Einfluß der Bodentemperatur und organischer Stoffe im Boden auf die Wirkung der vesikulär-arbuskulären Mykorrhiza / Pierre Nyabyenda.

Tese (doutor)- Georg-August-Universität, 1977

Development of vesicular-arbuscular mycorrhiza and its effect on plant growth depend on many environmental factors. Of these, the organic matter content of the soil and soil temperature were studied. The inter­actions of fertilization and light intensity with soil temperature were included in these investigations. Eupatorium odoratum, a species highly responsive to mycorrhiza, was used throughout this study. In addition, Solanum melongena, Sorghum bicolor, and Guizotia abyssinica were included in some experiments. The fungus used was an isolate originally derived from E. odoratum, probably belonging to the genus Glomus. The soil was acidic (pH 5.5) with low phosphate availability. The general source of fertilizer phosphate was hydroxylapatite, Ca5(P04)30H, other phosphates used in one experiment were FeP04, AlPO4 and Ca (H2P04) 2 . H20 . The organic materials added to the soil were sucrose, starch, cellulose, straw, sawdust and peatmoss; they were used in amounts corresponding to 0.025-0.1 per cent C in the soil. At the highest rate only peatmoss and only with S.melongena improved the mycorrhiza effect, the others inhibited plant growth. Small amounts of sucrose, starch and cellulose did not interfere with or (cellulose) induced a slight increase of the mycorrhizal effect. probably, the few and small positive effects of organic materials on the mycorrhiza were due to changes in other soil properties, e.g. structure, which influence plant growth and thereby indirectly the mycorrhiza. lf insoluble phosphates were supplied, E. odoratum without mycorrhiza in no way responded to soil temperature between 20ºC and 35ºC (Tab. 5, 9, 11, 17, 48, 50; Fig. 7, 9, 10, 24). This corresponded with the P uptake which was identically low at alI the temperatures (Tab. 6,9,11,18,48,54; Fig. 1, 11, 12,25). Mycorrhizal plants of E.odoratum supplied with insoluble phosphates, on the other hand, showed a very strong response to temperature with a steep rise from 20ºC to 30ºC and a falI from 30ºC to 35ºC (Tab. 5, 9, 11, 17, 48, 54; Fig. 7, 9, 10, 24). Growth of the mycorrhizal plants was closely correlated with P uptake whose changes with temperature were even of a higher order than those of growth (Tab. 9, 11, 18,48,54; Fig. 1, 11, 12,25), with the consequence that mycorrhizal plants had a higher P con­centration than non-mycorrhizal. The uptake of N, K, Ca, AI and Fe paralleled growth; no specific effect of mycorrhiza on the absorption of these elements was apparent (Tab. 7, 9, 10, 11, 12, 19, 20, 21, 46, 47; Fig. 2). Reduction of light intensity (shading) had no effect on non­mycorrhizal plants, but decreased the efficacy of the mycorrhiza. At 30ºC, shading had less effect on mycorrhizal plants (growth and P uptake) than at 25ºC and 35ºC (Tab. 50-55). Counts of vesicles, arbuscles and mycelium in the roots showed that at the highest temperature (35ºC) the development of mycelium and arbuscles was inhibited, whereas at low temperatures (20º and 25ºC) the number of vesicles was reduced (Tab. 8,22,49). However, temperature seems to affect the physiological activity of the mycorrhiza more than its development, since plants kept at the optimum temperature (30ºC) for 20 days before being moved to lower or higher temperatures showed the same influence of temperature on growth and P uptake as plants kept from the beginning at the different temperatures (Chapter 3.2.5). In the presence of suluble phosphate (Ca(H2P04)2'H20) , non-mycorrhizal E.odoratum plants responded well to temperature (Tab. 15-21; Fig. 9-12). The optimum temperature was 30ºC, the drop at 35ºC was as pronounced as in mycorrhizal plants. At the lowest temperature (20ºC), the non-mycorthizal plants grew better and took up more phosphate than the mycorrhizal, i.e., the mycorrhiza was detrimental. However, at the highest temperatures (30ºC and 35ºC) the mycorrhizal plants always were superior even in the presence of soluble phosphate, although the effect was not as striking as with insoluble phosphate. In an experiment with diurnally changing temperatures it was shown that 35ºC are not harmful to the development and physiological effect of the mycorrhiza if the high temperature was given only during the day, followed by night temperatures of 25ºc or 30ºC (Tab. 45, 46, 47; Fig. 24, 25). Contrary to E.odoratum, non-mycorrhizal plants of G.abyssinica and S.bicolor did respond to temperature in the presence of insoluble phosphate, G.abyssinica less than S.bicolor (Tab. 23,29,34,40; Fig. 13, 15, 17, 18). The optimum temperature for both plants without and with mycorrhiza was 30ºC. At temperatures of 25ºC and higher, both species can absorb considerable amounts of phosphorus from insoluble compounds in the absence of mycorrhiza (Tab. 24, 30, 35, 41; Fig. 19, 2o), Sorghum more efficiently than Guizotia; this ability is completely lacking in E.odoratum. In both plants the mycorrhiza increased P uptake and growth at 25ºC and 30ºC, not or very little at 20ºC and 35ºC. At the latter temperature non-mycorrhizal Sorghum took up as much P as mycorrhizal. There is an indication that two mechanisms with different response to temperature are involved in P uptake by non-mycorrhizal and mycorrhizal plants since the increase in P uptake and growth from 20ºC was much steeper in mycorrhizal than in non-mycorrhizal plants. The adaptation of G. abyssinica to relatively low temperatures led to very poor growth at 35ºC.