Microplastics accumulate during saline-alkali land improvement from agricultural inputs such as fertilizers and plastic films, forming a composite stress on crop growth. This study investigated the response mechanisms of maize (Zea mays L.) seedling roots to individual and combined stresses from microplastics and salt. Maize seedlings were exposed to 100 mM NaCl and 50 mg l-1 Polystyrene microplastics. Transcriptomic and metabolomic analyses were conducted to elucidate molecular responses. Salt (NaCl) and microplastics (MPs), both individually and in combination (PNaCl), significantly inhibited root growth and water metabolism. NaCl and PNaCl stresses upregulated phenylalanine ammonia-lyase and 4-coumaroyl-CoA ligase in the phenylpropanoid pathway, promoting the accumulation of phenolic metabolites such as ferulic acid, while MPs stress had the opposite effect. Under NaCl stress, catechol-O-methyltransferase expression increased, enhancing caffeic acid conversion and antioxidant capacity. Additionally, NaCl and PNaCl stresses also promoted the expression of genes involved in the biosynthesis of cutin, suberin, and wax, whereas MPs stress suppressed these genes. Overall, maize roots respond to NaCl and PNaCl stresses by activating phenylpropanoid metabolism, accumulating phenolic compounds, and enhancing the biosynthesis of cutin, suberin, and wax, thereby improving stress resistance and providing insights into plant adaptation to complex environmental conditions.

Global climate change increases abiotic stresses, such as heat and salinity, which pose significant challenges to agriculture and food security. These environmental stressors adversely affect plant growth, development, and productivity through various physio-biochemical and molecular mechanisms. Heat stress disrupts cellular metabolism, alters membrane fluidity, and impairs photosynthetic processes, while salt stress induces ionic toxicity, osmotic stress, and nutrient imbalances. To cope with these abiotic stresses, plants have evolved intricate defense strategies, including the production of compatible solutes, antioxidants, and stress-responsive transcription factors. Additionally, the soil microbiome plays a critical role in plant adaptation, as beneficial microbes can enhance stress tolerance. However, climate change-induced shifts in temperature and salinity can disrupt plant-microbiome interactions, leading to reduced microbial diversity and activity. This review highlights the current understanding of the impacts of heat and salt stress on plants, soil microbes, and their interactions. It also explores the potential of multi-omics approaches, microbe-mediated strategies, and genetic engineering to enhance crop yields under stress conditions. A comprehensive understanding of the complex networks underlying plant stress responses and the optimization of beneficial plant-microbe associations are essential for developing sustainable agricultural practices and ensuring global food security.

Due to the similar phytotoxicity symptoms induced by chloride (Cl-) and ammonium (NH4+) in citrus, which complicate diagnosis and nutrient management, this study examined the individual and combined effects of NH4+ (4, 8, 16 mM) and Cl- (0, 8, 32 mM) on the growth, nitrogen metabolism, and antioxidant responses of Poncirus trifoliata seedlings. Moderate concentrations of 8 mM Cl- and 4 mM NH4+ (Cl8N4) significantly increased growth parameters, including plant height, biomass, and leaf chlorophyll content, while reducing oxidative stress indicators such as malondialdehyde (MDA) and proline in leaves. In contrast, higher ion concentrations led to leaf chlorosis, membrane damage, and impaired nitrogen metabolism, with NH4+ exhibiting a stronger toxic effect than Cl-. Nitrogen metabolism analysis demonstrated that the combined treatment Cl8N4 optimized the levels of soluble sugar, glutamate, and free amino acids, while maintaining the activity of key enzymes such as nitrate reductase, glutamine synthetase, and glutamate synthase. Additionally, Cl8N4 enhanced photosynthetic efficiency (Fv/Fm), reduced MDA levels, and boosted antioxidant enzyme activity, thereby minimizing oxidative damage. In contrast, other combined treatments significantly inhibited plant growth and disrupted metabolic functions. Redundancy analysis further confirms the beneficial role of the Cl8N4 combination in enhancing plant adaptation to ionic stress. These findings highlight the importance of balanced NH4+ and Cl- levels in promoting citrus growth and stress resilience. Accordingly, chloride containing fertilizers may be beneficial in citrus cultivation, but their application alongside excessive NH4+ should be avoided due to the risk of increased toxicity.

