Denaturing gradient gel electrophoretic analysis of dominant 2,4-diacetylphloroglucinol biosynthetic phlD alleles in fluorescent Pseudomonas from soils suppressive or conducive to black root rot of tobacco

In Switzerland, similar types of rhizosphere pseudomonads producing the biocontrol compound 2,4-diacetylphloroglucinol (Phl) have been found in soils suppressive to Thielaviopsis basicola-mediated black root rot of tobacco as well as in conducive soils. However, most findings were based on the analysis of a limited number of Pseudomonas isolates, obtained from a single experiment and only from T. basicola-inoculated plants. Here, an approach based on denaturing gradient gel electrophoresis (DGGE) of dominant phlD alleles from tobacco rhizosphere provided different phlD migration patterns. Sequencing of phlD-DGGE bands revealed a novel phylogenetic cluster of phlD sequences found in both suppressive and conducive soils in addition to previously-documented phlD alleles. phlD-DGGE bands and alleles differed little from one plant to the next but more extensively from one sampling to the next during the three-year study. Three of the 13 bands and 12 of the 31 alleles were only found in suppressive soil, whereas five bands and 13 alleles were found exclusively in conducive soil. The population structure of phlD⁺ pseudomonads depended more on the individual soil considered and its suppressiveness status than on inoculation of tobacco with T. basicola. In conclusion, phlD-DGGE revealed additional phlD diversity compared with earlier analyses of individual Pseudomonas isolates, and showed differences in phlD⁺Pseudomonas population structure in relation to disease suppressiveness.     

Survival of the biocontrol agents Coniothyrium minitans and Bacillus subtilis MBI 600 introduced into pasteurised, sterilised and non-sterile soils

The biocontrol agents Coniothyrium minitans and Bacillus subtilis MBI 600 were added separately to three soil types that had been either sterilised, pasteurised or left non-sterile. Applied as a conidial suspension of 1×10⁶ cfu g⁻¹ soil, C. minitans showed good survival in all sterilised, pasteurised and non-sterile soils, remaining at the numerical level at which it was applied for the duration of the 30 d experiment. Applied at a lower rate of 1×10³ cfu g⁻¹ soil, C. minitans proliferated in sterilised soil to numbers slightly over 1×10⁶ cfu g⁻¹ soil, whereas no increase was seen in pasteurised or non-sterile soils from this lower application rate. However, although C. minitans was not easily recovered on plates from non-sterile soil, it did survive at the lower numerical level in pasteurised soil, and was recoverable throughout the experiment at the rate at which it was applied. B. subtilis MBI 600 survived well following introduction as a cell suspension into sterilised soil at a rate of 1×10⁶ cfu g⁻¹ soil. Spores were formed rapidly and, after 14 d, the introduced microorganism survived in this form rather than as vegetative cells. However, in non-sterile soil, the introduced microorganism did not compete well and decreased in number, with spores being formed in low numbers. Survival of B. subtilis MBI 600 in pasteurised soil was variable, but resembled the survival seen in non-sterile soil more than that seen in sterilised soil. More B. subtilis MBI 600 spores were formed in pasteurised soil than in non-sterile soil, however, and may have been important for survival in pasteurised soil. In conclusion, this work has shown that the biocontrol agent C. minitans can survive well in soil irrespective of whether the soil has been pasteurised or not and shows good promise as a soil inoculant for control of Sclerotinia sclerotiorum. Although soil pasteurisation does improve establishment of B. subtilis MBI 600 compared to non-sterile soil, survival is relatively poor when applied as cells. The best survival of B. subtilis MBI 600 occurred as spores in sterilised soil, and spore applications to pasteurised soil in an integrated control strategy may allow sufficient establishment of the biocontrol agent to target pathogens causing damping-off.     

