Grass species composition,yield and quality under and outside tree crowns in a semi‐arid rangeland in south‐western Zimbabwe

Abstract

A two‐year study was conducted in lightly grazed areas of Matopos Research Station, Zimbabwe, to evaluate the impact of widely spaced trees on understorey grass composition, yield and quality. The study trees were Terminalia sericea and Acacia karroo. Ordination techniques using grass density and biomass as indices separated quadrats according to soil type but not grass species according to understorey or open areas or according to tree species. Grass yield under tree crowns was similar to open areas, in contrast with most reports where understorey areas had higher yields. The high understorey grass quality that has been reported from savanna areas exhibiting grass composition differences was not expressed. Selective grazing of palatable perennial grasses growing in association with tree crowns and their eventual replacement by low‐yielding and less‐palatable grasses that normally grow in open areas is proposed as an explanation of the unique tree‐grass interaction scenario of this study. In areas where this replacement has occurred, recovery may require management interventions.     

Involvement of spleen components of mature fowl in the primary and secondary humoral antibody response following experimental EDS'76 virus infection

Summary

Cellular changes in spleens of mature fowl in relation to both the primary and secondary humoral antibody response following experimentalEDS'76 virus infection were studied. The influence of splenectomy on humoral antibody response was also examined.

Experimental fowl had been naturally infected with fowl adenovirus (FAV) but did not possess precipitins to these viruses at the time of EDS’ 76 virus infection. Since EDS'76 infection provokes a recall of the group antibody to FAV, this infection simultaneously induces a primary response against EDS’ 76 virus and a secondary response due to the recall of the group antibody to FAV.

HI and precipitating antibodies toEDS'76 virus (primary response) werefirst detected at 6 and 8 days p.i. respectively. Curves of HI, precipating and neutralising antibody titres were biphasic; the first peak (IgM peak) occurred at 10–11 days p.i., the second (IgG peak) at 16–28 days p.i.

Precipitating antibodies to FAV (secondary response) were demonstrated from 4 days p.i. The curve of these antibody titres was also biphasic, with peaks at the same times as in the primary response.

Based on HI and AGP testing of primary and secondary immune response in both splenectomised and non‐splenectomised fowl it is concluded that in the primary response the spleen of the adult fowl is involved significantly in only IgM secretion, while in the secondary response it is likely that bothIgM and IgG are secreted in considerable amounts.

Clusters of lymphoblasts and plasmablasts were observed at 3 days p.i. in the red pulp. It is very likely that antigen‐antibody complexes are formed from that time and circulate bound to the surface of lymphocytes. These antigen‐loaded lymphocytes are ‘picked up’ from the blood stream by

– red pulp macrophages, leading to enhanced formation of lymphoblasts in the red pulp. Great numbers of these cells (which are very probably IgM secreting cells) were present on days 6 and 7 p.i., but were no longer detectable after day 10 p.i.

– macrophages of the macrophagalellipsoidal corona (MEC), leading to significant enlargement of the periellipsoidal lymphoid tissue(PELT) by an increase of the number of lymphocytes observedfrom days 4–12 p.i. The MEC was significantly enlarged from 7–12 days p.i., very likely due to an increased number of macrophages.

Following deposition of antigen in the white pulp, formation of follicles begins. The number of small, intact follicles includingfollicle precursors increasedfrom 6 days p.i. From 15 days p.i. to the end of the experiment both the number and size of follicles increased significantly.

Uptake and processing of antigen by macrophages is probably accompanied by death of some of these cells. This might explain the degenerative changes observed in large mesenchymal cells, probably macrophages, at 3 and 5 days p.i. in the red pulp and at 5 and 6 days especially in the MEC. Splenitis which was present at 3 and 5 days p.i. and oedema observed in and around ellipsoidal cells at 5 days p.i. may be due to mediators released from these degenerative macrophages.

