The role of land plants,phosphorus weathering and fire in the rise and regulation of atmospheric oxygen

The evolution of vascular plants and their spread across the land surface, beginning ～420 Ma, progressively increased the rate of weathering of phosphorus from rocks. This phosphorus supply promoted terrestrial and marine productivity and the burial of organic carbon, which has been the major source of O₂ over geological timescales. Hence, it is predicted that the rise of plants led to an increase in the O₂ content of the atmosphere from ～12 vol %, 570–400 Ma to its present level of ～21 vol % by ～340 Ma. Previous modelling studies suggest that O₂ then rose to ～35 vol % ～300 Ma. Such high concentrations are difficult to reconcile with the known persistence of forests, because rising O₂ increases the frequency and intensity of vegetation fires, tending to decrease biomass and cause ecological shifts toward faster regenerating ecosystems. Rising O₂ also directly inhibits C3 photosynthetic carbon assimilation and increases the production of toxic reactive oxygen species in cells. These effects suppress plant‐induced phosphorus weathering and hence organic carbon burial, providing a sensitive negative feedback on O₂. A revised model predicts that this mechanism could have regulated atmospheric O₂ within the range 15–25 vol % for the last 350 million years.     

Effects of Wind Speed and Atmospheric Pressure on Mate Searching Behavior in the Aphid Parasitoid Aphidius nigripes (Hymenoptera: Aphidiidae)

The effects of wind speed and atmospheric pressure on male mate searching behavior, modulated by a female sex pheromone, were investigated in the aphid parasitoid Aphidius nigripes (Hymenoptera: Aphidiidae). Male A. nigripe generally did not reach females at wind speeds of 100 cm/sec, as the majority of individuals taking flight in the pheromone plume (81.8%) were unable to sustain upwind flight. At lower wind velocities, male responsiveness to females generally decreased with distance from the source. However, wind speeds approaching the upper threshold (100 cm/sec) tended to eliminate this distance effect. Therefore, there appears to be a trade-off between the need for higher wind speeds to detect the pheromone source from long distances, and a reduction in male flight capacity as wind velocity increases. Our results also indicate that chemical communication in A. nigripes could be affected by variations in atmospheric pressure, as we observed a relationship between pressure fluctuations in the 24 hr prior to testing and male responsiveness to females. The importance of these abiotic factors on mate searching behavior is discussed within the context of the reproductive biology of A. nigripes.     

Savanna Fires in East-Central Senegal: Distribution Patterns, Resource Management and Perceptions

The temporal and spatial distribution of fires for an area in east-central Senegal was determined on the basis of multi-temporal NOAA AVHRR satellite images. Three years of data (1990–1992) were analyzed defining the boundary between two different fire regimes: very few and scattered fires to the north with the majority of fires south of the boundary. This boundary was stable for the three dry seasons examined and was identical to the northernmost extension of fires as determined by visual inspection of a hard copy Landsat image mosaic. Fire frequencies were analyzed in relation to dominant vegetation types and yearly precipitation, and the findings compared to results of a field survey of the local population's perceptions of the causes and implications of fires. Survey results clearly showed that the use of fire in the study area is closely linked to the utilization of the environment for livestock grazing and crop production. We conclude that the local population has a high degree of awareness about the application of fire, that different fire use practices concerning can be identified respectively in the grasslands of the northern and the savanna of the southern parts of the study area, and that these practices reflect a well adapted production strategy. Finally, we recommend policy decisions be more flexible in the light of local understanding of fire use.     

Hyposensitive canopy conductance renders ecosystems vulnerable to meteorological droughts

Increased meteorological drought intensity with rising atmospheric demand for water (hereafter vapor pressure deficit [VPD]) increases the risk of tree mortality and ecosystem dysfunction worldwide. Ecosystem-scale water-use strategy is increasingly recognized as a key factor in regulating drought-related ecosystem responses. However, the link between water-use strategy and ecosystem vulnerability to meteorological droughts is poorly established. Using the global flux observations, historic hydroclimatic data, remote-sensing products, and plant functional-trait archive, we identified potentially vulnerable ecosystems, examining how ecosystem water-use strategy, quantified by the percentage bias (δ) of the empirical canopy conductance sensitivity to VPD relative to the theoretical value, mediated ecosystem responses to droughts. We found that prevailing soil water availability substantially impacted δ in dryland regions where ecosystems with insufficient soil moisture usually showed conservative water-use strategy, while ecosystems in humid regions exhibited more pronounced climatic adaptability. Hyposensitive and hypersensitive ecosystems, classified based on δ falling below or above the theoretical sensitivity, respectively, achieved similar net ecosystem productivity during droughts, employing different structural and functional strategies. However, hyposensitive ecosystems, risking their hydraulic system with a permissive water-use strategy, were unable to recover from droughts as quickly as hypersensitive ones. Our findings highlight that processed-based models predicting current functions and future performance of vegetation should account for the greater vulnerability of hyposensitive ecosystems to intensifying atmospheric and soil droughts.     

