Mechanism of rapid adaptive responses of macrophytes Vallisneria denseserrulata (Makino) to varying visible light transmittance: A mesocosm study

Light transmittance is a closely related and inseparable key environmental limiting factor shaping the presence and distribution of macrophytes in aquatic environments. However, little is known about the responses of the morphology and photosynthetic capacity of macrophytes to different light conditions. Here, we conducted a short-term mesocosm experiment with Vallisneria denseserrulata as subjects, exposing them to the light transmittance of 10%, 20%, 30%, 60%, and 100%. Plant growth indicators and photosynthesis-related indicators were monitored during the 28-day experiment. The results showed that V. denseserrulata responded rapidly to changes in the light environment. Under high light transmittance conditions, V. denseserrulata rapidly expanded to obtain more resources. In low light transmittance conditions, V. denseserrulata mainly maintained its growth, rarely forming ramet, and grew longer leaves and larger leaf areas to improve light acquisition ability. There were 158, 47, 192, and 554 differentially expressed genes (DEGs) were identified in the pairwise comparison of 10%VS100%, 20%VS100%, 30%VS100%, and 60%VS100%, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis suggested that the DEGs were mainly involved in “pigment biosynthetic” and “photosynthesis”. Furthermore, genes involved in the photosynthesis pathway obtained different expression levels in V. denseserrulata between different treatments. The lower the light transmittance, the higher the expression of genes involved in photosynthesis in V. denseserrulata. Therefore, macrophytes have strong plasticity to maintain growth in stressful environments. Synthesis: V. denseserrulata exhibits strong plasticity in morphology, cytochrome production, and photosynthetic pathway regulation to maintain its growth in low-light environments. However, our results also indicated that the degraded underwater light climate surely results in a decreased macrophyte community. These results help elucidate the degradation process of submerged macrophytes in turbid lakes and guide the restoration of aquatic plants in eutrophic lakes.