A comparison of a number of annual cool season legumes under dryland conditions in the Dohne Sourveld

Abstract

Fifteen annual cool season legumes were compared under dryland conditions on two sites in the Dohne Sourveld. These sites were Dohne, with a mild but dry winter and an average rainfall of 743 mm per year, and Grasslands, a colder, wetter site.

Vicia spp were among the highest‐yielding cultivars at both sites. At Dohne the mean yield of the legumes that performed best was slightly more than that of the veld and their use does not seem worthwhile. At Grasslands, the mean yield of the highest‐yielding legumes was above 6 t/ha/year and their use does seem economical.

The high yield of the legumes during wet seasons suggests that their cultivation under irrigation should be profitable. Under these or high rainfall conditions seed production may be lucrative.     

Secondary succession in the Mopani veld of the Limpopo Valley,South Africa

The long-term establishment sequences of the herbaceous and woody component of the Mopani veld of the Limpopo Valley were studied and documented. Based on vegetation surveys conducted at three enclosed sites at the Messina Experimental Farm during the period 1964 to 2001, no clear fixed grass species establishment sequence was observed. The classic plant succession model of the grass component, as usually found in other veld types, is absent in Mopani veld of the Limpopo Valley. Shallow, nutrient poor, gravelly, severely eroded soils with low moisture retention and a high runoff rate are mainly colonised by annual grasses and forbs. Perennial grasses take long to establish. This results in an unstable herbaceous component that is vulnerable to changes, which in turn depends on the erratic availability of soil moisture. Where the woody component is concerned, eight tree species appeared to be early colonisers, five intermediate colonisers and seven late colonisers. Tree numbers increased at sites with deeper soils, indicating that bush encroachment is a general, natural process that occurs irrespective of rest treatments applied to the herbaceous component. At a site with an extremely shallow soil, bush density decreased, suggesting that the bush encroachment process in the Limpopo Valley is much more affected by soil and climate than in other veld types and climatic zones of the Limpopo Province.     

光照、温度、土壤水分和播种深度对披针叶黄华种子萌发及幼苗生长的影响

披针叶黄华(Thermopsis lanceolate)是我国北方草地广泛分布的一种有毒多年生草本植物,且具有一定的药用价值。本研究分析了光照、温度、水分和播种深度等环境因子对披针叶黄华种子萌发的影响。结果表明,持续光照、持续黑暗和16 h/8 h光暗交替时披针叶黄华种子萌发最适宜的温度为25 ℃;16 h/8 h光暗交替下,25 ℃/15 ℃日夜变温是披针叶黄华种子萌发最适宜温度;其种子萌发对光照不敏感;种子萌发最适宜的土壤含水量为7%～12%,最适宜播深为0.5～2.0 cm。     

A preliminary investigation of area‐selective grazing in the Southern Tall Grassveld of Natal

The consequences of area‐selective grazing by cattle under three stocking rates and at two sites in the Southern Tall Grassveld of Natal were investigated. Soil compaction was found to significantly distinguish area‐selected patches from non‐selected veld (P≤0.01), while non‐significant differences in soil nutrient and moisture status were recorded. Area‐selected and non‐selected patches may be distinguished on the basis of species composition. Area‐selected patches are characterized by Aristida congesta subsp. barbicollis, Microchloa caffra and Eragrostis racemosa. Non‐selected veld is characterized by Themeda iriandra, Tristachya leucothrix and Hyparrhenia hirta.     

The effect of veld condition on the quality of diet selected by cattle grazing the Natal Sour Sandveld

The quality of diet selected by steers fistulated at the oesophagous was related to veld condition in a simulated rotational grazing system on the Natal Sour Sandveld. Six camps, ranging in veld condition score from 8,5 to 53%, were grazed simultaneously for a two‐week period in spring, summer, autumn and winter. Fistula samples were collected on the first, middle and last day of a period of occupation in a camp. Samples were analysed in terms of crude protein (CP), in vitro digestibility (IVD) and plant‐part (% leaf, % stem and % dead material) composition. Dietary quality in terms of CP, IVD and plant‐part composition was not related to veld condition but was dependent largely (P≤0,01) upon season and to a lesser extent upon period of occupation in a camp. It was concluded that in sourveld areas, where dietary quality may be limiting, the veld condition score may be a poor index of potential animal production.     

