CARAGANA FABR. PROMOTES REVEGETATION AND SOIL REHABILITATION IN SALINE-ALKALI WASTELAND

To determine how plantations of Caragana microphylla shrubs affect saline-alkali soil amelioration and revegetation, we investigated the vegetation and sampled soils from saline-alkali wasteland (SAW), perennial Caragana forestland (PCF), Caragana forest after fire disturbance (CFF). Results showed that with the development of Caragana Fabr., highly dominant species of Poaceae family, including Elymus dahuricus, Thermopsis lanceolata, Stipa tianschanica, died out in PCF. Moreover, Papilionaceae family, including Lespedeza indica, Oxytropis psammocharis, and Astragalus scaberrimus, was established both in PCF and CFF. Phytoremediation of saline-alkali wasteland (SAW) was achieved by plantation, resulting in the reduced soil pH, sodium adsorption ratio, exchangeable sodium percentage, salinity, and Na⁺ concentration around Caragana shrubs. Greater amounts of soil organic, total nitrogen, ammonium nitrogen, available phosphorus, and available potassium were observed in PCF topsoil than in SAW topsoil. The concentration of mineralized N in PCF soil was significantly lower than that in SAW soil at all sampled depths, indicating that Caragana shrubs were just using N and therefore less measured in soils. Fire disturbance resulted in decreased soil pH and salinity, but increased organic content, total nitrogen, and ammonium nitrogen. The improved soil parameters and self-recovery of shrubs indicated that Caragana shrubs were well established after burning event.     

Canopy height variation and environmental heterogeneity in the tropical dry forests of coastal Oaxaca,Mexico

Despite its importance for carbon storage and other ecosystem functions, the variation in vegetation canopy height is not yet well understood. We examined the relationship between this community attribute and environmental heterogeneity in a tropical dry forest of southern Mexico. We sampled vegetation in 15 sites along a 100‐km coastal stretch of Oaxaca State, and measured the heights of all woody plants (excluding lianas). The majority of the ca. 4000 individuals recorded concentrated in the 4–8 m height range. We defined three plant sets to describe overall community canopy height at each site: a set including all plants, a set made up by the tallest plants representing 10 percent of all individuals, and a set comprising the 10 tallest plants. For each site we computed maximum height and the mean and median heights of the three sets. Significant collinearity was observed between the seven resulting height variables, but null distributions constructed through bootstrap revealed their different behaviors as functions of species richness and density of individuals. Through linear modeling and a model selection procedure, we identified 21 models that best described the variation in canopy height variables. These models pointed out to soil (measured as PC1 of a principal component analysis performed on 10 soil variables), water stress, and elevation as the main drivers of canopy height variation in the region. In the event of increasing water stress resulting from global climate change, the studied tropical dry forests could become shorter and thus decrease their carbon storage potential.     

Insights into discharge argon-mediated biofilm inactivation

Formation of bacterial biofilms at solid–liquid interfaces creates numerous problems in biomedical sciences. Conventional sterilization and decontamination methods are not suitable for new and more sophisticated biomaterials. In this paper, the efficiency and effectiveness of gas discharges in the inactivation and removal of biofilms on biomaterials were studied. It was found that although discharge oxygen, nitrogen and argon all demonstrated excellent antibacterial and antibiofilm activity, gases with distinct chemical/physical properties underwent different mechanisms of action. Discharge oxygen- and nitrogen-mediated decontamination was associated with strong etching effects, which can cause live bacteria to relocate thus spreading contamination. On the contrary, although discharge argon at low powers maintained excellent antibacterial ability, it had negligible etching effects. Based on these results, an effective decontamination approach using discharge argon was established in which bacteria and biofilms were killed in situ and then removed from the contaminated biomaterials. This novel procedure is applicable for a wide range of biomaterials and biomedical devices in an in vivo and clinical setting.     

Organic carbon cycling in Taylor Valley, Antarctica: quantifying soil reservoirs and soil respiration

Organic carbon reservoirs and respiration rates in soils have been calculated for most major biomes on Earth revealing patterns related to temperature, precipitation, and location. Yet data from one of the Earth's coldest, driest, and most southerly soil ecosystems, that of the McMurdo Dry Valleys of Antarctica, are currently not a part of this global database. In this paper, we present the first regional calculations of the soil organic carbon reservoirs in a dry valley ecosystem (Taylor Valley) and report measurements of CO₂ efflux from Antarctic soils. Our analyses indicate that, despite the absence of visible accumulations of organic matter in most of Taylor Valley's arid soils, this soil environment contained a significant percentage (up to 72%) of the seasonally unfrozen organic carbon reservoir in the terrestrial ecosystem. Field measurements of soil CO₂‐efflux in Taylor Valley soils were used to evaluate biotic respiration and averaged 0.10 ± 0.08 μmol CO₂ m^?2 s^?1. Laboratory soil microcosms suggested that this respiration rate was sensitive to increases in temperature, moisture, and carbon addition. Finally, a steady‐state calculation of the mean residence time for organic carbon in Taylor Valley soils was 23 years. Because this value contradicts all that is currently known about carbon cycling rates in the dry valleys, we suggest that the dry valley soil carbon dynamics is not steady state. Instead, we suggest that the dynamic is complex, with at least two (short‐ and long‐term) organic carbon reservoirs. We also suggest that organic carbon in the dry valley soil environment may be more important, and play a more active role in long‐term ecosystem processes, than previously believed.     

