三叶鬼针草与不同本地植物竞争对土壤 微生物和土壤养分的影响

入侵植物三叶鬼针草(Bidens pilosa)对我国农牧业生产造成了重大的损失。本文主要研究三叶鬼针草入侵与不同本地植物竞争对土壤微生物群落结构和土壤养分的影响。利用磷脂脂肪酸方法(phospholipid fatty acids, PLFAs)测定土壤微生物群落组成, 同时测定土壤养分和酶活性, 并利用Canoco4.5软件分析了土壤微生物、土壤养分和土壤酶活性的相关性。结果表明: (1)三叶鬼针草对革兰氏阳性菌、革兰氏阴性菌、丛枝菌根真菌等土壤微生物具有较强的聚集能力, 且其根际土壤聚集的微生物类群与本地植物种类密切相关。(2)三叶鬼针草入侵显著增加了入侵地土壤的有机碳含量, 降低了铵态氮的含量; 土壤中的速效钾、速效磷和硝态氮的含量则与本地植物种类密切相关。(3)相关性分析表明, 16:00和16:1 ω5c对铵态氮的含量影响较大, 而三叶鬼针草入侵地16:00和16:1 ω5c的含量显著高于裸土对照, 进而推测这一状况导致了铵态氮含量的降低。(4) 15:1 anteiso A和18:1 ω5c与速效钾的含量呈显著正相关, 而其含量在狗尾草(Setaria viridis)中显著高于其他处理, 三叶鬼针草与狗尾草混种处理中土壤中速效钾的含量高于其他处理。以上结果说明, 三叶鬼针草通过改变土壤微生物群落结构影响了土壤酶活性和土壤养分, 且这种改变与入侵地本地植物种类有关。     

滇中退化山地不同植被恢复下土壤碳氮磷储量与生态化学计量特征

植被恢复对土壤营养元素的存赋及其生态化学计量特征的影响广受关注,为了深入了解不同植被恢复类型下土壤碳、氮、磷储量与生态化学计量特征,选择滇中地区退化山地飒马场流域具有代表性的4种不同修复阶段的典型植被(荒坡灌草丛、云南松林、针阔混交林和次生常绿阔叶林)为研究对象,分析了不同植被类型下不同深度土壤中有机碳(SOC)、全氮(TN)、全磷(TP)储量和化学计量变化特征。结果表明,退化山地的植被恢复显著改变土壤碳氮磷储存能力和化学计量比,这种改变作用整体上随土壤深度增加而降低。其中,在0—60 cm土层上,SOC储量在次生常绿阔叶林最高,达123.41 t/hm²,其次是针阔混交林(115.69 t/hm²)和云南松林(93.08 t/hm²),荒坡灌草丛(89.56 t/hm²)最低;TN储量针阔混交林(4.91 t/hm²)>次生常绿阔叶林(4.58 t/hm²)>云南松林(4.43 t/hm²)>荒坡灌草丛(3.98 ...     

香椿不同种源和优良单株的种子品质差异性分析

对13个省份14个产地香椿(Toona sinensisRoem.)种子的播种品质和营养成分含量差异进行分析,发现14个种源香椿种子的长度(6.07~8.22 mm)、宽度(3.68~4.65 mm)、千粒重(7.86~15.37 g)和发芽率(36.00%~96.00%)均存在显著差异,不同单株之间也存在一定的差异。播种品质与场圃发芽率较好的种源为河北邢台、江西崇义、江西九连山和湖南洞口;江西九连山种源的5个单株中,种子品质最好的为5号单株。各种源香椿种子的蛋白质含量为12.514~97.150 mg.g-1,可溶性糖含量为0.048~0.084 mg.g-1,淀粉含量为0.576%~1.410%,游离氨基酸含量为1.545~3.226 mg.g-1,粗脂肪含量为26.407%~38.158%,表明不同种源香椿种子的营养成分有显著差异。     

Long‐term experiment manipulating community assembly results in favorable restoration outcomes for invaded prairies

