Luis Ramírez-Díaz

SEED GERMINATION, GROWTH, AND OSMOTIC ADJUSTMENT IN RESPONSE TO NaCl IN A RARE SUCCULENT HALOPHYTE FROM SOUTHEASTERN SPAIN

In this paper, some issues of the autoecology of Halocnemum strobilaceum (a rare succulent halophyte that occurs in southeastern Spain) are examined, particularly the germination process and the first stages of plant development. In regards to germination, this species shows the general pattern of halophytes under increased salt stress (reduced germination and germination rate). What stands out is the extreme salt tolerance of H. strobilaceum seeds. The stimulation of root length by the presence of salt probably plays an important role in avoiding salt stress at surface-level soils, within salt concentrations where germination still occurs. Halocnemum strobilaceum typically accumulates Na+ ions, which, combined with Cl−, contributes to the internal osmotic potential. The accumulation of both ions clearly increases with an increase in salinity stress. In contrast, accumulation of K+, Mg2+, and Ca2+ decreases with an increase in salinity stress. Glycinebetaine contents are approximately 100 times greater than proline contents, although their contribution was significant only if cell compartmentalization was considered. The accumulation of ions along with the osmoprotective compounds glycinebetaine and proline allows seedlings to mantain a lower internal osmotic potential than that of the growth medium, which is necessary for water uptake in saline soils.

On the use of three performance measures for fitting species response curves

response models: density (stem counts per unit area),cover, biomass - or some alternative non-destructivemeasures such as volume -, etc. However, most of theavailable information for examining the species responseshape is based on qualitative data (presence/absence),and little attention has been paid to ascertaining whetherthis shape is independent (or not) of the response meas-ures considered.This paper examines quantitative response surfacesobtained from several species performance measures,i.e. density, cover and volume, of Periploca angustifolia(Asclepiadaceae ), in southeastern Spain. The main aimis to compare the shape of the responses, which weredetermined with the help of generalized linear models(GLM; McCullagh & Nelder 1989). This method wassuggested by Austin et al. (1984) as an approach thatallows an explicit rigorous analysis to be made of theshape of species response to a number of environmentalfactors considered simultaneously (cf. Austin et al. 1990).The response variables were related to complex gra-dients (sensu Whittaker 1956, 1967) of aspect, slopeangle and elevation as their use assumes that manysingle factors that change together in space - incomingsolar radiation, temperature, humidity, wind velocity -may be important for plant distribution. Therefore, meas-ures of aspect, slope angle and altitude are used here ascrude indices of relative position along complex envi-ronmental gradients.MethodsData collection43 10 × 10 m plots were located on limestone anddolomite substrate around two hills of the Sierra deCartagena (Murcia Region, SE Spain), with every expo-sition (N, NE, E, SE, etc.) represented. Topographicalvariation was represented in the sample as well (seeFerrer Castan 1994 for sampling details). On the other

The Use of Multivariate Analysis for the Ecological Characterization of Landscape: the Mula River Watershed, South-east Spain

Ordination and classification techniques have been applied to an integrated study of the ecological characteristics of the Mula River watershed (Murcia, south-east Spain), as environmental background for use and management. These techniques facilitate an objective determination of the main tendencies in environmental variation within the study area, and how this variation may be viewed from ecological and geographical points of view. Moreover, their use permits the delimitation of internally homogeneous environmental units based on their topographic, geologic, vegetation and land use characteristics. A description of six environmental units in the study area was derived using information theory parameters.

An approach to the ecological characterization of arid and semiarid basins

A morphometric study of 61 sub-basins of the River Segura basin (SE Spain) enables us to attribute ecological processes in streams of these arid and semiarid watersheds to altered patterns of discharge resulting from human activity.Methods used are compared to other, commonly used limnological indexes.