PARAMOS The paramos constitute both a region and a vegetation type in the high equatorial Andes of northern South America (Ecuador, Colombia and Venezuela) (Vareschi 1988). They occur above 2,800 m elevation, and are characterized by highly diversified, complex genus Espeletia (Asteraceae), with life forms similar to those found within other genera of the same family in the Kilimanjaro (Senecio), Hawaii (Argyroxiphium). This life form is described as a giant rosette, with leaves covered with a dense, whitish hair layer. Leaves are not shed during senescence but remain adpressed to the succulent stem (marcescent leaves), providing thermal isolation to the water conducting tissue (Goldstein et al. 1991). Plants in this tropical alpine environment show adaptations to high irradiation, extreme diurnal temperature oscillations, and seasonal dry conditions (Monasterio and Sarmiento (1991). Paramos: 10 N, 67W Squeo F.A., Rada F., Azcar A., Goldstein G. (1991) Freezing tolerance and avoidance in high tropical Andean plants: is it equally represented in species with different plant height? Oecologia 86: SpeciesLife-form Altitudinal distribution Arenaria jahnii Brake (Caryophyllaceae) cushion Azorella julianii Math (Apiaceae) cushion Lucilia venezuelensis Stmk. (Asterac.)cushion Castilleja fissifolia L.f. (Scrophulariaceae) perennial herb Geranium multiceps Tourez (Geraniaceae) perennial herb Senecio formosus H.B.K. (Asteraceae) perennial herb Draba chionophylla Blake (Cruciferae) small rosette Espeletia moritziana Sch. Bip. (Asteraceae) giant rosette Espeletia schultzii Wedd. (Asteraceae) giant rosette Espeletia spicata Sch. Bip. (Asteraceae) giant rosette Espeletia timotensis Cuatr. (Asterac.) giant rosette Hinterhubera lanuginosa Cuatr et Arist (Asterac)shrub Hypericum laricifolium Juess. (Guttiferae) shrub Polylepis sericeus Wedd. (Rosaceae)small tree Summary of morphological and physical characteristics of five Espeletia schultzii populations occurring along an elevation gradient (after Meinzer and Goldstein 1985) Elevation (m) Pith volume Leaf area PV/LA Pubescence thicknessLeaf absorptance (cm 3 ) (cm ) (cm 3 cm- 2 ) (mm) nm 2,600 ( 13C) , , , ,200 ( 2.8C) Site characteristics where Espeletia species were studied to estimate the period of time during which the water removed from the pith could replace the water transpired (T) (Meinzer and Goldstein 1986) Paramo site Annual Mean and elevation precipitation temperature Species PV/LA M T Hours (m) (mm) (C) (cm 3 cm -2 )(g)(g h -1 ) of T Piedras Blancas E. lutescens ,200 E. moritziana E. spicata Mucubaji, E. schultzii ,600 E. floccosa Batallon E. marcana ,100 E. atropurpurea Hours of transpiration were calculated by dividing the mass of available water in the pith (M) by the transpiration rate (T) of the entire rosette. Pith volume per unit leaf area (PV/LA) is a measure of relative capacitance Temperature for 50% injury, supercooling points, and relative apoplastic water content of leaves (3-5 pressure-volume curves) of 10 Espeletia species occurring along an altitudinal gradient. Leaf water potential range was -0.4 to -0.9 Mpa (after Goldstein et al. Oecologia 68: ) Species Elevation Supercooling 50% injury Relative apoplastic (m)point C C water content % E. lindenii E. angustifolia E. atropurpurea E. marcana E. atropurpurea E. jahnii E. schultzii E. floccosa E. schultzii E. moritziana E. spicata E. lutescens Relationship between cold injure temperature, and appearance of the first exhotherm for leaf tissues; n 6 (modified from Squeo et al. Oecologia 86: ) Species Temperatures C Cold resistance Life form Injury Freezing mechanism Espeletia moritziana Super CoolingGiant Rosette E. schultzii Super CoolingGiant Rosette E. spicata Super CoolingGiant Rosette E. timotensis Super CoolingGiant Rosette Polylepis sericea Super CoolingSmall Tree Hinterhubera lanuginosa Super CoolingShrub Hypericum laricifolium Super CoolingShrub Senecio formosus Freezing TolerancePerennial Herb Castilleja fissifolia Freezing TolerancePerennial Herb Arenaria jahnii Freezing ToleranceCushion plant Azorella julianii Freezing ToleranceCushion plant Draba chionophylla Freezing ToleranceSmall Rosette Lucilia venezuelensis Freezing ToleranceCushion plant Cold injury measured with Triphenyl-tetrazolium chloride (Steponkus and Laphear Plant Physiology 42, Cold resistance mechanism: difference between injure temperature (IT) and freezing temperature (FT) (Larcher 1982) IT larger than FT---> freezing avoidance by insulation IT similar to FT ---> supercooling IT lower than FT ---->freezing tolerance