To investigate the characteristics of plant diversity in the understory of eucalyptus plantations in Hainan, vegetation surveys were conducted in different areas of eucalyptus plantations, and the biomass of the upper part of the interior of the sample plots was measured by combining the standard wood method and the harvesting method, then theα-diversity index of the irrigation and grass layers was combined with the biomass of the above-ground part to construct a comprehensive functional index, and the new index was compared with the α diversity index. There were 101 species of understory plants in eucalyptus plantation, among which 49 species appeared in shrub layer, belonging to 45 genera of 31 families, and 52 species appeared in herb layer, belonging to 48 genera of 28 families. There was no significant difference in the diversity index of understory shrub layer in different regions of eucalyptus plantations. The α diversity index of herbaceous layer in Lingao was significantly higher than that of other areas. It means the diversity level of shrub layer was similar, while the diversity level of herb layer was more affected by environment. There were significant differences in aboveground biomass allocation between shrub layer and grass layer in different regions. Although shrub layer was larger than herb layer, the distribution ratio fluctuated widely. Yd indices of shrub layer of eucalyptus plantations in different areas had no significant difference, and Yd indices of herb layer in Lingao and Ding'an were significantly higher than those in Tunchang and Dongfang. It means that the ecological functions of shrub layer in different areas were similar, while the ecological functions of herbaceous layer were obviously stronger than those of Lingao and Ding'an. The Yd index of the shrub layer was strongly correlated with the α-diversity index; the Yd index of the herb layer was generally correlated with the α diversity index and strongly correlated with above-ground biomass. The results show that the plant diversity characteristics of the eucalyptus understory are influenced by the regional environment, with the herbaceous layer being more susceptible than the shrub layer; the α-diversity index of the shrub layer has a greater influence on the Yd index, while the above-ground biomass of the herbaceous layer has a greater influence on the Yd index. The Yd index can reflect both the α-diversity level and biomass of the understory, and is a good complement to evaluate the ecological functions of the understory vegetation of eucalyptus plantations.

Low temperature is an important factor limiting the growth, development and yield of pitaya. 2,4-Epibrassinolide (EBR) can enhance the resistance of plants to various stresses such as low temperature. In order to improve the cold resistance of pitaya and alleviate the damage caused by low temperature, the cutting seedlings of red pulp pitaya 'Taiwan No. 6' was sprayed with 0.5 mg/L EBR, and treated under low temperature stress (4℃/0℃, 12 h/12 h) for 7 days. Reactive oxygen species (ROS) content, antioxidant enzyme activity, relative conductivity (REC), malondialdehyde (MDA) content, fatty acid composition and content were determined to clarify the regulatory effect of EBR on the cold tolerance of pitaya seedlings. Furthermore, the relationship between antioxidant system and fatty acid unsaturation of membrane lipids under low temperature stress was studied. Low temperature stress (4℃/0℃, 12 h/12 h) increased the content of reactive oxygen species (ROS), significantly decreased the content of unsaturated fatty acids. The fatty acids unsaturation (UFA/SFA) and double bond index (DBI) reduced by 32.1% and 32.4% respectively, and significantly increased the content of malondialdehyde (MDA) and relative conductivity (REC), resulting in decreased membrane stability and increased membrane permeability. The plants showed obvious watery stains and slight wilting, and the index of chilling injury reached 0.60. Under low temperature, exogenous EBR treatment increased the activities of superoxide dismutase, peroxidase and catalase, effectively removed the excessive accumulated ROS, significantly reduced the production rate of superoxide anion and the content of hydrogen peroxide, alleviated the oxidation reaction between ROS and unsaturated fatty acids in membrane lipids, and increased the relative content of unsaturated fatty acids in pitaya seedlings. The proportion of saturated fatty acids decreased significantly, UFA/SFA and DBI increased significantly, EBR maintained the stability of cell membrane, reduced REC and the content of membrane lipid peroxidation products MDA, greatly reduced watery stains of plants, and the index of chilling injury was reduced to 0.25. It is becouse EBR can activate the antioxidant enzyme system and effectively remove a large number of accumulated ROS under stress, leading to reduce the double-bond fracture of unsaturated fatty acids in membrane lipids, alleviate the degree of membrane lipid peroxidation, maintain the stability and function of membrane membrane. In conclusion, under low temperature stress, exogenous EBR can effectively improve the cold tolerance of pitaya seedlings. Its mechanism is by increasing the activity of antioxidant enzymes in pitaya seedlings, remove excess accumulated ROS, and significantly increase the unsaturation of cell membrane fatty acids, so as to reduce the degree of membrane lipid peroxidation and electrolyte leakage, maintain the stability and function of cell membranes.

