Inorganic Pool Research Articles

Biogenic-to-lithogenic handoff of particulate Zn affects the Zn cycle in the Southern Ocean.

Zinc (Zn) is vital to marine organisms. Its active uptake by phytoplankton results in a substantial depletion of dissolved Zn, and Zn bound to particulate organic matter replenishes dissolved Zn in the ocean through remineralization. However, we found that particulate Zn changes from Zn bound to phosphoryls in cells to recalcitrant inorganic pools that include biogenic silica, clays, and iron, manganese, and aluminum oxides in the Southern Ocean water column. The abundances of inorganic pools increase with depth and are the only phases preserved in sediments. Changes in the particulate-Zn speciation influence Zn bioavailability and explain the decoupling of Zn and phosphorus and the correlation of Zn and silicon in the water column. These findings reveal a new dimension to the ocean Zn cycle, implicating an underappreciated role of inorganic Zn particles and their impact on biological productivity.

Extracting Insoluble Inorganic Phosphorus from Organic Farm Soils in Mountains: Identifying Effective Organic Acid Extractants

Phosphorus, among others, is quite a vital nutrient for the life of a plant. Because of the dominance of iron and aluminium oxides in acidic soils, they facilitate the fixation of phosphorus which results into phosphorus deficiency in large amounts. Hence, proper replenishment of the soil phosphorus (P) is very much important to cater the need of plant P requirement for better yield and development. The agricultural soils of Meghalaya (India) are by default rich in organic contents and organic P pool contributes 15-80% of the total plant P nutrition. Moreover, a different nature of nutrient pools is present in organic farming system compared to the conventional farming system. Lack of knowledge of these pools results in an imbalanced manuring plan, which hinders successful production system. The dynamic fraction of P cannot represent the correct status of phosphorus in soils under organic production systems, as the conventional soil testing protocols do not take into account the potentially available inorganic pools of phosphorus. Hence, a different extractant that can extract such potentially available P in an acidic soil under organic production system is highly required. The mineralization, solubilization and extraction (of the potentially available P pool) by using various organic acids produced through the beneficial soil microorganisms can serve this purpose. Therefore, the present research work was carried out to identify the best suitable P extractant to extract such potentially available inorganic P pool. The result of the present investigation revealed that out of 6 different extractants selected, 2% citric acid and double lactate extractants were found to be strongly correlated to the total P of the selected sites. Conventional Bray 1 extractant was taken as a check extractant. The outcome of the research is to develop a proper recommendation of fertilizer dose and an appropriate soil testing protocol for phosphorus being used in organic cultivation.

Speciation and cycling of iodine in the subtropical North Pacific Ocean

Iodine intersects with the marine biogeochemical cycles of several major elements and can influence air quality through reactions with tropospheric ozone. Iodine is also an element of interest in paleoclimatology, whereby iodine-to-calcium ratios in marine carbonates are widely used as a proxy for past ocean redox state. While inorganic iodine in seawater is found predominantly in its reduced and oxidized anionic forms, iodide (I−) and iodate (IO3−), the rates, mechanisms and intermediate species by which iodine cycles between these inorganic pools are poorly understood. Here, we address these issues by characterizing the speciation, composition and cycling of iodine in the upper 1,000 m of the water column at Station ALOHA in the subtropical North Pacific Ocean. We first obtained high-precision profiles of iodine speciation using isotope dilution and anion exchange chromatography, with measurements performed using inductively coupled plasma mass spectrometry (ICP-MS). These profiles indicate an apparent iodine deficit in surface waters approaching 8% of the predicted total, which we ascribe partly to the existence of dissolved organic iodine that is not resolved during chromatography. To test this, we passed large volumes of seawater through solid phase extraction columns and analyzed the eluent using high-performance liquid chromatography ICP-MS. These analyses reveal a significant pool of dissolved organic iodine in open ocean seawater, the concentration and complexity of which diminish with increasing water depth. Finally, we analyzed the rates of IO3− formation using shipboard incubations of surface seawater amended with 129I−. These experiments suggest that intermediate iodine species oxidize to IO3− much faster than I− does, and that rates of IO3− formation are dependent on the presence of particles, but not light levels. Our study documents the dynamics of iodine cycling in the subtropical ocean, highlighting the critical role of intermediates in mediating redox transformations between the major inorganic iodine species.

