Measured Soil pH Research Articles

The efficiency of Cd phytoextraction by S. plumbizincicola increased with the addition of rice straw to polluted soils: the role of particulate organic matter

The addition of organic amendments to soils can significantly increase soil organic matter (SOM) content as well as the mass of large (e.g. 2000–250 μm) particulate organic matter (POM) fractions. Here we address whether the addition of organic amendments might affect both POM pools and the phytoextraction efficiency of Sedum plumbizincicola (S. plumbizincicola) in cadmium (Cd) polluted soils. We carried out a 442-days long pot experiment and measured Cd uptake by S. plumbizincicola for four successive plant crops in two polluted paddy soils subjected to rice straw (RS) amendment. We also measured soil pH, nutrient availability, pore water dissolved organic carbon (DOC) and Cd concentrations across different soil particle-size fractions. We found that RS amendments had no significant effects on soil pH, DOC or Cd concentrations in bulk soils during repeated phytoextraction. However, RS amendments were associated with significant (1) increases (i.e. 14.3 to 20.7%) in Cd uptake by S. plumbizincicola plants from the first crop harvest, (2) increases in available soil nutrients content, (3) increases in the percentage of oxidizable Cd fractions and the mass of soil POM fractions, and (4) decreases in POM Cd concentrations after repeated phytoextraction. These findings suggest that POM fractions may represent important accessible pools of Cd for uptake by S. plumbizincicola plants. RS amendments enhance both Cd bioavailability within soil POM pools and Cd uptake by the hyperaccumulator S. plumbizincicola thus providing an effective management practice to improve Cd removal from polluted soils through phytoextraction.

The application of a spectrophotometric method to determine pH in acidic (pH

pH is a “master variable” controlling many biogeochemical processes in soils. Acid sulfate soils undergo rapid and large pH changes from circumneutral pH under anaerobic soil conditions to sulfuric soils with ultra (pH < 3.5) and extremely (pH 3.5–4.4) acidic properties following oxidation. Measuring soil pH using a glass electrode has several potential drawbacks including liquid junction errors, drift, suspension effects and clogging. Spectrophotometric pH measurement, involving addition of an indicator dye to the sample, is widely used in seawater and has recently been developed for soil extracts at circumneutral pH ranges. The aim of this study was to extend the spectrophotometric method for application in ultra and extremely acidic soils. The acid dissociation constant (pKa = 5.02) and molar absorptivities of the indicator dye bromocresol green were determined and shown to enable spectrophotometric pH measurement between pH 3 − 5.3. To demonstrate the performance and application of the method, pH and metal availability (Fe, Al, Zn) were measured during the incubation of two acid sulfate soils, which both classified as hypersulfidic soils (pH > 4) and transformed to sulfuric soils (pH < 4) after incubation for 12 weeks. The method compared well (r2 > 0.99) to glass electrode measurements under acidic conditions with high metal availability. The method has potential to improve understanding of biogeochemical processes in ultra and extremely acidic soils.

Assessment of Error Sources in Measurements of Field pH: Effect of Operator Experience, Test Kit Differences, and Time-Of-Day

ABSTRACTVarious methods exist to measure soil pH, and while there is general agreement between the existing published laboratory and field-based methods, the latter are subject to uncertainties including test kit reliability, accuracy, precision, and environmental factors. The contribution of this study is to quantify three uncertainties that affect the conversion between field pH and laboratory pH measurements, namely operator experience, choice of test kit, and the time-of-day for measurement. Soil samples from western Victoria, representing the pH range 4.5–10.0, were used in a randomized complete block design with 10 assessors split into two groups representing experienced and inexperienced users. Statistical analysis of laboratory and field pH was based on using the Maximum Likelihood Functional Relationship (MLFR) to determine if there was any bias between the two methods. Significant differences were found between experienced and inexperienced users, and between test kits.

