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Limitation of grain crop productivity by phosphorus (P) is widespread and will probably increase in the future. Enhanced P efficiency can be achieved by improved uptake of phosphate from soil (P-acquisition efficiency) and by improved productivity per unit P taken up (P-use efficiency). This review focuses on improved (P-use efficiency, which can be achieved by plants that have overall lower P concentrations, and by optimal distribution and redistribution of P in the plant allowing maximum growth and biomass allocation to harvestable plant parts. Significant decreases in plant P pools may be possible, for example, through reductions of superfluous ribosomal RNA and replacement of phospholipids by sulfolipids and galactolipids. Improvements in P distribution within the plant may be possible by increased remobilization from tissues that no longer need it (e.g. senescing leaves) and reduced partitioning of P to developing grains. Such changes would prolong and enhance the productive use of P in photosynthesis and have nutritional and environmental benefits. Research considering physiological, metabolic, molecular biological, genetic and phylogenetic aspects of P-use efficiency is urgently needed to allow significant progress to be made in our understanding of this complex trait.

The pqqC and phoD genes encode pyrroloquinoline quinone synthase and alkaline phosphomonoesterase (ALP), respectively. These genes play a crucial role in regulating the solubilization of inorganic phosphorus (Pi) and the mineralization of organic phosphorus (Po), making them valuable markers for P-mobilizing bacterial. However, there is limited understanding of how the interplay between soil P-mobilizing bacterial communities and abiotic factors influences P transformation and availability in the context of long-term fertilization scenarios. We used real-time polymerase chain reaction and high-throughput sequencing to explore the characteristics of soil P-mobilizing bacterial communities and their relationships with key physicochemical properties and P fractions under long-term fertilization scenarios. In a 38-year fertilization experiment, six fertilization treatments were selected. These treatments were sorted into three groups: the non-P-amended group, including no fertilization and mineral NK fertilizer; the sole mineral-P-amended group, including mineral NP and NPK fertilizer; and the organically amended group, including sole organic fertilizer and organic fertilizer plus mineral NPK fertilizer. The organically amended group significantly increased soil labile P (Ca2-P and enzyme-P) and Olsen-P content and proportion but decreased non-labile P (Ca10-P) proportion compared with the sole mineral-P-amended group, indicating enhanced P availability in the soil. Meanwhile, the organically amended group significantly increased soil ALP activity and pqqC and phoD gene abundances, indicating that organic fertilization promotes the activity and abundance of microorganisms involved in P mobilization processes. Interestingly, the organically amended group dramatically reshaped the community structure of P-mobilizing bacteria and increased the relative abundance of Acidiphilium, Panacagrimonas, Hansschlegelia, and Beijerinckia. These changes had a greater positive impact on ALP activity, labile P, and Olsen-P content compared to the abundance of P-mobilizing genes alone, indicating their importance in driving P mobilization processes. Structural equation modeling indicated that soil organic carbon and Po modulated the relationship between P-mobilizing bacterial communities and labile P and Olsen-P, highlighting the influence of SOC and Po on the functioning of P-mobilizing bacteria and their impact on P availability. Overall, our study demonstrates that organic fertilization has the potential to reshape the structure of P-mobilizing bacterial communities, leading to increased P mobilization and availability in the soil. These findings contribute to our understanding of the mechanisms underlying P cycling in agricultural systems and provide valuable insights for enhancing microbial P mobilization through organic fertilization.

