Flooding timing and frequency may have different effects on the growth and carbon metabolism of plants in wetlands. We tested this hypothesis using three marsh plants in Sanjiang Plain, which were growing in different flooding timing and frequency environments for 24 days. The three marsh plants in different elevations along a water-level gradient, high-elevation species Calamagrostis angustifolia, mid-elevation species Carex limosa and low-elevation species Carex lasiocarpa. Our experiment included 6 kinds of treatments: control, longer flooding timing, medial flooding timing and frequency (2 treatments), and higher flooding frequency (2 treatments). Longer flooding timing and higher flooding frequency treatments led to similar reductions in biomass accumulation and relative growth rate of Calamagrostis angustifolia, whereas growth of Carex limosa was not affected by either flooding timing or frequency. However, biomass accumulation and relative growth rate of Carex lasiocarpa was only reduced by the higher flooding frequency. Starch and soluble sugar contents of Calamagrostis angustifolia were negatively affected by flooding frequency. On Carex limosa, higher flooding frequency resulted in higher starch content, but longer flooding timing led to accumulated starch content in Carex lasiocarpa. Soluble sugar contents of Carex lasiocarpa and Carex limosa were not affected by either flooding timing or flooding frequency. These results indicated that growth responses of the three marsh plants to flooding timing and frequency was closely related to the different physiology of carbohydrate metabolism.
