Mg, K, Fe, Cu, Ca, Ba, and pH were identified as important influencing factors for the community structure of Sphingomonas, Pseudarthrobacter, Nocardioides, and Thiobacillus. The metabolites such as sucrose, raffinose, L-valine, D-fructose 2, 6-bisphosphate, and oxoglutaric acid were found to have the greatest effect on the bacterial community in the rhizosphere soils for arboreal plants. The results of the study demonstrated that long-term planting for woody plants in gangue dumps could regulate microbial abundance and symbiotic patterns through the accumulation of rhizosphere metabolites in the soil, increase soil enzyme activity, reduce heavy metal levels, and improve the soil environment in coal gangue dumps.

Soil Nutrient, Enzyme Activity, and Microbial Community Characteristics of E. urophylla × E. grandis Plantations in a Chronosequence

The effects of continuous Eucalyptus cropping on soil properties and microbial characteristics and the specific factors influencing tree species growth remain elusive. In this study, three Eucalyptus stands of three different ages were selected, and soil nutrients, microbial biomass, enzyme activity, microbial community composition, and diversity were quantified for each. The findings indicated a significant decline in soil pH, soil cation exchange, soil organic matter, and available phosphorus content with the plantation age. Simultaneously, there was an observed increase in soil alkaline hydrolyzed nitrogen content. In addition, urease and acid phosphatase activities did not show a significant difference with age. In spite of this, catalase activity exhibited a decline corresponding to the advancement in plantation age. The carbon and nitrogen content of the soil microbial biomass increased with the progression of Eucalyptus planting time. The high-throughput sequencing data demonstrated a reduction in microbial diversity in Eucalyptus soils as the planting age increased. Interestingly, the microbial community structure exhibited minimal alterations, and did not exhibit a predominantly oligotrophic state overall. In conclusion, the study results showed that short-term successive Eucalyptus cropping exerts a significant negative impact on the soil system.

Non-targeted impact of cyantraniliprole residues on soil quality, mechanism of residue degradation, and isolation of potential bacteria for its bioremediation.

Cyantraniliprole (CY), an anthranilic diamide insecticide widely used in grape farming for controlling various sucking pests, poses ecological concerns, particularly when applied as soil drenching due to the formation of more toxic and persistent metabolites. This study established the dissipation and degradation mechanisms of CY in grape rhizosphere soil using high-resolution Orbitrap-LC/MS analysis. The persistence of CY residues beyond 60days was observed, with dissipation following biphasic first + first-order kinetics and a half-life of 15 to 21days. The degradation mechanism of CY in the soil was elucidated, with identified metabolites such as IN-J9Z38, IN-JCZ38, IN-N7B69, and IN-QKV54. Notably, CY was found to predominantly convert to the highly persistent metabolite IN-J9Z38, raising environmental concerns. The impact of CY residues on soil enzyme activity was investigated, revealing a negative effect on dehydrogenase, alkaline phosphatase, and acid phosphatase activity, indicating significant implications for phosphorous mineralization and soil health. Furthermore, bacterial isolates were obtained from CY-enriched soil, with five isolates (CY3, CY4, CY9, CY11, and CY20) demonstrating substantial degradation potential, ranging from 66 to 92% of CY residues. These results indicate that the identified bacteria hold potential for commercial use in addressing pesticide residue contamination in soil through bioremediation techniques.

Freeze-thaw aged polyethylene and polypropylene microplastics alter enzyme activity and microbial community composition in soil

In cold regions, microplastics (MPs) in the soil undergo freeze-thaw (FT) aging process. Little is known about how FT aged MPs influence soil physico-chemical properties and microbial communities. Here, two environmentally relevant concentrations (50 and 500 mg/kg) of 50 and 500 µm polyethylene (PE) and polypropylene (PP) MPs treated soils were subjected to 45-day FT cycles (FTCs). Results showed that MPs experienced surface morphology, hydrophobicity and crystallinity alterations after FTCs. After 45-day FTCs, the soil urease (SUE) activity in control (MPs-free group that underwent FTCs) was 33.49 U/g. SUE activity in 50 µm PE group was reduced by 19.66 %, while increased by 21.16 % and 37.73 % in 500 µm PE and PP groups compared to control. The highest Shannon index was found in 50 µm PP-MPs group at 50 mg/kg, 2.26 % higher than control (7.09). Compared to control (average weighted degree=8.024), all aged MPs increased the complexity of network (0.19–1.43 %). Bacterial biomarkers of aged PP-MPs were associated with pollutant degradation. Aged PP-MPs affected genetic information, cellular processes, and disrupted the biosynthesis of metabolites. This study provides new insights into the potential hazards of MPs after FTCs on soil ecosystem in cold regions.

