The pH change in rhizosphere of Pinus koraiensis seedlings as af-fected by different nitrogen sources and its effect on phosphorus availability

Root mat method described by Kuchenbuch and Jungk was used to study the rhizosphere processes. The experi-ment was carried out on two years old Pinus koraiensis seedlings. Soil samples collected from the upper 20-cm soil layer in Changbai Mountain were treated with three different forms of nitrogen fertilizers: NO3--N, NH4+-N and NH4NO3. The results showed that the soil pH and available P near the roots were all lower than in the bulk soil in control treatment. NH4+-N applica-tion greatly decreased the soil pH near the roots compared to the control treatment and promoted the absorption of phosphorus, which led to a more remarkable depletion region of available P. On the contrary, the rhizosphere soil pH was higher than in the bulk soil in treatments with NO3--N and retarded the P absorption, which led to a nearly equal available P contents to the bulk soil. In treatment with NH4NO3, the rhizosphere soil pH was only a little lower than that in the control treatment and its effects on P absorption is mediate between the treatments with NH4+-N and NO3--N.

Effect of Submergence on Iron Transformation and Phosphorus Availability in Calcareous Soils

A thermostatic incubation experiment was carried out to estimate the effects of flooding periods, stalk application and P addition on Fe transformation and P availability in calcareous soils. Submergence increased amorphous Fe, especially in the case of stalk application. The newly formed amorphous Fe with a great surface area played an important role in P sorption; and submergence also stimulated the dissolution of inorganic P, thus increasing the availability of soil P in calcareous soils. Meanwhile, a part of soluble P was adsorbed and fixed again on the surface of newly formed amorphous Fe, thus resulting in a decrease of P availability. Soil rapidly available P increased after ISO-day incubation. There existed significantly negative correlations between soil amorphous Fe content and soil Fe-P and rapidly available P contents. Submerged conditions promoted the transformation of inorganic P added to-ward Fe-P in calcareous soils, especially in the case of stalk application.

Effect of N and P addition on soil organic C potential mineralization in forest soils in South China

Atmospheric nitrogen deposition is at a high level in some forests of South China. The effects of addition of exogenous N and P on soil organic carbon mineralization were studied to address: (1) if the atmospheric N deposition promotes soil C storage through decreasing mineralization; (2) if the soil available P is a limitation to organic carbon mineralization. Soils (0–10 cm) was sampled from monsoon evergreen broad-leaved forest (MEBF), coniferous and broad-leaved mixed forest (CBMF), and Pinus massoniana...

Phosphorus fertilizer induced changes in the soil available P,the P nutrition and the growth of Pinus radiata seedlings grown in association with understory

A study was carried out to investigate changes in the soil plant-available P,the P nutrition and the growth of Pinus radiata seedlings grown in association with understory,broom（Cytisus scoparius L.） or ryegrass（Lolium multiflorum） on Orthic Allophanic Soil,following the application of three rates of triple superphosphate（TSP）（0,50,and 100 mg·kg^-1P） under a glasshouse condition.The application of P fertilizer enhanced P availability in the rhizospheric of radiata seedlings and the bulk soils in a P-deficient site.P availability in the rhizospheric soils of ryegrass and broom,grown in association with radiata,were also increased by the presence of radiata roots.P concentrations in new shoot needles,old shoot needles,stem and roots of radiata pine increased with increase rates of TSP application,but the effects of ryegrass and broom on P nutrition of radiata seedlings depended on the soil P status.In the absence of P fertilizer addition（control treatment）,P concentrations in new shoot needles,old shoot needles,stem,and roots of radiata grown in association with broom were higher than those with ryegrass,whereas,when P fertilizer was added（50 and 100 mg·kg^-1） the P concentration was lower.This is probably related to the growth of broom that may have removed much of the plant-available P in the soil as indicated by the consistently lower Bray-2 P concentration in the rhizosphere soil of radiata in association with broom than that in the rhizosphere soil of radiata in association with grass at the two high P rates.Furthermore,in the high P fertile soil（application rate of 100 mg·kg^-1）,the dry matter yield of radiata was lower when it was grown with broom than with ryegrass.This result suggests that in moderate to high P fertile soils,P.radiata seedlings grow better with ryegrass than with broom,because broom grows vigorously in high P fertile soil and competes with P.radiata for P and perhaps for other nutrients as well.

