Phosphorus Turnover Research Articles

Biologisation impact on soil condition, grapevine mineral nutrition and productivity

The research aimed to study the combined effect of inter-row sodding with perennial grasses and biofertiliser applications (microbial preparations, MPs) on soil fertility and biological activity, as well as on mineral nutrition, productivity and quality of grapes. The experiment was conducted at a vineyard of the Shasla x Berlandieri 41B-rootstock Muskat Belyy variety nearby Sevastopol. The two-factor design was as follows. Sodding: with segetal vegetation (SV) or a mixture of seeded cereal and leguminous herbs (MHs). Microbial preparations: grapevine root system and soil bacterisation with MPs of various action, including Diazophyte nitrogen fixer, Phosphoenterin (PE) phosphate-mobiliser and a complex of microbial preparations (CMP) additionally containing Biopolycide bioprotector. In control, MPs were not applied with SV or MH sodding. Preparations were introduced in soil once a year prior to grapevine flowering at a dose of 200 g MP suspension per bush. Herbs were mown 5–6 times per season at 30–40 cm height. A combined sodding—MPs usage has been found to increase the nitrate content by 24–45, mobile P2O5 – by 16–21, exchangeable K2O – by 28–50 and organic matter – by 0.06–0.13 % relative to control. The greatest increase in N-NO3–K2O content was registered for the combination of MHs, Diazophyte and CMP; combined SV—CMP–MHs had the greatest impact on mobile P2O5 and organic matter. Biologisation enriched mineral grapevine nutrition, especially for P and K, as well as increased the bush productivity by 10–14 % (maximum in CMP–MHs) via improving the berry and bunch mass and grape quality via significantly increasing the sugar content and lowering acidity of wort. MHs–CMP maximized counts of agronomically valuable microorganisms involved in the organic and mineral nitrogen and phosphorus turnover (ammonifiers and oligotrophs by 120–130, amylolytics and phosphate mobilisers by 50–70 and oligonitrophilic by 50– 80 %). All usages contributed to soil enrichment with nutrients and humus.

Organic material with balanced C‐nutrient stoichiometry and P addition could improve soil P availability with low C cost

AbstractBackgroundCarbon (C) addition to promote phosphorus (P) turnover by microbes is recommended to increase soil P availability. The C‐nutrient stoichiometry of organic materials (OM) are the primary factors in controlling soil P availability and C storage.MethodsA pot experiment was carried out to investigate the effects of different organic matter (OM) with equal carbon input [soybean dregs (SD), chicken manure (CM), and vermicompost (VC), 1000 mg C kg–1 soil] under three P levels (0, 10, and 20 mg P per kg dry soil) on soil P availability, C content, and plant growth in high P fixing soils.ResultsPlant biomass and shoot P content were significantly increased in P and OM addition treatment. Application of OM or P alone had no effect on soil available P (AP) but increased the microbial P (MBP). Compared with P addition alone, soil potential AP pool (the sum of soil AP and MBP content) was increased by 89%–200% in both OM and P addition soil. Soil potential AP pool and dissolved organic carbon (DOC) in VC treatment were significantly increased compared with those in CM and SD treatments. On day 60, compared with VC treatment, SD and VC treatments significantly increased alkaline phosphatase (ALP) but decreased soil organic carbon (SOC) content, in which ALP was negatively correlated with SOC and net C balance.ConclusionA small amount of P and vermicompost addition, which had a balanced carbon‐nutrient stoichiometric ratio, was an effective measurement in improving soil AP pool and C content in P‐fixing soil.

