Disproportionate single-species contribution to canopy-soil nutrient flux in an Amazonian rainforest

Rainfall, throughfall and stemflow were monitored on an event basis in an undisturbed open tropical rainforest with a large number of palm trees located in the southwestern Amazon basin of Brazil. Stemflow samples were collected from 24 trees with a diameter at breast height (DBH) > 5 cm, as well as eight young and four full-grown babassu palms (Attalea speciosa Mart.) for 5 weeks during the peak of the wet season. We calculated rainfall, throughfall and stemflow concentrations and fluxes of Na+, K+, Ca2+, Mg2+,, Cl-, SO42-, NO3- and H+ and stemflow volume-weighted mean concentrations and fluxes for three size classes of broadleaf trees and three size classes of palms. The concentrations of most solutes were higher in stemflow than in rainfall and increased with increasing tree and palm size. Concentration enrichments from rainfall to stemflow and throughfall were particularly high (81-fold) for NO3-. Stemflow fluxes of NO3- and H+ exceeded throughfall fluxes but stemflow fluxes of other solutes were less than throughfall fluxes. Stemflow solute fluxes to the forest soil were dominated by fluxes on babassu palms, which represented only 4% of total stem number and 10% of total basal area. For NO3-, stemflow contributed 51% of the total mass of nitrogen delivered to the forest floor (stemflow + throughfall) and represented more than a 2000-fold increase in NO3- flux compared what would have been delivered by rainfall alone on the equivalent area. Because these highly localized fluxes of both water and NO3- persist in time and space, they have the potential to affect patterns of soil moisture, microbial populations and other features of soil biogeochemistry conducive to the creation of hotspots for nitrogen leaching and denitrification, which could amount to an important fraction of total ecosystem fluxes. Because these hotspots occur over very small areas, they have likely gone undetected in previous studies and need to be considered as an important feature of the biogeochemistry of palm-rich tropical forest. (C) 2011 Elsevier B.V. All rights reserved.

A Two-Stage Aerobic/Anaerobic Denitrifying Horizontal Bioreactor Designed for Treating Ammonium and H2S Simultaneously

A two-stage bioreactor was operated for a period of 140 days in order to develop a post-treatment process based on anaerobic bioxidation of sulfite. This process was designed for simultaneously treating the effluent and biogas of a full-scale UASB reactor, containing significant concentrations of NH4 and H2S, respectively. The system comprised of two horizontal-flow bed-packed reactors operated with different oxygen concentrations. Ammonium present in the effluent was transformed into nitrates in the first aerobic stage. The second anaerobic stage combined the treatment of nitrates in the liquor with the hydrogen sulfide present in the UASB-reactor biogas. Nitrates were consumed with a significant production of sulfate, resulting in a nitrate removal rate of 0.43 kg N m(3) day(-1) and a parts per thousand yen92 % efficiency. Such a removal rate is comparable to those achieved by heterotrophic denitrifying systems. Polymeric forms of sulfur were not detected (elementary sulfur); sulfate was the main product of the sulfide-based denitrifying process. S-sulfate was produced at a rate of about 0.35 kg m(3) day(-1). Sulfur inputs as S-H2S were estimated at about 0.75 kg m(3) day(-1) and Chemical Oxygen Demand (COD) removal rates did not vary significantly during the process. DGGE profiling and 16S rRNA identified Halothiobacillus-like species as the key microorganism supporting this process; such a strain has not yet been previously associated with such bioengineered systems.

Farming Nitrifiers: Main factors and parameters for maintaining healthy cultures

[EN] The atmospheric CO2 level is rising. Its greenhouse effect is partially mitigated by terrestrial (plants) and marine photosynthetic organisms (algae, phytoplankton), and also by the less-known chemosynthetic bacteria. Within this group of bacteria, nitrifiers have a direct and indirect impact on carbon fixation because, on one hand, they are autotrophs and, on the other, they release inorganic nitrogenous nutrients that feed other photoautotrophs. A new assay which simplifies the measurement of nitrification would improve our knowledge about the ocean’s capacity to fix CO2. Knowing how to cultivate these microbes from marine water samples is a first step towards developing new nitrification detection techniques. During the last six months, we have isolated and cultured a natural assembledge of marine nitrifiers. Our larger objective is to develop a way to enzymatically detect nitrification. However, to do this, we need large quantities of nitrifiers. Consequently, at this point, culturing this marine nitrifier community is our priority. We have learned that pH, nutrient levels, air flow, temperature, low light and sterility are critical for growing healthy nitrifiers. With this knowledge we will now be able to conduct experiments with the nitrifiers and develop the methodology that we seek.

