Tree species-mediated spatial patchiness of the composition of microbial community and physicochemical properties in the topsoils of a tropical montane forest

To evaluate the importance of plant-soil feedbacks in forest ecosystems, it is fundamental to understand the spatial range within which plant species control soil physicochemical and microbial properties. We investigated the spatial pattern of soil properties associated with canopy trees in a tropical montane forest on Mt. Kianbalu, Borneo. We analyzed soil physicochemical properties and microbial communities (biomarker lipid abundance) as a function of soil depth and distance from the tree trunk of a conifer (Dacrydium gracilis) or a broadleaf tree (Lithocarpus clementianus). The concentration of condensed tannins and fungi-to-bacteria were higher beneath Dacrydium than beneath Lithocarpus. Furthermore, carbon-degrading enzyme activities were lower beneath Dacrydium. These effects of the tree species were more distinct on soil properties beneath the tree crown than on those outside the tree crown. These effects appeared to be largely due to differences in litter chemistry, and the distinct set of soil properties formed corresponding to the above canopy crown. In conclusion, the species-rich forest on the tropical mountain contains spatially distinct units of soil properties associated with canopy trees, and this spatial pattern can influence ecosystem dynamics in the forest through plant-soil feedback effects.     

Soil fauna abundance and diversity in a secondary semi-evergreen forest in Guadeloupe (Lesser Antilles): influence of soil type and dominant tree species

The importance of secondary tropical forests regarding the maintenance of soil fauna abundance and diversity is poorly known. The aims of this study were (1) to describe soil fauna abundance and diversity and (2) to assess the determinants of soil fauna abundance and diversity in two stands of a tropical semi-evergreen secondary forest. Soil macrofauna and microarthropod abundance and soil macrofauna diversity were described at two sites developed on different soils and with different site histories: (1) a natural secondary stand (natural forest) under two dominant tree species, Pisonia subcordata and Bursera simaruba, and (2) a planted secondary forest (planted forest) under three tree species, B. simaruba, Swietenia macrophylla, and Tabebuia heterophylla. The effects of both soil and main tree species’ litter quality were assessed to explain soil fauna abundance and diversity. The abundance of soil macrofauna was significantly higher in the soil under the planted forest, and soil fauna communities were contrasted between the two sites. In the planted forest, a soil-dwelling macrofauna community developed (mainly consisting of the anecic earthworm Polypheretima elongata). In the natural forest, soil macrofauna and microarthropod communities were located at the soil surface. The effect of plant litter quality varied according to each dominant tree species and was superimposed to soil effect. The lowest macrofauna abundance was associated with B. simaruba in the natural forest. T. heterophylla supported a much greater macrofauna community than the two other tree species studied at the same soil, and it appears likely that this is due to the palatability of its leaves compared with the other trees (low lignin, tannins, soluble phenols).     

Spatial distribution of Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae) in the soil of a poultry house along a breeding cycle

Alphitobius diaperinus (Panzer) is an insect pest of tropical origin introduced in temperate areas. Its spatial distribution in the soil of poultry houses was studied during a winter breeding cycle. Soil sampling was done after the chickens’ removal in three plots (walls, feeders and central area). Three physical parameters were measured: soil moisture, soil density and soil surface compactness. Furthermore, soil and litter temperatures were recorded during the chickens’ breeding period and the following cleaning period. Spatial structure of the insect population in the soil revealed a high heterogeneity: late instar larvae, nymphae and adults were located in the soil (down to 10 cm depth) under the feeders where soil density, surface compactness and moisture content were lower. Management practices greatly influence this spatial structure. Soil constitutes a favourable site for pupation and a refuge (overwintering site) for adults and larvae during stressful periods (decrease of soil temperature during the cleaning period). A. diaperinus reacts to more than one stimulus to locate suitable sites (structural edaphic parameters, hygrotaxis, thermotaxis). The survival of A. diaperinus in temperate area depends on the opportunistic use of suitable warm sites such as the soil layer in poultry houses.     

