Traits of an invasive grass conferring an early growth advantage over native grasses

Aims Invasive species often have higher relative growth rates (RGR) than their native counterparts. Nutrient use efficiency, total leaf area and specific leaf area (SLA) are traits that may confer RGR differences between natives and invasives, but trait differences are less prominent when the invasive species belongs to the same plant functional type as the dominant native species. Here, we test if traits displayed soon after germination confer an early size advantage. Specifically, we predicted that invasive species seedlings grow faster than the natives because they lack trade-offs that more strongly constrain the growth of native species.Methods We quantified plant morphological and physiological traits and RGR during early seedling growth at high and low nutrient levels in three dominant perennial native C₄ grasses: Panicum virgatum L. (switchgrass), Schizachyrium scoparium (Michx.) Nash (little bluestem) and Andropogon gerardii Vitman (big bluestem); and a perennial C₄ exotic invasive grass, Sorghum halepense (L.) Pers. (Johnsongrass).Important findings After 2 weeks of growth, Johnsongrass seedlings had greater biomass, SLA and photosynthetic nitrogen use efficiency, but lower leaf N concentrations (% leaf N) and root:shoot ratio than natives. As growth continued, Johnsongrass more quickly produced larger and thicker leaves than the natives, which dampened the growth advantage past the first 2 to 3 weeks of growth. Investment in carbon gain appears to be the best explanation for the early growth advantage of Johnsongrass. In natives, growth was constrained by an apparent trade-off between allocation to root biomass, which reduced SLA, and production of leaves with high N content, which increased carbon gain. In Johnsongrass, root:shoot ratio did not interact with other traits, and % leaf N was decoupled from RGR as a result of a trade-off between the positive indirect association of % leaf N with RGR and the negative direct association of % leaf N with RGR.     

Trait Values,Not Trait Plasticity,Best Explain Invasive Species' Performance in a Changing Environment

The question of why some introduced species become invasive and others do not is the central puzzle of invasion biology. Two of the principal explanations for this phenomenon concern functional traits: invasive species may have higher values of competitively advantageous traits than non-invasive species, or they may have greater phenotypic plasticity in traits that permits them to survive the colonization period and spread to a broad range of environments. Although there is a large body of evidence for superiority in particular traits among invasive plants, when compared to phylogenetically related non-invasive plants, it is less clear if invasive plants are more phenotypically plastic, and whether this plasticity confers a fitness advantage. In this study, I used a model group of 10 closely related Pinus species whose invader or non-invader status has been reliably characterized to test the relative contribution of high trait values and high trait plasticity to relative growth rate, a performance measure standing in as a proxy for fitness. When grown at higher nitrogen supply, invaders had a plastic RGR response, increasing their RGR to a much greater extent than non-invaders. However, invasive species did not exhibit significantly more phenotypic plasticity than non-invasive species for any of 17 functional traits, and trait plasticity indices were generally weakly correlated with RGR. Conversely, invasive species had higher values than non-invaders for 13 of the 17 traits, including higher leaf area ratio, photosynthetic capacity, photosynthetic nutrient-use efficiency, and nutrient uptake rates, and these traits were also strongly correlated with performance. I conclude that, in responding to higher N supply, superior trait values coupled with a moderate degree of trait variation explain invasive species'' superior performance better than plasticity per se.     

Leaf trait co-ordination in relation to construction cost, carbon gain and resource-use efficiency in exotic invasive and native woody vine species

Background and Aims

Success of invasive plant species is thought to be linked with their higher leaf carbon fixation strategy, enabling them to capture and utilize resources better than native species, and thus pre-empt and maintain space. However, these traits are not well-defined for invasive woody vines.

Methods

In a glass house setting, experiments were conducted to examine how leaf carbon gain strategies differ between non-indigenous invasive and native woody vines of south-eastern Australia, by investigating their biomass gain, leaf structural, nutrient and physiological traits under changing light and moisture regimes.