Application of lineament density extracted from dual orbit of synthetic aperture radar (SAR) images to detecting fluids paths in the Wayang Windu geothermal field (West Java, Indonesia)

Lineaments appearing on satellite images were used to characterize a regional fracture system. Manual extraction of lineaments is subjective and difficult to extend to a wide area because smaller lineaments may be overlooked. To increase the extraction accuracy of fracture-related lineaments and specify fractures that act as geothermal fluid paths with high permeability, this study adopts Synthetic Aperture Radar (SAR) data because the backscattering intensities of SAR images can enhance small topographical reliefs relevant to fractures by using oblique microwave irradiation. We used two Phased Array type L-band SAR (PALSAR) images from the Advanced Land Observing Satellite with opposing irradiation directions to reduce the effect of topographic distortion caused by the oblique irradiation. Lineaments are extracted using the modified Segment Tracing Algorithm filtered by the Laplacian of Gaussian for linear features enhancement and noise removal. Surface geothermal features at the Wayang Windu geothermal field, West Java, Indonesia, were confirmed by comparing with soil pH, magnetic susceptibility, and surface roughness measurements. The calculated lineament distribution was spatially characterized by the intersection, occurrence frequency, and length densities of the lineaments. An ordinary kriging map of the lineament length density using 1×1-km cells showed good agreement with the geothermal surface features (hydrothermally altered zones, mud pools, and hot springs), which were probably formed by highly permeable fractures and fluid ascent. The high-anomaly zones of length density overlapped two fluid ascent sites and three water recharge sites in the water- and steam-dominated geothermal systems, respectively.

Development of a Spectrophotometric Method for Determining pH of Soil Extracts and Comparison with Glass Electrode Measurements

Core Ideas Soil pH is a critical parameter in soils as it influences many biogeochemical processes. There are problems in pH measurements in soils using glass electrodes. A new spectrophotometric method was developed to measure pH in soils. The method compared well to measurements using glass electrodes in a range of soils. A reflectance probe technique was also successfully trialed for in situ measurement. Soil pH measurement using conventional glass electrodes has several limitations. A spectrophotometric method was developed for determining soil pH involving indicator dye (bromocresol purple or phenol red) addition to soil extracts. Results were compared against values determined using a glass electrode for a range of soils (n = 13) with varying properties using different extraction conditions (1:1 w/v soil/water, 1:1 soil/0.01 mol L–1 CaCl2, 1:5 soil/water and 1:5 soil/0.01 mol L–1 CaCl2) and high and low ionic strength buffer calibrations of the electrode. For all extraction conditions, there was a strong relationship (r2 &gt; 0.95, slope ≈ 1) between values of the spectrophotometric (pHspec) and glass electrode (pHelec) methods. The precision of pHspec was similar to pHelec measurements across the different extraction conditions (±0.02–0.08 average standard deviation of triplicate measurements, n = 39). Large and variable differences were observed between pHelec measured following calibration with high (µ = 0.1 mol L–1) and low (µ = 0.005 mol L–1) ionic strength buffers. In contrast, ionic strength effects on the indicator dye and resulting pHspec calculation are implicitly accounted for. A spectrophotometric reflectance probe in situ method was also successfully trialed. The spectrophotometric pH method circumvents many of the problems associated with the use of glass electrodes in soil solutions.

Three‐Dimensional Electrical Resistivity Tomography of the Solfatara Crater (Italy): Implication for the Multiphase Flow Structure of the Shallow Hydrothermal System

