Notes On The Flora Of Caithness

Summary

216 species of diatoms have been found epiphytic on common intertidal marine algae from Great Cumbrae Island, Firth of Clyde, Scotland. Green and red algae had larger epiphytic floras than brown algae. Cocconeis spp. (especially C. scutellum var. scutellum) were common and abundant, and the endophytic Navicula endophytica was found in large numbers in fucoid algae. Similar epiphytic floras were observed on Cladophora rupestris, Polysiphonia lanosa, Gigartina stellata, and Palmaria palmata, but that on Enteromorpha intestinalis was quite distinct.     

腾格里沙漠人工固沙植被演替生物土壤结皮盖度对沙埋的响应

生物土壤结皮(简称结皮)的形成与发展是沙区固沙植被建设成功的重要标志之一,其盖度随固沙植被演替的变化趋势是表征该植被系统地表稳定性的一个直观性生态学指标。利用空间代时间的方法,以腾格里沙漠不同始植年代(1956、1973、1981和1987年)固沙植被区发育的4种优势结皮-真藓(Bryum argenteum Hedw.)结皮、土生对齿藓(Didymodon vinealis(Brid.)Zand.)结皮、齿肋赤藓(Syntrichia caninervis Mitt.)结皮和藻-地衣-藓类混生结皮(Mixed crust)为研究对象,在测定结皮盖度、高度以及粗糙度随沙埋厚度逐渐增加变化的基础上,计算了使结皮盖度(从99.99%)开始降低的初始沙埋厚度(D1)和盖度降低为0%的临界沙埋厚度(D2),研究了该区固沙植被演替过程中结皮盖度对沙埋厚度增加的响应特征及其相关机制。结果显示:(1)4种结皮的盖度随沙埋厚度的增加呈logistic曲线逐渐降低。(2)在同一年代固沙区不同种间比较,混生结皮的D1值最小,D2值最大;真藓结皮的D1和D2值均小于其他两种藓类结皮;土生对齿藓结皮和齿肋赤藓结皮因固沙年限的不同而不同,在1956年固沙区,土生对齿藓结皮齿肋赤藓结皮,而在1973年固沙区和1981年固沙区,齿肋赤藓结皮土生对齿藓结皮。(3)随固沙植被演替,4种结皮盖度随沙埋厚度增加的降低速率逐渐减小,D1和D2值逐渐增大。(4)结皮总盖度随沙埋厚度增加的降低速率逐渐减小,表明随固沙植被演替,结皮对沙埋的抵御能力逐渐增强,固沙区植被系统地表稳定性增加。(5)结皮的粗糙度和高度随固沙植被演替逐渐增加,并显著影响了4种结皮盖度随沙埋厚度增加的降低速率、D1及D2值。研究为全面评估沙埋对沙区结皮结构、功能的影响乃至固沙植被稳定性提供了参考。     

Change in striation density and systematics ofCocconeis scutellum var.Ornata (Bacillariophyceae)

Cocconeis scutellum var.ornata Grun. from three localities of Japan was studied. The striation density in 10 μm showed a marked tendency to increase with the decrease of the valve length in both raphe and rapheless valves, and this tendency did not vary with locality or environmental condition. The striation densities of rapheless valves were 4–6 in 10 μm for a valve length of 40μm, 4–6.5 for 30 μm, 6–9 for 20μm and 6.5–11 for 15μm. Those of raphe valves were 10–11 in 10μm for a valve length of 40μm, 10–12 for 30μm, 11–14.5 for 20μm and 12.5–17 for 15μm. According to the range of changing value in striation density obtained by the present study,C. scutellum var.schmidti Frenguelli andC. japonica Schmidt are identical withC. scutellum var.ornata. Dedicated to Prof. Munenao Kurogi on the occasion of his academic retirement. Culture experiment in the present study was undertaken at the Institute of Algological Research, Faculty of Science, Hokkaido University at Muroran.     

