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1.
We investigated how soil disturbance from roadworks affects the population structures of roadside shrubs in an agricultural landscape of southern New South Wales, Australia. Size structures of Acacia pycnantha, A. montana and A. decora were assessed, and a separate dendroecological study undertaken. On a regional scale, populations were expanding, but classification of structures showed distinct groups of colonising, stable and senescent populations. Soil disturbance from previous roadworks was recorded in 88% of populations, and there was a significant relationship between major recruitment and roadworks events in Acacia populations situated along bitumen roads. For Acacia species, soil disturbance from roadworks are analogous to periodic disturbance from a natural fire regime, which in conjunction with historical changes in grazing pressure, are suggested as the main causes of increased Acacia recruitment. Ongoing management of disturbance regimes in roadside environments may be critical to Acacia persistence and associated fauna habitat.  相似文献   

2.
Flowering phenology, soil seedbank and the impact of fire, weeds and grazing were investigated in two rare Acacia taxa restricted to the agricultural district north of Perth Western Australia. Acacia aprica is known from six extant populations and one extinct population. Five of the extant populations are restricted to linear road reserves with the sixth population located in a small native vegetation remnant. Acacia cochlocarpa ssp. cochlocarpa is known from a single population also situated on a road verge. Size class structure, levels of canopy death and an absence of juveniles indicated that all populations are in decline. Flowering intensity and success varied between populations and years in A. aprica and between years in A. cochlocarpa ssp. cochlocarpa. Seed bank analysis indicated that seeds were patchily distributed while experimental fires demonstrated that such events could break seed dormancy and promote germination. Both taxa have similar germination physiologies and showed increased germination after seeds were exposed to heat. Following emergence, however, competition with annual weeds had a negative impact on seedling growth and survival in both taxa. While vertebrate grazing had some influence, weeds were the major inhibitory influence on recruitment. Reduced fire frequencies since fragmentation may be responsible for population decline in both taxa but other site specific factors such as weeds and grazing may affect the establishment of seedlings following fire.  相似文献   

3.
An endemic dwarf birch, Betula apoiensis, is critically endangered, and two populations of this species are restricted to the ridges of Mt. Apoi in Hokkaido, Japan. We observed the flowering phenology, pollen dispersal, and viable seed production and conducted pollination experiments in order to examine pollen limitation and hybridization with a sympatric congener, B. ermanii. B. apoiensis flowered earlier than B. ermanii but had a more variable flowering time among trees than B. ermanii. The female flowering of B. apoiensis temporally overlapped with the male flowering of B. ermanii as well as with that of B. apoiensis. Pollination experiments demonstrated that seed set and seed germination were higher in female flowers outcrossed than in those that were non-pollinated, selfed, hybridized with B. ermanii pollen, or pollinated naturally. A few selfed or hybrid seeds were filled and germinated, which indicates that self-incompatibility and reproductive barriers are not complete. Logistic regressions of local density of conspecific trees on natural seed set and seed germination were significantly positive. These results suggest that B. apoiensis is pollen-limited.  相似文献   

4.
With the rapid conversion of tropical forests in Asia to plantation forests for timber or biofuel production there is a need to determine if these forests serve any viable role in wildlife conservation. We used infra-red trip cameras to survey for large terrestrial mammals within an Acacia/secondary forest matrix being created for pulpwood production in Sarawak, Malaysia. We detected at least 27 species of mammals within the matrix and 18 species were detected in both Acacia and secondary forest. Using occupancy modeling to determine important covariates for seven mammal species within the project area, six of these species were sensitive to forest type, and most were sensitive to the amount of secondary forest within 1 km of the sample point. For four species (sun bear, Helarctos melayanus; common porcupine, Hystrix brachyura; mousedeer, Tragulus spp.; and pig-tailed macaque, Macaca nemestrina), the mean distance of detection from large secondary forest blocks was significantly closer than expected from the distribution of sample points. Most species used Acacia forest less frequently than secondary forest, possibly for transit or foraging, with the exception of bearded pigs (Sus barbatus), sambar (Rucervus unicolor), and civets which were more common in Acacia stands. The amount of secondary forest preserved within forest plantations seems to be the best measure of conservation potential for these industrial forests. Forest plantations can provide a conservation value if managed properly and those retaining significant amounts of secondary forest should be eligible for a base level of certification as they comprise a significant portion of the landscape in this region.  相似文献   

