Ecotypic differentiation within Festuca rubra L. occurring in a heterogeneous coastal environment

In order to study the genetic differentiation between Festuca rubra L. individuals growing in a heterogeneous environment, indices of salt tolerance, mean relative growth rates and the numbers of tillers formed by plants grown in a Hoagland solution, were determined. It was found that plants from salt marsh sites have a high index of salt tolerance, a high mean relative growth rate and numerous tillers; plants from coastal sand dunes are less tolerant, grow slowly and form few tillers; plants from the inland polder sites are rather salt sensitive, fast growing and form a high number of tillers. The heritability of the mean relative growth rate and the tiller number appeared to differ from zero. Apparently, these characters have been under recent selection and thus give a picture of the adaptations of individual plants to the different environments encountered. An indication of gene flow has been found, although the effect of gene flow seems to be small in the face of the force of selection. It was concluded that the distinction of three ecotypes within the species F. rubra is insufficient to describe the differentiation found. Considering the differences observed, it seems more reasonable to speak of ecotypic variation.     

Light quality effects on the appearance of tillers of different order in wheat (Triticum aestivum)

Plants of Triticum aestivum cvs Norkin Pan 70, La Paz Inta, Buck Cencerro and Buck Cimarron were grown outdoors in individual pots with two sowing dates and irradiated at the end of the day either with red or far-red light. In red-treated plants the number of tillers was close to the potential calculated from the number of leaves on the main shoot but far-red treated plants produced less tillers. The magnitude of the effect was larger for secondary and tertiary than primary tillers. Thus, the proportion of primary to secondary and tertiary tillers was larger in FR-treated plants. Leaf sheath and lamina were longer under FR in the second sowing date, possibly due to warmer nights. These responses were greatly affected by the genotype. Significant differences in ear number were not found but in one of the sowing dates red-light-treated plants showed a lower grain number and yield than those treated with far-red.     

Flowering Phenology and Gender Variation in Pennisetum typhoides

Because of the modular structure of pearl millet (an annual grass crop, Poaceae), different tillers of a plant share the same genotype but are subjected to different environmental conditions during their maturation. This allows investigation of the effects of tiller flowering phenology on allocation to resource-producing photosynthetic biomass, sexual functions, and thus tiller gender. All tillers of plants of two families collected from individual maternal plants (represented by 33 and 31 plants each) were analyzed. In both families, allocation to aboveground vegetative biomass decreased as flowering was delayed. On average, late-flowering tillers were 65% smaller than the first ones to flower. The proportion of biomass allocated to reproduction significantly increased with the flowering rank of the tillers, suggesting that translocations of assimilates occurred between early- and late-flowering tillers. In both families, late-flowering tillers produced significantly fewer pollen grains per stamen than early-flowering ones, and female reproductive allocation (expressed as seed mass per tiller) was also affected by flowering phenology. Tillers became increasingly female as flowering phenology progressed. This gender variation is possibly adaptive because pollination efficiency is maximized by plant height. Natural selection may favor a shift toward femaleness to maximize reproductive fitness in small, late-developing tillers.     

浑善达克沙地榆树疏林幼苗更新空间格局

榆树疏林广泛分布于浑善达克沙地,是适应半干旱、半湿润气候的沙地植被类型.采用Ripley的K函数统计方法,分析了浑善达克沙地固定沙丘与丘间低地封育状态下的榆树幼苗空间分布及更新格局.结果表明:两种生境下榆树幼苗密度分别为88株/hm2和77株/hm2,丘间低地更适合幼苗的生长.固定沙丘和丘间低地榆树幼苗均呈聚集分布,但丘间低地的幼苗聚集强度更高.固定沙丘上榆树幼苗与成熟树种群在小尺度上呈负关联,而丘间低地幼苗与成熟树种群呈现较显著的正关联,但二者在大尺度上均无关联性.研究对揭示浑善达克沙地榆树幼苗分布、更新空间格局及其恢复保护具有重要意义.     

Cocksfoot (Dactylis glomerata) Grown for Production of Seed

In grasses grown for production of seed under field conditions,it has been found that only a small proportion of tillers produceinflorescences. For a period of 23 weeks from 4 February 1963a study was made of cocksfoot grown for production of seed inan attempt to discern whether the ability of tillers to becomereproductive was related to specific morphological features.Most tillers which initiated spikelets were rooted, and rootsquickly developed on unrooted tillers which had initiated spikelets.It appeared that larger tillers, judged on the basis of dry-weight,were more likely to become fertile than smaller tillers; importantfeatures of tiller size were the length of the stem and theweight of green leaf (lamina) borne by the tiller. The potentialnumber of inflorescences was reduced considerably by the death,in June, of tillers with completely differentiated apices.     

