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1.
2.
Atmospheric CO2 enrichment usually changes the relative contributions of plant species to biomass production of grasslands, but the types of species favored and mechanisms by which change is mediated differ among ecosystems. We measured changes in the contributions of C3 perennial forbs and C4 grasses to aboveground biomass production of tallgrass prairie assemblages grown along a field CO2 gradient (250–500 μmol mol?1) in central Texas USA. Vegetation was grown on three soil types and irrigated each season with water equivalent to the growing season mean of precipitation for the area. We predicted that CO2 enrichment would increase the forb contribution to community production, and favor tall‐grasses over mid‐grasses by increasing soil water content and reducing the frequency with which soil water fell below a limitation threshold. CO2 enrichment favored forbs over grasses on only one of three soil types, a Mollisol. The grass fraction of production increased dramatically across the CO2 gradient on all soils. Contribution of the tall‐grass Sorghastrum nutans to production increased at elevated CO2 on the two most coarse‐textured of the soils studied, a clay Mollisol and sandy Alfisol. The CO2‐caused increase in Sorghastrum was accompanied by an offsetting decline in production of the mid‐grass Bouteloua curtipendula. Increased CO2 favored the tall‐grass over mid‐grass by increasing soil water content and apparently intensifying competition for light or other resources (Mollisol) or reducing the frequency with which soil water dipped below threshold levels (Alfisol). An increase in CO2 of 250 μmol mol?1 above the pre‐industrial level thus led to a shift in the relative production of established species that is similar in magnitude to differences observed between mid‐grass and tallgrass prairies along a precipitation gradient in the central USA. By reducing water limitation to plants, atmospheric CO2 enrichment may alter the composition and even structure of grassland vegetation. 相似文献
3.
Some streams near Dorset in south-central Ontario suffer from acid precipitation via run-off and seepage from thin soils with little buffering capacity. A spring-summer survey of eight headwater streams revealed some characteristics of their insect communities which could be correlated with pH. The streams could be divided into three groups according to pH and community structure. In the most acid group (annual pH range 4.3–4.8), Ephemeroptera were absent from two streams although mature Leptophlebia were collected just after spring thaw from the most acid one (pH 4.3–4.5). One of these three streams also lacked Plecoptera but the others had two or three genera, all shredders. The second group of three streams (pH 5.0–6.3), with one exception, did support Ephemeroptera (3–4 genera) and Plecoptera (1–4 genera), most of the latter being shredders. In all six of these acid streams, Trichoptera were more diverse and more dense than Ephemeroptera and Plecoptera; again, shredders were clearly dominant, especially the limnephilid caddisfly, Frenesia difficilis (Walker). These six streams also had similar chironomid communities (densities were an order of magnitude higher than other insects). Dominance by Chironomini and abundant Tanypodinae typified the most acid streams. In contrast, the two streams in the third group (pH 5.3–6.7) had richer and more balanced communities in general with relatively fewer shredders (no Frenesia), more collectors, and fewer Chironomini and Tanypodinae. As a field experiment showed that autumn-shed leaves decomposed more slowly in acid than in non-acid streams, summer-growing shredders may benefit from the pulse of acidity at snowmelt. 相似文献
4.
ANNA M. MIKA ROSS M. WEISS† OWEN OLFERT† REBECCA H. HALLETT JONATHAN A. NEWMAN 《Global Change Biology》2008,14(8):1721-1733
Climate change may dramatically affect the distribution and abundance of organisms. With the world's population size expected to increase significantly during the next 100 years, we need to know how climate change might impact our food production systems. In particular, we need estimates of how future climate might alter the distribution of agricultural pests. We used the climate projections from two general circulation models (GCMs) of global climate, the Canadian Centre for Climate Modelling and Analysis GCM (CGCM2) and the Hadley Centre model (HadCM3), for the A2 and B2 scenarios from the Special Report on Emissions Scenarios in conjunction with a previously published bioclimatic envelope model (BEM) to predict the potential changes in distribution and abundance of the swede midge, Contarinia nasturtii, in North America. The BEM in conjunction with either GCM predicted that C. nasturtii would spread from its current initial invasion in southern Ontario and northwestern New York State into the Canadian prairies, northern Canada, and midwestern United States, but the magnitude of risk depended strongly on the GCM and the scenario used. When the CGCM2 projections were used, the BEM predicted an extensive shift in the location of the midges' climatic envelope through most of Ontario, Quebec, and the maritime and prairie provinces by the 2080s. In the United States, C. nasturtii was predicted to spread to all the Great Lake states, into midwestern states as far south as Colorado, and west into Washington State. When the HadCM3 was applied, southern Ontario, Saskatchewan, and Washington State were not as favourable for C. nasturtii by the 2080s. Indeed, when used with the HadCM3 climate projections, the BEM predicted the virtual disappearance of ‘very favourable’ regions for C. nasturtii. The CGCM2 projections generally caused the BEM to predict a small increase in the mean number of midge generations throughout the course of the century, whereas, the HadCM3 projections resulted in roughly the same mean number of generations but decreased variance. Predictions of the likely potential of C. nasturtii spatial spread are thus strongly dependent on the source of climate projections. This study illustrates the importance of using multiple GCMs in combination with multiple scenarios when studying the potential for spatial spread of an organism in response to climate change. 相似文献
5.
