Which Has a Greater Impact on Plant Functional Traits: Plant Source or Environment?

The deterioration of water quality caused by human activities has triggered significant impacts on aquatic ecosystems. Submerged macrophytes play an important role in freshwater ecosystem restoration. Understanding the relative contributions of the sources and environment to the adaptive strategies of submerged macrophytes is crucial for freshwater restoration and protection. In this study, the perennial submerged macrophyte Myriophyllum spicatum was chosen as the experimental material due to its high adaptability to a variable environment. Through conducting reciprocal transplant experiments in two different artificial environments (oligotrophic and eutrophic), combined with trait network and redundancy analysis, the characteristics of the plant functional traits were examined. Furthermore, the adaptive strategies of M. spicatum to the environment were analyzed. The results revealed that the plant source mainly influenced the operational pattern among the traits, and the phenotypic traits were significantly affected by environmental factors. The plants cultured in high-nutrient water exhibited a higher plant height, longer leaves, and more branches and leaves. However, their physiological functions were not significantly affected by the environment. Therefore, the adaptation strategy of M. spicatum to the environment mainly relies on its phenotypic plasticity to ensure the moderate acquisition of resources in the environment, thereby ensuring the stable and efficient operation of plant physiological traits. The results not only offered compelling evidence on the adaptation strategies of M. spicatum in variable environments but also provided theoretical support for the conservation of biodiversity and sustainable development.

The distinctive level of interaction between carbon and nitrogen metabolisms in the leaves of submerged macrophytes plays a key role in ammonium detoxification.

Possible ammonium detoxification mechanisms have been proposed recently, on submerged macrophytes, evidently illustrating that glutamate dehydrogenase (GDH) plays a greater role in ammonium detoxification compared to the primary glutamine synthetase/glutamate oxaloacetate transaminase (GS/GOGAT) pathway. In the current investigation, we cultured three submerged macrophytes to extreme concentrations of [NH4+-N] of up to 50 mg/L with the aim of clarifying the interaction between carbon and nitrogen metabolisms. The activities of carboxylation enzymes pyruvate orthophosphate dikinase (PPDK) and phosphoenolpyruvate carboxylase (PEPC), in lieu of Rubisco, increased almost two-fold for ammonium tolerant species P. maackianus and M. spicatum, compared with the sensitive species P. lucens. While these enzymes are well known for their central role in CO2 fixation, their inference in conferring resistance to ammonium stress has not been well elucidated before. In this study, we demonstrate that the overproduction of PEPC and PPDK led to improved photosynthesis, better ammonium assimilation and overall ammonium detoxification in M. spicatum and P. maackianus. These findings propose likelihood for the existence of a complementary ammonium detoxification pathway that targets carbon metabolism, thus, presenting a relatively efficient linkage between nitrogen and carbon metabolisms and identify candidate species for practical restoration of fresh water resources.

Transcriptome Analysis of Macrophytes' Myriophyllum spicatum Response to Ammonium Nitrogen Stress Using the Whole Plant Individual.

Ammonium toxicity in macrophytes reduces growth and development due to a disrupted metabolism and high carbon requirements for internal ammonium detoxification. To provide more molecular support for ammonium detoxification in the above-ground and below-ground parts of Myriophyllum spicatum, we separated (using hermetic bags) the aqueous medium surrounding the below-ground from that surrounding the above-ground and explored the genes in these two regions. The results showed an upregulation of asparagine synthetase genes under high ammonium concentrations. Furthermore, the transcriptional down and/or upregulation of other genes involved in nitrogen metabolism, including glutamate dehydrogenase, ammonium transporter, and aspartate aminotransferase in above-ground and below-ground parts were crucial for ammonium homeostasis under high ammonium concentrations. The results suggest that, apart from the primary pathway and alternative pathway, the asparagine metabolic pathway plays a crucial role in ammonium detoxification in macrophytes. Therefore, the complex genetic regulatory network in M. spicatum contributes to its ammonium tolerance, and the above-ground part is the most important in ammonium detoxification. Nevertheless, there is a need to incorporate an open-field experimental setup for a conclusive picture of nitrogen dynamics, toxicity, and the molecular response of M. spicatum in the natural environment.

Comparative chloroplast genome analysis of Sambucus L. (Viburnaceae): inference for phylogenetic relationships among the closely related Sambucus adnata Wall. ex DC Sambucus javanica Blume.

