Deeper Mineral Soil Research Articles

Imbalances in Dissolved Elemental Export Fluxes Disclose “Hidden” Critical Zone Compartments

AbstractIn streams, short‐term element‐specific solute fluxes are often not balanced with long‐term chemical weathering fluxes determined in the residual solids from fractional element loss and denudation rate. The ratio of both estimates—the “Dissolved Export Efficiency” (DEE)—is frequently <1, indicating deficits in the stream dissolved load. To explore the cause of the stream deficits, we performed a daily water sampling campaign for one year in a forested headwater watershed in Southern Germany. We sampled surface runoff, above‐canopy and below‐canopy precipitation, subsurface flow from the organic soil layer, upper, and deep mineral soil, and groundwater. Regolith samples were obtained from a drill core and revealed the weathering front to lie between 7 and 15 m depth. We found a DEE < 1 for K, Si, Al, Fe. These elements are characterized by shallow slopes in C‐Q relationships, and the imbalances were found to originate in the deep saprolite. Their export pathway potentially includes “hidden” Critical Zone compartments or fluxes, presumably unsampled colloids that are exported preferentially during rare flushing events with stochastic temporal distribution. The DEE of nutritive elements like Ca, Mg, and P is also <1. These elements are characterized by steeper C‐Q slopes, and their imbalance can be explained by deep nutrient uptake followed by nutrient retainment in re‐growing forest biomass or export in plant debris. The collective evidence for these imbalances, including previous evidence from metal stable isotopes, suggests that the deep Critical Zone represents the location for chemical or biogenic retention and release of solutes.

Missing nitrogen source during ecosystem succession within retrogressive thaw slumps in Alaska

Retrogressive thaw slumps (RTS)—thermal erosion of soil and vegetation after ground ice thaw—are increasing. Recovery of plant biomass after RTS is important for maintaining Arctic carbon (C) stocks and is regulated by nutrient availability for new plant growth. Many RTS are characterized by verdant shrub growth mid-succession, atypical of the surrounding nutrient-limited tundra. Here, we investigated the potential for internal and external sources of nitrogen (N) and phosphorus (P) to support mid-successional shrub growth at three Alaskan RTS chronosequences. We assessed patterns of soil and microbial CNP, soil NP cycling rates and stocks, N inputs via biological N2-fixation, and thaw leachate over time after disturbance. We found a clear transfer of P stocks from mineral to organic soils with increasing site age, yet insufficient N from any one source to support observed shrub growth. Instead, multiple mechanisms may have contributed to mid-successional shrub growth, including sustained N-cycling with reduced plant biomass, N leaching from undisturbed tundra, uninvestigated sources of N2-fixation, and most promising given the large resource, deep mineral soil N stocks. These potential mechanisms of N supply are critical for the regulation of the Arctic C cycle in response to an increasingly common climate-driven disturbance.

