Long-term nitrogen fertilization and sweetpotato cultivation in the wheat-sweetpotato rotation system decrease alkaline phosphomonoesterase activity by regulating soil phoD-harboring bacteria communities.

The alkaline phosphomonoesterase (ALP)-harboring community (phoD-harboring community) plays a crucial role in the conversion of organic phosphorus (P) into available P (AP). However, the response mechanisms of phoD-harboring communities to fertilization strategies, crop types, and their interactions within the wheat-sweetpotato rotation are poorly understood. A nine-year field experiment of different fertilization strategies was established under the wheat-sweetpotato rotation. After harvesting the crop, we collected soil samples without fertilization (CK), inorganic NK fertilization (NK), inorganic NPK fertilization (NPK), and a combined application of inorganic NPK and organic fertilizer (NPKM). We employed high-throughput sequencing and enzymology techniques to analyze the composition and functional activity of phoD-harboring bacterial communities as well as their correlation with soil physicochemical properties. The results showed that long-term nitrogen (N) fertilization, especially inorganic N, significantly reduced soil pH and ALP activity while increasing AP compared with CK. The AP content in sweetpotato season was significantly higher than that in wheat season. Inorganic N fertilization dramatically reshaped the communities of phoD-harboring bacteria and decreased diversity. The phoD-harboring bacterial communities in sweetpotato season were significantly different from those in wheat season. The N fertilization significantly reduced the relative abundance of Acuticoccus, Methylibium, Rhizobacter, and Roseivivax, which was positively correlated with ALP activity. These groups in sweetpotato season decreased significantly compared with wheat season. A structural equation model indicates that pH and AP play a significant role in regulating the phoD-harboring bacteria communities, ALP activity, and their interactions. We demonstrate that fertilization strategies and crop types have a substantial impact on the phoD-harboring bacteria communities and functions, which are closely linked to soil pH and AP levels. Our study highlights the detrimental effects of soil acidification resulting from inorganic N fertilization on P-cycling bacterial communities and functions. However, the combination of inorganic and organic fertilizer can mitigate these adverse effects.

Reduced nitrogen fertilization under flooded conditions cut down soil N2O and CO2 efflux: An incubation experiment.

Unreasonable water (W) and inorganic nitrogen (N) fertilization cause an intensification of soil greenhouse gas (GHGs) emissions. W-N interactions (W × N) patterns can maximise the regulation of soil GHGs efflux through the rational matching of W and N fertilization factors. However, the effects of W × N patterns on soil GHGs efflux and the underlying mechanism remain unclear. In this study, urea fertilizers were applied to paddy soils in a gradient of 100 (N100), 80 (N80), and 60 mg kg-1 (N60) concentrations. Flooding (W1) and 60% field holding capacity (W2) was set for each N fertilizer application to observe the effects of W × N patterns on soil properties and GHGs efflux through incubation experiments. The results showed that W significantly affected soil electrical conductivity and different N forms (i.e., alkali hydrolyzed N, ammonium N, nitrate N and microbial biomass N) contents. Soil organic carbon (C) content was reduced by 14.40% in W1N60 relative to W1N100, whereas microbial biomass C content was increased by 26.87%. Moreover, soil methane (CH4) fluxes were low in all treatments, with a range of 1.60-1.65 µg CH4 kg-1. Soil nitrous oxide (N2O) and carbon dioxide (CO2) fluxes were significantly influenced by W, N and W × N. Global warming potential was maintained at the lowest level in W1N60 treatment at 0.67 g CO2-eq kg-1, suggesting W1N60 as the preferred W × N pattern with high environmental impact. Our findings demonstrate that reduced N fertilization contributes to the effective mitigation of soil N2O and CO2 efflux by lowering the soil total N and organic C contents and regulating soil microbial biomass C and N.

Preparation of a novel rape pollen shell microencapsulation and its use for protein adsorption and pH-controlled release.

This study aims to synthesize hollow microspheres (HMS) from rape pollen via H3PO4 hydrothermal carbonization. The rape pollen hollow shell was used as the carrier and bovine serum albumin as a model protein. The properties of HMS were characterized by scanning electron microscope (SEM), solid-state nuclear magnetic resonance and elemental analysis. The SEM images clearly showed that the HMS had perfect spherical morphology and porous hollow surface. In the separated filtrate, a large number of sucroses were detected by high-performance liquid chromatography, suggesting that the hydrolysis of starch molecules occurred during the hydrothermal process. The formation of HMS was that the rape pollen inclusion was removed from rape pollen shell to preserve integral HMS by H3PO4 hydrothermal. The HMS possessed amphiphilic surfaces, which was suitable for protein adsorpion and pH-controlled release application.

Calcium involved in the poly(γ-glutamic acid)-mediated promotion of Chinese cabbage nitrogen metabolism.

Plant growth can reportedly be promoted by poly(γ-glutamic acid) (γ-PGA). However, the underlying mechanism is unknown. To reveal the mechanism of γ-PGA, we designed an experiment that investigated the effect of γ-PGA on the nitrogen metabolism of Chinese cabbage hydroponic cultured at different calcium (Ca) levels and varied exogenous Ca(2+) inhibitors. The results showed that nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase, and glutamate dehydrogenase activities in leaves and roots were obviously enhanced by γ-PGA at the normal Ca(2+) level (4.0 mM). Meanwhile, γ-PGA increased the content of total nitrogen, soluble protein, and soluble amino acids in leaves. However, the promotional effect of γ-PGA on fresh weight weakened when Ca(2+) was inadequate. Moreover, γ-PGA not only induced the influx of extracellular Ca(2+) and Ca(2+) in organelles into cytoplasm, but also increased the Ca(2+)-ATPase level to modify Ca(2+) homeostasis in plant cells. In addition, exogenous Ca(2+) inhibitors significantly suppressed the γ-PGA-mediated promotion of cytoplasmic free Ca(2+) level, calmodulin (CaM) content, GS and glutamate dehydrogenase activities. In summary, γ-PGA accelerated the nitrogen metabolism of plants through the Ca(2+)/CaM signaling pathway, thereby improving the growth of the plant.

[Effects of long-term fertilization on pH buffer system of sandy loam calcareous fluvor-aquic soil].

Soil samples (0-80 cm) were collected from a 30-year fertilization experimental site in Xuzhou, Jiangsu Province of East China to study the variations of the pH, calcium carbonate and active calcium carbonate contents, and pH buffer capacity of sandy loam calcareous fluvor-aquic soil under different fertilization treatments. Thirty-year continuous application of different fertilizers accelerated the acidification of topsoil (0-20 cm), with the soil pH decreased by 0.41-0.70. Under different fertilization, the soil pH buffer capacity (pHBC) varied from 15.82 to 21.96 cmol x kg(-1). As compared with no fertilization, single N fertilization decreased the pHBC significantly, but N fertilization combined with organic fertilization could significantly increase the pHBC. The soil pHBC had significant positive correlations with soil calcium carbonate and active calcium carbonate contents, but less correlation with soil organic matter content and soil cation exchange capacity, suggesting that after a long-term fertilization, the sandy loam calcareous fluvor-aquic soil was still of an elementary calcium carbonate buffer system, and soil organic matter and cation exchange capacity contributed little to the buffer system. The soil calcium carbonate and active calcium carbonate contents were greater in 0-40 cm than in 40-80 cm soil layer. Comparing with soil calcium carbonate, soil active calcium carbonate was more sensitive to reflect the changes of soil physical and chemical properties, suggesting that the calcium carbonate buffer system could be further classified as soil active calcium carbonate buffer system.