Physiological and Biochemical Aspects of Iron Nutrition in Grapevine

The objective of this thesis was to study the response mechanisms of grapevine to Fe-deficiency and to potential Fe chlorosis prevention strategies. The results show that the presence of bicarbonate in the nutrient solution shifted the activity of PEPC and TCA cycle enzymes and the accumulation/translocation of organic acids in roots of Fe-deprived plants. The rootstock 140 Ruggeri displayed a typical behavior of calcicole plants under bicarbonate stress. The Fe chlorosis susceptible rootstock 101-14 reacted to a prolonged Fe-deficiency reducing the root activity of PEPC and MDH. Noteworthy, it accumulates high levels of citric acid in roots, indicating a low capacity to utilizing, transporting and/or exudating organic acids into the rhizosfere. In contrast, 110 Richter rootstock is capable to maintain an active metabolism of organic acids in roots, accumulating them to a lesser extent than 101-14. Similarly to 101-14, SO4 genotype displays a strong decrease of mechanisms associated to Fe chlorosis tolerance (PEPC and MDH enzymes). Nevertheless it is able to avoid excessive accumulation of citric acid in roots, similar as 110 Richter rootstock. Intercropping with Festuca rubra increased leaf chlorophyll content and net photosynthesis. In addition, intercropping reduces the activity of PEPC in roots, similary to Fe-chelate supply. Applications of NH4+ with nitrification inhibitor prevents efficiently Fe-deficiency, increases chlorophyll content, and induces similar root biochemical responses as Fe-EDDHA. Without the addition of nitrification inhibitors, the effectiveness of NH4+ supply on Fe chlorosis prevention resulted significantly lower. The aspects intertwined in this investigation highlight the complexity of Fe physiology and the fine metabolic tuning of grapevine genotypes to Fe availability and soil-related environmental factors. The experimental evidences reveal the need to carry out future researches on Fe nutrition maintaining a continous flow of knowledge between theoretical and agronomical perspectives for fully supporting the efforts devoted to convert science into practice.

Use of isotopes for studying nitrogen processes in a wetland within the Venice Lagoon watershed

The present study is based on the use of isotopes for evaluating the efficiency of nutrients removal of a wetland, in particular nitrogen and nitrates, also between the different habitats present in the wetland. Nutrients like nitrogen and phosphorus, normally distributed as fertilizers, are among the principal causes of diffuse pollution. This is particularly important in the Adriatic Sea, which is frequently subjected to eutrophication phenomena. So it is very crucial requalification of wetland, in which there are naturally depurative processes such as denitrification and plant uptake, which allow the reduction of pollutant loads that flow in water bodies. In this study nutrient reduction is analyzed in the wetland of the Comuna drain, which waters flow in the Venice lagoon. Chemical and isotopical analyses were performed on samples of water, vegetation, soil and sediments taken in the wetlands of the Comuna drain in four different periods of the year and on data of nitrogen and phosphorus concentration obtained by the LASA of the University of Padova. Values of total nitrogen and nitrates were obtained in order to evaluate the reduction within the different systems of the wetland. Instead, the isotopic values of nitrogen and carbon were used to evaluate which process influence more nitrogen reduction and to understand the origin of the nutrient, if it is from fertilizers, waste water or sewage. To conclude, the most important process in the wetland of the Comuna drain is plant uptake, in facts the bigger percentage of nitrogen reduction was in the period of vegetative growth. So it is important the study of isotopes in plant tissues and water residence time, whose increase would allow a greater reduction of nutrients.

