Ontogeny of Themeda triandra tillers in the false thornveld of the eastern cape

Abstract

Marked populations of Themeda triandra tillers were sequentially sampled at fortnightly intervals under normal conditions and without moisture stress respectively, covering a period from tiller initiation through to senescence after flowering. Parameters recorded were height of shoot apex, tiller mass, leaf area, leaf number, secondary tiller development and premature tiller mortality. Tillers of irrigated plants had a significantly higher mass, more elevated shoot apices, and produced a greater total number of leaves than those of non‐irrigated plants. Fewer unstressed tillers senesced prematurely than those experiencing moisture stress.     

Veld burning in giant's castle game reserve,natal Drakensberg

A basic aim in the management of a wildlife reserve is to maintain ecological diversity. In the Giant's Castle Game Reserve the vegetation is largely composed of fire sub‐climax grasslands. Under the natural fire‐regime, before man influenced the system much, fires probably occurred at any time of the year, but mostly in summer. At present there are acute problems in controlling wildfires which occur mostly in late winter when there is an extreme fire hazard. Most of the Natal Drakensberg is now burnt by wildfires in late winter and deliberate fires in early spring. The ecological effect of the natural and present fire regimes are discussed, and a burning plan for Giant's Castle is outlined.     

A gradient analysis of grassed mountain catchments in the natal Drakensberg

Abstract

An indirect gradient analysis was carried out on vegetation and environmental data from the Mdedelelo Wilderness Area of Cathedral Peak State Forest in Highland Sourveld. Vegetation ordination axes were correlated with environmental variables deduced to have influenced species‐composition. Altitude proved a significant conjugate variable in the absence of tractable fire data.     

Tiller population dynamics in eight cultivars of elephant grass during undisturbed growth

The aim of the study was to assess tiller population dynamics of aerial and basal tillers in eight cultivars of Pennisetum purpureum (Schumach.), syn. Cenchrus purpureus (Schumach.) Morrone, in a warm humid climate in Veracruz, Mexico. This is a pioneer study on tiller population dynamics in elephant grass under conditions of undisturbed growth. The tiller population assays included data from 14 days after cutting until 154 and 182 days after cutting for the dry and wet seasons, respectively. On each sampling date, a distinctive ring was placed on every new tiller, and rings were removed from dead tillers. Tiller density, mortality and appearance were determined. In wet seasons, copious tillering occurred on initial regrowth (by day 42, mostly aerial tillers, with a ratio of 2:1 to 4:1 for aerial to basal tiller appearance), and on day 98 (a higher proportion of basal tillers, with an aerial to basal tiller ratio of 1.5:1). Aerial tillers showed a higher overall mortality rate than basal tillers (29.0 vs 14.4). Younger basal tillers showed higher mortality than older tillers. Higher tiller density occurred during the dry season, where it increased gradually until day 70 and then declined. The cultivars ‘Cameroon‘, ‘CT115‘ and ‘OM22‘ showed remarkably high tillering ability. The findings indicate that harvesting a forage bank is possible from day 70 during a dry season.     

辽东半岛不同生境结缕草种群有性生殖株的数量特征

通过对结缕草种子成熟期有性生殖株的测定,分析了辽东半岛不同生境结缕草种群有性生殖株的种子数量(每花序种子数)和质量(千粒质量)以及生长量(株高)和生殖生长量(花序长,生殖生长比率)的数量特征及其差异。结果表明,生态条件较差生境的结缕草种群,其有性生殖株的株高、花序长、每花序种子数及千粒质量均最低,而生殖生长比率最高,说明不同生境结缕草种群有性生殖株的生殖生长、生育力、其种子生存与竞争力主要受到环境的限制,但有性生殖株个体自身具有生殖生长调节策略,生态条件较差的生境结缕草种群有性生殖株将更多的生长量用于生殖生长。     

松嫩平原光稃茅香种群生殖分蘖株数量特征分析

在松嫩平原天然割草场光稃茅香种群的籽实成熟期，将广泛取样的588个生殖分蘖株样本分为10个高度级进行测定，分析的结果表明，株高与花序长度，营养生物量，生殖生物量，总生物量，籽粒千粒重均呈显著的正相关，与生殖生长比率，生殖分配I，生殖分配Ⅱ，每个花序种子生产的数量，结实率均呈显著的负相关，生殖分蘖株数量特征的生态可塑性及其规律性变化，蕴涵着个体生长与生殖策略。     

