Synergistic interactions of CO2 enrichment and nitrogen deposition promote growth and ecophysiological advantages of invading Eupatorium adenophorum in Southwest China

Molecular bases for the stronger plastic response to high nitrate in the invasive plant Xanthium strumarium compared with its native congener

MAIN CONCLUSION

High expressions of nitrate use and photosynthesis-related transcripts contribute to the stronger plasticity to high nitrate for the invader relative to its native congener, which may be driven by hormones. Strong phenotypic plasticity is often considered as one of the main mechanisms underlying exotic plant invasions. However, few studies have been conducted to investigate the related molecular mechanisms. Here, we determined the differences in the plastic responses to high nitrate between the invasive plant X. strumarium and its native congener, and the molecular bases by transcriptome analysis and quantitative real-time PCR validation. Our results showed that the invader had higher plasticity of growth, nitrogen accumulation and photosynthesis in responses to high nitrate than its native congener. Compared with its congener, more N utilization-related transcripts, including nitrate transporter 1/peptide transporter family 6.2 and nitrate reductase 1, were induced by high nitrate in the root of X. strumarium, improving its N utilization ability. More transcripts coding for photosynthetic antenna proteins were also induced by high nitrate in the shoot of X. strumarium, enhancing its photosynthesis. Hormones may be involved in the regulation of the plastic responses to high nitrate in the two species. Our study contributes to understanding the molecular mechanisms underlying the stronger plasticity of the invader in responses to high nitrate, and the potential function of plant hormones in these processes, providing bases for precise control of invasive plants using modern molecular techniques.

Nitrogen fertilization and CO2 concentration synergistically affect the growth and protein content of Agropyron mongolicum

Background

The nitrogen (N) and protein concentrations in plant tissues exposed to elevated CO₂ (eCO₂) generally decline , such declines in forage grass composition are expected to have negative implications for the nutritional and economic value of grass. Plants require N for the production of a photosynthetically active canopy and storage proteins in the tissues, whose functionality will strongly influence productivity and quality. The objective of this study was to investigate whether eCO₂ plus N-fertilization increases growth and N nutrition of Agropyron mongolicum, and the dependence of this improvement on the coordination between root and leaf development.

Methods

We analyzed A. mongolicum from field-grown within the open-top chambers (OTCs) facility under two atmospheric CO₂ (ambient, 400 ± 20 µmol mol^-1, aCO₂, and elevated, 800 ± 20 µmol mol^-1, eCO₂) and three N-fertigation treatments (control, low N-fertigation , and high N-fertigation) for two months.

Results

Elevated CO₂ plus N-fertigation strongly increased shoot and root biomass, and the nitrogen and protein concentrations of A. mongolicum compared to those plants at aCO₂ levels. Increased N content in leaves and reduced specific leaf area (SLA) at a high N supply could alleviate photosynthetic acclimation to eCO₂ and drive the production of greater shoot biomass with the potential for higher photosynthesis, productivity, and nutritional quality. The increased root length (RL), the ratio of total aboveground N taken up per RL (TN/RL), stomatal conductance (Gs), and transpiration rate (Tr) contribute to the transpiration-driven mass flow of N, consequently increasing N uptake by roots. In addition, a smaller percentage of N remained as unassimilated nitrate ( NO 3 - ) under eCO₂, indicating that assimilation of NO 3 - into proteins was not inhibited by eCO₂. These findings imply that grass productivity and quality will enhance under anticipated elevated CO₂ concentration when effective management measures of N-fertilization are employed.

Elevated CO2 and Increased N Intensify Competition between Two Invasive Annual Plants in China