Influence of temperature on the motility of Pseudomonas oryzihabitans and control of Globodera rostochiensis

The motility and efficacy of Pseudomonas oryzihabitans as a biocontrol agent against the potato cyst nematode Globodera rostochiensis were studied with respect to temperature. The influence of soil moisture on bacterial movement was also tested. In a closed container trial, P. oryzihabitans significantly reduced invasion of second stage juveniles (J2) of G. rostochiensis in potato roots, its effect being more marked at 25 and 21 °C than at 17 °C. P. oryzihabitans motility in vitro was optimal at 26 °C and inhibited at temperatures below 18 °C. In soil, both temperature and matric potential affected bacterial movement. At 16 °C its movement and survival were suppressed, but they were unaffected at 25 °C. At both temperatures the biocontrol agent moved faster in the wetter (−0.03 MPa) than in the drier soil (−0.1 MPa). These results suggest that temperature is a key factor in determining the potential of P. oryzihabitans as a biocontrol agent.     

Effects of Pseudomonas aeruginosa on the diversity of culturable microfungi and nematodes associated with tomato: impact on root-knot disease and plant growth

The available information on Pseudomonas biocontrol inoculants on the non-target fungal and nematode community is scant. The current paper addresses this issue and investigates the effects of biocontrol agents Pseudomonas aeruginosa IE-6 and IE-6S⁺ (previously shown to suppress several soil-borne plant pathogens) on soil microfungi and plant-parasitic nematodes as well as on the root-knot development and growth of tomato (Lycopersicon esculentum). Furadan, a granular nematicide was included as a treatment for comparative purposes. Treatments were applied to soil at the start of each 52-day-long tomato growth cycle, and their effects on the composition and diversity of rhizosphere and endophytic microfungi and plant-parasitic nematodes were examined at the end of first and fourth growth cycle. Several diversity indices were employed to assess community diversity. A total of 16 genera comprising 23 microfungal species were isolated from the tomato rhizosphere. The most abundant fungal species belonged to the genera Aspergillus, Fusarium, and Penicillium. With a few exceptions, fungi were neither exclusively inhibited nor specifically promoted by the application of treatments at any of the growth cycles studied. However, Paecilomyces lilacinus, an egg and female parasite of root-knot nematode, though exclusively absent in the controls was isolated from the treatments. Both general diversity and equitability of rhizosphere microfungi were greater at first compared to the fourth growth cycle while species richness remained uninfluenced across the growth cycles and treatments. However, Furadan and IE-6S⁺ treatments considerably abated general diversity and equitability. Of the microfungal species isolated from the rhizosphere seven were also recovered from surface-sterilized root tissue of tomato suggesting that all the endophytes are primarily rhizosphere organisms. Diversity of endophytic fungi was consistently lower compared with that of the rhizosphere. Both general diversity and equitability declined in all three treatments relative to controls in the root tissue but species richness remained unaltered. Diversity and equitability of plant-parasitic nematodes in soil were reduced by all three treatments over the controls at fourth growth cycle whilst species richness did not change at either growth cycle. The biocontrol agents significantly reduced root-knot development and enhanced shoot growth of tomato over the controls. The possible implications of fungal composition and abundance because of biocontrol by Pseudomonas application are discussed.     

Short-term C4 plant Spartina alterniflora invasions change the soil carbon in C3 plant-dominated tidal wetlands on a growing estuarine Island

Spartina alterniflora is an invasive C₄ perennial grass, native to North America, and has spread rapidly along the east coast of China since its introduction in 1979. Since its intentional introduction to the Jiuduansha Island in the Yangtze River estuary, Spartina alterniflora community has become one of the dominant vegetation types. We investigated the soil carbon in the Spartina alterniflora community and compared it with that of the native C₃Scirpus mariqueter community by measuring total soil carbon (TC), soil organic carbon (SOC), total soil nitrogen (TN), and the stable carbon isotope composition (δ¹³C) of various fractions. TC and SOC were significantly higher in Spartina alterniflora in the top 60 cm of soil. However, there was no significant difference in soil inorganic carbon (IC) between the two communities. Stable carbon isotopic analysis suggests that the fraction of SOC pool contributed by Spartina alterniflora varied from 0.90% to 10.64% at a soil depth of 0-100 cm with a greater percentage between 20 and 40 cm deep soils. The δ¹³C decreased with increasing soil depth in both communities, but the difference in δ¹³C among layers of the top 60 cm soil was significant (p<0.05), while that for the deeper soil layers (>60 cm) was not detected statistically. The changes in δ¹³C with depth appeared to be associated with the small contribution of residues from Spartina alterniflora at greater soil depth that was directly related to the vertical root distribution of the species.     

