Effects of clonal integration on species composition and biomass of sand dune communities

Many studies tested individual-level effects of clonal integration, but few addressed those at community level. In dune communities dominated by Hedysarum laeve, we severed rhizome connections of Hedysarum in 3 m × 3 m plots (preventing integration), or added water/nitrogen in areas surrounding the plots (increasing integration), with untreated plots as control. We expected that severance would decrease, and water/nitrogen addition would increase, performance of Hedysarum, change that of some other species, and thus modify species composition and community biomass. After two growth seasons, neither severance nor resource addition affected growth of Hedysarum, and thus affected growth of most other species or species diversity of the dune communities. However, community aboveground biomass was larger in the nitrogen-addition treatment than in the control, due to higher biomass of the annual herb Corispermum candelabrum. The biomass increase was likely because lateral roots of Corispermum at the inner edge of the plots reached and thus used the nitrogen added surrounding the plots. An alternative explanation is that nitrogen added in the surrounding area was translocated into the plots through the rhizomes of Hedysarum and released at least in part to the soils, which increased the growth of the Corispermum plants close to Hedysarum.