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Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/16/2002 Publication Date: 10/10/2003 Citation: Schreiner, R.P., Bethlenfalvay, F.J. CROP RESIDUE AND COLLEMBOLA INTERACT TO DETERMINE THE GROWTH OF MYCORRHIZAL PEA PLANTS. Biology and Fertility of Soils. 2003. (39) p. 1-8. Interpretive Summary: The effects of collembola (fungal grazing soil insects) on arbuscular mycorrhizal (AM) fungi and plant growth were studied in a controlled experiment. Collembola (+/- Col) effects were examined in the presence and absence of crop residue (+/- Litter) incorporated into the experimental soil. In the absence of crop residue, collembola reduced root length colonized by AM fungi, total plant dry mass and seed yield. However, in the presence of crop residue, collembola had no effect on root colonization by AM fungi, and increased total plant mass and seed yield. Crop residue also increased root colonization by AM fungi, numbers of bacteria and saprophytic fungi in soil, fungal hyphae lengths in soil, and the final population of collembola in soil. Collembola reduced both small and large diameter hyphae in soil and the number of saprophytic fungi in soil. Food choice tests of collembola showed that these soil insects preferred to consume mycorrhizal roots over uncolonized roots when given only these two choices. However, when crop residue was added as a food choice, the insects preferred to ingest the crop residue over either type of roots. These findings show that collembola can reduce plant growth and yield by consuming beneficial mycorrhizal fungi, but collembola may enhance plant growth and yield by consuming decomposer fungi instead of mycorrhizal fungi if ample crop residue is returned to soil. Technical Abstract: The effects of collembola grazing on arbuscular mycorrhizal (AM) fungi and plant growth were studied in a controlled experiment utilizing a mix of AM fungi and the dominant collembolan species (Isotoma sp.) indigenous to the experimental soil. Collembola (+/- Col) effects were examined in the presence and absence of crop residue (+/- Litter) incorporated into the experimental soil. Significant interactions between collembola and crop residue occurred for mycorrhizal colonization of roots and plant growth. In the absence of crop residue, collembola reduced root length colonized by AM fungi, total plant dry mass and seed pod yield. However, in the presence of crop residue, collembola had no effect on root colonization by AM fungi, and increased total plant mass and pod yield. Crop residue increased root colonization by AM fungi, numbers of bacteria and saprophytic fungi (colony forming units), small (< 5 'm) and large (> 5 'm) diameter hyphal lengths in soil, and the final population of collembola in soil. Collembola reduced both small and large diameter hyphae in soil and the number of saprophytic fungi (colony forming units, p=0.052). Feeding preference experiments conducted in vitro showed that Isotoma sp. preferred to graze on mycorrhizal roots over nonmycorrhizal roots when given no other food choice. However, when crop residue was added as a food choice, Isotoma sp. showed a clear feeding preference on crop residue. We conclude that collembolan grazing on mycorrhizae can be detrimental to plant growth when other fungal food sources are limited, but grazing on mycorrhizal fungi does not occur when ample organic matter and associated saprophytic fungi are present in soils. |