As multiple invaders often co-occur, understanding the interactions between different invasive species is important. Previous studies have reported on invasional meltdown and neutral and interference relationships between invasive species. However, interspecific interactions may vary with environmental change owing to the different responses of interacting invaders. To better understand the interaction of notorious invasive alien plants under CO₂ enrichment and N deposition, the growth characteristics of common ragweed (Ambrosia artemisiifolia) and redroot pigweed (Amaranthus retroflexus) were studied when they were planted in monoculture (4Rag and 4Pig) or mixture (1Rag:3Pig, 2Rag:2Pig, 3Rag:1Pig) under four environmental treatments: elevated CO₂, increased N, elevated CO₂ + increased N and a control. Increased N positively affected almost all the traits (basal stem diameter, height, shoot biomass, root biomass and total biomass) of common ragweed, except for branch number and root-shoot ratio. But increased N only promoted redroot pigweed's height and basal stem diameter. interspecific competition promoted basal stem diameter and number of branches but decreased root biomass of common ragweed, and the basal stem diameter was significantly higher in 1Rag:3Pig and 2Rag:2Pig compared to the other two treatments. interspecific competition inhibited almost all the characteristics of redroot pigweed. The interaction between elevated CO₂ and increased N also increased the biomass characteristics (shoot biomass, root biomass and total biomass) of common ragweed. However, elevated CO₂ inhibited the root biomass of redroot pigweed. The results indicated that common ragweed was a superior competitor under conditions of elevated CO₂ and increased N. Moreover, environmental change might strengthen the super-invasive plant common ragweed's competitive ability.

Differences and related physiological mechanisms in effects of ammonium on the invasive plant Xanthium strumarium and its native congener X. sibiricum

Few studies explore the effects of nitrogen forms on exotic plant invasions, and all of them are conducted from the perspective of nitrogen form utilization without considering the effects of ammonium toxicity. The invasive plant Xanthium strumarium prefers to use nitrate, while its native congener X. sibiricum prefers to use ammonium, and the invader is more sensitive to high ammonium based on our preliminary observations. To further reveal the effects of nitrogen forms on invasiveness of X. strumarium, we studied the difference and related physiological mechanisms in sensitivity to ammonium between these species. With increasing ammonium, total biomass, root to shoot ratio and leaf chlorophyll content of X. strumarium decreased, showing ammonium toxicity. For X. sibiricum, however, ammonium toxicity did not occurr. With increasing ammonium, ammonium concentration increased in leaves and roots of X. strumarium, which is associated with the decreased activities of glutamine synthetase and glutamate synthase and the increased ammonium uptake; and consequently the contents of hydrogen peroxide and malondialdehyde also increased, which is associated with the decreased contents of reduced glutathione and ascorbic acid. By contrast, the abilities of ammonium assimilation and antioxidation of X. sibiricum were less affected by the increase of ammonium, and the contents of ammonium nitrogen, hydrogen peroxide and malondialdehyde in leaves and roots were significantly lower than those in X. strumarium. Our results indicate that ammonium accumulation and oxidative damage may be the physiological mechanisms for the ammonium toxicity of X. strumarium, providing a possible explanation that it generally invades nitrate-dominated and disturbed habitats and a theoretical basis for future studies on the control of invasive plants by regulating soil nitrogen.

Induction of apoptosis and autophagy via mitochondria- and PI3K/Akt/mTOR-mediated pathways by E. adenophorum in hepatocytes of saanen goat

E. adenophorum has reported to cause hepatotoxicity. But, the precise effects of E. adenophorum on hepatocytes is unclear. Saanen goats were fed on E. adenophorum to detect the cytotoxicity effects of E. adenophorum on hepatocytes. Our study has shown that the typical apoptotic features, the increasing apoptotic hepatocytes and activated caspase-9, −3 and the subsequent cleavage of PARP indicated the potent pro-apoptotic effects of E. adenophorum. Moreover, the translocation of Bax and Cyt c between mitochondria and cytosol triggering the forming of apoptosome proved that the mitochondria-mediated apoptosis was triggered by E. adenophorum. Furthermore, E. adenophorum increased the MDC-positive autophagic vacuoles and the subcellular localization of punctate LC3, the ratio of LC3-II/LC3-I and the protein levels of Beclin 1, but decreased that of P62, indicating the potent pro-autophagic effects of E. adenophorum. In addition, E. adenophorum significantly inhibited the protein leves of p-PI3K, p-Akt and p-mTORC1, but increased PTEN and p-AMPK. Also, the p-mTORC2 and p-Akt Ser473 were inhibited, indicating that the supression of mTORC2/Akt pathway could induce the autophagy of hepatocytes. The autophagy-realted results indicated that the inhibition of PI3K/Akt/mTORC1- and mTORC2/Akt-mediated pathways contributed to the pro-autophagic activity of E. adenophorum. These findings provide new insights to understand the mechanisms involved in E. adenophorum-caused hepatotoxicity of Saanen goat.

