A method is described which permits measurement of sap pressure in the xylem of vascular plants. As long predicted, sap pressures during transpiration are normally negative, ranging from -4 or -5 atmospheres in a damp forest to -80 atmospheres in the desert. Mangroves and other halophytes maintain at all times a sap pressure of -35 to -60 atmospheres. Mistletoes have greater suction than their hosts, usually by 10 to 20 atmospheres. Diurnal cycles of 10 to 20 atmospheres are common. In tall conifers there is a hydrostatic pressure gradient that closely corresponds to the height and seems surprisingly little influenced by the intensity of transpiration. Sap extruded from the xylem by gas pressure on the leaves is practically pure water. At zero turgor this procedure gives a linear relation between the intracellular concentration and the tension of the xylem.

https://science.sciencemag.org/content/sci/148/3668/339.full.pdf

Sap Pressure in Vascular Plants: Negative hydrostatic pressure can be measured in plants.

INTRODUCTION 89 BACKGROUND: THE BASIC PHYSIOLOGY 91 Conclusions 9S ION RELATIONS 96' Ion Uptake and Osmotic Adjustment 96 Nutrient Uptake: NalK Specificity 99 Ion Distribution within the Plant 100 Ion Distribution within the Cell 100 Metabolic evidence 100 Physical measurements .... .... ......... ...... 104 Energetics 106 ROLE OF ORGANIC SOLUTES ........ 108 OrganiC Acids 108 Nitrogen Compounds 109 Carbohydrotes 110 CONCLUSIONS 114

The mechanism of salt tolerance in halophytes

The Ecology of Mangroves

Mangroves are woody plants that grow at the interface between land and sea in tropical and sub-tropical latitudes where they exist in conditions of high salinity, extreme tides, strong winds, high temperatures and muddy, anaerobic soils. There may be no other group of plants with such highly developed morphological and physiological adaptations to extreme conditions.

Because of their environment, mangroves are necessarily tolerant of high salt levels and have mechanisms to take up water despite strong osmotic potentials. Some also take up salts, but excrete them through specialized glands in the leaves. Others transfer salts into senescent leaves or store them in the bark or the wood. Still others simply become increasingly conservative in their water use as water salinity increases Morphological specializations include profuse lateral roots that anchor the trees in the loose sediments, exposed aerial roots for gas exchange and viviparous waterdispersed propagules.

Mangroves create unique ecological environments that host rich assemblages of species. The muddy or sandy sediments of the mangal are home to a variety of epibenthic, infaunal, and meiofaunal invertebrates Channels within the mangal support communities of phytoplankton, zooplankton and fish. The mangal may play a special role as nursery habitat for juveniles of fish whose adults occupy other habitats (e.g. coral reefs and seagrass beds).

Because they are surrounded by loose sediments, the submerged mangroves' roots, trunks and branches are islands of habitat that may attract rich epifaunal communities including bacteria, fungi, macroalgae and invertebrates. The aerial roots, trunks, leaves and branches host other groups of organisms. A number of crab species live among the roots, on the trunks or even forage in the canopy. Insects, reptiles, amphibians, birds and mammals thrive in the habitat and contribute to its unique character.

Living at the interface between land and sea, mangroves are well adapted to deal with natural stressors (e.g. temperature, salinity, anoxia, UV). However, because they live close to their tolerance limits, they may be particularly sensitive to disturbances like those created by human activities. Because of their proximity to population centers, mangals have historically been favored sites for sewage disposal. Industrial effluents have contributed to heavy metal contamination in the sediments. Oil from spills and from petroleum production has flowed into many mangals. These insults have had significant negative effects on the mangroves.

Habitat destruction through human encroachment has been the primary cause of mangrove loss. Diversion of freshwater for irrigation and land reclamation has destroyed extensive mangrove forests. In the past several decades, numerous tracts of mangrove have been converted for aquaculture, fundamentally altering the nature of the habitat. Measurements reveal alarming levels of mangrove destruction. Some estimates put global loss rates at one million ha y−1, with mangroves in some regions in danger of complete collapse. Heavy historical exploitation of mangroves has left many remaining habitats severely damaged.

These impacts are likely to continue, and worsen, as human populations expand further into the mangals. In regions where mangrove removal has produced significant environmental problems, efforts are underway to launch mangrove agroforestry and agriculture projects. Mangrove systems require intensive care to save threatened areas. So far, conservation and management efforts lag behind the destruction; there is still much to learn about proper management and sustainable harvesting of mangrove forests.

