Introduction

Exotic plant invasion, one of the most pressing environmental problems, has caused great concern to ecologists worldwide (Mack et al. 2000; Pimentel et al. 2000a). However, recently it was reported that some native species might also become invasive, and the large amount of damage that they cause in natural ecosystems is no less than the damage caused by exotic invasive species (Wright et al. 2004b; Peng et al. 2009). For example, Lactuca serriola, one of Europe’s native annual herbs, has come to occupy at least 60% of the Netherlands by enlarging its geographic range and rapidly broadening its ecological amplitude (Hooftman et al. 2006). In addition, some native lianas in the forests of Panama and across the Neotropics have increased in size and density over the last two decades and are likely to influence stand dynamics in these forests (Phillips et al. 2002; Bragg 2004; Allen et al. 2007). Furthermore, other indigenous plants (e.g., Humulus scandens and Pueraria lobata) have also threatened forest health and restoration by becoming “plant killers” in Zhejiang Province, southeast China (Li et al. 2006). Any species, whether native or exotic, that grows vigorously and spreads in a region can be qualified as invasive (Valéry et al. 2008). Thus, in this paper we refer to invaders that are native to a region as “native invaders,” while we refer to species from outside the native region as “exotic invaders.”

The ultimate causes of the invasiveness of exotics are tightly related to the ecological and life history characteristics of species (Kotiaho et al. 2005; van Kleunen and Richardson 2007). High resource capture ability is important for the success of plants involved in interspecific competition (Grime 1974; Shi and Ma 2006). An invasive species can grow very fast, allowing it to kill or displace native species. The degree of invasiveness of exotic invaders has been closely related to a number of ecophysiological traits that promote higher resource capture and utilization efficiency (Nagel et al. 2004; Feng et al. 2008). Previous studies comparing leaf traits of exotic invasive species and native species have shown that invasives have larger SLA than native species (Baruch and Goldstein 1999; Leishman et al. 2007). Exotic invasive species have also been shown to have higher relative growth rates (Pattison et al. 1998; Grotkopp et al. 2002), foliar nutrients and photosynthetic capacity (Baruch and Goldstein 1999; Durand and Goldstein 2001; McDowell 2002; Leishman et al. 2007). It seems likely that exotic invaders often have a higher photosynthetic rate (A), specific leaf area (SLA), photosynthetic nitrogen use efficiency (PNUE), photosynthetic energy use efficiency (PEUE) and low leaf construction cost (CCmass and CCarea; Pattison et al. 1998; Baruch and Goldstein 1999; Feng et al. 2008).

Identifying traits that may be associated with invasiveness (Pyšek and Richardson 2007) may improve our ability to predict and control potential invaders, including native invaders. To date, we know much more about exotic invaders than about native invaders, though the damage caused by native invaders is similarly severe. Little is known about the mechanisms underlying native invasion, though a few previous studies have separated native and exotic species into invasive and noninvasive (Lake and Leishman 2004; Leishman and Thomson 2005).

Do native invaders have similar characteristics to exotic invaders, e.g., higher resource capture and utilization efficiency? Our previous studies in Guangdong have shown that many forest ecosystems suffer from the serious damage caused by native invasive plants. There are 39 invasive species on Baiyun Mountain and Xiqiao Mountain in our study site in Guangzhou. Of these, 33 are native to the local region in China and can suppress and cover other dominant trees, ultimately resulting in the death of a large number of local trees (Peng et al. 2009). Successful invasion depends on a number of factors, including the traits of the invaders (e.g., resource capture ability and utilization), resource availability and the condition of the invaded ecosystem. In this paper we focus on the traits of the invaders themselves as a determinant of successful invasion. We hypothesized that native invaders, like exotic invaders, may have higher resource capture ability and utilization efficiency compared to native nonivaders, traits which are beneficial for successful invasion. To test this hypothesis, we compared leaf-level physiological traits (Amax, SLA, PNUE, PEUE, CCmass and CCarea) of three native invasive (NI) species and three exotic invasive (EI) species with noninvasive controls. All the plants used in the study are common in southern China.

