Growth reduction and alteration of nonstructural carbohydrate (NSC)allocation in a sympodial bamboo (Indocalamus decorus) under atmospheric O3 enrichment

Regional increases in atmospheric O3, mainly produced photochemically from anthropogenic precursor gases, have phytotoxicity due to its strong oxidizing properties. To determine the response of bamboo physiology to elevated O3 levels, three-year-old dwarf bamboo (Indocalamus decorus) clones were exposed to three O3 concentrations (Ambient-AA, 21.3 to 80.9 ppb in the daytime; AA+70, 70 ppb O3 above ambient; AA+140, 140 ppb O3 above ambient) in open-top chambers for one growing season in Beijing, China. Gas exchange, biomass, growth, soluble sugar, and starch contents were examined at the end of the experiment. Our findings indicated that: (1) elevated O3 treatments decreased the photosynthesis rate, total biomass, and bud numbers but increased individual bud biomass and rhizome bud to rhizome biomass ratio. The most severe reduction was observed in new rhizome biomass (35.9% reduction in AA+70 and 57.2%reduction in AA+140), whereas individual bud biomass increased by 50%and 75%in the AA+70
and AA+140 groups compared with AA, respectively; (2) the starch contents in the rhizome decreased by 28.4%, whereas soluble sugar increased by 38.1% in the AA+140 rhizome buds compared to AA; (3) only the culm numbers of pachymorph rhizomes (clumped) decreased, whereas no changes in leptomorph rhizomes were observed. However, the mean distance between two ramets was lengthened by 49.4% and 86.5% in AA+70 and AA+140, respectively. In conclusion, Indocalamus decorus allocated more nonstructural carbohydrates (NSCs) from the rhizome to the buds to form stronger buds and ensure the survival of newer generations as a high priority in response to O3 exposure. Indocalamus decorus may be conducive to escaping from disadvantaged habitats and decreasing resource competition by lengthening the distance between two ramets.