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ABSTACT This study investigated the fermentation of liquid feed for pigs and the effect of lactic acid bacteria (LAB) supplementation on fermentation rate, dry matter losses (DML), formation of biogenic amines and degradation of phytate-P. The basal substrate in all three in-vitro batch experiments consisted of 50% canola meal, 25% wheat, and 25% barley. The mixed substrates were adjusted to a dry matter (DM) content of 28.4% and fermented in 1L-vessels at 37° C for 24 h. Experiment 1 focused on changes in pH profiles over time. Treatments were: (1) liquid feed without additive (control) and (2) liquid feed supplemented with a mixture of Lactobacillus plantarum, Pediococcus pentosaceus, and Lactobacillus lactis (adLAB) at 2.0 × 10 5 CFU/g liquid feed (wet wt.; n = 8). Substrate pH was measured every 2 h. Experiment 2 focused on DML and the impact of fermentation on phytate-P. Treatments were identical to experiment 1 (control and adLAB; n = 8). Measured parameters included concentration of lactic acid, acetic acid, ethanol, and phytate-P, and DML after 24 h of fermentation. Counts of molds, Enterobobacteriaceae, yeasts and LAB were determined in one combined sample of all replicates. Dry matter losses were lower in LAB supplemented fermentations (5.89%) compared to the control (11.8%; P < 0.001). Supplementation with LAB reduced the phytate-P content (2.66 g/kg DM) compared to the control (3.07 g/kg DM; P = 0.002). Experiment 3 evaluated DML and the impact of fermentation on formation of biogenic amines. Treatments were: (1) control, (2) adLAB (2.0 × 10 5 CFU LAB/g liquid feed), (3) adLys (0.60% DM supplemented lysine) and (4) adLAB+Lys (combination of adLAB and adLys; n = 8). The fermentation of adLys resulted in a nearly complete breakdown of supplemented lysine, while only 10% of supplemented lysine was lost in adLAB+Lys. Furthermore, all adLys samples tested positive for cadaverine (mean concentration 0.89% DM), while no adLAB samples contained cadaverine above the detection limit (P < 0.001). Results indicate that DML is reduced in fermentations supplemented with homofermentative LAB. Fermentation of liquid feed with homofermentative LAB can effectively reduce the degradation of supplemental lysine, and has the potential to further improve P availability.

In this study, Shewanella oneidensis MR-1, an iron (Fe)-reducing bacterium, was inoculated to a red soil, which was then incubated. Soil samples were taken regularly to analyse the variation of iron oxides and phosphorus (P) fractions. The results showed that the MR-1 inoculation increased the content of the free iron oxides, but decreased the activity of the iron oxides in the soil, and had no significant influence on the amorphous iron oxides. The MR-1 inoculation increased the resin-P and residual-P, decreased the NaHCO₃-extracted inorganic P (NaHCO₃-P_i) and NaOH-extracted inorganic P (NaOH-P_i), but did not significantly influence the diluted HCl-extracted inorganic P (D.HCl-P_i) and concentrated HCl-extracted inorganic P (C.HCl-P_i). The presence of MR-1 influenced the correlation between the free iron oxides and NaOH-P_i. In the CK where deactivated MR-1 was applied, there was a significant positive correlation between the free iron oxides and the NaOH-P_i; in the treatment with the live MR-1 inoculation, there was no correlation between them. In addition, there was a significant positive correlation between the free iron oxides and the C.HCl-P_i, and there was a significant negative correlation between the NaHCO₃-P_i, resin-P, and residual-P. Therefore, the MR-1 inoculation improved the P availability by decreasing the activity of the iron oxides and consequently improved the P use efficiency in the red soil.

The over-supplementation of animal feeds with phosphorus (P) within livestock-production systems leads to high rates of P excretion and thus to high P loads and losses, which negatively impact the natural environment. The addition of phytase to pig and poultry diets can contribute to reducing P excretion; however, cascading effects of phytase on plant–soil systems remain poorly understood. Here, we addressed how three different diets containing various levels of exogenous phytase, i.e., (1) no-phytase, (2) phytase (250 FTU), and (3) superdose phytase (500 FTU) for pigs (Sus scrofa domesticus) and broilers (Gallus gallus domesticus) might affect P dynamics in two different plant–soil systems including comfrey (Symphytum ×uplandicum) and ryegrass (Lolium perenne). We found that differences in phytase supplementation significantly influenced total P content (%) of broiler litter and also pig slurry (although not significantly) as a result of dietary P content. P Use Efficiency (PUE) of comfrey and ryegrass plants was significantly higher under the intermediate ‘phytase’ dose (i.e., commercial dose of 250 FTU) when compared to ‘no-phytase’ and ‘superdose phytase’ associated with pig slurry additions. Soil P availability (i.e., water soluble P, WSP) in both comfrey and ryegrass mesocosms significantly decreased under the intermediate ‘phytase’ treatment following pig slurry additions. Dietary P content effects on P losses from soils (i.e., P leaching) were variable and driven by the type of organic amendment. Our study shows how commercial phytase levels together with higher dietary P contents in pig diets contributed to increase PUE and decrease WSP thus making the plant–soil system more P conservative (i.e., lower risks of P losses). Our evidence is that dietary effects on plant–soil P dynamics are driven by the availability of P forms (for plant uptake) in animal excretes and the type of organic amendment (pig vs. broiler) rather than plant species identity (comfrey vs. ryegrass).