Variation of phosphorus pools as affected by land use in acidic soil of eastern Himalayan region of India

Soil phosphorus (P), an essential major element is mostly low in many tropical and sub-tropical soils and its characterization into different pools and relationship with other soil properties is crucial in understanding the adsorption chemistry and its release to available forms. Three soil depths (0–15, 15–30 and 30–45 cm) from six major land use were studied to elucidate the effect of land use on different pools of soil P and its relationship with other soil properties. The studied soils were acidic in nature (pH: 5.03–6.33) and land use significantly increased the soil pH for lowland rice (LR: 6.1), the higher soil pH in LR soil also significantly increased the available P forms (available P: P and Mehlich P: M-P) while the higher clay content in Teak (T) plantation decreased the available P forms implying that P was fixed. In addition, soil pH was positively related to the labile inorganic pool (NaHCO3-PI) and stable pool (HCLP). The moderately labile pool, NaOH-P (16–44%) was higher compared to labile pool, NaHCO3-P (11–15%) and stable, HCL-P (2–13%) due to the acidic soil pH where Fe and Al oxide dominates in sub-tropical weathered soils. The organic P pools (NaOH and NaHCO3) which is important for long term P cycling were higher than the inorganic pools in T, F and R land uses. Management strategy for increasing SOC is important to maintain organic P cycling to supply available P for long term.

Modelling the terrestrial nitrogen and phosphorus cycle in the UVic ESCM

Abstract. Nitrogen (N) and phosphorus (P) biogeochemical dynamics are crucial for the regulation of the terrestrial carbon cycle. In Earth system models (ESMs) the implementation of nutrient limitations has been shown to improve the carbon cycle feedback representation and, hence, the fidelity of the response of land to simulated atmospheric CO2 rise. Here we aimed to implement a terrestrial N and P cycle in an Earth system model of intermediate complexity to improve projections of future CO2 fertilization feedbacks. The N cycle is an improved version of the Wania et al. (2012) N module, with enforcement of N mass conservation and the merger with a deep land-surface and wetland module that allows for the estimation of N2O and NO fluxes. The N cycle module estimates fluxes from three organic (litter, soil organic matter and vegetation) and two inorganic (NH4+ and NO3-) pools and accounts for inputs from biological N fixation and N deposition. The P cycle module contains the same organic pools with one inorganic P pool; it estimates influx of P from rock weathering and losses from leaching and occlusion. Two historical simulations are carried out for the different nutrient limitation setups of the model: carbon and nitrogen (CN), as well as carbon, nitrogen and phosphorus (CNP), with a baseline carbon-only simulation. The improved N cycle module now conserves mass, and the added fluxes (NO and N2O), along with the N and P pools, are within the range of other studies and literature. For the years 2001–2015 the nutrient limitation resulted in a reduction of gross primary productivity (GPP) from the carbon-only value of 143 to 130 Pg C yr−1 in the CN version and 127 Pg C yr−1 in the CNP version. This implies that the model efficiently represents a nutrient limitation over the CO2 fertilization effect. CNP simulation resulted in a reduction of 11 % of the mean GPP and a reduction of 23 % of the vegetation biomass compared to the baseline C simulation. These results are in better agreement with observations, particularly in tropical regions where P limitation is known to be important. In summary, the implementation of the N and P cycle has successfully enforced a nutrient limitation in the terrestrial system, which has now reduced the primary productivity and the capacity of land to take up atmospheric carbon, better matching observations.

Do carbon farming practices build bioavailable nitrogen pools?

