Calcium weathering in forested soils and the effect of different tree species

Soil weathering can be an important mechanism to neutralize acidity inforest soils. Tree species may differ in their effect on or response to soilweathering. We used soil mineral data and the natural strontium isotope ratio⁸⁷Sr/⁸⁶Sr as a tracer to identify the effect of treespecies on the Ca weathering rate. The tree species studied were sugar maple(Acer saccharum), hemlock (TsugaCanadensis), American beech (Fagusgrandifolia),red maple (Acer rubrum), white ash (FraxinusAmericana) and red oak (Quercus rubra) growingin a forest in northwestern Connecticut, USA. Three replicated sites dominatedby one of the six tree species were selected. At sugar maple and hemlock sitesthe dominant mineral concentrations were determined at three soil depths. Ateach site soil, soil water and stem wood of the dominant tree species weresampled and analyzed for the ⁸⁷Sr/⁸⁶Sr ratio, total SrandCa content. Atmospheric deposition was collected and analyzed for the sameconstituents. Optical analysis showed that biotite and plagioclaseconcentrations were lower in the soil beneath hemlock than beneath sugar mapleand suggested species effects on mineral weathering in the upper 10cm of the mineral soil. These results could not be confirmed withdata obtained by the Sr isotope study. Within the sensitivity of the Sr isotopemethod, we could not detect tree species effects on Ca weathering andcalculatedCa weathering rates were low at all sites (< 60mgm^–2yr^–1). Wefound a positive correlation between Ca weathering and the total Caconcentration in the surface soil. These results indicate that the absolutedifferences in Ca weathering rate between tree species in these acidic surfacesoils are small and are more controlled by the soil parent material(plagioclasecontent) than by tree species.     

'Clay hutches': a novel interaction between bacteria and clay minerals

Biofilm formation on a low-energy substratum floating on the surface of a water column overlying a polychlorinated biphenyl (PCB)-contaminated sandy clay soil was followed by light and electron microscopy. The biofilms that developed consisted of a dense lawn of clay aggregates, each one of which contained one or more bacteria, phyllosilicates and grains of iron oxide material, all held together by bacterial extracellular polysaccharides (EPS). The clay leaflets were arranged in the form of 'houses of cards' and gave the aggregates the appearance of 'hutches' housing the bacteria. Interestingly, although the soil is poor in carbon, and the weakly bioavailable PCBs constitute the principal source of carbon in this system, the bacteria contained electron-transparent structures presumed to be carbon storage granules. These, and the EPS material present in the hutches, indicate that carbon is not limiting in this system and, as PCBs have been found associated with the clay mineral fraction of the floating substratum, the clay particles may serve as carbon shuttles. The interesting possibilities that the 'clay hutches' may represent a 'soil microhabitat', a 'minimal nutritional sphere' and an 'effective survival unit' for autochthonous bacteria are noted. The formation of clay hutches by bacteria would seem to merit further investigation, particularly regarding their roles in bacterial processes in soil and in geological processes.     

A major role for nitrification in the weathering of minerals of brown acid forest soils

Experiments employing lysimeters and a comparison of soil leachates at >‐0.03 MPa and soil solutions extracted at ‐2.5 MPa showed the importance of nitrification in the weathering of minerals of brown acid forest soils (dys‐trochrept) which are formed over large areas in temperate climates.

Mineralization of litter from plants characteristic of such soils (in particular Festuca silvatica and Abies pectinata) produces large amounts of nitric acid. This bacterial nitrification is responsible for the solubilization of Ca²⁺, Mg²⁺, and K⁺ and must be involved in the slow weathering of minerals by acidolysis and in the biogeochemical cycling of Ca²⁺, Mg²⁺, and K⁺ in these soils. Soil solutions extracted at ‐2.5 MPa reflect much more the microbial activity than the leachates from soil and provide interesting information.     

