Competitive interactions between established grasses and woody plant seedlings under elevated CO2 levels are mediated by soil water availability

• Published in: Oecologia 2015-02, Vol.177 (2), p.499-506
• Main Authors: Manea, A, Leishman, M. R
• Format: Article
• Language: English
• Subjects: Biomass; Biomedical and Life Sciences; Carbon dioxide; Carbon Dioxide - metabolism; Carbon Dioxide - pharmacology; COMMUNITY ECOLOGY; Community ecology - Original research; Competition; Ecological effects; Ecology; Grasses; Grasslands; Hydrology/Water Resources; Interception; leaf area index; Life Sciences; Moisture content; plant available water; Plant Leaves - physiology; Plant Roots - physiology; Plant Sciences; Plant Shoots - physiology; Poaceae - physiology; rain; seedling growth; Seedlings; Seedlings - growth & development; shoots; Soil - chemistry; soil texture; Soil water; Stomatal conductance; Water - metabolism; Water availability; Wood - physiology; Woody plants
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-014-3143-z

The expansion of woody plants into grasslands has been observed worldwide and is likely to have widespread ecological consequences. One proposal is that woody plant expansion into grasslands is driven in part by the rise in atmospheric CO₂concentrations. We have examined the effect of CO₂concentration on the competitive interactions between established C₄grasses and woody plant seedlings in a model grassland system. Woody plant seedlings were grown in mesocosms together with established C₄grasses in three competition treatments (root competition, shoot competition and root + shoot competition) under ambient and elevated CO₂levels. We found that the growth of the woody plant seedlings was suppressed by competition from grasses, with root and shoot competition having similar competitive effects on growth. In contrast to expectations, woody plant seedling growth was reduced at elevated CO₂levels compared to that at the ambient CO₂level across all competition treatments, with the most plausible explanation being reduced light and soil water availability in the elevated CO₂mesocosms. Reduced light and soil water availability in the elevated CO₂mesocosms was associated with an increased leaf area index of the grasses which offset the reductions in stomatal conductance and increased rainfall interception. The woody plant seedlings also had reduced ‘escapability’ (stem biomass and stem height) under elevated compared to ambient CO₂levels. Our results suggest that the expansion of woody plants into grasslands in the future will likely be context-dependent, with the establishment success of woody plant seedlings being strongly coupled to the CO₂response of competing grasses and to soil water availability.