Abstract
Cushion plants are widely
representative species of the alpine ecosystem due to their vital roles
in the abiotic and biotic environments, ecological succession processes,
and
ecosystem engineering. Importantly, Cushion plants, such asAndrosace L. and Arenaria L., can be regarded as critical
pioneers of ecosystem health, restoration and sustainability across the
Tibetan Plateau because these plants (i) exhibit tenacious vitality,
regulate regional climates, substrates and soil nutrients and keep
warmth in extreme regions; (ii) facilitate relationships with
surrounding and maintain the diversity of above- and below-ground
communities; and (iii) have high sensitivity to environmental changes,
which can indicate grassland ecosystem health and resilience in the
context of global change.
KEYWORDS: Cushion plants; Androsace L.;ArenariaL.; Tibetan Plateau; ecosystem succession.
The cushion plant is a key builder of abiotic environments
Cushion plants, with more than 70 kinds, are widely distributed in high
elevations and inhabit extreme environments across the Tibetan Plateau
(Badano & Cavieres, 2006; Yang & Sun, 2006). The Tibetan Plateau is an
important centre of global cushion plants, e.g., Androsace L. andArenariaL., which play a vital role in the development of modern flora and
vegetation (Luo et al., 2018). Firstly, the ”microspace” formed by
convex structure and developed root system of cushion plants could
function in heat, nutrient and water preservation (Fig. 1a-c) (Cavieres
et al., 2006; Zhao et al, 2020). Actually, these plants act as an
ecological engineer to accelerate the enrichment of nutrients for the
substrate, which can last for hundreds of years for tenacious vitality
(Fig. 1d) (Yang et al., 2010). Second, the special structure and strong
adaptability of cushion plants reduce the damage of wind and water
erosion and maintain the warmth of extreme regions (Byers et al., 2006).
Ultimately, dead cushion plants provide sufficient fertilizer for the
soil and promote nutrient cycling.
Fig. 1 (a-c) The cushion plant, such as Androsace L.,
has the median uplifting structure to create ”micro space” with
developed root system; (f) The death cushion plant provides sufficient
fertilizer for the surrounding plants.
The cushion plant is a critical facilitator for biotic
environments
Cushion plants provide physical protection in extreme environments and
promote the growth and reproduction of surrounding species, especially
species of pioneer settlers (Cavieres et al., 2006; Francisco et al.,
2020). Thus, cushion plants exhibit interspecific facilitation, which
may be beneficial to maintain species diversity (Fig. 2) (Erfanzadeh et
al., 2020). The main effects of cushion plants on the below-ground
community are the promotion of the activity of soil microorganism and
the enhancement fungal communities to increase the absorption area of
roots and maintain microbial community diversity (Fig. 3) (Casanovakatny
et al., 2011; Chang et al., 2018; Wang et al., 2020).
Fig. 2 The cushion plant promotes the propagation of other
plants, such as Leontopodium, Carex and Artemisia .
Fig. 3 The cushion plant and fungi form symbionts to improve
the activity of soil microbe.
The cushion plant is an indicator of ecosystem health and
resilience
Cushion plants have high sensitivity to global change (e.g., climate,
nitrogen deposition, species invasion and land use), such as their
response to freezing-thawing and stress gradients, which may indicate
ecosystem health and resilience (Gorsuch et al., 2001). Besides, cushion
plants may be indicators of whether the ecosystem is healthy or
degradation succession occurs (Erfanzadeh et al., 2020; Luo et al.,
2018). Specifically, in the context of alpine grassland ecosystem
degradation, the cushion plants play an important role in improving
abiotic and biotic environments and the maintenance of alpine ecosystem
stability (Fig. 4).