Soil Phosphatase Activity Research Articles

Biochar addition to forest plantation soil enhances phosphorus availability and soil bacterial community diversity

Depletion of soil nutrients is a major cause of decline in productivity of forest plantations in successive rotations. Biochar amendment in agricultural systems has been shown to yield various beneficial effects, including increasing soil phosphorus (P) availability. However, the direct and indirect effects of biochar addition on forest soil P dynamics have largely been unexplored. The objective of this study was to examine how biochar produced from harvest residue (leaves and woodchips) affect the P dynamics in second rotation Cunninghamia lanceolata (Chinese fir) plantation soil. An incubation experiment which involved mixing of forest soil with 1% or 3% w/w leaf or woodchip biochar, pyrolyzed at 300 °C or 600 °C, was conducted for 80 days at 20 °C. After 7, 40 and 80 days of incubation, soil samples were analyzed for total and available P, inorganic and organic P pools, and soil phosphatase activity. At the end of the incubation period, bacterial community composition and diversity were analyzed by 16S rDNA sequencing. The leaf biochar produced at both pyrolysis temperatures was more alkaline and had significantly higher soluble P, nitrogen and calcium contents than the woodchip biochar. Soil total and available P increased significantly in all leaf biochar treatments after 80 days incubation compared to the untreated control soil, but the woodchip biochar treatments had no significant effects. At the end of the experiment, Al-P content was significantly lower and Ca10-P content higher in soil amended with both biochar types compared to the control soil, and Fe-P content was significantly higher in the leaf biochar treatments. Contrary to expectations, acid and alkaline phosphatase enzyme activities were significantly lower in some of the biochar treatments after 80 days incubation compared to the control soil. Nevertheless, the diversity of the bacterial community was higher in leaf biochar-amended forest soil than the woodchip biochar-amended and untreated soil at the end of the experiment. In particular, the abundance increased in the leaf biochar soil treatments of P-solubilizing bacteria, such as Burkholderia-Paraburkholderia, Planctomyces, Sphingomonas and Singulisphaera, which can indirectly improve P availability in soil. Thus, conversion of tree harvest residues, particularly leaves, into biochar and recycling back into the soil could be a viable option to boost P availability and help to conserve nutrients or reduce nutrient losses for the next rotation. Before recommending plantation management with biochar, long-term studies are required assessing the life cycle of biochar under field conditions and its promoting effect on growth of C. lanceolata.

Lithological and bioclimatic impacts on soil phosphatase activities in California temperate forests

Organic phosphorus (Po) biogeochemical cycling is known to be impacted by soil-forming factors, yet little is known about interactions among soil-forming factors on the drivers of Po cycling, soil phosphatases. A comprehensive assessment of lithological and bioclimatic impacts on soil phosphatase activities was conducted using lithological and vegetation-constrained climatic (i.e., bioclimatic) gradients in temperate California forests. Soils (0–5, 5–15 cm depth) from twelve combinations of three lithologies (andesite, basalt, granite) and four bioclimatic zones (blue oak, ponderosa pine, red fir, white fir) encompassing a wide range of MAP (330–1400 mm) and MAT (5.0–17.0 °C) were analyzed for resin P (Presin), Po, microbial biomass P and total P (Pt), activities of three phosphatases, and soil properties (e.g., organic carbon [OC], pedogenic minerals). Across soil depths, lithology influenced phosphomonoesterase (ACP, ALP) activities more than bioclimate, whereas the opposite occurred for phosphodiesterase (PDE). Correlations of phosphatases with edaphic (e.g., pedogenic minerals, clay content) and climatic variables (MAP, MAT) varied by lithology (e.g., ACP and OC, Rbasalt = 0.61, p < 0.01 and Rgranite = 0.20, p = 0.28), indicating lithological dependence of bioclimatic impacts. Within bioclimates, phosphomonoesterase but not PDE activities were correlated with OC much more strongly than with pedogenic minerals, suggesting limited lithological impacts in vegetation- and climate-constrained ecosystems. This study demonstrates that the enzymes that catalyze the two distinct steps of Po mineralization, phosphomonoesterase versus phosphodiesterase, can express differential and even opposite relationships with edaphic variables depending on the combination of lithology and bioclimate. Additionally, OC, Presin, and Po may not necessarily be the best predictors of phosphatase activities as commonly proposed. Lithology type and/or pedogenic minerals that integrate lithology and bioclimate context may enable a more comprehensive assessment of phosphatases in soil P cycling sensitive to bioclimatic variability.

