Matrix-bound phosphine, phosphorus fractions and phosphatase activity through sediment profiles in Lake Chaohu, China

Adsorption of Phosphorus Oxyanions at the FeOOH(goethite)/Water Interface: The Importance of Basicity

P^III-containing H-phosphonate (HPO₃^2-) and its monoethyl ester (fosetyl), essential pesticides for control of oomycete and fungal pathogens, are among the few pesticides transported by both xylem and phloem, making application as folia spray, soil spray, and trunk injection equally effective. To understand bioavailability and efficacy within soils, knowledge of adsorption to soil minerals is important. FeOOH(goethite) is often selected as an archetypal mineral surface. In the present work, H-phosphonate (with pK_a values of 1.5 and 6.78) adsorption onto FeOOH is nearly complete below pH 6 and decreases to negligible amounts by pH 11, following an S-shaped curve. Fosetyl (pK_a: 0.9), in contrast, does not adsorb to any significant extent, regardless of pH. To place these observations in context, adsorption of six other phosphorus oxyanions was investigated, and fitted using a CD-MUSIC model. Phosphate defines a similar S-shaped curve but adsorbs more strongly than H-phosphonate. Despite moderate differences in basicity, pH dependence and extents of adsorption for the four additional diprotic oxyanions methylphosphonate (pK_as: 2.40, 8.00), benzylphosphonate (2.24, 7.93), phenylphosphonate (1.9, 7.47), and phenyl phosphate (1.1, 6.28) are quite similar to those of H-phosphonate. As with fosetyl, the other low pK_a monoprotic oxyanion in our study, phenylphosphinate (pK_a: 1.75), does not adsorb. Basicity, that is, pK_a, is revealed to be the principal determinant of extents of adsorption.

Phosphine as a Biosignature Gas in Exoplanet Atmospheres

A long-term goal of exoplanet studies is the identification and detection of biosignature gases. Beyond the most discussed biosignature gas O₂, only a handful of gases have been considered in detail. In this study, we evaluate phosphine (PH₃). On Earth, PH₃ is associated with anaerobic ecosystems, and as such, it is a potential biosignature gas in anoxic exoplanets. We simulate the atmospheres of habitable terrestrial planets with CO₂- and H₂-dominated atmospheres and find that PH₃ can accumulate to detectable concentrations on planets with surface production fluxes of 10¹⁰ to 10¹⁴ cm^-2 s^-1 (corresponding to surface concentrations of 10s of ppb to 100s of ppm), depending on atmospheric composition and ultraviolet (UV) irradiation. While high, the surface flux values are comparable to the global terrestrial production rate of methane or CH₄ (10¹¹ cm^-2 s^-1) and below the maximum local terrestrial PH₃ production rate (10¹⁴ cm^-2 s^-1). As with other gases, PH₃ can more readily accumulate on low-UV planets, for example, planets orbiting quiet M dwarfs or with a photochemically generated UV shield. PH₃ has three strong spectral features such that in any atmosphere scenario one of the three will be unique compared with other dominant spectroscopic molecules. Phosphine's weakness as a biosignature gas is its high reactivity, requiring high outgassing rates for detectability. We calculate that tens of hours of JWST (James Webb Space Telescope) time are required for a potential detection of PH₃. Yet, because PH₃ is spectrally active in the same wavelength regions as other atmospherically important molecules (such as H₂O and CH₄), searches for PH₃ can be carried out at no additional observational cost to searches for other molecular species relevant to characterizing exoplanet habitability. Phosphine is a promising biosignature gas, as it has no known abiotic false positives on terrestrial planets from any source that could generate the high fluxes required for detection.

Emission and distribution of phosphine in paddy fields and its relationship with greenhouse gases

Phosphine (PH₃), as a gaseous phosphide, plays an important role in the phosphorus cycle in ecosystems. In this study, the emission and distribution of phosphine, carbon dioxide (CO₂) and methane (CH₄) in paddy fields were investigated to speculate the future potential impacts of enhanced greenhouse effect on phosphorus cycle involved in phosphine by the method of Pearson correlation analysis and multiple linear regression analysis. During the whole period of rice growth, there was a significant positive correlation between CO₂ emission flux and PH₃ emission flux (r=0.592, p=0.026, n=14). Similarly, a significant positive correlation of emission flux was also observed between CH₄ and PH₃ (r=0.563, p=0.036, n=14). The linear regression relationship was determined as [PH₃]_flux=0.007[CO₂]_flux+0.063[CH₄]_flux-4.638. No significant differences were observed for all values of matrix-bound phosphine (MBP), soil carbon dioxide (SCO₂), and soil methane (SCH₄) in paddy soils. However, there was a significant positive correlation between MBP and SCO₂ at heading, flowering and ripening stage. The correlation coefficients were 0.909, 0.890 and 0.827, respectively. In vertical distribution, MBP had the analogical variation trend with SCO₂ and SCH₄. Through Pearson correlation analysis and multiple stepwise linear regression analysis, pH, redox potential (Eh), total phosphorus (TP) and acid phosphatase (ACP) were identified as the principal factors affecting MBP levels, with correlative rankings of Eh>pH>TP>ACP. The multiple stepwise regression model ([MBP]=0.456∗[ACP]+0.235∗[TP]-1.458∗[Eh]-36.547∗[pH]+352.298) was obtained. The findings in this study hold great reference values to the global biogeochemical cycling of phosphorus in the future.

Stimulus Response of Au-NPs@GMP-Tb Core-Shell Nanoparticles: Toward Colorimetric and Fluorescent Dual-Mode Sensing of Alkaline Phosphatase Activity in Algal Blooms of a Freshwater Lake

In this study, we demonstrate a colorimetric and fluorescent dual-mode method for alkaline phosphatase activity (APA) sensing in freshwater lake with stimuli-responsive gold nanoparticles@terbium-guanosine monophosphate (Au-NPs@GMP-Tb) core-shell nanoparticles. Initially, the core-shell nanoparticles were fabricated based on Au-NPs decorated with a fluorescent GMP-Tb shell. Upon being excited at 290 nm, the as-formed Au-NPs@GMP-Tb core-shell nanoparticles emit green fluorescence, and the decorated GMP-Tb shell causes the aggregation of Au-NPs. However, the addition of ALP destroys GMP-Tb shell, resulting in the release of Au-NPs from the shell into the solvent. As a consequence, the aggregated Au-NPs solubilizes with the changes in the UV-vis spectrum of the dispersion, and in the meantime, the fluorescence of GMP-Tb shell turns off, which constitutes a new mechanism for colorimetric and fluorescent dual-mode sensing of APA. With the method developed here, we could monitor the dynamic change of APA during an algal bloom of a freshwater lake, both by the naked eye and further confirmed by fluorometric determination. This study not only offers a new method for on-site visible detection of APA but also provides a strategy for dual-mode sensing mechanisms by the rational design of the excellent optical properties of Au-NPs and the adaptive inclusion properties of the luminescent infinite coordination polymers.