香蕉假茎生物炭对根际土壤细菌丰度和群落结构的影响

【目的】将香蕉假茎生物炭施加到土壤,探讨香蕉假茎生物炭对香蕉根际土壤微生物的影响。【方法】以香蕉假茎生物炭(BPB)0、1%、2%、3%的质量比与土壤均匀混合。盆栽培养3个月后分离香蕉根际土壤。采用16S rRNA高通量测序技术对根际土壤细菌群落结构和丰度进行表征。【结果】提高BPB施用量可增加土壤有机质、有效钾、有效磷含量,提高土壤pH值,但降低有效氮浓度。在1%BPB样品中获得2278个OTUs,其显示细菌群落中的最大多样性。施加3%的BPB处理土壤,拟杆菌门、疣微菌门和厚壁菌门的相对丰度显著增加;放线菌门、酸杆菌门、芽单胞菌门明显减少。主成分分析发现,1%BPB和2%BPB处理的样本之间土壤细菌群落相似。【结论】施加不同比例BPB改变了根际土壤中细菌丰度和群落结构,且高比例添加改变更加明显。     

不同生长季节黑果枸杞的根际细菌群落结构

【目的】黑果枸杞是一种耐盐植物,是我国西北干旱区盐渍土改良的优良植物物种,其根际土壤细菌群落结构在不同生长时期的变化特征尚不清楚。【方法】本研究采用Illumina MiSeq高通量测序研究了黑果枸杞3个生长阶段的根际土壤细菌群落结构的动态变化。【结果】所有样品中共获得317467条序列,对应于7028个细菌/古细菌OTUs。根际土壤细菌群落的α多样性显著高于非根际土壤。衰老期根际细菌的多样性和丰富度明显低于营养生长期和花/果期。变形菌门和酸杆菌门的相对丰度随生长时期的演变而逐渐降低,而蓝细菌门则相反。厚壁菌门的丰度在衰老期明显高于营养生长期和花/果期。优势属的组成也随生长期的演变而改变,营养生长期、花/果期、衰老期的优势属数量分别为17、16、4,且组成也具有差异。相似性分析表明营养生长期和花/果期的根际细菌群落具有很高的相似性,衰老期根际细菌群落组成与生长期和花/果期具有很高差异,然而与非根际土壤的群落结构具有较高的相似性。【结论】根际土壤细菌群落多样性和组成随生长期的改变而表现出明显的动态变异性,表明黑果枸杞生长时期对根际土壤细菌群落结构具有重要的影响。     

不同生长季节黑果枸杞的根际细菌群落结构（英文）

【目的】黑果枸杞是一种耐盐植物,是我国西北干旱区盐渍土改良的优良植物物种,其根际土壤细菌群落结构在不同生长时期的变化特征尚不清楚。【方法】本研究采用Illumina MiSeq高通量测序研究了黑果枸杞3个生长阶段的根际土壤细菌群落结构的动态变化。【结果】所有样品中共获得317467条序列,对应于7028个细菌/古细菌OTUs。根际土壤细菌群落的α多样性显著高于非根际土壤。衰老期根际细菌的多样性和丰富度明显低于营养生长期和花/果期。变形菌门和酸杆菌门的相对丰度随生长时期的演变而逐渐降低,而蓝细菌门则相反。厚壁菌门的丰度在衰老期明显高于营养生长期和花/果期。优势属的组成也随生长期的演变而改变,营养生长期、花/果期、衰老期的优势属数量分别为17、16、4,且组成也具有差异。相似性分析表明营养生长期和花/果期的根际细菌群落具有很高的相似性,衰老期根际细菌群落组成与生长期和花/果期具有很高差异,然而与非根际土壤的群落结构具有较高的相似性。【结论】根际土壤细菌群落多样性和组成随生长期的改变而表现出明显的动态变异性,表明黑果枸杞生长时期对根际土壤细菌群落结构具有重要的影响。     