Toxicity of cadmium to twoStreptomyces species as affected by clay minerals

Summary The effect of cadmium on the growth ofStreptomyces rimosus andS. bottropensis (both isolated from soil) was investigated. The modifying effect of the presence of the clay minerals kaolinite, bentonite and vermiculte on Cd toxicity was also included. After four days no growth was observed at 100 ppm CdCl₂ ofS. bottropensis and at 150 ppm in case ofS. rimosus. After six days some growth ofS. rimosus occurred at 150 ppm CdCl₂ and ofS. bottropensis at 100 ppm. Addition of the three clay minerals decreased the Cd toxicity considerably.     

Interactions between clay minerals and siderophores affect the respiration of Histoplasma capsulatum

The reduction in the respiration of Histoplasma capsulatum in broth culture caused by montmorillonite appeared to be the result, in part, of the interference by the clay with the iron nutrition of the fungus. This interference was apparently the result of the adsorption by the clay of the iron-transporting siderophore (deferricoprogen B) produced by the fungus, as the reduction in respiration was partially alleviated by the addition of foreign siderophores. Neither kaolinite nor attapulgite (palygorskite) appeared to adsorb significant amounts of the siderophores, probably because of the low cation exchange capacity and specific surface area of kaolinite and the inaccessibility of adsorption sites in the fibrous attapulgite. These observations, in addition to the adhesion of montmorillonite to the hyphae, suggest mechanisms that may explain the discrete geographic distribution of this fungus, which is pathogenic to humans and which has been isolated essentially only from soils that do not contain montmorillonite.     

Maximum tree: a consistent estimator of the species tree

We propose a model based approach to use multiple gene trees to estimate the species tree. The coalescent process requires that gene divergences occur earlier than species divergences when there is any polymorphism in the ancestral species. Under this scenario, speciation times are restricted to be smaller than the corresponding gene split times. The maximum tree (MT) is the tree with the largest possible speciation times in the space of species trees restricted by available gene trees. If all populations have the same population size, the MT is the maximum likelihood estimate of the species tree. It can be shown the MT is a consistent estimator of the species tree even when the MT is built upon the estimates of the true gene trees if the gene tree estimates are statistically consistent. The MT converges in probability to the true species tree at an exponential rate.     

Biological inhibition of soil nitrification by forest tree species affects Nitrobacter populations

Some temperate tree species are associated with very low soil nitrification rates, with important implications for forest N dynamics, presumably due to their potential for biological nitrification inhibition (BNI). However, evidence for BNI in forest ecosystems is scarce so far and the nitrifier groups controlled by BNI-tree species have not been identified. Here, we evaluated how some tree species can control soil nitrification by providing direct evidence of BNI and identifying the nitrifier group(s) affected. First, by comparing 28 year-old monocultures of several tree species, we showed that nitrification rates correlated strongly with the abundance of the nitrite oxidizers Nitrobacter (50- to 1000-fold changes between tree monocultures) and only weakly with the abundance of ammonia oxidizing archaea (AOA). Second, using reciprocal transplantation of soil cores between low and high nitrification stands, we demonstrated that nitrification changed 16 months after transplantation and was correlated with changes in the abundance of Nitrobacter, not AOA. Third, extracts of litter or soil collected from the low nitrification stands of Picea abies and Abies nordmanniana inhibited the growth of Nitrobacter hamburgensis X14. Our results provide for the first time direct evidence of BNI by tree species directly affecting the abundance of Nitrobacter.     

Ectomycorrhizal weathering of the soil minerals muscovite and hornblende

Ectomycorrhizal fungi are hypothesized to enhance mineral weathering in forest soils. Several studies have shown an increased uptake of mineral-derived nutrients by trees when in symbiosis with ectomycorrhizal fungi. However, it is difficult to determine from these studies if the improved nutrient uptake is the result of increased weathering or better exploitation of the substrate by the ectomycorrhizal fungi. In a pot experiment, Pinus sylvestris (Scots pine) seedlings were grown with or without ectomycorrhizal fungi, and with or without the mineral muscovite as the only potassium (K) source or the mineral hornblende as the only magnesium (Mg) source. After 27 wk, all pools of non-mineral-bound K or Mg were determined. The ectomycorrhizal fungus Paxillus involutus increased weathering of muscovite but not hornblende. The other ectomycorrhizal fungi tested, Piloderma croceum and Suillus bovinus, did not increase weathering of either muscovite or hornblende compared with the nonmycorrhizal trees. The P. involutus-mediated mobilization of K from muscovite resulted in increased K content of root plus adhering hyphae, but not of shoots. In conclusion, ectomycorrhizal fungi may increase weathering of minerals in response to nutrient deficiencies, but this response is species specific.     

