Open AccessEffects of CO 2 enrichment on photosynthesis, growth, and nitrogen metabolism of the seagrass Z ostera noltii
Author(s) -
Alexandre Ana,
Silva João,
Buapet Pimchanok,
Björk Mats,
Santos Rui
Publication year - 2012
Publication title -
ecology and evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.17
H-Index - 63
ISSN - 2045-7758
DOI - 10.1002/ece3.333
Subject(s) - photosynthesis , seagrass , zostera , glutamine synthetase , nitrate , nitrate reductase , nitrogen , ammonium , botany , mesocosm , nitrogen cycle , zostera marina , carbon fixation , biology , chemistry , ecosystem , ecology , glutamine , biochemistry , organic chemistry , amino acid
Abstract Seagrass ecosystems are expected to benefit from the global increase in CO 2 in the ocean because the photosynthetic rate of these plants may be C i ‐limited at the current CO 2 level. As well, it is expected that lower external p H will facilitate the nitrate uptake of seagrasses if nitrate is cotransported with H + across the membrane as in terrestrial plants. Here, we investigate the effects of CO 2 enrichment on both carbon and nitrogen metabolism of the seagrass Z ostera noltii in a mesocosm experiment where plants were exposed for 5 months to two experimental CO 2 concentrations (360 and 700 ppm). Both the maximum photosynthetic rate (P m ) and photosynthetic efficiency ( α ) were higher (1.3‐ and 4.1‐fold, respectively) in plants exposed to CO 2 ‐enriched conditions. On the other hand, no significant effects of CO 2 enrichment on leaf growth rates were observed, probably due to nitrogen limitation as revealed by the low nitrogen content of leaves. The leaf ammonium uptake rate and glutamine synthetase activity were not significantly affected by increased CO 2 concentrations. On the other hand, the leaf nitrate uptake rate of plants exposed to CO 2 ‐enriched conditions was fourfold lower than the uptake of plants exposed to current CO 2 level, suggesting that in the seagrass Z . noltii nitrate is not cotransported with H + as in terrestrial plants. In contrast, the activity of nitrate reductase was threefold higher in plant leaves grown at high‐ CO 2 concentrations. Our results suggest that the global effects of CO 2 on seagrass production may be spatially heterogeneous and depend on the specific nitrogen availability of each system. Under a CO 2 increase scenario, the natural levels of nutrients will probably become limiting for Z . noltii . This potential limitation becomes more relevant because the expected positive effect of CO 2 increase on nitrate uptake rate was not confirmed.