The Free Air CO 2 Enrichment (FACE) system has proved suitable for exposing plants to elevated [CO 2 ] with minimal disturbance of their natural environment. Here we describe a FACE facility in a floodplain wetland in detail and, additionally, its performance after the first year of operation (2012). The FACE system consisted of six 3-m diameter emission rings in which Phragmitesaustralis was grown. The target [CO 2 ] was 550 µmol mol-1 and fertilization was carried out continuously. Daily temporal [CO 2 ] performance was adequate with 61% and 83% of air samples at the ring's centre having a [CO 2 ] within 10% and 20% of the target, respectively, with values closest to their target during summer months and daytime. Spatial [CO 2 ] distribution showed no significant gradients across the ring. Increased wind speed improved the system's spatial performance, as [CO 2 ] was within ±10% of the target in the whole ring. Across the entire fertilization season, CO 2 requirements for maintaining a mean [CO 2 ] of 582 µmol mol-1 in wetland plots averaged 17.4 kg CO 2 ring-1 day-1. Our requirements (2.5 kg CO 2 m-2 day-1) were very low compared to other FACE systems, demonstrating its high potential to study the effects of elevated CO 2 in wetlands at low cost.
Clonal reproduction of Azolla filiculoides Lam.: implications for invasivenessClonal reproduction of Azolla filiculoides Lam., an aquatic floating fern, native from the American subtropics and a recent invader of Mediterranean wetlands, was assessed experimentally. Shoot fragmentation of the species was quantified under suitable room conditions for optimum growth. Azolla fililculoides showed high longevity, a low mortality percentage and a high potential for clonal reproduction (biomass obtained by shoot fragmentation from only one individual was multiplied by 100). This last attribute changed over time: first generations developed a high number of propagules, a number which decreased progressively in later generations until the end of the experiment. The results of this experiment will be useful for understanding Azolla's success within invaded habitats.
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