Co-inoculation of fungi and desert cyanobacteria facilitates biological soil crust formation and soil fertility.

The inoculation of cyanobacteria for enriching soil nutrients and forming biological soil crusts (BSCs) is considered an effective means to restore degraded soil. However, there are limited studies on the application of co-inoculation of fungi and cyanobacteria for degraded soil remediation. In this study, a high exopolysaccharide-secreting fungi Zh2 was isolated from lichen BSCs in Hobq Desert, and co-inoculated with a cyanobacterial strain identified as Phormidium tenue in different proportions to form BSCs on sand during a 35 days incubation period. Results revealed significant differences in crust biomass and soil properties among crusts with different cyanobacterial/fungal inoculation ratios. Microbial biomass, soil nutrient content and enzyme activities in crusts co-inoculated with cyanobacteria and fungi were higher than those inoculated with cyanobacteria and fungi alone. The inoculation of cyanobacteria contributed to the fulvic-like accumulation, and the inoculated fungi significantly increased the humic-like content and soil humification. Redundancy analysis showed that the inoculation of cyanobacteria was positively correlated with the activities of urease and phosphatase, and the content of fulvic-like. Meanwhile, the inoculation of fungi was positively correlated with the contents of total carbon, total nitrogen and humic-like, the activities of catalase and sucrase. Cyanobacteria and fungi play distinct roles in improving soil fertility and accumulating dissolved organic matter. This study provides new insights into the effects of cyanobacteria and fungi inoculations on the formation and development of cyanobacterial-fungus complex crusts, offering a novel method for accelerating induced crust formation on the surface of sand.

Differences in dissolved organic matter and analysis of influencing factors between plantations pure and mixed forest soils in the loess plateau

The dissolved organic matter (DOM) in forest ecosystems significantly impacts soil carbon cycling due to its active turnover characteristics. However, whether different plantation forest soil profiles exhibit distinct DOM characteristics remains unclear. Hence, utilizing fluorescence spectroscopy and the parallel factor analysis (PARAFAC) method, a 1-meter soil profile analysis was carried out on three distinct artificial forests (Pinus tabuliformis (PT), Quercus crispula (QC), and a mixed forest of PT and QC (MF)), concurrently assessing the impact of soil chemical properties and enzyme activity on dissolved organic matter (DOM). The findings indicated that the mean concentration of dissolved organic carbon (DOC) was greatest in the MF and lowest in PT, exhibiting considerable variation with soil depth, suggesting that mixed tree species may promote the discharge of organic matter. The fluorescence spectra revealed two distinct peaks: humic-like fluorescence peaks (Peaks A and C) and a protein-like fluorescence peak (Peak T), with the most intense fluorescence observed in MF soil. As the soil depth increased, the fluorescence intensity of Peaks A and C steadily declined, while the intensity of Peak T rose. Four DOM components were identified in three types of plantations forests: surface soil was dominated by humic acid-like fluorescent components (C1 and C2), while the deep soil was primarily characterized by protein-like fluorescence components (C3 and C4). Different soil profile fluorescence parameter indices indicated that the source of DOM in the surface soil (i.e., 0–20 cm) was mainly allochthonous inputs, whereas, in the deep soil (i.e., 60–100 cm), it was mainly autochthonous, such as microbial activity. The findings from the partial least squares path modeling (PLS-PM) revealed that TP, aP, NH4+-N, and the combined impact of soil enzymes were influential in shaping the diversity of DOM attributes. Put differently, alterations in DOM concentration were concomitantly influenced by forest classification, soil characteristics, and depth. It has been demonstrated that, in contrast to monoculture forests, the establishment of mixed forest models has been more advantageous in enhancing the soil dissolved organic matter (DOM). These discoveries offer innovative perspectives on the dynamic characteristics of DOM in soil profiles and its influencing factors under different plantations forest planting patterns.