Soil organic carbon stocks by soil group for afforested soils in Ireland

Forest ecosystems are recognised as Natural Climate Solutions because forest soils are such important carbon stores, containing almost half of the total soil organic carbon of terrestrial ecosystems. Here we present the results of a synthesis of soil carbon stocks by World Reference Base soil group, and forest litter carbon stocks for afforested soils in the Republic of Ireland. We report soil carbon stocks of mineral soils separately from organo-mineral soils. We estimated mean soil carbon stocks in a 100 cm deep mineral soil to be between 162 ± 87 t C/ha (Gleysols) and 416 ± 0 t C/ha (Umbrisols, n = 1), and between 173 ± 65 t C/ha (Phaeozems) and 602 ± 226 t C/ha (Regosols) in a 100 cm deep organo-mineral soil; both less than the estimated soil carbon stocks in organic soils (Histosols): 645 ± 222 t C/ha. The entire soil carbon stocks in mineral Leptosols (100 ± 0 t C/ha, n = 1), Stagnosols (144 ± 39 t C/ha), Luvisols (159 ± 52 t C/ha) and Fluvisols (231 ± 0 t C/ha, n = 1) was contained in the upper 50 cm of soil. Based on a 100 cm deep soil, Histosols hold 1.6–4 times the amount of soil C than mineral soils and 1.1–3.7 times the amount in organo-mineral soils for the same profile depth. Certain mineral (e.g. Umbrisols) and organo-mineral soils (e.g Gleysols, Regosols) contain substantial soil carbon stocks relative to Histosols. We found considerable soil carbon stocks below 30 cm depth, which highlights the importance of depth extent for cumulative soil carbon stocks estimates. The upper third of the 100 cm profile contained 33% (Histosols) to 70% (Luvisols) of the soil carbon stocks and the upper half of a 100 cm profile contained the entire soil carbon stocks for Leptosols, Stagnosols, Luvisols and Fluvisols and organo-mineral Leptosols. Unfortunately, there were few samples available for mineral Leptosols, Umbrisols, Luvisols and Fluvisols, and the organo-mineral Stagnosols and Regosols, which precludes the drawing of conclusions for these groups. Relative to the soil carbon stocks, we found low mean forest litter stocks: 4.1 ± 5.5 t C/ha, 4.8 ± 3.3 t C/ha and 2.7 ± 2.9 t C/ha for broadleaf, coniferous and mixed forests respectively. Few exceptions existed for individual sites: 22.7 and 131.3 t C/ha for broadleaf forests. Our results are evidence that soil carbon stocks in mineral, organo-mineral and organic soils need to be protected, appropriately managed, and enhanced to be beneficial for greenhouse gas mitigation. Assessments are needed to identify which soil-site-management practice combinations risk soil carbon stock depletion. The large range observed in soil and litter carbon stocks stresses the importance of adequately accounting for soil group differences when GHG inventories are compiled. The synthesised dataset will contribute to improved SCS estimation for afforested lands in Ireland.

Natural 15N abundance of ammonium and nitrate in soil profiles: New insights into forest ecosystem nitrogen saturation

AbstractAssessment of nitrogen (N) saturation of forests is critical to the evaluation of the manner in which ecosystems will respond to current and future global changes such as N deposition. However, quantifying N saturation remains a challenge. We developed a conceptual model of N saturation stages in forest ecosystems based on (1) a hypothetical relative rate of ammonification, nitrification, and denitrification, (2) concentrations of ammonium and nitrate in the soil, and (3) 15N enrichment pattern of bulk soil N, ammonium, and nitrate in the soil profile. We tested the hypotheses using data from forests located at five sites across eastern Asia. The fraction of nitrate in total inorganic N indicated that the sites represent an N saturation gradient with one boreal forest at stage 1 (least saturated), three temperate forests at stage 2, and one tropical forest at stage 3 (most saturated). The δ15N of bulk soil N increased from topsoil to subsoil more sharply at N‐limited sites than at the N‐rich sites along the N deposition gradient. We also found distinct 15N enrichment patterns of bulk soil N, ammonium, and nitrate in the soil profile across the study sites. At stage 1, nitrate was more 15N‐depleted than ammonium only in the organic soil horizon, indicating limited nitrification, while the 15N depletion of nitrate to ammonium was observed in the deeper mineral soil at stages 2 and 3. Furthermore, ammonium was more 15N‐depleted than bulk soil N at stages 1 and 2 but more 15N‐enriched than bulk soil N at stage 3. Our study suggests that soil profile patterns of δ15N of bulk soil N, ammonium, and nitrate provide information about the relative rates of mineralization, nitrification, and denitrification and thus can be an additional measure of N saturation of forest ecosystems across broad environmental gradients.

Effects of Moderate Nitrate and Low Sulphate Depositions on the Status of Soil Base Cation Pools and Recent Mineral Soil Acidification at Forest Conversion Sites with European Beech (“Green Eyes”) Embedded in Norway Spruce and Scots Pine Stands