Understanding how long-term organic amendments increase soil phosphatase activities: Insight into phoD- and phoC-harboring functional microbial populations

In context of the use of organic materials as alternatives for mineral fertilizer, it is important to understand how organic amendments influence soil extracellular phosphatase activities which accelerate the mineralization of organic phosphorus (P). To address this, the current study investigates the influence of organic amendments on acid (ACP) and alkaline (ALP) phosphatase activities in soils and how organic amendments influence these activities from the perspective of microbially-mediated pathways. Herein, a comprehensive meta-analysis of 599 measurements from 106 published studies around the world was performed as well as a field component sourced from a 30-year-old field experiment on fertilization. Based on meta-analysis, organic amendments increased average extracellular ACP and ALP activities by 22% and 53%, respectively, in comparison to the mineral-only fertilization. Observed increases in activities were consistent with significant increases in soil organic carbon (C), total nitrogen (N) and available P contents, and microbial biomass C and N pools. According to the data from the long-term field experiment, we found phoD-harboring species encoding ALP were more closely correlated with phoC-harboring species encoding ACP in organically amended soils, and more network hubs were also observed by organic amendment. Soil C:P and N:P ratios, and microbial biomass C were the main predictors of the abundance, diversity, and composition of the phoC- and phoD-harboring populations. Further analysis revealed that the soil C:P ratio was identified as the dominant predictor of potential ACP and ALP activities. Our work highlights the importance in understanding how soil C:N:P stoichiometry mediates phosphatase-harboring populations in order to determine the downstream consequences of using organic amendments for increasing phosphatase activities.

The better suppression of pepper Phytophthora blight by arbuscular mycorrhizal (AM) fungus than Purpureocillium lilacinum alone or combined with AM fungus

Phytophthora blight caused by Phytophthora capsici (Pc) is one of the most economically destructive soilborne diseases of pepper (Capsicum annum L.) on a global scale. Biocontrol using antagonistic microbes, such as Purpureocillium lilacinum (Pl) and arbuscular mycorrhizal (AM) fungus Funneliformis caledonium (Fc), is one of the significant strategies for ecologically sound plant disease management. The purpose of this work was to investigate the sole and combined suppression of pepper Phytophthora blight by Fc and Pl. The 14-week pot experiment with three pepper plants per pot included five treatments: control (non-inoculation), inoculation with Pc, inoculation with Pc and Pl (Pc + Pl), inoculation with Pc and Fc (Pc + Fc), and inoculation with Pc, Pl, and Fc (Pc + Pl + Fc). Pots were randomly arranged with eight replicates per treatment. The incidence and severity of Phytophthora blight at plant full productive stage were recorded. The biomasses and N, P, and K concentrations of pepper shoots, roots, and fruits were all measured. In addition, root mycorrhizal colonization rate and soil pH, phosphatase activity, and available P concentration were also tested. The inoculation of Pc induced both high incidence (92%) and severity (33%) of pepper Phytophthora blight, and the alleviating effects of Pl, Fc, and Pl + Fc were 46%, 79%, and 59%, respectively. The Fc significantly increased (P < 0.05) root mycorrhizal colonization, nutrient (N, P, and K) acquisition, plant biomass, and fruit yield of pepper, while Pl only significantly increased (P < 0.05) plant nutrient (N and P) acquisition and tended to increase the fruit yield. The Pc, Pl, and Fc all had additive effects on decreasing soil pH, but only Fc significantly increased (P < 0.05) soil phosphatase activity and available P concentration, contributing partly to the elevated P acquisition as well as the increased P concentrations in both shoot and root. Compared with the sole inoculation of Fc, the extra inoculation of Pl had negative effects on mycorrhizal colonization, soil P mobilization, and plant growth and nutrient acquisition. It suggests that AM fungus (Fc) has the superiority of formatting symbioses with plant roots and enhancing soil P mobilization for the suppression of pepper Phytophthora blight compared with Pl, and the joint application of different fungal agents to improve plant health needs careful consideration.