With the rapid development of the livestock industry, the demand for forage is increasing, and it is urgent to screen new forage crop varieties. In this study, two national forage sugarcane varieties were used as the control. The biological yield of 15 sugarcane varieties and the routine nutritional components of 10 green fodder were measured and analyzed to explore the principal component variation of sugarcane at different cutting stages, and evaluate the feeding value of sugarcane, so as to provide scientific basis for more than one year of sugarcane harvest and whole plant feeding. Crude protein (CP), acid detergent fiber (ADF), water-soluble carbohydrate (WSC) and crude fat (EE) were selected by factor principal component analysis, which basically contained all the information of the indexes measured. Among the 15 sugarcane varieties, 'Yunzhe 12-201' had the highest CP content, which was 8.80 %, 'ROC22' with the lowest ADF content, 35.25 %. The highest WSC content was from 'Yunzhe 00-290', 6.16 %. The highest EE content was from 'Yunzhe 01-286', 1.40 %. The CP content of 'ROC22' and 'Yunzhe 12-201' was higher than that of CK1 and CK2. The ADF content of 'Q27','ROC22','Yunzhe 01-286', 'Yunzhe 06-160','Yunzhe 12-142-1-J', 'Dianzhe 11-728' was lower than that of CK1 and CK2. The WSC content of 'Q27', 'Yunzhe 00-290', 'Yunzhe 12-142-1-J', 'Yunzhe 16-16', 'Dianzhe 11-726' and 'Dianzhe 11-728' was higher than that of CK1 and CK2. There was no significant difference in EE content between 15 sugarcane varieties and CK1 (P>0.05), except 'Yunzhe 06-160'. There was no significant difference in EE content between 14 sugarcane varieties and CK2. Except for 'Dianzhe 11-726', there was no significant difference in Ca content between 14 varieties and CK1 and CK2. The CP content of all sugarcane varieties in the first cutting period was higher than that in the second cutting period, and the ADF, WSC, EE and Ca content in the first cutting period was higher than that in the second cutting period, with 12, 5, 4 and 14 sugarcane varieties, respectively. The total yield of 15 sugarcane was 71.40-163.95 t/hm², higher than that of CK1 and CK2. The yield of CP, ADF, WSC and EE per unit area of 15 sugarcane varieties exceeded that of CK1 and CK2, and the Ca yield of 15 sugarcane varieties exceeded that of CK2. Comprehensive evaluation showed that sugarcane could be used as ruminant feed with high nutritional value and economic benefit. In this study, five varieties 'Q27', 'ROC22', 'Yunzhe 01-286', 'Yunzhe 12-201', 'Dianzhe 11-728' were selected as the sources of forage sugarcane, which could not only meet the raw material needs of forage animals, but also form an industrial development model of sugar-animal linkage..

