锦鸡儿属灌丛化对草原化荒漠区土壤线虫群落组成和代谢足迹的影响

调查了内蒙古草原化荒漠区3种锦鸡儿[垫状锦鸡儿(Caragana tibetica)、荒漠锦鸡儿(C.roborovskyi)和狭叶锦鸡儿(C.stenophylla)]灌丛内、外土壤线虫群落多样性、组成和代谢足迹,以及相关的土壤理化性质和植物群落特征,旨在探讨锦鸡儿属灌丛对土壤线虫群落的影响,并分析这种影响是否具有灌木种间差异,同时从线虫功能团水平上探究灌丛如何通过非生物因素和生物因素影响线虫群落组成。结果表明：锦鸡儿属灌丛对土壤线虫多度、丰富度和多样性无显著影响,但却显著影响土壤线虫群落组成。原因是灌丛对土壤线虫群落具有物种选择性;灌丛可能主要是通过根系分泌物、凋落物质量等因素,而不是通过土壤理化性质和林下植物影响线虫群落组成。土壤线虫组成的变化引起线虫代谢足迹发生明显变化。灌丛内土壤线虫功能代谢足迹大于灌丛外(除狭叶锦鸡儿外),说明灌丛内土壤线虫群落对碳的利用率更高。3种锦鸡儿属灌木中,狭叶锦鸡儿的结构代谢足迹最大,表明狭叶锦鸡儿对捕食杂食类线虫代谢活性的促进作用更强。土壤线虫组成的变化通过线虫代谢足迹导致土壤食物网结构发生显著性变化。狭叶锦鸡儿灌丛土壤干扰程度低,营养富集状况好...     

锦鸡儿属灌木阻止干旱草地沙漠化生态过程

纵观全球沙漠化的研究进展,从宏观上研究沙漠化现状和后果的报道较多,对沙漠化内在过程的综合研究较少,灌木在阻止干旱区草原沙漠化中的生态作用缺乏研究。研究假设：在干旱地区,灌木的存在提高土壤营养水平,提升土壤保水能力,促进林下植物和土壤生物群落,进而减轻风蚀和固结土壤,这些相互联系的生态过程共同阻止了草原沙漠化。为了验证上述假设,我们以内蒙古阿拉善地区的荒漠化草原为样地,研究锦鸡儿属灌木的固土能力、提高土壤保水能力、改善土壤营养能力和促进生物群落能力,从生物、土壤、水分和沙物质运动等多过程来探讨锦鸡儿属灌木在阻止草原沙漠化中的作用。目的是弄清灌木阻止干旱草地沙漠化的生态过程。在阿拉善荒漠化草原区,锦鸡儿属灌木盖度大约为12.40%。在100 m²的土地上现有灌木固土2.01 m³,固土效率为167 cm³/g鲜重,每年灌木生长可以增加固土能力0.264 m³/100 m²土地。锦鸡儿属灌木提高了土壤湿度(灌丛效应SE=0.120)和土壤对雨水的保持能力(SE 0.155),改善了土...     

Intercropping <Emphasis Type="Italic">Caragana arborescens</Emphasis> with <Emphasis Type="Italic">Salix miyabeana</Emphasis> to Satisfy Nitrogen Demand and Maximize Growth

Willow shows great promise as a biomass crop and is now used worldwide. However, willow is a nutrient and water demanding plant that often requires the use of nitrogen (N) fertilizer to maximize growth on poor soils. The intercropping of Salix miyabeana with the atmospheric N₂-fixing Caragana arborescens on poor soils of the Canadian Prairies could provide a portion of the N demand of the willow. The main objectives were to: (1) determine the yield potential, N nutrition and water use efficiency (WUE) of willow and Caragana grown in pure and mixed plantations across a range of soil productivity and (2) assess the extent of atmospheric N₂-fixation by the Caragana within the first rotation in central Saskatchewan. We found large differences in willow yields, foliar N and WUE across the sites. The willow yields (1.24 to 15.6 t dry matter ha⁻¹ over 4 years) were low compared to northeastern North American values and reflect the short and dry summers of the region. The yields were positively correlated to foliar N (ranging between 14.3 and 32.4 mg g⁻¹), whereas higher WUE (expressed as δ¹³C) were not positively correlated to water availability but to higher yields. Caragana N₂-fixation (measured using ¹⁵N isotope dilution) was not active at the most productive site but up to 60% of the foliar N was of atmospheric origin at the two other sites. Willow growth increased with Caragana proportions at the least productive site, which is typical of the benefits of N₂-fixing plants on the growth of other plants on poor soils. At the most productive site, Caragana decreased the growth of willow early on due to competition for resources, but willow eventually shaded Caragana to a point of significant canopy decline and dieback. It is therefore more appropriate to intercrop the two species on less productive soils as Caragana is more likely to add N to the system via N₂-fixation and is less likely to be shaded out by willow.     