High N depositions of past decades brought changes to European forests including impacts on forest soil nutrition status. However, the ecosystem responses to declining atmospheric N inputs or moderate N depositions attracted only less attention so far. Our study investigated macronutrient (N, S, Ca2+, Mg2+, K+) pools and fluxes at forest conversion sites over 80 years old in Central Germany with European beech (so-called “Green Eyes” (GE)). The GE are embedded in large spruce and pine stands (coniferous stands: CS) and all investigated forest stands were exposed to moderate N deposition rates (6.8 ± 0.9 kg ha−1 yr−1) and acidic soil conditions (pHH2O < 4.7). Since the understanding of forest soil chemical and macronutrient status is essential for the evaluation of forest conversion approaches, we linked patterns in water-bound nutrient fluxes (2001–2018) and in predicted macronutrient storage in the herbaceous and tree layer to patterns in litter fall (2016–2017) and in forest floor and mineral soil macronutrient stocks at GE and CS assessed in 2018. Our results exhibited 43% (Nt) and 21% (S) higher annual throughfall fluxes at CS than at GE. Seepage water at 100 cm mineral soil depth (2001–2018) of CS is characterized by up to fivefold higher NO3− (GE: 2 ± 0.7 µmolc L−1; CS: 9 ± 1.4 µmolc L−1) and sevenfold higher SO42− (GE: 492 ± 220 µmolc L−1; CS: 3672 ± 2613 µmolc L−1) concentrations. High base cation (∑ Ca2+, Mg2+, K+) concentrations in CS mineral soil seepage water (100 cm depth: 2224 ± 1297 µmolc L−1) show significant positive correlations with SO42−. Tree uptake of base cations at GE is associated especially with a Ca2+ depletion from deeper mineral soil. Foliar litter fall turns out to be the main pathway for litter base cation return to the topsoil at GE (>59%) and CS (>66%). The litter fall base cation return at GE (59 ± 6 kg ha−1 yr−1) is almost twice as large as the base cation deposition (30 ± 5 kg ha−1 yr−1) via throughfall and stemflow. At CS, base cation inputs to the topsoil via litter fall and depositions are at the same magnitude (24 ± 4 kg ha−1 yr−1). Macronutrient turnover is higher at GE and decomposition processes are hampered at CS maybe through higher N inputs. Due to its little biomass and only small coverage, the herbaceous layer at GE and CS do not exert a strong influence on macronutrient storage. Changes in soil base cation pools are tree species-, depth- and might be time-dependent, with recently growing forest floor stocks. An ongoing mineral soil acidification seems to be related to decreasing mineral soil base cation stocks (through NO3− and especially SO42− leaching as well as through tree uptake).

Simulation of dissolved organic carbon concentrations and fluxes in Chinese monsoon forest ecosystems using a modified TRIPLEX-DOC model

Dissolved organic carbon (DOC) plays an important role in global and regional carbon cycles. However, the quantification of DOC in forest ecosystems remains uncertain. Here, the processed-based biogeochemical model TRIPLEX-DOC was modified by optimizing the function of soil organic carbon distribution with increasing depths, as well as DOC sorption-desorption efficiency. The model was validated by field measurements of DOC concentration and flux at five forest sites and Beijiang River basin in monsoon regions of China. Model validation indicated that seasonal patterns of DOC concentration across climatic zones were different, and these differences were captured by our model. Importantly, the modified model performed better than the original model. Indeed, model efficiency of the modified model increased from −0.78 to 0.19 for O horizon predictions, and from −0.46 to 0.42 for the mineral soils predictions. Likewise, DOC fluxes were better simulated by the modified model. At the site scale, the simulated DOC fluxes were strongly correlated with the observed values (R2 = 0.97, EF = 0.91). At the regional scale, the DOC flux predicted in the Beijiang River basin was 16.44 kg C/ha, which was close to the observed value of 17 kg C/ha. Using sensitivity analysis, we showed that temperature, precipitation and temperature sensitivity of DOC decomposition (Q10) were the most sensitive parameters when predicting DOC concentrations and fluxes in forest soils. We also found that both the percentage of DOC flux to forest net ecosystem productivity, and the retention of DOC by mineral soil were highly correlated with the amount of precipitation. Overall, our model validations indicated that the modified TRIPLEX-DOC model is a useful tool for simulating the dynamics of DOC concentrations and fluxes in forest ecosystems. We highlight that more accurate estimates of parameter Q10 in deep mineral soils can reduce model uncertainty, when simulating DOC concentrations and fluxes in forest soils.

