UBL-UBA protein functions as a shuttle factor in the 26S ubiquitin degradation pathway, playing a critical role in plant growth and development, and responding to various biotic and abiotic stresses.  Although RAD23, a type of UBL-UBA protein, has been extensively studied in several plants, there is currently no comprehensive analysis available for kiwifruit (Actinidia chinensis).  In this study, we identified six AcRAD23 genes in kiwifruit and further analyzed their phylogenetic relationships, gene structure, conserved motif composition and cis-acting element in the promoter.  Subcellular localization experiments revealed that all AcRAD23 were localized in the nucleus and the cell membranes.  Quantitative real-time PCR (qRT-PCR) analysis demonstrated differential expression patterns of these AcRAD23 genes across different tissues and under various stress conditions (drought, waterlogging, salt stress, etc.), with AcRAD23D1 showing the highest responsiveness to abiotic stress.  Additionally, we investigated the biological function of AcRAD23D1 using VIGS-mediated gene silencing methods under drought stress conditions.  Suppression of AcRAD23D1 expression resulted in reduced relative water content (RWC) but increased malondialdehyde (MDA) content and relative electrolyte leakage (REL) levels in D1-VIGS lines compared to control lines.  Furthermore, D1-VIGS lines exhibited a higher accumulation of reactive oxygen species (ROS) along with decreased superoxide dismutase (SOD) and peroxidase (POD) enzyme activities.  These findings suggest that AcRAD23D1 may play a positive role in regulating kiwifruit’s response to drought stress.  Our results provide new insights into the potential involvement of AcRAD23 under abiotic stress conditions while offering a theoretical foundation for understanding the molecular mechanisms underlying kiwifruit’s adaptation to stresses. 

The practice of conservation tillage or straw return to the farmland influences the grain yield and quality of rice (Oryza sativa).  The key volatile compound responsible for the fragrance of fragrant rice is 2-acetyl-1-pyrroline (2-AP), which is significantly affected by field management measures.  The purpose of this study was to investigate the impact of tillage management and straw return on the grain yield and biosynthesis of 2-AP in fragrant rice.  This study was conducted over two years in 2016 and 2017 and used two fragrant rice cultivars (Meixiangzhan 2 and Xiangyaxiangzhan) as materials.  The experimental design consisted of different tillage management and straw return treatments, which included three tillage management regimes: rotary tillage (T0), minimum tillage (T1), and no tillage (T2); and two straw return treatments: without straw return (S0) and straw return (S1).  The straw used for the experiment was sourced from the residue of the corresponding fragrant rice cultivar harvested in the early season.  Tillage management and straw return substantially affected the grain yields, grain quality, and 2-AP contents of both fragrant rice cultivars.  Compared with the T0S0 treatment, tillage management and straw return resulted in 2-AP content improvements in 2016 (12.41–116.85%) and 2017 (34.85–103.89%) on average.  Higher 2-AP contents were also detected in both fragrant rice cultivars in the T2S1 and T1S1 treatments.  A structural equation model (SEM) demonstrated that the activities of enzymes related to fragrance metabolism in the leaves and grain jointly regulated the biosynthesis of precursors of fragrance metabolism in the grain, which further promoted the accumulation of 2-AP.  In addition, a principal component analysis indicated that the T1S1 treatment was positively correlated with both 2-AP and grain yield.  The SEM demonstrated that the enzymes related to nitrogen metabolism, parameters related to photosynthesis, and yield components contributed to the grain yield.  The T1S1 treatment resulted in the highest average grain yield of 760.75 g m^–2, which could be attributed to increases in various attributes, such as the leaf area index, SPAD value, nitrogen metabolism, panicle number m^–2, and grain number per panicle.  In summary, the minimum tillage and straw return (T1S1) treatment is more effective at simultaneously improving both the grain yield and 2-AP content in fragrant rice.

