Interpretation of sulfur cycling in two catchments in the Black Forest (Germany) using stable sulfur and oxygen isotope data

The isotopic composition of SO ₄ ^2- in bulk precipitation, canopy throughfall, seepage water at three different soil depths, stream water, and groundwater was monitored in two forested catchments in the Black Forest (Germany) between November 1989 and February 1992. Isotope measurements on aqueous sulfate were complemented by ³⁴S-analyses on SO₂ in the air, total sulfur and inorganic sulfate in the soil, and bedrock sulfur, in order to identify sources and biogeochemical processes affecting S cycling in catchments with base poor, siliceous bedrock. Stable S isotope data indicated that atmospheric deposition and not mineral weathering is the major source of S in both catchments since ³⁴S-values for sulfate in the soil, in seepage water, and in stream water were generally found to be similar to the mean ³⁴S-values of precipitation SO ₄ ^2- (+2.1. However, ¹⁸O-values of seepage water SO ₄ ^2- at 30 cm and especially at 80 cm depth were depleted by several per mil with respect to those of the atmospheric deposition (+7.5 to +13.5. This indicates that in both catchments a considerable proportion of the seepage water SO ₄ ^2- is derived from mineralization of carbon-bonded soil S and must therefore have cycled through the organic soil S pool. ³⁴S-values for different S compounds in the solid soil were found to differ markedly depending on S fraction and soil depth. Since atmospheric S deposition with rather constant ³⁴S-values was identified as the dominant S source in both catchments, this is interpreted as a result ofin situ isotope fractionation rather than admixture of isotopically different S. The differences between the ³⁴S-values of seepage water and soil sulfate and those of organic soil S compounds are consistent with a model in which SO ₄ ^2- uptake by vegetation and soil microorganisms favours³⁴SO ₄ ^2- slightly, whereas during mineralization of organic soil S to aqueous SOSO ₄ ^2- ,³²S reacts preferentially. However, the data provide evidence for negligible isotope fractionation during physico-chemical S transformations such as adsorption/desorption in aerated forest soils.     

基于典范对应分析的滨海湿地土壤季节性盐渍化特征

为了更好地开发利用黄河三角洲湿地土壤资源和生态环境建设,运用单因素方差分析(One-way ANOVA)和典范对应分析方法(CCA),对黄河口湿地0—10 cm土壤全盐量(TS)、盐分离子组成、pH、钠吸附比(SAR)、电导率(EC)的季节性变化特征及数量关系进行了分析。结果表明:该区土壤属于盐土类型,春季(5月)、夏季(8月)、秋季(10月)全盐含量均高于17.9 g/kg,且春季、秋季的含盐量高于夏季,造成春、秋季积盐,夏季脱盐。盐分阳离子以Na~+为主,阴离子以Cl~-为主,除Mg~(2+)在夏季、秋季和Cl~-在秋季表现出强烈的变异性外,其余离子在不同季节均表现出中等强度的变异性。春季,Cl~-与Na~+、Mg~(2+),SO■与K~+;夏季,Cl~-与HCO~-_3,SO■与Mg~(2+)、Ca~(2+),Ca~(2+)与Mg~(2+);秋季,Cl~-与SO■,SO■与Mg~(2+),Ca~(2+)与Mg~(2+),均有很好的关联性。pH值均介于7.7—8.1之间,各个季节受盐分离子的影响较小,分布较为均匀。SAR介于3.08—5.29之间,春季受控于HCO~-_3;夏季受控于K~+;秋季受各离子的影响均较小,分布较为均匀。EC介于7.16—13.04 mS/cm,春季受各离子的影响均较小,其空间分布较为均匀;夏季受控于SO■、Ca~(2+)、Mg~(2+);秋季受控于Na~+。TS与Cl~-、Na~+、Mg~(2+)在季节变化上的差异性一致,且各个季节均受控于Cl~-。故通过合理的措施控制或减少Cl~-来源是一条减轻黄河口湿地土壤盐渍化的合适途径。     

