Long-term nitrogen addition increases denitrification potential and functional gene abundance and changes denitrifying communities in acidic tea plantation soil.

The response of soil denitrification to nitrogen (N) addition in the acidic and perennial agriculture systems and its underlying mechanisms remain poorly understood. Therefore, a long-term (12 years) field trial was conducted to explore the effects of different N application rates on the soil denitrification potential (DP), functional genes, and denitrifying microbial communities of a tea plantation. The study found that N application to the soil significantly increased the DP and the absolute abundance of denitrifying genes, such as narG, nirK, norB, and nosZ. The diversity of denitrifying communities (genus level) significantly decreased with increasing N rates. Moreover, the denitrifying communities composition significantly differed among the soils with different rates of N fertilization. Further variance partitioning analysis (VPA) revealed that the soil (39.04%) and pruned litter (32.53%) properties largely contributed to the variation in the denitrifying communities. Dissolved organic carbon (DOC) and soil pH, pruned litter's total crude fiber (TCF) content and total polyphenols to total N ratio (TP/TN), and narG and nirK abundance significantly (VIP >1.0) influenced the DP. Finally, partial least squares path modeling (PLS-PM) revealed that N addition indirectly affected the DP by changing specific soil and pruned litter properties and functional gene abundance. Thus, the findings suggest that tea plantation is a major source of N2O emissions that significantly enhance under N application and provide theoretical support for N fertilizer management in an acidic tea plantation system.

Metagenomics reveals N-induced changes in carbon-degrading genes and microbial communities of tea (Camellia sinensis L.) plantation soil under long-term fertilization.

Soil organic carbon (SOC) is an important C pool of the global ecosystem and is affected by various agricultural practices including fertilization. Excessive nitrogen (N) application is an important field management measure in tea plantation systems. However, the mechanism underlying the impact of N fertilization on SOC, especially the microscopic mechanism remain unclear. The present study explored the effects of N fertilization on C-cycling genes, SOC-degrading enzymes and microbes expressing these enzymes by using a metagenomic approach in a tea plantation under long-term fertilization with different N rates. Results showed that N application significantly changed the abundance of C-cycling genes, SOC-degrading enzymes, especially those associated with labile and recalcitrant C degradation. In addition, the beta-glucosidase and chitinase-expressing microbial communities showed a significant difference under different N rates. At the phylum level, microbial taxa involved in C degradation were highly similar and abundant, while at the genus level, only specific taxa performed labile and recalcitrant C degradation; these SOC-degrading microbes were significantly enriched under N application. Redundancy analysis (RDA) revealed that the soil and pruned litter properties greatly influenced the SOC-degrading communities; pH and DOC of the soil and biomass and total polyphenol (TP) of the pruned litter exerted significant effects. Additionally, the random forest (RF) algorithm revealed that soil pH and dominant taxa efficiently predicted the beta-glucosidase abundance, while soil pH and DOC, pruned litter TP, and the highly abundant microbial taxa efficiently predicted chitinase abundance. Our study indicated that long-term N fertilization exerted a significant positive effect on SOC-degrading enzymes and microbes expressing these enzymes, resulting in potential impact on soil C storage in a perennial tea plantation ecosystem.

[Status of Heavy Metal in Organic Fertilizers in Main Tea Growing Regions of China].

To provide guidance for the safe use of organic fertilizers and improve soil quality and tea safety, it is necessary to conduct systematic analyses of the heavy metal content of organic fertilizers applied in the main tea producing areas of China. In this study, we analyzed the heavy metal contents in organic fertilizer samples collected from 2017 to 2019. The risks of collected organic fertilizers from different areas and sources were calculated. The results showed that the average concentrations of ω(As), ω(Hg), ω(Pb), ω(Cd), ω(Cr), ω(Cu), ω(Zn), and ω(Ni) in the collected organic fertilizers were 4.60, 0.22, 27.1, 0.78, 27.9, 58.3, 250.1, and 16.3 mg·kg-1, respectively. According to the assessment standard in NY/T 525- 2021, the over-limit rates of As, Hg, Pb, Cd, and Cr were 6.19%, 1.33%, 4.42%, 4.42%, and 1.33%, respectively. With respect to the area, the qualified rates were 100% in Shaanxi, Jiangsu, Anhui, Fujian, and Guangxi; 80%-90% in Shandong, Zhejiang, Hubei, Sichuan, Yunnan, and Guangdong; and only 54.5% in Jiangxi. The qualified rates of sources were 100% in rapeseed cake, soybean cake, and pig manure; 95.8% in sheep manure; 91.7% in cow manure; 90.7% in chicken manure; 87.2% in manure of other animals; 82.4% in the mixture of plant and animal sources; 65.2% in other plant sources; and 63.6% in other sources. According to the recommended application rate, the accumulation rate of heavy metals in soil with pig manure, cow manure, chicken manure, and sheep manure would be much higher than that with rapeseed cake and soybean cake. The average accumulation rate of organic fertilizer from animal sources was 7-30 times higher than that from plant sources. Therefore, it is recommended to use rapeseed cake or soybean cake fertilizer in tea plantation and to increase the supervision of heavy metal accumulation in soil and tea in those high-risk areas.

