Age,growth and architecture of the historic Big Tree at Victoria Falls,Zimbabwe assessed by radiocarbon dating

The article discloses the AMS (accelerator mass spectrometry) radiocarbon dating results of the historic Big Tree at Victoria Falls, Zimbabwe. The research aimed to determine the age, growth and architecture of this renowned African baobab. The superlative baobab is composed of five main stems, three young stems and one false stem. It exhibits an open ring-shaped structure, an architecture that allows baobabs to reach large sizes and old ages. Several wood samples extracted from four stems were dated by radiocarbon. The oldest sample had a radiocarbon date of 978 ± 14 BP, corresponding to a calibrated age of 955 ± 20 calendar years. By this value, the Big Tree at Victoria Falls is 1150 ± 50 years old. We found that the eight common stems belong to three generations, which are 1000–1100, 600–700 and 200–250 years old, respectively. The false stem is 550 years old. The stems belonging to the oldest generation stopped growing over 100 years ago.     

Stem demography and post-fire recruitment of a resprouting serotinous conifer

Abstract. The contribution of resprouts and seedling recruitment to post-fire regeneration of the South African fynbos conifer Widdringtonia nodiflora was compared eight months after wildfires in 1990. Stems on all trees were killed by fire but resprouting success was > 90 % at all but one site. A demographic study of burned skeletons revealed that prior to these fires, nearly all plants were multi-stemmed (4–9 stems/plant) and multi-aged, indicating continuous sprout production between fires. All stems were killed by these 1990 fires and at most sites > 90 % of the stems were burned to ground level. All diameter stems were susceptible to such incineration as, at most sites, there was no difference in average diameter of stems burned to ground level and those left standing. Individual genets usually had all ramets incinerated to ground level or all ramets charred, but intact, suggesting certain micro-sites burned hotter, whereas other sites were somewhat protected. Although not true of the 1990 fires, there was evidence that occasionally Widdring-tonia stems may survive fire. At one site, four of the 16 plants sampled had a burned stem twice as old as the oldest burned stem on the other 12 plants at the site, suggesting some stems had survived the previous fire (ca. 1970) and this conclusion was supported by fire-scars on these four stems that dated to ca. 1970. Based on the highly significant correlation between stem diameter and cone density left standing after the 1990 fires, we calculated that for most sites > 80 % of the initial cone crop was incinerated by fire. This is important because we observed a strong relationship between size of the canopy cone crop surviving fire and post-fire seedling recruitment. Under these conditions we hypothesize that sprouting confers a selective advantage to genets when fires cause heavy losses of seed. The infrequent occurrence of sprouting in the Cupressaceae suggests the hypothesis that resprouting is an apomorphic or derived trait in Widdringtonia. Data from this study suggests resprouting provides a selective advantage under severe fynbos fires, which are not only 'stand-replacing fires,’but also are intense enough to incinerate cone-bearing stems.     

克隆乔木黄牛奶树枝条的功能特征

黄牛奶树(Symplocos laurina)是一种乔木克隆植物,其枝担负着支撑叶进行光合作用和克隆苗繁殖两种功能。由于枝功能的特异性在形态上表现出独特的特征:上部的枝生长比较旺盛,主要进行光合作用负责整个植株的碳水化合物供应与积累;下部的枝在形态上有所变化,基部细长而端部较基部明显增粗,并下垂呈“V”状,在生长过程中增长明显而无明显增粗现象,主要进行克隆繁殖。黄牛奶树的枝在由营养功能转变为繁殖功能的过程中年萌发次数显著增加;枝分化成克隆苗后在截取光能方面采取了不同的策略:克隆苗作为一个新的生命体,主要通过增加叶量占据更大的水平空间来增大总叶面积以截取更多阳光,不同于营养枝通过增加单叶面积占据更大的垂直空间来增大总叶面积以截取更多阳光的方式,但在不同的生境下对照枝与压枝克隆苗达到的总叶面积却无显著差异;从各构件的生物量特征看, 对照枝的生物量主要分配在叶和叶柄等光合构件上,而枝分化成克隆苗后生物量主要分配在茎上。即黄牛奶树的枝随着着地后功能的变化,在形态等各方面都有相应的变化,这可能是由于功能变化后内源激素发生变化的结果,但这有待于进一步研究。     

