Base cations release in soils along the 127‐year Hailuogou glacial retreat chronosequence

At the Hailuogou glacial retreat chronosequence, a mature forest has surprisingly fast developed in ∼120 yr, although the glacial debris is dominated by nutrient-poor granite with a small contribution of carbonate minerals. In previous work, we hypothesized that the fast vegetation development is synchronized with initial fast carbonate weathering followed by slow silicate weathering. To test this hypothesis, we (a) characterized the composition of the glacial debris to elucidate the sources of base cations and (b) determined the base cation release kinetics from topsoils (0–10 cm) along the chronosequence with a weathering experiment at a constant pH value (pH$_{stat}$). Besides granitic rocks, the glacial debris contained some meta-sedimentary and meta-volcanic calc-silicate rocks, amphibolite, mica schist, and quartzite. Although the total Ca concentration of the glacial debris was only about double that of Mg, K, and Na, during the 1st day of the pH$_{stat}$ experiment, the released mass of Ca was >10 times higher than that of Mg and K, and even about 100 times higher than that of Na. The size of the fast-reacting Ca-carbonate pool decreased quickly in the first approximately 40 yr, after which a slow-reacting Ca-silicate pool matched the fast-reacting pool with a size of 1.9 ± 0.6 g kg$^{–1}$ Ca. In contrast, for Mg, K, and Na the slow-reacting pool dominated from the beginning, suggesting that these elements mainly originated from silicate weathering. Our findings support the view that the well-synchronized interplay between carbonate and silicate weathering facilitated the fast vegetation succession

Equilibrium isotope fractionation factors of H exchange between steam and soil clay fractions

Rationale Steam equilibration overcomes the problem of the traditional measurements of H isotope compositions, which leave an arbitrary amount of adsorbed water in the sample, by controlling for the entire exchangeable H pool, including adsorbed water and hydroxyl-H. However, the use of steam equilibration to determine nonexchangeable stable H isotope compositions in environmental media (expressed as δ2Hn values) by mathematically eliminating the influence of exchangeable H after sample equilibration with waters of known H-isotopic composition requires the knowledge of the equilibrium isotope fractionation factor between steam-H and exchangeable H of the sample (αex-w), which is frequently unknown. Methods We developed a new method to determine the αex-w values for clay minerals, topsoil clay fractions, and mica by manipulating the contributions of exchangeable H to the total H pool via different degrees of post-equilibration sample drying. We measured the δ2H values of steam-equilibrated mineral and soil samples using elemental analyzer-pyrolysis-isotope ratio mass spectrometry. Results The αex-w values of seven clay minerals ranged from 1.071 to 1.140, and those of 19 topsoil clay fractions ranged from 0.885 to 1.216. The αex-w value of USGS57 biotite, USGS58 muscovite, and of cellulose was 0.965, 0.871, and 1.175, respectively. The method did not work for kaolinite, because its small exchangeable H pool did not respond to the selected drying conditions. Structurally different mineral groups such as two- and three-layer clay minerals or mica showed systematically different αex-w values. The αex-w value of the topsoil clay fractions correlated with the soil clay content (r = 0.63, P = 0.004), the local mean annual temperature (r = 0.68, P = 0.001), and the δ2H values of local precipitation (r = 0.72, P < 0.001), likely to reflect the different clay mineralogy under different weathering regimes. Conclusions Our new αex-w determination method yielded realistic results in line with the few previously published values for cellulose. The determined αex-w values were similar to the widely assumed values of 1.00–1.08 in the literature, suggesting that the adoption of one of these values in steam equilibration approaches is appropriate

Initial carbonate weathering is linked with vegetation development along a 127-year glacial retreat chronosequence in the subtropical high mountainous Hailuogou region (SW China)

