|Blank, Robert - Bob|
Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2003
Publication Date: 4/15/2004
Citation: Blank, R.R., Derner, J.D. 2004. Effects of CO2 enrichment on plant-soil relationships of lepidium latifolium. Plant and Soil. 262:159-167. Interpretive Summary: Elevated atmospheric CO2 has been proposed as a mechanism by which certain weeds increase their invasiveness. We tested a hypothesis that the exotic invasive crucifer, perennial pepperweed (Lepidium latifolium), increases soil nutrient availability in response to elevated atmospheric CO2. This hypothesis was tested at the Temple, TX ARS, CO2 controlled greenhouse facility. Pepperweed plants (and unplanted controls) were grown in a high fertility and low fertility soil and exposed to ambient and elevated atmospheric CO2. Response variables measured included plant mass, plant tissue nutrient concentration and uptake, and several measures of soil nutrient availability. Growth of perennial pepperweed was significantly increased by CO2 enrichment. In addition, plants exposed to elevated atmospheric CO2 overall had less of a particular nutrient per unit mass than plants exposed to ambient CO2. Although several measures of nutrient availability were higher with CO2 enrichment, there is no overwhelming evidence that the interaction of perennial pepperweed growth with exposure to elevated CO2 facilitated greater nutrient availability. The data does suggest that soil nutrient availability is influenced by an interaction of CO2 treatment with soil microflora.
Technical Abstract: The exotic crucifer Lepidium latifolium (perennial pepperweed) is invading wetland and riparian habitats throughout the western United States. Based on previous field studies, our working hypothesis proposed that L. latifolium elevates soil nutrient acquisition ability in response to CO2 enrichment. Replicates of L. latifolium were grown in a high fertility and low fertility soil (along with unplanted controls) in a glasshouse at ambient and elevated CO2 concentrations (360 and 699 µmol mol-1, respectively). Plants were harvested after 81 days and numerous plant and soil attributes measured. Aboveground plant mass was influenced by a significant CO2 treatment x soil interaction (p<0.001) with CO2 enrichment inducing a greater proportional increase in mass for the low fertility soil. Root concentrations of citrate, malate, and ortho-phosphate and enzyme activities of amidase and asparaginase did not differ between the CO2 treatments across soils. Aboveground tissue concentrations of N, S, P, Mg, K, Fe, and Zn showed a consistent decreasing trend for both soils with CO2 enrichment, corresponding with higher biomass per unit nutrient. Plants grown in the low fertility soil had higher concentrations of N, S, P, Ca, and Mg in aboveground tissue than plants grown in the high fertility soil. Carbon dioxide enrichment decreased tissue N:S ratios by >20 % and increased, though not significant, tissue C:N ratio by 38% in high fertility soil and by 51 % in low fertility soil. Carbon dioxide enrichment increased aboveground uptake of C and S, and most other elements displayed a trend toward greater uptake with CO2 enrichment. For most soil attributes measured there was a main effect or interaction with soil fertility level. Soil attributes differed between soil fertility levels and, with the exception of SO4-2, were not influenced by the presence of L. latifolium. Soil attributes enhanced by CO2 enrichment included acetate extractable Mg+2 (high fertility soil only), net 30 day N mineralization potential (unplanted control soils only), available N (high fertility soil), bicarbonate extractable P, soil-solution SO4-2 (L. latifolium planted pots only), and soil-solution Mg+2 (high fertility control soil only). Collectively, these data tangentially support our working hypothesis that CO2 enrichment increases nutrient availability. That availability of some nutrients increases without plant growth (control soils) however, suggests an interaction of elevated CO2 with soil microflora.