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 importance of the ecological view of agriculture

Abstract

Marked populations of Themeda triandra and Sporobolus fimbriatus tillers were sequentially harvested at fortnightly intervals both under irrigation and under unamended moisture conditions. Sampling covered a period from tiller initiation through to senescence after flowering.

Tiller masses and green leaf areas were used to derive absolute growth rates, relative growth rates, net assimilation rates and leaf area ratios respectively. Growth rates of Themeda triandra were higher, or were maintained at high levels for longer than those of Sporobolus fimbriatus. Moisture stress resulted in considerably depressed growth rates. Photosynthetic efficiency of spring emerging tillers was potentially greatest in midsummer, but this seasonal influence was masked by moisture stress on non‐irrigated treatments.     

Growth and tiller production of Themeda triandra as affected by NPK fertilisation

Themeda triandra Forssk. is a common perennial grass in southern African grasslands that tolerates low nutrient soils. Establishment of the species into degraded or transformed areas is difficult, but there have been some advances with clonal propagation using tillers. To generate propagules (tillers), tiller production of plants must be maximised. This research focused on the growth response of T. triandra to fertilisation with nitrogen (N), phosphorus (P), and potassium (K) each at three levels in a fully factorial pot experiment. Fertilisation increased growth. The number of tillers and aerial shoot mass were controlled by an N × P interaction, and total mass and root mass were controlled by N and by P, with N having a larger effect. Mass per tiller was not related to treatment. Shoot:root ratio and root mass per tiller were controlled by N. Potassium had no effect on any response. For maximum tiller production of T. triandra, plants should be fertilised with high levels of N and P.     

The dynamics of Themeda Triandra tillers in relation to burning in the natal Drakensberg

Abstract

Marked tillers of Themeda triandra were sampled regularly over a two year period in Highland Sourveld burnt annually in winter, biennially in spring and after a single summer and early winter burning treatment. Parameters recorded were height of shoot apex, tiller mass, number of new lateral tillers and time of flowering. Monitoring of marked tillers before and after each burn enabled the life history of populations of tillers to be followed.

There were no significant differences in survivorship between tillers in the annual winter and biennial spring burn treatments but winter burning stimulated the development of a greater number of daughters per parent. Both populations exhibited a constant death rate over the two year period. Only 8% of the marked T. triandra tillers survived the single summer burning treatment.     

Growth patterns and annual growth cycle of Acacia karroo Hayne in relation to water stress I. Leaf and shoot growth

Abstract

A field study was conducted to describe the growth patterns of A. karroo at different levels of water stress in different edaphic situations.

Shoots are heterophyllous and are formed by free growth. The degree of development of a shoot, relative to others in the canopy, is governed by branch and position in the canopy. At least six phenological phases were identified in the annual growth cycle.

The pattern of growth and the phenological cycle are not changed by water stress. Initiation, emergence and development of shoots and leaves are governed by how favourable environmental conditions are. If there is little shoot growth early in the season, these plants can partially compensate by producing more leaf per unit of shoot if environmental conditions improve.

Leaf and shoot growth at the beginning of the season took place only if there was sufficient moisture available, and if the minimum temperature had risen above a threshold amount. Where there was insufficient soil moisture, no growth was observed before rains had fallen. The growth strategy of A. karroo differs markedly from that of broadleaved African savanna tree species. Growth in A. karroo is dominated by current growing conditions, rather than those of the previous season. They are able to make opportunistic growth at any time.

Soil depth had a marked influence on plant growth, presumably due to a larger available nutrient and moisture pool.     

The response of Acacia karroo plants to defoliation by hand compared to defoliation by goats

Abstract

The leaf and shoot growth of Acacia karroo plants defoliated by goats was compared to that of plants in which leaf only or leaf plus shoot‐tips were removed by hand, to simulate goat browsing.