Materials and methods

Study site

This study was carried out in Guangzhou (23°6′32″N, 114°15′53′E), which lies in central-south Guangdong Province, Southern China. The region has a subtropical monsoon climate with a mean annual temperature of 22.8°C (ranging from 0°C in January to 38°C in July or August), a mean annual precipitation of 1,982.7 mm and a relative humidity of 68%. Guangzhou is located on hilly land, and the prevalent soil type is lateritic red soil (Cui et al. 2003). The three study sites were all located in Guangzhou: Baiyun Mountain (a park in Guangzhou), the south campus of Sun Yat-sen University and Guangzhou Higher Education Mega Center. The sites were separated by a distance of about 20 to 30 km. Detailed information on the vegetation and soil properties of the sites is provided by Guan and Chen (2003). The soil here is latosolic red soil and the soil organic matter content is medium; soil fertility is poor because nutrient elements such as nitrogen (N) and phosphorus (P) are scarce. In the study area, human activities are more intense than in natural forests, thus the vegetation and condition of the forest in the study area differ greatly from natural vegetation. Details of each plant species used in the study are shown in Table 1.

Table 1 The plant species in the present study
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Plant species

Each pair of species was selected from the same family and had a similar life form. To minimize the impact of environmental factors on plant growth, we choose the species of each pair from similar habitats. Although there are many invasive plant species in the studied area, only six of them were found to have the respective noninvasive species pair to meet our standards as controls in this area. Thus, we selected six pairs of plant species that were divided into two groups: invasive (including native invasive, NI, and exotic invasive, EI) and noninvasive (including native noninvasive, NN, and exotic noninvasive, EN; details in Table 1). The three NI species, Paederia scandens, Pueraria phaseoloides and Stephania longa, are perennial vines that grow rapidly and can reach the top of the canopy, causing other plants to die from lack of light. These species have caused severe damage to forest development and function in some areas in Guangzhou (Peng et al. 2009). The three NN species, Mussaenda pubescens, Lablab purpureus and Tinospora sinensis, are widely grown as common species in South China and cause no damage to the local ecosystem. In addition, the three EI species, Ipomoea cairica, Lantana camara and Oxalis corymbosa, were compared with the respective noninvasive species Pharbitis nil, Lantana montevidensis and Oxalis corniculata. Ipomoea cairica, a perennial herb native to North America, was introduced into China in the 1970s (Lin and Liu 2008). Lantana camara, a shrub native to Tropical America, was introduced into China in the middle of the 16th century (Lin et al. 2008). Oxalis corymbosa, a perennial herb native to Brazil, was introduced into China in the middle of 19th century (Feng et al. 2008). All of these exotic invasives were introduced as ornamental plants and have been naturalized in the subtropics and tropics of China. These species often form monocultures, causing a serious disruption to the structure and function of the local ecosystem (Huang et al. 2009). Pharbitis nil and Lantana montevidensis are exotic species. They were introduced into China as ornamental plants but did not cause damage to the local ecosystem. Oxalis corniculata, a native perennial herb, is widely distributed throughout China (details of the species are shown in Table 1).

Measurements

Photosynthetic characteristics

Net photosynthetic rate in relation to varying photosynthetic photon flux density (P n—PPFD curves) was determined on the youngest fully expanded leaves with a Li-6400 Portable Photosynthesis System (Li-6400, Li-Cor, USA). Measurements were made on 2–3 representative leaves on 3–4 randomly selected individuals of each species in a pair over consecutive days from 09:00 to 12:00 am in the field in the summer of 2008. All leaves of the two species in a pair were of similar age and position on the canes. Three replicates for each species were used for each measurement. Light response curves were generated by decreasing PAR. PPFD was decreased in a stepwise fashion from 2,000 to 0 μmol photon m−2 s−1. During the measurements, CO2 concentration, temperature and relative humidity within the leaf chamber were similar to those of ambient conditions. Each leaf was acclimated for 10–25 min to 2,000 μmol m−2 s−1 mol of PPFD prior to the measurement.

Leaf structural and biochemical characteristics

Around fifty leaves per species were selected, and specific leaf area (SLA, in square centimeters per gram) for each individual was measured using a leaf area meter (Li-3100A, Li-Cor, USA) and leaf dry weight. Leaves were dried for 48 h at 72°C in an oven and weighed. The dried leaves were ground into a fine powder using a micro-plant mill and stored with a desiccant to maintain dryness for subsequent analysis. Leaf N was determined using an azotometer (Kjeltec 2300, Foss, Sweden). Ash content (ASH) was measured by burning 1 g leaf powder samples in a 500°C muffle furnace (Vulcan A-550, Vulcan, UK) for 6 h and weighing the remaining mass, then dividing the ash mass by the sample mass. To obtain the leaf caloric value, ~0.5 g pellets of leaf powder from each sample were pressed and combusted using a calorimeter (IKA-C2000, IKA, Germany). The same leaf of each sample plant was used if the measurements of photosynthesis and leaf structural and biochemical characteristics were possible (Feng et al. 2008).