Soil and microbial C:N:P stoichiometries play vital roles in regulating P transformation in agricultural ecosystems:A review

Stoichiometry plays a crucial role in biogeochemical cycles and can modulate soil nutrient availability and functions. In agricultural ecosystems,phosphorus(P) fertilizers(organic or chemical) are often applied to achieve high crop yields. However, P is readily fixed by soil particles, leading to low P use efficiency. Therefore, understanding the role of carbon:nitrogen:P stoichiometries of soil and microorganisms in soil P transformation is of great significance for P management in agriculture. This paper provides a comprehensive review of the recent research on stoichiometry effect on soil P transformation in agricultural ecosystems. Soil microorganisms play an important role in the transformation of soil non-labile inorganic P to microbial biomass P by regulating microbial biomass stoichiometry. They also mobilize soil unavailable organic P into available P by changing ecoenzyme stoichiometry. Organic materials, such as manure and straw, play an important role in promoting the transformation of insoluble P into available P as well. Additionally, periphytic biofilms can reduce P loss from rice field ecosystems. Agricultural stoichiometries are different from those of natural ecosystems and thereby should receive more attention due to the influences of anthropogenic factors. Therefore, it is necessary to conduct further stoichiometry research on the soil biochemical mechanisms underlying P transformation in agricultural ecosystems. In conclusion, understanding stoichiometry impact on soil P transformation is crucial for P management in agricultural ecosystems.

Positive effects of biochar application and Rhizophagus irregularis inoculation on mycorrhizal colonization,rice seedlings and phosphorus cycling in paddy soils

Phosphorus(P)is an essential element for plant growth but is often limiting in ecosystems;therefore,improving the P fertilizer use efficiency is important.Biochar and arbuscular mycorrhizal fungi(AMF)may enhance P cycling in paddy soils that contain high content of total P but low content of available P(AP).In this study,the effects of biochar addition and Rhizophagus irregularis inoculation on the organic and inorganic P contents and phosphatase activities in paddy soils,rice seedling growth,and AMF colonization were investigated.Compared with no biochar addition,biochar addition enhanced the percentage of spore germination at day 7,hyphal length,most probable number,and mycorrhizal colonization rate of R.irregularis by 32%,662%,70%,and 28%on average,respectively.Biochar and R.irregularis altered soil P cycling and availability.Biochar and R.irregularis,either individually or in combination,increased soil AP content by 2%–48%.Rice seedlings treated with biochar and R.irregularis produced greater biomass,improved root morphology,and increased nutrient uptake compared with those of the control without biochar and R.irregularis.The results suggest that combined application of biochar and R.irregularis is beneficial to rice cultivation in paddy soils with high content of total P but low content of AP.

Increased phosphorus availability to corn resulting from the simultaneous applications of phosphate rock, calcareous rock, and biochar to an acid sandy soil

