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91.
The affinity of iron oxides and hydroxides for phosphorus is thought to contribute to phosphorus limitation to net primary
productivity in humid tropical forests on acidic, highly weathered soils. Perennially warm, humid conditions and high biological
activity in these soils can result in fluctuating redox potential that in turn leads to considerable iron reduction in the
presence of labile carbon and humic substances. We investigated the effects of reducing conditions in combination with the
addition of labile carbon substrates (glucose and acetate) and an electron shuttle compound on iron reduction and phosphorus
release in a humid tropical forest soil. Glucose or acetate was added to soils as a single dose at the beginning of the experiment,
and as pulsed inputs over time, which more closely mimics patterns in labile carbon availability. Iron reduction and phosphorus
mobilization were weakly stimulated by a single low level addition of carbon, and the addition of the electron shuttle compound
with or without added carbon. Pulsed labile carbon additions produced a significant increase in soil pH, soluble iron, and
phosphorus concentrations. Pulsed labile carbon inputs also promoted the precipitation of ferrous hydroxide complexes which
could increase the capacity for P sorption, although our results suggest that rates of P solubilization exceeded re-adsorption.
Plant and microbial P demand are also likely to serve as an important sinks for released P, limiting the role of P re-adsorption.
Our results suggest that reducing conditions coupled with periodic carbon inputs can stimulate iron reduction and a corresponding
increase in soil phosphorus mobilization, which may provide a source of phosphorus to plants and microorganisms previously
undocumented in these ecosystems. 相似文献
92.
Carbon monoxide uptake kinetics in unamended and long-term nitrogen-amended temperate forest soils 总被引:4,自引:0,他引:4
The effect of nitrogen (N) additions on the dynamics of carbon monoxide consumption in temperate forest soils is poorly understood. We measured soil CO profiles, potential rates of CO consumption and uptake kinetics in temperate hardwood and pine control plots and plots amended with 50 and 150 kg N ha-1 year-1 for more than 15 years. Soil profiles of CO concentrations were above atmospheric levels in the high-N plots of both stands, suggesting that in these forest soils the balance between consumption and production may be shifted so that either production is increased or consumption decreased. Highest rates of CO consumption were measured in the organic horizon and decreased with soil depth. In the N-amended plots, CO consumption increased in all but one soil depth of the hardwood stand, but decreased in all soil depths of the pine stand. CO enzyme affinities increased with soil depth in the control plots. However, enzyme affinities in the most active soil depths (organic and 0-5 cm mineral) decreased in response to low levels of N in both stands. In the high-N plots, affinities dramatically-increased in the hardwood stand, but decreased in the organic horizon and increased slightly in the 0-5 cm mineral soil in the pine stand. These findings indicate that long-term N addition either by fertilization or deposition may alter the size, composition and/or physiology of the community of CO consumers so that their ability to act as a sink for atmospheric CO has changed. This change could have a substantial effect on the lifetime of greenhouse gases such as CH4 and therefore the future of Earth's climate. 相似文献
93.
R. Milla S. Palacio-Blasco M. Maestro-Martínez G. Montserrat-Martí 《Plant and Soil》2006,280(1-2):369-372
Studies dealing with changes in the plant internal nutrient cycling in response to natural, long-term P-fertility gradients
are scarce. In this short report, we show some evidence on how leaf P dynamics can be drastically altered when plants typical
from nutrient-poor sites grow in long-term P-enriched soils. The study was conducted in two natural populations of the Mediterranean
evergreen shrub Pistacia lentiscus L.: one in a P-poor site and the other in a P-rich site. Soil texture and N, P, and organic matter contents were measured
at each site. Leaf N and P concentrations were also measured in current-year, 1-year-old, and 2-year-old leaves, and in the
senesced leaves. In the P-poor site, leaf P and N decreased as the leaves aged. This occurs because of nutrient reabsorption
to other plant organs and/or dilution of nutrients by carbon compounds. In contrast, the leaves from the P-rich site acummulated
P (but not N) during leaf lifespan. Consequently, P concentration in senesced leaves was very high in the P-rich site. These
results show that, in long-lived perennials living in the field, long-term P enrichment can switch the normal process of P
resorption during leaf aging to P accretion in the leaf. P accumulation in the leaves, which are periodically shed, might
constitute a simple P excretion mechanism for plants typical from P-poor soils. 相似文献
94.