AbstractThe Solfatara volcano is the main degassing area of the Campi Flegrei caldera, characterized by 60 years of unrest. Assessing such renewal activity is a challenging task because hydrothermal interactions with magmatic gases remain poorly understood. In this study, we decipher the complex structure of the shallow Solfatara hydrothermal system by performing the first 3‐D, high‐resolution, electrical resistivity tomography of the volcano. The 3‐D resistivity model was obtained from the inversion of 43,432 resistance measurements performed on an area of ~0.68 km2. The proposed interpretation of the multiphase hydrothermal structures is based on the resistivity model, a high‐resolution infrared surface temperature image, and 1,136 soil CO2 flux measurements. In addition, we realized 27 soil cation exchange capacity and pH measurements demonstrating a negligible contribution of surface conductivity to the shallow bulk electrical conductivity. Hence, we show that the resistivity changes are mainly controlled by fluid content and temperature. The high‐resolution tomograms identify for the first time the structure of the gas‐dominated reservoir at 60 m depth that feeds the Bocca Grande fumarole through a ~10 m thick channel. In addition, the resistivity model reveals a channel‐like conductive structure where the liquid produced by steam condensation around the main fumaroles flows down to the Fangaia area within a buried fault. The model delineates the emplacement of the main geological structures: Mount Olibano, Solfatara cryptodome, and tephra deposits. It also reveals the anatomy of the hydrothermal system, especially two liquid‐dominated plumes, the Fangaia mud pool and the Pisciarelli fumarole, respectively.

Soil microbial community responses to acid exposure and neutralization treatment

Changes in microbial community induced by acid shock were studied in the context of potential release of acids to the environment due to chemical accidents. The responses of microbial communities in three different soils to the exposure to sulfuric or hydrofluoric acid and to the subsequent neutralization treatment were investigated as functions of acid concentration and exposure time by using 16S-rRNA gene based pyrosequencing and DGGE (Denaturing Gradient Gel Electrophoresis). Measurements of soil pH and dissolved ion concentrations revealed that the added acids were neutralized to different degrees, depending on the mineral composition and soil texture. Hydrofluoric acid was more effectively neutralized by the soils, compared with sulfuric acid at the same normality. Gram-negative ß-Proteobacteria were shown to be the most acid-sensitive bacterial strains, while spore-forming Gram-positive Bacilli were the most acid-tolerant. The results of this study suggest that the Gram-positive to Gram-negative bacterial ratio may serve as an effective bio-indicator in assessing the impact of the acid shock on the microbial community. Neutralization treatments helped recover the ratio closer to their original values. The findings of this study show that microbial community changes as well as geochemical changes such as pH and dissolved ion concentrations need to be considered in estimating the impact of an acid spill, in selecting an optimal remediation strategy, and in deciding when to end remedial actions at the acid spill impacted site.

Oxidation of iron sulfides in subsoils of cultivated boreal acid sulfate soil fields – based on soil redox potential and pH measurements

Acid sulfate soil leachates deteriorate the aquatic ecosystems of their recipient waters around the world. In Finland, AS soils are located mainly on the coast of the Baltic Sea, where rivers and estuaries suffer from acid leachates and waters do not meet with the criteria of good water quality set by the EU. Field drainage of cultivated AS soils is attributable to leaching of acidity, but regardless of various mitigation measures, the acidity of discharge water in these areas has not decreased significantly. In order to better understand the pathways involved in the formation of acidity, the redox status of 56 Finnish AS soil fields was examined using redox potential and pH data measured down to 2m. The findings indicated that the oxidation of soils has occurred at depths below the drainage pipes, with the median being at a depth of 1.6m. In fields cultivated for a long time, soil texture had a stronger effect on the depth of the redox interface than the drainage method; open ditch drainage and subsurface drainage; oxidation being faster in sandy and silty soils than in clayey soils. The isostatic land uplift also seems to affect the depth of the redox interface in the long run. Most of the studied fields had been cultivated for at least 30years prior to the study. However, the pH values of the soils were still very low, probably due to actual and retained acidity. The prevention of oxidation of sulfidic materials in subsoils is important, but measures for neutralizing the acidity are needed. Without them it seems that the leaching of acidity will continue and may decrease only slowly. However, severe droughts during summers and the reclamation of unripe AS soils for any purpose will increase the leaching of acidity.

