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Journal of Resources and Ecology >

2022 , Vol. 13 >Issue 1: 107 - 112

DOI: https://doi.org/10.5814/j.issn.1674-764x.2022.01.012

Restoration Ecology and Ecological Engineering

The Facilitation of Restoration by Cushion Plant Androsace tapete in a Degraded Alpine Grassland

  • HE Yongtao , 1, 2, * ,
  • WANG Fang 1, 2 ,
  • NIU Ben 1 ,
  • WANG Zhipeng 1, 2 ,
  • LI Meng 1, 2 ,
  • SHI Peili 1, 2 ,
  • ZHANG Xianzhou 1, 2
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  • 1. Lhasa Plateau Ecosystem Research Station, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
  • 2. College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100190, China
* HE Yongtao, E-mail:

Received date: 2021-07-25

  Accepted date: 2021-10-21

  Online published: 2022-01-08

Supported by

The National Natural Science Foundation of China(31770477)

The Strategic Priority Research Program of the Chinese Academy of Sciences(XDA19050502)

The Strategic Priority Research Program of the Chinese Academy of Sciences(XDA20010201)

The National Key R&D Program of China(2017YFA0604801)

The National Key R&D Program of China(2016YFC0502001)

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Abstract

The cushion plant Androsace tapete is an endemic species that is widely distributed in the Qinghai-Tibetan Plateau, and also predominant in the alpine grassland that is locally degraded due to overgrazing and other reasons. As an ecosystem engineer cushion plant, its ability to facilitate the restoration of degraded alpine grassland was studied in a degraded alpine grassland at an elevation of 4500 m on the southern slope of the Nyainqentanglha Mountains in Damxung. The species diversity, soil nutrients and water content underneath and outside the cushion plant A. tapete were investigated. The results showed that soil nutrients underneath the A. tapete cushion were significantly increased by about 16%-48% compared to outside the cushion, of which the organic matter and total N were increased by 16.2% and 18.9% respectively, and the soil water content was increased about 12%. The index of species diversity of richness (S), Shannon-Wiener’s H and Simpson’s D all increased with the coverage of cushion plant A. tapete. Our results suggested that this cushion plant can facilitate restoration of the degraded alpine grassland by modifying the local soil environment and increasing the community diversity, so it should be conserved for the restoration of degraded alpine grasslands on the Qinghai-Tibetan Plateau.

Key words： cushion plant; facilitation; degraded alpine meadow; species diversity; soil nutrients

Cite this article

HE Yongtao , WANG Fang , NIU Ben , WANG Zhipeng , LI Meng , SHI Peili , ZHANG Xianzhou . The Facilitation of Restoration by Cushion Plant Androsace tapete in a Degraded Alpine Grassland[J]. Journal of Resources and Ecology, 2022 , 13(1) : 107 -112 . DOI: 10.5814/j.issn.1674-764x.2022.01.012

