Nitrogen mineralization and nitrification during incubation of East Pakistan ‘tea’ soils in relation to pH

Summary A study was made of the effects of increasing pH, by addition of varying levels of calcium carbonate, on N-mineralization and nitrification during aerobic incubation (30°C for 12 weeks) of two tea soils (original pH 4.1 and 4.2) from East Pakistan. Mineral-N (NH₃- plus NO₃-N) accumulation increased with pH in both soils. In the low-flat soil maximum nitrate accumulation occurred at pH 5.0, whilst at the higher pH levels mineral-N accumulated mainly as ammonia-N. In the high-flat soil nitrate accumulation increased considerably with pH; mineralized-N was accounted for largely as ammonia at pH 5.0 or less, and almost entirely as nitrate at higher pH levels. Results are discussed in relation to possible occurrence of heterotrophic nitrification in these soils.     

Comparison of ‘ignition’ and ‘extraction’ methods for the determination of organic phosphate in rocks and soils

Summary Ignition markedly increased the solubility in dilute acid of iron- and aluminium-bound inorganic phosphate in samples of weathered New Zealand greywacke rock. This observation supports the view that ignition methods may sometimes overestimate the total organic phosphate of soils.     

Can mineralization of soil organic nitrogen meet maize nitrogen demand?

Background and aims

It is generally assumed that very large herbivores, such as elephants, make foraging decisions at large spatial scales, but the extent to which seasonal foraging decisions are driven by soil quality, and its link to plant nutrient levels, is uncertain.

Methods

We studied the diet selection of African elephants Loxodonta africana in Ithala Game Reserve in northern KwaZulu-Natal, South Africa, using data on elephant feeding preferences and spatial distributions from a published paper. Elephants were present in the eastern half with granite soils in the wet season, and in the western half with sedimentary soils in the dry season. The quality of these two soil types and of seven key tree species for elephants was assessed in both seasons.

Results

Soil quality was higher on the sedimentary soils in terms of total nitrogen, soil respiration, water-holding capacity, organic carbon and pH. Leaf quality was higher on the sedimentary soils in the dry season, while in the wet season there was no significant difference in leaf quality of the seven key tree species growing on the two substrates.

Conclusion

Soil quality may explain elephants’ foraging decisions in the dry season, but not in the wet season. Elephants preferred trees with higher protein and lower concentrations of fibre on both granite and sedimentary soils.

     

Aspects of carbon and nitrogen cycling in soils of the Bornhöved Lake district II. Modelling the influence of temperature increase on soil respiration and organic carbon content in arable soils under different managements

Based on field measurements in two agriculturalecosystems, soil respiration and long-term response ofsoil organic carbon content (SOC) was modelled. Themodel predicts the influence of temperature increaseas well as the effects of land-use over a period ofthirty years in a northern German glacial morainelandscape. One of the fields carried a maizemonoculture treated with cattle slurry in addition tomineral fertilizer (maize monoculture), the otherwas managed by crop rotation and recieved organicmanure (crop rotation). The soils of both fieldswere classified as cambic Arenosols. The soilrespiration was measured in the fields by means of theopen dynamic inverted-box method and an infrared gasanalyser. The mean annual soil respiration rates were 268 (maizemonoculture) and 287 mg CO₂ m^-2 h^-1(crop rotation). Factors controlling soil respirationwere soil temperature, soil moisture, root respirationand carbon input into the soil. Q₁₀-valuesof soil respiration were generally higher in winterthan in summer. This trend is interpreted as anadaptive response of the soil microbial communities.In the model a novel mathematical approach withvariable Q₁₀-values as a result oftemperature and moisture adjustment is proposed. Withthe calibrated model soil respiration and SOC werecalculated for both fields and simulations over aperiod of thirty years were established. Simulationswere based on (1) local climatic data, 1961 until1990, and (2) a regional climate scenario for northernGermany with an average temperature increase of 2.1 K.Over the thirty years period with present climateconditions, the SOC pool under crop rotation wasnearly stable due to the higher carbon inputs, whereasabout 16 t C ha^-1 were lost under maizemonoculture. Under global warming the mean annualsoil respiration for both fields increased and SOCdecreased by ca. 10 t C ha^-1 under croprotation and by more than 20 t C ha^-1 undermaize monoculture. It was shown that overestimationof carbon losses in long-term prognoses can be avoidedby including a Q₁₀-adjustment in soilrespiration models.     