Key Results

Leaf construction cost (CC), calorific value and carbon : nitrogen (C : N) ratio were lower in the invasive group, while ash content, N, maximum photosynthesis, light-use efficiency, photosynthetic energy-use efficiency (PEUE) and specific leaf area (SLA) were higher in this group relative to the native group. Trait plasticity, relative growth rate (RGR), photosynthetic nitrogen-use efficiency and water-use efficiency did not differ significantly between the groups. However, across light resource, regression analyses indicated that at a common (same) leaf CC and PEUE, a higher biomass RGR resulted for the invasive group; also at a common SLA, a lower CC but higher N resulted for the invasive group. Overall, trait co-ordination (using pair-wise correlation analyses) was better in the invasive group. Ordination using 16 leaf traits indicated that the major axis of invasive-native dichotomy is primarily driven by SLA and CC (including its components and/or derivative of PEUE) and was significantly linked with RGR.

Conclusions

These results demonstrated that while not all measures of leaf resource traits may differ between the two groups, the higher level of trait correlation and higher revenue returned (RGR) per unit of major resource need (CC) and use (PEUE) in the invasive group is in line with their rapid spread where introduced.     

Growth of tree seedlings in a tropical dry forest in relation to soil moisture and leaf traits

"AimsThe growth of plant species in tropical dry forest (TDF) is expected to be largely governed by the availability of soil moisture. In this study we attempt to identify mechanisms by which seedlings of dry tropical trees cope with water stress by adjusting their leaf characteristics to water availability and micro environments, and address following questions: How are leaf traits and relative growth rate (RGR) of the dominant seedling species of TDF affected by seasonal changes in soil moisture content (SMC)? What is the relationship of functional traits with each other? Can leaf traits singly or in combination predict the growth rate of seedling species of TDF? The study was conducted in situ on four sites (viz., Hathinala, Gaighat, Harnakachar and Ranitali, listed in order of decreasing SMC) within the tropical dry deciduous forest in northern India. Methods Five leaf traits viz., specific leaf area (SLA), leaf dry matter content (LDMC), concentrations of leaf nitrogen (leaf N), phosphorus (leaf P) and chlorophyll (Chl) and two physiological processes, viz., stomatal conductance (Gs net) and photosynthetic rate (A net), and RGR, of four dominant tree seedling species of a TDF (viz., Buchanania lanzan, Diospyros melanoxylon, Shorea robusta and Terminalia tomentosa) on four sites were analysed for species, site and season effects over a 2-year period. Step-wise multiple regression was performed to predict RGR from mean values of SMC, leaf traits and physiological processes. Principal component analysis (PCA) was performed to observe the extent of intra- vs. inter-specific variability in the leaf traits and physiological rates.Important findings All the traits and physiological rates were interrelated and showed significant positive relationship with RGR except for the correlation of LDMC with RGR which was not significant. Further, relationships of SMC with all leaf traits, physiological rates and RGR were significant, except for that between SMC and SLA for B. lanzan and D. melanoxylon. The slope of seedling trait:SMC relationship, a measure of phenotypic plasticity in response to soil moisture gradient, varied among species. Among the four species, T. tomentosa was the most plastic and S. robusta the least. In conclusion, leaf traits and physiological processes were strongly related to soil water availability on the one hand and seedling growth on the other. Gs net is the most important variable which accounted for the greatest amount of variability (62%) in RGR, emphasizing the role of stomatal conductance in shaping growth patterns across spatial and temporal gradients of soil water availability. Gs net and SMC together explained 64% variability in RGR, indicating that other traits/factors, not studied by us are also important in modulating the growth of tropical tree seedlings.     

Influence of light and nutrient conditions on seedling growth of native and invasive trees in the Seychelles

Several recent studies have shown that plant invasions can occur in resource-poor and relatively undisturbed habitats. It is, therefore, important to investigate whether and how life-history traits of species invasive in such habitats differ from those of species that are only invasive in disturbed and resource rich habitats. We compared the growth of seedlings of native and invasive tree species from nutrient-poor secondary forests in the tropical Seychelles. We hypothesised that the relative performance of the two groups would change predictably along resource gradients, with native species performing better at low levels of resource availability and invasive species performing better at higher levels. To test this hypothesis, we performed a common garden experiment using seedlings of six invasive and seven native tree species grown under three levels of light (65, 11 and 3.5% of ambient light) and two of nutrients (low and high). Due to large variation among species, differences in growth rates (RGR) were not significant among seedlings of the native and the invasive species. However, seedlings of the invasive species showed higher specific leaf areas (SLA) and higher leaf nutrient contents than seedlings of the native species. They also exhibited greater plasticity in biomass and nutrient allocation (i.e., greater plasticity in LAR, RSR and leaf nutrient contents) in response to varying resource availability. However, differences between the mean values of these parameters were generally small compared with variation within groups. We conclude that successful invaders on nutrient-poor soils in the Seychelles are either stress-tolerant, possessing growth traits similar to those of the native species, or fast-growing but adapted to nutrient-poor soils. In contrast, the more typical, fast-growing alien species with no particular adaptations to nutrient-poor soils seem to be restricted to relative nutrient-rich sites in the lowlands. The finding—that some introduced species thrive in resource-poor habitats—suggests that undisturbed habitats with low resource availability may be less resistant to plant invasions than was previously supposed.     

