A chromosome-scale genome assembly of Malus domestica, a multi-stress resistant apple variety.

Hanfu apple is the main cultivar grown in the cool areas of Northeast, Northwest, and North China. Here, we proposed a chromosome-level Hanfu genome assembly using PacBio, Illumina and Hi-C sequencing data. The total contig length was 628.99 Mb, with scaffold and contig N50 sizes of 36.18 Mb and 1.25 Mb, respectively. The Hanfu genome had a total of 39,617 genes, of which we predicted the function for 38,816. Evolutionary analysis showed that Hanfu may have undergone a γ-event, a recent whole-genome duplication. A comparative analysis was conducted on the genomes of Hanfu and homozygous triploid HFTH1, which were cultured using the anthers of diploid Hanfu apples. Three variants were identified, including 2,155,184 single nucleotide polymorphisms (SNPs), 413,108 insertions/deletions (indels), and 7,587 structural variants (SVs).This high-quality genome will provide a reference for the genetic improvement of apples and the breeding of more varieties with high resistance and high quality.

Physiological and de novo transcriptome analysis of the fermentation mechanism of Cerasus sachalinensis roots in response to short-term waterlogging.

BACKGROUND: Cerasus sachalinensis is widely used in cool regions as a sweet cherry rootstock and is known for its sensitivity to soil waterlogging and waterlogging stress. However, the limited availability of Cerasus genomic resources has considerably restricted the exploration of its waterlogging response mechanism. To understand its reaction to short-term waterlogging, we analyzed the physiology and transcriptomes of C. sachalinensis roots in response to different waterlogging durations. RESULTS: In this study, 12,487 differentially expressed genes (DEGs) were identified from Cerasus sachalinensis roots under different waterlogging durations. Carbon metabolism and energy maintenance formed the first coping mechanism stage of C. sachalinensis in response to low oxygen conditions. Root energy processes, including root respiration and activities of the fermentation enzymes alcohol dehydrogenase, pyruvate decarboxylase, and lactate dehydrogenase, showed unique changes after 0 h, 3 h, 6 h, and 24 h of waterlogging exposure. Ribonucleic acid sequencing was used to analyze transcriptome changes in C. sachalinensis roots treated with 3 h, 6 h, and 24 h of waterlogging stress. After de novo assembly, 597,474 unigenes were recognized, of which 355,350 (59.47%) were annotated. To identify the most important pathways represented by DEGs, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases were used to compare these genes. The first stage of root reaction to waterlogging stress was activation of carbohydrate metabolism to produce more glucose and maintain energy levels. At 3 h, the glycolytic and fermentation pathways were activated to maintain adenosine triphosphate production. At 24 h, pathways involved in the translation of proteins were activated to further assist the plant in tolerating waterlogging stress. These findings will facilitate a further understanding of the potential mechanisms of plant responses to waterlogging at physiological and transcriptome levels. CONCLUSIONS: Carbon metabolism and energy maintenance formed the first coping mechanism C. sachalinensis in response to low oxygen conditions, and they may be responsible for its short-term waterlogging response. Our study not only provides the assessment of genomic resources of Cerasus but also paves the way for probing the metabolic and molecular mechanisms underlying the short-term waterlogging response in C. sachalinensis.

Exogenous Spermidine Alleviated Low-Temperature Damage by Affecting Polyamine Metabolism and Antioxidant Levels in Apples.

Low-temperature stress significantly limits the growth, development, and geographical distribution of apple cultivation. Spermidine (Spd), a known plant growth regulator, plays a vital role in the plant's response to abiotic stress. Yet, the mechanisms by which exogenous Spd enhances cold resistance in apples remain poorly understood. Therefore, the present study analyzed the effects of exogenous Spd on antioxidant enzyme activity, polyamine metabolism, and related gene expression levels of 1-year-old apple branches under low-temperature stress. Treatment with exogenous Spd was found to stabilize branch tissue biofilms and significantly reduce the levels of reactive oxygen species by elevating proline content and boosting the activity of antioxidants such as superoxide dismutase. It also upregulated the activities of arginine decarboxylase, S-adenosylmethionine decarboxylase, and spermidine synthase and the expression levels of MdADC1, MdSAMDC1, and MdSPDS1 under low-temperature stress and led to the accumulation of large amounts of Spd and spermine. Moreover, compared with the 2 mmol·L-1 Spd treatment, the 1 mmol·L-1 Spd treatment increased the expression levels of cold-responsive genes MdCBF1/2/3, MdCOR47, and MdKIN1, significantly. The findings suggest that exogenous Spd can enhance cold resistance in apple branches significantly. This enhancement is achieved by modulating polyamine metabolism and improving antioxidant defense mechanisms, which could be exploited to improve apple cultivation under cold stress conditions.

