Application of nitrogen in NO 3 − form increases rhizosphere alkalisation in the subsurface soil layers in an acid soil

Leaching of NO ₃ ^? derived from ammoniacal fertilizers in the topsoil and subsequent uptake of NO ₃ ^? by plants from deeper layers may be used as a method of biological amelioration of subsurface soil acidity. This paper reports a glasshouse column experiment testing the above concept. Nitrogen with labelled ¹⁵N was supplied with and without lime to the surface soil (0–10 cm) as urea, (NH₄)₂SO₄ or Ca(NO₃)₂ at a rate equivalent to 120 kg N ha^?1. Soil columns were regularly watered from the top to facilitate NO ₃ ^? leaching. An aluminium-tolerant wheat genotype was grown for 38 days. The application of lime with nitrogen fertilizers increased growth of shoot and roots in all soil layers. The application of Ca(NO₃)₂ resulted in about 66% of recovery efficiency irrespective of whether lime was applied in the surface. This in turn resulted in about 0.2 units increase in rhizosphere pH in the subsurface (10–15 cm) soil layer compared to the same layer of the unlimed control. The supply of urea and (NH₄)₂SO₄ alone or with lime did not increase rhizosphere pH in the subsurface soil layers. Importantly, this study indicates that it is possible to exploit the process of nitrate uptake by wheat to increase pH in acidic subsurface soil.     

Biological amelioration of subsoil acidity through managing nitrate uptake by wheat crops

Subsoil acidity occurs in many agricultural lands in the world, and is considered to be an irreversible constraint due to amelioration difficulties. This field study aimed to develop a biological method to ameliorate subsoil acidity through the root-induced alkalisation resulting from nitrate uptake. Aluminium (Al)-tolerant wheat variety Diamondbird and Al-sensitive variety Janz (Triticum aestivum L.) were grown at two contrasting field sites with mild and severe subsurface acidity, respectively, and were supplied with either Ca(NO₃)₂ at the soil surface, Ca(NO₃)₂ at 10 cm depth or urea at 10 cm depth. Application of nitrate increased rhizosphere pH up to 0.5 units and bulk soil pH to 0.3 units, and to a depth >30 cm in the Kandosol. The placement of nitrate at 10 cm increased subsoil pH more than the surface application. Nitrate application increased nitrate concentration in soil profiles as expected, whereas urea application increased NH ₄ ⁺ concentration which in turn favored acidification processes. Diamondbird generally produced more tillers and shoot biomass at anthesis but the two varieties did not differ in grain yield or rhizosphere alkalisation. Similar grain yields were achieved under supply of nitrate and urea. The results suggest that biological amelioration through managing nitrate uptake is possible as part of an integrated approach to combat subsoil acidity in farming systems.     

Nitrate leaching stimulates subsurface root growth of wheat and increases rhizosphere alkalisation in a highly acidic soil

Subsurface acidity is a major factor limiting crop yield in some agricultural soils. The surface application of lime has limited effect on the subsurface acidity due to the slow downward movement, while deep incorporation of lime is costly. This paper tested the concept of biologically ameliorating subsurface acidity in a highly acidic soil through the net uptake of anions by plant roots. Nitrogen was supplied to the top soil (0–10 cm) as Ca(NO₃)₂ at rates equivalent to 30–240 kg N ha^?1. Four water levels were imposed (40, 60, 80 and 100% of field capacity). Aluminium-tolerant wheat was grown for 58 days. The high N and high water treatments stimulated root growth below 15 cm, which in turn increased N capture, resulting in a greater excess anion uptake over cations and thus alkalisation of subsurface soil layers. This study suggests that it is feasible to exploit the process of nitrate uptake by an aluminium-tolerant wheat genotype to increase pH in acidic subsoil.     

Coupled response of soil carbon and nitrogen pools and enzyme activities to nitrogen and water addition in a semi-arid grassland of Inner Mongolia

Background and aims

Previous studies have demonstrated positive net primary production effects with increased nitrogen (N) and water availability in Inner Mongolian semi-arid grasslands. However, the responses of soil carbon (C) and N concentrations and soil enzyme activities as indicators of impacts of long-term N (urea) and water addition are still unclear. We tested the effect of 7 years of a N and water addition experiment on soil C, N, and specific soil-bound enzymes in a semi-arid grassland of Inner Mongolia.