盐碱地柠条根围土中黑曲霉的分离鉴定及解磷能力测定

在盐碱滩地的改良过程中,柠条具有提升土壤供氮、供磷、供钾的潜力.以盐碱滩地上建植的柠条灌木林为研究对象,以柠条根围土壤为培养基质,采用无机磷培养基筛选,用平板溶菌圈法分离获得1株具有溶磷能力的真菌.将测得的ITS基因序列在NCBI上进行同源性检索,结果表明,所测序列与黑曲霉(Aspergillus niger)同源性为100％.综合形态特征和ITS基因序列同源性两方面分析,该菌株鉴定为黑曲霉(Aspergillus niger).168h连续监测无机磷培养液pH值、速效磷含量、菌丝重量和菌体吸磷量,研究该菌株的解磷能力.研究结果表明:随着培养时间的延长,培养液pH值从7.0下降到2.0左右,溶液中速效磷含量逐渐增加到4.7 mg,菌体自身吸磷量由5.4 mg下降到0.5mg,在36-48h后各项指标达到稳定状态.可见,黑曲霉菌体可以有效利用难溶性磷源,并将其转化成可被植物吸收利用的有效磷.     

From rags to enriched: metagenomic insights into ammonia-oxidizing archaea following ammonia enrichment of a denuded oligotrophic soil ecosystem

Stored topsoil acts as a microbial inoculant for ecological restoration of land after disturbance, but the altered circumstances frequently create unfavourable conditions for microbial survival. Nitrogen cycling is a critical indicator for ecological success and this study aimed to investigate the cornerstone taxa driving the process. Previous in silico studies investigating stored topsoil discovered persistent archaeal taxa with the potential for re-establishing ecological activity. Ammonia oxidization is the limiting step in nitrification and as such, ammonia-oxidizing archaea (AOA) can be considered one of the gatekeepers for the re-establishment of the nitrogen cycle in disturbed soils. Semi-arid soil samples were enriched with ammonium sulfate to promote the selective enrichment of ammonia oxidizers for targeted genomic recovery, and to investigate the microbial response of the microcosm to nitrogen input. Ammonia addition produced an increase in AOA population, particularly within the genus Candidatus Nitrosotalea, from which metagenome-assembled genomes (MAGs) were successfully recovered. The Ca. Nitrosotalea archaeon candidates' ability to survive in extreme conditions and rapidly respond to ammonia input makes it a potential bioprospecting target for application in ecological restoration of semi-arid soils and the recovered MAGs provide a metabolic blueprint for developing potential strategies towards isolation of these acclimated candidates.     

