Biological and geochemical controls on phosphorus fractions in semiarid soils

This study examined the concentration of organic and inorganicphosphorus in surface soils of a Boutelouagracilis-Bouteloua eriopoda grassland, and a Larreatridentata shrubland, in the northern Chihuahuan Desert, NewMexico, U.S.A. In this desert where the grassland vegetation has auniform spatial distribution and individual shrubs have a patchy spatialdistribution across the landscape, vegetation strongly influences thedistribution of soil nutrients. Most studies of soil phosphorusfractions in desert soils have focused primarily on inorganic Pfractions and have demonstrated the importance of geochemical controlson soil P cycling. The research presented here addressed the question ofwhether organic phosphorus, determined by the presence of differentvegetation types, also contributes to soil P cycling. Within soils ofsimilar age, topography, parent material, and climatic regime, sampleswere collected under and between vegetation and analyzed for P fractionsfollowing a modified sequential fractionation scheme. Most soilinorganic P was found in the HCl- and cHCl-extractable forms in both thegrassland and shrubland soils, indicating CaCO₃ control overphosphorus availability. In contrast, most soil organic P was bound toAl and Fe minerals. Labile, plant-available P fractions summed to9.5% of total P in the grassland and 6.1% in theshrubland. Organic P comprised 13.3% of the total phosphorus poolin the grassland and 12.0% in the shrubland. Our results showthat the organic P pool may represent an important, yet oftenoverlooked, source of P in semiarid ecosystems.     

Determination of available phosphorus for phytoplankton populations in lakes and rivers of southeastern Norway

A biotest method with diluted phytoplankton populations was used to determine external concentrations of available phosphorus in water samples with high concentrations of inorganic seston from River Rømua. RP (total molybdate reactive P measured on unfiltered samples) was approximately the P fraction available for Synedra cf. acus, Asterionella formosa and Oscillatoria agardhii. In filtered samples RP_F was the available concentration of P.The ratio RP:RP_F may give valuable information on the ratio between total available P (including available P in seston) and available P in filtered water. Different filter types may give different RP: RP_F ratios. The ratio RP:RP_F was often high during spring and autumn in River Rømua and the lakes studied. During the period June–September RP:RP_F 1 in most of the lakes and periodically in River Rømua.     

土壤中积累态磷的化学耗竭

积累态P是指肥料P未被植物利用而积累于土壤中的那一部分P素,本文用一次平衡法、流动技术法和阴离子树脂膜等不同方法来研究土壤中积累态P的化学耗竭。研究表明,解吸出的P量随时间的增加而增加,P解吸过程符合二级动力学方程,各处理中P的释放过程快慢程度是PK＞NPK＞NK,红壤的释放量和释放速度均比潮土的要大且快。解吸P量与土壤速效P和植物吸收P均有显著相关。土壤中积累态P最大表观利用率为总P量的45％左右。     

Uptake of nitrogen and phosphorus in relation to soil structure and nutrient mobility

Summary Nitrogen and phosphate uptake by young plants was studied in experiments, mainly using artificial aggregates of different sizes. Large impenetrable aggregates brought about coarse rooting, while in the finer substrates dense root growth was possible. Coarse rooting resulted diminished uptake of the mainly immobile stock of phosphate. Nitrate uptake, however, was hardly influenced by rooting density on account of its high mobility and transport along with the extracted water. On the finer substrates the plants absorbed more phosphate and therefore the N/P ratio was lower.Implications of this effect of soil structure on uptake are indicated.     

Effects of water additions,chemical amendments,and plants on in situ measures of nutrient bioavailability in calcareous soils of southeastern Utah,USA