Increased nutrient availability can have a large impact in Australian woodland ecosystems, many of which are very poor in
nutrients, particularly phosphorus. A study was conducted in an urban Banksia woodland remnant in Perth, southwest Western Australia to test the hypothesis that the soil nutrient status in areas in good
condition (GC), poor condition invaded by the perennial grass Ehrharta calycina (PCe), and poor condition invaded by the perennial herb Pelargonium capitatum (PCp), is reflected in the nutrient status of the native and introduced species. Leaf concentrations of P, K, N, Na, Ca,
Mg, S, B, Cu, Fe, Mn and Zn of six native (Banksia attenuata, Banksia menziesii, Allocasuarina humilis, Melaleuca systena, Macrozamia fraseri and Conostylis aculeata) and four introduced species (Ehrharta calycina, Pelargonium capitatum, Gladiolus caryophyllaceus and Briza maxima), were measured. Soil pH, electrical conductivity, N (total), P (total), available P, K, S and organic C were assessed beneath
all species on all sites. Significantly higher concentrations of soil P (total) and P (HCO3) were found at PCe and PCp sites than GC sites, while PCp sites also had significantly higher soil concentrations for N (total)
and S. Principal Components Analysis of the leaf analyses showed (a) individual species have characteristically different
nutrient concentrations; (b) the introduced species Ehrharta calycina and Pelargonium capitatum clustered separately from each other and by vegetation condition. Leaf concentrations of P were significantly (P<0.05) higher, and K and Cu were significantly lower in PCe and PCp sites compared with those at GC sites. Introduced species
leaf nutrient concentrations were significantly greater than native species for all nutrients except Mn which was significantly
lower, with no differences for Mg and B. The results indicate a key role for P in the Banksia woodland, and we conclude that higher levels of available P at invaded sites are having a detrimental impact on the ecosystem.
These results provide new knowledge to enhance conservation practices for the management of the key threatening process of
invasion within a biodiversity hot spot.
Section Editor: T. Kalapos 相似文献
95.
Experiments addressing the role of plant species diversity for ecosystem functioning have recently proliferated. Most studies
have focused on plant biomass responses. However, microbial processes involved in the production of N2O and the oxidation of atmospheric CH4 could potentially be affected via effects on N cycling, on soil diffusive properties (due to changes in water relations and
root architecture) and by more direct interactions of plants with soil microbes. We studied ecosystem-level CH4 and N2O fluxes in experimental communities assembled from two pasture soils and from combinations of 1, 3, 6, 8 or 9 species typical
for these pastures. The soils contrasted with respect to texture and fertility. N2O emissions decreased with diversity and increased in the presence of legumes. Soils were sinks for CH4 at all times; legume monocultures were a smaller sink for atmospheric CH4 than non-legume monocultures, but no effect of species richness per se was detected. However, both the exchange of CH4 and N2O strongly depended on plant community composition, and on the interaction of composition with soil type, indicating that
the functional role of species and their interactions differed between soils. N2O fluxes were mainly driven by effects on soil nitrate and on nitrification while soil moisture had less of an effect. Soil
microbial C and N and N mineralisation rates were not altered. The driver of the interactive soil type×plant community composition-effects
was less clear. Because soil methanotrophs may take longer to respond to alterations of N cycling than the 1/2 year treatment
in this study, we also tested species richness-effects in two separate 5-year field studies, but results were ambiguous, indicating
complex interactions with soil disturbance. In conclusion, our study demonstrates that plant community composition can affect
the soil trace gas balance, whereas plant species richness per se was less important; it also indicates a potential link between the botanical composition of plant communities and global
warming. 相似文献
96.
Michael S. Ross Sherry Mitchell-Bruker Jay P. Sah Stuart Stothoff Pablo L. Ruiz David L. Reed Kris Jayachandran Charles L. Coultas 《Hydrobiologia》2006,569(1):37-59
Extensive portions of the southern Everglades are characterized by series of elongated, raised peat ridges and tree islands
oriented parallel to the predominant flow direction, separated by intervening sloughs. Tall herbs or woody species are associated
with higher elevations and shorter emergent or floating species are associated with lower elevations. The organic soils in
this “Ridge-and-Slough” landscape have been stable over millennia in many locations, but degrade over decades under altered
hydrologic conditions. We examined soil, pore water, and leaf phosphorus (P) and nitrogen (N) distributions in six Ridge and
Slough communities in Shark Slough, Everglades National Park. We found P enrichment to increase and N to decrease monotonically
along a gradient from the most persistently flooded sloughs to rarely flooded ridge environments, with the most dramatic change
associated with the transition from marsh to forest. Leaf N:P ratios indicated that the marsh communities were strongly P-limited,
while data from several forest types suggested either N-limitation or co-limitation by N and P. Ground water stage in forests
exhibited a daytime decrease and partial nighttime recovery during periods of surface exposure. The recovery phase suggested
re-supply from adjacent flooded marshes or the underlying aquifer, and a strong hydrologic connection between ridge and slough.
