Soil Phosphorus Bioavailability Research Articles

Drying and rewetting affect the chemical speciation and bioavailability of soil phosphorus in a hyper-arid desert ecosystem

Climate change is expected to alter the frequency and intensity of drying and rewetting cycles, impacting water availability and consequently soil nutrient availability. However, the effects of these fluctuations on the chemical speciation and bioavailability of phosphorus (P) in soil with or without desert species remain uncertain. We conducted a pot experiment involving bare soil and two desert species (Alhagi sparsifolia and Calligonum mongolicum) to determine the short-term impacts of drought (no water supply), drying-rewetting-1 (D-RW1, high frequency of low water amounts), and drying-rewetting-2 (D-RW2, low frequency of high-water amounts) treatments on soil Hedley-P pools, plant P concentration and biomass accumulation. Results demonstrated that the presence of plants significantly increased soil labile-P and organic P (Po) concentrations by 60–150% and 1–68%, respectively, compared to bare soil. Both D-RW1 and D-RW2 treatments significantly increased soil dissolved organic carbon concentration by 2–35% relative to the drought treatment. Moreover, soil resin-P and NaHCO3-Pi concentrations under Alhagi sparsifolia in D-RW1 treatment significantly increased by 31% and 75%, respectively, when compared to the drought treatment, with NaHCO3-Po and NaOH-Po concentrations under D-RW2 treatment rising by 14% and 32%, respectively. Furthermore, D-RW2 treatment significantly increased leaf P concentration and biomass compared to D-RW1 and drought treatments. Overall, compared to drought treatment, frequent low-intensity drying-rewetting cycles enhanced soil Pi turnover, whereas infrequent high-intensity drying-rewetting cycles increased Po turnover and P bioavailability. These findings will inform better water management strategies for desertification restoration in hyper-arid desert ecosystems.

Legacy soil phosphorus bioavailability in tropical and temperate soils: Implications for sustainable crop production

Improving phosphorus (P) use efficiency is key to improving the productivity and sustainability of cropping systems and slowing the exploitation rate of mineral P resources required for fertilizer production. At present, large amounts of added P in fertilizers and manure each year are retained in the soil and are not used by the crop. This ‘legacy P’ progressively accumulates in soil and represents an untapped P resource in tropical soils while in temperate soils it contributes to eutrophication. In the context of legacy P, the aim of this study was to quantify changes in soil P pools of contrasting bioavailability (determined using conventional chemical extraction procedures) during 12 successive brachiaria (Urochloa ruziziensis) cropping cycles in which no additional P was added. The study was undertaken in the greenhouse with 10 tropical (Brazil) and 6 temperate (UK) agricultural topsoils. Above-ground dry matter yield (DM) and P offtake was measured at each harvest alongside operationally-defined measures of the labile, moderately-labile and non-labile P pools at the start and end of the experiment. Over twelve repeated cultivation cycles, brachiaria demonstrated an ability to efficiently mine legacy P from all measurable soil pools across both sets of soils. This included the depletion of up to 87 % of non-labile soil P in some soils from the UK and up to 66 % from soils in Brazil after one year. While the amounts of initial labile P showed the closest positive relationship with plant P export, contrary to expectation the non-labile P pool also clearly contributed to plant nutrition across all the soils. As a cover crop, brachiaria clearly possesses traits which enable both the solubilization and efficient capture of soil P that can be harnessed to actively recycle historically non recalcitrant soil P fractions. Incorporating brachiaria into crop rotations or intercropping systems therefore shows promise as a strategy to enhance the longer-term sustainability of soil P management.