AbstractAgricultural soils contain large amounts of nitrogen (N), but only a small fraction is readily available to plants. Despite several methods developed to estimate the bioavailability of N, there is no consensus on which extraction methods to use, and which N pools are critically important. In this study, we measured six soil N pools from 20 farms, which were part of a multi‐year soil carbon sequestration on‐farm experiment (Carbon action, 2019–2023). The aim was to quantify the N pools and to evaluate if farming practices that aim to build soil carbon pools, also build bioavailable N pools. We also aimed to test if the smaller and rapidly changing N pools could serve as an indicator for the slower change in soil organic matter. The measured N pools decreased in size, when moving from total N (7700 ± 1500 kg/ha) to slowly cycling (Illinois Soil Nitrogen Test ISNT‐N: 1063 ± 220 kg/ha, autoclave citrate‐extracted ACE protein N: 633 ± 440 kg/ha), water‐soluble organic N (50 ± 17 kg/ha), potentially mineralizable N (33 ± 13 kg/ha) and finally readily plant available inorganic pools (nitrate and ammonium, total: 14 ± 8 kg/ha). In total, the measured pools covered only 18%–44% of total N, indicating a large unidentified N pool, which is either tightly bound to soil mineral fraction and not easily extractable or is bound to undecomposed plant residues and not hydrolysed by the methods. Of the large N pools (ISNT‐N, ACE protein and unidentified residual N), clay, carbon (C) and C:Clay ratios explained most of the variability (R2 = .90–.93), leaving a minor part of the variation to the management effect. A pairwise comparison of carbon farming and control plots concluded that farming practices had a small (3%–5%) but statistically significant (p < .05) effect on soil total N and ISNT‐N pools, and a moderate and significant effect (18%, p < .01) on potentially mineralizable N. The large variation in protein N, water‐soluble organic N and inorganic N reduced statistical significance, although individual C sequestration practices had large effects (−30% to +50%). In conclusion, carbon sequestration practices can build both slowly cycling N pools (ISNT) and increase the mineralisation rate of these pools to release plant available forms, resulting in an additional benefit to agriculture through reduced fertilizer application needs.

Toward a Global Model for Soil Inorganic Phosphorus Dynamics: Dependence of Exchange Kinetics and Soil Bioavailability on Soil Physicochemical Properties.

The representation of phosphorus (P) cycling in global land models remains quite simplistic, particularly on soil inorganic phosphorus. For example, sorption and desorption remain unresolved and their dependence on soil physical and chemical properties is ignored. Empirical parameter values are usually based on expert knowledge or data from few sites with debatable global representativeness in most global land models. To overcome these issues, we compiled from data of inorganic soil P fractions and calculated the fraction of added P remaining in soil solution over time of 147 soil samples to optimize three parameters in a model of soil inorganic P dynamics. The calibrated model performed well (r 2 > 0.7 for 122 soil samples). Model parameters vary by several orders of magnitude, and correlate with soil P fractions of different inorganic pools, soil organic carbon and oxalate extractable metal oxide concentrations among the soil samples. The modeled bioavailability of soil P depends on, not only, the desorption rates of labile and sorbed pool, inorganic phosphorus fractions, the slope of P sorbed against solution P concentration, but also on the ability of biological uptake to deplete solution P concentration and the time scale. The model together with the empirical relationships of model parameters on soil properties can be used to quantify bioavailability of soil inorganic P on various timescale especially when coupled within global land models.

Phosphorus dynamics during early soil development in a cold desert: insights from oxygen isotopes in phosphate

