Hydrology shapes microbial communities and microbiome-mediated growth of an Everglades tree island species

Plant-associated microbiomes can improve plant fitness by ameliorating environmental stress, providing a promising avenue for improving outplantings during restoration. However, the effects of water management on these microbial communities and their cascading effects on primary producers are unresolved for many imperiled ecosystems. One such habitat, Everglades tree islands, has declined by 54% in some areas, releasing excess nutrients into surrounding wetlands and exacerbating nutrient pollution. We conducted a factorial experiment, manipulating the soil microbiome and hydrological regime experienced by a tree island native, Ficus aurea, to determine how microbiomes impact growth under two hydrological management plans. All plants were watered to simulate natural precipitation, but plants in the “unconstrained” management treatment were allowed to accumulate water above the soil surface, while the “constrained” treatment had a reduced stage to avoid soil submersion. We found significant effects of the microbiomes on overall plant performance and aboveground versus belowground investment; however, these effects depended on hydrological treatment. For instance, microbiomes increased investment in roots relative to aboveground tissues, but these effects were 142% stronger in the constrained compared to unconstrained water regime. Changes in hydrology also resulted in changes in the prokaryotic community composition, including a >20 log₂fold increase in the relative abundance of Rhizobiaceae, and hydrology-shifted microbial composition was linked to changes in plant performance. Our results suggest that differences in hydrological management can have important effects on microbial communities, including taxa often involved in nitrogen cycling, which can in turn impact plant performance.     

Effects of legumes on soil physical quality in a maize crop

The effect of intercropped legumes and three N fertilizer rates in a continuous maize (Zea mays L.) cropping system on the physical properties of two soils were investigated for three years. The legumes, being a mixture of alfalfa, clover and hairy vetch, had a significant cumulative effect on some physical properties of both soil. The lowest stability and smallest mean weight diameter of soil aggregates were associated with monoculture maize plots. Aggregate size and stability were not affected by N fertilization at any of the rates of 0, 70, and 140 kg ha^-1 in intercropped plots, except that aggregate stability was actually reduced by N fertilization in one soil, the Ste. Rosalie clay. In maize plots in both soils, stability and size of soil aggregates were significantly increased with increased added N. Intercropped legumes significantly decreased dry bulk density and soil penetration resistance. Added N had no measurable influence on these compaction factors. Soil water properties were not significantly affected by either intercropping or N fertilization. Positive effects noted on soil aggregation and other physical properties in intercropped plots are the result of enhanced root activity, or incorporation of legumes as green manure, or both. Improvement of soil structure in maize plots associated with increasing N application was the result of increased maize-root residues.     

紫茎泽兰入侵对土壤酶活性和理化因子的影响

紫茎泽兰是我国危害最严重的外来入侵植物之一,为探明其入侵对土壤肥力的影响,比较研究了紫茎泽兰、云南菅、狗尾草群落和撂荒地下0~30 cm的4层土壤中6种酶活性和12种理化因子。结果表明群落类型和土壤深度对测定的各参数均有显著影响。随土壤深度的增加,多酚氧化酶、碱性磷酸酶、脲酶活性,以及有机质、全氮、全磷、全钙、水解氮、有效磷、速效钾含量和pH值均降低。总的看来,紫茎泽兰群落下碱性磷酸酶和脲酶活性,有机质、全氮、全磷、全钙、水解氮和有效磷含量,以及pH值均较高,全钾含量较低,但速效钾含量并不低,表明紫茎泽兰入侵多年后土壤肥力水平提高,形成了对其生长有利的土壤环境。     

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.     

The new higher level classification of eukaryotes with emphasis on the taxonomy of protists

This revision of the classification of unicellular eukaryotes updates that of Levine et al. (1980) for the protozoa and expands it to include other protists. Whereas the previous revision was primarily to incorporate the results of ultrastructural studies, this revision incorporates results from both ultrastructural research since 1980 and molecular phylogenetic studies. We propose a scheme that is based on nameless ranked systematics. The vocabulary of the taxonomy is updated, particularly to clarify the naming of groups that have been repositioned. We recognize six clusters of eukaryotes that may represent the basic groupings similar to traditional "kingdoms." The multicellular lineages emerged from within monophyletic protist lineages: animals and fungi from Opisthokonta, plants from Archaeplastida, and brown algae from Stramenopiles.     

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.     

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