Ecological Value Of Soil Organic Matter (SOM) at Tropical Evergreen Aglaia-Streblus Forest of Meru Betiri National Park, East Java, Indonesia

As part of carbon pools, forest soil stores soil organic matter (SOM) that contains many elements including organic C, N, P, and K. These elements contribute nutrients for biogeochemical cycles within the ecosystem. This study was done to determine the ecological value of forest soil organic matter at tropical evergreen Aglaia-Streblus forest of Meru Betiri National Park (MBNP), East Java, Indonesia. The data were sampled along gradient topography in Pringtali tropical forest of TMBNP. Direct measurements of soil moisture, temperature, and pH were taken in the field. The soil samples were extracted from 6 points of soil solum using soil auger, and then oven-dried to get value of dry-weight. The elements content of organic C, N, P, and K were analyzed and estimated at the laboratory. The ecoval of SOM was appraised using developed ecological valuation tool. The result showed that SOM contributed higher ecoval of organic C (66.03 Mg ha-1) than other elements. Compared to P and K elements, N had the highest stock of element content. However, comparing to other two tropical forest ecosystems of Asia the ecoval of SOM elements in TMBNP was relatively low because of its natural geomorphological features.The ecoval of SOM elements in TMBNP was relatively low because of its natural geomorphological features. The ecovals contributed about 2.440,64 - 6.955,50 USD or 31.271.923,73 - 89.120.837,23 IDR per hectare of ecological value (d) to the ecosystem. This value was mainly contributed by organic C stock in the TMBNP forest SOM. It means the forest SOM had higher element content of organic C than N, P, and K elements. This d value is an indicator for TMBNP to protect the SOM elements meaning protecting their resources to sustain the biogeochemical cycles in the forest ecosystem. All the management and policy correlated to this protected area should consider this valuable information for their plan and actions.

Quantification of Uncertainty in Mathematical Models: The Statistical Relationship between Field and Laboratory pH Measurements

The measurement of soil pH using a field portable test kit represents a fast and inexpensive method to assess pH. Field based pH methods have been used extensively for agricultural advisory services and soil survey and now for citizen soil science projects. In the absence of laboratory measurements, there is a practical need to model the laboratory pH as a function of the field pH to increase the density of data for soil research studies and Digital Soil Mapping. The accuracy and uncertainty in pH field measurements were investigated for soil samples from regional Victoria in Australia using both linear and sigmoidal models. For samples in water and CaCl2 at 1 : 5 dilutions, sigmoidal models provided improved accuracy over the full range of field pH values in comparison to linear models (i.e., pH &lt; 5 or pH &gt; 9). The uncertainty in the field results was quantified by the 95% confidence interval (CI) and 95% prediction interval (PI) for the models, with 95% CI &lt; 0.25 pH units and 95% PI = ±1.3 pH units, respectively. It was found that the Pearson criterion for robust regression analysis can be considered as an alternative to the orthodox least-squares modelling approach because it is more effective in addressing outliers in legacy data.

Water balance creates a threshold in soil pH at the global scale.

Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems. However, soil pH is not an independent regulator of soil fertility-rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep transition from alkaline to acid soils across natural climate gradients. Although the processes governing this threshold in soil pH are well understood, the threshold has not been quantified at the global scale, where the influence of climate may be confounded by the effects of topography and mineralogy. Here we evaluate the global relationship between water balance and soil pH by extracting a spatially random sample (n = 20,000) from an extensive compilation of 60,291 soil pH measurements. We show that there is an abrupt transition from alkaline to acid soil pH that occurs at the point where mean annual precipitation begins to exceed mean annual potential evapotranspiration. We evaluate deviations from this global pattern, showing that they may result from seasonality, climate history, erosion and mineralogy. These results demonstrate that climate creates a nonlinear pattern in soil solution chemistry at the global scale; they also reveal conditions under which soils maintain pH out of equilibrium with modern climate.