Abstract. At the early stages of pedogenesis, the dynamics of phosphorus (P) in soils are controlled by microbial communities, the physicochemical properties of the soil and the environmental conditions. While various microorganisms involved in carrying out biogeochemical processes have been identified, little is known about the actual contribution of microbial processes, such as organic P hydrolysis and microbial P turnover, to P cycling. We thus focused on processes driven by microbes and how they affect the size and cycling of organic and inorganic soil P pools along a soil chronosequence in the Chamser Kangri glacier forefield (Western Himalayas). The rapid retreat of the glacier allowed us to study the early stages of soil formation under a cold arid climate. Biological P transformations were studied with the help of the isotopic composition of oxygen (O) in phosphate (δ18OP) coupled to sequential P fractionation performed on soil samples (0–5 cm depth) from four sites of different age spanning 0 to 100–150 years. The P bound to Ca, i.e., 1 M HCl-extractable P, still represented 95 % of the total P stock after approximately 100 years of soil development. Its isotopic composition was similar to the parent material at the most developed site. Primary phosphate minerals, possibly apatite, mostly comprised this pool. The δ18OP of the available P and the NaOH-extractable inorganic P instead differed from that of the parent material, suggesting that these pools underwent biological turnover. The δ18OP of the available P was mostly controlled by the microbial P, suggesting fast exchanges occurred between these two pools possibly fostered by repeated freezing–thawing and drying–rewetting cycles. The release of P from organic P becomes increasingly important with soil age, constituting one-third of the P flux to available P at the oldest site. Accordingly, the lighter isotopic composition of the P bound to Fe and Al oxides at the oldest site indicated that this pool contained phosphate released by organic P mineralization. Compared to previous studies on early pedogenesis under alpine or cold climate, our findings suggest a much slower decrease of the P-bearing primary minerals during the first 100 years of soil development under extreme conditions. However, they provide evidence that, by driving short-term P dynamics, microbes play an important role in controlling the redistribution of primary P into inorganic and organic soil P pools.

Soil Phosphorus Exchange as Affected by Drying-Rewetting of Three Soils From a Hawaiian Climatic Gradient

Current understanding of phosphorus (P) dynamics is mostly based on experiments carried out under steady-state conditions. However, drying-rewetting is an inherent feature of soil behavior, and as such also impacts P cycling. While several studies have looked at net changes in P pool sizes with drying-rewetting, few studies have dynamically tracked P exchange using isotopes, which would give insights on P mean residence times in a given pool, and thus P availability. Here, we subjected three soils from a climatic gradient on the Kohala peninsula from Hawaii to 5-month drying-rewetting treatments. The hypotheses were that physico-chemical and biotic processes would be differently affected by repeated drying-rewetting cycles, and that response would depend on climatic history of the soils. Soils were labeled with 33P and 18O enriched water. At select time intervals, we carried out a sequential extraction and measured P concentration, 33P recovery (only first 3 months), and incorporation of 18O from water into phosphate. This allowed tracing P dynamics in sequentially extracted pools as well as O dynamics in phosphate, which are driven by biological processes. Results showed that P concentration and 33P recovery were predominantly driven by soil type. However, across all soils we observed faster dilution of 33P from resin-P into less mobile inorganic pools under drying-rewetting. On the other hand, O dynamics in phosphate were mostly governed by drying-rewetting treatment. Under drying-rewetting, considerably less O was incorporated from water into phosphate of resin-P, microbial-P and HCl-P, suggesting that drying-rewetting reduced biological P cycling. Hence, our results suggest that repeated drying-rewetting increases inorganic P exchange while reducing biological P cycling due to reduced microbial activity, independent of climatic history of the soils. This needs to be considered in P management in ecosystems as well as model representations of the terrestrial P cycle.

Effects of algae and hydrophytes on the inorganic phosphorus pool of shallow hypereutrophic Lake Taihu

Abstract Sedimentary phosphorus is a crucial potential source of phosphorus in the eutrophic lake ecosystem. Different ecological types are supposed to affect the presence and variation of sediment phosphorus. On the basis of field investigations, the total sediment phosphorus load in Zhushan Bay was 1,457.48 mg/kg, nearly four times that of the hydrophyte-dominated area. Thereinto, 41.1% was in the form of iron and aluminum-bound phosphorus, which explicitly indicated the phosphorus contamination there. Analytical methods such as Pearson correlation, contamination assessment and principal component analysis were conducted to find out that ‘contamination’ was not equivalent to ‘release risk’. The contamination classification of East Lake Taihu was ‘clean’ in general. However, 63.3% of the total phosphorus could be mobilized under certain conditions. Therefore, light phosphorus loading does not equate to less release risk. In the long run, the implicit phosphorus release by the activation of organic phosphorus in hydrophytic areas needs close attention. This study provides a reference to understand the influence of hydrophytes and algae on the phosphorus cycle of sediment.