1 Introduction

Natural restoration is important for the degraded ecosystems, and the positive interactions of plants can promote the natural restoration of degraded ecosystems. Research on this topic has received increasing attention, and the current research is mostly focused on trees, shrubs and perennial herbs (Padilla and Pugnaire, 2006), which can ameliorate the stressful microenvironment in important ways to improve soil fertility and productivity in degraded grasslands. A cushion plant is a type of plant with a special morphological structure that grows in the alpine environment. It not only has strong adaptability, but also can improve the local microenvironment and increase the availability of soil nutrients, thus providing better conditions for the settlement and growth of other plants and increasing the species diversity of the local community. Therefore, they are called the “engineers” in the alpine ecosystem (He et al., 2010; Meng et al., 2013; Wang et al., 2021). However, studies have also found that the engineer effect of cushion plants to the local microenvironment can be different due to the varieties and growing environments of the cushion plants (Liu et al., 2014a, b; Liu et al., 2016), which also affected the local plant diversity (Chen et al., 2015a). At present, there are few reports on the role of cushion plants and their ecosystem engineer effects in degraded alpine grasslands (Erfanzadeh et al., 2020).
Androsace tapete is one of the endemic and most widely distributed cushion plants on the Qinghai-Tibetan Plateau. It is also distributed in the locally disturbed area due to overgrazing and other reasons (Li et al., 1985; Li et al., 1987; Huang and Wang, 1991), and it occurs mixed with other plant communities. Existing research on A. tapete mainly focuses on its community distribution (Li et al., 2013; He et al., 2014), individual growth (Zhao et al., 2015) and genetic diversity (Zeng et al., 2010). Pugnaire et al. (2015) carried out a preliminary study on its role as an ecosystem engineer, and the results showed that A. tapete could help other plants to grow in stressful environments, and improve both local species diversity and plant growth traits. They also pointed out that the positive interaction of A. tapete conformed to the environmental stress gradient hypothesis, that is, the positive interaction will be stronger when the environment is more stressful (Pugnaire et al., 2015). However, the low levels of soil nutrients of degraded grasslands make them more infertile, so it is unclear whether the positive interaction of A. tapete as an ecosystem engineer would change in these environments.
In this study, A. tapete, in a severely degraded grassland in Damxung, was taken as an example to study the effects of A. tapete on community species diversity, soil microenvironment and nutrients, to explore the effects of this cushion plant as an ecosystem engineer in alpine degraded grasslands.

2 Materials and methods

2.1 Field site

The study area is located on the southern slope of Nyainqentanglha Mountains, about 5 km to the north of Damxung county, Tibetan Plateau. It has a continental plateau monsoon climate with strong solar radiation, low temperature and a wide diurnal temperature range. According to the observation records of the meteorological station (at elevation 4300 m) at Damxung, the annual average temperature in this area is 1.3 ℃, the average temperatures are -10.4 ℃ in the coldest month (January) and 10.7 ℃ in the hottest month (July), the diurnal temperature range is 18.0 ℃, the annual average temperature on the ground is 6.5 ℃, and the freezing period is 3 months (from November to January of the following year). The mean annual precipitation is 476.8 mm, 85.1% of which is concentrated from June to August (Zhang et al., 2009). The study area is located at the transition zone from humid to semi-arid areas, the zonal vegetation is alpine meadow, and the plant community composition is dominated by Kobresia and Carex of the family Cyperaceae.
The selected sample field is located on a gentle slope, on the lower part of the southern slope of the Nyainqentanglha Mountains (30°30'46"N, 91°3'57"E, 4473 m). The soil type is alpine meadow soil with a sandy texture and a depth of 0.1-0.3 m. The grassland is owned by herdsmen in nearby villages, and serves as a free grazing grassland. The grassland degradation is relatively serious. The plant community composition has changed from Cyperus to weeds. The coverage of the vegetation is sparse, and the overall coverage of the community is about 30%-40%. The dominant species are Artemisia desertorum, Gentiana squarrosa, Pleurospermum hookeri, Potentilla nivea, Anaphalis sp., etc. A. tapete is scattered among them, and individuals are mainly about 25-50 cm2. This site is also the lowest elevation where A. tapete is distributed along the slope (He et al., 2013; Li et al., 2013).

