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1.
Soil carbon and nitrogen stores and storage potential as affected by land-use in an agro-pastoral ecotone of northern China 总被引:6,自引:0,他引:6
Zhiyong Zhou Osbert J. Sun Jianhui Huang Linghao Li Ping Liu Xingguo Han 《Biogeochemistry》2007,82(2):127-138
Equilibrium carbon stock is the result of a balance between inputs and outflows to the pool. Changes in land-use are likely
to alter such balance, resulting in different carbon stores under different land-use types in addition to the impacts of global
climate change. In an agro-pastoral ecotone of Inner Mongolia, northern China, we investigated productivity and belowground
carbon and nitrogen stores under six different types of land-uses, namely free grazing (FG), grazing exclusion (GE), mowing
(MW), corn plantation (CP), fallow (FL), and alfalfa pasture (AP), and their impacts on litter and fine roots in semiarid
grassland ecosystems. We found that there were great variations in aboveground net primary production (ANPP) across the six
land-use types, with CP having markedly high ANPP; the FG had significantly reduced soil organic carbon (SOC) and nitrogen
stores (SON) to 100 cm depth compared with all other types of land uses, while very little litter accumulation was found on
sites of the FG and CP. The top 20 cm of soils accounted for about 80% of the root carbon and nitrogen, with very little roots
being found below 50 cm. About 60% of SOC and SON were stored in the top 30 cm layer. Land-use change altered the inputs of
organic matters, thus affecting SOC and SON stores accordingly; the MW and GE sites had 59 and 56% more SOC and 61% more SON
than the FG. Our estimation suggested that restoring severely degraded and overgrazed grasslands could potentially increase
SOC and SON stores by more than 55%; conversion from the native grasses to alfalfa could potentially double the aboveground
biomass production, and further increase SOC and SON stores by more than 20%. Our study demonstrated significant carbon and
nitrogen storage potential of the agro-pastoral ecotone of northern China through land-use changes and improved management
in the context of mitigating global climate change. 相似文献
2.
Effects of parentage,prior fruit set and pollen load on fruit and seed production in Campanula americana L 总被引:1,自引:0,他引:1
Summary We conducted a controlled crossing experiment to examine the effects of maternal and paternal parentage, the size of the pollen load, and prior fruit production on the proportion of flowers that set fruit, seed number per fruit and seed weight in a natural population of Campanula americana. Effects due to the maternal parent were large for all measures of fruit and seed production, while the paternal parent had a significant effect only upon mean seed weight. As the number of prior fruits on the maternal plant increased the probability that a flower would produce a mature fruit, the number of seeds per fruit, and total seed weight per fruit all decreased. We found no effect of the size of the pollen loads used in this study on fruit or seed production. These results are consistent with those of other studies that suggest in natural plant populations maternal effects, especially environmental maternal effects, can have an overwhelming effect on fruit and seed production and on seed characteristics. 相似文献
3.
继1989年以后,1991年大兴安岭林区兴安落叶松又出现一次结实,结实率平均为63.8%,且结实的林木多出现在过火的林地上。胸径28cm以上的林木结实率可达到80%以上,而且结实量多的林木绝大部分(85%以上)是树冠稀疏的。球果多集中于树冠的中部。短枝年龄结构格局对结实具有重要影响。短枝的数量以1、2年生最多,但结实的短枝主要属于3—7年生的短枝,一次种子丰收年,需要消耗大量的短枝数量,花芽中大部分为雄花,直接用于形成球果的雌花,一般尚不足20%。开花结实成熟年龄短枝的存蓄率愈高,其结实的潜力也愈大,出现种子年的可能性也愈大。 相似文献
4.
Populations of the obligate-seeder, Banksia ericifolia, were even-aged. Seedling recruitment occurred only after fire. Mean genet size (height + canopy diameter; H+D) increased progressively with elapsed time since fire in stands last burnt 2–23 years before 1981. Populations of a co-occurring resprouter, B. oblongifolia, were mixed-aged. Genet size varied significantly between stands, but this variation was not explained by regressions of H+D on years since fire. In addition B. oblongifolia seedlings were recruited both after fire and in patches of heath unburnt for 16 years.Most flower and seed production in B. oblongifolia occurred in the stands last burnt less than 10 years previously. More than 30% of genets had not produced cones since the last fire, irrespective of how many years had elapsed. In contrast, few B. ericifolia genets had produced cones five years after fire, but by 16 years after fire nearly 100% had. Overall, about 51% of B. ericifolia inflorescences and about 28% of B. oblongifolia inflorescences set seed. The number of seeds in seed-bearing cones was not significantly different between species.Resprouting B. oblongifolia genets began flowering sooner after fire, but B. ericifolia subsequently overtook them in accumulating a bank of serotinous seeds. In the stand unburnt for 23 years the largest B. ericifolia genets had more than twice as many cones as the largest co-occurring B. oblongifolia. However, when accumulated cone production was compared for genets of equal H+D over all stands, there was no difference between species.We thank the New South Wales National Parks & Wildlife Service for permission to do this work in Ku-ring-gai Chase National Park. We are grateful to Don Adamson, Lynn Day, David Haig and James Sim for constructive comments on earlier drafts. 相似文献
5.
