Vegetation-environment relationships in a heavy metal-dry grassland complex

Heavy-metal content is assumed to be the most important edaphic factor that determines vegetation composition on contaminated soil. We compared the effects of heavy metals on species composition and species richness in the heavy metal-dry grassland complex of the Bottendorf Hills (Central Germany) with those of other environmental factors. Based on 206 relevés, we distinguished nine communities of the classesKoelerio-Corynephoretea andFestuco-Brometea. Four communities in which the metallophytesArmeria maritima subsp.halleri andMinuartia verna subsp.hercynica occurred with high frequency were classified as heavy metal subassociations of four different dry grassland associations because of the dominance of dry grassland species. We measured the soil content of copper, zinc and lead, and the carbonate content, C/N ratio, pH and conductivity of the soil, soil depth and incident radiation per site. The first axis resulting from a DCA was positively correlated with the cover and height of the herb layer, the soil depth and soil carbonate content, and negatively with the soil content of copper, the proportion of rocks, the soil C/N ratio and incident radiation per site. The number of vascular plants, bryophyte and lichen species per plot increased with pH up to 7.5 and then decreased slightly. Species richness increased with carbonate content and conductivity of the soil and decreased with the soil C/N ratio. Heavy metal content of the soil and species richness were not correlated. The occurrence of the metallophytes was strongly related to the copper content of the soil. In conclusion our study has shown that heavy metal content is not necessarily the main factor determining the total composition and richness of grasslands on soil containing heavy metals. Heavy metal grasslands are not necessarily floristically distinct from “normal” dry grasslands.     

Species richness of vascular plants, bryophytes and lichens in dry grasslands: The effects of environment, landscape structure and competition

We studied the relative importance of local habitat conditions and landscape structure for species richness of vascular plants, bryophytes and lichens in dry grasslands on the Baltic island of Öland (Sweden). In addition, we tested whether relationships between species richness and vegetation cover indicate that competition within and between the studied taxonomic groups is important. We recorded species numbers of vascular plants, bryophytes and lichens in 4 m² plots (n=452), distributed over dry grassland patches differing in size and degree of isolation. Structural and environmental data were collected for each plot. We tested effects of local environmental conditions, landscape structure and vegetation cover on species richness using generalized linear mixed models. Different environmental variables explained species richness of vascular plants, bryophytes and lichens. Environmental effects, particularly soil pH, were more important than landscape structure. Interaction effects of soil pH with other environmental variables were significant in vascular plants. Plot heterogeneity enhanced species richness. Size and degree of isolation of dry grassland patches significantly affected bryophyte and lichen species richness, but not that of vascular plants. We observed negative relationships between bryophyte and lichen species richness and the cover of vascular plants. To conclude, effects of single environmental variables on species richness depend both on the taxonomic group and on the combination of environmental factors on a whole. Dispersal limitation in bryophytes and lichens confined to dry grasslands may be more common than is often assumed. Our study further suggests that competition between vascular plants and cryptogams is rather asymmetric.     

The Rengen Grassland Experiment: Effect of Soil Chemical Properties on Biomass Production, Plant Species Composition and Species Richness

The Rengen Grassland Experiment (RGE), set up on a Nardus grassland in 1941, consists of a control and five fertilizer treatments (Ca, CaN, CaNP, CaNP-KCl and CaNP-K₂SO₄). In 2005, soil chemical properties were analyzed to investigate the effect of soil variables on biomass production, plant species composition and species richness of vascular plants. Further, the effect of sampling scale (from 0.02 to 5.76 m²) on species richness was investigated. Soil properties (plant-available contents of K, P, C:N ratio, and pH) and biomass production were found to be strictly dependent on the fertilizers applied. Diversification of soil P content between treatments with and without P application is still in progress. Biomass production was most positively affected by P and K soil contents under N application. Furthermore, pH had a small positive effect on biomass production, and C:N ratio a moderately negative one. Two types of nutrient limitation were recognized: (1) limitation of total biomass production and (2) limitation of individual plant species. Long-term addition of a limiting nutrient affected the grassland ecosystem in three ways: (1) causing a change in plant species composition without significant increase in total biomass production, (2) causing no change in species composition but with significant increase in total biomass production, and (3) causing substantial change in plant species composition accompanied by significant increase in total biomass production. The explanatory power of all measured soil properties on plant species composition was almost the same as the power of the treatment effect (61.7% versus 62% of explained variability in RDA). The most powerful predictors of plant species composition were soil P, K and Mg contents, pH, and biomass production. The soil P content and biomass production were the only variables leading to a significant negative effect on species richness. An almost parallel increase in species richness with increasing sampling area was detected in all treatments. Constant differences among treatments were independent of sampling area.     

