Yanbao Lei

Evolutionary tradeoffs for nitrogen allocation to photosynthesis versus cell walls in an invasive plant

Many studies have shown that individuals from invasive populations of many different plant species grow larger than individuals from native populations and that this difference has a genetic basis. This increased vigor in invasive populations is thought to be due to life history tradeoffs, in which selection favors the loss of costly defense traits, thereby freeing resources that can be devoted to increased growth or fecundity. Despite the theoretical importance of such allocation shifts for invasions, there have been no efforts to understand apparent evolutionary shifts in defense-growth allocation mechanistically. Reallocation of nitrogen (N) to photosynthesis is likely to play a crucial role in any growth increase; however, no study has been conducted to explore potential evolutionary changes in N allocation of introduced plants. Here, we show that introduced Ageratina adenophora, a noxious invasive plant throughout the subtropics, appears to have evolved increased N allocation to photosynthesis (growth) and reduced allocation to cell walls, resulting in poorer structural defenses. Our results provide a potential mechanism behind the commonly observed and genetically based increase in plant growth and vigor when they are introduced to new ranges.

Effect of osmotic stress and sodium nitroprusside pretreatment on proline metabolism of wheat seedlings

Effect of osmotic stress and sodium nitroprusside (SNP, NO donor) pretreatment on growth and proline metabolism of wheat seedlings was investigated. Polyethylene glycol 6000 treatment for 2, 4 and 6 d could be termed as mild, moderate and severe stress, respectively, according to decrease in the relative water content. Severe osmotic stress significantly decreased the growth and photochemical efficiency, and increased proline content due to activation of its synthesis. 0.2 mM SNP pretreatment enhanced growth of wheat seedlings, increased variable to maximum fluorescence ratio (Fv/Fm) and fluorescence yield, while decreased proline content. However, 2 mM SNP retarded the seedlings growth and chlorophyll a fluorescence, and increased proline accumulation. Our results showed that NO might be involved in the regulation of osmotic stress in a concentration-dependent manner.

Adaptive responses of Populus przewalskii to drought stress and SNP application

In this study we used the cuttings of Populus przewalskii Maximowicz as experimental material and sodium nitroprusside (SNP) as nitric oxide (NO) donor to determine the physiological and biochemical responses to drought stress and the effect of NO on drought tolerance in woody plants. The results indicated that drought stress not only significantly decreased biomass production, but also significantly increased hydrogen peroxide content and caused oxidative stress to lipids and proteins assessed by the increase in malondialdehyde and total carbonyl contents, respectively. The cuttings of P. przewalskii accumulated many amino acids for osmotic adjustment to lower water potential, and activated the antioxidant enzymes such as superoxide dismutase, guaiacol peroxidase and ascorbate peroxidase to maintain the balance of generation and quenching of reactive oxygen species. Moreover, exogenous SNP application significantly heightened the growth performance of P. przewalskii cuttings under drought treatment by promotion of proline accumulation and activation of antioxidant enzyme activities, while under well-watered treatment the effect of SNP application was very little.

Different photosynthetic responses to night chilling among twelve populations of Jatropha curcas

Jatropha curcas, one of the most important energy plant resources, is vulnerable to chilling. To evaluate the effects of chilling on photosynthesis of J. curcas and intraspecific differences in chilling tolerance, seedlings of twelve populations were treated with the temperature of 4–6°C for five consecutive nights with normal environmental temperature during the day. Night chilling treatment decreased light-saturated photosynthetic rate (Pmax) significantly for all populations. Stomatal limitation could not explain the decreased Pmax because intracellular CO2 concentration was not significantly reduced by night chilling in all populations (with only one exception). The decreased soluble-protein content, which may be related to the increased malondialdehyde (MDA) content, contributed to the decreased Pmax. The increased MDA content indicated that oxidative stress occurred after night chilling, which was associated with the larger decrease in Pmax compared with the decrease in actual photochemical efficiency of photosystem II, and the slight increase in thermal dissipation of excessive energy. After five-day recovery, MDA (with two exceptions) and Pmax still did not recover to the levels as those before night chilling treatment for all populations, indicating that J. curcas was vulnerable to chilling. Chilling tolerance was significantly different among populations. Populations originating from high elevations had greater chilling-tolerant abilities than populations originating from low elevations, showing a local adaptation to environmental temperatures of origins. Our study shed light on the possibility to find or breed chilling-tolerant genotypes of J. curcas.