Methods

We determined concentrations of soil organic carbon (SOC) and soil total nitrogen (TN) in both the 0–10 and 10–20 cm soil layers. Concentrations of labile carbon (LC) and inorganic nitrogen (nitrate and ammonium), and soil pH were measured. Additionally, soil dehydrogenase (DHA), β-glucosidase (BG) and acid and alkaline phosphomonoesterase (PME) enzyme activities were determined in the 0–10 cm soil layer.

Results

SOC concentration in the 0–10 cm soil layer showed no response to N addition or N plus water addition, but increased with water addition alone by 0.3–15.7 %. N addition significantly increased nitrate by 46.0–138.4 % and ammonium by 19.0–73.3 % in the 0–10 cm soil layer, whereas water addition did not affect them. The activities of DHA and alkaline PME enzymes, as well as soil pH, in the 0–10 cm layer decreased with N addition, however water addition alone caused these enzyme activities to increase. Unlike the surface soil (0–10 cm), the lower soil layer (10–20 cm), was responsive to N and water addition in that SOC and TN concentrations decreased with N addition and increased with water addition.

Conclusions

The accumulation of SOC and TN in N and water addition plots may be caused by the input of plant biomass exceeding SOC decomposition. Decrease in microbial activity, derived from decreased DHA and alkaline PME activities might result from suppression effects of lower pH and decreased microbial N supply. Water availability is proved to be more important than N availability for soil C and N accumulation in this semi-arid grassland.     

Effect of trickle fertigation with three forms of nitrogen on soil pH,levels of extractable nutrients below the emitter and plant growth

The effects of application of nitrogen as calcium nitrate, urea or ammonium sulphate at two rates through the trickle irrigation system on pH and nutrient status of the wetted volume of soil below the emitters and on growth and nutrition of courgette (zucchini) plants (Cucurbita pepo L.) was investigated. Soil acidification, caused by nitrification, occurred to a large extent in the volume of soil immediately below the emitters in the urea and ammonium sulphate treatments. Acidification was greater at the high rate of N addition and more pronounced with ammonium sulphate than urea. A significant amount of applied urea appeared to move through the soil as urea and consequently, at the same rate of N addition, levels of ammonium were lower directly below the emitter and those of nitrate were higher further away from the emitters for the urea than ammonium sulphate treatments. Soil acidification below the emitters resulted in significant decreases in levels of exchangeable Ca, Mg and K and increases in levels of exchangeable Al, EDTA-extractable Fe, Mn, Zn and Cu and bicarbonate-extractable P. Vegetative growth and harvestable yields of courgettes were increased by both irrigation and nitrogen applications. Vegetative growth was generally greater at the low rate of N addition than at the high one and generally followed the order calcium nitrate > urea > ammonium sulphate. However, fruit yields followed the order urea > ammonium sulphate > calcium nitrate and were larger at the high rate of N for urea and ammonium sulphate treatments and unaffected by rate for the calcium nitrate treatments. It is suggested that with fertigation, the form of applied N can have significant physiological effects of plant growth and yields because N may be applied into the root zone on numerous occasions during the growing season.     

Acidification of a kaolinitic Alfisol under continuous cropping with nitrogen fertilization in West Africa

Increased use of N fertilizer and more intensive cropping due to the rising food demand in the tropics requires design and evaluation of sustainable cropping systems with minimum soil acidification. The objectives of this study were to quantify acidification of an Oxic Kandiustalf with different types of N fertilizer in two cropping systems under no-tillage and its effect on crop performance. Chemical soil properties in continuous maize (Zea mays L.) and maize-cowpea (Vigna unguiculata (L.) Walp) rotation were determined with three N sources (urea (UA), ammonium sulfate (AS) and calcium ammonium nitrate (CAN)) in Nigeria, West Africa, during five years. Chemical soil properties were related to grain yield and diagnostic plant nutrient concentrations. For the three N sources, the rate of decline in soil pH in maize-cowpea rotation was 57±7.5% of that in continuous maize, where double the amount of N fertilizer was applied. The rate of soil acidification during the five years was greater for AS than for UA or CAN in continuous maize, and not different for UA and CAN in both cropping systems. With AS, soil pH decreased from 5.8 to 4.5 during five years of continuous maize cropping. Exchangeable acidity increased with N fertilization, but did not reach levels limiting maize or cowpea growth. Return of residues to the soil surface may have reduced soluble and exchangeable Al levels by providing a source of organic ligands. Soil solution Mn concentrations increased with N fertilization to levels likely detrimental for crop growth. Symptoms of Mn toxicity were observed on cowpea leaves where AS was applied to the preceding maize crop, but not on maize plants. Soil acidification caused significant reductions in exchangeable Ca and effective CEC. Main season maize yield with N fertilization was lower with AS than with UA or CAN, but not different between UA and CAN during the six years of cropping. The lower maize grain yield with AS than with the other N sources was attributed to lower pH and a greater extractable Mn concentration with AS. When kaolinitic Alfisols are used for continuous maize cropping, even under no-tillage with crop residues returned as mulch, the soil may become acidifed to pH values of 5.0 and below after a few years. The no-till cereal-legume rotation with judicial use of urea or CAN as N sources for the cereal crop is a more suitable system for these poorly buffered, kaolinitic soils than continuous maize cropping. The use of AS as N source should be avoided. H Marschner Section editor     