冻融条件下生物结皮覆盖对土壤饱和导水率的影响

生物结皮(BSC)是广泛分布的地被物,每逢冬春季节,受冻融交替作用影响,结皮土壤的理化性质和水文学特征明显改变且与裸土差异显著,从而影响该地区土壤可蚀性评估和土壤侵蚀防治。采用室内模拟实验,以蓝藻结皮土壤为对象,研究不同冻融交替次数和初始含水量下,土壤三相对温度变化的响应特征并定量分析结皮覆盖土壤在此条件下饱和导水率(Ks)的变化趋势和突变点。结果表明:初始含水量对Ks无显著影响(P>0.05),冻融交替次数对Ks有极显著影响(P<0.01),冻融条件下裸土的平均Ks为1.941 mm/min,结皮覆盖土壤平均Ks为0.325 mm/min,两者具有极显著差异(P<0.01),且随交替次数增加,Ks差异逐渐增大,并在10次时达到最大值为10.13倍。不同冻融含水量下的结皮土壤的Ks在冻融10—20次时趋近,平均值为0.219mm/min。冻融作用显著改变土壤结构,且在冻融7次时土壤结构变化较明显,冻融过程中<0.1 mm的土壤颗粒显著变化。试验条件下,Ks受因子影响程度大小为:冻融交替次数>土壤结构>结皮厚度>结皮容重>下层土壤容重>...     

An experimental association between Chlorella xanthella and a streptomyces

An association in the form of a lichen-like crust (“actinolichen”) was obtained by seeding Chlorella xanthella cells and spores of a Streptomyces sp. isolated from soil on the surface of potato sections partially immersed in water at temperatures with a diurnal fluctuation of 9–19 C or 14–25 C, and with illumination continuous or during the hours of the higher temperatures. Sections of the crust showed a lichen-like organized tissue with layers of Streptomyces sp. spores, hyphae alone and associated hyphae and algae.     

Initial effects of experimental warming on carbon exchange rates, plant growth and microbial dynamics of a lichen-rich dwarf shrub tundra in Siberia

Biological soil crusts can affect seed germination and seedling establishment. We have investigated the effect of biological soil crusts on seed water status as a potential mechanism affecting seed germination. The seed water potential of two annual grasses, one exotic Bromus tectorum L. and another native Vulpia microstachys Nutt., were analyzed after placing the seeds on bare soil, on a crust that contains various lichens and mosses (mixed crust), or on a crust dominated by the crustose lichen Diploschistes muscorum (Scop.) R. Sant. (Diploschistes crust). Seed water potential and germination were similar on the bare soil and the mixed crust, except for the initial germination of V. microstachys, which was higher on the mixed crust than on the bare soil. For the two grasses studied, seed water potential was significantly higher on the bare soil and mixed crust than on the Diploschistes crust. These differences in water potential correlated with differences in germination, which was much lower on the lichen crust. Experiments were conducted under two watering regimens. Increasing the frequency of watering amplified the differences in seed water potential and germination between the Diploschistes crust and the other two surfaces. For a particular watering regimen, the bare soil, mixed crust, and Diploschistes crust received the same amount of water, but they reached significantly different water potentials. Throughout the experiments, the water potential of the soil and mixed crust remained above −0.6 MPa, while there was a marked decline in the water potential of the Diploschistes surface to about −4 MPa. To ascertain that water was the major factor limiting germination on the Diploschistes crust, we conducted germination tests in an environment with 100% relative humidity. Under these conditions, germination on the Diploschistes crust was similar to that on the bare soil. However, the seeds that germinated on the Diploschistes crust did not penetrate this surface and approximately 60% of their root tips became necrotic. Our results indicate that the presence of D. muscorum can inhibit seedling establishment by two mechanisms: a reduction in seed water absorption and an increase in root tip mortality.     