Growth and desiccation of Themeda triandra and Sporobolus fimbriatus in relation to diminishing moisture availability

Abstract

Water was withheld from individual plants of Themeda triandra and Sporobolus fimbriatus growing in pots in a greenhouse. Leaf extension growth, followed by successive degrees of tiller desiccation, were monitored on a daily basis and related to diminishing moisture availability. Leaf extension growth ceased after about 40 % soil water depletion in both species on the sandy clay loam used in the trial. Thereafter, leaves and growing points senesced progressively with increasing evaporative demand, despite a relatively small drop in soil moisture content. The tentative conclusion is that active leaf growth in semi‐arid grassveld takes place in short sporadic spells subsequent to each effective rainfall event. It seems, for example, that after a rain of 50 mm in midsummer, the duration of active leaf growth could be no more than a week.     

Flock dynamics of desert Barki sheep in relation to age structure

Reproduction data of 8689 ewe records spread over 40 years (from 1960 to 2000) representing 2952 breeding Barki ewes were used in this study. The flock belonged to the Desert Research Center in Egypt. Flock dynamics of nine age groups (2–10 yrs) were assessed. Two parameters were used to evaluate flock dynamics, net reproduction rate (R_o) (number of ewe- lambs reaching joining age and produced by each ewe during its lifetime in the flock) and intrinsic rate of increase (r_m) (flock growth when no resource is limiting). Age of ewe had a highly significant (P < 0.01) effect on number of ewes lambing per ewe joined (E_PJ), number of lambs born per ewe joined (L_BJ), number of lambs weaned per ewe joined (L_WJ) and number of ewe lambs reaching joining age per ewe joined (L_EJ.J). All estimates tended to increase with dams age up to four years and decreased thereafter. The results of R_o and r_m showed that the studied flock must consist of 5 age groups to maintain its size and replace itself. It may be recommended to cull the breeding ewe at the age of 6 years to accelerate genetic improvement.     

The function of the hygroscopic awn of Themeda triandra 1

The hygroscopic awn of species such as Themeda triandra is widely believed to be a device ensuring the early burial of its seed. This belief has been extensively tested and no tendency for such self‐burial has been found. It has been demonstrated that the propelling action of the awn does cause the seed to move along the surface and its possible function as a dispersal mechanism is tentatively suggested.     

松嫩平原碱化草甸野大麦无性系构件的定量分析

野大麦无性系构件的数量决定于丛径的大小,无性系中营养蘖构件组分的数量占较大比重,为69.15%,是生殖蘖的2.24倍,但生殖蘖和营养蘖的生长与物质生产相差悬殊,平均生殖蘖重是平均营养蘖重的2.17倍,致使无性系对营养生长和生殖生长的能量分配大体相等。无性系构件的生物量,以及营养蘖和生殖蘖构件组分的生物量与丛径和总蘖数间均存在着极显著的正相关关系;平均单蘖重、平均的生殖蘖重均随着无性系构件数量的增加呈幂函数形式下降;无性系的芽数随着丛径和总蘖数的增大而有规律地增加;抽穗率在大小不等的无性系间具有相对稳定性。     

The response of eragrostis curvula (schrad.) nees to fertilizers in the highland sourveld of natal*

The effects of five years of application of N, P and K fertilizers at three levels, and of agricultural lime at two levels, on the herbage yield of Eragrostis curvula are discussed. The experiment was carried out on leached soils under an average annual rainfall of 900mm. Significant responses in yield were obtained to N, P and K fertilizers but there was no response to lime.     

Ontogeny of sporobolus fimbriatus tillers in the false thornveld of the Eastern Cape

Abstract

Marked populations of Sporobolus fimbriatus tillers were sequentially sampled at fortnightly intervals under normal rainfall conditions and under irrigation respectively, covering a period from tiller initiation through to senescence after flowering. Parameters recorded included shoot apex elevation, tiller mass and leaf development.

Surviving tillers consisted of two sub‐populations, those that flowered in autumn and those that remained vegetative. Flowering of individual apices was rapid, but was spread over a number of months for the whole population. Moisture played an important role in determining tiller size, and at least some forage was lost through leaf drop on tillers rested for a whole season.     