2.2 Field investigation and sampling

The plant species diversity, soil moisture and nutrients were investigated in the A. tapete cushion area and the control area (without A. tapete) in the degraded grassland during August, the peak growth period of plateau plants. Because the size of A. tapete was mostly in the range of 25-50 cm2, in order to compare the plant diversity between the area with A. tapete and the control area, 28 quadrats of 1 m×1 m were randomly selected in an area with medium sized A. tapete distributed in the sample plot, and the interval between each quadrat was not less than 10 m (Zeng et al., 2010). By dividing the 1 m×1 m sample plots into 25 small subplots (20 cm×20 cm) evenly, the A. tapete and the other plant species and their coverage in each subplot were recorded (Sklenář, 2009).
In the sampled plots, 5 pairs of 0-20 cm soil samples were randomly collected with an auger of 3.5 cm diameter. Each mixed soil sample included the soil underneath three individuals of A. tapete (underneath A. tapete), and the soil collected from an area without A. tapete distribution nearby was used as the control (outside A. tapete). One soil sample was randomly taken from underneath each A. tapete, and a total of three soil samples were mixed. At the same time, three soil samples were randomly taken from the area without A. tapete as a control soil sample.
The collected soil was divided into two parts: one part was used for the determination of soil water content; while other part was used for the determination of soil organic matter, total nitrogen (N), inorganic nitrogen (ammonia nitrogen NH4+ and nitrate nitrogen NO3-), pH and other physical and chemical indexes.

2.3 Chemical analyses

The soil water content was determined by oven-drying at 65.0 ℃ for 48 h. Soil pH was measured by a pH meter with a water:soil ratio of 1:2.5. Soil organic matter was determined by the potassium dichromate volumetric method. Total nitrogen (N) was determined by a Vario MACRO cube element analyzer. The content of inorganic nitrogen (NH4+ and NO3-) was measured with an automatic continuous flow analyzer (Model AA3, produced by Seal Company, Germany). Available phosphorus (P) was determined by the sodium bicarbonate extraction-molybdenum antimony colorimetric method, and available potassium (a-K) and slow-acting potassium (s-K) were determined by a flame photometer method.

2.4 Statistical analyses

For the determination of species diversity, the following three types of diversity indices were used (Magurran et al., 1988).
(1) Richness (S): Number of species recorded in a plot.
(2) Shannon-Wiener index (H):
$H = –\underset{i=1}{\overset{S}{\mathop \sum }}\,~{{p}_{i}}~\text{ln }{{p}_{i}}$
(3) Simpson index (D):
$D = 1–\underset{i=1}{\overset{S}{\mathop \sum }}\,{{p}_{i}}^{2}$
where S is the number of species in the sample plot; pi is ratio of the coverage of species i to the total coverage of all plants in the sample plot; and i is the species from 1, 2, 3,…to S.
Data were statistically tested by SPSS 13.0. The T-test was used to test the significance of differences between inside and outside the A. tapete cushions.

3 Results

3.1 Community species composition

In the 28 surveyed 1 m×1 m plots, a total of 32 species of vascular plants were recorded. Most plants had a low coverage, with average coverage of the community being less than 43%. The coverage of A. tapete was about 6.9%, making it the most dominant species in the sampled plot, and its relative coverage was 17.3%. There were only 12 plant species with coverage of more than 1%, while there were 14 plant species with coverage of less than 0.5%, among which six species had coverage of less than 0.1%.
In addition, based on the grassland species classification, the sample field was dominated by weeds. Forbs such as the Kobresia humilis, Poa sp. and Stipa aliena, all had average coverage of less than 1.5%, except for Carex atrofusca. There were 21 species of weeds, mainly composed of Compositae, accounting for 66% of the total investigated species. Their coverage reached 27.62%, accounting for about two-thirds of the total community coverage, indicating that the sample field was a severely degraded alpine grassland (Wang et al., 2016; Yang et al., 2020).