紫茎泽兰和飞机草的形态和光合特性对磷营养的响应

比较研究了紫茎泽兰和飞机草的生长、形态、生物量分配和光合特性对磷营养的可塑性反应,及与其入侵性的关系.结果表明,两种入侵植物对磷营养变化表现出很强的可塑性和适应性.低磷时,两种植物的根生物量比增大,利于养分吸收;高磷时,两种植物的比叶面积、最大净光合速率、光饱和点、单位面积的叶绿素和类胡萝卜素含量增大,同化面积和同化能力增强,利于碳积累.相比之下,紫茎泽兰对磷的适应性更强.随供磷量的增加,紫茎泽兰和飞机草的相对生长速率、总生物量、株高、分枝数、叶面积指数和最大净光合速率均显著增大,过量磷素对上述参数抑制较小,表明两种入侵植物偏好较高的磷环境,土壤磷含量升高有利于其入侵,并在高磷时,通过增大株高、分枝数和叶面积指数荫蔽排挤本地种.在本地种基本停止生长的干季,紫茎泽兰和飞机草仍维持较高的相对生长速率.这也与其入侵性密切相关.     

Are plasticity in functional traits and constancy in performance traits linked with invasiveness? An experimental test comparing invasive and naturalized plant species

The role of phenotypic plasticity in plant invasions is among the most often discussed relationships in invasion ecology. However, despite the large number of studies on this topic, there is little consistency. Reconsideration of the role of plasticity by distinguishing two substantially distinct trait-groups, performance traits (contributing directly to fitness) and functional traits (influencing fitness indirectly), could form a more operative framework for comparative studies. In the current study we expect that invasive species benefit from being plastic in functional traits, which allows them to maintain a more constant performance across different environmental conditions compared to non-invasive alien species. We compared invasive and naturalized non-invasive alien plant species by their germination (20 species), their vegetative (10 species) and their reproductive (four species) responses to three different levels of water, light and nutrient availability in a common garden experiment. Used traits were classified into performance (germination ratio, total biomass, seed number) and functional traits (time to germination, root:shoot ratio, specific leaf area, reproductive allocation). We found that invasive and non-invasive species responded similarly to environmental factors, except for example that invasive species germinated earlier with decreasing light conditions or, surprisingly, non-invasive species reacted more intensely to increased nitrogen availability by having a superior ability to achieve greater biomass. The two groups were equally plastic in all the germination and vegetative traits measured but the reproductive traits, since higher plasticity in relative reproductive allocation and higher constancy in reproductive performance showed a pronounced relation with invasiveness.     

Variation in resource acquisition and utilization traits between native and invasive perennial forbs

Understanding the functional traits that allow invasives to outperform natives is a necessary first step in improving our ability to predict and manage the spread of invaders. In nutrient-limited systems, plant competitive ability is expected to be closely tied to the ability of a plant to exploit nutrient-rich microsites and use these captured nutrients efficiently. The broad objective of this work was to compare the ability of native and invasive perennial forbs to acquire and use nutrients from nutrient-rich microsites. We evaluated morphological and physiological responses among four native and four invasive species exposed to heterogeneous (patch) or homogeneous (control) nutrient distribution. Invasives, on average, allocated more biomass to roots and allocated proportionately more root length to nutrient-rich microsites than did natives. Invasives also had higher leaf N, photosynthetic rates, and photosynthetic nitrogen use efficiency than natives, regardless of treatment. While these results suggest multiple traits may contribute to the success of invasive forbs in low-nutrient environments, we also observed large variation in these traits among native forbs. These observations support the idea that functional trait variation in the plant community may be a better predictor of invasion resistance than the functional group composition of the plant community.     

