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Purpose: Rapid urbanization has altered regional nutrient cycles and consequently affected soil nutrient availability for plant growth. This study aims to explore the way in which urbanization shapes the spatial patterns of soil phosphorus (P) concentrations as well as the imprint on tree leaf P concentrations across gradients of urban-rural forests. Methods: We collected soil samples of the surface (0-10 cm) and subsurface (10-20 cm) layers and leaf samples of three common tree species (Chinese pine, Pinus tabuliformis; Chinese scholar tree, Sophora japonica; golden rain tree, Koelreuteria paniculata) from forest patches in twenty parks across urban-rural transects in the Beijing metropolitan region, China. By measuring soil total P, soil available P, and leaf P concentrations, we tested the urban soil P hotspot hypothesis and assessed the consequent imprint on tree leaf P concentrations. Results: Soil total P and available P concentrations in the surface and subsurface layers both increased significantly with closer distance to the urban core. Spatially, leaf P concentrations showed an increase with soil available P concentrations only for the legume Chinese scholar tree, while leaf P concentrations of Chinese pine and broadleaf golden rain tree both increased significantly with the diameter at breast height. Conclusion: Our results confirmed the occurrence of an urban soil P hotspot and identified its significant imprint on leaf P nutrition of legume trees across transects of urban-rural forests. The findings improve the understanding of the way that urbanization alters regional P cycles and consequent P availability for plant growth. [ABSTRACT FROM AUTHOR]

Background: Over fertilization with nitrogen (N) is considered the main driver of agricultural soil acidification in China. However, the contribution of this driver compared to other causes of soil acidification on intensive croplands has seldom been quantified under field conditions.Methods: We measured the fate of major nutrients, and calculated the related H+ production, based on the difference between inputs and leaching losses of those nutrients for a wheat-maize rotation system on a moderate acid silty clay loam soil in a two-year field experiment.Results: Topsoil pH decreased 0.3 units in the plots with conventional (current farmer practice) high N fertilization after two years, with a proton production of 13.1 keq H+ ha−1 yr.−1. No apparent changes in topsoil pH were observed in the plots without N application, in spite of a proton production of 4.7 keq H+ ha−1 yr.−1. Crop uptake was the primary driver of H+ production, followed by N transformation processes and HCO3− leaching in both plots.Conclusions: Nitrogen fertilization had a relative small direct impact on soil acidification due to a very limited nitrate leaching, induced by large N losses to air by denitrification in this specific moderately acid soil, whereas elevated base cation uptake by crops induced by N fertilization indirectly had a relative large impact. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus (P) availability in calcareous soils is limited. Acidifying the soil by adding sulfur (S) or enhancing microbial activity by adding carbon (C) can increase P bioavailability. However, understanding of the impact of the combined application of P, S and C on P availability in calcareous soils is lacking. In this study, we investigated the effects of heterogeneous (co-localized) supply of different combinations of P, S and C on the maize (Zea mays L.) shoot and root growth and soil P availability in calcareous soil with low available P.A rhizo-box experiment with heterogeneous supply of P, S and C was conducted to assess the responses of maize growth, root morphology and physiology, as well as soil P availability.Heterogeneous low P (P1) with S supply significantly increased shoot and root biomass, shoot P content and P-use efficiency (PUE) compared to homogenous or heterogeneous P1 supply alone. Application of S decreased the rhizosphere soil pH and stimulated the proliferation of maize roots. By contrast, heterogeneous P1 and C supply did not change shoot biomass, P uptake or PUE but decreased root biomass. The addition of C, however, enhanced acid phosphatase activity and carboxylates concentration in the rhizosphere, and increased NaHCO3-extractable P, implying enhanced P availability.Adding S combined with P is an effective approach to engineer the rhizosphere by increasing maize growth and PUE in calcareous soil, whereas adding C increased NaHCO3-extractable soil P but did not influence maize shoot growth.Methods: Phosphorus (P) availability in calcareous soils is limited. Acidifying the soil by adding sulfur (S) or enhancing microbial activity by adding carbon (C) can increase P bioavailability. However, understanding of the impact of the combined application of P, S and C on P availability in calcareous soils is lacking. In this study, we investigated the effects of heterogeneous (co-localized) supply of different combinations of P, S and C on the maize (Zea mays L.) shoot and root growth and soil P availability in calcareous soil with low available P.A rhizo-box experiment with heterogeneous supply of P, S and C was conducted to assess the responses of maize growth, root morphology and physiology, as well as soil P availability.Heterogeneous low P (P1) with S supply significantly increased shoot and root biomass, shoot P content and P-use efficiency (PUE) compared to homogenous or heterogeneous P1 supply alone. Application of S decreased the rhizosphere soil pH and stimulated the proliferation of maize roots. By contrast, heterogeneous P1 and C supply did not change shoot biomass, P uptake or PUE but decreased root biomass. The addition of C, however, enhanced acid phosphatase activity and carboxylates concentration in the rhizosphere, and increased NaHCO3-extractable P, implying enhanced P availability.Adding S combined with P is an effective approach to engineer the rhizosphere by increasing maize growth and PUE in calcareous soil, whereas adding C increased NaHCO3-extractable soil P but did not influence maize shoot growth.Results: Phosphorus (P) availability in calcareous soils is limited. Acidifying the soil by adding sulfur (S) or enhancing microbial activity by adding carbon (C) can increase P bioavailability. However, understanding of the impact of the combined application of P, S and C on P availability in calcareous soils is lacking. In this study, we investigated the effects of heterogeneous (co-localized) supply of different combinations of P, S and C on the maize (Zea mays L.) shoot and root growth and soil P availability in calcareous soil with low available P.A rhizo-box experiment with heterogeneous supply of P, S and C was conducted to assess the responses of maize growth, root morphology and physiology, as well as soil P availability.Heterogeneous low P (P1) with S supply significantly increased shoot and root biomass, shoot P content and P-use efficiency (PUE) compared to homogenous or heterogeneous P1 supply alone. Application of S decreased the rhizosphere soil pH and stimulated the proliferation of maize roots. By contrast, heterogeneous P1 and C supply did not change shoot biomass, P uptake or PUE but decreased root biomass. The addition of C, however, enhanced acid phosphatase activity and carboxylates concentration in the rhizosphere, and increased NaHCO3-extractable P, implying enhanced P availability.Adding S combined with P is an effective approach to engineer the rhizosphere by increasing maize growth and PUE in calcareous soil, whereas adding C increased NaHCO3-extractable soil P but did not influence maize shoot growth.Conclusion: Phosphorus (P) availability in calcareous soils is limited. Acidifying the soil by adding sulfur (S) or enhancing microbial activity by adding carbon (C) can increase P bioavailability. However, understanding of the impact of the combined application of P, S and C on P availability in calcareous soils is lacking. In this study, we investigated the effects of heterogeneous (co-localized) supply of different combinations of P, S and C on the maize (Zea mays L.) shoot and root growth and soil P availability in calcareous soil with low available P.A rhizo-box experiment with heterogeneous supply of P, S and C was conducted to assess the responses of maize growth, root morphology and physiology, as well as soil P availability.Heterogeneous low P (P1) with S supply significantly increased shoot and root biomass, shoot P content and P-use efficiency (PUE) compared to homogenous or heterogeneous P1 supply alone. Application of S decreased the rhizosphere soil pH and stimulated the proliferation of maize roots. By contrast, heterogeneous P1 and C supply did not change shoot biomass, P uptake or PUE but decreased root biomass. The addition of C, however, enhanced acid phosphatase activity and carboxylates concentration in the rhizosphere, and increased NaHCO3-extractable P, implying enhanced P availability.Adding S combined with P is an effective approach to engineer the rhizosphere by increasing maize growth and PUE in calcareous soil, whereas adding C increased NaHCO3-extractable soil P but did not influence maize shoot growth. [ABSTRACT FROM AUTHOR]