Phosphorus(P)deficiency is one of the main constraints on crop production in Arenosols(acid sandy soil).The high cost of P fertilizers may represent an insurmountable obstacle in many poor countries,leaving the exploitation of their own calcareous and phosphate rocks as the only low-cost and long-term alternative.Biochar is suggested to have positive effects on soil properties;however,there is no published research on the synergistic effects of biochar and rocky materials in modifying soil properties.The aim of this study was to investigate the chemical and biochemical responses of an acid Arenosol treated with phosphate rock(PR),calcareous rock(CR),and biochar(BC),and the implications for corn yield.A soil from Marracuene District,Mozambique was used,where corn was grown for 90 d with the soil treated with:no addition(control),water-soluble zinc phosphite fertilizer(WSP),PR,WSP+CR,WSP+BC,WSP+CR+BC,PR+BC,and PR+CR+BC.Biochar was produced by pyrolysis of babycorn peels for 4 h at 450?C and applied at 11 g kg-1.The soil pHH2 Oincreased from about 4.54 in the control to 7.38 in the PR+CR+BC treatment.Easily oxidizable organic carbon,cation exchange capacity,and available P were higher in the treatments containing BC than in the control.The treatments containing CR and/or BC led to the highest activities of alkaline phosphomonoesterase,phosphodiesterase,andα-glucosidase,which increased P availability and gave the greatest biomass and yields.We suggest that biochar provides additional soluble P and supplies adsorption sites for phosphate,preventing its evolution to unavailable forms.Thus,PR applied together with BC contributed to an 840%yield increase compared to the control.The treatments containing WSP and BC facilitated phosphite oxidation to phosphate and increased crop yield.

Biochar and soil properties limit the phytoavailability of lead and cadmium by Brassica chinensis L.in contaminated soils

The current study investigated the effect of biochars derived from cinnamomum woodchip,garden waste and mulberry woodchip on soil phytoavailable lead(Pb),cadmium(Cd)pools,and their uptake by Chinese cabbage(Brassica chinensis L.).The biochars were produced at 450℃of pyrolysis temperature.The contaminated soils were collected from Yunfu(clas-sified as Udept),Jiyuan(Ustalf)and Shaoguan(Udult)cities in China at the depth of 0-20 cm and amended with biochars at the rate of 3%w/w.After mixing the soil with biochar for 14 days,the Chinese cabbage was planted in the amended soils.Then,it was harvested on the 48th day after sowing period.In Udult soil,Chinese cabbage died 18 days after sowing period in control and soils amended with cinnamomum and mulberry biochars.Although only plants grown with the garden waste biochar treatment survived in Udult soil,amendment of garden waste or mulberry biochars at 3%w/w(450℃)to Udult soil significantly increased(4.95-6.25)soil pH compared to other biochar treatments.In Udept and Ustalf soils,the application of garden waste and mulberry biochars significantly improved plant biomass compared to control,albeit it was dependent on both biochar and soil properties.Garden waste biochar significantly decreased soil Cd phytoavailable concentration by 26%in the Udult soil,while a decrease of soil Cd phytoavailable concentration by 16%and 9%was observed in Ustalf and Udept soils,respectively.The available phosphorus in biochar and soil pH were important factors controlling toxic metal phytouptake by the plant.Thus,the amendment of soil with biochar at 3%can effectively reduce the mobility of Cd and Pb in soil and plant uptake.However,biochar and soil properties should be well-known before being used for soil toxic metal immobilization.

Synergistic Effects of Biochar and NPK Fertilizer on Soybean Yield in an Alkaline Soil

Biochar effects on legume growth and biological nitrogen fixation have been studied extensively, mostly in acidic soils with laboratory produced biochar. In the present study, a pot experiment in a full factorial experimental design was performed to examine soybean yield and nodulation of three genotypes grown with or without biochar and NPK fertilizers in an alkaline soil. We observed synergistic effects of biochar and NPK fertilizer applications on biomass and seed yields for all three soybean genotypes. Total biomass production and seed yield increased on average by 67% and 54%, respectively, with biochar and by 201% and 182% with NPK fertilizer application compared to the control. When applications of biochar and NPK fertilizer were combined, the increases were 391% and367%, respectively. However, the biomass production in the control was very low(692 kg ha-1) due to a high soil p H(8.80). The nodulation increased with biochar and NPK fertilizer applications, and was largest with the combined application. A correlation was found between leaf chlorophyll content(single photon avalanche diode value) and nodule number. We suggested that the synergistic increase in yield was due to a decrease in soil p H caused by biochar and NPK fertilizer applications thereby increasing P availability in this alkaline soil.