Contrasting responses in the growth and energy utilization properties of sympatric Populus and Salix to different altitudes: implications for sexual dimorphism in Salicaceae

An interesting ecological and evolutionary puzzle arises from the observations of male-biased sex ratios in genus Populus, whereas in the taxonomically related Salix, females are generally more dominant. In the present study, we combined results from a field investigation into the sex ratios of the Salicaceous species along an altitudinal gradient on Gongga Mountain, and a pot experiment by monitoring growth and energy utilization properties to elucidate the mechanisms governing sexual dimorphism. At middle altitudes 2000 and 2300 m, the sex ratios were consistent with a 1:1 equilibrium in sympatric Populus purdomii and Salix magnifica. However, at the lower and higher ends of the altitudinal gradient, skewed sex ratios were observed. For example, the male:female ratios were 1.33 and 2.36 in P. purdomii at 1700 and 2600 m respectively; for S. magnifica the ratio was 0.62 at 2600 m. At 2300 m, the pot-grown seedlings of both species exhibited the highest biomass accumulation and total leaf area, simultaneously with the balanced sex ratios in the field. At 3300 m, the specific leaf area in male P. purdomii was 23.9% higher than that of females, which may be the morphological cause for the observed 19.3% higher nitrogen allocation to Rubisco, and 20.6% lower allocation to cell walls. As such, male P. purdomii showed a 32.9% higher foliar photosynthetic capacity, concomitant with a 12.0% lower construction cost. These properties resulted in higher photosynthetic nitrogen- and energy-use efficiencies, and shorter payback time (24.4 vs 40.1 days), the time span that a leaf must photosynthesize to amortize the carbon investment. Our results thus suggested that male P. purdomii evolved a quicker energy-return strategy. Consequently, these superior energy gain-cost related traits and the higher total leaf area contributed to the higher growth rate and tolerance in stress-prone environments, which might, in part, shed new light on the male-biased sex ratios in Populus. However, no significant sexual difference was observed in S. magnifica for all the above parameters, thereby implying that the female-biased sex ratios in Salix cannot be explained in terms of the energy-use properties studied here.

Nutrient enrichment alters impacts of Hydrocotyle vulgaris invasion on native plant communities

Nutrients may affect the invasiveness of alien plants and the invasibility of native plant communities. We performed a greenhouse experiment to investigate the interactive effect of invasion by a clonal herb Hydrocotyle vulgaris and nutrient enrichment on biomass and evenness of native plant communities. We established three types of plant communities (H. vulgaris alone, native plant communities without or with H. vulgaris) under low and high levels of nutrients. Native communities consisted of eight native, terrestrial species of three functional groups, i.e. four grasses, two legumes, and two forbs. Invasion of H. vulgaris had no effect on biomass of the native community, the functional groups, or the individual species. High nutrients increased biomass of grasses, but reduced evenness of the community. High nutrients also decreased the competitive effect, and the relative dominance index of H. vulgaris. Therefore, high nutrients reduced the competitive ability of H. vulgaris and enhanced the resistance of the native community to invasion. The results provide a basis for management strategies to control the invasion and spread of H. vulgaris by manipulating resource availability to support native communities.

Physiological and proteomic analysis reveals the different responses of Cunninghamia lanceolata seedlings to nitrogen and phosphorus additions