Aims The retreat of glaciers is exposing new terrains to primary plant succession around the globe. To improve the understanding of vegetation development along a glacier retreat chronosequence, we (i) evaluated a possible link between base metal (Ca, Mg, K, Na) supply and vegetation establishment, (ii) determined the rates of the establishment of soil and plant base metal stocks, and (iii) estimated the size of the main base metal fluxes. Methods We determined base metal stocks in the soil organic layer, the mineral topsoil (0–10 cm), and in leaves/needles, trunk, bark, branches and roots of the dominating shrub and tree species and estimated fluxes of atmospheric deposition, plant uptake and leaching losses along the 127-yr Hailuogou chronosequence. Results Total ecosystem Ca and Mg stocks decreased along the chronosequence, while those of K and Na were unrelated with ecosystem age. Fortyfour and 30% of the initial stocks of Ca and Mg, respectively, were leached during the first 47 years, at rates of 130 ± 10.6 g m$^{-2}$ year$^{-1}$ Ca and 35 ± 3.1 g m$^{-2}$ year$^{-1}$ Mg. The organic layer accumulated at a mean rate of 288 g m$^{-2}$ year$^{-1}$ providing a bioavailable base metal stock, which was especially important for K cycling. Conclusions We suggest that the initial high Ca bioavailability because of a moderately alkaline soil pH and carbonate depletion in 47 years, together with the dissolution of easily-weatherable silicates providing enough Mg and K to the pioneer vegetation, contributed to the establishment of the mature forest in ca. 80 years

Influence of modelled soil biogenic NO emissions on related trace gases and the atmospheric oxidizing efficiency

The emission of nitric oxide (NO) by soils (SNOx) is an important source of oxides of nitrogen (NO&lt;sub&gt;x&lt;/sub&gt;=NO+NO&lt;sub&gt;2&lt;/sub&gt;) in the troposphere, with estimates ranging from 4 to 21 Tg of nitrogen per year. Previous studies have examined the influence of SNOx on ozone (O&lt;sub&gt;3&lt;/sub&gt;) chemistry. We employ the ECHAM5/MESSy atmospheric chemistry model (EMAC) to go further in the reaction chain and investigate the influence of SNOx on lower tropospheric NO&lt;sub&gt;x&lt;/sub&gt;, O&lt;sub&gt;3&lt;/sub&gt;, peroxyacetyl nitrate (PAN), nitric acid (HNO&lt;sub&gt;3&lt;/sub&gt;), the hydroxyl radical (OH) and the lifetime of methane (&amp;tau;&lt;sub&gt;CH&lt;sub&gt;4&lt;/sub&gt;&lt;/sub&gt;). We show that SNOx is responsible for a significant contribution to the NO&lt;sub&gt;x&lt;/sub&gt; mixing ratio in many regions, especially in the tropics. Furthermore, the concentration of OH is substantially increased due to SNOx, resulting in an enhanced oxidizing efficiency of the global troposphere, reflected in a ~10% decrease in &amp;tau;&lt;sub&gt;CH&lt;sub&gt;4&lt;/sub&gt;&lt;/sub&gt; due to soil NO emissions. On the other hand, in some regions SNOx has a negative feedback on the lifetime of NO&lt;sub&gt;x&lt;/sub&gt; through O&lt;sub&gt;3&lt;/sub&gt; and OH, which results in regional increases in the mixing ratio of NO&lt;sub&gt;x&lt;/sub&gt; despite lower total emissions in a simulation without SNOx. In a sensitivity simulation in which we reduce the other surface NO&lt;sub&gt;x&lt;/sub&gt; emissions by the same amount as SNOx, we find that they have a much weaker impact on OH and &amp;tau;&lt;sub&gt;CH&lt;sub&gt;4&lt;/sub&gt;&lt;/sub&gt; and do not result in an increase in the NO&lt;sub&gt;x&lt;/sub&gt; mixing ratio anywhere

Non‐exchangeable stable hydrogen isotope ratios in clay minerals and soil clay fractions: A method test