Mobilization of Inorganic Phosphorus from Soils by Ectomycorrhizal Fungi

Ectomycorrhizal(EM) fungi could form symbiosis with plant roots and participate in nutrient absorption; however, many EM species commonly found in forest soils, where phosphorus(P) concentration and availability are usually very low, particularly in tropical and subtropical areas, have not yet been investigated for their efficiencies to mobilize soil P. In this study, fungal growth, P absorption,efflux of protons and organic acids, and soil P depletion by four isolates of EM fungi isolated either from acidic or calcareous soils were compared in pure liquid culture using soil as a sole P source. Boletus sp. 7(Bo 7), Lactarius deliciosus 3(Ld 3), and Pisolithus tinctorius 715(Pt 715) from acidic and P-deficient soils of southwestern China showed higher biomass and P concentration and accumulation than Cenococcum geophilum 4(Cg 4) from a calcareous soil of Inner Mongolia, northern China, after 4 weeks of liquid culture. Oxalate, malate, succinate, acetate, and citrate concentrations in the culture solutions varied significantly with fungal species,and oxalate accounted for 51.5%–91.4% of the total organic acids. Organic acids, particularly oxalate, in the culture solutions may lead to the solubilization of iron-bound P(Fe-P), aluminum-bound P(Al-P), and occluded P(O-P) from soil phosphates. Fungal species also varied greatly in proton efflux, which decreased the culture solution pH and may dissolve calcium-bound P(Ca-P) in soil.This could be the reason for the increment of both inorganic P in the culture solutions and Olsen P in the soil when EM fungi were present. Total inorganic P, the sum of Al-P, Fe-P, O-P, and Ca-P, in the culture solutions was positively correlated with the total concentration of organic acids in the culture solutions(r = 0.918*, n = 5), but negatively with both the total inorganic P in soil(r =-0.970**, n = 5) and the culture solution pH(r =-0.830*, n = 5). These suggested variable efficiencies of EM fungal species to mobilize inorganic P fractions from soil, which could make EM trees to utilize inorganic P in the same way like EM fungi and adapt to the soils with various P concentrations and availabilities.

Biosolid Application to Agricultural Land a Contribution to Global Phosphorus Recycle： A Review

Phosphorus(P) is an essential nutrient required for plant development.Continuous population growth and rising global demand for food are expected to increase the demand for phosphate fertilizers.However,high-quality phosphate rock reserves are progressively becoming scarce.Part of the increased pressure on P resources could be alleviated by recycling P present in biosolids.Therefore,it is crucial to understand the dynamics of P in biosolid-amended soils,the effects of residual biosolid-borne P in soils,the way in which microorganisms may control P dynamics in biosolid-amended soils and the environmental implications of the use of biosolids as a source of P.Further research is needed to maximize biosolid-borne P uptake by crops and minimize its loss from biosolid-amended soils.The analysis of the microbiological control of P dynamics in biosolid-amended soils indicates interactions of biosolid P with other nutrients such as carbon(C) and nitrogen(N),suggesting that harmonization of the current regulation on the use of biosolids in agriculture,mainly based on total N and pollutant contents,is needed to better recycle P in agriculture.