黄河三角洲盐碱地花生根层土壤菌群结构多样性

花生属豆科固氮作物,具较强的抗旱耐盐性,土壤微生物在盐碱土生态系统中具有重要的生态功能。以花生平作、花生/棉花间作为对象,通过16S rRNA基因克隆文库技术分析了黄河三角洲滨海盐碱地花生旺盛生长期不同含盐量盐碱地和非盐碱地0—40cm根层非培养土壤微生物群落组成及其多样性,分析了盐碱地花生根层土壤细菌群落与非盐碱地花生根层土壤细菌群落的差异,为揭示盐碱地花生根层土壤微生物的多样性以及土地利用变化与生态环境效应间的关系奠定基础。利用免培养技术直接从土壤样品提取总DNA,针对细菌基因组16S rRNA基因的V3高变区进行PCR扩增;利用焦磷酸测序的方法对V3高变区PCR产物进行高通量测序,并对测序数据进行生物信息学分析。结果表明,(1)黄河三角洲滨海盐碱土较高含盐量土壤中根层土壤微生物种类、优势种群数量和群落功能多样性较非盐碱土壤较为丰富。(2)盐碱土花生平作或花生//棉花间作两种种植方式基本不影响二者0—40cm根层土壤微生物优势类群;不同土壤类型和种植模式下,花生和棉花根层土壤中优势菌群均为变形菌门(Proteobacteria)、放线菌门(Actinobacteria)、绿弯菌门(Chloroflexi)和酸杆菌门(Acidobacteria) 4种菌群,其总丰度为80%—90%。非盐碱土壤中花生根层的酸杆菌门(Acidobacteria)丰度是盐碱土壤中的3倍以上,嗜热油菌纲(Thermoleophilia)和放线菌纲(Actinomycetales)丰度远高于各种盐碱土壤花生平作和花生//棉花间作两种植模式下的花生根层土壤;非盐碱土平作花生0—40cm土层中Rubellimicrobium、Pontibacter和Lamia细菌则显著缺失。(3)土壤类型对土壤微生物菌群类型影响较大,聚类分析表明,10个土壤样本依据土壤含盐量高低和根系分布深度聚为3类,即非盐碱土壤归为1类,盐碱土壤根系密集分布层0—20cm、20—40cm各归为1类。     

Phenotypic and genetic diversity in <Emphasis Type="Italic">Sinorhizobium meliloti</Emphasis> and <Emphasis Type="Italic">S. medicae</Emphasis> from drought and salt affected regions of Morocco

Background  

Sinorhizobium meliloti and S. medicae are symbiotic nitrogen fixing bacteria in root nodules of forage legume alfalfa (Medicago sativa L.). In Morocco, alfalfa is usually grown in marginal soils of arid and semi-arid regions frequently affected by drought, extremes of temperature and soil pH, soil salinity and heavy metals, which affect biological nitrogen fixing ability of rhizobia and productivity of the host. This study examines phenotypic diversity for tolerance to the above stresses and genotypic diversity at Repetitive Extragenic Pallindromic DNA regions of Sinorhizobium nodulating alfalfa, sampled from marginal soils of arid and semi-arid regions of Morocco.     

晋西北不同年限小叶锦鸡儿灌丛土壤氮矿化和硝化作用

利用PVC管顶盖埋管法研究了晋西北黄土高原区小叶锦鸡儿人工灌丛不同定植年限(5,10,20,30,40a)土壤氮矿化与硝化速率的动态和净矿化与硝化总量。结果表明,⑴小叶锦鸡儿灌丛土壤无机氮主要以NO_-~3-N形式存在,不同生长年限相同月份的土壤硝态氮(NO-3-N)含量分别是铵态氮(NH+4-N)含量的1.5—15.4倍;⑵土壤氮素硝化速率和矿化速率随生长年限延长而加快,30年生时达到高峰,数值达40.2,44.1 mg m~(-2)d~(-1)。从季节性变化看,7—8月份是硝化速率和矿化速率快速增长期,30年生小叶锦鸡儿灌丛土壤硝化速率和矿化速率分别达到86.9,93.1 mg m~(-2)d~(-1),显著高于其它生长年限(P0.05);(3)土壤氮素硝化与矿化总量同样随小叶锦鸡儿生长年限延长而增加,30年生时达到最高,与5年生相比,分别增加了3.7和3.1倍。(4)5—10月份小叶锦鸡儿生长期内,各年限土壤全氮量的2.3%被矿化成无机氮,其中87%最终被转化成NO-3-N形式存在于土体中。     

Differences in Earthworm Densities and Nitrogen Dynamics in Soils Under Exotic and Native Plant Species