Effect of slope and plant cover on run‐off,soil loss and water use efficiency of natural veld

Abstract

Run‐off and soil loss were monitored from a climax, subclimax and pioneer veld, each on a 5,9%, 4,1% and 2,1% slope, by means of a rainfall simulator on a Valsrivier soil form. With rainfall intensity, soil moisture content at the beginning of each rain storm, and soil texture the same for each treatment, plant cover and composition had a significant (positive) (P≤0,05) influence on the amount of soil loss and run‐off that occurred, as against the insignificant influence of the slope.

An average of 6,2 t/ha soil loss and 80,6% run‐off of the amount of water applied occurred from the pioneer veld (0,7% basal cover) on the steepest slope. In all the successional stages more run‐off and less soil loss occurred from wet soil than from dry soil. Significant (P≤0,01) relationships between basal and canopy cover were obtained with run‐off and soil loss.

The climax, subclimax and pioneer veld produced on average 0,57 g, 0,23 g and 0,07 g aboveground phytomass for each litre of water evapotranspirated.     

Effect of continuous grazing in the dohne sourveld on species composition and basal cover

Abstract

In a grazing trial conducted at the Dohne Agricultural Research Station, natural grassland was grazed continuously for 36 years with cattle. In a second investigation conducted on similar grassland, paddocks were grazed or rested, in all combinations of the four seasons of the year, over a ten year period. Changes in botanical composition and cover of the sward were monitored at regular intervals. The results of these investigations indicate that under a regime of non‐selective grazing the composition of Dohne Sourveld is remarkably stable. After 36 years of continuous grazing the species composition of the sward was largely maintained. Floristically Dohne Sourveld is dominated by a small number of grass species of which Andropogon appendiculatus, Elionurus muticus, Heteropogon contortus, Sporobolus africanus, Themeda triandra and Tristachya leucothrix are the most important. These species react differently to under‐utilization or increasingly severe defoliation, enabling them to be classified into decreaser or increaser categories. Severe defoliation resulted in a marked decrease in basal cover but only small changes in relative species composition. As the intensity of defoliation increases, decrease in grass cover is associated with an increase of forbs, such as Senecio retrorsus.     

高山植物种子萌发、幼苗存活和定居对气候变化的响应

高山植物的自然更新,是高寒山区植物群落多样性的维持以及群落生产力高低的重要前提条件。弄清其在未来气候变化下的响应特征,可为准确评估高山生态系统响应气候变化的演变方向和格局提供数据支撑,并为探索内在的演变机制提供理论依据。本文从高山植物种子萌发、幼苗存活与定居的3个关键更新环节展开,综述了生物因素(植物自身因素、植物间相互作用、动物干扰、昆虫授粉等)和非生物因素(温度、水分、土壤性质等)对这3个关键环节影响的研究结果。在种子萌发阶段,极端干旱和高山积雪提前融化改变植物–传粉昆虫相互关系和营养结构网络。升温和降水增加促进植物种子萌发,升温能打破种子休眠改变种子生理状况,而增加土壤水分能为种子萌发提供充足的水分供应。而温度过高和水分过多却对种子萌发产生阻碍作用,归因于温度高于萌发阈值造成高温胁迫,土壤水分过多产生病原体。幼苗存活和定居阶段,植食动物干扰和植物种间竞争对幼苗的存活和定居有利有弊,适当的动物干扰增加幼苗生长空间,资源贫乏山地的植物种间竞争促使幼苗相互协调共生,促进存活和定居。动物对幼苗的高强度取食和干扰及资源富足的区域植物种间竞争造成植物资源获取受阻,都抑制幼苗存活和定居。迄今为止,有关升温对高山植物幼苗存活的影响还存在争议(促进或者没有影响),但升温和增加降水可以促进幼苗生长的结论比较一致,这可能是更温暖湿润的土壤可以为幼苗的生长提供良好的环境条件,有利于养分吸收利用。本文阐明了高山植物早期更新3个阶段的生物与非生物因素对其的影响,也指出了忽略生物和非生物因子的多重效应等方面的研究不足,同时提出了需要继续深入探索的科学问题,以期为气候变化对高山生态系统的影响研究提供文献借鉴。     

Controlling bush encroachment with fire in the savanna areas of South Africa

The savanna areas of South Africa can be divided into the moist and arid savanna types according to the availability of soil moisture. Bush encroachment is a serious veld management problem in all the savanna areas and veld burning is a potential eradication technique in situations with an adequate grass cover to support an intense fire. In the moist savannas fire per se can be used to control bush encroachment but in the arid savannas it has the role of maintaining trees and shrubs at an available height and in acceptable state for browsing animals. Intense head fires applied at the end of the dormant season are used for bush eradication. The frequency of burning is relatively high in the moist savannas but is very low in the arid savannas, being usually limited to years with above average rainfall when adequate grass fuel loads can be accumulated. Veld burning provides an attractive economic and energy saving technique of solving the problem of bush encroachment in the savanna areas of South Africa.     