Hotspots of Legacy Phosphorus in Agricultural Landscapes: Revisiting Water-Extractable Phosphorus Pools in Soils

Controlling phosphorus (P) losses from intensive agricultural areas to water bodies is an ongoing challenge. A critical component of mitigating P losses lies in accurately predicting dissolved P loss from soils, which often includes estimating the amount of soluble P extracted with a laboratory-based extraction, i.e., water-extractable P (WEP). A standard extraction method to determine the WEP pool in soils is critical to accurately quantify and assess the risk of P loss from soils to receiving waters. We hypothesized that narrower soil-to-water ratios (1:10 or 1:20) used in current methods underestimate the pool of WEP in high or legacy P soils due to the equilibrium constraints that limit the further release of P from the solid-to-solution phase. To investigate P release and develop a more exhaustive and robust method for measuring WEP, soils from eight legacy P fields (Mehlich 3–P of 502 to 1127 mg kg−1; total P of 692 to 2235 mg kg−1) were used for WEP extractions by varying soil-to-water ratios from 1:10 to 1:100 (weight:volume) and in eight sequential extractions (equivalent to 1:800 soil-to-water ratio). Extracts were analyzed for total (WEPt) and inorganic (WEPi) pools, and organic (WEPo) pool was calculated. As the ratios widened, mean WEPi increased from 23.7 mg kg−1 (at 1:10) to 58.5 mg kg−1 (at 1:100). Further, WEPi became the dominant form, encompassing 92.9% of WEPt at 1:100 in comparison to 79.0% of WEPt at 1:10. Four of the eight selected soils were extracted using a 1:100 ratio in eight sequential extractions to fully exhaust WEP, which removed a cumulative WEPt of 125 to 549 mg kg−1, equivalent to 276–416% increase from the first 1:100 extraction. Although WEP concentrations significantly declined after the first sequential extraction, WEP was not exhausted during the subsequent extractions, indicating a sizeable pool of soluble P in legacy P soils. We conclude that (i) legacy P soils are long-term sources of soluble P in agricultural landscapes and (ii) the use of a 1:100 soil-to-water ratio can improve quantification and risk assessment of WEP loss in legacy P soils.

Estimating the Impact of Seep Methane Oxidation on Ocean pH and Dissolved Inorganic Radiocarbon Along the U.S. Mid‐Atlantic Bight

AbstractOngoing ocean warming can release methane (CH4) currently stored in ocean sediments as free gas and gas hydrates. Once dissolved in ocean waters, this CH4 can be oxidized to carbon dioxide (CO2). While it has been hypothesized that the CO2 produced from aerobic CH4 oxidation could enhance ocean acidification, a previous study conducted in Hudson Canyon shows that CH4 oxidation has a small short‐term influence on ocean pH and dissolved inorganic radiocarbon. Here we expand upon that investigation to assess the impact of widespread CH4 seepage on CO2 chemistry and possible accumulation of this carbon injection along 234 km of the U.S. Mid‐Atlantic Bight. Consistent with the estimates from Hudson Canyon, we demonstrate that a small fraction of ancient CH4‐derived carbon is being assimilated into the dissolved inorganic radiocarbon (mean fraction of 0.5 ± 0.4%). The areas with the highest fractions of ancient carbon coincide with elevated CH4 concentration and active gas seepage. This suggests that aerobic CH4 oxidation has a greater influence on the dissolved inorganic pool in areas where CH4 concentrations are locally elevated, instead of displaying a cumulative effect downcurrent from widespread groupings of CH4 seeps. A first‐order approximation of the input rate of ancient‐derived dissolved inorganic carbon (DIC) into the waters overlying the northern U.S. Mid‐Atlantic Bight further suggests that oxidation of ancient CH4‐derived carbon is not negligible on the global scale and could contribute to deepwater acidification over longer time scales.