Calculation

Photosynthetic characteristics

Entire light response curves were fitted using the standard quadratic equation (Y = aX2 + bX + c). Light-saturated photosynthetic rate (Amax, μmol m−2 s−1) = c − (b2/4a) (Wen et al. 2000).

Leaf structural and biochemical characteristics

Specific leaf area (SLA, cm2 g−1) = leaf area/leaf dry weight. Area-based leaf nitrogen content (Narea, g m−2) = Nmass/SLA. Leaf construction cost per unit of mass (CCmass, equivalent to grams glucose per gram dry mass) was calculated according to the following equation (Williams et al. 1987): CCmass = [(0.06968ΔHc-0.065) (1−ASH) + 7.5(k N/14.0067)]/EG. Where ΔHc was ash-free heat of combustion: ΔHc = Caloric value/(1−Ash content), k was the oxidation state of the N substrate (+5 for nitrate or −3 for ammonium) and EG was the growth efficiency. EG has been estimated to be 0.87 across species (Penning de Vries et al. 1974). Because the form of N utilized by the plants was unknown in our samples, CC for all species was estimated as the mean of CC values calculated with each NH4 + and NO3 − oxidation state.

Resource use efficiency

Photosynthetic energy use efficiency (PNUE, μmol g−1 s−1) = Amax/Narea (Field and Mooney 1986). Energy use efficiency (PEUE, CO2 g glucose−1 s−1) = Amax/CCarea (Funk and Vitousek 2007). Water use efficiency (WUE, μmol mmol−1) = A/E (transpiration). Light use efficiency (LUE, μmolCO2 μmol−1 proton) = A/PPFD.

Statistical analyses

Independent-sample t tests were conducted to evaluate the differences in resource capture ability and utilization efficiency between each native invasive and noninvasive native pair, and between each exotic invasive and noninvasive pair. Furthermore, the differences between the pooled native invasive and their corresponding noninvasive native species as well as the differences between the pooled exotic invasive and their corresponding noninvasive species were analyzed with paired t tests All analyses were carried out using SPSS 16.0 (SPSS, Chicago, USA).

Results

The resource capture and utilization properties of NI species

NI species were more efficient in capturing and utilizing resources than were their corresponding NN species (Table 2), and the NI group was more efficient in capturing and utilizing resources than was the NN group (Fig. 1). For family Rubiaceae, the native invader P. scandens had higher SLA, PNUE, PEUE and LUE but lower Narea, CCmass and CCarea than M. pubescens. Similarly, for family Menispermaceae and Leguminosae, native invader S. longa and P. phaseoloides had higher Amax, PNUE, PEUE or SLA, but had lower Nmass, CCmass and WUE than their controls (Table 2). When the data from the different species was pooled, the NI group showed the same tendency. About 78% of the traits in the NI group were significantly different from those of the NN group, and SLA, PNUE and PEUE in the NI group were significantly higher than those of the NN group (Fig. 1), while Narea, CCmass and CCarea in the NI group were significantly lower than in the NN group (Table 2; Fig 1). However, Nmass, WUE and LUE had no significant differences (Fig. 1).

Table 2 The differences between each native invasive and noninvasive native pair in ecophysiological traits according to independent-sample t tests
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Fig. 1
figure 1

a Specific leaf area in cm2 g−1 (SLA), b net photosynthetic rate in μmol m−2 s−1 (Amax), c biomass-based leaf nitrogen content in % (Nmass), d photosynthetic nitrogen use efficiency in μmol g−1 s−1 (PNUE), e mass-based leaf construction cost in g glucose g−1 (CCmass), f area-based leaf construction cost in g glucose m−2 (CCarea), g mean photosynthetic energy-use efficiency in μmol CO2 g glucose−1 s−1 (PEUE), h water use efficiency in μmol mmol−1 (WUE), i light use efficiency in μmolCO2 μmol−1 proton (LUE) of the native invasive (NI) species (filled black bars) and the noninvasive species (open bars) in the study site. Error bars represent 1 ± SE. * P ≤ 0.05; ** P ≤ 0.01; *** P ≤ 0.001

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Resource capture and utilization properties of EI species

Similar to the NI species, EI species had higher resource capture and resource utilization efficiency than the corresponding EN species (Table 3). Likewise, the EI group had higher resource capture and resource utilization efficiency than the EN group (Fig. 2). The exotic invader I. cairica had higher SLA and Nmass but lower CCarea than exotic noninvader P. nil. Exotic invaders L. camara and O. corymbosa were also more efficient at capturing and utilizing resources because of their higher Amax, SLA, PNUE and PEUE but lower Narea, CCmass and CCarea than their respective controls. Correspondingly, the EI group not only had higher Amax, Nmass, PNUE, PEUE and LUE, but also had lower CCmass and CCarea (Fig. 2) than noninvasive species. The WUE of exotic invaders was not significantly different from that of the noninvasive species.