An automated method for the analysis of ‘particulate’ carbon and nitrogen in natural waters

A method is described for the measurement of the carbon and nitrogen content of particulate material in natural waters. Particulate material is separated by filtration through GF/C filters. The dried filter is encapsulated in silver foil using a purpose made press. Analysis is carried out using high temperature combustion with thermal conductivity detection of emission gasses. Analytical performance characteristics obtained with both standards and natural materials are given.     

Fluxes and concentrations of dissolved organic carbon and nitrogen – a synthesis for temperate forests

Dissolved organic carbon (DOC) and nitrogen (DON)represent an important part of the C and N cycles inforest ecosystems. Little is known about the controlson fluxes and concentrations of these compounds insoils under field conditions. Here we compiledpublished data on concentrations and fluxes of DOC andDON from 42 case studies in forest ecosystems of thetemperate zone in order to evaluate controls on alarger temporal and spatial scale. The focus was onannual fluxes and concentrations in throughfall,forest floor leachates and soil solutions. In allcompartments considered, concentrations and fluxesdiffered widely between the sites. Highestconcentrations of DOC and DON were generally observedin forest floor leachates and in A horizons. Highestfluxes occurred in forest floor leachates. The fluxesof DOC and DON in forest floor leachates increasedwith increasing annual precipitation and were alsopositively related to DOC and DON fluxes withthroughfall. Variation in throughfall fluxes couldexplain 46% and 65% of the variation in DOC and DONfluxes from the forest floor, respectively. No generaldifference in DOC and DON concentrations and fluxes inforest floor leachates was found when comparingconiferous and hardwood sites. Concentrations of DOCin forest floor leachates were positively correlatedto the pH of the forest floor. Furthermore, there wasno relationship between organic C and N stocks, soilC/N, litterfall or mineral N inputs and concentrationsand fluxes of DOC and DON in forest floor leachates.Including all compartments, fluxes of DOC and DON werehighly correlated. Ratios of DOC to DON calculatedfrom fluxes from the forest floor were independent ofthe amount of annual precipitation, pointing to asimilar response of DOC and DON to precipitationconditions. A decrease in the ratio of DOC to DON withsoil depth as observed on a plot-scale, was notconfirmed by data analysis on a large scale. Thecontrols observed on annual fluxes and concentrationsof DON and DOC at regional scale differed from thosereported for smaller time and space scales.     

Plant–microbial competition for nitrogen increases microbial activities and carbon loss in invaded soils

Many invasive plant species show high rates of nutrient acquisition relative to their competitors. Yet the mechanisms underlying this phenomenon, and its implications for ecosystem functioning, are poorly understood, particularly in nutrient-limited systems. Here, we test the hypothesis that an invasive plant species (Microstegium vimineum) enhances its rate of nitrogen (N) acquisition by outcompeting soil organic matter-degrading microbes for N, which in turn accelerates soil N and carbon (C) cycling. We estimated plant cover as an indicator of plant N acquisition rate and quantified plant tissue N, soil C and N content and transformations, and extracellular enzyme activities in invaded and uninvaded plots. Under low ambient N availability, invaded plots had 77% higher plant cover and lower tissue C:N ratios, suggesting that invasion increased rates of plant N acquisition. Concurrent with this pattern, we observed significantly higher mass-specific enzyme activities in invaded plots as well as 71% higher long-term N availability, 21% lower short-term N availability, and 16% lower particulate organic matter N. A structural equation model showed that these changes were interrelated and associated with 27% lower particulate organic matter C in invaded areas. Our findings suggest that acquisition of N by this plant species enhances microbial N demand, leading to an increased flux of N from organic to inorganic forms and a loss of soil C. We conclude that high N acquisition rates by invasive plants can drive changes in soil N cycling that are linked to effects on soil C.     

Dynamics of soil carbon,nitrogen, and phosphorus in calcareous soils after land-use abandonment – A chronosequence study

Aims

The objective of this study was to investigate changes in soil total organic C (TOC), total nitrogen (TN), phosphorus (P) fractions, and microbial community structure during secondary succession after abandonment of vineyards on calcareous soils.

Methods

Two chronosequences covering 200 years and differing in aspect and slope were established in Hungary, and the upper 10 cm of the mineral soils were studied.

Results

We found strong increases in TOC concentrations after land-use abandonment, especially at the south-exposed sites. The TOC/TN ratio increased by a factor of 1.3 in the south-west exposed chronosequence and by a factor of 1.6 in south exposed chronosequence. The concentration of labile P (NaHCO₃-extractable P) diminished during the first 50 years after land-use abandonment, leading to low P availability at the later stages of the succession. The total organic P (TOP) concentration increased during the first 40 years after abandonment. At the later stages of succession, TOP concentrations decreased again, while the ratio of TOC/TOP increased continuously over 200 years. The ratio of arbuscular-mycorrhizal-fungi-to-bacteria (AMF/bacteria) increased strongly during the first decade after abandonment of the vineyards.