Regional differences in soil pH niche among dry grassland plants in Eurasia

Soil pH is a key predictor of plant species occurrence owing to its effect on the availability of nutrients and phytotoxic metals. Although regional differences in realized soil pH niche (‘niche shifts’) have been reported since the 19th century, no study has disentangled how they are influenced by spatial differences in substrate availability, macroclimate, and competitors. We linked plot‐level data on species occurrence and measured soil pH from dry grasslands in eight regions across Eurasia (n = 999 plots), spanning a geographic gradient of 6862 km. We calculated regional shifts in niche optimum (Dopt) and width (Dwidth) for 73 Species × Region 1 × Region 2 combinations (SRRs; 38 study species) using extended Huisman–Olff–Fresco models. Next, we used commonality analysis to partition the contribution of substrate availability, precipitation, and species traits indicative of competitive ability to variation in regional niche shifts. Shifts in optimum were rare (5% of SRRs with Dopt ≥ 1 pH units) but many species did not show optima within regions. By contrast, shifts in niche width were common (22% of SRRs with Dwidth ≥1 pH units) and there were pronounced interspecific differences. Whereas none of the three predictors significantly explained shifts in niche optimum, common and unique effects of substrate availability and precipitation accounted for 85% of variation in niche width. Our results suggest that substrate availability and precipitation could be the driving factors behind species regional shifts in niche width. Studies that address additional factors, such as other edaphic niches, and their variability at the regional and micro‐scale will improve our understanding of the mechanisms underlying species distributions.

Effects of Dolomite and Oyster Shell on Nitrogen Processes in an Acidic Mine Soil Applied with Livestock Manure Compost

Mine soils are usually unfavorable for plant growth due to their acidic condition and low contents of organic matter and nutrients. To investigate the effect of organic material and lime on nitrogen processes in an acidic metal mine soil, we conducted an incubation experiment with treating livestock manure compost, dolomite, and oyster shell and measured soil pH, dehydrogenase activity, and concentration of soil inorganic N (<TEX>$NH_4{^+}$</TEX> and <TEX>$NO_3{^-}$</TEX>). Compost increased not only soil inorganic N concentration, but also soil pH from 4.4 to 4.8 and dehydrogenase activity from 2.4 to <TEX>$3.9{\mu}g\;TPF\;g^{-1}day^{-1}$</TEX>. Applying lime with compost significantly (P<0.05) increased soil pH (5.9-6.4) and dehydrogenase activity (<TEX>$4.3-7.0{\mu}g\;TPF\;g^{-1}day^{-1}$</TEX>) compared with applying only compost. Here, the variation in dehydrogenase activity was significantly (P<0.05) correlated with that in soil pH. Soil inorganic N decreased with time by 14 days after treatment (DAT) due to N immobilization, but increased with time after 14 DAT. At 28 DAT, soil inorganic N was significantly (P<0.05) higher in the lime treatments than the only compost treatment. Especially the enhanced dehydrogenase activity in the lime treatments would increase soil inorganic N due to the favored mineralization of organic matter. Although compost and lime increased soil microbial biomass and enzyme activity, ammonia oxidation still proceeded slowly. We concluded that compost and lime in acidic mine soils could increase soil microbial activity and inorganic N concentration, but considerable ammonium could remain for a relatively long time.

Context-dependent environmental quality standards of soil nitrate for terrestrial plant communities

Environmental quality standards (EQS) specify the maximum permissible concentration or level of a specific environmental stressor. Here, a procedure is proposed to derive EQS that are specific to a representative species pool and conditional on confounding environmental factors. To illustrate the procedure, a dataset was used with plant species richness observations of grasslands and forests and accompanying soil nitrate-N and pH measurements collected from 981 sampling sites in the Netherlands. Species richness was related to soil nitrate-N and pH with quantile regression allowing for interaction effects. The resulting regression models were used to derive EQS for nitrate conditional on pH, quantified as the nitrate-N concentrations at a specific pH level corresponding with a species richness equal to 95% of the species pool, for both grasslands and forest communities. The EQS varied between 1.8 mg/kg nitrate-N at pH 9–65 mg/kg nitrate-N at pH 4. EQS for forests and grasslands were similar, but EQS based on Red List species richness were considerably lower (more stringent) than those based on overall species richness, particularly at high pH levels. The results indicate that both natural background pH conditions and Red List species are important factors to consider in the derivation of EQS for soil nitrate-N for terrestrial ecosystems.