A method for collecting soil percolate and soil solution in the field

Summary A soil-water extractor is described which uses an absorbent sponge material for sampling soil percolate and solution. Good agreement existed between soil extracts (1:5 soil:water) and extracts obtained from the extractor sponge after equilibration at low water tensions (pF 0–2.5) in the range, 0–100 g/g soil (0–1400 g/ml solution) for solute anions (Cl^-, NO₂ ^- and NO₃ ^–, R² > 0.98), and for ammonium ions (NH₄ ⁺, R²=0.93).Percolate was recovered in a field soil in volumes sufficient to permit analysis of constituents. Concentrations of solute Cl^- ions in these percolates were similar to those in the added water and in percolate from a zero-tension lysimeter. Poor relationships were obtained in the field between soil solution extracts from the sponge and 1:10 soil water extracts. For the present, the soil extractor may be used for sampling and monitoring movement of percolate and solute fronts, in the wetter range of soil water content.     

Microbial N turnover processes in three forest soil layers following clear cutting of an N saturated mature spruce stand

Microbial N turnover processes were investigated in three different forest soil layers [organic (O) layer, 0–10 cm depth (M₁), 10–40 cm depth (M₂)] after the clear cutting of a nitrogen (N) saturated spruce stand at the Höglwald Forest (Bavaria, Germany). The aim of the study was to provide detailed insight into soil-layer specific microbial production and the consumption of inorganic N within the main rooting zone. Furthermore, we intended to clarify the relevance of each soil layer investigated in respect of the observed high spatial variation of seepage water nitrate (NO ₃ ^? ) concentration at a depth of 40 cm. The buried bag and the ¹⁵N pool dilution techniques were applied to determine the net and gross N turnover rates. In addition, soil pH, C:N ratio, pool sizes of soil ammonium (NH ₄ ⁺ ) and NO ₃ ^? , as well as quantities of microbial biomass carbon (C_mic) and nitrogen (N_mic) were determined. The 40 cm thick upper mineral soil was found to be the main place of NO ₃ ^? production with a NO ₃ ^? supply or net nitrification three times higher than in the considerably thinner O layer. Nevertheless, O layer nitrification processes determined via in situ field experiments showed significant correlation with seepage water NO ₃ ^? . An improved correlation noted several months after the cut may result from a transport-induced time shift of NO ₃ ^? with downstream hydrological pathways. In contrast, the soil laboratory incubation experiments found no indication that mineral soil is relevant for the spatial heterogeneity of seepage water NO ₃ ^? . The results from our study imply that in situ experiments may be better suited to studies investigating N turnover in relation to NO ₃ ^? loss via seepage water in similar ecosystems in order to gain representative data.     

Forest soil solutions: Acid/base chemistry and response to calcite treatment

Soil solution chemistry was investigated at a forested watershed draining into Woods Lake. N.Y. as part of the Experimental Watershed Liming Study (EWLS). The objective of this study was to assess the response of soil water to watershed treatment of calcite (CaCO₃). This material was applied in an effort to mitigate the effects of acidic atmospheric deposition. Soil solutions draining Oa and Bs horizons in reference subcatchments were characterized by low pH and acid neutralizing capacity (ANC) due to elevated concentrations of SO ₄ ^2– , NO ₃ ^– and organic anions relative to the sum of base cation (C_B Ca²⁺, Mg²⁺, Na⁺, K⁺) concentrations. Seasonal and spatial variation of pH andANC in soil solutions appeared to belargely controlled by variations in the concentrations of dissolved organic acids which, in turn, were regulated by reactions of Al with soil organic matter. Nitrate was positively correlated and SO²⁺ was negatively correlated with Ca²⁺ and Al concentrations in reference soil solutions, indicating that changes in NO ₃ ^– influences spatial and seasonal variations in Ca²⁺ and Al concentrations. On this basis, NO ₃ ^– appears to be important in soil acidification and the dynamics of drainage water acidity. Comparison of our results with historical data for the site showed declines in concentrations of SO ₄ ^2– , which are consistent with decreases in emissions of SO₄, in the eastern U.S. and atmospheric deposition of SO ₄ ^2– , to the Adirondack region. Mineral soil solutions have shown large increases in concentrations of NO ₃ ^– . Declines in concentrations of C_B and increases in concentrations of Al have occurred over the last ten years, suggesting depletion of soil pools of exchangeable basic cations and increased sensitivity to acidic deposition. Calcite (CaCO₃) treatment of 6.89 Mg/ha resulted in a significant increase of Ca²⁺, ANC and pH in both Oa and Bs horizon soil solutions. Soil water response to CaCO₃ addition was most evident during the first year after treatment, apparently due to macropore transport of particulate and dissolved CaCO₃ However, increases in ANC and pH in the mineral soil waters were not sustained and appeared insufficient to result in substantial improvement in surface water quality over the 43 month study period.     