Adult plants incapable of producing viable offspring inflate our perception of the size of population distribution. We propose that species occurrence is limited to a subset of the environmental gradient and that it changes as ontogenetic development progresses. Moreover, fruit production is associated with site-specific environmental conditions. We sampled 2988 adult individuals from nine palm species in 30 plots (40 × 250 m) and used a larger data set including 42 other plots distributed along a continuous topo-edaphic gradient in a terra firme forest near Manaus, Brazil. Five out of nine palm species were more restricted to a sub-section of the topo-edaphic gradient in the adult-size phase. More specifically, reproductive individuals of species Attalea attaleoides and A. microcarpa had even more restricted distributions than adult-sized, non-reproductive plants. Successive environmental filtering and competition probably acting through selective mortality led to increasing habitat restriction, with reproductive adults being restricted to a smaller part of the region than juveniles and adults. Water availability and nutrients limited both the ability to produce fruits and the amount of fruit production. Previous studies have reported stronger habitat associations for older plants than for seedlings or juveniles, but we show here that some species are more restricted at their reproductive stage. Plant specializations to local conditions may be more common than currently acknowledged, and a significant portion of individuals in a population might represent sinks. Such strong environmental limitations of reproductive plants should also be considered in management of species with economic value and in conservation planning. 相似文献
6.
Ulf Sperens 《Oecologia》1997,109(3):368-373
Variation in fruit production and pre-dispersal seed predation by Argyresthia conjugella was studied in␣four populations of Sorbus aucuparia in northern Sweden.␣The number of infructescences, fruits per infructescence, consumed seeds and developed unattacked seeds
per fruit were scored in marked trees from 1984 to 1990. The results showed that the number of fruits produced in each population
determined the number of seed predators occurring in the host population, as the yearly number of seed predators was significantly
and positively correlated with yearly number of fruits, in all but one population. The seed predators showed a delay in response
to variation in number of fruits produced. This lag in response resulted in a large proportion of fruits being attacked and
seeds consumed in a bad fruiting year that followed a good fruiting year, and vice versa. The proportion of fruits attacked
and seeds consumed was largest in the population showing the greatest between-year variation in fruit production and lowest
in the population showing the lowest between-year variation in fruit production. Furthermore, the individuals within the former
population were synchronised, while they were not in the latter population. These results contradict one of the possible explanations
of mast-seeding, where large synchronised between-year variation is supposed to reduce pre-dispersal seed predation. Instead,
differences in attraction of the seed predator to differences in fruit crop size could explain the observed difference in
seed predation between the two populations with opposite fruiting patterns. Within each population, irrespective of year,
the proportion of fruits attacked and seeds consumed was independent of a tree's fruiting display. Therefore, trees with high
fruit production, despite harbouring the largest number of seed predators, produced the largest number of developed seeds
in absolute numbers, compared to trees that produced few fruits.
Received: 25 February 1996 / Accepted: 30 November 1996 相似文献
7.
Marek Sammul Tiiu Kull Kaire Lanno Merit Otsus Merike Mägi Silja Kana 《Biodiversity and Conservation》2008,17(14):3531-3550
Large-scale changes in regional floras provide direct information about changes in biodiversity through time and enable the
evaluation of conservation targets. We compared the distribution ranges in 2004 of Estonian native terrestrial flora with
the distribution ranges before 1970, using the Atlas of Estonian Flora. Relative persistence was related to species endemism,
commonness, occurrence at its border of the global distribution range, main habitat type, sensitivity to human impact, life-form,
conservation category, and Red List category. A literature-based database of the flora of Estonian habitat types was used
to evaluate relative persistence of the flora of different habitats. Changes in the flora are largely dependent on human activities.
The decrease in mire and grassland habitats and the increase in forests are reflected in the persistences of related species.