Gaziantep Yöresi Tarım Topraklarının Besin Elementi Durumları ve Bunların Bazı Toprak Özellikleri ile İlişkileri

Calismada, Gaziantep yoresi topraklarinin verimlilik durumlarinin toprak analizleriyle belirlenmesi amaclanmistir. Bu amacla, yoreyi temsilen 53 noktadan, iki farkli derinlikten (0-30 ve 30-60 cm) alinan toplam 106 toprak orneginde bunye, toplam kirec (CaCO 3 ) , reaksiyon (pH), toplam tuz, organik madde (OM), katyon degisim kapasitesi (KDK) ve makro–mikro besin elementlerinin analizleri yapilmistir. Elde edilen bulgulara gore, arastirma alani topraklarinin % 65.11’ inin killi, % 27.35’ inin killi tinli, % 7.54’ unun kumlu-killi-tinli bunyeye sahip oldugu, topraklarin buyuk bir cogunlugunun hafif alkalin ve alkalin reaksiyonlu, topraklarin organik madde iceriklerinin yetersiz oldugu ve yaklasik yarisinin tuzlu sinifinda yer aldiklari belirlenmistir. Topraklarin % 55.65’ inin azot, % 35.86’ sinin fosfor, % 39.63’ unun potasyum, % 29.24’ unun demir, % 43.40’ inin cinko ve % 2.8’ inin bakir bakimlarindan yetersiz oldugu belirlenmistir. Topraklarda CaCO 3 ile pH, Tuz, KDK, K ve Zn; OM ile P, Tuz, KDK ve pH; pH ile Zn, KDK ve P; KDK ile Kil, Kum, Tuz ve P; Kil ile K, Kum ve Silt; Kum ile Silt ve Cu arsinda onemli iliskiler belirlenmistir. Anahtar kelimeler: Gaziantep, toprak verimliligi, toprak ozellikleri, besin elementleri Nutrient Status of Gaziantep Agricultural Soils and Their Relationships with Some Soil Properties ABSTRACT: The goal of this study is to determine soil fertility levels of Gaziantep Province, Turkey, through soil analyses. For this objective, a representative soil survey of 53 samplings with two different depths (0-30 ve 30-60 cm), totaling 106 soil samples, was performed to determine soil texture, lime content, soil pH, total salt, soil organic matter content (SOM), cation exchange capacity (CEC), and macro and micronutrient concentrations. The results showed that clayey, clay loam, and sandy clay loam soils covered 65.11, 27.35, and 7.54 % of the study area, respectively. Most of the soil pH measurements in the area fell between slightly alkaline and alkaline reactions. Soil organic matter content was deficient in all the region’s soils and approximately half of the soils were categorized as saline soils. Deficiency of nitrogen, phosphorous, potassium, iron, zinc, and cupper was determined in 55.65, 35.86, 39.63, 29.24, 43.4, and 2.8 % of the soils, respectively. Significant relationships were found for lime with pH, Salt, CEC, K, Zn; SOM with P, Salt, CEC, and pH; pH with Zn, CEC, and P; CEC with Clay, Sand, Salt, and P; Clay with K, Sand, and Silt; Sand with Silt and Cu in the soils of the study area. Key words: Gaziantep, soil fertility, soil properties, nutrient elements

Gaziantep Yöresi Tarım Topraklarının Besin Elementi Durumları ve Bunların Bazı Toprak Özellikleri ile İlişkileri