Nitrogen addition mediates the response of foliar stoichiometry to phosphorus addition: a meta-analysis

Background:Changes in foliar nitrogen(N)and phosphorus(P)stoichiometry play important roles in predicting the efects of global change on ecosystem structure and function.However,there is substantial debate on the efects of P addition on foliar N and P stoichiometry,particularly under diferent levels of N addition.Thus,we conducted a global meta-analysis to investigate how N addition alters the efects of P addition on foliar N and P stoichiometry across different rates and durations of P addition and plant growth types based on more than 1150 observations.Results:We found that P addition without N addition increased foliar N concentrations,whereas P addition with N addition had no efect.The positive efects of P addition on foliar P concentrations were greater without N addition than with N addition.Additionally,the efects of P addition on foliar N,P and N:P ratios varied with the rate and duration of P addition.In particular,short-term or low-dose P addition with and without N addition increased foliar N concentration,and the positive efects of short-term or low-dose P addition on foliar P concentrations were greater without N addition than with N addition.The responses of foliar N and P stoichiometry of evergreen plants to P addition were greater without N addition than with N addition.Moreover,regardless of N addition,soil P availability was more efective than P resorption efciency in predicting the changes in foliar N and P stoichiometry in response to P addition.Conclusions:Our results highlight that increasing N deposition might alter the response of foliar N and P stoichiometry to P addition and demonstrate the important efect of the experimental environment on the results.These results advance our understanding of the response of plant nutrient use efciency to P addition with increasing N deposition.

Influences of Long-Term Fertilizer and Tillage Management on Soil Fertility of the North China Plain

In the North China Plain, fertilizer management and tillage practices have been changing rapidly during the last three decades; however, the influences of long-term fertilizer applications and tillage systems on fertility of salt-affected soils have not been well understood under a winter wheat (Triticum aestivum L.)-maize (Zea mays L.) annual double cropping system. A field experiment was established in 1985 on a Cambosol at the Quzhou Experimental Station, China Agricultural University, to investigate the responses of soil fertility to fertilizer and tillage practices. The experiment was established as an orthogonal design with nine treatments of different tillage methods and/or fertilizer applications. In October 2001, composite soil samples were collected from the 0–20 and 20–40 cm layers and analyzed for soil fertility indices. The results showed that after 17 years of nitrogen (N) and phosphorous (P) fertilizer and straw applications, soil organic matter (SOM) in the top layer was increased significantly from 7.00 to 9.30–13.14 g kg-1 in the 0–20 cm layer and from 4.00 to 5.48–7.75 g kg-1 in the 20–40 cm layer. Soil total N (TN) was increased significantly from 0.37 and 0.22 to 0.79–1.11 and 0.61–0.73 g N kg-1 in the 0–20 and 20–40 cm layers, respectively, with N fertilizer application; however, there was no apparent effect of straw application on TN content. The amounts of soil total P (TP) and rapidly available P (RP) were increased significantly from 0.60 to 0.67–1.31 g kg-1 in the 0–20 cm layer and from 0.52 to 0.60–0.73 g kg-1 in the 20–40 cm layer with P fertilizer application, but were decreased with combined N and P fertilizer applications. The applications of N and P fertilizers significantly increased the crop yields, but decreased the rapidly available potassium (RK) in the soil. Straw return could only meet part of the crop potassium requirements. Our results also suggested that though some soil fertility parameters were maintained or enhanced under the long-term fertilizer and straw applications, careful soil quality monitoring was necessary as other nutrients could be depleted. Spreading straw on soil surface before tillage and leaving straw at soil surface without tillage were two advantageous practices to increase SOM accumulation in the surface layer. Plowing the soil broke aggregates and increased aeration of the soil, which led to enhanced organic matter mineralization.

Dynamics of Soil and Grain Micronutrients as Affected by Long-Term Fertilization in an Aquic Inceptisol