Improvement of nitrogen and phosphorus availability by Pseudoalteromonas sp. during salt-washing in saline-alkali soil

In saline-alkali soils, the inactivation of phosphorus and loss of nitrogen resulting in soil infertility could be intensified by salt, which simultaneously leads to pollution of water sphere. However, there is no complete solution for this challenge due to the weak nutrients biological turnover caused by salt dynamic accumulation. In this study, halophilic marine bacteria strains with carriers were screened to decrease the leaching of nitrogen and phosphorus inactivation in saline-alkali soil during salt-washing. Results showed the combination of Pseudoalteromonas sp. CF8-6 and corn cob significantly increased not only soil available phosphorus by 37.03%, but also the soil bioavailable phosphorus content. Moreover, the concentration of TN, NO3−, TP and PO43− in salt washing eluents reduced by corn cob colonized with CF8-6 significantly. It was also found that the abundance of nitrogen-fixing bacteria (such as Azotobacter), and abundance of Proteobacteria and Actinobacteria in soil were all increased by this combination, which were corresponding for the turnover of nitrogen and phosphorus. We demonstrated that the combination of CF8-6 and corn cob has promising potential in improvement of bioavailability of soil nitrogen and phosphorus during the salt-washing process in saline-alkali soil.

Cyanophage Diversity and Community Structure in Dead Zone Sediments.

Up to 20% of prokaryotic organisms in the oceans are estimated to die every day due to viral infection and lysis. Viruses can therefore alter microbial diversity, community structure, and biogeochemical processes driven by these organisms. Cyanophages are viruses that infect and lyse cyanobacterial cells, adding bioavailable carbon and nutrients into the environment. Cyanobacteria are photosynthesizing bacteria, with some species capable of N2 fixation, which are known to form large blooms as well as resistant resting cells known as akinetes. Here, we investigated cyanophage diversity and community structure plus cyanobacteria in dead zone sediments. We sampled surface sediments and sequenced DNA and RNA, along an oxygen gradient-representing oxic, hypoxic, and anoxic conditions-in one of the world's largest dead zones located in the Baltic Sea. Cyanophages were detected at all stations and, based on partial genome contigs, had a higher alpha diversity and different beta diversity in the hypoxic-anoxic sediments, suggesting that cyanobacteria in dead zone sediments and/or environmental conditions select for specific cyanophages. Some of these cyanophages can infect cyanobacteria with potential consequences for gene expression related to their photosystem and phosphate regulation. Top cyanobacterial genera detected in the anoxic sediment included Dolichospermum/Anabaena, Synechococcus, and Cyanobium RNA transcripts classified to cyanobacteria were associated with numerous pathways, including anaerobic carbon metabolism and N2 fixation. Cyanobacterial blooms are known to fuel oxygen-depleted ecosystems with phosphorus (so-called internal loading), and our cyanophage data indicate the potential for viral lysis of cyanobacteria which might explain the high nutrient turnover in these environments.IMPORTANCE Cyanophages are viruses that target cyanobacteria and directly control their abundance via viral lysis. Cyanobacteria are known to cause large blooms in water bodies, substantially contributing to oxygen depletion in bottom waters resulting in areas called dead zones. Our knowledge of cyanophages in dead zones is very scarce, and so far, no studies have assembled partial cyanophage genomes and investigated their associated cyanobacteria in these dark and anoxic sediments. Here, we present the first study using DNA and RNA sequencing to investigate in situ diversity of cyanophages and cyanobacteria in dead zones. Our study shows that dead zone sediments contain different cyanophages compared to oxic sediments and suggest that these viruses are able to affect cyanobacterial photosystem and phosphate regulation. Furthermore, cyanophage-controlled lysis of cyanobacteria might also increase the turnover of carbon, phosphorus, and nitrogen in these oxygen-free environments at the bottom of the sea.

Changes in the Bio-Availability of Phosphorus in Pyrochars and Hydrochars Derived from Sewage Sludge after Their Amendment to Soils