Climatic effects on vertical mixing and deep-water oxygen content in the subalpine lakes in Italy

Acidification has adversely affected freshwater ecosystems in many areas, and recovery from acidification is often interrupted by acidic events. We lack detailed information about how benthic algae react to short-term acidic events and long-term recovery from acidification. We sampled 15 stream sites in the Czech Republic to study the effects of (a) water pH, aluminium and lead concentrations, (b) short-term acidic events, (c) 20 years of recovery from acidification and (d) high phosphorus concentrations combined with low pH on soft-bodied benthic algae. Water pH and aluminium concentrations affected benthic algal assemblages, but the acidification index periphyton (AIP) mainly reflected pH. Benthic algal assemblages reflected recent acidic events more closely than maximum or average pH. Our results indicate that the reaction of benthic algae to pH results from a fast effect of pH minima that cause sensitive species to disappear within a few months, and a slower process of dispersal and competition for resources during periods of higher pH. After an acidic event, recolonization of stream sites by sensitive species had started within 2 years, and was largely completed after 9 years. Our data indicate that acidification may mask the effect of enhanced phosphorus concentrations on benthic algal eutrophication indices.     

Positive and negative impacts of plants on acid production in exposed acid sulphate soils

This study examined the impact of plants on acid sulphate soils with the aim of determining whether plants are able to reduce acid production. The study was conducted with clayey acid sulphate soil under controlled conditions with treatments lasting up to 24 weeks and measurements made in the top 0?C60 mm of soil. pH profiles in the soil were strongly dependent on soil moisture and the pattern of irrigation. When bare soil was allowed to dry down without further irrigation, there was very little acidification of either the surface or subsurface layers. Planting of Phragmites accelerated soil drying and caused extensive cracking and acidification of the subsoil under simulated drought conditions. Under a wetting and drying regime, both Phragmites and a surface spreading grass Paspalum increased soil acidification, while a surface spreading herbaceous shrub Cotula had little effect on acidification. There was no evidence that live plants could ameliorate acid sulphate soils. However, application of dead plant matter to the surface of the soil was effective in reducing acidification, especially if submerged.     

Nitrogen nutrition of ginger (Zingiber officinale)

Summary Two fertilizer experiments were conducted in the field at Beerwah, South-East Queensland. In the first experiment leaf nitrogen concentrations, and the yield of ginger shoots and rhizomes at early and late harvests increased both with the total amount of nitrogen applied up to the highest level studied (336 kg N/ha as ammonium nitrate) and with the number of applications making up the total. At all levels of nitrogen application the apparent recovery of fertilizer nitrogen increased in the order 1 application <2 applications <4 applications. At 33.6 kg N/ha there appeared to be no advantage in dividing the total N applied into more than 4 applications but the data suggested higher recoveries of nitrogen with 8 applications at 112 kg N/ha and 336 kg N/ha. In the second experiment, ammonium nitrate, urea, and ammonium sulphate were found to be equally effective as nitrogen fertilizers for ginger when applied at equal rates of nitrogen per hectare. However, in terms of cost effectiveness they rated in the order urea > ammonium nitrate > ammonium sulphate.All three nitrogen sources acidified the soil, the decrease in soil pH during the growing season increasing with increasing rate of application. In Experiment 1 split applications, which increased the recovery of applied nitrogen in the crop, also increased the extent of acidification. In Experiment 2 ammonium sulphate tended to be more strongly acidifying than the other fertilizers but the difference was statistically significant only at the highest rate of nitrogen application. Because of the strong effects of nitrogen supply on both yield and soil pH, the highest yields were associated with end-of-season pH values below 5.0.     