Nitrogen (N) uptake is regulated by water availability, and a water deficit can limit crop N responses by reducing N uptake and utilization.  The complex and multifaceted interplay between water availability and the crop N response makes it difficult to predict and quantify the effect of water deficit on crop N status.  The nitrogen nutrition index (NNI) has been widely used to accurately diagnose crop N status and to evaluate the effectiveness of N application.  The decline of NNI under water-limiting conditions has been documented, although the underlying mechanism governing this decline is not fully understood.  This study aimed to elucidate the reason for the decline of NNI under water-limiting conditions and to provide insights into the accurate utilization of NNI for assessing crop N status under different water–N interaction treatments.  Rainout shelter experiments were conducted over three growing seasons from 2018 to 2021 under different N (75 and 225 kg N ha^–1, low N and high N) and water (120 to 510 mm, W0 to W3) co-limitation treatments.  Plant N accumulation, shoot biomass (SB), plant N concentration (%N), soil nitrate-N content, actual evapotranspiration (ET_a), and yield were recorded at the stem elongation, booting, anthesis and grain filling stages.  Compared to W0, W1 to W3 treatments exhibited NNI values that were greater by 10.2 to 20.5%, 12.6 to 24.8%, 14 to 24.8%, and 16.8 to 24.8% at stem elongation, booting, anthesis, and grain filling, respectively, across the 2018–2021 seasons.  This decline in NNI under water-limiting conditions stemmed from two main factors.  First, reduced ET_a and SB led to a greater critical N concentration (%N_c) under water-limiting conditions, which contributed to the decline in NNI primarily under high N conditions.  Second, changes in plant %N played a more significant role under low N conditions.  Plant N accumulation exhibited a positive allometric relationship with SB and a negative relationship with soil nitrate-N content under water-limiting conditions, indicating co-regulation by SB and the soil nitrate-N content.  However, this regulation was influenced by water availability.  Plant N accumulation sourced from the soil nitrate-N content reflects soil N availability.  Greater soil water availability facilitated greater absorption of soil nitrate-N into the plants, leading to a positive correlation between plant N accumulation and ET_a across the different water–N interaction treatments.  Therefore, considering the impact of soil water availability is crucial when assessing soil N availability under water-limiting conditions.  The findings of this study provide valuable insights into the factors contributing to the decline in NNI among different water–N interaction treatments and can contribute to the more accurate utilization of NNI for assessing winter wheat N status.

Tobacco (Nicotiana tabacum) and tomato (Solanum lycopersicum) are two major economic crops in China.  Tobacco mosaic virus (TMV; genus Tobamovirus) is the most prevalent virus infecting both crops.  Currently, some widely cultivated tobacco and tomato cultivars are susceptible to TMV and there is no effective strategy to control this virus.  Cross-protection can be a safe and environmentally friendly strategy to prevent viral diseases.  However, stable attenuated TMV mutants are scarce.  In this study, we found that the substitutions in the replicase p126, arginine at position 196 (R¹⁹⁶) with aspartic acid (D), glutamic acid at position 614 (E⁶¹⁴) with glycine (G), serine at position 643 (S⁶⁴³) with phenylalanine (F), or D at position 730 (D⁷³⁰) with S, significantly reduced the virulence and replication of TMV.  However, only the mutation of S⁶⁴³ to F reduced the RNA silencing suppression activity of TMV p126.  A double-mutant TMV-E614G-S643F induced no visible symptom and was genetically stable through six successive passages in tobacco plants.  Furthermore, our results showed that TMV-E614G-S643F double-mutant could provide effective protection against the wild-type TMV infection in tobacco and tomato plants.  This study reports a promising mild mutant for cross-protection to control TMV in tobacco and tomato plants.