THE ECOLOGICAL IMPACT OF ALLELOPATHY IN AILANTHUS ALTISSIMA (SIMAROUBACEAE)

Compounds inhibitory to the growth of neighboring plant species were found in significant concentrations in the leaves and stems of young Ailanthus altissima ramets. The surrounding soil also contained appreciable concentrations of similarly acting toxins. Individuals of neighboring plant species have either incorporated active portions of inhibitory compounds or responded to Ailanthus by producing growth-inhibiting substances. Under greenhouse conditions, individuals of neighboring plant species previously unexposed to Ailanthus in the field were found to be more susceptible to the Ailanthus toxins than individuals previously exposed. Moreover, seeds produced by unexposed populations were also more susceptible to Ailanthus toxins than seeds produced by previously exposed populations. These differences demonstrated that the allelochemicals of Ailanthus altissima exhibited a measurable impact upon neighboring plant species. Since the progeny of these populations displayed a differential response to Ailanthus toxin, this phenotypic difference between the two populations may have a heritable basis.     

松嫩平原不同生境芦苇种群分株的生物量分配与生长分析

在松嫩平原8月中旬,4个旱地生境芦苇种群分株的生长和生产力以季节性临时积水的低洼地为最高,以碱斑地为最低,两个生境之间分株高度相差2.8倍,分株生物量相差4.4倍,其它2个生境沙地和草甸混生 少也达到了显著或极显著水平,不同生境芦苇种群分株生物量分配的差异,蕴涵着重要的生长调节和物质分配策略。在分株株较小而又有充分生长空间的沙地生境和三斑生境,以及具有种间竞争的草句生境,分株将50％以上的物质分配给叶的建造上,以保证充分的物质生产;在环境条件相对较好的低洼地生境,分株将近40％的物质分配给茎的伸长生长,以提高个体对空间和光资源的竞争力。4个生境芦苇种群在分株增高与增重,以及茎、叶与分株的相对增重均具有相同的幂函数异速生长规律。     

The role of nodding stems in the goldenrod-gall-fly interaction: A test of the "ducking" hypothesis

Herbivores are among the most pervasive selective forces acting on plants, and the number of plant chemicals that presumably evolved for defense against herbivory is immense. In contrast, biologists are only beginning to appreciate the important roles that architectural traits can play in antiherbivore defense. One putative architectural-resistance trait is the nodding stem apex of some goldenrods (Solidago; Asteraceae). Individuals of S. altissima genets that undergo temporary nodding in the late spring (i.e., "candy-cane" ramets) have been shown to be more resistant than individuals of erect-stemmed genets to certain apex-attacking herbivores. We tested the hypothesis that the greater resistance of candy-cane ramets is accomplished by the ramets' "ducking" from the herbivores. In a greenhouse experiment, nodding candy-cane ramets were significantly more resistant to oviposition by the gall-inducing fly Eurosta solidaginis than were ramets of the same genets that had been experimentally straightened. The straightened candy-cane stems were just as susceptible to ovipositions as were ramets of erect-stemmed genets. Thus, ducking indeed appears to confer a resistance advantage to candy-cane genets of S. altissima.     

Strong but opposing effects of associational resistance and susceptibility on defense phenotype in an African savanna plant

