Sedimentary Organic Matter Load Influences the Ecological Effects and Potential Risks of Submerged Macrophyte Restoration Through Rhizosphere Metabolites

Aims Rehabilitation of submerged vegetation is one of the commonly used techniques for the ecological restoration of shallow lakes. The changes of pollution structure in sediments caused by plant recovery and the rhizosphere chemical process under different sediment organic matter (SOM) levels are theoretical basis for the rational application of plant rehabilitation technology in lake management.Methods A circulating extraction system was designed for in situ collection of rhizospheric metabolites especially for the submerged plants. We explored how Vallisneria natans (V. natans) mediate the changes in sediment N and P through rhizospheric metabolites under low (4.94%) and high (17.35%) SOM levels. Results By analysing 63 rhizospheric metabolites from V. natans, glucitol was found to be 146.82% lower in the low SOM than in the high SOM treatment. NH4-N and NO2-N increased by 57% and 68.39%, respectively, in the high SOM treatment, while approximately one-seventh Inorg-P was transferred from Fe/Al-P to Ca-P in the low SOM treatment. The metabolites lactic acid, 3-hydroxybutyric acid, and phosphoric acid mediated NH4-N accumulation. Additionally, 3-hydroxy-decanoic acid and adipic acid mediated the transformation of Fe/Al-P to Ca-P.Conclusions The growth of V. natans significantly changed Inorg-N or Inorg-P fractions. The changes were SOM level-dependent and rhizosphere metabolites related. This study emphasised the benefit of V. natans rehabilitation at low SOM level. When restoring submerged macrophytes from high SOM sediment, care should be taken due to the release potential of labile N and P forms.

Role of DIN and DON in nitrogen cycle in a humid subtropical forest catchment in northeast Taiwan

<p>Although global models of nitrogen (N) cycling typically focus on nitrate of ecosystem N saturation, dissolved organic nitrogen (DON) is the dominant form of nitrogen export from many watersheds. In previous hypotheses, DON dynamics in the watersheds was treated as being functionally equivalent to inorganic N forms. However, unlike inorganic N, the dynamics of N contained within organic molecules is controlled not only by direct biological demand for N, but also by heterotrophic demand for the reduced C, to which N is attached. During 2016-2018, we evaluated the DON release hypothesis and the passive carbon vehicle hypothesis by comparing streamwater DON, DOC, and DIN concentrations across Fushan experimental forested watershed in the northeast Taiwan. We found that (1) the export of the Fushan Experimental Forest (FEF) is N saturated and (2) the altering nature of the DON release hypothesis and passive carbon vehicle hypothesis between non-event days and typhoon events. Results show that DON concentrations change systematically with increasing nitrate concentrations in all surveys. Among which, DON concentration correlates negatively with nitrate concentration in non-event days but positively during typhoon events. Our results support the coupling between DIN, DON, and DOC concentrations in forested watersheds that are subject to high rates of anthropogenic N loading. In non-event days, the N-containing dissolved organic matter may be in a labile form of carbon. Thus, alleviating heterotrophic N limitation may result in a decrease in DON export (passive carbon vehicle hypothesis), while during typhoon events, DON losses increase as demand for labile N forms attenuates (DON release hypothesis). These hypotheses are not mutually exclusive but represent the potentially contrasting roles of DON within C and N cycles. Our study suggests that bioavailability assays and addition experiments will present variations in the direct biological demand for N and heterotrophic demand for the reduced C, which is informative and necessary for characterizing the processes controlling DON export.<br><br></p><p><strong>Keywords:</strong> DON, DIN, N saturation, DON release hypothesis, passive carbon vehicle hypothesis</p>

Mannan molecular sub-structures control nanoscale glucan exposure in Candida

N-linked mannans (N-mannans) in the cell wall of Candida albicans are thought to mask β-(1,3)-glucan from recognition by Dectin-1, contributing to innate immune evasion. Lateral cell wall exposures of glucan on Candida albicans are predominantly single receptor-ligand interaction sites and are restricted to nanoscale geometries. Candida species exhibit a range of basal glucan exposures and their mannans also vary in size and complexity at the molecular level. We used super resolution fluorescence imaging and a series of protein mannosylation mutants in C. albicans and C. glabrata to investigate the role of specific N-mannan features in regulating the nanoscale geometry of glucan exposure. Decreasing acid labile mannan abundance and α-(1,6)-mannan backbone length correlated most strongly with increased density and nanoscopic size of glucan exposures in C. albicans and C. glabrata, respectively. Additionally, a C. albicans clinical isolate with high glucan exposure produced similarly perturbed N-mannan structures and exhibited similar changes to nanoscopic glucan exposure geometry. We conclude that acid labile N-mannan controls glucan exposure geometry at the nanoscale. Furthermore, variations in glucan nanoexposure characteristics are clinically relevant and are likely to impact the nature of the pathogenic surface presented to innate immunocytes at dimensions relevant to receptor engagement, aggregation and signaling.

Tuning of electronic properties via labile N→B-coordination in conjugated organoboranes

In this report we demonstrate that labile intramolecular N→B-Lewis pair formation can serve to tailor the properties of π-conjugated electronic materials.