Epiphytic diatom communities on intertidal seaweeds from Iceland

Epiphytic diatom communities on macroalgae from Iceland coastal waters were investigated during July 2005. Ten species of seaweeds have been collected belonging to brown, red and green algae. The analysis of epiphytic diatom community was carried out under scanning electron microscopy. The epiphytic diatom abundances varied from 7 ± 5 to 7524 ± 3491 cells mm⁻². Erect growth forms were the most abundant, representing on average 50% of the total diatoms (Achnanthes cf. brevipes var. parvula, Tabularia investiens, T. fasciculata, Hyalosira cf. delicatula, Gomphoseptatum aestuarii, Pseudogomphonema plinskii), followed by adnate (29%) (Cocconeis stauroneiformis, C. scutellum) and motile forms (21%) (Nitzschia cf. amphibia and Navicula perminuta). Highly branched seaweeds with articulated thallus surface, offering a number of microenvironments to be occupied by the epiphytes, showed a high level of colonization, mainly due to erect and motile diatoms. Flat thalli with smooth surface allowed for the growth of mainly erect diatoms.     

Algal crust formation in the inland dune area,Laarder Wasmeer,the Netherlands

The aim of this study is to acquire insight in the initial vegetation development on active drifting sands in relation to geomorphological processes. For this purpose the algal vegetation and surface dynamics were monitored on a sand hill with active drifting sand, and on a bare slope within a terrain covered with Polytrichum piliferum located in the Laarder Wasmeer (The Netherlands).There is a successional development from an algal community dominated by the cyanobacterium Oscillatoria spp., through the crust in which initially the green alga Klebsormidium and later the cyanobacterium Synechococcus predominates, eventually succeeded by the green alga Zygogonium ericetorum. In this phase the sand is stabilized. The areal extent of algal crusts on the active drifting sand area is greatest during the winter, contrastingly highest biomass values are found during the summer and autumn in mature Zygogonium crusts.Substrate instability due to the action of wind clearly limits algal growth and vegetational development on the sand hill. The algal crust seldom reaches the stage of maturity. Near-flat ground is more easily stabilized. Unlike the algae found in coastal dune area and the initial pioneers in the Laarder Wasmeer area, the Zygogonium crust is water repellent when dry. Consequently increasing surface stability by algal crust development is accompanied by higher surface runoff on sloping areas.     

Biological crust of <Emphasis Type="Italic">Nostoc flagelliforme</Emphasis> (cyanobacteria) on sand bed materials

Nostoc flagelliforme in liquid culture was cultivated on sand bed materials as inoculum and formed a biological crust. The biological crust had no common appearance of wild N. flagelliforme thallus in naked eye observation, but it had natural morphology of wild N. flagelliforme thallus in microscopic observation. By examining the photosynthetic activity, N. flagelliforme cells on sand were found to be heat resistant. The sand grain size had some influence on N. flagelliforme growth, and the growth rate on fine sand was higher than on coarse sand. It is necessary to consider the characteristics of sand particle size to prevent desertification. N. flagelliforme cells could form the algal biological crust, which indicates that the biological crust has potential application in soil desertification and was extremely important to improve desertification.     

Soil stabilization by a prokaryotic desert crust: Implications for Precambrian land biota

