Photosynthate Partitioning in Split-Root Citrus Seedlings with Mycorrhizal and Nonmycorrhizal Root Systems

Abstract

Photosynthate partitioning was examined in seedings of sour orange (Citrus aurantium L.) and Carrizo citrange (Poncirus trifoliata jL.j Raf.x C. sinensis [L.] Osbeck) grown with split root systems inoculated on one side with vesicular-arbuscular mycorrhizal fungus (Glomus intraradices Schenck and Smith). Source-sink relations were studied without mitipting differences in mineral content or physiological age that can occur in separate plant comparisons, because phosphorus was evenly distributed between leaves on opposite sides of the seedlings. Aboveground portions of each plant were exposed to '4CO2 for 8.5 minutes and ambient air for 2 hours, followed by extraction and identification of labeled assimilates. Mycorrhizal halves of root systems accumulated 66 and 68% of the '4C-labeled photosynthates translocated to roots of sour orange and 'Carrizo' citrange, respectively, as well as an average of 77% greater disintegrations per minute per gram fresh weight. Distribution of '4C-labeled assimilates was independent of phosphorus effects on photosynthate partitioning in leaves and did not reflect fresh or dry weights of roots or degree of mycorrhizal dependency of the species. Differences in radioactivity between mycorrhizal and nonmycorrhizal root halves after 2 hours indicated at least 3 to 5% of the whole plant '4C-labeled pbotosynthates were allocated to mycorrhizae-related events on one side and that twice this amount, or 6 to 10%, might be expected if the entire root system was infected.

ACCUMULATION OF PHOSPHORUS, DRY MATTER AND BETAINE DURING NaCl STRESS OF SPLIT‐ROOT CITRUS SEEDLINGS COLONIZED WITH VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI ON ZERO, ONE OR TWO HALVES

“…Hirrel & Gerdemann (1980) found that NaCl at 12 g kg~^ soil reduced colonization of onion and bell pepper plants from the typical, respective values of 55 to 70% and 60 to 80% for non-salinized plants to only 15 to 40% and 5 to 20%,. The 53% colonization at the highest salt concentration in the present study was still at a level considered adequate for mycorrhizal enhancement of plant growth (Koch & Johnson, 1984) and in fact showed a substantial beneficial effect even at this reduced level (Pigs 2 and 3).…”

“…x Citrus sinensis (L.) Osbeck] seedlings were grown as described by Koch & Johnson (1984). Seedling root halves were potted into two 500 ml square plastic containers joined together along one side.…”

“…A common problem in mycorrhtzal research is the difference in growth of colonized vs non-colonized plants due to levels of phosphorus nutrition. Koch & Johnson (1984) showed that the split-root technique offers a means of studying mycorrhizal effects on physiological responses without the interference of phosphorus nutrition.…”

The growth of the extramatrical mycelium of ectomycorrhizal fungi and the growth response of Pinus sylvestris L.

“…This has been demonstrated and discussed for VA mycorrhizas (Koch & Johnson, 1984;Koide &: Elliot, 1989;Jakobsen & Rosendahl, 1990) as well as for ectomycorrhizas (Reid, Kidd & Ekwebelam, 1983;Finlay & Read, 1986a). The experiments of Miller, Durall & Rygiewicz (1989) are of particular interest for the interpretation of our results.…”

Carbon partitioning patterns of mycorrhizal versus non‐mycorrhizal plants: real‐time dynamic measurements using 11CO2

“…One-half of the root system from the cluster of tillers was placed on each side of the split-root apparatus (Fig. 1), modelled on that of Koch & Johnson (1984).…”