Resumen La repelencia al agua del suelo (RAS) se atribuye a la acumulación de compuestos hidrofóbicos (lípidos), pero su extracción no siempre elimina la RAS, lo que sugiere que componentes macromoleculares no extraíbles también pueden estar relacionados con una RAS. Se han estudiado suelos quemados (B) y control (UB) del Parque Nacional de Doñana (Huelva, España) bajo dos tipos de vegetación (alcornoque y brezo) y fracciones de suelo: gruesa (1-2 mm) y fina (<0.05 mm). La composición molecular de la materia orgánica del suelo (MOS) se analizó mediante espectrometría de masas de ultra-alta resolución. Además, se empleó la regresión por mínimos cuadrados parciales (PLS) para explorar la relación entre la RAS y la MOS definida por la abundancia de los 1221 compuestos orgánicos comunes. También se utilizaron índices para obtener gráficas que faciliten la identificación de biomarcadores de la RAS. En los suelos quemados, la RAS estaba significativamente relacionada (P<0.05) con compuestos aromáticos y condensados, mientras que, en los suelos control, la MOS incluía compuestos aromáticos y ligninas. En las fracciones finas, la RAS estuvo relacionada principalmente con lípidos, pero, no se encontró correlación en las fracciones gruesas. Los resultados permiten concluir que la hidrofobicidad depende de varias famílias de compuestos orgánicos. La combinación de la FT-ICR/MS con herramientas estadísticas ha facilitado la obtención de nuevos biomarcadores de RAS.

Abstract Soil water repellency (SWR) is often attributed to the accumulation of hydrophobic organic compounds, mainly lipids. Nonetheless, lipid extraction not always suppress SWR and unextractable soil constituents may be related with residual SWR. Burnt (B) and unburnt (UB) soils (Doñana National Park, Huelva) under two vegetations (cork oak and heather) and two soil fractions, coarse (1-2 mm) and fine (<0.05 mm) were studied. Soil organic matter (SOM) molecular composition was studied by ultra-high resolution mass spectrometry. Partial least squares regression (PLS) was employed to explore SWR in function the abundance of the 1221 common compounds found. An omic approach using various indices (e.g., factor loadings of PLS models, etc,) was applied to identify compounds which could be used as proxies for SWR. In the case of B soils, SWR was related (P< 0.05) to aromatic and condensed compounds, while in UB soils it relied mainly on aromatics and lignins. In the fine fractions, lipids were associated with SWR, and no correlation was found in the coarse fractions. In conclusion, hydrophobicity was related to lipids as expected, but also to lignin and aromatic components. The combination of FT-ICR/MS with graphical statistical approach was effective in finding molecular predictors of SWR.

Resumo O presente estudo teve como objetivo identificar a flora e a vegetação dos afloramentos rochosos isolados e de baixa altitude (lajedos), na vegetação de Caatinga Arbustiva Aberta, que se encontram nos municípios de Sobral, Groaíras e Santa Quitéria, no estado do Ceará, Brasil e propor uma classificação fitossociológica para estas comunidades xerófilas. Foram definidas cinco áreas de coleta de dados com elevada proporção de rochas expostas (> 80%) onde as excursões de campo decorreram em março de 2014 e 2015 (3º56’S e 40º23’W, 4º01’S e 40º05’W, 4º07’S e 40º08’W, 4º09’S e 40º09’W e 4º03’S e 40º00’W). No estudo da vegetação aplicou-se os métodos TWINSPAN (two-way indicator species analysis) e o clássico sigmatista de Braun-Blanquet. As áreas mínimas dos inventários fitossociológicos variaram de 8 a 16 m2. Foram coletadas as espécies vegetais que crescem em fissuras, fendas e ilhas de vegetação que se encontram em afloramentos rochosos. Foram registradas 88 espécies, distribuídas em 59 gêneros e 30 famílias botânicas. Fabaceae foi a família que se destacou em riqueza específica (20 spp.), seguida por Poaceae (dez spp.), Euphorbiaceae (sete spp.) e Convolvulaceae (seis spp.). Quanto ao endemismo foram registradas, em vegetação rupestre, 19 espécies endêmicas para o Brasil. Na análise fitossociológica da vegetação propôs-se estudar a comunidade de Pilosocereus gounellei (FA.C.Weber) Byles & Rowley e Encholirium spectabile Mart. ex Schult. & Schult.f. e a de Crateva tapia L. e Combretum leprosum Mart.

Abstract In this study, we aim to identify flora and vegetation of low-elevation rocky outcrops (lajedos) in “Caatinga Arbustiva Aberta” (open shrublands) to propose a phytosociological classification for xerophilous communities. The study areas are located at the municipalities of Sobral, Groaíaras and Santa Quitéria (Ceará state, Brazil). We selected five stations comprising areas with high proportion of bare rocks (> 80%), and the field work were conducted in March 2014 and 2015 respectively (3º56’S and 40º23’W, 4º01’S and 40º05’W, 4º07’S and 40º08’W, 4º09’S and 40º09’W and 4º03’S and 40º00’W). We have applied the TWINSPAN (two-way indicator species analysis) and Braun-Blanquet methods. The minimum areas of phytosociological inventories ranged from 8 to 16 m2. Floristic relevés were made and all the plant species growing in cracks, crevices and small vegetation "islands" were identified. The floristic list is composed of 88 species, distributed in 59 genera and 30 families. Fabaceae was the most representative in species richness, 20 species, followed by Poaceae (10 spp.), Euphorbiaceae (7 spp.) and Convolvulaceae (6 spp.). We identified 19 Brazilian endemisms. Following phytosociological analysis of vegetation we found two different communities: Pilosocereus gounellei FA.C.Weber) Byles & Rowley and Encholirium spectabile Mart. ex Schult. & Schult.f. and the Crateva tapia L. and Combretum leprosum Mart.