A cyanophyte dominated mat, desert crust, forms the ground cover in areas measuring hundreds of square meters in Utah and smaller patches in Colorado. The algal mat shows stromatolitic features such as sediment trapping and accretion, a convoluted surface, and polygonal cracking. Sand and clay particles are immobilized by a dense network of filaments of the two dominating cyanophyte species,Microcoleus vaginatus andM. chthonoplastes, which secrete sheaths to which particles adhere. These microorganisms can tolerate long periods of desiccation and are capable of instant reactivation and migration following wetting. Migration occurs in two events: 1. immediately following wetting of dry mat, trichomes are mechanically expelled from the sheath as it swells during rehydration, and 2. subsequently, trichomes begin a self-propelled gliding motility which is accompanied by further production of sheath. The maximum distance traveled on solid agar by trichomes ofMicrocoleus vaginatus during a 12 hour period of light was 4.8 cm. This corresponds to approximately 500 times the length of the fastest trichome, and provides a measure of the potential for spreading of the mat in nature via the motility of the trichomes.Dehydration resistence of the sheath modifies the extracellular environment of the trichomes and enables their transition to dormancy. Following prolonged wetting and evaporative drying of the mat in the laboratory, a smooth wafer-like crust is formed by the sheaths ofMicrocleus trichomes that have migrated to the surface. Calcium carbonate precipitates among the algal filaments under experimental conditions, indicating a potential for mat lithification and fossilization in the form of a caliche crust. It is suggested that limestones containing tubular microfossils may, in part, be of such an origin.The formation of mature Precambrian soils may be attributable to soil accretion, stabilization, and biogenic modification by blue-green algal land mats similar to desert crust.     

Developmental Morphology of Roots and root-borne shoots ofPodostemum subulatum as compared withZeylanidium olivaceum (Podostemaceae—Podostemoideae) Part VII of the series ‘Morphology of Podostemaceae’

The root structure ofPodostemum subulatum is investigated and compared with that ofZeylanidium olivaceum. Podostemum has thread- or ribbon-like roots. The root tip consists of an inner apical meristem and a single-layered root cap. From roots arise numerous shoots of endogeneous origin. Their vascular bundle isab initio connected with the root bundle.By the simple (reduced) apical zonation, the roots ofPodostemum subulatum appear more advanced than the crustose roots ofZeylanidium olivaceum, which bear an ordinary (though asymmetrical) root cap. With regard to the endogeneous root-borne shoots, however,Zeylanidium appears more advanced because of the shoot dimorphism. The floriferous shoots have a short axis that grows plagiotropously above the crust surface, whereas the axes of the vegetative shoots are extremely short and remain, together with the apical meristem, within the crust. Only the leaves protrude from the crust surface.     

A protein phosphorylation module patterns the Bacillus subtilis spore outer coat

Assembly of the Bacillus subtilis spore coat involves over 80 proteins which self-organize into a basal layer, a lamellar inner coat, a striated electrodense outer coat and a more external crust. CotB is an abundant component of the outer coat. The C-terminal moiety of CotB, SKR^B, formed by serine-rich repeats, is polyphosphorylated by the Ser/Thr kinase CotH. We show that another coat protein, CotG, with a central serine-repeat region, SKR^G, interacts with the C-terminal moiety of CotB and promotes its phosphorylation by CotH in vivo and in a heterologous system. CotG itself is phosphorylated by CotH but phosphorylation is enhanced in the absence of CotB. Spores of a strain producing an inactive form of CotH, like those formed by a cotG deletion mutant, lack the pattern of electrondense outer coat striations, but retain the crust. In contrast, deletion of the SKR^B region, has no major impact on outer coat structure. Thus, phosphorylation of CotG by CotH is a key factor establishing the structure of the outer coat. The presence of the cotB/cotH/cotG cluster in several species closely related to B. subtilis hints at the importance of this protein phosphorylation module in the morphogenesis of the spore surface layers.     

Biodiversity and ecology of epilithic diatoms in the Agnéby River,Ivory Coast

The ecology and taxonomy of the epilithic diatom flora of the Agnéby River, Ivory Coast were studied in 2012. Ten sites were investigated and diatoms were sampled on glass slides immersed for a period of 30 days during the wet and dry seasons. Physico-chemical parameters were measured at each site while sampling diatoms. Five taxa were largely dominant: Planothidium comperei CE Wetzel, N’Guessan and Tison-Rosebery, Eolimna minima (Grunow) Lange-Bertalot, Planothidium piaficum (JR Carter and Denny) CE Wetzel and Ector, Cocconeis schroederi Foged and Cocconeis scutellum var. parva (Grunow in Van Heurck) Cleve. Electrical conductivity, temperature, dissolved oxygen, nitrite and phosphorus were found to influence the distribution of taxa.     

