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1.
侧柏抗病单株对叶枯病抗性机制研究   总被引：1，自引：0，他引：1       下载免费PDF全文
本文比较测定了对叶枯病具有高度抗性的侧柏单株叶片中木质素和纤维素含量、苯丙氨酸解氨酶（ＰＡＬ）和超氧化物歧化酶（ＳＯＤ）、以及细胞含水量和肉质化程度。结果表明,抗病单株叶片细胞中木质素和纤维素的含量显著地高于普通的感病侧柏;抗病单株的ＰＡＬ活性和ＳＯＤ活性也明显高于感病株。并且发现ＰＡＬ活性和木质素含量之间具有高度相关性。抗病单株的细胞含水量和肉质化程度则显著地低于感病株。综上指标说明,抗病单株在生理生化和遗传上,明显地区别于普通感病株。  相似文献   

2.
The exotic tree Melaleuca quinquenervia (melaleuca) forms dense forests usually characterized by low plant diversities and dense litter biomass accumulations on forest floors of ecologically sensitive ecosystems, including portions of the Florida Everglades. We quantified litter accumulation in mature melaleuca stands and compared decomposition rates of melaleuca leaves with a sympatric native plant, either Cladium jamaicense (sawgrass) in sawgrass marshes or Pinus elliottii (slash pine) in pine flatwoods habitats that varied in soil types. Total litter accumulation in mature melaleuca forests prior to June 1997 ranged from 12.27 to 25.63 Mg ha−1. Overall, melaleuca leaves decomposed faster in organically rich versus arenaceous soils. Decomposition rates were lower for melaleuca leaves than for sawgrass in both melaleuca-invaded and uninvaded sawgrass marshes. In arenaceous soils of pine flatwoods, melaleuca leaf and pine needle decomposition rates were similar. Complete mineralization of sawgrass leaves occurred after 258 weeks, whereas melaleuca leaves had up to 14% and pine foliage had up to 19% of the original biomass remaining after 322 weeks. Total carbon (C) in intact decomposing leaves varied slightly, but total nitrogen (N) steadily increased for all three species; the greatest being a fourfold in sawgrass. Increases in N concentrations caused decreases in the C/N ratios of all species but remained within an optimal range (20–30) in sawgrass resulting in higher decomposition rates compared to melaleuca leaves and pine needles (C/N ratio >30). Slower decomposition of melaleuca leaves results in denser litter layers that may negatively affect recruitment of other plant species and impede their establishment in invaded communities.  相似文献   

3.
Vegetation recovery is a key measure to improve ecosystems in the Loess Plateau in China. To understand the evolution of soil microorganisms in forest plantations in the hilly areas of the Loess Plateau, the soil microbial biomass, microbial respiration and physical and chemical properties of the soil of Robinia pseudoacacia plantations were studied. In this study, eight forest soils of different age classes were used to study the evolution of soil microbial biomass, while a farmland and a native forest community of Platycladus orientalis L. were chosen as controls. By measuring soil microbial biomass, metabolic quotient, and physical and chemical properties, it can be concluded that soil quality was improved steadily after planting. Soil microbial biomass of C, N and P (SMBC, SMBN and SMBP) increased significantly after 10 to 15 years of afforestation and vegetation recovery. A relatively stable state of soil microbial biomass was maintained in near-mature or mature plantations. There was an increase of soil microbial biomass appearing at the end of the mature stage. After 50 years of afforestation and vegetation recovery, compared with those in farmland, the soil microbial biomass of C, N and P increased by 213%, 201% and 83% respectively, but only accounting for 51%, 55% and 61% of the increase in P. orientalis forest. Microbial soil respiration was enhanced in the early stages, and then weakened in the later stage after restoration, which was different from the change of soil organic carbon. The metabolic quotient (qCO2) was significantly higher in the soils of the P. orientalis forest than that in farmland at the early restoration stage and then decreased rapidly. After 25 years of afforestation and vegetation recovery, qCO2 in soils of the R. pseudoacacia forest was lower than that in the farmland soil, and reached a minimum after 50 years, which was close to that of the P. orientalis forest. A significant relationship was found among soil microbial biomass, qCO2 and physical and chemical properties and restoration duration. Therefore, we conclude that it is possible to artificially improve the ecological environment and soil quality in the hilly area of the Loess Plateau; a long time, even more than 100 years, is needed to reach the climax of the present natural forest. __________ Translated from Acta Ecologica Sinica, 2007, 27(3): 909–917 [译自: 生态学报]  相似文献   