Soil respiration response to three years of elevated CO2 and N fertilization in ponderosa pine (Pinus ponderosa Doug. ex Laws.)

We measured growing season soil CO₂ evolution under elevated atmospheric [CO₂] and soil nitrogen (N) additions. Our objectives were to determine treatment effects, quantify seasonal variation, and compare two measurement techniques. Elevated [CO₂] treatments were applied in open-top chambers containing ponderosa pine (Pinus ponderosa L.) seedlings. N applications were made annually in early spring. The experimental design was a replicated factorial combination of CO₂ (ambient, + 175, and +350 L L^–1 CO₂) and N (0, 10, and 20 g m^–2 N as ammonium sulphate). Soils were irrigated to maintain soil moisture at > 25 percent. Soil CO₂ evolution was measured over diurnal periods (20–22 hours) in October 1992, and April, June, and October 1993 and 1994 using a flow-through, infrared gas analyzer measurement system and corresponding pCO₂ measurements were made with gas wells. Significantly higher soil CO₂ evolution was observed in the elevated CO₂ treatments; N effects were not significant. Averaged across all measurement periods, fluxes, were 4.8, 8.0, and 6.5 for ambient + 175 CO₂, and +350 CO₂ respectively).Treatment variation was linearly related to fungal occurrence as observed in minirhizotron tubes. Seasonal variation in soil CO₂ evolution was non-linearly related to soil temperature; i.e., fluxes increased up to approximately soil temperature (10cm soil depth) and decreased dramatically at temperatures > 18°C. These patterns indicate exceeding optimal temperatures for biological activity. The dynamic, flow-through measurement system was weakly correlated (r = 0.57; p < 0.0001; n = 56) with the pCO₂ measurement method.     

Temporal variability of solution Cd2+ concentration in metal-contaminated soils as affected by soil temperature: consequences on lettuce (Lactuca sativa L.) exposure

The aim of this study was to assess how the solubility and the speciation of Cd in soil solution were affected over time by the soil temperature for three metal-contaminated soils. The changes of solution Cd concentration (either total or free ionic) and other physico-chemical parameters (e.g. pH, ionic strength, the concentrations of ${\text{NO}}_3^ - $ , ${\text{SO}}_4^{2 - } $ , Ca, Mg and dissolved organic carbon) were monitored over a 28-day culture of lettuce (Lactuca sativa L.) in soils incubated at 10°C, 20°C or 30°C. The major result of this study was that Cd²⁺ concentration greatly varied over time in soil solution. The Cd²⁺ concentration declined over time in soil solution as did the concentration of cations that may compete for adsorption (Ca²⁺, Mg²⁺). The rise in soil temperature primarily impacted on the concentration of Cd²⁺ via promoting the microbial C-degradation and, thus, the complexation of Cd in soil solution. The integration of the temporal variations in Cd²⁺ concentration through the calculation of the root exposure to solution Cd (E _Cd) provided a fairly close and robust prediction of Cd concentration in lettuce roots. The present work thus provided new insights on the fate of Cd in contaminated soils that may be relevant for predicting the root uptake of Cd.     

The Occurrence,Sources and Spatial Characteristics of Soil Salt and Assessment of Soil Salinization Risk in Yanqi Basin,Northwest China