苦豆子种子形态特性及发芽条件研究

野生苦豆子种子硬实率高,因种皮不透水和不透气,而具有深休眠性。本研究观测了野生苦豆子种子的形态特征、种子大小、千粒重和硬实率,并对H₂SO₄破除种子硬实的处理浓度和时间,植物生长调节剂和聚乙二醇(PEG)处理对种子萌发和幼苗生长的影响,以及种子田间萌发的适宜土壤含水量和播种深度进行了研究。结果表明:苦豆子种子长为3.865mm,宽为3.358mm,厚为2.321mm,千粒重为20.775g,硬实率达99%;破除硬实处理适宜的H₂SO₄浓度为65%,时间是20min;0.02%GA3对提高种子发芽速度和幼苗生长量具有显著的作用,此外PEG处理种子能显著提高幼苗的生物量;苦豆子种子田间萌发的适宜土壤含水量为8%～12%,播种的最适深度是1～3cm。     

偃麦草属5种植物种子发育过程中生理生化的研究

对偃麦草属5种植物种子发育特性研究表明,其种子在成熟过程中水分含量呈下降的趋势,达50%含水量后下降非常迅速;干物质重量随种子的成熟逐渐增加,进入生理成熟期趋于稳定;偃麦草属植物种子成熟后含水量、干鲜重和千粒重存在种间显著差异,其中长根茎的巴顿硬叶偃麦草种子含水量、干鲜重和千粒重最低,种子较小。发芽实验结果表明,偃麦草属5种植物种子发育存在明显种间差异,种子发芽率与根茎的发育程度呈负相关,根茎越长,其休眠程度越严重。采用电导率值能够较好地反映种子间活力差异。偃麦草属植物种子发育过程中种子活力逐渐提高,直至种子进入生理成熟期（水分含量40%～50%）达到最高。     

A flexible system of management for sourveld in Natal

The conventional systems of veld management have a number of shortcomings, the main one being that the period of absence from grazing during the growing period is normally too short. This is due to the fact that a particular group of animals is allocated to a specific set of camps for the whole growing season.

A more flexible system of veld management would allow the grazing procedure to be manipulated in such a way that the period of absence could be varied in relation to the rate of regrowth of the grass.

The application of such a flexible system would involve the following: (a) the minimum number of camps required is calculated on the basis of at least four to five camps for each group of animals; (b) one quarter of the area of veld is rested; (c) the remaining camps are grazed whenever sufficient regrowth has taken place, and no group of animals is confined to particular camps or set of camps; (d) each camp is well grazed down and the number of camps grazed for the season will depend on weather conditions; during a dry year, more camps will be grazed and fewer camps during a wet year; (e) the camps grazed most selectively, are rested during the following season; and (f) burning of the veld is confined to those camps that have been rested during the previous year.     

三种药用甘草种子位置效应对幼苗建植特性的影响

通过对甘草属3种植物,光果甘草、胀果甘草、乌拉尔甘草植株不同部位种子的萌发特性、幼苗生长特性、叶绿素含量、叶绿素荧光参数的测定和比较,探讨了3种药用甘草植株不同部位种子的萌发策略、幼苗的生长适应性,为更清楚地认识甘草属植物种子萌发与幼苗建植策略提供科学依据。结果表明,1)光果甘草植株中、上部,胀果甘草和乌拉尔甘草植株中、下部种子具有较高的出苗率,是种子繁殖的主要保障,但存活率无差异。2)具有较高出苗率的种子萌发形成的幼苗具有较大的生物量、较长的根长,且根冠比也相对较高,其分配到地下部分生物量多于地上部分,发达的根系可增强幼苗的抗逆性和对环境的适应性;而地上部分叶片的叶绿素相对含量、可变荧光(F_v)、最大荧光产量(F_m)、PSⅡ光化学效率(F_v/F_m)、PSⅡ潜在的光化学活性(F_v/F₀)和光反应阶段电子传递的速率也相对较高,荧光动力学曲线也反映出其具有较强的荧光强度、电子捕获和光能利用率,进而增强了幼苗建植能力。3)具有较低出苗率的种子萌发形成的幼苗具有较高的株高,较多的叶片数,可以通过优先占领空间和光源来维持生长。综上所述,3种药用甘草不同位置的种子具有不同种子萌发和幼苗生长策略,这对野生甘草自然种群的幼苗建植和种群更新有着重要的生态学意义。     

