Cultivation effects on soil texture and fertility in an arid desert region of northwestern China

In arid desert regions of northwestern China, reclamation and subsequent irrigated cultivation have become effective ways to prevent desertification, expand arable croplands, and develop sustainable agricultural production. Improvement in soil texture and fertility is crucial to high soil quality and stable crop yield. However, knowledge on the long-term effects of the conversion of desert lands into arable croplands is very limited. To address this problem, we conducted this study in an arid desert region of northwestern China to understand the changes in soil physical-chemical properties after 0, 2, 5, 10, 17, and 24 years of cultivation. Our results showed that silt and clay contents at the 17-year-old sites increased 17.5 and 152.3 folds, respectively, compared with that at the 0-year-old sites. The soil aggregate size fraction and its stability exhibited an exponential growth trend with increasing cultivation ages, but no significant change was found for the proportion of soil macroaggregates (>5.00 mm) during the 17 years of cultivation. The soil organic carbon (SOC) content at the 24-year-old sites was 6.86 g/kg and increased 8.8 folds compared with that at the 0-year-old sites. The total (or available) nitrogen, phosphorus, and potassium contents showed significant increasing trends and reached higher values after 17 (or 24) years of cultivation. Changes in soil physical-chemical properties successively experienced slow, rapid, and stable development stages, but some key properties (such as soil aggregate stability and SOC) were still too low to meet the sustainable agricultural production. The results of this long-term study indicated that reasonable agricultural management, such as expanding no-tillage land area, returning straw to the fields, applying organic fertilizer, reducing chemical fertilizer application, and carrying out soil testing for formula fertilization, is urgently needed in arid desert regions.     

土地确权对农户地权稳定性感知的影响——基于村庄内土地不平等视角的分析

稳定的农地产权能够激励农户农地投资,有助于促进农地资源可持续利用和农业可持续发展。土地确权是稳定农地产权的重要正式制度安排,即稳定地权是新一轮土地确权承载的重要功能。基于诱致性制度变迁理论和社会心理学理论,以黄土高原苹果优势区为研究对象,利用实地调研数据,采用Logit和Ologit模型,从村庄内家庭土地不平等视角分析土地确权对农户地权稳定性感知的影响及其作用机制,探讨新一轮农地确权的地权稳定效应。结果表明,在研究区域,33.79%的农户已完成新一轮土地确权颁证,62.64%的农户认为研究地块在未来不会被重新调整,即感知的地权稳定性水平较高。新一轮土地确权显著强化了农户的地权稳定性感知,且在控制村庄内土地不平等的情境中具有更高的强化效果;村庄内家庭土地不平等对农户地权稳定性感知具有显著的弱化效应,且土地不平等在土地确权对农户地权稳定性感知的影响中具有负向调节作用。因此,在"三权分置"产权制度改革中,政府应重视规范土地确权程序,加强产权制度改革宣传和信息披露,同时,注重以政策调整和市场配置相结合的方式,降低土地不平等造成的负面影响,强化土地产权制度改革的政策效果。     

乡土物种补播对青藏高原高寒草甸群落稳定性的影响

为了探究高寒草甸天然草地补播乡土物种对草地群落稳定性的影响，本试验以垂穗披碱草（Elymus nutans）、异针茅（Stipa aliena）、中华羊茅（Festuca sinensis）、溚草（Koeleria cristata）、星星草（Puccinellia tenuiflora）、扁蓿豆（Melissitus rutenica）、冷地早熟禾（Poa crymophila）为试验材料，设置5种混播组合，于2017年在青海省贵南县天然草地上进行补播。试验采用方差比率法（Variance ratio，VR）、M.Godron贡献定率法（Contribution law）以及生物量稳定性分析方法，结果表明：5种组合补播后使得群落联结性降低、生物量稳定性增大，群落整体稳定性增强，正向着稳定方向发展；5种组合中，组合D （扁蓿豆+星星草+垂穗披碱草+异针茅+溚草）的生物量稳定性最大，是对草地恢复最有效的物种组合。本试验筛选出了对草地生态修复最有效的物种组合，为草地保护及利用提供了科学依据。     

海洋食物网结构稳定性及干扰响应研究综述

针对当前全球环境急剧变化的背景,本文归纳了海洋食物网结构复杂性常用的量化指标,梳理了食物网稳定性不同维度的概念并深入探究其与复杂性之间的内在联系。根据海洋生态系统的不同干扰类型,分析了各种类型干扰的发生方式以及食物网在应对干扰时的适应机理,最后总结了海洋生态系统数据获取分析以及食物网构建时有待解决的问题,并指出开展初级生产者与消费者之间的相互作用研究能更利于解析全球变化对海洋食物网结构和功能的影响。     