There were no differences in leaf or shoot production between plants whose leaf only was removed compared to those that had both leaf and shoot‐tips removed. Leaf growth on the plants defoliated by goats at moderate levels was approximately three‐fold that on plants defoliated moderately by hand. The plants defoliated by hand produced approximately twice the amount of leaf that the undefoliated plants produced. Heavy defoliation by both hand and goat, produced approximately half the leaf growth that moderately defoliated plants produced, following equivalent defoliation. Shoot production of all plants defoliated by hand was no different to that of the undefoliated control plants and was considerably less than that of the plants defoliated by goats.     

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.     

Influence of grazing frequency and intensity on aerial and reproductive tillering in Lolium perenne L. under subtropical conditions

Abstract

Reproductive and aerial tillering dynamics in Lolium perenne L. (perennial ryegrass) was monitored for two years under grazing. Reproductive tillers were observed from winter (June) to midsummer (February) with the main period of initiation occurring in spring to early summer (August to October). For infrequent lenient grazing, reproductive tiller densities ranged from 102 (July 1993) to 1 900 (September 1993) tillers m^?2, and from 29 (June 1994) to 980 (September 1994) tillers m^?2. By contrast, simulated continuous grazing (CG) resulted in reproductive tiller densities ranging from 13 (August 1993) to 100 (October 1993) tillers m^?2, and from 25 (July 1994) to 46 (September 1994) tillers m^?2. Aerial tillers were initiated mainly during spring, and to a lesser extent autumn and winter, with no appreciable number being recorded during summer. For infrequent lenient grazing, aerial tiller densities ranged from 25 (February 1993) to 1 620 (September 1993) tillers m^?2, and from 362 (August 1994) to 1 524 (September 1994) tillers m^?2. By contrast, CG resulted in aerial tiller densities ranging from 123 (May 1993) to 14 (June 1993) tillers m^?2, and from 5 (July 1994) to 29 (May 1994) tillers m^?2. There was no indication that reproductive or aerial tillers contribute to the persistence of perennial ryegrass under the grazing frequencies and intensities tested.     

行距与播种量对无芒雀麦生产性状的影响

采取二因素随机区组试验,分析不同行距（30、50、70和90 cm）与播种量（0.46、0.77和1.08 g·m-2）对无芒雀麦(Bromus inermis)群体株高、生殖蘖数、营养蘖数、总分蘖数、地上生物量、叶面积指数（LAI）和冠层底部光合有效辐射（PAR）的影响,旨在为无芒雀麦种子生产提供理论依据。结果表明,行距对无芒雀麦群落特性具有显著影响（P<0.05）。随着行距的增加,株高和PAR呈上升趋势,其余指标呈下降趋势。30 cm行距处理的生殖蘖数、营养蘖数、总分蘖数和LAI显著高于70和90 cm行距处理（P<0.05）,而PAR显著低于50、70和90 cm行距处理（P<0.05）。播种量对LAI和PAR的影响显著,对株高、生殖蘖数、营养蘖数、总分蘖数和地上生物量没有显著影响。生殖蘖数、营养蘖数、总分蘖数与LAI呈极显著正相关（P<0.01）,与PAR呈显著负相关（P<0.05）。12个播种组合处理可聚合成窄行距类与宽行距类两类,类之间群落特性差异显著。     

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.     

The influence of tiller age and time of year on the growth of Themeda tri andra and Sporobolus fimbriatus in semi‐arid grassveld

Abstract

Sequential growth measurements were made on successive populations of Themeda triandra and Sporobolus fimbriatus tillers initiated at different times of the year. The independent influences of tiller age and time of year on tiller growth were isolated by deriving growth indices for tillers of the same age at different times of the year and for tillers of all ages at each time of the year respectively.

Isolating the effect of plant age on growth showed that T. triandra is most productive under a regime of long periods of undisturbed growth, while S. fimbriatus is better suited to frequent interruptions in growth. Isolating the effect of time of year shows that both species are particularly sensitive to perturbations in spring. However, the photosynthetic efficiency of T. triandra is strongly influenced by time of year while S. fimbriatus seems to be a more opportunistic assimilator of sunlight.     