Exchange of nitrogen dioxide (NO 2) between plants and the atmosphere under laboratory and field conditions

Nitrogen is an essential nutrient. It is for human, animal and plants a constituent element of proteins and nucleic acids. Although the majority of the Earth’s atmosphere consists of elemental nitrogen (N2, 78 %) only a few microorganisms can use it directly. To be useful for higher plants and animals elemental nitrogen must be converted to a reactive oxidized form. This conversion happens within the nitrogen cycle by free-living microorganisms, symbiotic living Rhizobium bacteria or by lightning. Humans are able to synthesize reactive nitrogen through the Haber-Bosch process since the beginning of the 20th century. As a result food security of the world population could be improved noticeably. On the other side the increased nitrogen input results in acidification and eutrophication of ecosystems and in loss of biodiversity. Negative health effects arose for humans such as fine particulate matter and summer smog. Furthermore, reactive nitrogen plays a decisive role at atmospheric chemistry and global cycles of pollutants and nutritive substances.rnNitrogen monoxide (NO) and nitrogen dioxide (NO2) belong to the reactive trace gases and are grouped under the generic term NOx. They are important components of atmospheric oxidative processes and influence the lifetime of various less reactive greenhouse gases. NO and NO2 are generated amongst others at combustion process by oxidation of atmospheric nitrogen as well as by biological processes within soil. In atmosphere NO is converted very quickly into NO2. NO2 is than oxidized to nitrate (NO3-) and to nitric acid (HNO3), which bounds to aerosol particles. The bounded nitrate is finally washed out from atmosphere by dry and wet deposition. Catalytic reactions of NOx are an important part of atmospheric chemistry forming or decomposing tropospheric ozone (O3). In atmosphere NO, NO2 and O3 are in photosta¬tionary equilibrium, therefore it is referred as NO-NO2-O3 triad. At regions with elevated NO concentrations reactions with air pollutions can form NO2, altering equilibrium of ozone formation.rnThe essential nutrient nitrogen is taken up by plants mainly by dissolved NO3- entering the roots. Atmospheric nitrogen is oxidized to NO3- within soil via bacteria by nitrogen fixation or ammonium formation and nitrification. Additionally atmospheric NO2 uptake occurs directly by stomata. Inside the apoplast NO2 is disproportionated to nitrate and nitrite (NO2-), which can enter the plant metabolic processes. The enzymes nitrate and nitrite reductase convert nitrate and nitrite to ammonium (NH4+). NO2 gas exchange is controlled by pressure gradients inside the leaves, the stomatal aperture and leaf resistances. Plant stomatal regulation is affected by climate factors like light intensity, temperature and water vapor pressure deficit. rnThis thesis wants to contribute to the comprehension of the effects of vegetation in the atmospheric NO2 cycle and to discuss the NO2 compensation point concentration (mcomp,NO2). Therefore, NO2 exchange between the atmosphere and spruce (Picea abies) on leaf level was detected by a dynamic plant chamber system under labo¬ratory and field conditions. Measurements took place during the EGER project (June-July 2008). Additionally NO2 data collected during the ECHO project (July 2003) on oak (Quercus robur) were analyzed. The used measuring system allowed simultaneously determina¬tion of NO, NO2, O3, CO2 and H2O exchange rates. Calculations of NO, NO2 and O3 fluxes based on generally small differences (∆mi) measured between inlet and outlet of the chamber. Consequently a high accuracy and specificity of the analyzer is necessary. To achieve these requirements a highly specific NO/NO2 analyzer was used and the whole measurement system was optimized to an enduring measurement precision.rnData analysis resulted in a significant mcomp,NO2 only if statistical significance of ∆mi was detected. Consequently, significance of ∆mi was used as a data quality criterion. Photo-chemical reactions of the NO-NO2-O3 triad in the dynamic plant chamber’s volume must be considered for the determination of NO, NO2, O3 exchange rates, other¬wise deposition velocity (vdep,NO2) and mcomp,NO2 will be overestimated. No significant mcomp,NO2 for spruce could be determined under laboratory conditions, but under field conditions mcomp,NO2 could be identified between 0.17 and 0.65 ppb and vdep,NO2 between 0.07 and 0.42 mm s-1. Analyzing field data of oak, no NO2 compensation point concentration could be determined, vdep,NO2 ranged between 0.6 and 2.71 mm s-1. There is increasing indication that forests are mainly a sink for NO2 and potential NO2 emissions are low. Only when assuming high NO soil emissions, more NO2 can be formed by reaction with O3 than plants are able to take up. Under these circumstance forests can be a source for NO2.