Fertilizers and Manures Enhance the Bioavailability of Soil Phosphorus Fractions in Karst Grassland

Phosphorus is one of the major constraints to karst grassland productivity. Understanding the effects of different fertilization practices on soil phosphorus dynamics is essential for enhancing phosphorus bioavailability and rational management of soil phosphorus in karst grasslands. Here, we investigated the effects of fertilizers and manures on soil bioavailability of phosphorus fractions and explored the relationship between soil properties and soil phosphorus fractions. The four fertilizer application designs were as follows: control (CK; no fertilizer or manure); fertilization (F); manure application (M); fertilization and manure application (FM). The results showed that total phosphorus (TP) concentration was elevated by 23%, 1%, and 42% in F, M, and FM treatments, respectively, compared with CK. F and FM treatments enhanced the total inorganic phosphorus (Pi) concentration by 65% and 66%, respectively, while M and FM treatments enhanced the total organo-phosphorus (Po) concentration by 21% and 35%, respectively. FM treatment elevated bioavailable P, active Po, secondary mineral P, primary mineral P, and occluded P by 69%, 39%, 50%, 31%, and 41%, respectively. Fertilizers inhibited soil acid phosphatase activity, whereas alkaline phosphatase did not respond significantly to fertilizer management in low-latitude karst regions. SOM, TN, AP, and MBP are the key factors affecting the bioavailability of phosphorus fractions. The combined application of fertilizer and manure is the most beneficial measure for enhancing soil phosphorus bioavailability. This research helps deepen our understanding of soil phosphorus dynamics in the karst areas and provides a basis for further enhancement of nutrient availability and vegetation productivity of grassland ecosystems.

Chlorella-Bacillus biofertilizers interact with varying nitrate addition amounts to increase soil phosphorus bioavailability

Chlorella-Bacillus biofertilizers interact with varying nitrate addition amounts to increase soil phosphorus bioavailability

Isolation of a potential rock phosphate solubilizing Aspergillus sp. towards development of biofertilizer

Phosphorus (P) is one of the key bio elements that limits agricultural production. Although Sri Lanka is endowed with rock phosphate deposits, practical means to utilize this resource are limited. Phosphate-solubilizing fungi (PSF) play an important role in enhancing the bioavailability of soil phosphorus to plants. In this study, fungi from eight soil samples in Kaikawala, Sri Lanka, were isolated using spread plate method and analyzed for its phosphate solubility capacity. One fungal isolate with significant halo zones on Pikovskaya’s agar (PVK) plates, containing 0.5% tricalcium phosphate, was identified. After purification, the isolate was transferred to three media setups: PVK with 0.5% apatite (ERP) as the phosphate source, PVK with 0.5% tricalcium phosphate as a positive control, and PVK without P source as a negative control and analyzed for the solubilization index (SI). DNA sequences of the internal transcribed spacers with 5.8S region of ribosomal DNA (ITS1-5.8S-ITS2) was analyzed with universal primer pair ITS4-F/ITS5-R to determine the identity of the species. Fungal isolate PSF01 showed a phosphate solubilizing activity on both PVK media, ERP (1.07 ± 0.03 cm SI) and tricalcium phosphate (1.07 ± 0.01 cm), with similar effects (p > 0.05). However, the SI in the negative control was 1.00 ± 0.00 cm without halo zone (p < 0.05). The fungal strain is fast growing with initially white but quickly changing to black colonies after producing conidial spores on potato dextrose agar with distinctive conidial heads and pale-yellow lower surface characterized as Aspergillus. Sanger DNA sequencing identified the fungus as Aspergillus niger (99%) and a phylogenetic tree was constructed using MEGA11 software using reference data obtained from NCBI GenBank data to identify the isolated PSF01. Consequently, our preliminary studies demonstrate the importance of examining more soil samples to identify PSF for sustainable agricultural applications in the future.

Effects of maize and soybean intercropping on soil phosphorus bioavailability and microbial community structure in rhizosphere.

