Comparative diversity and abundance of ammonia monooxygenase genes in mulched and vegetated soils

Soil microbial habitats are altered by mulching, a common practice in urban areas during which vegetation is removed and soils covered to suppress weeds and retain moisture. Soil microorganisms drive nitrogen-cycling processes in mulched soils, because living plants no longer take up ammonium-N released during decomposition of residual organic matter. Because ammonia oxidizers carry out the first, rate-limiting step of nitrification, we compared ammonia oxidizers in experimental, unfertilized plots of mulched and vegetated soils. We hypothesized that mulched and vegetated soils would support contrasting communities of bacterial and archaeal ammonia oxidizers, as determined by quantitative PCR and primers specific for genes encoding ammonia monooxygenase subunit A (amoA). Clone libraries of archaeal amoA also were constructed to compare diversity in soil cores, duplicate blocked plots, and treatments (bark-mulched, gravel-mulched, and unmanaged old field vegetation). Gene copies from ammonia-oxidizing bacteria (AOB) ranged from 2.2 × 10⁶ to 2.7 × 10⁷ gene copies per gram dry soil and did not differ across treatments. In contrast, gene copies from ammonia-oxidizing archaea (AOA) ranged from 9.1 × 10⁵ to 1.0 × 10⁸ copies per gram dry soil, with bark-mulched soils having significantly lower abundance. Community structure of AOA in gravel-mulched soils was distinct from the other two treatments. At 97% amino acid similarity, 22 operational taxonomic units, or OTUs, were identified, with only one OTU found in all 18 clone libraries. This ubiquitous OTU-1, which was highly similar to published amoA sequences recovered from soils, comprised 55% of all 482 translated sequences. Greater variability in OTU richness was observed among cores from mulched soils than from vegetated soils. Our observations supported our hypothesis that AOA communities differ in mulched and vegetated soils, with mulched soils providing altered and variable microniches for these N cycling microorganisms.     

Tree species effects on microbial respiration from decomposing leaf and fine root litter

Tree species have an impact on decomposition processes of woody litter, but the effects of different tree species on microbial heterotrophic respiration derived from decomposing litter are still unclear. Here we used leaf and fine root litter of six tree species differing in chemical and morphological traits in a temperate forest and elucidated the effects of tree species on the relationships between litter-derived microbial respiration rates and decomposition rates and morphological traits, including specific leaf area (cm² g⁻¹) and specific root length (m g⁻¹) of litter at the same site. Litterbags set in forest soil were sequentially collected five times over the course of 18 months. During litter decomposition, microbial respiration from leaf and fine root litter differed among the six tree species. Temporal changes in the remaining mass and morphology (specific leaf area and specific root length) were observed, and the magnitude of these changes differed among species. Positive correlations were observed between respiration and mass loss or morphology across species. These results revealed that litter mass loss and morphological dynamics during decomposition jointly enhanced microbial respiration, and these carbon-based litter traits explained species differences in decomposition of leaves and fine roots. In conclusion, tree species influenced the magnitude and direction of microbial respiration during leaf/fine root litter decomposition. Tree species also affected the relationship between microbial respiration and litter decomposition through direct effects of litter traits and indirect effects mediated by regulation of heterotroph requirements.     

控释肥对菇渣基质电导率及容器苗生长的影响

通过木槿容器苗栽培试验,研究了控释肥、控释肥+少量普通复合肥(BB肥)、普通复合肥、营养液对菇渣基质电导率及木槿苗叶片数、枝条长度、最大叶面积、叶绿素含量、植株鲜重等生长指标的影响。结果表明:普通肥料处理前期菇渣基质电导率过高,后期电导率偏低,木槿容器苗生长不理想;控释肥处理前期菇渣基质EC值稍低,但后期木槿各项生长指标与营养液处理相当;控释肥加入少量普通复合肥制成的BB肥,养分释放与木槿容器苗的养分需求基本一致,木槿生长总体优于其他施肥处理。控释肥施肥方法简单,效果理想,是基质容器育苗值得推广的一种施肥方法。     

