The recent widespread increase in iron chlorosis on acid, sandy soils in Florida has led to studies of the underlying causes. The leaves on affected trees are deficient in iron (10). Field (3,5).Little is known about the fundamentals of heavy-metal nutrition of citrus. There is actually little information on the relative toxicities, antagonistic reactions, or the nature and extent of the accumulation of heavy metals in roots of any plant. Much additional research is needed to elucidate the processes of their absorption and accumulation. The present studies were made with the hope that some information on these aspects of nutrition could be gained and it is felt that the results presented will contribute toward this end.
Materials and methodsThe plants tested were young citrus seedlings grown in seedbeds of vermiculite as described elsewhere (9). Valencia orange seedlings were used mostly; however, some Sunki mandarin seedlings were included in one experiment. The seedlings were one to two months old when used and the experiments were continued two or three months, which gave sufficient time for a widely differential growth response.Two systems of culture were used. The first involved use of clay pots filled with vermiculite and placed in glazed pottery vessels which permitted sub-irrigation with the desired nutrient solution. The solution was flushed through the pot twice weekly and adjusted frequently to keep the pH near 4 and to maintain the liquid level. Fresh solutions were applied about every two weeks. The second system was a solution culture in one-quart glass jars that had been painted successively on the outside with asphalt and 371 www.plantphysiol.org on May 9, 2018 -Published by Downloaded from
Synopsis
Organic amendments in addition to flooding were injurious to rice yields and increased plant Fe uptake but decreased Mn. The Fe levels in plants grown submerged in water and unsubmerged without organic amendments were found comparable, but the submerged yields were higher and were accompanied by a Mn uptake more than tenfold that of rice grown unsubmerged. Marked yield response to Mn was obtained in upland cultures. Levels of Mn found in plants indicate that rice has a high requirement for and an exceptionally high tolerance to Mn.
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