Centrifuge modeling of a large-scale surcharge on adjacent foundation

This study investigates the ground and structural response of adjacent raft foundations induced by largescale surcharge by ore in soft soil areas through a 130g centrifuge modeling test with an innovative layered loading device.The prototype of the test is a coastal iron ore yard with a natural foundation of deep soft soil.Therefore,it is necessary to adopt some measures to reduce the influence of the large-scale surcharge on the adjacent raft foundation,such as installing stone columns for foundation treatment.Under an acceleration of 130 g,the model conducts similar simulations of iron ore,stone columns,and raft foundation structures.The tested soil mass has dimensions of 900 mm×700 mm×300 mm(lengthwidthdepth),which is remodeled from the soil extracted from the drilling holes.The test conditions are consistent with the actual engineering conditions and the effects of four-level loading conditions on the composite foundation of stone columns,unreinforced zone,and raft foundations are studied.An automatic layer-by-layer loading device was innovatively developed to simulate the loading process of actual engineering more realistically.The composite foundation of stone columns had a large settlement after the loading,forming an obvious settlement trough and causing the surface of the unreinforced zone to rise.The 12 m surcharge loading causes a horizontal displacement of 13.19 cm and a vertical settlement of 1.37 m in the raft foundation.The stone columns located on both sides of the unreinforced zone suffered significant shear damage at the sand-mud interface.Due to the reinforcement effect of stone columns,the sand layer below the top of the stone columns moves less.Meanwhile,the horizontal earth pressure in the raft foundation zone increases slowly.The stone columns will form new drainage channels and accelerate the dissipation of excess pore pressure.

T-RFLP技术在森林土壤微生物多样性研究中的应用

土壤微生物在物质循环转化中具有重要的作用,与森林植被类型、土壤理化性质存在密切的关系。森林土壤微生物多样性及其变化在一定程度上反映了土壤环境的生产力和稳定性,对森林演替,土壤生境改善等有重要意义。末端限制性酶切片段长度多态性分析(T-RFLP)技术具有快捷、高效和可重复性高等优点。本文简要介绍T-RFLP技术的原理和特点,分析这一技术的局限性和优化方法。以及该技术在森林土壤微生物多样性研究中的应用现状,展望该技术的发展前景,以期能为今后这一领域的研究提供科学依据。

Developing conservation strategies for Pinus koraiensis and Eleutherococcus senticosus by using model-based geographic distributions

We described potential changes in the geo- graphic distribution and occurrence probability of Pinus koraiensis Sieb. et Zucc. and Eleutherococcus senticosus （Rupr. et Maxim.） Maxim. in the counties of northeast China. This information was used to identify priority areas for protection and provide protection and management recommendations within each studied county. The two species were mapped in 2884 study plots throughout this region over a 4-year period （38°40＇N-53°30＇N, 115°05＇E- 135°02＇E）. We used the species distribution models （Maxent）, systematic conservation planning models （Marxan）, and Geographic Information Systems （ArcGIS 10.0）. The distributions of two species were correlated in the study area, enabling unique and economically viable joint conservation measures to be implemented. Three models were combined to identify feasible priority con- servation sites. We used local spatial statistics to assess all identified conservation areas in relation to potential climate change based shifts in the geographic distribution of the two species. Model-based conservation strategies were used to identify effective measures to protect and utilize these two tree species in the study region. This study pre- sents a novel technique for assessing wild plant distribu- tions, in addition to serving as a model for the conservation of other species within the framework of general forest management, ecological construction, and geographical surveying.

The effect of soil moisture on the response by fungi and bacteria to nitrogen additions for N_(2)O production

In addition to bacteria,the contribution of fungi to nitrous oxide(N_(2)O)production has been recognized but the responses of these two broad and unrelated groups of microorganisms to global environmental changes,atmospheric nitrogen(N)deposition,and precipitation in terms of N_(2)O production are unclear.We studied how these two microbial-mediated N_(2)O production pathways responded to soil moisture conditions and to N addition in an N-limited temperate forest.Soils from a long-term N addition experiment in Changbai Mountain,northeastern China were incubated.Varied concentrations of cycloheximide and streptomycin,both inhibitors of fungal and bacterial activity,were used to determine the contributions of both to N_(2)O production in 66%,98%and 130%water-filled pore spaces(WFPS).The results showed that N_(2)O production decreased significantly with increasing cycloheximide concentration whereas streptomycin was only inhibiting N_(2)O emissions at 98%and 130%WFPS.The bacterial pathway of N_(2)O production in N-addition(Nadd)soil was significantly more dominant than that in untreated(Namb)soil.The difference in the fungal pathway of N_(2)O production between the soil with nitrogen addition and the untreated soil was not significant.Net N_(2)O emissions increased with increasing soil moisture,especially at 130%WFPS,a completely flooded condition.Bacteria dominated carbon dioxide(CO_(2))and N_(2)O emissions in Nadd soil and at 130%WFPS regardless of N status,while fungi dominated CO_(2)and N_(2)O emissions in soil without N addition at 66%and 98%WFPS.The results suggest that flooded soil is an important source of N_(2)O emissions and that bacteria might be better adapted to compete in fertile soils under anoxic conditions.