Plant-soil feedback in spruce (Picea abies) and mixed spruce-beech (Fagus sylvatica) stands as indicated by dendrochemistry

Ten pairs of secondary pure spruce (Picea abies) and adjacent mixed spruce-beech (Fagus sylvatica) stands on comparable sites were selected on two different bedrocks for soil formation (Flysch: nutrient rich and high soil pH; Molasse: poor nutrient supply and acidic) to study how an admixture of beech to spruce stands affects nutrient cycling and consequently soil chemistry. Soil analyses indicated accumulation of Ca under the mixed stands while the top soil under pure spruce was acidified. It was hypothesized that changes of soil chemical properties due to species composition over the last six decades are reflected in the stem wood of spruce. Three healthy dominant spruce trees per plot were selected for coring. Cores were crossdated and half-decadal samples were analyzed for Ca, Mg, Mn and Al. Calcium and Mg concentrations in stem wood of spruce were significantly higher for the pure spruce than for the mixed stands in spite of lower Ca and Mg stores in the soil. We assume that acidification caused by pure spruce mobilized these cations temporarily, increasing soil solution contents and consequently stem wood concentrations. It was possible to reconstruct soil pH from the element ratios Ca/Al (pure stands) and Ca/Mg (mixed stands), since these ratios in the stem wood of the last half-decade did correlate with soil pH for selected soil depths. Reconstructed soil pH showed a decline over the last 60 years under both species compositions due to accumulation of base cations in the increasing biomass. Comparisons of reconstructed soil pH in 0–5 and 10–20 cm soil depth indicated more pronounced top soil acidification (lower soil pH in 0–5 cm) by spruce on the nutrient rich soil (Flysch) than on the acidic soil (Molasse). However, admixture of beech caused higher pH values in 0–5 cm than in 10–20 cm soil depth on Flysch due to the observed Ca-pump effect of beech (uptake of Ca from deeper soil horizons).     

Impact of Nitrogen Fertilization to Short-Rotation Willow Coppice Plantations Grown in Sweden on Yield and Economy

A fertilization trial was carried out in established short-rotation willow coppice (SRWC) plantations of two bred varieties of willow (Salix spp.; "Tora" and "Jorr") at five sites in central Sweden between 2008 and 2010. Mineral nitrogen was applied at four different rates: No fertilization (Control), 160 kg nitrogen ha^?1 as a single dose after harvest (Economy), 60–100–60 kg nitrogen ha^?1 in year 1–2–3 (Normal), and 160 kg nitrogen ha^?1 year^?1 in years 1–3 (Intensive), using a randomized block design with four replicates. The yield response (biomass increase per kg fertilizer nitrogen) was 65, 67 and 46 kg kg^?1 in the Economy, Normal and Intensive treatments, respectively. The results from the fertilization trial were used for economic calculations of different fertilization strategies given varying costs for fertilization and marginal value of the increased yield (price received for wood chips minus the costs for harvest and transportation of wood chips to a district heating plant). Comparative calculations were made based on data from a previous fertilization trial during the first cutting cycle of old, non-bred varieties. The calculations showed positive net present values of fertilizing bred willow varieties given a realistic fertilization response and a price for wood chips close to the market price for forestry-based wood chips in Sweden.     

Low temperature,autotrophic microbial denitrification using thiosulfate or thiocyanate as electron donor

Wastewaters generated during mining and processing of metal sulfide ores are often acidic (pH < 3) and can contain significant concentrations of nitrate, nitrite, and ammonium from nitrogen based explosives. In addition, wastewaters from sulfide ore treatment plants and tailings ponds typically contain large amounts of inorganic sulfur compounds, such as thiosulfate and tetrathionate. Release of these wastewaters can lead to environmental acidification as well as an increase in nutrients (eutrophication) and compounds that are potentially toxic to humans and animals. Waters from cyanidation plants for gold extraction will often conjointly include toxic, sulfur containing thiocyanate. More stringent regulatory limits on the release of mining wastes containing compounds such as inorganic sulfur compounds, nitrate, and thiocyanate, along the need to increase production from sulfide mineral mining calls for low cost techniques to remove these pollutants under ambient temperatures (approximately 8 °C). In this study, we used both aerobic and anaerobic continuous cultures to successfully couple inorganic sulfur compound (i.e. thiosulfate and thiocyanate) oxidation for the removal of nitrogenous compounds under neutral to acidic pH at the low temperatures typical for boreal climates. Furthermore, the development of the respective microbial communities was identified over time by DNA sequencing, and found to contain a consortium including populations aligning within Flavobacterium, Thiobacillus, and Comamonadaceae lineages. This is the first study to remediate mining waste waters by coupling autotrophic thiocyanate oxidation to nitrate reduction at low temperatures and acidic pH by means of an identified microbial community.     