Organic amendments improved soil quality and reduced ecological risks of heavy metals in a long-term tea plantation field trial on an Alfisol.

Tea plantation can cause strong soil degradation, e.g. acidification, basic nutrient decrease and microbial diversity loss, naturally by its root activity and secondary by practically tremendous synthetic N input. Organic amendments application is considered a practical way to mitigate the above adverse consequence. However, the trade-off between agronomic and environmental effects on the application of the organic amendments is still under debate. Herein, we conducted a long-term field experiment with four treatments, including control (without and fertiliser) (CK), chemical fertiliser treatment (CF), chicken manure treatment (CM) and chicken manure combined with biochar treatment (CMB) to investigate the effects of organic amendments application on soil quality, heavy metal contamination and tea production in a tea plantation. Totally 16 plots were arranged randomly with a completely randomised design. The results showed that CM and CMB treatments improved soil nutrient, mitigated soil acidification and ameliorated soil porosity compared to CF treatment. CMB treatment displayed a relatively high tea yield and quality in three consecutive years of monitoring. However, CM and CMB treatments elevated the heavy metal (HM) potential ecological risk (RI) and Nemerow's composite index (Ps). CM treatment significantly increased available As, Pb, Cu and Zn concentrations compared to CF treatment, while CMB treatment significantly decreased available Cr and Cu concentrations and slightly decreased available Cd, Pb and Ni concentrations compared to CM treatment. But the increase of available As and Zn in CMB treatment compared to CM treatment also indicated adverse effects of biochar addition. The PLS-PM model showed HM risk had direct negative effects on tea quality. Moreover, soil fungal community revealed positive effects on tea yield and negative effects on tea quality. Overall, our study proved that CMB treatment could improve soil quality, reduce available Cr and Ni concentrations, maintain tea yield and increase tea quality.

Extracellular polymeric substance induces biogenesis of vivianite under inorganic phosphate-free conditions.

Vivianite is often found in reducing environments rich in iron and phosphorus from organic debris degradation or phosphorus mineral dissolution. The formation of vivianite is essential to the geochemical cycling of phosphorus and iron elements in natural environments. In this study, extracellular polymeric substances (EPS) were selected as the source of phosphorus. Microcosm experiments were conducted to test the evolution of mineralogy during the reduction of polyferric sulfate flocs (PFS) by Shewanella oneidensis MR-1 (S. oneidensis MR-1) at EPS concentrations of 0, 0.03, and 0.3 g/L. Vivianite was found to be the secondary mineral in EPS treatment when there was no phosphate in the media. The EPS DNA served as the phosphorus source and DNA-supplied phosphate could induce the formation of vivianite. EPS impedes PFS aggregation, contains redox proteins and stores electron shuttle, and thus greatly promotes the formation of minerals and enhances the reduction of Fe(III). At EPS concentration of 0, 0.03, and 0.3 g/L, the produced HCl-extractable Fe(II) was 107.9, 111.0, and 115.2 mg/L, respectively. However, when the microcosms remained unstirred, vivianite can be formed without the addition of EPS. In unstirred systems, the EPS secreted by S. oneidensis MR-1 could agglomerate at some areas, resulting in the formation of vivianite in the proximity of microbial cells. It was found that vivianite can be generated biogenetically by S. oneidensis MR-1 strain and EPS may play a key role in iron reduction and concentrating phosphorus in the oligotrophic ecosystems where quiescent conditions prevail.

Ecological management model for the improvement of soil fertility through the regulation of rare microbial taxa in tea (Camellia sinensis L.) plantation soils.