Richard Y. Morita 《Geomicrobiology journal》2013,30(3-4):213-214
Microcosm experiments were performed to identify the influence of bacterial cell surfaces on the morphology, mineralogy, size and solubility of CaCO3 precipitated in response to the enzymatic hydrolysis of urea in an artificial groundwater (AGW) by the ureolytic bacteria, Bacillus pasteurii. In each microcosm, B. pasteurii were contained within a cellulose dialysis membrane (10 K Dalton MWCO), resulting in bacteria-inclusive and bacteria-free AGW solution. Urea hydrolysis by B. pasteurii resulted in the production of ammonium and an increase in pH in the whole AGW solution. This initiated predominantly rhombohedral calcite precipitation at the same critical saturation state ( S critical = 12) in the B. pasteurii-inclusive and bacteria-free zone of the AGW, indicating the mineralogy and morphology of CaCO3 precipitation is not controlled by B. pasteurii surfaces. However, the temporal evolution of distinctly different lognormal crystal-size-distributions in the B. pasteurii-inclusive and bacteria-free zone of the AGW resulted from identical changes in bulk solution chemistry. Specifically, B. pasteurii increased the size and size variance of crystals, and led to a greater crystal growth rate throughout the experiments, relative to bacteria-free AGW. Calculated crystal solubility (ln K S0 ) was lower for crystals > 4000 nm in diameter, reflecting smaller molar surface areas. This suggests that the larger crystals generated in the presence of B. pasteurii have a lower affinity for re-dissolution than those generated in the bacteria-free AGW, which may act as a positive feedback to maintain larger crystal sizes in the presence of B. pasteurii. During ureolysis, higher bacterial concentrations may therefore generate larger and less soluble carbonate crystals. This has important implications for the adaptation of bacterial ureolysis as a method for precipitating calcium carbonate and co-precipitating metals and radionuclides in contaminated aquifers. 相似文献
6.
Climate change can affect biotic interactions, and the impacts of climate on biotic interactions may vary across climate gradients. Climate affects biotic interactions through multiple drivers, although few studies have investigated multiple climate drivers in experiments. We examined the effects of experimental watering, warming, and predator access on leaf water content and herbivory rates of woolly bear caterpillars (Arctia virginalis) on a native perennial plant, pacific silverweed (Argentina anserina ssp. pacifica), at two sites across a gradient of precipitation in coastal California. Based on theory, we predicted that watering should increase herbivory at the drier end of the gradient, predation should decrease herbivory, and watering and warming should have positive interacting effects on herbivory. Consistent with our predictions, we found that watering only increased herbivory under drier conditions. However, watering increased leaf water content at both wetter and drier sites. Warming increased herbivory irrespective of local climate and did not interact with watering. Predation did not affect herbivory rates. Given predictions that the study locales will become warmer and drier with climate change, our results suggest that the effects of future warming and drying on herbivory may counteract each other in drier regions of the range of Argentina anserina. Our findings suggest a useful role for range‐limit theory and the stress‐gradient hypothesis in predicting climate change effects on herbivory across stress gradients. Specifically, if climate change decreases stress, herbivory may increase, and vice versa for increasing stress. In addition, our work supports previous suggestions that multiple climate drivers are likely to have dampening effects on biotic interactions due to effects in different directions, though this is context‐dependent. 相似文献
7.