Long term cultivation effects on nitrogen dynamics in polyhouse and open field vegetable growing soils of North-Western Himalayas

Aim: The present study was undertaken to assess the differences in the transformations of native nutrients between protected and open field conditions, affecting their availability to plants. Methodology: The geo-referenced soil samples were collected from farmers' field growing vegetables under polyhouse and adjacent open fields for last 5 to 6 years. Collected soil samples were analysed for organic and inorganic pools of nitrogen. Means of the different land use types were compared by using Tukey HSD Procedure.? Results: Hydrolysable NH4-N was found as second most dominant form of nitrogen after amino acid-N, both under conventional and protected cultivation. In general, an increase was observed in hydrolysable NH4-N both under protected and conventional cultivation with respect to their fallow plots Interpretation: Various fractions of nitrogen were found to be affected by the management practices and consequently status of nitrogen fractions was observed higher under polyhouse soil. Soil nutrient release under protected environment as compared to open field is necessary to observe the changes and adverse effect with ages of intensive cultivation under protected conditions.

Non-Redfieldian C:N:P ratio in the inorganic and organic pools of the Bay of Bengal during the summer monsoon

Nitrogen (N) and phosphorus (P) determine the strength of the ocean’s biological carbon (C) pump, and variation in the N:P ratio is key to phytoplankton growth. A fixed C:N:P ratio (106:16:1) in organic matter and deep-water nutrients was observed by Alfred C. Redfield. However, recent studies have challenged the concept of the Redfield Ratio, and its veracity remains to be examined in oceanic basins like the Bay of Bengal. For this purpose, we sampled the water in the Bay of Bengal for C, N, and P content in the organic and inorganic pools from the surface to 2000 m. Overall, the C:N:P ratio deviated greatly from the Redfield Ratio. The C:N:P ratio in particulate organic matter varied from 232:25:1 in the top layer (surface to the depth of the chlorophyll maximum) to 966:72:1 in the deep water (300-2000 m). In dissolved organic matter, the ratio varied from 357:30:1 in the top layer to 245:66:1 in the deep water. The N:P ratio in nutrients varied from 3 in the top layer to 12 in the deep water. The nutrient-depleted top layer (average NO3- + NO2- ~ 0.7 µmol l-1) with a low N:P ratio coupled with reported low primary production rates in the Bay suggested that the production was N limited. Concurrent N2 fixation rates were not sufficient to alter the observed C:N:P ratio. Eddies showed a mixed effect on the C:N:P ratio. Our C:N:P ratios in particulate organic matter are comparable to other tropical basins and supports the nutrient supply hypothesis for low latitude ecosystems.

Effect of common bean (Phaseolus vulgaris) on apatite weathering under elevated CO2

Plants accelerate chemical weathering of minerals through the production of carbonic acid during root respiration, root exudation, and uptake of ions. These plant processes are increased by elevated concentrations of atmospheric CO2 and may in turn affect mineral weathering. We seek to understand the effect of predicted atmospheric CO2 concentrations on plant-mediated soil mineral weathering. Phaseolus vulgaris (common bean) was grown in flow-through microcosms consisting of a mixture of 85% quartz and 15% apatite sands (by weight). Nutrient release from apatite was measured using plants grown under two atmospheric conditions: ambient CO2 (~400 ppm) and elevated CO2 (~1000 ppm). To sustain plant growth, a nutrient solution without calcium (Ca) or phosphorous (P) was supplied to the plants using peristaltic pumps. Unplanted microcosms receiving the same nutrient solution served as abiotic controls in both CO2 treatments. Using atomic absorption spectroscopy and colorimetry, Ca and P concentrations of the leachate and plant tissue were measured as proxies for apatite dissolution. Plants were harvested every 2 weeks during the 8-week experiment to understand how Ca and P release in the two CO2 treatments changed over time. After 8 weeks, P. vulgaris grown in elevated CO2 had a greater root to shoot ratio than plants grown in ambient CO2. Plants grown in elevated CO2 released more P than plants grown in ambient conditions, possibly due to greater demands for mineral nutrients. P was preferentially released by the plants and there were no significant differences in Ca released by plants. Both elevated and ambient planted microcosms had a lower pH than abiotic controls, likely due to root respiration, nutrient uptake and exudation of organic acids. Organic acids were not identified in the leachate likely due to their low concentrations and rapid breakdown. Plants released as much as 7 times more Ca than abiotic controls, regardless of CO2 concentrations. Biotic experiments released over 200 times more P than abiotic experiments. Our results show increased atmospheric CO2 can determine rhizosphere processes, which in turn affect weathering products. Thus, mineral nutrient fluxes and C sequestration in inorganic pools are likely to increase as CO2 concentrations rise.

