Biomass production and species composition change in a tallgrass prairie ecosystem after long‐term exposure to elevated atmospheric CO₂

Abstract

To determine the long‐term impact of elevated CO2 on primary production of native tallgrass prairie, we compared the responses of tallgrass prairie at ambient and twice‐ambient atmospheric CO2 levels over an 8‐year period. Plots in open‐top chambers (4.5 m diameter) were exposed continuously (24 h) to ambient and elevated CO2 from early April to late October each year. Unchambered plots were monitored also. Above‐ground peak biomass was determined by clipping each year in early August, and root growth was estimated by harvesting roots from root ingrowth bags. Plant community composition was censused each year in early June. In the last 2 years of the study, subplots were clipped on 1 June or 1 July, and regrowth was harvested on 1 October. Volumetric soil water content of the 0–100 cm soil layer was determined using neutron scattering, and was generally higher in elevated CO2 plots than ambient. Peak above‐ground biomass was greater on elevated CO2 plots than ambient CO2 plots with or without chambers during years with significant plant water stress. Above‐ground regrowth biomass was greater under elevated CO2 than under ambient CO2 in a year with late‐season water stress, but did not differ in a wetter year. Root ingrowth biomass was also greater in elevated CO2 plots than ambient CO2 plots when water stress occurred during the growing season. The basal cover and relative amount of warm‐season perennial grasses (C4) in the stand changed little during the 8‐year period, but basal cover and relative amount of cool‐season perennial grasses (C3) in the stand declined in the elevated CO2 plots and in ambient CO2 plots with chambers. Forbs (C3) and members of the Cyperaceae (C3) increased in basal cover and relative amount in the stand at elevated compared to ambient CO2. Greater biomass production under elevated CO2 in C4‐dominated grasslands may lead to a greater carbon sequestration by those ecosystems and reduce peak atmospheric CO2 concentrations in the future.

Final Report on "Rising CO2 and Long-term Carbon Storage in Terrestrial Ecosystems: An Empirical Carbon Budget Validation"

“…Nitrogen and water availability are key regulators of plant and microbial responses to elevated CO 2 in upland ecosystems (Curtis and Wang 1998; Geiger et al 1999;Owensby et al 1999;Henry et al 2005) and our analysis of long term data suggests that this generalization applies to a tidal marsh ecosystem exposed to elevated CO 2 for two decades. However, the precise mechanisms at work in this wetland ecosystem can sometimes be quite different from other terrestrial ecosystems.…”

“…As a result, increases in photosynthesis can either increase or decrease soil carbon pools (Jastrow et al 2005), although a small increase in soil carbon is more common. Elevated CO 2 generally enhances plant growth, but growth responses are also highly variable (Lloyd and Farquhar 1996;Owensby et al 1999;Oren et al 2001;Nowak et al 2004). Many of these feedbacks are mediated by microbial communities and microbial-plant interactions.…”

“…Elevated CO 2 generally enhances plant growth, but growth responses are also highly variable (Lloyd and Farquhar 1996;Owensby et al 1999;Oren et al 2001;Nowak et al 2004). Many of these feedbacks are mediated by microbial communities and microbial-plant interactions.Nitrogen and water availability are key regulators of plant and microbial responses to elevated CO 2 in upland ecosystems (Curtis and Wang 1998; Geiger et al 1999;Owensby et al 1999;Henry et al 2005) and our analysis of long term data suggests that this generalization applies to a tidal marsh ecosystem exposed to elevated CO 2 for two decades. However, the precise mechanisms at work in this wetland ecosystem can sometimes be quite different from other terrestrial ecosystems.…”

Spatial and temporal variations of C3/C4 relative abundance in global terrestrial ecosystem since the Last Glacial and its possible driving mechanisms

“…170-360 L L 1 ) should be in the range of the so-called "low atmospheric CO 2 concentration" that suitable for the growth of C 4 plants. A field experimental study over eight years carried out in the United States demonstrates that atmospheric CO 2 concentration shows no significant influence on the relative C 4 biomass production even if it reaches twice of the natural concentrations [67].…”

Grazing primarily drives the relative abundance change of C4 plants in the typical steppe grasslands across households at a regional scale

“…A series of studies on paleoclimate climate modelling, and vegetation changes have confirmed the fact that the relative abundance of C 4 plants will decrease with increasing atmospheric CO 2 concentration (Cerling et al 1993;Scheiter et al 2012;Ripley et al 2013). However, some studies did not fully support this view (Owensby et al 1999;Tooth and Leishman 2013). Then researchers gradually realised the importance of temperature.…”