Soil biological activity and their seasonal variations in response to long-term application of organic and inorganic fertilizers

The objectives of this study were to explore the effects of long-term and continued application of fertilizers and manures on microbial biomass, soil biological activity and their seasonal variations in surface and subsurface soils in relation to soil fertility. For this, soils were sampled in spring, summer and autumn from Shenyang Long-term Experimental Station, northeastern China. The results showed that soil total nitrogen (N), organic carbon (C), basal respiration, microbial biomass and enzymatic activity increased in manure-amended surface soils, but decreased with soil depth. Long-term application of inorganic fertilizers significantly decreased soil pH value, sucrase activity and microbial biomass C, but increased soil metabolic quotient (qCO₂). However, no significant effect of inorganic fertilizers on soil total N, urease activity and microbial biomass N was observed in comparison with CK0 (neither tillage nor fertilization) and CK (no fertilizers). There was no significant difference between CK0 and CK in soil total N, organic C and microbial activity in surface soil layer (0–20 cm), but these parameters in subsurface soil layer (20–40 cm) were higher in CK than in CK0. Moreover, seasonal changes were observed in terms of soil nutrient contents, enzymatic activity, microbial biomass and soil respiration. There were significant correlations between soil microbial biomass C and N, between organic C and sucrase activity and between total N and urease activity, respectively. It is recommended that combined use of organic manure with inorganic fertilizers should be considered to maintain higher microbial biomass, soil biological activity and soil fertility. Considering considerably high nutrients reserve and microbial activity in subsurface layers of soil and wind-erosion-caused nutrient loss in spring in north China, we also propose that low tillage should be considered to make use of nutrients in soils.     

Phosphate solubilization by stress-tolerant soil fungus <Emphasis Type="Italic">Talaromyces funiculosus</Emphasis> SLS8 isolated from the Neem rhizosphere

A promising biotechnological strategy in the management of phosphorus (P) fertilization is the use of phosphate-solubilizing fungi to solubilize rock phosphates and allow the recovery of unavailable P fixed to soil particles. Phosphate-solubilizing rhizosphere fungus, Talaromyces funiculosus SLS8, isolated from Neem (Azadirachta indica) on saline soil, was tolerant to environmental stressors, salinity and agricultural systemic fungicides. Phosphate solubilization under different nutritional conditions was investigated by culturing T. funiculosus SLS8 in Pikovskaya liquid medium containing different nitrogen sources (ammonium sulfate, casein, urea, potassium nitrate or sodium nitrate) and carbon sources (glucose, fructose, galactose or sucrose), NaCl, and three systemic fungicides. The highest concentration of solubilised phosphate (187 mg P L^?1) was achieved after 5 days of incubation in the medium with glucose and ammonium sulphate. The culture pH decreased from 6.5 to 4.2 and HPLC demonstrated organic acid production. Phosphate solubilized was highly negatively correlated with pH (r?=??0.96). Increasing salinity had no effect on phosphate solubilization. The maximum tolerance limits to systemic fungicides carbendazim, mancozeb, and hexaconazole were 12.5 μg mL^?1, 2,000 μg mL^?1 and 250 μl mL^?1 respectively. At these concentrations carbendazim, mancozeb and hexaconazole were found to decrease phosphate solubilization by 55 %, 37 %, and 30 %, respectively. Our results indicate that T. funiculosus SLS8 may be a potential candidate for the development of a biofertilizer for maintaining available phosphate levels in environmentally stressed soils such as saline agricultural soils impacted by systemic fungicide application or seed treatment.     

