Jianyun Ruan

Tea cultivar genotype plays a critical role in shaping rhizosphere microbiome assembly, yet the underlying mechanisms remain poorly understood. This study employed a controlled pot experiment with five widely cultivated Chinese tea cultivars (Camellia sinensis) to investigate how cultivar-specific variation influences rhizosphere microbial communities and their assembly processes. Rhizosphere soil microbiomes (bacterial and fungal communities) and metabolomes were characterized using 16S rRNA and ITS2 amplicon sequencing combined with untargeted metabolomics. Significant differences in rhizosphere metabolite composition, primarily organic acids, fatty acids, and carbohydrates, were observed among cultivars, which corresponded to distinct bacterial and fungal community structures. Redundancy analysis (RDA) revealed that rhizosphere metabolites explained 19.87% of bacterial and 21.63% of fungal community compositional variation, second only to soil physicochemical properties. Neutral community model and modified stochasticity ratio analyses indicated that microbial assembly across cultivars was predominantly deterministic, and rhizosphere metabolite profiles were strongly correlated with microbial community structure. Notably, arbuscular mycorrhizal fungi made up about 11% of the fungal communities in minimally fertilized pot systems, contrasting sharply with their near-absence in conventionally managed systems plantations. These findings demonstrate that tea cultivar genotype significantly shapes rhizosphere microbiome assembly through metabolic differentiation, providing a theoretical foundation for integrating microbiome considerations into tea breeding programs and developing cultivar-specific management strategies.

Nitrogen (N) plays a dual role in tea plants, serving as both an essential nutrient for growth, and a key regulator of quality-related secondary metabolism. Recent research has concentrated on elucidating how different levels or forms of N influence key secondary metabolites, such as amino acids, flavonoids, caffeine, and aroma compounds, and how these metabolites collectively determine the flavor of tea. However, excessive N application can adversely affect tea quality and reduce nitrogen use efficiency (NUE). This review systematically examines recent advances in understanding how N signaling modulates these pathways, with particular emphasis on the molecular mechanisms underlying N-regulated gene expression, enzyme activity, and inter-pathway crosstalk. We further discuss how this knowledge informs the development of targeted agronomic practices and breeding strategies aimed at achieving sustainable tea production—optimizing quality while enhancing NUE under reduced N input.

Anji Baicha is produced from 'Baiye 1', which is an albino cultivar of tea (Camellia sinensis). It is highly prized for its unique characteristic of accumulating high levels of free amino acids, especially theanine. Conventional fertilization practices used to maintain leaf albinism often compromise yield and quality. Therefore, the present study used an optimized fertilization strategy, combining adjusted N-P-K ratios with Mg supplementation, to enhance plant nutrition while preserving the desired albinism feature. Field experiments were carried out to compare farmers' practice (FFP), optimized N-P-K (OPT), and OPT+Mg. Compared with FFP, OPT, and OPT+Mg treatment significantly increased tea yield by 22%–29% and the amino acid (including theanine) content in new shoots (p > 0.05), while successfully maintaining leaf albinism. They also improved soil nutrient availability, microbial diversity, and enhanced soil quality by 19.4%–75%. Both OPT and OPT+Mg treatments reshaped soil bacterial and fungal communities, enriching specific beneficial microbial taxa. Random Forest predictive analysis indicated that bacterial biomarkers exerted a greater influence on tea yield and amino acid content than fungal biomarkers, accounting for 57% and 51.4% of the predicted variance for yield and amino acids, respectively (compared to 43% and 48.6% for fungi). Acidicaldus and Deniquelata were identified as key biomarkers for yield, while Cupriavidus and Aspergillus were key biomarkers associated with variation in amino acid content. Thus, findings demonstrate that adequate N fertilization is crucial for optimal growth of this albino tea cultivar, and Mg supplementation under optimal N supply provides synergistic advantages. The study establishes a scientific framework for the sustainable production of Anji Baicha.

Applying a top dressing of nitrogen fertilizer before harvesting spring tea is vital for producing high-quality spring tea. However, the interaction between the sprouting phenological characteristics of various cultivars and the timing of top dressing remains unclear. A field trial was conducted to investigate such interaction. Urea enriched with ¹⁵N was applied to soil of the early-sprouting cultivar Jia-ming-1 (JM1) and the late-sprouting cultivar Tie-guan-yin (TGY) on 29 January (early application, EApp) or 10 March (late application, LApp), respectively. The bud density and yield of young spring shoots were significantly decreased in LApp compared to EApp. Such differences were more remarkable in the early-sprouting cultivar (JM1) than in the late-sprouting cultivar (TGY). The N_dff (N derived from ¹⁵N-enriched urea) in mature leaves and young spring shoots as well as the amount of ¹⁵N in young spring shoots were all higher in EApp than in LApp. N_dff in both mature leaves (R² = 0.99, p < 0.001) and young spring shoots (R² = 0.61–0.89, p < 0.01) could be well predicted by the growing degree days of the duration between the N fertilization and sampling. N_dff and ¹⁵N concentrations in mature leaves were significantly correlated with the content of nitrate and the ratio of ammonium to total inorganic nitrogen. Partial least squares path modeling revealed that thermal condition directly affected soil N supply and soil pH and thereby affected N_dff in mature leaves and young spring shoots. Our findings highlight the importance of early pre-spring topdressing of N fertilizer to improve the yield and N use efficiency of spring tea in both early- and late-sprouting tea cultivars. The work identified a synergistic effect of N uptake by tea plants, N transformation, and soil pH related to the thermo-conditions of early and late N topdressing.