3.2 Effects of Androsace tapete on the species diversity of the community

The results of species diversity showed that species richness (S), Shannon-Wiener’s H and Simpson’s D all increased with the coverage of A. tapete. The species richness in the area without A. tapete was about 5.6. With increasing coverage of A. tapete, the species richness gradually increased to more than 6; and when coverage of A. tapete more than 75%, the species richness in the sample plot increased to 7.4. The Shannon-Wiener index (H) increased from 1.5 to 1.8, while the Simpson index (D) increased from 0.7 in sample plots without A. tapete to 0.8 with A. tapete.
Table 1 Community species composition in the sampled plots
Species Coverage (%) Species Coverage (%)
Androsace tapete 6.88 Leontopodium sp. 0.59
Gentiana squarrosa 6.40 Kobresia pygmae 0.53
Artemisia desertorum 4.58 Stellera chamaejasme 0.39
Carex atrofusca 4.06 Koeleria cristata 0.37
Pleurospermum hookeri 3.68 Aster flaccidus 0.33
Potentilla nivea 2.62 Taraxacum sp. 0.23
Anaphalis sp. 2.01 Pedicularis kansuensis 0.20
Kobresia humilis 1.37 Veronica biloba 0.17
Poa sp. 1.20 Unidentified species 0.16
Stipa aliena 1.20 Kobresia robusta 0.16
Polygonum macrophyllum 1.13 Iris sp. 0.09
Silene repens 1.01 Allium sp. 0.08
Oxytropis sp. 0.90 Anemone obtusiloba 0.08
Androsace mariae 0.89 Thalictrum sp. 0.08
Stipa purpurea 0.76 Rhodiola sp. 0.06
Saussurea sp. 0.60 Microula sikkimensis 0.04
Fig. 1 Species diversity increase with coverage of the cushion plant A. tapete

3.3 Effects of Androsace tapete on soil nutrients

The results of soil nutrients showed that organic matter, total nitrogen, ammonium nitrogen, available potassium, and slow-acting potassium underneath A. tapete were all significantly higher than in areas outside A. tapete (P < 0.05). Although there were no significant differences in pH or available phosphorus, their values underneath A. tapete were also higher than those outside A. tapete. Soil nutrients increased by 16%-48%, of which organic matter and total nitrogen increased by 16.2% and 18.9%, respectively; and available potassium and slow-acting potassium increased by 38%, 48%, respectively.

3.4 Effect of Androsace tapete on soil water content

A. tapete had the ability to change the soil water content significantly. The results showed that the soil water contents underneath and outside cushion plants were significantly different (P < 0.01). Average soil water content underneath A. tapete was 15.5%, while that outside A. tapete was 13.9%. Cushion plants increased the soil water content by about 12%.
Table 2 Soil nutrients underneath and outside the cushion plant A. tapete
Sample area pH Organic matter
(g kg-1)		 Total N
(g kg-1)		 NO3-
(mg kg-1)		 NH4+
(mg kg-1)		 Available P
(mg kg-1)		 Available K
(mg kg-1)		 Slow-acting K
(mg kg-1)
Underneath A. tapete 6.26±0.06a 28.93±6.78a 1.49±0.23a 0.24±0.03a 1.40±0.21a 5.72±1.72a 68.52±12.99a 463.31±78.70a
Outside A. tapete 6.19±0.20a 24.89±7.96b 1.25±0.38b 0.34±0.08b 0.98±0.24b 4.46±2.29a 49.54±7.12b 311.83±20.47b

Note: Different letters (a, b) show the significant differences between underneath and outside the cushion plant A. tapete (P < 0.05).

