Abstract. The contribution of photosynthesis and soil respiration to net land-atmosphere carbon dioxide (CO 2 ) exchange can be estimated based on the differential influence of leaves and soils on budgets of the oxygen isotope composition (δ 18 O) of atmospheric CO 2 . To do so, the activity of carbonic anhydrases (CAs), a group of enzymes that catalyse the hydration of CO 2 in soils and plants, needs to be understood. Measurements of soil CA activity typically involve the inversion of models describing the δ 18 O of CO 2 fluxes to solve for the apparent, potentially catalysed, rate of CO 2 hydration. This requires information about the δ 18 O of CO 2 in isotopic equilibrium with soil water, typically obtained from destructive, depth-resolved sampling and extraction of soil water. In doing so, an assumption is made about the soil water pool that CO 2 interacts with, which may bias estimates of CA activity if incorrect. Furthermore, this can represent a significant challenge in data collection given the potential for spatial and temporal variability in the δ 18 O of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by inferring the rate of CO 2 hydration and the δ 18 O of soil water from the relationship between the δ 18 O of CO 2 fluxes and the δ 18 O of CO 2 at the soil surface measured at different ambient CO 2 conditions. This approach was tested through laboratory incubations of air-dried soils that were re-wetted with three waters of different δ 18 O. Gas exchange measurements were made on these soils to estimate the rate of hydration and the δ 18 O of soil water, followed by soil water extraction to allow for comparison. Estimated rates of CO 2 hydration were 6.8-14.6 times greater than the theoretical uncatalysed rate of hydration, indicating that CA were active in these soils. Importantly, these estimates were not significantly different among water treatments, suggesting that this represents a robust approach to assay the activity of CA in soil. As expected, estimates of the δ 18 O of the soil water that equilibrates with CO 2 varied in response to alteration to the δ 18 O of soil water. However, these estimates were consistently more negative than the composition of the soil water extracted by cryogenic vacuum distillation at the end of the gas measurements with differences of up to −3.94 ‰ VSMOW-SLAP. These offsets suggest that, at least at lower water contents, CO 2 -H 2 O isotope equilibration primarily occurs with water pools that are bound to particle surfaces and are depleted in 18 O compared to bulk soil water.
Los trópicos albergan la mayor biodiversidad del planeta, pero todavía son zonas inexploradas. Entre estas áreas remotas se encuentran los Tepuyes del Valle de Nangaritza, en la provincia de Zamora Chinchipe, al sureste de Ecuador. Constituyen sistemas montañosos aislados de gran importancia biológica y con altos niveles de endemicidad. Debido a estas características, el objetivo principal del estudio es elaborar el primer catálogo de líquenes epifitos de varios Tepuyes del Valle de Nangaritza. Como resultado de dos expediciones realizadas en los Tepuyes, entre 900 y 2000 m de altitud, se recolectaron aproximadamente 1.000 muestras de líquenes en diferentes hábitats: bosque denso piemontano, bosque denso montano bajo, bosque chaparro y páramo arbustivo atípico. Se identificaron 174 especies, pertenecientes a 57 géneros y 26 familias. De ellas, trece especies son nuevos registros para Sudamérica, 64 para Ecuador y 132 para la provincia de Zamora Chinchipe. Se encontraron nuevos quimiótipos para especies de la familia Cladoniaceae. La forma de crecimiento crustácea fue dominante, con alrededor del 40 % de la riqueza total, siendo Graphidaceae la familia con mayor riqueza (27 especies). Predominaron las especies de líquenes con alga verde como fotobionte, presentando Trenthepholia un gran número de especies (66 especies). Este catálogo es una primera aproximación al conocimiento de la diversidad de líquenes de los Tepuyes del Valle de Nangaritza, donde el alto número de nuevos registros indican la falta de conocimiento de la diversidad asociada a estos bosques tropicales.
Deforestation is the most important cause of biodiversity loss in tropical ecosystems. Epiphytic species, lichens and bryophytes, are very sensitive to environmental changes, including those produced by conversion of primary forests into secondary vegetation. However, little is known about the differences between different secondary forests and plantations regarding the epiphytic biota. We compared epiphytic communities among different secondary forests and non-native plantations in southern Ecuador. Four forest types were considered: non-native Pinus patula plantations, monospecific secondary forests of Alnus acuminata, monospecific secondary forests of Andesanthus lepidotus and mixed secondary forests. Within each forest type, two stands were surveyed, establishing a total of 80 plots and analyzing four trees per plot. We estimated lichen and bryophyte cover in four inventories per tree and calculated and compared different metrics for taxonomic and functional diversity, as well as community composition. The results revealed forest type as the major predictor for the species and functional traits richness, and for diversity and composition. In total, 422 taxa were identified (312 lichens and 110 bryophytes), with mixed secondary forests having the richest communities (194 species) and non-native plantations having the lowest richness (105 species). Bryophyte richness was highest in A. lepidotus forests. Taxonomic and functional diversity, and species composition differed greatly among forest types and followed a different pattern depending on the organism considered. Lichens were the most sensitive indicators of environmental conditions associated with different tropical forest types.
Figure S1: IRIS measurement stability for a cylinder of compressed air containing about 500 ppm of CO2. (a) 1 Hz time-series of total CO2 concentration, (b) 1 Hz time-series of δ 18 O of CO2, (c) Allan plot of total CO2 concentration and (d) Allan plot of δ 18 O of CO2.
The contribution of photosynthesis and soil respiration to net land-atmosphere carbon dioxide (CO 2 ) exchange can be estimated based on the differential influence of leaves and soils on budgets of the oxygen isotope composition (δ 18 O) of atmospheric CO 2 . To do so, the activity of carbonic anhydrases (CAs), a group of enzymes that catalyse the hydration of CO 2 in soils and plants, needs to be understood. Measurements of soil CA activity typically involve the inversion of models describing the δ 18 O of CO 2 fluxes to solve for the apparent, potentially catalysed, rate of CO 2 hydration. This requires information about the δ 18 O of CO 2 in isotopic equilibrium with soil water, typically obtained from destructive, depth-resolved sampling and extraction of soil water. In doing so, an assumption is made about the soil water pool that CO 2 interacts with, which may bias estimates of CA activity if incorrect. Furthermore, this can represent a significant challenge in data collection given the potential for spatial and temporal variability in the δ 18 O of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by inferring the rate of CO 2 hydration and the δ 18 O of soil water from the relationship between the δ 18 O of CO 2 fluxes and the δ 18 O of CO 2 at the soil surface measured at different ambient CO 2 conditions. This approach was tested through laboratory incubations of air-dried soils that were re-wetted with three waters of different δ 18 O. Gas exchange measurements were made on these soils to estimate the rate of hydration and the δ 18 O of soil water, followed by soil water extraction to allow for comparison. Estimated rates of CO 2 hydration were 6.8-14.6 times greater than the theoretical uncatalysed rate of hydration, indicating that CA were active in these soils. Impor-tantly, these estimates were not significantly different among water treatments, suggesting that this represents a robust approach to assay the activity of CA in soil. As expected, estimates of the δ 18 O of the soil water that equilibrates with CO 2 varied in response to alteration to the δ 18 O of soil water. However, these estimates were consistently more negative than the composition of the soil water extracted by cryogenic vacuum distillation at the end of the gas measurements with differences of up to −3.94 ‰ VSMOW-SLAP. These offsets suggest that, at least at lower water contents, CO 2 -H 2 O isotope equilibration primarily occurs with water pools that are bound to particle surfaces and are depleted in 18 O compared to bulk soil water.
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