Integrated water and fertilizer management is important for promoting sustainable development of facility agriculture, and biochar plays an important role in guaranteeing food production, as well as alleviating water shortages and the overuse of fertilizers.  The field experiment had twelve treatments and a control (CK) trial including two irrigation amounts (I₁, 100% ET_m; I₂, 60% ET_m; where ET_m is the maximum evapotranspiration), two nitrogen applications (N₁, 360 kg ha^–1; N₂, 120 kg ha^–1) and three biochar application levels (B₁, 60 t ha^–1; B₂, 30 t ha^–1 and B₃, 0 t ha^–1).  A multi-objective synergistic irrigation–nitrogen–biochar application system for improving tomato yield, quality, water and nitrogen use efficiency, and greenhouse emissions was developed by integrating the techniques of experimentation and optimization.  First, a coupled irrigation–nitrogen–biochar plot experiment was arranged.  Then, tomato yield and fruit quality parameters were determined experimentally to establish the response relationships between irrigation–nitrogen–biochar dosage and yield, comprehensive quality of tomatoes (TCQ), irrigation water use efficiency (IWUE), partial factor productivity of nitrogen (PFPN), and net greenhouse gas emissions (NGE).  Finally, a multi-objective dynamic optimization regulation model of irrigation–nitrogen–biochar resource allocation at different growth stages of tomato was constructed which was solved by the fuzzy programming method.  The results showed that the application of irrigation and nitrogen to biochar promoted increase in yield, IWUE and PFPN, while it had an inhibitory effect on NGE.  In addition, the optimal allocation amounts of water and fertilizer were different under different scenarios.  The yield of the S1 scenario increased by 8.31% compared to the B₁I₁N₂ treatment; TCQ of the S2 scenario increased by 5.14% compared to the B₂I₂N₁ treatment; IWUE of the S3 scenario increased by 10.01% compared to the B₁I₂N₂ treatment; PFPN of the S4 scenario increased by 9.35% compared to the B₁I₁N₂ treatment; and NGE of the S5 scenario decreased by 11.23% compared to the B₂I₁N₁ treatment.  The optimization model showed that the coordination of multiple objectives considering yield, TCQ, IWUE, PFPN, and NGE increased on average from 4.44 to 69.02% compared to each treatment when the irrigation–nitrogen–biochar dosage was 205.18 mm, 186 kg ha^–1 and 43.31 t ha^–1, respectively.  This study provides a guiding basis for the sustainable management of water and fertilizer in greenhouse tomato production under drip irrigation fertilization conditions.

The constant evolution of pathogens poses a threat to wheat resistance against diseases, endangering food security.  Developing resistant wheat varieties is the most practical approach for circumventing this problem.  As a close relative of wheat, Aegilops geniculata, particularly accession SY159, has evolved numerous beneficial traits that could be applied to improve wheat.  In this study, we established the karyotype of SY159 by fluorescence in situ hybridization (FISH) using the oligonucleotide probes Oligo-pTa535 and Oligo-pSc119.2 and a complete set of wheat–Ae. geniculata accession TA2899 addition lines as a reference.  Using specific-locus amplified fragment sequencing (SLAF-seq) technology, 400 specific markers were established for detecting the SY159 chromosomes with efficiencies reaching 81.5%.  The SY159-specific markers were used to classify the different homologous groups of SY159 against the wheat–Ae. geniculata addition lines.  We used these specific markers on the 7M^g chromosome after classification, and successfully confirmed their suitability for studying the different chromosomes of SY159.  This study provides a foundation for accelerating the application of SY159 in genetic breeding programs designed to improve wheat. 