In order to evaluate the soil salinization risk of the oases in arid land of northwest China, we chose a typical oasis-the Yanqi basin as the research area. Then, we collected soil samples from the area and made comprehensive assessment for soil salinization risk in this area. The result showed that: (1) In all soil samples, high variation was found for the amount of Ca²⁺ and K⁺, while the other soil salt properties had moderate levels of variation. (2) The land use types and the soil parent material had a significant influence on the amount of salt ions within the soil. (3) Principle component (PC) analysis determined that all the salt ion values, potential of hydrogen (pHs) and ECs fell into four PCs. Among them, PC1 (C1^-, Na⁺, SO₄ ^2-, EC, and pH) and PC2 (Ca²⁺, K⁺, Mg²⁺and total amount of salts) are considered to be mainly influenced by artificial sources, while PC3 and PC4 (CO₃ ^- and HCO₃ ^2-) are mainly influenced by natural sources. (4) From a geo-statistical point of view, it was ascertained that the pH and soil salt ions, such as Ca²⁺, Mg²⁺ and HCO₃ ^-, had a strong spatial dependency. Meanwhile, Na⁺ and Cl^- had only a weak spatial dependency in the soil. (5) Soil salinization indicators suggested that the entire area had a low risk of soil salinization, where the risk was mainly due to anthropogenic activities and climate variation. This study can be considered an early warning of soil salinization and alkalization in the Yanqi basin. It can also provide a reference for environmental protection policies and rational utilization of land resources in the arid region of Xinjiang, northwest China, as well as for other oases of arid regions in the world.     

Nutrient concentration in wheat and soil under allelopathy treatments

Allelopathy is related to soil nutrient availability and allelochemicals can change the soil and therefore the plant nutrient status. Wheat is one of the most important crops for the production of human food in the world. Alhagi maurorum and Cardaria draba are the most important weeds in wheat fields. We performed experiments to assess the allelopathic effect of A. maurorum and C. draba shoots on mineral nutrient concentrations in pot-grown wheat plants and soil. The presence of dry powder of A. maurorum and C. draba shoots reduced concentrations of macronutrients (NO₃ ^?, K⁺, Ca²⁺ and P) and micronutrients (Fe²⁺ and Cu²⁺) in roots and shoots of wheat plants, whereas it did not affect concentrations of Mg²⁺, Mn²⁺ and Zn²⁺. Allelopathic effect of A. maurorum was significantly greater than that of C. draba. There was a significantly positive correlation between wheat growth and ion concentration. There was a significantly negative correlation between the soil nutrient concentration and plant nutrient concentration across the treatments. These results suggest that allelopathy increases the nutrient availability in the soil because of the decrease in absorption by plants.     

Plant induced alteration in the rhizosphere and the utilisation of soil heterogeneity

Plant-soil interactions result in a special rhizosphere soil chemistry, differing from that of the bulk soil found only a few mm from the root. The aim of this study was to investigate adaptation mechanisms of herbs growing in acid soils through studying their rhizosphere chemistry in a greenhouse experiment and in a field study. Ten herbs were grown in acid soil (pH 4.2 in the soil solution) in the greenhouse. The concentrations of NO₃ ^-, SO₄ ^2-, phosphates, Ca²⁺, Mg²⁺, Mn²⁺, K⁺, Na⁺, NH₄ ⁺ and pH were analysed in soil solutions obtained by centrifugation. The general pattern found was a depletion of nutrients in the rhizosphere compared with their concentrations in the bulk soil. The pH increase (up to 0.7 units) in the rhizosphere soil appeared to be caused by plant uptake of NO₃ ^- (r²=0.88). The ion concentrations in the soil solution of the rhizosphere were dependent on plant species and biomass increase. Although species with a larger biomass and higher growth rates showed a higher degree of ion depletion (except for Na⁺, SO₄ ^2-) in the rhizosphere, there were also species specific responses. A field study of five herbs at five oak forest sites in Southern Sweden (Scania) was also carried out. In addition to the soil solution concentrations, the loss on ignition (LOI) and the concentrations of 0.1 M BaCl₂ extractable K⁺, Mg²⁺, Mn²⁺, Ca²⁺, and Al ions were measured. The amount of soil solution Al was determined as free ionic (quickly reacting) Al. For all species and sites, the LOI and the concentrations of exchangeable cations were higher in the rhizosphere than in the bulk soil, apparently due to the roots preferably growing at organic-rich microsites. The concentrations of the ions as measured in the centrifuged soil solution, were either higher in the rhizosphere than in the bulk soil or were the same in both, except for NO₃ ^- and quickly reacting Al. The lower concentrations of quickly reacting Al in the rhizosphere, compared with the bulk soil could indicate the uptake of Al by the plant or the exudation of complexing substances. The pH differences were only small and mostly non-significant. Plant-soil interactions and the ability of plants to utilise heterogeneity of the soil appear to be more important for plant growth in acid soils than recognised heretofore. Rhizosphere studies provide an important means of understanding plant strategies in acid soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of prescribed burning and drought on the solute chemistry of mixed-conifer forest streams of the Sierra Nevada, California