Previous studies of the invasion of two exotic plants – Berberis thunbergii and Microstegium vimineum – in hardwood forests of New Jersey have shown a significant increase of pH in soils under the invasive plants as compared with soils from under native shrubs (Vaccinium spp). We present a further investigation of soil properties under the exotic plants in question. We measured the densities of earthworms in the soil under the two exotics and the native shrubs in three parks in New Jersey. In the same populations we also measured the extractable ammonium and nitrate in the top 5 cm of the soil, as well as the respiration of the soils and the potential rates of mineralization (aerobic lab incubation). In addition, we measured the nitrate reductase activity in leaves of the two exotic plants and several native shrubs and trees. Although there were differences between parks, we observed significantly higher earthworm densities in the soil under the exotic species. The worms were all European species. Soil pH, available nitrate and net potential nitrification were significantly higher in soils under the two exotic species. In contrast, total soil C and N and net ammonification were significantly higher under native vegetation. Nitrate reductase activities were much higher in the leaves of exotic plants than in the leaves of native shrubs and trees. Changes in soil properties, especially the change in nitrogen cycling, associated with the invasion of these two plant species may permit the invasion of other weedy or exotic species. Our results also suggest that even if the two exotic species were removed, the restoration of the native flora might be inhibited by the high nitrate concentrations in the soil.     

Shrubs as ecosystem engineers in a coastal dune: influences on plant populations,communities and ecosystems

Question: How do two shrubs with contrasting life‐history characteristics influence abundance of dominant plant taxa, species richness and aboveground biomass of grasses and forbs, litter accumulation, nitrogen pools and mineralization rates? How are these shrubs – and thus their effects on populations, communities and ecosystems – distributed spatially across the landscape? Location: Coastal hind‐dune system, Bodega Head, northern California. Methods: In each of 4 years, we compared vegetation, leaf litter and soil nitrogen under canopies of two native shrubs –Ericameria ericoides and the nitrogen‐fixing Lupinus chamissonis– with those in adjacent open dunes. Results: At the population level, density and cover of the native forb Claytonia perfoliata and the exotic grass Bromus diandrus were higher under shrubs than in shrub‐free areas, whereas they were lower under shrubs for the exotic grass Vulpia bromoides. In contrast, cover of three native moss species was highest under Ericameria and equally low under Lupinus and shrub‐free areas. At community level, species richness and aboveground biomass of herbaceous dicots was lower beneath shrubs, whereas no pattern emerged for grasses. At ecosystem level, areas beneath shrubs accumulated more leaf litter and had larger pools of soil ammonium and nitrate. Rates of nitrate mineralization were higher under Lupinus, followed by Ericameria and then open dune. At landscape level, the two shrubs – and their distinctive vegetation and soils – frequently had uniform spatial distributions, and the distance separating neighbouring shrubs increased as their combined sizes increased. Conclusions: Collectively, these data suggest that both shrubs serve as ecosystem engineers in this coastal dune, having influences at multiple levels of biological organization. Our data also suggest that intraspecific competition influenced the spatial distributions of these shrubs and thus altered the distribution of their effects throughout the landscape.     