不同载畜率下短花针茅分蘖数量对内源激素浓度的响应

放牧是荒漠草原最主要的利用方式之一,载畜率的变化严重影响着植物的生长发育;而内源植物激素是调节植物生长发育的开关,且植物在不同的生长发育阶段具有不同的生理要求和环境适应能力。通过测定放牧条件下短花针茅(Stipa breviflora)分蘖叶内源激素的变化,研究短花针茅分蘖生长对放牧的响应,并分析了分蘖数量受内源激素影响的机制。结果表明,(1)内源激素与载畜率之间存在显著二次相关关系,说明放牧能够显著增加内源激素的浓度(P0.05),但这种相关只存在于中、小株丛的短花针茅中。(2)其次,放牧能够在一定程度上影响短花针茅植株个体分蘖的数量(P0.05),重度放牧是增加短花针茅植株个体分蘖数量最显著的载畜率。(3)过高浓度的生长素(IAA)会抑制短花针茅的分蘖数量(P0.01)。而细胞分裂素(CTK)与短花针茅的分蘖数量之间尚未发现相关关系。     

A New Species of Gall Midge (Diptera: Cecidomyiidae) Infesting Switchgrass in the Northern Great Plains

A new species of gall midge, Chilophaga virgati Gagn?? (Diptera: Cecidomyiidae), collected from tillers of switchgrass at Brookings, South Dakota (44.31134?? N, 96.78374?? W) is described here. Plant morphological symptoms of infestation and frequency of tillers infested are also provided. Full-grown larvae of C. virgati were found inside the sheath of the flag leaf of reproductive tillers of clonally replicated spaced plants of a selected southern upland population of switchgrass during October 2008 and 2009. Infested tillers were shorter and lighter than normal tillers and had panicles that were partially encased in the sheath of the flag leaf due to reduced elongation of the peduncle as a result of the feeding of larvae of C. virgati at the proximal end of the panicle and in the intercalary meristem area of the peduncle. Variation was found among 10 genotypes for percentage of tillers infested by C. virgati, with a range from 7.2% to 21.8%. No difference was found between years for infestation rate (12.7% in 2008 and 14.3% in 2009). The mass of infested tillers was 35% that of normal tillers, and infested tillers produced no appreciable amount of viable seeds. Results of this research revealed that C. virgati had direct negative impacts on biomass and seed production in spaced plant nurseries of switchgrass. C. virgati was also observed in seeded swards of northern upland switchgrass cultivars, but its impact in seeded swards has not yet been determined.     

Ecophysiological behavior ofArtemisia ordosica on the process of sand dune fixation

The population structure and water relations ofArtemisia ordosica were studied at different stages of the sand dune fixation process. Vegetation coverage and biomass increased as the sand dune fixation process progressed. In contrast, individual growth rate decreased in the late fixation stage. On fixed sand dunes the modal age ofA. ordosica plants was higher and seedlings or saplings were rearely observed. On active sand dunes, settlement of seedlings was regulated by sand mobility; that is, seedlings were observed only when sand mobility was below 10 cm per year. Leaf transpiration was highest in active sand dunes. Stand transpiration in fixed sand dunes was lower than in semi-fixed sand dunes. These differences in transpiration were related to a decrease in soil water availability, which was affected by the increase in the aeolian fine soil component during the course of sand dune fixation. The reduction in soil water status and the cessation of sand movement were considered to be important factors in the decline of theArtemisia ordosica community.     

Tolerance and compensatory response of rice to sugarcane borer (Lepidoptera: Crambidae) injury