Responses of soil microorganisms, enzyme activities and nutrient contents to inter-row grass ploughing and returning to the field in a natural sod culture apple orchard.

Natural sod culture in orchard is an effective measure to improve the orchard productivity and promote the sustainable production. To explore the effects of inter-row grass ploughing and returning on soil biological cha-racteristics and nutrient contents, we examined the effects of different grass returning to the field on the amount of soil microorganisms, enzyme activities and nitrogen and potassium contents of 0-20 cm soil layer. There are three treatments, cleaning tillage as the control (CK), conventional mowing management (NG), and soil ploughing annually under natural sod culture with conventional mowing condition (NGR) treatments. The results showed that soil microorganisms were dominated by bacteria, followed by actinomycetes, with the least fungi. Compared with CK, both NG and NGR treatments significantly improved the abundance of soil bacteria and fungi, with the strongest effects in NGR treatment, and significantly increased the soil urease, sucrase and catalase activities by 59.0%, 20.7%, 38.3% and 73.5%, 45.9%, 67.8%, respectively. NGR treatment significantly increased soil nitrogen and potassium contents, with the contents of ammonium nitrogen, nitrate nitrogen, particulate organic nitrogen, microbial biomass nitrogen, available potassium and water-soluble potassium being 1.5, 1.8, 1.6, 2.0, 1.3 and 1.4 times of that in CK, respectively. NGR significantly increased soluble sugar content and sugar acid ratio and subsequently improved fruit quality. Overall, NGR increased soil microbial abundance, enzyme activities, nitrogen, potassium contents and fruit quality, which could be a feasible management of inter-row grasses in the natural sod culture apple orchard.

Abnormal static and dynamic amplitude of low-frequency fluctuations in multiple brain regions of methamphetamine abstainers.

Methamphetamine (meth) addiction is a significant social and public health problem worldwide. The relapse rate of meth abstainers is significantly high, but the underlying physiological mechanisms are unclear. Therefore, in this study, we performed resting-state functional magnetic resonance imaging (rs-fMRI) analysis to detect differences in the spontaneous neural activity between the meth abstainers and the healthy controls, and identify the physiological mechanisms underlying the high relapse rate among the meth abstainers. The fluctuations and time variations in the blood oxygenation level-dependent (BOLD) signal of the local brain activity was analyzed from the pre-processed rs-fMRI data of 11 meth abstainers and 11 healthy controls and estimated the amplitude of low-frequency fluctuations (ALFF) and the dynamic ALFF (dALFF). In comparison with the healthy controls, meth abstainers showed higher ALFF in the anterior central gyrus, posterior central gyrus, trigonal-inferior frontal gyrus, middle temporal gyrus, dorsolateral superior frontal gyrus, and the insula, and reduced ALFF in the paracentral lobule and middle occipital gyrus. Furthermore, the meth abstainers showed significantly reduced dALFF in the supplementary motor area, orbital inferior frontal gyrus, middle frontal gyrus, medial superior frontal gyrus, middle occipital gyrus, insula, middle temporal gyrus, anterior central gyrus, and the cerebellum compared to the healthy controls ($ P < 0.05 $). These data showed abnormal spontaneous neural activity in several brain regions related to the cognitive, executive, and other social functions in the meth abstainers and potentially represent the underlying physiological mechanisms that are responsible for the high relapse rate. In conclusion, a combination of ALFF and dALFF analytical methods can be used to estimate abnormal spontaneous brain activity in the meth abstainers and make a more reasonable explanation for the high relapse rate of meth abstainers.

