[Effects of light intensity contrast on clonal integration of Spartina anglica]

We conducted a greenhouse experiment to test how clonal integration affected the growth responses of Spartina anglica to light intensity heterogeneity in light availability and whether such effects depended on contrast light intensity. The experiment had three homogeneous treatments and two heterogeneous treatments. In the homogeneous treatments, both ramets of a connected ramet pair were unshaded (high light intensity), moderately shaded (medium light intensity, 70% of the high light intensity) and deeply shaded (low light intensity, 30% of the high light intensity). In the heterogeneous treatments, one ramet of a pair was unshaded, but its connected ramet was either moderately shaded (low light intensity contrast) or deeply shaded (high light intensity contrast). In the homogeneous treatments, biomass of S. anglica was significantly higher in the high light intensity treatment than in the medium and low light intensity treatments. Number of leaves, root length, and total biomass were significantly higher in the shaded ramet in the heterogeneous treatment with low light intensity contrast than in the ramet in the homogeneous treatment with medium light intensity. Final size and mass were not significantly different between the unshaded ramet in the heterogeneous treatment with low light intensity contrast and the ramets in the homogeneous high light intensity treatment. These results suggested that clonal integration benefitted a shaded ramet with little cost to an unshaded ramet when contrast in light intensity was low. However, effects of clonal integration were not significant when contrast was high. It therefore appeared that effects of clonal integration on the growth of S. anglica did not increase with increasing light intensity contrast. In natural habitats, clonal integration might improve growth of S. anglica when its ramets are moderately shaded by other plants but not when they are deeply shaded.