Barren, subgrade serpentine substrates are difficult to revegetate due to N, P, and K deficiencies, low Ca:Mg molar ratios, potentially high levels of heavy metals including Ni, Cr, and Co, low organic matter, low CEC, and poor water holding capacity. Several large, bare roadcuts exist in the North Coast Ranges along the west coast of California, USA. Substrate was collected from a large roadcut that has remained barren for more than a decade despite conventional surface amendment with NPK fertilizer and seeding with a mix including nonserpentine grasses and herbs. Although serpentine plant communities have been studied globally in great detail, very little information exists on how to effectively restore these communities after drastic disturbance (removal of topsoil and loss of biological activity). This rhizotron study examined how surface layering and mixing yard waste compost into serpentine substrate affected biomass production, rooting distribution, and tolerance of native, as well as invasive grass species that grow on serpentine. Roots of less serpentine-tolerant species became necrotic upon contact with the serpentine substrate in the layered compost application treatment. The roots of highly serpentine-tolerant species, however, displayed a superior tolerance to the serpentine substrate and were able to grow through its entire depth. Mixing the compost into the serpentine substrate significantly improved the Ca content of the growing medium, allowing the less serpentine-tolerant species to root through the entire depth. Although the compost surface layer treatment promoted growth of the highly serpentine-tolerant species in the serpentine substrate, mixing the compost amendment into the substrate would also permit additional desirable revegetation species to become established.     

Chemical speciation and risks of heavy metals in sediment of urban wetlands in southeastern China

Dredging, remediation, and other management of sediment in polluted urban wetlands require the information of environmental risks associated with heavy metals (HMs). In this study, sediment samples collected from three typical wetlands in the urban area of Wenzhou City, China, were analyzed to evaluate their risks posed by five HMs. Sediments from an industrial area stored higher Cr and Cu but lower Cd and Pb than those from the residential and agricultural areas. The assessment by the pollution load index method indicated that all of the three study wetlands were polluted. An ecological risk index approach identified low risk for wetlands in forested and residential areas but high risk for wetlands in an industrial area as well as in mixed residential and agricultural area, which was also confirmed by the geo-accumulation index (I_geo) method. Furthermore, the ratio of the secondary phase and primary phase and risk assessment code methods recognized that Cd poses a high pollution risk. The results indicated that sediment pollution by HMs in urban wetlands is possibly a widespread problem in China and needs great attention.     

Docking of axonal mitochondria by syntaphilin controls their mobility and affects short-term facilitation

Proper distribution of mitochondria within axons and at synapses is critical for neuronal function. While one-third of axonal mitochondria are mobile, a large proportion remains in a stationary phase. However, the mechanisms controlling mitochondrial docking within axons remain elusive. Here, we report a role for axon-targeted syntaphilin (SNPH) in mitochondrial docking through its interaction with microtubules. Axonal mitochondria that contain exogenously or endogenously expressed SNPH lose mobility. Deletion of the mouse snph gene results in a substantially higher proportion of axonal mitochondria in the mobile state and reduces the density of mitochondria in axons. The snph mutant neurons exhibit enhanced short-term facilitation during prolonged stimulation, probably by affecting calcium signaling at presynaptic boutons. This phenotype is fully rescued by reintroducing the snph gene into the mutant neurons. These findings demonstrate a molecular mechanism for controlling mitochondrial docking in axons that has a physiological impact on synaptic function.     

Effects of land use in the drainage area on phosphorus binding and mobility in the sediments of four drinking-water reservoirs

The study of four drinking-water reservoirsdemonstrates how the anthropogenic land use of acatchment may affect binding and mobility ofphosphorus in the sediment. P_diss concentrationgradients at the sediment–water interface weremeasured to calculate potential diffusive releaserates. P binding forms were determined by sequentialextraction of fresh sediment and settling seston. Mainstudy sites were Saidenbach Reservoir (mesotrophic,densely populated drainage area with 73% agriculturalland use) and Neunzehnhain Reservoir (oligotrophic,unpopulated drainage area forested to 80%) in thesilicate-rich Erzgebirge mountains of eastern Germany.Tot-P concentrations and P binding forms of typicalerosive matter from each catchment were similar to thesediment of both pre-reservoirs and reservoirs' mouth.In Saidenbach Reservoir, diatoms responded to highnutrient loading by incorporating ortho-P. Whilesettling, the org-P was partly transformed toFe(OOH)P. Apart from hypolimnetic O₂depletion, this P binding form dominated in thesurface sediment mainly in front of the dam. Withincreasing sediment depth, org-P and Fe(OOH)Pnot only redissolved into the pore water, but alsoadsorbed onto Al compounds. In Neunzehnhain Reservoir,acidification of the low buffered catchment favouredloading of humic compounds and Al³+ ions, whichprecipitated and redox-independently adsorbed ortho-Pdue to a pH increase in the lake. Neunzehnhainsediment was able to immobilize Fe(OOH)P fromSaidenbach sediment in a batch experiment. Comparativesequential P extraction of sediment from SosaReservoir (oligo-mesotrophic, sparsely populateddrainage area forested to 94%) and Kleine KinzigReservoir (nearly unpopulated drainage area forestedto 98%) also demonstrated effective P immobilizationby Al-/humic compounds.It is concluded that the absence of settlements in thecatchment, together with forestry as dominating landuse, favour not only oligotrophic conditions in thereservoir but also confine internal P loading from thesediment. But attention should be paid toacidification problems.     

