Nitrogen deposition alters soil chemical properties and bacterial communities in the Inner Mongolia grassland

Nitrogen deposition has dramatically altered biodiversity and ecosystem functioning on the earth; however, its effects on soil bacterial community and the underlying mechanisms of these effects have not been thoroughly examined. Changes in ecosystems caused by nitrogen deposition have traditionally been attributed to increased nitrogen content. In fact, nitrogen deposition not only leads to increased soil total N content, but also changes in the NH₄⁺-N content, NO₃^--N content and pH, as well as changes in the heterogeneity of the four indexes. The soil indexes for these four factors, their heterogeneity and even the plant community might be routes through which nitrogen deposition alters the bacterial community. Here, we describe a 6-year nitrogen addition experiment conducted in a typical steppe ecosystem to investigate the ecological mechanism by which nitrogen deposition alters bacterial abundance, diversity and composition. We found that various characteristics of the bacterial community were explained by different environmental factors. Nitrogen deposition decreased bacterial abundance that is positively related to soil pH value. In addition, nitrogen addition decreased bacterial diversity, which is negatively related to soil total N content and positively related to soil NO₃^--N heterogeneity. Finally, nitrogen addition altered bacterial composition that is significantly related to soil NH₄⁺-N content. Although nitrogen deposition significantly altered plant biomass, diversity and composition, these characteristics of plant community did not have a significant impact on processes of nitrogen deposition that led to alterations in bacterial abundance, diversity and composition. Therefore, more sensitive molecular technologies should be adopted to detect the subtle shifts of microbial community structure induced by the changes of plant community upon nitrogen deposition.     

Degradation of pyrene by immobilized microorganisms in saline-alkaline soil

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) is very difficult in saline-alkaline soil due to the inhibition of microbial growth under saline-alkaline stress. The microorganisms that can most effectively degrade PAHs were screened by introducing microorganisms immobilized on farm byproducts and assessing the validity of the immobilizing technique for PAHs degradation in pyrene-contaminated saline-alkaline soil. Among the microorganisms examined, it was found that Mycobacterium sp. B2 is the best, and can degrade 82.2% and 83.2% of pyrene for free and immobilized cells after 30 days of incubation. The immobilization technique could increase the degradation of pyrene significantly, especially for fungi. The degradation of pyrene by the immobilized microorganisms Mucor sp. F2, fungal consortium MF and co-cultures of MB+MF was increased by 161.7% (P < 0.05), 60.1% (P < 0.05) and 59.6% (P < 0.05) after 30 days, respectively, when compared with free F2, MF and MB+MF. Scanning electron micrographs of the immobilized microstructure proved the positive effects of the immobilized microbial technique on pyrene remediation in saline-alkaline soil, as the interspace of the carrier material structure was relatively large, providing enough space for cell growth. Co-cultures of different bacterial and fungal species showed different abilities to degrade PAHs. The present study suggests that Mycobacterium sp. B2 can be employed for in situ bioremediation of PAHs in saline-alkaline soil, and immobilization of fungi on farm byproducts and nutrients as carriers will enhance fungus PAH-degradation ability in saline-alkaline soil.     

Soil warming effect on net ecosystem exchange of carbon dioxide during the transition from winter carbon source to spring carbon sink in a temperate urban lawn

The significant warming in urban environment caused by the combined effects of global warming and heat island has stimulated widely development of urban vegetations. However, it is less known of the climate feedback of urban lawn in warmed environment. Soil warming effect on net ecosystem exchange (NEE) of carbon dioxide during the transition period from winter to spring was investigated in a temperate urban lawn in Beijing, China. The NEE (negative for uptake) under soil warming treatment (temperature was about 5℃ higher than the ambient treatment as a control) was -0.71 μmol/(m².sec), the ecosytem was a CO₂ sink under soil warming treatment, the lawn ecosystem under the control was a CO₂ source (0.13 μmol/(m².sec)), indicating that the lawn ecosystem would provide a negative feedback to global warming. There was no significant effect of soil warming on nocturnal NEE (i.e., ecosystem respiration), although the soil temperature sensitivity (Q₁₀) of ecosystem respiration under soil warming treatment was 3.86, much lower than that in the control (7.03). The CO₂ uptake was significantly increased by soil warming treatment that was attributed to about 100% increase of α (apparent quantum yield) and A_max (maximum rate of photosynthesis). Our results indicated that the response of photosynthesis in urban lawn is much more sensitive to global warming than respiration in the transition period.     