Solute concentrations in atmospheric depositionand stream water were measured in two mixed-conifercatchments (Tharps and Log creeks) in the SierraNevada of California from 1984 through 1995, a periodincluding a 6-year drought and a prescribed burn inone catchment. The effects of prescribed burning inthe Tharps Creek catchment significantly increasedthe concentrations of most solutes in stream water. In the first year after prescribed burning, the VWM(volume-weighted mean) concentrations of acid anionsin stream water increased proportionally more thanthose of the base cations, and ANC (acid neutralizingcapacity) more than doubled. Sulfate and NO ₃ ^- increased proportionally more in streamwater than any other ions after the fire, but pre- andpost-burn VWM pH were not significantlydifferent. VWM SO ₄ ^2- and NO ₃ ^- concentrations the first year after burning occurredwere about 16- and 2,000-fold above pre-burnbaselines, respectively, while that of Cl^-increased 4-fold. Net retention (precipitationinputs minus streamwater outputs) of H⁺,NO ₃ ^- , NH ₃ ⁺ , SO ₄ ^2- and Cl^- occurred in both catchments, except afterprescribed burning of the Tharps Creek catchment inthe fall of 1990, which caused a net export ofSO ₄ ^2- , Cl^- and K⁺ thefirst year after the burn. Most solutes remained abovepre-disturbance concentrations by the end of the thirdyear after burning, whereas H⁺ and SiO₂remained below. Periodic increases in theconcentrations of Na⁺, Ca²⁺ and SO ₄ ^2- , and decreases in ANC and SiO₂occurred during a 6-year drought monitored in theadjacent undisturbed catchment of Log Creek.     

Soil temperature and biotic factors drive the seasonal variation of soil respiration in a maize (Zea mays L.) agricultural ecosystem

The diurnal and seasonal variation of soil respiration (SR) and their driving environmental factors were studied in a maize ecosystem during the growing season 2005. The diurnal variation of SR showed asymmetric patterns, with the minimum occurring around early morning and the maximum around 13:00 h. SR fluctuated greatly during the growing season. The mean SR rate was 3.16 μmol CO₂ m⁻² s⁻¹, with a maximum of 4.87 μmol CO₂ m⁻² s⁻¹ on July 28 and a minimum of 1.32 μmol CO₂ m⁻² s⁻¹ on May 4. During the diurnal variation of SR, there was a significant exponential relationship between SR and soil temperature (T) at 10 cm depth: . At a seasonal scale, the coefficient α and β fluctuated because the biomass (B) increased α, and the net primary productivity (NPP) of maize markedly increased β of the exponential equation. Based on this, we developed the equation to estimate the magnitude of SR and to simulate its temporal variation during the growth season of maize. Most of the temporal variability (93%) in SR could be explained by the variations in soil temperature, biomass and NPP of maize. This model clearly demonstrated that soil temperature, biomass and NPP of maize combined to drive the seasonal variation of SR during the growing season. However, only taking into account the influence of soil temperature on SR, an exponential equation over- or underestimated the magnitude of SR and resulted in an erroneous representation of the seasonal variation in SR. Our results highlighted the importance of biotic factors for the estimation of SR during the growing season. It is suggested that the models of SR on agricultural sites should not only take into account the influence of soil temperature, but also incorporate biotic factors as they affect SR during the growing season.     

Diel plant water use and competitive soil cation exchange interact to enhance NH<Subscript>4</Subscript><Superscript>+</Superscript> and K<Superscript>+</Superscript> availability in the rhizosphere

Aims

Hydro-biogeochemical processes in the rhizosphere regulate nutrient and water availability, and thus ecosystem productivity. We hypothesized that two such processes often neglected in rhizosphere models — diel plant water use and competitive cation exchange — could interact to enhance availability of K⁺ and NH₄ ⁺, both high-demand nutrients.