Nutrient Biogeochemistry During the Early Stages of Delta Development in the Mississippi River Deltaic Plain

Nutrient biogeochemistry associated with the early stages of soil development in deltaic floodplains has not been well defined. Such a model should follow classic patterns of soil nutrient pools described for alluvial ecosystems that are dominated by mineral matter high in phosphorus and low in carbon and nitrogen. A contrast with classic models of soil development is the anthropogenically enriched high nitrate conditions due to agricultural fertilization in upstream watersheds. Here we determine if short-term patterns of soil chemistry and dissolved inorganic nutrient fluxes along the emerging Wax Lake delta (WLD) chronosequence are consistent with conceptual models of long-term nutrient availability described for other ecosystems. We add a low nitrate treatment more typical of historic delta development to evaluate the role of nitrate enrichment in determining the net dinitrogen (N₂) flux. Throughout the 35-year chronosequence, soil nitrogen and organic matter content significantly increased by an order of magnitude, whereas phosphorus exhibited a less pronounced increase. Under ambient nitrate concentrations (>60 μM), mean net N₂ fluxes (157.5 μmol N m^?2 h^?1) indicated greater rates of gross denitrification than gross nitrogen fixation; however, under low nitrate concentrations (<2 μM), soils switched from net denitrification to net nitrogen fixation (?74.5 μmol N m^?2 h^?1). As soils in the WLD aged, the subsequent increase in organic matter stimulated net N₂, oxygen, nitrate, and nitrite fluxes producing greater fluxes in more mature soils. In conclusion, soil nitrogen and carbon accumulation along an emerging delta chronosequence largely coincide with classic patterns of soil development described for alluvial floodplains, and substrate age together with ambient nitrogen availability can be used to predict net N₂ fluxes during early delta evolution.     

CO2-induced fertilization impairment in Strongylocentrotus droebachiensis collected in the Arctic

Fertilization depends on distribution and aggregation patterns of sea urchins which influence gamete contact time and may potentially enhance their vulnerability to ocean acidification. In this study, we conducted fertilization experiments to assess the effects of selected pH scenarios on fertilization success of Strongylocentrotus droebachiensis, from Spitsbergen, Arctic. Acidification was achieved by aerating seawater with different CO₂ partial pressures to represent pre-industrial and present conditions (measured ~180–425 µatm) and future acidification scenarios (~550–800, ~1,300, ~2,000 µatm). Fertilization success was defined as the proportion of successful/unsuccessful fertilizations per treatment; eggs were classified according to features of their fertilization envelope (FE), hyaline layer (HL) and achievement of cellular division. The diagnostic findings of specific pathological aberrations were described in detail. We additionally measured intracellular pH changes in unfertilized eggs exposed for 1 h to selected acidification treatments using BCECF/AM. We conclude that (a) acidified conditions increase the proportion of eggs that failed fertilization, (b) acidification may increase the risk of polyspermy due to failures in the FE formation supported by the occasional observation of multiple sperms in the perivitelline space and (c) irregular formation of the embryo may arise due to impaired formation of the HL. The decrease in fertilization success could be also related to the observed changes in intracellular pH at pCO₂ ~ 1,000 μatm or higher.     

Responses of soil chemical and biological properties to nitrogen addition in a Dahurian larch plantation in Northeast China

Soil microbial properties play a key role in belowground ecosystem functioning, but are not well understood in forest ecosystems under nitrogen (N) enrichment. In this study, soil samples from 0–10 cm and 10–20 cm layers were collected from a Dahurian larch (Larix gmelinii Rupr.) plantation in Northeast China after six consecutive years of N addition to examine changes in soil pH, nutrient concentrations, and microbial biomass and activities. Nitrogen addition significantly decreased soil pH and total phosphorus, but had little effect on soil total organic carbon (TOC) and total N (TN) concentrations. The NO ₃ ^? -N concentrations in the two soil layers under N addition were significantly higher than that in the control, while NH ₄ ⁺ -N concentrations were not different. After six years of N addition, potential net N mineralization and nitrification rates were dramatically increased. Nitrogen addition decreased microbial biomass C (MBC) and N (MBN), and MBC/TOC and MBN/TN in the 0–10 cm soil layer, but MBC/MBN was increased by 67% in the 0–10 cm soil layer. Soil basal respiration, microbial metabolic quotient (qCO₂), and β-glucosidase, urease, acid phosphomonoesterase and nitrate reductase activities in the two soil layers showed little change after six years of N addition. However, soil protease and dehydrogenase activities in the 0–10 cm layer were 41% and 54% lower in the N addition treatment than in the control, respectively. Collectively, our results suggest that in the mid-term N addition leads to a decline in soil quality in larch plantations, and that different soil enzymes show differentiated responses to N addition.     