Characteristics of cadmium accumulation and tolerance in apple plants grown in different soils.

Cadmium (Cd) is a nonessential element and highly toxic to apple tree. However, Cd accumulation, translocation and tolerance in apple trees planted in different soils remain unknown. To investigate soil Cd bioavailability, plant Cd accumulation, physiological changes as well as gene expression patterns in apple trees grown in five different soils, 'Hanfu' apple seedlings were planted in orchard soils collected from Maliangou village (ML), Desheng village (DS), Xishan village (XS), Kaoshantun village (KS) and Qianertaizi village (QT), and subjected to 500 µM CdCl2 for 70 d. Results showed that soils of ML and XS had higher content of organic matter (OM), clay and silt, and cation exchange capacity (CEC) but lower sand content than the other soils, thereby reduced Cd bioavailability, which could be reflected by lower concentrations and proportions of acid-soluble Cd but higher concentrations and proportions of reducible and oxidizable Cd. The plants grown in soils of ML and XS had relatively lower Cd accumulation levels and bio-concentration factors than those grown in the other soils. Excess Cd reduced plant biomass, root architecture, and chlorophyll content in all plants but to relatively lesser degree in those grown in soils of ML and XS. The plants grown in soils of ML, XS and QT had comparatively lower reactive oxygen species (ROS) content, less membrane lipid peroxidation, and higher antioxidant content and enzyme activity than those grown in soils of DS and KS. Transcript levels of genes regulating Cd uptake, transport and detoxification such as HA11, VHA4, ZIP6, IRT1, NAS1, MT2, MHX, MTP1, ABCC1, HMA4 and PCR2 displayed significant differences in roots of plants grown in different soils. These results indicate that soil types affect Cd accumulation and tolerance in apple plants, and plants grown in soils with higher OM content, CEC, clay and silt content and lower sand content suffer less Cd toxicity.

MdSWEET23, a sucrose transporter from apple (Malus × domestica Borkh.), influences sugar metabolism and enhances cold tolerance in tomato.

Photosynthetic products in most fleshy fruits are unloaded via the apoplasmic pathway. Sugar transporters play an important role in the apoplasmic unloading pathway and are involved in sugar transport for fruit development. The MdSWEET23, cloned from ''Hanfu'' apple (Malus × domestica Borkh.) fruits, belongs to Clade III of the SWEET family. Subcellular localization revealed that MdSWEET23 is localized on the plasma membrane. ß-glucuronidase activity assays showed that MdSWEET23 was primarily expressed in the sepal and carpel vascular bundle of apple fruits. Heterologous expression assays in yeast showed that MdSWEET23 functions in sucrose transport. The overexpression of MdSWEET23 in the ''Orin" calli increased the soluble sugar content. The silencing of MdSWEET23 significantly reduced the contents of sucrose and sorbitol in apple fruits. Ectopic overexpression of MdSWEET23 in tomato altered sugar metabolism and distribution in leaves and fruits, causing a reduction in photosynthetic rates and plant height, enhanced cold stress tolerance, and increased the content of sucrose, fructose, and glucose in breaking color fruits, but did not increase sugar sink potency of tomato fruits.

Alleviation effect of GR24, a strigolactone analogue, on low-nitrogen stress in Malus baccata seedlings.