Nutritional enhancement has been reported to effectively relieve infected symptoms of Huanglongbing, one of the most destructive diseases of citrus. However, few studies focused on the role of plant nutrition in citrus plant-vector (Asian citrus psyllid; Diaphorina citri Kuwayama) interactions, which is regarded as an important part to develop an effective management strategy.METHOD:In the present study, a hydroponic culture was carried out to evaluate the effects of boron deficiency on psyllid feeding process to decode the molecular/biochemical basis of host-psyllid interaction.RESULTS:Boron deficiency was observed to play a major role in accelerating the release of volatile organic compounds, especially methyl salicylate, affecting the shikimic acid pathway through an elevated synthesis of shikimic acid, l-phenylalanine, 3-phenylpyruvic acid and salicylic acid. These changes made citrus leaf more attractive to psyllid adults. Meanwhile, boron deficiency evidently decreased the boron concentration of leaf cell wall fractions, thereby, weakened the structural stability by affecting pectin and cellulose formations. A significant decrease of cell wall mechanical strength was observed in boron-deficiency leaf, which could be the critical reasons to reduce piercing and to increase phloem ingestion during psyllid feeding.CONCLUSION:Our study demonstrated that boron deficiency facilitated the feeding behavior of psyllid adults through elevated release of methyl salicylate, coupled with weakened mechanical properties of cell wall.

Magnesium (Mg) has been found to promote the color change citrus peel, but the underlying mechanism remains unclear. In this study, Mg application treatment significantly increased the Mg content in the peel of Satsuma mandarin fruit during the expansion stage (90–150 days after flowering). Mg fertilizer treatment was also found to significantly reduce chlorophyll (Chl) a content and increase β, β-xanthophyll (β-cryptoxanthin, zeaxanthin, neoxanthin), and abscisic acid (ABA) content in the flavedo during the key period of color change in Satsuma mandarin (165–195 days after flowering). Under Mg fertilizer treatment, Chl biosynthesis genes (CitGGDR, CitCHLH, CitCHLM, CitCHL27, and CitPORA) was down-regulated and that of Chl degradation genes (CitNYC, CitPPH, CitPAO, and CitRCCR) was up-regulated, which resulted in a lower Chl content in the flavedo than the control. Moreover, Mg fertilizer treatment up-regulated carotenoid biosynthesis genes (CitPSY, CitPDS, CitZDS, CitLCYb1, CitLCYb2, CitZEP, CitNCED2, and CitNCED3), leading to the accumulation of β, β-xanthophyll and ABA in the flavedo. Mg fertilizer treatment also promoted sugar (mainly fructose, glucose, and sucrose) accumulation in fruit flavedo, which showed significant negative correlations with Chl, α-carotene, lutein, and β-carotene, but positive correlations with β, β-xanthophyll compositions, and ABA in the flavedo. An analysis integrating transcriptome and metabolome data revealed that Mg may promote the color change of Satsuma mandarin fruit flavedo by regulating various metabolic pathways related to peel coloration, such as sugar accumulation, Chl degradation, carotenoid and ABA biosynthesis, and carbon fixation. The results can explain the regulatory pathways and networks of Mg-induced citrus peel coloration.