Calismada, Gaziantep yoresi topraklarinin verimlilik durumlarinin toprak analizleriyle belirlenmesi amaclanmistir. Bu amacla, yoreyi temsilen 53 noktadan, iki farkli derinlikten (0-30 ve 30-60 cm) alinan toplam 106 toprak orneginde bunye, toplam kirec (CaCO 3 ) , reaksiyon (pH), toplam tuz, organik madde (OM), katyon degisim kapasitesi (KDK) ve makro–mikro besin elementlerinin analizleri yapilmistir. Elde edilen bulgulara gore, arastirma alani topraklarinin % 65.11’ inin killi, % 27.35’ inin killi tinli, % 7.54’ unun kumlu-killi-tinli bunyeye sahip oldugu, topraklarin buyuk bir cogunlugunun hafif alkalin ve alkalin reaksiyonlu, topraklarin organik madde iceriklerinin yetersiz oldugu ve yaklasik yarisinin tuzlu sinifinda yer aldiklari belirlenmistir. Topraklarin % 55.65’ inin azot, % 35.86’ sinin fosfor, % 39.63’ unun potasyum, % 29.24’ unun demir, % 43.40’ inin cinko ve % 2.8’ inin bakir bakimlarindan yetersiz oldugu belirlenmistir. Topraklarda CaCO 3 ile pH, Tuz, KDK, K ve Zn; OM ile P, Tuz, KDK ve pH; pH ile Zn, KDK ve P; KDK ile Kil, Kum, Tuz ve P; Kil ile K, Kum ve Silt; Kum ile Silt ve Cu arsinda onemli iliskiler belirlenmistir. Anahtar kelimeler: Gaziantep, toprak verimliligi, toprak ozellikleri, besin elementleri Nutrient Status of Gaziantep Agricultural Soils and Their Relationships with Some Soil Properties ABSTRACT: The goal of this study is to determine soil fertility levels of Gaziantep Province, Turkey, through soil analyses. For this objective, a representative soil survey of 53 samplings with two different depths (0-30 ve 30-60 cm), totaling 106 soil samples, was performed to determine soil texture, lime content, soil pH, total salt, soil organic matter content (SOM), cation exchange capacity (CEC), and macro and micronutrient concentrations. The results showed that clayey, clay loam, and sandy clay loam soils covered 65.11, 27.35, and 7.54 % of the study area, respectively. Most of the soil pH measurements in the area fell between slightly alkaline and alkaline reactions. Soil organic matter content was deficient in all the region’s soils and approximately half of the soils were categorized as saline soils. Deficiency of nitrogen, phosphorous, potassium, iron, zinc, and cupper was determined in 55.65, 35.86, 39.63, 29.24, 43.4, and 2.8 % of the soils, respectively. Significant relationships were found for lime with pH, Salt, CEC, K, Zn; SOM with P, Salt, CEC, and pH; pH with Zn, CEC, and P; CEC with Clay, Sand, Salt, and P; Clay with K, Sand, and Silt; Sand with Silt and Cu in the soils of the study area. Key words: Gaziantep, soil fertility, soil properties, nutrient elements

High-Resolution Denitrification Kinetics in Pasture Soils Link N2O Emissions to pH, and Denitrification to C Mineralization.

Denitrification in pasture soils is mediated by microbial and physicochemical processes leading to nitrogen loss through the emission of N2O and N2. It is known that N2O reduction to N2 is impaired by low soil pH yet controversy remains as inconsistent use of soil pH measurement methods by researchers, and differences in analytical methods between studies, undermine direct comparison of results. In addition, the link between denitrification and N2O emissions in response to carbon (C) mineralization and pH in different pasture soils is still not well described. We hypothesized that potential denitrification rate and aerobic respiration rate would be positively associated with soils. This relationship was predicted to be more robust when a high resolution analysis is performed as opposed to a single time point comparison. We tested this by characterizing 13 different temperate pasture soils from northern and southern hemispheres sites (Ireland and New Zealand) using a fully automated-high-resolution GC detection system that allowed us to detect a wide range of gas emissions simultaneously. We also compared the impact of using different extractants for determining pH on our conclusions. In all pH measurements, soil pH was strongly and negatively associated with both N2O production index (IN2O) and N2O/(N2O+N2) product ratio. Furthermore, emission kinetics across all soils revealed that the denitrification rates under anoxic conditions (NO+N2O+N2 μmol N/h/vial) were significantly associated with C mineralization (CO2 μmol/h/vial) measured both under oxic (r2 = 0.62, p = 0.0015) and anoxic (r2 = 0.89, p<0.0001) conditions.