To investigate the effect of maize/soybean intercropping on rhizosphere soil microbial communities and phosphorus (P) bioavailability, we examined the changes of soil bioavailable P fractions and microbial community characteristics in the monoculture and intercropping systems based on high-throughput sequencing. The results showed that maize/soybean intercropping increased the contents of rhizosphere soil organic matter (SOM), available phosphorus (AP), microbial biomass phosphorus (MBP), and aboveground biomass. The increase of AP was mainly related to the increasing enzyme extracted phosphorus (Enzyme-P) and hydrochloric acid extracted phosphorus (HCl-P) contents. The dominant bacterial phyla under each treatment were Proteobacteria, Actinobacteria, Acidobacteria and Chloroflexi, while the dominant bacterial genera were Nocardioides, Solirubacter, Sphingomonas and Arthrobacter, with Proteobacteria and Sphingomonas having the highest relative abundance. The relative abundance of Proteobacteria and Sphingomonas in intercropping maize rhizosphere soil was significantly higher than that in monoculture, and that of Proteobacteria in intercropping soybean rhizosphere soil was significantly higher than monoculture. Soil properties and P fractions were closely related to the rhizosphere soil microbial composition. In all, maize/soybean intercropping could affect the rhizosphere soil P bioavailability by altering the structure of rhizosphere microbial communities.

Seed phytic acid concentration affects rice seedling vigor irrespective of soil phosphorus bioavailability.

Rice with a black-colored pericarp (hereafter, black rice) is well-known as an antioxidant-rich food, but a high grain phytic acid (PA) concentration affects its nutritional quality. However, phytic acid helps improve seedling vigor, which is crucial for enhancing subsequent plant growth. This study investigated the effect of seed phytic acid concentration in black rice on seedling vigor compared to the effects on white rice. In the first experiment, three phytic acid concentrations in the seeds of black rice, low (LPA, 15.5 mg g-1 per seed), medium (MPA, 24.7 mg g-1 per seed), and high (HPA, 35.4 mg g-1 per seed) were tested for seedling vigor in phosphorus-deficient soils. The HPA seedlings showed substantially increased seedling vigor and shoot P uptake due to early root development and enhanced physiological processes. LPA grown seedlings showed increased ethylene production in response to P stress, which is the main physiological mechanism modulating seedling growth under P stress conditions. In the second experiment, the three phytic acid concentrations in black and white rice seeds were tested under low and high soil P conditions. Again, LPA seedlings showed significantly reduced seedling vigor in both rice varieties in P-deficient soils. Interestingly, seed phytic acid and external P application had an additive effect on seedling vigor, suggesting that the combined effect further improved seedling growth. Our results reveal that black rice seeds with a HPA concentration can be used as a seed source for planting in P-deficient ecosystems for rice plants as they can increase seedling vigor and subsequent growth, thus reducing dependence on finite P resources.

Effects of pH, Calcium, and Phosphate on the Solubility of Arsenic in Paddy Soil Based on Surface Complexation Modeling

This study aimed to obtain a better understanding on the environmental behavior of As in paddy soil and to reveal the influence mechanisms of different environmental factors on the availability of As in the soil solution. The effects of pH, calcium, and phosphate on the solubility and speciation distribution of As in the paddy soil collected from Zhuzhou of Hunan province were studied by combining the adsorption experiments with the NOM-CD model. The results showed that the minimum concentration of soluble As in the soil was at approximately a pH of 6.0, which was mainly affected by both electrical interactions and site competition between Ca2+, PO43-, As(Ⅲ), and As(Ⅴ). The adsorption of As onto soil particles could be increased by an increase in Ca2+ in the soil system, leading to the decrease in soluble As concentration. This effect became significant at a higher pH, because adsorbed Ca2+ increased the positive charge on (hydr)oxide surfaces. With phosphate addition, the reduction in As(Ⅴ) in the soil was inhibited at pH<5.5, whereas it was promoted at pH>5.5. Moreover, the concentration of soluble As(Ⅲ) and As(Ⅴ) in the soil solution was dramatically increased with the addition of phosphate owing to the competitive adsorption between As and phosphate. At a lower background of Ca2+, there was a higher fraction of As(Ⅲ) in the soil either with or without phosphate addition. This phenomenon might be caused by the higher bioavailability of phosphorus in soil at a lower concentration of Ca2+, which favors the dissimilatory reduction of As or iron (hydr)oxides. The results indicated that the NOM-CD model could predict the influence of pH, calcium, and phosphate on the solubility and speciation distribution of As in paddy soil and reveal its main mechanisms. Therefore, the NOM-CD model would provide the quantitative and scientific method for evaluating the risk of As in soils or other solid-water systems.