Synergistic effect of colonization with arbuscular mycorrhizal fungi improves growth and drought tolerance of Plukenetia volubilis seedlings

The objective of this study was to investigate the effects of arbuscular mycorrhizal fungus (AMF) inoculation on plant growth and drought tolerance in seedlings of a promising oilseed crop, Sacha Inchi (Plukenetia volubilis L.), under well-watered or drought conditions. AMF inoculation was applied in four treatments: without AMF inoculation, Glomus versiforme, Paraglomus occultum, or combination of both microorganism inoculations. The results showed that AMF colonization significantly enhanced the growth of Sacha Inchi seedlings regardless of soil water conditions, and the greatest development was reached in plants dually inoculated under well-watered conditions. G. versiforme was more efficient than P. occultum. Plants inoculated with both symbionts had significantly greater specific leaf area, leaf area ratio and root volume when compared with the uninoculated control, G. versiforme, and P. occultum treatments alone, indicating a synergistic effect in the two AMF inoculation. Photosynthetic rate and water-use efficiency were stimulated by AMF, but not stomatal conductance. Inoculation with AM fungus increased antioxidant enzymes activities including guaiacol peroxidase and catalase, thus lowering hydrogen peroxide accumulation and oxidative damage, especially under drought stress conditions. However, proline content showed little change during drought stress and AMF colonization conditions, which suggested that proline accumulation might not serve as the main compound for osmotic adjustment of the studied species. These results indicate that AMF inoculation stimulated growth and enhanced drought tolerance of Sacha Inchi seedlings, through alterations in morphological, physiological and biochemical traits. This microbial symbiosis might be an effective cultivation practice in improving the performance and development for Sacha Inchi plants.

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

Global environmental change and ongoing biological invasions are the two prominent ecological issues threatening biodiversity worldwide, and investigations of their interaction will aid to predict plant invasions and inform better management strategies in the future. In this study, invasive Eupatorium adenophorum and native congener E. stoechadosmum were compared at ambient and elevated atmospheric carbon dioxide (CO2) concentrations combined with three levels of nitrogen (N; reduced, control and increased) in terms of growth, energy gain, and cost. Compared with E. stoechadosmum, E. adenophorum adopted a quicker-return energy-use strategy, i.e. higher photosynthetic energy-use efficiency and shorter payback time. Lower leaf mass per area may be a pivotal trait for the invader, which contributed to an increased N allocation to Rubisco at the expense of cell walls and therefore to higher photosynthetic energy gain. CO2 enrichment and N deposition synergistically promoted plant growth and influenced some related ecophysiological traits, and the synergistic effects were greater for the invader than for the native congener. Reducing N availability by applying sugar eliminated the advantages of the invader over its native congener at both CO2 levels. Our results indicate that CO2 enrichment and N deposition may exacerbate E. adenophorum’s invasion in the future, and manipulating environmental resources such as N availability may be a feasible tool for managing invasion impacts of E. adenophorum.

Comparisons of plastic responses to irradiance and physiological traits by invasive Eupatorium adenophorum and its native congeners