Table 3 The differences between each exotic invasive and noninvasive pair in ecophysiological traits according to independent-sample t tests
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Fig. 2
figure 2

a Specific leaf area in cm2 g−1 (SLA), b net photosynthetic rate in μmol m−2 s−1 (Amax), c biomass-based leaf nitrogen content in % (Nmass), d photosynthetic nitrogen use efficiency in μmol g−1 s−1 (PNUE), e mass-based leaf construction cost in g glucose g−1 (CCmass), f area-based leaf construction cost in g glucose m−2 (CCarea), g mean photosynthetic energy-use efficiency in μmol CO2 g glucose−1 s−1 (PEUE), h water use efficiency in μmol mmol−1 (WUE), i light use efficiency in μmol mmol−1 (LUE) of the exotic invasive (EI) species (filled bars) and the exotic noninvasive (EN) species (open bars) in the study site. Error bars represent 1 ± SE. * P ≤ 0.05; ** P ≤ 0.01; *** P ≤ 0.001

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Discussion

Higher resource capture ability and utilization efficiency has been proposed as one of the potential mechanisms explaining the success of plant invasion (Baruch and Goldstein 1999; Grotkopp and Rejmánek 2007; Funk and Vitousek 2007). With higher resource capture ability and utilization efficiency, invasive species have advantages in competing for sunlight and other resources. Our study illustrated that native invasives, like exotic invasives, have higher resource capture and use efficiency than native noninvasives. In addition, several ecophysiological traits, including high Amax, SLA, PNUE, PEUE, and low CCmass and CCarea, are tightly related to resource capture and use efficiency. The results suggest that high resource capture ability and utilization efficiency might be the common biological foundation for both exotic invasives and native invasives.

Differences in resource capture ability among plant types

The ability to capture and utilize sunlight plays an important role in plant growth (Durand and Goldstein 2001). SLA is of great importance in regulating and controlling carbon assimilation and allocation (Lambers and Poorter 1992; Reich et al. 1997). A higher SLA has been demonstrated in invasive species vs. noninvasive species (Zou et al. 2007; Grotkopp and Rejmánek 2007), and is thus commonly thought to be associated with invasiveness. Species with greater SLA may increase their capacity to assimilate CO2 because a larger leaf area could be produced for a given mass of carbon invested in photosynthetic tissues (Lambers and Poorter 1992; Reich et al. 1997). Consequently, species with high SLA have a greater potential for fast growth than low SLA species. Like SLA, the higher rate of Amax may give invasive species a larger potential to accumulate more carbon for allocation to reproduction and growth (Ewe and Sternberg 2003). Based on a broad survey of 280 plant species in different ecosystems, Reich et al. (1997) found that variation in leaf traits among species was strongly related to whole-plant properties. Having a higher SLA and Amax may translate into a higher relative growth rate (Davis et al. 2000; Nagel et al. 2004; Grotkopp and Rejmánek 2007).

In the present study, SLA was significantly different among plant types, and the invasives (both EI and NI) had higher SLA than the pairwise noninvasives. The SLA of NI species was 49.3% higher than that of NN species, and the SLA of EI species was 44.2% higher than that of the noninvasives, suggesting that the invaders could produce larger assimilatory surfaces for a given amount of fixed carbon. However, some studies indicate that rapid carbon capture via high SLA may not always be advantageous for invasive plants and the studies highlight the importance of ecological context for each individual species in determining whether particular plant traits will confer an advantage (Pyšek et al. 2009; Leishman et al. 2010). The work by Leishman et al. (2010) has shown that exotic invasive and native species do not have fundamentally different carbon capture strategies, suggesting that differences between exotic invasives and natives may reflect differences in the environmental conditions of the sites where they occur rather than differences between exotic invasives and natives per se. It should be mentioned that Leishman et al. (2010) focused on exotic invasive species and native species in disturbed and undisturbed areas in eastern Australia. By contrast, the present study focused on differences in the traits of not only exotic invasives vs. exotic noninvasives, but also of native invasives vs. native noninvasives in southern China.

