Effects of ants on plant diversity in semi-natural grasslands

Ants (L. niger and L. flavus) build conspicuous mounds that are covered with vegetation. The aim of this study was to investigate whether the vegetation on ant mounds in semi-natural grasslands differed from that around the mounds. Another aim was to investigate whether the changes in the vegetation on ant mounds were influenced by grazing management or by habitat characteristics, semi-dry versus moist. Here, the total number of plant species and total plant cover were lower on ant mounds than in patches off-mound. The plant cover of perennials that form rosettes was twice as high on mounds inhabited by L. niger than on those inhabited by L. flavus. Only a few plant species were restricted to either ant mounds or adjacent field and the effects of ants on the plant diversity in semi-natural grasslands seemed to be low. Grazing management did not affect the differences in the vegetation on ant mounds and in equal-sized patches off-mound, whereas habitat characteristics affected ant-induced changes in vegetation cover of some plant species.     

南极地区苔藓地衣植物的地球化学元素营养富集特征

研究南极苔藓地衣中地球化学元素的营养富集特征,发现K,Ca为苔藓地衣中最活跃元素,主要以主动吸收的方式累积于苔藓地衣植物中,P极易富集在地衣的藻层,参与藻类的有机合成过程,苔藓容易富集环境中的S,Al,Si以被动吸收的方式累积于地衣中,同时Fe,Mg以被动吸收的方式累积于苔藓体内,根据元素的含量和营养作用,研究认为K,Ca苔地衣的大量无机营养元素,S,P为苔藓地衣的中等营养元素,Al,Si为苔藓地衣的环境累积元素。     

Phototolerance of lichens, mosses and higher plants in an alpine environment: analysis of photoreactions

 Adaptation to excessive light is one of the requirements of survival in an alpine environment particularly for poikilohydric organisms which in contrast to the leaves of higher plants tolerate full dehydration. Changes in modulated chlorophyll fluorescence and 820-nm absorption were investigated in the lichens Xanthoria elegans (Link) Th. Fr. and Rhizocarpon geographicum (L.) DC, in the moss Grimmia alpestris Limpr. and the higher plants Geum montanum L., Gentiana lutea L. and Pisum sativum L., all collected at altitudes higher than 2000 m above sea level. In the dehydrated state, chlorophyll fluorescence was very low in the lichens and the moss, but high in the higher plants. It increased on rehydration in the lichens and the moss, but decreased in the higher plants. Light-induced charge separation in photosystem II was indicated by pulse-induced fluorescence increases only in dried leaves, not in the dry moss and dry lichens. Strong illumination caused photodamage in the dried leaves, but not in the dry moss and dry lichens. Light-dependent increases in 820-nm absorption revealed formation of potential quenchers of chlorophyll fluorescence in all dehydrated plants, but energy transfer to quenchers decreased chlorophyll fluorescence only in the moss and the lichens, not in the higher plants. In hydrated systems, coupled cyclic electron transport is suggested to occur concurrently with linear electron transport under strong actinic illumination particularly in the lichens because far more electrons became available after actinic illumination for the reduction of photo-oxidized P700 than were available in the pool of electron carriers between photosystems II and I. In the moss Grimmia, but not in the lichens or in leaves, light-dependent quenching of chlorophyll fluorescence was extensive even under nitrogen, indicating anaerobic thylakoid acidification by persistent cyclic electron transport. In the absence of actinic illumination, acidification by ca. 8% CO₂ in air quenched the initial chlorophyll fluorescence yield F_o only in the hydrated moss and the lichens, not in leaves of the higher plants. Under the same conditions, 8% CO₂ reduced the maximal fluorescence yield F_m strongly in the poikilohydric organisms, but only weakly or not at all in leaves. The data indicate the existence of deactivation pathways which enable poikilohydric organisms to avoid photodamage not only in the hydrated but also in the dehydrated state. In the hydrated state, strong nonphotochemical quenching of chlorophyll fluorescence indicated highly sensitive responses to excess light which facilitated the harmless dissipation of absorbed excitation energy into heat. Protonation-dependent fluorescence quenching by cyclic electron transport, P700 oxidation and, possibly, excitation transfer between the photosystems were effectively combined to produce phototolerance. Received: 10 December 1999 / Accepted: 13 April 2000     

