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Acidic soils are hotspots of global nitrous oxide (N 2 O) emission. The application of organic fertilizer with low carbon (C) to nitrogen (N) ratio (C:N) often stimulated N 2 O emission in acidic soils. However, how its use increases acidic soil N 2 O emission remains largely unclear. We thus conducted an aerobic 15  N tracing incubation experiment to quantify the effects of organic fertilizer input with low C:N on the contribution of denitrification and autotrophic and heterotrophic nitrification to N 2 O emission in an acidic soil. We found a shift from nitrification to denitrification-dominated N 2 O emission after adding organic fertilizer with low C:N into the studied acidic soil, and this shift was more pronounced with increasing the application rate of organic material. Therefore, organic fertilizer application with low C:N may stimulate N 2 O emission in acidic soils due to the stimulation of denitrification.

Aluminium (Al) toxicity is one of the major abiotic stress problems around the globe where acidic soil is present. Al shows a toxic effect between the soil pH 4.5 and 5.5. Root growth inhibition is the most prodigious symptom of Al toxicity in plants. Aluminium toxicity adversely affects the plant growth and development which ultimately reduces the yield. However, the extent of toxicity depends on the genotype of the plant, that is the plant is either the Al-sensitive or Al-tolerant type. Plants have several mechanisms to cope with the toxic effects of aluminium which include exclusion mechanism and internal tolerance mechanism. This review discusses the harmful impacts of aluminium on morphological, anatomical, physio-biochemical, and molecular aspects of the plant. This review also discusses the strategies to reduce the toxic effects of aluminium in plant and various aluminium-responsive genes which can be used in genetic manipulation for better crop development.

AimsOrganic manure (OM) is an effective amelioration measure for acidic soils. Acid (ACP) and alkaline phosphatases (ALP) encoded by bacterial phoC and phoD genes, respectively, are responsible for organic phosphorus (P) mineralization. However, the short-term influence of OM application on phosphatase activity and organic P-mineralizing bacterial communities of bulk and rhizosphere soils in acidic soils is less known.MethodsMaize was grown in acidic soil (pH 4.40) supplied with 0, 1, 5, 10, 20 and 50 g OM kg− 1 dry soil for six weeks. Maize biomasses and nutrients, soil physicochemical properties and phosphatase activities, and P-mineralizing bacterial communities were observed.ResultsRhizosphere showed higher ACP and ALP activities than bulk soils, and the rhizosphere effects were stronger than OM application. The Shannon index of phoC- and phoD-harboring bacteria responded differently to both rhizosphere effect and OM application, with a stronger influence from maize rhizosphere. The rhizosphere effect significantly affected both phoC- and phoD-harboring bacterial community structures, but OM application only influenced phoD-harboring bacterial community structure. Co-occurrence network of the phoD-harboring bacteria had higher average degree and more nodes and edges than phoC-harboring bacteria. PLS-PM results suggested that the rhizosphere effect exhibited greatest contribution to soil ACP and ALP activities than OM treatment.ConclusionCompared with short-term OM application, maize rhizosphere effect showed stronger influences on soil phosphatase activities and P-mineralizing bacterial communities in acidic soils. The phoD-harboring bacteria showed the more sensitive response to the rhizosphere effect and OM application, while phoC-harboring bacteria was only influenced by rhizosphere effect.

In agro-ecosystems, the relationship between soil fertility and crop yield is mediated by manure application. In this study, an 8-year field experiment was performed with four fertilizer treatments (NPK, NPKM 1 , NPKM 2 , and NPKM 3 ), where NPK refers to chemical fertilizer and M 1 , M 2 , and M 3 refer to manure application rates of 15, 30, and 45 Mg ha −1  year −1 , respectively. The results showed that the NPKM (NPKM 1 , NPKM 2 , and NPKM 3 ) treatments produced greater and more stable yields (4.95–5.45 Mg ha −1 and 0.59–0.75) than the NPK treatment (4.01 Mg ha −1 and 0.50). Crop yields under the NPKM treatments showed two trends, with a rate of decrease of 0.48–0.83 Mg ha −1  year −1 during the first 4 years and a rate of increase of 0.10–0.25 Mg ha −1  year −1 during the last 4 years. The soil organic carbon (SOC) significantly increased under all treatments. The estimated annual SOC decomposition rate was 0.35 Mg ha −1  year −1 and the equilibrium SOC level was 6.22 Mg ha −1 . Soil total nitrogen (N), available N, total phosphorus (P) and available P under the NPKM treatments increased by 0.15–0.26, 15–33, 0.17–0.66 and 45–159 g kg −1 , respectively, compared with the NPK treatment. Manure application mainly influenced crop yield by affecting the soil TN, available N, and available P, which accounted for up to 64% of the crop yield variation. Taken together, applying manure can determine or at least improve the effects of soil fertility on crop yield in acidic soils in South China.