Stable hydrogen isotope ratios (δ$^{2}$H values) in structural hydroxyl groups of pedogenic clay minerals are inherited from the surrounding water at the time of their formation. Only non-exchangeable H preserves the environmental forensic and paleoclimate information (δ$^{2}$H$_{n}$ value). To measure δ$^{2}$H$_{n}$ values in structural H of clay minerals and soil clay fractions, we adapted a steam equilibration method by accounting for high hygroscopicity. Our δ$^{2}$H$_{n}$ values for USGS57 biotite (−95.3 ± SD 0.9‰) and USGS58 muscovite (30.7 ± 1.4‰) differed slightly but significantly from the reported δ$^{2}$H values (−91.5 ± 2.4‰ and −28.4 ± 1.6‰), because the minerals contained 1.1%–4.4% of exchangeable H. The low SD of replicate measurements (n = 3) confirmed a high precision. The clay separation method including destruction of Fe oxides, carbonates and soil organic matter, and dispersion did not significantly change the δ$^{2}$H$_{n}$ values of five different clay minerals. However, we were unable to remove all organic matter from the soil clay fractions resulting in an estimated bias of 1‰ in two samples and 15‰ in the carbon-richest sample. Our results demonstrate that δ$^{2}$H$_{n}$ values of structural H of clay minerals and soil clay fractions can be reliably measured without interference from atmospheric water and the method used to separate the soil clay fraction

Biodiversität und Ökosystemfunktionen - Ergebnisse von Experimenten in den Tropen und den gemäßigten Breiten

Die Artenvielfalt beeinflusst den Nährstoffkreislauf und damit für den Menschen wichtige Ökosystem-funktionen, wie z.B. die Nährstoff-retention. Ob dieses Ergebnis für komplexe Waldsysteme und längere Zeiträume gilt, blieb bisher ungeklärt. Wir untersuchten die oberirdischen N-Vorräte in Abhängigkeit von der pflanzlichen Diversität im Sardinilla-Projekt (Panama) und im Jena-Experiment (Deutschland). Außerdem verfolgten wir den zeitlichen Verlauf des Diversitätseffektes auf oberiridische N-Vorräte und N-Verfügbarkeit im Boden (Jena). Wir fanden effektivere Ressourcenausnutzung im Baumexperiment in Panama und im Grünlandexperiment in Jena. In Jena blieb der negative Zusammenhang zwischen N-Verfügbarkeit im Boden über die Zeit nicht bestehen. Der Grund waren positive Rückkopplungseffekte, die durch den Landnutzungswechsel von Acker zu Grünland induziert waren. Die Dauer des Experimentes muss bei der Betrachtung des Diversitätseinflusses auf Prozesse im Boden mit einbezogen werden

Does biochar contribute to close nutrient cycles of tree plantations on degraded Ultisols in the Ecuadorian Amazonia?

The use of biochar is expected to improve soil fertility and close nutrient cycles in degraded strongly weathered tropical soils. We, therefore, hypothesized that biochar amendment to tree plantations (a) increases nutrient fluxes with litterfall alone and with mineral fertilizer plus lime and (b) reduces N losses reflected by lower $\delta$$^{15}$N values of litterfall and soils than in unamended controls. We grew the native leguminous Schizolobium parahyba var. amazonicum (Ducke) Barneby and the exotic Gmelina arborea Roxb at two sites. We used a replicated full factorial split–split plot design of amendment of mineral fertilizer plus lime, 3 and 6 t ha$^{–1}$ biochar, and a control. We collected litterfall biweekly (2012–2013) and topsoil samples (0–0.25 m) in 2009 before tree planting, in 2011 and 2013. Fertilizer plus lime increased the mean annual concentrations of P, Ca and Zn in litterfall but decreased that of Mn. At the same time, fertilizer plus lime increased the annual fluxes of nutrients, Na and Al with litterfall. During the dry season, biochar decreased the N concentration in litterfall and the K flux with litterfall. During the rainy season, biochar increased the concentrations of Ca and Zn in litterfall and their fluxes with litterfall. Biochar did not influence the $\delta$$^{15}$N values of soil and litterfall after 51 months of tree growth. Fertilizer plus lime decreased the $\delta$$^{15}$N values of soil, because of the lower $\delta$$^{15}$N value of the used urea (−0.30‰) than the soil (4.5‰–7.8‰). Moreover, fertilizer plus lime increased the $\delta$$^{15}$N values of litterfall, possibly because of enhanced 14N leaching from the N-rich canopies. The amendment of up to 6 t ha$^{–1}$ biochar did not contribute to close nutrient cycles