Deciphering the rhizobium inoculation effect on spatial distribution of phosphatase activity in the rhizosphere of alfalfa under copper stress

Legume–rhizobium symbiosis plays an important role in agriculture and ecological restoration. However, the regulatory mechanisms of rhizobium in alleviating heavy metal stress through the biochemical response of plant-soil system is limited. In this study, alfalfa was inoculated with a copper (Cu)-resistant rhizobium, and its effect on plant growth and the spatial distribution of phosphatase in the rhizosphere under Cu stress was assessed. Our results showed that rhizobium inoculation alleviated Cu-induced growth inhibition, and increased the nitrogen and phosphorus content in alfalfa tissues. Moreover, inoculated plants had a higher Cu uptake than non-inoculated plants, with a much higher increase in the roots than in the shoots; thus, inoculation with rhizobium was shown to decrease the transfer coefficient and promote Cu phytostabilization. The zymograms illustrated that the distribution of phosphatase activities was associated with the presence of roots. Compared with the non-inoculated treatment, the rhizobium inoculation increased the hotspot areas of phosphatase by 26.1% and 39.3% at the Cu 0 and Cu 800 treatments, respectively. In addition, the available phosphorus in the soil showed negative correlations with soil phosphatase activity (p < 0.05). The model of partial least squares path modelling (PLS-PM) indicated that soil Cu content directly influenced the hotspot areas of phosphatase activities in the rhizosphere and explained most (86%) of the variation. Thus, the enzymatic hotspots were concluded to mainly be affected by the Cu content of soil, and the phosphatase activities in the rhizosphere were mainly regulated by the ratio of nitrogen to phosphorus. These findings provide a basis for the spatio-temporal dynamics of biogeochemical reactions in the rhizosphere of polluted soils.

The application of Klebsiella sp. and Rhizobium radiobacter as biofertilizer and Palm Oil Mills Effluent (POME) as organic fertilizer on growth of Paraserianthes falcataria

The Bio and organic fertilizers are cheap and environmentally friendly source of plant nutrients for agricultural yields and environmental quality improvement. The study aimed to evaluate the application of biofertilizer and Palm oil mills effluent (POME) either singly or in combination on growth of Paraserianthes falcataria under greenhouse condition. The study was laid out in factorial based Completely Randomized Design (CRD) design which was comprised of biofertilizer treatments (Control without bacteria, Klebsiella sp, Rhizobium radiobacter, Klebsiella sp + Rhizobium radiobacter) and five concentrations of POME treatments (0%, 10%, 25%, 50%, 100%) with 3 replicates for each treatment. The results revealed that inoculation with biofertilizer treatments along with POME significantly enhanced plant growth parameters, soil available P, soil phosphatase activity and soil bacterial population. Combination of Rhizobium radiobacter and POME 50% induced the highest increase of shoot length (10.17 ± 0.83cm), root length (28.67±0.88cm), shoot dry weight (0.48± 0.006g), and root dry weight (0.25±0.013g). The highest soil phosphatase activity was obtained in the combination Klebsiella sp. and POME 25% treated soil. The application of Rhizobium radiobacter along with POME at 10% and 25% concentrations reached its highest level of soluble soil P (4.07 ppm) and soil bacterial population (48.33 107 cfu/g of soil) respectively.