We therefore developed a simple steady-state model to explore a mechanism by which a phosphorus conveyor belt driven by both
evapotranspiration and the regional flow gradient can contribute to the characteristic Ridge and Slough pattern. The model
demonstrated that evapotranspiration sinks at higher elevations can draw in low concentration marsh waters, raising local
soil and water P concentrations. Focusing of flow and nutrients at the evapotranspiration zone is not strong enough to overcome
the regional gradient entirely, allowing the nutrient to spread downstream and creating an elongated concentration plume in
the direction of flow. Our analyses suggest that autogenic processes involving the effects of initially small differences
in topography, via their interactions with hydrology and nutrient availability, can produce persistent physiographic patterns
in the organic sediments of the Everglades. 相似文献
97.
【目的】采用传统的纯培养技术,分离新疆阿克苏地区典型的盐碱地中的粘细菌,并初步分析盐碱地土壤中可培养粘细菌资源的多样性。【方法】采用传统的水琼脂法、滤纸法和改良的土壤浸出液法分离新疆阿克苏地区25份盐碱地的粘细菌。结合分析土样的酸碱度、含盐量、地理位置及其植被分布情况分析新疆阿克苏地区盐碱地粘细菌资源多样性。【结果】共分离到58株粘细菌,它们被鉴定为:粘球菌属(Myxococcus)33株;珊瑚球菌属(Corallococcus)14株;孢囊杆菌属(Cystobacter)6株;堆囊菌属(Sorangium)2株;侏囊菌属(Nannocystis)2株;多囊菌属(Polyangium)1株。其中粘球菌抗逆性强,分离的菌株数最多,在pH值7.5-8.5范围的盐碱地中普遍存在;其次为珊瑚球菌属;而侏囊菌属、多囊菌属的菌株较少见。【结论】新疆阿克苏地区盐碱地粘细菌多样性不高,可能受分离纯化方法、含盐量以及土壤性质影响较大。 相似文献
98.
Tumor hypoxia may be an indicator of poor survival in cancer patients. Thus, an understanding of the molecular mechanism responsible for hypoxic tumor selection is essential to gain further insight into tumor biology. Our aim in this study was to investigate whether hypoxia-responsive GLTSCR2 contributes to death resistance and increased invasiveness of hypoxia-selected glioblastoma cells. We found that repeated hypoxia downregulates p53-upstream regulator, GLTSCR2, which resulted in increased death resistance and invasive potential of glioblastoma cells. Restoration of GLTSCR2 expression suppressed the malignant potential of hypoxia-selected cells. Our results indicate that GLTSCR2 participates in hypoxia-induced malignant potential. 相似文献
99.
Catello Pane Domenica Villecco Francesco Campanile Massimo Zaccardelli 《Biocontrol Science and Technology》2012,22(12):1373-1388
A stepwise screening strategy made it possible to identify five new Bacillus spp. strains for biocontrol of Rhizoctonia solani, Sclerotinia minor and Fusarium solani. In vitro and in vivo biocontrol activity and M13-PCR DNA-fingerprinting led to the selection of these valuable biological control agents (BCAs) from a wide collection of over 250 candidates. At the end of this selection, the highest potential antagonists were identified at species level by 16S-rRNA gene sequence analysis, and results assigned them to Bacillus subtilis group as Bacillus amyloliquefaciens- and Bacillus methylotrophicus-related strains. In the current study, spore-forming bacteria provided substantial biocontrol of telluric diseases on cress and other different host plants. The strains named 15S and 09C were effective in disease control on Brassica oleracea/R. solani pathosystem, whereas Sclerotinia drop of lettuce was reduced by treatments with the strains 17S and 08C. Finally, the strains 17S and 12S were equally effective to control potato Fusarium rot. The evident zone of inhibition seen in dual culture plates suggested antibiosis-like antagonisms as the main mechanisms used by these bacterial isolates in interaction with the pathogens. Additionally, the API-ZYM method revealed constitutive activity of certain extracellular enzymes that could be involved in plant fortification. Bacillus strains isolated from compost and compost-amended soils are promising BCAs that have potential for practical application as biofungicides. 相似文献
100.
R. Vijayakumar K. Panneerselvam C. Muthukumar N. Thajuddin A. Panneerselvam R. Saravanamuthu 《Indian journal of microbiology》2012,52(2):230-239
Totally 25 marine soil samples were collected from the region of Palk Strait of Bay of Bengal, Tamil Nadu, and were subjected to the isolation of actinomycetes. Sixty-eight morphologically distinct isolates were obtained and 37% (25) of them had antimicrobial activity. The potential producer was named as Streptomyces sp. VPTS3-1 and the phylogenetic evaluation on the basis of 16S rDNA sequence further categorized the organism as Streptomyces afghaniensis VPTS3-1. Further, the antimicrobial compound was extracted from the isolate using various solvents and the antimicrobial efficacies were tested against bacterial and fungal pathogens. In addition, in vitro optimization of parameters for the antimicrobial compound production revealed that the suitable pH as 7–8, the period of incubation as 9 days, temperature (30°C), salinity (2%), and starch and KNO3 as the suitable carbon and nitrogen sources respectively in starch–casein medium. 相似文献