To investigate the efficacy of foliar application of GR24, a strigolactone analogue, in alleviating low-nitrogen stress in Malus baccata, we applied GR24 with different concentrations (0, 1, 5, 10, and 20 µmol·L-1) to leaves of plants under low nitrogen stress. We evaluated the changes in photosynthetic characteristics of leaves, reactive oxygen metabolism, and nitrogen assimilation in roots. The results showed that shoot biomass of seedling significantly decreased and root-shoot ratio increased under low-nitrogen stress. The chlorophyll contents decreased, the carotenoid content increased, and the photosynthetic activity decreased. The activities of superoxide dismutase and catalase enzymes in roots changed little, while the activities of peroxidase and ascorbic acid peroxidase enzymes, along with the levels of soluble sugar, free proline, and reactive oxygen species showed a significant increase, and the soluble protein content decreased. The NO3- content in roots decreased, the NH4+ content increased, while activities of nitrate reductase and glutamine synthase decreased. Compared to the control group without GR24 application, foliar sprays of 10 and 20 µmol·L-1 GR24 under both normal and low-nitrogen increased biomass and root-shoot ratio to varying degrees. Additionally, GR24 application increased chlorophyll content, photosynthesis indices (net photosynthetic rate, transpiration rate and stomatal conductance), and fluorescence (maximum photochemical efficiency of PSⅡ and quantum yield of electron transfer per unit area) performance parameters, as well as the contents of osmotic regulation substances (soluble protein, soluble sugar, and free proline) and glutamine synthase activity. Application of 10 and 20 µmol·L-1 GR24 under low-nitrogen stress decreased carotenoid, reactive oxygen species, and NH4+ contents, while increased the activities of antioxidases and key enzymes in nitrogen metabolism (nitrate reductase and glutamine synthase) and NO3- content. The 10 µmol·L-1 GR24 treatment was the most effective in alleviating low nitrogen stress, which has potential for application in apple orchards with low nitrogen soil.

Glucose addition promotes C fixation and bacteria diversity in C-poor soils, improves root morphology, and enhances key N metabolism in apple roots.

The interaction between plant, soil and microorganism plays a crucial role in sustainable development of terrestrial ecosystem function and diversity. However, little information is known about how plant growth, soil organic carbon (C) fractions and microorganism respond to exogenous C addition in soils with low organic C content. Three levels of 13C-glucose (equal to 0, 100% and 500% of initial microbial biomass C) were added to non-sterilized (corresponding to treatment abbreviation of CK, Glu-1, Glu-2, respectively) and sterilized soils (corresponding to treatment abbreviation of SS, SS+Glu-1, SS+Glu-2, respectively) planted with apple rootstock (Malus baccata (L.) Borkh.) seedings. The objectives of this study were to analyse the dynamics of soil organic C (SOC) fractions and soil bacterial community diversity with glucose levels and soil sterilization, and to explore the morphology of roots and nitrogen (N) metabolism by plant after glucose addition to sterilized/non-sterilized soils. Results showed that the contents of labile organic C fractions were significantly varied (P<0.05) with the levels of glucose addition and soil sterilization. SS+Glu-2 and Glu-2 treatments increased the contents of labile organic C fractions, on average, by 48.47% and 35.33% compared with no glucose addition, respectively. About 21.42% and 16.17% of glucose-C remained in sterilized and non-sterilized soils, respectively at the end of experiment (day 45). Regardless of soil sterilized or not, the glucose addition increased the richness and diversity indices of soil bacterial community compared with no-glucose addition. The glucose addition optimized root zone conditions, and enhanced root vitality, morphology and biomass. Both SS+Glu-2 and Glu-2 treatments significantly enhanced (P<0.05) the contents of nitrate (NO3-N) and nitrite (NO2-N), but sharply decreased (P<0.05) the ammonium (NH4+-N) content compared with no glucose addition. Also, these two treatments significantly (P<0.05) increased the enzymic activities and gene transcript levels involved in root N metabolism, which demonstrated that the high level of glucose addition promoted N assimilation and transformation into free amino acids by root. Overall, the addition of exogenous C to not only promotes its fixation and bacterial community diversity in C-poor soils, but also improves root morphology and N absorption by plant.

Differential pulp cell wall structures lead to diverse fruit textures in apple (Malus domestica).

In this study, we aimed to elucidate the effect of pulp cell wall structure on fruit hardness and crispness in apples. To this end, we studied the cell wall polysaccharides in two apple varieties, "Hanfu" and "Honeycrisp," during fruit development. Compared with Hanfu, the crispness of Honeycrisp was higher, whereas its harness was lower. The intensity and distribution of immunofluorescence signals indicated that galactose and arabinose contributed to the higher hardness of Hanfu, whereas arabinose, egg-box structure, and fucosylated xyloglucans, distributed in the corners of tricellular junctions, enhanced the cell-cell adhesion and improved the crispness of Honeycrisp. Besides, fucosylated xyloglucan played an important role in promoting the formation and maintaining the strength of the cell wall skeleton and, consequently, retaining the fruit crispness. The esterification state of pectin had little effect on the fruit hardness and crispness in both varieties. Collectively, our findings provided information on the underlying mechanism of fruit texture formation in apples.