4.
In this paper, we present a two-stage approach for characterizing the structure of Pinus sylvestris L. stands in forests of central Spain. The first stage was to delimit forest stands using eCognition and a digital canopy height model (DCHM) derived from lidar data. The polygons were then clustered (k-means algorithm) into forest structure types based on the DCHM data within forest stands. Hypsographs of each polygon and field data validated the separability of structure types. In the study area, 112 polygons of Pinus sylvestris were segmented and classified into five forest structure types, ranging from high dense forest canopy (850 trees ha−1 and Loreýs height of 17.4 m) to scarce tree coverage (60 tree ha−1 and Loreýs height of 9.7 m). Our results indicate that the best variables for the definition and characterization of forest structure in these forests are the median and standard deviation (S.D.), both derived from lidar data. In these forest types, lidar median height and standard deviation (S.D.) varied from 15.8 m (S.D. of 5.6 m) to 2.6 m (S.D. of 4.5 m). The present approach could have an operational application in the inventory procedure and forest management plans.  相似文献   

5.
In order to offer a scientific basis for cultivation and management of forests, effects of light radiation intensity on photosynthetic characteristics and water use efficiency of Platycladus orientalis and Pinus tabulaeformis were studied under different soil moisture contents. By adopting artificial control methods to soil moisture, and under simulated photosynthetic radiation (SPR), the net photosynthetic rate (P N), transpiration rate (T r), water use efficiency (WUE) and intercellular CO2 concentration (C i) of Platycladus orientalis and Pinus tabulaeformis in the semi-arid region of the Loess Plateau, were studied. Results are as follows: within the photon range of 0–2,200 μmol/(m2·s), P N, T r and WUE were enhanced with an increase in SPR in both species. P N and WUE of Platycladus orientalis and Pinus tabulaeformis, however, declined with continued increase in SPR. P N, T r, WUE and light saturation point (LSP) of Platycladus orientalis were higher than those of Pinus tabulaeformis, while light compensation point (LCP) of Platycladus orientalis was lower than that of Pinus tabulaeformis at the same soil moisture content. The efficiency of light energy utilization of Platycladus orientalis was higher than that of Pinus tabulaeformis; P N, T r and C i of Platycladus orientalis and Pinus tabulaeformis were enhanced by increasing soil moisture content, whereas WUE declined. At soil moistures of 7.90%, 13.00% and 19.99%, LSP of Platycladus orientalis was 1,275, 1,450 and 1,675 μmol/(m2·s) respectively, and LCP was 42, 25 and 13 μmol/(m2·s) respectively, with corresponding maximal net CO2 photosynthetic rates (P max) of 3.04, 4.06 and 5.53 μmol/(m2·s). At soil moistures of 7.83%, 13.04% and 20.15%, the LSP of Pinus tabulaeformis was 1,100, 1,325 and 1,500 μmol/(m2·s) respectively, and LCP was 60, 30 and 23 μmol/(m2·s), with P max of 1.08, 3.35 and 4.36 μmol/(m2·s) respectively. __________ Translated from Science of Soil and Water Conservation, 2006, 4(3): 108–113 [译自: 中国水土保持科学]  相似文献   

