Differential phosphorus and nitrogen effects drive species and community responses to elevated CO sub(2) in semi-arid grassland

Productivity of dryland communities is often co-limited by water and nutrients. Since atmospheric CO sub(2) enrichment induces water savings by plants, elevated CO sub(2) and nutrients could interact to reduce growth limitation, irrespective of the direct influence of CO sub(2) on photosynthesis. We...

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Bibliographic Details
Published in:Functional ecology 2003-12, Vol.17 (6), p.766-777
Main Authors: Gruenzweig, J M, Koerner, C
Format: Article
Language:English
Online Access:Get full text
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Summary:Productivity of dryland communities is often co-limited by water and nutrients. Since atmospheric CO sub(2) enrichment induces water savings by plants, elevated CO sub(2) and nutrients could interact to reduce growth limitation, irrespective of the direct influence of CO sub(2) on photosynthesis. We studied CO sub(2) effects in model communities from the semi-arid Negev of Israel with 17 mostly annual C sub(3) species at three CO sub(2) concentrations and three nutrient treatments. Community biomass increased at elevated (440 and 600 mu L L super(-1)) compared to pre-industrial CO sub(2) (280 mu L L super(-1)) by 34% on average in the low-nutrient control, by 45% in the high P and by 50% in the high NPK treatment. Less evapotranspiration at elevated CO sub(2) increased soil water content by 30-40% on average. Significant CO sub(2)-fertilization interactions indicated that plant responses to CO sub(2) enrichment were constrained by nutrient availability. Responses of biomass and water-use efficiency (dry-matter accumulation per cumulative evapotranspiration) to CO sub(2) enrichment were non-linear and were saturated at 440 mu L L super(-1) at low nutrient and high P supply. CO sub(2) effects were further increased up to 600 mu L L super(-1) only under full NPK fertilization. The overall CO sub(2) effect on biomass depended on the differential response of plant functional groups, with the P-dependent legume response dominating at low nutrient and high P supply, and the N-dependent grass response dominating at high NPK. With the exception of grasses, species responded differently to combinations of CO sub(2) enrichment and nutrient addition, even within functional groups. Biomass production was co-limited by CO sub(2) and nutrients in this semi-arid seasonal community, with both effects possibly mediated by water availability. Nutrient losses associated with desertification will thus diminish potential gains in biomass due to elevated CO sub(2). Growth stimulation by CO sub(2) enrichment beyond close-to-current concentrations will only be seen under nutrient-rich conditions in semi-arid and possibly other drought-stressed grasslands.
ISSN:0269-8463
DOI:10.1111/j.1365-2435.2003.00797.x