Invasive alien plants can severely threaten biodiversity conservation, ecosystem function and human health (Lodge, 1993; Feng et al., 2007a; Vilà et al., 2011). Numerous studies have been conducted to assess functional traits that can contribute to the invasion success of alien plants (Lodge, 1993; Alpert et al., 2000; Levine et al., 2003; Roiloa et al., 2016; He et al., 2021). An emerging pattern is that many of the world’s most invasive plant species are able to regenerate clonally (i.e., asexually) and thus have unique clonal life-history traits (McDowell, 2002; van Kleunen et al., 2002; Liu et al., 2006; Song et al., 2013; Wang et al., 2017). Thus, it is likely that these clonal traits have played a key role in the successful invasion of alien clonal plants into native plant communities (Kolar and Lodge, 2001; Song et al., 2013; Wang et al., 2017; Wang et al., 2022).

The environment that plants face is commonly not spatially uniform, but heterogeneous (Hutchings and Wijesinghe, 1997; Ikegami et al., 2008; Keser et al., 2014). Spatial heterogeneity in resource supply makes resource capture more costly and challenging for sessile organisms (Magyar et al., 2007; Ikegami et al., 2008; Wang et al., 2017; Li et al., 2018; Xue et al., 2020). However, clonal growth allows many clonal plants to produce interconnected ramets that are situated in patches (microsites) of different resource availability (Price and Marshall, 1999; Roiloa and Retuerto, 2006; Ikegami et al., 2008; You et al., 2016; Xue et al., 2020). Via clonal integration, interconnected ramets can transfer and share resources so that ramets growing in low-quality resource patches can get support from ramets growing in high-quality resource patches (Roiloa et al., 2010; Song et al., 2013; Wang et al., 2017). Such clonal integration can promote the performance of the whole clone because it commonly greatly benefits the ramets in the low-quality patches at no or low cost to the ramets in the high-quality patches (Song et al., 2013; You et al., 2016; Wang et al., 2021). Previous studies have shown that under such a type of heterogeneous environments (i.e., consisting of low- and high-quality patches) clonal integration can benefits invasive alien clonal plants more than their native congeners, suggesting that clonal integration can contribute to the invasion success of invasive alien clonal plants (Wang et al., 2017).

However, under some circumstances, environments can consist of reciprocal resource patches (Alpert and Stuefer, 1997; Stuefer, 1998; He et al., 2011; Zhang and Zhang, 2013). For instance, open patches with high light intensity are commonly short of soil water and nutrients and their adjacent shade patches with low light intensity are frequently abundant in soil water and nutrients (Alpert and Stuefer, 1997; Stuefer, 1998; Zhang and Zhang, 2013). Neither of these patches are favorable for individual plant (ramet) growth, but interconnected ramets that are situated in both types of patches are potentially beneficial because they can specialize to acquire locally abundant resources via changes in morphology, physiology and/or biomass allocation and mutually exchange acquired resources via clonal integration (Ikegami et al., 2008; Wang et al., 2011; Roiloa et al., 2014). For instance, ramets in the high-light but low-water/nutrient condition can increase leaf photosynthesis rate, leaf nitrogen content, leaf chlorophyll content, leaf size and/or biomass allocation to shoots and their connected ramets in the low-light but high-water/nutrient condition can increase water/nutrient uptake rate, specific root length and/or biomass allocation to roots, showing division of labor (Stueffer et al., 1996; Liao et al., 2003; Roiloa et al., 2007). Such clonal division of labor can greatly increase the efficiency of resource harvesting (Bloom et al., 1985; Stuefer, 1998; Freschet et al., 2018) and thus promote the performance of the whole clone (Friedman and Alpert, 1991; Stueffer et al., 1996; Roiloa et al., 2007; Roiloa et al., 2014; Lin et al., 2018).