Interactions between clay minerals and siderophores affect the respiration of Histoplasma capsulatum.

The reduction in the respiration of Histoplasma capsulatum in broth culture caused by montmorillonite appeared to be the result, in part, of the interference by the clay with the iron nutrition of the fungus. This interference was apparently the result of the adsorption by the clay of the iron-transporting siderophore (deferricoprogen B) produced by the fungus, as the reduction in respiration was partially alleviated by the addition of foreign siderophores. Neither kaolinite nor attapulgite (palygorskite) appeared to adsorb significant amounts of the siderophores, probably because of the low cation exchange capacity and specific surface area of kaolinite and the inaccessibility of adsorption sites in the fibrous attapulgite. These observations, in addition to the adhesion of montmorillonite to the hyphae, suggest mechanisms that may explain the discrete geographic distribution of this fungus, which is pathogenic to humans and which has been isolated essentially only from soils that do not contain montmorillonite.     

Relationship between leaf characteristics, tree sizes and species distribution along a slope in a warm temperate forest

The relationships between some leaf characteristics, tree size and species distribution were investigated for evergreen tree species along a slope in a warm temperate forest in Japan. Tree species were classified into three groups based on their dominance on the slope: ridge species that were aggregated in an uppersite, valley species that were aggregated in a lowersite, and uniform species that were distributed almost uniformly. The ridge species had a more positive leaf carbon isotope ratio than the valley species, which suggests that the ridge species have larger water use efficiency than the valley species. This may give some advantage to the ridge species over the valley species in the uppersite where water availability would be limited. However, the ridge species had smaller leaf nitrogen content on a mass basis and larger leaf mass per area than the valley species, which suggests that the ridge species had a smaller mass-based leaf photosynthetic capacity than the valley species. This may be disadvantageous to ridge species in the lowersite, because smaller leaf photosynthetic capacities cause lower leaf carbon gain and thus lower growth than the valley species. These differences in leaf characteristics between the ridge and the valley species were affected by microenvironments, and were also partly affected by the difference in species specific responses to microenvironments on the slope.     

Influence of tree species and ground vegetation on nitrification in an acid forest soil

Soil N transformations were studied at Ironhill, near Liphook, UK as part of a forest fumigation experiment. Nitrification potential was measured in a humoferric podzol soil, of pH 3 (in 0.01 M CaCl₂). An initial experiment into nitrogen mineralisation potential indicated that nitrification was linked strongly to the species of coniferous tree growing in the soil. Transfer of soil solution between soils had no influence on mineralisation potential and allelopathic effects of the trees were not demonstrated. The initial finding was attributed subsequently to the type of ground vegetation and its management. Attempts to reproduce soil conditions, which promoted nitrification, were partially successful.Soil, from the Ironhill site, was incubated with various nitrogenous substrates and other nutrients and sources of carbon to test whether heterotrophs were responsible for nitrification. Organic N (which was ammonified) promoted nitrification, but the addition of ammonium was inhibitory unless supplied with a readily available carbon source such as acetate. Nitrification potential was unaffected when soils were incubated with an inhibitor of autotrophic nitrification. The results of these experiments supported strongly the hypothesis that heterotrophic organisms were responsible for nitrification in this soil.     