不同盐分处理对黑果枸杞种子萌发和幼苗生长的影响

为了比较黑果枸杞(Lycium ruthenicum Murr.)种子在萌发期对不同类型盐溶液的耐盐性强弱,对黑果枸杞种子在不同浓度NaCl,Na2SO4,NaHCO3和混合盐(NaCl:NaHCO3为1:1)4种盐溶液中进行模拟盐胁迫,以蒸馏水为对照(CK),通过种子萌发试验,测定黑果枸杞种子在不同浓度和种类盐处理下...     

野榆钱菠菜三种异型种子幼苗的生长特性

野榆钱菠菜是新疆重要的荒漠野生牧草资源,具有褐色(非休眠类型)、黑色大、黑色小(休眠类型)3种异型种子。以种子异型性植物野榆钱菠菜为材料,对3种异型种子在自然条件下进行培育,对比观察研究3种异型种子的萌发物候及幼苗的生长特性。结果表明:1) 异型种子萌发物候不同步,萌发策略不同,褐色种子集中萌发,出苗率为74.30%,萌发期为3 d;两种黑色种子萌发期长,分散萌发,出苗率分别为6.58%(黑色大种子)和1.55%(黑色小种子),萌发期分别为21和17 d。2) 异型种子子叶存留时间长,但存留时间有差异,种子越小子叶存留时间越短。3) 褐色种子幼苗在初期其子叶长宽、根长、地上地下生物量均显著大于黑色种子幼苗,但随着幼苗的生长,3种异型种子幼苗在这些指标方面的差异逐渐缩小。4) 异型种子幼苗具有不同的生物量分配策略,褐色种子幼苗主要将养分输送到地上部分,两种黑色种子幼苗主要将养分输送到地下部分,这种不同的生物量分配策略能够使种子异型性植物在面对荒漠异质环境时具有不同的应对方式,是种子异型性植物能够长期适应荒漠异质环境的重要生态适应机制。研究结果为揭示种子异型性植物长期适应荒漠异质环境提供新的科学依据,也为“两头下注”对策理论提供新的理论基础。     

Effects of fire,bruchid beetles and soil type on germination and seedling establishment of Acacia drepanolobium

The effects of fire, bruchid seed beetles and soil type on the germination and seedling establishment of Acacia drepanolobium were experimentally investigated. Seeds subjected to three seed treatments (bruchid damaged, bruchid-free burnt, and bruchid-free unburned) were germinated in three different soil types (black cotton, red sandy, and clay loam soils). Undamaged seeds had significantly higher germination (85.3%) than either beetle damaged (20.6%), or burnt seeds (3.4%). Soil type did not influence germination or seedling survival. Burnt seeds had an average germination of 2% in clay loams and 5.4% in red sandy soils, while beetle damaged seeds had an average germination of 15.6% in clay loams and 28.7% in black cotton soils. Treatment effects on seedling mortality or survival were not significant but seedlings from undamaged seeds had higher survival rates than those damaged by bruchid beetles.     

Korttermyn invloed van strawwe droogte op veldtoestand en waterverbruiksdoeltreffendheid van grasveld in die sentrale Oranje‐Vrystaat

Short‐term effect of severe drought on veld condition and water use efficiency of grassveld in the central Orange Free State. The impact of an intensive drought (1982/1983 and 1983/84‐growing seasons) on botanical composition, basal cover, mortality of grazing plants and water use efficiency (WUE) of veld in good, moderate and poor condition was identified. Increaser II species were apparently more capable of surviving drought than the Decreaser species. Under optimal soil moisture conditions the Decreaser species increased and the Increaser II species decreased. During the drought extensive grass mortality took place. Veld condition plays an important role in determining mortality during drought. Decreaser species have a high water requirement for optimal WUE, while Increaser II species can reach maximum WUE with less water. Under water stress conditions Increaser II species significantly (P≤0.01) do not use the water as efficiently as do Decreaser species. The WUE under water stress conditions for veld in good, moderate and poor condition was on average, during the study period, 0.90; 0.90 and 0.40 kg ha^?1 mm^?1, respectively, and towards under optimal water conditions, 2.47; 1.67 and 0.23 kg ha^?1 mm^?1, respectively.     