Variations in the natural 13C and 15N abundance of plants and soils under long-term N addition and precipitation reduction:interpretation of C and N dynamics

Background:The nitrogen isotope natural abundance(δ^(15)N)provides integrated information on ecosystem N dynamics,and carbon isotope natural abundance(δ^(13)C)has been used to infer how water-using processes of plants change in terrestrial ecosystems.However,howδ^(13)C andδ^(15)N abundances in plant life and soils respond to N addition and water availability change is still unclear.Thus,δ^(13)C andδ^(15)N abundances in plant life and soils were used to investigate the effects of long-time(10 years)N addition(+50 kg N·ha^(−1)·yr^(−1)and precipitation reduction(−30%of throughfall)in forest C and N cycling traits in a temperate forest in northern China.Results:We analyzed theδ^(13)C andδ^(15)N values of dominant plant foliage,litterfall,fungal sporophores,roots,and soils in the study.The results showed thatδ^(15)N values of foliage,litterfall,and surface soil layer’s(0–10 cm)total N were significantly increased by N addition,whileδ^(15)N values of fine roots and coarse roots were considerably decreased.Nitrogen addition also significantly increased theδ^(13)C value of fine roots and total N concentration of the surface soil layer compared with the control.The C concentration,δ^(13)C,andδ^(15)N values of foliage andδ^(15)N values of fine roots were significantly increased by precipitation reduction,while N concentration of foliage and litterfall significantly decreased.The combined effects of N addition and precipitation reduction significantly increased theδ^(13)C andδ^(15)N values of foliage as well as theδ^(15)N values of fine roots andδ^(13)C values of litterfall.Furthermore,foliarδ^(15)N values were significantly correlated with foliageδ^(13)C values,surface soilδ^(15)N values,surface soil C concentration,and N concentrations.Nitrogen concentrations andδ^(13)C values of foliage were significantly correlated withδ^(15)N values and N concentrations of fine roots.Conclusions:This indicates that plants increasingly take up the heavier 15N under N addition and the heavier 13C and 15N under precipitation reduction,suggesting that N addition and precipitation reduction may lead to more open forest ecosystem C and N cycling and affect plant nutrient acquisition strategies.

A vehicle-mounted dual-smog chamber:Characterization and its preliminary application to evolutionary simulation of photochemical processes in a quasi-realistic atmosphere

Smog chambers are the effective tools for studying formation mechanisms of air pollution.Simulations by traditional smog chambers differ to a large extent from real atmospheric conditions,including light,temperature and atmospheric composition.However,the existing parameters for mechanism interpretation are derived from the traditional smog chambers.To address the gap between the traditional laboratory simulations and the photochemistry in the real atmosphere,a vehicle-mounted indoor-outdoor dual-smog chamber(JNUVMDSC)was developed,which can be quickly transferred to the desired sites to simulate quasi-realistic atmosphere simultaneously in both chambers using“local air”.Multiple key parameters of the smog chamber were characterized in the study,demonstrating that JNUVMDSC meets the requirements of general atmospheric chemistry simulation studies.Additionally,the preliminary results for the photochemical simulations of quasi-realistic atmospheres in Pearl River Delta region and Nanling Mountains are consistent with literature reports on the photochemistry in this region.JNU-VMDSC provides a convenient and reliable experimental device and means to study the mechanism of atmospheric photochemical reactions to obtain near-real results,and will make a great contribution to the control of composite air pollution.

