While many clonal plants are highly successful invaders, not all clonal plants share resources, often making the contribution of clonal integration (i.e., the translocation of resources among ramets) to invasion unclear. To determine if photosynthate translocation augments performance of emerging daughter ramets for a globally invasive grass (Imperata cylindrica), we combined a 13CO2 pulse-chase experiment with a greenhouse experiment manipulating light levels and rhizome attachment. Model simulations were also used to determine if clonal integration facilitated photosynthate translocation, if the performance of daughter ramets was enhanced by clonal integration, and if shaded ramets benefited relatively more from transferred photosynthate. We found that acropetal photosynthate transfer occurred between all sampled parent-daughter ramet pairs and that this resource sharing led to higher biomass and tiller production when rhizomes between parent and daughter ramets were intact. We also found that the benefits of integration to recipient clones outweighed the costs to donors, since there was no reduction in parent plant performance due to sharing. Additionally, analysis of our data show that photosynthate transfer was likely of greater benefit in overcoming growth constraints in the shade than in the full sun (posterior probability ~ 96.5%), a result that is further supported by our numerical simulations from a basic growth model. Thus, photosynthate transfer is a probable mechanism that explains why clonal integration can be particularly beneficial in heterogeneous resource environments. More generally, resource sharing among clonal plants may be a critical but underappreciated trait of invasive species.

Data originate from a greenhouse study of clonal integration in Cogongrass (Imperata cylindrica). Cogongrass ramets were transplanted into one end of a rectangular window box mesocosm, and allowed to grow linearly along length of box. In this way, the planted half constituted the "parent patch", while the colonized half constituted the "daughter patch". To assess the impact of clonal integration, rhizomes were severed at the midpoint of the mesocosm halfway through the growth cycle. Aboveground biomass, root biomass, rhizome biomass, tiller count, and tillers added post-severing were all assessed in both parent and daughter patches. If clonal integration (i.e. sharing of resources such as photosynthate) is important to Cogongrass performance, than severing should reduce performance in the daughter patch relative to unsevered plants. Likewise, if clonal integration incurs an expense to the parent plants, we would expect the parent patch in unsevered plants to have less biomass and tiller production relative to severed plants. We tested the role of clonal integration across two light environments (ambient and shaded) in order to check the importance of environmental heterogeneity in modulating the benefits of clonal integration.

Each row in the dataset represents observations of biomass or tiller count from a single unique pot, and separates out by daughter versus parent patch.

Variable names and definitions:

Tillers_P : tiller count in parent patch

AGB_P: aboveground biomass (g) in parent patch

Tillers_D: tiller count in daughter patch

AGB_D: aboveground biomass (g) in daughter patch

Tillers_added: tillers added in daughter patch after rhizome severing

Light: light environment (A=ambient, S = shade)

Rh: rhizome severing condition (C=cut/severed, I = intact)

Block: block within greenhouse.

RH_P: rhizome biomass (g) in parent patch

Root_P: root biomass (g) in parent patch

Total_P: total biomass (g) in parent patch

RH_D: rhizome biomass (g) in daughter patch

Root_D: root biomass (g) in daughter patch

Total_D: total biomass (g) in daughter patch