Internal phosphorus loading (IPL), as an important part of lake phosphorus cycle and the key to solve the eutrophication problem, is still an important cause of regional and seasonal algal blooms for some mesotrophic lakes located in plateau areas. We investigated the composition, distribution of P fractions in sediments and suspended particulate matter (SPM) of Erhai Lake, southwest China, and explored the relationships between environmental variables and spatial-temporal variations of P fractions. The total P (TP) in surface sediments ranged from 817 to 1216 mg/kg, with inert Ca-P (32%) and Res-P (24%) predominating, at a moderate level. The comparison of short-term release fluxes (0.08 mg/(m 2 ·d)) and long-term release fluxes (0.09 mg/(m 2 ·d)) reflected that the northern region was recovering slowly from the previous P pollution. Mobile-P (the sum of loosely adsorbed P, iron bound P, and organic P) accounted for 52.3% of the TP in SPM and showed high spatial-temporal variations, which were closely related to the growth of algae throughout the investigation. The results suggested that sediments could make a sustained contribution to IPL, and that the P in SPM was highly active and significantly contributed to eutrophication in Erhai Lake especially at the time of seasonal alternations. Our data provided important theoretical bases for the relationship between internal phosphorus loading and eutrophication in plateau lakes.

Background and Aims Phosphorus (P) plays a vital role in plant physiology, and the soils of Chinese fir-producing areas are rich in aluminum and iron ions, making phosphorus highly susceptible to fixation. Insufficient phosphorus nutrient supply is a main constraint to the sustainability of Chinese fir plantations. The aim of this study is to ameliorate the problem of soil available phosphorus deficiency in Chinese fir plantations by changing the management mode, introducing local broad-leaved tree species to form multiple layers of different ages, thereby enhancing soil productivity. Methods The properties and phosphorus fractions of the surface soils (0-20 cm), litter and leaf nutrients were determined, and macro-genomic technique was used to explore changes of soil phosphorus cycling (P-cycling) genes. Results (1) The close-to-nature management (CNM) significantly increased soil organic carbon (SOC) and available phosphorus (AP) content and affected litter and plant nutrients. (2) The CNM affected the availability of soil phosphorus. The labile phosphorus (resin-P, NaHCO 3 -Pi) and moderately labile phosphorus (NaOH-Pi) were significantly higher in CNM forests than in Chinese fir plantation. (3) The relative abundances of most of the P-cycling genes differed between the forests, with higher abundances of P-solubilization ( ppa ), P-mineralization ( phnL and opd ) and P-regulatory ( phoB ) genes in CNM forests. Moreover, MBC (microbial biomass carbon), SOC, total nitrogen (TN) and LTP (litter total phosphorus) were the main factors affecting the composition of soil P-cycling genes. Conclusions The CNM affected properties (soil, litter and plant) and improved soil phosphorus availability and the relative abundance of P-cycling genes. This study revealed the regulation mechanism of P-cycling in the CNM of Chinese fir plantation from microbial P-cycling genes perspective, which highlights the importance of P supply and microbial metabolic strategy by CNM of Chinese fir plantation.

Aims Rational intercropping is crucial for improving phosphorus (P) uptake and utilization. This study aimed to investigate the effects of intercropping on the activation of soil P fractions and available P in acid soil under different P application rates. Methods Field experiments were conducted to investigate the effects of maize intercropping with soybean at different P application rates (0, 60, 90, and 120 kg P ha −1 ) on soil P fractions and P pool turnover over two consecutive years. Results Intercropping of maize and soybean showed an advantage in increasing P uptake and reducing apparent P balance at all P application rates, and promoting soil P pool activation. Compared with monoculture maize, intercropping significantly increased maize P uptake by 43.6–74.3% and 45.5–76.8% in consecutive years, reduced apparent P balance by 17.1–33.4% and 19.9–32.4% in those years. Additionally, intercropping maize increased labile P pools by 32.5–38.4% and 14.4–82.1% over consecutive years and reduced non-labile P pools by 7.4–10.9% and 6.6–11.6% compared with monoculture maize. Moreover, intercropping depleted NaOH-Po, conc. HCl-Pi, conc. HCl-Po and Residual-P fractions, and increased Resin-P, NaHCO 3 -Pi, NaHCO 3 -Po, NaOH-Pi, and 1 M HCl-Pi fractions compared with monoculture maize. Resin-P, NaHCO 3 -Pi, NaHCO 3 -Po increased by 4.3–41.2%, 21.1–84.6%, and 9.7–98.8%, respectively. Furthermore, intercropping at different P application rates significantly increased acid phosphatase activity (ACP) by 13.8–27.1% and 9.5–13.4%, and significantly increased alkaline phosphatase activity (ALP) by 21.2–42.6% and 19.9–28.6% in those years. Structural equation modelling (SEM) showed that both ACP and ALP played a crucial role in increasing available P directly or indirectly through their effects on organic P turnover. Conclusions These results demonstrate that intercropping maize with soybean increases soil P bioavailability by transforming NaOH-Po and conc. HCl-Po into soluble P (Resin-P and NaHCO 3 -Pi) by facilitating the accumulation of soil phosphatase activity.