Invasive species are a common problem in restoration projects. Manipulating soil fertility and species arrival order has the potential to lower their abundance and achieve higher abundances of seeded native species. In a 7‐year experiment in Missouri, United States, we tested how nutrient addition and the timing of arrival of the invasive legume Lespedeza cuneata and seeded native prairie grass and forb species influenced overall community composition. Treatments that involved early arrival of seeded forb and grass species and late arrival of L. cuneata were most successful at creating community structure that fulfilled our restoration goals, displaying high abundance of seeded native forb species, low abundances of L. cuneata, and non‐native species. There were few treatment interactions, with the exception that timing seeded native forbs and timing of L. cuneata arrival interactively influenced the abundance of seeded native forbs. This suggests that the individual treatments are supporting the restoration goals, such as creating a community with low abundance of L. cuneate or high abundance of native seeded species, without restricting each other. This study demonstrates the importance of priority effects in disturbed habitats prone to invasion, the lasting effects of initial seeding on long‐term community composition, and the potential for fertilization to positively benefit restoration of degraded grasslands.     

Influence of pastoral fallow on plant root growth and soil physical and chemical characteristics in a hill pasture

Pastoral fallowing over a growing season (October–May) has a profound effect on standing biomass and sward structure, and should have an impact on below ground plant growth and soil biological activities. Two field studies were conducted to compare the effects of pastoral fallow with rotational grazing on root growth and soil physical and chemical properties. Root growth and distribution was altered by pastoral fallowing and there was significantly (P < 0.01) less root biomass at 0–50 mm depth of soil in the fallowed sward than the grazed sward. Compared with the grazed treatment, pastoral fallow increased soil air permeability at 500 mm tension by 38%, saturated hydraulic conductivity by 26%, unsaturated hydraulic conductivity at 20 mm tension by 67% and soil moisture by 10–15%, and reduced soil bulk density by 11%. Fallowing had little effect on soil nutrients both at the end of fallowing, except for small reductions in K and Mineral N levels at 0–75 mm soil depth, and two to three years after fallowing.     

低营养浓度培养基分离培养生物膜中的细菌及其鉴定

室内潮湿环境固体表面很容易形成细菌生物膜,这些生物膜生长在不易清除或不被人注意的固体表面,研究这一类生物膜中的细菌类群可以了解其中是否滋生着对人体健康有威胁性的致病菌或条件致病菌。选择某公共浴室内塑料表面生长的生物膜作为分离培养对象,同时使用实验室最常用的LB培养基及其10倍稀释培养基(LB/10)作为分离培养基。结果表明在LB培养基上生长的细菌类群相对单一,并且有单一类群占优势或抑制其他类群生长的现象;而在LB/10培养基上生长的细菌具有更丰富的多样性,并且各类菌的数量分布较均匀,没有出现LB培养基中一种细菌占绝对生长优势的现象。对LB/10上生长的8个菌株的16SrDNA片段序列进行测定和系统发育分析,发现与所分离的细菌系统发育相近的包括多株人体临床分离的病原菌以及未培养细菌(Uncultured bacterium)。     

土壤抑真菌作用与细菌群落结构的关系

自然清洁土壤所具有的抑真菌作用,是健康土壤的一种自然属性,也是土壤质量的重要指标之一,对控制农作物土传病原真菌的爆发具有积极的生态学意义.本试验以中国科学院沈阳生态实验站近10年未受农药和肥料影响的撂荒地土壤作为自然清洁土壤样品,通过高温（对照、100 ℃、110 ℃、121 ℃）处理得到具有不同抑真菌作用的土壤模型,采用PCR DGGE(变性梯度凝胶电泳)方法对上述土壤样品的细菌群落结构进行分析.结果表明：土壤抑真菌作用与土壤细菌群落结构紧密相关;对照清洁土壤抑真菌作用最强,处理后土壤细菌群落结构偏离自然清洁土壤愈远,土壤抑真菌能力愈差;DGGE特异性条带切胶测序结果表明,Sphingomonas asaccharolytica、Nitrospira sp.、Hyphomicrobiaceae sp.、Bacillus megaterium和Micrococcus sp.可能与土壤抑真菌作用密切相关.     