内蒙古高原荒漠区四种锦鸡儿属植物灌丛沙包形态和固沙能力比较

测定了内蒙古高原荒漠区4种锦鸡儿属优势植物(柠条锦鸡儿、狭叶锦鸡儿、荒漠锦鸡儿和垫状锦鸡儿)不同大小灌丛的灌丛形态参数、沙包形态参数和沙包体积,目的是掌握这些锦鸡儿属植物灌丛的沙包形态特征、沙包发育特征和固沙能力随着灌丛发育的变化,比较4种锦鸡儿属植物灌丛沙包的形态、发育特征和固沙能力的差异。研究发现:柠条锦鸡儿沙包形态呈球冠状,狭叶锦鸡儿沙包呈圆锥状,荒漠锦鸡儿沙包呈圆台状,垫状锦鸡儿沙包呈半球状。同种锦鸡儿属灌丛沙包的底面直径与地上枝条鲜重呈极显著正相关关系(P<0.01),沙包高度与地上枝条鲜重无显著相关性(P>0.05),沙包高度与植物株高呈显著正相关关系(P<0.05),沙包坡角与地上枝条鲜重呈显著负相关关系(P<0.05),沙包半径与沙包高度呈显著正相关关系(P<0.05)。灌丛水平扩展快于垂向生长,灌丛沙包的水平发育也快于垂向发育。随着灌丛地上生物量的增加,4种锦鸡儿属植物不仅沙包体积增大,而且固沙效率也显著增加(P<0.01)。不同锦鸡儿属植物灌丛和沙包形态参数存在显著差异。柠条锦鸡儿和狭叶锦鸡儿的灌丛水平和垂直方向成比例扩展,而荒漠锦鸡儿和垫状锦鸡儿无论灌丛面积多大,高度基本不变。随着灌丛地上枝条鲜重的增加,4种锦鸡儿灌丛沙包底面积都在增大,其中荒漠锦鸡儿增长最快,垫状锦鸡儿次之,柠条锦鸡儿排位第三,狭叶锦鸡儿增长最慢。随着灌丛沙包水平方向的扩展,荒漠锦鸡儿沙包垂向扩展最慢,最终导致其沙包垂向尺度最小;柠条锦鸡儿、垫状锦鸡儿和狭叶锦鸡儿沙包两个方向发育较为均衡。4种锦鸡儿属植物的固定沙包体积和固沙效率都表现为:荒漠锦鸡儿>柠条锦鸡儿>狭叶锦鸡儿>垫状锦鸡儿。这些研究结果表明,灌丛地上生物量的不同决定了种内沙包的体积、形态和植物固沙能力的差异;灌丛形态和发育特征的不同决定了种间沙包形态、沙包发育和植物固沙能力的差异。     

温带荒漠灌丛和藓类结皮对土壤养分的贡献

灌丛与生物土壤结皮镶嵌分布是温带荒漠常见的地表景观之一,二者的发育均显著影响了地表土壤养分的空间分布特征及循环过程。然而,灌丛和生物土壤结皮对荒漠土壤表层养分的影响存在怎样的差异,二者对养分变化的贡献度如何尚不清楚。因此,选择中国北方典型温带荒漠古尔班通古特沙漠为研究区,以荒漠中的优势灌丛膜果麻黄(Ephedra przewalskii)灌丛和生物土壤结皮发育高级阶段的藓类结皮的结皮层及结皮下层土壤为研究对象,采集不同微生境(裸露地、灌丛下)的裸沙与藓类结皮的土壤样品。为探究不同微生境下不同土层碳、氮、磷和钾养分变化特征,测定了不同土层土壤有机碳(SOC)、全氮(TN)、全磷(TP)、全钾(TK)、速效氮(AN)、速效磷(AP)和速效钾(AK)含量。结果表明:(1)相较于裸露地,灌丛显著提高了藓类结皮不同土层有机碳、全氮和全钾的含量和裸沙全磷的含量,降低了灌丛下藓类结皮土壤全磷的含量。(2)对于速效养分而言,与裸沙相比,裸露地藓类结皮覆盖降低了土壤速效氮含量,增加了速效磷和速效钾含量;而灌丛下藓类结皮覆盖提高了土壤速效氮和速效钾的含量,但降低了速效磷的含量。 (3) 相关性分析显示,在0-2 cm土壤中速效磷与速效氮呈现显著负相关,而在2-6 cm速效磷与速效氮呈现显著正相关(P<0.01)。(4)贡献度分析表明,土壤中灌丛效应对养分的贡献(42.54%)要远大于藓类结皮的贡献(2.43%),但二者交互作用却降低了除速效氮以外的其他土壤养分含量。综上,灌丛、藓类结皮覆盖和土层深度变化对土壤碳、氮、磷和钾养分均具有显著影响(P<0.05),但三者间的交互效应对养分的影响不显著(P>0.05)。相对于裸露地,灌丛与藓类结皮的覆盖均对表层土壤碳、氮、磷和钾养分具有促进作用,且随着土层深度的下降,土壤养分含量呈现显著的下降趋势(P<0.05)。因此,在荒漠生态系统中耐旱灌丛与生物土壤结皮这两个最重要的斑块单元联合调控了微尺度土壤养分的空间异质性变化。     

