Biol Rev Camb Philos Soc. 2015 Feb;90(1):1-18. doi: 10.1111/brv.12092.
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.
植物对特定土壤类型的适应长期以来一直令生物学家着迷。石膏土壤在世界许多地区占据着大片区域，拥有引人注目的生物多样性，但它们的植被研究却比开发蛇纹石或盐渍土的植被研究少得多。在此，我们综述了石膏生态系统中植物生命的各个方面，讨论了驱动其结构和功能的主要过程，并强调了它们面临的主要保护威胁。石膏生境中的植物群落通常在非常小的空间尺度上表现出独特的带，这些带主要由地形决定。生活在石膏土壤上的植物可以分为三类：（i）广布的石膏喜盐植物是专性种，它们可以在早期生活阶段穿透物理土壤壳，并通过生理调节来应对石膏土壤带来的化学限制；（ii）窄布的石膏喜盐植物是避难植物，它们成功地应对物理土壤壳，并能耐受这些化学限制，但没有针对这种土壤的特殊适应；（iii）非专性的石膏植物是在物理土壤壳不存在或减少时才能在石膏土壤中茁壮成长的非专性种。它们在石膏土壤中的生存能力也可能通过与土壤微生物的地下相互作用来介导。石膏喜盐植物和非专性石膏植物在低温下表现出高效的萌发，种群内和种群间的种子和果实异型性，以及植物和种群间种子休眠的变异。在石膏生态系统中，地上植被组成和结构的时空变化与土壤种子库的变化密切相关。以蓝细菌、地衣和苔藓为主的生物土壤结皮（BSC）在世界范围内的石膏环境中非常明显，是碳和氮循环、水分渗透和径流以及土壤稳定性等生态系统过程的重要驱动因素。这些生物也是生活在石膏土壤上的一年生植物群落结构的重要决定因素。石膏喜盐植物的短距离种子扩散是导致石膏露头中通常发现的大量非常狭窄特有种的原因之一，这表明这些物种是由于它们需要时间来偶然殖民孤立的石膏露头而成为进化古老的类群。气候变化和栖息地破碎化对石膏生境中的植物和生物土壤结皮都有负面影响，是这些生态系统的主要威胁之一。石膏生境和专性种为我们提供了一个深入了解限制土壤的机会，它们不仅是测试土壤中低钙/镁比例耐受等重要进化问题的理想模型，也是完善群落生态学和生态系统功能理论框架的理想模型。