丛枝菌根真菌参与下植物-土壤系统的养分交流及调控

近几年随着有机农业的发展,丛枝菌根的作用受到特别关注。丛枝菌根是由植物根系与丛枝菌根真菌(AMF)形成的一种共生体。在植物-AMF-土壤系统中,AMF为植物提供N、P等营养的同时从根系得到所需的C。概述了植物-AMF-土壤系统中C、N、P等营养物质的交流以及AMF与土壤微生物的互作关系。丛枝菌根的形成可显著提高植物对P的吸收,且在高P条件下多余的P可储存于AMF中。AMF对土壤N循环的影响相当复杂,可能参与调控N循环的多个过程,如硝化作用、反硝化作用和氨氧化作用等。在有机质丰富的土壤中AMF菌丝可快速扩增并吸收其中的N,主要供菌丝自身所需,只有一小部分传递给植物。AMF对土壤C库的影响尚存争议,可能存在时间尺度的差异。短期内可活化土壤C,而在长期尺度上可能有利于土壤C的储存。AMF能够通过改变土壤微生物群落结构而影响植物-土壤体系的物质交流。AMF与解磷菌、根瘤菌和放线菌的协同增效作用可促进土壤有机质的降解或增强其固氮能力;AMF对氨氧化菌的抑制作用可降低氨的氧化减少N2O的释放。AMF与外生共生真菌EMF共存时,表现出协同增效作用,但EMF的优先定殖会限制AMF的侵染。AMF不同类群之间则主要表现为竞争和拮抗关系。AMF与土壤微生物之间的互作关系受土壤无机环境的影响,在养分亏缺条件下微生物之间往往表现为竞争关系。因植物、AMF与土壤微生物之间存在复杂的互作关系,为此AMF并不总是表现出其对植物营养的促进作用。目前关于AMF的作用机理仍以假说为主,需要进一步的实验验证。在植物-AMF-土壤系统中N与C的交流和P与C的交流并未表现出一致性,对N、P循环相互关系的进一步探讨有助于深入理解植物-土壤体系中的养分循环。植物、AMF和土壤微生物的养分来源及其对养分的相对需求强度和吸收效率尚未可知,因此无法深入理解AMF在植物-土壤体系中养分交流和转化的作用。在方法上,传统的土壤学方法在养分动态研究中存在局限性,现代分子生物学手段和化学计量学的结合值得尝试。     

干旱胁迫条件下AMF促进小马鞍羊蹄甲幼苗生长的机理研究

采用温室水分控制试验,在干旱胁迫条件下,定量化研究优势丛枝菌根真菌(AMF)影响优势乡土植物小马鞍羊蹄甲(Bauhinia faberi var.microphylla)幼苗生长的机理,主要通过研究干旱胁迫条件下摩西球囊霉菌(Funneliformis mosseae)与小马鞍羊蹄甲的共生关系,阐明AMF在植物生长初期的作用。结果表明,干旱胁迫条件下,摩西球囊霉菌能够很好地侵染幼苗,侵染率高达89%—97%,并且不受水分条件影响。接种的幼苗最大光合速率、水分利用效率随着干旱胁迫程度从重度到轻度(水分从低到高)逐渐增大,相反地,叶片脯氨酸含量逐渐减小。接种显著地促进幼苗株高、叶片数、叶面积、根长、根面积等生长指标,提高幼苗各部分生物量、地上地下磷(P)含量。当含水量为60%田间持水量时,AMF促进小马鞍羊蹄甲幼苗吸收P的效果最好。接种还显著影响幼苗的生物量分配,在重度干旱胁迫时影响P分配,水分条件也显著影响幼苗的生物量分配。此外,接种和水分的交互作用对叶生物量、总生物量、生长指标以及地上部氮(N)总量影响显著。结果表明干旱胁迫条件下菌根效应显著,并在干旱条件下显著促进了小马鞍羊蹄甲幼苗的生长,这为进一步干旱河谷植被恢复提供了理论依据。     

Seasonal changes in element contents in mangrove element retranslocation during leaf senescene

The concentrations of nitrogen (N), phosphorus (P), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg) and chlorine (Cl) were followed monthly in pre-senescence leaves and post-abscission leaves of Kandelia candel (L.) Druce at the Jiulongjiang estuary, and Fujian, China. The element retranslocation efficiency (RE) was studied during leaf senescence. The element RE's evaluated using different methods were compared and a new method was put forward to evaluate element RE during leaf senescence in evergreen trees without concentrated leaf fall. The results showed that during leaf senescence, 77.22% N, 57.53% P, and 44.51% K were translocated out of senescing leaves. Translocation of nutrients out of senescing leaves back into shoots was an important nutnent-conservation mechanism for N and P, was less important for K, and did not occur for Ca, Mg, Na, or Cl. One of the reasons for the high primary productivity of mangroves in nutrient poor sites (especially with low N) is the high nutrient use efficiency.