A significantly increased number of follicles with lymphoblasts was seen from 2–15 days p.i. while lymphoblasts and plasmablasts were present in the PELT from 5–15 days p.i., but predominantly at 6 and 7 days p.i. It is likely that disruption of follicles and blast transformation of white pulp lymphoid cells are secondary response events. White pulp lymphoblastsand plasmablastsare probably IgG secreting cells.

Splenomegaly was observed at 3, 5 and 6 days after infection and was mainly due to swelling of red pulp macrophages and infiltration of granulocytes in the red pulp. Ellipsoidal and periellipsoidal changes could contribute to the splenomegaly at 5 and 6 days p.i.     

酵母铬与L-肉碱对蛋鸡生产性能及脂质代谢的影响

选用21周龄海兰褐壳蛋鸡288只,随机分为9组,每组32只,采用3×3(铬×L-肉碱)2因子3水平有重复交叉试验设计,预试2周后,在玉米-豆粕型日粮的基础上添加不同水平的酵母铬(以铬计:0、400、600μg/kg)与L-肉碱(0、50、100mg/kg),以饲喂基础日粮组为对照组,用以研究二者对蛋鸡生产性能及脂质代谢的影响,并初步探讨二者的互作效应,试验期7周。结果表明:600μg/kg铬或100mg/kgL-肉碱对脂质代谢多数指标效果显著(P<0.05或0.01);二者同时添加对蛋黄胆固醇、肝脏甘油三酯及腹脂率等均产生显著互作效应(P=0.0003～0.0500),且400μg/kg铬和100mg/kgL-肉碱混合添加对降低蛋黄胆固醇比其它各组均表现出优势,400μg/kg铬和50mg/kgL-肉碱混合添加对降低腹脂率比其它各组均表现出优势。铬或(与)L-肉碱在降低蛋鸡肝脂、腹脂及蛋黄胆固醇的同时并未影响蛋鸡的生产性能。     

水肥空间耦合对冬小麦光合特性的影响

在防雨棚管栽试验条件下,以品种“3279”为研究材料,通过7种不同处理来研究水肥空间耦合对冬小麦光合特性的影响,试验结果表明:不同的水肥耦合处理中,冬小麦的光合速率、气孔导度、细胞间隙CO2浓度有所不同,三者之间有很好的平衡关系。其中,深层施肥处理其小麦在生长后期能够维持较高的光合速率,但气孔导度却有所降低,有效地减少了水分散失,表现出很好的节水潜力。同样水分条件下维持同样高的光合速率时,深层施肥的肥上灌水与肥下灌水相比,其受水分影响小,叶绿素含量下降快。深施肥20 cm处灌水处理,在开花后小麦叶片光合作用最强,气孔导度小,细胞间隙CO2浓度高,具有更好的节水潜力。     

Including an additional systematic environmental effect within a generation in an evaluation model improves accuracy of prediction of breeding values in a closed herd of pigs

The present study evaluated the advantage of mixed‐model techniques over a selection index under different magnitudes of an additional systematic environmental effect (ASEE) in terms of accuracy of prediction and expected genetic gain. The data attempted to simulate a closed herd in a pig breeding program. The base population (G₀) consisted of 10 males and 50 females. Six generations (G₀ to G₅) were selected by using a selection index of three traits without overlapping. Additional systematic environmental constants with four levels in a generation were assigned from a uniform distribution at different ranges. Breeding values of animals in the last generation (G₅) were estimated on the basis of an index of individual phenotype (SI‐U), SI‐U adjusted for ASEE using a least‐squares mean (SI‐A), best linear unbiased prediction using an animal model excluding ASEE (AM‐E), and an animal model including ASEE (AM‐I). Accuracy of prediction and expected genetic gain were larger by the animal model than by the selection index, even if heritability of the traits selected was high and ASEE was set to zero. When ASEE was zero, the accuracy of prediction and expected genetic gain given by SI‐U and AM‐I were similar to those given by SI‐A and AM‐E, respectively. However, the differences in accuracy and expected gain between SI‐U and AI‐A and between AM‐I and AM‐E increased as the range of ASEE increased. It was concluded that selection based on an animal model was more effective than index selection, even if the herd environment was uniform and traits with high heritability were selected, and that it should be always included in an evaluation model, however slight any systematic environmental effect may be in a closed herd.     