Phenotypic plasticity of lianas in response to altered light environment

The growth, morphology and biomass allocation of 11 liana species (six light-demanding and five shade-tolerant) were investigated by growing plants in three contrasting light environments (i.e., field, forest edge and forest interior). Our objectives were to determine: (1) changes in plant traits at the species level; and (2) differences in light-demanding and shade-tolerant species in response to altered light environment. We found that all seedlings of liana species increased in total biomass, total leaf area, relative growth rate (RGR), net assimilation rate (NAR), height, basal diameter, root length, leaf number, root mass/total plant mass (RMR) and root-to-shoot dry biomass (R/S ratio), and decreased in leaf area ratio (LAR), specific leaf area (SLA), leaf size, stem mass-to-total plant mass ratio (SMR) and leaf mass-to-total plant mass ratio (LMR) with increasing light availability. Under the three light environments, the two types of species differed significantly in total biomass, total leaf area, RGR, NAR, LAR, SLA and leaf number, and not in leaf area. Only light-demanding species differed significantly in height, root length, basal diameter, RMR, SMR, LMR and R/S ratio. The mean plasticity index of growth and biomass allocation were relatively higher than the morphological variables, with significant differences between the two groups. Our results showed that liana species respond differently to changing light environments and that light-demanding species exhibit higher plasticity. Such differences may affect the relative success of liana species in forest dynamics.     

紫茎泽兰和飞机草的形态、生物量分配和光合特性对氮营养的响应

比较研究了紫茎泽兰(Ageratina adenophora)和飞机草(Chromolaena odorata)的形态、生物量分配、生长和光合特性对氮营养的可塑性反应,探讨其与入侵性的关系。结果表明:1) 两种入侵植物对氮营养变化表现出很高的可塑性。随供氮量的增加,两种植物的根冠比、根生物量比降低,叶生物量比(LMR)、叶面积比和叶根比升高。低氮时,增加吸收器官的生物量分配,有利于养分吸收;高氮时,更多的生物量投入同化器官,有利于碳积累。相比之下紫茎泽兰对氮素的适应性更强。2) 两种入侵植物偏好较高的氮营养环境,土壤氮含量升高利于紫茎泽兰和飞机草的入侵。在较大的氮范围内,其相对生长速率(RGR)、总生物量、株高、分枝数、叶面积指数、最大净光合速率和光合色素含量都随供氮量的增加而显著增加,过量氮素对上述参数的抑制不显著。在本地种基本停止生长的干季,紫茎泽兰和飞机草仍维持较高的RGR,这与它们的入侵性密切相关。3) 在决定RGR对氮营养的响应过程中,平均叶面积比和净同化速率同等重要。LMR对两种植物的RGR有重要的影响,是决定处理间和种间RGR差异的重要因素。随氮素的增加,紫茎泽兰的比叶面积(SLA)降低,飞机草的SLA升高,但在所有氮水平下,前者的SLA都高于后者,紫茎泽兰SLA的变化规律更利于植物适应氮环境。     

Testing the effect–response framework: key response and effect traits determining above‐ground biomass of salt marshes

Question: How do species traits respond to environmental conditions and what is their effect on ecosystem properties? Location: Salt marshes, Northwest Germany. Methods: On 113 plots along the German mainland coast and on one island, we measured environmental parameters (soil nutrient content, inundation frequency, groundwater level and salinity), collected traits from 242 individuals (specific leaf area [SLA], whole plant C:N ratio, and dry weights of plant organs) and sampled above‐ground biomass as an ecosystem property. We constructed a path model combining environmental parameters, functional traits at community level and above‐ground biomass, which was tested against a dependence model using path analysis; model fit was evaluated by structural equation modelling (SEM). Results: The final model showed good consistency with the data and highlights the major role of groundwater level, salinity and nutrient availability as the most important factors influencing biomass allocation in salt marshes. Above‐ground living biomass was mostly determined by stem biomass, which was mediated through an allometric allocation of biomass to all other plant organs, including leaf mass. C:N ratio and SLA were the major drivers for dead biomass. Conclusion: We emphasize an indirect link between standing biomass and environmental conditions and recognize stem biomass, plant C:N ratio and SLA as keystone markers of species functioning in determining the relationship between environment and ecosystem properties.     