碳源对工业污染场地土壤中HCHs和DDTs降解的促进作用

我国对有机氯农药的大量需求使得在农药生产、加工和分装等过程中造成了许多城镇中存在有机氯农药污染场地,限制了土地的后续开发利用.本研究选取3种类型的碳源组成有机修复剂A、B、C,添加到受有机氯工业污染场地土壤中进行微生物降解试验,并对比了3种修复剂的效果.试验过程中,反应体系水分含量为50％,添加零价金属调节氧化还原电位,采用好氧/厌氧交替循环方式进行生物降解.实验结果表明:3种修复剂对HCHs和DDTs的降解都有显著促进作用.与DDTs相比,HCHs较易降解.90 d内,添加修复剂(A、B、C)的处理中∑HCH的浓度分别从73.37~85.71 mg·kg^-1降解到了15.88~38.21 mg·kg^-1.与未添加修复剂的对照相比较,∑HCH的降解率提高了19%~52%,90 d内,ΣHCH的降解率最高可达81%.添加修复剂(A、B、C)的处理中ΣDDT的浓度分别从91.68~119.79 mg·kg^-1降解到了45.1~60.7 mg·kg^-1,相对未添加修复剂的对照试验,∑DDT的降解率提高了39%~45%,30 d内∑DDT的降解率最高可达到51%,但30 d后降解效率无明显增加.就不同类型碳源的促进作用来看,C/N最高,而含水率最低的修复剂B的效果最好,而C/N比最低而含水率最高的修复剂A效果最差.     

集约化种植区硝态氮在土壤剖面中的分布与累积特征

采用GPS定位、土钻取样的方法,在北京市大兴区14个乡镇的农田土壤中选取了91个土壤剖面,分别在0～20cm、20～40cm、40～60cm、60～80cm4个不同深度取得土壤样品,并在一次种植期结束后,综合考虑种植类型和土壤质地后选取24个重复取样点.在此基础上,分析了种植类型及土壤质地对硝态氮分布及累积情况的影响.结果表明,研究区土壤中的硝态氮含量有随土壤深度的增加呈降低的趋势.露地菜田和设施菜田最容易出现硝态氮淋洗现象,果园和粮田的总体状况较好,但粮田个别地区有一定的污染风险,细质地土壤具有较强的保水保肥能力.大兴区采育镇及长子营镇地区有较高的硝态氮累积量,为硝态氮淋洗污染危险区,应进行合理施肥,以免在一个种植期结束后造成较深层土壤中硝态氮的累积.研究结果可为大兴区地下水环境保护提供参考.     

广州市“南肺”果园土壤H g和A s的形态分析

采用Tessier连续提取法、BCR连续提取法和Leleyter连续提取法,研究广州"南肺"果园土壤Hg和As的形态分布和生物可给性。结果表明,果园土壤Hg和As形态分布都以残渣态为主;3种方法的土壤生物可给性分析均表明,Hg和As生物可利用态的含量较少;生物不可利用态是主要形态,其次是潜在可利用态。     

生态减污袋去除模拟污水中氨氮及磷的效果试验

研究利用砂土与粘土混合制成的生态减污袋对于模拟污水中氨氮及磷的去除效果。研究发现砂土与粘土比例为1∶1的减污袋对于高浓度模拟污水中氨氮和磷的去除率分别达到73%和63%;而砂土与粘土比例为10∶1的减污袋对于低浓度模拟污水中磷的去除率最高达到49%。对于高浓度污水,采用砂土与粘土比例为1∶1的生态减污袋能取得最好的除磷去氮效果;而对于低浓度污水,采用砂土与粘土比例为10∶1的生态减污袋除磷去氮效果较好并且成本相对较低。     

有机氯农药污染土壤的Fenton氧化修复研究

研究了Fenton氧化对某实际有机氯农药污染场地土壤的修复效果。结果显示:Fenton氧化能够快速有效地降解污染土壤中的六氯和DDTs。当Fe2+浓度为80 mmol/L,Fe2+与H2O2的摩尔浓度比为1∶5,水土比10∶1时,反应6 h,土壤中六氯和总DDT的去除率分别为:96.7%和78.2%。每方土的修复成本估算为951元。     

异位稳定化技术处理重金属复合污染土壤的工程应用研究

异位稳定化技术处理重金属污染土壤在国内外已有应用,但鲜有大规模工程应用时的控制关键及操作要求的报道。本研究根据异位稳定化处理技术的特点,采用该技术处理重金属复合污染且修复时间有限的目标污染场地,通过合理控制稳定剂投加量、土壤理化性质、施工工艺及养护条件等各项影响因素,取得了很好的处理效果,可为类似污染场地提供借鉴和经验。     

西安表土中多环芳烃的污染特征及其来源解析

通过2008年采集西安不同功能区表层土壤样品,运用GC/MS质谱联用仪对美国EPA优控的16种多环芳烃(PAHs)进行定性、定量分析,来探讨西安表层土壤种多环芳烃的污染特征及其来源。结果表明,16种PAHs均被检出,西安表土中ΣPAHs浓度范围为125~9 057 ng/g,平均值为2 727 ng/g,主要以4~6环PAHs为主,共占总量的69%。PAHs的空间分布规律为:工业区>文教区>绿化区>郊区>农村。应用特征比值判断法可知,西安表土中PAHs主要是煤的不完全燃烧和机动车尾气排放所产生的混合源污染。借鉴国外土壤污染标准可知西安城区表土污染较为严重。