健康与感染青枯病烟株根际土壤与茎秆细菌群落结构与多样性

【目的】了解健康烟株与感染青枯病烟株在根际土壤、茎杆发病部位、茎杆病健交界部位以及未发病茎杆的细菌群落结构与多样性。【方法】分别对土壤与茎杆样品中细菌的16S rRNA基因V3-V4区进行扩增,采用Illumina MiSeq测序技术对扩增片段进行高通量测序,然后对健康烟株与感染青枯病烟株不同部位细菌群落结构与多样性进行分析。【结果】感染青枯病烟株发病茎杆及根际土壤的细菌群落多样性高于健康烟株茎杆及其根际土壤样品,病健交界茎杆样品细菌群落多样性低于健康烟株。变形菌门(Proteobacteria)在所有样品中均为优势菌门;所有烟株根际土壤的优势菌门为拟杆菌门(Bacteroidetes)、酸杆菌门(Acidobacteria)、放线菌门(Actinobacteria)和绿弯菌门(Chloroflexi);健康烟株茎杆部位的优势菌门为蓝细菌门(Cyanobacteria);感染青枯病烟株发病茎杆和病健交界茎杆部位的优势菌门为蓝细菌门(Cyanobacteria)和厚壁菌门(Firmicutes)。所有根际土壤样品的优势菌属为劳尔氏菌属(Ralstonia)、假单胞菌属(Pseudomonas)、鞘脂单胞菌属(Sphingomonas)、黄杆菌属(Flavobacterium)和代尔夫特菌属(Delftia),而感染青枯病烟株根际土壤的劳尔氏菌属(Ralstonia)和假单胞菌属(Pseudomonas)相对丰度显著高于健康烟株根际土壤,鞘脂单胞菌属相对丰度显著低于健康烟株根际土壤。烟株茎杆的优势菌属为劳尔氏菌属和假单胞菌属等。感染青枯病烟株病健交界茎杆中劳尔氏菌属、肠杆菌属(Enterobacter)和泛菌属(Pantoea)相对丰度显著低于健康烟株样品。【结论】健康与感染青枯病烟株茎杆样品细菌群落的丰富度和多样性明显低于相应的根际土壤样品。较健康烟株而言,感染青枯病烟株根际土壤和茎杆样品细菌群落丰富度和多样性均表现出不同程度地增加,且根际土壤细菌群落结构变化较茎杆样品明显,而病健交界茎杆样品细菌群落丰富度和多样性降低。烟草青枯病为典型土传病害,其病原茄科劳尔氏菌尽管能在烟株维管束中蔓延扩增,但主要还是分布于土壤中;它的存在似乎对土壤细菌群落的影响大于茎杆样品的。该研究结果提示对于青枯病的防治不能局限于烟株本身,田间土壤也应加大防治力度。     

盐碱胁迫对小麦幼苗生长和根际细菌群落结构的影响

【背景】植物可通过改变根际微生物群落结构来减轻胁迫,但盐碱胁迫下小麦生长和根际细菌群落结构变化尚待明晰。【目的】明确盐碱胁迫下小麦幼苗生长及根际细菌群落结构变化。【方法】以添加NaCl和Na2CO3调节Hoagland营养液Na+浓度和pH来模拟盐碱胁迫,通过MiSeq高通量测序分析细菌群落结构。【结果】与无胁迫对照相比,单纯盐胁迫使小麦幼苗地上和地下部干重、叶绿素和根际土壤速效氮含量分别显著降低了25.0%、57.1%、21.2%和42.9%(P<0.05);小麦幼苗生长指标和根际土壤速效氮、速效磷、有机质含量及酶活性(除过氧化氢酶)随碱度升高而降低;所有处理的小麦幼苗根际优势菌门(丰度7.1%-71.5%)均为变形菌门(Proteobacteria)、放线菌门(Actinobacteria)和厚壁菌门(Firmicutes),优势属(丰度0.5%-5.1%)有肠杆菌属(Enterobacter)、嗜多甲基菌属(Methyloversatilis)、固氮菌属(Azotobacter)、假单胞菌属(Pseudomonas)和异根瘤菌属(Allorhizobium)。盐碱胁迫未显著...     

广东省本地油茶和引种油茶根际土壤微生物群落特征

【背景】近年来,油茶低效林面积较大,根际土壤微生物影响林木抗性和生长,对林业可持续发展具有重要意义。【目的】了解广东省本地油茶和引种油茶根际土壤微生物群落特征。【方法】利用高通量测序分析油茶根际土壤微生物群落组成。【结果】油茶根际土壤细菌有26门77纲201目377科593属676种,真菌有14门50纲121目266科502属631种。油茶根际土壤中的优势细菌为酸杆菌门和变形菌门,优势真菌为子囊菌门和担子菌门。两种油茶根际土壤微生物组成差异显著,本地油茶根际土壤的细菌多样性显著高于引种油茶。在门水平上,脱硫杆菌门细菌和罗兹菌门、被孢霉门真菌的相对丰度在两种油茶间差异显著,Amorphotheca在本地油茶根际土壤中特异性富集。两种油茶根际土壤细菌碳代谢相对丰度差异显著,真菌以腐生营养型为主,其次为病理营养型和共生营养型。本地油茶根际土壤中显著富集土壤腐生菌,而共生营养型真菌(尤其是丛枝菌根真菌)相对丰度(6.43%)显著低于引种油茶中(21.83%)。此外,有机质和养分含量是影响油茶根际土壤微生物群落的关键因子。【结论】本地油茶和引种油茶根际土壤微生物群落组成和结构差异显著,Amorp...     