Dissolved organic phosphorus uptake by marine phytoplankton is enhanced by the presence of dissolved organic nitrogen

Organic nutrients can constitute the major fractions (up to 70%) of aquatic nitrogen (N) and phosphorus (P), but their cycling is poorly understood relative to the inorganic pools. Some phytoplankton species access P from the dissolved organic phosphorus (DOP) pool through expression of alkaline phosphatase (AP), which hydrolyses orthophosphate from organic molecules, and is thought to occur either at low concentrations of dissolved inorganic P (DIP), or elevated ratios of dissolved inorganic N (DIN) to DIP. Three algal strains native to the North-East Atlantic Ocean (coccolithophore, dinoflagellate and diatom species) were grown under representative, temperate conditions, and the dissolved N and P components amended to include dissolved organic N (DON) and DOP. The activity of AP was measured to determine the rate of DOP uptake by each algal species. The addition of DON and DOP enhanced the growth of the algal species, regardless of DIN and DIP concentrations. In cultures where the total concentrations and absolute N: P ratio was unchanged but the N pool included both DON and DIN, an increase in alkaline phosphatase activity (APA) was measured. This suggested that the presence of DON triggered the selective uptake of DOP. The uptake of organic P was confirmed by detection of adenosine in DOP-amended culture media, indicating that P had been cleaved from ADP and ATP added to the media as DOP, and cellular P concentration in these cultures exceeded the calculated concentration based on uptake of DIP only. Our data demonstrates that organic nutrients can enhance and sustain marine algal productivity. The findings have implications for marine ecosystem function and health, since climate change scenarios predict variable riverine inputs to coastal areas, altered N: P ratios, and changes in the inorganic to organic balance of the nutrient pools.

Effect of Pasture Management System Change on In-Season Inorganic Nitrogen Pools and Heterotrophic Microbial Communities

It has been assumed that the system of long-term pasture management exerts a significant impact on the soil microorganisms count, subsequently affecting the availability of mineral nitrogen (Nmin). This hypothesis was tested in a three-year experiment on a long-term pasture with two distinct systems of grass sward management, i.e., grazing and mowing. Mowing significantly increased the microorganisms count by 13%, 28%, 86%, and 2% for eubacteria (EU), actinobacteria (AC), molds (MO), and Azotobacter (AZ), respectively. The main reason was drought in 2006, which resulted in the domination of Dactylis glomerata L. in the grass sward, instead of Lolimum perenne L. and Poa pratensis L. The content of Nmin decreased through the vegetative growing season, reaching its lowest value after the 3rd grazing cycle. The impact of microorganisms on the Nmin pools increased in the order: molds < eubacteria < actinobacteria. The count of actinobacteria in the alkaline organic soil increased in response to drought, contribution of Dactylis glomerata L. in the sward, and the shortage of available phosphorus. The sound pasture management system is possible by introducing alternate grazing and mowing cycles. The core of sustainability is the enhanced activity of actinobacteria after changing the system from grazed into mowed.

Role of soluble and exchangeable nitrogen pools in N cycling and the impact of nitrogen added in forest soil.