6.
北京九龙山侧柏生态公益林空间结构分析与评价   总被引：2，自引：0，他引：2       下载免费PDF全文
[目的]分析侧柏生态公益林空间结构并进行经营迫切性评价,为侧柏生态公益林空间结构的优化调整及区域内其它生态公益人工林空间结构优化调整奠定理论基础。[方法]基于北京九龙山侧柏生态公益林的实测数据,选取混交度、大小比数、角尺度、密集度、林层指数、开敞度和竞争指数7个空间结构参数分析侧柏生态公益林的空间结构特征,并从密度、格局、竞争和混交等方面选取10个指标构建了经营迫切性评价指标体系并确定评价标准,进而对侧柏林进行了经营迫切性评价。[结果]侧柏生态公益林空间结构较为简单,林分呈均匀分布,树种组成单一,以零度和弱度混交为主,呈现单种聚集趋势;林木大小分化不明显,侧柏的优势度最大;林木之间较为密集,处于很密集和比较密集的林木比例较高;林分中所有林木几乎都分布在中林层与上林层,林层指数为0.288,林层结构不太明显;林分开敞度和竞争指数分别为0.274和0.318,总体处于生长空间不足、中度竞争状态;侧柏林的经营迫切性指数为0.8,经营迫切性等级为特别迫切,说明侧柏人工林大多数状态特征不符合标准,急需通过采取有效的经营措施优化林分配置,改善森林状况,以实现侧柏人工林可持续发展的目的。[结论]林分空间结构的分析与经营迫切性评价,不仅能够发现林分结构的不合理方面,还能针对性的制定空间结构调整措施,促进侧柏生态公益林不断向健康稳定的方向发展,实现其生态、经济和社会效益的持续发挥。  相似文献   

7.
Defined populations of American (Periplaneta americana), German (Blattella germanica), and Oriental (Blatta orientalis) cockroaches, and silverfish (Lepisma saccharina) were observed after exposure to deposits (25 g/m2) of a new 1,1,1–trimethyl-N-trimethylsilane-modified, highly hydrophobic diatomaceous earth (DE) formulation by using a computer-aided device measuring motility, circadian rhythm, and mortality under defined environmental and climatic field-simulating and exposure-enforced conditions. In a humid climate (85% relative humidity) with water and food offered ad libitum, complete population eradication could be achieved on the sixth day against B. germanica, on the eighth day against P. americana, and on the ninth day against L. saccharina, respectively. No population eradication occurred within 10 days of exposure when testing B. orientalis, showing a mean survival rate of 29.4 ± 6.7 % of the populations. When comparing the species-specific mortality rates with the results obtained from corresponding reference control groups, significantly higher mortality rates could be observed in B. germanica (F = 66; df = 52; P < 0.00001), P. americana (F = 344; df =66; P < 0.00001), L. saccharina (F = 253; df = 24; P < 0.00001), and B. orientalis (F = 422; df = 11; P < 0.00001). Overall, the efficacy of the hydrophobised DE examined ranked as follows: B. germanica > P. americana (F = 51; df = 24; P < 0.00001) > L. saccharina (F = 43; df = 24; P < 0.00001) >> B. orientalis (F = 9; df = 15; P < 0.000001). DE exposure resulted in complete disruption of the circadian activity in B. germanica and P. americana, but not when tested against B. orientalis, where the species-specific circadian motility peak was still preserved at lower levels after 10 days of exposure. In contrast to the cockroach species examined, no specific circadian rhythm could be measured in the L. saccharina control and treatment groups. Results indicate that hydrophobised DE originating from freshwater diatoms modified with 1,1,1-trimethyl-N-trimethylsilane can be successfully used for the control of infestations with German and American cockroaches as well as silverfish, but not against Oriental cockroaches. It is concluded that species-specific morphological, physiological and behavioural characteristics of insects influencing DE efficacy as well as the toxicological risk of modified DE to humans deserve further investigation.  相似文献   