土壤侵蚀对植被发育演替的干扰与植物的抗侵蚀特性研究进展

植被与土壤侵蚀之间的关系因其重要的科学意义和实际应用价值而备受关注。大多研究集中在植被的防蚀机理与功效方面,有关土壤侵蚀对植被生长发育与恢复演替的影响及植物抵抗土壤侵蚀的特性与能力的研究国内外都较少且不系统。笔者就国内外有关土壤侵蚀对种子生产、种子流失与再分布、幼苗存活与建植、植物群落组成结构与功能、植被空间分布格局及植被恢复过程、速率与方向等方面的干扰与胁迫,以及植物在各方面所表现的抵抗土壤侵蚀特性的研究进行了总结与分析,认为只有明确了一个区域土壤侵蚀对植被恢复过程的干扰程度及不同植物抵抗土壤侵蚀所表现出的特性与能力大小,才能提出有效防治土壤侵蚀的对策。     

干旱荒漠区4种一年生植物种子萌发期耐盐性

采用不同浓度的NaCl溶液对4种一年生草本植物雾冰藜(Bassia dasyphylla)、白茎盐生草(Halogeton arachnoideus)、沙米(Agriophyllum squarrosum)和画眉草(Eragrostis pilosa)种子进行处理,通过测定种子相对发芽率、相对发芽势、发芽指数等指标,分析了种子萌发期耐盐差异性。结果表明:1)随着NaCl溶液浓度的增大,种子发芽率呈逐渐下降的趋势,在蒸馏水中第3天达到了发芽高峰,发芽基本结束,在NaCl溶液中第7天结束发芽。2)随NaCl溶液浓度逐渐增大,4种植物种子发芽率和发芽势均呈先增加后降低的趋势,同一植物种子发芽率和发芽势在不同浓度NaCl溶液中存在显著差异(P<0.05)。NaCl溶液浓度对白茎盐生草种子发芽率和发芽势影响较大,画眉草次之,其余两种较小。3)随NaCl溶液浓度逐渐增大,4种植物种子发芽指数呈下降趋势,雾冰藜活力指数显著高于白茎盐生草、沙米和画眉草种子;盐胁迫对画眉草发芽指数和活力指数影响较大,当NaCl溶液浓度达到2.1%时,幼苗活力指数降到最低。4)4种植物幼苗长度均随NaCl浓度增大表现出先增加后快速降低的趋势,0~0.3%NaCl浓度有促进幼苗生长的作用。0.6%及以上NaCl溶液浓度对画眉草幼苗长度产生了较大影响,而0.9%及以上NaCl溶液浓度对雾冰藜、白茎盐生草和沙米幼苗长度影响较大。综合各项指标分析表明,4种一年生植物种子萌发期耐盐性大小依次为沙米>雾冰藜>画眉草>白茎盐生草,根据发芽率、发芽势、幼苗长度等指标综合分析,最适宜萌发NaCl浓度分别为雾冰藜0~0.6%、白茎盐生草0~0.6%、沙米0~0.9%、画眉草0~0.6%。     

疆3种锦鸡儿属植物种子萌发对温度和土壤水分的响应

白皮锦鸡儿Caragana leucophloea、草原锦鸡儿C.pumila和刺叶锦鸡儿C.acanthophylla均为旱生灌木,在植被恢复中具有潜在的价值。通过萌发试验,研究3种锦鸡儿种子萌发对昼夜变温和土壤水分的响应,及其萌发物候。结果表明：3种锦鸡儿种子在10/6 ℃、15/6 ℃、20/10 ℃、25/15 ℃和30/20 ℃昼夜变温（昼12 h/夜12 h）均能萌发。试验条件下,启动它们萌发的最低土壤水分含量为2.50%。白皮锦鸡儿和草原锦鸡儿种子萌发速度快,在种子成熟的当年就能萌发出苗,刺叶锦鸡儿由于部分硬实种子,直到来年还有幼苗出土。