Methods

A rhizosphere model with competitive cation exchange was used to investigate how diel plant water use (i.e., daytime transpiration coupled with no nighttime water use, with nighttime root water release, and with nighttime transpiration) affects competitive ion interactions and availability of K⁺ and NH₄ ⁺.

Results

Competitive cation exchange enabled low-demand cations that accumulate against roots (Ca²⁺, Mg²⁺, Na⁺) to desorb NH₄ ⁺ and K⁺ from soil, generating non-monotonic dissolved concentration profiles (i.e. ‘hotspots’ 0.1–1 cm from the root). Cation accumulation and competitive desorption increased with net root water uptake. Daytime transpiration rate controlled diel variation in NH₄ ⁺ and K⁺ aqueous mass, nighttime water use controlled spatial locations of ‘hotspots’, and day-to-night differences in water use controlled diel differences in ‘hotspot’ concentrations.

Conclusions

Diel plant water use and competitive cation exchange enhanced NH₄ ⁺ and K⁺ availability and influenced rhizosphere concentration dynamics. Demonstrated responses have implications for understanding rhizosphere nutrient cycling and plant nutrient uptake.

     

Soil water content and temperature as independent or confounded factors controlling soil respiration in a temperate mixed hardwood forest

Variation in soil temperature can account for most of the seasonal and diel variation in soil CO₂ efflux, but the temperature effect is not always consistent, and other factors such as soil water content are known to influence soil respiration. The objectives of this research were to study the spatial and temporal variation in soil respiration in a temperate forested landscape and to evaluate temperature and soil water functions as predictors of soil respiration. Soil CO₂ fluxes were measured with chambers throughout an annual cycle in six study areas at the Harvard Forest in central Massachusetts that include soil drainage classes from well drained to very poorly drained. The mean annual estimate of soil CO₂ efflux was 7.2 Mg ha^–1, but ranged from 5.3 in the swamp site to 8.5 in a well-drained site, indicating that landscape heterogeneity is related to soil drainage class. An exponential function relating CO₂ fluxes to soil temperature accounted for 80% of the seasonal variation in fluxes across all sites (Q₁₀ = 3.9), but the Q₁₀ ranged from 3.4 to 5.6 for the individual study sites. A significant drought in 1995 caused rapid declines in soil respiration rates in August and September in five of the six sites (a swamp site was the exception). This decline in CO₂ fluxes correlated exponentially with decreasing soil matric potential, indicating a mechanistic effect of drought stress. At moderate to high water contents, however, soil water content was negatively correlated with soil temperature, which precluded distinguishing between the effects of these two confounded factors on CO₂ flux. Occurrence of high Q₁₀ values and variation in Q₁₀ values among sites may be related to: (i) confounding effects of high soil water content; (ii) seasonal and diel patterns in root respiration and turnover of fine roots that are linked to above ground phenology and metabolism; and (iii) variation in the depth where CO₂ is produced. The Q₁₀ function can yield reasonably good predictions of annual fluxes of CO₂, but it is a simplification that masks responses of root and microbial processes to variation in temperature and water content throughout the soil.     

Nutrient fluxes in a snow-dominated, semi-arid forest: Spatial and temporal patterns

We tested five hypotheses regarding the potential effects of precipitation change on spatial and temporal patterns of water flux, ion flux, and ion concentration in a semiarid, snowmelt-dominated forest in Little Valley, Nevada. Variations in data collected from 1995 to 1999 were used to examine the potential effects of snowpack amount and duration on ion concentrations and fluxes. Soil solution NO₃ ^–, NH₄ ⁺, and ortho-phosphate concentrations and fluxes were uniformly low, and the variations in concentration bore no relationship to snowmelt water flux inputs of these ions. Weathering and cation exchange largely controlled the concentrations and fluxes of base cations from soils in these systems; however, soil solution base cation concentrations were affected by cation concentrations during snowmelt episodes. Soil solution Cl^– and SO₄ ^2– concentrations closely followed the patterns in snowmelt water, suggesting minimal buffering of either ion by soils. In contrast to other studies, the highest concentration and the majority of ion flux from the snowpack in Little Valley occurred in the later phases of snowmelt. Possible reasons for this include sublimation of the snowpack and dry deposition of organic matter during the later stages of snowmelt. Our comparison of interannual and spatial patterns revealed that variation in ion concentration rather than water flux is the most important driver of variation in ion flux. Thus, it is not safe to assume that changes in total precipitation amount will cause concomitant changes in ion inputs to this system.     