8.
The sustainability of plantation forests is closely dependent on soil nitrogen availability in short-rotation forests established on low-fertility soils. Planting an understorey of nitrogen-fixing trees might be an attractive option for maintaining the N fertility of soils. The development of mono-specific stands of Acacia mangium (100A:0E) and Eucalyptus grandis (0A:100E) was compared with mixed-species plantations, where A. mangium was planted in a mixture at a density of 50% of that of E. grandis (50A:100E). N2 fixation by A. mangium was quantified in 100A:0E and 50A:100E at age 18 and 30 months by the 15N natural abundance method and in 50A:100E at age 30 months by the 15N dilution method. The consistency of results obtained by isotopic methods was checked against observations of nodulation, Specific Acetylene Reduction Activity (SARA), as well as the dynamics of N accumulation within both species. The different tree components (leaves, branches, stems, stumps, coarse roots, medium-sized roots and fine roots) were sampled on 5–10 trees per species for each age. Litter fall was assessed up to 30 months after planting and used to estimate fine root mortality. Higher N concentrations in A. mangium tree components than in E. grandis might be a result of N2 fixation. However, no evidence of N transfer from A. mangium to E. grandis was found. SARA values were not significantly different in 100A:0E and 50A:100E but the biomass of nodules was 20–30 times higher in 100A:0E than in 50A:100E. At age 18 months, higher δ15N values found in A. mangium tree components than in E. grandis components prevented reliable estimations of the percentage of N derived from atmospheric fixation (%Ndfa). At age 30 months, %Ndfa estimated by natural abundance and by 15N dilution amounted to 10–20 and 60%, respectively. The amount of N derived from N2 fixation in the standing biomass was estimated at 62 kg N ha−1 in 100A:0E and 3 kg N ha−1 in 50A:100E by the 15N natural abundance method, and 16 kg N ha−1 in 50A:100E by the 15N dilution method. The total amount of atmospheric N2 fixed since planting (including fine root mortality and litter fall) was estimated at 66 kg N ha−1 in 100A:0E and 7 kg N ha−1 in 50A:100E by the 15N natural abundance method, and 31 kg N ha−1 in 50A:100E by the 15N dilution method. The most reliable estimation of N2 fixation was likely to be achieved using the 15N dilution method and sampling the whole plant.  相似文献   

9.
Effects of different forest floor vegetation types in secondary forest and of conversion to plantation on the quality and quantity of ectomycorrhizas are mostly unknown.Betula platyphylla var.japonica seedlings were used for bioassays of ectomycorrhizal fungal inoculum using soils from four 50-year-oldB. platyphylla var.japonica forests that had different types of forest floor vegetation: two with shrub types, one with aSasa type, and one with a grass type. Seedlings were also grown in soil from a nearby monospecific plantation ofChamaecyparis obtusa. Ectomycorrhizas formed 13 to 26% of root length of seedlings grown in soil from the five different sites. The maximum percentage of ectomycorrhizal formation was obtained from the grass-type forest. The dominant type of ectomycorrhiza in the two shrub-type forest soils was the same as that in theSasa-type forest soil. The dominant types of ectomycorrhizas in the grass-type forest soil and in theC. obtusa plantation soil were different from that in the two shrub-type forest soils and in theSasa-type forest soil. The results of this investigation suggest that the type of forest floor vegetation, accompanied with changes in thickness of the A0 horizon, might affect the ectomycorrhizal fungi in the soils ofB. platyphylla var.japonica forests. Establishment of artificial plantations ofC. obtusa might change the ectomycorrhizal fungi that could associate withB. platyphylla var.japonica seedlings in soil.  相似文献   

10.
Forage value of 10 deciduous woody fodder species during six stages of maturity as well as their acceptance by goats in July and August were studied in Macedonia, northern Greece. The fodder species studies wereAmorpha fruticosa L.,Carpinus orientalis Mill.,Colutea arborescens L.,Corylus avellana L.,Fraxinus ornus L.,Ostrya carpinifolia Scop.,Pyrus amygdaliformis Vill.,Quercus pubescens Willd.,Quercus sessiliflora Salich, andRobinia pseudoacacia L. with two accessions, common and spineless. All these species are integral components of the mediterranean silvo-pastoral systems. Monthly forage samples were collected throughout their growing period (May to November), which coincides with the long dry summer when herbaceous plants are dormant, and analyzed for crude protein content, neutral detergent fiber (NDF), lignin and in vitro organic matter digestibility (IVOMD). Comparing the leguminous species (Robinia pseudoacacia, Amorpha fruticosa, Colutea arborescens) with the remaining species, the leguminous one had on average a higher (P0.05) content of crude protein (21.1%, 21.0% and 17.1% vs. 10.5–13.3%, respectively) and higher (P0.05) IVOMD values (58.4%, 56.0% and 60.0% vs. 47.3–52.8, respectively). Moreover, the leguminous species were among species with lower NDF (42.3%, 45.0% and 35.2% vs. 36.0–48.9%, respectively) and lignin content (7.1%, 8.3% and 9.1% vs. 7.6–10.9%). All species showed a significant increase in crude protein when new leaves appeared (May). Most of the fodder species had digestibilities in the higher range (>55% IVOMD) and low NDF content (<53.5%) during the growing season (first five stages). Lignin contents ranged from 5.9% (A. fruticosa, May) to 16.0% (O. carpinifolia, Nov.).Robinia pseudoacacia had the highest relative acceptance index whileAmorpha fruticosa, Colutea arborescens andCorylus avellana the lowest. It is concluded that deciduous woody fodder species may play a significant role as sources of nutrients in the mediterranean silvo-pastoral systems during the summer period of seasonal nutritional shortage.  相似文献   