自然林下与田间根腐三七根际微生物群落特征及比较分析

【背景】三七根际微生物群落特征与其土传根腐病害密切相关,而针对自然林下根腐三七的相关研究鲜见报道。【目的】比较分析自然林下与田间根腐三七根际土壤微生物群落的组成特征,结合土壤理化性质与酶活性分析,为三七根腐病害防治与仿野生栽培提供科学依据。【方法】采集自然林下与田间根腐三七根际土壤,利用高通量测序技术,分析土壤细菌与真菌群落的物种组成与多样性,并测定土壤理化性质和酶活性。【结果】自然林下与田间根腐三七根际土壤中细菌和真菌群落组成具有明显差异,自然林下根腐三七根际土壤中担子菌门(Basidiomycota)、酸杆菌门(Acidobacteria)和疣微菌门(Verrucomicrobia)的相对丰度较高,而田间根腐三七根际土壤中子囊菌门(Ascomycota)、变形菌门(Proteobacteria)和绿弯菌门(Chloroflexi)的相对丰度较高。在属分类水平,镰刀菌属(Fusarium)是自然林下根腐三七根际土壤中的优势菌群,相对丰度为17.30%,而癣囊腔菌属(Plectosphaerella)是田间根腐三七根际土壤中的优势菌群,相对丰度为22.55%;Candidatus Ba...     

两种盐生植物根际土壤细菌多样性和群落结构

应用高通量测序技术对西北干旱区两种盐生植物黑果枸杞和里海盐爪爪根际土壤细菌的多样性和群落结构进行研究,旨在揭示两种耐盐植物根际土壤细菌之间以及根际与非根际细菌群落结构间的差异,为深入研究盐生植物根际土壤微生物与耐盐性之间的关系提供理论基础。结果表明:黑果枸杞、里海盐爪爪根际细菌多样性丰度高于非根际土,黑果枸杞根际土壤细菌多样性丰度高于里海盐爪爪。根际和非根际土壤细菌群落的组成和丰度存在差异,从黑果枸杞和里海盐爪爪根际土壤中分别检测出细菌21门289属和22门304属,而从非根际土壤中分别检测出28门285属和24门336属;在两种盐生植物根际土壤中,变形菌门和厚壁菌门均为优势门;拟杆菌门、放线菌门、蓝细菌门及浮霉菌门在根际土壤中的丰度显著高于非根际土壤,而厚壁菌门在根际土壤中的丰度低于非根际土壤。两种植物根际土壤中的细菌优势门和优势属的数量均高于非根际土壤,在黑果枸杞和里海盐爪爪的根际土壤中的细菌优势属分别有10个和9个,而二者非根际土壤中的细菌优势属各有4个,其中假单胞菌属是根际和非根际土壤中的共有优势属。黑果枸杞和里海盐爪爪根系细菌群落组成和丰度存在差异,只有假单胞菌属和盐单胞菌属是两种植物根际土壤中的共有优势属。Unifrac分析和聚类分析表明,两种盐生植物根际土壤细菌之间的相似性大于根际和非根际细菌群落间的相似性。细菌多样性与土壤有机碳、有机质、总氮正相关,与pH、电导率负相关,电导率和pH,有机碳和总氮分别是非根际土,根际土壤细菌群落物种组成的主要影响因素。     