The susceptibility of plants to herbivores can be strongly influenced by the identity, morphology and palatability of neighboring plants. While the defensive traits of neighbors often determine the mechanism and strength of associational resistance and susceptibility, the effect of neighbors on plant defense phenotype remains poorly understood. We used field surveys and a prickle‐removal experiment in a semi‐arid Kenyan savanna to evaluate the efficacy of physical defenses against large mammalian herbivores in a common understory plant, Solanum campylacanthum. We then quantified the respective effects of spinescent Acacia trees and short‐statured grasses on browsing damage and prickle density in S. campylacanthum. We paired measurements of prickle density beneath and outside tree canopies with long‐term herbivore‐exclusion experiments to evaluate whether associational resistance reduced defense investment by decreasing browsing damage. Likewise, we compared defense phenotype within and outside pre‐existing and experimentally created clearings to determine whether grass neighbors increased defense investment via associational susceptibility. Removing prickles increased the frequency of browsing by ~25%, and surveys of herbivory damage on defended leaves suggested that herbivores tended to avoid prickles. As predicted, associational resistance and susceptibility had opposing effects on plant phenotype: individuals growing beneath Acacia canopies (or, analogously, within large‐herbivore exclosures) had a significantly lower proportion of their leaves browsed and produced ~ 70–80% fewer prickles than those outside refuges, whereas plants in grass‐dominated clearings were more heavily browsed and produced nearly twice as many prickles as plants outside clearings. Our results demonstrate that associational resistance and susceptibility have strong, but opposing, effects on plant defense phenotype, and that variable herbivore damage is a major source of intraspecific variation in defense phenotype in this system.     

五叶木通营养器官解剖结构与三萜皂苷的积累关系

采用显微制片技术、组织化学定位和三萜皂苷定量分析方法,对五叶木通的营养器官分别进行了三萜皂苷的组织化学定位、含量和解剖结构特征研究。结果表明：三萜皂苷在五叶木通不同营养器官中的含量不同,含量测定与组织化学定位推测的结果吻合,叶＞根＞茎;三萜皂苷在同一营养器官的不同发育时期含量不同,总的规律是：老叶＞幼茎＞幼根＞幼叶﹥老根﹥老茎。三萜皂苷在不同器官中具有明确的积累位置：根中主要是次生韧皮部和周皮;皮层和次生韧皮部是茎中三萜皂苷积累部位;叶内则以栅栏组织为主。五叶木通根中初生木质部二原型,次生木质部内导管多为单管孔,少数为管孔链,纤维含量丰富。茎中韧皮纤维丰富,在幼茎中纤维成束状罩在初生韧皮部的外方,在次生韧皮部中纤维呈带状环绕在外方。叶为异面叶。     

松嫩平原全叶马兰种群不同龄级分株的生长策略

全叶马兰为根蘖性多年生草本菊科植物,种群由3个龄级无性系分株组成,在松嫩平原6月份,是全叶马兰营养生长的旺盛期,研究结果表明,分株的生长与生产力以1龄级最低,2、3龄级依次增高,3个龄级分株的生物量分配均为茎>叶>主根,叶的生物量分配为1龄级>2龄级>3龄级,茎和主根的均为1龄级<2龄级<3龄级,3个龄级分株总重与分株高度、分株叶重与茎重、分株主根重与枝条重之间均为幂函数异速生长规律,主根的生物量分配则随着分株高度的增加呈线性减少,全叶马兰无性系分株的生长与分配策略是在分株幼小时将较多的物质分配给叶,以保证物质生产器官叶的建造上,随着分株生长逐渐将生产的物质分配到茎和主根的生长与贮藏;分株不向主根投入较多的能量,但在分株幼小时向主根中分配的物质相对较多,随着分株的生长则按比例较小,并保持相对稳定的分配比率     

Two enzymatic sources of nitric oxide in different organs of apple plant

Nitric oxide production, nitric oxide synthase (NOS) and mitochondrial nitrite-reducing activities in roots, leaves and stems of different developmental stages were investigated, using potted 3-year-old apple (Malus domestica Borkh.) trees. The arginine-dependent NOS activity is sensitive to NOS inhibitor L-NAME and aminoguanidine (AG), with L-NAME being more effective than AG. Endogenous NO production, NOS and mitochondrial nitrite-reducing activities are predominately presented in young leaves and especially in young white roots and young stems. Root and stem mitochondria can reduce nitrite to nitric oxide at the expense of NADH, however, this mitochondrial nitrite-reducing activity is absent in leaves.     