While division of labor has been observed in a number of clonal plants and also in both invasive alien and native species under environments with reciprocal patchiness of resources (Friedman and Alpert, 1991; Roiloa et al., 2007; Ikegami et al., 2008; Wang et al., 2011; Roiloa et al., 2014; Huang et al., 2018), few studies have compared the ability of division of labor between invasive alien and native clonal plants. Comparing invasive alien species with their phylogenetically closely related native species (e.g., congeneric species) that occur in the same habitats is a powerful approach to understand the mechanisms underlying the invasion success of alien species (McDowell, 2002; Burns, 2004; van Kleunen et al., 2010; van Kleunen et al., 2014). Additionally, while clonal integration has been found to benefit invasive alien clonal plants more than their native congeners under heterogeneous environments consisting of low- and high-quality patches (Wang et al., 2017), it is still unknown whether clonal integration also benefits invasive alien clonal plants more than their native congeners under reciprocal patchiness of resources.

We grew connected (allowing clonal integration) and disconnected (preventing clonal integration) clonal fragments (each consisting of a developmentally older ramet and a developmentally younger ramet) of an invasive plant Wedelia trilobata and its congeneric native plant Wedelia chinensis under reciprocal patches of light and soil nutrients. Specifically, we tested the following hypotheses: (1) clonal integration increases the performance of both the invasive and the native plant under reciprocal patchiness of resources; (2) clonal integration benefits the invasive plant more than the native plant under such a type of heterogeneous environment; (3) both the invasive and the native plant show division of labor in terms of physiology, morphology and/or biomass allocation in the presence of clonal integration; (4) the ability of labor division is higher in the invasive than in the native plant.

Clonal integration can confer invasive alien clonal plants a competitive advantage over native ones under heterogeneous environments consisting of favorable and unfavorable patches (Wang et al., 2017). We found that clonal integration could also benefit the invasive plant W. trilobata more than that of its native congener W. chinensis heterogeneous environments with reciprocal patchiness of light and soil nutrients. However, the invasive species did not show a large ability of division of labor in such an environment.

The ability of plants to capture and utilize resources is an important determinant of their growth and fitness (Alpert, 1999; Feng et al., 2007b; Huang et al., 2018). To increase resources capture, plants are able to adjust the morphology and physiology of their roots and leaves, as well as biomass allocation to roots vs. to shoots, in response to the availability of above- and belowground resources (Burns and Winn, 2006; Magyar et al., 2007; Song et al., 2010; Roiloa et al., 2013; Keser et al., 2014). For non-clonal plants or isolated ramets, such responses are commonly in the way that is potentially helpful for them to increase the capture of the limiting resources (Bloom et al., 1985; Feng et al., 2007a; Roiloa et al., 2007). For connected ramets growing in heterogeneous environments, however, clonal integration may modify the responses of ramets so that they can respond in the way that is potentially helpful for them to increase the capture of the abundant resources (Stuefer, 1998; Ikegami et al., 2008; Wang et al., 2011; Roiloa et al., 2014; Huang et al., 2018).

Such specialization for abundance was observed in the younger ramet of the invasive plant W. trilobata growing in the high-light but low-nutrient patch in terms of photosynthetic physiology (i.e., greater net photosynthesis rate and chlorophyll content with than without clonal integration; Figure 2 ) and also in terms of biomass allocation (i.e., smaller root to shoot ratio with than without clonal integration; Figure 4 ). These physiological and allocational responses of the younger ramet can potentially increase its efficiency to take up light (Ikegami et al., 2008; Wang et al., 2011; Roiloa et al., 2014; Roiloa et al., 2016; Xi et al., 2019), which was abundant in the patch where the younger ramet grew. Specialization for abundance was also observed in the older ramet of W. trilobata growing in the low-light but high-nutrient patch in terms of root morphology (i.e., greater specific root surface area, total root length and total root surface area in the presence vs. absence of clonal integration) to increase nutrient capture ( Figures 3C, E, F ). These results suggest that, in the environment with reciprocal patchiness of light and soil nutrients, the interconnected ramets of the invasive plant W. trilobata demonstrated division of labor. Similarly, the interconnected ramets of the native plant W. chinensis also demonstrated division of labor in terms of root morphology of the older ramet ( Figures 3C–F ) and biomass allocation of the younger ramet ( Figure 4 ).