The expected shortage of global phosphate has enforced the search for alternative resources for P fertilizers. Therefore, the present study focuses on the turnover of phosphorus (P) of hydrochars and pyrochars derived from sewage sludge (SS) in soils during plant growth. We designed a pot experiment in which Lolium perenne L. was allowed to grow on a Calcic Cambisol amended with SS-derived chars. Hydrothermal carbonization (HTC) yielded the SS-hydrochars (200 °C, 260 °C; 30 min, 3 h), whereas the SS-pyrochars were obtained after dry pyrolysis (600 °C, 1 h). Increasing severity of HTC lowered the recovery of total P (PT) from the feedstock to 76%. The Olsen-P diminished from 4% PT in the untreated sludge to 1% PT in the hydrochars, whereas the pyrochars exhibited an Olsen-P between 3 and 6%. At the end of the pot experiment, the soils amended with pyrochars and with hydrochars produced at 200 °C contained more Olsen-P than the unamended soils, proving that P-rich chars can indeed serve as a P fertilizer. Part of the P sequestered in the chars turned into a mobile form during the experiment. After addition of our chars, the soil pH remained alkaline, allowing the conclusion that P could not have been solubilized through just abiotic processes. We suggest that biological and biochemical processes are involved in this mobilization. This work demonstrates that, in order to evaluate the efficiency of an organic amendment as a P fertilizer, the knowledge of their P availability alone is not sufficient and a better understanding of the biochemical processes involved in the cycling of its immobilized P is certainly required.

Straw Returning Mediates Soil Microbial Biomass Carbon and Phosphorus Turnover to Enhance Soil Phosphorus Availability in Rice-Oilseed Rape Rotation

Straw Returning Mediates Soil Microbial Biomass Carbon and Phosphorus Turnover to Enhance Soil Phosphorus Availability in Rice-Oilseed Rape Rotation

Correlation of the abundance of bacteria catalyzing phosphorus and nitrogen turnover in biological soil crusts of temperate forests of Germany

Soil P pools are strongly driven by microbial activities, and vice versa, P pools shape bacterial communities and their functional potential. Biological soil crusts (biocrusts) represent a microbial hotspot for nutrient turnover. We compared biocrusts and bulk soil samples from different temperate beech (Fagus sylvatica L.) forests representing a gradient in soil texture, nutrient concentrations, and pH values at biocrust peak biomass. We measured the total and plant-available P and N concentrations and assessed the bacterial potential to mineralize (phoD, phnX), solubilize (gcd), and take up P (pstS and pitA) and mineralize (chiA, apr) and fix N (nifH) by quantifying the respective marker genes (qPCR). We found an increase of absolute and relative bacterial abundance involved in P turnover in biocrusts, but the strategy to acquire P differed between the regions as bacteria harboring the starvation-induced pstS gene were most abundant where labile P was lowest. In contrast, the region with lowest total P concentrations has a higher potential to utilize more stable phosphonates. N mineralization was strongly correlated to P turnover at regions with increased labile N and P concentrations. Interestingly, the potential to fix N was highest in the bulk soil where total P concentrations were highest. Even though the correlation of N and P turnover is strongest if their ratio is low, the acquisition strategy strongly depends on soil properties.

Assessing Dietary Phosphorus Intake and Serum Phosphorus in Adults with Liver Conditions: NHANES 2015–2016

Abstract Objectives Patients with liver conditions may have increased phosphorus turnover which can increase the risk of severe hypophosphatemia and other complications. The objective of this cross-sectional study was to quantify the usual intake of phosphorus, assess serum phosphorus (SP) levels across levels of liver conditions, and to estimate and assess the odds for having critically low phosphorus levels across adults with and without liver conditions. Methods Data were obtained from the NHANES 2015–2016 cycle. Adults were divided into four groups based on self-reported responses from the NHANES medical history questionnaire: liver cancer (LC), unspecified current liver condition (CLC), unspecified resolved liver condition (RLC), and no liver condition. Usual intake was estimated using the NCI method and all analyses were adjusted to account for the complex, multistage, probability sampling design. Results Usual phosphorus intake was highest in participants with RLC (1399 ± 26.5 mg) and lowest in participants with LC (1267 ± 140.7 mg). Although the percentage of those meeting the EAR for phosphorus was high (>95%), SP levels are lowest in participants with LC. SP levels differed slightly across liver conditions: participants with LC had a SP level of 1.0 ± 0.07 mmol/L, while participants with CLC, RLC, or no liver conditions had SP levels of 1.2 ± 0.01 mmol/L, 1.2 ± 0.01 mmol/L, and 1.2 ± 0.02 mmol/L, respectively. Participants with CLC had a usual phosphorus intake of 1350 ± 49.6 mg, and those who had no liver conditions had a usual phosphorus intake of 1387 ± 18.5 mg. The odds for normal phosphorus levels in participants with LC was low (Odds = 0.06; 95% CI: 0.01–0.45); the odds for CLC participants having normal SP levels was 1.6 (95% CI: 1.2–2.15); the odds for normal SP levels in participants with RLC were 2.2 (95% CI: 1.3–3.75), and the odds for normal SP in participants with no liver conditions odds for low were 1.9, (95% CI: 1.71–2.14). Conclusions These results indicate that patients with liver cancer are at higher risk of hypophosphatemia, and that phosphorus recommendations for patients with liver cancer may need to be adjusted. However, the variability in this subpopulation with liver cancer is high and warrants further investigation. Funding Sources None.