Green Manure Amendment Increases Soil Phosphorus Bioavailability and Peanut Absorption of Phosphorus in Red Soil of South China

Peanut (Arachis hypogaea L.) is one of the most important crops produced worldwide. Peanut is the dominant crop in the typical upland red soil areas of China; however, phosphorus bioavailability in red soil is very low, which severely affects peanut production. To improve the phosphorus bioavailability, which substantially promotes the green development of peanut production, a peanut–green manure rotation field experiment was conducted with six treatments (milkvetch; radish; brassica rape; mustard rape; winter fallow and no-tillage), commencing in September 2017 in the red soil area of Jiangxi province, China. The results show that compared with no-tillage (NT) treatments, different green manure returning treatments had significant effects on soil pH, soil phosphorus components and available potassium content. The particulate phosphorus and soil available phosphorus contents in the green manure treatments were significantly higher than those in the winter fallow (WF) treatment. Compared with the WF treatment, the content of particulate phosphorous in brassica rape (BR), radish (R) and milkvetch (MV) treatments was significantly increased by 6.55%, 3.66% and 2.50%, respectively; the available phosphorus content in mustard rape (MR), BR, R and MV was significantly increased by 20.93%, 25.60%, 23.76% and 18.10%, respectively. In addition, the total phosphorus content of peanut shell in the MV and R treatment was significantly higher than that in the WF treatment, increasing by 33.47% and 60.66%, respectively. Compared with the WF treatment, the peanut biomass of MR, BR and R treatments increased significantly by 19.51%, 29.83% and 19.77%, respectively. The total phosphorus accumulation in all green manure treatments was higher than that in the WF treatment, and the MV treatment reached a significant level at 18.83%. Based on these results, the particulate phosphorus (PP) and available phosphorus were significantly affected by different green manure treatments; green manure amendment improves peanut phosphorus uptake. The use of green manure (especially milkvetch and brassica rape) can be recommended to improve phosphorus bioavailability and yield of peanut in red soil areas.

Cotton-maize intercropping increases rhizosphere soil phosphorus bioavailability by regulating key phosphorus cycling genes in northwest China

Intercropping is widely used as an important means to promote crop productivity; but the underpinning mechanisms of rhizosphere soil microbial processes in shaping soil phosphorus (P) bioavailability under cotton-based intercropping systems have not been investigated in arid northwest China. Therefore, taking cotton-maize intercropping as an example, biologically based P (BBP) and metagenomics methods were used to investigate changes of soil P bioavailability, microbial community and functional P-cycling genes in the rhizosphere. Three treatments were cotton monoculture, maize monoculture and cotton-maize intercropping. We found that rhizosphere soils from cotton-maize intercropping exhibited higher soil organic matter (SOM), available P (AP), and alkaline phosphatase (ALP) than those of crop monocultures (p < 0.05). The change of bioavailable-P fractions in the order HCl-P > Citrate-P > Enzyme-P > CaCl2-P, and higher mount of CaCl2-P, Citrate-P and Enzyme-P were observed in soil samples from cotton-maize intercropping. These results indicated that P bioavailability were improved after two crops intercropping. The dominate soil microbial community from all treatments belonged to the phyla Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi and Gemmatimonadetes. In addition, we observed that the expression of functional genes which involved in soil microbial inorganic phosphate transportation (phoR), inorganic phosphate solubilization (phoD, glpA, glpK, glpQ), phosphate ester mineralization (gcd, ppk, ppx), and phosphate ester mineralization (pstABC, pit) were also up-regulated in cotton-maize intercropping (p < 0.05). Redundancy analysis showed that SOM, CaCl2-P and AP significantly correlated genes gcd, ppx, pstABC, pit, and phoD, suggesting that SOM, CaCl2-P and available P are important factors in influencing expression of these P-cycling functional genes. It is concluded that cotton-maize intercropping increased P bioavailability via changing rhizosphere soil microbial composition and functional genes.

Does pyrolysis temperature determine soil phosphorus bioavailability and uptake on peri-urban cropland amended with poultry litter biochar?

Does pyrolysis temperature determine soil phosphorus bioavailability and uptake on peri-urban cropland amended with poultry litter biochar?