Flooding in rainfed lowlands greatly impairs the mutualistic relationship between indigenous arbuscular mycorrhizal fungi (AMF) and rice. In flooded soils, root colonization by AMF is arrested, but some AMF genera, defined as the core AMF, remain present. However, the core AMF in rainfed lowlands and their symbiotic roles remain unknown. Here, we showed that Acaulospora fungi were the core AMF in rice seedling roots of the Sangyod Muang Phatthalung (SMP) landrace rice variety grown in non-flooded and flooded paddy soils. Subsequently, indigenous Acaulospora spores were propagated by trap cultures using maize as the host plants. Therefore, to clarify the roles of cultured Acaulospora spores in a symbiotic partnership, the model japonica rice variety Nipponbare was grown in sterile soil inoculated with Acaulospora spores, and recolonized with a native microbial filtrate from the organic rice paddy soil. Our data demonstrated that the inoculation of Acaulospora spores in well-drained soil under a nutrient-sufficient condition for six weeks enabled 70 percent of the rice roots to be colonized by the fungi, leading to higher phosphate (Pi) accumulation in the mycorrhizal roots. Unexpectedly, the growth of rice seedlings was significantly suppressed by inoculation while photosynthetic parameters such as fractions of incoming light energy and relative chlorophyll content were unaltered. In the soil, the Acaulospora fungi increased soil phosphorus (P) availability by enhancing the secretion of acid phosphatase in the mycorrhizal roots. The findings of this work elucidate the symbiotic roles of the dominant Acaulospora fungi from lowland rice paddies.

Abstract. Soil represents the largest phosphorus (P) stock in terrestrial ecosystems. Determining the amount of soil P is a critical first step in identifying sites where ecosystem functioning is potentially limited by soil P availability. However, global patterns and predictors of soil total P concentration remain poorly understood. To address this knowledge gap, we constructed a database of total P concentration of 5275 globally distributed (semi-)natural soils from 761 published studies. We quantified the relative importance of 13 soil-forming variables in predicting soil total P concentration and then made further predictions at the global scale using a random forest approach. Soil total P concentration varied significantly among parent material types, soil orders, biomes, and continents and ranged widely from 1.4 to 9630.0 (median 430.0 and mean 570.0) mg kg−1 across the globe. About two-thirds (65 %) of the global variation was accounted for by the 13 variables that we selected, among which soil organic carbon concentration, parent material, mean annual temperature, and soil sand content were the most important ones. While predicted soil total P concentrations increased significantly with latitude, they varied largely among regions with similar latitudes due to regional differences in parent material, topography, and/or climate conditions. Soil P stocks (excluding Antarctica) were estimated to be 26.8 ± 3.1 (mean ± standard deviation) Pg and 62.2 ± 8.9 Pg (1 Pg = 1 × 1015 g) in the topsoil (0–30 cm) and subsoil (30–100 cm), respectively. Our global map of soil total P concentration as well as the underlying drivers of soil total P concentration can be used to constraint Earth system models that represent the P cycle and to inform quantification of global soil P availability. Raw datasets and global maps generated in this study are available at https://doi.org/10.6084/m9.figshare.14583375 (He et al., 2021).

Tremendous progress has been made on molecular aspects of plant phosphorus (P) nutrition, often without heeding information provided by soil scientists, ecophysiologists, and crop physiologists. This review suggests ways to integrate information from different disciplines. When soil P availability is very low, P-mobilizing strategies are more effective than mycorrhizal strategies. Soil parameters largely determine how much P roots can acquire from P-impoverished soil, and kinetic properties of P transporters are less important. Changes in the expression of P transporters avoid P toxicity. Plants vary widely in photosynthetic P-use efficiency, photosynthesis per unit leaf P. The challenge is to discover what the trade-offs are of different patterns of investment in P fractions. Less investment may save P, but are costs incurred? Are these costs acceptable for crops? These questions can be resolved only by the concerted action of scientists working at both molecular and physiological levels, rather than pursuing these problems independently. Expected final online publication date for the Annual Review of Plant Biology, Volume 73 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Abstract The vegetation in the Arabian Peninsula experiences drought, heat, soil salinity, and low fertility, mainly due to low phosphorus (P) availability. The beneficial mycorrhizal symbiosis between plants and arbuscular mycorrhizal fungi (AMF) is a key factor supporting plant growth under such environmental conditions. Therefore, AMF strains isolated from these soils might be useful as biotechnological tools for agriculture and revegetation practices in the region. Here we present a pioneering program to isolate, identify, and apply AMF isolated from rhizosphere soils of agricultural and natural habitats, namely date palm plantations and five native desert plants, respectively in the Southern Arabian Peninsula. We established taxonomically unique AMF species as single-spore cultures as part of an expanding collection of AMF strains adapted to arid ecosystems. Preliminary experiments were conducted to evaluate the abilities of these AMF strains to promote seedling growth of a main crop Phoenix dactylifera L. and a common plant Prosopis cineraria L. (Druce) in the Arabian Peninsula. The results showed that inoculation with certain AMF species enhanced the growth of both plants, highlighting the potential of these fungi as part of sustainable land use practices in this region.