Occurrence and intensity of wild boar disturbances, effects on the physical and chemical soil properties of alpine grasslands

Background and aims

Physical and chemical soil properties determine local plant conditions and resources, affecting plants’ ability to respond to disturbances. In alpine grasslands, wild boar disturbances occur at different intensities, what may affect differently their soil properties. Alpine soils from five contrasted plant communities were explored within and outside disturbances, accounting for an overall and community scale effect. Additionally, we analysed the effect of disturbance intensity on soil NO₃ ^--N and NH₄ ⁺-N.

Methods

Soils were analyzed for physical (bulk density, moisture content and electrical conductivity), and chemical properties (pH, total N and C, oxidizable C, C:N ratio, available K, P, Ca²⁺, Na⁺ and Mg²⁺). Resin bags were used to compare the effect of the disturbance occurrence and intensity on soil NO₃ ^--N and NH₄ ⁺-N.

Results

Bulk density, total N and NO₃ ^--N concentration were significantly higher in disturbed areas, while soil moisture, C:N, NH₄ ⁺-N, Na⁺, Mg²⁺ and Ca²⁺ concentrations were significantly lower. However, low disturbance intensity reduced NO₃ ^--N and increased NH₄ ⁺-N concentrations.

Conclusions

Wild boar occurrence and intensity strongly alter physical and chemical conditions of alpine soils, increasing soil compaction, and altering the availability of N forms. These changes may affect most plant species, thus affecting the structure and dynamics of alpine plant communities.     

In-situ soil solution chemistry in an acid forest soil as influenced by growing roots of Norway spruce (Picea abies [L.] Karst.)

A new approach for non-destructive monitoring of soil solution chemistry in high spatial and temporal resolution for rhizosphere studies is presented. In a 5×10 mm grid, 30 micro suction cups (1mm) were installed in a rhizotron with Norway spruce (Picea abies [L.] Karst.) growing in low pH B-horizon soil. Roots grew through the grid, closely passing the suction cups. Soil solution composition before, during and after root passage was determined. For K⁺ and Mg²⁺ a significant decrease of soil solution concentration near root tips and elongation zones was observed, indicating a marked uptake of these elements. Mg²⁺ concentration was also significantly lowered when the root system aged, suggesting that this ion might also be taken up in older parts of the root system. No influence of growing roots was found on Na⁺-concentrations.     

黑河天涝池流域典型林分生态水文化学特征

采集了黑河天涝池流域典型林分林外雨、穿透雨、树干径流和枯透水,并检测水体pH值和12种离子(K~+、Ca~(2+)、Na~+、Mg~(2+)、NH_4~+、Cu~(2+)、Zn~(2+)、Pb~(2+)、Cd~(2+)、Cl~-、SO_4~(2-)、NO_3~3)的质量浓度。结果表明:天涝池流域大气降水pH均值为7.74,呈碱性,降水中离子绝对质量浓度较低,最高的是NO_3~-,质量浓度为1.1111 mg/L,最低的为Na~+,质量浓度为0.0108 mg/L;两种林分冠层有降低降雨pH值的作用,青海云杉林冠层对NH_4~+有升高作用,祁连圆柏林冠层对NH_4~+有降低作用,两种林冠层对NO_3~-和Cu~(2+)质量浓度有降低作用,对其它离子质量浓度均表现为升高作用;两种林分树干径流有提高穿透雨pH值的作用,与穿透雨相比,两种林分树干径流中阴离子均有升高,圆柏树干径流中所有阳离子质量浓度均有下降,云杉树干径流中Ca~(2+)、K~+、Mg~(2+)和Na~+减少,NH_4~+和Cu~(2+)增加;典型林分枯透水有提升穿透雨pH值的作用,与穿透雨相比,两种林分枯透水中阴离子质量浓度均有升高,云杉枯透水各阳离子均有降低,圆柏枯透水中Ca~(2+)、K~+和Mg~(2+)质量浓度升高,NH_4~+、Na~+和Cu~(2+)质量浓度下降;在采集的所有样本中,Pb~(2+)和Cd~(2+)均未检出,而Zn~(2+)仅在云杉树干径流中检出。     