Selecting and breeding tea plant varieties with low nitrogen tolerance is crucial for reducing the application of nitrogen fertilizer in tea gardens and promoting the green and sustainable production of tea. Thus, a split-plot designed field experiment was conducted in a subtropical tea garden in China, where ten distinct cultivars were planted and exposed to two different levels of nitrogen (N) supply. This study aimed to assess the response of these cultivars to normal (450 kg ha⁻¹) and low (150 kg ha⁻¹) N fertilization treatments and to evaluate their tolerance to low N conditions. The results revealed notable differences in both the growth and biomass responses of the tea cultivars to N supply levels. Under low N supply, tea tree height, pruned litter biomass, and its nitrogen accumulation were all significantly lower than those under the normal N level. There was also a significant interaction effect between the cultivar and N level in the one-hundred-bud weight, new shoot yield, and its nitrogen content, respectively. The amount of total N uptake by harvested new shoots was relatively low, whereas a considerable amount of N was returned to the garden through pruned biomass. The aboveground biomass and its nitrogen accumulation could be considered as critical indicators for identifying nitrogen-tolerant cultivars with a variation coefficient by 20% and 20.57%, respectively. Additionally, cluster analysis showed that BY1 and LJ43 were strong low N-tolerant cultivars, while HJY was the most N-sensitive cultivar, closely followed by the ZN117 tea plants. In conclusion, significant disparities were observed in the adaptability of different tea cultivars to low N fertilization under the ambient field conditions. This study provided valuable theoretical insights and practical references for selecting N-tolerant tea varieties and reducing N fertilizer consumption in tea gardens.

Nitrate (NO3−), a key form of inorganic nitrogen (N) in soils, is typically lost in tea gardens through leaching. However, NO3− utilization efficiency (NiUE) and its characteristic mechanism in tea plants remain unclear. This study screened contrastive genotypes of NiUE using leaf chlorate sensitivity and explored the potential genes that regulate this process. Fresh branches of 10 cultivars were hydroponically cultivated and subjected to potassium nitrate (KNO3) and potassium chlorate (KClO3) treatments, with the former as the control group. The sensitive cultivar, Zhenong 117 (ZN117), showed a decrease in SPAD and Fv/Fm values following KClO3 treatment, while the tolerant cultivar, Teiguanyin (TGY), exhibited minimal significant changes. After 5 days of cultivation, the 15N concentration and proportion in new shoots of ZN117 were significantly higher than those in TGY. Transcriptome analysis revealed that the expression of genes responsible for NO3− transport, including the nitrate transporters NRT2.4, NPF4.6, NPF6.1, NPF1.10, and NPF1.11, significantly increased in ZN117 after NO3− supply. Genes involved in NO3− reduction, chlorophyll synthesis, and photosynthesis were progressively induced. Coexpression network analysis indicated that the squamosa promoter-binding protein activated the onset of NO3− signaling, while basic helix–loop–helix transcripts were triggered to higher levels during NO3− supply. This study proposes a rapid characterization method of NiUE in woody plants and a speculative molecular regulatory mechanism for the NO3− transfer and remobilization of tea plants. A set of specific genes involved in NO3− transport, reduction, and mobilization were identified and proposed as marker genes for NiUE in tea plants.

Nitrogen (N) remobilization from mature leaves to new shoots (NSs) is closely related to the quality of green tea in the spring season, which subsequently determines its economic value. However, the underlying N remobilization mechanism remains poorly understood. Here, we demonstrate that >80% of the recovered 15N was partitioned in the first mature leaves that supply NSs. N-remobilization efficiency (NRE) from mature leaves to NSs varied significantly among tea cultivars. N-fertilization level and NRE showed a significantly positive correlation. Based on weighted gene co-expression network analysis, glutamate metabolism-related genes, including glutamine synthetase genes, CsGSs, were dissected from the interaction network of hub genes regulating N remobilization. Gene expression patterns and the localization of CsGS1.1 in the cytosol and vascular tissue suggest its potential role in N remobilization. Consistent with these findings, source-to-sink N remobilization at the reproductive stage was enhanced in transgenic CsGS1.1-overexpressing plants. Furthermore, we demonstrated that the Dof transcription factor CsDof16 directly binds to the −526 to −426 region of the CsGS1.1 promoter, thereby activating its transcription and regulating N remobilization. Taken together, our findings suggest that the CsDof16-CsGS1.1 module regulates the remobilization of N in the form of glutamate/glutamine from mature leaves to NSs, constituting an important control point in the regulation of source-to-sink N partitioning in tea plants. Our findings can be employed to reduce fertilizer application and promote the development of sustainable tea production.