三种锦鸡儿属植物水力结构特征及其干旱适应策略

水分胁迫是干旱半干旱区限制植物生长的主要因素。以干旱半干旱区的3种锦鸡儿属植物为研究对象,从生态适应策略角度来分析3种锦鸡儿植物产生生态分离的原因。对三种锦鸡儿属植物茎干叶片的显微结构、生理功能(导水率、光合速率以及水分利用效率)进行测定,并统计了3种锦鸡儿植株的形态特征,如一、二级枝的直径、长度、末端叶面积。结果表明:三种锦鸡儿属植物都能形成较小的导管直径来适应旱生环境,但是在导水结构上又表现出一定的差异性。中间锦鸡儿的导管直径最小,次脉密度和最大净光合速率最大;柠条锦鸡儿的导管直径、叶片厚度和比叶重(LMA)最大。小叶锦鸡儿在导水率下降50%时的水势(P_(50))最大,水分胁迫时极易发生栓塞,但正是由于导管的栓塞降低了水分运输效率,使其在旱生环境中能够通过减少水分的供应来降低水分的丧失,从而保证自身生长的水分需求;而中间锦鸡儿则主要通过减小导管直径来适应旱生环境;柠条锦鸡儿的水分利用效率最高,抗栓塞能力最强,抗旱性最好,同时柠条锦鸡儿可以通过减少蒸腾面积来减少水分的丧失。植物的导管直径大小、叶片厚度、LMA、叶脉密度对植物导水速率、光合速率等生理功能都有一定的影响。     

植物种类对野芷湖湖岸带土壤反硝化作用的影响

反硝化作用是湖岸带有效去除氮素的关键氮循环过程,受到植物、土壤理化性质及微生物等因素的影响。为探究湖岸带不同植物对土壤反硝化作用的影响,通过调查测定野芷湖湖岸带9种常见植物的根际与非根际土壤的反硝化功能基因丰度和反硝化潜势,分析其与土壤理化性质的关系,阐明植物种类影响反硝化作用的机制。研究结果表明:(1)种植植物会改变湖岸带土壤的理化指标,植物根际土的硝态氮(NN)、铵态氮(AN)、总碳(TC)、总氮(TN)和可溶性有机碳(DOC)含量等显著高于非根际土,其中柳树、黄素馨、喜旱莲子草根际土的TC、DOC、TN、NN显著高于其他物种,桂树的根际和非根际土的pH均显著低于其他物种;(2)植物根际土的微生物反硝化功能基因(narG、napA、nirS、nirK和nosZ)丰度显著高于非根际土,其中柳树、黄素馨、喜旱莲子草根际土的基因丰度显著高于其他物种, pH、TN、NN和DOC等对反硝化功能基因丰度影响较大;(3)根际土的反硝化潜势显著高于非根际土,其中柳树、桂树、黄素馨根际土的反硝化潜势显著高于其他物种,黄素馨非根际土的反硝化潜势也较高,pH、DOC、TN以及napA、nirS、norB基因丰度等对土壤的反硝化潜势具有显著影响。本研究说明植物根际微环境更有利于反硝化微生物的生长与繁殖,湖岸带种植植物时可考虑不同的常绿和落叶乔木、灌木、草本植物的合理配置来提高湖岸带的氮素截留能力,以减少由过量氮素进入水生生态系统导致的面源污染。     

Some studies on field distribution and seed germination ofSuaeda fruticosa andSporobolus arabicus with reference to salinity and sodicity of the medium

Summary Vegetation of two wasteland sites near Dera Chahl, 30 km from Lahore, was studied quantitatively. Soil samples obtained from the two sites were analysed.Suaeda fruticosa (L.) Forssk. was a dominant species on saline and sodic soil whereas soil underSporobolus arabicus Boiss. was saline and non-sodic. Seed germination studies show thatSporobolus arabicus is relatively more affected by Nasalinity than by Ca-salinity. This species tolerates salinity to some extent but is sensitive to sodicity.Suaeda fruticosa is relatively more tolerant to salinity and sodicity thanSporobolus arabicus and is capable of growing on saline and sodic soils.     