Evolution in situ: hybrid origin and establishment of willows (Salix L.) on alpine glacier forefields.

Little attention has been paid to the evolutionary consequences of the colonizing dynamics and succession processes following glacier retreat. Here we studied hybrid populations that have recently formed and established on glacier forefields of the European Alps owing to secondary contact of a lowland colonizer with a subalpine species. We analyzed the composition of two hybrid populations between Salix purpurea and Salix helvetica with nine microsatellite markers by using Bayesian methods (structure and NewHybrids), and simulations. We also studied niche differentiation between the hybrids and the parental species based on indicator values, soil pH and water retention potential measurements. Allelic structure of hybrids confirms the assumed parentage and in situ origin of the crosses on two independent sites within the last decades. Both hybrid populations comprised F1 and later generation hybrids (F2 and backcrosses), confirming hybrid fertility. The parental species showed significant differences in niche characteristics for temperature, soil pH, nutrients and moisture. Remarkably, the hybrids exhibited a higher tolerance to cold temperatures, nutrient-poor and acidic soils than either parent. Our results show that willow hybrids originated after glacier retreat and have established persistent populations within a few decades. One factor contributing to hybrid establishment in sympatry with their parents is their ability to occupy more extreme niches than either parental species within a mosaic-like pattern of microhabitats on the forefield. Introgression and/or transgressive segregation may have resulted in novel genotypes that are able to expand the ecological spectrum of either parent.

Effect of topography and litterfall input on fine-scale patch consistency of soil chemical properties in a tropical rainforest

Spatial aggregation of soil chemical properties, or nutrient patches, may be generated by topography and plants and can seasonally fluctuate because of climate. Whether nutrient patches maintain consistency (no change in ranking through sequential sampling), through temporal scales, and whether topography and litterfall contribute to the persistence of such ranking is rarely tested. In a 1-ha tropical rainforest plot in Southwest China, we measured soil pH, total N, NH4–N, NO3–N, and available P and K for four times and assessed the patch structure (patterns of patch distribution) and their temporal consistency. We then tested how structure and consistency of chemical soil properties were affected by topography and chemical inputs from litterfall. All soil chemical properties showed significant seasonal fluctuations, but patch consistency was higher for soil pH, total N, and available P and K compared to NH4–N or NO3–N. Topography influenced pH patch consistency while annual litterfall input was important for maintaining patch consistency in total N and available P and K. Fine-scale consistency of patches in soil pH, total N, and available P and K suggest they may exert stable selection pressures on species for niche differentiation, while consistency of soil NH4–N and NO3–N require further study.

Short-term variability in labile soil phosphorus is positively related to soil moisture in a humid tropical forest in Puerto Rico

Primary productivity in tropical forests is often considered limited by phosphorus (P) availability. Microbial activity is a key regulator of available P through organic matter decomposition (supply) as well as microbial immobilization (depletion). Environmental conditions, such as soil moisture and temperature can fluctuate significantly on hourly to daily time-scales in tropical forested ecosystems. Given the ability of microbes to respond rapidly to changing environmental conditions we would expect concomitant changes in the available soil P pool. Despite the potential for soil P availability to vary on short time-scales, research that investigates hourly to daily changes in the available soil P pool in tropical forests is extremely rare. We quantified diurnal fluctuations in labile soil P and the importance of biotic and abiotic factors in driving these patterns in a wet tropical forest in Puerto Rico. Hourly measurements of Bray-extractable P were made from sunrise to sunset on five separate days along with measurements of soil temperature, moisture, pH, soil respiration, and solar radiation. While we found no significant diurnal variation in labile P, it did, however, vary significantly across the five sample days (2.8–3.8 µg/g). The day-to-day variation in labile P was positively related to soil moisture (R2 = 0.42, p = 0.009). These findings illustrate the potential for rapid change in the available P pool in response to variable soil moisture status as well as the importance of considering soil moisture conditions when estimating P availability in the humid tropics.