Uptake of natural and man-made radionuclides by lichens and mushrooms

Summary Due to the large absorbing surface of the mycelium that grows in the upper parts of the soil mushrooms take up higher amounts of¹³⁷Cs and⁴⁰K than lichens. Besides these nuclides only the long-lived radionuclides¹²⁵Sb and⁶⁰Co could be measured; but not the short-lived fission-products¹⁴⁴Ce,⁹⁵Zr and⁹⁵Nb which probably decayed before absorption into the mycelium. These nuclides, however, are present in lichens because of their surface structures which enable high foliar deposition.The¹³⁷Cs-content of lichens is probably due to absorption by the mycobiont and seems to be used to satisfy their potassium-requirements. Mushrooms on the other hand are characterized by a relatively stable potassium-content and a wide ranging¹³⁷Cs-content which depends on the availability in different substrates. Occasionally the natural radionuclides²³⁸U and²²⁶Ra could be detected in mushroom and lichen samples, showing no correlation with the natural radionuclide content of the soil.     

Comparisons of photosynthesis-related traits among understory lichens,mosses and vascular plant leaves in a high-elevation subalpine forest

对比高海拔亚高山森林林下地衣、藓类及维管植物叶片的光合相关性状 在高海拔亚高山森林中,许多地衣和藓类植物欣欣向荣,甚至成为林地表层的优势物种。尽管它们在森林生态系统中承担着不可替代的功能,但我们对其光合作用相关的功能性状水平知之甚少,对相同生境下藓类植物和维管植物的比较研究也较为匮乏。因此,本研究选择中国青藏高原东缘亚高山林下常见的3种地衣、3种藓类和4种维管植物,测定并对比了它们的碳、氮、磷含量及化学计量比、单位面积光合组织干重、叶绿素含量及光合光响应曲线的异同。研究结果表明,林下地衣的氮含量高于藓类植物,二者的氮、磷、叶绿素、光合速率及光合氮利用效率均低于维管植物叶片。不同种类地衣的光合相关性状与其生长环境相符,而林地表层的3种藓类植物和3种草本植物的功能性状在各自功能群中的种间差异均不显著。总之,这些结果表明高海拔亚高山林下地衣和藓类植物的优势与其光合相关性状关系不大,对严酷环境较强的适应能力可能是它们得以繁荣生长的关键。     

A survey of metal concentrations in higher plants, mosses, and lichens collected on King George Island in 1988

Antarctica is considered to be one of the least polluted regions on earth, and therefore, it is important to survey and control the level of contamination. Antarctic vegetation is very sparse and is essentially restricted to seashore oases and nunataks. Therefore, any data concerning metal levels in plants and lichens are of crucial value for this area. Our first goal was to determine metal concentrations in two higher plants and the most dominant species of mosses and lichens collected in 1988. We then compared the results of our survey with recent studies employing similar methodology. In our study, Cr, Cu, Fe, Ni, Pb, V, and Zn concentrations in mosses, C. quitensis and D. antarctica were also higher than typical values for mosses and vascular plants from unpolluted areas indicating anthropogenic influence. Mosses were determined to be better bioindicators of metals than lichens. Hg concentrations in mosses were significantly higher than those in shoots of C. quitensis and D. antarctica. Increases in Cr, Pb, and V concentrations over time were observed in moss when concentrations from samples collected in 1988 were compared with more recent data from other studies. Our results for King George Island may apply at least to all the maritime Antarctic where climate and plant communities are similar.     

Fatal interactions between Scots pine and Sphagnum mosses in bog ecosystems

In this study, we explore how Sphagnum mosses and Scots pine, Pinus sylvestris , interact on different spatial and temporal scales in a boreal bog ecosystem. We were particularly interested in relationships between the occurrence of Sphagnum- dominated habitats and the occurrence of Scots pines of different age and size.
Juvenile and adult pines occurred in different habitats. While juveniles mainly occurred in Sphagnum- dominated habitats, predominantly with Sphagnum rubellum , adult pines were found in habitats dominated by lichens, or with a sparse vegetation cover. Examination of surface peat cores sampled close to adult pines revealed that almost all pines (97%) had established in a Sphagnum -dominated environment and that the habitat had changed since pine establishment. Scots pine is thus capable of changing and exterminating the Sphagnum -dominated environment preferred for germination and establishment. Pines impede Sphagnum growth and peat accumulation significantly once they have reached a stem diameter of approximately 20 mm. It takes from 30 to 90 yr for a pine to reach that size.
Our results show the importance of interactions between Scots pine and Sphagnum mosses in bog ecosystems. We conclude that interactions between trees and Sphagnum mosses are important driving forces behind the vegetation change that has characterised boreal bogs during the Holocene.     