Biochar in perennial crops: nutritional, agronomical and environmental implications

Biochar is the solid C-rich matrix obtained by pyrolysis of biomasses, currently promoted as a soil amendment with the aim to offset anthropogenic C emissions, while ameliorating soil properties and growth conditions. Benefits from biochar seem promising, although scientific understandings are beginning to be explored. In this project, I performed a suite of experiments in controlled and in field conditions with the aims to investigate the effect of biochar on: a) the interaction with minerals; b) Fe nutrition in kiwifruit; c) soil leaching, soil fertility, soil CO2 emissions partitioning, soil bacterial profile and key gene expression of soil nitrification-involved bacteria; d) plant growth, nutritional status, yield, fruit quality and e) its physical-chemical changes as affected by long-term environmental exposure. Biochar released K, P and Mg but retained Fe, Mn, Cu and Zn on its surface which in turn hindered Fe nutrition of kiwifruit trees. A redox reaction on the biochar surface exposed to a Fe source was elucidated. Biochar reduced the amount of leached NH4+-N but increased that of Hg, K, P, Mo, Se and Sn. Furthermore, biochar synergistically interacted with compost increasing soil field capacity, fertility, leaching of DOC, TDN and RSOC, suggesting a priming effect. However, in field conditions, biochar did not affect yield, nutritional status and fruit quality. Actinomadura flavalba, Saccharomonospora viridis, Thermosporomyces composti and Enterobacter spp. were peculiar of the soil amended with biochar plus compost which exhibited the highest band richness and promoted gene expression levels of Nitrosomonas spp., Nitrobacter spp. and enzymatic-related activity. Environmental exposure reduced C, K, pH and water infiltration of biochar which instead resulted in a higher O, Si, N, Na, Al, Ca, Mn and Fe at%. Oxidation occurred on the aged biochar surface, it decreased progressively with depth and induced the development of O-containing functional groups, up to 75nm depth.

Charakterisierung von optischen Partikelspektrometern und in-situ Messungen zur Mikrophysik der polaren Stratosphärenwolken

Polare Stratosphärenwolken (PSC), die unterhalb einer Temperatur von etwa -78 °C in polaren Regionen auftreten, üben einen starken Einfluss auf die stratosphärische Ozonschicht aus. Dieser Einfluss erfolgt größtenteils über heterogene chemische Reaktionen, die auf den Oberflächen von Wolkenpartikeln stattfinden. Chemische Reaktionen die dabei ablaufen sind eine Voraussetzung für den späteren Ozonabbau. Des Weiteren verändert die Sedimentation der Wolkenpartikel die chemische Zusammensetzung bzw. die vertikale Verteilung der Spurengase in der Stratosphäre. Für die Ozonchemie spielt dabei die Beseitigung von reaktivem Stickstoff durch Sedimentation Salpetersäure-haltiger Wolkenpartikeln (Denitrifizierung) eine wichtige Rolle. Durch gleichen Sedimentationsprozess von PSC Elementen wird der Stratosphäre des weiteren Wasserdampf entzogen (Dehydrierung). Beide Prozesse begünstigen einen länger andauernden stratosphärischen Ozonabbau im polaren Frühling.rnGerade im Hinblick auf die Denitrifikation durch Sedimentation größerer PSC-Partikel werden in dieser Arbeit neue Resultate von in-situ Messungen vorgestellt, die im Rahmen der RECONCILE-Kampagne im Winter des Jahres 2010 an Bord des Höhenforschungs-Flugzeugs M-55 Geophysica durchgeführt wurden. Dabei wurden in fünf Flügen Partikelgrößenverteilungen in einem Größenbereich zwischen 0,5 und 35 µm mittels auf der Lichtstreuung basierender Wolkenpartikel-Spektrometer gemessen. Da polare Stratosphärenwolken in Höhen zwischen 17 und 30 km auftreten, sind in-situ Messungen vergleichsweise selten, so dass noch einige offene Fragen bestehen bleiben. Gerade Partikel mit optischen Durchmessern von bis zu 35µm, die während der neuen Messungen detektiert wurden, müssen mit theoretischen Einschränkungen in Einklang gebracht werden. Die Größe der Partikel wird dabei durch die Verfügbarkeit der beteiligten Spurenstoffe (Wasserdampf und Salpetersäure), die Sedimentationsgeschwindigkeit, Zeit zum Anwachsen und von der Umgebungstemperatur begrenzt. Diese Faktoren werden in der vorliegenden Arbeit diskutiert. Aus dem gemessenen Partikelvolumen wird beispielsweise unter der Annahme der NAT-Zusammensetzung (Nitric Acid Trihydrate) die äquivalente Konzentration des HNO 3 der Gasphase berechnet. Im Ergebnis wird die verfügbare Konzentration von Salpetersäure der Stratosphäre überschritten. Anschließend werden Hypothesen diskutiert, wodurch das gemessene Partikelvolumen überschätzt worden sein könnte, was z.B. im Fall einer starken Asphärizität der Partikel möglich wäre. Weiterhin wurde eine Partikelmode unterhalb von 2-3µm im Durchmesser aufgrund des Temperaturverhaltens als STS (Supercooled Ternary Solution droplets) identifiziert.rnUm die Konzentration der Wolkenpartikel anhand der Messung möglichst genau berechnen zu können, muss das Messvolumen bzw. die effektive Messfläche der Instrumente bekannt sein. Zum Vermessen dieser Messfläche wurde ein Tröpfchengenerator aufgebaut und zum Kalibrieren von drei Instrumenten benutzt. Die Kalibration mittels des Tröpfchengenerators konzentrierte sich auf die Cloud Combination Probe (CCP). Neben der Messfläche und der Größenbestimmung der Partikel werden in der Arbeit unter Zuhilfenahme von Messungen in troposphärischen Wolken und an einer Wolkensimulationskammer auch weitere Fehlerquellen der Messung untersucht. Dazu wurde unter anderem die statistische Betrachtung von Intervallzeiten einzelner Messereignisse, die in neueren Sonden aufgezeichnet werden, herangezogen. Letzteres ermöglicht es, Messartefakte wie Rauschen, Koinzidenzfehler oder „Shattering“ zu identifizieren.rn