To explore the traits contributing to invasiveness of Eupatorium adenophorum and to test the relationship between plasticity of these traits and invasiveness, we compared E. adenophorum with its two native congeners at four irradiances (10%, 23%, 40%, and 100%). The invader showed constantly higher performance (relative growth rate and total biomass) across irradiances than its native congeners. Higher light-saturated photosynthetic rate (P(max)), respiration efficiency (RE), and nitrogen (PNUE) and water (WUE, at 40% and 100% irradiances only) use efficiencies contributed directly to the higher performance of the invader. Higher nitrogen allocation to, stomatal conductance, and the higher contents of leaf nitrogen and pigments contributed to the higher performance of the invader indirectly through increasing P(max), RE, PNUE and WUE. The invader had consistently higher plasticity only in carotenoid content than its native congeners in ranges of low (10-40%), high (40-100%) and total (10-100%) irradiances, contributing to invasion success in high irradiance by photo protection. In the range of low irradiances, the invader had higher plasticity in some physiological traits (leaf nitrogen content, nitrogen contents in bioenergetics, carboxylation and in light-harvesting components, and contents of leaf chlorophylls and carotenoids) but not in performance, while in the ranges of high or total irradiances, the invader did not show higher plasticity in any variable (except Car). The results indicated that the relationship between invasiveness and plasticity of a specific trait was complex, and that a universal generalization about the relationship might be too simplistic.

Populus from high altitude has more efficient protective mechanisms under water stress than from low-altitude habitats: a study in greenhouse for cuttings.

Cuttings of Populus przewalskii and P. cathayana, which originated from high and low altitudes in southwest China, were used to examine the effect of water stress on the morphological, physiological and biochemical traits of plants in a greenhouse for one growing season. The dry mass accumulation and allocation, gas exchanges, extent of peroxidation damage, osmotic adjustment and antioxidative defenses, and amounts of pigments were measured to characterize the differences in peroxidation damage and protective mechanisms of two poplar species that contrast in drought tolerance. Under water stress, poplars showed a series of biochemical adjustments and morphological changes as follows: a decrease in leaf relative water content, gas exchanges, plant growth and dry mass accumulation; an increase in relative allocation to roots; an increase in the osmolyte contents (e.g. total amino acids). Additionally, water deficit induced an increase in peroxidation damage [as indicated by an increase in electrolyte leakage, malondialdehyde (MDA), carbonyl (C = O ) and hydrogen peroxide (H(2) O(2) ) content], enhanced activities or contents of antioxidants (e.g. ascorbate peroxidase, guaiacol peroxidase, glutathione redutase and ascorbic acid) and reduced amounts of leaf pigments (e.g. chlorophyll and carotenoid). Furthermore, there were significant differences in the extent of morphological and biochemical changes between the two poplar species. Compared with P. cathayana, P. przewalskii responded to water stress by allocating relatively more to root dry mass, possessing a higher net photosynthesis rate, and having more efficient protective mechanisms, such as more osmolyte accumulation, stronger antioxidant activities and lower chlorophyll/carotenoid ratio. Thus, P. przewalskii suffered less damage as deduced from lower levels of electrolyte leakage, MDA, C=O and H(2) O(2) content. Therefore, P. przewalskii originating from high altitude could possess more efficient protective mechanisms than P. cathayana, which is from low-altitude habitats.

Evolutionary increases in defense during a biological invasion

Abstract Invasive plants generally escape from specialist herbivores of their native ranges but may experience serious damage from generalists. As a result, invasive plants may evolve increased resistance to generalists and tolerance to damage. To test these hypotheses, we carried out a common garden experiment comparing 15 invasive populations with 13 native populations of Chromolaena odorata, including putative source populations identified with molecular methods and binary choice feeding experiments using three generalist herbivores. Plants from invasive populations of C. odorata had both higher resistance to three generalists and higher tolerance to simulated herbivory (shoot removal) than plants from native populations. The higher resistance of plants from invasive populations was associated with higher leaf C content and densities of leaf trichomes and glandular scales, and lower leaf N and water contents. Growth costs were detected for tolerance but not for resistance, and plants from invasive populations of C. odorata showed lower growth costs of tolerance. Our results suggest that invasive plants may evolve to increase both resistance to generalists and tolerance to damage in introduced ranges, especially when the defense traits have low or no fitness costs. Greater defenses in invasive populations may facilitate invasion by C. odorata by reducing generalist impacts and increasing compensatory growth after damage has occurred.

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.