Youjiang River Valley in Baise is one of the famous dry and hot river valleys in China. Drought is the most serious meteorological disaster in the region. It has a unique suitable environment for mango and is the main mango producing area in China. However, the research on the water use strategy of Mango in Baise dry-hot river valley region is still lacking. Based on based on the measuring of hydrogen and oxygen stable isotope of precipitation, soil water at different layers, groundwater, and mango xylem water, the variation characteristics of hydrogen-oxygen isotope an its influencing factors of precipitation were analyzed, and the water absorption sources of mango roots at different growth stages were quantified. The hydrogen-oxygen stable isotopes and d-excess had obvious seasonal changes in the year, which were low in rainy season and high in dry season. The local meteoric water line was δD=8.2587δ¹⁸O+12.308 (r=0.9968, n=35, P<0.001) for the area. Under the influence of monsoon climate, the stable isotope value of precipitation had a significantly negative linear relationship with precipitation amounts and air temperature (P<0.05). During mango flowering stage, young fruit stage, fruit expansion stage, and mature stage, the stable isotopes of soil water became poor with the increase of soil depth. In the flowering stage and young fruit stage, mango trees used a relatively uniform proportion of soil water at different depths and groundwater, while in the expansion stage and maturity stage, mango trees mainly used deep soil water and groundwater, indicating that mango trees in this area mainly use deep soil water and groundwater as water sources, as mango trees' roots are mainly distributed in deep layers, and reveals its conservative water use strategies. The variation of hydrogen-oxygen stable isotopes of precipitation indicates the xerothermic environment of Baise dry-hot river valley region, and mango mainly uses deeper soil water and groundwater, the above results are expected to provide a basis for the sustainable development of mango industry in this area.

The effects of phosphorus (P) and lime application on yield and biomass and P uptake and utilization of sweet corn were evaluated with a field experiment. Research on the appropriate rate of P application would provide a theoretical basis in improving sweet corn yield and P use efficiency. The field experiment was a split-plot design with main-plot randomly assigned into each of four blocks. The main-plot treatments were four P application rates (0, 60, 120 and 180 kg/hm², expressed as P₀, P₆₀, P₁₂₀ and P₁₈₀). The split-plot factors were two lime levels (0 and 750 kg/hm², expressed as L₀ and L₁). The responses of sweet corn yield, P uptake, soil available P and P fertilizer utilization efficiency to P fertilizer application and lime application were studied. The yield of sweet corn increased significantly under P₁20 and P₁₈₀ treatments without lime by 19.4% and 18.5%, respectively, compared with P₀ treatment. Compared to P₀, the yield of sweet corn increased significantly by 14.0% under P₆₀ treatment with lime. Under P₆₀ treatment, lime increased the yield of sweet corn significantly by 12.7%. P fertilizer application increased both total biomass and P uptake of sweet corn significantly. After two sweet corn growing seasons, soil available P under P₆₀ treatment had no significant difference comparing with the original value. Soil available P basically maintained a balance under P₆₀ treatment. Soil available P in P₁₂₀ and P₁₈₀ treatments increased by 103.8% and 228.4%, respectively, compared with the original value, and soil available P increased obviously in 0-20 cm soil layer. The fresh ear yield per P uptake and P physiological efficiency decreased significantly with P application rates. Also, the P use efficiency of sweet corn declined with P application rates. P agronomic efficiency, recovery efficiency, and partial factor productivity increased significantly under lime treatments with P₆₀ treatment, compared with no-lime treatments. Together, these results indicated that the application of 60 kg/hm² P fertilizer combined with lime can be an efficient way to obtain high yield and P utilization efficiency of sweet corn and maintain the balance of soil available P.

This article aims to study the differences in the photosynthetic characteristics of different tea cultivars. The photosynthetic parameters in the leaves of nine tea cultivars were determined under field conditions, and the light response curves were drawn. The photosynthetic indicators of different tea cultivars were comprehensively evaluated by statistical analysis, principal component analysis, cluster, discrimination analysis and correlation analysis. There were great differences in net photosynthesis rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), intercellular CO₂ concentration (C_i). Among them, P_n, T_r of 'Yunshan' and 'Yunkang 10^#' were significantly higher than those of the other tea cultivars (P<0.05), G_s of 'Tian', 'Baohong' and 'Shilixiang' was significantly lower than that of the other tea cultivars (P<0.05), C_i of 'Changningdayezhong' was significantly lower than that of the other tea cultivars (P<0.05). At the beginning of photosynthetically active radiation (PAR), differences in the P_n between tea cultivars were not distinct. However, with the increase in PAR, great differences in P_n between tea cultivars appeared. The G_s and T_r of the nine tea cultivars showed two trends with the increase of PAR, 'Xiangguiyinhao' showing a first upward and then trend till to be stable, while other tea cultivars showing an overall upward trend. The C_i of the nine tea cultivars decreased rapidly at first and then tended to be stable. The WUE and iWUE increased first and then decreased with the increase of PAR, and the ability to tolerance of strong drought for 'Changningdayezhong' and 'Xiangguiyinhao' was better than that of the other tea cultivars with a higher WUE and iWUE, and both of them could be used as the drought tolerance tea cultivars suitable for breeding needs. The photosynthetic potential for 'Yunkang 10^#', 'Xiangguiyinhao', 'Yunashan' was better than the other tea cultivars with a higher P_nmax, and they could be used as the high-light-efficiency tea cultivars suitable for breeding needs. The LSP of 'Shilixiang', 'Changningdayezhong' and 'Zijuan' was significantly higher than that of other tea cultivars (P<0.05), and had a strong ability to use strong light. The strong ability to use low light for 'Xiangguiyinhao' and 'Shilixiang' was better than that of the other tea cultivars with a lower LCP (P<0.05). The nine tea cultivars were divided into four groups by principal components and cluster analysis. Correlation analysis indicated that P_n was significantly positively correlated with G_s and T_r (P<0.01).