5.
Seeds stored for a long time may be difficult to germinate under standard conditions and are thus considered not to be viable. By using conductivity test an accession of Brassica rapa L. ssp. rapa with viable seeds was identified among seed material previously declared dead based on traditional filter paper germination tests. The identified accession was germinated by means of long time germination on aseptic agar based growth medium. After transplanting, weaning and vernalisation 0.8% of the seeds could be grown to plants, which flowered and produced seeds.  相似文献   

6.
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7.
A collection of seeds from five Acacia species was made in Egypt in 1856. Since then, the seeds have been stored at room temperature in different Swedish museums. Due to the extreme longevity within the seeds of Acacia and related species, germination tests were performed on the now 151-year old seed. Seeds of two of the five species tested germinated. The first, Acacia farnesiana (L.) Willd., had two seeds germinate, and Acacia melanoxylon R. Br. ex Ait. f. had one seed germinate. In addition, DNA was extracted from the aged seed and DNA preservation was analyzed. Four of the tested species displayed well preserved DNA, whereas DNA from Albizia lebbeck (L.) Benth. showed signs of degradation. The 151-year longevity of the Acacia seeds is among the longest of dry-stored seeds reported. Several independent studies now report on extreme survival capacity for Acacia and related genera suggesting that these genera are suitable for studies on the characteristics of seeds with long storage performance. The results also demonstrate that herbaria and seed collections stored in museums and institutional depositories can be alternate sources of plants genetic material and should be given conservation attention.  相似文献   

8.
Terrestrial orchids typically produce numerous small seeds that contain very small nutrient reserves. The seeds are structurally adapted for wind dispersal but little is known about their fate after dispersal. Some studies of seed viability in situ indicate survival for up to two years in temperate orchid species. Seeds stored in the laboratory may last much longer. We investigated seed viability of seven North American orchid species with seed packets buried in a range of soil and wood substrates within their natural habitats. In Goodyera pubescens most seeds germinated within one year. Four other species continued to germinate sparsely during the observation period, but after almost seven years many seeds were still viable. In one species, Liparis liliifolia, seeds that had been in situ for four years had germination rates as high as 68% when sown in vitro with a compatible fungus. The remaining two species did not germinate during the observation period but the seeds were judged to be intact and tested positively for viability after four years in the ground. These observations are interpreted as different species-specific strategies for in situ germination and their seed bank potential is discussed.  相似文献   

9.
Many ecological studies have pointed out maternal effects in plants and shown that plant maternal environment influences germination of their seed and subsequent seedling growth. However, few have tested for maternal effects induced by soil macroorganisms. We tested whether two earthworm species (Aporrectodea caliginosa and Lumbricus terrestris) trigger such maternal effects on seed germination and seedling growth of three plant species (Veronica persica, Poa annua and Cerastium glomeratum). Our results show that, through maternal effects, A. caliginosa enhanced seed germination (V. persica and P. annua) and seedling growth (C. glomeratum and P. annua) while L. terrestris reduced seed germination only in V. persica. In some cases, the increase in germination rates of seeds produced in the presence of earthworms was associated with a reduction of nitrogen content in seeds. These results show that earthworms induce maternal effects in plants and that the size and direction of these effects depend on the combination of plant and earthworm species.  相似文献   

10.
The short-term belowground transfer of nitrogen from nitrogen-fixing trees to companion trees has never been studied in the field. A 15N pulse-labeling study was conducted in a mixed plantation of Acacia mangium and Eucalyptus grandis at the peak of leaf area, 26 months after planting. 15N–NO3− was injected into the stem of one big Acacia tree in three plots. 15N was traced over 2 months in the labeled Acacia tree as well as in neighboring Eucalyptus trees. For both species, young leaves were sampled, as well as fine roots and the rhizosphere at a distance of 0.75 m and 2.25 m from the labeled tree. The 15N atom% was also determined in the wood, bark, branches and total foliage of the 3 labeled Acacia trees and 9 Eucalyptus trees, 60 days after labeling. Most of the leaves, fine roots and rhizosphere samples of both species were 15N enriched from 5 days after labeling. The δ15N values were higher at a distance of 0.75 m than at 2.25 m in Acacia roots, but were similar at both distances in Eucalyptus roots and the rhizospheres. The wood and bark of Eucalyptus trees sampled at a distance of 6.2 m from the labeled Acacia trees were 15N enriched. This shows belowground N transfer from Acacia to Eucalyptus trees in the field during the first few days after labeling. This facilitation process may provide a significant amount of the nitrogen requirements of trees close to N-fixing trees in mixed forests.  相似文献   

