Plant life on gypsum: a review of its multiple facets

Abstract

The adaptation of plants to particular soil types has long intrigued biologists. Gypsum soils occupy large areas in many regions of the world and host a striking biological diversity, but their vegetation has been much less studied than that developing over serpentine or saline soils. Herein, we review all aspects of plant life on gypsum ecosystems, discuss the main processes driving their structure and functioning, and highlight the main conservation threats that they face. Plant communities in gypsum habitats typically show distinctive bands at very small spatial scales, which are mainly determined by topography. Plants living on gypsum soils can be classified into three categories: (i) wide gypsophiles are specialists that can penetrate the physical soil crust during early life stages and have physiological adjustments to cope with the chemical limitations imposed by gypsum soils; (ii) narrow gypsophiles are refugee plants which successfully deal with the physical soil crust and can tolerate these chemical limitations but do not show specific adaptations for this type of soils; and (iii) gypsovags are non-specialist gypsum plants that can only thrive in gypsum soils when the physical crust is absent or reduced. Their ability to survive in gypsum soils may also be mediated by below-ground interactions with soil microorganisms. Gypsophiles and gypsovags show efficient germination at low temperatures, seed and fruit heteromorphism within and among populations, and variation in seed dormancy among plants and populations. In gypsum ecosystems, spatio-temporal changes in the composition and structure of above-ground vegetation are closely related to those of the soil seed bank. Biological soil crusts (BSCs) dominated by cyanobacteria, lichens and mosses are conspicuous in gypsum environments worldwide, and are important drivers of ecosystem processes such as carbon and nitrogen cycling, water infiltration and run-off and soil stability. These organisms are also important determinants of the structure of annual plant communities living on gypsum soils. The short-distance seed dispersal of gypsophiles is responsible for the high number of very narrow endemisms typically found in gypsum outcrops, and suggests that these species are evolutionarily old taxa due to the time they need to colonize isolated gypsum outcrops by chance. Climate change and habitat fragmentation negatively affect both plants and BSCs in gypsum habitats, and are among the major threats to these ecosystems. Gypsum habitats and specialists offer the chance to advance our knowledge on restrictive soils, and are ideal models not only to test important evolutionary questions such as tolerance to low Ca/Mg proportions in soils, but also to improve the theoretical framework of community ecology and ecosystem functioning.

The crystallization water of gypsum rocks is a relevant water source for plants

“…They are particularly prevalent in arid and semiarid regions of Africa, Western and Central Asia 3 , where they affect ca. 40%, 75% and 25% of the total surface, respectively 4 . Gypsum is also a key water-holding mineral of Mars 5 .…”

Floral similarity and vegetative divergence in a new species of Bletia (Orchidaceae) from Mexico

“…However, B. parkinsonii is one of the most widespread Mexican species of Bletia and is not restricted to gypsum, but it grows in a variety of soil conditions, both on volcanic and limestone or gypsum substrates (i.e. it is a 'gypsovag'; see Palacio et al 2007;Escudero et al 2015). Gypsum soils have stressful physical and chemical properties for plants, including a hard surface crust that could limit plant establishment, mechanical instability, an excess of S, and Ca/Mg imbalances, among others (Parsons 1976;Palacio et al 2007;Escudero et al 2015).…”

“…it is a 'gypsovag'; see Palacio et al 2007;Escudero et al 2015). Gypsum soils have stressful physical and chemical properties for plants, including a hard surface crust that could limit plant establishment, mechanical instability, an excess of S, and Ca/Mg imbalances, among others (Parsons 1976;Palacio et al 2007;Escudero et al 2015). The aerial thickened stems of B. mixtecana may represent an adaptation to gypsum outcrops in ravines and steep slopes by allowing the plant to grow on the surface, instead of within and across the surface crust (Fig.…”

Trees as Ecosystem Engineers Driving Vegetational Restoration/Retrogradation of Industrial Deposits in Cultural Landscape

“…Edges are susceptible to create firm layers of gypsum in various depths under the substrate surface (several tens of centimeters) which represents an unconquerable barrier for the roots of trees and determines high limits of water permeability into bottom horizons. It is also the cause of rapid chemical changes in overlying substrate profile (desalinization, renewal of acidification, secondary accumulation of Fe-, Mn-and Al-oxides) which requires adaptive traits of plants (e.g., Escudero et al, 2015). All this implies extinction of relative mature tree individuals (mainly birches) after approx 4 decades of their growth at the edge of sedimentation body.…”