Impact of Arbuscular Mycorrhizal Fungi, Phosphate Solubilizing Bacteria and Selected Chemical Phosphorus Fertilizers on Growth and Productivity of Rice

Phosphorus is the second most significant macro nutrient in rice productivity. Phosphorus fixation in Egyptian soil makes it unavailable for rice to absorb. The goal of this study was to examine the effects of microbial and chemical sources of phosphorus fertilizers on the Egyptian Sakha 106 rice cultivar by applying different sources of phosphorus to increase the bioavailability of soil phosphorus for plants and to allow it to be fixed biologically to change it from an insoluble form to a soluble and available form for rice to absorb. So, in the 2019 and 2020 seasons, a field experiment was conducted at the experimental farm of Sakha Agricultural Research Station, Sakha, Kafr El-Sheikh, Egypt. The experiment was carried out using a Randomized Complete Block Design with four replications to determine the best phosphorus source for rice and soil among various treatments, which included 100% single super phosphate (SSP) basal application (P1), 75% single super phosphate (SSP) basal application (P2), P2 + phosphate-solubilizing bacteria (PSBs) top-dressing, P2 + arbuscular mycorrhizal fungi (AMFs) top-dressing P2 + phosphorus nanoparticles (PNPs) foliar spraying, P2 + phosphoric acid (PA) foliar spraying, P2 + (PSBs + AMFs) foliar spraying, P2 + (PSBs + PNPs) foliar spraying, P2 + (PSBs + PA) foliar spraying, P2 + (PNPs + PA) foliar spraying, P2 + (PSBs + PNPs + PA) foliar spraying and zero-phosphorus fertilizer. The results showed that the highest values were mostly obtained using the combination of 75% SSP basal application with the foliar spraying of PSBs, PNPs and PA, with substantial beneficial impacts on the leaf area index (3.706 and 3.527), dry matter accumulation (464.3 and 462.8 g m2), plant height (96.33 and 95.00 cm), phosphorus uptake in grain (24.3 and 24.49 Kg ha−1), phosphorus uptake in straw (17.7 and 17.0 Kg ha−1) and available phosphorus in the soil at harvest (21.75 and 21.70 ppm) in the 2019 and 2020 seasons, respectively; moreover, 75% SSP basal application with the foliar spraying of PSBs, PNPs and PA or 100% SSP basal application alone improved the number of panicles (506.3 or 521.1 and 521.9 or 547.1 m−2), filled grain weight (3.549 or 3.534 and 3.627 or 3.767 g panicle−1), the percentage of filled grain (96.19 or 96.47 and 95.43 or 96.24%), grain yield (9.353 or 9.221 and 9.311 or 9.148 t ha−1) and straw yield (11.51 or 11.46 and 11.82 or 11.69 t ha−1) in the 2019 and 2020 seasons, respectively. Chemical P fertilizers combined with the foliar spraying of PSBs, PNPs and PA obtained the highest crop productivity and improved most of the examined characteristics without any significant changes with respect to chemical P application alone in some other characteristics, followed by 75% SSP + top-dressing with PSBs + AMFs. The treatment that included the combination of 75% SSP basal application and the foliar spraying of PSBs +PNPs +PA is recommended, as it might be utilized to boost rice yield by solubilizing P in soil and increasing the absorption efficiency. In addition, it reduces chemical P fertilizers by 25%, which would guarantee a cleaner environment and soil conservation.

Increase of soil phosphorus bioavailability with ectomycorrhizal tree dominance in subtropical secondary forests