11.
Preliminary research to understand the flammability of 14 species of shrubs and 8 species of trees based on silica-free ash content was done in order to recognize which shrubs or trees are more flammable. The results show that the silica-free ash content of shrubs and trees leaves was greater than the stems ranging between 1.7% and 11.4% for leaf and 0.4% and 7.8% for the stems. The shrubsDicranopteris linearis, Imperata cylindrica, Eupatorium pubescens, Lantana camara, Eugenia sp.,Cliforia laurifolia, Pterospermum sp.,Hibiscus similis, Clidemia hirta andTrema orientalis must be considered when fire invades the plantation as well as the treeParaserianthes falcataria, Eucalyptus urophylla, Calliandra callothyrsus, andPeronema canescens.  相似文献   

12.
Growth of regenerating trees in different light environments was studied for the mountainous, mixed-species forests in the Carpathian Mountains of Romania. The primary species in these mixtures were silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). Seedlings/saplings of these species were selected and measured in different stands from two different geographical locations. Regenerating trees were measured for height and diameter growth during the summer of 2002. For each seedling/sapling, percentage of above canopy light (PACL) and stand basal area (BA) were used to assess available and occupied growing space respectively. Regeneration growth was compared against these two variables and regression relationships were developed. Using these models, we predicted the dynamics of regeneration as both growth and species composition. Our results showed that in low-light environments (PACL<20–35%; BA>30 m2/ha), shade tolerant fir and beech clearly outcompeted the spruce. Therefore, in dense stands, spruce could be eliminated by the shade tolerant species. For intermediate levels of cover (PACL=35–70%; BA=15–35 m2/ha) the spruce grew at comparable rates as the beech and fir. All three species showed similar growth rates in open conditions (PACL>80–90%; BA<15–20 m2/ha) with the spruce having a tendency to outgrow the others. However, in terms of establishment, such conditions favor spruce and inhibit fir and beech.  相似文献   

13.
Charcoal was produced from short rotation tropical species ofLeucaena leucocephala andTectona grandis. The combustion-related properties, moisture content, specific gravity and percentage element composition of carbon, hydrogen, oxygen, nitrogen, sulphur and ash in wood and charcoal from the two species were determined. The gross heat of combustion of wood and charcoal was also determined.There were significant differences in the moisture content, specific gravity and percentage element composition between wood and charcoal from the two species. The carbon and ash content of charcoal were higher than those of wood. The average heat of combustion of charcoal 25.25 MJKg–1 was higher than that of wood 13.75 MJKg–1.  相似文献   

14.
The chemical and spectroscopic properties of humic acids (HAs) isolated from four litters and their corresponding underlying soils at three depths in a protected forest area in Southern Italy were investigated as a function of four different plant coverings: Quercus ilex L., mixed Carpinus betulus L. and C. orientalis Mill., Pinus halepensis L., and mixed Quercus trojana Webb. and Q. ilex L.. The forested site is a part of a calcareous plateau, characterized by homogeneous soils classified as Eutric Cambisols associated with Calcic Luvisols. The changes in the composition of HAs with soil depth have been evaluated on the basis of chemical (elemental and COOH groups) and spectroscopic analyses (E4/E6 ratio and FT IR spectra), and lignin-derived CuO oxidation products. A different distribution of the main elements was found in the various HAs which is apparently related to the type of humic acid-precursor biomolecules in the parent litters. The HAs isolated from soils under Q. ilex and mixed Carpinus species showed a slight increase in the C/H ratio and COOH content downward the soil profile, suggesting increasing aromatic polycondensation and humification degree with depth. On the contrary, no trend was observed for HAs from soils under Pinus halepensis L. and mixed Quercus species, indicating a partial incorporation of residues deriving from litter degradation into these HAs. Further, the content of lignin-derived phenols was higher in Pinus halepensis L. and mixed Quercus species layers, with the same trend measured for the corresponding HAs, thus confirming a lignin contribution related to the lignin type of plant covering.  相似文献   