Carbon recycling efficiency and phosphate turnover by marine nitrifying archaea.

Thaumarchaeotal nitrifiers are among the most abundant organisms in the ocean, but still unknown is the carbon (C) yield from nitrification and the coupling of these fluxes to phosphorus (P) turnover and release of metabolites from the cell. Using a dual radiotracer approach, we found that Nitrosopumilus maritimus fixed roughly 0.3 mol C, assimilated 2 mmol P, and released ca. 10-2 mol C and 10-5 mol P as dissolved organics (DOC and DOP) per mole ammonia respired. Phosphate turnover may influence assimilation fluxes by nitrifiers in the euphotic zone, which parallel those of the dark ocean. Collectively, marine nitrifiers assimilate up to 2 Pg C year-1 and 0.05 Pg P year-1 and thereby recycle roughly 5% of mineralized C and P into marine biomass. Release of roughly 50 Tg DOC and 0.2 Tg DOP by thaumarchaea each year represents a small but fresh input of reduced substrates throughout the ocean.

High starter phosphorus fertilization facilitates soil phosphorus turnover by promoting microbial functional interaction in an arable soil

Microbial phosphorus (P) turnover is critical in C utilization efficiency in agroecosystems. It is therefore necessary to understand the P mobilization processes occurring during P fertilization in order to ensure both crop yield and environmental quality. Here, we established a controlled pot experiment containing soil amended with three different levels of starter P fertilizer and collected soil samples after 30, 60, and 90 days of incubation. Quantitative microbial element cycling (QMEC) smart chip technology and 16S rRNA gene sequencing were used to investigate functional gene structures involved in carbon, nitrogen and P cycling and the bacterial community composition of the collected samples. Although P fertilization did not significantly affect the structure of the soil microbial community, some rare microbiota were changed in particular phosphorus-solubilizing bacteria were enriched at the high P fertilization level, suggesting that the rare taxa make an important contribution to P turnover. P fertilization also altered the functional gene structure, and high P concentrations enhanced the functional gene diversity and abundance. Partial redundancy analysis further revealed that changes in rare taxa and functional genes of soil microorganisms drive the alteration of soil P pools. These findings extend our understanding of the microbial mechanisms of P turnover.

Pectin drives microbial phosphorus solubilization in soil: Evidence from isolation-based and community-scale approaches

A considerable part of soil phosphorus is bound to metal cations or metal oxides, and cannot be used in these forms by soil microbes and plants. Phosphate-solubilizing bacteria (PSB) are abundant in pectin-rich rhizosphere, and their pectin-degrading activity has been reported. Therefore, we hypothesized that pectin activates PSB and promotes soil phosphorus solubilization. To test this hypothesis, we first tested the phosphate-solubilizing activity of pectin-degrading bacteria. PSB were more frequently isolated from pectin-containing medium, compared with other media (P < 0.001). Further in a soil microcosm experiment, we examined whether pectin amendment accelerated soil phosphate solubilization. Pectin amendment decreased the concentrations of labile metallophosphate but increased the content of microbial biomass phosphorus in soils, meaning that phosphate solubilization was promoted by pectin amendment. In addition, PSB-like clades of bacteria increased by up to three times in response to pectin addition. This indicated that pectin amendment encouraged proliferation of PSB, accelerating soil phosphorus turnover processes initiated by solubilization of metallophosphate. In line with these results, genomic analysis indicated the widespread distribution of pectin-degrading genes among PSB, suggesting the possible co-evolution of pectin-degrading and phosphate solubilizing functions.