Growth,biomass allocation and plant nitrogen concentration in Chilean temperate rainforest tree seedlings: effects of nutrient availability

Seedlings of nine southern Chilean trees were grown at three nutrient supply rates, to examine the roles of growth rate, biomass distribution and nutrient use traits in determining species natural distributions on resource gradients. Relative growth rate (RGR) showed no overall relationship with species site requirements, although RGR of fertile-site species tended to be more responsive to nutrient supply. In the low-nutrient treatment, infertility-tolerant Fitzroya cupressoides showed a higher RGR rank than a fertility-demanding species (Laurelia philippiana) which outgrew it substantially at the highest supply rate. This reversal of RGR ranks was associated with divergent nutrient use responses: at high nutrient supply both spp. had similar plant nitrogen concentrations (PNC), whereas at the low supply rate Fitzroya’s production of biomass per unit of assimilated N was twice that of Laurelia’s. However, this pattern does not appear to serve as a general explanation of the respective distributions of the study species, as RGR ranks of most species were unaltered by nutrient supply. At low nutrient availability, no clear differences in shoot:root ratio (SRR) were apparent between poor-site and fertile-site species. However, at high nutrient availability, SRR was markedly higher in the latter, resulting from differences in biomass allocation to stems (not leaves). Leaf area ratios (LAR) were higher in fertile-site species than in those tolerant of low fertility, because of differences in specific leaf area rather than leaf weight ratio. Very high LAR at high nutrient supply was characteristic of most shade-tolerant angiosperms, but not of shade-tolerant conifers. Although PNC showed no overall differences between poor- and fertile-site species, sensitivity of PNC to external supply rate was greatest in two infertility-tolerant conifers. In contrast, the angiosperm Weinmannia trichosperma, although tolerant of low fertility, responded to increased nutrient supply with greatly increased RGR and little change in PNC. Results show little trait convergence between conifers and angiosperms in adaptation both to shade and to infertile soils; i.e. fitness of different taxa in a given environment may hinge on different trait combinations. Received: 12 September 1995 /Accepted: 14 June 1996     

Specific leaf area relates to the differences in leaf construction cost,photosynthesis, nitrogen allocation,and use efficiencies between invasive and noninvasive alien congeners

Comparisons between invasive and native species may not characterize the traits of invasive species, as native species might be invasive elsewhere if they were introduced. In this study, invasive Oxalis corymbosa and Peperomia pellucida were compared with their respective noninvasive alien congeners. We hypothesized that the invasive species have higher specific leaf (SLA) than their respective noninvasive alien congeners, and analyzed the physiological and ecological consequences of the higher SLA. Higher SLA was indeed the most important trait for the two invaders, which was associated with their lower leaf construction cost, higher nitrogen (N) allocation to photosynthesis and photosynthetic N use efficiency (PNUE). The higher N allocation to photosynthesis of the invaders in turn increased their PNUE, N content in photosynthesis, biochemical capacity for photosynthesis, and therefore light-saturated photosynthetic rate. The above resource capture-, use- and growth-related traits may facilitate the two invaders' invasion, while further comparative studies on a wider range of invasive and noninvasive congeners are needed to understand the generality of this pattern and to fully assess the competitive advantages afforded by these traits.     

Biomass partitioning in response to resources availability: A comparison between native and invaded ranges in the clonal invader Carpobrotus edulis

Identifying the mechanism underlying plant invasiveness is a fast-moving research topic in current ecology. Phenotypic plasticity has been pointed out as a trait that can contribute to plant invasiveness. This experiment examines the presence of rapid adaptive evolution favoring plastic biomass partitioning during the invasion process. With that aim, we tested differences in patterns of biomass allocation between populations of Carpobrotus edulis from South Africa (native area) and the Iberian Peninsula (invaded area) growing under different nutrient, water and light availabilities in a common garden experiment. Here we demonstrate that biomass partitioning in response to nutrient availability in C. edulis differs between populations from native and invaded ranges, indicating that this trait could be under selection during the invasion process. Thus, nutrient shortage significantly increased the proportional production of roots in populations from the invaded range, but not in populations from the native area. This plastic root-foraging response may contribute to the optimization of nutrient uptake by plants, and therefore could be considered as an adaptive strategy. Understanding the ecological implications of rapid evolution for plastic biomass partitioning is important in determining processes of plant adaptation to new environments, and contributes to disentangling the mechanisms underlying plant invasiveness.     

Predicting invasiveness in exotic species: do subtropical native and invasive exotic aquatic plants differ in their growth responses to macronutrients?