Processes influencing the nitrate concentration in an aquifer for drinking water production in Bremen-Nord - Northern Germany

Groundwater represents the most important raw material. Germany struggles to maintain the best water quality possible by providing advanced monitoring systems and legal measures to prevent further pollution. In areas involved in the intensive growing of plantations, one of the major contamination factors derives from nitrate. The aim of this master thesis is the characterisation of the Water Protection Area of Bremen (Germany). Denitrification is a natural process, representing the best means of natural reduction of the hazardous nitrate ion, which is dangerous both for human health and for the development of eutrophication. The study has been possible thanks to the collaboration with the University of Bremen, the Geological Service of Bremen (GDfB) and Peter Spiedt (Water Supply Company of Bremen). It will be defined whether nitrate amounts in the groundwater still overcome the threshold legally imposed, and state if the denitrification process takes place, thanks to new samples collected in 2015 and their integration with historical data. Gas samples have been gathered to test them with the “N2/Ar method”, which is able to estimate the denitrification rate quantitatively. Analyses stated the effective occurrence of the reaction, nevertheless showing that it only affects the chemical of the deep aquifers and not shallow ones. Temporal trends concentrations of nitrate have shown that no real improvement took place in the past years. It will be commented that despite the denitrification being responsible for an efficacious lowering in the nitrate ion, it needs reactive materials to take place. Since the latter are finite elements, it is not an endless process. It is thus believed that is clearly necessary to adopt a better attitude in order to maintain the best chemical qualities possible in such an important area, providing drinking water.

Temporal and spatial variation of nitrogen transformations in nitrogen-saturated soils of a central Appalachian hardwood forest

We studied temporal and spatial patterns of soil nitrogen (N) dynamics from 1993 to 1995 in three watersheds of Fernow Experimental Forest, W.V.: WS7 (24-year-old, untreated); WS4 (mature, untreated); and WS3 (24-year-old, treated with (NH4)2SO since 1989 at the rate of 35 kg Nha–1year–1). Net nitrification was 141, 114, and115 kg Nha–1year–1, for WS3, WS4, and WS7, respectively, essentially 100% of net N mineralization for all watersheds. Temporal (seasonal) patterns of nitrification were significantly related to soil moisture and ambient temperaturein untreated watersheds only. Spatial patterns of soil water NO3–of WS4 suggest that microenvironmental variabilitylimits rates of N processing in some areas of this N-saturated watershed, in part by ericaceous species in the herbaceous layer. Spatial patterns of soil water NO3–in treated WS3 suggest that later stages of N saturation may result inhigher concentrations with less spatial variability. Spatial variability in soil N variables was lower in treated WS3 versus untreated watersheds. Nitrogen additions have altered the response of N-processing microbes to environmental factors, becoming less sensitive to seasonal changes in soil moisture and temperature. Biotic processes responsible forregulating N dynamics may be compromised in N-saturated forest ecosystems.