Chemical insecticides targeting the digestive system of diamondback moth (DBM), Plutella xylostella, have not been developed.  The discovery of an insecticide with novel mode of action is a challenge for the control of DBM.  In this study, a class of selenium- and difluoromethyl-modified azoles (fluoroazole selenoureas, FASU) were designed and synthesized for the control of DBM.  Of these azoles, compound B4 showed the highest insecticidal activity against DBM.  The LC₅₀ of third- and second-instar larvae reached 32.3 and 4.6 μg mL^–1, respectively.  The midgut tissue of larvae was severely disrupted, and the larval intestinal tissue was dotted with unique red spots after treatment with compound B4.  Compound B4 led to disintegration of the peritrophic matrix, swelling of the midgut epithelium, fracture of the microvilli, and extensive leakage of cellular debris in the midgut lumen.  Surviving larvae grew very slowly, and the larval duration was significantly prolonged after exposure to compound B4 at sublethal doses (LC₁₀, LC₂₅ and LC₅₀).  Furthermore, the pupation rate, emergence rate and pupae weight were significantly decreased.  Compound B4 also induced abnormal pupae, causing adults to be trapped in the cocoon or failure to fly due to twisted wings.  These results demonstrated that FASU could reduce the population of DBM in sublethal doses.  FASU is the first synthetic insecticidal lead compound that has been shown to disrupt the midgut tissue of the larvae of DBM, and its mode of action totally differs from that of commercial chemical insecticides.

Methane (CH₄) emissions from ruminant production are a significant source of anthropogenic greenhouse gas production, but few studies have examined the enteric CH₄ emissions of lactating dairy cows under different feeding regimes in China.  This study aimed to investigate the influence of different dietary neutral detergent fiber/non-fibrous carbohydrate (NDF/NFC) ratios on production performance, nutrient digestibility, and CH₄ emissions for Holstein dairy cows at various stages of lactation. It evaluated the performance of CH₄ prediction equations developed using local dietary and milk production variables compared to previously published prediction equations developed in other production regimes.  For this purpose, 36 lactating cows were assigned to one of three treatments with differing dietary NDF/NFC ratios: low (NDF/NFC=1.19), medium (NDF/NFC=1.54), and high (NDF/NFC=1.68).  A modified acid-insoluble ash method was used to determine nutrient digestibility, while the sulfur hexafluoride technique was used to measure enteric CH₄ emissions.  The results showed that the dry matter (DM) intake of cows at the early, middle, and late stages of lactation decreased significantly (P<0.01) from 20.9 to 15.4 kg d^–1, 15.3 to 11.6 kg d^–1, and 16.4 to 15.0 kg d^–1, respectively, as dietary NDF/NFC ratios increased.  Across all three treatments, DM and gross energy (GE) digestibility values were the highest (P<0.05) for cows at the middle and late lactation stages.  Daily CH₄ emissions increased linearly (P<0.05), from 325.2 to 391.9 kg d^–1, 261.0 to 399.8 kg d^–1, and 241.8 to 390.6 kg d^–1, respectively, as dietary NDF/NFC ratios increased during the early, middle, and late stages of lactation.  CH₄ emissions expressed per unit of metabolic body weight, DM intake, NDF intake, or fat-corrected milk yield increased with increasing dietary NDF/NFC ratios.  In addition, CH₄ emissions expressed per unit of GE intake increased significantly (P<0.05), from 4.87 to 8.12%, 5.16 to 9.25%, and 5.06 to 8.17% respectively, as dietary NDF/NFC ratios increased during the early, middle, and late lactation stages.  The modelling results showed that the equation using DM intake as the single variable yielded a greater R2 than equations using other dietary or milk production variables.  When data obtained from each lactation stage were combined, DM intake remained a better predictor of CH₄ emissions (R²=0.786, P=0.026) than any other variables tested.  Compared to the prediction equations developed herein, previously published equations had a greater root mean square prediction error, reflecting their inability to predict CH₄ emissions for Chinese Holstein dairy cows accurately.  The quantification of CH₄ production by lactating dairy cows under Chinese production systems and the development of associated prediction equations will help  establish regional or national CH₄ inventories and improve mitigation approaches to dairy production.