中国水土流失问题的初探

长期以来,水土流失直接威胁着人们赖以生存的环境,在所有的生态破坏中,水土流失称之为“环境破坏第一杀手”。针对我国山地丘陵面积大、地质条件复杂、人为破坏加速、水土流失严重的实际情况,通过丰富的历史资料和整治经验及野外工作所积累的大量数据分析,以生态恢复学为指导,总结了水土流失的基本特点,研究了水土流失治理与经济可持续发展的关系,探讨了水土流失给生态安全造成的巨大危害,展望了水土保持的预期目标,根据中国的实际情况,提出了综合治理的基本思路。     

肉仔鸡体内锌和维生素A互作效应初探

本研究以艾维因肉仔鸡为模型 ,采用2×3(VA×Zn)实验设计来探讨肉仔鸡体内锌对维生素A代谢的影响。锌的添加量为0 ,40mg/kg和160mg/kg;维生素A的添加量为1500IU/kg 和8800IU/kg。结果证明在肉仔鸡体内锌对动员肝脏维生素A入血有重要作用 ;日粮锌和维生素A水平对血清维生素A浓度有互补作用。锌、维生素A及其交互作用对各脏器的锌沉积有不同程度的影响     

Neotyphodium属禾草内生真菌和球囊霉属菌根真菌对野大麦生长的影响

禾草内生真菌提高宿主对生物及非生物胁迫抗性的同时也促进植物生长, 丛枝菌根真菌促进植物根系对营养元素尤其是磷的吸收和贮存, 野大麦(Hordeum brevisubulatum)中同时存在这两种共生体。本研究比较了温室条件下这两种共生体共存及单独存在时对野大麦生长的影响和其相互作用。结果表明, 内生真菌可抑制丛枝菌根真菌的侵染;内生真菌和菌根真菌均可显著增加野大麦地上生物量, 菌根真菌可显著增加其地下生物量。二者共存时野大麦的全N含量显著小于单个共生体的处理;仅带菌根的野大麦P含量显著大于二者共存时的处理, 内生真菌通过对菌根真菌的抑制降低了野大麦对P的吸收和积累。     

早期营养干预对幼龄反刍动物瘤胃微生物区系发育的影响

正常稳定的瘤胃微生物区系是反刍动物瘤胃健康的重要指标,且在瘤胃结构形态发育、微生物定植模式、免疫功能调节及抵御外源致病因子侵袭等方面发挥着重要积极作用.最近研究表明,新生反刍动物瘤胃微生物组成相对单一,但随着早期瘤胃发育过程中不同微生物群落相继开始定植并占据不同的生态位,此时的营养干预可能会形成特定的微生物群落组合并产...     

猪圆环病毒2型感染PK-15细胞差异表达miRNA和mRNA互作网络

旨在筛选猪圆环病毒2型感染猪肾上皮细胞(PK-15)后差异表达miRNA和mRNA,并探究miRNA和mRNA之间的互作关系。使用茎环定量PCR检测多个热点miRNA在PCV2感染组和未接种病毒组之间的差异表达水平以发现差异表达miRNA,分析PCV2感染后第12小时的蛋白质组学研究结果(GEO登录号:GSE71945)以获得差异表达mRNA,并分析差异表达miRNA和mRNA之间的互相作用关系。结果显示,在PCV2感染后第12小时miR-10b、miR-128、miR-155-5p、miR-21、miR-29b、miR-361-3p等表达量显著性变化,使用miRecords预测其靶基因,分别发现7 105、9 741、7 451、7 183、7 971、8 793个靶基因;PCV2感染后第12小时共有158个差异表达mRNA,分属于多种细胞结构成分并参与多条重要的细胞生物途径,且差异miRNA的靶基因和差异mRNA之间有大量的交集基因。上述结果表明,PCV2感染能导致细胞内多种miRNA差异表达,造成miRNA的靶基因表达紊乱,进而影响细胞正常的生命进程。