Hydrotaxis of Cyanobacteria in Desert Crusts

We studied the migration of cyanobacteria in desert crusts from Las Bárdenas Reales (Spain). The crusts were almost exclusively colonized by the filamentous cyanobacterium Oscillatoria, which formed a dense layer approximately 600 µm thick located between 1.5 and 2.1 mm deep. Laboratory and field experiments showed that saturation of the crust with liquid water induced a migration of the cyanobacteria leading to a significant greening of the surface within a few minutes. Under light and rapid evaporation, the green color rapidly disappeared and the crust surface was completely devoid of filaments within 60 min. In contrast, 260 min was required to recover the original white color of the crust when slow evaporation was experimentally imposed. The up and down migration following wetting and drying occurred also in the dark. This demonstrates that light was not a required stimulus. Addition of ATP synthesis inhibitors prevented the cyanobacterium from migrating down into the crust, with filaments remaining on the surface. Therefore, the disappearance of the green color observed during desiccation can only be attributed to an active cyanobacterial motility response to the decrease in the water content. The simplest explanation that can account for the evidence gathered is the presence of a mechanism that links, directly or indirectly, these motility responses to gradients in water content, namely a form of hydrotaxis.     

Cyanobacterial soil crusts and woody shrub canopies in Kalahari rangelands

Intensive grazing of Kalahari rangelands has led to woody plant encroachment, notably of Acacia mellifera and Grewia flava. The mechanisms causing this process, and the ecological stability of woody plant encroached ecosystems, remain uncertain. Past studies suggest that canopy–soil relations may enhance woody plant competitive dominance. This study aims to investigate one element of this ecological change by examining the spatial distribution of cyanobacterial soil crusts in two vegetation sub‐habitats at sites of different disturbance. Crust burial by litter was also assessed to analyse the dynamics of canopy–crust relations. Our results show there is enhanced cyanobacterial crust cover under A. mellifera canopies and that unlike G. flava canopies, the crust cover remains under A. mellifera even at highly disturbed sites. This canopy–crust association suggests A. mellifera encroachment exhibits intrinsic resilience because of the crusts ability to stabilize the soil surface and increase nutrient retention. Crust burial by litter that accumulates under larger woody plants restricts crust development under canopies. Disturbance restricts crust development in plant interspaces and under G. flava. These two mechanisms combine to restrict crust development to an observed 40% threshold, with nonlinear models required to explain spatial patterns of crust dynamics.     

Effects of Biological Soil Crusts on Seed Bank, Germination and Establishment of Two Annual Plant Species in the Tengger Desert (N China)

The presence of biological soil crusts can affect the germination and survival of vascular plants, but the reasons are not well investigated. We have conducted a field investigation and greenhouse experiments to test the effect of crusts on two desert annual plants, which occur on the stabilized dunes of the Tengger Desert in N China. The results showed that biological soil crusts negatively influenced the seed bank of Eragrostis poaeoides and Bassia dasyphylla. The important effect of biological soil crusts on seed germination and establishment were performed indirectly through reducing the amount of germinating seeds. Field investigation and experimental results with regard to the seed bank indicated that higher seedling density was found in disturbed crust soil and bare soil surface than in intact crust soils. Greenhouse experiments showed that the effects of biological soil crusts on germination and establishment of the two plants are not obvious in moist condition, while disturbed crusts are more favorable to seed germination in dry treatment. Significant differences in biomass were found between disturbed crust soil and bare soil. Survival and growth of the two annual plants were enhanced in both algal and moss crusts during the season of rainfall or in moist environment, but crusts did not affect seedling survival in the dry period. The small seeded E. poaeoides has higher germination than larger-seeded B. dasyphylla in crust soils, but B. dasyphylla has a relatively higher survival rate than E. poaeoides in crust soils.     

