Effects of clonal integration on growth of stoloniferous herb Centella asiatica suffering from heterogeneous heavy metal Cd~(2+) stress
异质性重金属镉胁迫下克隆整合对匍匐茎草本植物积雪草生长的影响

Aims A pot experiment to examine the effects of clonal integration on growth of the stoloniferous herb Centella asiatica suffering from heterogeneous heavy metal Cd2+ stress was conducted to address two questions: (1) does clonal integration alleviate the negative effects on growth of clonal plants suffering from heterogeneous heavy metal stress; and (2) do the ramets growing in unfavorable microhabitats incur increased photosynthetic efficiency in the connected ramets? Methods Relatively young, distal ramets of C. asiatica were assigned to normal or Cd2+ stressed soil, and the stolon connections between the relatively old proximal ramets and the young distal ramets were either severed or left intact. The net photosynthetic rate (Pn), chlorophyll fluorescence (maximum quantum yield of PSII, Fv/Fm) and chlorophyll contents of distal ramets and Pn of proximal ramets were measured. The growth performance of distal and proximal ramets was investigated at the end of the experiment. Important findings Cd2+ stress treatment significantly decreased the Pn, Fv/Fm, chlorophyll contents and growth of distal ramets. Clonal integration significantly alleviated the negative effect of Cd2+ stress to distal ramets in terms of Pn, Fv/Fm, chlorophyll contents and biomass of distal ramets. There was no significant cost to the connected proximal ramets, and clonal integration did not incur increased photosynthetic efficiency in the proximal ramets. In addition, clonal integration significantly decreased root to shoot ratio of distal ramets suffering from Cd2+ stress, and reduced the uptake of the heavy metal. Petiole length of proximal and distal ramets was not significantly affected by stolon severing and Cd2+ stress. It is suggested that clonal integration may enhance growth of clonal plants suffering from heterogeneous heavy metal stress.