Factors Influencing Spatial Variability in Nitrogen Processing in Nitrogen-Saturated Soils

Nitrogen (N) saturation is an environmental concern for forests in the eastern U.S. Although several watersheds of the Fernow Experimental Forest (FEF), West Virginia exhibit symptoms of Nsaturation, many watersheds display a high degree of spatial variability in soil N processing. This study examined the effects of temperature on net N mineralization and nitrification in N-saturatedsoils from FEF, and how these effects varied between high N-processing vs. low N-processingsoils collected from two watersheds, WS3 (fertilized with [NH4]2SO4) and WS4 (untreated control). Samples of forest floor material (O2 horizon) and mineral soil (to a 5-cm depth) were taken from three subplots within each of four plots that represented the extremes of highest and lowest ratesof net N mineralization and nitrification (hereafter, high N and low N, respectively) of untreated WS4 and N-treated WS3: control/low N, control/high N, N-treated/low N, N-treated/high N. Forest floor material was analyzed for carbon (C), lignin,and N. Subsamples of mineral soil were extractedimmediately with 1 N KCl and analyzed for NH4+and NO3– to determine preincubation levels. Extracts were also analyzed for Mg, Ca, Al, and pH. To test the hypothesis that the lack of net nitrification observed in field incubations on the untreated/low N plot was the result of absence ofnitrifier populations, we characterized the bacterial community involved in N cycling by amplification of amoA genes. Remaining soil was incubated for 28 d at three temperatures (10, 20, and30°C), followed by 1 N KCl extraction and analysis for NH4+ and NO3–. Net nitrification was essentially 100% of net N mineralization for all samples combined. Nitrification rates from lab incubation sat all temperatures supported earlier observations based on field incubations. At 30°C, rates from N- t reated/high N were three times those of N-treated/low N. Highest rates were found for untreated/high N (two times greater than those of N-treated/high N), whereas untreated/low N exhibited no net nitrification. However, soils exhibitingno net nitrification tested positive for presence of nitrifying bacteria, causing us to reject our initial hypothesis. We hypothesize that nitrifier populations in such soil are being inhibited by a combination of low Ca:Al ratios in mineral soil and allelopathic interactions with mycorrhizae of ericaceous species in the herbaceous layer.

Effects of Silvicultural Practices on Soil Carbon and Nitrogen in a Nitrogen Saturated Central Appalachian (USA) Hardwood Forest Ecosystem

Silvicultural treatments represent disturbances to forest ecosystems often resulting in transient increases in net nitrification and leaching of nitrate and base cations from the soil. Response of soil carbon (C) is more complex, decreasing from enhanced soil respiration and increasing from enhanced postharvest inputs of detritus. Because nitrogen (N) saturation can have similar effects on cation mobility, timber harvesting in N-saturated forests may contribute to a decline in both soil C and base cation fertility, decreasing tree growth. Although studies have addressed effects of either forest harvesting or N saturation separately, few data exist on their combined effects. Our study examined the responses of soil C and N to several commercially used silvicultural treatments within the Fernow Experimental Forest, West Virginia, USA, a site with N-saturated soils. Soil analyses included soil organic matter (SOM), C, N, C/N ratios, pH, and net nitrification. We hypothesized the following gradient of disturbance intensity among silvicultural practices (from most to least intense): even-age with intensive harvesting (EA-I), even-age with extensive harvesting, even-age with commercial harvesting, diameter limit, and single-tree harvesting (ST). We anticipated that effects on soil C and N would be greatest for EA-I and least with ST. Tree species exhibited a response to the gradient of disturbance intensity, with early successional species more predominant in high-intensity treatments and late successional species more predominant in low-intensity treatments. Results for soil variables, however, generally did not support our predictions, with few significant differences among treatments and between treatments and their paired controls for any of the measured soil variables. Multiple regression indicated that the best predictors for net nitrification among samples were SOM (positive relationship) and pH (negative relationship). This finding confirms the challenge of sustainable management of N-saturated forests.