Background and aims Understanding how long-term intercropping and phosphorus (P)-fertilizer application affect soil P fractions through P-acquisition strategies is critical to maintaining soil P balance in agroecosystems. Methods We established a long-term field experiment with three P-fertilizer application rates (0, 40, and 80 kg P ha −1 ) and continuously used four intercropping systems of chickpea/maize, faba bean/maize, oilseed rape/maize, soybean/maize and corresponding five monocultures in 2009. We measured aboveground biomass, shoot P content, soil P fractions, P-related root physiological traits, and soil microbe-related parameters of crop species in 2020. We also calculated the apparent soil P balance (P input into soil minus P harvested from crops) using data from 2009 to 2020. Results Intercropping enhanced aboveground biomass and shoot P content by 31.2% and 49.4% compared with the weighted means of corresponding monocultures, respectively; intercropping decreased the apparent soil P balance by 37.8% compared with monocultures across three P-fertilizer application rates. Over the 12-year period, chickpea/maize and soybean/maize intercropping systems significantly decreased the soil organic P concentration compared with sole maize; faba bean/maize and oilseed rape/maize intercropping systems significantly decreased soil non-labile P but increased organic P and labile P pool relative to sole maize. Rhizosheath phosphatases and carboxylates (proxied by leaf manganese concentration) might contribute to the depletion of sparingly-available soil P (organic P or non-labile P) in different crop combinations. Conclusion The higher rhizosheath acid phosphatase activities and carboxylate concentrations may correlate with efficient utilization of sparingly-available soil P resources in intercropping; effective P-fertilizer input enhanced soil P availability and decreased the P surplus in soil which is crucial to enhance crop P uptake.

Background Soil phosphorus (P) availability is crucial for the restoration of degraded ecosystems, but how soil organic P transforms during post-agricultural succession remains poorly understood in karst ecosystems. Methods A typical recovery gradient including manual (orchard) and natural (grassland and secondary forest) vegetation restoration after agricultural abandonment was established in a karst region of southwest China. Sequential fractionation, solution 31 P nuclear magnetic resonance (NMR) and enzyme assays were performed to investigate the chemical nature and biochemical transformation of organic P during post-agricultural succession in a karst region of southwest China. Results We found significant redistributions of soil P fractions from inorganic P to organic P after agricultural abandonment. Specifically, orthophosphate decreased by 10.5% to 34.6%, while phosphomonoester and phosphodiester increased from 9.0% to 33.9% and 0.79% to 2.64%, respectively, during post-agricultural succession. The increased P limitation and organic P substrates induced higher phosphatase activities, with the highest acid phosphomonoesterase activity observed in secondary forest while the highest phosphodiesterase and alkaline phosphomonoesterase activities observed in grassland. Moreover, structural equation modelling demonstrated a clear increase in microbial production of alkaline phosphomonoesterase and the potential hydrolysis of phosphomonoesters under elevated P limitation. Conclusions In summary, our findings suggested that agricultural abandonment caused redistributions of soil inorganic P to organic P, with alkaline phosphomonoesterase-mediated phosphomonoester turnover playing a crucial role in soil P availability during post-agricultural succession in karst ecosystem.