Chemical mobility and bioavailabity of sediment-bound heavy metals influenced by salinity

The transfer of metals from contaminated sediments to algal cell walls (Scenedesmus quadricauda) and organisms from various trophic levels (euryhaline osmoconform hydroid Cordylophora caspia and algae Brachiomonas submarina) was studied with a multichamber device. The system consists of a central chamber which contained the mud suspension and six external chambers containing the different biological indicators. The solids in the central and external chambers are separated by 0.45 m-diameter membranes which allow diffusion of the mobilized, dissolved metal compounds. Experiments were performed with dredged sediments at various salinities (0.5, 1.0, 1.5, and 2.0 percent, respectively) and the kinetic of re-adsorption was obtained by taking samples after different time intervals. High enrichment of Cd was found in the living alga Brachiomonas submarina, but on the other side only a weak influence of salinity on re-adsorption could be observed. Model experiments with ionic Cd showed a clear dependency on Cd-sorption on the algae, Cd-concentration in solution, and salinity. These results indicate that the transfer of metals mainly depends on the specific surface properties of the substrates and on the specific chemical form of the dissolved mobilized metal.     

A new species of Eremogone (Caryophyllaceae) from northern Utah and southeastern Idaho, U.S.A.

A name (Eremogone loisiae) is provided for those plants from northern Utah and southeastern Idaho that have gone under the misapplied name Eremogone kingii subsp. uintahensis. Eremogone loisiae, named in honor of Lois A. Arnow, is distinguished from E. kingii by its longer and narrower, flexuous leaves and its longer sepals, petals, styles, capsules, and seeds.     

Soil phosphorus supply controls P nutrition strategies of beech forest ecosystems in Central Europe

Phosphorus availability may shape plant–microorganism–soil interactions in forest ecosystems. Our aim was to quantify the interactions between soil P availability and P nutrition strategies of European beech (Fagus sylvatica) forests. We assumed that plants and microorganisms of P-rich forests carry over mineral-bound P into the biogeochemical P cycle (acquiring strategy). In contrast, P-poor ecosystems establish tight P cycles to sustain their P demand (recycling strategy). We tested if this conceptual model on supply-controlled P nutrition strategies was consistent with data from five European beech forest ecosystems with different parent materials (geosequence), covering a wide range of total soil P stocks (160–900 g P m^?2; <1 m depth). We analyzed numerous soil chemical and biological properties. Especially P-rich beech ecosystems accumulated P in topsoil horizons in moderately labile forms. Forest floor turnover rates decreased with decreasing total P stocks (from 1/5 to 1/40 per year) while ratios between organic carbon and organic phosphorus (C:P_org) increased from 110 to 984 (A horizons). High proportions of fine-root biomass in forest floors seemed to favor tight P recycling. Phosphorus in fine-root biomass increased relative to microbial P with decreasing P stocks. Concomitantly, phosphodiesterase activity decreased, which might explain increasing proportions of diester-P remaining in the soil organic matter. With decreasing P supply indicator values for P acquisition decreased and those for recycling increased, implying adjustment of plant–microorganism–soil feedbacks to soil P availability. Intense recycling improves the P use efficiency of beech forests.     

Chemical state analysis of sulfur and phosphorus in biological samples by X-ray fluorescence

Double-crystal high-resolution X-ray fluorescence spectroscopy was applied to the chemical state analysis of sulfur and phosphorus in biological samples of leaves and bones. Both S²⁻ and S⁶⁺ states are present in all leaves. In plants infected with the mosaic virus, the abundance of S²⁻ state was found to be less than normal. Furthermore, the total sulfur content of leaves with the mosaic virus was less than that in normal leaves. From these results we have concluded that the mosaic virus is related to the decrease in cysteine sulfur (S²⁻), which is an essential component in amino acids. Most of the phosphorus in leaves and bones was found to be in P⁵⁺ state. A small amount of P³⁺ state, however, was also detected.     