土地利用方式对黄河漫滩土壤微生物群落结构和多样性的影响

土壤微生物群落及其多样性是土壤碳和养分循环的重要生物指标。土地利用变化是影响漫滩生态系统土壤微生物群落组成的主要决定因素。然而,土壤微生物群落的结构和多样性如何响应土地利用变化,以及这些变化的主要驱动因素是什么,仍不清楚。本研究在黄河漫滩进行,以检验土地利用变化对土壤微生物群落的影响。选取了4种土地利用类型(灌丛、农田、草地和森林),其中以灌木地为对照,用磷脂脂肪酸测量了土壤微生物组成和多样性。研究结果表明,土地利用变化显著影响了总细菌、真菌和革兰氏阳性/阴性细菌。与灌丛相比,农田的总磷脂脂肪酸和细菌较高,森林的真菌较高。土壤pH值和全磷是微生物组成的最佳预测因子,分别解释了37%和26%的变异性。土壤全氮和硝态氮是影响微生物多样性的主要因素。花生农田的土壤碳含量、土壤碳储量、磷脂脂肪酸总量和微生物多样性最高,表明漫滩具有巨大的碳汇潜力。这些研究结果表明,黄河漫滩的农田对于维持土壤微生物群落和土壤碳固存至关重要。

Long-time precipitation reduction and nitrogen deposition increase alter soil nitrogen dynamic by influencing soil bacterial communities and functional groups

The effects of precipitation reduction and nitrogen deposition increase on soil bacterial communities and functions impact soil nitrogen cycling. Seasonal changes could modify the effects of precipitation reduction and nitrogen deposition increase on bacterial communities and functions by changing soil environments and properties. Understanding soil microbial communities and the seasonal response of functions to precipitation reduction and nitrogen deposition increase may be important for the accurate prediction of changes in the soil nitrogen dynamics. Thus, a long-term field simulation experiment of nitrogen deposition increase and throughfall exclusion was established to investigate soil bacterial communities’ response to nitrogen deposition increase and/or precipitation reduction, with no nitrogen deposition increase and no precipation reduction as a control, in a temperate forest. We examined soil bacterial communities(Illumina sequencing) under different treatments during the winter, freezing-thawing cycle periods(FTCs), and growing season. The bacterial functional groups were predicted by the FAPROTAX database. The results showed that nitrogen deposition increase, precipitation reduction, the combined effect of nitrogen deposition increase and precipitation reduction, and seasonal changes significantly altered the soil bacterial community composition.Interestingly, by combining the result of a previous study in which nitrogen deposition increase increased the nitrous oxide flux in the same experimental system, the loss of soil nitrogen was increased by the decrease in denitrification and increase of nitrification bacteria under nitrogen deposition increase,while ammonification bacteria significantly increased and N-fixing bacteria significantly decreased with precipitation reduction compared to the control. In relation to seasonal changes, the aromatic-degrading, cellulolytic, and ureolytic bacteria were lowest during FTCs, which indicated that FTCs might inhibit biodegradation. Nitrification and nitrite-oxidizing bacteria increased with nitrogen deposition increase or precipitation reduction and in FTCs compared to the control or other seasons. The interaction between treatment and season significantly changed the soil bacterial communities and functions. These results highlight that nitrogen deposition increase, precipitation reduction, seasonal changes, and their interactions might directly alter bacterial communities and indirectly alter the dynamics of soil N.

Effects of warming on soil respiration during the non-growing seasons in a semiarid temperate steppe

Aims The response pattern of terrestrial soil respiration to warming during non-growing seasons is a poorly understood phenomenon,though many believe that these warming effects are potentially significant.This study was conducted in a semiarid temperate steppe to examine the effects of warming during the non-growing seasons on soil respiration and the underlying mechanisms associated therewith.Methods This experiment was conducted in a semiarid temperate grassland and included 10 paired control and experimental plots.Experimental warming was achieved with open top chambers(OTCs)in October 2014.Soil respiration,soil temperature and soil moisture were measured several times monthly from November 2014 to April 2015 and from November 2015 to April 2016.Microbial biomass carbon(MBC),microbial biomass nitrogen(MBN)and available nitrogen content of soil were measured from 0 to 20 cm soil depth.Repeated measurement ANOVAs and paired-sample t tests were conducted to document the effect of warming,and the interactions between warming and time on the above variables.Simple regressions were employed to detect the underlying causality for the observed effects.Important Findings Soil respiration rate was 0.24μmol m^(−2) s^(−1) in the control plots during the non-growing seasons,which was roughly 14.4%of total soil carbon flux observed during growing seasons.Across the two non-growing seasons,warming treatment significantly increased soil temperature and soil respiration by 1.48℃(P<0.001)and 42.1%(P<0.01),respectively,when compared with control plots.Warming slightly,but did not significantly decrease soil moisture by 0.66%in the non-growing seasons from 2015 to 2016.In the non-growing seasons 2015–16,experimental warming significantly elevated MBC and MBN by 19.72%and 20.99%(both P<0.05),respectively.In addition,soil respiration responses to warming were regulated by changes in soil temperate,MBC and MBN.These findings indicate that changes in non-growing season soil respiration impact other components in the carbon cycle.Additionally,these findings facilitate projections regarding climate change–terrestrial carbon cycling.