Rhizosphere processes play a critical role in phosphorus (P) acquisition by plants and microbes, especially under P-limited conditions. Here, we investigated the impacts of nutrient addition and plant species on plant growth, rhizosphere processes, and soil P dynamics. In a glasshouse experiment, blue lupin (Lupinus angustifolius), white clover (Trifolium repens L.), perennial ryegrass (Lolium perenne L.), and wheat (Triticum aestivum L.) were grown in a low-P pasture soil for 8 weeks with and without the single and combined addition of P (33 mg kg−1) and nitrogen (200 mg kg−1). Phosphorus addition increased plant biomass and total P content across plant species, as well as microbial biomass P in white clover and ryegrass. Alkaline phosphatase activity was higher for blue lupin. Legumes showed higher concentrations of organic anions compared to grasses. After P addition, the concentrations of organic anions increased by 11-,10-, 5-, and 2-fold in the rhizospheres of blue lupin, white clover, wheat, and ryegrass, respectively. Despite the differences in their chemical availability (as assessed by P fractionation), moderately labile inorganic P and stable organic P were the most depleted fractions by the four plant species. Inorganic P fractions were depleted similarly between the four plant species, while blue lupin exhibited a strong depletion of stable organic P. Our findings suggest that organic anions were not related to the acquisition of inorganic P for legumes and grasses. At the same time, alkaline phosphatase activity was associated with the mobilization of stable organic P for blue lupin.

Wetlands act as filters, retaining phosphorus (P). The objective of this study was to evaluate the degree of P lability of hydromorphic (Histosol) and non-hydromorphic (Cambisol) soils under natural condition (no P addition) and with mineral P addition. The mineral P added was equivalent to 100% of the maximum phosphorus adsorption capacity, incubated during 0 and 120 days, at depths of 0-10 and 40-60 cm. The sequential P extraction was: labile, moderately labile, low lability, and residual. Under the natural condition, the moderate and low lability fractions were predominant in the Histosol, indicating lower P lability compared to the Cambisol. Total phosphorus (Pt) and organic phosphorus (Po) were higher in the Histosol compared to the Cambisol. After 120 days incubation with mineral P, the labile fraction decreased and the moderately labile fraction increased in the Histosol, demonstrating the effect of time on P stability. The addition of mineral P increased inorganic P (Pi) and also Po in both soils, indicating a strong interaction of mineral P with soil organic matter. The Po extracted with NaOH 0.1 mol L-1 (moderately labile) was predominant in both soils and it was higher in the Histosol when compared to the Cambisol. In general, under both conditions (natural and mineral P addition), the Histosol stored P in more stable forms, reinforcing the need for permanent preservation of wetlands.

Nitrogen (N) and phosphorus (P) are critical to pasture productivity; however, limited information is available on how the single and combined additions of N and P affect soil P fractions and seasonal changes in microbial and biochemical processes linked to P cycling under pasture systems. A two-year field trial was conducted where N (0 or 250 kg ha −1  yr −1 ) and P (0 or 50 kg ha −1  yr −1 ) were applied in a full factorial design to an intensively managed grass-pasture system. Changes in plant growth and nutrient uptake, soil microbial biomass P, soil phosphatase activities, and soil inorganic and organic P fractions were assessed by regular sampling. Phosphorus addition increased Olsen P and shoot P uptake but not shoot biomass compared to the control. In contrast, N addition decreased Olsen P by 23% but increased both shoot biomass and P uptake by 1.6-fold, compared to the control. Microbial biomass P was irresponsive to N and P additions. Phosphatase enzyme activity significantly increased in summer under N addition, which was linked to labile organic P mineralization. After two growing seasons, N addition alone significantly decreased readily-available inorganic P, labile inorganic P, moderately labile inorganic P, and labile organic P by 75, 19, 7, and 28%, respectively, compared to the control. On the other hand, combined N and P addition significantly decreased readily-available inorganic P, labile inorganic P, and labile organic P by 39, 26, and 28%, respectively, but had no impact on moderately labile inorganic P compared to P addition alone. The findings of this study revealed that short-term N fertilization to N-limited grass-pastures can accelerate P cycling by mobilizing labile inorganic and organic P as well as moderately labile inorganic P pools. However, N fertilization combined with P applications exceeding plant requirements cannot mobilize moderately labile inorganic P, which accumulates under high P sorbing soils.