白三叶与不同禾草混播群落17年稳定性经较研究

在适度放牧条件下开展了白三叶与多年生黑麦草、紫羊茅、草地早熟禾和无芒雀麦的两两豆禾混播群落的种间相容性、群落生产力和稳定性的研究。17年的研究结果表明,白三叶 紫羊茅组合的年均干物质产量502g/m2,显著高于其他组合(P<0.05),但前期以白三叶 多年生黑麦草最高(P<0.05)。在时间序列混播比例的变化上,白三叶逐渐增加,然后维持在一定的范围;多年生黑麦草第1年最高,后逐渐下降;紫羊茅和草地早熟禾变化不大,而无芒雀麦减少最快,并最终消失;白三叶 紫羊茅组合的比例动态变化最小,组分稳定,而且群落抵抗力最强,年均杂草侵入量仅为2.4 g/m2,极显著地低于其他处理(P<0.01)。参试禾本科牧草与白三叶的种间相容性为紫羊茅>多年生黑麦草≥草地早熟禾>无芒雀麦。种间相容性是混播群落长期稳定性的重要决定因素。时间梯度上的群落生产力变化趋势,白三叶 紫羊茅和白三叶 草地早熟禾呈平稳略升,而白三叶 多年生黑麦草和白三叶 无芒雀麦呈前高后低模式。对混播群落稳定性的判断存在时间尺度和空间尺度。     

The effects of replacement of whole‐plant corn with oat and common vetch on the fermentation quality,chemical composition and aerobic stability of total mixed ration silage in Tibet

The objective of this experiment was to evaluate the effects of replacement of whole‐plant corn with oat and common vetch on the fermentation quality, chemical composition and aerobic stability of total mixed ration (TMR) silage in Tibet. Four TMR that varied in the forage sources on dry matter basis were used: (i) 52% whole‐plant corn (Control); (ii) 43% oat + 12% common vetch (OC3.6); (iii) 38% oat + 18% common vetch (OC2.2); and (iv) 33% oat + 23% common vetch (OC1.5). Silos were opened on day 45 and then subjected to an aerobic stability test for 12 days. The results showed that all silages were well preserved with low pH and NH₃‐N, and high lactic acid and V‐scores. With the increasing proportion of common vetch, crude protein, ether extract increased (P < 0.05), and neutral detergent fiber and acid detergent fiber decreased (P < 0.05). Under aerobic conditions, treated silages were more stable than the control silage as indicated by lower (P < 0.05) pH and yeast population. It was concluded that replacement of whole‐plant corn with oat and common vetch had no unfavorable effects on the fermentation quality and improved crude protein content and aerobic stability of TMR silage. OC2.2 silage was the best among three treated TMR silages.     

耐受自身代谢产物及耐二甲基亚砜红霉素高产菌株的选育

为提高红霉素发酵单位,考察了二甲基亚砜(DMSO)添加时间和体积分数对红霉素合成的影响,采用筛选自身代谢产物突变株的方法,将突变株进行常压室温等离子体(ARTP)诱变和耐受高浓度DMSO处理。结果显示,在36 h向发酵瓶中添加30000μg/m L红霉素,筛选得到化学效价比对照提高22.4%的菌株。DMSO最适添加时间为发酵48 h,最适添加剂量为0.2%,其可提高发酵单位10.1%。     

不同类型竹地板物理力学性能对比分析

对同一厂家生产的8种不同类型竹地板的物理力学性能进行了对比分析。结果表明：本色平压竹地板的物理力学性能最好;本色竹地板的物理力学性能优于炭化竹地板;平压竹地板的物理力学性能优于侧压竹地板、重竹地板及3 mm重竹贴面竹木复合地板;重竹地板密度最大,吸水率最低,在提高竹材利用率的同时,仍具有优良的物理力学性能,3 mm重竹贴面竹木复合地板可以有效降低重竹地板密度;重竹地板和3 mm重竹贴面竹木复合地板尺寸稳定性较差,炭化侧压竹地板更易使用受环境温湿度的影响。     

乙酰化处理对樟子松木材耐光性和热稳定性的影响

【目的】探讨乙酰化处理对人工林木材耐光性和热稳定性的影响,为木材颜色调控技术及高耐光染色木材的研发提供理论依据。【方法】以樟子松木粉为试样,加入乙酸酐和二甲苯溶液,在120℃条件下分别反应5,10,20,40,60 min,测试乙酰化处理时间对木粉增重率的影响;分别称取1 g经不同时间乙酰化处理的木粉和未处理木粉,置于 UV老化试验箱内辐射100 h,利用红外光谱分析 UV辐射前后乙酰化木粉化学官能团的变化,通过热重和扫描电镜分析乙酰化木粉的热稳定性及其形貌变化。【结果】随着乙酰化处理时间的延长,樟子松木粉的增重率呈现先增加后降低的趋势,在处理40 min 时木粉增重率最大;乙酰化木粉在1741 cm －1和1385 cm －1处的CO,C—H特征吸收峰强度均大于原木粉,处理时间40 min 时木粉的吸收峰强度最大;UV 辐射后,乙酰化木粉在1508 cm －1处木质素苯环特征吸收峰强度明显大于原木粉,处理时间40 min 时木粉的吸收峰强度最大,表明木粉经乙酰化处理后光稳定性得到提升;热重分析显示,经乙酰化处理后,木粉热分解所需的温度明显提高,表明乙酰化木粉的热稳定性好于原木粉;扫描电镜分析表明,乙酰化处理可增强木粉微观构造抵抗光劣化的能力。【结论】乙酰化处理能有效抑制樟子松木材的光降解反应并提升其热稳定性。     

菊花发酵乳饮料工艺优化

以菊花提取液和鲜牛奶为主要原料，杀菌后接种乳酸菌进行乳酸发酵，通过单因素与正交试验确定原料的配比、发酵条件及产品的配方。结果表明，原料最佳配比为菊花提取汁20％、蔗糖8％、鲜牛奶40％；制备该乳饮料的最佳发酵工艺条件为接种量3％、发酵时间4h、温度42℃。