Chilling injury during tobacco seedling stage is an important problem affecting tobacco agricultural production, and enhancement of the chilling resistance by various agronomic measures has practical significance. In this study, using two main cultivars Yunyan97 and K326 as the experimental materials, the seedlings were pretreated with salicylic acid (SA) at concentrations 0, 0.5, 1.0 and 1.5 mmol/L. Then the pretreated seedlings were transferred to 10℃ for 12 days for chilling treatment. Compared with the control without SA pretreatment, the SA pretreatment could significantly reduce the malondialdehyde (MDA) content and ratio of electrolyte leakage, slowed down the consumed rate of dry matter, increased chlorophyll content and root vigor, improve root length, surface area, volume and number of roots, promoted the growth of root system under the chilling stress, and finally enhanced the chilling resistance of 'Yunyan 97' and 'K326' seedlings. The optimum SA concentration of different tobacco varieties varied, that for 'Yunyan 97' and 'K326' was 1.5 mmol/L and 1.0 mmol/L respectively. After the SA pretreatment, the content of reduced ascorbic acid (ASA) and glutathione (GSH) in the antioxidant defense system in the seedlings remained a higher level, but oxidized ASA and GSH maintained a lower level, and ratio of the reduced antioxidants in total antioxidants increased. Ascorbate peroxidase (APX), catalase (CAT), guaiacol peroxidase (GPX), glutathione reductase (GR) and superoxide dismutase (SOD) maintained high activities compared with the control before and during the chilling treatment. The results indicated that after the SA pretreatment, the seedlings could maintain higher reduced antioxidant level and antioxidant enzyme activity, and remain higher antioxidant capacity, which would lay an important biochemical foundation for SA-induced chilling resistance in tobacco seedlings. The results would not only have reference significance for raising chilling-resistant tobacco seedlings, but also referential value for culture of seedlings and early cultivation of other crops and vegetables.

In this paper, a 3-factor fertilization experiment with N, P and K in an incomplete orthogonal design of "3414" was conducted to validate the optimal fertilization effect model, and the dry weight of single fruit and hesperidin content of Citrus medica 'Fingered' (CM) were used as the indicators for statistical analysis. The results showed that nitrogen, phosphorus and potassium fertilizers had effects on the dry weight of single fruit and hesperidin content in CM and N₂P₂K₂ (40g/plant for N, 40g/plant for P and 45g/plant for K) had the best effect among the different fertilization treatments, and no or less fertilization led to the decrease of quality of CM in Wanzhou to different degrees. The two-factor interaction analysis showed that when any of the N, P and K fertilizers were at the level of 2, with the increase of the other two factors, the single fruit dry weight and hesperidin content of CM showed a trend of increasing and then decreasing, indicating that any two factors interacted with each other within a certain range, and two of the N, P and K factors had an interaction effect. The optimization results of the fertilization model indicated that the suitable fertilization rates of N, P and K for cultivation of CM in Wanzhou ranged from 38.78 g to 51.25 g per plant, 35.67 g to 42.35 g per plant and 48.17 g to 60.37 g per plant, respectively. The results of the validation experiments under the intermediate conditions of the optimal fertilizer application effect model showed that the dry weight yield of single fruit of CM was 8.14% higher than that of the highest group of "3414", and the hesperidin content was 1.94% higher than that of the highest group of "3414". This indicates that the optimal formulation fertilization model is reasonable which has some practical guidance for the field cultivation of C. Sarcodactylis Fructus.

