Soil fungal‐arthropod responses to Populus tremuloides grown under enriched atmospheric CO₂ under field conditions

Abstract

We investigated the influence of elevated CO2 and soil N availability on the growth of arbuscular mycorrhizal and non‐mycorrhizal fungi, and on the number of mycophagous soil microarthropods associated with the roots of Populus tremuloides. CO2 concentration did not significantly affect percentage infection of Populus roots by mycorrhizal or non‐mycorrhizal fungi. However, the extra‐radical hyphal network was altered both qualitatively and quantitatively, and there was a strong interaction between CO2 and soil N availability. Under N‐poor soil conditions, elevated CO2 stimulated hyphal length by arbuscular mycorrhizal fungi, but depressed growth by non‐mycorrhizal fungi. There was no CO2 effect at high N availability. High N availability stimulated growth by opportunistic saprobic/pathogenic fungi. Soil mites were not affected by any treatment, but collembolan numbers were positively correlated with the increase in non‐mycorrhizal fungi. Results indicate a strong interaction between CO2 concentration and soil N availability on mycorrhizal functioning and on fungal‐based soil food webs.

Spatial and temporal deployment of crop roots in CO2‐enriched environments

“…Klironomos et al (1996) found that exposure of plants to elevated [CO # ] resulted in a shift in the balance between mycorrhizal and nonmycorrhizal fungi and bacteria. They later reported that exposure to elevated [CO # ] resulted in a stimulation of a mycorrhizal-based soil food web when soil N was limiting, and a stimulation of the opportunistic-saprobic\pathogenic-fungus-based food web when N was nonlimiting (Klironomos et al, 1997). The increase in pathogenic fungi in high N could result in more root disease and higher mortality.…”

Interspecific differences in the response of arbuscular mycorrhizal fungi to Artemisia tridentata grown under elevated atmospheric CO2

“…However, studies of AM and plant responses to elevated CO # have shown variable results. Several studies have reported an increase in percent AM fungal colonization and enhanced plant biomass under elevated CO # conditions (Morgan et al, 1994 ;Klironomos, Rillig & Allen, 1996), while other studies have found percent colonization or the plants themselves to be unresponsive to CO # enrichment (Curtis et al, 1994 ;Jongen, Fay & Jones, 1996 ;Klironomos et al, 1997 ;Schenk, Jager & Weigel, 1997). There is also evidence of plant speciesspecific responses to the same AM fungal inoculum under elevated CO # (O' Neill et al, 1991 ;Monz et al, 1994).…”

“…In studies with Artemisia tridentata, Klironomos et al (1996) found that proportions of arbuscules, internal hyphae and external hyphae increased, whereas proportions of vesicles and spores were unresponsive to CO # enrichment. In Populus tremuloides, CO # enrichment caused an increase in extra-radical hyphal length but no change in intra-radical colonization levels (Klironomos et al, 1997). It has been suggested that under conditions of environmental stress, AM fungi will respond by favouring vesicle over arbuscule formation (Duckmanton & Widden, 1994 ;Klironomos et al, 1996).…”

“…It has been suggested that under conditions of environmental stress, AM fungi will respond by favouring vesicle over arbuscule formation (Duckmanton & Widden, 1994 ;Klironomos et al, 1996). However, the proliferation of only external AM structures in association with P. tremuloides (Klironomos et al, 1997), and both internal and external structures in association with A. tridentata (Klironomos et al, 1996) under elevated CO # remains unexplained. One avenue that has not been explored with regard to CO # studies is the role different AM species play in controlling plant and mycorrhizal responses.…”

“…Concurrent with this trend is a rise in nitrogen deposition that has also been shown to affect plant and soil biota (Shafer & Schoeneberger, 1991 ;Zak et al, 1993). Elevated CO # and N fertilization can act synergistically on plant interactions above-and below-ground (Klironomos et al, 1997 ;Schenk et al, 1997), and future research efforts should be directed towards studying interspecific AM responses to both these treatments with a wider range of plant species. …”