Division of labor was also reported in many other clonal plants, including the invader Carpobrotus edulis and the native Fragaris chiloensis when their connected ramets grew in heterogenous environments with reciprocal patchiness of light and soil nutrients (Friedman and Alpert, 1991; Roiloa et al., 2007; Roiloa et al., 2014). The invader Mikania micrantha and the native plant Trifolium repens when their connected ramets grew in heterogenous environments with reciprocal patchiness of light and soil water (Stueffer et al., 1996; Huang et al., 2018). Additionally, connected ramets of C. edulis from both the native and invaded regions showed division of labor in terms of morphology and physiology (Roiloa et al., 2016) and connected ramets collected from dunes showed a greater capacity of division of labor than those from grasslands (Roiloa et al., 2007).

While the younger ramet of W. chinensis did not show specialization for abundance in terms of photosynthesis physiology ( Figure 2 ), specialization for abundance in terms of biomass allocation of the younger ramet and specific root surface area and specific root length of the older ramet were significantly stronger in W. chinensis than in W. trilobata ( Figure 3 ). Thus, in the heterogeneous environment consisting of reciprocal patches of light and nutrients, the overall ability of division of labor was not stronger in the invasive species W. trilobata than in the native one W. chinensis. The results also suggest that different species may show division of labor in terms of different sets of traits (morphological, physiological and allocational traits), as reported before (Roiloa et al., 2007; Wang et al., 2011; Roiloa et al., 2016; Huang et al., 2018; Xi et al., 2019).

In heterogeneous environments with reciprocal patchiness of resources, division of labor can commonly increase resource harvesting for ramets in both types of patches and consequently promote the growth of the whole clone (Roiloa et al., 2007; Roiloa et al., 2014). We indeed observed that, when connected ramets of the clonal invader W. trilobata grew in the heterogeneous environment with reciprocal patchiness of light and soil nutrients, clonal integration significantly increased the growth of both types of ramets and also promoted that of the whole clone ( Figures 5 , 6 ). Surprisingly, however, this growth promotion was not observed in the native plant W. chinensis, despite the fact that clonal integration also resulted in division of labor in this species. These results suggest that division of labor may not always result in growth promotion, as its induction may incur greater costs (Alpert and Stuefer, 1997; Stuefer, 1998). The results also suggest at the first time that clonal integration can benefit invasive clonal species more than native ones when they grow in heterogeneous environments consisting of reciprocal patches of resources.

We conclude that in heterogeneous environments consisting of reciprocal patches of resources, which are common in natural habitats (Alpert and Mooney, 1996; Stuefer, 1998; Liao et al., 2003; Chu et al., 2006), clonal integration can confer invasive plants a competitive advantage over natives, but this difference is not related to their capacity of labor division. One caveat is that we used only one pair of invasive and native plant species so that the generality of the findings is limited. Further studies could consider using multiple species pairs to test the generality of our findings. Additionally, roles of clonal integration and division of labor in mediating competition between invasive and native clonal plants should also be tested. This study highlights the importance of clonal integration for plants in heterogeneous environments consisting of reciprocal patches of resources and suggests that clonal integration can contribute to the invasion success of alien clonal plants (Song et al., 2013; Wang et al., 2017; Roiloa et al., 2019).

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

J-SC and L-XH contributed to conception and design of the study. L-XH, X-MZ, and XX conducted the experiments. L-XH, J-PL, and N-FL performed the statistical analysis. L-XH, F-HY, and MT wrote the first draft of the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.

This research was funded by NSFC (grant 32071527).

We gratefully thank Min Su and Hao Wang for assistance with the experiment.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.