Agricultural management is essential to enhance soil ecosystem service function through optimizing soil physical conditions and improving nutrient supply, which is predominantly regulated by soil microorganisms. Several studies have focused on soil biodiversity and function in tea plantation systems. However, the effects of different agriculture managements on soil fertility and microbes remain poorly characterized, especially for what concerns perennial agroecosystems. In this study, 40 soil samples were collected from 10 tea plantation sites in China to explore the effects of ecological and conventional managements on soil fertility, as well as on microbial diversity, community composition, and co-occurrence network. Compared with conventional management, ecological management was found to significantly enhance soil fertility, microbial diversity, and microbial network complexity. Additionally, a significant difference in community composition was clearly observed under the two agriculture managements, especially for rare microbial taxa, whose relative abundance significantly increased under ecological management. Random forest modeling revealed that rare taxa (e.g., Rokubacteria and Mortierellomycota), rather than dominant microbial taxa (e.g., Proteobacteria and Ascomycota), were key variables for predicting soil fertility. This indicates that rare taxa might play a fundamental role in biological processes. Overall, our results suggest that ecological management is more efficient than conventional management in regulating rare microbial taxa and maintaining a good soil fertility in tea plantation systems.

Characterization of three different classes of non-fermented teas using untargeted metabolomics.

Non-fermented teas, which are widely consumed in China, Japan, Korea, and elsewhere, have refreshing flavors and valuable health benefits. Various types of non-fermented teas look and taste similar and have no obvious differences in appearance, making their classification challenging. To date, there are very few reports about characterization and discrimination of different types of non-fermented teas. To characterize non-fermented teas and build a standard model for their classification based on their chemical composition, we employed multi-platform-based metabolomics to analyze primary and secondary metabolites in three main categories of non-fermented teas (green, yellow, and white), using 96 samples collected from China. Five hundred and ninety unique tea metabolites were identified and quantified in these three types of teas. Moreover, a partial least squares discriminant analysis (PLS-DA) model was established based on metabolomics data, in order to classify non-fermented teas into these three classes. Furthermore, our results speculate that the health benefits (e.g., antioxidant content) of these three types of non-fermented tea differ primarily because of variation in their metabolic components (e.g., ascorbate, vitexin).

Soil fluoride fractions and their bioavailability to tea plants (Camellia sinensis L.).

Drinking teas containing high fluoride (F) imposes fluorosis risk. The soil F bioavailability is an important factor influencing its uptake and contents in teas. The present work was conducted to investigate F fractions in soil and their bioavailability to tea plants. Tea seedlings were cultivated on 6 typical soils treated with a mixture consisting of dolomite, lime, peat and KCl at variable rates in the pot experiment. Soils and young shoots were collected in pairs from 63 sites of 21 plantations in a field experiment. Soil fluoride was sequentially separated into hot water soluble [Formula: see text], exchangeable [Formula: see text] (by 1 mol L-1 MgCl2, pH = 7.0), F bound to Mn and Fe hydroxides [F(oxides,s)], and organic matter [F(OM,s)] or extracted independently by water [Formula: see text] or 0.01 mol L-1 CaCl2 solution [Formula: see text]. Averaged [Formula: see text], [Formula: see text], F(oxides,s) and F(OM,s) accounted for 51, 14, 5 and 30 % of the total sequential extracts, respectively. There were significant correlations among [Formula: see text], [Formula: see text] and F(OM,s). Fluoride contents in leaves correlated with [Formula: see text] (r = 0.71, p < 0.001), [Formula: see text] (r = 0.93, p < 0.001) and F(OM,s) (r = 0.69, p < 0.01) but not other fractions in the pot experiment and with [Formula: see text] (r = 0.43-0.57, p < 0.001) and [Formula: see text] (r = 0.42-0.79, p < 0.001) in the field experiment. It was concluded that 0.01 M CaCl2 extractable fluoride can be a good indicator of soil F bioavailability to tea plants. The significant correlations among some of the F fractions suggested that F in solution, AlF complexes (AlF2+, AlF2+) and those bound to organic matter likely represent the available pools to tea plants.

Metabolomic analysis using ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC-Q-TOF MS) uncovers the effects of light intensity and temperature under shading treatments on the metabolites in tea.

To investigate the effect of light intensity and temperature on the biosynthesis and accumulation of quality-related metabolites, field grown tea plants were shaded by Black Net and Nano-insulating Film (with additional 2-4°C cooling effect) with un-shaded plants as a control. Young shoots were subjected to UPLC-Q-TOF MS followed by multivariate statistical analysis. Most flavonoid metabolites (mainly flavan-3-ols, flavonols and their glycosides) decreased significantly in the shading treatments, while the contents of chlorophyll, ß-carotene, neoxanthin and free amino acids, caffeine, benzoic acid derivatives and phenylpropanoids increased. Comparison between two shading treatments indicated that the lower temperature under Nano shading decreased flavonols and their glycosides but increased accumulation of flavan-3-ols and proanthocyanidins. The comparison also showed a greater effect of temperature on galloylation of catechins than light intensity. Taken together, there might be competition for substrates between the up- and down-stream branches of the phenylpropanoid/flavonoid pathway, which was influenced by light intensity and temperature.