Conclusions

Our study indicates that impacts of former cultivation on secondary ecosystems persisted for more than a century, and that especially P concentrations showed long lasting legacy effects.

     

Mineralisation of carbon and plant uptake of phosphorus from microbially-derived organic matter in response to 19 years simulated nitrogen deposition

Here we test the hypotheses that 19 years of simulated pollutant N deposition increases both losses of carbon (C) and the ability of plants to access P from organic material in upland heathland. The grass, Dactylis glomerata, and the dwarf shrub, Calluna vulgaris, were grown in soil containing microbial-derived organic matter labelled with ¹⁴C and ³³P. We found that both soil and root-surface phosphatase activity increased significantly in response to N deposition. We also found a significant positive relationship between root-surface phosphatase activity and ³³P uptake for Calluna, but a negative relationship for Dactylis. Efflux of ¹⁴C from the microbial-derived organic matter was strongly dependent on an interaction among plant presence, plant species and N deposition. Our results show that mineralisation of C and P, and subsequent plant uptake of P from organic sources is decoupled. In our experimental conditions, stimulation of P turnover coupled with subsequent plant uptake through up-regulation of root phosphatases is little affected by N addition. However, our data indicate that root-surface phosphatases are likely to be more important for uptake of P derived from organic sources for Calluna than for Dactylis.     

Anthocyanin and pH in the color of ‘Heavenly Blue’ morning glory

The major anthocyanin in blue morning glory flowers, peonidin 3-(dicaffeylsophoroside)- 5-glucoside, is stable in a neutral aqueous solution and is solely responsible for the color of the flowers. Co-ocurring flavonols based on quercetin at the pH's of epidermal cells have no effect on the color of the anthocyanin. Deep or strong reddish-purple buds change to moderate or light blue open flowers within a 4 hr period, and during this time the pH of epidermal tissue increases from ca 6.5 to 7.5.     

Drying and wetting in saline and saline-sodic soils—effects on microbial activity, biomass and dissolved organic carbon

Aims

There are few studies on the interactive effect of salinity and sodicity in soils exposed to drying and wetting cycles. We conducted a study to assess the impact of multiple drying and wetting on microbial respiration, dissolved organic carbon and microbial biomass in saline and saline-sodic soils.

Methods

Different levels of salinity (EC_1:5 1.0 or 2.5) and sodicity (SAR?<?3 or 20) were induced by adding NaCl and CaCl₂ to a non-saline/non-sodic soil. Finely ground wheat straw residue was added at 20?g?kg^?1 as substrate to stimulate microbial activity. The constant moist (CM) treatment was kept at optimum moisture content for the length of the experiment. The drying and rewetting (DW) treatments consisted of 1 to 3 DW cycles; each DW cycle consisted of 1?week drying after which they were rewet to optimum moisture and then maintained moist for 1?week.

Results

Drying reduced respiration more strongly at EC2.5 than with EC1.0. Rewetting of dry soils produced a flush in respiration which was greatest in the soils without salt addition and smallest at high salinity (EC2.5) suggesting better substrate utilisation by microbes in soils without added salts. After three DW events, cumulative respiration was significantly increased by DW compared to CM, being 24% higher at EC1.0 and 16% higher at EC2.5 indicating that high respiration rates after rewetting may compensate for the low respiration rates during the dry phase. The respiration rate per unit MBC was lower at EC2.5 than at EC1.0. Further, the size of the flush in respiration upon rewetting decreased with each ensuing DW cycle being 50–70% lower in the third DW cycle than the first.

Conclusions

Both salinity and sodicity alter the effect of drying and rewetting on soil carbon dynamics compared to non-saline soils.     