15.
The use of municipal sewage sludge as a fertiliser could be a more adequate means of disposal of this residue than its transport to the dump. The objective of this experiment was to evaluate the effects of different doses of sludge and sowing a mixture of cocksfoot (Dactylis glomerata) and clover (Trifolium repens) on pasture production, botanical composition of the pasture, forage quality, and changes in soil chemical properties. Treatments applied were: (1) no fertilisation (L0), (2) fertilisation with 26 Mg ha–1 of sewage sludge with no sowing (L40), (3) fertilisation with 26 Mg ha–1 of sewage sludge and sowing with 25 kg of Dactylis glomerata L. cv Artabro (Dg) and 3 kg Trifolium repens cv Huia per hectare and (4) 52 Mg ha–1 of sewage sludge with no herbage sowing (L80). Plots were established in a silvopastoral system with Pinus radiata D. Don at a density of 1666 trees ha–1 (3 × 2 m). The improvement of soil fertility due to organic fertiliser application and the use of Dactylis glomerata increased the production and quality of pasture as well as reduced the risk of fire and erosion, as grasses dominated shrubs. Fertilisation with sewage sludge in soils of acid origin increased the concentration of copper in the pasture and, if cocksfoot was not sown, the levels of this element exceeded the maximum tolerable dietary levels for sheep. On the other hand, fertilisation also increased the levels of zinc in pasture, but values were not above toxic limits for sheep, horses and cattle.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

16.
In a Cryptomeria japonica plantation, we examined the composition and seasonal abundance of microarthropods in communities associated with habitat substrates in the canopy (defined as dead leaves, dead branches, and living leaves) and compared them with those in soil communities. Habitat substrates and microarthropods were periodically collected by the branch-clipping and washing method from the canopy and by the Tullgren method from the soil. Oribatida, Collembola, and larvae of the Chironomidae, most of which are detritivorous or fungivorous, were dominant in the canopy. The dominant oribatid and collembolan families differed markedly between the canopy and the soil. Numbers of all microarthropods per unit dry weight of leaf or per unit area of branch ranged from 4.2 to 11.7g–1 dry wt on dead leaves, 0.13–0.48cm–2 on dead branches, and 1.3–6.4g–1 dry wt on living leaves. In the soil, the number of individuals per unit ground area ranged from 24000 to 220000m–2. The total abundances of microarthropods on dead leaves and dead branches were almost constant throughout the year. These results suggest that the arboreal litter characteristic of C. japonica canopies is utilized consistently by large numbers of detritivorous and fungivorous microarthropods, and that the decomposition of dead foliage and branches is initiated in the canopy.  相似文献   

17.
Lowland evergreen rainforests in southern Chile growing on highly productive soils and accessible sites have been subjected to traditional and industrial logging of valuable timber trees. Old-growth rain forests in this area are characterized by highly conservative N cycles, which results in an efficient N use of ecosystems. We hypothesize that different logging practices, by changing forest structure and species composition, can alter the quantity and quality (i.e. C/N ratio) of litterfall and soil organic matter and soil microbial processes that determine N storage and availability. To test this hypothesis we investigated chemical properties, microbial N transformations, N fluxes and N storage in soils of lowland evergreen rainforests of Chiloé Island after 10 years since industrial selective logging (ISL) and in stands subjected to traditional selective logging (TSL) by landowners in small properties. We compared them to reference unlogged old-growth stands (OG) in the same area. Tree basal area was more reduced in the stands subjected to ISL than to TSL. Litterfall inputs were similar in both logging treatments as in OG stands. This was due to greater biomass of understory species after logging. In TSL understory tree species determined a higher litterfall C/N ratio than ISL. We found higher soil N availability and content of base cations in surface soils of logged forests than in OG. The litter horizon of OG forest had significantly higher rates of non-symbiotic N fixation than logged forests. In the ISL treatment there was a trend toward increasing soil denitrification and significantly higher NO3–N/Nt ratio in spring waters, which led to a stronger δ15N signal in surface and deep soils. We conclude that massive understory occupation by the shade-intolerant native bamboo Chusquea quila in ISL led to enhanced litter quality (lower C/N ratios) relaxing the tightness of the N cycle, which increased soil N availability leading to a higher proportion of nitrate in spring waters and higher gaseous N losses. In contrast, under TSL a higher litterfall C/N ratio slowed decomposition and net N mineralization rates thus reducing the chances for N losses, and enhancing C and N storage in soil. We suggest that sustainable logging practices in these rain forests should be based on lower rates of canopy removal to enhance colonization of the understory by shade-tolerant trees, which are associated with a more efficient N cycle.  相似文献   