A pathogenic myxoma virus in vaccinated and non-vaccinated commercial rabbits

A case of a myxoma virus strain in vaccinated and non-vaccinated rabbits is described, and genetic identification of that strain was performed in this study. In two commercial farms being 150 km apart, myxomatosis has been occurred after the import of animals from a common supplier. The disease was manifested firstly in the existing non-immune population of does and fatteners, and later in all vaccinated animals, being 2–3 months immune at the time of first symptoms. Morbidity was almost 100% with nasal discharge, listlessness, fever, eyelid swelling, eye and nasal purulent discharge, papules in the ears, facial oedema, and swelling of the anagenital region, with result always the death of the animals. Examination by PCR had shown the presence of a 492-bp specific product in all the symptomatic animals tested from both farms, having 100% nucleotide sequence identity with the homologous region of the myxoma virus Lausanne strain. The simultaneous occurrence of myxomatosis in the vaccinated and non-vaccinated rabbits of both farms, suggests that the supplier was possibly the source of a viral isolate with increased virulence.     

基于不同人为干扰的土壤全量氮磷钾空间变异性研究

采用地统计学与GIS技术相结合的方法，对无人为干扰区25个样本、人为干扰区30个样本土壤全量氮磷钾的空间异质性进行了研究。结果表明：人为干扰区土地多被开发成林地、育苗地，自然植被残体等被移除，土壤腐殖质来源减少，加之由于土层翻动，土壤透气性变好，加快了养分分解与利用，土壤全量氮磷钾含量均值分别降低至0.433、0.902、15.325 g·kg-1，数据间的差异性和分布状态也发生变化;球状模型能较好地拟合无人为干扰区土壤全磷分布,而高斯模型则能较高地拟合两区其余养分指标的分布,两区理论模型的R²介于0.66和0.90之间，拟合精度高;土壤全量氮磷钾的理论模型中，均以无人为干扰区模型的R²高且RSS小;无人为干扰区全量氮磷钾的高值区均在植被覆盖度高的区域内。干扰程度较大的区域，土壤全氮和全磷含量较低，因此应补充适量氮肥和磷肥，满足养分需求。     

Phylogenetic structure of arbuscular mycorrhizal community shifts in response to increasing soil fertility

Understanding the underlying mechanisms driving responses of belowground communities to increasing soil fertility will facilitate predictions of ecosystem responses to anthropogenic eutrophication of terrestrial systems. We studied the impact of fertilization of an alpine meadow on arbuscular mycorrhizal (AM) fungi, a group of root-associated microorganisms that are important in maintaining sustainable ecosystems. Species and phylogenetic composition of AM fungal communities in soils were compared across a soil fertility gradient generated by 8 years of combined nitrogen and phosphorus fertilization. Phylogenetic patterns were used to infer the ecological processes structuring the fungal communities. We identified 37 AM fungal virtual taxa, mostly in the genus Glomus. High fertilizer treatments caused a dramatic loss of Glomus species, but a significant increase in genus richness and a shift towards dominance of the lineage of Diversispora. AM fungal communities were phylogenetically clustered in unfertilized soil, random in the low fertilizer treatment and over-dispersed in the high fertilizer treatments, suggesting that the primary ecological process structuring communities shifted from environmental filtering (selection by host plants and fungal niches) to a stochastic process and finally to competitive exclusion across the fertilization gradient. Our findings elucidate the community shifts associated with increased soil fertility, and suggest that high fertilizer inputs may change the dominant ecological processes responsible for the assembly of AM fungal communities towards increased competition as photosynthate from host plants becomes an increasingly limited resource.     