Bacillus subtilis strain NCD-2 is an excellent biocontrol agent for plant soil-borne diseases, and the lipopeptide fengycin is one of the active antifungal compounds in strain NCD-2.  The regulator phoP and its sensor kinase PhoR compose a two-component system in B. subtilis.  In this study, the phoR- and phoP-knockout mutants were constructed by in-frame deletion and the role of PhoR/phoP on the production of fengycin was determined.  Inactivation of phoR or phoP in  B. subtilis decreased its inhibition ability against Botrytis cinerea growth in vitro compared to the strain NCD-2 wild type.  The lipopeptides were extracted from strain NCD-2 wild type and its mutant strains by hydrochloric acid precipitate, and the lipopeptides from phoR-null mutant or phoP-null mutant almost lost the inhibition ability against B. cinerea growth compared to the lipopeptides from strain NCD-2 wild type.  Fast protein liquid chromatography (FPLC) analysis of the lipopeptides showed that inactivation of phoR or phoP genes reduced the production of fengycin by strain NCD-2.  The fengycin production abilities were compared for bacteria under low-phosphate medium (LPM) and high-phosphate medium (HPM), respectively.  Results indicated that the regulation of fengycin production by the PhoR/PhoP two-component system occurred in LPM but not in HPM.  Reverse transcriptional-PCR confirmed that the fengycin synthetase gene fenC was positively regulated by phoP when cultured in LPM.  All of these characteristics could be partially restored by complementation of intact phoR or phoP gene in the mutant.  These data indicated that the PhoR/PhoP two-component system greatly regulated fengycin production and antifungal ability in B. subtilis NCD-2 mainly under low-phosphate conditions.

The importance of nutrient provisions and weaning methods for calves has been well established over the past few years, while as increasing interest has focused on contribution of animal behavior and their overall performance in production regimes.  The present study investigated the effects of feeding methods and space allowance on growth performance, individual and social behaviors in Holstein calves.  Twenty-four Chinese Holstein male and female calves were allocated to either an individual or group of 6 and fed either with a bucket or a teat.  Milk replacer, calf starter, and Chinese wildrye were offered during the experiment.  A fecal index used in the present study was defined as the total fecal scores/total number of calves in each treatment.  The results showed that there was no significant difference among the 4 treatments in terms of feed intake, body weight, average daily gain, and fecal index.  For the feeding behaviors, the ingesting milk time and ingesting milk rate were significantly affected by space allowance, while the feeding methods showed a significant influence on the bunting behavior of the calves.  There was no significant difference among the 4 treatments in terms of licking fixtures, self-grooming, and lying down behaviors, irrespective of the feeding method or space allowance.  However, sucking an empty bucket or the teat was significantly affected by the feeding method.  Several selected group behaviors were examined in the present study, and similar values for sniffing the other calves, social grooming, and cross-sucking behaviors were observed.  Overall, the present study demonstrated that different feeding methods and space allowances had a significant effect on the feeding behavior of calves, while the feed intake, growth performance, health condition, individual and group social behaviors were not significantly influenced.  Furthermore, under intensified production systems, Holstein calves raised in a group may obtain a similar production performance, thus reducing management input and profitability compared with those kept individually.  However, there may be competition during the feeding period.

Thinopyrum ponticum (2n=10x=70), a wild relative of common wheat (Triticum aestivum L.), is considered an invaluable genetic resource for wheat improvement due to its abundance of genes that confer resistance to biotic and abiotic stresses.  This study focused on the CH97 line, derived from the BC₁F₇ progeny of a cross between wheat cv. 7182 and Th. ponticum.  Cytological evidence showed that CH97 has 42 chromosomes, forming 21 bivalents at meiotic metaphase I, with the bivalents subsequently separating and moving to opposite poles during meiotic anaphase I.  Through a combination of FISH (fluorescence in situ hybridization), GISH (genomic in situ hybridization), mc-GISH (multicolor genomic in situ hybridization), and liquid array analysis, it was determined that CH97 comprises 40 wheat chromosomes and two alien chromosomes from the E^e genome of Th. ponticum, featuring the absence of a pair of 5D chromosomes and variations in 1B, 6B, and 7B chromosomes.  These findings confirm that CH97 is a stable wheat-Th. ponticum 5E (5D) alien disomic substitution line.  Inoculation experiments revealed that CH97 exhibits high resistance to wheat powdery mildew and stripe rust throughout the growth period, in contrast to the highly susceptible common wheat parent 7182.  Compared to 7182, CH97 displayed improvements in spikelets per spike, thousand-kernel weight, and kernel length.  Additionally, utilizing SLAF-seq technology, chromosome 5E-specific molecular markers were developed and validated, achieving a 33.3% success rate, which facilitates marker-assisted selection to enhance disease resistance in wheat.  Overall, the CH97 substitution line, with its resistance to diseases and improved agronomic traits represents valuable new germplasm for wheat chromosome engineering and breeding.