The structure of feeding behavior in the colorado potato beetle,Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Feeding behavior, in an ad libitum situation on potato plants in the laboratory, was continuously observed for approximately 7 h/day on 2 successive days for 18 adult femaleLeptinotarsa decemlineata. Additional behaviors were also recorded including resting, walking, biting, local movements, grooming, defecating, and regurgitating. These data were used to calculate a time budget for the various behaviors. The feeding data were analyzed to describe the structure of feeding for young adult females on their normal host plant. The criterion for a meal (minimum intermeal interval) was determined to be 286 s. This criterion was used to distinguish between intra- and intermeal interruptions in feeding for all subsequent analyses. Meals taken from leaves that were young, medium aged, or old did not differ, but on average beetles took 60% of their meals from young leaves. Meal size and meal duration were equally good predictors of when a meal would end. Feeding from stems was a prominent feature for most beetles. The stem meals had much longer durations than leaf meals, but stem feeding did not affect subsequent leaf feeding. The structure of feeding by these beetles is compared with that found in other insects, especiallyLocusta migratoria.     

Trade-off among antiherbivore defences in a south american blackberry (Rubus bogotensis)

Summary The idea of trade-offs among antiherbivore defences in plants is examined using data from a South American blackberry (Rubus bogotensis). Two distinct morphs of R. bogotensis, one with glandular trichomes and one without, were compared with respect to leaf toughness, number of prickles and prickle length. The two morphs were sympatric and grew under similar environmental conditions. The morph lacking trichomes had significantly tougher leaves and also tended to have more and longer prickles. Bioassay showed that Ithomiid larvae fed to a lesser extent on tough leaves than on more tender ones. Correlations between antiherbivore defences within each phenotype revealed three significant or almost significant negative relationships. The comparisons support the hypothesis that trade-offs exist among antiherbivore defences.     

Effects of Bean Leaf Age on Pathogenicity by Botrytis fabae

Leaves from field bean plants grown out of doors were inoculated with conidia of B. fabae immediately after detaching from stems. The oldest leaves developed more lesions than youngest ones, although they were not chlorotic. On intact plants at high humidities, established lesions on young leaves increased in size at only half the rate of those on old. but still green leaves. Seven days after inoculation a higher proportion of lesions on old leaves bore conidia than those on young leaves, but leaf age had no significant effect on numbers of conidia per mm² of lesion area. Young leaflets from bean plants grown in a controlled environment or in the field challenged with β. cinerea accumulated more phytoalexins than did old ones.     

Microclimate and ecophysiological significance of the tree-like life-form of Lobelia rhynchopetalum in a tropical alpine environment

The microclimate and the adaptive significance of the tree-like plant life-form for growth in a tropical alpine environment was investigated with the pachycaul arborescent giant rosette plant, Lobelia rhynchopetalum (Hochst. A. Rich.) Hemsl. in the Bale and Simen Mountains, Ethiopia. The microclimate of plants of three height classes was examined with respect to temperature, relative humidity and the effect of wind. Although the total heat gains were rather similar, leaves of young, still stemless (acaulescent) individuals of Lobelia were subjected to a high diurnal temperature fluctuation of up to 29 K compared to a 14-K fluctuation for the leaves of an individual 3.5 m in height. During the cold nights, temperatures of the inner rosette leaves and inside leaf buds of caulescent plants were 4–5 K above air temperature, while corresponding temperatures of acaulescent individuals were 1–2 K below air temperature. The inner temperature of the stem tissue was higher than the surface temperature of the stem by about 5 K for most of the cold night. The annual rates of increment in whole plant, stem and rosette height, and stem diameter of L. rhynchopetalum showed that the young, still acaulescent individuals, with an annual increment of 5.6 cm in plant height, had the lowest growth rate, compared to 12.1 and 22.1 cm for caulescent life-forms. The results show that the most important advantage gained by the tree-like life-form of adult L. rhynchopetalum is probably a more favourable microclimate in which the strong diurnal temperature fluctuations at the ground are mitigated and nocturnal temperatures do not drop below freezing point. Received: 16 August 1996 / Accepted: 9 September 1997     

