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Influence of vesicular-arbuscular mycorrhiza on Leucaena leucocephala growth, water relations and nutrient acquisition
|Title:||Influence of vesicular-arbuscular mycorrhiza on Leucaena leucocephala growth, water relations and nutrient acquisition|
|Abstract:||Knowledge of the dynamics of VA mycorrhizal plant systems is fundamental to the understanding of the relationships between VA mycorrhiza, plants and soil. Pot experiments were conducted to: 1) determine early physiological responses to VA mycorrhizal inoculation, 2) measure the acquisition and utilization of water and nutrients, dry matter production and assimilate partitioning in mycorrhizal and non-mycorrhizal plants, and 3) develop a model of VA mycorrhizal influence and its consequences to the physiology and ecology of VA mycorrhizal plants.|
Leucaena leucocephala seedlings, with and without the VA mycorrhizal fungus (Glomus aggregatum), were grown in a Wahiawa soil (Tropeptic Eutrustox) with soil P levels ranging from 0.005 to 0.429 mg L-1 of P in 0.01 M CaCl2 extract. Without mycorrhizal infection, leucaena plant growth was stunted under low soil P conditions. Even with high P fertilization, the growth of non-mycorrhizal plants was less than the growth of mycorrhizal plants.
Daily pinnule sampling, pot weighing methods and multiple 5-day-interval harvests revealed a series of changes in nutrient uptake, dry matter production and water transpiration between mycorrhizal and non-mycorrhizal plants. The series of changes was as follows: 1) Five days after inoculation, plant roots had about 7% mycorrhizal infection. 2) At 10 days, root P concentrations were higher in mycorrhizal plants than in non-mycorrhizal plants. By 15 days after inoculation, increases in shoot P, K and S concentrations were observed in mycorrhizal plants. Shoot Mg and Ca concentrations in mycorrhizal plants were greater than in non-mycorrhizal plants at 20 and 25 days after inoculation, respectively. From 10 to 15 days after inoculation, the flux of P into mycorrhizal roots was greater than that into non-mycorrhizal roots. 3) Elevated nutrient contents in shoots of mycorrhizal plants was followed by superior growth rates. Mycorrhizal plants also allocated more assimilate to leaf growth than did non-mycorrhizal plants. Increased leaf growth was followed by increased transpiration. 4) Leaf area expansion rates and net assimilation rates were greater for mycorrhizal plants than for non-mycorrhizal plants. Greater dry weight was observed in mycorrhizal plants, supporting further growth of the mycorrhizal roots (positive feedback), and 5) Greatest soil volume was explored by the mycorrhizal roots. A scheme to explain these changes is pressed and used to describe processes involved in the soil-mycorrhiza-plant system.
In contrast, the flux of P into non-mycorrhizal roots decreased during the period 10 to 15 days after transplanting. The resulting low P content in non-mycorrhizal plants further reduced relative leaf expansion rates, net assimilation rates and later reduced relative root expansion rates (negative feedback). Nevertheless, when non-mycorrhizal plants were subsequently inoculated they eventually attained a similar size and weight as mycorrhizal plants. The stunting of non-mycorrhizal plants thus appears to be reversible and probably is part of a survival strategy which reduces energy use while retaining the potential for mycorrhizal infection.
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Ph.D. - Agronomy and Soil Science|
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