模拟增温对青海湖鸟岛土壤微生物的影响

【背景】土壤微生物对其生存的微环境变化极为敏感,鸟岛作为湖滨湿地,对气候变化具有敏感性,但目前关于青海湖鸟岛的土壤微生物鲜有研究。【目的】探究气候变暖后青海湖鸟岛土壤微生物群落特征的变化。【方法】利用开顶箱模拟增温,通过高通量测序方法了解温度升高后土壤细菌及真菌的群落结构以及多样性的变化情况。【结果】温度的升高并未改变青海湖鸟岛土壤微生物的优势菌群,细菌优势菌群为变形菌门和酸杆菌门;真菌优势菌门为子囊菌门,优势菌纲为座囊菌纲。但增温改变了土壤微生物的群落结构,显著升高了拟杆菌门、蓝细菌门、Patescibacteria及球囊菌纲的相对丰度,显著降低了锤舌菌纲的相对丰度。土壤微生物群落的多样性指数也发生了变化,温度上升后微生物的ACE指数及Chao1指数均降低,细菌的Simpson指数及真菌的Shannon指数降低。【结论】青海湖鸟岛土壤微生物对温度升高的响应明显,增温改变了土壤细菌拟杆菌门、蓝细菌门、Patescibacteria的相对丰度及真菌的球囊菌纲、锤舌菌纲的相对丰度,降低了土壤微生物的多样性。     

黄渤海海草分布区日本鳗草根际微生物群落结构特征及其功能分析

日本鳗草(Zostera japonica)是亚洲特有的海草种类,具有重要生态价值。近年来,黄渤海海草分布区中的日本鳗草海草床持续退化,引起了研究人员的广泛关注。【目的】基于根际微生物的分布与日本鳗草的健康生长密切相关的设想,本文旨在探究黄渤海海草分布区日本鳗草根际细菌群落结构多样性并分析其与海草健康生长的内在联系。【方法】选取黄渤海海草分布区中东营、威海、大连3个地点的日本鳗草根际与非草区表层沉积物,采用高通量测序技术(Illumina HiSeq PE300)解析根际微生物群落特征,并结合相关环境参数分析其环境功能。【结果】日本鳗草根际表层沉积物中主要存在的细菌类群有:变形菌门(Proteobacteria)所占比例为41.1%,蓝细菌门(Cyanobacteria)占15.4%,拟杆菌门(Bacteroidetes)占12.6%,放线菌门(Actinobacteria)占9.3%。不同地点之间以及样品类型(海草床根际与非根际)之间的微生物群落存在显著差异,主要表现为根际富含硫酸盐还原菌和固氮菌。环境因素:TN (total nitrogen)、TC (total carbon)、TOC (total organic carbon)、黏土(Clay)、砷(As)与根际群落组成与分布显著相关。【结论】从功能的角度来看,不同地点、不同样品类型之间的差异物种多与硫、氮代谢相关,硫酸盐还原菌对维持日本鳗草的生态健康起关键作用;日本鳗草根际微生物群落分布与环境因子、空间分布有一定相关性。     

The effect of competition and edaphic conditions on the establishment of halophytes on brine effected soils

In order to test the feasibility of using native halophytes to reclaim brinecontaminated soil, seedlings of five inland halophytes, Atriplexprostrata, Hordeum jubatum, Salicornia europaea, Spergularia marina, and Suaeda calceoliformis, were planted at threedensities on a site near Athens, Ohio which had been contaminated by oilwell brine water. Ten replicates of each density treatment weretransplanted on two distinct areas of high and low salinity in May of 1993. Seedling survivorship, soil moisture, and soil salinity were monitored weeklythroughout the growing season. Biomass production and ion uptake weredetermined for each plant surviving until harvest. Soil analyses wereperformed prior to planting and after harvest to determine overall changesin soil chemistry and to determine the amount of Na⁺ reductionfrom the soil due to leaching by precipitation during the course of theexperiment. Survival was determined to be density independent for all ofthe species with the exception of S. marina where survival wasfacilitated at high density. Increased salinity negatively affected the survivaland yield of A. prostrata. The remaining species had greater survivalunder high salinity conditions, and density appeared to be the key factorinfluencing yield. Sodium and chloride ions were accumulated in planttissues in much greater amounts than K⁺, Ca⁺²or Mg⁺². Salicornia europaea plants grown in high densityon the high salinity site accumulated the highest amount of Na⁺ andH. jubatum grown in low density on the high salinity site accumulatedthe lowest amount of Na⁺. Soil salinities measured directly from theroot zone were significantly reduced (p<0.05) at the end of thegrowing season when compared to their controls. Atriplex prostrata(high density/low salinity) plots produced the greatest reduction in soilsalinity (15.8%) and S. marina (high density/high salinity) plots hadthe least reduction (1.2%).     