A 3-yr field experiment was conducted to evaluate the tolerance and compensatory response of rice (Oryza sativa L.) to injury caused by sugarcane borer, Diatraea saccharalis (F.), as affected by cultivar (Cocodrie, Francis, and Jefferson), stage of crop growth during which the injury occurred (third tiller stage, panicle differentiation stage, and heading stage), and sugarcane borer density. The proportion of rice tillers with sugarcane borer injury (leaf and leaf sheath injury and/or stem injury) was lower when injury occurred at the third tiller stage (0.05) than at panicle differentiation (0.19) and heading (0.18). When injury occurred at the two latter stages, both the proportion of tillers with injury and the proportion of tillers with stem injury were negatively correlated with rainfall. Rainfall resulted in dislodgement and mortality of sugarcane borer eggs and larvae before the larvae entered the stems. Rice plant density in this study (111.1 plants/m2) was higher than recorded for previous research on rice compensation using potted rice or conducted in low-density hill production systems (26.7-51.3 plants/m2). Two mechanisms of within-plant tolerance/compensation were observed. Stem injured plants produced approximately 0.69 more tillers than uninjured plants, whereas tillers with leaf and leaf sheath injury produced larger panicles, up to 39.5 and 21.0% heavier than uninjured tillers, when injury occurred at third tiller stage and at panicle differentiation, respectively. Rice yield was not reduced with up to 23% injured tiller and up to 10% injured stems at the third tiller stage, 42% injured tillers and 17% injured stems at panicle differentiation, and 28% injured tillers and 14% injured stems at heading. Significant between-plant compensation was not detected, suggesting competition between adjacent plants is not significantly reduced by injury. Our results suggest that rice can tolerate and/or compensate for a level of stem borer injury previously considered to be economically damaging.     

Environmental factors and ground disturbance affecting the composition of species and functional traits of ground layer lichens on grey dunes and dune heaths of Estonia

A unique, species‐rich and endangered lichen biota can be found on European coastal and inland sand dunes. However, it is increasingly affected by natural succession as well as by anthropogenic disturbances. We studied lichen diversity on the grey dunes and dune heaths of coastal and inland regions of Estonia. A total of 28 study plots were investigated; in each 0.1 ha study plot general environmental variables and anthropogenic disturbances were described and all epigeic lichen species were identified. We found 66 lichenized fungus (lichen) species, including several rare and ten red‐listed lichens. Multivariate analysis (DCA, CCA) was performed to examine gradients in species composition and to relate variation in species data to environmental factors. In addition, we used redundancy analysis (RDA) to relate variation in species’ trait composition to environmental factors. Species composition on grey dunes differed significantly from that on dune heaths. The characteristic species for grey dunes are, besides several Cladonia species, foliose lichens, e.g. Hypogymnia physodes, Parmelia sulcata and Peltigera spp. Also species’ traits composition was different for either habitat, indicating that sorediate lichens, foliose lichens, lichens with cyanobacterium as the main photobiont, and sparsely branched Cladonia species dominate on grey dunes, while esorediate, green‐algal, crustose and richly branched fruticose lichens are common on dune heaths. Soil pH was the most essential environmental variable for determining both species composition and species’ traits composition. The composition of lichen species was also significantly influenced by forest closeness, soil Mg content and cover of bare sand; the effect of ground disturbances was low compared to the effect of these environmental factors. To protect and conserve the species‐rich lichen biota, it is necessary to protect the dune habitats from building activity, to avoid overtrampling in recreation areas and to regularly remove shrubs and trees.     

Studies on Selection of Valuable Somaclonal Mutants in Silage Maize

The calli were induced from young embryo, shoot apex, young leaf, young infiorescences, and hypocotyl of silage maize (Zea mays). The inducing freguency of young embryo was higher than the hypocotyL but the latter was not affected by season changes. The induction of calli were different in response to different kinds and concentration of hormones. Plantlet were regenerated from repetitive subcultured calli, among which three plant lines with characteristics of more tillers and early maturity were selected. Two of the plant lines with characteristics of more tillers and early maturity were selected. Two of the plant lines have become new inbred lines: 8501 and 8502. Through several generations of experimental hybrid combination "Baidan~ 8502" characterized by high silage yield, disease resistant, prolong green period and abundant tillers, has been obtained. The silage yield was 75000~105000 kg/hm2 which accounted for 40% more than the CK variety and commercial varieties.     

Water mites as indicators of natural aquatic ecosystems of the coastal dunes of the Netherlands and northwestern France

A large number of coastal dune waters in the Netherlands and northwestern France have been investigated for the occurrence of water mites. Dune waters turned out to be very rich in water mite species. In the Dutch dunes, 110 species of water mites have been found; this is 50 % of the total number of water mite species present in the Netherlands. In the French dunes 64 species have been found. The water mites most characteristic of the coastal dunes are the temporary water species. Dune areas with a high-lying hinterland have a water mite composition much different from dune areas with a low-lying hinterland. This can be explained by the existence of a very different hydrology. During the last century human activity affected the ground water of dunes. Afforestation and extraction of ground water for drinking water purposes caused a lowering of the ground water table. As a result, many dune slacks dried out. Moreover, the infiltration of river water caused an eutrophication of the ground water. Nowadays, the dunes most rich in typical water mite species are the dunes in which neither infiltration of river water nor extraction for drinking water purposes, occur. It can be concluded that water mites are good indicators for dune areas with a natural hydrology.     

