Quantifying the Effects of Reciprocal Assimilate and Water Translocation in a Clonal Plant by the Use of Steam-Girdling

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Abstract
Experimental studies have shown that clonal plants can reciprocally translocate assimilates and water between interconnected ramets, if grown in heterogeneous environments with complementary resource supplies. Internal exchange of different resources between spatially scattered ramets is a unique trait of clonal plants which can considerably enhance their performance in terms of biomass and clonal offspring production. Cost-benefit analyses have often been used to quantify the effects of clonal integration. The classical version of this analysis, however, is not applicable to the translocation of different resources in two directions, because each ramet can serve as a sink and as a source at the same time. We used steam-girdling to disentangle and to quantify the effects of reciprocal assimilate and water translocation. This method specifically disables assimilate transport, while leaving water integration unaffected. We grew ramet pairs of the clonal herb Potentilla anserina in Spatially heterogeneous environments with complementary availabilities of light and water. The stolen connection between ramets was left intact, steam-girdled or severed. Total biomass and clonal offspring production was highest when the stolen connection was left intact, intermediate when it was steam-girdled and lowest when it was severed, confirming our hypothesis that the degree of clonal integration is positively correlated with plant performance. Cost-benefit analyses revealed that ramets benefited significantly from assimilate and water import. Costs of resource export were absent or small. Fully integrated ramets specialized functionally in the uptake of a locally abundant resource. The degree of functional specialization decreased from intact to steam-girdled and severed ramet pairs. Disconnected ramets specialized in the uptake of the locally most limiting resource. Our results provide evidence that interconnected ramets of P. anserina can benefit from bi-directional resource translocation, and that the scale of these benefits is related to the type and degree of physiological integration within clonal fragments.

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