Many forest tree species form symbiotic associations with either arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi to increase access to nutrients. ECM and AM differ in strategies for acquiring nitrogen (N) and phosphorus (P), however, little is known about the degree to which mycorrhiza mediate the effects of tree species on soil P bioavailability outside of the temperate zone. Here, we established a natural gradient with increasing ECM tree dominance in subtropical secondary forests, and investigated the linkages between the ECM tree dominance and soil bioavailable P content. We quantified the contents of four soil bioavailable P pools (CaCl2-P, citric-P, enzyme-P and HCl-P) using the recently developed biologically-based P extraction method, as well as acid phosphatase activity, litter biomass and quality, microbial biomass carbon (C), and soil abiotic variables. We found that CaCl2-P, citric-P and HCl-P increased with ECM tree dominance, while enzyme-P did not. Specially, ECM-dominated soils displayed markedly higher (1.2–2.9 times) citric-P and HCl-P than AM soils, indicating that ECM forests can effectively obtain inorganic P by releasing organic acids and through proton excretion. The acid phosphatase involved in the acquisition of organic P had similar activity between AM and ECM forests. Structural equation models indicated that increasing ECM tree dominance increases litter C/N ratio and soil organic matter, but decreases pH and microbial biomass C/P ratio, all of which are critical in mediating P bioavailability. Collectively, our findings confirm that tree mycorrhizal associations affect soil P bioavailability, which have implications for understanding species coexistence and guiding forest managements in subtropics.

Remarkable effects of microbial factors on soil phosphorus bioavailability: A country-scale study.

Low soil phosphorus (P) bioavailability causes the widespread occurrence of P-limited terrestrial ecosystems around the globe. Exploring the factors influencing soil P bioavailability at large spatial scales is critical for managing these ecosystems. However, previous studies have mostly focused on abiotic factors. In this study, we explored the effects of microbial factors on soil P bioavailability of terrestrial ecosystems using a country-scale sampling effort. Our results showed that soil microbial biomass carbon (MBC) and acid phosphatase were important predictors of soil P bioavailability of agro- and natural ecosystems across China although they appeared less important than total soil P. The two microbial factors had a positive effect on soil P bioavailability of both ecosystem types and were able to mediate the effects of several abiotic factors (e.g., mean annual temperature). Meanwhile, we revealed that soil phytase could affect soil P bioavailability at the country scale via ways similar to those of soil MBC and acid phosphatase, a pattern being more pronounced in agroecosystems than in natural ecosystems. Moreover, we obtained evidence for the positive effects of microbial genes encoding these enzymes on soil P bioavailability at the country scale although their effect sizes varied between the two ecosystem types. Taken together, this study demonstrated the remarkable effects of microbial factors on soil P bioavailability at a large spatial scale, highlighting the importance to consider microbial factors in managing the widespread P-limited terrestrial ecosystems.

Methods for assessing laterally-resolved distribution, speciation and bioavailability of phosphorus in soils

Methods for assessing laterally-resolved distribution, speciation and bioavailability of phosphorus in soils

Interaction and Mechanism Between Conditioning Agents and Two Elements in the Soil Enriched with Phosphorus and Cadmium

Focusing on agricultural soil enriched in phosphorus and cadmium (total Cd=0.94 mg·kg-1 and total P=0.86g·kg-1), indoor cultivation experiments were conducted according to the length of the middle rice growth period and the following crop planting period in Hubei. The bioavailability of soil phosphorus and cadmium were examined along with their morphological changes and coupling effect under the influence of material biochar (BC), calcium magnesium phosphate fertilizer (CMP), and fly ash (FA). The results showed that:① When cultured for 140 days, the content of available phosphorus in the soil treated with the conditioning agents was significantly increased compared with the control soil, available phosphorus reached 22.47-37.81mg·kg-1, and the optimal growth requirements of rice were met without additional application of phosphate fertilizer, and adding BC had the best effect. ② The phosphorus in the test soil is mainly inorganic orthophosphate, and the content of different forms of inorganic phosphorus increased under the action of the conditioning agents. The fixed O-P and Ca10-P in the soil gradually changed to more active forms (Ca2-P, Ca8-P, Al-P and Fe-P) over time. ③ The effective Cd content of the soil treated with the conditioning agents was significantly reduced by 8.74%-17.48% relative to the control treatment, which was mainly related to the effect of the three conditioning agents on soil pH. At the same time, compared with the control, the addition of a conditioning agent significantly reduced the exchangeable Cd, and the carbonate-bound Cd and the residual Cd were increased. The abundance of active groups at the surface is related to the adsorption and chelation of Cd2+. The results showed that the three conditioners have the dual functions of phosphorus activation and cadmium passivation in phosphorus-and cadmium-enriched soil, and the effect of biomass carbon and calcium magnesium phosphate fertilizer was greatest, which persisted across the entire rice growth period to the sowing date of the next crop.