The role of regional and local scale predictors for plant species richness in Mediterranean forests

Abstract

Both local and regional predictors play a role in determining plant community structure and composition. Climate, soil features as well as different local history and management affect forest understorey and tree species composition, but to date their specific role is relatively unknown. Few studies have addressed the importance of these predictors, especially in the Mediterranean area, where environmental conditions and human impacts have generated heterogeneous forest communities. In this study, the relationships between environmental variables and species richness of different groups of vascular plants (vascular species, woody species and open habitat species) and bryophytes were investigated in Tuscan forests. A total of 37 environmental variables were used by generalised linear model fitting in order to find parsimonious sub-sets of environmental factors (predictors) that are able to explain species diversity patterns at the local scale. Moreover, the role of regional and local variable groups on species richness of the considered plant groups was estimated by using the variance partitioning approach. We found that local variables, such as forest management and structure, explained more variance than regional variables for total species richness, open habitat species richness and bryophyte species richness. On the other hand, regional variables (such as elevation) played a central role for woody species richness.     

Possible Impacts of the Invasive Plant Rubus niveus on the Native Vegetation of the Scalesia Forest in the Galapagos Islands

Originally from Asia, Rubus niveus has become one of the most widespread invasive plant species in the Galapagos Islands. It has invaded open vegetation, shrubland and forest alike. It forms dense thickets up to 4 m high, appearing to displace native vegetation, and threaten the integrity of several native communities. This study used correlation analysis between a R. niveus cover gradient and a number of biotic (vascular plant species richness, cover and vegetation structure) and abiotic (light and soil properties) parameters to help understand possible impacts in one of the last remaining fragments of the Scalesia forest in Santa Cruz Island, Galapagos. Higher cover of R. niveus was associated with significantly lower native species richness and cover, and a different forest structure. Results illustrated that 60% R. niveus cover could be considered a threshold for these impacts. We suggest that a maximum of 40% R. niveus cover could be a suitable management target.     

Local and regional patterns of species richness in Central European vegetation types along the pH/calcium gradient

We investigated the relationship between soil pH/calcium content and species richness of vascular plants in seven broadly defined Central European vegetation types, using Ellenberg indicator values for soil reaction and a phytosociological data set of 11,041 vegetation sample plots from the Czech Republic. The vegetation types included (A) broad-leaved deciduous forests, (B) meadows, (C) dry grasslands, (D) reed-bed and tall-sedge vegetation, (E) fens and transitional mires, (F) perennial synanthropic vegetation and (G) annual synanthropic vegetation. Relationships between local species richness (alpha diversity) and pH/calcium were positive for vegetation types A and C, negative for D and G, unimodal for E, and insignificant for B and F. Ellenberg soil reaction values explained 37% of variation in local species richness for vegetation type E, 24% for A, 13% for D, but only less than 4% for the others. Species pool size, i.e., the number of species that can potentially occur in a given habitat, was calculated for each plot using Beals index of sociological favourability applied to a large phytosociological database. For most vegetation types, the relationships between species pool size and pH/calcium were similar to the relationships between local species richness and pH/calcium, with the exception of meadows (weak unimodal) and perennial synanthropic vegetation (weak negative).These patterns suggest that for those types of Central European vegetation that developed independently of human influence in the Pleistocene or early Holocene (dry grasslands, deciduous forests), there are larger pools of calcicole than calcifuge species. This pattern is also found at the level of local species richness, where it is, however, less clearly pronounced, possibly due to the predominance of a few widespread and generalist calcifuges in acidic habitats. The unimodal pattern found in mires may result from similar underlying mechanisms, but in high pH environments mineral-rich spring waters probably decrease species richness by having toxic effects on plant growth. By contrast, vegetation types developed under direct human influence (meadows, synathropic vegetation) show weak negative or no relationships of local species richness or species pool to pH/calcium gradient. These results support the hypothesis ofPärtel (Ecology 83: 2361–2366, 2002) andEwald (Folia Geobot. 38: 357–366, 2003), that the modern calcicole/calcifuge disparity in the species pool of Central European flora has resulted from historical and evolutionary processes that took place on high pH soils. In the Pleistocene, calcareous soils dominated both the dry continental landscapes of Central Europe and glacial refugia of temperate flora, which were mostly situated in southern European mountain ranges with abundant limestone and dolomite. The negative pattern of species richness along the pH/calcium gradient found in reed-bed and tall-sedge vegetation, however, is not consistent with this historical explanation.     