Effects of biological organic fertilizer on rhisosphere soil bacteria community and root rot diseases of continuous cropping Angelica sinensis

Understanding the effects of biological organic fertilizer DZF-363 on the growth, root rot diseases, and the structure and function of soil microbial community of Angelica sinensis could provide theoretical basis for the adjustment and improvement of soil environment in the rhizosphere of continuous cropping. Taking 2-year continuous cropping A. sinensis and its rhizosphere soil as test objects, with control (without any pesticides, micro-fertilizer, CK), pesticides groups (15% chlorpyrifos and 50% carbendazim, N), and DZF-363 (DZF) treatments, microbial community structure, and urease and phosphatase activities in rhizosphere soil were figured out by high throughput sequencing and colorimetric method. The results showed that the yield of DZF-363 group was 18.8% higher than CK and 6.8% higher than N. The root rot disease index in the DZF was reduced, with a control effectiveness of 52.0%. The activities of urease, neutral phosphatase and alkaline phosphatase in rhizosphere soil were significantly increased during the growing season, and the urease acti-vity increased by 52.4%, 13.9%, 10.3%, neutral phosphatase activity by 15.5%, 10.2%, 10.3%, alkaline phosphatase activity by 10.3%, 4.4%, 4.0% compared with CK during seedling and middle, and harvesting stages, respectively. The acid phosphatase activity increased by 15.6% and 8.2% at middle and harvesting stages, respectively. The proportion of Actinobacteria in CK, N and DZF groups was 11.3%, 10% and 20%, respectively. The proportion of unidentified Bacillibacteria and Actinobacteria was larger in DZF than in the CK and N groups. The Shannon index was significantly increased by DZF. There was positive correlation between Shannon and Simpson indices with the yield of A. sinensis, while negative correlation with the root rot disease. Therefore, the application of DZF-363 could strongly improve the diversity of soil bacteria in the rhizosphere, alter the soil bacterial community structure and rhizosphere soil urease and phosphatase activities, reduce the occurrence of root rot diseases, and thus increase the yield.

Засвоєння фосфору рослинами кукурудзи за впливу фосфатмобілізувальних бактерій

The purpose. To study action of phosphate mobilizing bacteria on the level of assimilation of phosphorus by plants of corn at cultivation on leached chernozem. Methods. Field, microbiological, biochemical, agrochemical, statistical. Results. They determined in dynamics amount of phosphate mobilizing bacteria capable to dissolve minerals-phosphates of insoluble complexes with cations of Ca++, Fe+++, Al+++ and bacteria which hydrolyze organic forms of phosphate, phosphatase activity of rhizosphere soil, level of assimilation of phosphorus by plants of corn at action of bacterization of seeds. It is fixed the following: amount of bacteria which dissolve Ca3 (PO4) 2 increased from 12,7 (in control) up to 27,5 millions/g of soil (in alternative with Agrobacterium radiobacter 5006), AlPO4 — from 9,2 (in control) up to 17,9 millions/g of soil (in alternative with A. radiobacter 5006), FePO4 — from 8,9 (in control) up to 17,3 millions/g of soil (at action of Enterobacter aerogenes 3271), and bacteria which hydrolyze organic forms of phosphate — from 12,7 (in control) up to 29,5 millions/g of soil (in alternative with Basillus sp. 2473). The highest phosphatase activity was observed at action of Basillus sp. 2473 — 4,34 accordingly at indexes of control of 2,84 mg P2O5/100 g of soil/hour. Conclusions. Bacterization of seeds of corn by active strains of phosphate mobilizing bacteria A. radiobacter 5006, Paenibacillus polymyxa KV, Bacillus sp. 2473, E. aerogenes 3271, E. nimipressuralis 5213 promotes increase of: amount of bacteria converting joints of phosphorus, phosphatase activity and level of mobility of phosphates in root zone, that positively influences phosphorous nutrition of plants. Biological factor of intensification of root nutrition of plants ensures increase of content of phosphorus in grain on 0,08-0,14%, as well as its removal with yield of crop on 24,8-35,9% concerning control.

