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Hydrobiologia (2010) 656:514 DOI 10.1007/s10750-010-0441-2
AQUATIC WEEDS
Response of the oating aquatic fern Azolla liculoides to elevated CO2, temperature, and phosphorus levels
Weiguo Cheng Hidemitsu Sakai
Miwa Matsushima Kazuyuki Yagi
Toshihiro Hasegawa
Published online: 3 September 2010 Springer Science+Business Media B.V. 2010
Abstract Azolla liculoides is a oating aquatic fern growing in tropical and temperate freshwater ecosystems. As A. liculoides has symbiotic nitrogen-xing cyanobacteria (Anabaena azollae) within its leaf cavities, it is cultivated in rice paddies to improve N availability and suppress other wetland weeds. To understand how C assimilation and N accumulation in A. liculoides respond to elevated atmospheric carbon dioxide concentration (CO2) in combination with P addition and higher temperatures,
we conducted pot experiments during the summer of 2007 and 2008. In 2007, we grew A. liculoides in pots at two treatment levels of added P fertilizer and at two levels of [CO2] (380 ppm for ambient and 680 ppm for elevated [CO2]) in controlled-environment chambers. In 2008, we grew A. liculoides in four controlled-environment chambers at two [CO2]
levels and two temperature levels (34/26C (day/ night) and 29/21C). We found that biomass and C assimilation by A. liculoides were signicantly increased by elevated [CO2], temperature, and P level (all P \ 0.01), with a signicant interaction between elevated [CO2] and added P (P \ 0.01).
Tissue N content was decreased by elevated [CO2]
and increased by higher temperature and P level (all P \ 0.01). The acetylene reduction assay showed that the N-xation activity of A. liculoides was not signicantly different under ambient and elevated [CO2] but was signicantly stimulated by P addition.
N-xation activity decreased at higher temperatures (34/26C), indicating that 29/21C was more suitable for A. azollae growth. Therefore, we conclude that the N accumulation potential of A. liculoides under future climate warming depends primarily on the temperature change and P availability, and C assimilation should be increased by elevated [CO2].
Keywords Azolla liculoides Carbon
assimilation Elevated atmospheric carbon dioxide
High temperature Nitrogen xation Phosphorus
nutrient
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