18.
Trees of the family Dipterocarpaceae are the dominant trees in Southeast Asian tropical forests where they play an important ecological role and are also important commercially. An experiment was conducted to determine the effect of ectomycorrhizal fungi on the growth of dipterocarp species in peat soils. Seedlings of Shorea pinanga were inoculated with spores of two ectomycorrhizal fungi, Pisolithus arhizus and Scleroderma sp. were grown in pots containing sterilized peat soil for 7 months. The percentage of ectomycorrhizal colonization on S. pinanga exceeded 86%. Colonization of S. pinanga roots by ectomycorrhizal fungi resulted in increased shoot height, stem diameter, number of leaves, and shoot fresh and dry weight. Survival rates of S. pinanga were greater for inoculated seedlings than control seedlings. These results suggest that inoculation of ectomycorrhizal fungi can improve the early growth of S. pinanga grown in tropical forests and that this technique will accelerate the rehabilitation of degraded dipterocarp forests.  相似文献   

19.
Beech leaf disease (BLD) is a currently undiagnosed and seemingly lethal disease that was discovered in 2012 on American beech trees (Fagus grandifolia) in north‐east Ohio in the United States. Since its discovery, BLD has spread rapidly and can now be found in forests in 10 counties in Ohio, eight counties in Pennsylvania and five counties in Ontario, Canada. The initial symptoms of the disease appear as a dark green, interveinal banding pattern on the lower canopy foliage. These initial symptoms typically occur in the shrub or sampling layer of a beech stand. The later symptoms result in solidly darkened leaves that are shrunken and crinkled. The symptoms appear to progress through the buds as the affected buds are eventually aborted and no new leaves are produced. We fear this disease has the potential to drastically alter the Eastern deciduous forests of the United States on its own and through potential compounding disease effects. In addition, BLD poses a threat to global forests as symptoms of the disease were detected on European (F. sylvatica) and Oriental (F. orientalis) beech species in nurseries in north‐eastern Ohio. Due to its rapid spread and variability in environmental conditions where it has been detected, it seems unlikely that BLD is an abiotic disorder. Thus, intense efforts are underway to determine the causal agent of BLD. Relevant stakeholders are advised to be alert for BLD symptoms in beech forests in the Northern Hemisphere, and substantial resources should be invested in understanding this emerging forest disease.  相似文献   

20.
A study was carried out in the Lama forest reserve of Benin to characterize the habitat of Afzelia africana Sm., an endangered multipurpose tree species (found in African humid, dry forests and woodlands), in order to define a sustainable management strategy for its conservation. An estimation of species density was done on 100 square plots of 1 ha each, while tree height and dbh of all the species were measured on subplots of 50 m × 30 m within the 1 ha plots. The regenerations of A. africana (dbh < 10 cm) were counted in the diagonal quadrats of the principal plots. Presence–absence data of the species was subjected to multidimensional scaling and results showed four vegetation communities including: young fallow, old fallow, typical dense forest and degraded dense forest. Significant differences were noted between the four communities with respect to dendrometric parameters of the species. High values of these parameters were noted for the species in typical dense forest (5.2 stems/ha, 66.7 cm, 17.9 m, 7.9 m2/ha and 38.8% for the tree-density, the mean diameter, the mean height, basal area and basal area contribution of the species, respectively) whereas the lowest values were obtained for the old preforest fallow as far as the mean diameter (59.7 cm), the mean height (15.7 m) and the basal area contribution (27.7%) of the species were concerned. In general, the basal area of A. africana in the over vegetation types was less than 3 m2/ha. No A. africana tree was found in the young preforest fallow while more than 80% of A. africana trees were found in the typical dense forest community. Stem diameter and height structures of the species in all the four communities showed a left dissymmetric Gaussian shape and were well adjusted to Weibull distribution.  相似文献   

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