The application of Bacillus Megaterium alters soil microbial community composition, bioavailability of soil phosphorus and potassium, and cucumber growth in the plastic shed system of North China

The long-term continuous mono-cropping and application of large amount of chemical fertilizers have led to a dramatic degradation of soil quality in the intensive vegetable production system. It is important to develop more sustainable, environmentally friendly and high-efficiency agroecosystems for vegetable production in plastic shed systems. Field experiments were performed to explore the impacts of Bacillus megaterium application on cucumber yields, the bioavailability of soil phosphorus (P) and potassium (K), properties of soil microbial communities in a plastic shed production system with cucumber mono-cropped for more than 15 years. The field trails were set up with four treatments of conventional fertilization as control (CON), conventional fertilization with Bacillus megaterium (CON + BM), conventional fertilization reduced by 10 % P and 10 % (or 5 %) K from chemical fertilizer with Bacillus megaterium (CON + BM - PK1), conventional fertilization reduced by 20 % P and 20 % (or 10 %) K from chemical fertilizer with Bacillus megaterium (CON + BM - PK2). Results illustrated that CON + BM treatment significantly increased the cucumber yields by 11.8 %–15.2 % and P and K accumulation in cucumber fruits and roots by 27.5 %–46.1 % and 17.8 %–45.1 %, respectively. The treatments of CON + BM - PK1 and CON + BM - PK2 did not decrease the yields and quality of cucumber, and the bioavailability of soil P and K compared with CON + BM. Moreover, the strain of Bacillus megaterium can efficiently colonize the soil at the early stage of inoculation and improved the richness of soil bacterial and fungal communities significantly. High-throughput sequencing identified that the application of Bacillus megaterium did not change the compositions of the predominant bacterial phyla Proteobacteria, Acidobacteria, Actinobacteria, Firmicutes, and predominant fungal phylum Ascomycota in soil, but increased the relative abundances of the beneficial bacterial genera and fungal orders and suppressed the development of pathogenic bacterial genus significantly. Principal coordinate analysis revealed that the structures of soil bacterial and fungal communities in the CON + BM treatment were dramatically separated from CON at the early stage of inoculation. Moreover, soil pH, available K (AK), total P (TP), and total K (TK) were dramatically related to the changes of soil bacterial community structure, while soil AK and TK were dramatically linked to the variations of soil fungal community structure. The findings indicated that the application of Bacillus megaterium might contribute to the development of a more sustainable production system of vegetables in plastic shed via improving the properties of soil microbial community and the bioavailability of soil P and K.

Long-term effects of white-tailed deer overabundance, hybrid poplar genotype and planting stock type on tree growth and ecosystem services provision in bioenergy buffers

Populus hybrids are increasingly planted in multifunctional bioenergy buffers bordering crop fields. However, such small agroforestry systems are vulnerable to damage caused by overabundant deer populations. We measured after 8 years the effects of white-tailed deer (Odocoileus virginianus), genotype and planting stock type on tree growth and ecosystem services provision (biomass production; energy, nutrient and carbon storage; and phytoaccumulation of soil nitrate and phosphorus) in 15-m wide buffers located downslopes of hayfields in southern Québec (Canada). Two deer protection treatments (fenced and unfenced), two genotypes (P. deltoides × P. nigra, genotype D×N-3570 and P. maximowiczii × P. balsamifera, genotype M×B-915311) and two stock types (bare-root stocks: ±1.8 m in height and whips: 2.5 m in height) were studied. In unfenced plots, deer heavily browsed poplars (increase in the height of the first branch by 59 cm), repeatedly rubbed tree bark (36% of trees with rubs for genotype D×N-3570, and 59% for genotype M×B-915311), slightly decreased survival (by 2.9%), which reduced tree-level and stand-level productivity. Proportion of trees with rubs, first branch height and survival were correlated (p < 0.001) with woody biomass yields. Fenced poplars increased wood volume, biomass and energetic content by 20–21%, and C, N and P stocks in aboveground biomass by 13–20%. Higher soil phosphorus bioavailability was also found in unfenced plots. Genotype D×N-3570, which allocates less biomass to branches, grows its first branches farther from the ground and rapidly develops a rough and thick bark, was the least affected by deer, despite its high palatability. Genotype M×B-915311, which had higher biomass allocation to branches, a smooth and thin bark, but low palatability, was the most affected by deer. Soils in plots of genotype M×B-915311 had the lowest macronutrients availability, except for nitrate. Biomass feedstock quality (i.e. low nutrient concentrations and high heating value of woody biomass) was highest for genotype M×B-915311. In both fenced and unfenced plots, whips were more productive than bare-root stocks, especially for genotype D×N-3570. Optimizing ecosystem services provision in bioenergy buffers can be achieved by fencing, and by genotype and stock type selection.

