不同微喷弥雾调控方式下微气候因子对极端干旱区葡萄果实生长及糖度的影响

通过对极端干旱区葡萄在不同微喷弥雾调控方式（WP1,架上喷水1 h;WP2，架下喷水1 h；WP3，地上喷水1 h）下微气候因子与葡萄果实生长形态及糖度的监测，分析葡萄园微气候因子变化规律及其与葡萄果实生长形态和糖度的关系。结果显示：采用微喷弥雾调控可有效降低葡萄园温度和增加湿度，与CK处理（常规滴灌，不喷水）相比，白天平均温度低2.9℃~3.3℃，平均温度低2.5℃~2.9℃，夜晚平均湿度高4.7%~5.5%，同时可促进葡萄果实生长和糖度累积，WP1、WP2和WP3与CK处理相比，果粒纵茎高出2.88、1.76、0.9 mm，果粒横茎高出1.33、1.80、1.76 mm，果粒均重高出0.22、0.26、0.25 g，糖度分别高出7.75%、3.96%和5.53%。在葡萄果实生长发育过程中，白天平均温度和平均温度是影响葡萄纵径和横径的关键微气候因子，晚上平均湿度是影响葡萄果实重量和糖度的关键微气候因子，在白天平均温度为30.4℃~33.8℃、晚上平均湿度为49.5%~50.5%时接近葡萄果实纵径、横径和果粒均重拟合值最大值。根据其相互关系和建立的回归模型，得出可以用白天平均温度、平均温度和晚上平均湿度对该地区葡萄生长和糖度变化进行分析和预测。     

Genetic bases of source-,sink-,and yield-related traits revealed by genome-wide association study in Xian rice

The source-sink relationship determines the ultimate grain yield.We investigated the genetic basis of the relationship between source and sink and yield potential in rice.In two environments,we identified quantitative trait loci(QTL)associated with sink capacity(total spikelet number per panicle and thousand-grain weight),source leaf(flag leaf length,flag leaf width and flag leaf area),source-sink relationship(total spikelet number to flag leaf area ratio)and yield-related traits(filled grain number per panicle,panicle number per plant,grain yield per plant,biomass per plant,and harvest index)by genome-wide association analysis using 272 Xian(indica)accessions.The panel showed substantial variation for all traits in the two environments and revealed complex phenotypic correlations.A total of 70 QTL influencing the 11 traits were identified using 469,377 high-quality SNP markers.Five QTL were detected consistently in four chromosomal regions in both environments.Five QTL clusters simultaneously affected source,sink,source–sink relationship,and grain yield traits,probably explaining the genetic basis of significant correlations of grain yield with source and sink traits.We selected 24 candidate genes in the four consistent QTL regions by identifying linkage disequilibrium(LD)blocks associated with significant SNPs and performing haplotype analysis.The genes included one cloned gene(NOG1)and three newly identified QTL(qHI6,qTGW7,and qFLA8).These results provide a theoretical basis for high-yield rice breeding by increasing and balancing source–sink relationships using marker-assisted selection.     

覆盖作物多样性对猕猴桃园土壤微生物群落功能的影响

以丹江口水源涵养区猕猴桃园为研究对象,运用Biolog微平板技术,研究不同种类覆盖作物处理(2、4、8种和清耕对照)下土壤微生物群落功能多样性的差异。结果表明,覆盖作物处理土壤微生物群落对碳源的利用程度、功能多样性指数和丰富度指数均高于清耕对照。覆盖作物及清耕对照处理土壤微生物Shannon-Wiener多样性指数、丰富度指数与土壤含水量、有机碳、pH、微生物量碳氮呈显著正相关关系。主成分分析与碳代谢图谱分析表明,猕猴桃园增加覆盖作物种类提高了土壤微生物对碳源的利用能力,且对D-甘露醇、L-精氨酸、L-天门冬酰胺、L-苯丙氨酸、γ-羟丁酸、α-丁酮酸、4-羟基苯甲酸、吐温40的利用能力显著高于清耕对照。此外,4种覆盖作物处理对猕猴桃园土壤生态环境的影响优于2种和8种。研究表明,猕猴桃园增加覆盖作物多样性改变了土壤环境因子,影响了土壤微生物群落的代谢活性和功能多样性。     

Weed community responses to soil type during transition to no-till practice on smallholder farms in Zimbabwe