Differential effects of lichens,mosses and grasses on respiration and nitrogen mineralization in soils of the New Jersey Pinelands

In the New Jersey Pinelands, severely disturbed areas often do not undergo a rapid succession to forest; rather, a patchy cover of lichens, mosses and grasses persists for decades. We hypothesized that these plant covers affect soil microbial processes in different ways, and that these effects may alter the successional dynamics of the patches. We predicted that the moss and grass covers stimulate soil microbial activity, whereas lichens inhibit it, which may in turn inhibit succession. We collected soil cores from beneath each type of cover plus bare soil within two types of highly disturbed areas—sites subjected to hot wildfires, and areas mined for sand. Organic matter (OM) content, soil respiration and potential N mineralization were measured in the cores. Soils under mosses were similar to those under grasses; they accumulated more OM and produced more mineral N, predominantly in the form of ammonium, than either the bare soils or the soils beneath lichens. Mineralization under lichens, like that of the bare soils but unlike the soils beneath mosses or grasses, was dominated by net nitrification. These patterns were reproduced in experimentally transplanted moss and lichen mats. Mosses appear to create high-nutrient microsites via high rates of OM accumulation and production of ammonium, whereas lichens maintain low-nutrient patches similar to bare soil via low OM accumulation rates and production of mineral N predominantly in the mobile nitrate form. These differences in soil properties may explain the lack of vascular plant invasion in lichen mats, in contrast to the moss-dominated areas.     

Ecological effects of atmospheric reactive nitrogen deposition on semi-natural terrestrial ecosystems

Evidence that enhanced reactive nitrogen deposition is affecting semi-natural terrestrial ecosystems comes from historic increases in plant tissue N concentrations, correlations between tissue N concentrations and present-day total atmospheric N deposition, changes in plant amino-acid composition and effects on N assimilation. The ecological significance of such changes in biomarkers is uncertain. This paper explores the ecological significance of reactive atmospheric N deposition through a review of previous experimental findings and new experimental evidence from an acidic and a calcareous grassland, both showing phosphorus limitation, and a N-limited Calluna vulgaris (L.) Hull heathland in upland Britain. Nitrogen addition in the range 0–20 g N m⁻² yr⁻¹ initially (years 0–4) increased the growth of Calluna and a decline in some subordinate species. In subsequent years, shoot extension was not stimulated, but winter injury was observed from 1993 onwards, suggesting a strong interaction between N supply and climatic conditions. By contrast, the grasslands showed a small decrease in the cover of higher plants in later years (6–7) of the experimental treatments (0–14 g N m⁻² yr⁻¹) and no growth stimulation. All N treatments reduced the bryophyte cover in the acidic grassland. There were marked effects on below-ground processes, including a sustained stimulation of N mineralization in the grassland soils, and an increase in the bacterial utilization of organic substrates in the heathland, as measured in BIOLOG plates. The results strongly suggest the importance of atmospheric N deposition on microbially driven processes in soils, and are discussed in relation to the scale of potential ecosystem changes and their reversibility by pollution abatement.     

Epiphytic lichens and bryophytes of forest ecosystems in Tuscany (Central Italy)

The distribution of epiphytic bryophytes and lichens on three species of trees (Quercus ilex, Quercus cerris and Fagus sylvatica, representing the forest ecosystems of central Italy at low, medium and high elevations, respectively) was examined with respect to host specificity and habitat differences. Although most species were host-specific, the results suggested that habitat characteristics are more important than phorophyte properties in determining the distribution of lichens and bryophytes. Factors affecting the diversity of the epiphytic flora were different for lichens and bryophytes. In the case of lichens, climatic parameters and forest monospecificity were important factors, whereas tree cover (i.e. shade) and to a certain extent the number of available trees seemed more important for bryophytes.     

Protection of the photosynthetic apparatus against damage by excessive illumination in homoiohydric leaves and poikilohydric mosses and lichens