Low Rather Than High Level Nitrogen Additions Accelerate Carbon Release Process and Inhibit Recalcitrant Carbon Allocation via Stirring Soil Enzymatic Activities in Plateau Meadows

Low Rather Than High Level Nitrogen Additions Accelerate Carbon Release Process and Inhibit Recalcitrant Carbon Allocation via Stirring Soil Enzymatic Activities in Plateau Meadows

Unraveling the effect of phenolic extract derived from olive mill solid wastes on agro-physiological and biochemical traits of pomegranate and its associated rhizospheric soil properties

Agricultural waste management poses a significant challenge in circular economy strategies. Olive mill wastes (OMW) contain valuable biomolecules, especially phenolic compounds, with significant agricultural potential. Our study evaluate the effects of phenolic extract (PE) derived from olive mill solid wastes (OMSW) on pomegranate agro-physiological and biochemical responses, as well as soil-related attributes. Pomegranate plants were treated with PE at doses of 100 ppm and 200 ppm via foliar spray (L100 and L200) and soil application (S100 and S200). Results showed increased biomass with PE treatments, especially with soil application (S100 and S200). Proline and soluble sugar accumulation in leaves suggested plant adaptation to PE with low-level stress. Additionally, PE application reduced malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents. Higher doses of PE (S200) significantly improved net photosynthesis (Pn), transpiration rate (E), water use efficiency (WUEi), and photosynthetic efficiency (fv/fm and PIabs). Furthermore, PE treatments enhanced levels of chlorophylls, carotenoids, polyphenols, flavonoids, and antioxidant activity. Soil application of PE also increased soil enzyme activities and microbial population. Our findings suggest the beneficial impact of PE application on pomegranate agro-physiological responses, laying the groundwork for further research across various plant species and soil types to introduce nutrient-enriched PE as an eco-friendly biostimulant.

Cottonseed meal improved, nutrient uptake, biochemical attributes of cotton (Gossypium hirsutum L.) and activities of soil enzymes on saline soil

Cottonseed meal improved, nutrient uptake, biochemical attributes of cotton (Gossypium hirsutum L.) and activities of soil enzymes on saline soil

Comprehensive bioremediation effect of phosphorus-mineralized bacterium Enterobacter sp. PMB-5 on cadmium contaminated soil-crop system

Phosphate-mineralizing bacteria (PMBs) have been widely studied by inducing phosphate heavy metal precipitation, but current researches neglect to study their effects on soil-microbe-crop systems on cadmium (Cd) contaminated. Based on this, a strain PMB, Enterobacter sp. PMB-5, was inoculated into Cd contaminated pots to detect soil characteristics, Cd occurrence forms, soil biological activities, plant physiological and biochemical indicators. The results showed that the inoculation of strain PMB-5 significantly increased the available phosphorus content (85.97%−138.64%), Cd-residual fraction (11.04%−29.73%), soil enzyme activities (31.94%−304.63%), plant biomass (6.10%−59.81%), while decreased the state of Cd-HOAc (11.50%−31.17%) and plant bioconcentration factor (23.76%−44.24%). These findings indicated that strain PMB-5 could perform the function of phosphorus solubilization to realize the immobilization of Cd in the complex soil environment. Moreover, SEM-EDS, FTIR, XPS, and XRD analysis revealed that strain PMB-5 does not significantly alter the soil morphology, structure, elemental distribution, and chemical composition, which suggested that remediation of Cd contamination using strain PMB-5 would not further burden the soil. This research implies that PMB-5 could be a safe and effective bioinoculant for remediating Cd-contaminated soils, contributing to the sustainable management of soil health in contaminated environments.

Changes in Microbial Community and Activity of Chernozem Soil under Different Management Systems in a Long-Term Field Experiment in Hungary

The effects of intensive and reduced tillage, fertilization, and irrigation on soil chemical and microbiological parameters were studied in a long-term field experiment in Hungary. The treatments were plowing tillage, ripper tillage, strip tillage; control (without fertilization), NPK fertilization (N: 160 kg/ha; P: 26 kg/ha; K: 74 kg/ha); and non-irrigation and irrigation. Soil samples were collected through maize monoculture in the fall of 2021 in the 30th year of the experiment. The soil organic carbon, total nitrogen, soil microbial biomass (based on PLFA analysis), and soil enzyme activity were observed to be significantly high in the strip tillage plots, but were lower in the ripper tillage plots, and even lower in the plowing tillage plots. The fungal, arbuscular mycorrhiza fungal, and bacterial biomasses were significantly higher in the strip tillage and ripper tillage plots compared to the plowing tillage plots. The strip tillage treatment was found to be the most favorable cultivation method for improving the microbial biomass and activity of Chernozem soil, followed by the ripper tillage and plowing tillage treatments. The long-term use of chemical fertilizers greatly reduced the soil microbial biomass and negatively impacted the soil microbial community, leading to a decrease in fungi and Gram-negative bacteria. The ratio of cyclopropyl PLFA precursors to cyclopropyl PLFAs, as a “stress factor”, indicated the most stressful bacterial environment was that found in the fertilized, non-irrigated plowed soil.