Understanding drivers of weed density and diversity is essential for the development of weed management strategies. Here, we compared temporal changes in weed density and diversity under no-till (NT) and conventional (CONV) tillage systems in cotton–maize rotations on loam, clay loam and sandy loam soils immediately after transition to NT in Kadoma, Zimbabwe. The effect of tillage system on weed density varied through the growth season and was dependent upon soil type and species composition of the weed community. Although weed responses to tillage system varied amongst species, we identified general trend effects on weed density on specific soils. At 3 weeks after crop emergence (WACE), weed density on loam soils was 76% and 96% higher in NT than in CONV during the 2009/2010 and 2010/2011 seasons, respectively, and on clay loam soils it was 37% and 33% higher in NT than CONV, respectively. Weed densities in NT and CONV were similar across all soil types at 6 WACE during the 2009/2010 and 2010/2011 seasons and at 9 WACE in 2009/2010. Tillage system did not affect weed density during the growth season on sandy loam soils. Weed diversity (Shannon index) was at least 75% higher in NT than CONV on loam and clay loam soils at 3 WACE during both seasons. It is likely these increases in weed densities following conversion to NT will exacerbate already prevalent weed management problems in the smallholder sector. Earlier weeding is recommended to suppress weed emergence and reduce likely associated crop yield losses.     

China's alfalfa market and imports: Development,trends, and potential impacts of the U.S.–China trade dispute and retaliations

This study examines the development and trends of China's alfalfa market and imports, identifies key factors for the rapid increase in China's alfalfa imports, and discusses potential impacts of the U.S.–China trade dispute and retaliations on the alfalfa markets and trade in both nations. China's rapid transition toward larger-scale commercial dairy production, with enhanced feed and cost management as well as quality and safety control, and its limited resources for high-quality alfalfa production are key factors for the dramatic increase in its alfalfa imports, from 19 601 metric tons in 2008 to 1.38 million metric tons (mmt) in 2018. While the United States dominated China's alfalfa imports with an average share of 97.01% from 2007 to 2017, the share dropped to 83.76% in 2018 and 63.28% in January 2019 due to the trade dispute and retaliations started in 2018. China will likely remain a large importer of alfalfa because of both its growing demand and the comparative advantages of imported alfalfa in quality and price, but the imports from the United States will be highly affected by the ongoing trade dispute and negotiations. China is also expected to make more efforts to reduce its dependence on U.S. alfalfa through increased investment in domestic alfalfa production and identification of alternative sources of alfalfa and other hay imports.     

Nutritional Qualities of the Low-Value Bivalve Mollusks Paphia malabarica and Villorita cyprinoides at the Estuarine Waters of the Southwestern Coast of India

The bivalve mollusks Paphia malabarica and Villorita cyprinoides collected from the estuarine system located in the southwest coastal waters of India were evaluated for their nutritional composition. A balanced essential to nonessential amino acid ratio (> 1.0) with a greater quantity of sulfur-containing amino acids in these species demonstrated that they could provide well-balanced protein depositions. The n-3/n-6 polyunsaturated fatty acid ratio in P. malabarica was found to be greater than 2, and, therefore, can be considered as a healthy diet. The C₂₀–C₂₂ long-chain polyunsaturated n-3 fatty acids (for example, docosahexaenoic acid and eicosapentaenoic acid) accounted for more than 23% of the total fatty acid content in P. malabarica as compared to about 7% in V. cyprinoides. P. malabarica showed greater hypocholesterolemic/hypercholesterolemic ratio (1.7) and lesser atherogenicity (0.7), thrombogenicity (0.3) indices when contrasted with those in V. cyprinoides, thereby indicating the nutritional superiority of the former. A greater content of vitamin D₃ (> 150 IU), along with significant quantities of calcium and phosphorus (> 500 mg/100 g) in the clams, signified their importance in preventing osteoporosis. This study demonstrated the importance of bivalves, in particular, P. malabarica as a valued species for human consumption.     