油藏注入水靶向脱硫潜力的高温脱硫菌群富集驯化

【背景】海上油田见聚后产出水硫化物超标,影响到注聚水的配聚黏度,采用生物脱硫时,由于常规除硫菌难以适应除油后产出液的高温,使得脱硫效果不佳。【目的】分析海上采出液水处理过程的菌群结构,明确生物处理各节点的菌群构成变化;开展耐高温脱硫菌驯化筛选,获得耐高温的高效脱硫菌。【方法】采集来自胜利油田海三站的水样,以16S rRNA基因高通量测序技术分析样本菌群结构,并分别在不同温度(55、60和65℃)下的无机富集培养基中进行多轮转接驯化,结合常压室温等离子体(atmospheric and room temperature plasma, ARTP)诱变技术筛选获得耐高温的脱硫菌群,采用宏基因组测序技术分析富集菌群的组成,并测定其脱硫能力。【结果】处理前的采出液水样含有较多的嗜热菌和硫酸盐还原菌,如Thermodesulfovibrio、Pseudothermotoga、Thermolithobacter、Fervidobacterium、Thermovenabulales和Pseudomonas;以厌氧气浮除油工艺处理的出水中,嗜氢菌属(Hydrogenophilus)成为最主要的优势菌,...     

Nutrient budgets in a dry heathland watershed in northeastern Spain

Dissolved nutrient inputs in bulk precipitation and outputs in streamwater were measured during 3 years of contrasting hydrological conditions in a 6.3-ha, grazed heathland watershed on schists in the Montseny mountains (NE Spain), drained by an intermittent stream. On average, 39% of the precipitation became streamflow. Bulk precipitation delivered positive net alkalinity (mean 0.22 keq/ha/yr), sulphate input was moderate (9.0 kg SO₄-S/ha/yr), and the mean input of inorganic N was not exceptionally high (6.6 kg/ha/yr). Ion concentrations were relatively low in streamwater; SO₄ ^2- was the dominant anion. Most concentrations in streamwater varied seasonally, with maxima in late summer or early autumn and minima in spring. This pattern probably resulted from increased availability of ions for leaching due to decomposition of organic matter and chemical weathering during the warm period. Nitrate concentrations were relatively high in winter and dropped sharply in early spring, probably because of biological uptake. Annual element outputs in streamwater varied between years and seemed to be controlled by both the amount of annual streamflow and its seasonal distribution. Annual inputs exceeded outputs for dissolved inorganic N. The watershed accumulated H⁺ and Ca²⁺, had net losses of Na⁺ and Mg²⁺, and was close to steady state for K⁺, SO₄ ^2-, Cl^- and alkalinity. The chloride budgets gave no evidence of substantial dry deposition in this system. The cationic denudation rate was negative (-0.14 keq/ha/yr) because Ca²⁺ retention was higher than net exports of Na⁺ and Mg²⁺ from silicate weathering. Low nutrient export and little production of alkalinity suggest that this watershed has a low buffering capacity.     

Variability of entrainment of cohesive sediments in freshwater

Estimates of sediment entrainment are required for models of particle transport in lakes and estuaries but are difficult to make because of the multiplicity of factors affecting cohesiveness of surficial sediments. We present results of sediment resuspension studies performed in an annular flume calibrated with laser-Doppler velocimetry. In our experiments, using sediments collected from two sites in the R. Raisin which flows into L. Erie and from one site in the western basin of L. Erie near the mouth of the R. Raisin, we applied shear stresses at the sediment-water interface in steps from 2 to 12 dyne/cm². Percent water content at the surface of the sediments was either 77 or 74%, and trials were run with and without oxygenating the water overlying the sediments. Entrainment rates as a function of shear stress at the sediment-water interface were best described by a power-law relationship. All but 14% of the variability in the power law expression was due to shear stress and percent water content; the variability not accounted for was due to differences in particle size distributions, chemical properties, and biological activity in the sediments.     

Atmospheric input of inorganic nitrogen to the Western Mediterranean

Bulk inorganic nitrogen deposition was monitored over a period of 3 years at the Bavella Pass (Corsica, France). Annual fluxes range between 126 and 150mol.m^–2.d-^–1, increasing slightly with annual rainfall. Natural background average concentrations of rain water and associated fluxes were estimated from a classification of rain events into natural (Oceanic and Saharan), polluted and composite. Long range transport of incoming polluted air masses increases the atmospheric wet nitrogen input by at least a factor of 1.6 in this Mediterranean area. Extrapolation of atmospheric dissolved inorganic nitrogen input to the Western Mediterranean leads to fluxes of 80 to l00mol.m^–2.d-^–1. This atmospheric input is in the same order of magnitude as the inorganic nitrogen riverine input. As a consequence, the nitrogen budget for the Mediterranean has had to be reassessed. Atmospheric wet inorganic nitrogen input is of noticeable importance to marine Mediterranean ecosystems, representing on average 10 to 25% of new production in the Western Basin, with values of up to 60% in oligotrophic zones.     

The effects of low concentrations of particulates from paper mill effluent on the macroinvertebrate community of a fast-flowing stream

The effects of a paper mill effluent on the macroinvertebrate community were assessed for the riffle areas of a large fast-flowing stream, the lower reaches of the Saranac River of northern New York State, U.S.A. The effluent caused few changes in dissolved oxygen concentration, pH, biochemical oxygen demand, temperature or nutrient content; however, significant differences in transmitted light, concentrations of particulates and accumulated debris on the substrate were observed. A moderate decrease in invertebrate diversity correlated with increased levels of particulates and substrate debris. An analysis of the response of invertebrate functional groups revealed the effluent had little effect on the density of gathering collector organisms. The functional groups most severely reduced in density were the filtering collectors and scrapers. Predators showed a moderate reduction in density in response to the effluent. The alterations in invertebrate densities were attributed largely to the alterations in seston and substrate caused by the introduction of particulates composed mainly of paper fiber and inert dye.