Nitrogen addition effects on tree growth and soil properties mediated by soil phosphorus availability and tree species identity

Increasing evidence has suggested that nitrogen (N) deposition has great effects on forest productivity and nutrient cycling, but how these effects are mediated by soil phosphorus (P) availability and tree species identity remains unclear. Here, a two-year factorial experiment was conducted to examine the short-term effects of N addition (100 kg N ha−1 year−1), P addition (50 kg P ha−1 year−1) and their interactions on tree growth and soil nutrient cycling of a Mongolian pine (Pinus sylvestris var. mongolica) plantation and a neighboring Simon poplar (Populus simonii) plantation in Northeast China. Results showed that N addition promoted tree growth (stem increment), reduced soil microbial biomass carbon (C) and N in the Mongolian pine plantation, but did not affect those in the Simon poplar plantation, and these N addition effects were not interacted by P addition. P addition significantly increased microbial biomass C and N in the Simon poplar plantation. N addition elevated soil phosphatase activities and reduced net N mineralization rate, and these N addition effects were alleviated by simultaneous P addition in both plantations. N addition decreased soil labile inorganic P concentration in both plantations and elevated labile organic P in the Mongolian pine plantation, but only the decrease in labile inorganic P with N addition in the Mongolian pine plantation was counteracted by P addition. N addition significantly reduced soil pH, with a greater extent in the Mongolian pine plantation than in the Simon poplar plantation. Moreover, soil pH response explained most of the microbial and nutrient transformation response. Above results indicated that short-term N addition impacts on tree growth and soil microbial biomass were more strongly influenced by tree species identity than by P addition, while N addition effects on soil N and P transformations were strongly influenced by P addition. Drought resistance of trees and acid buffering capacity of soils are key traits influencing the short-term N addition impacts on the growth of trees and microorganisms in this semiarid region.

Community composition and catabolic functional diversity of soil microbes affected by Hedysarum scoparium in arid desert regions of northwest China

The soil microbial community and edaphic factors in the rhizosphere and bulk soils of Hedysarum scoparium were investigated at seven arid desert locations in northwest China in July 2016. Plant and edaphic factors had significant effects on the community composition and functional diversity of soil microbes. Bacteria (ranging from 2.57 to 4.23 nmol g−1) contributed the most to the microbial community composition, followed by actinomycetes, followed by fungi. Carbohydrates, polymers, and carboxylic acids were the main carbon sources for soil microorganisms. Principal component analysis showed that the carbon source catabolism of soil microorganisms was higher in the rhizosphere than in bulk soils. Spearman correlation analyses revealed that the content of Gram-negative bacteria was significantly negatively correlated with the amino acids and that the content of AM fungi was significantly positively correlated with the carbohydrates and amines. Soil organic carbon, pH, and ammoniacal-N were significant predictors of microbial community composition, whereas soil organic carbon, phosphatase activity, and soil moisture were closely correlated with microbial carbon catabolism. This study indicated that soil microbial community composition and functional diversity are influenced by plants, nutrient availability, and enzymatic activity in the arid desert and serve as useful indicators for evaluating the soil quality and function of the desert ecosystem based on their relationships with the microbial community and soil nutrient distribution.

Soil Properties as Influenced by Long Term Herbicide with or without Organic Manure Application in Transplanted Rice-Rice System

Transplanted autumn rice-winter rice is one of the major rice-based cropping systems followed under specific soil type and land situation that faces diverse weed flora and intensity. The soil physical, chemical and biological properties of a long-term trial, being conducted since 2001 at Assam Agricultural University, Jorhat, India were evaluated after completion of tenth crop cycles of rice-rice cropping sequence. Rotational application of pre-emergence, followed by post-emergence herbicide significantly increased grain yield in both the crops. The pH of the soil increased and fractions of soil acidity decreased significantly, while the cation exchange capacity and exchangeable Ca2+, Mg2+ and NH4+ increased significantly by organic manure application for partial N-fertilizer substitution. The application of organic manure significantly increased organic carbon and positively influenced available nitrogen and phosphorous content in soil. The microbial biomass carbon, urease activity were unaffected by herbicide application but were enhanced by organic manure addition. Application of herbicide significantly reduced the acid phosphatase activity in soil, while it had a positive effect on dehydrogenase activity and the effect was pronounced by addition of the organic manure. The effect of rotation of herbicide was not obvious and was limited to a few biological properties.

