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The effects of elevated atmospheric CO 2 on the amount and depth distribution of plant water uptake in a California annual grassland
Author(s) -
MOORE LISA A.,
FIELD CHRISTOPHER B.
Publication year - 2006
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2006.01105.x
Subject(s) - monoculture , agronomy , microcosm , water content , growing season , grassland , biomass (ecology) , environmental science , ecosystem , moisture , chemistry , ecology , environmental chemistry , biology , geotechnical engineering , organic chemistry , engineering
Soil moisture profiles can affect species composition and ecosystem processes, but the effects of increased concentrations of atmospheric carbon dioxide ([CO 2 ]) on the vertical distribution of plant water uptake have not been studied. Because plant species composition affects soil moisture profiles, and is likely to shift under elevated [CO 2 ], it is also important to test whether the indirect effects of [CO 2 ] on soil water content may depend on species composition. We examined the effects of elevated [CO 2 ] and species composition on soil moisture profiles in an annual grassland of California. We grew monocultures and a mixture of Avena barbata and Hemizonia congesta – the dominant species of two phenological groups – in microcosms exposed to ambient (∼370 μmol mol −1 ) and elevated (∼700 μmol mol −1 ) [CO 2 ]. Both species increased intrinsic and yield‐based water use efficiency under elevated [CO 2 ], but soil moisture increased only in communities with A . barbata , the dominant early‐season annual grass. In A. barbata monocultures, the [CO 2 ] treatment did not affect the depth distribution of soil water loss. In contrast to communities with A. barbata , monocultures of H. congesta , a late‐season annual forb, did not conserve water under elevated [CO 2 ], reflecting the increased growth of these plants. In late spring, elevated [CO 2 ] also increased the efficiency of deep roots in H. congesta monocultures. Under ambient [CO 2 ], roots below 60 cm accounted for 22% of total root biomass and were associated with 9% of total water loss, whereas in elevated [CO 2 ], 16% of total belowground biomass was associated with 34% of total water loss. Both soil moisture and isotope data showed that H. congesta monocultures grown under elevated [CO 2 ] began extracting water from deep soils 2 weeks earlier than plants in ambient [CO 2 ].