Spatial pattern of soil organic carbon of the main forest soils and its influencing factors in Guangxi,China北大核心CSCD

Aims Our objectives were to study the spatial distribution of soil organic carbon (SOC) density and its influencing factors in the main forest ecosystems in Guangxi. Methods A total of 345 sample plots were established in Guangxi, and the size of each plot was 50 m × 20 m. Based on the forest resource inventory data and field investigation, the SOC storage of the main forests in Guangxi was estimated. Geostatistics was applied to analyze the spatial pattern of SOC density and the main influencing factors on SOC density were also explored by principal component analysis and stepwise regression. Important findings The total SOC storage in the main forests in Guangxi was 1 686.88 Tg, and the mean SOC density was 124.70 Mg•hm2, which is lower than that of China. The best fitted semivariogram model of SOC density was exponential model, and the spatial autocorrelation was medium. The contour map based on Kriging indicated that northeastern Guangxi had high SOC density and northwestern Guangxi had low SOC density, which corresponded to high SOC density in non-karst region and low SOC density in karst region. The SOC density followed the sequence of bamboo forest > deciduous broadleaf forest > warm coniferous forest > mixed evergreen and deciduous broadleaf forest > evergreen broadleaf forest, and yellow soil > red soil >lateritic red soil > limestone soil. The dominant environment factors affecting SOC density included soil depth, longitude, latitude, and altitude. Soil depth was the most influential factor, which was mainly attributed to the karst landscape.     

Metabolism of organic acids, nitrogen and amino acids in chlorotic leaves of ‘Honeycrisp’ apple (Malus domestica Borkh) with excessive accumulation of carbohydrates

Metabolite profiles and activities of key enzymes in the metabolism of organic acids, nitrogen and amino acids were compared between chlorotic leaves and normal leaves of ‘Honeycrisp’ apple to understand how accumulation of non-structural carbohydrates affects the metabolism of organic acids, nitrogen and amino acids. Excessive accumulation of non-structural carbohydrates and much lower CO₂ assimilation were found in chlorotic leaves than in normal leaves, confirming feedback inhibition of photosynthesis in chlorotic leaves. Dark respiration and activities of several key enzymes in glycolysis and tricarboxylic acid (TCA) cycle, ATP-phosphofructokinase, pyruvate kinase, citrate synthase, aconitase and isocitrate dehydrogenase were significantly higher in chlorotic leaves than in normal leaves. However, concentrations of most organic acids including phosphoenolpyruvate (PEP), pyruvate, oxaloacetate, 2-oxoglutarate, malate and fumarate, and activities of key enzymes involved in the anapleurotic pathway including PEP carboxylase, NAD-malate dehydrogenase and NAD-malic enzyme were significantly lower in chlorotic leaves than in normal leaves. Concentrations of soluble proteins and most free amino acids were significantly lower in chlorotic leaves than in normal leaves. Activities of key enzymes in nitrogen assimilation and amino acid synthesis, including nitrate reductase, glutamine synthetase, ferredoxin and NADH-dependent glutamate synthase, and glutamate pyruvate transaminase were significantly lower in chlorotic leaves than in normal leaves. It was concluded that, in response to excessive accumulation of non-structural carbohydrates, glycolysis and TCA cycle were up-regulated to “consume” the excess carbon available, whereas the anapleurotic pathway, nitrogen assimilation and amino acid synthesis were down-regulated to reduce the overall rate of amino acid and protein synthesis.     

Radiocaesium in an organic soil and the effect of treatment with the fungicide ‘Captan’

Soil fungi accumulate radiocaesium from contaminated soil and it has been hypothesised that this may alter the plant availability and movement of the radionuclide in soil. The effect of twice-monthly addition of an aqueous suspension of the fungicide ‘Captan’ on the changes in a peaty podzol soil at 2 sites, contaminated 2 or 3 years earlier by the injection of ¹³⁴Cs, has been quantified. The sites had different soil acidity and vegetation cover. The less acid soil (pH_water 5.0) had been improved by the addition of lime and fertilizer and was reseeded with grass and clover. The more acid soil (pH_water 3.8) was under hill grasses, herbs and heather. On both sites the addition of fungicide did not alter the amount or concentration of radiocaesium in plant material sampled monthly or the depth distribution of radiocaesium in the soil profile. The concentration of the fungal constituent, ergosterol, in the soil, measured monthly, was unaffected by the fungicide treatment but evidence was obtained from a pot experiment to show that ergosterol decomposes slowly in cold, wet soils. On the more acid soil, two weeks after the last application of fungicide, there was a decline in active fungi as measured by fluorescein diacetate staining. Chloroform fumigation of the more acid soil resulted in a small increase in the amount of ¹³⁴Cs exchangeable with 1 M ammonium acetate. Radiocaesium in seven different fungi grown in pure culture was found to be almost entirely extractable (> 95%) with 1 M ammonium acetate. Another, Amanita rubescens, showed some retention and 88% was extractable. These findings do not preclude the fungal biomass as an important soil component controlling plant availability of radiocaesium from acid, organic soils by maintaining radiocaesium in a biological cycle, but make it unlikely that any fixation by fungi in a chemical sense is involved.     