Biodiversity of arbuscular mycorrhizas in three vegetational types from the semiarid of Ceará State,Brazil

Semiarid lands are the object of a limited number of studies, very few among them aimed at characterizing root-associated fungal communities. The diverse vegetation occurring in the tropical dry forest from the Ceará State, Brazil, core area of the Brazilian tropical semiarid, has been attributed to its soil, topography and climatic variation. However, the arbuscular mycorrhizal (AM) symbiosis may have an important role in the function of these ecosystems. We examined AM association in 29 semiarid Brazilian species from three different locations: thorny dry woody savanna vegetation, known as caatinga; non-thorny dry forest and closed, non thorny dry tall-shrubby vegetation, known as carrasco. AM fungal diversity was also compared among the different sites. Twenty of the 22 trees and two of the seven herbs examined had AM association. Arum-type AM morphology was the dominant association occurring in 19 trees and in 3 hemicryptophyte plants. AM morphology is reported for the first time in 21 trees and two herbaceous species. Over the different sites, spore densities in the soil ranged from 5 to 32 per 100 g air-dried soil. Spores of 32 AM fungal taxa were isolated from the soil samples of trees of which twelve belonged to Acaulospora, two to Scutellospora, three to Gigaspora, four to Racocetra, three to Glomus, one to Clareoideoglomus, one to Ambispora, one to Pacispora, one to Sclerocystis, one to Dentiscutata, one to Orbispora, one to Quatunica and one to Entrophospora. Species richness was high in woody caatinga and Glomus macrocarpum, Gigaspora gigantea and Cetraspora pellucida were the most frequent species at different sites. Species diversity (Shannon–Weaver index) did not differ significantly among sites. Water content and phosphorus availability was found to influence the AMF species composition at the plant community level, providing information about the caatinga dominium biodiversity, mainly for its conservation.     

Nutrient relations and root mycorrhizal status of healthy and declining beech (Fagus sylvatica L.) in Southern Britain

Many studies have been carried out to investigate the wide scale problem of forest decline that is affecting vast numbers of trees throughout Europe and North American. Evidence of nutritional disturbances, both above- and below-ground, has been found for a variety of species. Furthermore, it has been suggested that differences in above-ground tree health are often reflected below ground, particularly in the root systems of declining trees. An investigation of root vitality, soil and leaf chemistry of healthy and unhealthy beech (Fagus sylvatica L.) was carried out at a number of sites in southern Britain, covering a range of different soil types. At each site, healthy and unhealthy trees growing in very close proximity were compared in order to avoid large scale environmental differences that might be expected when comparing stands of trees at different locations. Healthy trees were found to have significantly greater proportions of live mycorrhizal roots than their unhealthy neighbours at most of the sites investigated. In addition, significant differences in soil chemistry were found between trees in contrasting health, with healthy trees generally growing in soil containing higher concentrations of calcium, magnesium and potassium and lower aluminium/calcium ratios. Very few differences were found in leaf nutrient content, suggesting that soil chemistry is not yet limiting nutrient uptake. The importance of root system differences in the tolerance of unfavourable edaphic and climatic conditions is discussed with respect to tree health.     

Conservation of bats in suburban landscapes: roost selection by Myotis yumanensis in a residential area in California

Protection of roosting habitat is essential to the conservation of bats in human-dominated landscapes. To help define bat roosting needs in suburban settings, we used radio telemetry to locate day roosts of a common North American species (Myotis yumanensis) within a residential area in California. Between June and August 2000, we tracked 16 bats to 20 roosts in two buildings and 18 trees. We used multiple logistic regression to assess roost selectivity at multiple spatial scales. Of 15 tree, plot, and site characteristics considered, only three helped distinguish roosts from random comparisons: tree diameter, distance to water, and forest cover. Myotis yumanensis preferred large trees (mean diameter 115 cm), and roosted only in the five species of largest mean diameter (Sequoia sempervirens, Pseudotsuga menziesii, Quercus agrifolia, Quercus lobata, and Acer macrophyllum). At the site level, these bats selected roosts that were close to water and had substantial forest cover in the surrounding 100-m radius. Unlike other North American bats, they often roosted in live trees (89% live). Relatively high roost fidelity (mean 4.8 days) and large travel distances between consecutive roosts (mean 1130 m) and between capture sites and roosts (mean 2007 m) may indicate a greater degree of roost limitation at this site versus other research sites. We recommend the preservation of large trees and forested parkland, particularly along stream corridors, to help maintain bat populations in urbanizing landscapes.     