Effects of nitrogen deposition on growth and survival of montane Racomitrium lanuginosum heath

Montane heaths dominated by the moss Racomitrium lanuginosum are in decline, for which increased atmospheric nitrogen (N) deposition may be partially responsible. To test this, field plots in northeast Scotland were treated with either low or high (10 or 40 kg N ha⁻¹year⁻¹) doses of nitrogen (as NO₃⁻ or NH₄⁺) for 2 years. Although Racomitrium tissue N increased after treatment, with greater response for low than high N application, activity of the enzyme nitrate reductase and Racomitrium growth were severely inhibited by increasing N addition. Racomitrium cover declined following N addition and graminoid cover increased, also with greatest effect at high doses. Of all measurements, only nitrate reductase showed a distinction between NO₃⁻ and NH₄⁺ application. The results demonstrate the detrimental effects of even low increases in nitrogen deposition on the moss heath, suggesting that loss of Racomitrium and its replacement by graminoids is strongly linked to increased levels of anthropogenic N pollution.     

Towards an ecologically-sustainable forestry in the Atlantic Forest

Since pristine Atlantic Forest remnants are vanishing, and biological reserves are in short, conservation of biodiversity will largely depend on proper management of the anthropogenic matrix. Here, we test (1) the effectiveness of ecologically-managed tree monocultures in maintaining Araucaria Forest biodiversity, (2) how this effectiveness change among taxa, and (3) we discuss management principles that can be used by the forestry industry in order to contribute positively to biodiversity conservation. The study was conducted in the São Francisco de Paula National Forest, southern Brazil, an environmental mosaic composed mostly of patches of Araucaria Forest and ecologically-managed monocultures of Araucaria, Pinus and Eucalyptus. Using standardized sampling methods in these four main habitats, we have recorded the richness and species composition of small mammals, birds, leaf-litter frogs, butterflies, galling insects, spiders, opiliones, flatworms, woody plants, epiphytic angiosperms, epiphytic ferns, lichens, and fruit-body producing fungi. Overall, we recorded 506 species in Araucaria Forest, 181 (36%) of which were exclusive of this habitat while 325 (64%) could be found in at least one monoculture. Distribution patterns of species richness and number of records across taxonomic groups showed that a large biodiversity can be found inside ecologically-managed plantations of Araucaria, Pinus, and Eucalyptus. For all studied taxa, except for epiphytic angiosperms and fruit-body producing fungi, more than half of the Araucaria Forest species could be found living on monocultures. We discuss how the actual management practices of the forest industry can be improved to contribute positively to the conservation of the Atlantic Forest biodiversity.     

Plant growth promoting properties of a strain of Enterobacter ludwigii isolated from Lolium perenne rhizosphere

The capability of native bacterial strains isolated from Lolium perenne rhizosphere to behave as plant growth promoting bacteria and /or biocontrol agents was investigated. One strain (BNM 0357) over 13 isolates from the root tips of L. perenne resulted proved to be nitrogenase positive (ARA test) and an IAA producer. Conventional tests and the API 20E diagnostic kit indicated that BNM 0357 behaves to the Enterobacteriaceae family and to the Enterobacter genus. Molecular identification by 16S rRNA sequence analysis indicated that BNM 0357 had the highest similarity to Enterobacter ludwigii (EN-119). Isolate BNM 0357 had the capability to solubilize calcium triphosphate and to antagonize Fusarium solani mycelial growth and spore germination. Strain BNM 0357 also showed the ability to improve the development of the root system of L. perenne. This study disclosed features of E. ludwigii BNM 0357 that deserve further studies aimed at confirming its putative importance as a PGPR.     