Selenium and Bacillus proteolyticus SES increased Cu-Cd-Cr uptake by ryegrass: highlighting the significance of key taxa and soil enzyme activity.

Many studies have focused their attention on strategies to improve soil phytoremediation efficiency. In this study, a pot experiment was carried out to investigate whether Se and Bacillus proteolyticus SES promote Cu-Cd-Cr uptake by ryegrass. To explore the effect mechanism of Se and Bacillus proteolyticus SES, rhizosphere soil physiochemical properties and rhizosphere soil bacterial properties were determined further. The findings showed that Se and Bacillus proteolyticus SES reduced 23.04% Cu, 36.85% Cd, and 9.85% Cr from the rhizosphere soil of ryegrass. Further analysis revealed that soil pH, organic matter, soil enzyme activities, and soil microbial properties were changed with Se and Bacillus proteolyticus SES application. Notably, rhizosphere key taxa (Bacteroidetes, Actinobacteria, Firmicutes, Patescibacteria, Verrucomicrobia, Chloroflexi, etc.) were significantly enriched in rhizosphere soil of ryegrass, and those taxa abundance were positively correlated with soil heavy metal contents (P < 0.01). Our study also demonstrated that in terms of explaining variations of soil Cu-Cd-Cr content under Se and Bacillus proteolyticus SES treatment, soil enzyme activities (catalase and acid phosphatase) and soil microbe properties showed 42.5% and 12.2% contributions value, respectively. Overall, our study provided solid evidence again that Se and Bacillus proteolyticus SES facilitated phytoextraction of soil Cu-Cd-Cr, and elucidated the effect of soil key microorganism and chemical factor.

Response of bacterial communities, enzyme activities and dynamic changes of soil organic nitrogen fractions to six-year different application levels of biochar retention in Northeast China

Composition and availability of soil organic nitrogen play a key role in soil N retention and supply. The application of traditional chemical fertilizers can improve soil production and crop yields. However, it also leads to low N utilization efficiency and soil solidification. Previous studies have shown that fertilizers added with biochar can improve soil fertility and facilitate soil nutrient transformation by regulating soil biological indicators. However, whether biochar used with fertilizers can promote nutrient cycling in the long term, which remains to be tested. Therefore, this study aims to explore the long-term effects of biochar with different levels used with fertilizers on soil fertility, N supply potential of organic N, and microbial communities, thus, providing a theoretical reference for the rational management of biochar applications. In this study, a field experiment was carried out from 2013 to 2018 assess dynamic changes in organic N fractions and diversity and richness of microbial communities under the impacts of chemical fertilizers combined with different levels of biochar. Biochar with no amendment (CK), biochar with 15.75 t ha−1 (BC1), biochar with 31.5 t ha−1 (BC2), and biochar with 47.25 t ha−1 (BC3) are four biochar levels that were tested in this study. The results show that compared with CK, those other three biochar levels can increase soil organic matter, C/N, and pH values. Acid-hydrolysable N (AHN) makes a major contribution to organic N in soil. Biochar retention for six years has significantly affected AHN levels, as well as its four fractions, namely, amino acid N (AAN), acid-hydrolysable ammonium N (AN), amino sugar N (ASN), and hydrolysable unknown N (HUN). Some vital biological characteristics, with which each AHN fraction is primarily regulated, can be altered with the application of biochar. That is, AAN is mainly controlled by enriched Verrucomicrobia, Cyanobacteria, Glucosylbacteria, and Nitrospira, and reduced soil urease, while AN is mainly controlled by enriched Verrucomicrobia, Bacteroidetes, Gemmatimonadetes, Acidobacteria, and Proteobacteria. ASN is regulated by enriched Acidobacteria and depleted soil protease, while HUN is regulated by Gemmatimonadetes and enriched soil nitrate reductase. It has been found that microbial and soil enzyme activities are involved in N cycle processes, indicating that the formation of AHN fractions is closely associated with biochar-induced specific microbial and enzyme activities. This study has provided new insights into the influences of biochar with different levels on distribution of soil organic N fractions, and shifts in soil enzyme activities and microbial communities.