In the present study, Amax values of the NI and EI species were 47.6 and 26.3% higher than those of the NN species, respectively. This result was consistent with previous studies (Pattison et al. 1998; Baruch and Goldstein 1999; Durand and Goldstein 2001; Feng et al. 2008), which indicated that higher Amax might be a significant trait contributing to successful invasion by exotic species. Thus, the higher Amax together with the higher SLA of NI species might have important implications for their invasion success.

It should be noted that environmental conditions might play an important role in resource capture, which might then affect plant invasion. In our study, a slight difference in growing conditions may have existed that could affect the relationship between plant traits (SLA, Amax) and resource capture or invasiveness, though both the invasives and the noninvasives grew under similar conditions and in the same region, Guangzhou. Future studies should pay more attention to disturbance and growing conditions in addition to the traits of the plants per se.

Differences in resource utilization ability among plant types

The expenditure of energy, in addition to being related to resource capture ability, is also related to plant productivity. Some studies suggest that leaf construction cost might be considered a general index for predicting invasiveness, as some studies have found that invasive species have a lower cost of leaf construction, irrespective of how they compared with native species or compared with their noninvasive congeners (Baruch and Goldstein 1999; Song et al. 2007; Feng et al. 2008). As a quantifiable measure of energy demand for biomass production, having a low leaf construction cost suggests that these species require less energy to construct biomass and can allot more energy to other competitive strategies, such as seed production, biomass productivity, and relative growth rate, based on a study that researched exotic invasive species and one native species in a desert system (Nagel et al. 2004). Our results showed that both CCmass and CCarea of native invasive species were lower than those of noninvasive native species, indicating that lower leaf construction cost may not only be intrinsic to EI species, but may also be an intrinsic property of NI species.

Plants with lower leaf nutrient concentrations generally tend to use nutrition more efficiently (Chapin 1980), but high leaf nutrient concentration, especially N, promotes growth and allows a more efficient use of radiant energy by increasing instantaneous photosynthetic nitrogen use (Field and Mooney 1986). Our results showed that leaf N of NI species was lower than that of NN species, while there was no significant difference in Nmass between the pair of Rubiaceae species and no significant difference in Narea between the pair of Menispermaceae species. However, the leaf N of EI species was higher than that of noninvasive species, though there was no significant difference in Nmass between the pair of Oxalidaceae species, and in Narea between the pairs of Convolvulaceae and Oxalidaceae species. Interestingly, in the present study, NI have lower leaf N than the NN controls, while EI have higher leaf N than the noninvasive species. Previous studies suggested that exotic invaders were the result of higher Nmass (Baruch and Goldstein 1999; Leishman et al. 2007) and Narea (Song et al. 2007; Feng et al. 2008). Leaf nutrient concentration was higher for invasive species in general and also in species-specific comparisons between native and invasive plants. In particular, N was nearly always significantly higher for invasive species. However, few studies have focused on leaf N in native invasive plants. Is it general, like the results in the present study? More attention should be paid to N dynamics of NI species, such as whether lower leaf N for NI species compared with NN species is a general phenomenon.

The lower leaf construction cost of invaders resulted from a higher SLA and lower leaf nitrogen and carbon concentrations (Song et al. 2007). Plants with higher SLA will have thinner leaves and invest less carbon in structural carbohydrates. Additionally, as the respective constituents of many more expensive biochemical plant compounds (Penning de Vries et al. 1974) such as proteins and amino acids (Williams et al. 1987), the concentration of nitrogen was typically positively correlated with leaf construction cost (Griffin et al. 1996). Therefore, with high SLA and low nitrogen concentrations, invasive species may require less energetic costs for construction, and consequently may be more efficient in resource utilization to some extent. In this study, NI species generally had higher SLA, lower leaf N and lower CC than NN species, while EI species had higher leaf N but lower CC than the respective controls. On the whole, it is likely that NI species have the potential for invasiveness no less than EI species.