Performance of two Picea abies (L.) Karst. stands at different stages of decline

Summary The annual replacement of tillers of Agropyron desertorum (Fisch. ex Link) Schult., a grazing-tolerant, Eurasian tussock grass, was examined in the field following cattle grazing. Heavy grazing before internode (culm) elongation seldom affected tiller replacement. Heavy grazing during or after internode elongation, which elevates apical meristems, increased overwinter mortality of fall-produced tillers and reduced the number and heights of these replacement tillers. Unexpectedly, tussocks grazed twice within the spring growing season tended to have lower overwinter tiller mortality, greater tiller replacement, and larger replacement tillers than tussocks grazed only once in late spring. These responses of twice-grazed tussocks, however, were still less than those of ungrazed tussocks or tussocks grazed moderately in early spring. The presence of ungrazed tillers on partially grazed tussoks did not increase the replacement of associated grazed tillers relative to tillers on uniformly grazed plants. This result indicates that resource sharing among tillers, if present, is short-lived or ecologically unimportant in this species. Although A. desertorum is considered grazing-tolerant, tiller replacement on heavily grazed tussocks, particularly those grazed during or after internode elongation when apical meristems were removed, was usually inadequate for tussock maintenance. These observations at the tiller (ramet) level of organization in individual tussocks (genet) may explain the often noted reduction in stand (population) longevity with consistent heavy grazing.     

Spatial arrangement of tiller replacement in Agropyron desertorum following grazing

Summary The spatial arrangement of tiller replacement was assessed on grazed and ungrazed tussocks of Agropyron desertorum (Fisch. ex Link) Schult. for three annual cycles. Frequency distributions of the number of replacement tillers per single progenitor were also determined. Tiller replacement was usually greater on the perimeter of tussocks than within the core, with or without grazing. Replacement was inversely related to grazing intensity, both on the perimeter and within the core of tussocks. Heights of replacement tillers on the perimeter or within the core seldom differed. Furthermore, grazing seldom affected the number of replacement tillers per progenitor. Greater tillering on the perimeter than within the core indicates that the tussocks were expanding. Apparently, grazing neither enhances tussock expansion and subsequent disintegration, nor does it necessarily lead to patches of tillers (multiple tillering per progenitor) within tussocks of A. desertorum.     

Insights on the role of tillering in salt tolerance of spring wheat from detillering

Tillering is reduced by salinity, with the primary and secondary tillers being more affected than is the mainstem. To understand the importance of tillering in the salt tolerance of wheat plants, two contrasting genotypes of spring wheat (Triticum aestivum L.) were grown in a greenhouse under saline or non-saline conditions and were subjected to five progressive levels of detillering. Regardless of the genotype and salinity, shoot dry weight, seed yield and seed number per plant were all significantly decreased in the treatments where only one or two tillers per plant remained compared with the untouched treatment (more than three tillers), whereas these same variables per tiller tended to be increased on a per tiller (mainstem or substem tiller) basis. The increased seed yield per tiller observed with tiller reduction may be attributed to the enhanced seed number within the spikelet. Under saline conditions, the reductions in shoot dry weight, seed yield and seed number per plant for the salt-tolerant genotype Kharchia were of a greater magnitude in the treatments where only one or two tillers per plant were present compared with the untouched treatment, whereas the magnitude of this reduction in the salt-sensitive genotype Sakha 61 was decreased.     

Effects of fire frequency on survival,growth and fecundity of Paspalum quadrifarium (Lam.) in a grassland of the Flooding Pampa (Argentina)

Abstract Fire and grazing are important factors in the regulation of the grassland structure of the Flooding Pampa (Buenos Aires Province, Argentina dominated by Paspalum quadrifarium plants (henceforth ‘pajonal’)). Winter burning of pajonal is a practice that increases P. quadrifarium growth and its nutritious value for cattle. The objective of this work was to determine the responses of different demographic variables of P. quadrifarium growing in a grassland managed with different fire frequencies. The work was carried out in a pajonal situated in San Ignacio (Ayacucho county, Buenos Aires Province, Argentina). The treatments were: high fire frequency (0.8 fires per year) and low fire frequency (0.4 fires per year). The population of P. quadrifarium was affected by fire frequency. Biomass, number of tillers, and the relative production of tillers per plant did not change with fire frequency. Plant height was negatively affected by fire frequency. Whereas no plant mortality was observed in high fire frequency, 30% of the mature plants died at the end of the experiment in low fire frequency. In both treatments, plant mortality was size‐dependent and juvenile plants were more affected than mature ones. Burning had an immediate negative effect on mature and juvenile plants in terms of fecundity, survival of tillers and basal cover. Tiller survival and fecundity were significantly lower in burned plants than in unburned ones. In the high fire frequency treatment the number of ramets and/or genets and basal cover were greater than in the low fire frequency treatment.     