Toxic aluminum ions (Al 3+ ) found in acidic soils are absorbed by plants and interact with multiple sites during plant development, affecting especially the root growth. The mechanisms by which plants cope with Al 3+ stress are variable, and Al 3+ can be excluded or accumulated internally. The molecular and physiological mechanisms associated with Al 3+ response have been substantially studied. Thus, reviewing the findings about these mechanisms is important to portrait the state-of-the-art of Al 3+ response in plants, highlight key results, identify research gaps, and ask new questions. In this paper, we discuss the current knowledge about DNA damage response induced by Al 3+ , as well as membrane transporters that avoid Al 3+ toxicity in the apoplast, Al 3+ exclusion mechanisms, how Al 3+ influences plant nutrition, signaling pathways evoked by Al 3+ affecting gene expression, changes in plant growth regulators concentrations caused by Al 3+ toxicity, and beneficial effects of microorganisms on plants exposed to Al 3+ stress. The future research on these topics is also discussed. The current and future knowledge of how plants cope with Al 3+ stress is important to comprehend the inter- and intraspecies variability of Al 3+ response and to pave the way for new molecular breeding targets that can improve plant performance under Al 3+ stress.

Increasing evidence demonstrated the involvement of ammonia-oxidizing archaea (AOA) in the global nitrogen cycle, but the relative contributions of AOA and ammonia-oxidizing bacteria (AOB) to ammonia oxidation are still in debate. Previous studies suggest that AOA would be more adapted to ammonia-limited oligotrophic conditions, which seems to be favored by protonation of ammonia, turning into ammonium in low-pH environments. Here, we investigated the autotrophic nitrification activity of AOA and AOB in five strongly acidic soils (pH<4.50) during microcosm incubation for 30 days. Significantly positive correlations between nitrate concentration and amoA gene abundance of AOA, but not of AOB, were observed during the active nitrification. 13 CO 2 -DNA-stable isotope probing results showed significant assimilation of 13 C-labeled carbon source into the amoA gene of AOA, but not of AOB, in one of the selected soil samples. High levels of thaumarchaeal amoA gene abundance were observed during the active nitrification, coupled with increasing intensity of two denaturing gradient gel electrophoresis bands for specific thaumarchaeal community. Addition of the nitrification inhibitor dicyandiamide (DCD) completely inhibited the nitrification activity and CO 2 fixation by AOA, accompanied by decreasing thaumarchaeal amoA gene abundance. Bacterial amoA gene abundance decreased in all microcosms irrespective of DCD addition, and mostly showed no correlation with nitrate concentrations. Phylogenetic analysis of thaumarchaeal amoA gene and 16S rRNA gene revealed active 13 CO 2 -labeled AOA belonged to groups 1.1a-associated and 1.1b. Taken together, these results provided strong evidence that AOA have a more important role than AOB in autotrophic ammonia oxidation in strongly acidic soils.

PurposeThe aims of this study were to investigate the links between potassium (K) uptake by crops and soil K, exchangeable calcium (Ca2+), magnesium (Mg2+), and aluminum (Al3+) when using lime in acidic soil in southern China.Materials and methodsSoil samples of three treatments (chemical NP fertilizers, NPK, and NPK plus straw (NPKS)) were collected from a 26-year field experiment (0–20 cm) and then a rhizobox experiment was conducted with seven lime application rates (0–2.26 g kg−1). We investigated the soil exchangeable K+, Ca2+, Mg2+, and Al3+ and non-exchangeable K (NEK) in the rhizosphere soil (RS) and non-rhizosphere soils (NRS), and K uptake by crops.Results and discussionAs lime addition rates increased, the average concentration of exchangeable K (EK) in RS under NPK and NPKS treatments decreased to 46.5 mg kg−1 and 70.4 mg kg−1 for maize and wheat, respectively. In treatments with lime application, the NEK concentration was higher in RS and NRS compared with the no-lime in NP treatment but was lower in RS in treatments with K fertilizer input (NPK and NPKS). The K uptake by crops under lime application significantly (p < 0.05) increased by 37.6% to 155.1% compared with the no-lime treatments. Lime application significantly increased soil exchangeable Ca2+ (42.9 to 255.7%) and decreased exchangeable Al3+ (23.7 to 86.6%). According to structural equation modeling, lime indirectly influenced K uptake by crops through its effects on soil exchangeable Ca2++Mg2+ and Al3+, EK, and NEK, which accounted for up to 39% (RS) and 46% (NRS) of the variation in the K uptake by crops. Lime directly and negatively affected EK and NEK in NRS but had no direct effects on EK and NEK in RS.ConclusionsOur results suggested that lime-induced K uptake by crops was mediated by K+, Ca2+, and Al3+, and that lime application resulted in higher soil K availability.