Lateral mobility of the light-harvesting complex in chloroplast membranes controls excitation energy distribution in higher plants

Chloroplast thylakoid protein phosphorylation produces changes in light-harvesting properties and in membrane structure as revealed by freeze-fracture electron microscopy. Protein phosphorylation resulted in an increase in the 77 °K fluorescence signal at 735 nm relative to that at 685 nm. In addition, a decrease in connectivity between Photosystem II centers (PS II) and a dynamic quenching of the room temperature variable fluorescence was observed upon phosphorylation. Accompanying these fluorescence changes was a 23% decrease in the amount of stacked membranes. Microscopic analyses indicated that 8.0-nm particles fracturing on the P-face moved from the stacked into the unstacked regions upon phosphorylation. The movement of the 8.0-nm particles was accompanied by the appearance of chlorophyll b and 25 to 29 kD polypeptides in isolated stroma lamellae fractions. We conclude that phosphorylation of a population of the light-harvesting chlorophyll $\text{a}\text{b}$ protein complexes (LHC) in grana partitions causes the migration of these pigment proteins from the PS II-rich appressed membranes into the Photosystem I (PS I) enriched unstacked regions. This increases the absorptive cross section of PS I. In addition, we suggest that the mobile population of LHC functions to interconnect PS II centers in grana partitions; removal of this population of LHC upon phosphorylation limits PS II → PS II energy transfer and thereby favors spillover of energy from PS II to PS I.     

Performance of Bromus tectorum L. in relation to soil properties, water additions, and chemical amendments in calcareous soils of southeastern Utah, USA

In drylands of southeastern Utah, USA, the invasive exotic grass Bromus tectorum L. occurs in distinct spatial patterns suggesting soil control of ecosystem susceptibility to invasion. To improve our understanding of these patterns, we examined performance of B. tectorum in relation to additions of water, KCl, MgO, and CaO at seventeen 1600 m² sites distributed across a calcareous soil gradient in Canyonlands National Park. Water additions resulted in a 57% increase in B. tectorum establishment. Fall establishment was significantly correlated with silt and clay content in wet plots but not in dry plots, suggesting that texture effects on B. tectorum establishment patterns may be greater in wet years than in dry years. Applications of MgO resulted in a 49% decrease in B. tectorum establishment, although MgO had no effect on whole-plot biomass at the end of the growing season. B. tectorum–soil relations were strongest during winter (December–March) when relative growth rates were negatively related to soil acid-neutralizing potential, sand and CaCO₃ content, and a measure of bioavailable Mg; and positively related to silt and clay content, total N, measures of bioavailable Mn, P, and K, and a measure of magnetite indicating distributional patterns of eolian dust. As soils were persistently moist during this period, we attribute strong B. tectorum–soil patterns in winter to effects of low temperature on diffusion, microbial activity, and/or production of root exudates important for nutrient mobilization and uptake. In spring, there was a reversal in B. tectorum–soil relations such that loamy soils with higher B. tectorum densities were unfavorable for growth relative to sandy soils with higher warm-season water potentials. We conclude that resource limitations for B. tectorum in this study area shift seasonally, from water limitation of fall establishment, to nutrient limitation of winter growth, and back to water limitation of spring growth. Because study sites generally were arrayed along a hillslope gradient with downslope trends in soil vtexture and nutrient content, close B. tectorum–soil relations documented in this study indicate that a geomorphic framework is useful for understanding and predicting B. tectorum invasion patterns in dryland ecosystems of this region.Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users. Section Editor: T. KalaposThe U.S. Government’s right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged     

Mediterranean drylands: The effect of grain size and domain of scale on landscape metrics