3种锦鸡儿属植物过氧化物酶基因的克隆及表达分析

采用同源克隆技术分离了3种锦鸡儿属植物柠条锦鸡儿(Caragana korshinskii)、小叶锦鸡儿(C.microphylla)和中间锦鸡儿(C.intermedia)的过氧化物酶(POD)基因(分别命名为CkPOD、CmPOD和CiPOD),并对它们在干旱胁迫条件下的表达特征进行了分析。CkPOD、CiPOD、CmPOD基因的cDNA序列均包含有1 074bp的开放阅读框(ORF),编码的蛋白质由357个氨基酸构成,分子量为38.7kD。系统进化分析结果显示:3种锦鸡儿属植物的POD可以和鹰嘴豆等豆科植物的POD聚为一类,且CkPOD和CmPOD具有较近的亲缘关系,CiPOD与CkPOD和CmPOD的亲缘关系相对较远,这一结果与3种锦鸡儿属植物的进化地位一致,显示POD基因较为保守,可以为锦鸡儿属植物的系统分类提供参考。PEG模拟干旱胁迫能够强烈诱导CkPOD、CiPOD和CmPOD基因的表达,显示POD基因在锦鸡儿属植物抵御干旱胁迫过程中发挥着重要作用。研究结果可为解析锦鸡儿属植物的耐旱机理以及利用锦鸡儿属植物进行荒漠改良和生态修复提供理论和实验依据。     

Root tensile strength and root distribution of typical Mediterranean plant species and their contribution to soil shear strength

In Mediterranean environments, gully erosion is responsible for large soil losses. It has since long been recognized that slopes under vegetation are much more resistant to soil erosion processes compared to bare soils and improve slope stability. Planting or preserving vegetation in areas vulnerable to erosion is therefore considered to be a very effective soil erosion control measure. Re-vegetation strategies for erosion control rely in most cases on the effects of the above-ground biomass in reducing water erosion rates, whereas the role of the below-ground biomass is often neglected or underestimated. While the above-ground biomass can temporally disappear in semi-arid environments, roots may still be present underground and play an important role in protecting the topsoil from being eroded. In order to evaluate the potential of plant species growing in Mediterranean environments to prevent shallow mass movements on gully or terrace walls, the root reinforcement effect of 25 typical Mediterranean matorral species (i.e. shrubs, grasses herbs, small trees) was assessed, using the simple perpendicular model of Wu et al. (Can Geotech J 16:19–33, 1979). As little information is available on Mediterranean plant root characteristics, root distribution data were collected in SE-Spain and root tensile strength tests were conducted in the laboratory. The power root tensile strength–root diameter relationships depend on plant species. The results show that the shrubs Salsola genistoides Juss. Ex Poir. and Atriplex halimus L. have the strongest roots, followed by the grass Brachypodium retusum (Pers.) Beauv. The shrubs Nerium oleander L. and the grass Avenula bromoides (Gouan) H. Scholz have the weakest roots in tension. Root area ratio for the 0–0.1 m topsoil ranges from 0.08% for the grass Piptatherum miliaceum (L.) Coss to 0.8% for the tree Tamarix canariensis Willd. The rush Juncus acutus L. provides the maximum soil reinforcement to the topsoil by its roots (i.e. 304 kPa). Grasses also increase soil shear strength significantly (up to 244 kPa in the 0–0.1 m topsoil for Brachypodium retusum (Pers.) Beauv.). The shrubs Retama sphaerocarpa (L.) Boiss. and Anthyllis cytisoides L. are increasing soil shear strength to a large extent as well (up to 134 and 160 kPa respectively in the 0–0.10 m topsoil). Whereas grasses and the rush Juncus acutus L. increase soil shear strength in the topsoil (0–0.10 m) to a large extent, the shrubs Anthyllis cytisoides (L.), Retama sphaerocarpa (L.) Boiss., Salsola genistoides Juss. Ex Poir. and Atriplex halimus L. strongly reinforce the soil to a greater depth (0–0.5 m). As other studies reported that Wu’s model overestimates root cohesion values, reported root cohesion values in this study are maximum values. Nevertheless, the calculated cohesion values are used to rank species according to their potential to reinforce the soil.     