Sambucus L. is found in the family Viburnaceae (syn. Adoxaceae) and encompasses approximately 29 accepted species. The complex morphology of these species has caused continued confusion concerning their nomenclature, classification, and identification. Despite previous attempts to resolve taxonomic complexities in the Sambucus genus, there are still unclear phylogenetic relationships among several species. In this study, the newly obtained plastome of Sambucus williamsii Hance. as well as the populations of Sambucus canadensis L., Sambucus javanica Blume, and Sambucus adnata Wall. ex DC were sequenced, and their sizes, structural similarity, gene order, gene number, and guanine-cytosine (GC) contents were analyzed. The phylogenetic analyses were conducted using the whole chloroplast genomes and protein-coding genes (PCGs). The findings revealed that the chloroplast genomes of Sambucus species exhibited typical quadripartite double-stranded DNA molecules. Their lengths ranged from 158,012 base pairs (bp) (S. javanica) to 158,716 bp (S. canadensis L). Each genome comprised a pair of inverted repeats (IRs), which separated the large single-copy (LSC) and small single-copy (SSC) regions. In addition, the plastomes contained 132 genes, encompassing 87 protein-coding, 37 tRNA, and four rRNA genes. In the simple sequence repeat (SSR) analysis, A/T mononucleotides had the highest proportion, with the most repetitive sequences observed in S. williamsii. The comparative genome analyses showed high similarities in structure, order, and gene contents. The hypervariable regions in the studied chloroplast genomes were trnT-GGU, trnF-GAA, psaJ, trnL-UAG, ndhF, and ndhE, which may be used as candidate barcodes for species discrimination in Sambucus genus. Phylogenetic analyses supported the monophyly of Sambucus and revealed the separation of S. javanica and S. adnata populations. Sambucus chinensis Lindl. was nested within S. javanica in the same clade, collaborating their conspecific treatment. These outcomes indicate that the chloroplast genome of Sambucus plants is a valuable genetic resource for resolving taxonomic discrepancies at the lower taxonomic levels and can be applied in molecular evolutionary studies.

The Above-Ground Part of Submerged Macrophytes Plays an Important Role in Ammonium Utilization.

As a paradoxical nutrient in water ecosystems, ammonium can promote plants growth under moderate concentration, but excess of it causes phytotoxic effects. Previous research has revealed that glutamate dehydrogenase in the above-ground part of submerged macrophytes plays an important role in ammonium detoxification. However, the strategies of ammonium utilization at the whole plant level of submerged macrophytes are still unclear and the role of the above-ground part in nutrient utilization has not been clearly elucidated in previous studies, hence, directly influencing the application of previous theory to practice. In the present research, we combined the methods of isotopic labeling and enzyme estimation to investigate strategies of ammonium utilization by the submerged macrophytes. The results showed that when [NH4 +-N] was 50 mg L-1, 15N taken up through the above-ground parts was 13.24 and 17.52 mg g-1 DW, while that of the below-ground parts was 4.24 and 8.54 mg g-1 DW in Potamogeton lucens and Myriophyllum spicatum, respectively. The ratios of 15N acropetal translocation to uptake were 25.75 and 35.69%, while those of basipetal translocation to uptake were 1.93 and 4.09% in P. lucens and M. spicatum, respectively. Our results indicated that the above-ground part was not only the main part for ammonium uptake, but also the major pool of exogenous ammonium. Besides, the dose-response curve of GDH (increased by 20.9 and 50.2% under 15 and 50 mg L-1 [NH4 +-N], respectively) exhibited by the above-ground parts of M. spicatum indicates that it is the main site for ammonium assimilation of the tolerant species. This study identifies the ammonium utilization strategy of submerged macrophytes and reveals the important role of the above-ground part in nutrient utilization providing new insight into the researches of nutrient utilization by plants and theoretical supports for water restoration by phytoremediation.

Exploring the ammonium detoxification mechanism of young and mature leaves of the macrophyte Potamogeton lucens.

Toxicity in aquatic plants, caused by excess ammonium in the environment, is an important ecological problem and active research topic. Recent studies showed the importance of the enzyme Glutamate Dehydrogenase (GDH) in detoxifying ammonium. However, these results mainly derived from species comparisons, hence some mechanisms may have been obscured due to species differences. Our recent finding that young leaves of Potamogeton lucens were less sensitive to ammonium enrichment, than mature leaves allowed us to study ammonium detoxification within a species. We found that, unlike mature leaves, ammonium-tolerant young leaves of P. lucens could assimilate ammonium mainly through GDH. There was a 38% increase of NADH-dependent GDH in 50 mg/L ammonium concentration compared with 0.1 mg/L. Therefore, this study confirms the hypothesis that the GDH pathway plays a major role in the detoxification of ammonium in freshwater macrophytes.