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: : Liviidae) is the primary vector of pathogenic bacteria disseminating Huanglongbing. Nutrients enhancement have been reported to be few optional methods to relieve Huanglongbing. However, limited studies have focused on the interactions between citrus plants and psyllid under nutritional enhancement. The present work was conducted to study psyllid feeding and psyllid feeding with nutrients enhancement. Our results suggested that psyllid feeding up-regulated the amino acid metabolism especial phenylalanine of leaf, which hence attracted more insect adults. Psyllid feeding significantly decreased palisade tissue pectin methylation but increased fibrous ring tissue, with increasing the concentration of different nutrients of leaves, resulted in an increased leaf thickness, leaf weight, and leaf dry mass per unit area. These changes facilitated psyllid feeding process, embodied in increased phloem ingestion and decrease in piercing process. While, foliar supply of nutrients affected the leaf nutrient composition, having cascading effect on down-regulation of amino acids mediated metabolism coupled with poor growth of palisade tissues, but accelerated the growth of fibrous ring tissues inhibited the ability of psyllid to recognize host, thereby, reduced the feeding efficiency of psyllid. Compared with the pesticide treatment, pesticide+nutrients treatment showed a higher reduction rate of psyllid population. Our study, hence, provided some evidences about behavior of psyllid under three distinct feeding environments, for insightful analysis of behavioral dynamics of psyllid feeding, an issue considered important for uncontrolled spread of Huanglongbing.

The amount and time of fertilization play an important role in the quality and yield of citrus. Moreover, twice fertilization in the spring (March) and summer (July) are generally applied in citrus orchards, of which the appropriate proportion is unclear, especially in Ganzhou. Therefore, the two-year field experiment containing three proportions (60/40, 80/20, 100/0) of spring and summer fertilization was carried out with a 15-year-old Newhall orange orchard to recommend the optimum fertilization proportion for orchard. Results showed that variations of soil available N, P, K concentrations resulting from different spring and summer fertilization proportion significantly affected orange fruit quality and yield. The soil available nitrogen (N), phosphorus (P), and potassium (K) concentrations fertilized with a proportion of 80/20 spring and summer were higher overall the year. The spring and summer fertilizer application with 80/20 increased fruit yield by 35.14%, and had higher total soluble solids and lower titrated acid. Moreover, the only one-time fertilization exhibited almost the same fruit yield, fruit N, P, K removal, but lower fruit titrated acid content and higher solid acid ratio. The present study results demonstrated that increasing the proportion of spring fertilization particularly the proportion of 80/20 could be a recommended dose for obtaining higher fruit yield and quality.

Due to long-term excessive fertilization, the fruit quality of the Guanxi pomelo (Citrus grandis) has been declining. The classification of fruit quality and its relationship with nutrients in soils and trees were studied to declaim the characteristics of nutrients in Guanxi pomelo orchards, ultimately guiding the fertilization for high-quality fruit production. By cluster analysis, 281 samples were grouped into four clusters. High-quality fruit (HF) showed a gourd shape with moderate weight size, high sweetness, edible rate (ER) up to 73%, and vitamin C content over 40 mg/100 g. Compared to sub-quality fruit (SF), common fruit (CF), and inferior fruit (IF), the content of magnesium (Mg) in the leaves of HF was 11.76, 11.76, and 18.75% higher, while the content of iron (Fe) was 6.45, 5.76 and 10.97% higher, respectively. Meanwhile, the contents of Zinc (Zn, 8.51, 6.44, and 11.22% higher than SF, CF, and IF, respectively) and Boron (B, 13.47, 13.83, and 25.40% higher than SF, CF, and IF, respectively) were also found to increase. However, the contents of Mn (35.34, 27.51, and 25.53% higher) and Cu (31.90, 31.99, and 5.64% higher) in IF were significantly higher than in HF, SF, and CF. Acid soils (4.24–4.40) with low OM content (23.00–26.71 g kg−1) led to an imbalance uptake of nutrients of citrus, ultimately resulting in poor quality. These results indicated that farmers should reduce the application of nitrogen (N), phosphorus (P), and K fertilizer and pesticides and increase micronutrient and organic fertilizer, which provides a theoretical basis for scientific fertilization to improve the fruit quality of Guanxi pomelo (Citrus grandis) of Pinghe County.