Phyllostachys edulis (moso bamboo) rhizosphere increasing soil microbial activity rather than biomass

Rhizosphere and fertilization might affect soil microbial activities, biomass, and community. This study aimed to evaluate the impacts of Phyllostachys edulis (moso bamboo) rhizospheres on soil nutrient contents and microbial properties in a moso bamboo forest with different fertilizer applications and to link soil microbial activities with abiotic and biotic factors. The experiment included three treatments: (1) application of 45% slag fertilizer (45%-SF); (2) application of special compound fertilizer for bamboos (SCF); and (3) the control without any fertilizer application (CK). Simultaneously, bulk soils and 0.5, 2.5, 4.5, and 6.5-year-old (y) bamboo rhizosphere soils were selected. Soil nutrient contents were analyzed. Microbial activities were evaluated based on the activities of soil enzymes including β-glucosidase, urease, protease, phosphatase, and catalase. The total microbial biomass and community were assessed with the phospholipid fatty acids (PLFAs) method. In the CK and SCF treatments, organic matter contents of rhizosphere soils were significantly higher than those of bulk soils. Soil β-glucosidase, urease, protease, phosphatase, and catalase activities in rhizosphere soils were higher than those of bulk soils, with the sole exception of β-glucosidase of 0.5 y rhizosphere soil in the 45%-SF treatment. Compared with the CK treatment, fertilizer applications tended to increase soil total PLFAs contents and changed soil microbial community. Moso bamboo rhizospheres did not significantly increase the total microbial biomass. In the SCF treatment, the Shannon index of bulk soil was significantly lower than those of rhizosphere soils. Our results suggested that both rhizospheres and fertilizer applications could change the soil microbial community structures and that moso bamboo rhizosphere could increase microbial activity rather than biomass in the forest soils with different fertilizer applications.

Soil microbial character response to plant community variation after grazing prohibition for 10 years in a Qinghai-Tibetan alpine meadow

In addition to improving vegetation, grazing prohibition changes the soil micro-environment. Soil enzymes and microbes, which are the chief constituents responsible for mediation of most of the processes involved in energy and material fluxes of ecosystems, are very sensitive to changing environments. This study aimed to illustrate the effects of grazing prohibition on vegetation and soil enzyme characteristics, and to elucidate the responses of soil fungal and bacterial function and community composition on grazing prohibition for 10 years in a Qinghai-Tibetan alpine meadow. About 6 hm2 lightly degraded alpine meadows were selected in 2006, and half of which were fenced to completely prohibit grazing throughout the year, while the other half were subjected to free yak grazing. Four different plots in each site were selected as experimental fields in 2016. Soil microbial characteristics were analyzed by high-throughput gene detection. Grazing prohibition had no significant impact on vegetable Shannon-Wiener diversities or below-ground biomass, but dramatically changed the above-ground biomass and soil phosphatase activity. In the Qinghai-Tibetan alpine meadow, bacteria are dominant members of the soil microbial community. Grazing prohibition significantly increased the fungal species diversity and the abundance of pathotrophs, saprotrophs and symbiotrophs, while it had no effect on soil bacterial diversity and functional structure. A total of 100.0% of the variations in fungi and bacteria could be explained by plant variables. The reciprocal action among plant biomass (i.e. above-ground biomass, below-ground biomass), plant diversities (i.e. Shannon-wiener diversity, species number, coverage) and species important value have a great impact on soil microbial composition variations. Long-term grazing prohibition restrained the phosphatase activity and increased the abundance of pathotrophic fungi but had no effect on the abundance of functional bacteria, which participate in the soil biogeochemistry cycling process. Grazing prohibition for 10 years did not improve the community structure of functional microorganisms related to carbon, nitrogen and sulfur, and appropriate grazing could maintain the sustainable utilization of grassland resources.