Flora of mire habitats decreased the most. The fact that an almost ten-fold decrease of grasslands has not resulted in as
large a decrease in the ranges of grassland species could serve as evidence of the extinction debt of these habitats. We also
found a greater decrease among habitat specialists than habitat generalists and lower average persistence of the species of
species-rich habitats. Our data show that current prioritization of species for conservation is in concordance with needs,
as reflected in the changes in the range of species. However, conservation has not been entirely successful: the decrease
of protected species continues. Our simple method for summarizing large databases was effective for the evaluation of large
scale effects of conservation actions. 相似文献
8.
Kazuaki Takahashi Tadatoshi Shiota Hiroo Tamatani Masaru Koyama Izumi Washitani 《Ecological Research》2008,23(2):471-478
Fruit use by the Japanese black bear (Ursus thibetanus japonicus) and seed clumping in bear scat were studied in central Japan using fecal analyses. Between May and November 2003 and 2004,
the life form and fruit size of plants consumed by bears and the species composition and intactness of seeds contained in
scat were examined in five transects (approximately 10 km × 10 m) in broad-leaved deciduous forests. In 2003, scats with seeds
were found only in the autumn, when fruiting trees and shrubs were abundant. In 2004, scats with seeds occurred intermittently
from the summer, when fruiting plants were rare, up to the autumn. Yearly and seasonal variation in fruit use reflects the
opportunistic foraging behavior of Japanese black bears. Seven of the nine plant species detected in scats had medium-sized
fruits (6–15 mm width), whereas the other two species had relatively large fruits (20–100 mm width). In total, 14,492 seeds
were detected, of which 97.6% were intact; the remainder were damaged. Intact seeds of one or two species were found in each
scat. The number of intact seeds per scat ranged from 1 to 5476. Japanese black bears seldom digest ingested seeds, thereby
contributing to the seed dispersal of their food plants, including species with fruits that are too large to be swallowed
by frugivorous birds. 相似文献
9.
Pyrus calleryana var. dimorphophylla, a variety of Callery pear (Pyrus calleryana), is endemic to the Tokai district of central Japan, and is currently listed as “Endangered”. The remnant habitats and trees are of limited number, and highly fragmented. As the first step in determining appropriate conservation units, genetic diversity and differentiation in this species were investigated using chloroplast DNA (cpDNA) and nuclear simple sequence repeat (SSR) polymorphisms. All possible remnant trees were genotyped, then six populations were defined based on the results of cpDNA haplotype determination and Bayesian clustering approaches performed using the SSR locus data. Some trees appeared to originate from artificial propagation. Some individuals were difficult to differentiate genetically from the related species, Pyrus × uyematsuana, which is considered to be a hybrid between P. calleryana var. dimorphophylla and a possibly naturalized species, Pyrus pyrifolia, implying that introgression between these species may have occurred. In P. calleryana var. dimorphophylla, anthropogenic factors such as propagation and related species planting are probably major causes of complexity in the genetic structure. 相似文献
10.
Effects of acid irrigation and liming on the production of fruit bodies by ectomycorrhizal fungi 总被引:1,自引:0,他引:1
The aim of this work was to examine the effects of an increase in acid rain upon community diversity and productivity of the ectomycorrhizal fungi in a Norway spruce stand and the possible amelioratory effects of liming. No obvious adverse effects on either the diversity or productivity were found. Acid irrigation appeared to enhance the fruiting of Russula ochroleuca, as did irrigation with normal rain. A combination of acid irrigation and liming resulted in a large increase in the fruiting of Hygrophorus pustulatus. Thirty times more fruit bodies were recorded from this treatment than from the control. A principal component analysis of the fruit body data suggested that soil organic horizon pH may be an important determinant of ectomycorrhizal community structure within the spruce stand. 相似文献
11.
A global analysis of fine root production as affected by soil nitrogen and phosphorus 总被引:1,自引:0,他引:1
Fine root production is the largest component of belowground production and plays substantial roles in the biogeochemical cycles of terrestrial ecosystems. The increasing availability of nitrogen (N) and phosphorus (P) due to human activities is expected to increase aboveground net primary production (ANNP), but the response of fine root production to N and P remains unclear. If roots respond to nutrients as ANNP, fine root production is anticipated to increase with increasing soil N and P. Here, by synthesizing data along the nutrient gradient from 410 natural habitats and from 469 N and/or P addition experiments, we showed that fine root production increased in terrestrial ecosystems with an average increase along the natural N gradient of up to 0.5 per cent with increasing soil N. Fine root production also increased with soil P in natural conditions, particularly at P < 300 mg kg(-1). With N, P and combined N + P addition, fine root production increased by a global average of 27, 21 and 40 per cent, respectively. However, its responses differed among ecosystems and soil types. The global average increases in fine root production are lower than those of ANNP, indicating that above- and belowground counterparts are coupled, but production allocation shifts more to aboveground with higher soil nutrients. Our results suggest that the increasing fertilizer use and combined N deposition at present and in the future will stimulate fine root production, together with ANPP, probably providing a significant influence on atmospheric CO(2) emissions. 相似文献
12.