Variation in small-scale spatial heterogeneity of soil properties and vegetation with different land use in semiarid grassland ecosystem

Soil properties (i.e. soil organic carbon, SOC; soil organic nitrogen, SON; and soil C/N ratio) and vegetation in a semiarid grassland of Inner Mongolia, northern China, were studied with the method of geostatistical analysis. We examined the spatial heterogeneity of soil and plants, and possible impacts of land use on their heterogeneity and on the relationship between soil resources and plant richness. Land use affected small scale spatial heterogeneity in plants and soil. SOC, SON and C/N ratio displayed autocorrelation over a range of ～2 m under most circumstances on sites where livestock grazing had been excluded. The uncontrolled grazing site (UG, i.e. unregulated grazing by excessive livestock) displayed an increased range of spatial autocorrelation and the total amount of variability in soil nitrogen over the other land use types. Plant life forms and plant species exhibited spatial autocorrelation over a range of about 2 m on the grazing exclusion (GE) and mowed (MW) sites, while pattern of spatial autocorrelation for several less common species on the UG site were difficult to predict. Plant species richness was positively related with spatial heterogeneity of SOC, SON and C/N on both GE and MW sites, and with only SOC heterogeneity on the UG site. These suggest that spatial soil heterogeneity plays an active role in maintaining plant species richness. However, we call for caution in generalization of the control of spatial soil heterogeneity over plant richness when multiple modes of disturbances are present, as we found in this study that higher total amount of variation in soil nitrogen and C/N ratio on the over-grazed UG site did not lead to increased plant species richness, and that land use had apparent effects on the patterns of spatial heterogeneity in both vegetation and soil.     

Plant species diversity and composition of wet grasslands in relation to environmental factors

Relationships between environmental factors and plant species-richness as well as the composition of plant species in wet grasslands from the order Molinietalia caeruleae were studied with a view to quantifying the relative contribution of different abiotic factors, such as soil chemical parameters, climatic conditions and human impact to diversity of vascular plants and floristic composition. Data and soil samples were collected from 88 plots across Slovenia from regions at the eastern edge of the Po plain, karstic and pre-Alpine mountain regions and the western part of the Pannonian plain, which are classified to sub-Mediterranean, Dinnaric, pre-Alpine and sub-Pannonian phytogeographic areas. Plant diversity was positively correlated with the content of exchangeable Ca²⁺ in soil and the amount of annual precipitation, while significant negative correlation was calculated in case of the plant-available phosphorous content and altitude. Moreover, plant species richness was also negatively correlated with altitude. Among the groups of environmental factors the group of soil factors revealed the strongest correlation with species richness, followed by climatic and topographic group. The order of these groups was the same in the explanation of species composition. Variance of plant species composition was best explained with altitude, soil pH, geographical gradient, frequency of flooding, mean annual temperature, date of mowing, humidity, annual amount of precipitation as well as with the content of plant-available phosphorous, total nitrogen, exchangeable Mg²⁺ and Ca²⁺ in the soil.     