降水对鄂尔多斯高原克隆植物分布的影响

鄂尔多斯高原地处半干旱区到干旱区的过渡带。通过沿鄂尔多斯高原从东到西的天然降水梯度的样带调查,分析了克隆植物的分布特征与降水的关系。结果表明:克隆植物的物种数量、占物种总数的比例和重要值以及根状茎型克隆植物的物种数量均与降水量呈显著正相关。5种优势植物克氏针茅、本氏针茅、黑沙蒿、赖草和短花针茅均为克隆植物,它们的分布也受降水影响。克氏针茅的密度、本氏针茅的盖度和密度、黑沙蒿的高度、盖度和密度以及赖草的高度均与降水量呈显著正相关。然而,赖草的盖度以及短花针茅的高度、盖度和密度均与降水量成负相关。因此,克隆植物在鄂尔多斯高原植被中具有重要作用,而且其作用随着降水量的增加而加强。     

A comparative study on the influence of manganese on the bactericidal response of marine invertebrates

Manganese, Mn, is a naturally abundant metal in marine sediments. During hypoxic conditions the metal converts into a bioavailable state and can reach levels that have been shown immunotoxic to the crustacean Nephrops norvegicus. For this species it has previously been shown that exposure to 15 mg L⁻¹ of Mn decreased the number of circulating haemocytes while it for the echinoderm Asterias rubens increased the number of coelomocytes. Here, we compared if five days of exposure to the same concentration of Mn affects the bactericidal capacity of these two species and the mollusc Mytilus edulis when inoculated with the bacterium Vibrio parahaemolyticus. Viable counts of the bacteria were investigated at a time-course post-injection in the blood and the digestive glands of Mn-exposed and un-exposed (controls) animals. Accumulation of Mn was also analyzed in these tissues. When exposed to Mn the haemocyte numbers were significantly reduced in M. edulis and it was shown that the bactericidal capacity was impaired in the mussels as well as in N. norvegicus. This was most obvious in the digestive glands. These two species also showed the highest accumulation of the metal. In A. rubens the bactericidal capacity was not affected and the metal concentration was similar to the exposure concentration. After a recovery period of three days the concentration of Mn was significantly reduced in all three species. However, in M. edulis and N. norvegicus it was still double that of A. rubens which could explain the remaining bactericidal suppression observed in N. norvegicus. This study pointed out that exposure to such Mn-levels that are realistic to find in nature could have effects on the whole organism level, in terms of susceptibility to infections. The effect seemed associated to the accumulated concentration of Mn which differed on species level.     

Distribution of VA mycorrhiza on halophytes on inland salt playas

The value of mycorrhizal association for higher plants has been well established. However, the impact of high salinity on the mycorrhizal relationship has not been investigated to any great extent. Inland salt playas represent an opportunity to test the impact of salinity because it is possible to obtain a gradient by following a transect from the centre of the salt playa to the higher outer zones. In a salt playa near Goshen, Utah, the sodium concentration ranged from 27,150 ppm in the centre to 25 ppm in the outer zone. In the playas with sodium concentrations of 20,000 ppm, no mycorrhiza were detected on the halophytes and no spores of mycorrhizal fungi were found in the soil. One percent of the roots of salt grass in soils containing 8,450 ppm of sodium were mycorrhizal. In soils containing 622 ppm of 45 percent of the roots of a salt-tolerant grass (hybrid ofAgropyron repens × Agropyron spicatum) were mycorrhizal. Halophytes such asSalicornia pacifica var.utahensis which are among the most salt tolerant halophytes of the inland salt playas rarely had mycorrhizal roots. The mycorrhizal associations appear to be very limited in inland salt playas with sodium content.     

Dry deposition of pollutants and effects on vegetation

Summary Dry deposition of gases and airborne particles is reviewed in particular relation to their interaction with vegetation. Once deposited, pollutants overcome the system of resistances (air, cuticular, stomatal and mesophyll) and penetrate key physiological points that affect the plant's biochemistry. Strong relationships have been found between gases in the environment and the chlorophyll content of leaves, production and partitioning of dry matter, relative growth rate and net assimilation rate. Physical modes of dry deposition involving anthropogenic pollutants present in the surface layer and micrometeorological conditions allowing their diffusion in the canopy are also discussed, with emphasis on measurement techniques.     