大豆-柑桔间作磷的迁移与分配规律

A mini-plot field experiment was conducted on a loamy clay Oxisol to compare and evaluate P absorption and transfer in plant organs and P movement in soil profile at three P application depths under the soybean-citrus intercropping versus the monoculture using a ^32p tracer technique. Total P absorption （Pt） by soybean and P accumulation （Pa） in soybean organs decreased significantly （P 〈 0.05） under the intercropping in contrast to the monoculture. With intercropping, when ^32p was applied in topsoil （15 cm soil layer）, total ^32p absorption （^32pt） in soybeans was significantly lower （P 〈 0.05）, but when ^32p was applied to deeper soil layers （35 or 55 cm soil layer）, ^32pt in soybeans was significantly greater （P 〈 0.05）. The percentage of P in leaves to total P （Pa/Pt） and 32p in leaves to total ^32p （^32pa/^32pt） for soybean were ≥ 25% and those of root ≥ 12%. When P was applied ia topsoil and 55 cm soil layer, no significant differences were found between intercropping and monoculture for Pt of citrus. The P absorbed by citrus was transferred rapidly to the growing organs of aboveground during the experiment, and the speed of transferring to the growing organs slowed when P was applied to the deeper soil layers. In intercropping, P mobility was heightened in the soil profile, and P in deeper soil layers moved up to topsoil more rapidly.     

Quantification of Wautersia [Ralstonia] basilensis in the mycorrhizosphere of Pinus thunbergii Parl. and its effect on mycorrhizal formation

The bacterium Wautersia [Ralstonia] basilensis has been shown to enhance the mycorrhizal symbiosis between Suillus granulatus and Pinus thunbergii (Japanese black pine). However, no information is available about this bacterium under field conditions. The objectives of this study were to detect W. basilensis in bulk and mycorhizosphere soils in a Japanese pine plantation in the Tottori Sand Dunes, determine the density of W. basilensis in soil, and determine the optimal cell density of W. basilensis for mycorrhizal formation in pine seedlings. We designed and validated 16S rRNA gene-targeted specific primers for detection and quantification of W. basilensis. SYBR Green I real-time PCR assay was used. A standard curve relating cultured W. basilensis cell density (10³-10⁸ cells ml⁻¹) to amplification of DNA showed a strong linear relationship (R = 0.9968). The specificity of the reaction was confirmed by analyzing DNA melting curves and sequencing of the amplicon. The average cell density of W. basilensis was >4.8 × 10⁷ cells g⁻¹ of soil in the mycorrhizosphere and 7.0 × 10⁶ cells g⁻¹ in the bulk soil. We evaluated the W. basilensis cell density required for mycorrhizal formation using an in vitro microcosm with various inoculum densities ranging from 10² to 10⁷ cells g⁻¹ soil (10⁴-10⁹ cells ml⁻¹). Cell densities of W. basilensis of >10⁶ cells g⁻¹ of soil were required to stimulate mycorrhizal formation. In vivo and in vitro experiments showed that W. basilensis was sufficiently abundant to enhance mycorrhizal formation in the mycorrhizosphere of Japanese black pine sampled from the Tottori Sand Dunes.     

Surface water and ground-water thresholds for maintaining Populus-Salix forests, San Pedro River, Arizona