Quantifying the legacy of snowmelt timing on soil greenhouse gas emissions in a seasonally dry montane forest.

The release of water during snowmelt orchestrates a variety of important belowground biogeochemical processes in seasonally snow-covered ecosystems, including the production and consumption of greenhouse gases (GHGs) by soil microorganisms. Snowmelt timing is advancing rapidly in these ecosystems, but there is still a need to isolate the effects of earlier snowmelt on soil GHG fluxes. For an improved mechanistic understanding of the biogeochemical effects of snowmelt timing during the snow-free period, we manipulated a high-elevation forest that typically receives over two meters of snowfall but little summer precipitation to influence legacy effects of snowmelt timing. We altered snowmelt rates for two years using black sand to accelerate snowmelt and white fabric to postpone snowmelt, thus creating a two- to three-week disparity in snowmelt timing. Soil microclimate and fluxes of carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O) were monitored weekly to monthly during the snow-free period. Microbial abundances were estimated by potential assays near the end of each snow-free period. Although earlier snowmelt caused soil drying, we found no statistically significant effects (p<0.05) of altered snowmelt timing on fluxes of CO2 or N2 O, or soil microbial abundances. Soil CH4 fluxes, however, did respond to snowmelt timing, with 18% lower rates of CH4 uptake in the earlier snowmelt treatment, but only after a dry winter. Cumulative CO2 emission and CH4 uptake were 43% and 88% greater, respectively, after the dry winter. We conclude that soil GHG fluxes can be surprisingly resistant to hydrological changes associated with earlier snowmelt, likely because of persistent moisture and microbial activities in deeper mineral soils. As a result, a drier California in the future may cause seasonally snow-covered soils in the Sierra Nevada to emit more GHGs, not less.

Effects of Serpentinite Fertilization with N, P, and K Fertilizers on Soil Properties and Needle Chemistry

ABSTRACTThe aim of the present research was to study the long-term effect of serpentinite fertilization with additional nitrogen, phosphorous, and potassium fertilizers on some physicochemical properties and the enzyme activity of acidic soils and needle chemistry in stands of Norway spruce (Picea abies (L.) Karst.). Experimental plots were located in spruce stands in the middle forest zone (900–950 m) on two nappes of the Carpathian flysch: Magura and Silesian. Serpentinite was introduced in autumn 2008 on all plots while the other fertilizers in spring 2009. The effect of fertilization was visible mainly in the humus horizon. No significant changes were found in the deeper mineral soil. The acidity and Al toxicity in the surface horizon were ameliorated through serpentinite fertilization. Five years after fertilization, no significant difference in the fertilization treatments was noted in the chemistry of the spruce needles.

Influence of transient flooding on methane fluxes from subtropical pastures

AbstractSeasonally flooded subtropical pastures are major methane (CH4) sources, where transient flooding drives episodic and high‐magnitude emissions from the underlying landscape. Understanding the mechanisms that drive these patterns is needed to better understand pasture CH4 emissions and their response to global change. We investigated belowground CH4 dynamics in relation to surface fluxes using laboratory water table manipulations and compared these results to field‐based eddy covariance measurements to link within‐soil CH4 dynamics to ecosystem fluxes. Ecosystem CH4 fluxes lag flooding events, and this dynamic was replicated in laboratory experiments. In both cases, peak emissions were observed during water table recession. Flooding of surface organic soils and precipitation driven oxygen pulses best explained the observed time lags. Precipitation oxygen pulses likely delay CH4 emissions until groundwater dissolved oxygen is consumed, and emissions were temporally linked to CH4 production in surface soil horizons. Methane accumulating in deep soils did not contribute to surface fluxes and is likely oxidized within the soil profile. Methane production rates in surface organic soils were also orders of magnitude higher than in deep mineral soils, suggesting that over longer flooding regimes CH4 produced in deep horizons is not a significant component of surface emissions. Our results demonstrate that distinct CH4 dynamics may be stratified by depth and flooding of surface organic soils drives CH4 fluxes from subtropical pastures. These results suggest that small changes in pasture water table dynamics can drive large changes in CH4 emissions if surface soils remain saturated over longer time scales.