Anthocyanins, key quality components of tea, act as an important bridge between plants and the environment due to their function on protecting plants from biotic and abiotic irritants. This study aimed to assess the interactions between anthocyanins metabolism and the environment. Purple (P) and green (G) leaves with different anthocyanin contents were inoculated with tea plant anthracnose. High-throughput metabolomics and 16S microbial diversity sequencing methods were used to screen the anthocyanin fractions of tea plant leaves responsive to anthracnose. The interconnections between metabolites and the resistance of phyllosphere microorganisms to fungal pathogens were then analyzed. The results showed that leaves with high anthocyanin content (0.14% of diseased area ratio) were less impacted by anthracnose infestation than leaves with low anthocyanin (3.12%). The cyanidin content decreased after infection in purple leaves (PR) and increased in green leaves (GR). The relative abundance of Cyanobacteria was suppressed by the significant enrichment of Proteobacteria after anthracnose infection in green leaves. However, there were no significant differences between these two groups of microorganisms in purple leaves. Collinear network analysis revealed a strong correlation between Cyanobacteria and Dihydrosorbinol and between Proteobacteria and cyanidin metabolites. Among them, OTU456 (Bosea) was identified as the key taxonomic group of bacterial communities in the green-infected leaf network. In summary, the anthracnose resistance benefits from cyanidin mediated by proteobacteria in tea plants. These results deepen our understanding of the regulation of secondary metabolism in tea plants and the formation of plant resistance.

Great concern has long been raised about nitrate leaching in cropland due to its possible environmental side effects in ground water contamination. Here we employed two common techniques to measure nitrate leaching in tea plantation soils in subtropical China. Using drainage lysimeter as a reference method, the adaptability of estimating drainage and nitrate leaching by combining the water balance equation with the suction cup technique was investigated. Results showed that the final cumulative leachate volume for the calculated and measured method was 721.43 mm and 729.92 mm respectively during the study period. However, nitrate concentration exerted great influence in the estimation of nitrate leaching from the suction cup-based method. The cumulative nitrate leaching loss from the lysimeter and suction cup-based method was 47.45 kg ha⁻¹ and 43.58 kg ha⁻¹ under lysimeter nitrate concentrations ranging from 7 mg L⁻¹ to 13 mg L⁻¹, 156.28 kg ha⁻¹ and 79.95 kg ha⁻¹ under lysimeter nitrate concentrations exceeding 13 mg L⁻¹. Therefore, the suction cup-based method could be an alternative way of monitoring nitrate leaching loss within a range of 7–13 mg L⁻¹ of nitrate concentrations in leachate. Besides, lower results occurred in suction cup samplers due to lack of representative samples which mainly leached via preferential flow when in strong leaching events. Thus, it is advisable to increase sampling frequency under such special conditions. The results of this experiment can serve as a reference and guidance for the application of ceramic cups in monitoring nitrogen and other nutrient-ion leaching in tea plantation soils.

Proper nutrient management is crucially important to the sustainable development of tea production. Compared to normal green-leaf cultivars, albino tea cultivars produce green tea of superior quality characterized by high contents of amino acids as a result of the hydrolysis of chloroplast proteins at albinism. However, the advantage of albino tea cultivars was offset by inferior growth and yield performance because of low contents of chlorophylls and limited photosynthesis capacity. Our understanding about the nutrition characteristics of albino tea cultivars was very limited. A four-year field experiment was conducted to develop proper nutrient management for Baiye-1 to overcome its weakness of low productivity without a tradeoff in tea quality and environmental risks. The nutrient management schemes were formulated by optimizing the rate and ratio of nitrogen (N), phosphorus, potassium and magnesium together with substitution of chemical fertilizers with organic manures. The total amounts of nutrients in the optimized schemes were reduced by 25% compared to the local farmers’ practice (FP). Results showed that optimized rates and ratio of nutrients together with partial substitution of chemical fertilizers with rapeseed cake manure more considerably improved albino tea yield, the contents of free amino acids, total polyphenol and catechins relative to FP. Partial substitution of chemical fertilizers with commercial livestock manure decreased tea quality, which was likely caused by a dilution effect of increasing tea yield and decreasing N status of tea plants. Full organic substitution of chemical fertilizers by rapeseed cake manure improved tea yield and quality but had relatively low agronomic efficiency and profit. The effect of optimized nutrient management schemes was associated with the improvement of nutritional status in tea plants. The present work demonstrated that the optimization of nutrient management considerably improved albino tea yield, quality and profit while decreased the application rate of fertilizers and the intensity of greenhouse gas emissions.