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ARS Home » Plains Area » Temple, Texas » Grassland Soil and Water Research Laboratory » Research » Publications at this Location » Publication #310564
Title: Dominant plant taxa predict plant productivity responses to CO2 enrichment across precipitation and soil gradients

Author
item Fay, Philip
item Newingham, Beth
item Polley, Herbert
item Morgan, Jack
item Lecain, Daniel
item NOWAK, ROBERT - University Of Nevada
item SMITH, STANLEY - University Of Nevada

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2015
Publication Date: 3/30/2015
Publication URL: http://handle.nal.usda.gov/10113/61375
Citation: Fay, P.A., Newingham, B.A., Polley, H.W., Morgan, J.A., Lecain, D.R., Nowak, R.S., Smith, S.D. 2015. Dominant plant taxa predict plant productivity responses to CO2 enrichment across precipitation and soil gradients. Annals Of Botany Plants. DOI: 10.1093/aobpla/plv027.

Interpretive Summary: Increasing enrichment of Earth’s atmosphere with the gas carbon dioxide (CO2), a well-known ‘greenhouse gas’, is predicted to stimulate the biomass production of rangeland plant communities, in part by increasing the moisture contained in the soil and in part by altering the abundances of different members of the plant community. These changes have consequences for the amount and quality of forage for grazing animals and for the sustainability of rangeland agriculture in future climates. Previous research suggests that CO2 enrichment will more strongly stimulate biomass production in rangelands in drier compared to wetter climates, and on drier compared to wetter soils. We tested this expectation by comparing the results of five CO2 enrichment experiments located in sub-humid, semi-arid, and desert rangeland and in sub-humid grassland on a sequence of fine- to coarse-textured soils. In the sub-humid and semi-arid rangelands and on the two more coarse-textured soils, the only predictor of the yearly CO2 enrichment effect on biomass production unexpectedly was the yearly change in the abundance of the most common species. Desert rangeland biomass production had no cumulative response even after 10 years of CO2 enrichment. These results show that extremely dry rangelands may experience little forage production benefit from continued atmospheric CO2 enrichment, and that the identity of the dominant species will control forage amount and quality in more responsive rangelands.

Technical Abstract: The responses of water-limited ecosystems to rising atmospheric CO2 concentration (eCO2) depend on the supply and availability of soil moisture and on change in abundance of dominant plant taxa. Soil moisture supply and availability depends primarily on precipitation amount and soil texture. Responses to eCO2 in yearly plant aboveground biomass ('AGB) and in the abundance of the dominant plant taxa ('DPT) should be more coupled to eCO2 responses in soil moisture ('SM) in drier ecosystems and on coarser soils, but variation in interactions among 'SM, 'AGB, and 'DPT have not been examined. Data from five CO2 manipulation experiments, including experiments in mesic and semi-arid grasslands and in a xeric shrubland were used to determine how the effects of 'SM and 'DPT on 'AGB varied along gradients of precipitation and soil texture, whether 'SM followed a ‘sequential’ model by influencing 'AGB primarily by driving 'DPT, or a ‘concurrent’ model by interactively affecting 'AGB. Our analyses found no correlations of 'SM with 'DPT or 'AGB in the grassland experiments, and thus did not support either model. Instead, 'AGB was correlated only with 'DPT in both mesic and semi-arid grasslands (R2 0.65 – 0.85), and on sandy loam and silty clay (R2> 0.90) but not on clay soils in mesic grassland, despite increases in mean soil moisture over the multiple years of CO2 enrichment. In the xeric shrubland, eCO2 caused no response in soil moisture, plant species composition, or cumulative change in aboveground biomass after 10 years of CO2 treatment, suggesting a threshold in soil moisture supply or availability below which eCO2 does not alter plant communities and productivity. Thus, dry ecosystems were unlike coarse-textured soils with low water-holding capacity, and were more like fine-textured soils in terms of low eCO2 responses. Conceptual models of ecosystem responses to chronic resource change such as eCO2 can be advanced by devising heterarchical, rather than hierarchical models, incorporating multiple temporal scales on which limiting resources vary, multiple points at which resources control response, and alternate pathways not strictly linked to levels of ecological organization.