Plant functional type affects nitrogen use efficiency in high-Arctic tundra

To unravel the potential effects of climate warming on soil N availability in a high Arctic tundra ecosystem we studied temperature effects on soil mineralization, and N uptake from different soil depths (−3, −10 and −30 cm) by tundra plants. Uptake was assessed using 15N tracer injected directly into mineral soil as 15NH4Cl solution to specifically mimic altered N availability from enhanced mineralization. Net N mineralization rates were very low, suggesting that N is strongly limiting in this system. There was no apparent temperature effect (−2 °C, 5 °C, 10 °C) on mineralization, but net nitrification was strongly limited by temperature – under the −2 °C treatment no nitrification occurred. As a consequence of ongoing mineralization and limited nitrification under freezing conditions, mineral NH4 may accumulate during the winter season and be available for plant uptake without risk of loss via NO3− leaching immediately after snowmelt. Nitrogen uptake niches were clearly stratified by depth. Graminoids (Carex misandra and Luzula arctica) were most effective at taking up N from deep soil horizons, and recovery in graminoid biomass after one year was independent of 15N injection depth. Recovery of N by the dwarf shrub Salix polaris was significantly higher following shallow application (−3 cm) compared to deeper treatments (−10 and −30 cm). Lichens and mosses also showed a decline in N uptake with application depth, and very little N was recovered by lichens and mosses even from −3 cm, in contrast to the strong uptake that has been observed in mosses when N is applied to the vegetation surface. The ability of graminoids to access nutrients from deeper mineral soil may give them an advantage over mosses and dwarf shrubs in warmer high Arctic tundra in acquiring limited available nutrient resources.

Changes in forest soil properties and spruce stands characteristics after dolomite, magnesite and serpentinite fertilization

We have to deal with spruce dieback in recent years in Europe. Fertilization can be used to reduce susceptibility to forest dying through improving the chemical properties of soil. The aim of this study was to assess the condition of soil and spruce stand after dolomite, magnesite and serpentinite fertilization. The fertilization was used to sustain a stable condition and extended the life of spruce stands by several years which allows the reconstruction of the stand. The experimental plots were set up in the areas of two Carpathian nappes, differing in terms of lithological deposits, in Wisla and Ujsoly Forest Districts. Fertilization improves the chemical properties and enzymes activity of soil. The used fertilization variants did not cause inhibition of soil enzymatic activity. The effect of liming is visible mainly in the humus horizon, and in the deeper mineral soil, a significant change was not found. Heavy metals, mainly nickel introduced with serpentinite, did not inhibit the activity of enzymes. As a result of fertilization, the process of dying spruce was delayed. Three years after fertilization, a clear improvement in the chemistry of spruce needles was not recorded.

Nanoscale evidence of contrasted processes for root-derived organic matter stabilization by mineral interactions depending on soil depth

Up to now stabilization of organic matter (OM) in soils due to mineral interactions has been assessed mainly by correlations between carbon and iron and/or aluminum oxides evidencing that metal oxides may be principal stabilization agents. The nature and morphology of stabilized OM are poorly known. Taking advantage of a field experiment, the aim of our study was to analyze the fate of 13C and 15N labeled root material at 30 and 90 cm depths after three years of incubation and to characterize the nature of OM stabilized by interactions with metal oxides. Our methodological approach included isolation of metal oxides by physical fractionation and visualization of their interaction with OM using NanoSIMS. We concentrated metal oxides in a fraction corresponding to our objectives: the heavy fraction (>3 g cm−3) of fine silt. NanoSIMS analyses of this fraction allowed us to locate unlabeled OM and OM either double labeled or carrying one single label in association with metal oxides. Our results suggest that decoupling of C and N may have happened during OM stabilization within the timeframe of the 3 year field experiment. Scanning electron microscopy (SEM) after NanoSIMS analyzes, indicated that 15N labeled OM at 90 cm were well-defined ovoid OM particles resembling to microbial cells in interaction with Fe, Al and Ti oxides. At 30 cm depth, OM associated with metal oxides was 13C and 15N labeled unstructured material, possibly derived from plant debris. We suggest that at the two soil depths under investigation different processes might be at work, leading to association of OM with mineral compounds of the isolated fraction: in upper soil layers, decomposed plant material may directly interact with metal oxides, whereas in deep mineral soil, OM could mainly interact with metal oxides after microbial turnover. Both types of interactions may be fairly stable as they persisted after ultrasonication and salt extraction.