Ecological biogeography of southern ocean islands: species-area relationships, human impacts, and conservation

ABSTRACT Previous studies have concluded that southern ocean islands are anomalous because past glacial extent and current temperature apparently explain most variance in their species richness. Here, the relationships between physical variables and species richness of vascular plants, insects, land and seabirds, and mammals were reexamined for these islands. Indigenous and introduced species were distinguished, and relationships between the latter and human occupancy variables were investigated. Most variance in indigenous species richness was explained by combinations of area and temperature (56%)-vascular plants; distance (nearest continent) and vascular plant species richness (75%)-insects; area and chlorophyll concentration (65%)-seabirds; and indigenous insect species richness and age (73%)-land birds. Indigenous insects and plants, along with distance (closest continent), explained most variance (70%) in introduced land bird species richness. A combination of area and temperature explained most variance in species richness of introduced vascular plants (73%), insects (69%), and mammals (69%). However, there was a strong relationship between area and number of human occupants. This suggested that larger islands attract more human occupants, increasing the risk of propagule transfer, while temperature increases the chance of propagule establishment. Consequently, human activities on these islands should be regulated more tightly.     

Humboldt's spa: microbial diversity is controlled by temperature in geothermal environments

Over 200 years ago Alexander von Humboldt (1808) observed that plant and animal diversity peaks at tropical latitudes and decreases toward the poles, a trend he attributed to more favorable temperatures in the tropics. Studies to date suggest that this temperature–diversity gradient is weak or nonexistent for Bacteria and Archaea. To test the impacts of temperature as well as pH on bacterial and archaeal diversity, we performed pyrotag sequencing of 16S rRNA genes retrieved from 165 soil, sediment and biomat samples of 36 geothermal areas in Canada and New Zealand, covering a temperature range of 7.5–99 °C and a pH range of 1.8–9.0. This represents the widest ranges of temperature and pH yet examined in a single microbial diversity study. Species richness and diversity indices were strongly correlated to temperature, with R² values up to 0.62 for neutral–alkaline springs. The distributions were unimodal, with peak diversity at 24 °C and decreasing diversity at higher and lower temperature extremes. There was also a significant pH effect on diversity; however, in contrast to previous studies of soil microbial diversity, pH explained less of the variability (13–20%) than temperature in the geothermal samples. No correlation was observed between diversity values and latitude from the equator, and we therefore infer a direct temperature effect in our data set. These results demonstrate that temperature exerts a strong control on microbial diversity when considered over most of the temperature range within which life is possible.     

Plant communities and landscape diversity along a Canadian Arctic river

Abstract. We analysed the structure and diversity of the vegetation along an Arctic river to determine the relationship between species richness and plant community structure. We examined whether variation in species richness along the corridor is structured as (1) an increase in the number of communities due to increasing landscape heterogeneity, (2) an increase in the floristic distinctiveness (β-diversity) of communities, or (3) an increase in within-community richness (α-diversity) as species-poor communities are replaced by species-rich communities. We described 24 community types and analysed the relationship between site vascular species richness (γ-diversity) and β-diversity, α-diversity, site environmental heterogeneity, and the number of distinct plant communities. We also measured diversity patterns of vascular, bryophyte, and lichen species within communities and examined their relationship to community-level estimates of environmental factors. We found that an increase in site species richness correlated with an increase in the number of communities (r²= 0.323, P= 0.0173) and β-diversity (r²= 0.388, P= 0.0075), rather than an increase in the α-diversity of individual communities. Moisture and pH controlled most of the differences in composition between communities. Measures of species richness and correlations with moisture and pH within communities differed among vascular, bryophyte, and lichen species. Bryophyte richness was positively correlated with moisture (r²= 0.862, P= 0.0010) and lichen richness was negatively correlated with moisture (r²= 0.809, P= 0.0031). Vascular plants had a peak in richness at pH 6.5 (r²= 0.214, P < 0.0001). We conclude that site variation in vascular richness in this region is controlled by landscape heterogeneity, and structured as variation in the number and distinctiveness of recognizable plant communities.     