The current investigation aimed at evaluating the impact of as-is biochar (BC) and phosphorous (P)-loaded biochar (PBC) (3%) on the growth and biochemical characteristics of rice under exposure to vanadium (V) (60 mg L^-1).  The results indicate that rice plants exposed to V-only treatment experienced a decline in growth parameters.  Conversely, the inclusion of BC and PBC caused a noteworthy increase in physiological traits.  PBC performed well in stress environments, specifically, shoot and root fresh weight increased by 82.86 and 53.33%, respectively, when compared to V-only treatment.  Additionally, the SPAD chlorophyll of the shoot increased by 13.05% than V-amended plants.  Moreover, the antioxidant enzyme traits of plant shoot and root, such as superoxide dismutase (SOD by 56.11&117.35%), catalase (CAT by 34.19&35.77%), and peroxidase (POD 25.90&18.74%), exhibited significant increases when compared to V-only amended plants, respectively.  These findings strongly suggest that the application of BC and PBC can trigger biochemical pathways that facilitate biomass accumulation in meristematic cells.  However, further investigations are required to elucidate the underlying mechanisms responsible for this growth promotion.

Black point, a black discoloration of the grain embryo, downgrades the grain quality and commodity grade.  Identification of the underlying genetic loci can facilitate the improvement of black point resistance in wheat.  Here, 262 recombinant inbred lines (RILs) from the cross of Zhongmai 578/Jimai 22 were evaluated for black point reaction in five environments.  A high-density genetic linkage map of the RIL population was constructed with the wheat 50K single nucleotide polymorphism (SNP) array.  Six stable QTLs for black point resistance, QBp.caas-2A, QBp.caas-2B1, QBp.caas-2B2, QBp.caas-2D, QBp.caas-3A and QBp.caas-5B were detected, explaining 2.1-28.8% of the phenotypic variances.  The resistance alleles of QBp.caas-2B1 and QBp.caas-2B2 were contributed by Zhongmai 578 while the others were from Jimai 22.  QBp.caas-2B2, QBp.caas-2D and QBp.caas-3A are overlapped with previously reported loci, whereas QBp.caas-2A, QBp.caas-2B1 and QBp.caas-5B are likely to be new.  Five KASP markers, Kasp_2A_BP, Kasp_2B1_BP, Kasp_2B2_BP, Kasp_3A_BP and Kasp_5B_BP were validated in a natural population of 165 cultivars.  The findings provide useful QTL and molecular markers for improvement of black point in wheat resistance in marker-assisted breeding.