Structure and activity of soil-inhabiting methanotrophic communities in northern forest of Japan

In a Japanese forest, CH₄ uptake rate and methanotrophic community structure in the soil were investigated at four sites of different vegetation. At two of these sites, undergrowth was dominated by Sasa senanensis, and that of another was dominated by Sasa kurilensis. At the rest site, undergrowth had been removed artificially. The tree-layer composition differed between the two sites with S. senanensis, but tree layer of the other two sites were dominated by the same species. At the site lacking undergrowth, observed CH₄ uptake rate was twice as high as that at the other sites. Under laboratory conditions, soil sample from the site lacking undergrowth exhibited CH₄ consumption rate higher than that of the adjacent site with the same dominating tree species. The community structures of methanotrophs were investigated with denaturing gradient gel electrophoresis (DGGE) of the gene encoding particulate methane monooxygenase (pmoA). The banding patterns observed were different depending on the type of undergrowth vegetation. The sequences of the DGGE bands were closely related to each other and belonged to the “upland soil cluster alpha” (USCα). These results imply possible close relationship between the undergrowth vegetation and methanotrophic communities in forest soils.     

Deforestation effects on vegetative regeneration and soil quality in tropical semi‐evergreen degraded and protected forests of Bangladesh

Tropical forests of the world are degrading at an alarming rate because of human‐induced activities. This study was conducted to determine the consequences of deforestation on the natural regeneration of vegetation and soil quality in tropical, semi‐evergreen protected and degraded forest ecosystems of Bangladesh. In each forest ecosystem, 20 matured trees were randomly selected for laid‐out experimental plots by placing the tree stand at the center of the plot. The number of vegetative species, height, basal area, crown percentages and species richness were measured. The selected soil properties were determined. The vegetation in the protected forest site was denser with an abundance of species than in the degraded forest site. The primary forest regenerative species were dominated by the dipterocarps in both forest sites. The most alarming difference was that of an abrupt decline in regenerative forest species accompanied by an increase in exotic shrubs, grasses and vines typical of open habitats in the degraded forest site. These shrubs (e.g. Melastaoma, Lantana camara, Clerodendrum infortunatum and Jasminium spp.) and grasses and vines (e.g. Imperata cylindrica, Imperata arundinacea, Mikania scandenes, Saccharum spontaneum and Eupatorium odoratum) are gradually replacing the primary forest regenerative species in the degraded forest site. The soil quality of the degraded forest site has deteriorated over time due to preferential removal of finer particles and organic matter by accelerated water erosion. As a result, natural regeneration of primary forest species, especially dipterocarps, is severely affected by the direct effects of biotic interferences and attendant processes of soil quality degradation from deforestation. In contrast, degraded forest sites under regular protection have shown slow, but gradual, increase in crown frequency, enhanced recruitment and recovery of primary forest species, species abundance, and an improvement in soil quality. Copyright © 2001 John Wiley & Sons, Ltd.     

Assessment of VA mycorrhizal inoculum potential in relation to the establishment of cactus seedlings under mesquite nurse-trees in the Sonoran Desert

A commonly observed preferential association was quantified between mature native mesquite (Prosopis articulata) trees and the seedlings of six cactus species (Pachycereus pringlei, Opuntia cholla, Lophocereus schottii, Machaerocereus gummosus, Lemaireocereus thurberi, Mammilaria sp.) in a previously-disturbed area of the Sonoran Desert of Baja California, Mexico. We hypothesized that, in addition to more favorable edaphic factors, the inoculum potential of beneficial vesicular–arbuscular mycorrhizal (VAM) fungi was higher, and therefore, more favorable for cactus seedling establishment under the mesquite tree canopy (UC) compared to adjacent barren areas (BAs) away from the trees. In the greenhouse inoculum potential assays, VAM fungi were detected in onion (Allium cepa) trap plants from all soil samples regardless of collection site, but cardon cactus (P. pringlei) trap seedlings formed no VAM even after 6.5 months. Test soils were further used to preinoculate new onion seedlings transplanted into pots, to serve as nurse plants to inoculate adjacent cardon seedlings by vegetative transfer. After 15 months, cardon seedlings did develop slight VAM colonization, confined exclusively to the outermost cortical layers. Examination of test soils for spores or root fragments revealed very few to none, and spore production on onion trap plant roots was also sparse even though colonization was high. Analysis of UC and BA soils revealed that the water holding capacity, nutrient content, cation exchange capacity, total carbon, and total nitrogen contents of the UC soils were all higher than those of the BA soils. Since the VAM inoculum density in this study was not different between sites under and away from the mesquite tree canopy, we concluded that VAM inoculum density is not the primary factor for the establishment of cactus seedlings and that edaphic factors probably play a more important role. Our results suggest, however, that VAM inoculum potential in these hot desert soils, although relatively low, is probably maintained in the upper layers by means of hyphal fragments rather than spores.     