Dispersal patterns of Lonicera periclymenum determined by genetic analysis

Colonization of Lonicera periclymenum L. (honeysuckle) was studied by RAPD analysis of young ramets in two woodlots planted 20 years ago, and in all ramets in older woodlots within a range of 1 km. Mature ramets that climbed in a particular tree always belonged to one individual. Twenty-five percent of the mature individuals had reproduced vegetatively to other trees or patches nearby, which indicates that the larger part of reproduction is sexual. Some young plants that were growing at close distances from each other were genetically highly similar and shared high similarities to the same mature plants. They may be the product of one dispersal event. Detection of parents of young individuals by exclusion was not successful, because of the dominant nature of the bands. Average distances from young plants to genetically most similar mature plants were variable, due to the small number of colonization events. However, four ways of analysis of genetic similarity among all individuals indicated that exchange of genetic material by seed and pollen occurs to a large extent over small distances and within woodlots: (i) using the Mantel test, pairs of individuals with highest similarity were found significantly more often in the same woodlot than in different woodlots; (ii) genetic similarities between individuals decreased significantly with geographical distance, but only for distances up to 300 m; (iii) individuals of woodlots in the Western part of the study area were hardly related to individuals in the Eastern part of the study area, a distance of 2–3 km; (iv) Φ_ST in the study area was 0.186, indicating a limited gene flow between woodlots. These results are consistent with the dispersal distance as estimated from the average distance between colonized woodlots and the nearest occupied old woodlot in earlier research.     

Variation in the nutritional value of leaf and stem fractions of nineteen leucaena lines

In two experiments, 2.5-month-old edible regrowth of the genus Leucaena (varying in tolerance to the leucaena psyllid pest attack) were analysed for nutritive value. In Experiment 1, forage of nine lines was separated into young leaves, young stems (within woody fraction < 5 mm diameter), old leaves and old stems (within a woody fraction 5-10 mm diameter) whereas in Experiment 2, forage of the other 10 lines was separated in main stem leaves, branch leaves, young branches, young main stems, old main stems and old branches for analysis. Major differences were recorded between lines and forage fractions. Nutrient contents in dry matter were: nitrogen 0.7-4.8%, phosphorus 0.1-0.3%, potassium 0.2-2.5%, calcium 0.2-1.6%, magnesium 0.1-0.6%, acid detergent fibre 20-63%, lignin 8-23% and in vitro dry matter digestibility 15-69%. The leaves and immature fractions were higher in nitrogen, phosphorus, potassium and digestibility but lower in calcium, magnesium and fibre. Nutrient content in L. Leucocephala lines exceeded that in L. esculenta, L. diversifolia, leucaena hybrids and the composites. Based on the data, a management strategy that will promote young growth is suggested as appropriate for high quality forage production.     

Persistence in Sarcopoterium spinosum dwarf-shrub communities

Our study aimed at identifying mechanisms that permit the long-termpersistence of Sarcopoterium spinosum, a dwarf-shrub thatdominates large areas of hilly landscape in eastern Mediterranean countries.Data were obtained from 16 1×1 m quadrats distributed amongwell-established S. spinosum communities in Israel thathadnot been burned or otherwise disturbed for well over 20 years. We sampled threecommunities that represent different climatic and habitat conditions andanalysed the growth rings in the root crowns of 604 uprooted plants, todetermine the age structures of the sampled stands. Many older'shrubs that appeared to be individual plantswere in fact clusters of ramets with their root crowns concentrated in a verysmall area. The morphology of these ramets indicates that they arose by rootingof peripheral stems. Seedlings and young plants were rare. Ramets seldomexceeded 17 years of age, although a few were 18–21 years old and one had34 growth rings. The average ramet age on the different sites varied between 9and 11 years. The ramets appeared to separate from the mother plant when theywere older than 7 years, after which they had an estimated average half-life ofca. 2.8 years. Young shrubs grew rapidly in height, but their basal cover waslow; it increased when they were much older, presumably as the older plantsdied. Consequently, three or four cohorts of older ramets between 12 and 17years old often dominated stand cover. The continuing profuse production ofseeds even where seedlingrecruitment is normally rare could be related to the relatively short averagelife-span of the ramets. We conclude that where resources are irregularlydistributed and establishment sites are fully occupied by perennial species,localised phalanx-type clonal proliferation can reduce the risk of genetextinction. On favourable sites this strategy confers upon S.spinosum genets the tenacity required to hold off replacement byother species and to dominate large areas of the landscape for much longer thanthe average life span of individual ramets.     