Ground-water and surface flow depletions are altering riparian ecosystems throughout the southwestern United States, and have contributed to the decline of forests of the pioneer trees Populus fremontii (Fremont cottonwood) and Salix gooddingii (Goodding willow). On some rivers, these forests have been replaced by shrublands of Tamarix ramosissima (tamarisk), a drought-tolerant species from Eurasia. The physiological response of these three riparian plant species to decreases in water availability is well studied, but little attention has been given to shifts in community and population structure in response to declines in surface flow and ground-water levels. Based on study of 17 sites spanning a hydrologic gradient, this research identified hydrologic thresholds above which P. fremontii-S. gooddingii maintain tall dense stands with diverse age classes, and above which they are more abundant than T. ramosissima stands along the San Pedro River in Arizona. Surface flow permanence was the hydrologic variable that explained most of the variance in species abundance and relative importance, with inter-annual ground-water fluctuation and depth to ground water also contributing. P. fremontii and S. gooddingii were dominant over T. ramosissima at sites where surface flow was present more than 76% of the time, inter-annual ground-water fluctuation was less than 0.5 m, and average maximum depth to ground water was less than 2.6 m, during a two-year period of data collection. Because T. ramosissima is a shrub species with smaller leaves and lower canopy heights than P. fremontii and S. gooddingii, these shifts in species composition corresponded to decreases in maximum canopy height and upper stratum (above 8 m) vegetation volume as site water availability declined. As well, sites with deeper water tables and more intermittent flows had greater areal coverage of shrublands and less of woodlands. The altered vegetation structure along dewatered rivers may lower wildlife habitat quality. This study provides river managers with quantitative hydrologic guidelines for conserving tall dense P. fremontii-S. gooddingii stands and emphasizes the importance of maintaining long-term hydrologic conditions that are favorable to these species. The study also has implications for riparian restoration and invasive species management by suggesting that desired outcomes may be achieved through restoration of physical processes.     

Mycorrhizal fungi increase biocontrol potential of Pseudomonas fluorescens

Wheat roots are susceptible to colonisation by soil-borne pathogens, such as Gaeumannomyces graminis var. tritici (Ggt), which causes the globally important disease take-all, and mutualistic arbuscular mycorrhizal fungi (AMF). Certain rhizosphere fluorescent Pseudomonas strains have received much attention as potential biocontrol agents given their ability to produce antibiotics, such as 2,4-diacetylphloroglucinol (DAPG), that confer a measure of plant protection. Here we show that Pseudomonas fluorescens only produced DAPG in the presence of soluble carbon from soil containing either Ggt or AMF, and production increased by two orders of magnitude in response to both AMF and Ggt. Encouragement of mycorrhizal colonisation may therefore offer a sustainable strategy for protection against take-all.     

3 种挺水植物吸收水体NH4+、NO3-、H2PO4- 的动力学特征比较

本文用动力学试验研究了具有景观价值的3 种挺水植物—— 水生美人蕉(Canna generalis)、细叶莎草(Cyperus papyrus)、紫芋(Colocasia tonoimo)对H₂PO₄^-、NH₄⁺、NO₃^- 的吸收特征及差异。试验结果表明: 3 种挺水植物吸收H₂PO₄^- 时, 美人蕉的吸收速率最快, 且在较低离子浓度条件下也可以吸收该离子, 说明其具有嗜磷特性, 能够适应广范围浓度H₂PO₄^- 环境; 吸收NO₃^- 时, 细叶莎草的速率最快, 但对低浓度NO₃^- 环境的适应能力较差, 美人蕉吸收NO₃^- 的特性与细叶莎草刚好相反; 吸收NH₄⁺ 时, 细叶莎草的吸收速率最快, 且在低浓度NH₄⁺ 环境下仍能吸收该离子, 而美人蕉的吸收速率最慢, 但能在低浓度NH₄⁺ 环境下吸收该离子。说明不同植物对养分的吸收特性存在较大差异, 各自的污染水体修复适用范围也不同。美人蕉可用于各种浓度H₂PO₄^- 污染的水体修复; 而NO₃^- 污染严重的水体最适宜用细叶莎草作先锋植物, 修复到一定程度后再种植美人蕉来维持水质; 细叶莎草在各种浓度NH₄⁺ 污染的水体中均适用, NH₄⁺ 污染较轻的水体也可用美人蕉修复。     

Wheat-rhizoplane pseudomonads as antagonists of Gaeumannomyces graminis

The role of rhizoplane-inhabiting Pseudomonas spp as inhibitors of take-all on wheat was investigated. Apparent numbers of pseudomonads in wheat rhizoplanes and numbers that were antagonistic in vitro toward Gaeumannomyces graminis var, tritici did not differ when wheat was supplied with NH⁺₄-N or NO^?₃-N. More intense antagonism was expressed by colonies selected from soil treated with NH⁺₄-N than with NO^?₃-N, and from isolation media prepared at pH 5.5 rather than at 7.0. Antagonists were not recovered from methyl bromide-treated soil. Highly antagonistic pseudomonads were recovered from a wheat-monoculture soil which is considered suppressive toward the pathogen in the field, and were not recovered from a “nonsuppressive” soil. Pseudomonad antagonism ratings were inversely correlated with take-all severity in the suppressive soil, but not in the nonsuppressive soil. Pseudomonads were considered to be antagonists of G. graminis on rhizoplanes of wheat in a soil exhibiting the “take-all decline” phenomenon, but the significance of this interaction remains to be determined.     