Responses of springtail and mite populations to prolonged periods of soil freeze-thaw cycles in a sub-arctic ecosystem

The effect of temperature changes on soil communities is an important aspect when estimating the effects of a predicted climate change. The aim of this investigation was to increase knowledge on how freeze-thaw cycles alter the soil microarthropod community in the sub-arctic. The abundance of springtails and mites was investigated after three seasons of prolonged periods of freeze-thaw cycles in the field, and the presence or absence of migration barriers, at two different field sites. Dome shaped transparent plastic greenhouses were successfully used as a novel method to increase freeze-thaw cycle frequencies in the soil. At a fellfield site, freeze-thaw treatment did not lead to significant differences in the five main soil faunal groups, but increased abundance were seen in a number of separate taxa. There was no freeze-thaw treatment effect on soil microbial biomass or soil nutrients, although treatments interacted as inorganic N increased in the separate freeze-thaw and migration barrier treatments. By contrast, at a glade site responses were strong due to more pronounced increases in the number of freeze-thaw cycles. The highest numbers of Collembola after 2 years of treatment were found in the freeze-thaw plots, in combination with migration barriers. The freeze-thaw treatment here also resulted in more Oribatida, microbial biomass C and dissolved organic C. A common hypothesis is that an increased number of freeze-thaw cycles would result in elevated winter mortality in microarthropods due to increased risk of inoculative freezing. However, we observed no increased mortality due to freeze-thaw events. Rather, there was a stimulation of soil microarthropods and microbial biomass, perhaps due to a prolonged period of microbial and faunal activity when the soil is repeatedly frozen and thawed compared to a constantly frozen soil.     

Creation of multi-layered canopy structures in young oak-dominated urban woodlands – The ‘ecological approach’ revisited

We investigated the stand structure of ten young urban woodlands established in Southern Scandinavia during the 1970s and 1980s according to the ecological approach, which advocated the use of many different species of trees and shrubs to create complex canopy structures as soon as possible after establishment to promote recreation and biodiversity. Tree height and live crown depths were measured and analysed using a combination of quantitative and qualitative approaches to assess the forest structure in terms of canopy stratification. The results show that the current canopy structures could be classified into seven different two- and three-layered structural types which had evolved as a combination of differences in management frequency and the initial species composition. Two layered stands were characterized by lower management frequency compared to three layered stands and stands in transition to three layers. They were also established with a lower proportion of understory species and a higher proportion of shade tree species. The total number of species at the establishment did not influence how stands were categorized. The two main conclusions are that recurrent thinnings is a key factor for successful management of young, species rich forest plantations, and that species composition can increase the resilience towards management neglect. Instead of aiming at maximising total species number it is more reasonable to focus on a few key species in each layer. We conclude that three-layered canopy structures can be created already after twenty five years, which should encourage planners and practitioners to incorporate multilayered stands in future urban woodland creation.     

Carbon storage and sequestration by urban forests in Shenyang,China

Urban forests can play an important role in mitigating the impacts of climate change by reducing atmospheric carbon dioxide (CO₂). Quantification of carbon (C) storage and sequestration by urban forests is critical for the assessment of the actual and potential role of urban forests in reducing atmospheric CO₂. This paper provides a case study of the quantification of C storage and sequestration by urban forests in Shenyang, a heavily industrialized city in northeastern China. The C storage and sequestration were estimated by biomass equations, using field survey data and urban forests data derived from high-resolution QuickBird images. The benefits of C storage and sequestration were estimated by monetary values, as well as the role of urban forests on offsetting C emissions from fossil fuel combustion. The results showed that the urban forests in areas within the third-ring road of Shenyang stored 337,000 t C (RMB92.02 million, or $ 13.88 million), with a C sequestration rate of 29,000 t/yr (RMB7.88 million, or $ 1.19 million). The C stored by urban forests equaled to 3.02% of the annual C emissions from fossil fuel combustion, and C sequestration could offset 0.26% of the annual C emissions in Shenyang. In addition, our results indicated that the C storage and sequestration rate varied among urban forest types with different species composition and age structure. These results can be used to help assess the actual and potential role of urban forests in reducing atmospheric CO₂ in Shenyang. In addition, they provide insights for decision-makers and the public to better understand the role of urban forests, and make better management plans for urban forests.