Chemical recovery of acidified Bohemian lakes between 1984 and 2012: the role of acid deposition and bark beetle induced forest disturbance

Assessment of temporal trends and rates of change in hydrochemical parameters and forest cover has been conducted to elucidate key drivers of surface water acidification in glacial lakes in the Czech Republic. Since 1984, the key driver in acidification reversal was sulphate (SO₄) concentration (median decrease of ?3.58 μeq L^?1 yr^?1) which fell in line with reductions in sulphur (S) deposition. Reduction of nitrogen (N) deposition was followed by proportional reduction in nitrate (NO₃) leaching although decline in NO₃ concentrations was more pronounced at two sites, the ?ertovo Lake (CT) and Prá?ilské Lake (PR) until 2006; only ??árské pond showed effective catchment N immobilization. Coherent decline of chloride concentration was detected across all sites. The decrease of strong mineral acids was partly compensated by decrease of inorganic aluminium (Al_in), especially at sites most acidified in the beginning of observations (ANC_1984–1986 between ?160 and ?90 μeq L^?1 at CT, ?erné Lake—CN and Ple?né lake—PL) and by reductions of base cations and increases of pH. All lakes (CN, CT, PL, PR and LK) moved to the ANC range between ?29 and 30 μeq L^?1 (2010–2012) where sensitivity of pH to further reductions in acid anions may be expected. Concurrently, charge of weak organic acids (OAs) increased and partly balanced the strong mineral acid decrease as a consequence of (i) significant DOC (dissolved organic carbon) increase (median change of 0.13 mgC L^?1 yr^?1 since 1993) and (ii) deprotonation of weak OAs caused by pH rise. Since 2000s, bark beetle induced forest decline accelerated NO₃ leaching at most of the catchments (by 200 % at LK, PL and PR). However, elevated N leaching was effectively neutralized by base cations (K, Mg, Ca) originating from decaying fresh litter, thus acidification recovery was not reversed, but slowed down. After cessation of NO₃ leaching we hypothesise that collapsed tree canopy across catchments (from 12 to 87 % compared to 1984) will cause lower total acid input in precipitation (S + N) and regrowth of vegetation may stimulate higher N immobilization (in biomass and soil); processes which could lead to further increase of ANC and pH, key indicators for biological recovery.     

Fine-root dynamics in sugi (Cryptomeria japonica) under manipulated soil nitrogen conditions

Aims

Nitrogen deposition affect fine-root dynamics, a key factor in forest carbon and nutrient dynamics. This study aimed to elucidate the effects of increased soil inorganic nitrogen (N) levels on the fine-root dynamics of Cryptomeria japonica, which is tolerant to excess N load.

Methods

An ammonium nitrate solution (28 kg ha^?1 month^?1) was applied for 3 years to plots (1 m?×?2 m) in a C. japonica plantation. The elongation and disappearance of the fine roots were examined using the minirhizotron technique.

Results

The N fertilization increased soil inorganic N content and lowered the soil pH. Fine-root elongation rates increased with fertilization, whereas patterns of their seasonal changes were not affected. The ratio of cumulative disappearance to cumulative elongation of fine roots was lower in the N-fertilized plots than in the control plots. The mean diameter of the fine roots was not affected by N fertilization.

Conclusions

Our results suggest that C. japonica can respond to increased levels of soil inorganic N by increasing both the production and residence time of the fine roots. However, the effects of the changing soil N content are less evident for the phenology and morphology of the fine roots in C. japonica.     

Assessment of soil acidification due to a natural gas‐fired power plant by using two different approaches

Potential soil acidification impacts of a proposed natural gas‐fired combined cycle power plant were assessed using an integrated approach coupling an atmospheric deposition model with soil acidification quantification. The deposition model was used to estimate the rates of nitrogen oxide (NO_x) deposition on the air‐soil boundary. The expected changes in the soil column were then predicted by utilizing mechanistic and experimental methods, and the number of years required to reach critical pH values were predicted using the two methods mentioned above under different rates of acidic deposition. The number of years predicted by the mechanistic modeling approach was lower for all soils exhibiting calcareous character.