Differences in resource utilization efficiency among plant types

A plant’s efficiency at utilizing resources has implications for its survival, growth and reproductive capacity (Lambers and Poorter 1992; Chen et al. 2005). Light is one of the most important resources for plant growth. LUE of exotic species was higher than that of noninvasive species. LUE of native invaders was 26.6% higher than noninvasive native species, but this difference was not significant, and further studies are needed to confirm it. These results suggest that the invaders may be able to make full use of light, producing more organic matter conducive for their growth, especially the exotic invaders. Furthermore, PNUE is an indicator of resource capture per unit of N investment (Field and Mooney 1986). Plants with high PNUE often have high growth rates (Lambers and Poorter 1992; Schieving and Poorter 1999). Previous studies have shown that the high level of PNUE potentially provides a competitive edge for exotic plants (Ewe and Sternberg 2003; Xu et al. 2007; Feng et al. 2008). In the present study, compared to native noninvasive species, the native invaders had significantly higher PNUE, with a difference that was 3.5 times greater than the difference in PNUE between exotic invasive species and exotic noninvasive ones. The results suggest that PNUE is a common trait in native invasive species and exotic invaders and provides a competitive advantage for successful invasion. Additionally, photosynthesis can be limited by low water availability. Therefore, maximizing A relative to water costs may be another mechanism of invasive plant success (McDowell 2002). However, in our study, there was no significant difference in WUE between invaders and noninvasive species. This may be because that there is typically a trade-off between WUE and PNUE in plants (Van den Boogaard and Villar 1998). Plants achieve high WUE by closing their stomata, which at the same time reduces the supply of CO2, thereby decreasing the rate of PNUE (Chen et al. 2005). Furthermore, in our study site in Guangzhou, water was not the limiting resource for plant growth as precipitation in the summer is abundant. WUE differences should not be expected under non-stressed conditions; consequently, no significant difference in WUE was observed. PEUE is another useful metric of plant invasion, as it considers both of the supply and demand functions in plant energy budgets (Nagel and Griffin 2004; Funk and Vitousek 2007). With higher PEUE, plants may be better at acquiring resources and competing with native species (Song et al. 2010). This suggests that the dramatically greater PEUE of native invasive species could allow them to assimilate more carbon per unit of energy invested than either of the noninvasive native species measured, which would promote vigorous growth and large areal spread.

Although PEUE provides an instantaneous assessment of energy utilization, the energetic gains and costs are affected by the leaf lifespan when considered over the lifetime of a leaf or plant (Kikuzawa 1991; Kitajima et al. 1997; Nagel and Griffin 2004). Numerous studies have found that leaves with higher PEUE have a shorter leaf lifespan than leaves with lower PEUE (Eamus et al. 1999; Funk and Vitousek 2007). While the leaf-longevity of all the species were not measured in this study, we might speculate that both the native and exotic invaders have shorter leaf lifespans than noninvasive species based on the findings we mentioned above. Species with short leaf lifespans, together with high SLA and Amax, can realize higher growth rates (Reich et al. 1997) and may represent a specific growth strategy with quick returns on investment of nutrients and dry mass in leaves (Wright et al. 2004a). However, the importance of resource-use efficiency (RUE) to invasion success might vary across habitats and timescales, based on a broad survey of 19 pairs of phylogenetically related invasive and native species from three habitats in Hawaii where light, water or nutrient availability was limited (Funk and Vitousek 2007). Their findings suggested that high RUE is a plausible mechanism for plant invasion and persistence in low-resource systems, as the invaders were more efficient at using limiting resources than native species on short timescales, but no advantage or disadvantage was evident over long timescales. Thus, further research should be pursued on how resource-use efficiency plays a role in promoting plant invasion under different levels of resource availability and over the long term.

In conclusion, our study provides evidence that native invasive species, like exotic invasive species, have higher Amax, SLA, PNUE, and PEUE, and lower CC than native noninvasive species. The results suggest that high resource capture ability and utilization efficiency might be a common biological foundation in plant invasion. Unlike exotic invasives that have higher leaf N, the leaf N of native invasives was lower than in control noninvasives. More attention should be paid to the lower leaf N of native invasive species. In addition, other factors are important for plant invasion such as reproductive efforts, seed dispersal, seedling establishment capabilities, growth and carbon fixation rate, acclimation potential, susceptibility to herbivores and pathogens, phenology, age of reproductive maturity and genetics (Bazzaz 1986; Rejmánek 1996; Williamson and Fitter 1996; Pyšek 1997). Resource capture ability and the utilization efficiency of plants will vary across different species and habitat conditions. Thus, future research should address how these traits act synergistically to promote invasiveness, especially for native invaders. In addition, further comparative studies should be carried out on more species in a wider range of environments to better understand the general traits that play key roles in successful invasions.