We investigated whether plasticity in growth responses to nutrients could predict invasive potential in aquatic plants by measuring the effects of nutrients on growth of eight non-invasive native and six invasive exotic aquatic plant species. Nutrients were applied at two levels, approximating those found in urbanized and relatively undisturbed catchments, respectively. To identify systematic differences between invasive and non-invasive species, we compared the growth responses (total biomass, root:shoot allocation, and photosynthetic surface area) of native species with those of related invasive species after 13 weeks growth. The results were used to seek evidence of invasive potential among four recently naturalized species. There was evidence that invasive species tend to accumulate more biomass than native species ( P  = 0.0788). Root:shoot allocation did not differ between native and invasive plant species, nor was allocation affected by nutrient addition. However, the photosynthetic surface area of invasive species tended to increase with nutrients, whereas it did not among native species ( P  = 0.0658). Of the four recently naturalized species, Hydrocleys nymphoides showed the same nutrient-related plasticity in photosynthetic area displayed by known invasive species. Cyperus papyrus showed a strong reduction in photosynthetic area with increased nutrients. H. nymphoides and C. papyrus also accumulated more biomass than their native relatives. H. nymphoides possesses both of the traits we found to be associated with invasiveness, and should thus be regarded as likely to be invasive.     

Seedling growth of five tropical dry forest tree species in relation to light and nitrogen gradients

Aims Increasing anthropogenic nitrogen (N) deposition has been claimed to induce changes in species composition and community dynamics. A greenhouse experiment was conducted to examine the effect of increased N availability on growth and functional attributes of seedlings of five tree species with different life history characteristics under varying irradiances. The following questions have been addressed: (i) how do the pioneer and non-pioneer species respond in absolute growth and relative growth rate (RGR) to the interaction of light and nitrogen? (ii) how does the interaction between irradiance and nitrogen availability modulate growth attributes (i.e. functional attributes)? (iii) is there any variation in growth responses between leguminous and non-leguminous species along the light and nitrogen gradients?Methods Seedlings of five tree species (Acacia catechu, Bridelia retusa, Dalbergia sissoo, Lagerstroemia parviflora and Terminalia arjuna) were subjected to twelve combinations of irradiance and N levels. Various growth traits, including height (HT), basal area (BA), whole plant dry biomass (M D), leaf mass per unit area (LMA), leaf area ratio (LAR), net assimilation rate (NAR), RGR, biomass fractions, root-to-shoot ratio (R:S) and leaf nitrogen content, were studied to analyse intra- and inter-specific responses to interacting light and N gradients.Important findings Significant interactions for irradiance and N availability for majority of growth attributes indicates that growth and biomass allocation of seedlings were more responsive to N availability under high irradiance. However, species responded differentially to N addition and they did not follow successional status. Slow growers (B. retusa, a shade-tolerant species and L. parviflora, a light demander) exhibited greater response to N enrichment than the fast growers (A. catechu, D. sissoo and T. arjuna). However, N-mediated increment in growth traits was greater in non-legumes (B. retusa, L. parviflora and T. arjuna) compared with that of legumes (A. catechu and D. sissoo). Allocation of biomass to root was strongly suppressed at the highest N supply across species; however, at high irradiance and high N availability, a greater suppression in R:S ratio was observed for B. retusa. NAR was a stronger determinant of RGR relative to LAR, suggesting its prominent role in increased RGR along increasing irradiances. Overall, a higher growth response of slow-growing species to elevated N levels, particularly the non-pioneers (B. retusa and L. parviflora) suggests that future N deposition may lead to perturbations in competition hierarchies and species composition, ultimately affecting community dynamics in nutrient-poor tropical dry forests.     

Functional traits,growth patterns,and litter dynamics of invasive alien and co-occurring native shrub species of chir pine forest in the central Himalaya,India