Micronutrient status in soils can be affected by long-term fertilization and intensive cropping.A 19-year experiment (1990-2008) was carried out to investigate the influence of different fertilization regimes on micronutrients in an Aquic Inceptisol and maize and wheat grains in Zhengzhou,China.The results showed that soil total Cu and Zn markedly declined after 19 years with application of N fertilizer alone.Soil total Fe and Mn were significantly increased mainly due to atmospheric deposition.Applications of P and organic fertilizer with incorporation of straws resulted in dramatic increases in soil total Cu,Zn,Fe,and Mn.Soil diethylenetriamine pentaacetic acid (DTPA)-extractable Cu in all treatments sharply decreased from initially 1.12 to about 0.8 mg kg -1 .The treatments with organic fertilizer had the highest soil DTPA-extractable Cu,Zn,Fe,and Mn after 19 years of cropping and fertilization,thus demonstrating the important role of organic fertilizer application in improving available micronutrient status.Cu and Zn contents in wheat grains in the no-P treatments were significantly higher than those of the treatments with P application.In addition,Fe and Mn contents in wheat grains were positively correlated with their soil DTPA-extractable concentrations.These indicated that the long-term application of organic fertilizer resulted in significant increases in soil total and available micronutrient concentrations and remarkable reduction in wheat grain Cu and Zn contents,which was due to high soil available P.

Effects of Slope Aspects on Soil Bacterial and Arbuscular Fungal Communities in a Boreal Forest in China

The effects of slope aspects on soil biogeochemical properties and plant communities in forested environments have been studied extensively; however, slope aspect influence on soil microbial communities remains largely unexamined, despite the central role of soil biota in ecosystem functioning. In this study, the communities of both soil bacteria and arbuscular mycorrhizal fungi （AMF） were investigated using tagged pyrosequencing for three types of slope aspects （south-facing aspect, north-facing aspect and flat area） in a boreal forest of the Greater Khingan Mountains, China. The bacterial and AMF community composition differed with slope aspects. Bacterial diversity was the lowest on the north-facing aspect, and AMF diversity was the lowest on the flat area. Aspects also had a significant impact on soil pH and available phosphorus （P） and shrubby biomass. Soil pH and understory shrub biomass were significantly correlated with bacterial communities, and soil available P and shrub biomass showed significant correlations with AMF communities. Our results suggested that slope aspects affected bacterial and AMF communities, mediated by aspect-induced changes in plant community and soil chemical properties （e.g., pH and available P）, which improved the knowledge on the effects of forest slope aspects on aboveground and belowground communities.

Phosphorus Speciation and Nutrient Stoichiometry in the Soil-Plant System During Primary Ecological Restoration of Copper Mine Tailings

The effects of plant vegetation on phosphorus （P） speciation, pH, total carbon concentration, total nitrogen concentration, and alkaline phosphatase activities were investigated to explore the P uptake strategy of plants in low-P soil and to determine the nutrient stoichiometric ratio changes in the rhizosphere of plants （Imperata cylindrica, Miscanthus floridulus, Zoysia sinica, Artemisia lavandulaefolia, Indigofera pseudotinctoria, and Conyza canadensis） which had grown for approximately 15 years in copper mine tailings, East China. The results showed that the average pH values in the rhizosphere decreased by 0.06 1.37 compared with those in the non-rhizosphere. The alkaline phosphatase activities of the rhizosphere were significantly higher than those in the non-rhizosphere. The mean concentrations of aluminum （A1）- and iron （Fe）-bound P and Ca2-P （CaHPO4） in the rhizosphere of all plants were 5.4% to 87.7%, 49.2% to 214.2%, and 86.6% to 147.6% higher than those in the non-rhizosphere, respectively. Except for Cas-P （CasH2（PO4）6） and Cal0-P （Cal0（PO4）6（OH）2） in the rhizosphere, all kinds of inorganic P forms were negatively correlated with pH. Significant correlation was also observed among the concentrations of dominant forms of inorganic P, C, and N and alkaline phosphatase activities in the rhizosphere. Among the studied species, I. pseudotinetoria showed the most significant effect on enhancing soil available P concentration. The stoichiometric ratios of C：P and N：P were apparently higher in the rhizosphere than the non-rhizosphere, whereas these ratios were far below the ratios commonly observed in Chinese soils. These results indicated that the plant growth effectively affected P fractions possibly by changing pH, C and N concentrations, and alkaline phosphatase activity, in the rhizosphere in copper mine railings.