Experimental work on the control of photosystem II in the photosynthetic apparatus of higher plants, mosses and lichens is reviewed on a background of current literature. Transmembrane proton transport during photoassimilatory and photorespiratory electron flows is considered insufficient for producing the intrathylakoid acidification necessary for control of photosystem II activity under excessive illumination. Oxygen reduction during the Mehler reaction is slow. Together with associated reactions (the water-water cycle), it poises the electron transport chain for coupled cyclic electron transport rather than acting as an efficient electron sink. Coupled electron transport not accompanied by ATP consumption in associated reactions provides the additional thylakoid acidification needed for the binding of zeaxanthin to a chlorophyll-containing thylakoid protein. This results in the formation of energy-dissipating traps in the antennae of photosystem II. Competition for energy capture decreases the activity of photosystem II. In hydrated mosses and lichens, but not in leaves of higher plants, protein protonation and zeaxanthin availability are fully sufficient for effective energy dissipation even when photosystem II reaction centres are open. In leaves, an additional light reaction is required, and energy dissipation occurs not only in the antennae but also in reaction centres. Loss of chlorophyll fluorescence during the drying of predarkened poikilohydric mosses and lichens indicates energy dissipation in the dry state which is unrelated to protonation and zeaxanthin availability. Excitation of photosystem II by sunlight is not destructive in these dry organisms, whereas photosystem II activity of dried leaves is rapidly lost under strong illumination.     

Metals in some dominant vascular plants, mosses, lichens, algae, and the biological soil crust in various types of terrestrial tundra, SW Spitsbergen, Norway

Arctic environments are commonly considered to be relatively pristine because of minimal local human activity. However, these areas receive air pollution from lower latitude regions. Our goal was to determine concentrations of metals (Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn) in dominant species of vascular plants, mosses, lichens, algae, and in the biological soil crust (BSC), and topsoil (0–3 cm) from various types of tundra in the southwestern part of Spitsbergen, Norway. Results indicate that mosses are more efficient bioaccumulators of Cd, Co, Cr, Cu, Fe, Mn, and Zn than lichens. The highest levels of Co, Cr, Cu, Fe, Hg, Mn, Ni, and Pb were found in the BSC, and the moss species Racomitrium lanuginosum, Sanionia uncinata, and Straminergon stramineum from the polygonal tundra, initial cyanobacteria-moss wet tundra, snow bed cyanobacteria-moss tundra, and flow water moss tundra alimented by melting ice or snow. The observed higher concentrations of Cu and lower concentrations of Hg in mosses, lichens, and vascular plants compared with values observed 20 years earlier were apparently associated with changes in the atmospheric deposition of contaminants over Spitsbergen due to changes in the long-distance transport of anthropogenic emissions from industrialized areas. Prasiola crispa and Salix polaris may be useful bioindicators of Cd and Zn, and the BSC, R. lanuginosum, S. uncinata, and S. stramineum as bioindicators of Co, Cr, Cu, Fe, Hg, Mn, Ni, and Pb. These results may be extrapolated across other areas of Spitsbergen with similar climates.     

Diversity of winter photoinhibitory responses: a case study in co‐occurring lichens,mosses, herbs and woody plants from subalpine environments

Winter evergreens living in mountainous areas have to withstand a harsh combination of high light levels and low temperatures in wintertime. In response, evergreens can activate a photoprotective process that consists of the downregulation of photosynthetic efficiency, referred to as winter photoinhibition (WPI). WPI has been studied mainly in woody evergreens and crops even when, in many instances, other functional groups such as lichens or bryophytes dominate in alpine and boreal habitats. Thus, we aimed to (1) assess the occurrence of WPI within overwintering evergreens comprising woody species, herbs, mosses and lichens, (2) compare the recovery kinetics among those groups and (3) clarify the role of thylakoid proteins and pigments in both processes: WPI and recovery. With this aim, WPI was analyzed in 50 species in the field and recovery kineticcs were studied in one model species from each functional group. Results showed that high levels of WPI are much more frequent among woody plants than in any other group, but are also present in some herbs, lichens and mosses. Winter conditions almost always led to the de‐epoxidation of the xanthophyll cycle. Nevertheless, changes in the de‐epoxidation level were not associated with the activation/deactivation of WPI in the field and did not match changes in photochemical efficiency during recovery treatments. Seasonal changes in thylakoid proteins [mainly D1 (photosystem II core complex protein) and PsbS (essential protein for thermal dissipation)] were dependent on the functional group. The results highlight the diversity of physiological solutions and suggest a physical–mechanical reason for the more conservative strategy of woody species compared with other groups.     

Transfer of Bt corn byproducts from terrestrial to stream ecosystems

The review deals with the pathways of Bt corn (Zea mays L.) byproduct entry to the environment. Bt plants are genetically modified plants containing the genes of a gram-positive aerobic spore-forming bacterium Bacillus thuringiensis encoding δ-endotoxins. Special attention was given to decomposition of corn detritus in fresh water and migration of Bt toxins to stream ecosystems. The results of field and laboratory experiments on the effect of Bt corn byproducts on stream detritophages are summarized.     