11.
The impact of forest tree leaf litters on microbial activity and nutrient status of red laterite soil was tested for the ecological suitability of Cassia siamea, Shorea robusta, Acacia auriculiformes and Dalbergia sissoo, which are typically used for afforestation of wastelands in eastern India. The objectives were to compare seasonal variation in soil enzyme activity in 30-years old afforested sites, and to study nutrient status and microbial biomass and function during short-term in-situ incubation of litter in decomposition pits. In afforested soils, enzyme activities significantly varied between litters and seasons. All enzyme activity except invertase dominated in the soils containing Dalbergia and Cassia litters compared to the others. The seasonal effect was enzyme-dependent, with amylase and cellulase reaching peaks during the rainy season but invertase activity showed a reverse trend with lowest values in rainy season, except in Acacia soil, and protease activity was lowest in the soil containing Cassia and Dalbergia during the rainy season. Dehydrogenase activity was negligible in the soils containing Shorea and Acacia, but remained high with respect to Dalbergia and Cassia during all seasons. The decomposition pit study showed significant increase of soil nutrients with respect to litter types and intervals, except with respect to electrical conductivity. Cassia and Dalbergia litters enabled notable increase of soil nutrients than Shorea and Acacia. The soil enzyme activity, in general, increased with duration of litter decay, but microbial biomass C (MBC) decreased over time except in Shorea. Therefore, the enzyme rates normalized to the MBC indicated inverse relations for all enzymes, except in the soil containing Shorea. A positive relationship existed between MBC and soil respiration in Cassia, Acacia and Dalbergia. Analysis of variance revealed main effects of litter types for increasing protease, MBC and CO2 output, and a main effect of intervals for enhancing enzymes other than cellulase. Rates of soil respiration were greater in soils contain Cassia and Dalbergia, and showed significant differences between litters and between intervals. All enzymes were significantly correlated with electrical conductivity, organic carbon and available phosphorus contents, and all enzymes except invertase were correlated with nitrate concentrations. The acidic soil pH did not affect enzyme activities, and soil nutrients exerted only weak effect on MBC and respiration. Our study showed that leaf litters of Cassia and Dalbergia trees improved the nutrient status and microbial activity in soil more so than Shorea and Acacia litters, and therefore, afforestation using Cassia and Dalbergia trees may be particularly suitable for soil restoration in tropical laterite wastelands.  相似文献   

12.
Investigations of vegetation stress along non-paved roads treated with a range of magnesium chloride (MgCl2) application rates utilized 60 roadside and 79 drainage plots on 15 and 18 roads, respectively. Evaluations were completed of foliar damage, plant health, biotic and abiotic damage incidence and severity, soil and foliar chemistry and other common site and stand characteristics of Pinus contorta, Populus tremuloides, Picea engelmannii, Abies lasiocarpa, and lower elevation plots dominated by shrubs and grasses. High concentrations of soil magnesium and chloride (400–500 ppm), high foliar chloride (2,000–16,000 ppm depending on species) and high incidence of foliar damage were measured in roadside plots along straight road segments in the first 3 to 6.1 m adjacent to treated roads. In drainage plots, where water is channeled off roads, high concentrations of both magnesium and chloride ions and associated foliar damage were measured between 3 and 98 m from the road. High incidence of foliar damage and elevated ion concentrations were not apparent in control plots along non-treated roads. Lodgepole pine appeared to be the most sensitive species, while aspen accumulated the most chloride and exhibited the least amount of damage. Foliar chloride concentrations strongly correlated with percent foliar damage for all species (r?=?0.53 to 0.74, p?<?0.0001) while the incidence of biotic damages did not correlate well. Positive relationships between foliar chloride and magnesium chloride application rates were strong and can be used to predict foliar concentrations and subsequent damage to roadside trees.  相似文献   

13.
针对玉米繁种阶段亲本种子播前分级效率低、筛面自净效果差的问题,该研究提出一种变幅振动筛分方法,并设计了种子分级振动筛装置,对驱动机构和自净清筛装置进行设计与分析。在喂入量2.5 kg/s的条件下,以京科968玉米种子为试验对象,以分级合格率、作业时间和卡种数量为试验指标,通过四因素（进料口高度、振幅、振动频率和筛面倾角）三水平Box-Behnken试验,建立各因素与试验指标间的回归模型,并对参数进行优化。结果表明,影响变幅振动式分级装置分级合格率的主次因素顺序为振动频率、筛面倾角、振幅和进料口高度,影响作业时间的主次因素顺序为振动频率、振幅、筛面倾角和进料口高度;卡种数量具有较大的随机性,当振幅和振动频率都较低时,筛面卡种数量急剧增多,自净效果极差。最优参数组合为进料口高度19 mm、振幅5 mm、振动频率8.25 Hz、筛面倾角7°,模型优化预测结果为分级合格率88.04%,作业时间40 s。在最优条件下的验证试验结果为分级合格率89.55%、作业时间39 s,平均卡种数量8粒,与预测结果基本一致,较等幅振动式分级装置的分级合格率提高3.25个百分点,作业时间减少4 s,平均卡种数量减少2粒,作业性能优于等幅振动式分级装置。分级装置分级效率达0.33 t/h,各项指标均满足相关设计要求。研究结果可为繁种阶段种子分级装备的设计提供参考。  相似文献   