Recently, Diammonium phosphate (DAP, (NH 4 ) 2 HPO 4 ) has gradually replaced fused calcium-magnesium phosphate (FCMP) as the primary source of phosphorus in sugarcane fields in China. FCMP is a thermally processed phosphate fertilizer primarily containing α-Ca 2 (PO 4 ) 2 and CaMgP 2 O 7 . Despite its possible impacts on sustainable sugarcane production, the effect of this substitution on accelerating soil acidification has not yet been investigated. In this study, a three-year-long experiment was performed in Tuolu Town of Jiangzhou District, and field experiments were conducted with five treatment groups with different substitution ratios of DAP replacing FCMP (0%, 25%, 50%, 75%, and 100% of P 2 O 5 ). The results indicated that the replacement of FCMP with DAP decreased soil pH. The decrease in soil pH is closely related to the increase in soil exchangeable aluminum and the decrease in soil exchangeable calcium and magnesium. In acidic soil, FCMP can release and increase Ca 2+ and Mg 2+ to compensate for the losses of Ca 2+ and Mg 2+ over time. With an increase in the proportion of DAP replacing FCMP, soil exchangeable Ca 2+ and Mg 2+ decreased and soil exchangeable Al 3+ increased simultaneously. Complete replacement of FCMP with DAP increased soil exchangeable aluminum by 0.23 cmol kg −1 yr −1 . The accumulation of soil exchangeable Al 3+ and loss of exchangeable (Ca 2+ + Mg 2+ ) had an approximately 1:1 linear negative correlation. Our study shows that applying FCMP further prevents soil acidification in acidic sugarcane field, but replacing FCMP with DAP leads to a decrease in soil pH and an increase in soil exchangeable aluminum. Therefore, FCMP should be favored in acidic sugarcane fields to mitigate acidification. These results can provide an important reference for decision-making in China’s fertilizer and sugarcane industries.

Background and aims Soil acidification impedes crop growth. Seed pelletization was used to improve crop resistance to various stress environments but not acidic soil. This study aimed to develop rapeseed seed pelletization and to assess the promotional effects of pelletization on rapeseed growth under acidic conditions. Methods Two main acid-resistant functional agents (Ca(OH) 2 , and biochar) and a basic formula including sodium carboxymethyl cellulose, H 3 BO 3 , nano-silica, brassinolide, sodium naphthalene acetate, indoleacetic acid, and yeast metabolite were used to evaluate the effects on rapeseed growth by seed pelletization. Then, the mechanism of alleviating acidic stress by seed pelletization was investigated. Results A basic formula were developed by soil test. Three acid-resistant seed pelletization cases (① 0.5% Ca(OH) 2  + a basic formula; ② 10% biochar + a basic formula; ③ 0.25% Ca(OH) 2  + 5% biochar + a basic formula) were confirmed to have significant plant growth promotion. Compared to the unpelletized treatment, seed pelletization significantly increased root length and dry weight of rapeseed seedling by 67.32%-78.34% and 46.47%-74.12%, respectively. It also increased nutrient uptake and reduced the accumulation of toxic Al by 11.72%-16.23% in rapeseed roots. Moreover, seed pelletization modulated the local soil environment at the sowing site, increased soil pH by 0.88–1.11 in the microzone, thereby reducing the adverse effects of acidic stress. Conclusion Seed pelletization in rapeseed can enhance its tolerance to acidic stress and promote plant growth. Additionally, our results provide new insights into the strategies to alleviate the inhibitory effects of acidic soil.

Aims Although phosphorus (P) availability and plant cultivation affect diazotrophic populations, studies often consider individual factors rather than their combined effects. Their relative importance to diazotrophs remains poorly understood, especially in acidic soils with P deficiency. It is hypothesized that the influences of P fertilization and plant cultivation on diazotrophic communities differ in acidic soils. The objectives were to investigate these influences and identify the key determining factors. Methods Maize was grown in an acidic soil that was supplemented with 0, 20, and 50 mg P kg − 1 for 42 days. Maize biomasses, plant nutrient contents, and soil physicochemical properties were determined. Based on the nifH gene, the abundances and community compositions of diazotrophs in the different plant/soil compartments (bulk soils, rhizosphere soils, and roots) were respectively investigated using quantitative PCR and high-throughput sequencing. Results P fertilization significantly improved the diazotrophic abundances in the bulk and rhizosphere soils, but not in the roots. The plant/soil compartments had stronger effects on the abundance and diversity of diazotrophs than did P fertilization. Furthermore, the plant/soil compartments influenced diazotrophic community composition, but P fertilization did not. However, in the same sampling site, P fertilization caused community variations in the bulk and rhizosphere soils, rather than in the roots. Conclusions Although P fertilization affected the abundances and compositions of diazotrophic communities in the bulk and rhizosphere soils, the plant/soil compartments resulting from maize cultivation had more noticeable effects than did P fertilization. These findings improved the understanding of biological nitrogen fixation in acidic soils.