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.

Heterophylly, the plasticity of leaf form in response to environmental conditions, occurs in aquatic and amphibious plants where it modulates water availability, gas exchange and photosynthesis to maximize plant productivity. Rorippa aquatica produces simple leaves in terrestrial conditions but dissected leaves under submerged conditions. Regulation of CIN-TCP transcription factors by miR319 controls leaf complexity in a number of species and we provide evidence that this regulatory module acts in R. aquatica heterophylly. RaTCP1 was identified as the most likely target of Raq-miR319b. Under conditions that induced increased leaf complexity, RaTCP1 expression was reduced whereas Raq-miR319b expression was increased. Overexpression of Raq-miR319 in Arabidopsis thaliana reduced TCP gene expression and increased leaf serration. Similarly, a repressive form of RaTCP1 expressed in either A. thaliana or R. aquatica resulted in more complex leaves. Our results indicate that the environmental induction of dissected leaves in R. aquatica occurs through down-regulation of RaTCP by Raq-miR319.

Macrophytes are critical primary producers in freshwater ecosystem and provide potential crop output to feed the expanding human population, they also have been used to mitigate eutrophication and upgrade the water quality. Aquatic plants adapt themselves to the more complicated, changeable and unstable conditions compared to terrestrial plants, especially the fluctuated nutrient environments. Nitrogen (N) and phosphorus (P) are the key nutrient elements for plants, and their cycles have been massively altered by anthropogenic activities in diverse ecosystems. However, there is still a lack of comprehensive understanding about the adapt mechanisms of N and P stress in aquatic plants. Therefore, we investigated the response mechanisms at the molecular, physiological, and morphological levels in the macrophyte Spirodela polyrhiza under N deficiency, P deficiency, combined N and P deficiency, and total nutrient deficiency using RNA-seq, physiological, and biochemical measurements in this study. We found that the similar response mechanisms are shared between terrestrial plants and this tiny aquatic plant, such as nutrient deficiency-induced root system architecture (RSA) changes and photosynthetic inhibition, interacting of N/P signaling networks and uptake, and the consistent changes of gene expression profiles at transcriptional level. Encouragingly, novel findings have been found in S. polyrhiza. The dramatic accumulation of starch or protein without significantly growth inhibition under nutrient deficiencies, improve the crop output of S. polyrhiza. It has a more complex P-signaling network, which is made up of miR399, PHO2, PHT1 and lncRNAs, and miR399 should be a dual-function regulator in Pi homeostasis of S. polyrhiza. The N assimilation process explained the prioritizing usage of ammonium (NH 4 +)-N in duckweed, enhancing its application to phytoremediation of NH 4 + waste water.

Macrophyte habitats exhibit remarkable heterogeneity encompasses the spatial variation of abiotic and biotic components such as water condition changes, climates and anthropogenic stressors. Environmental factors have been proposed as important drivers in shaping genetic and epigenetic variation of aquatic plants, yet the linking between genetic diversity, epigenetic variation and environmental variables remain largely unclear, especially in clonal aquatic plants. Here, we applied population genetic and epigenetic analysis, in conjunction with the habitats discriminations to detail the environmental factors of which drive intraspecies genetic and epigenetic variations of Ceratophyllum demersum from a subtropical lake. Our results demonstrated that environmental factors were highly correlated to the genetic and epigenetic variation of C. demersum, temperature was a key driver in generating the genetic variation of this aquatic herb. Genetic and epigenetic variation were positively driven by water temperature, climate temperature was defined to exert negative effects on genetic and epigenetic variation. These findings indicate that the genetic and epigenetic variations of this clonal aquatic herb could not be related to the geographic feature, but driven by environmental hierarchal, which confers new benefits of temperature to local genetic and epigenetic variation in aquatic systems.