The effects of elevated CO2 on clonal growth and nutrient content of submerge plant Vallisneria spinulosa

An approximately four months long glasshouse experiment was conducted to examine the effects of elevated carbon dioxide (CO2) concentration (1000 ± 50 μmol mol−1) in the atmosphere on biomass accumulation and allocation pattern, clonal growth and nitrogen (N), phosphorus (P) accumulation by the submerged plant Vallisneria spinulosa Yan. Elevated CO2 significantly increased V. spinulosa total fresh biomass (≈130%) after 120 days, due to more biomass accumulation in all morphological organs than in those at ambient CO2 (390 ± 20 μmol mol−1). About 75% of the additional total biomass at elevated CO2 was accounted for by leaf and rhizome (above ground) biomass and only 25% of it belonged to root and turion (below ground). However, the turions biomass exhibited a greater increase rate than that of organ above ground, which caused reduction in the above/below ground biomass ratio. The clonal growth of V. spinulosa responded positively to elevated CO2. The number of primary ramets increased up to 1.4-folds at elevated CO2 and induced a dense growth pattern. For nutrients absorption, concentration of N in leaf and in turion was significantly (p ⩽ 0.05) reduced by 13.4% and by 15.7% in elevated CO2 and were not affected in both root and rhizome. Percent P, in contrast, was significantly (p ⩽ 0.05) enhanced in all of the organs, ranging from 35% to 147%, except for turion. Compared with those in ambient CO2, the mean accumulation per ramet of N and P significantly higher in elevated CO2. These results showed that elevated CO2 could promote submerged plant biomass accumulation, and it should be an adaptive strategy for clonal plants to increase the nutrient absorption efficiency of root and reproduce more clonal ramets to exploit enough resources to match with higher growth in elevated CO2.