Changes in the molecular composition of dissolved organic matter (DOM) and its light-absorbing component (CDOM) along the river–coastal ocean continuum are crucial for better understanding the source and fate of DOM in coastal oceans. Both optical (absorbance and fluorescence) techniques and ultrahigh-resolution mass spectrometry have been widely used to trace DOM cycling. However, to the best of our knowledge, the linkage between these two techniques is rarely investigated along the river–coastal ocean continuum. In this regard, bulk characterization, optical techniques, and ultrahigh-resolution mass spectrometry [Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS)] were applied to determine the DOM chemistry along a spatial transect from the Yangtze River Estuary (YRE) to the East China Sea. The results showed that DOM in the YRE was mainly controlled by the mixing of freshwater and seawater. Besides terrestrial input, multiple sources (tributary input from the Huangpu River, wastewater input, and sediment resuspension and subsequent release at the turbidity maximum zone) have been identified. In addition, the linkages between CDOM and thousands of formulas were developed based on Spearman’s rank correlations between optical parameters and FT-ICR MS peaks. The linkages showed that the molecular groups associated with the optical parameters generally agreed with conventional biogeochemical interpretations. Nevertheless, each technique has its unique advantage and weakness in interpreting DOM composition. Therefore, the combination of the untargeted FT-ICR MS approach and optical techniques could be valuable for studying the DOM sources and transformation in large river estuarine systems.

Desertification reversal is globally significant for the sustainable development of land resources. However, the mechanisms of desertification reversal at the level of plant community are still unclear. We hypothesized that desertification reversal has clear effects on plant community composition, plant functional types (PFTs), and other vegetation characteristics, including plant diversity and biomass, and their changes in the early stages of reversal are more dramatic than in later stages. We investigated the vegetation of four to five different stages of desertification reversal at each of seven large study sites in southwestern Mu Us Sandy Land, China. The results show that the dominant species in very severe desertification areas were replaced by perennial grasses in potential desertification areas. The importance values of annual forbs and perennial sub-shrubs decreased dramatically (from 42.59 and 32.98 to 22.13 and 5.54, respectively), whereas those of perennial grasses and perennial forbs increased prominently (from 13.26 and 2.71 to 53.94 and 11.79, respectively) with the reversal of desertification. Desertification reversal increased the complexity of plant community composition by increasing plant species in each PFT, and C₃ plants replaced C₄ plants to become the dominant PFT with reversal. Plant species richness and species diversity rose overall, and aboveground plant biomass significantly (p < 0.05) increased with the reversal of desertification. Most vegetation characteristics changed more strikingly in the early stages of desertification reversal than in later stages. Our results indicate that the type and composition of the plant community were dramatically affected by desertification reversal. Anthropogenic measures are more applicable to being employed in early stages than in later stages, and Amaranthaceae C₄ plants are suggested to be planted in mobile dunes for the acceleration of desertification reversal. This study is useful for designing strategies of land management and ecological restoration in arid and semiarid regions.

Cotton (Gossypium hirsutum L.) is a promising candidate for an Arsenic (As)-tolerant plant due to its low As accumulation in fibers. The individual arbuscular mycorrhizal fungi (AMF) inoculation or exogenous calcium (Ca²⁺) application is known to enhance heavy metal tolerance in higher plants; however, their synergistic mechanisms in alleviating As stress in cotton remain poorly understood. A three-factor pot experiment was conducted, including two levels of AMF (Funneliformis mosseae C.Walker & A.Schüßler) inoculation (non-inoculated/inoculated), As stress (0/100 mgAs⁵⁺·kg⁻¹soil), and exogenous Ca²⁺ (CaCl₂) application (0/20 mmol·L⁻¹ CaCl₂). AMF inoculation and Ca²⁺ application were investigated for their effects on cotton growth, root morphology, photosynthetic characteristics, osmotic regulators, antioxidant enzyme activities, and ion homeostasis under As stress. Results showed As stress significantly disrupted cotton growth (decreased plant height, shoot and root dry weight) and root morphology (reduced total root length, root area, and root fork number), photosynthetic capacity (reduced Pn, Ci, Fv/Fm, and ΦPSII), osmotic adjustment (decreased proline, soluble sugar and protein), antioxidant defense (inhibited SOD, POD, CAT activities), and K⁺/Ca²⁺ homeostasis (reduced concentration of K⁺ and Ca²⁺, and K⁺/Ca²⁺ ratio). Both AMF inoculation and Ca²⁺ application independently alleviated these adverse effects of As stress. At the same time, AMF symbiosis combined with exogenous Ca²⁺ was better than AMF inoculation or Ca²⁺ application alone in optimizing root architecture, improving stomatal function and photosynthetic efficiency, enhancing osmotic regulator accumulation and antioxidant enzyme activities, and restoring ion balance under As stress. Three-way ANOVA confirmed significant As×AMF×Ca²⁺ interactions on key parameters such as Pn and ΦPSII. In summary, both AMF inoculation and Ca²⁺ application synergistically enhanced cotton As tolerance through regulating growth, root morphology, photosynthetic characteristics, osmotic regulators, antioxidant enzyme activities, and ion homeostasis, demonstrating its potential for sustainable cotton cultivation in As-contaminated soils.