Across the continents, plant invasion is identified as one of the main threats to ecosystem functioning and stability. The main objective of this research was to evaluate the differences in the functional traits between invasive alien (Ageratina adenophora (Spreng.) and Lantana camara L.) and native (Berberis asiatica Roxb. Ex DC., Pyracantha crenulata (D. Don.) M. Roemer and Rubus ellipticus Sm.) shrub species of chir pine (Pinus roxburghii Sarg.) forest in the central Himalaya. Three 0.5 hectare chir pine forest stands were selected and individuals of similar diameter were tagged for comparative studies of leaf traits, growth pattern, and biomass accumulation in structural organs of each invasive alien and native species. Our one-way ANOVA and Tukey’s post hoc test results showed that both the invasive alien species have significantly (p?<?0.05) higher SLA, LWC, total chlorophyll content, foliar nutrient (N and P), RGR, LMR, SMR, nutrient uptake, and nutrient use efficiencies than native species. Leaf litter decomposition rate and nutrient release were also significantly (p?<?0.05) higher in both the invasive alien species. Native species, R. ellipticus, shared some of the traits, such as leaf area, chlorophyll content, RGR, LAR, LMR, and nutrient uptake efficiency with invasive alien species. The majority of traits differed among invasive alien and native species, implying that the success of invasive alien species is best described by being functionally distinct from native species. These findings indicate that invasive alien species had advanced functional traits which may be playing an important role in a rapid spread in the central Himalaya.

     

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.     

Invasive plants do not display greater phenotypic plasticity than their native or non‐invasive counterparts: a meta‐analysis

Phenotypic plasticity is commonly considered as a trait associated with invasiveness in alien plants because it may enhance the ability of plants to occupy a wide range of environments. Although the evidence of greater phenotypic plasticity in invasive plants is considerable, it is not yet conclusive. We used a meta‐analysis approach to evaluate whether invasive plant species show greater phenotypic plasticity than their native or non‐invasive counterparts. The outcome of such interspecific comparisons may be biased when phylogenetic relatedness is not taken into account. Consequently, species pairs belonged to the same genus, tribe or family. The meta‐analysis included 93 records from 35 studies reporting plastic responses to light, nutrients, water, CO₂, herbivory and support availability. Contrary to what is often assumed, overall, phenotypic plasticity was similar between invasive plants and native or non‐invasive closely related species. The same result was found when separate analyses were conducted for trait plasticity to nutrients, light and water availability. Thus, invasive plant species and their native or non‐invasive counterparts are equally capable of displaying functional responses to environmental heterogeneity. The colonization of a wide range of environments by invasive plants could be due to their capacity to undergo adaptive ecotypic differentiation rather than to their ability to display plastic responses. Alternatively, phenotypic plasticity might play a role in plant invasion, but only during the initial phases, when tolerance of the novel environment is essential for plant survival. Afterwards, once alien plants are identified as invaders, the magnitude of phenotypic plasticity might be reduced after selection of the optimum phenotypes in each habitat. The identification of plant traits that consistently predict invasiveness might be a futile task because different traits favor invasiveness in different environments. Approaches at the local scale, focusing on the ecology of specific invasive plants, could be more fruitful than global macro‐analyses.     

Phenotypic plasticity in rice: responses to fertilization and inoculation with arbuscular mycorrhizal fungi

Aims Changes in the phenotype of crops (phenotypic plasticity) are known to play an important role in determining responses to nutrient availability, with the direction and magnitude of plasticity of individual traits being crucial for grain yields. Our study analysed the direction, magnitude and hierarchy of plastic responses of yield-related traits (i.e. biomass allocation and yield components) of rice (Oryza sativa L.) to nutrient availability. We estimated the effect of inoculation with arbuscular mycorrhizal fungi (AMF) on these characteristics of phenotypic plasticity.Methods A field experiment was carried out in northeast China, providing rice with six NPK fertilizer levels with or without inoculation with Glomus mosseae. At maturity, we quantified biomass allocation traits (shoot:root ratio and panicle:shoot ratio) and yield component traits (panicle number per hill, spikelet number per panicle, percentage of filled spikelets and seed weight). We also assessed the direction of change in each trait and the magnitude of trait plasticity.Important findings In non-inoculated plants, we found that biomass allocation and seed-number traits (i.e. panicle number per hill, spikelet number per panicle and percentage of filled spikelets) responded to fertilization in the same direction, increasing with rising fertilization. Panicle formation was the most plastic trait, while seed mass was the least plastic trait. AMF inoculation nullified the relationship between most biomass allocation and seed-number traits (except for that between panicle:shoot ratio and the percentage of filled spikelets) but increased the magnitude of plasticity in biomass allocation traits without altering the hierarchy of traits' plasticity. These results underscore the importance of plasticity of yield-related traits per se, and the impact of AMF on plasticity, for maintaining rice yields under low fertilization regimes.