Crop and cattle production responses to tillage and cover crop management in an integrated crop–livestock system in the southeastern USA

Integrated crop–livestock systems can help achieve greater environmental quality from disparate crop and livestock systems by recycling nutrients and taking advantage of synergies between systems. We investigated crop and animal production responses in integrated crop–livestock systems with two types of winter cover cropping (legume-derived N and inorganic fertilizer N), two types of tillage [conventional disk (CT) and no tillage (NT)], and whether cover crops were grazed by cow/calf pairs or not. The 13-ha field study was a modification of a previous factorial experiment with four replications on Ultisols in Georgia, USA. Recurring summer drought severely limited corn and soybean production during all three years. Type of cover crop had little influence and grazing of cover crops had minor influence on crop production characteristics. Cattle gain from grazing of winter cover crops added a stable component to production. No-tillage management had large positive effects on corn grain (95 vs. 252 g m⁻² under CT and NT, respectively) and stover (305 vs. 385 g m⁻²) production, as well as on soybean grain (147 vs. 219 g m⁻²) and stover (253 vs. 375 g m⁻²) production, but little overall effect on winter wheat grain (292 g m⁻²) and stover (401 g m⁻²) production. Our results suggest that robust, diversified crop–livestock systems can be developed for impoverished soils of the southeastern USA, especially when managed under no tillage to control environmental quality and improve resistance of crops to drought.     

Effects of supplementary feeds with different protein levels on growth and economic performances of Nile tilapia (Oreochromis niloticus) cultured in a rain-fed rice–fish ecosystem

This study investigated the effects of supplementary feeds with different crude protein (CP) levels on the growth and economic performances of sex-reversed Nile tilapia (Oreochromis niloticus) reared in a rain-fed rice–fish ecosystem for a period of 120 days. There were four treatments—namely, traditional feed (21% CP), formulated feed (26% CP), commercial feed (30% CP), and control (no feed was used)—with three replicates per treatment. Fish (30.04 g) were stocked in ditches at a rate of 0.5 fish m^?2 considering the total area and fed one of the tested feeds twice daily at the rate of 2%–5% of body weight. Water-quality parameters of the ditches were monitored fortnightly, and these parameters were found suitable for fish farming. Organic matter, total nitrogen, and available phosphorous in soil were increased significantly (P < 0.05) in the feed treatments after fish cultivation. Highly significant weight gain and SGR were observed with fish fed the commercial feed as compared with other treatments. The highest benefit-cost ratio (2.15) was found in the control, followed by formulated feed (1.90), but in the case of numerical net return, it was the opposite. However, commercial feed showed the lowest benefit-cost ratio (1.67) due to higher feed cost than other supplementary feeds. Therefore, this study suggests that fish fed with a formulated feed (26% CP) produced significantly higher net economic return in the rice–fish farming system.     

马铃薯中耕前期圆盘式中耕机设计与试验

针对现有马铃薯中耕机在第1次中耕作业时存在作业效果不佳、易伤苗的问题,对圆盘式马铃薯中耕机进行设计与试验。阐述了该机的工作原理,通过理论计算对其关键部件进行设计,根据农艺培土、除草等作业要求,确定了圆盘式马铃薯中耕机主要结构参数和作业参数;采用单因素和二次旋转正交组合试验,以耕作深度、机车前进速度、调节角为试验因素,以除草率及伤苗率为试验指标进行了样机试验。试验结果表明,当耕作深度为0.13 m、机车前进速度为4.6 km/h、调节角为52°时,除草率为95.2%,伤苗率为3.9%,满足国家标准伤苗率不大于5%、除草率不小于90%的要求。     

Rodent abundance triggered switch between the relative mutualism and predation in a rodent–seed system of the subtropical island forest

Density-dependent non-monotonic species interactions are important in maintaining ecosystem stability and function, but empirical evidences are still rare. Rodents, as both seed dispersers and seed predators, have dual effects on plant regeneration and may result in non-monotonic rodent-plant interactions. According to the non-monotonic models, the relative positive or negative effects of rodents on seedling establishment can be measured based on the positive or negative association of seedling recruitment rate and rodent abundance. In this study, we investigated the fates of acorns of Quercus serrata by tracking tagged seeds on 21 fragmented subtropical islands in the Thousand Island Lake, China. We found that the proportion of germinated seeds of all released seeds showed a dome-shaped association with rodent abundance per seed. The proportion of removed seeds and cached seeds showed a saturated- and a weak dome-shaped association with rodent abundance per seed, respectively. Our results demonstrated a clear empirical evidence that rodent abundance per seed triggered a switch between the relative mutualism and predation in a rodent–seed system. Our study implied that the observed non-monotonic interactions between plants and animals may play a significant role in maintaining biodiversity and ecosystem function. We appeal for more investigations of the complex non-monotonic interactions in various ecosystems.