Magnesium (Mg) deficiency is a major factor limiting citrus production. Here, we performed Mg treatments (0, 100, 150, 200 and 250 g MgO plant-1) on 15-year-old navel orange (Citrus sinensis Osb.) trees to investigate the effect of Mg application on fruit yield and quality. Mg application obviously enhanced the fruit yield of navel orange, particularly at the dose of 150 g MgO plant-1, which significantly improved the fruit yield by 27.87% in 2019 and by 17.89% in 2020 compared with the control. At the fruit color turning stage, Mg application increased the sucrose content in the pulp, especially at the doses of 150 and 200 g MgO plant-1, which signif-icantly increased the sucrose content by 20.38-29.85% and 7.01-7.36% in 2019 and 2020, respectively. Moreover, application of Mg fertilizer significantly decreased the Chl a and total Chl contents in the peel, as well as increased the peel brightness and chroma, accelerated fruit ripening. Furthermore, the pulp sucrose content was negatively correlated with Chl a and total Chl in the peel. Overall, we proposed a recommended amount of Mg fertilization (142 to 177 g MgO plant-1) for high yield and good quality of navel orange fruit.

The phenomenon of magnesium (Mg) deficiency in citrus is widespread and has become an important limiting factor for the yield and quality of citrus. Thus, the 15-year-old‘Newhall’navel orange ( Citrus sinensis Osb.) trees were carried out with 0, 100, 150, 200, and 250 g plant -1 , Mg application to investigate beneficial role of Mg application on navel orange yield and quality in the experiment. We found that Mg application improved fruit yield, and enhanced levels of sugars (e.g., fructose, glucose and sucrose) and organic acids (e.g., malic and citric acids) in the fruits of Mg application treated‘Newhall’navel orange, indicating that it had a positive impacts on the improvement of fruit quality and nutritional values. Meantime, Mg application significantly increased color difference value (e.g., L , a , b and C ), the brightness and chroma of pericarp. Additionally, Mg application decreased pericarp of Chl a and total Chl contents significantly at fruit color turning stage. Take together, the relationship analysis among each sugar, organic acid component and pericarp pigment by curve estimation revealed that sucrose was negatively correlated with the Chl a and total Chl in fruit color turning stage. Therefore, we speculate that chlorophyll degradation was possibly due to sugar content response of citrus by Mg application, which was attributed to their ability to promote fruit ripening, and the recommended amount of Mg for high yield and good quality of navel orange fruit is 150~200 g plant -1 . Overall, Our results show that appropriate Mg fertilizer significantly improves the citrus fruit yield, sugar and organic acid, and promoted colouration of pericarp, and provides references for Mg application in a rational way.

为确定镁肥在柑橘的合理施用量并提高柑橘果实的内外品质,以20年生枳砧温州蜜柑(Citrus un?shiu Marc.)为材料,设置5个镁肥水平,分别为MgO 0、100、150、200、250 g/株(记为CK、T1、T2、T3、T4),研究镁对温州蜜柑果实转色期及成熟期果肉糖酸组分、果皮色差值和色素含量的影响.结果显示:与不施镁相比,施镁能明显提高果实膨大期叶片镁含量;显著提高果实产量,且产量随镁肥用量的增加呈先增后减的变化规律,2019年及2020年分别以MgO 124、122 g/株时果实理论产量最高.镁肥能提高温州蜜柑果实转色期果肉蔗糖含量,显著增加果皮L、a、b、C值,显著降低果皮H值、叶绿素a、叶绿素b和总叶绿素含量,提高果皮亮度、彩度及纯度;但对果实成熟期果肉糖酸组分、果皮L、a、b、C值及叶绿素含量无显著影响.在果实转色期,T2、T3及T4处理果实内外品质整体较好,但T4处理得分最高,果实品质更佳.结果表明,本试验条件下,温州蜜柑果实产量最高且品质较佳的推荐施镁量为MgO 122～150 g/株,果实品质最佳推荐施镁量为MgO 200～250 g/株.