Denitrification and total nitrogen gas production from forest soils of Eastern China

Reactive forms of nitrogen (Nr) are accumulating at local, regional and global levels largely due to human activities, particularly N-fertilizer production and use as well as fossil fuel combustion. This has resulted in a change in the nitrogen (N) cycle and excess Nr in the environment, which has negative environmental effects. Therefore, characterizing denitrification and the edaphic variables controlling denitrification and its products is the first step in predicting the long-term effects of Nr accumulation. In the present study, six forest soil types in different climatic zones were collected from East China and evaluated for denitrification products following a K¹⁵NO₃ amendment and subsequent incubation. The results showed that denitrification, indicated by production of nitric oxide (NO), nitrous oxide (N₂O) and dinitrogen (N₂), was higher in the studied temperate forest soils than in the studied subtropical and tropical forest soils and was negatively correlated with soil redox potential at the beginning of incubation (r = −0.94, P < 0.01), but not with soil pH. The ratios of NO/total N gas and N₂O/total N gas produced during denitrification varied among the soils, and were generally higher in the subtropical and tropical soils. Spearman's correlation analysis showed that the NO ratio was positively correlated with soil oxidation capacity (OXC) (r = 0.94, P < 0.01) and redox potential at the beginning of incubation (r = 0.86, P < 0.05), but negatively correlated with soil pH (r = −0.83, P < 0.05). The N₂O ratio was not significantly correlated with these edaphic variables, but showed a significant correlation to NO ratio (r = 0.83, P < 0.05). These results suggested that the OXC value might be the key factor affecting denitrification rates in soils. One possible explanation for these effects is that large OXC values would result in a higher level soil redox potential, thus suppressing denitrification and enhancing NO and N₂O ratios during denitrification.     

Chemische Eigenschaften von Waldböden im Nordwestdeutschen Pleistocän und deren Gruppierungen nach Pufferbereichen

Chemical properties of forest soils in the pleistocene of Northwest Germany and their classification based on soil buffering systems In order to characterize the chemical characteristics of forest soils of Hamburg, 800 soil samples and 400 root samples from 172 sites were used to obtain suitable soil chemical and ecochemical parameters. A strong and deep reaching soil acidification was observed on all sites with exception of those on till. The sulfate concentration in the equilibrium soil solution allows the conclusion that deposition of acid plays a significant role in this acidification. Classification of sites based on edaphic factors did not provide useful information on the chemical status of soils. However, grouping of soil horizons using pH measured in 0.01 M CaCl₂ lead to a stratification according to the soil buffering systems. Distinction between the exchanger and the aluminium buffer ranges was, however, not quite satisfactory.     

Differences in the growth and ectomycorrhizal community of Dryobalanops lanceolata (Dipterocarpaceae) seedlings grown in ultramafic and non-ultramafic soils

Ultramafic soils have naturally high concentrations of metals and are often low in major plant nutrients. Plant species of non-ultramafic origin, such as Dryobalanops lanceolata (Dipterocarpaceae), generally grow less well on these soils. I found minimal changes in growth, but a 17% reduction in foliar potassium, when seedlings of D. lanceolata were grown in a non-native ultramafic soil when compared with a ‘normal’ tropical ultisol. There were, however, marked changes in the ectomycorrhizal community structure on the roots of D. lanceolata. Cenococcum geophilum was at least 10 times more common and Inocybe sp. was one and a half times more common in non-ultramafic soils, whereas Boletales sp. was over 30 times more common in the non-ultramafic soil. These changes may have been brought about by a number of edaphic differences between the two soil types, including high metal concentrations and differences in organic matter content.     

