Light Requirement Dynamics in Three Common Submerged Macrophytes: From Establishment to Peak Biomass.

The deterioration of the underwater light environment is a key driver of submerged vegetation decline in shallow lakes. However, previous studies have largely focused on the short-term light needs of plants, failing to capture their dynamic requirements across the entire growth period. To quantify these stage-specific dynamics, we investigated three common submerged macrophytes: the rosette-type Vallisneria natans, erect-type Hydrilla verticillata, and canopy-forming Myriophyllum spicatum. Using mesocosm enclosures, we established eight bottom light gradients (0-20% of ambient light intensity) during both seedling and rapid growth stages to assess growth responses. Key findings are as follows: (1) Light requirements varied by species: V. natans < H. verticillata < M. spicatum. (2) Growth traits exhibited distinct responses: shoot density and biomass increased progressively with light, while plant height showed a unimodal response (increasing then declining), reflecting a shift in energy allocation. (3) Light requirements increased with developmental stage: the light compensation point for V. natans, H. verticillata, and M. spicatum increased from 2.1%, 4.4%, and 4.7% (seedling stage) to 3.3%, 10.5%, and 24.1% (rapid growth stage), respectively. (4) An integrated light-biomass model showed that achieving specific biomass targets required 2.4 to 4.7 times more light during rapid growth than during the seedling stage. This study quantifies stage-specific light requirements for submerged macrophytes, providing a theoretical basis for vegetation restoration and light management in shallow lakes.