Nitrogen (N) cycle in forest soils is altered by water, salt, or acid solutions, and its internal transfers to and from each existing inorganic pools are not known comprehensively. To evaluate the soluble and exchangeable N pools, bulk soil (B soil), water-extracted soil (W soil), and the 0.5 mol L-1 K2SO4-treated soil (K soil) were incubated for up to 48 days to comprehend the dynamics of inorganic (NH4+ and NO3-) and soluble organic N (SON) in water-soluble, exchangeable, 2.5 mol L-1 H2SO4 (labile pool I, LPI) and 13 mol L-1 H2SO4 (labile pool II, LPII) pools. To test the N deposition effects, additional NH4NO3 solution was added to B, W, and K soils at amount of 40 mg N kg-1 soil. The results showed that though there was more NO3- removed when W soil was prepared, the similar net nitrification rate in W soil to B soil and more than 20 mg N kg-1 water-soluble NO3- were observed in W soil, which indicated that the loss of NO3- would be enhanced. In contrast, there was more water-soluble and exchangeable NH4+ for K soil compared with B soil. The different dynamic of NO3- between W and K soil suggested that nitrifiers might dominate in the soil matrix rather than the soil solution. After incubation, each N form in the LPI decreased, which can be attributed to the allocation of remaining N into the recalcitrant pool, except the increase of NH4+ for B soil and NO3- for K soil, and NO3- in LPII for B soil. Compared with control, N addition increased mineralization of exchangeable SON to promote nitrification regardless of soils, but weakened the immobilization of NO3-. In addition, N in LPI and LPII pools have increased, which might be related to decomposition of recalcitrant organic matter induced by N addition to transform when the water-soluble and exchangeable N was removed. Therefore, the changes of soluble and exchangeable nitrogen pools impact the N cycling. Our findings can give some explanation for whole soil N transformation responses to N deposition.

Thermal stability of soil carbon pools: Inferences on soil nature and evolution

The quantification of soil carbon pools is a pressing topic both for the agriculture productivity and to evaluate the Greenhouse Gases (GHG) sequestration potential, therefore a rapid and precise analytical protocol for carbon speciation is needed. Temperature-dependent differentiation of soil carbon in compliance with the DIN (German Institute for Standardization) 19539 standard has been applied for the first time on 24 agricultural soil samples from the Po River Plain (Italy), with the aim of investigate their thermal behavior in the 50−900 °C interval. The results invariably show the existence of three soil carbon pools having different thermal stabilities, namely, thermally labile organic carbon (TOC400), residual oxidizable carbon (ROC) and total inorganic carbon (TIC900), in the intervals of 300−400 °C, 510−600 °C and 700−900 °C, respectively. Significant relationships have been observed between the above mentioned organic and inorganic carbon pools and the associated isotopic composition: 1) inverse correlation between TOC400/ROC and δ13C links thermal stability and soil organic matter (SOM) composition; 2) direct correlation between carbonate breakdown temperature and δ13C denotes the mineralogical association of the inorganic pool. The results give clues regarding the nature and evolution of soil carbon pools.

Phosphorus pool responses under different P inorganic fertilizers for a eucalyptus plantation in a loamy Oxisol

Phosphate fertilizers play an important role in plant nutrition. Different P fertilizer sources such as high-solubility (simple superphosphate, SSP), low-solubility (rock phosphate, RP) and complex superphosphate (CSP) are available for plant supplementation. The objective of this study was to investigate the short- and long-term redistribution of soil P after application of different P sources at establishment of an Eucalyptus forest stand. We carried out two experiments to identify the short- and long- term changes in a Brazilian Oxisol. To property identify the P pools in different times, Hadleýs fractionation methodology was applied to a long-term studies and citrate and oxalate to short-term. From zero to 180 days, the soluble P fractions were not altered in the non-fertilized treatment. Under SSP, a slight increase in this P fraction was found until 30 days, followed by a decrease in later evaluations. During the same period, a slight reduction in Pi extracted by citrate and oxalate was found under the control and a large reduction (approximately 50%) under the SSP treatment. Intermediate behavior was observed under the CSP and RP treatments, whereas there was an increase in P-citrate and P-oxalate until 30 days followed by a reduction afterwards. These results suggest that this pool comprises a potential bioavailability of P to plants. Different fertilizer sources did not increase the most recalcitrant P pool. However, different sources increased the organic P pool, mainly organic moderately labile P at long-term evaluations. Organic labile pools showed a fertilizer-specific response where CSP and RP increased respectively by 43% and 41% during the first year, and decreased to 39% in CSP treatment and 50% in RP treatment during the third year. Available P pool was highly dependent on inorganic and occluded pools and the organic pool acted predominantly as a sink of P on available and inorganic pools. The results reinforce the high level of recalcitrance of the organic pool and the fact that Eucalyptus plants must access pools of residual P in order to maintain their nutritional demands.