Mineral soil carbon and nitrogen still low three decades following clearcut harvesting in a typical Acadian Forest stand

Intensive forest management practices can alter forest soil organic matter (SOM) storage (kgCha−1) due to changes in the environmental variables that control SOM cycling and stability. Here we investigate whether SOM losses are observed three decades following clearcut harvesting in a temperate forest ecosystem that includes the deep mineral soil (to a depth of 50cm). We compared SOM stored as carbon (C) and nitrogen (N) in paired (35-year-old; 110-year-old reference) Acadian Forest sites that differed only in their time since harvest. We found lower mineral soil carbon (C) and nitrogen (N) storage (27% and 26% respectively), and lower C and N concentrations at the 35-year-old site compared with the 110-year-old reference site. Isotopic compositions of C and N through the soil profile did not provide insight into the dominant mechanisms driving SOM losses at the 35-year-old site in this study. This is the second study to document decreases in mineral soil C and N storage in a red spruce forest within the Acadian Forest Region three decades following clearcut harvesting.

Investigating the role of moisture as an environmental constraint in the decomposition of shallow and deep mineral soil organic matter of a temperate coniferous soil

Temperature and moisture are primary environmental drivers of soil organic matter (SOM) decomposition, and an improved understanding of how they interact to control SOM cycling processes in temperate forest soils is needed. Intact soil cores from shallow (0–25 cm) and deep (25–50 cm) mineral soils were incubated under constant and/or diurnal temperature regimes, and subjected to a series of moisture manipulations within a climate-controlled facility. Soil temperature, moisture, and CO2 efflux were monitored daily for all intact cores and monitored continuously on a subset of cores in order to establish predictive relationships between these variables. Moisture constraints upon the decomposition of SOM were observed below 0.20 and above 0.60 water filled pore space (WFPS) for all shallow mineral soils, and below 0.40 WFPS for shallow soils that had been recently rewet. These thresholds were also evidenced in phase lags between respiration and temperature at 5 cm at high moisture contents, suggesting that while biological responses drive soil respiration at low moisture contents, diffusivity limits the response at high soil moisture. While the shallow mineral soil dominated the contribution to CO2 flux and consistently generated short term responses to rewetting events, deep mineral soil layers respired an order of magnitude lower than shallow layers (per gram C) with no short term measured response to rewetting events. The temperature sensitivity, measured using a Q10 function, was close to 2 for all soil cores, regardless of soil depth or (steady state) moisture content. The exclusion of fluxes collected following precipitation events from field-derived estimates of CO2 flux–temperature relationships, improved these relationships. This study provides insights into how we consider the role of moisture in evaluating SOM decomposition-temperature responses for temperate forest soils.

Biogeochemical Processes in the Soil-Groundwater System of a Forest-Peatland Complex, North Coast British Columbia, Canada

Abstract There is a limited understanding of the distribution and transport of solutes in the coastal forest-peatland systems of northern British Columbia, Canada. The purpose of this research was to evaluate the sources, concentration and flux of major ions and dissolved organic carbon (DOC) in the soil-groundwater system of a forest-peatland complex in the coastal western hemlock (CWH) forest zone. DOC dominated the groundwater flux, with most of it exported during high flow conditions. Inorganic ion concentration increased and DOC decreased with ground surface slope and community type from open peatland to bog woodland, bog forest, swamp forest and upland forest. Base cations, HC03 - and DOC in the peatland forest communities differed significantly (P < 0.05) from concentrations in the upland forest. The greatest concentrations of ions derived from mineral weathering were found in the upland forest where the absence of peat, deep mineral soil (85-465 cm) and steep surface slope (26%) combined to increa...