Huanglongbing (HLB) is one of the most complex and destructive diseases of citrus, which has left a great negative impact on growth of world citrus industry. The characteristic symptoms of HLB include leaves with blotchy mottles and stunted growth of infected plants. These symptoms are often confused with the symptoms of nutritional deficiencies. Mineral nutrition not only plays an important role in triggering an untimely decline in citrus productivity, but also acts as a pre-disposing factor in offering plant defense against HLB. Although, nutritional management showed no determinacy and consistency in results, the application of macro-and micronutrients inducing Systemic Acquired Resistance (SAR) is one of the measures followed worldwide to maintain the normal production of HLB-infected orchards. Therefore, understanding the detailed process of interaction between nutrient disorders and HLB development is the key to effective nutritional management vis-à-vis prolonged orchard productivity. In this review, recent advances on pathogen-host-nutritional interaction and vector-host-nutrition interaction are discussed with updated global studies.

Chlorine (Cl) is indispensable for the growth of plants. While rarely systematic reports are available for the effect of Cl-containing fertilizers on citrus production. This study aimed to investigate the impacts of various Cl-containing fertilizers on the nutrients in the leaves, the yield and quality of sweet orange, and the Cl migration in the plant-soil-leaching system. A 5-year field experiment (2016-2020) with five Cl treatments (0, 75, 150, 450, and 900 kg ha-1), and soil core lysimeter test with five Cl levels (0, 150, 225, 300, and 450 kg ha-1) were carried out. The results showed that 77.0% of Cl leached into above 60 cm deeper soil layer, with calcium as the main accompanying ions, resulting in less Cl being absorbed by the citrus plants. The content of Cl in the leaves and soil was enhanced by the increasing input of Cl-containing fertilizer, without yearly increased characteristics, under a mean annual rainfall of 1,474 mm. Chlorine significantly increased the yield (13.24-37.8 9%), fruit weight, and vitamin C (Vc), in addition to enhancing the flavor and the juice yield of sweet orange via improving the absorption of N and K. Moreover, the long-term application of potassium sulfate has elevated the accumulation of sulfur in the soil and in leaves; it is becoming a potential risk factor for citrus production. Taken together, the application of Cl-containing fertilizer in sweet orange is feasible, and trace absorbance of Cl could improve the yield and fruit quality of sweet orange.

[目的]调查不同种类柑橘果实矿质养分含量,结合土壤及树体养分含量状况,对我国主要种类柑橘进行推荐施肥研究.[方法]根据土壤类型 、 柑橘种类(宽皮柑橘类、甜橙类、柚类、柠檬类和杂柑类)、树龄及产量水平,将我国柑橘主产区湖北、湖南、江西、四川、广东、广西、福建、云南、浙江、陕西、重庆等11省(市、区)的柑橘园划分为1200个采样单元,每个采样单元为3.3～6.7 hm2,于2010—2017年在柑橘成熟期(9—12月),采集土壤、叶片及果实样品,调查柑橘产量、施肥量,分析叶片养分含量、土壤速效氮磷钾含量,并依据柑橘产量进行氮磷钾肥施用量及施用比例的推荐.[结果]低产水平果园氮(N)、磷(P2O5)、钾(K2O)肥推荐用量:宽皮柑橘类分别为189.75～253.00、76.20～96.13、133.20～159.84 kg/hm2,甜橙类分别为176.94～235.92、101.02～123.47、128.03～153.64 kg/hm2;柚类分别为134.76～179.68、69.04～84.38、125.21～150.25 kg/hm2;柠檬类分别为91.33～121.77、55.43～67.75、79.68～95.62 kg/hm2;杂柑类分别为109.42～145.89、70.06～85.63、93.18～111.81 kg/hm2.中产水平果园氮(N)、磷(P2O5)、钾(K2O)肥推荐用量:宽皮柑橘类分别为216.86～337.33、83.82～139.70、145.31～245.91 kg/hm2;甜橙类分别为202.22～314.56、111.12～185.20、139.67～236.37 kg/hm2;柚类分别为154.01～239.57、75.95～126.58、136.59～231.15 kg/hm2;柠檬类分别为104.37～162.36、60.98～101.63、86.92～147.10 kg/hm2;杂柑类分别为125.05～194.52、77.07～128.45、101.65～172.02 kg/hm2.高产水平果园氮(N)、磷(P2O5)、钾(K2O)肥推荐用量:宽皮柑橘类分别为303.60～474.38、118.06～190.50、222.00～330.00 kg/hm2;甜橙类分别为283.10～442.35、156.51～252.55、213.39～320.08 kg/hm2;柚类分别为215.62～336.90、106.96～172.60、208.68～313.01 kg/hm2;柠檬类分别为146.12～243.54、85.88～147.82、132.80～212.48 kg/hm2;杂柑类分别为175.07～273.54、108.55～175.16、155.29～232.94 kg/hm2.[结论]5类柑橘对氮、磷、钾素需求量不同,其中宽皮柑橘类对氮、钾素需求较其它柑橘种类高,甜橙类对磷素需求量较其它柑橘种类高.5类柑橘对氮、磷、钾需求比例也有所不同,N:P2O5:K2O需求比例分别为宽皮柑橘类1:0.37～0.41:0.63～0.73,甜橙类1:0.52～0.59:0.65～0.75,柚类1:0.47～0.53:0.84～0.97,柠檬类1:0.56～0.63:0.79～0.91,杂柑类1:0.59～0.66:0.77～0.89.