Estimates of mean residence times of phosphorus in commonly considered inorganic soil phosphorus pools

Abstract. Quantification of turnover of inorganic soil phosphorus (P) pools is essential to improve our understanding of P cycling in soil–plant systems and improve representations of the P cycle in land surface models. Turnover can be quantified using mean residence time (MRT); however, to date there is little information on MRT of P in soil P pools. We introduce an approach to quantify MRT of P in sequentially extracted inorganic soil P pools using data from isotope exchange kinetic experiments. Our analyses of 53 soil samples from the literature showed that MRT of labile P (resin- and bicarbonate-extractable P) was on the order of minutes to hours for most soils, MRT in NaOH-extractable P (NaOH-P) was in the range of days to months, and MRT in HCl-extractable P (HCl-P) was on the order of years to millennia. Multiple-regression models were able to capture 54 %–63 % of the variability in MRT among samples and showed that land use was the most important predictor of MRT of P in labile and NaOH pools. MRT of P in HCl-P was strongly dependent on pH, as high-pH soils tended to have longer MRTs. This was interpreted to be related to the composition of HCl-P. Under high pH, HCl-P contains mostly apatite, with a low solubility, whereas under low-pH conditions, HCl-P may contain more exchangeable P forms. These results suggest that current land surface models underestimate the dynamics of inorganic soil P pools and could be improved by reducing model MRTs of the labile and NaOH-P pools, considering soil-type-dependent MRTs rather than universal exchange rates and allowing for two-way exchange between HCl-P and the soil solution.

模拟不同春季降雨量下典型草原土壤微生物磷周转特征

模拟不同春季降雨量下典型草原土壤微生物磷周转特征

Energy Flows and Phosphorus Turnover in the System of Shallow Reservoir under Anthropogenic Stress

Abstract—We investigated the magnitude and intensity of phosphorus turnover and energy flows in the plankton and zoobenthos communities of a shallow, highly eutrophied reservoir. Due to a high degree of reservoir eutrophication, the energy flow through zooplankton significantly exceeded energy flow through zoobenthos. The role of biota in the phosphorus turnover was very high. During the growing season, plankton organisms regenerated 1.5 times more phosphorus than the external load per year, and five times more than the internal load of this element. Maximum value of primary plankton production was observed in the year with the highest rate of phosphorus turnover.

Phosphorus forms affect the hyphosphere bacterial community involved in soil organic phosphorus turnover.

Interactions between bacteria and arbuscular mycorrhizal (AM) fungi play a significant role in mediating organic phosphorus (P) transformations and turnover in soil. The bacterial community in soil is largely responsible for mobilization of the soil organic P pool, and the released P is taken up by extraradical AM hyphae, which mediate its use for plant growth. However, the functional microbiome involved in organic P mineralization in the hyphosphere remains poorly understood. The aim of this study was to determine how AM hyphae-associated bacterial communities related to P turnover in the hyphosphere of leek (Allium porrum) respond to different forms of soil P. Using a compartmented microcosm, leek was grown with the AM fungus Funneliformis mosseae, and the extraradical mycelium of F. mosseae was allowed to grow into a separate hyphal compartment containing either no added P, or P as KH2PO4 or phytin. High-throughput sequencing showed that the alkaline phosphatase (ALP)-harboring bacterial community associated with the AM hyphae was dominated by Sinorhizobium, Bradyrhizobium, Pseudomonas, and Ralstonia and was significantly changed in response to different P treatments, with Pseudomonas showing higher relative abundance in organic P treatments than in control and inorganic P treatments. Pseudomonas was also the major genus harboring the β-propeller phytase (BPP) gene in the hyphosphere, but the BPP-harboring community structure was not affected by the presence of different P forms. These results demonstrate the profound differences in ALP- and BPP-harboring bacterial communities in the hyphosphere at bacterial genus level, providing new insights to link bacteria and biogeochemical P cycling driven in association with mycorrhizal hyphae.