干旱-复水对菊芋苗期根、茎、叶形态特征的影响

通过盆栽试验研究干旱-复水对菊芋(Helianthus tuberosus)苗期根、茎、叶、茎叶比、根冠比和物质积累量的影响,探讨菊芋苗期干旱适应机制,干旱半干旱地区菊芋栽培管理提供参考。结果表明:干旱-复水处理菊芋根、茎、叶生物量和总生物量均低于正常水分管理;干旱-复水增加了主根和须根的直径;干旱-复水过程中除复水第16天外,处理须根长度均高于对照;处理前期主根长度高于对照,后期主根长度低于对照;干旱-复水处理提高了菊芋平均叶面积,降低了叶片数量,抑制新叶片的形成;干旱胁迫第2天测定的茎叶比对照高于处理,而其他取样时间处理均高于对照;干旱-复水过程中菊芋根冠比胁迫第2天高于对照,胁迫第4天、第8天和复水第8天处理根冠比低于对照,复水第16天处理高于对照。     

Ranking of grass species according to visible wilting order and rate of recovery in the central orange free state

Abstract

A number of grasses were ranked according to the order in which they wilted with diminishing moisture availability, and according to their ability to recover after water replenishment. Digitaria eriantha and Digitaria argyrograpta were the most sensitive to moisture stress, whereas Sporobolus fimbriatus and Panicum stapfianum were last to show signs of wilting. The latter two grass species were the first to recover from wilting during optimum soil water conditions. The leaf water potential and soil water content at which each grass species wilted were recorded.     

Presidential address

In intact plants C¹⁴‐assimilates were translocated from the treated leaf on the primary tiller to young leaves on that tiller, to secondary tillers, and also to the roots. Plants defoliated after labelling revealed movement of materials from the storage organs to all the new leaves. Here these materials were used as a respiratory substrate and for the production of structural materials. Although initially after defoliation new leaves retained all their assimilates, presumably for their own growth, assimilates were soon translocated from these leaves to the roots.     

Effects of selective defoliation and height of defoliation on tiller dynamics and herbage yield of Themeda triandra in a semi-arid rangeland in Zimbabwe

Understanding the impacts of intensity and selection of grazing on the performance of grasses is important in the management of grazing areas. It is especially important in semi-arid environments where, apart from moisture, the levels at which grasses are utilized has a major influence on their persistence in the environment. The effects of selective defoliation and height of defoliation (5 cm and 10 cm stubble heights) on the performance of the grass, Themeda triandra, were investigated in a field experiment for two growing seasons. Performance was measured as tiller production, rate of production, tiller mortality, herbage yield and quality. Tiller production was greater (81 tillers per plant) under non-selective defoliation than under selective defoliation (49 tillers per plant) in the 1995/1996 season. Tiller mortality was higher (66.45%) under heavy selective defoliation than under nonselective defoliation (21.98%). Herbage yield, apart from the control treatment, was high (13.6 g per plant) under light non-selective defoliation. Heavy selective defoliation reduced the nutrient levels (e.g. levels of soluble carbohydrates under heavy selective defoliation were 6 g kg^?1 glucose compared to 20 g kg^?1 glucose under light non-selective defoliation).     