Claire Fortunel Cyrille Violle Catherine Roumet Bruno Buatois Marie-Laure Navas Eric Garnier 《Perspectives in Plant Ecology, Evolution and Systematics》2009,11(4):267-283
Species performance depends on ecological strategies, revealed by suites of traits, conferring different relative ecological advantages in different environments. Although current knowledge on plant strategies along successional gradients is derived from studies conducted in situ, actually quantifying these strategies requires disentangling the effects of environmental factors from intrinsic differences between species.Here we tested whether allocation strategies and seed traits differ among successional stages and nitrogen levels. To this aim, we assessed biomass and nitrogen allocations and seed traits variations for 18 species, differing in life history and belonging to three stages of a Mediterranean old-field succession. These species were grown as monocultures in an experimental garden under limiting and non-limiting nitrogen supply.Early successional species allocated allometrically more nitrogen and proportionally more biomass to reproduction, and set more seeds than later successional species. Seed mass increased with successional status and was negatively related to seed number. Early successional species thus produced more but less-provisioned seeds, suggesting better colonization abilities. These patterns were not the sole consequence of the replacement of annuals by perennials along the successional gradient, since comparable trends were also observed within each life history. Allocation patterns were generally not altered by nitrogen supply and the higher nitrogen content in vegetative organs of plants grown under high nitrogen supply was not retranslocated from leaves to seeds during seed development.We therefore conclude that differences in plant ecological strategies in species characteristics from contrasting successional stages appear to be intrinsic properties of the studied species, and independent from environmental conditions. 相似文献
13.
水杉人工林树冠结构及生物生产力的研究 总被引:15,自引:2,他引:15
研究了水杉人工林的树冠结构和林分生物生产力。结果表明,不同密度及林龄的林分树冠结构存在较大差异,随着树冠部位上升和林分密度增大,分枝角度逐渐减小;径阶大小与枝叶率成反比,与树冠重量成正比,径阶增大,树冠最大叶量层的集团上移,有效光合面积相对减少,树冠结构的变化直接影响到林分的生物量生产、分配分配和经济生物量,林分干、枝、叶的干物质累积趋势可用Richard方程描述;林龄增大,分配到主干的生物量比例 相似文献
14.
The strength and periodicity of D. melanogaster circadian rhythms are differentially affected by alterations in period gene expression 总被引:6,自引:0,他引:6
The per gene of D. melanogaster influences or participates in the generation of biological rhythms. Previous experiments have identified the head as the location from which per exerts its effect on circadian rhythms. To localize further this region and to examine the effects of altered levels and altered spatial expression patterns of the per gene on circadian rhythms of locomotor activity, we have characterized transformed lines containing per gene constructs missing substantial cis-acting regulatory information. The data suggest that wild-type levels of per gene expression are necessary in only a small fraction of the nervous system for near wild-type periods, whereas a larger fraction of per-expressing cells in the brain contributes to the strength of the circadian rhythms. 相似文献
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16.
ROBERT C. JOHNSON HWA‐SEONG JIN MARGARET M. CARREIRO JEFFREY D. JACK 《Freshwater Biology》2013,58(5):843-857
1. Despite non‐point‐source (NPS) pollution being perhaps the most ubiquitous stressor affecting urban streams, there is a lack of research assessing how urban NPS pollution affects stream ecosystems. We used a natural experimental design approach to assess how stream macroinvertebrate community structure, secondary production and trophic structure are influenced by urban NPS pollution in six streams. 2. Differences in macroinvertebrate community structure and secondary production among sites were highly correlated with stream‐water specific conductivity and dissolved inorganic phosphorus (DIP) concentrations. Macroinvertebrate richness, the Shannon diversity index and the Shannon evenness index were all negatively correlated with specific conductivity. These patterns were driven by differences in the richness and production of EPT and other intolerant taxa. Production of the five most productive taxa, tolerant taxa, non‐insect taxa and primary consumers were all positively correlated with stream‐water DIP. 3. Despite the positive correlation between primary consumer production and DIP, there was no correlation between macroinvertebrate predator production and either total or primary consumer macroinvertebrate production. This was observed because DIP was positively correlated with the production of non‐insect macroinvertebrate taxa assumed to be relatively unavailable for macroinvertebrate predator consumption. After removing production of these taxa, we observed a strong positive correlation between macroinvertebrate predator production and production of available prey. 4. Our results suggest that urban NPS pollution not only affects macroinvertebrate community structure, but also alters secondary production and trophic‐level dynamics. Differences in taxon production in our study indicate the potential for altered energy flow through stream food webs and potential effects on subsidies of aquatic insect prey to riparian food webs. 相似文献
17.