Screening of Phosphate-Solubilizing Fungi From Air and Soil in Yunnan, China: Four Novel Species in Aspergillus, Gongronella, Penicillium, and Talaromyces.

Phosphate-solubilizing fungi (PSF) play an important role in increasing the bioavailability of phosphorus in soils for plants. Thirteen fungal strains, one collected from air and 12 from soil, were screened and described here in detail. These fungal strains were tested for their ability to solubilize tricalcium phosphate (TCP) on both solid and liquid Pikovskaya (PVK) media in vitro. The airborne fungal strain KUMCC 18-0196 (Aspergillus hydei sp. nov.) showed the most significant phosphate solubilizing activity on a solid PVK medium with the solubilization index (SI) (2.58 ± 0.04 cm) and the highest solubilized phosphates (1523.33 ± 47.87 μg/mL) on a liquid PVK medium. To the best of our knowledge, A. hydei sp. nov. is the first phosphate-solubilizing fungus reported from air. We also provide the identification especially for Aspergillus, Penicillium and Talaromyces, generally reported as PSF. It is important to not only screen for PSF but also identify species properly so that researchers have a clearer taxonomic picture for identifying potential taxa for future plant growth-promoting applications. Herein, A. hydei (section Nigri), Gongronella hydei, Penicillium soli (section Lanata-Divaricata) and Talaromyces yunnanensis (section Talaromyces) are fully described and introduced as new to science. These four new species are identified based on both morphological characteristics and multigene phylogenetic analyses, including the genealogical concordance phylogenetic species recognition method where necessary. Penicillium austrosinense is considered to be a synonym of P. guaibinense.

Effects of bioavailable phosphorus and soil biota on typical Nardus grassland species in competition with fast-growing plant species

The restoration of Nardus grasslands is often hampered by high bioavailability of soil phosphorus and disturbed soil communities. In order to better understand these bottlenecks, we studied Nardus grassland species grown together in communities with fast-growing species in 50-liter pots along a gradient of bioavailable phosphorus with or without inoculated soil biota. These mesocosms allowed the plants to freely interact, including competition for light and nutrients.We investigated changes in the plant community composition along the phosphorus gradient using Threshold Indicator Taxa Analysis (TITAN). We found a negative threshold of 11.5 mg POlsen kg−1 with six significant indicator plant species. Above the threshold, a small increase in phosphorus resulted in a disproportionally large drop in biomass for the indicator species, including four typical Nardus grassland species. The decline in these ‘oligotrophic indicator species’ was also linked to increasing plant community biomass, so we suggest the oligotrophic indicator species to be outcompeted for light by fast-growing plant species. We did not find an effect of the soil biota treatment on the biomass of the oligotrophic indicator species, but did observe a positive effect of inoculation with soil biota on the total biomass of the plant community.Interestingly, the threshold for the plant communities in the mesocosm experiment was comparable to the upper bioavailable phosphorus concentrations in remnant Nardus grasslands in northern Belgium. For the restoration of Nardus grasslands, such phosphorus-poor soil conditions appear to be essential, because the plant species that typically occur in these grasslands are able to handle nutrient limitation, but not light limitation.