Fate of 15N labelled urine on four soil types

A field lysimeter experiment was conducted over a 406 day period to determine the effect of different soil types on the fate of synthetic urinary nitrogen (N). Soil types included a sandy loam, silty loam, clay and peat. Synthetic urine was applied at 1000 kg N ha^-1, during a winter season, to intact soil cores in lysimeters. Leaching losses, nitrous oxide (N₂O) emissions, and plant uptake of N were monitored, with soil ¹⁵N content determined upon destructive sampling of the lysimeters. Plant uptake of urine-N ranged from 21.6 to 31.4%. Soil type influenced timing and form of inorganic-N leaching. Macropore flow occurred in the structured silt and clay soils resulting in the leaching of urea. Ammonium (NH ₄ ⁺ –N), nitrite (NO ₂ ^- –N) and nitrate (NO₃ ^-–N) all occurred in the leachates with maximum concentrations, varying with soil type and ranging from 2.3–31.4 g NH ₄ ⁺ –N mL^-1, 2.4–35.6 g NO ₂ ^- –N mL^-1, and 62–102 g NO ₃ ^- –N mL^-1, respectively. Leachates from the peat and clay soils contained high concentrations of NO ₂ ^- –N. Gaseous losses of N₂O were low (<2% of N applied) over a 112 day measurement period. An associated experiment showed the ratio of N₂–N:N₂O–N ranged from 6.2 to 33.2. Unrecovered ¹⁵N was presumed to have been lost predominantly as gaseous N₂. It is postulated that the high levels of NO ₂ ^- –N could have contributed to chemodenitrification mechanisms in the peat soil.     

Differential responses to copper in rainbow trout (Oncorhynchus mykiss) acclimated to sea water and brackish water

Rainbow trout, Oncorhynchus mykiss, acclimated to 33% sea water (12 mg·ml^-1 salinity) experienced significant (10 meq·1^-1) increases in plasma [Na⁺] and [Cl^-] within 5 h of exposure to 6.3 mol copper·1^-1 indicating severe impairment of branchial ionoregulatory capacity. All plasma ion levels subsequently stabilised once the transbranchial [Na⁺] gradient was reduced to zero. The similar ionic strength of the external medium and their body fluids appeared to protect trout maintained in 33% sea water from further ionoregulatory stress and any secondary physiological disturbances during exposure to copper. Despite three- and fourfold greater transbranchial [Na⁺] and [Cl^-] gradients, trout acclimated to full-strength sea water (35 mg·ml^-1 salinity) suffered no major changes in plasma Na⁺, Cl^-, K⁺, or Ca²⁺, blood gases or haematology during 24 h exposure to 6.3 mol copper·1^-1. This reduction in toxicity in full strength sea water cannot be explained by differences in copper speciation. We suggest that during acute exposure to waterborne copper, active NaCl extrusion is unaffected due to the basolateral location of the gill Na⁺/K⁺-ATPase, but that ionoregulatory disturbances can occur due to gill permeability changes secondary to the displacement of surface-bound Ca²⁺. However, in full strength sea water the three-fold higher ambient [Ca²⁺] and [Mg²⁺] appear to be sufficient to prevent any detrimental permeability changes in the presence of 6.3 mol copper·1^-1. Plasma [NH ₊ ⁴ ] and [HCO _- ³ ] were both significantly elevated during exposure to copper, indicating that some aspects of gill ion transport (specifically the apical Na⁺/NH ₊ ⁴ and Cl^-/HCO _- ³ exchanges involved in acid/base regulation and nitrogenous waste excretion) are vulnerable to inhibition in the presence of waterborne copper.Abbreviations C _aO₂ arterial oxygen content - Hb haemoglobin - Hct haematocrit - MABP mean arterial blood pressure - MCHC mean cell haemoglobin content - MO₂ rate of oxygen consumption - P _a CO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen partial pressure - S salinity - SW sea water - T _Amm total ammonia (=NH₃+NH ₊ ⁴ ) - T _{CO 2} total carbon dioxide - TEP transepithelial potential - TOC total organic carbon - %Hb-O₂ percentage of haemoglobin saturated with oxygen