Soil nitrogen patterns induced by colonization of Polygonum cuspidatum on Mt. Fuji

Summary The spatial pattern of soil nitrogen was analyzed for a patchy vegetation formed by the colonization of Polygonum cuspidatum in a volcanic desert on Mt. Fuji. Soils were sampled radially from the bare ground to the center of the patch, and analyses were done for bulk density, water content, soil acidity, organic matter, organic nitrogen, and ammonium and nitrate nitrogen. The soils matured with succession from the bare ground through P. cuspidatum to Miscanthus oligostachyus and Aster ageratoides sites: bulk density decreased, and water content, organic matter, organic nitrogen, and ammonium nitrogen increased. Nitrate nitrogen showed the highest values at the P. cuspidatum site. Application of principal component analysis to the soil data discriminated two component factors which control the variation of soil characteristics: the first factor is related to soil formation and the second factor to nitrogen mineralization and nitrification. The effect of soil formation on nitrogen mineralization and nitrification was analyzed with a first-order kinetic model. The decreasing trends with soil formation in the ratios of mineral to organic nitrogen and of nitrate to ammonium nitrogen could be accounted for by the higher activity of immobilization by microorganisms and uptake by plants in the more mature ecosystem.     

Leaf photosynthesis, chlorophyll fluorescence, ion content and free amino acids in Caragana korshinskii Kom exposed to NaCl stress

To understand the physiological response under salt stress, photosynthesis, PSII efficiency, contents of ions and free amino acids in leaves of Caragana korshinskii Kom (Caragana) exposed to three levels of salinity were investigated. Results showed that the decrease in photosynthesis of Caragana with salt stress was largely dependent on stomatal closure during the experimental period. In the early period of stress, due to the dissipation of excess excitation energy which occurred by the increase in non-photochemical quenching, photodamage was avoided and maximum efficiency of PSII was not affected. However, with increased salt stress, the photoprotective mechanism was not sufficient to avoid oxidative damage. Thus, damage to PSII and its resulting non-stomatal inhibition of photosynthesis may occur. At 18 days with 300 mM NaCl treatment, a non-stomatal factor was responsible for the inhibition of photosynthesis. Accumulation of Na⁺ and K⁺ in leaves indicated no competition between Na⁺ and K⁺ absorption, which suggests the potential for a unique pathway of Na⁺ absorption in Caragana. There was a critical salinity level for the accumulation of free amino acids in salt-treated leaves of Caragana, i.e., free amino acids accumulated slowly below critical level, but rapidly above the critical level. In addition, proline was the most abundant among all individual free amino acids.     

载畜率对短花针茅荒漠草原灌木及其邻近土壤养分含量的影响

草地灌丛化现象在草地生态系统上广泛发生。放牧是人类利用草原的重要方式,通过分析不同载畜率下荒漠草原灌木种群及其邻近土壤养分含量的变化,可研究放牧干扰下不同灌木种群的耐牧特性,对深入了解荒漠草原植物群落演替机制具有重要意义。以荒漠草原灌木小叶锦鸡儿(Caragana microphylla)、半灌木驼绒藜(Ceratoides latens)及小半灌木冷蒿(Artemisia frigida)和木地肤(Kochia prostrata)(下称为“灌木”)为研究对象,探究不同载畜率下各个灌木种群的密度、高度、盖度及地上生物量(下称为“数量特征值”)及其邻近土壤养分含量。结果表明:冷蒿的数量特征值均随着载畜率的增加而降低,其他植物种群的数量特征值均在CK或LG区出现最大值,且不同灌木邻近土壤养分含量随着土壤深度的增加而下降(P < 0.05)。不同灌木邻近土壤全氮含量随着载畜率增加而下降;冷蒿邻近有机碳含量在CK区最高,小叶锦鸡儿邻近速效磷含量在HG区最高,其余灌木邻近有机碳、速效磷含量在LG区最高。灌木种群数量特征与土壤养分的关系为:土壤有机碳与冷蒿和驼绒藜的高度、盖度、地上生物量呈正相关,土壤速效磷与木地肤高度、地上生物量呈显著负相关。因此,载畜率均会对灌木植物种群的数量特征值及其邻近土壤养分含量产生影响。