Soil–plant relationships and tree distribution in old growth Nothofagus betuloides and Nothofagus pumilio forests of Tierra del Fuego

The evergreen Nothofagus betuloides and deciduous Nothofagus pumilio live close together in Tierra del Fuego. The fact that these two species rarely form mixed forests suggests that the soil factor can contribute to the distribution of two species on a local scale. Most of these forests are undisturbed; therefore, soil characteristics may reflect both the influence of the species and of the dominant pedogenetic processes. In this paper, we aim to study how soil characteristics can affect nutrient cycling, the strategies of tree nutrition and the distribution of Nothofagus forests in Tierra del Fuego. Twenty-two soils in these two types of forests in contrasted topographic positions were sampled and analysed. The dominant soil processes were waterlogging in the evergreen forest and podzolisation in the deciduous one. Within each type of forest we observed large variability in soils. Nutrient-poor litter slowed down nitrogen cycling. However, phosphorus mobilisation was high in nutrient-poor environments because of low pH and waterlogging. Chemical and biological characteristics of the Oa horizon were able to discriminate between forest types while mineral soil characteristics were not. Biological activity of the organic horizons was limited by low pH and, in N. betuloides forests, also by waterlogging conditions. According to this pattern, N. betuloides grows in less fertile soils and thus has lower nutrient concentrations in leaves. In contrast, N. pumilio grows in soils with higher fertility and consequently has high nutrient content in leaves. Despite growing in low fertility sites, N. betuloides grows at a rate similar to that of N. pumilio. This suggests that the evergreen species is more efficient in using nutrients and better adapted to waterlogging conditions.     

The influence of American Chestnut (Castanea dentata) on nitrogen availability, organic matter and chemistry of silty and sandy loam soils

American chestnut trees once dominated vast areas of deciduous forest in eastern North America, but the exotic chestnut blight almost eliminated the species from the region. Introduction of blight-resistant American chestnut hybrids will probably start in the next decade after many years of tree breeding. What were the historic effects of chestnut on forest soils, and what changes may follow reintroduction of hybrid chestnuts? A site in southern Wisconsin provided an opportunity to examine the effect of chestnut trees on soil properties. At this site, 600 km northwest of chestnut's historic distribution, naturalized chestnuts have spread throughout an intact mixed-species forest from nine planted trees. The site contains soil developed on a silty loess-mantled ridge that abuts sandier hillslopes, allowing the effects of individual chestnuts to be examined on two soil types. I sampled and analyzed forest floor and mineral soils beneath canopies of individual American chestnuts and the surrounding mixed-species deciduous forest on fine-silt and sandy-loam soil types. On sandy loam soils, total soil carbon (C) and nitrogen (N), inorganic N and net mineralization and nitrification rates were 10–17% higher beneath chestnut canopies compared to soils beneath mixed-species deciduous forest. The pool of total soil N beneath chestnut canopies was positively related to the silt content of the sandy loam soils. In contrast, there were no differences between properties of chestnut canopy and mixed-species deciduous forest soils on the fine silt texture class. On sandy loam soil conditions common throughout the pre-blight distribution of American chestnut, soil biogeochemical processes differ beneath individual chestnut trees relative to a diverse mixture of deciduous species. These findings suggest that widespread chestnut reintroduction has the potential to alter both stand- and watershed-scale processes.     

Feeding preferences of native terrestrial isopod species (Oniscoidea,Isopoda) for native and introduced leaf litter

Due to current predictions for Central Europe that forecast higher frequencies of hot and dry summers, Mediterranean drought-tolerant oak species are being evaluated as future forest trees for German forest sites that are becoming increasingly damaged by water deficit. As a result of planting foreign tree species, the leaf litter composition and thus the food resources of native saprophagous macroarthropods will change, possibly altering primary decomposition processes. Therefore, experiments concerning the acceptance and palatability of introduced versus native litter for native isopods were undertaken. Consumption rates of four native isopod species (Porcellio scaber, Oniscus asellus, Trachelipus rathkii, Trachelipus ratzeburgii) were investigated in laboratory choice tests with introduced (Quercus pubescens, Quercus frainetto, Quercus ilex) and comparable native (Fagus sylvatica, Quercus robur) leaf litter. Litter was characterized by measurement of C/N-ratios and lignin content. Although species-specific preferences of isopods could be observed in the experiments, Mediterranean oak litter was consumed by all investigated species. Furthermore, two isopod species even preferred the leaf litter of the introduced Q. ilex. Compared to native beech or oak litter, litter from these introduced tree species thus apparently do not negatively influence the consumption rates of terrestrial isopods. Possible reasons for the determined preferences are discussed.     