Relative susceptibility to predation of two species of caterpillar on plantain

Summary The relative susceptibility to predators of a cryptic generalist caterpillar (Spilosoma congrua: Arctiidae) and a non-cryptic specialist (Junonia coenia: Nymphalidae) using the same hostplant species (Plantago lanceolata) was examined. In a laboratory experiment using predatory stinkbugs (Podisus maculiventris), more Junonia caterpillars than Spilosoma caterpillars were killed (70% vs. 16%). This result was a consequence of the Spilosoma spending some time under cover, moving frequently, feeding on leaves while under or adjacent to them, and spending little time on the leaves. In a field experiment using predatory wasps (Polistes fuscatus), the wasps found 7 times as many of the Junonia as the Spilosoma, and overall 6 times as many Junonia were killed as Spilosoma. Initially, 71% of the Junonia caterpillars encountered by wasps were killed, but by the fourth day of the test, only 22% of the Junonia encountered by wasps were killed. Over three full days of observations, a constant 50% of the Spilosoma caterpillars encountered by the wasps per day were killed. For the Junonia, evasion of predators rested on passive chemical defense. For the Spilosoma, evasion depended on being unapparent, speedy movement between feeding and resting sites and, if found, on fleeing immediately and quickly. These results indicate that Spilosoma caterpillars, by way of cryptic and escape behaviors, can be less susceptible to insect predators than Junonia caterpillars.     

Structures of acidic O-linked polylactosaminoglycans on human skim milk mucins

O-Linked glycans were isolated from human skim milk mucins or mucin-derived high-molecular weight glycopeptides and fractionated by anion exchange chromatography into neutral and acidic alditols. Major oligosaccharides contained in the acidic fraction were purified by high performance liquid chromatography and structurally characterized by a combination of fast atom bombardment mass spectrometry, methylation analysis and 500 MHz 1H-nuclear magnetic resonance spectroscopy. The structural aspects exhibited by these major species in the acidic fraction resemble those established previously for the neutral oligosaccharides from human skim milk mucins: 1) the size of the alditols varies from tri- to decasaccharides, 2) the core structure is of the ubiquitous type 2, 3) the backbone sequences are of the poly-N-acetyllactosamine type with a particular preponderance of linearly extended GlcNAc beta(1-3)Gal (major) or GlcNAc beta(1-6)Gal units (minor).     

In vitro studies on the effects of fungicides on beneficial fungi of peach twig mycoflora

In vitro studies were carried out to investigate a possible integrated use of chemical and biological means to control the peach twig blight pathogen,Monilinia laxa. Three fungal antagonists ofM. laxa (Penicillium purpurogenum, Penicillium frequentans andEpicoccum nigrum) and six fungicides (vinclozolin, iprodione, thiram, captan, benomyl and thiophanate-methyl) were used in the study. Sensitivity of the fungal isolates to the fungicides was determined in vitro by calculating ED50 values. Benomyl and thiophanate-methyl were the most fungitoxic compounds and captan was the least fungitoxic.M. laxa andP. purpurogenum were the most sensitive to all chemicals tested, whileE. nigrum andP. frequentans presented bigger differences in their sensitivity to chemicals compared toM. laxa. E. nigrum was consistently less sensitive to benomyl (ED50=2.26 ppm), thiophanate-methyl (ED50=9.61 ppm) and vinclozolin (ED50=3.89 ppm) than the other fungi.P. frequentans was less sensitive to captan, vinclozolin, iprodione, thiophanate-methyl and thiram thanM. laxa (8, 7, 5, 4 and 2 times respectively). These results suggest thatE. nigrum andP. frequentans could be successfully used in an integrated control programme that combines biological and chemical methods.     

Effect of algalization on seed germination of vegetable crops

Soaking seeds of cucumber and pumpkin with an extract of Westiellopsis prolifica, an N₂-fixing cyanobacterium, promoted germination and their subsequent growth and development. An extract of Lyngbya sp., a non-N₂-fixing cyanobacterium, had no significant effect.The authors are with the Algal Physiology Laboratory, Department of Botany, Berhampur University, Berhampur-760007, Orissa, India.     

Effects of irrigation frequency on germination and on root and shoot yields ofAcacia species

Summary Maximum germination response and root + shoot yields of Acacias were obtained at daily irrigation. Any deviation from daily irrigation resulted in variations of performance (germination and growth yield) between the six Acacia species studied. Species of relatively dry habitse.g. A. nubica andA. seyal were more sensitive to water supply compared with those of relatively wet habitatse.g. A. nilotica andA. albida. This was reflected at the establishment phase by the greater production of root + shoot yields of species of drier zones than by those of wetter ones. It is concluded that variations in water supply may account for species adaptation and distribution in semi-arid zones.