Temporal and spatial responses of the branch and leaf growth relationship to human water flow regulation: a case study on remnant Myricaria laxiflora populations.

Regulation of water flow by dams for flood control and power generation has changed the patterns of water level fluctuation in the lower Yangtze River. By investigating the branch and leaf traits of M. laxiflora plants at various growth recovery stages along the water fluctuation gradient, this study uncovered the spatiotemporal response in the relationships among branch and leaf traits during growth to the regulated water level fluctuations. Results indicated leaf number (LN) and leaf-and-branch volume (LV) rapidly increased during the first 30 d of growth recovery. Afterwards, the increase in LN gradually slowed, while LV continued to increase steadily and was isometric to the increase in leaf-and-branch dry mass (LM). The investment strategy of this plant species changed from 'fast return' to 'slow return' as plant growth was restored. In the upper hydro-fluctuation zone, the LN vs. LM and leaf-and-branch water content (LWC) vs. LM comparisons exhibited negative allometric growth, while the LV vs. LM comparison exhibited positive allometric growth. In the middle hydro-fluctuation zone, the LN vs. LM and LV vs. LM comparisons exhibited isometric growth patterns, while the LWC vs. LM comparison exhibited positive allometric growth. In the lower hydro-fluctuation zone, the LN vs. LM comparison exhibited positive allometric growth, while the LWC vs. LM comparison exhibited negative allometric growth. As water level decreased, the investment strategies of the plants switched from prioritizing LV and LWC to LN, and shifted from 'slow return' to 'fast return'. The above results indicate that changes in water level fluctuation patterns have greatly affected branch and leaf growth, as well as the growth relationships among branch and leaf traits in the remnant populations of M. laxiflora. Growth of these remnant populations, especially those at the lower hydro-fluctuation zone, was seriously affected and exhibited signs of degradation as a result. Regulation of water flow by dams for flood control and power generation has changed the patterns of water level fluctuation in the lower Yangtze River. The human water flow regulation impacts the allometric growth of M. laxiflora in terms of branch and leaf traits, as well as the investment strategies during growth. Clear differences were observed in the growth patterns of branches and leaves at different levels along the water fluctuation gradient. [ABSTRACT FROM AUTHOR]