草地群落类型对乳白香青种群特征和雌雄株形态及抗性的影响

为探究亚高山雌雄异株草本植物乳白香青对生境的适应方式,通过测定5个草地群落(A-老芒麦改良草地,B-虉草改良草地,C-天然草地,D-天然草甸,E-沙化草地)中乳白香青种群数、种群密度和面积、分布系数、性比组成,以及雌雄株构件性状、生物量配比、水分分配及抗性物质含量等参数,研究群落组成对乳白香青种群特征、雌雄株形态可塑性及抗性的影响。结果表明,5个草地群落的优势种、群落密度、基盖度、物种密度和优势种高度及土壤理化性状的显著差异(P<0.05),使不同群落中乳白香青种群特征显著不同,群落类型对种群特征参数影响顺序为种群面积>种群密度>性比>年龄结构>种群数>分布系数;D群落中乳白香青种群数和分布系数最高,C中乳白香青种群面积和密度最大,E中乳白香青种群数仅分别为D和C中的30.21%和35.11%,分布系数仅为C中的36.04%;群落类型对乳白香青种群年龄结构和性比有显著影响(P<0.05),雌株数为雄株的2.22~7.03倍;叶数和叶面积、株高和茎径、根长、小花数和苞片层数有显著的性别差异(P<0.05),群落类型对雌雄株的叶数和叶面积、株高、根数、花序数和小花数有显著影响,对雄株茎径和苞片层数有显著影响;雄株总生物量和花分配比显著高于雌株,而根分配比显著低于雌株(P<0.05),群落类型对乳白香青生物量配比有显著影响,雌株生物量配比受影响顺序为花>总生物量>叶>根>茎,雄株受影响顺序为花>茎>叶>总生物量>根;雄株茎、叶、花含水量显著高于雌株(P<0.05),根含水量在性别间和群落间差异较小,雌株构件含水量受群落类型影响顺序为花>茎>叶>根,雄株为叶>茎>花>根。雄株中MDA含量高于雌株,雌株中H₂O₂含量及T-AOC活性大于雄株(P<0.05),群落组成对雌、雄株中H₂O₂和MDA含量及T-AOC活性有极显著影响(P<0.01)。A和B中H₂O₂和MDA含量最低,E中H₂O₂和MDA达最大值,而T-AOC活性最低。雌、雄个体均能依据群落生境调整生长策略,通过构件性状、生物量配比、水分分配和抗性生理等适应性变化,使种群具有与生境匹配的种群特征,利于提高种群适合度和生活史完成。     

水氮供应对地下滴灌紫花苜蓿生长特征及草地小气候的影响

为探讨不同水氮处理条件下紫花苜蓿生长状况与草地小气候特征的关系,以2年生紫花苜蓿“巨能7号”为研究对象,采用田间试验和室内分析相结合的方法,研究了宁夏引黄灌区地下滴灌条件下不同滴灌量和施氮量处理下紫花苜蓿生长特征和草地小气候的变化。结果表明:1)滴灌量和施氮量对紫花苜蓿的株高、叶面积和鲜草产量都有显著的影响,表现为紫花苜蓿的株高、叶面积和鲜草产量均随滴灌量和施氮量的增加而增加,当施氮量增加到一定值时,继续增施氮肥,其鲜草产量增产效果在不同滴灌量处理下表现出不同的趋势。2)与不施氮处理相比,增施氮肥降低了紫花苜蓿株间空气温度、浅层土层温度和株间光照强度,而增加了群体内部空气相对湿度。3)不同滴灌量对紫花苜蓿的生长微环境的调节作用不同,随着滴灌量的增加,紫花苜蓿群体相对湿度逐渐提高,而紫花苜蓿株间气温和浅层土层温度降温效应越明显。4)紫花苜蓿生育期间株高与叶面积、草产量和群体内部相对湿度呈极显著正相关(P<0.01),与群体内光照强度、株间气温、浅层土壤温度呈极显著负相关(P<0.01)。合理减少滴灌量和施氮量不仅能维持紫花苜蓿良好的生长特征,而且能提高鲜草产量和改善草地生态环境条件。本研究旨在为紫花苜蓿群体微环境生态因子的改善及高产优质栽培措施提供科学依据。     

In situ provision of drinking water to grazing dairy cows improves milk production

AIMS: To determine the effect of providing water within the area grazed by dairy cows on milk yield and quality, compared to requiring cows to walk to a distant water trough, on a dairy farm in the Pampa region of Argentina during summer.

METHODS: Holstein dairy cows were allocated to two herds with similar parity, days in milk and milk production. They were grazed in one paddock that was divided in two, with a fixed water trough at one end. Cows were moved twice daily to grazing plots within the paddock. Control cows (n=66) could only access water from the fixed trough, whereas supplemented cows (n=67) also received water from a mobile trough within the grazing plot. Milk production of each cow, and water consumption of the two herds were measured daily over 62 days. Milk composition for each herd was determined weekly from Days 18 to 60 of the study, and grazing behaviour was observed between 08:00 and 16:00 hours on Days 11–15, 19–22 and 39–43.