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To explore the effects of zinc levels on the synthesis and translocation of photosynthetic products from leaves to fruits, and to lay a theoretical foundation for improving fruit quality through zinc supplementation during the critical period of apple fruit development, a field experiment was carried out with a eight-year old 'Hanfu'/GM256/Malus baccata Borkh apple. We used the 13C tracer method to examine the effects of different zinc levels (ZnSO4·H2O 0, 0.1%, 0.2%, 0.3%, 0.4%, expressed by CK, Zn1, Zn2, Zn3, Zn4, respectively) on translocation of photosynthate to fruit during the stage of fruit expanding. The results showed that, with increasing zinc concentration, Rubisco enzyme activity, net photosynthetic rate, sorbitol and sucrose content, sorbitol 6-phosphate dehydrogenase, and sucrose phosphate synthase enzyme activities of leaves first increased and then decreased, with the highest values being observed in Zn3 treatment. Zn3 treatment significantly increased the 13C assimilation capability of leaves. Compared with other treatments, the 13C of self-retention (labeled leaves and labeled branches) was lowest in Zn3 treatment (61.2%) and the output of 13C photoassimilates was highest in Zn3 treatment (38.8%). 13C absorption of apple fruit showed a trend of Zn3 ＞ Zn2 ＞ Zn4 ＞ Zn1 ＞ CK. In summary, foliar zinc application under appropriate concentration (0.3% ZnSO4·H2O) enhanced photosynthesis, increased the assimilation capability of leaves, and promoted the directional transportation of photosynthate to fruit.

Malus rootstocks affect copper accumulation and tolerance in trees by regulating copper mobility, physiological responses, and gene expression patterns.

We investigated the roles of rootstocks in Cu accumulation and tolerance in Malus plants by grafting 'Hanfu' (HF) scions onto M. baccata (Mb) and M. prunifolia (Mp) rootstocks, which have different Cu tolerances. The grafts were exposed to basal or excess Cu for 20 d. Excess Cu-treated HF/Mb had less biomass, and pronounced root architecture deformation and leaf ultrastructure damage than excess Cu-challenged HF/Mp. Root Cu concentrations and bio-concentration factor (BCF) were higher in HF/Mp than HF/Mb, whereas HF/Mb had higher stem and leaf Cu concentrations than HF/Mp. Excess Cu lowered root and aerial tissue BCF and translocation factor (Tf) in all plants; however, Tf was markedly higher in HF/Mb than in HF/Mp. The subcellular distribution of Cu in the roots and leaves indicated that excess Cu treatments increased Cu fixation in the root cell walls, which decreased Cu mobility. Compared to HF/Mb, HF/Mp sequestered more Cu in its root cell walls and less Cu in leaf plastids, nuclei, and mitochondria. Moreover, HF/Mp roots and leaves had higher concentrations of water-insoluble Cu compounds than HF/Mb, which reduced Cu mobility and toxicity. Fourier transform infrared spectroscopy analysis showed that the carboxyl, hydroxyl and acylamino groups of the cellulose, hemicellulose, pectin and proteins were the main Cu binding sites in the root cell walls. Excess Cu-induced superoxide anion and malondialdehyde were 28.6% and 5.1% lower, but soluble phenolics, ascorbate and glutathione were 10.5%, 41.9% and 17.7% higher in HF/Mp than HF/Mb leaves. Compared with HF/Mb, certain genes involved in Cu transport were downregulated, while other genes involved in detoxification were upregulated in HF/Mp roots and leaves. Our results show that Mp inhibited Cu translocation and mitigated Cu toxicity in Malus scions by regulating Cu mobility, antioxidant defense mechanisms, and transcription of key genes involved in Cu translocation and detoxification.

Rootstock-Scion Interaction Affects Cadmium Accumulation and Tolerance of Malus.