Richness and Composition of Vascular Plants and Cryptogams along a High Elevational Gradient on Buddha Mountain, Central Tibet

We explored patterns of plant species richness and composition along an elevational gradient (4,985?C5,685?m a.s.l.) on Buddha Mountain, 100?km northwest of Lhasa, Tibet. We recorded the presence of plants and lichens in 1-m² quadrats separated by 25-m elevational intervals (174 quadrats in 29 elevational bands) along a vertical transect with a SE aspect. We recorded 143 total species, including 107 angiosperms, 2 gymnosperms, 27 lichens, and 7 mosses. We measured stone cover in each quadrat, and soil pH, C, N and C/N ratio from two randomly located samples collected from 10-cm depth within each band. C, N and C/N decreased with elevation, stoniness increased and soil pH did not change with altitude. We employed detrended correspondence analysis (DCA), canonical correspondence analysis (CCA) and generalized linear models (GLMs) to assess the relationships of species richness and species composition to the environment. The first two axes of the CCA biplot explained 87.7% of total variation in the species-environment relationship, and 27.7% of total variance of species data. The first CCA axis is associated with elevation, while the second axis is related to soil pH and stone cover. We also compared patterns in species richness against expectations from species pools interpolated from the literature. Total species richness was relatively constant between 4,985 and 5,400?m a.s.l. and declined continuously above 5,400?m a.s.l. Similar declining patterns were observed for forbs and graminoids. Cushion plants and lichens abundance exhibited a unimodal relationship with altitude while shrubs declined monotonically. Except for lichens, models derived from our observations and the literature were quite similar in shape. The proportion of the species pool represented in each elevational band increased as a function of elevation for non-vascular plants, but decreased markedly for vascular plants. Thus, vascular plants are more likely to be constrained by dispersal at higher elevations, resulting in more local endemism, while the relatively easily-dispersed high-elevation cryptogams have little local differentiation. Our comparative approach demonstrates that complex scale-dependent differences between life forms may underlie the apparent simplicity of elevational gradients. Furthermore, elevational gradients summarized from distributional notes cannot be assumed to be proxies for elevational gradients on individual mountain slopes.     

Niche characteristics ofCladonia lichens associated with geothermal vents in Japan

To characterize the niche preferences ofCladonia species associated with geothermal areas, we sampled ten thermal areas in Japan. It appears from the current study and related studies that some members of theCladonia genus can have a wide tolerance for both soil temperature and pH conditions.Cladonia mitis is the most abundantCladonia and occurs throughout most of the vent system.Cladonia theiophila occurs most frequently at a soil pH of less than 3.5, but occurs mostly at lower soil surface temperatures (below 29°C).Cladonia floerkeana is very restricted in its distribution and is most abundant where the root zone temperature (15 cm) is above 70°C, the surface temperature is above 40°C, and the pH is 5–5.5. Tolerances to low pH, high soil temperatures, and low to moderate humidity permitCladonia species to grow where vascular plants and even mosses cannot grow and thus they avoid the competition such plants would provide to these slow-growing organisms. Contribution from the Phytotaxonomical and Geobotanical Laboratory, Hiroshima University, N. Ser. No. 390.     

Effects of invasive Typha × glauca on wetland nutrient pools,denitrification, and bacterial communities are influenced by time since invasion

Invasive plants dramatically shift the structure of native wetland communities. However, less is known about how they affect belowground soil properties, and how those effects can vary depending on time since invasion. We hypothesized that invasion of a wetland by a widespread invasive plant (Typha × glauca) would result in changes in soil nutrients, denitrification, and bacterial communities, and that these effects would increase with time since invasion. We tested these hypotheses by sampling Typha-invaded sites of different ages (~40, 20, and 13 years), a Typha-free, native vegetation site, and a restored site (previously invaded ~30–40 years ago) but that had Typha return within 2 years of the restoration. At each site, we measured Typha stem density, plant species richness, soil nutrients, denitrification rates, and the abundance and composition of bacterial denitrifier communities. All Typha-dominated sites had the least plant species richness regardless of time since invasion. Additionally, sites that were invaded the longest exhibited significantly higher concentrations of soil organic matter, nitrate, and ammonium than the native site. In contrast, denitrification was higher in sites invaded more recently. Denitrifier diversity for the nirS gene was also significantly different, with highest nirS diversity in sites invaded the longest. Interestingly, the denitrifier communities within the restored site were most similar to the ones in T. × glauca sites, suggesting a legacy effect. Our study suggests this invader can alter important ecosystem properties, such as native species richness, nutrient pools, and transformations, as well as bacterial community composition depending on time since invasion.     