This study first sought to isolate a select group of landscape metrics particularly well-suited for describing dryland Mediterranean landscapes in Jordan. We examined the response of 50 landscape metrics to a large range of imagery grain sizes. Most of the metrics exhibited an expected behavior, similar to what has been previously reported in literature such as (a) a predictable (linear or power law) response to changing grain size, and (b) an unpredictable (staircase-like or erratic) response to changing grain size. Some metrics, however, exhibited a domain of scale effect, in particular the core area metrics. Using correlation analysis, the original 50 metrics were placed into 19 groups such that all metrics within a group were strongly correlated with each other, and were represented by a single representative metric. Using these representative metrics in the context of principal components analysis, we then found that six factors explained 95.35% of the total variation found in the landscape pattern. The highest loadings for these six factors, in order, were the number of patches (NP), mean proximity index (PROX_MN), largest patch index (LPI), patch cohesion index (COHESION), total core area (TCA), and the proximity index coefficient of variation (PROX_CV). It was concluded that east Mediterranean landscapes with a long history of anthropogenic-driven change showed a domain of scale for core area metrics. We also recommend that the majority of the pattern in dry Mediterranean landscapes, particularly those in Jordan, can be described with six metrics. We suggest that our procedure for landscape metric selection can be utilized in other regions of study as well.     

Chemical and phylogenetic relationships among Aristolochia L. (Aristolochiaceae) from southeastern Brazil

In this report, a molecular phylogeny based on the plastid gene matK and on the region between the genes trnL and trnF, and a chemical relationship based on the pattern of sesquiterpenes, is proposed for Aristolochia species from southeastern Brazil. We found that Aristolochia is a monophyletic genus and species considered to be derived contain labdanoic acids (LAs) in their leaves. The phenetic relationship recovered with sesquiterpenes did not agree with the phylogenetic relationships for Aristolochia, and three main clusters were recognized, namely, germacrene-D, germacrene-C and Z-caryophyllene groups. The presence of different sesquiterpene structures in species that are phylogenetically closely related may reflect adaptations to avoid predation of herbivores specialized in feeding on Aristolochiaceae plants.     

Impact of hydrodynamics (ex- and infiltration) on the microbially controlled phosphorus mobility in running water sediments of a cultivated northeast German wetland

To gain insight into the impact of hydrodynamics (ex- and infiltration) on microbial activities, the microbial community structure, and the dynamics of phosphate and other chemical parameters in running water sediments of two transects in a German wetland have been studied. Flow directions and Darcy flow rates at canal bottom were determined using temperature profiles in the groundwater zone near and beneath the canal. Besides the chemical composition of pore water and sediment, a suite of enzyme activities and phosphorus fractions have been analyzed in the sediment. Hydrological analysis proved that at one transect infiltrating and stagnant conditions alter frequently, whereas at the other transect exfiltration dominates. We found significant differences between the transects in microbial activities and organic and iron-bound phosphorus as well as significant correlations between Darcy flux, microbial activities and phosphorus fractions. We conclude that not only the direction and rates of the flow, but also the quantity of changes between ex- and infiltration have an impact on microbial activity, and thus on phosphorus dynamics in the sediment of wetlands.     

Controls of Bedrock Geochemistry on Soil and Plant Nutrients in Southeastern Utah

The cold deserts of the Colorado Plateau contain numerous geologically and geochemically distinct sedimentary bedrock types. In the area near Canyonlands National Park in Southeastern Utah, geochemical variation in geologic substrates is related to the depositional environment with higher concentrations of Fe, Al, P, K, and Mg in sediments deposited in alluvial or marine environments and lower concentrations in bedrock derived from eolian sand dunes. Availability of soil nutrients to vegetation is also controlled by the formation of secondary minerals, particularly for P and Ca availability, which, in some geologic settings, appears closely related to variation of CaCO₃ and Ca-phosphates in soils. However, the results of this study also indicate that P content is related to bedrock and soil Fe and Al content suggesting that the deposition history of the bedrock and the presence of P-bearing Fe and Al minerals, is important to contemporary P cycling in this region. The relation between bedrock type and exchangeable Mg and K is less clear-cut, despite large variation in bedrock concentrations of these elements. We examined soil nutrient concentrations and foliar nutrient concentration of grasses, shrubs, conifers, and forbs in four geochemically distinct field sites. All four of the functional plant groups had similar proportional responses to variation in soil nutrient availability despite large absolute differences in foliar nutrient concentrations and stoichiometry across species. Foliar P concentration (normalized to N) in particular showed relatively small variation across different geochemical settings despite large variation in soil P availability in these study sites. The limited foliar variation in bedrock-derived nutrients suggests that the dominant plant species in this dryland setting have a remarkably strong capacity to maintain foliar chemistry ratios despite large underlying differences in soil nutrient availability.