The effect of defoliation and competition on the regrowth of Themeda triandra and Aristida junciformis subsp. junciformis

Abstract

The effects of a cutting trial, conducted to study the combined influence of defoliation and competition from surrounding vegetation on the vigour of Themeda triandra and Aristida junciformis, were evident after the single season of treatment implementation. Aristida junciformis was more sensitive to defoliation than T. triandra, whereas competition reduced yield to a greater extent in T. triandra than in A. junciformis. The two species differed in their ability to tolerate defoliation under competition. Defoliation reduced the yield of A. junciformis, at all levels of competition, to a greater extent than T. triandra. Aristida junciformis was particularly sensitive to a combination of severe defoliation and full competition. It is suggested that manipulation of grazing patterns may shift the competitive balance between palatable (e.g. T. triandra) and unpalatable (e.g. A. junciformis) components of the sward.     

黑麦草有害动物群落动态研究

对合肥地区多年生黑麦草Lolium perenne有害动物群落进行了研究,共记录有害动物13种,分属3个动物门、4个纲,以节肢动物门为主,占总数量的95.7%。主要优势种为麦圆叶爪螨Penthaleus major、黑草蚁Lasius fuliginosus、麦杆蝇Meromyza saltatrix、鼠妇Armadillidium unlgare、麦长管蚜Macrosiphmavenae和大青叶蝉Cicadella viridis;优势种中麦长管蚜、大青叶蝉和麦杆蝇主要分布于上部和中部,黑草蚁和鼠妇主要分布于下部和中部,麦圆叶爪螨主要集中在中部。群落均匀度和多样性变化一致,均以群落形成初期较高。聚类分析结果表明,黑麦草从早春萌芽到抽穗期间有害动物群落比较稳定。     

The porcine sperm reservoir in relation to the function of hyaluronan

The oviduct plays a role in successful animal reproduction not only in spermatozoa and ova transport to the fertilization site but also by affording a microenvironment for fertilization and early embryonic development. The sperm reservoir (SR) is restricted in the uterotubal junction (UTJ) and caudal isthmus. Billions of porcine spermatozoa are distributed to the female reproductive tract during/after insemination, and small amounts of them are stored for about 36–40 hours in the SR, which maintains sperm viability in the pre-ovulation period through its surface epithelium and production of fluid. The SR regulates the release of spermatozoa so that only a small population moves towards the fertilization site (ampulla) to decrease polyspermy. This review attempts to provide information about the structure and function of the porcine SR, its intraluminal content (hyaluronan, HA), and the influences of HA on porcine spermatozoa in vivo. In pigs, the spermatozoa are stored in a mucous-like fluid within the UTJ and caudal isthmus in the pre-ovulation period. The oviduct fluid contains sulfated glycosaminoglycans (GAGs) and non-sulfated GAGs, i.e., HA. It is interesting to note that HA is synthesized by hyaluronan synthase-3 (HAS-3), and its receptor, CD44, is found in the epithelium of the porcine SR site. Additionally, sperm capacitation does not occur in vivo in the SR during the pre- and peri-ovulation periods, but spermatozoa in the SR will attempt to capacitate if exposed to bicarbonate. However, capacitation in the SR will rise in the post-ovulation period, indicating the role of HA in modulating sperm capacitation after ovulation. All data support the understanding that the porcine SR ensures the viability of fertile spermatozoa and maintains the non-capacitated status during the pre-ovulation period. This basic knowledge about the SR is believed to be useful to advance sperm preparation procedures for in vitro fertilization (IVF) and improve the preservation process of porcine semen.     

林间草地硬质早熟禾无性分株构件的定量分析

通过对硬质早熟禾单优群落随机取样的调查与测定,就该种群的分株构件进行了定量化分析。结果表明,硬质早熟禾无性系构件的数量决定于丛径的大小,无性系中生殖蘖构件组分的数量占较大比重,取样中最高比例为95.98%;无性系分株的数量及生殖蘖的数量,随着丛径的增加均呈幂函数形式增大;无性系的生物量及生殖蘖的生物量随着丛径的增加也呈幂函数形式增大;硬质早熟禾无性系对生殖生长有着较高的能量投入,以此维持种群的更新与发展。