Interplay of phosphorus doses, cyanobacterial inoculation, and elevated carbon dioxide on yield and phosphorus dynamics in cowpea.

Phosphorus (P) demand is likely to increase especially in legumes to harness greater benefits of nitrogen fixation under elevated CO2 condition. In the following study, seed yield and seed P uptake in cowpea increased by 26.8% and 20.9%, respectively, under elevated CO2 level. With an increase in phosphorus dose up to 12mgkg-1, seed yield enhanced from 2.6 to 5.4gplant-1. P application and cyanobacterial inoculation increased the microbial activity of soil, leading to increased availability of P. Under elevated CO2 condition, microbial activity, measured as dehydrogenase, acid phosphatase, and alkaline phosphatase activities showed stimulation. Soil available P also increased under elevated CO2 condition and was stimulated by both P application and cyanobacterial inoculation. Higher P uptake in elevated CO2 condition led to lower values of inorganic P in soil. Stepwise regression analysis showed that aboveground P uptake, soil available P, and alkaline phosphatase activity of soil influenced the yield while available P, and organic and inorganic P influenced the aboveground P uptake of the crop. This study revealed that under elevated CO2 condition, P application and cyanobacterial inoculation facilitated P uptake and yield, mediated through enhanced availability of nutrients, in cowpea crop.

Effect of vegetables and nano-particle hydroxyapatite on the remediation of cadmium and phosphatase activity in rhizosphere soil through immobilization

Nano-hydroxyapatite (n-HAP) and two types of plants (rape plant and cabbage) were used in this study to investigate their combined remediation effect on the removal of heavy metal contaminated soil. Different n-HAP concentrations (5, 10, 15, 20, and 25 g kg−1) with two kinds of plants were used in the experiments and compared with two control groups without adding n-HAP. Compared with the control group, the total Cd concentration increased and the amount of available Cd decreased significantly in soil (p < 0.05) in text groups. Cd toxicity decreased, and the rape plant and cabbage biomass increased after adding n-HAP. Cd accumulation in rape plant and cabbage decreased when more n-HAP was added; Cd accumulated less in rape plant than in cabbage. The phosphatase activity in soil also increased after adding n-HAP. Results showed that the total Cd concentration was positively correlated with phosphatase activity, the concentration of the available Cd and Cd accumulated in root has a significant effect on phosphatase activity in Cd-contaminated soil (p < 0.05). Cd-contaminated soil could be remediated effectively with rape plant and n-HAP with a concentration of 15 g kg−1.

The accuracy in the assessment of arsenic toxicity using soil alkaline phosphatase depends on soil water contents

Soil phosphatase is commonly used as an indicator to evaluate the arsenic (As) toxicity in soil. However, the As ageing process and the accuracy of using soil phosphatase activity to assess As contamination under various soil water contents are not clearly known. This study explored the effects of soil moisture condition on the As fractions (soil solid phase species) and soil alkaline phosphatase (ALP) over time. Results showed that elevated soil moisture would increase the content of F1-F4 (water soluble, exchangeable, carbonate and organic-bound) and decrease the ratio of F6 (residual). Whereas, the F5 fraction (bound to Fe and Mn/Al oxides), although did not show significant variation in the early period (up to 15 d), showed an increase at later period (30 d). The As bioavailability (K) increased with increasing soil moisture. Ageing process exhibited two stages. In the stage1, as the ageing progress the fractions, F1, F2 and F3 (former) gradually transformed into F4, F5 and F6 (later) under all tested As concentrations. The second stage is that under the low As concentrations, F1 and F4 transformed to F5 fraction. While, under the high As concentrations (200 mg kg−1 and 400 mg kg−1), F1 and F2 transformed to F4 and F5. Meanwhile, soil moisture had a significant influence on soil ALP activity. Soil ALP activity under 110% WHC was smaller than the activity of soil ALP under 35% WHC. The variation partitioning analysis (VPA) showed that soil moisture contributed 63.19% for this effect on soil ALP activity and was identified as the dominant factor. The value of ED10 indicated that the As toxicity under 35% WHC was greater than that under 110% WHC. This could be due to that the excessive moisture content depressed soil ALP activity. Therefore, it is important to consider soil moisture content while assessing the As toxicity to soil ALP.