10 Jahre Ökosystemforschung in Ecuador: Bergregenwald-Böden unter dem Einfluss klimaabhängiger Telekonnektionen

Seit 1998 erfassen wir in einem tropischen Bergregenwald in Südecuador alle wichtigen Stoffflüsse. Der Standort ist ostexponiert und liegt im Einflussbereich des Nordostpassates. In den ersten fünf Messjahren konnten wir im Zusammenhang mit einem extremen La Niña-Ereignis Ca- und Mg-Einträge durch Ferntransport von Sahara-Staub nachweisen. In der Zeit außerhalb der Staubeinträge kam es zu N- und Säureeinträgen aus Waldbränden im Amazonas-becken. Nach Auswertung der 10-Jahres-Datenreihe stellte sich heraus, dass es zwar zu wiederholten Saharastaubeinträ-gen während der La Niña-Ereignisse 2005 und 2007 kam, dass aber insgesamt die Bodenversauerung überwog, was sich in einem abnehmenden pH-Wert des Streuperkolates manifestierte. Die Versauerung wurde nicht nur durch direk-te Säureinträge verursacht, sondern auch durch kontinuierlich ansteigende NH4+-Einträge

Does biochar improve nutrient availability in Ultisols of tree plantations in the Ecuadorian Amazonia?

The application of biochar to strongly weathered soils is thought to supply nutrients and improve nutrient retention. We hypothesized that biochar increases (a) total N, bioavailable macronutrient (NH$_{4}$–N, P, K, Ca, Mg), micronutrient (Fe, Mn, Zn, Cu), and plant-beneficial Na concentrations; and (b) nutrient retention in the topsoil. We grew the native leguminous Brazilian firetree [Schizolobium parahyba var. amazonicum (Ducke) Barneby] and the exotic beechwood (Gmelina arborea Roxb.) in a full factorial split-split-plot design at La Victoria and Los Zapotes, Ecuadorian Amazonia. The treatments included amendment of mineral fertilizer plus lime, 3 and 6 t ha−1 biochar (locally produced charcoal), and a control. We sampled the 0-to-0.25- and 0.25-to-0.50-m soil depth layers before the start of the experiment in 2009 and six times until 2013. The site at Los Zapotes was more fertile as reflected by a significant site effect on most studied soil properties in both depth layers. Biochar increased modified Olsen (NaHCO3+EDTA)-extractable Ca (p < .05) and Zn concentrations (p < .1) and total N concentrations (p < .05) in topsoil. Mineral fertilizer plus lime increased Olsen-extractable P, K, Ca, Mg, and Zn concentrations (all p < .05) but reduced Olsen-extractable Fe concentrations (p < .05) in topsoil. Biochar increased Ca (p < 0.1) and Zn (p < .05) retention in mineral fertilized topsoils but decreased total N retention (p < .05) in unfertilized topsoils. The amendment of up to 6 t ha$^{-1}$ biochar did not increase the fertility of the studied degraded Amazonian Ultisols sufficiently to enhance tree growth

Optimierte Demineralisierung von Bodenproben mittels Flusssäure

Die Trennung von organischer Bodensubstanz und mineralischer Matrix kann eine wichtige Voraussetzung für die Anwendung vieler analytischer Verfahren der organischen Chemie sein. Durch Optimierung verbreiteter Verfahren zur Demineralisierung mittels Flusssäure (HF) war es uns möglich, einige Nachteile der HF-Demineralisierung zu beseitigen. Wir konnten die Corg-Gehalte (vor allem Corg-armer Proben) um einen Faktor von bis zu 100 steigern sowie die Wiederfindung des organischen Kohlen-stoffs (Corg) im Vergleich zu gängigen Demineralisierungsmethoden teilweise mehr als verdoppeln. Gleichzeitig war es uns möglich, den Zeit- und Materialaufwand zu reduzieren