Macromolecular structures, such as lignin and cellulose, are important components of soil organic carbon, the major terrestrial global carbon pool. The degradation of these macromolecules, including lignin and cellulose, in plant-derived soil organic matter, is important to the global carbon cycle. In grasslands, saprotrophic (decomposer) fungi are major decomposers of such organic material. Some of these compounds, such as lignin are relatively resistant to decay by the microbial community if compared with other compound classes such as cellulose. In this work we investigate the involvement of fungi in the decomposition of both lignin and cellulose and look to link the decomposition processes observed in the field to those observed in a laboratory-controlled environment. The key findings of this work are:- Field based experiments in both tropical and temperate environments indicated that lignin can be degraded completely, most likely by white-rot fungi, as shown by the shifts in the [Ac/Al]S, [Ac/Al]G and [S/G] relative lignin decomposition state proxies. The results confirm that even in a very low carbon environment, fungi are able to completely degrade lignin over time. However, lignin is degraded much faster in tropical environments. Culturing experiments showed that it was possible to isolate a number of fungi present on the degraded wheat straw collected in the field, especially soft-rot fungi. When used in microcosm experiments using a range of organic substrates, the relative lignin decomposition state proxies indicated that Absidia cylindrospora and Trichoderma koningii are not able to completely degrade lignin but preferentially degrade cellulose. Cellulose degradation rates are much higher than those of lignin in degraded field samples over time, confirming previous work.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Tropical plant species resist seasonal drought by avoidance or tolerance, keeping or losing leaves, respectively. Since drought resistance is influenced by wood attributes and lignin is a major component of wood, we investigated whether lignin is related to foliar retention time (LR). We selected 22 species, determined the stem lignin content by thioglycolic acid and quantified guaiacyl (G) and syringyl (S) monomers by thioacidolysis and GC-MS analysis. Among these species, we selected 15 species to measure vulnerability to embolism by pneumatic method. In our analyses, were considered measures of wood density, stem water saturation and stem water potential in the dry season, published by other authors. Our analyses showed that there are two ways of surviving drought. A small group of species, for which the lignin does not seem to matter, stores water in the stem and loses leaves right at the end of the rainy season. A large group of species, from early deciduous to evergreens, retains leaves in the dry season for increasingly longer periods the higher the S/G ratio is. Higher values of the S/G ratio allow greater LR by reducing vulnerability to embolism. / EspÃcies de plantas de clima tropical sazonalmente resistem à seca por tolerÃncia ou evitaÃÃo, mantendo ou perdendo folhas, respectivamente. Atributos da madeira estÃo relacionados à resistÃncia à seca e a lignina à um dos principais componentes da madeira. Investigamos se a lignina està relacionada ao tempo de retenÃÃo foliar (LR). Selecionamos 22 espÃcies, determinamos o teor de lignina do caule pelo Ãcido tioglicÃlico e quantificamos os monÃmeros guaiacil (G) e siringil (S) by thioacidolysis e GC-MS analysis. Dentre as espÃcies, selecionamos 15 espÃcies para medir a vulnerabilidade ao embolismo pelo mÃtodo pneumÃtico. IncluÃmos medidas da densidade da madeira, saturaÃÃo de Ãgua no caule e potencial hÃdrico do caule na estaÃÃo seca, publicadas por outros autores. Nossas anÃlises mostraram haver duas maneiras de sobreviver à seca. Um pequeno grupo de espÃcies, para as quais a lignina parece nÃo ter importÃncia, armazena Ãgua no caule e perde folhas logo no final da estaÃÃo chuvosa. Um grande grupo de espÃcies, que vÃo desde decÃduas precoces atà sempre verdes, retÃm folhas na estaÃÃo seca por tempos cada vez mais longos quanto maior a razÃo S/G. Maiores valores da razÃo S/G permitem maior LR por diminuir a vulnerabilidade ao embolismo.

<p dir="ltr">The chemical constituents of terrestrial and atmospheric waters originate from biomass burning, fertilizer runoff, and anthropogenic activity, among other sources, and their multi-phase chemistry is complex. Sunlight plays an essential role in aquatic chemistry. Photosensitizers in terrestrial and atmospheric waters absorb light to form highly reactive species such as triplet excited carbon (³C*), hydroxyl radical (•OH), and singlet oxygen (¹O₂), driving the photochemical transformations of dissolved organic matter (DOM) in the aqueous phase. Of note, these reactive species transform DOM compounds that do not undergo direct photolysis. DOM frequently undergoes a change in optical properties following photochemical processing, with implications for air quality, water quality, and human and animal health. The presence of inorganic minerals, such as the fertilizer compound struvite, in terrestrial or atmospheric waters introduces further complexity and impacts the photochemical processes that occur. Simplified proxy systems are created in the laboratory to simulate aquatic photochemical processes and evaluate the formation and/or photodegradation of photoproducts. These mixtures typically consist of a representative organic carbon (OC) compound and a photosensitizer, along with struvite or another inorganic mineral.</p>