Hydrocarbon Degradation and Biosurfactant Production by an Acenaphthene-degrading Pseudomonas Species

An acenaphthene-degrading bacterium putatively identified as Pseudomonas sp. strain KR3 and isolated from diesel-contaminated soil in Lagos, Nigeria was investigated for its degradative and biosurfactant production potentials on crude oil. Physicochemical analysis of the sampling site indicates gross pollution of the soil with high hydrocarbon content (2100 mg/kg) and detection of various heavy metals. The isolate grew luxuriantly on crude oil, engine oil and acenaphthene. It was resistant to septrin, amoxicillin and augmentin but was susceptible to pefloxacin, streptomycin and gentamycin. It was also resistant to elevated concentration of heavy metals such as 1–15 mM lead, nickel and molybdenum. On acenaphthene, the isolate exhibited specific growth rate and doubling time of 0.098 day^?1 and 3.06 days, respectively. It degraded 62.44% (31.2 mg/l) and 91.78% (45.89 mg/l) of 50 mg/l acenaphthene within 12 and 21 days. On crude oil, the specific growth rate and doubling time were 0.375 day^?1 and 1.85 days with corresponding percentage degradation of 33.01% (903.99 mg/l) and 87.79% (2403.71 mg/l) of crude oil (2738.16 mg/l) within 9 and 18 days. Gas chromatographic analysis of residual crude oil at the end of 18 days incubation showed significant reductions in the aliphatic, alicyclic and aromatic fractions with complete disappearance of benzene, propylbenzene, pristane, phytane, and nC₁₈-octadecane fractions of the crude oil. The isolate produced growth-associated biosurfactant on crude oil with the highest emulsification index (E₂₄) value of 72% ± 0.23 on Day 10 of incubation. The partially purified biosurfactant showed zero tolerance for salinity and had its optimal activity at 27°C and pH 2.0.     

Stability in the patterns of long‐term development and growth of the Canadian spruce–moss forest

Aim The spruce–moss forest is the main forest ecosystem of the North American boreal forest. We used stand structure and fire data to examine the long‐term development and growth of the spruce–moss ecosystem. We evaluate the stability of the forest with time and the conditions needed for the continuing regeneration, growth and re‐establishment of black spruce (Picea mariana) trees. Location The study area occurs in Québec, Canada, and extends from 70°00′ to 72°00′ W and 47°30′ to 56°00′ N. Methods A spatial inventory of spruce–moss forest stands was performed along 34 transects. Nineteen spruce–moss forests were selected. A 500 m² quadrat at each site was used for radiocarbon and tree‐ring dating of time since last fire (TSLF). Size structure and tree regeneration in each stand were described based on diameter distribution of the dominant and co‐dominant tree species [black spruce and balsam fir (Abies balsamea)]. Results The TSLF of the studied forests ranges from 118 to 4870 cal. yr bp . Forests < 325 cal. yr bp are dominated by trees of the first post‐fire cohort and are not yet at equilibrium, whereas older forests show a reverse‐J diameter distribution typical of mature, old‐growth stands. The younger forests display faster height and radial growth‐rate patterns than the older forests, due to factors associated with long‐term forest development. Each of the stands examined established after severe fires that consumed all the soil organic material. Main conclusions Spruce–moss forests are able to self‐regenerate after fires that consume the organic layer, thus allowing seed regeneration at the soil surface. In the absence of fire the forests can remain in an equilibrium state. Once the forests mature, tree productivity eventually levels off and becomes stable. Further proof of the enduring stability of these forests, in between fire periods, lies in the ages of the stands. Stands with a TSLF of 325–4870 cal. yr bp all exhibited the same stand structure, tree growth rates and species characteristics. In the absence of fire, the spruce–moss forests are able to maintain themselves for thousands of years with no apparent degradation or change in forest type.     

