Water relations and gas exchange in Coespeletia moritziana (Sch. Bip) Cuatrec., a giant rosette species of the high tropical Andes

Abstract

Giant rosettes are ones of the most striking features of the vegetation in the high tropical Andes, with Coespeletia moritziana reaching the highest altitudes up to 4,600 m a.s.l. Different from other giant rosettes, this species grows on rock outcrops with poorly developed soils and where water availability may be limited. Two questions are addressed in this study: How does this species respond in terms of water relations to maintain favorable gas-exchange conditions? Considering that adult plants rely on a water-reserving central pith, how do early stages respond to this environment´s extreme conditions? Water relations and gas-exchange studies were carried out on juveniles, intermediate and adult C. moritziana plants during wet and dry seasons in Páramo de Piedras Blancas at 4,200 m a.s.l. Adult plants maintained higher leaf water potentials (Ψ L ) during the wet season, however, no differences between stages were found for the dry season. Minimum dry season Ψ L were never near the turgor loss point in any of the stages. Juveniles show a more strict stomatal control during the dry season to maintain a favorable water status. Net photosynthesis significantly decreased in intermediate and juvenile stages from wet to dry seasons. Our results suggest that C. moritziana resists more extreme conditions compared to other Andean giant rosettes.

Water relations and gas exchange in <i>Ruilopezia atropurpurea</i> (Asteraceae), a giant rosette growing under contrasting microclimates in the high tropical Andes

“…Maximum CO 2 assimilation rates (10-13 mmol m -2 s -1 ) measured for R. atropurpurea in this study are remarkably higher than any other of the giant rosettes investigated in the Venezuelan paramos (Goldstein et al 1989, Rada et al 1998, Rada et al 2012, Rada 2016 or Lobelia rhynchopetalum (Hochst. Ex A.…”

“…Different reports have highlighted the particularly positive leaf water potentials that Andean giant rosettes maintain, even under drought conditions (Goldstein et al 1984, Rada et al 1998, Rada 2016. Coespeletia moritziana diverges from this pattern with significantly more negative Y L min (-1.8 MPa) and Y L tlp (-2.3) compared to other giant rosettes (Rada et al 2012). These authors also report important osmotic adjustments for C. moritziana, surviving under drought conditions and on poorly developed soils in rocky sites in one of the driest Venezuelan paramos at higher elevations (4300 m).…”

“…Cuatrec. which at extreme elevations (> 4000 m altitude) in a particularly dry paramo reaches lower Y L and rely on osmotic adjustments under drought periods (Rada et al 2012).…”

Measurement of actual evapotranspiration in a páramo ecosystem using portable closed chambers: Comparison between giant rosettes, tussock grasses and shrubs

“…Moreover, a high stomatal conductance has not shown to be directly correlated to a higher ET in the páramos (Jarvis & McNaughton, 1986; Martin et al, 1999). The higher stomatal conductance of giant rosettes could be explained by the presence of a reservoir of water in the stem pith, which helps with the regulation of the water potential gradient and allows a higher control on the water loss through stomata; therefore, the species has the ability to continuously move water and transpire (Cárdenas et al, 2018; Mora Osejo, 2001; Rada et al, 2012).…”