Spatial heterogeneity of soil nutrients and plant species in herb-dominated communities of contrasting land use

Recent interest in spatial pattern in terrestrial ecosystems has come from an awareness of theintimate relationship between spatial heterogeneity of soil resources and maintenance of plant species diversity. Soil and vegetation can vary spatially inresponse to several state factors of the system. In this study, we examined fine-scale spatial variability of soil nutrients and vascular plant species in contrasting herb-dominated communities (a pasture and an oldfield) to determine degree of spatial dependenceamong soil variables and plant community characteristics within these communities by sampling at 1-m intervals. Each site was divided into 25 1-m 2 plots. Mineral soil was sampled (2-cm diameter, 5-cm depth) from each of four 0.25-m2 quarters and combined into a single composite sample per plot. Soil organic matter was measured as loss-on-ignition. Extractable NH4 and NO3 were determined before and after laboratory incubation to determine potential net N mineralization and nitrification. Cations were analyzed using inductively coupled plasma emission spectrometry. Vegetation was assessed using estimated percent cover. Most soiland plant variables exhibited sharp contrasts betweenpasture and old-field sites, with the old field having significantly higher net N mineralization/nitrification, pH, Ca, Mg, Al, plant cover, and species diversity, richness, and evenness. Multiple regressions revealedthat all plant variables (species diversity, richness,evenness, and cover) were significantly related to soil characteristics (available nitrogen, organic matter,moisture, pH, Ca, and Mg) in the pasture; in the old field only cover was significantly related to soil characteristics (organic matter and moisture). Both sites contrasted sharply with respect to spatial pattern of soil variables, with the old field exhibiting a higher degree of spatial dependence. These results demonstrate that land-use practices can exert profound influence on spatial heterogeneity of both soil properties and vegetation in herb-dominated communities.

The nitrogen cycle of tropical montane forest in Ecuador turns inorganic under environmental change

Water-bound nitrogen (N) cycling in temperate terrestrial ecosystems of the Northern Hemisphere is today mainly inorganic because of anthropogenic release of reactive N to the environment. In little-industrialized and remote areas, in contrast, a larger part of N cycling occurs as dissolved organic N (DON). In a north Andean tropical montane forest in Ecuador, the N cycle changed markedly during 1998–2010 along with increasing N deposition and reduced soil moisture. The DON concentrations and the fractional contribution of DON to total N significantly decreased in rainfall, throughfall, and soil solutions. This inorganic turn of the N cycle was most pronounced in rainfall and became weaker along the flow path of water through the system until it disappeared in stream water. Decreasing organic contributions to N cycling were caused not only by increasing inorganic N input but also by reduced DON production and/or enhanced DON decomposition. Accelerated DON decomposition might be attributable to less waterlogging and higher nutrient availability. Significantly increasing NO3-N concentrations and NO3-N/NH4-N concentration ratios in throughfall and litter leachate below the thick organic layers indicated increasing nitrification. In mineral soil solutions, in contrast, NH4-N concentrations increased and NO3-N/NH4-N concentration ratios decreased significantly, suggesting increasing net ammonification. Our results demonstrate that the remote tropical montane forests on the rim of the Amazon basin experienced a pronounced change of the N cycle in only one decade. This change likely parallels a similar change which followed industrialization in the temperate zone of the Northern Hemisphere more than a century ago.

Central European hardwood trees in a high-CO 2 future: synthesis of an 8-year forest canopy CO 2 enrichment project

Rapidly increasing atmospheric CO2 is not only changing the climate system but may also affect the biosphere directly through stimulation of plant growth and ecosystem carbon and nutrient cycling. Although forest ecosystems play a critical role in the global carbon cycle, experimental information on forest responses to rising CO2 is scarce, due to the sheer size of trees. Here, we present a synthesis of the only study world-wide where a diverse set of mature broadleaved trees growing in a natural forest has been exposed to future atmospheric CO2 levels (c. 550ppm) by free-air CO2 enrichment (FACE). We show that litter production, leaf traits and radial growth across the studied hardwood species remained unaffected by elevated CO2 over 8years. CO2 enrichment reduced tree water consumption resulting in detectable soil moisture savings. Soil air CO2 and dissolved inorganic carbon both increased suggesting enhanced below-ground activity. Carbon release to the rhizosphere and/or higher soil moisture primed nitrification and nitrate leaching under elevated CO2; however, the export of dissolved organic carbon remained unaltered.Synthesis. Our findings provide no evidence for carbon-limitation in five central European hardwood trees at current ambient CO2 concentrations. The results of this long-term study challenge the idea of a universal CO2 fertilization effect on forests, as commonly assumed in climate-carbon cycle models.