Both nitrogen (N) and phosphorus (P) additions in soils can increase tree photosynthetic rate (Pn), biomass accumulation and further increase primary production of plantation. However, the improved photosynthetic ability is varied from the added nutrient types and the mechanisms are sophisticated. In this study, an iTRAQ-based quantitative proteome combined with physiological analysis of Chinese fir (Cunninghamia lanceolata) leaves was performed to determine the common and different responses on photosynthetic process to the N and P additions. The results showed that, either N or P added in soils significantly increased Pn, but N addition had more positive effects than P addition in improving photosynthetic ability. Physiologically, N addition caused more in improving photosynthetic rate than P addition, which attributes to higher leaf N and chlorophyll contents, enlarged chloroplast size and more number of thylakoids. Proteomic data revealed that the increased Pn to N and P additions may attribute to the increased abundance of proteins involved in carbon fixation and RuBP regeneration during the light-independent reactions. However, N addition increased the abundance of photosystem II related proteins and P addition increased the abundance of photosystem I related proteins. Additionally, proteomic data also gave some clues on the different metabolic processes caused by N and P additions on glycolysis and TCA cycle, which were potentially related to higher growth and developmental rates of C. lanceolata. Therefore, this study provides new insights into the different photosynthesis and metabolic processes of Chinese fir in response to N and P additions.

BIOLOGICAL SIGNIFICANCE

Fertilization is an important management measure to improve timber yield and primary production of Cunninghamia lanceolata, which is the largest planted coniferous species in southeast China. Nitrogen (N) and phosphorus (P) additions into soils can improve tree photosynthesis, and further increase plantation production. However, the mechanism of N and P additions in improving photosynthesis is still unclearly. In this study, a physiological measurement combined with proteomic analysis was performed on a controlled experiment in the greenhouse. These results improve understanding of the essentially photosynthetic activity and metabolic process of C. lanceolata responding to N and P fertilization.

Aphicidal Activity of an Ageraphorone Extract From Eupatorium adenophorum Against Pseudoregma bambucicola (Homoptera: Aphididae, Takahashi)

The bamboo aphid, Pseudoregma bambucicola, is an important insect pest of bamboo that affects normal bamboo growth and induces sooty molds. The control of P. bambucicola involves the application of chemicals, such as imidacloprid, to which many species are resistant. In this study, we isolate a novel botanical pesticide (9-oxo-10,11-dehydro-ageraphorone) from an Eupatorium adenophorum(Asteraceae: Compositae) petroleum ether extract and test the aphicidal activity of this compound against P. bambucicola in laboratory bioassay and field-based experiments. This ageraphorone compound at a concentration of 2 mg/ml caused 73.33% mortality (corrected mortality [Subtracted the mortality of the negative control]: 70%) of P. bambucicola by laboratory bioassay within 6 h. Even at lower concentrations, this compound caused greater 33% mortality (corrected mortality: 30%) of aphids. Field experiments with naturally infested bamboo plants showed that two applications of 2 mg/ml ageraphorone to infested plants completely cleared infestations within 30 d. These effects were similar to those of the positive control (imidacloprid). These results reveal that 9-oxo-10,11-dehydro-ageraphorone exhibits significant aphicidal activity against bamboo aphids. We suggest that future research be directed at developing this ageraphorone compound from E. adenophorum as an aphicidal agent for biocontrol.

Belowground advantages in construction cost facilitate a cryptic plant invasion

The energetic cost of plant organ construction is a functional trait that is useful for understanding carbon investment during growth (e.g. the resource acquisition vs. tissue longevity tradeoff), as well as in response to global change factors like elevated CO2 and N. Despite the enormous importance of roots and rhizomes in acquiring soil resources and responding to global change, construction costs have been studied almost exclusively in leaves. We sought to determine how construction costs of aboveground and belowground organs differed between native and introduced lineages of a geographically widely dispersed wetland plant species (Phragmites australis) under varying levels of CO2 and N. We grew plants under ambient and elevated atmospheric CO2, as well as under two levels of soil nitrogen. We determined construction costs for leaves, stems, rhizomes and roots, as well as for whole plants. Across all treatment conditions, the introduced lineage of Phragmites had a 4.3 % lower mean rhizome construction cost than the native. Whole-plant construction costs were also smaller for the introduced lineage, with the largest difference in sample means (3.3 %) occurring under ambient conditions. In having lower rhizome and plant-scale construction costs, the introduced lineage can recoup its investment in tissue construction more quickly, enabling it to generate additional biomass with the same energetic investment. Our results suggest that introduced Phragmites has had an advantageous tissue investment strategy under historic CO2 and N levels, which has facilitated key rhizome processes, such as clonal spread. We recommend that construction costs for multiple organ types be included in future studies of plant carbon economy, especially those investigating global change.