No abstract

Despite the high relevance of communities dominated by lichens, mosses and cyanobacteria living on the soil surface (biocrusts) for ecosystem functioning in drylands worldwide, no study to date has investigated the decomposition of biocrust-forming lichen litter in situ. Thus, we do not know whether the drivers of its decomposition are similar to those for plant litter (e.g., importance of abiotic degradation through UV radiation), the magnitude of lichen decomposition rates and whether they will be affected by climate change. Here we report results from a litter decomposition experiment carried out with two biocrust-forming lichens (Diploschistes diacapsis and Cladonia convoluta) in central Spain. We evaluated how lichen decomposition was affected by warming, rainfall exclusion and the combination of both. We also manipulated the incidence of UV radiation using mesh material that blocked 10% or 90% of incoming UV radiation. Our results indicate that lichens decompose as fast as some plants typical of the region (k~0.3) and that the chemical composition of their thallus drives litter decomposition rates.Warming increased decomposition rates of both lichen species, and mediated the effects of photodegradation. While UV exposure accelerated the decomposition of D. diacapsis, it slowed down that of C. convoluta. Our results indicate that biocrust-forming lichens can decompose in the field at a rate similar to that of vascular plants, and that this process will be affected by warming. Our findings further highlight the need of incorporating biocrusts into carbon cycling models to better understand and forecast climate change impacts on terrestrial biogeochemistry.

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25Despite the high relevance of communities dominated by lichens, mosses and cyanobacteria 26 living on the soil surface (biocrusts) for ecosystem functioning in drylands worldwide, no study 27 to date has investigated the decomposition of biocrust-forming lichen litter in situ. Thus, we do 28 not know whether the drivers of its decomposition are similar to those for plant litter (e.g., 29importance of abiotic degradation through UV radiation), the magnitude of lichen decomposition 30 rates and whether they will be affected by climate change. Here we report results from a litter 31 decomposition experiment carried out with two biocrust-forming lichens (Diploschistes 32 diacapsis and Cladonia convoluta) in central Spain. We evaluated how lichen decomposition 33 was affected by warming, rainfall exclusion and the combination of both. We also manipulated 34 the incidence of UV radiation using mesh material that blocked 10% or 90% of incoming UV 35 radiation. Our results indicate that lichens decompose as fast as some plants typical of the region 36 (k~0.3) and that the chemical composition of their thallus drives litter decomposition rates. 37Warming increased decomposition rates of both lichen species, and mediated the effects of 38 photodegradation. While UV exposure accelerated the decomposition of D. diacapsis, it slowed 39 down that of C. convoluta. Our results indicate that biocrust-forming lichens can decompose in 40 the field at a rate similar to that of vascular plants, and that this process will be affected by 41 warming. Our findings further highlight the need of incorporating biocrusts into carbon cycling 42 models to better understand and forecast climate change impacts on terrestrial biogeochemistry. 43 Lichen litter decomposition 3 44

El CO2 del suelo se produce por la mineralización de la materia orgánica y la respiración de organismos del suelo. Las biocostras contribuyen a dicho f lujo y son claves en el funcionamiento de ecosistemas áridos y semiáridos. Esta investigación se realizó en áreas de matorral desértico micróf ilo donde se seleccionaron cuatro microambientes: área abierta sin biocostras (Aa), área abierta con biocostras (AaC), bajo planta sin biocostras (Bp) y bajo planta con biocostras (BpC). Las biocostras estuvieron constituidas predominantemente por líquenes y cianobacterias. Se probaron las siguientes hipótesis: i) las biocostras contribuyen, en mayor medida que las plantas vasculares de estas áreas, a la respiración del suelo; ii) la respiración del suelo es mayor en los microambientes con biocostras que en áreas abiertas sin biocostras; iii) las tasas de respiración del suelo aumentan conforme aumenta la temperatura del suelo, independientemente de la presencia/ausencia de biocostras. La respiración se midió in situ con un equipo EGM-4 con cámara cerrada de respiración de suelo. Los datos se analizaron mediante pruebas de Kruskal Wallis y U de Mann Whitney. La relación entre temperatura y tasa de respiración de suelo se evaluó mediante correlación de Spearman. Los análisis estadísticos se realizaron en el programa SPSS® Statistics versión 19. Los resultados mostraron que la tasa de respiración promedio (3.03 μmol CO2 m-2 s-1) fue mayor en suelo con biocostras que sin éstas. Las tasas de respiración dif irieron entre micrositios. Los microambientes AaC, BpC y Bp presentaron mayores tasas de respiración y fueron iguales entre sí y diferentes de Aa; si bien este último fue igual a Bp. Los resultados mostraron una relación positiva entre respiración y temperatura del suelo para todos los microambientes. Se concluye que las tasas de respiración fueron mayores en las áreas que presentaban cobertura de biocostras ≥ 40%, tanto en presencia como en ausencia de plantas vasculares, que en suelo sin biocostras.