Microbial Inoculants Assisted Growth of Chrysopogon zizanioides Promotes Phytoremediation of Salt Affected Soil.

Restoration of salt-affected soil through cultivation Chrysopogon zizanioides is a promising approach. The two way benefit of such an approach is that reclamation of salt-affected soil concomitant to improve plant growth and increased yield of essential oil produced in the plants roots. Earlier studies showed physiological changes and reduced growth of C. zizanioides under salinity. In the present study, plant growth promoting microorganisms viz. Pseudomonas monteilii, Bacillus megaterium, Azotobacter chroococcum and Rhizophagus intraradices were used as bio-inoculants for cultivation of C. zizanioides under salt-affected soil. Bio-inoculants in combination with vermicompost significantly increased the growth and productivity of C. zizanioides under salt-affected soil, and simultaneously improved soil health. When compared to control, the soil physico-chemical and biological properties of bio-inoculants treated plants was significantly improved. The reclamation of salt-affected soil was evident by the significant decrease in the level of soil pH (11.0%), electrical conductivity (23.5%), sodium adsorption ratio (15.3%), and exchangeable sodium percent (12.4%) of bio-inoculants treated plants. The improvement of soil cation exchange capacity indicated the decrease in soil salinity. Whereas increase in the microbial count (four-fold), AMF spores (447 spores), dehydrogenase (six-fold), acid (two-fold) and alkaline phosphatase (five-fold) activities in rhizosphere soil of bio-inoculant treated plants indicated the improved biological properties. A positive correlation of plant biomass production to soil organic carbon, total Kjeldahl nitrogen, available phosphorus and cation exchange capacity depicted improved nutrients content in rhizosphere soil of bio-inoculant treated plants. The findings of this study suggest that P. monteilii and R. intraradices with vermicompost can be effectively used as bio-inoculants for encouragement of phytoremediation in salt-affected soil.

Phosphate solubilizing microorganisms and phosphatase activities in the rhizosphere soil of organically grown winter wheat cultivars

Phosphate solubilizing microorganisms and phosphatase activities in the rhizosphere soil of organically grown winter wheat cultivars

Short-Term Response of the Soil Microbial Abundances and Enzyme Activities to Experimental Warming in a Boreal Peatland in Northeast China

Global warming is likely to influence the soil microorganisms and enzyme activity and alter the carbon and nitrogen balance of peatland ecosystems. To investigate the difference in sensitivities of carbon and nitrogen cycling microorganisms and enzyme activity to warming, we conducted three-year warming experiments in a boreal peatland. Our findings demonstrated that both mcrA and nirS gene abundance in shallow soil and deep soil exhibited insensitivity to warming, while shallow soil archaea 16S rRNA gene and amoA gene abundance in both shallow soil and deep soil increased under warming. Soil pmoA gene abundance of both layers, bacterial 16S rRNA gene abundance in shallow soil, and nirK gene abundance in deep soil decreased due to warming. The decreases of these gene abundances would be a result of losing labile substrates because of the competitive interactions between aboveground plants and underground soil microorganisms. Experimental warming inhibited β-glucosidase activity in two soil layers and invertase activity in deep soil, while it stimulated acid phosphatase activity in shallow soil. Both temperature and labile substrates regulate the responses of soil microbial abundances and enzyme activities to warming and affect the coupling relationships of carbon and nitrogen. This study provides a potential microbial mechanism controlling carbon and nitrogen cycling in peatland under climate warming.

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.