A new Neocalamites (Sphenophyta) with prickles and attached cones from the Upper Triassic of China

Remains of the extinct sphenophyte (horsetail) Neocalamites are most widespread in the Middle–Upper Triassic and are typically represented by stem and leaf fragments. Here we report on spectacular new finds of Neocalamites from the Late Triassic Yangcaogou Formation in Liaoning Province, China that include bedding surfaces dominated by nearly complete aerial stems with attached leaf whorls and rare bractless cones. They reveal a monopodial growth habit for the stems, which are covered with downward projecting prickles that probably provided protection against herbivores. These features provide the basis for a new proposed species, Neocalamites horridus. The nodes bear whorls of very long leaves mainly free to their bases, and one specimen bears an attached cone on a long peduncle. Identical dispersed cones have also been recovered. The leaves of adjacent monopodial stems most likely interlocked to support growth in large stands akin to the role now played by branches in large modern Equisetum species. The new Chinese Neocalamites is among the most confidently reconstructed species, and indicates a greater diversity of sphenophyte morphology during the Mesozoic than previously realized.     

Assessment of heavy metal accumulation in Anzali wetland,Iran, using a submerged aquatic plant,Ceratophyllum demersum

The objective of this study in 2009 was to examine whether levels of cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb) and chromium (Cr) were higher in the leaves than in the stems of a submerged aquatic plant Ceratophyllum demersum in Anzali wetland. Cadmium, Pb and Cr concentrations were highest in the leaves. The mean concentrations of Cd and Cr in the leaves at all the sampling sites ranged between 0.94–1.26 μg g^?1 and 1.03–2.71 μg g^?1, respectively. Lead also had its highest concentrations in the leaves. The mean concentration of Pb in the leaves at all sampling sites ranged between 7.49–11.88 μg g^?1. Copper and Zn concentrations were highest in the stems. The mean concentrations of Cu and Zn in the stems at all sampling sites ranged between 10.79–17.91 μg g^?1 and 19.89–40.01 μg g^?1, respectively. Cadmium and Pb concentrations were higher in the leaves than in the stems, while Zn concentration was higher in the stems than in the leaves. Accumulation of Cu and Cr in the organs of C. demersum was in descending order of leaf ～ stem, since there was no significant difference between their mean concentrations in the leaves and stems.     

Ants,Stem Borers,and Pubescence in Endospermum in Papua New Guinea1

The stems of the ant-plant, Endospermum labios Schodde, serve as colonization sites for the ant, Camponotus quadriceps F. Smith. They are also subject to damage by insect borers. We sampled young E. labios trees in distutbed forest to compare evidence of stem boring insect and stem miner damage in plants with and without colonies of C. quadriceps. Dissections of a subsample of plants showed that dipteran stem borers and stem miner damage were significantly more common in plants lacking C, quadriceps colonies than in plants with established colonies. Evidence from these dissections and from field counts of meristem damage caused by emerging borers suggested that coleopteran stem borers were also more abundant when ants were not present. In addition to the incidence of stem boring insects and ant colonies, we examined relative levels of leaf pubescence by measuring trichome density and leaf size for E. labios trees. We found that trichome density was significantly greater in trees with evidence of prior shoot damage (presumably from stem borer emergence at the meristem) but was not significantly related to the presence or absence of an ant colony. This prompted us to compare trichome density on leaves of nearby small trees and of different branches of the same tree, pairing a stem/branch that appeared damaged with one that appeared healthy. Trichome densities on leaves from damaged stems and branches were significantly greater than were trichome densities on healthy branches and stems. Based on these empirical data, we present several possible explanations for the patterns of association between ants, stem borers, and pubescence. Although feeding preference tests with a common folivore showed no effect of trichome densities on leaves, we suggest further study on how trichomes may affect ovipositing stem borers.