COLONIZATION PATTERNS OF WOODY SPECIES ON LANDS MINED FOR COAL IN SPAIN: PRELIMINARY INSIGHTS FOR FOREST EXPANSION

In this study, we combined the analysis of a coenocline with Huisman–Olff–Fresco (HOF) modelling of species behaviour to describe colonization patterns of woody species on reclaimed coal wastes in northern Spain. We hypothesize that fine‐scale variation in abiotic factors along the forest‐grassland gradient that appears after mining restoration affects colonization pattern of woody species. To understand these factors, we analysed changes in floristic composition and abundance of the main woody colonizers according to the spatial distance from forest limit, as well as the spatial variability of some edaphic and microclimatic parameters. Our results showed how the primary coenocline extracted from DCA1 reflected a gradient in environmental conditions influencing the species composition of the woody plant communities, from the more shade, moist and dense forest on acid and rich soils to the open, dry and oligotrophic grassland. The colonization pattern of woody species is affected by fine‐scale variations in abiotic factors, such as the increase in pH, P, light, and the decrease in K, N, C/N, organic matter and soil moisture, from the forest to the restored mine. Most species HOF modelled showed monotone responses with decreasing trends along the environmental gradient from forest to mine, being Quercus petraea the species clearly dominant in the forest. On the contrary, Cytisus scoparius and Genista florida colonize intensely in the mine area, reaching the maximum abundance around 15 and 10 m distance from the forest limit, respectively. We conclude that the composition of woody species in the forest is not a good predictor of the colonizing intensity, not even of the species composition in the mine area. Copyright © 2011 John Wiley & Sons, Ltd.     

Remnant sugar maple (Acer saccharum subsp. skutchii) populations at their range edge: Characteristics,environmental constraints and conservation implications in tropical America

Relationships between environmental conditions and persistence of populations at edges of ranges should be useful for predicting consequences of climate change. We characterized environmental conditions of six disjunct sites in Mexico and Guatemala that contain all known relict populations of the most southern subspecies of sugar maple, cloud forest sugar maple (Acer saccharum subsp. skutchii). We also sampled abundance and basal area of all tree species, recording 164 species, 92 genera (61% tropical), and 54 families at these sites. Temperate genera decreased in number from north to south, but mixtures of temperate and tropical species were co-dominant with cloud forest sugar maple at all sites. For all species, basal area was 24–52 m² ha^?1 and density was 990–2986 trees/ha at the six sites. Cloud forest sugar maple comprised 7–43% of total basal area and 1–16% of total densities at each site. Populations of cloud forest sugar maple currently are vulnerable to environmental change. Anthropogenic disturbance is negatively affecting four populations, and regeneration is successfully occurring in only two sites. As a result, densities and basal area are much reduced compared to more northern temperate populations. NMS-ordination indicated that elevation and hurricane frequency are major environmental constraints related to abundance. Maple recruitment is associated with short hurricane return intervals that maintain higher elevation cloud forests in states conducive for regeneration. We establish the conservation status of cloud forest sugar maple at the southern end of its range relative to expected climate change and propose this subspecies be included in the IUCN-Red List.     

Parent material and vegetation influence bacterial community structure and nitrogen functional genes along deep tropical soil profiles at the Luquillo Critical Zone Observatory