不同放牧强度下高寒草甸矮嵩草无性系分株构件的研究

对放牧强度分别为０、２、４、８（藏羊只／ｈｍ２）的矮嵩草无性系各构件数量和地上生物量进行了研究。结果表明随放牧强度的加重每分株生殖分蘖数、分蘖地上生物量、营养和生殖地上生物量呈下降的趋势，而营养生物量占分蘖生物量的分配比例呈上升趋势。在不放牧的情况下，矮嵩草无性系分株总数小，其各构件地上生物量和生殖分蘖数高（Ｐ＜０．００１）；每分株分蘖数、营养分蘖数及杆叶比低（Ｐ＜０．００１）。     

Effect of intensity of defoliation by goats at different phenophases on leaf and shoot growth of acacia karroo hayne

Abstract

Defoliation by goats (leaves plus shoots) during the growing phenophases resulted in a considerable stimulation of leaf and shoot growth relative to non‐defoliated plants. The response differed considerably depending on the intensity and phenophase of defoliation. Plants were most susceptible to defoliation and young shoot removal during the spring flush when carbohydrate levels were at their lowest. During the rest of the growing season carbohydrate levels were high. At these times moderate to heavy (50 % to 75 % leaf removal) defoliations resulted in the greatest leaf and shoot growth.

In contrast, the initial and continuing impact of avian and insect consumption of leaves only reduced leaf and shoot production. The stimulatory effect of defoliation in one season carried through the dormant season to the following growing season. Defoliations during the dormant season did not have any positive or negative impact on plants relative to non‐defoliated plants. Leaf and shoot material removed when the plants were growing, was replaced within weeks of defoliation.     

行距对老芒麦种群构件组成、生物量结构及能量分配的影响

试验对30,45,60,75,90 cm行距下,第3年盛花期老芒麦种群的根、茎、叶、花序等构件数量性状、生物量结构、能量累积及分配比例进行比较分析。结果表明,行距对单位面积分蘖数与生殖枝比例有极显著影响;对叶长、叶宽、单蘖叶片数均无显著影响;对单蘖节数、节间长有显著影响,致使自然高度间差异极显著;根系深度与分布范围、花序柄及小穗数显著受行距影响;叶、茎、花序、根系的生物量均显著受行距的影响,顺序为茎＞叶＞根系＞花序;行距对叶、茎、根、花序的单位生物量能量值均无显著影响;对叶、茎、根、花序的能量累积有显著影响,影响由大到小的顺序为茎＞叶＞花序＞根;行距极显著影响老芒麦能量在构件间的分配,影响由大到小为叶＞茎＞花序＞根。30 cm是适合饲草生产的最佳行距,60 cm是适合种子生产的最佳行距。     

过表达FaSAMDC基因提高黑麦草属植物的抗旱性和耐热性

主要探讨了在黑麦草属植物中导入高羊茅S-腺苷甲硫氨酸脱羧酶基因(FaSAMDC)对转基因植株抗旱耐热性的提高效果,为培育黑麦草抗旱耐热新品种提供种质新材料。选择黑麦草成熟种子为外植体,采用贵州省草业研究所分子生物学实验室构建的过表达载体以及黑麦草胚性愈伤组织高频植株再生和农杆菌介导的遗传转化体系,将克隆自高羊茅的FaSAMDC基因转入贵州地区主栽品种多花黑麦草特高和多年生黑麦草四季的基因组内,经抗性筛选、PCR检测和Southern杂交分析验证,获得45株特高与44株四季的转基因植株,转化频率分别为2.93%和2.28%。抗旱耐热试验表明,在30 ℃高温和中度干旱胁迫条件下,特高转基因株系的根冠比比对照组培苗高出7.08%,叶片相对含水量(RWC)比对照高出13.12%,RWC降低幅度比对照少5.49个百分点;四季转基因株系的根冠比比对照组培苗高出6.54%,RWC比对照高出12.54%,RWC降低幅度比对照少6.50个百分点,差异均达到显著水平(P<0.05),证明转入FaSAMDC基因的黑麦草阳性株系的抗旱耐热能力得到了明显提高。形态与生长特征观测结果显示,与非转基因组培苗相比,转基因株系的叶长、株高、主茎节数减小,叶宽、单株分蘖数增加,叶色变深,植株形状趋向于叶片丛生的紧凑型,推测导入的FaSAMDC基因参与了基因表达、细胞分裂等生理功能的调节。     

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。