Effects of microorganism on carbon,nitrogen and phosphorus of Dodonaea viscosa and the soils from different elevations in Yuanmou,Yunnan, China北大核心CSCD

Aims Understanding the effects of soil microorganism at different elevations on plant C:N:P stoichiometry can help us to understand the plant-soil interactions in the context of climate change. Our aim was to quantify the independent and interactive effects of soil microbial communities and temperatures on the C, N, and P in the leaves of Dodonaea viscosa-a global widespread species. Methods Rhizosphere soils of D. viscosa were collected from two elevation zones in Yuanmou County, Yunnan Province. A 2 × 3 factorial experiment with six replications was conducted using climate chambers. The leaf C, N and P contents and the soil properties were measured after three months of the treatments. Important findings Compared with the autoclaved treatment, inoculated rhizosphere soils from both high and low elevations had higher nutrient absorption, especially P uptake. Temperature produced no significant effect on leaf C:N:P stoichiometry, but the interactive effect of temperature and microbial treatment appeared significant. For inoculated rhizosphere soils from high elevation, temperature had no significant effect on leaf C:N:P stoichiometry. For inoculated rhizosphere soils from low elevation, leaf N and P contents under low temperature were significantly lower than those with warmer soils. The promoting effect of soil microorganisms on nutrient uptake may be due to the direct effect of beneficial microorganisms (e.g., mycorrhizal fungi), but not through the alteration of nutrient cycling process. Because D. viscosa in the inoculated rhizosphere soils absorbed more N and P from the soil than those in autoclaved soil, the available N and P in inoculated rhizosphere soils were lower than those in autoclaved soils. As predicted future temperature will be lower in the studied region, the growth of D. viscosa may be negatively affected through plant-microbe feedbacks.     

Organic carbon in soils of Central Asia—status quo and potentials for sequestration

Expectations have been raised that carbon sequestration in soils could provide a short-term bridge to reduce the impacts of increasing carbon emissions until low-carbon technologies are available. To assess the role of Central Asia in this regard, the organic carbon in soils of Central Asia and losses in response to land use were quantified in a spatially explicit way. Based on literature information on soil organic carbon contents and in combination with the FAO-UNESCO Soil Map of the Word, the organic carbon stocks in the upper 30 cm of native soils of Central Asia were estimated to amount to 20,17?±?4,03 Pg. The extent of conversion of native land into agricultural land and the degradation of rangelands was assessed by a land use land cover change map of the region. This type of land use (change) was responsible for a reduction of the soil organic carbon by about 828?±?166 Tg C, or on average 4.1% of the total stocks. To this reduction, degradation of rangeland (observed on 4.9 Mha) with 50 Tg contributed only 6%. Most of the losses resulted from past conversion of rangelands into rainfed or irrigated agricultural land in the north of Kazakhstan. Hotspots of high soil organic matter depletion were former wetlands, drained for cultivation during the last decades. Assuming that improved agronomic and grazing management could be put in place and that therewith SOC levels in all of Central Asia’s cropland and degraded rangeland could be brought back to native levels in the next 50 years, each year 16.6 Tg C could be sequestered. This is equal to the sizeable amount of 15.5% of the 2004 annual anthropogenic C-emissions of the five Central Asian countries (107 Tg C yr^?1). However, Central Asia contributed only 1.4% of CO₂ that is set free worldwide by fossil fuel burning. Therefore, the mitigation effect on rising atmospheric CO₂ levels and climate change of such ambitious sequestration plans, if put into practice, would be hardly notable. The central Asian example shows that, unfortunately, the strategy of soil C sequestration as a stand-alone measure is not a viable bridge to a future in which alternative energy source can substitute fossil fuel burning, but can only be part of a set of mitigating measures.     

Microbial transformations of some particulate pollution deposits in soils — A source of plant-available nitrogen and sulphur

Summary Atmospheric pollution deposits, largely consisting of soot, were removed from sycamore leaves growing downwind of a coking plant, and added to soil. Increases in plant available S-ions (S₂O₃ ²⁻; S₄O₆ ²⁻ and SO₄ ²⁻) and N (NH₄ ⁺ and NO₃ ⁻) occurred due to the action of soil microorganisms on the deposits. Although the detrimental effects of air pollution on plant growth have been previously emphasised, supply of nutrients resulting from the microbial transformation of particulate pollutants may prove important to the growth of pollution-resistant plant communities.