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.

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.

[Effects of zinc levels on synthesis and translocation of 13C-photoassimilates in leaves to fruit of apple during fruit expanding stage]. / 锌对苹果果实膨大期叶片13Cå ‰åˆäº§ç‰©åˆæˆåŠå‘æžœå®žè½¬ç§»åˆ†é çš„å½±å“.

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.

[Effects of exogenous glucose on growth and root nitrogen metabolism in Malus baccata]. / å¤–æºè‘¡è„ç³–å¯¹å±±å®šå­ç”Ÿé•¿åŠæ ¹ç³»æ°®ç´ ä»£è°¢çš„å½±å“.

To examine the effects of external glucose on growth, root architecture and nitrogen metabolism of Malus baccata seedlings in low carbon soil condition, Malus baccata seedlings were grown in sandy soil with the concentration of soil organic matter being 0.65%. The experiment consisted of three treatments: Control, with 2 g·kg-1 glucose that equal to the ambient microbial biomass carbon (MBC), and with 10 g·kg-1 glucose that was five times higher than the ambient MBC. The plant height, biomass, total root length and superficial area of the five times MBC group were 12.3%, 26.4%, 23.2% and 14.6% higher than that of the control, respectively. Root diameter, root volume and average diameter exhibited no significant difference under glucose treatments. The root activity was significantly increased under equal and five times MBC-glucose treatments, and reached its peak at 3 d and 15 d, about 119.1% and 75.7% higher than the control, respectively. Exogenous glucose addition significantly enhanced the concentrations of NO3-, NO2- and NH4+ in roots. The activities of nitrate reductase, glutamine synthetase, glutamate dehydrogenase, glutamate synthase, glutamic-oxalacetic transaminase and glutamic-pyruvic transaminase were substantially increased in the roots, especially under five times MBC treatment. Five times higher than the ambient MBC of external carbon source promoted biomass accumulation, root growth, morphogenesis and N absorption of plants in low carbon sandy soil.

[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.