Streptomyces acidiscabies (SA), Ralstonia solanacearum (RS) and Erwinia carotovora subsp carotovora borgey (ECCB) cause plant scab, brucellosis and soft rot of carrot, respectively. These are common and prevalent bacterial disease in crop production. The volatile oil of Guava leaves consists of a variety of active substances with broad-spectrum anti-microbial activity. The aim of this study was to extract and configure an antimicrobial solution of guava leaves volatile oil to conduct a volatile oil resistance study against three disease bacteria, SA, RS and ECCB, to reserve resources for biological control agents. The volatile oil of guava leaves was extracted by the addition of lithium salt combined with microwave-assisted hydrodistillation, the antibacterial effect of guava leaf volatile oil on three test strains was evaluated by the filter paper diffusion method and minimum inhibitory concentration (MIC), and the extraction process was optimized by single factor combined with response surface experiments. The chemical components of guava leaf volatile oil were determined by gas chromatography-mass spectrometry (GC-MS). The results showed that the oil exhibited excellent inhibitory effects against SA, RS and ECCB, with the inhibition circle diameters ranging from 20.57 to 23.24 mm and the inhibition rates reaching more than 60%, and the MIC values of 3.13 μg/mL, 1.56 μg/mL and 3.13 μg/mL, respectively. The oil had the greatest inhibitory effect on RS, the diameter of the inhibition circle was (23.24±0.47)mm, which was highly sensitive, and also had certain inhibitory effect on SA and ECCB. The optimum process conditions for the extraction process were liquid to material ratio of 10 mL/g DW, microwave power of 660 W and microwave time of 43 min. The yield of the oil obtained under the conditions was (10.23±0.17)mL/kg DW, and the validity and reproducibility of the method were verified by three parallel experiments. The components of the oil were detected to be mainly terpenes and alcohols, with relatively high content of β-caryophyllene (28.36%), l-calamenene (11.47%), (-)-globulol (11.31%) and α-pinene (10.01%). The substances that played a major role in the antibacterial experiment were β-caryophyllene, α-pinene, eugenol, and D-limonene. It was speculated that the mechanism of guava leaf volatile oil inhibition on the test strain was the damage to its cell structure, which resulting in the leakage of intracellular material. The above results demonstrated that the guava leaf volatile oil has an excellent antimicrobial activity and considerable extraction rate, the results of the study would provide a reference for the development and application of guava leaves and integrated control of crop diseases.

To investigate the effects of different coating treatments on the quality of betel nut fresh fruits during storage, three groups of coating agents, aseptic distilled water (CK), chitosan (T₁), and chitosan-chitosan-thymol (T₂), were used to coat the surface of betel nut fresh fruits and then packed in PE bags with perforations to determine the quality changes of fresh fruits stored at 13℃ and 65% relative humidity for 40 days. The results showed that the T₁ and T₂ film treatments effectively delayed and inhibited fruit decay and softening, kernel browning, yellowing, water loss and shrinkage, and extended the shelf life from 5 days to 35 days. Compared with the CK group, the T₁ treatment effectively inhibited fruit yellowing, but the T₂ treatment had the best overall preservation effect, which not only enhanced the initial antioxidant capacity of fresh fruits, but also significantly inhibited the increase of weight loss and decay rate, and the decay rate was only 8% at the 35th day. At the same time, the color of fresh fruits was more stable and the browning of kernels was not obvious in T₂ treatment. In addition, the changes of respiratory intensity, hardness, cellulose and lignin content had showed that the T₂ coating treatment could maintain the physiological and metabolic capacity of fresh fruits during the storage period after 25 days, and the freshness preservation effect was significantly better than that of the CK group, so the T₂ coating treatment can be used as a green, safe, economic and effective method to preserve fresh fruits of betel nut.