Population structure of Salmonella investigated by amplified fragment length polymorphism 总被引:2,自引:0,他引:2
AIMS: This study was undertaken to investigate the usefulness of amplified fragment length polymorphism (AFLP) in determining the population structure of Salmonella. METHODS AND RESULTS: A total of 89 strains were subjected to AFLP analysis using the enzymes BglII and BspDI, a combination that is novel in Salmonella. Both species S. bongori and S. enterica and all subsp. of S. enterica were represented with emphasis on S. enterica subsp. enterica using a local strain collection and strains from the Salmonella Reference Collection B (SARB). The amplified fragments were used in a band-based cluster analysis. The tree resulting from the subgroup analysis clearly separated all subgroups with high bootstrap values with the species S. bongori being the most distantly related of the subgroups. The tree resulting from the analysis of the SARB collection showed that some serotypes are very clonal whereas others are highly divergent. CONCLUSIONS: AFLP clearly clustered strains representing the subgroups of Salmonella together with high bootstrap values and the serotypes of subspecies enterica were divided into polyphyletic or monophyletic types corresponding well with multilocus enzyme electrophoresis (MLEE) and sequence-based studies of the population structure in Salmonella. SIGNIFICANCE AND IMPACT OF THE STUDY: AFLP with the enzyme combination BglII and BspDI allows discrimination of individual strains and provides evidence for the usefulness of AFLP in studies of population structure in Salmonella. 相似文献
18.
Population genetic structure determines speed of kill and occlusion body production in Spodoptera frugiperda multiple nucleopolyhedrovirus 总被引:1,自引:0,他引:1
Oihane Simn Trevor Williams Miguel Lpez-Ferber Jean-Marie Taulemesse Primitivo Caballero 《Biological Control》2008,44(3):321-330
A Nicaraguan isolate of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfNIC) survives as a complex mixture of genotypes (named A to I). The speed of kill, time-mortality distribution, and occlusion body (OB) production of single genotypes (A, B and F) and co-occluded mixtures of genotypes, in a 75% + 25% ratio, were compared to determine the contribution of each genotype to the transmissibility of the viral population. Pure genotypes differed markedly in their speed of kill in second instar S. frugiperda. The speed of kill of SfNIC was attenuated compared to that of the dominant genotype B, indicating that interactions involving two or more genotypes likely determine host killing traits in the virus population. Genotypes A, F and defective genotype C, had no significant effects on the distribution of insect deaths over time when present as minority components in mixtures comprising 75% of genotype B. Similarly, the mortality pattern over time of insects infected by genotype F, the fastest-killing genotype tested, was not affected by the presence of genotypes A or C. Semi-quantitative PCR studies indicated that the genetic composition did not differ significantly between SfNIC-infected insects that died soon (67 h) or late (139 h) after inoculation, suggesting that stability in genotypic composition is important for virus survival. Median OB production per insect was correlated with mean time to death so that attenuated speed of kill of SfNIC resulted in high OB yields. We conclude that (i) minority genotypes play a functional role in determining the timing of mortality of infected hosts and (ii) the genotypic structure of the virus population is stably maintained to maximize the likelihood of survival. 相似文献
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20.
Adults of the parasiteApanteles sp. groupultor were held unter constant temperatures (15, 20, 26, 30°C) each within ±1°C. Total progeny production was significantly greater at 26°C, averaging 85 per female and decreased at 15°C and 30°C. Mating behavior showed that both sexes were a polygamous. The range of constant temperature did not greatly alter the progeny sex ratio when female parent had been mated. At 15°C, male activity was adversely affected when both sexes were exposed to it without previous mating, resulting in a higher number of male progeny. A temperature of 26°C was the most appropriate for normal sex ratio. 相似文献