Relationship between the timing of vessel formation and leaf phenology in ten ring-porous and diffuse-porous deciduous tree species

The goal of this study is to clarify how different aspects of plant function are coordinated developmentally for species of ring-porous versus diffuse-porous deciduous trees, comparing the timing of leaf phenology and vessel formation in twigs and stems from an ecophysiological viewpoint. Cylindrical stem cores and twigs were collected at intervals from early spring through summer from five ring-porous and five diffuse-porous species in a cool temperate forest, and leaf and vessel formation were observed simultaneously. We found that the first-formed vessels of the year were lignified in twigs around the time of leaf appearance and at or before full leaf expansion of each tree in both groups of species with flush-leaves. Vessels in stems were lignified 2 weeks before to 4 weeks after leaf appearance and before or around full leaf expansion of the tree in ring-porous species. This was significantly earlier than in diffuse-porous species, in which stem vessel lignification was 2–8 weeks after leaf appearance and at or after full leaf expansion of the tree. The timing of vessel formation in twigs compared to stems was significantly earlier in ring-porous species than in diffuse-porous species. Lignification of vessels in stems occurred within 2 weeks of lignification in the twigs of ring-porous species and 2–8 weeks after lignification in twigs of diffuse-porous species. These results indicate the order and time-lag of leaf and vessel formation. Ring-porous species showed intensive leaf/vessel production, whereas diffuse-porous species showed less intensive leaf/vessel production.     

南亚热带混交人工林树种丰富度与土壤微生物多样性和群落组成的关系

森林植被与土壤微生物作为森林生态系统的重要组成部分,它们之间的相互作用对维持森林生态系统功能和稳定性起着重要作用。以往多在天然草地和森林生态系统开展植物多样性与土壤微生物多样性关系的研究,但人工构建的多树种混交林生态系统中树种多样性对土壤微生物群落组成的影响及其机制尚不完全清楚。因此,以南亚热带人工块状造林后自然恢复形成的多树种混交森林生态系统为研究对象,利用高通量测序技术研究了随树种丰富度(1—10种)变化土壤细菌和真菌多样性的变化规律及主要影响因子。结果表明,随树种丰富度增加,土壤真菌α多样性显著提高,但土壤细菌α多样性差异不显著;不同树种丰富度梯度间土壤细菌和真菌的群落结构组成均差异显著;Pearson相关分析表明土壤细菌α多样性主要受土壤pH和土壤铵态氮影响,而土壤pH和有效磷是土壤真菌α多样性的主要影响因子。距离冗余分析(db-RDA)表明,对土壤细菌群落组成产生显著影响的环境因子分别为土壤pH、硝态氮和芳香碳组分,而土壤有机碳、硝态氮、细根生物量和氧烷基碳组分是影响土壤真菌群落组成的主要因子。本研究的结果说明了南亚热带人工林不同树种混交后形成多树种混交林生态系统的过程中,树...     

Chemical weathering of soil minerals and the role of biological processes

Existing weathering models based on direct, abiotic factors, and biological factors through systemic feedbacks seem to describe the weathering rates observed in the field with good accuracy. The Swedish weathering rate model, PROFILE is the only existing model with this capacity. The PROFILE model is widely used and has been used successfully in sustainability assessments for forests and agriculture. The author has reviewed available experiments, as well as existing knowledge on chemical weathering kinetics and concludes that the physical and chemical conditions existing in forest soils do not allow any significant direct surface actions on minerals by microorganisms or tree roots. The reported tracks and holes in minerals have been mistakenly identified as being produced by roots, but this misunderstanding is caused by a lack of understanding of crystallography and chemical dissolution mechanisms. The holes and tracks have been produced by known chemical mechanisms.     