Problematic megafossils in Cambrian palaeosols of South Australia

Abstract: Red calcareous Middle Cambrian palaeosols from the upper Moodlatana Formation in the eastern Flinders Ranges of South Australia formed in well‐drained subhumid floodplains and include a variety of problematic fossils. The fossils are preserved like trace fossil endichnia but do not appear to be traces of burrows or other animal movement. They are here regarded as remains of sessile organisms, comparable with fungi or plants living in place, and are formally named as palaeobotanical form genera under provisions of the International Code of Botanical Nomenclature. Most common are slender (0.5–2 mm) branching filaments flanked by green‐grey reduction haloes within the red matrix of palaeosol surface horizons (Prasinema gracile gen. et sp. nov.). Other axial structures (Prasinema nodosum and P. adunatum gen. et spp. nov.) are larger and show distinctive surface irregularities (short protuberances and irregular striations, respectively). The size and form of these filaments are most like rhizines of soil‐crust lichens. Other evidence of life on land includes quilted spheroids (Erytholus globosus gen. et sp. nov.) and thallose impressions (Farghera sp. indet.), which may have been slime moulds and lichens, respectively. These distinctive fossils in Cambrian palaeosols represent communities comparable with modern biological soil crusts.     

Germination and seedling establishment of two annual grasses on lichen-dominated biological soil crusts

Biological soil crusts dominated by lichens are common components of shrub-steppe ecosystems in northwestern US. We conducted growth chamber experiments to investigate the effects of these crusts on seed germination and initial seedling establishment of two annual grasses; the highly invasive exotic Bromus tectorum L. and the native Vulpia microstachys Nutt. We recorded germination time courses on bare soil and two types of biological soil crusts; one composed predominantly of the lichen Diploschistes muscorum (Scop.) R. Sant. (lichen crust) and the other comprised of an assortment of lichens and mosses (mixed crust). Final germination on the lichen crust for both grass species was about a third of that on the bare soil surface. Mean germination time (MGT) was 3–4 days longer on the lichen crust compared with the bare soil. In contrast, there was no difference in germination percentage or MGT between the mixed crust and bare soil, and results were similar for both grass species. For both species, root penetration of germinating seeds on the lichen crust was lower than on the bare soil or mixed crust surfaces. The combined effects of the lichen crust on germination and root penetration resulted in an overall reduction in seedling establishment of 78% for V. microstachys and 85% for B. tectorum relative to the bare soil treatment. Our results clearly demonstrate that lichen-dominated biological soil crust can inhibit germination and root penetration, but the extent of these effects depends on the composition of the crust. Responsible Editor: Tibor Kalapos     

Are epiphytes a significant component of intertidal Zostera noltii beds?

The role of epiphytes in an intertidal Zostera noltii seagrass bed in Marennes-Oléron Bay was assessed in comparison with the other main benthic primary producers (Z. noltii, microphytobenthos) at two bathymetric levels and on a seasonal basis. Assemblage and biomass of epiphytes were studied using scanning electron microscopy (SEM). Z. noltii and its detrital matter followed a typical seasonal pattern: microphytobenthos was present in large quantities throughout the year representing 21% of the total biomass while detrital matter, above-ground parts and below-ground parts accounted for 65, 9 and 5%, respectively. Only two species of epiphytic diatoms, Cocconeis scutellum and Cocconeis placentula, were observed on seagrass leaves. Epiphyte biomass was very low, representing on average less than 0.001% of that of microphytobenthos or leaves. This low epiphyte biomass is linked with the absence of macroalgae and also with the low biovolume of Cocconeis, which formed a monolayer of cells on leaves. This can be explained by the severe conditions of the intertidal and the high leaf turn-over of Z. noltii leaves.