Mangroves have enormous ecological value. They protect and stabilize coastlines, enrich coastal waters, yield commercial forest products and support coastal fisheries. Mangrove forests are among the world's most productive ecosystems, producing organic carbon well in excess of the ecosystem requirements and contributing significantly to the global carbon cycle. Extracts from mangroves and mangrove-dependent species have proven activity against human, animal and plant pathogens. Mangroves may be further developed as sources of high-value commercial products and fishery resources and as sites for a burgeoning ecotourism industry. Their unique features also make them ideal sites for experimental studies of biodiversity and ecosystem function. Where degraded areas are being revegetated, continued monitoring and thorough assessment must be done to help understand the recovery process. This knowledge will help develop strategies to promote better rehabilitation of degraded mangrove habitats the world over and ensure that these unique ecosystems survive and flourish.

Biology of mangroves and mangrove Ecosystems

The Botany of Mangroves

5 Weissmann, C., P. Borst, R. H. Burdon, M. A. Billeter, and S. Ochoa, these PROCEEDINGS, 51, 682 (1964). 6Ibid., 890 (1964). 7Burdon, R. H., P. Borst, and C. Weissmann, Federation Proc., 23, 319 (1964). 8 Ochoa, S., C. Weissmann, P. Borst, R. H. Burdon, and M. A. Billeter, Federation Proc., in press. 9 Fenwick, M. L., R. L. Erikson, and R. M. Franklin, Federation Proc., 23, 319 (1964). '0Kaerner, H. C., and H. Hoffmann-Berling, Z. Naturforsch., in press. \"Weissmann, C., L. Simon, and S. Ochoa, these PROCEEDINGS, 49, 407 (1963). 12 Langridge, R., and P. J. Gomatos, Science, 141, 694 (1963). 13Langridge, R., H. R. Wilson, C. W. Hooper, M. H. F. Wilkins, and L. D. Hamilton, J. Mol. Biol., 2, 19 (1960). 14 Mejbaum, W., Z. Physiol. Chem., 258, 117 (1939). 1Dische, Z., in The Nucleic Acids, ed. E. Chargaff and J. N. Davidson (New York: Academic Press, 1955), vol. 1, p. 294. 16 We are indebted to Dr. R. C. Warner for these determinations. 17 Strauss, J. H., Jr., and R. L. Sinsheimer, J. Mol. Biol., 7, 43 (1963). 18 A replicative form isolated by Kaerner and Hoffmann-Berling (ref. 10) from E. coli infected with the RNA phage fr shows the same melting profile, Tm, RNAase resistance, and buoyant density in CS2SO4 as the replicative form of MS2. Although the replicative form of phage fr, purified by the method A of these authors, also sediments with an s20 of about 8.5, their improved method B yielded a preparation containing a minor component with an s20 of 14.5 S. This is the value expected for a duplex containing twice as much RNA as the viral strand. A similar value, of 12-16 S, was obtained by Fenwick et al. (ref. 9) for material tentatively identified as the replicative form of the RNA phage R17 by sucrose gradient analysis of infected E. coli extracts.

https://www.pnas.org/content/pnas/52/1/119.full.pdf

Hydrostatic pressure and osmotic potential in leaves of mangroves and some other plants.

Freezing point depression in xylem sap of mangroves was found to range from 005 to 05°, in desert plants from 001 to 016° In crush juices from leaves of Batis and Salicornia, 90% or more of the freezing point depression was made up of sodium and chlorine ions; in mangroves they constituted 50 to 70%, the rest probably being organic solutes Plants growing in seawater have −30 to −60 atmospheres pressure in the xylem sap As shown earlier, at zero turgor pressure the intracellular freezing point of the parenchyma cells matches closely the negative pressure in the xylem sap This agrees with the present data, that the fluid which exudes from the xylem by applying gas pressure on the leaves is practically pure water; freezing point is rarely above 001 to 002° To perform this ultrafiltration, the plasma membrane is subjected to a hydrostatic pressure gradient which in some cases may exceed 100 atmospheres

Edda Bradstreet

Papers

Sap Pressure in Vascular Plants: Negative hydrostatic pressure can be measured in plants.

Hydrostatic pressure and osmotic potential in leaves of mangroves and some other plants.

Sap Concentrations in Halophytes and Some Other Plants

Metabolic changes in the mud-skipper during asphyxia or exercise.

Lactic acid response in the grunion.