周期性土壤干旱和叶片水势对气孔响应木质部ABA灵敏度的影响

研究了周期性土壤干旱期间气孔对木质部ＡＢＡ响应的灵敏度的变化以及叶片水势对灵敏度的影响。实验结果证明了木质部ＡＢＡ浓度是反映根系周围土壤水分状况的一个指标的结论。土壤周期性干旱不影响木质部ＡＢＡ浓度对土壤水分状况的依赖关系,但显著地提高了气孔对木质部ＡＢＡ 响应的灵敏度。根据对实测数据的数学模拟结果显示,引起气孔导度下降５０％ 所需的木质部ＡＢＡ浓度从第一轮土壤干旱的７５０ ｎｍｏｌ／Ｌ降至第二轮土壤干旱的５５０ ｎｍｏｌ／Ｌ。分根实验的结果表明,叶片水分亏缺显著提高了气孔对木质部ＡＢＡ 的响应的灵敏程度,全根干旱中引起气孔导度下降５０ ％ 所需的木质部ＡＢＡ 浓度比半根干旱的小２ ～４ 倍。这表明,气孔对木质部ＡＢＡ响应的灵敏度不是一个固定的特性,可随植物生长环境及许多其他因素的变化而表现出很大的差异     

Assessing facilitative responses to a nurse shrub at the community level: the example of Potentilla fruticosa in a sub‐alpine grassland of northwest China

Biotic interaction studies have revealed a large discrepancy among experiments in target responses to the effects of neighbours, which may in part be due to both high species‐specificity of plant responses and low number of target species used in experiments. Our aim was to assess facilitative responses at the community level and the role of both functional groups and ecological attributes of target species. In a sub‐alpine grassland on the eastern Tibet plateau, we assessed growth responses of all species in the community to removal of a dominant shrub. We also measured changes in the main environmental variables. Species responses were analysed by functional group and in relation to their mean regional altitudinal distribution. All significant interactions were positive and affected one‐third of the total species richness of the community. All functional groups were facilitated but forbs were less strongly facilitated than in the two other groups. High‐alpine species were less strongly facilitated than low‐sub‐alpine species, but the strength of this relationship was weaker than that reported in previous work. There was evidence of a decrease in extreme temperatures below the canopy of the shrub but no variations in soil moisture. We conclude that the highly stressful conditions induced by the dry continental climate of the eastern Tibet plateau are a main driver of the exclusive dominance of positive interactions. Assessing interactive responses at the community level is likely to provide a useful tool to better understand the role of biotic interactions in community responses to environmental changes.     

黄土高原半干旱偏旱区草粮轮作田土壤水分恢复效应模拟

采用实地调查和EPIC模型相结合的方法,模拟研究了黄土高原半干旱偏旱区不同草粮轮作模式的土壤水分恢复效应.结果表明：多年生苜蓿地和苜蓿翻耕后种植粮食作物农田0～10 m土层土壤湿度调查值与模拟值间的相关系数均超过0.9（P<0.01）,相对均方根误差在0.05～0.16,相对误差均低于10%;模拟与实测的土壤湿度剖面分布变化趋势一致.在黄土高原半干旱偏旱区,苜蓿地深层土壤干层恢复难度较大,在种植苜蓿期间应避免8～10 m土层土壤湿度降到5.7%以下.苜蓿地适宜种植年限为4～6 a,最长不应超过8 a.苜蓿翻耕后适宜采用马铃薯→马铃薯→春小麦轮作模式进行土壤水分恢复,32～33 a后可以再次种植苜蓿.     

Bioavailable cadmium during the bioremediation of phenanthrene-contaminated soils using the diffusive gradients in thin-film technique

AIMS: To study the impact of fungal bioremediation of phenanthrene on trace cadmium solid-solution fluxes and solution phase concentration. METHODS AND RESULTS: The bioremediation of phenanthrene in soils was performed using the fungus Penicillium frequentans. Metal behaviour was evaluated by the techniques of diffusive gradient in thin-films (DGT) and filtration. Fluxes of cadmium (Cd) show a significant (P < 0.002) increase after the start of bioremediation, indicating that the bioremediation process itself releases significant amount of Cd into solution from the soil solid-phase. Unlike DGT devices, the solution concentration from filtration shows a clear bimodal distribution. We postulate that the initial action of the fungi is most likely to breakdown the surface of the solid phase to smaller, 'solution-phase' material (<0.45 microm) leading to a peak in Cd concentration in solution. CONCLUSIONS: Phenanthrene removal from soils by bioremediation ironically results in the mobilization of another toxic pollutant (Cd). SIGNIFICANCE AND IMPACT OF THE STUDY: Bioremediation of organic pollutants in contaminated soil will likely lead to large increases in the mobilization of toxic metals, increasing metal bio-uptake and incorporation into the wider food chain. Bioremediation strategies need to account for this behaviour and further research is required both to understand the generality of this behaviour and the operative mechanisms.