14.
The emission of Platinum–group elements (PGE) from automobile catalytic converters has led to rapid increases in Pt, Pd and Rh concentrations in roadside media. This paper examines the temporal variability of PGE levels in road dusts and roadside soils on a seasonal basis over a 12 month period. Road dust and roadside soil samples were analysed by ICP–MS following microwave digestion and cation exchange. Concentrations of PGE in all road dust and roadside soil samples are elevated above local background concentrations with maximum levels of Pt?440 ng g?1, Rh?91 ng g?1 and Pd?440 ng g?1. Systematic seasonal variations in PGE levels are observed in both sample types and the temporal distribution of PGE levels is affected by a number of factors including surface morphology and rainfall. PGE ratios in road dusts and soils are consistent with known catalytic converter composition throughout the sampling period indicating the PGE remain associated during mobilisation and transport.  相似文献   

15.
The incorporation of biological control organisms in seeds may help control pathogens and improve seedling performance. The aim of this study was to determine the effects of biopriming bean seeds with Trichoderma spp. and Bacillus subtilis using physiological conditioning, suspensions of biological structures and film coating techniques. Biopriming treatments with suspensions of biological structures were performed using the commercial products Agrotrich plus® and Rhizoliptus®. Water restriction was achieved using a PDA?+?Manitol (?0.7?MPa) medium for both Trichoderma spp. and Bacillus subtilis. Fifty disinfected bean seeds were placed in each petri dish. When the first radicle protrusion appeared in a seed, the other seeds were removed and dried in the laboratory environment for 48?h. Film coating was performed with the addition of the Color Seed® (150?mL kg?1) polymer to a treatment solution containing either the Trichoderma spp. or the Rhizoliptus product. Seeds were dried for 48?h in the laboratory. Seeds were covered and treated with one or both organisms. Biopriming with spore or bacterial cell suspensions promoted bean seedling growth, and the other techniques were not required to potentiate these benefits. Covering the primed bean seeds reduced seed quality. Both Trichoderma spp. and Bacillus subtilis promote bean seedling growth, benefitting the seedling even after it becomes independent of the seed reserves.  相似文献   

16.
电磁振动式拌浆育秧水稻芽种播种机优化试验   总被引：2，自引：1，他引：1  
为了探明电磁振动式拌浆育秧水稻芽种播种机工作性能的影响规律并获得因素的最优组合,该文对拌浆育秧水稻芽种播种机进行了单因素和多因素播种试验。通过回归分析建立了挡种板开口高度、行走速度、排种盘振动速度和隔振橡胶垫刚度4个因素与播种量和播种合格率的单因素、多因素数学模型,分析了各影响因素及交互作用对播种量和播种合格率的影响规律及机理,进行了参数优化。结果表明,挡种板开口高度小于7mm时,堵种现象较严重;挡种板开口高度和排种盘振动速度大,播种量和播种合格率大,行走速度大,播种量和播种合格率小;小的行走速度与大的排种盘振动速度组合,有利于提高播种合格率。参数的最优组合为挡种板开口高度9.3mm,行走速度50.1mm/s,排种盘振动速度13.1m/s,隔振橡胶垫刚度1248.9N/mm。可靠性为95%的播种合格率总区间为86.72%～93.54%。该文为播种机的优化设计提供依据。  相似文献   

17.
Nutrient seed priming is a strategy to increase the seed reserves of mineral nutrients as primary source for mineral nutrition during seedling development and early growth. The present study investigates the effects of zinc (Zn) and manganese (Mn) seed priming on growth and nutritional status of soybean under conditions of Zn and Mn limitation. Nutrient seed priming increased the natural seed reserves for Zn by, approximately, sixfold and by fivefold for Mn; however, 40–60% of the primed nutrients were adsorbed to the seed coat. Zinc seed priming was able to maintain plant growth for 5 weeks in the same way as Zn supply via the nutrient solution. It is concluded that nutrient seed priming offers perspectives to improve seed quality of soybean for early seedling development under limited nutrient supply or availability and needs further investigation on performance under various stress conditions.  相似文献   