Effects of bison grazing on Andropogon gerardii and Panicum virgatum in burned and unburned tallgrass paririe

Summary Responses to clipping and bison grazing in different environmental contexts were examined in two perennial grass species, Andropogon gerardii and Panicum virgatum, on the Konza Prairie in northeastern Kansas. Grazed tillers had lower relative growth rates (RGR) than clipped tillers following defoliation but this difference was transient and final biomass was not affected by mode of defoliation. Grazed tillers of both species had higher RGR throughout the season than ungrazed tillers, resulting in exact compensation for tissue lost to defoliation. However, A. gerardii tillers which had been grazed repeatedly the previous year (1988) had reduced relative growth rates, tiller biomass and tiller survival in 1989. This suggests that the short-term increase in aboveground relative growth rates after defoliation had a cost to future plant growth and tiller survival.In general, the two species had similar responses to defoliation but their responses were altered differentially by fire. The increase in RGR following defoliation of A. gerardii was relatively greater on unburned than burned prairie, and was influenced by topographic position. P. virgatum responses to defoliation were similar in burned and unburned prairie. Thus grazing, fire, and topographical position all interact to influence tiller growth dynamics and these two species respond differently to the fire and grazing interaction. In addition, fire may interact with grazing pattern to influence a plants' grazing history and thus its long-term performance.     

古尔班通古特沙漠西部梭梭种群退化原因的对比分析

古尔班通古特沙漠植被的建群种梭梭在沙漠的低平地和小沙丘(高度<5 m)区域发生大面积退化死亡,而在大沙丘(高度>10 m)生境中梭梭却长势良好。对此分析了梭梭林枯死植株的空间分布、活株和死株的年龄结构,研究了地下水埋深以及对比低平地、小沙丘和大沙丘3种生境土壤理化性质对梭梭生存的影响。发现梭梭死亡植株在观测的19个样点中的15个呈显著的集群分布,表明梭梭植株死亡并非是种内自疏。梭梭各年龄级植株均在死亡,说明死亡与植株年龄关系不大。退化区地下水埋深过浅或过深均对梭梭生长不利,表明地下水埋深对梭梭生长产生显著影响。低平地和小沙丘区土壤电导率高,土壤水分入渗速率慢,且0-90 cm深度范围梭梭侧根数和成活的梭梭幼苗幼株数较少,与梭梭正常生长的大沙丘区明显不同。综合分析认为梭梭退化主要是由自身的根系分布特性,以及地下水位、土壤盐分、土壤水分入渗变化等综合作用,实质是梭梭水分利用受限和种群更新不良引起的。     

Soil pH and species diversity in coastal dunes

Soil pH was measured at two different spatial scales in coastal dunes on Norderney, North Sea, and in Mecklenburg-Vorpommern, Baltic Sea, Germany. Relationships between the variability in soil pH, species richness and species diversity are presented. Species richness and diversity were highest in grey dunes, where soil pH was at intermediate levels; both variables were lower in yellow and brown dunes. The variability in pH increased with increasing species diversity and also with scale. Overall, soil pH variability decreased with increasing vegetation cover. The lowest pH heterogeneity was found in heath dominated by Empetrum nigrum L. and grey dunes dominated by Campylopus introflexus (Hedw.) Brid. Increasing abundance of dominant species and decreasing species diversity of vegetation apparently reduces soil heterogeneity. Decreasing species diversity of vegetation is likely to explain decreasing variability in soil pH.     

Tiller demography in seashore populations of Agrostis stolonifera,Festuca rubra and Poa irrigata

Abstract. The dynamics of tillers in natural populations of three cohabiting perennial grass species, Agrostis stolonifera, Festuca rubra and Poa irrigata (= Poa pratensis ssp. irrigata) were studied for five years in a Baltic seashore meadow. The process of tiller population maintenance was very dynamic. Both birth and death rates of tillers were high, particularly in A stolonifera, and the turnover rate of the populations was high. Recruitment was mainly by vegetative tillers, produced continuously throughout the growing season. The proportion of flowering tillers was low, but varied between years. Considerable year-to-year variation was also found in birth and death rates. Despite this between-year variation and the differences found between species in flowering frequency, pattern of survivorship and tiller longevity, population sizes of the species remained relatively constant.