2013年5月,在青藏高原高寒沼泽化草甸收集优势种黑褐苔草(Carex atrofusca)立枯体凋落物。6月初,选择3个样带:长期积水带、周期性积水带和无积水带,并结合凋落物分解袋的方法,在每个样带区设置网孔大小分别为大(4.5 mm)、中(2.0 mm)、小(0.1mm)的3种凋落物分解袋,研究积水状态和网孔大小对凋落物早期分解的影响。结果显示:长期积水显著抑制凋落物的分解,而周期性积水和无积水环境中凋落物的质量损失率在大、中、小网孔凋落物袋中没有显著性的差异;网孔显著影响凋落物质量损失率,表现为大网孔中网孔小网孔;在早期分解过程中,凋落物的氮、磷均表现为富集;积水状态显著影响凋落物分解后氮、磷的富集;网孔大小对凋落物氮富集的影响显著,而对磷富集的影响不显著;积水状态和网孔大小对凋落物氮富集影响的交互作用极显著,但对磷富集没有显著的交互作用。研究发现,积水状态和网孔大小影响高寒沼泽化草甸凋落物分解以及氮、磷养分动态,由于不同网孔对凋落物分解的影响可用来反映不同土壤生物对凋落物分解的影响,因此,积水和土壤生物对维持高寒沼泽化草甸生态系统的结构和功能起着非常重要的作用。 相似文献
8.
通过研究小牛血清对CHO-C28细胞培养及HBsAg表达的影响,探讨小牛血清的不同采集时间对血清质量的影响。采集出生后4、8、12h(未进食)小牛的血清,对CHO-C28细胞进行传代、换液培养,并检测乙肝表面抗原(HBsAg)表达量。结果可见:①在细胞传代4次时,4h采集的血清细胞生长状态良好,8h采集的血清细胞出现明显的衰老,12h采集的血清细胞大面积死亡;②在细胞维持换液方面,4h采集的血清可维持细胞换液25次以上,8h采集的血清可勉强维持20次,12h采集的血清维持细胞换液10次时已大部分死亡;③乙肝表面抗原(HBsAg)表达量的检测结果,同批培养上清,4h采集的血清培养细胞表达量最高。可见,小牛出生后采集血清时间越早越好。 相似文献
9.
目的 以兰州兴隆山不同区域的土壤微生物为研究对象,分析比较土壤微生物数量与土壤酶活性之间的相关性。 方法 利用不同方法测定土壤理化性质、微生物数量以及土壤相关酶活特性;采用三区划线法进行土壤微生物的分离与纯化,通过16S rDNA和ITS方法进行优势菌株鉴定。 结果 兰州兴隆山土壤中微生物菌群数量由多到少依次为细菌、放线菌、真菌。通过分离纯化后,对其中的2株优势菌进行了鉴定,初步推断X2为萎缩芽胞杆菌属(Bacillus atrophaeus)细菌,Z2为栎生青霉属(Penicillium glandicola)真菌。从酶活特性可知,阳面的土壤过氧化氢酶活性比阴面高;随着海拔高度的增加,过氧化氢酶活性呈现增加趋势;阳面的土壤脱氢酶活性总体比阴面高,并且随着海拔梯度的升高,土壤脱氢酶活性也在不断升高。从相关性分析可知,不同海拔土样间微生物数量与酶活性之间表现出明显的相关性。 结论 兰州兴隆山土壤微生物数量丰富,且细菌数量居多;不同阴、阳面土壤微生物的层次分布以及活性也各有不同。以上研究可为兰州兴隆山土壤生态系统演替等提供参考依据,并为土壤生态环境的治理做铺垫。 相似文献
10.
Nitrogen (N) is one of the most important factors limiting plant productivity, and N fixation by legume species is an important source of N input into ecosystems. Meanwhile, N resorption from senescent plant tissues conserves nutrients taken up in the current season, which may alleviate ecosystem N limitation. N fixation was assessed by the 15N dilution technique in four types of alpine grasslands along the precipitation and soil nutrient gradients. The N resorption efficiency (NRE) was also measured in these alpine grasslands. The aboveground biomass in the alpine meadow was 4–6 times higher than in the alpine meadow steppe, alpine steppe, and alpine desert steppe. However, the proportion of legume species to community biomass in the alpine steppe and the alpine desert steppe was significantly higher than the proportion in the alpine meadow. N fixation by the legume plants in the alpine meadow was 0.236 g N/m2, which was significantly higher than N fixation in other alpine grasslands (0.041 to 0.089 g N/m2). The NRE in the alpine meadows was lower than in the other three alpine grasslands. Both the aboveground biomass and N fixation of the legume plants showed decreasing trends with the decline of precipitation and soil N gradients from east to west, while the NRE of alpine plants showed increasing trends along the gradients, which indicates that alpine plants enhance the NRE to adapt to the increasing droughts and nutrient‐poor environments. The opposite trends of N fixation and NRE along the precipitation and soil nutrient gradients indicate that alpine plants adapt to precipitation and soil nutrient limitation by promoting NRE (conservative nutrient use by alpine plants) rather than biological N fixation (open sources by legume plants) on the north Tibetan Plateau. 相似文献