The mycorrhizal fungus Glomus intraradices and rock phosphate amendment influence plant growth and microbial activity in the rhizosphere of Acacia holosericea

Plants inoculated with arbuscular mycorrhizal (AM) fungi utilize more soluble phosphorus from soil mineral phosphate than non-inoculated plants. However, there is no information on the response of soil microflora to mineral phosphate weathering by AM fungi and, in particular, on the catabolic diversity of soil microbial communities.The AM fungus, Glomus intraradices was examined for (i) its effect on the growth of Acacia holosericea, (ii) plant-available phosphate and (iii) soil microbial activity with and without added rock phosphate.After 4-months culture, AM fungal inoculation significantly increased the plant biomasses (by 1.78× and 2.23× for shoot and root biomasses, respectively), while mineral phosphate amendment had no effect in a sterilized soil. After 12-months culture, the biomasses of A. holosericea plants growing in a non-sterilized soil amended with mineral phosphate were significantly higher than those recorded in the control treatment (by 2.5× and 5× for shoot and root biomasses, respectively). The fungal inoculation also significantly stimulated plant growth, which was significantly higher than that measured in the mineral phosphate treatment. When G. intraradices and mineral phosphate were added together to the soil, shoot growth were significantly stimulated over the single treatments (inoculation or amendment) (1.45×). The P leaf mineral content was also higher in the G. intraradices+mineral phosphate treatment than in G. intraradices or rock phosphate amendment. Moreover, the number of fluorescent pseudomonads has been significantly increased when G. intraradices and/or mineral phosphate were added to the soil. By using a specific type of multivariate analysis (co-inertia analysis), it has been shown that plant growth was positively correlated to the metabolization of ketoglutaric acid, and negatively linked to the metabolisation of phenylalanine and other substrates, which shows that microbial activity is also affected.G. intraradices inoculation is highly beneficial to the growth of A. holosericea plants in controlled conditions. This AM symbiosis optimises the P solubilization from the mineral phosphate and affects microbial activity in the hyphosphere of A. holosericea plants.     

Nitrate leaching in soil: Tracing the NO3 sources with the help of stable N and O isotopes