18.
Morphological differences were observed between roadside (R) and agricultural field (F) biotypes of Ambrosia artemisiifolia, in which R-type seedlings were shorter and produced larger and heavier seeds under greenhouse grown conditions. Previous findings indicated that A. artemisiifolia R-types exhibited greater salt tolerance with respect to germination. However, the impact of biotype and salt tolerance on morphological variation has not been investigated in A. artemisiifolia plants. After performing replicated greenhouse experiments with both biotypes, it was shown that salinity level was a critical factor influencing both seedling and mature plant size and this response was dependent upon biotype. The R-type exhibited slight but significant increases in growth at low/mild salinity levels (50–100 mM) compared with non-saline conditions, while the F-type exhibited significantly reduced growth at the low/mild salinity levels. The reductions in growth of F-type plants in low/mild salinity were similar to those reductions of R-types observed in non-saline conditions. As both biotypes produced seeds at low/mild salinity levels, we conclude that low/mild salinity affects A. artemisiifolia plant size and overall growth rate, and secondly, certain F-type plants may acclimate to the roadside environment over time by reducing their size while producing larger seed under saline conditions. It is possible that this species may exhibit changes in morphology after several generations of exposure to saline roadside conditions. Toxicity due to salt treatment at high salinity (400 mM) was observed in both biotypes, whereas the R-type was more tolerant to both low and high salinity levels with respect to seed germination. Differential A. artemisiifolia growth responses which occur from seed germination to plant maturity may be partially attributed to its ability to tolerate saline soil conditions both under greenhouse and field conditions. This ability to tolerate saline conditions may be especially important in early spring when roadside soils experience increased salinity, caused by de-icing salt treatments applied during the winter season.  相似文献   

19.
In Arnica montana L. (Asteraceae) two subspecies are described, A. montana subsp. atlantica (AMA), present only on the Iberian Peninsula and A. montana subsp. montana (AMM) with a very wide distribution area. The morphological differences between the two subspecies are small and variable. Therefore, this concept is sometimes questioned. To establish the genetic background of the two subspecies, populations of AMA and AMM together with herbarium samples and DNA Bank material of AMM were tested with 12 microsatellite markers. A. montana propagates by seeds or by clonal propagation of its rhizome. In AMA, clonality was frequent while in AMM only one case of clonality could be identified. Therefore, further results were clone-corrected. Genetically, AMA separated very well from AMM with a GST between the subspecies of 0.81, genetically justifying the subspecies concept of A. montana. Genetic variability in AMA (Hexp?=?0.28) was lower than in the AMM populations (Hexp?=?0.70). A somewhat higher fixation index of AMA (FST?=?0.17, compared to an FST?=?0.08 for AMM) may indicate that geneflow in AMA is a bit more restricted than in alpine AMM. However, the fixation index of AMA is not deviating from Hardy–Weinberg equilibrium. No inbreeding was observed for AMA (FIS?=?0.10) and AMM (FIS?=?0.08).  相似文献   

20.
紫茎泽兰叶片凋落物对入侵地4 种草本植物的化感作用   总被引：5，自引：2，他引：3  
为了明确紫茎泽兰叶片凋落物对入侵地草本植物的化感作用, 研究了不同浓度紫茎泽兰叶片凋落物水提液对入侵地草本植物多年生黑麦草、白三叶、辣子草和紫花苜蓿种子萌发和幼苗生长的影响, 同时结合土培试验研究了叶片凋落物在入侵地土壤中的化感作用。结果表明, 除多年生黑麦草外, 水提液对其他3 种草本植物种子萌发均产生了显著的化感抑制作用, 且水提液的浓度越高抑制效果越强; 低浓度水提液对紫花苜蓿和辣子草的幼苗生长存在显著化感促进作用, 高浓度的水提液对除多年生黑麦草外的其他3 种植物幼苗的生长存在显著化感抑制作用, 水提液对多年生黑麦草幼苗生长的影响不显著; 土壤中按照50 g·kg-1的比例添加叶片凋落物后, 显著抑制了白三叶的生长, 而添加活性炭后, 白三叶的单株生物量相对于未添加活性炭的处理增加71.25%, 进一步证实叶片凋落物在土壤中的化感抑制作用。这说明外来入侵植物紫茎泽兰可能通过其叶片凋落物在入侵地土壤中降解, 释放化感物质, 抑制伴生植物的种子萌发和幼苗生长, 为自身创造有利的生长环境, 实现其成功入侵和扩张。  相似文献   

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