NADC34-like porcine reproductive and respiratory syndrome virus (PRRSV) has been circulating in China for several years and became the dominant field strain in some provinces. Current commercial vaccines could not provide complete cross-protection to NADC34-like PRRSV infection, which led to huge economic losses on pig farms. Co-infections of NADC34-like PRRSV with some other PRRSV strains are commonly found in many clinical cases, and successful isolation of NADC34-like PRRSV strain from the clinical samples has been a challenge to study its biological characters and perform animal experiments to evaluate its pathogenicity. In this study, we constructed a NADC34-like PRRSV infectious clone derived from the isolated JS2021NADC34 PRRSV strain using the reverse genetics technique and investigated its virulence and pathogenicity for nursery pigs. The rescued (rNADC34) strain could proliferate well in porcine alveolar macrophages (PAMs), and the viral copy number and titers were comparable to parental strain. For pathogenicity, the rNADC34 strain-infected pigs showed high body temperature and body weight loss. The histopathological results presented interstitial pneumonia and severe hemorrhage, infiltration of neutrophils and lymphocyte in lungs, lymph nodes, and tonsils. The viral proteins were also detectable in rNADC34 strain-infected pigs using immunohistochemistry staining. Moreover, the trends of PRRSV-specific antibody and viremia in PRRSV rNADC34-infected pigs were similar with the parental strain-infected pigs. These data indicated that rNADC34 strain manifested strong virulence and high pathogenicity for nursery pigs. 

Maize (Zea mays L.) is a globally significant crop that plays a crucial role in feeding the growing global population.  Among its various traits, plant height is particularly important as it affects yield, lodging resistance, ecological adaptability, and other important factors.  Traditional methods for measuring plant height often lack cost-efficiency and accuracy.  In this study, we employed a light detection and ranging (LiDAR) sensor mounted on an unmanned aerial vehicle (UAV) to collect point cloud data from 270 doubled haploid (DH) lines.  This innovative application of UAV-based LiDAR technology was explored for high-throughput phenotyping in maize breeding.  We constructed high-density genetic maps and assessed plant height at both single-plant and row scales across multiple developmental stages and genetic backgrounds.  Our findings revealed that for many varieties and small areas, single-plant-scale estimation accuracy was superior to row-scale estimation, with an R² of 0.67 versus 0.56 and an RMSE of 0.12 m vs. 0.17 m, respectively.  Two high-density genetic maps were constructed based on SNP markers.  In Sanya and Xinxiang, the F₁DH and F₂DH populations identified 12 and 20 QTLs (quantitative trait loci) for plant height, respectively.  The study successfully identified and validated QTLs associated with plant height, revealing novel genetic loci and candidate genes.  This research highlights the potential of UAV-based remote sensing to advance precision agriculture by enabling efficient, large-scale phenotyping and gene discovery in maize breeding programs.

Magnesium (Mg) deficiency is becoming a limiting factor for citrus production in acid soils of subtropical and tropical zones. It is speculated that soil Mg leaching and thereby its imbalance may be a major cause of yield decline, yet Mg deficiency in citrus receives little attention. A two-year field experiment was therefore conducted to quantify soil Mg leaching in a typical citrus orchard in China fertilized with varying levels of Mg (0 (Mg₀), 45 (Mg₄₅), 90 (Mg₉₀) and 180 (Mg₁₈₀) kg MgO ha^-1 yr^-1). Results showed that Mg application significantly increased citrus fruit yield by 4.1-16.4% compared with where MgO was not added. The average amount of soil Mg leaching was 65.7 kg ha^-1 yr^-1 where no Mg fertilizer was added, while it reached up to 91.3 kg Mg ha^-1 yr^-1 where MgO was added at the rate of 180 kg ha^-1. Over the 4 treatments, Mg leaching accounted for 12.1-42.4% of the applied Mg fertilizer. Mg leaching and its removal through harvested fruits resulted in an orchard soil Mg balance of -69.9, -51.1, -27.4 and 10.9 kg ha^-1 in the Mg_0, Mg_45, Mg₉₀ and Mg₁₈₀, treatments, respectively. The pH values of leachate from the acid soil were alkaline and it contained higher amounts of calcium and potassium than that of Mg. Considering the high leaching of Mg from the acid soils of citrus orchards, applications of Mg fertilizer or Mg-fortified soil conditioner are vital to sustain soil Mg balance, high fruit yield and fruit quality in citrus production systems in humid subtropical regions.