To understand the roles of Malus rootstock, scion, and their interaction in Cd accumulation and tolerance, four scion/rootstock combinations consisting of the apple cultivars "Hanfu" (HF) and "Fuji" (FJ) grafted onto M. baccata (Mb) or M. micromalus "qingzhoulinqin" (Mm) rootstocks differing in relative Cd tolerance were exposed either to 0 µM or 50 µM CdCl2 for 18 d. Cd accumulation and tolerance in grafted Malus plants varied within rootstock, scion, and rootstock-scion interaction. Cd-induced decreases in photosynthesis, photosynthetic pigment level, and biomass were lower for HF grafted onto Mb than those for HF grafted onto Mm. Reductions in growth and photosynthetic rate were always the lowest for HF/Mb. Cd concentration, bioconcentration factor (BCF), and translocation factor (Tf ) were always comparatively higher in HF and FJ grafted onto rootstock Mm than in HF and FJ grafted on Mb, respectively. When HF and FJ were grafted onto the same rootstock, the root Cd concentrations were always higher in HF than FJ, whereas the shoot Cd concentrations displayed the opposite trend. The shoot Cd concentrations and Tf were lower for HF/Mb than the other scion/rootstock combinations. Rootstock, scion, and rootstock-scion interaction also affected subcellular Cd distribution. Immobilization of Cd in the root cell walls may be a primary Cd mobility and toxicity reduction strategy in Malus. The rootstock and scion also had statistically significant influences on ROS level and antioxidant activity. Cd induced more severe oxidative stress in HF and FJ grafted onto Mm than it did in HF and FJ grafted onto Mb. Compared with FJ, HF had lower foliar O2 -, root H2O2, and root and leaf MDA levels, but higher ROS-scavenging capacity. The rootstock, scion, and rootstock-scion interaction affected the mRNA transcript levels of several genes involved in Cd uptake, transport, and detoxification including HA7, FRO2-like, NRAMP1, NRAMP3, HMA4, MT2, NAS1, and ABCC1. Hence, the responses of grafted Malus plants to Cd toxicity vary with rootstock, scion, and rootstock-scion interaction.

The impact of cover crop shoot decomposition on soil microorganisms in an apple orchard in northeast China.

Mowing can facilitate the incorporation of cover crop shoots into soil and improve the properties of soils in apple orchards. This article evaluated how apple orchard soil responds to the decomposition of the shoot residues of three cover crops[native mixed herbs (NMS), red clover (RCS), and ryegrass (RES)] in terms of microbial metabolism and biomass, and discussed the relationships between microbial responses and shoot chemistry. The chemical composition of shoots was analysed and a buried bag experiment was carried out to simulate shoot decomposition in an apple orchard. The results revealed significant differences in the chemical compositions and shoot C:N ratios (NMS: 10.9, RCS: 19.1, and RES: 12.9) of the three cover crops. The decomposition of the cover crop shoots promoted microbial metabolism and boosted soil bacterial reproduction (increase in the biomass indicator muramic acid: 19.44, 124.15, and 14.83 mg kg-1, respectively. But there are different types of effects on soil fungal reproduction (change in the biomass indicator glucosamine: 712.51, 887.45, and 103.97 mg kg-1), and they are obviously negative, significantly positive, and non-significant respectively. Thus, the native mixed herbs and red clover are preferable swards for better shoot enhancement in apple orchard.

[Effects of exogenous glucose and starch on soil carbon metabolism of root zone and root function in potted sweet cherry].

