Effects of elevated carbon dioxide and arbuscular mycorrhizal infection onTrifolium repens

Abstract

SUMMARYTrifolium repens L. cv. aran was grown for 58 d at ambient (350//mol moi"^) and elevated (700//moi mol"') atmospheric CO^, with and without the arbuscular mycorrhizal fungus Glo?nus mosseae (Nicol. & Gerd.) Gerd. & Trappe cv. YV. Plant biomass, mycorrhizal infeciion, non-structural carbohydrates, C, N and P content were examined. Ele\'ated CO., (a) significantly increased above-and below-ground biomass, (b) decreased specific leaf area and specific root lengtb, (c) decreased tissue "^N and increased tbe C:X ratio, and (d) significantly increased total non-structural carbohydrates. Inoculating T. repens with Glomus mosseae (a) significantly increased abo\ e-and below-ground biomass, (h) increased the total root length and total leaf area, and (c) significantly decreased tissue°o P-Evidence of an increased influence of mycorrhiza on the P nutrition of T. repens at elevated CO^ was found in the 22 "<, increase in leaf total P (P ^ 005) of mycorrhizal plants grown at elevated CO^ compared with nonmycorrhizal plants. No significant interactions were found between CO^ and mycorrhiza treatments.The proportion of T. repens root length colonized by Glomus mosseae was not affected by CO^ concentration. The percentage mycorrhizal infection was 29 % at ambient CO^ and 35 "o at elevated CO^. However, exposure to elevated CO., significantly increased the total mycorrbizal root length from 3-4 to 6-1 m per plant.The results show little evidence that the role of arbuscular mycorrhiza in the growth and nutrition of T. repens would increase if atmospheric CO., were to increase as predicted.

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 addition to the inherent genotypic differences between the species, the fact that the former study used a higher CO # concentration and a distinctive nutrient regime might have contributed to the different response. Jongen et al (1996) found that elevated CO # treatment caused no increase in the proportion of total root length of T. repens that was colonized at 58 d, and even found reduced colonization which was smaller than that seen in P. lanceolata at 41 d. However, subsequent harvests of P. lanceolata demonstrated an increasingly large influence of C ELEV on colonization, to the extent that by 104 d in this treatment the mycorrhizal root length was four times that seen in C AMB . It was a feature of the present study that most of the differences between M plants exposed to CO # treatment only became apparent at 76 d, these effects becoming progressively more pronounced towards the final harvest.…”

“…Greater amounts of colonization were observed in roots of the C % grass Bouteloua gracilis at elevated CO # (Monz et al, 1994 ;Morgan et al, 1994) but not in those of the C $ grass Pascopyrum smithii (Monz et al, 1994), in cotton (Gossypium hirsutum) or in clover (Trifolium repens) (Jongen, Fay & Jones, 1996). 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.…”

“…However some trends in response of mycorrhizal plants to elevated CO # are detectable. Jongen et al (1996) examined the responses of Trifolium repens to C ELEV and mycorrhizal colonization using a relatively high CO # concentration (700 µl l −" ), a short growing season (58 d), and nutrient-enriched quartz sand as substrate. They found greater yields of whole plants, shoots and roots in C ELEV than in C AMB , the differences between the CO # treatments being bigger in the M than in the NM plants.…”

Effects of mycorrhizal colonization on biomass production and nitrogen fixation of black locust (Robinia pseudoacacia) seedlings grown under elevated atmospheric carbon dioxide

“…However, only one study has been performed that examines the response of mycorrhiza to elevated CO # using symbiotic N # -fixing plant species (Jongen et al, 1996). Elevated CO # has been shown to stimulate the productivity of symbiotic N # -fixing plants (Norby, 1987 ;Arnone & Gordon, 1990 ;Thomas et al, 1991 ;Tissue et al, 1997 ;Vogel et al, 1997).…”