Aims : Special fertilizer and soil mulching have been used to improve crop yield worldwide. However, the effects of special fertilizer with mulching on soil characteristics of citrus orchards were not yet fully understood. This study aimed at assessing the effects of different mulch patterns including plastic mulching and grass mulching on improving fruit quality of Ponkan and providing a new insight of mulching development in citrus orchards. Methods : In this study, a two-year field experiment was conducted to investigate the effects of citrus special fertilizer (FR), grass mulching (RGM), and plastic mulching (RPM) on fruit quality, soil organic carbon fractions, physicochemical properties, and plant nutrition in Ponkan citrus orchard. Results : The study resulted showed that special fertilizer treatment and grass mulching treatment increased Total soluble solid contents by 6.76% and 3.97%, while plastic mulching decreased Titratable acid contents by 19.44%, resulting in increases of fruit TSS: TA by 6.14%, 3.61%, and 22.76%, respectively. Correlation analyses showed that citrus fruit quality was associated with soil bulk density, Total porosity, Capillary porosit, Aeration porosity, Total organic carbon, Readily oxidized organic carbon, Microbial biomass carbon and Soil available phosphorus. Soil physical properties were improved by RPM, but FR and RGM had better effects on soil nutrients and organic carbon, as evidenced by the results of principal component analysis and loading matrix plot. Conclusions : This study suggested that the different effects of special fertilizer, plastic mulching, and grass mulching on improving fruit quality were associated with their diverse effects on improving soil characteristics.

Soil fertility plays a key role in citrus productivity. Therefore, it is necessary to explore the effects of soil amendments on soil fertility and citrus productivity and estimate carbon fractions’ suitability, which response to soil fertility and citrus productivity. A field experiment in a citrus orchard was conducted containing five treatments: local habit fertilization (LF), special fertilizer [25% lower NPK than LF, (SF)], special fertilizer, and rice straw mulching [0%, 12.5%, and 25% NPK higher than LF (SFRS25, SFRS37.5, and SFRS50, respectively)]. Total organic carbon (TOC), microbial biomass carbon (MBC), water-soluble organic carbon (WSOC), permanganate oxidizable carbon (ROC), available N, P, K, fruit yield, and quality were analyzed. Straw mulching and special fertilizer significantly increased soil carbon fractions, such as MBC and ROC. Such treatments also enhanced the soil available N, P, and K, subsequently elevated the fruit yield. MBC, available K, and available P showed a significantly positive correlation with citrus yield. Redundancy analysis indicated that MBC and ROC significantly explained 61.87% of the variation for available nutrients, suggesting that the increase of organic carbon fractions and microbial biomass could accelerate nutrient cycling for the plant. It proved that decrement application of special compound fertilizer with straw mulching raised fruit yield by altering soil carbon fractions to improve soil available nutrients or fertility. The MBC of soil labile carbon responded more sensitively to not only soil fertility but also citrus fruit yield.