Legumes increase the plant-available N pool in soil, but might also increase NO₃⁻ leaching to groundwater. To minimize NO₃⁻ leaching, N-release processes and the contribution of legumes to NO₃⁻ concentrations in soil must be known. Our objectives were (1) to quantify NO₃⁻-N export to >0.3 m soil depth from three legume monocultures (Medicago x varia Martyn, Onobrychis viciifolia Scop., Lathyrus pratensis L.) and from three bare ground plots. Furthermore, we (2) tested if it is possible to apply a mixing model for NO₃⁻ in soil solution based on its dual isotope signals, and (3) estimated the contribution of legume mineralization to NO₃⁻ concentrations in soil solution under field conditions. We collected rainfall and soil solution at 0.3 m soil depth during 1 year, and determined NO₃⁻ concentrations and δ¹⁵N and δ¹⁸O of NO₃⁻ for >11.5 mg NO₃⁻-N l⁻¹. We incubated soil samples to assess potential N release by mineralization and determined δ¹⁵N and δ¹⁸O signals of NO₃⁻ derived from mineralization of non-leguminous and leguminous organic matter.Mean annual N export to >0.3 m soil depth was highest in bare ground plots (9.7 g NO₃⁻-N m⁻²; the SD reflects the spatial variation) followed by Medicago x varia monoculture (6.0 g NO₃⁻-N m⁻²). The O. viciifolia and L. pratensis monocultures had a much lower mean annual N export (0.5 and 0.3 g NO₃⁻-N m⁻²). The averaged NO₃⁻-N leaching during 70 days was not significantly different between field estimates and incubation for the Medicago x varia Martyn monoculture.The δ¹⁵N and δ¹⁸O values in NO₃⁻ of rainfall (δ¹⁵N: 3.3±0.8‰; δ¹⁸O: 30.8±4.7‰), mineralization of non-leguminous SOM (9.3±0.9‰; 6.7±0.8‰), and mineralization of leguminous SOM (1.5±0.6‰; 5.1±0.9‰) were markedly different. Applying a linear mixing model based on these three sources to δ¹⁵N and δ¹⁸O values in NO₃⁻ of soil solution during winter 2003, we calculated 18-41% to originate from rainfall, 38-57% from mineralization of non-leguminous SOM, and 18-40% from mineralization of leguminous SOM.Our results demonstrate that (1) even under legumes NO₃⁻-N leaching was reduced compared to bare ground, (2) the application of a three-end-member mixing model for NO₃⁻ based on its dual isotope signals produced plausible results and suggests that under particular circumstances such models can be used to estimate the contributions of different NO₃⁻ sources in soil solution, and (3) in the 2nd year after establishment of legumes, they contributed approximately one-fourth to NO₃⁻-N loss.     

Pathways and dynamics of NO3 and NH4 applied in a mountain Picea abies forest and in a nearby meadow in central Switzerland

To evaluate the pathways and dynamics of inorganic nitrogen (N) deposition in previously N-limited ecosystems, field additions of ¹⁵N tracers were conducted in two mountain ecosystems, a forest dominated by Norway spruce (Picea abies) and a nearby meadow, at the Alptal research site in central Switzerland. This site is moderately impacted by N from agricultural and combustion sources, with a bulk atmospheric deposition of 12 kg N ha⁻¹ y⁻¹ equally divided between NH₄⁺ and NO₃⁻. Pulses of ¹⁵NH₄⁺ and ¹⁵NO₃⁻ were applied separately as tracers on plots of 2.25 m². Several ecosystem pools were sampled at short to longer-term intervals (from a few hours to 1 year), above and belowground biomass (excluding trees), litter layer, soil LF horizon (approx. 5-0 cm), A horizon (approx. 0-5 cm) and gleyic B horizon (5-20 cm). Furthermore, extractable inorganic N, and microbial N pools were analysed in the LF and A horizons. Tracer recovery patterns were quite similar in both ecosystems, with most of the tracer retained in the soil pool. At the short-term (up to 1 week), up to 16% of both tracers remained extractable or entered the microbial biomass. However, up to 30% of the added ¹⁵NO₃⁻ was immobilised just after 1 h, and probably chemically bound to soil organic matter. 16% of the NH₄⁺ tracer was also immobilised within hours, but it is not clear how much was bound to soil organic matter or fixed between layers of illite-type clay. While the extractable and microbial pools lost ¹⁵N over time, a long-term increase in ¹⁵N was measured in the roots. Otherwise, differences in recovery a few hours after labelling and 1 year later were surprisingly small. Overall, more NO₃⁻ tracer than NH₄⁺ tracer was recovered in the soil. This was due to a strong aboveground uptake of the deposited NH₄⁺ by the ground vegetation, especially by mosses.     

How well does a botanical garden collection of a rare palm capture the genetic variation in a wild population?