One-year-old potted sweet cheery trees were treated with 4 g · kg(-1) exogenous glucose or starch and with non-addition of exogenous carbon as the control for up to 60 days. Soil of root zone was sampled to analyze soil microbial biomass carbon, activities of invertase and amylase and microbial community functional diversity during the 60-day treatment, and roots were sampled for analysis of root respiratory rate, respiratory pathways and root viability after treatment for 30 days. Results showed that the invertase activity and the microbial biomass carbon initially increased and decreased subsequently, with the maxima which were 14.0% and 13.1% higher in the glucose treatment than in the control treatment appeared after 15 and 7 days of treatments, respectively. Soil organic matter content increased first then decreased and finally moderately increased again. Amylase activity was 7.5-fold higher in the starch treatment than in the control treatment after 15-day treatment. Soil microbial biomass carbon was higher in the starch treatment than in the control treatment except after 7-day treatment. Soil organic matter content initially increased and then decreased, but it was still 19.8% higher than in the control after 60-day treatment. BIOLOG results showed that the maximum average well color development (AWCD) value and microbial activity appeared after 15-day treatment in the following order: starch>glucose>control. After 30-day treatment, glucose treatment resulted in a significant increase in the soil microbial utilization of carbohydrates, carboxylic acid, amino acids, phenolic acids and amines, and starch treatment significantly increased the soil microbial utilization of carbohydrates, carboxylic acid, polymers and phenolic acids. After 30-day treatment, the total root respiratory rate and root viability were 21.4%, 19.4% and 65.5%, 37.0% higher in glucose treatment than in the control and starch treatments, respectively. These results indicated exogenous glucose and starch affected soil carbon metabolism and enhanced soil microbial activity, the root respiratory rate and root viability.

[Effects of different organic matter mulching on water content, temperature, and available nutrients of apple orchard soil in a cold region].

The effects of different organic matter covers on soil physical-chemical properties were investigated in a 'Hanfu' apple orchard located in a cold region. Four treatments were applied (weed mulching, rice straw mulching, corn straw mulching, and crushed branches mulching), and physical-chemical properties, including orchard soil moisture and nutrient contents, were compared among treatment groups and between organic matter-treated and untreated plots. The results showed that soil water content increased in the plots treated with organic matter mulching, especially in the arid season. Cover with organic matter mulch slowed the rate of soil temperature increase in spring, which was harmful to the early growth of fruit trees. Organic matter mulching treatments decreased the peak temperature of orchard soil in the summer and increased the minimum soil temperature in the fall. pH was increased in soils treated with organic matter mulching, especially in the corn straw mulching treatment, which occurred as a response to alleviating soil acidification to achieve near-neutral soil conditions. The soil organic matter increased to varying extents among treatment groups, with the highest increase observed in the weed mulching treatment. Overall, mulching increased alkali-hydrolyzable nitrogen, available phosphorus, and available potassium in the soil, but the alkali-hydrolyzable nitrogen content in the rice straw mulching treatment was lower than that of the control.

[Microbial flora in Cerasus sachalinensis rhizosphere].

By using selected culture media, the microbes in Cerasus sachalinensis rhizosphere were isolated, identified and classified, with their community structure and dynamic changes at different growth stages of C. sachalinensis studied. The bacteria isolated were belonged to 15 genera, among which, Bacillus, Pseudomonas and Flavobacterium were the dominant ones. Flavus and Albosporus were the two dominant genera in seven groups of Actinomyces, and Mucor, Aspergillus and Penicillium were the main genera of fungi. The microbial flora varied with C. sachalinensis growth stage, being the richest at defoliation stage and the least at budding stage.

[Community structure and its dynamics of phosphobacteria in Cerasus sachalinensis rhizosphere and nonrhizosphere].

By using selective culture media, the phosphobacteria in Cerasus sachalinensis rhizosphere and nonrhizosphere were isolated and identified, with their community structure and dynamics studied. The phosphobacteria isolated from three test substrates belonged to 13 genera, and Bacillus, Pseudomonas and Serratia were the main ones. The substrate added with slag was most suitable for the growth of phosphobacteria, on which, phosphobacteria had the highest population number but the lowest diversity index. There was a difference in the population number of phosphobacteria in rhizosphere and nonrhizosphere during the growth period of C. sachalinensis. In rhizosphere, phosphobacteria had the highest number (6 genera) in withhold-growing period of shoot, less in fast growing period of shoot and in defoliation period, and the least in germination period. The diversity index of phosphobacteria in rhizosphere also varied with the growth period of C. sachalinensis, which was in the order of fast growing period of shoot > defoliation period > withhold-growing period of shoot. In nonrhizosphere, the population number and diversity index of phosphobacteria had a decreasing trend with the growth of C. sachalinensis. All of these indicated that there was an obvious rhizosphere effect on phosphobacteria.