The contribution of mosses to the carbon and water exchange of Arctic ecosystems: quantification and relationships with system properties

Water vapour and CO2 exchange were measured in moss-dominated vegetation using a gas analyser and a 0.3 x 0.3 m chamber at 17 sites near Abisko, Northern Sweden and 21 sites near Longyearbyen, Svalbard, to quantify the contribution of mosses to ecosystem level fluxes. With the help of a simple light-response model, we showed that the moss contribution to ecosystem carbon uptake varied between 14 and 96%, with an average contribution of around 60%. This moss contribution could be related to the normalized difference vegetation index (NDVI) of the vegetation and the leaf area index (LAI) of the vascular plants. NDVI was a good predictor of gross primary production (GPP) of mosses and of the whole ecosystem, across different moss species, vegetation types and two different latitudes. NDVI was also correlated with thickness of the active green moss layer. Mosses played an important role in water exchange. They are expected to be most important to gas exchange during spring when leaves are not fully developed.     

Dynamics of interaction between lichens and fallen deadwood in forest ecosystems of the eastern Baikal region

Successional stages of epixylic lichens in conjunction with fallen deadwood decomposition were studied in the eastern Baikal region. It was found that lichens passed through four stages of epixylic succession: from the epiphytic and epixylic stages to the epigeic stage. It was also determined that lichens could inhibit the decomposition of the higher layer of fallen deadwood, which served as a substrate to them.     

Impacts of tropospheric ozone and airborne nitrogenous pollutants on natural and semi-natural ecosystems: a commentary

Man's activities pose a number of threats to the functioning, structure and diversity of natural and semi-natural ecosystems. One of the main threats is the increase in concentrations in air pollutants in this century (Wellburn, 1988; Tamm, 1991). This paper is a commentary on the effects of tropospheric ozone (O₃) and airborne nitrogen deposition (both oxidized (NO_x) and reduced (NH_y) compounds) on natural and semi-natural ecosystems, based upon the oral presentations and the discussions during the Symposium, extended with a personal overview and some suggestions about future challenges for research. The most important effects of these air pollutants on natural and semi-natural vegetation are summarized and evaluated in ecological terms, with respect to the functioning and structure of unaffected systems. Air pollutants are transported over both short and long distances (as far as a few thousand km) before being deposited on surface water, vegetation or soil. In this way, vegetation over a large area or in remote regions can be influenced by airborne pollutants (see Fowler et al . (1998); Asman, Sutton & Schjørring (1998)).     

Effects of atmospheric deposition,soil pH and acidification on heavy metal contents in soils and vegetation of semi-natural ecosystems at Rothamsted Experimental Station,UK

The effects of acidification on the soil chemistry and plant availability of the metals Pb, Cd, Zn, Cu, Mn and Ni in new and archived soil and plant samples taken from the >100-year-old experiments on natural woodland regeneration (Geescroft and Broadbalk Wildernesses) and a hay meadow (Park Grass) at Rothamsted Experimental Station are examined. We measured a significant input of metals from atmospheric deposition, enhanced under woodland by 33% (Ni) to 259% (Zn); Pb deposition was greatly influenced by vehicle emissions and the introduction of Pb in petrol. The build up of metals by long-term deposition was influenced by acidification, mobilization and leaching, but leaching, generally, only occurred in soils at pH<4. Mn and Cd were most sensitive to soil acidity with effective mobilization occurring at pH 6.0–5.5 (0.01 M CaCl₂), followed by Zn, Ni and Cu at pH 5.5–5.0. Pb was not mobilized until pH<4.5. Acidification to pH 4 mobilized 60–90% of total soil Cd but this was adsorbed onto ion exchange surfaces and/or complexed with soil organic matter. This buffering effect of ion exchange surfaces and organic matter in soils down to pH 4 was generally reflected by all the metals investigated. For grassland the maximum accumulation of metals in herbage generally corresponded to a soil pH of 4.0. For woodland the concentration of Pb, Mn and Cd in oak saplings (Quercus robur) was 3-, 4- and 6-fold larger at pH 4 than at pH 7. Mature Oak trees contained 10 times more Mn, 4 times more Ni and 3 times more Cd in their leaves at pH 4 than at pH 7. At pH values <4.0 on grassland the metal content in herbage declined. Only for Mn and Zn did this reflect a decline in the plant available soil content attributed to long-term acid weathering and leaching. The chief cause was a long-term decline in plant species richness and the increased dominance of two acid-tolerant, metal-excluder species