Photomineralization of Effluent Organic Phosphorus to Orthophosphate under Simulated Light Illumination.

Organic phosphorus (OP), one of the main forms of phosphorus in effluent from biological wastewater treatment plants, may contribute to the bioavailable phosphorus pool as well as water eutrophication. However, little is known about the photomineralization of OP or the possible impacts on the phosphorus cycle in water bodies. Herein, the photomineralization of effluent OP was investigated. An increase in orthophosphate concentration was observed under illumination. The 31P liquid nuclear magnetic resonance spectra demonstrated that the release of orthophosphate resulted from photomineralization of OP. Furthermore, the photoproduced hydroxyl radicals (·OH) were proved to play a dominant role in the OP photomineralization. Nitrate, effluent organic matter (EfOM), and Fe(III) presented in effluent were the main chromophores for ·OH photoproduction, and their contributions to ·OH production and photomineralization of OP followed the order: nitrate > EfOM > Fe(III). Additionally, the carbonate (or bicarbonate) in the effluent and high pH were unfavorable for OP photomineralization. The present study revealed the photomineralization behavior of OP in actual effluent, suggesting that photomineralization of OP might contribute to eutrophication and may play a non-negligible role in phosphorus turnover in water bodies.

Soil microbial phosphorus turnover and identity of algae and fungi in biological soil crusts along a transect in a glacier foreland

Although biological soil crusts (BSCs) are known for a variety of ecological functions, the role of individual biocrust organism species in BSCs on their P cycling is almost unknown. To evaluate the hypothesis that the contribution of defined cultivable taxa of fungi and algea might influence the microbial P storage and mobilization in the underlying soil, a transect was investigated in a glacier foreland in the mountain plateau Hardangervidda in Southern Norway. Microbial biomass P storage in soil under BSC increased continuously with increasing distance to the glacier and increasing fungal species richness. Lowest soil phosphatase activity and soil organic matter content were linked with highest number of algal and fungal in the overlaying BSCs. Enhanced soil microbial biomass P was linked with an increasing water content and decreasing pHCaCl2 of the soil. Nine to 21 algal and 5 to 10 fungal taxa were identified per test site from BSCs along the transect. Members of the Eustigmatophyceae and Xanthophyceae were observed exclusively close to the glacier, those of Klebsormidiophyceae exclusively in larger distance. The most common fungal genera in the BSCs were Lecythophora, Penicillium, Rhizoscyphus and Pholiota, whereas Cosmospora sp., Thelebolus globosus and Mucor hiemalis were found exclusively close to the glacier. The presence of usually biomass-rich taxa in the soil crusts was related to an increased microbial P storage in total. An increasing impact of microbial P storage under BSCs on the subsequent successional vegetation development is suggested.

Bioturbation by mammals and fire interact to alter ecosystem-level nutrient dynamics in longleaf pine forests.

Activities of ecosystem engineers can interact with other disturbances to modulate rates of key processes such as productivity and nutrient cycling. Bioturbation, movement of soil by organisms, is a widespread form of ecosystem engineering in terrestrial ecosystems. We propose that bioturbation by southeastern pocket gophers (Geomys pinetis), an abundant but declining ecosystem engineer in longleaf pine (Pinus palustris Mill.) forests, accelerates nutrient dynamics of the forest floor by burying litter and then reduces litter consumption and nitrogen (N) volatilization losses in the presence of fire. We evaluated our hypothesis by measuring how litter burial alters decomposition and N and phosphorus (P) turnover of longleaf pine and turkey oak (Quercus laevis Walt.) litter over four years, and then simulated interactive ecosystem-level effects of litter burial and low-intensity fires on N and P dynamics of the litter layer. In the field, mass loss was over two times greater and N and P were released much more rapidly from litter buried beneath mounds than on the surface of the forest floor. At a measured rate of mound formation covering 2.3 ± 0.6% of the forest floor per year, litter mass and N and P content of the forest floor simulated over an eight-year period were approximately 11% less than amounts in areas without pocket gopher mounds. In contrast to unburied litter, litter beneath mounds is protected from consumption during fires, and as fire interval increased, consumption rates decreased because mounds cover more years of accumulated litter. Our research indicates that bioturbation and burial of litter by pocket gophers accelerates turnover of N and P on the forest floor, and in the presence of fire, conserves N in this ecosystem where productivity is known to be nutrient limited.