Microbial communities mediate every step of the soil nitrogen cycle, yet the structure and associated nitrogen cycle functions of soil microbial communities remain poorly studied in tropical forests. Moreover, tropical forest soils are often many meters deep, but most studies of microbial nitrogen cycling have focused exclusively on surface soils. The objective of our study was to evaluate changes in bacterial community structure and nitrogen functional genes with depth in soils developed on two contrasting geological parent materials and two forest types that occur at different elevations at the Luquillo Critical Zone Observatory in northeast Puerto Rico. We excavated three soil pits to 140 cm at four different sites representing the four soil × forest combinations (n = 12), and collected samples at ten-centimeter increments from the surface to 140 cm. We used bacterial 16S rRNA gene-DGGE (denaturant gradient gel electrophoresis) to fingerprint microbial community structures, and quantitative PCR to measure the abundance of five functional genes involved in various soil nitrogen transformations: nifH (nitrogen fixation), chiA (organic nitrogen decomposition), amoA (ammonia oxidation), nirS (nitrite reduction) and nosZ (nitrous oxide reduction). Multivariate analyses of DGGE fingerprinting patterns revealed differences in bacterial community structure across the four soil × forest types that were strongly correlated with soil pH (r = 0.69, P < 0.01) and nutrient stoichiometry (r² ≥ 0.36, P < 0.05). Across all soil and forest types, nitrogen functional genes declined significantly with soil depth (P < 0.001). Denitrification genes (nirS and nosZ) accounted for the largest proportion of measured nitrogen functional genes. Measured nitrogen functional genes were positively correlated with soil carbon, nitrogen and phosphorus concentrations (P < 0.001) and all genes except amoA were significantly more abundant in the Inceptisol soil type compared with the Oxisol soil type (P < 0.03). Greater abundances and a stronger vertical zonation of nitrogen functional genes in Inceptisols suggest more dynamic nitrogen transformation processes in this soil type. As the first study to examine bacterial nitrogen functional gene abundances below the surface 20 cm in tropical forest soils, our work provides insight into how pedogenically-driven vertical gradients control the nitrogen-cycling capacity of soil microbial communities. While previous studies have shown evidence for redox-driven hotspots in tropical nitrogen cycling on a watershed scale, our study corroborates this finding on a molecular scale.     

Priority areas for the conservation of Atlantic forest large mammals

Large mammal faunas in tropical forest landscapes are widely affected by habitat fragmentation and hunting, yet the environmental determinants of their patterns of abundance remain poorly understood at large spatial scales. We analysed population abundance and biomass of 31 species of medium to large-bodied mammal species at 38 Atlantic forest sites (including three islands, 26 forest fragments and six continuous forest sites) as related to forest type, level of hunting pressure and forest fragment size using ANCOVAs. We also derived a novel measure of mammal conservation importance for each site based on a “Mammalian Conservation Priority index” (MP_i) which incorporates information on species richness, population abundance, body size distribution, conservation status, and forest patch area. Mammal abundance was affected by hunting pressure, whereas mammalian biomass of which was largely driven by ungulates, was significantly influenced by both forest type and hunting pressure. The MP_i index, when separated into its two main components (i.e. site forest area and species-based conservation index C_i), ordered sites along a gradient of management priorities that balances species-focused and habitat-focused conservation actions. Areas with the highest conservation priority were located in semi-deciduous forest fragments, followed by lowland forests. Many of these fragments, which are often embedded within large private landholdings including biofuel and citrus or coffee crops, cattle ranches and pulpwood plantations, could be used not only to comply with environmental legislation, but also enhance the prospects for biodiversity conservation, and reduce edge effects and hunting.     

Seasonal pattern of total soil respiration in undisturbed and disturbed ecosystems of Central Himalaya

Summary The rates of CO₂ efflux were measured by an alkali absorption method (using 20 ml 0.5 N NaOH) from soils in four undisturbed sites [two evergreen oak forests, Quercus floribunda Lindl. (tilonj oak), Quercus leucotrichophora A Camus (banj oak), and two evergreen conifer forests, Cedrus deodara Loud. (deodar forest) and Pinus roxburghii Sarg. (chir pine forest)] and three disturbed sites. The sites were located between elevations of 1850 and 2360 m in the Central Himalaya. The seasonal pattern of soil respiration was similar in all the sites with a maximum during the rainy season, intermediate rates during the summer season and the lowest level of activity in winter. The rate of CO₂ efflux was higher in broadleaf than in conifer forests, and it was lowest in the disturbed sites. Among the edaphic conditions, soil moisture, N, organic C, pH, soil porosity, and root biomass positively affected total soil respiration. The proportion of root respiration to total soil respiration was higher in the disturbed sites than the undisturbed sites in winter. Conditions in the winter season were less favourable for microbial respiration than for root respiration.