Long-lasting Imprint of Former Glassworks on Vegetation Pattern in an Extremely Species-rich Grassland: A Battle of Species Pools on Mesic Soils

Increasing evidence suggests that past human activities have irreversibly changed soil properties and biodiversity patterns. In the White Carpathian Mts (Central-Eastern Europe), a mosaic of hyper-species-rich and species-rich patches have developed in a regularly mown dry grassland in the area of a glassworks abandoned in the eighteenth century. We tested whether and how anthropogenically changed soils affected the distribution of extraordinary species richness. Using magnetometry we detected former furnaces, workspace, waste deposit and unaffected surrounding grasslands and compared their vegetation and environmental conditions. Archaeological features, especially furnaces and waste deposits, showed a higher pH, higher soil concentrations of exchangeable phosphorus, manganese, lead and calcium, and higher productivity. Surrounding grassland showed higher iron and sodium concentrations in the soil, higher N:P ratio in the biomass and higher species richness. Moisture was uniformly lower in soils on archaeological features, where non-trivially a more ‘mesic’ vegetation in terms of European habitat classification occurred. Plant compositional variation was best explained by water-extractable phosphorus. Because nutrient-richer patches were not moister as common elsewhere, and because species richness was only poorly accounted for by productivity, the occurrence of a species-poor ‘mesic’ vegetation on archaeological features was evidently caused by a long-lasting phosphorus oversupply which favours a comparatively small species pool of rather recently arriving species. On the contrary, surrounding phosphorus-poorer grasslands still contain the ancient species pool whose extraordinary size determines the exceptional species richness of grasslands in the study region. Its maintenance or restoration demands a persistent phosphorus deficiency.     

浙江大雷山夏蜡梅群落植物物种多样性及其与土壤因子相关性

分别采用物种丰富度、物种多样性指数和群落均匀度等指标对浙江省大雷山夏蜡梅群落植物物种多样性进行测定,并通过相关分析对各种指数与土壤因子的关系进行研究。据10个样地统计,共有维管植物74科、165属、193种。从种子植物属的地理成分来看,温带分布的类型居多。不同群落木本植物的物种丰富度和多样性指数以杉木+木荷林最高,群落均匀度以杉木林最高,毛竹林的各项指数最低。草本植物的物种丰富度以杉木+马尾松林最高,杉木林最低;多样性指数和群落均匀度以竹林最高,短柄枹+格药柃林最低。在不同群落的垂直结构中,乔木层的物种丰富度和多样性指数均小于灌木层,草本层的物种多样性在不同群落间变化较大。相关分析表明,夏蜡梅群落物种多样性与土壤有机质含量相关性较大,其中,木本植物物种多样性与有机质含量显著正相关,草本植物与有机质含量显著负相关。     

Alpine vascular plant species richness: the importance of daily maximum temperature and pH