Bacterial potentials for uptake, solubilization and mineralization of extracellular phosphorus in agricultural soils are highly stable under different fertilization regimes.

Phosphorus is one of the most important macronutrient for plants. In agriculture, amending fertilizer with phosphorus (P) is common practice. However, natural phosphorus sources are finite, making research for more sustainable management practices necessary. We postulated that the addition of carbon (C) and nitrogen (N) would stimulate phosphorus mobilization by bacteria because of their desire to maintain a stable intracellular C:N:P stoichiometry. Therefore, we chose a metagenomic approach to investigate two agricultural soils, which only received mineral N fertilizer or mineral N and organic fertilizer for more than 20 years. The most abundant genes involved in the acquisition of external P sources in our study were those involved in solubilization and subsequent uptake of inorganic phosphorus. Independent of site and season, the relative abundance of genes involved in P turnover was not significantly affected by the addition of fertilizers. However, the type of fertilization had a significant impact on the diversity pattern of bacterial families harbouring genes coding for the different P transformation processes. This gives rise to the possibility that fertilizers can substantially change phosphorus turnover efficiency by favouring different families. Additionally, none of the families involved in phosphorus turnover covered all investigated processes. Therefore, promoting bacteria which play an essential role specifically in mobilization of hardly accessible phosphorus could help to secure the phosphorus supply of plants in soils with low P input.

Soil microbial biomass, phosphatase and their relationships with phosphorus turnover under mixed inorganic and organic nitrogen addition in a Larix gmelinii plantation

Atmospheric nitrogen (N) deposition can affect soil microbial biomass, phosphatase activity, and the concentrations of organic phosphorus (P), inorganic P and available P, but the changes in soil microbial biomass under mixed inorganic and organic N addition and their relationships with soil P turnover in forest ecosystems are not fully understood. In this study, a simulated N deposition experiment was conducted in a Larix gmelinii plantation in Northeastern China to investigate the variation of soil microbial biomass, phosphatase activity, P forms and available P concentrations as well as the relationships between these features. The experiment was arranged in a randomized block design with three replications for each treatment, including the control (no N addition, CK), total inorganic N (NH4NO3, TIN), mixed inorganic and organic N (inorganic N and organic N in the ratio of 7:3, ION), and total organic N (urea and glycine 1:1, TON). The results indicated that there was a significant difference in the response of soil biochemical characteristics to different types of N addition. Soil total microbial biomass, the biomass of bacteria and actinomycetes, alkaline phosphomonoesterase (AlP) activity, as well as oxalate-extracted aluminum (Al), cMonoesters, cDiesters and orthophosphate concentrations were significantly increased by the addition of mixed inorganic and organic N, whereas they were not affected by single inorganic or organic N addition. Compared to the CK treatment, the increase in soil microbial biomass and Al oxides concentrations under ION treatment significantly increased soil cMonoesters and cDiesters concentrations, and the increased bacterial biomass contributed to the increase of soil AlP activity. Moreover, the ION treatment also significantly increased soil total P concentration and enhanced microbial immobilization of P compared to the CK treatment. However, there was no significant difference in available P concentration between the ION treatment and other treatments, which could be attributed to increased orthophosphate concentration under the ION treatment. Overall, the findings suggest that bacteria and AlP can play important roles in maintaining soil P availability by accelerating P turnover under conditions of increased atmospheric N deposition in a Larix gmelinii plantation.