INTERACTIVE EFFECTS OF ATMOSPHERIC CO2 ENRICHMENT, SALINITY AND FLOODING ON GROWTH OF C-3 (ELYMUS-ATHERICUS) AND C-4 (SPARTINA-ANGLICA) SALT-MARSH SPECIES

The growth response of Dutch salt marsh species (C3 and C4) to atmospheric CO2 enrichment was investigated. Tillers of the C3 species Elymus athericus were grown in combinations of 380 and 720 mul l-1 CO2 and low (0) and high (300 mM NaCl) soil salinity. CO2 enrichment increased dry matter production and leaf area development while both parameters were reduced at high salinity. The relative growth response to CO2 enrichment was higher under saline conditions. Growth increase at elevated CO2 was higher after 34 than 71 days. A lower response to CO2 enrichment after 71 days was associated with a decreased specific leaf area (SLA). In two other experiments the effect of CO2 (380 and 720 mul l-1) on growth of the C4 species Spartina anglica was studied. In the first experiment total plant dry weight was reduced by 20% at elevated CO2. SLA also decreased at high CO2. The effect of elevated CO2 was also studied in combination with soil salinity (50 and 400 mM NaCl) and flooding. Again plant weight was reduced (10%) at elevated CO2, except under the combined treatment high salinity/non-flooded. But these effects were not significant. High salinity reduced total plant weight while flooding had no effect. Causes of the salinity-dependent effect of CO2 enrichment on growth and consequences of elevated CO2 for competition between C3 and C4 species are discussed.