Conservation is increasingly central to the botanic garden mission. Living plant collections are important components of conservation. Critical evaluation of living conservation collections with population genetic analysis can directly inform ex situ conservation strategy. Here, we quantify the degree of genetic variation captured through a population-based collection protocol, and explore optimal sampling for ex situ conservation. An extensive living collection derived from one population of Leucothrinax morrisii (Arecaceae) provided a model system. We compared 58 specimens from the ex situ collection with 100 individuals from throughout the parent population via 6 ISSR loci. Random bootstrapped resamples of the data were made to model differently structured ex situ collections. Mean diversity (He) differed little between the collection (0.204) and the population (0.216), and genetic distance (D) was very close (0.036). Very few private alleles were found between the collection and the population. Allelic capture, as measured by percent of private alleles, was greater than 94%. Resampled collections of different sizes captured from 48% to 94% of alleles. Pairwise comparison of bootstrapped resamples suggests that increasing the representation of half-sibling groups does not significantly increase allele capture. Increase in allele capture with increasing sample size is greatest at low resample sizes, and showed diminishing returns as resample size increased. No appreciable increase in allele capture was gained through maintaining different half-sibling groups. These data inform sampling for ex situ conservation purposes, and recommend sample sizes of at least 15 individuals, with the upper limit based on resources.     

Status of tiger and leopard in Rajaji-Corbett Conservation Unit, northern India

Rajaji-Corbett Tiger Conservation Unit (RCTCU), in northern India, is one of the 11 Level-I Tiger Conservation Units (TCU) identified in the Indian subcontinent for the long-term conservation of the tiger. This TCU of about 7500 km² stretches from the Yamuna River in the west to Sharda River in the east and includes portions of the Outer Himalaya and the Shivalik hills. Little less than one third of this TCU comes under protected area status (Rajaji National Park—820 km², and Corbett Tiger Reserve—1286 km²) and the rest are under 12 reserve forest divisions, five of which have largely been converted into monoculture plantations. Between November 1999 and March 2000, we evaluated the status of tiger and leopard in RCTCU by counting the number of different pug marks on 3-5 km transect walks along 52 dry stream beds (‘raus’), for a total distance of 479 km in these reserve forests and plantations. People and cattle seen along the transects, were also counted, as an index of disturbance. In this TCU, the tiger occurs in three isolated populations: between the west bank of River Ganges and River Yamuna, from the east bank of Ganges to Kathgodam-Haldwani-Lalkuan Highway and between the Highway and River Sharda. Owing to increasing biotic pressures, the tiger has become rare in Rajaji-Corbett corridor and has become extinct in four divisions. There is a growing threat of further degradation and fragmentation of its habitat. To implement a recovery programme, we suggest several management measures such as control of poaching, resettlement of local tribes (gujjars) and five villages, creation and strengthening of forest corridors, conversion of monocultures into polyculture plantations and establishment of several mini-core areas including Nandaur Valley National Park. We recommend the reliable and user-friendly method used by us to evaluate and monitor the status of leopard and tiger in this conservation unit. A suggested Greater Corbett Tiger Reserve (2000 km²) should be kept as inviolate as possible.     

Temperature sensitivity of respiration differs among forest floor layers in a Pinus resinosa plantation

Decomposer microorganisms contribute to carbon loss from the forest floor as they metabolize organic substances and respire CO₂. In temperate and boreal forest ecosystems, the temperature of the forest floor can fluctuate significantly on a day-to-night or day-to-day basis. In order to estimate total respiratory CO₂ loss over even relatively short durations, therefore, we need to know the temperature sensitivity (Q₁₀) of microbial respiration. Temperature sensitivity has been calculated for microbes in different soil horizons, soil fractions, and at different depths, but we would suggest that for some forests, other ecologically relative soil portions should be considered to accurately predict the contribution of soil to respiration under warming. The floor of many forests is heterogeneous, consisting of an organic horizon comprising a few more-or-less distinct layers varying in decomposition status. We therefore determined at various measurement temperatures the respiration rates of litter, F-layer, and H-layer collected from a Pinus resinosa plantation, and calculated Q₁₀ values for each layer. Q₁₀ depended on measurement temperature, and was significantly greater in H-layer than in litter or F-layer between 5 and 17 °C. Our results indicate, therefore, that as the temperature of the forest floor rises, the increase in respiration by the H-layer will be disproportionate to the increase by other layers. However, change in respiration by the H-layer associated with change in temperature may contribute minimally or significantly to changes of total forest floor respiration in response to changes in temperature depending on the depth and thickness of the layer in different forest ecosystems.