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Plant Physiology 43:1870-1873 (1968) © 1968 American Society of Plant Biologists Sap Tension in Flooded Trees and Bushes of the AmazonScripps Institution of Oceanography, UCSD, Brazilian Navy, Instituto de Pesquisas da Marinha, Brazilian Navy The water relations of the inundated forest of the Rio Negro in the Amazon have been investigated. The sap pressure in trees and bushes standing in several meters of water was found to average between 15 and 20 atm in sunshine. and above 10 in overcast. In rainy weather and at night. the pressure would remain close to ambient. Submerged leaves had ambient or sometimes very slightly positive pressure. Pinnate leaves of legumes folded when the pressure rose above a critical level characteristic of the species. Dehydration curves from full turgor to negative turgor showed 3 characteristic phases: A) a steep decline in pressure when the turgor disappeared; B) a linear decline at zero turgor proportional to the increase in osmotic pressure; and C) a steep decline as negative turgor (intracellular packing) developed. The tensions in the drowned forests were similar to those found in inundated plants of temperate lakes. and hence like many plants in a humid forest. However, in the daytime many flooded plants of the Amazon reached zero turgor without any external sign of wilting.
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