Species richness in the alpine zone varies dramatically when communities are compared. We explored (i) which stress and disturbance factors were highly correlated with species richness, (ii) whether the intermediate stress hypothesis (ISH) and the intermediate disturbance hypothesis (IDH) can be applied to alpine ecosystems, and (iii) whether standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone. Species numbers and standing crop were determined in 14 alpine plant communities in the Swiss Alps. To quantify the stress and disturbance factors in each community, air temperature, relative air humidity, wind speed, global radiation, UV-B radiation, length of the growing season, soil suction, pH, main soil nutrients, waterlogging, soil movement, number of avalanches, level of denudation, winter dieback, herbivory, wind damage, and days with frost were measured or observed. The present study revealed that 82% of the variance in␣vascular species richness among sites could be explained by just two abiotic factors, daily maximum temperature and soil pH. Daily maximum temperature and pH affect species richness both directly and via their effects on other environmental variables. Some stress and disturbance factors were related to species richness in a monotonic way, others in an unimodal way. Monotonic relationships suggest that the harsher the environment is, the fewer species can survive in such habitats. In cases of unimodal relationships (ISH and IDH) species richness decreases at both ends of the gradients due to the harsh environment and/or the interaction of other environmental factors. Competition and disturbance seemed only to play a secondary role in the form of fine-tuning species richness in specific communities. Thus, we concluded that neither the ISH nor the IDH can be considered useful conceptual models for the alpine zone. Furthermore, we found that standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone, even though there is no direct causality.     

Habitat is more important than climate and animal richness at shaping latitudinal variation in plant diversity in China

Species data from 249 National Nature Reserves in China were used to identify potential underlying drivers of latitudinal gradients in plant diversity. We used generalized linear models to assess correlations between predictor and plant species richness. Variance partitioning was then used to decompose the variation in plant richness into different taxonomic levels among the three groups of predictors (i.e., climate, habitat and animal). We found that species richness showed significant latitudinal trends in richness (p?<?0.001). This remained true when examining gymnosperms, angiosperms and ferns individually. Climate and habitat variables explained more variation in richness across different plant groups than did animal richness. Annual precipitation was the best climate variable across different taxonomic plants groups, and soil pH and elevation range were the best habitat variables across different taxonomic plant groups. The independent effects of habitat variables were higher than that of climate and animal variables across different taxonomic plant groups. Finally, climate, habitat heterogeneity, and animal richness explain 48.8% of the variation in total species richness, 28.2% in gymnosperm richness, 44.2% in angiosperm richness, and 38.9% in fern richness.     

Diversity of arbuscular mycorrhizal fungi in the rhizosphere of three host plants in the farming–pastoral zone, north China

The spatial diversity and distribution of AM fungi were investigated in three plots located in farming–pastoral zone, north China. The rhizospheres of Caragana korshinskii, Artemisia sphaerocephala and Salix psammophila were sampled and thirty AM fungal species belonging to five genera were isolated. The study demonstrated that AM fungal diversity and distribution differed significantly among the three host plants and the three studied plots. Spore density of AM fungi ranged between 2 and 22 spores per g^?1 of soil and species richness between 8 and 23. Correlation coefficient analysis demonstrated that spore density was significantly and positively correlated with soil organic matter and available N (P?<?0.01). Species richness was significantly and positively correlated with soil organic matter and available P (P?<?0.01), but significantly and negatively correlated with soil pH (P?<?0.01). Finally, the Shannon–Weiner index was significantly and positively correlated with soil organic matter (P?<?0.05). In this farming–pastoral zone, Glomus reticulatum and G.melanosporum may be more adaptable to the arid conditions than other AM fungal species. This research into AM fungal diversity may lead to exploitation of AM fungi for the mitigation of soil erosion and desertification using mycorrhizal plants, such as C.korshinskii, A.sphaerocephala and S. psammophila. The results of this study support the conclusion that diversity and distribution of AM fungi might be useful to monitor desertification and soil degradation.     

Fungi from Geothermal Soils in Yellowstone National Park

Geothermal soils near Amphitheater Springs in Yellowstone National Park were characterized by high temperatures (up to 70°C), high heavy metal content, low pH values (down to pH 2.7), sparse vegetation, and limited organic carbon. From these soils we cultured 16 fungal species. Two of these species were thermophilic, and six were thermotolerant. We cultured only three of these species from nearby cool (0 to 22°C) soils. Transect studies revealed that higher numbers of CFUs occurred in and below the root zone of the perennial plant Dichanthelium lanuginosum (hot springs panic grass). The dynamics of fungal CFUs in geothermal soil and nearby nongeothermal soil were investigated for 12 months by examining soil cores and in situ mesocosms. For all of the fungal species studied, the temperature of the soil from which the organisms were cultured corresponded with their optimum axenic growth temperature.