Tree species diversity increases fine root productivity through increased soil volume filling

Summary Although fine roots (&lt; 2 mm in diameter) account for a major share of the production of terrestrial ecosystems, diversity effects on fine root productivity and their mechanisms remain unclear. We hypothesized that: (i) fine root productivity increases with tree species diversity, (ii) higher fine root productivity is a result of greater soil volume filling due to species‐specific patterns of root placement and proliferation, and (iii) differences in fine root productivity and soil volume filling associated with tree species diversity are more pronounced in summer when plants are physiologically active and demand for water and nutrients is at its greatest. We investigated the effects of tree species diversity on fine root productivity and soil volume filling of boreal forest stands that have grown naturally for 85 years on similar sites. Annual fine root production was 19–83% higher in evenly mixed‐ than single‐species‐dominated stands, and increased with tree species evenness, but not tree species richness. Fine root biomass was higher in evenly mixed‐ than single‐species‐dominated stands in summer months, but not in spring or fall. Higher fine root productivity in evenly mixed‐ than single‐species‐dominated stands was realized by filling more soil volume horizontally and vertically in the forest floor in the mixtures of deep‐ and shallow‐rooted species vs. the deeper mineral soil in the mixtures of deep‐rooted species. Synthesis. Our results provide some of the first direct evidence for below‐ground species complementarity in heterogeneous natural forests, by demonstrating that tree species evenness increases fine root productivity by filling/exploiting the soil environment more completely in space and time, driven by differences in the inherent rooting traits of the component species and variations of root growth within species.

Long-term forest soil acidification, nutrient leaching and vegetation development: Linking modelling and surveys of a primeval spruce forest in the Ukrainian Transcarpathian Mts.

The biogeochemical model MAGIC was applied to simulate long-term (1880–2050) soil and stratified soil solution (30 and 90cm depth) chemistry at a spruce dominated site in the western Ukraine (Pop Ivan, 1480m a.s.l.) to evaluate the effects of acid deposition on soil acidification in a less polluted region of Europe.Since 2008, sulphur (S) deposition of 9kgha−1year−1 and nitrogen (N) deposition of 8.5kgha−1year−1 have been measured at Pop Ivan. The recent deposition of S and N is about 30% and 50% of those values estimated for the early 1980s, respectively. Acidic deposition caused the depletion of base cations (Ca, Mg, Na, K) from the soil cation exchange complex, which resulted in a decrease of calcium and magnesium saturation between 1935 and 2008 in the top mineral soil (0–30cm) and deeper mineral soil (30–80cm) by 67% and 88%, respectively. Base cation leaching acted as the major buffer mechanism against incoming acidity, therefore the measured inorganic aluminium (Al) concentration in soil solutions is ca. 10μmolL−1 and the subsequent molar (Ca+Mg+K)/Al ratio above 1. Recovery of the soil solution pH and Al is expected within the next 40 years, whereas the soil base saturation will only increase slowly, from 6% to 9.8% in the top soil and from 5.5% to 11% in the deeper mineral soil. Since the 1960s, modelled inorganic N leaching (as NO3) has started to increase following the trend in N deposition. Modelling and experimental evidence suggest that N availability from mineralization and deposition exceeds the rate of microbial and plant immobilization. Thus, soil N accumulation since the 1960s has been limited. A significant increase in nitrophilous species as well as a decrease of herb layer diversity was observed between 1936 and 1997.

Development of chemical soil properties in the western Ore Mts. (Czech Republic) 10 years after liming

The article focuses on changes in soil chemistry observed on plots limed in 2000 in the western Ore Mts.(Kru&amp;scaron;n&amp;eacute; hory) on the basis of chemical analyses done before liming and repeated in 2002, 2005 and 2010. In the deeper mineral soil (down to 30 cm), only the increase in pH and exchangeable magnesium was significant. The increase in exchangeable calcium in upper soil layers was significant in 2002 and 2005 only; ten years after liming the effect was negligible, although the number of Ca deficient samples was lower than in 2000. The exchangeable Mg content increased above the deficiency limit in all samples of upper soil, and an increase was also found in the deeper mineral soil. These changes were reflected in increasing base saturation and lower base cations/aluminium ratio in the organic and organomineral soil layer. Despite these positive shifts, calcium and magnesium deficiency and very low base saturation (&amp;lt; 10%) still prevail in the deeper mineral soil (2&amp;ndash;30 cm) and are common even in the upper mineral soil. The increased total nitrogen level observed two and five years after liming indicated enhanced decomposition of the humus layer. On the other hand, N content in the upper organic (FH) horizon as well as in deeper mineral soil did not change significantly. &amp;nbsp;

