Below-Ground Microbial and Microfaunal Responses to Artemisia tridentata Grown Under Elevated Atmospheric Co 2

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Summary 1. Soil microbes are fed primarily by root-derived substrates, fulfil functions such as mineralization, immobilization, decomposition, pathogeneity and improvement of plant nutrition, and form the basis of the below-ground food web. Hitherto, belowground processes have generally been monitored using a 'black-box' approach, thereby ignoring effects of global change at a finer level of resolution. We describe shifts in the activity between microbial functional groups associated with roots of Artemisia tridentata, and the influence of this change on higher trophic levels.2. We tested the hypothesis that elevated atmospheric CO2 causes the soil community to change qualitatively. We measured the responses of several soil microbe and' soil microfaunal parameters to a double-ambient CO2 concentration and nutrient additions. The soil community, as measured by those parameters, showed great changes in response to the treatments. There-was a very strong interaction between elevated CO2 and the nutrient addition. 3. Under low nutrient conditions, total microbial biomass did not change under elevated atmospheric C02, but doubled under conditions of elevated CO2 and added nutrients. As we increased the resolution of our analysis, however, results shifted. Under low nutrient conditions, mycorrhizal fungi responded positively to elevated C02, whereas with added soil nutrients they responded negatively to the same elevated CO2 concentration. Bacteria and non-mycorrhizal fungi did not respond under the former conditions but more than doubled in biomass under conditions of elevated CO2 and added nutrients. Soil fauna was also affected by the treatments. Overall, elevated CO2 shifted carbon flow in the plant-soil system to a more mutualistic-closed, mycorrhizal-dominated system, whereas the combination of elevated CO2 and nutrient addition shifted carbon flow to a more opportunistic-open, saprobe/pathogendominated one. 4. This indicates that elevated atmospheric CO2 may lead to far less predictable feedback patterns than previously thought and that qualitative shifts in the soil community may be far more important than mere changes in total C sink strength.

The role of mycorrhiza in determining the response of Plantago lanceolata to CO2 enrichment

“…The greater percentage of root length colonized in P. lanceolata under C ELEV contrasts with the situation reported not only for T. repens by Jongen et al (1996) but also for other C $ plants : Gossypium , Pascopyrum (Monz et al, 1994), Artemisia (Klironomos et al, 1996) and Liriodendron (O'Neill et al, 1991). Sequential harvests in the latter study revealed progressive increases in total root length with time without change in the proportion of colonized to non-colonized root.…”

“…In the case of the last species, however, although the proportions of root length colonized did not change, the total mycorrhizal root length almost doubled. Klironomos, Rillig & Allen (1996) found that significantly more root length was occupied by arbuscular hyphae and arbuscules at elevated CO # , but only under conditions of low nutrient supply.…”

“…Klironomos et al (1996) grew the C $ shrub Artemisia tridentata for 84 d at C AMB and C ELEV (700 µl l −" ) and examined the effects on hyphal, arbuscular and vesicular colonization. At the end of their experiment, as in the case of P. lanceolata, hyphal and arbuscular colonization were both significantly greater in the C ELEV than in the C AMB treatment, but unlike the situation in P. lanceolata, vesicular colonization was reduced in C ELEV .…”

“…Although this result might imply greater sensitivity of vesicle formation in A. tridentata to CO # elevation, it is not possible to determine, from a one-harvest experiment, whether vesicle production was at equilibrium at this stage. In the study of Klironomos et al (1996), it was shown that nutrient application had major effects upon the observed responses to CO # treatment, negative impacts of C ELEV upon the extent of mycorrhizal colonization being demonstrated. The results of the present study, which were obtained at low nutrient-availability, and those reported for A. tridentata under control conditions are likely to reflect the situation prevailing in the natural ecosystems of these plants, where nutritional constraints are normal.…”

“…It is suggested by Klironomos et al (1996) that the greater arbuscular frequency observed under the low-nutrient regime at C ELEV must be related to mycorrhizal ' activity '. Our results indicate that there might indeed be a relationship between number of arbuscules, P inflow and P content of the plant, but whereas the different arbuscule numbers in C AMB and C ELEV were significant at both H # and H $ , the Prelated parameters were significantly different only at the final harvest.…”