The Effects of Rock Zones and Tea Tree Varieties on the Growth and Quality of Wuyi Rock Tea Based on the OPLS-DA Model and Machine Learning

Rock zones have an important influence on the yield and quality of Wuyi rock tea. In this study, OPLS-DA combined with machine learning was used to analyze the effects of different rock zones and tea tree varieties on the physicochemical properties of rhizosphere soil, the growth of the tea tree and the quality of the tea leaves using tea trees in different rock zones. The results showed that rock zones had significant effects on rhizosphere soil physicochemical indexes, soil enzyme activities, tea tree growth and tea quality indexes, while there was little difference between different tea tree varieties. The interaction analysis showed that the physicochemical indexes of rhizosphere soil in different rock zones significantly affected tea quality, while also affecting growth indexes. The main indexes affecting tea yield and caffeine content were soil pH, available nitrogen, total phosphorus, total nitrogen and available phosphorus, while the main indexes affecting tea quality were available potassium, organic matter, total potassium, protease, polyphenol oxidase and urease. Analyses of PCA, OPLS-DA models and KNN and ANN machine learning showed that different rock zones could be effectively distinguished from each other with 100% accuracy, while different tea varieties had little difference and could not be distinguished. TOPSIS analysis found that the physicochemical indexes most affected by rock zone were available nitrogen, available potassium and sucrose, and the quality indexes most affected by rock zone were tea polyphenols and theanine. The growth index most affected by rock zone was tea yield. It was evident that the key difference between tea trees in different rock zones was yield and quality, with high yields in continent zones, and good quality in semi-rock zones and rock zones. This study provides a crucial foundation for tea-plantation management, the artificial regulation of tea yield and the quality of different rock zones of Wuyi rock tea.

Soil ecosystem multifunctionality is strongly linked with crop yield after four decades chemical fertilization in black soil

Soil ecosystem multifunctionality (EMF), the ability of an ecosystem to perform multiple functions, remains uncertain in its contribution to crop production, especially in the context of long-term fertilization ecosystems. This study was carried out on a 40-year-old long-term fertilization experiment in black soil in China. Soil samples were collected from four treatments: control (CK); nitrogen (N) fertilizer; phosphorus (P) fertilizer; and a combination of nitrogen and phosphorus (NP) in both maize and wheat planting seasons. The results showed significant effects of N, P fertilizers and crop season on soil biotic and abiotic properties, especially on soil enzyme activities. Crop productivity and soil EMF showed a similar pattern across different treatments and both crop seasons, with significant higher values recorded in treatments with N addition (i.e. N and NP). Soil EMF was strongly associated with crop productivity in both maize and wheat seasons, while soil pH had a negative impact on crop yield. Random forest analysis revealed that microbial functional gene structure was significantly correlated with both soil ecosystem multifunctionality and crop yield. This suggested that fertilization leads to alterations in soil nutrients and the composition of functional microbial communities, subsequently impacting ecological functions and crop growth. These findings indicated that mineral fertilizers can enhance crop yield through soil EMF in the black soils, while exerted substantial impact on soil properties, raising concerns about the sustainability of soils under continuous chemical fertilization.

Disturbance Level Mediates the Differential Resistance of Tropical Dry Forest Soil and Vegetation Attributes to High-Intensity Hurricanes

Hurricanes are extreme climatic events frequently affecting tropical regions such as the tropical dry forests (TDFs) in Mexico, where its frequency/intensity is expected to increase toward the year 2100. To answer how resistant is a Mexican tropical dry forest to a high-intensity hurricane, and if its degree of resistance was mediated by its conservation degree, we evaluated the effect of a category 4 hurricane over the tree community, soil nutrients, and soil enzymatic activity in two contrasting TDF ecosystems: Old-Growth Forest (OGF) and Secondary Forest (SF). In general, vegetation richness and diversity showed very high resistance one year after the hurricane, but several structural attributes did not, especially in the OGF where the tree mortality related to vegetation structure and spatial distribution of individuals was higher. Then, in the short term, SF vegetation appeared to be more resistant, whereas the OGF, with more biomass to lose, appeared to be more vulnerable. Conversely, most soil attributes showed low resistance in both stages, but especially in SF which could face more severe nutrient limitations. The response of TDF to high-intensity hurricanes, in terms of above- and belowground processes, was in part dependent on its disturbance level. Moreover, an increase in the intensity/frequency of hurricanes could lead this TDF toward a high nutrient limitation (especially by phosphorus) for the plants and consequently toward a loss of soil functioning, especially in the SF. This eventually could produce a severe degradation in fundamental attributes and functions of the ecosystem.