Urbanization is widely assumed to degrade soil ecosystem services, but the changes in the urban soil phosphorus (P) status due to urbanization and the associated environmental implications have rarely been studied. The objective of this study was to investigate the P forms and associated soil properties in urban soils. Thirty sites were selected along an urban–rural gradient in Nanchang, China, to examine the effects of urbanization on soil P fractions. Residual P and NaOH-extractable P (NaOH-Pi and NaOHPo) were the major P forms in the 0–30 cm of urban soils, comprising on average 37% and 43% of the total P pool, respectively, similar to the suburban and rural soils. Compared with non-urban soils, urban soil had higher contents of total P and P fractions (i.e., P_H2O, P_KCl, NaOH-Pi, P_HCl, and residual P), as well as higher contents of related soil P-retentive properties, especially soil pH and Mehlich 3-extractable Ca and Mg. Phosphorus enrichment in the urban soils may become a source of aquatic pollution because the soil labile P content (the sum of P_H2O and P_KCl) was positively related to total P, P_HCl, NaOH-Pi, and residual P, which implied that the labile P can be replenished by these P pools. This study increased the understanding of P stabilization characteristics (e.g., the specific P forms) of urban soils and has further implications for urban environmental management.

This study investigated the effects of long-term method of fertilization on growth and yield formation in early-season rice. Based on a 42-year field experiment initiated in 1981, three treatments: chemical N, P, and K (NPK), a double dose of chemical NPK (HNPK), and a combination of chemical and organic fertilizers (NPKM) were selected for comparison. Measurements included rice yield, yield components, tiller dynamic, dry matter accumulation, chlorophyll content (SPAD values), and transcriptome analysis of leaves at full heading stage in 2022. Results showed that rice yield followed the order NPKM > HNPK > NPK. The HNPK and NPKM treatments increased by 56.64% and 90.33%, respectively (p < 0.05). Spikelet density and 1000-grain weight increased by 9.16–22.89% and 3.74–4.28%, respectively. Both HNPK and NPKM enhanced the tillering rate by 43.84–72.73%, leading to an 18.95–57.54% increase in effective panicles. Dry matter accumulation from heading to filling stages was highest in NPKM-treated rice, with an increase of 3.31–4.25 g/plant in dry matter transport from leaves and stems to spikes during the filling to maturity stages. The SPAD values of NPKM-treated plants were consistently higher than those of HNPK and NPK treatments, with a smaller decline (6.94%) from heading to filling stages compared to 18.23% and 26.29% for HNPK and NPK, respectively. Correlation analysis indicated a positive relationship between yield and SPAD values or dry matter accumulation and a negative correlation with the decline in SPAD values from full heading to filling stage. Transcriptome analysis revealed significant enrichment of photosynthesis and plant senescence pathways among treatments. Overall, long-term combined application of chemical and organic fertilizers (NPKM) improved yield components, delayed chlorophyll degradation, promoted dry matter accumulation and transport, and regulated the expression of photosynthesis-related and senescence-related genes, ultimately optimizing growth and yield in early-season rice.

With irrigation using waste water, application of sewage sludge, and development of mine exploration, copper (Cu) contamination in some paddy fields has become increasingly serious. A greenhouse pot experiment was conducted using a factorial design with three sulfur (S) application rates (i.e., 0, 0.013, and 0.026 g S kg⁻¹ soil) and three silicon (Si) application rates (i.e., 0, 0.05, and 0.1 g Si kg⁻¹ soil) to test the effect of co-amendment of S and Si on alleviating Cu contamination in paddy soil. There were significant interaction effects between S and Si on soil Cu speciation and Cu uptake by rice plants (except brown rice). Sulfur addition decreased the content of soil-exchangeable Cu, whereas Si addition decreased the content of soil-reducible Cu, suggesting that co-amendment of S and Si generally reduced Cu availability. Copper was biominimized in the soil-rice plant system and rice root had the greatest Cu concentration (163–285 mg kg⁻¹). Co-amendment of S and Si decreased the translocation of Cu from soil to rice root, possibly due to decreased soil Cu mobility and enhancement of the formation of iron plaque on rice root. Co-amendment of S-Si at a rate of 0.013 (S)–0.1 (Si) g kg⁻¹ soil, respectively, was the optimal among all treatments.

Microbial necromass carbon (MNC) is the dominant contributor to soil organic carbon (SOC). However, the contribution of MNC in different soil compartments to SOC sequestration has not been comprehensively studied, especially under the organic fertilizers input. To address this gap, we conducted a rice root box experiment by adding organic fertilizer (straw and straw biochar) and chemical fertilizer alone to red loamy paddy soil, respectively. We found that although SOC accumulation was stimulated by both biochar and straw in the rhizosphere, more substantial SOC was sequestered in the rhizosphere due to biochar addition (increased by 25.82% compared to straw addition). Additionally, the input of organic fertilizers resulted in varying degrees of MNC retention in the different soil compartments. Compared with that in bulk soil, fungal necromass carbon (FNC) content was reduced by 1.37% and 7.06%, and bacterial necromass carbon (BNC) content was reduced by 5.53% and 9.49% in the rhizosphere and hyphosphere, respectively, following straw addition. Conversely, the addition of biochar leads to a significant increase of FNC (increased by 2.92%) and BNC (increased by 2.00%) in the rhizosphere compared with bulk soil. However, straw addition also significantly enhanced SOC thermal stability within the rhizosphere and hyphosphere soils. Based on partial least squares path modeling, we found that SOC thermal stability was significantly and positively influenced by FNC, which was strongly associated with carbon degradation gene abundance. These results emphasize the critical role of soil compartments in SOC sequestration under organic fertilizer application and underscore the importance of FNC in enhancing SOC stability in the rhizosphere.