RESULTS: Over the 62 days of the study, supplemented cows produced 1.39 (SE 0.11) L/cow/day more milk than Control cows (p=0.027). Estimated mean daily water intake was 50.4 (SE 2.1) L/cow/day for supplemented cows and 58.2 (SE 2.7) L/cow/day for Control cows (p=0.004). Percentage total solids in milk was higher for supplemented (12.5 (SE 0.06)%) than Control (12.4 (SE 0.04)%) cows (p=0.047). During the periods of behavioural observation, a higher percentage of cows in the water supplemented than the Control herd were observed in the grazing area (p=0.012).

CONCLUSIONS AND CLINICAL RELEVANCE: This preliminary study demonstrated that provision of water to dairy cows within the grazing plot was beneficial for milk production and composition, and may be associated with longer periods spent within the grazing area, during hot weather in the Pampa region of Argentina.     

Effect of water restriction on milk yield and quality in Lacaune breed ewes

The effect of water restriction on body weight, body condition score, milk yield, and milk composition and rheological characteristics in intensively reared Lacaune ewes was evaluated. After 7 days of adaptation, the trial lasted 28 days. Thirty lactating ewes (48 ± 5 months of age; mean value ± standard deviation) at the beginning of third lactation month were divided into three groups (n = 10), corresponding to the following water restriction treatment: a group control received no drinking water restriction (W100), and two groups received water to the extent of 80% and 60% of W100 daily consumption (W80 and W60 group respectively). The effects of water restriction were assessed at the beginning of experiment (D0), at D14 and D28. The W60 group resulted in a significant decrease in body weight, body condition score, milk yield and feed consumption of hay due to the experimental treatment; whereas a marked increase in both W60 and W80 groups of milk lactose, urea, sodium, sodium chloride content and titratable acidity was observed. Rheological parameters of milk, rennet coagulation time and curd‐firming time were positively affected by water restriction treatments, with a decrease in both experimental groups of the time required for the formation of a stable and firm curd. Results highlight the importance of water consumption in dairy sheep. The scarce availability of water, significantly affecting ewes milk production, is worthy of particular attention in arid area where water stress‐resistant breeds should be considered. This study underlines that milk yield, being closely linked to the availability of water of the breeding habitat due to its high water content (about 81%), could be reached in area where water is not a limiting factor without reducing the genetic expression of the animals. Less severe water restrictions, such as 20% of daily voluntary water intake, produce no detrimental effect on milk yield.     

The effects of late gestation nutrient restriction of dams on beef heifer intake,metabolites and hormones during an ad libitum feeding trial

This study's objective was to determine if nutrient restriction during late gestation affected beef heifer feed intake, body weight (BW) gain and endocrine regulation during a 10‐week feeding trial. During the last 100 days of gestation, control (CON) dams were fed to increase body condition score (BCS). Whereas, nutrient‐restricted dams (NR) and NR dams protein supplemented 3 days/week (NRS) were fed to decrease BCS by 1.2. After parturition, all cow‐calf pairs were moved to a common pasture and fed in excess of requirements until weaning. At 15 months of age, heifers were randomly sorted into two pens and adjusted to a commercial total mixed ration over a 2‐week period. Blood samples and BW were taken at the initiation of feeding and on a biweekly basis for the duration of the feeding trial. Feed intake was monitored for 10 weeks using a GrowSafe System. After 10 weeks, an intravenous glucose tolerance test (IVGTT) was performed on 21 randomly subsampled heifers. During the feeding trial, NR heifers consumed more feed than CON and NRS heifers. Heifers from NR dams tended to increase BW compared to NRS and CON heifers when adjusted for initial BW. Heifers from NR and NRS dams had a greater increase in BCS compared to heifers from CON dams. Plasma glucose and insulin concentrations during the feeding trial increased in NR heifers compared to the other groups beginning at 2 and 4 weeks respectively. Plasma leptin concentrations were increased in the NR and NRS heifers compared to the CON heifers beginning at week 4 of feeding. During the IVGTT at the conclusion of the feeding challenge, plasma glucose and insulin were increased in NR heifers compared to other treatment groups. These results show that nutrient restriction during late gestation alters appetite and endocrine regulation in heifer offspring.     