Calcium isotope constraints on the uptake and sources of Ca 2+ in a base-poor forest: A new concept of combining stable (δ 44/42Ca) and radiogenic ( εCa) signals

Plant-available reserves of major base cations, Ca 2+ and Mg 2+, decreased markedly in soils over the past century, thus posing a potential threat to forest ecosystem health. Trees are thought to obtain dissolved Ca 2+ ions mainly from an easily accessible soil–water reservoir also termed the ‘exchangeable cation pool’. The status of Ca reserves in this soil pool is sensitive to anthropogenic perturbations such as soil acidification induced by acid rain and/or excessive timber harvesting. Here we show that in a base-poor forest of the northeastern USA (i.e. Wachusett Mountain, Massachusetts) the ‘exchangeable Ca pool’ of deeper mineral soils has a unique isotope signature that is significantly enriched in the radiogenic 40Ca, due to the dissolution of K-rich silicate minerals such as biotite. Using a simple isotope mass balance, and assuming that the input of Ca from biotite has a ε Ca signature of ∼16, the results of our calculation indicate that the weathering of biotite may supply a sizeable fraction, up to 25%, of Ca 2+ ions into the ‘exchangeable cation pool’ of deeper mineral soils. Importantly, samples of local vegetation (i.e. woody tissues of red oak) show no detectable excess of the radiogenic 40Ca, and based on our model the upper limit of a possible biotite-derived Ca contribution in vegetation is estimated at ∼5%. We also found no evidence of the radiogenic 40Ca signal in the samples of forest floor and the uppermost organic-rich soils (0–15 cm depth), which in turn suggest that over the long-term development of the forest and its organic matter accumulation, the vegetation growth must have also relied primarily on the non-radiogenic Ca sources. Based on our experimental data, such sources may include (i) wet atmospheric deposition, (ii) the organically-complexed Ca in topsoil horizons, and (iii) chemical weathering and/or fungal-mediated dissolution of apatite and Ca-rich plagioclase. Hence, our stable and radiogenic Ca isotope data indicate that the studied base-poor forest is able to bypass the ‘exchangeable cation pool’ of deeper (i.e. below 15 cm) mineral soils, and still manages to meet its nutritional requirements with respect to Ca. Another important implication of this study is that the organically-complexed Ca in the topsoil horizon (0–15 cm depth) has to be tightly bound to the ion exchange sites, otherwise the large radiogenic 40Ca signatures present in the ‘exchangeable cation pool’ of deep mineral soils would be swamped by the downward gravitational flux of non-radiogenic Ca from the decaying organic matter and litterfall. Hence, the limited mobility of the organically-complexed Ca in soils and its tight biological cycling could explain the lack of a significant impact of vegetation on the Ca isotope systematics observed in large rivers.

Soil carbon release along a gradient of physical disturbance in a harvested northern hardwood forest

Changes in soil respiration associated with forest harvest could increase net loss of CO 2 to the atmosphere relative to pre-harvest values. By excavating quantitative soil pits across a gradient of physical disturbance in a harvested northern hardwood forest, this study examines C release from mineral soil. Mineral soil samples were analyzed for pH, percent organic matter (%OM), C and N concentration, δ 13C, and total C per unit area. Results show a relationship between degree of disturbance and C concentration in soil 10–30 cm beneath the O-horizon. Highly disturbed sites show C depletion, with horizons from disturbed sites containing 25% less total C than the least disturbed sites. δ 13C signatures of soil profiles at these sites show vertical mixing of plant-derived material into deeper mineral horizons. Mixing, as a result of physical disturbance, could have led to the observed C depletion by physical or chemical destabilization, or through the promotion of microbial respiration in deep mineral soil. Regardless of the mechanism, these results suggest elevated CO 2 emissions from soil following harvest, and, thus, have implications for the validity of wood biomass as a carbon neutral energy source.