Floodwater infiltration through root channels on a sodic clay floodplain and the influence on a local tree species Eucalyptus largiflorens

Dieback of riparian species on floodplains has been attributed to increased soil salinisation due to raised groundwater levels, resulting from irrigation and river regulation. This is exacerbated by a reduction in flooding frequency and duration of inundation. For the Chowilla floodplain on the River Murray raised water tables have increased the amount of salts mobilised in the soil profile, causing the trees to experience salt induced water stress. For the trees to survive in the long term, salts need to be leached from the root zone.This study investigated whether floodwater infiltrates through channels created by E. largiflorens (black box) roots, flushing salts away from roots, thereby allowing the trees to increase their water uptake. Trees at different sites on the floodplain were artificially flooded, by pumping 1.5 kL of creek water into impoundments constructed around the trees. Gas exchange parameters, and pre-dawn and midday water potential were measured the day before, the day after and one week after the artificial flood and compared against trees that were not flooded. Pre-dawn and midday water potentials were also measured one month after the flood. After flooding, the trees experienced less water stress, indicated by an increase in water potential of less than 0.2 MPa, in comparison to non-flooded control trees. However, this response was not evident one month after flooding. The response to flooding did not result in increased rates of transpiration, stomatal conductance or photosynthesis, even though flooding effectively doubled the trees yearly water supply.The infiltration of floodwater in the impoundments around E. largiflorens was also compared to that of impoundments on bare ground. Floodwater infiltrated 2 – 17 times faster around trees than on adjacent bare ground, for parts of the floodplain not grazed by livestock. Tracer dye experiments indicated that bulk flow of water through pores down the profile was the reason for the enhanced infiltration. Flooding leached salts in direct vicinity of tree roots, but only leached small amounts of salts from the bulk soil.     

Smoke-water effect on the germination of Amazonian tree species

Smoke stimulates seed germination of a range of species from ecosystems that may or may not be fire prone. We evaluated the effects of smoke-water on germination of ten tree species of economic value in the Amazon region. Two materials were burnt to produce smoke-water: germination paper and the wood of Cecropia palmata Willd. Seven dilutions of the solutions were tested. Seeds of nine forest trees were germinated under controlled laboratory conditions (25 °C ± 2 °C) in the laboratory. Bertholletia excelsa Humb. & Bonpl., was tested in the nursery (approximately 25–36 °C) because of its large seeds. Irrespective of the material burned, smoke-water significantly increased seed germination of three species: Cordia goeldiana Hub., Ochroma pyramidale (Cav. ex Lam.) Urb. and Jacaranda copaia (Aubl.) D. Don. and there was a significant inhibitory effect on Swietenia macrophylla King. Germination was accelerated by smoke in J. copaia, B. excelsa and Bellucia grossularioides (L.) Triana. The most pronounced effect was observed in B. excelsa, as the mean germination time of 108 d (control) was reduced to 76 d with smoke-water made from germination paper (dilution of 1:25) and to 61 d with the one from Cecropia wood (dilution of 1:250). For five of the ten species studied, smoke-water either increased or accelerated seed germination, irrespective of the materials used for its production. Seeds with low vigour and prolonged germination time seemed to be more receptive to smoke.     

美国白蛾危害前后树木蛋白质含量与抗虫性关系

以廊坊市主要园林绿化树种白蜡(Fraxinus chinensis Rosb.)、法国梧桐(Platanus orientalis L.)、桑树(Morus alba L.)、臭椿(Ailanthus altissima(Mill.)Swingle)、毛白杨(Populus tomentosa Carr.)和香椿(Toona sinensis(A.Juss.)Roem.)为目标树种,于2014年9月在其3年生林地中进行美国白蛾(Hyphantria cunea(Drury))人工接种试验,并用目标树种的离体叶片饲喂美国白蛾的幼虫,统计其食叶量,同时测定目标树种非自然侵染前后可溶性蛋白质含量的变化。结果表明:美国白蛾对目标树种取食量的高低顺序为桑树法国梧桐臭椿白蜡毛白杨香椿;美国白蛾取食2、4、6、8、10 d后,对美国白蛾抗性低的桑树、法国梧桐、臭椿、白蜡的可溶性蛋白质含量呈现先上升后下降的趋势,而对美国白蛾抗性高的毛白杨体内蛋白质含量首先表现出降低趋势,但二者均表现为被持续取食10 d后体内蛋白质含量低于取食前和对照;表明不同树种(耐虫和感虫)受美国白蛾侵害后蛋白质含量变化规律不同,抗虫性高低与蛋白质含量的高低没有对应关系。