基于冗余分析的高寒草原土壤与草地退化关系

在高寒草原退化草地设置研究样地,观测植物群落特征、采集土壤样品、分析土壤物理化学性质,依据数量生态学基本原理,探讨高寒草原退化草地与土壤因子间关系。结果表明:不同退化程度样地沿冗余分析排序图第一排序轴分布,第一排序轴反映草地退化程度的变化;草地植物群落中与第一排序轴负相关且按相关程度大小排序的指标为盖度>地上生物量>地下生物量;第一、第二排序轴能够解释97.1%的土壤因子与草地退化关系;土壤沙砾、p H与第一排序轴正相关,土壤有机碳、土壤含水量、容重、全氮、有效氮与第一排序轴负相关;第一排序轴及所有排序轴所反映的土壤因子均与草地退化之间呈极显著相关关系(P<0.01);不同土壤因子与草地退化之间相关程度不同,土壤有机碳(r=-0.890)、土壤含水量(r=-0.864)、容重(r=-0.847)、全氮(r=-0.836)、有效氮(r=-0.821)等与高寒草原退化相关程度更高且相关关系极显著(P<0.01)。利用退化草地群落特征和土壤因子数据矩阵进行冗余分析能够较好地综合反映土壤因子与草地退化之间的关系及相关程度,土壤有机碳、土壤含水量、容重、全氮、有效氮是反映高寒草原退化的重要土壤指标。     

Sex‐dependent responses of perch to changes in water clarity and temperature

Rising temperatures and decreasing water transparency of lakes have strong wide ranging effects on fish. Fish responses to various changes in the environment are usually species‐dependent, but responses may also vary within species. In general, large individuals are considered to be more sensitive to environmental variation due to higher energy demand, than smaller individuals. Similarly, large individuals require more food to maintain bodily functions and are thus more sensitive to resource and food scarcity. These size‐specific responses to environmental gradients are also sex‐dependent in species that exhibit sexual size dimorphism (SSD). We studied in enclosures with short‐term experiments how rising temperatures and decreasing water transparency regulate the feeding rates of female and male European perch (Perca fluviatilis L.). To explore experimental results, we calculated perch SSD in nine lakes with varying environmental conditions using previously collected field data. The results of the experiments revealed that the combined effect of water transparency and temperature on the feeding rate of fish is gender‐dependent: feeding rate of females decreased more than that of males. The experimental results were also supported by field data that revealed a negative relation between water transparency and the magnitude of SSD in perch. Our results suggest that rising temperatures and decreasing water transparency may potentially decrease fish size in a sex‐dependent manner. As female size is one of the main demographic traits determining the reproductive success of a fish population, changing environments may have unexpected and far‐reaching consequences on fish population dynamics.     

对农村机电提灌站存在的问题及应做好的工作分析

随着现代社会的不断进步发展,科学技术越来越成为一个行业的核心竞争力,对于农业来说,运用科学技术解决好农业的水利问题,这对于农业的发展有很大的促进作用。农村机电提灌站就是为了解决农业的水利问题而建设的,下面笔者就农村机电提灌站存在的问题及应作好的工作和大家展开讨论。     

叶面喷施吲哚乙酸对油菜蕾薹期渍水的缓解效应

以油菜品种秦优7号(敏感)和苏油4号(耐渍)为材料,通过盆栽试验研究吲哚乙酸(IAA)对油菜蕾薹期渍水的缓解效应。蕾薹期渍水持续10d,渍水结束后,叶面喷施浓度为0.1mmol/L的IAA,随后的0~15d调查油菜的生理变化。结果发现:渍水后生物量和叶片光合色素含量降低;谷胱甘肽、抗坏血酸含量和超氧化物歧化酶活性升高;丙二醛含量升高;蔗糖合成酶、蔗糖磷酸合成酶活性上升,蔗糖和可溶性糖含量增加。渍水结束后喷施IAA,对敏感的秦优7号缓解效应更明显;叶片中的光合色素含量升高,5d后显著恢复生长;蔗糖磷酸合成酶活性降低,降低蔗糖含量;蔗糖合成酶活性降低,减少蔗糖的分解;尤其是喷施15d后IAA对渍水胁迫的缓解作用最明显,苏油4号根干重显著增加,而秦优7号的根干重和茎干重均显著增加。叶面喷施IAA有效缓解单株角果数、每角粒数和产量的降低,但对抗氧化系统影响较小。     

一种准零刚度被动隔振系统的非线性共振响应分析

分析了一种机构的负刚度特性和它与线性主弹簧并联后而成的隔振系统的准零刚度特性，推导了准零刚度被动隔振系统的主谐波共振、亚谐波共振和超谐波共振的幅频特性表达式.结果表明，机构的负刚度区域随弹簧的初始变形与杆长的比值增大而变宽；隔振系统的准零刚度区域随主弹簧的刚度与机构中的弹簧总刚度的比值以及机构中的弹簧初始变形与杆长的比值增大而变宽；经比较发现，本文推得的被动隔振系统的同一种谐波共振幅频特性与杜芬方程的幅频特性均存在较大偏差.因此，对于这类被动隔振系统的运动微分方程，若以位移激励的幅值与激励频率平方的乘积代替单位质量的激励力幅值按杜芬方程的解来处理谐波共振问题将会带来较大误差.