Fig. 2 Soil water contents underneath and outside the cushion plant A. tapete

4 Discussion

Many studies have shown that the plant diversity and soil nutrients in degraded grasslands are all significantly decreased on the Tibetan Plateau (Zhan et al., 2019; Yang et al., 2020). In contrast to the results of Pugnaire et al. (2015), this study found the presence of A. tapete significantly improved the community biodiversity, soil water content and soil nutrients, which are important to the restoration of the degraded grassland. In this study, the research field was near a village, and the vegetation coverage was sparse and mainly dominated by weeds due to the long-term free grazing. Compared to the soil nutrition in other sites, the soil nutrition in our sample site is significantly lower (Ohtsuka et al., 2008; Wang et al., 2016; Yang et al., 2020), indicating that the grassland of the sample site was in a seriously degraded stage. A. tapete could effectively accumulate soil nutrients, improve soil water moisture and increase community diversity, thus promoting the restoration of the degraded grassland. Therefore, it may play an important role in the restoration of degraded alpine grassland due to the unique growth characteristics of the cushion plants.
The cushion plant A. tapete has a special dense structure which can adapt to the alpine environment, and according to estimations, its average age is about 60 years, and can even reach up to 100 years (Zhao et al., 2015). Many studies on cushion plants have shown that they can effectively change the microenvironment, such as regulating the local soil temperature, increasing the availability of soil moisture and nutrients, reducing wind erosion, and having positive interactions with other plants (Reid et al., 2010; Butterfield et al., 2013; Kikvidze et al., 2015), such as facilitating the survival rate of other plants and increasing the biodiversity locally (Arroyo et al., 2003; Cavieres et al., 2014). These findings were consistent with our results which showed that the local plant diversity significantly increased with the coverage of A. tapete. Other studies on the Tibetan Plateau also proved that the cushion plants play mutually beneficial roles in the alpine plant community, and the positive interactions had significant effects on increasing the community diversity, abundance and richness (Yang et al., 2010; Chen et al., 2015a; Liu et al., 2016).
Enhancing the availability of soil nutrients is an important function of cushion plants. Soil nutrient depletion is one of the indicators of grassland degradation, while strong winds and grazing would take away most of the plant litter, thus restricting the natural cycle of soil nutrients (Körner, 2003). Unlike most alpine plants, the leaves of cushion plants remain on their stem for many years, forming a large dense cushion, which can play a “nutrient trapping” role in alpine grasslands (Körner, 2003; Cavieres et al., 2008). The effectively maintained and aggregated cushion litter can improve the microenvironment, in which microbes and other decomposers are active, therefore, the soil underneath cushion plants often has a good nutrient cycle. This can effectively ameliorate the disadvantages caused by the infertility of the soil in alpine grasslands, and provide favorable conditions for the growth of plants. The retained litter of cushion plants is also an important source of soil nutrients, and it has been estimated that the cushion litter of A. tapete accounts for more than two-thirds of their existing biomass (He et al., 2013; He et al., 2014a). The cushion litter can keep the soil warm and promote soil nitrogen mineralization in winter when the temperature is low (He et al., 2014b). In this study, we also found the soil nutrient content was significantly higher underneath the cushion than in places where A. tapete was absent. This was consistent with the results of previous studies, where the contents of soil nitrogen (Badano et al., 2006; Cavieres et al., 2006) and other soil nutrients were higher due to the presence of the cushion plant (Yang et al., 2010; Liu et al., 2014a). This is an important mechanism of the engineer effects of cushion plants in alpine ecosystems (Liu et al., 2014b; Chen et al., 2015b).
Cushion plants improve the local microenvironment due to their special structure, which can also promote soil nutrient cycling and vegetation growth. Specifically, cushion plants can improve the soil water holding capacity by increasing the contents of litter and humus in the soil. In this study, we found the soil water content underneath the cushion plant increased by about 12%. In other studies, it was also revealed that the soil water content increased by 33%-70% compared with the areas without cushion plants (Badano et al., 2006; Cavieres et al., 2006). In addition, because of its special cushiony form, the cushion plant is an effective endothermic body, and its temperature rises faster than that of the soil. According to the field observation results, compared with the control area, A. tapete can increase the soil temperature in the daytime but decrease it in the nighttime (Arroyo et al., 2003; Badano et al., 2006). Increases of soil moisture and temperature would promote the mineralization of soil nitrogen (Koch et al., 2007), and the low temperature at night would inhibit the respiration of soil microorganisms and reduce the absorption of available nitrogen in the soil (He et al., 2014b), thus increasing the available nitrogen in the soil, improving the local microenvironment, promoting the settlement and growth of other plants, and enhancing the species diversity of the community.

5 Conclusions

The restoration of degraded grassland remains an urgent problem for alpine ecosystems. A cushion plant A. tapete can significantly improve the soil nutrient and water contents, as well as plant biodiversity, which plays a significant role in the natural succession and restoration of degraded grasslands. More research should be conducted on the cushion plants in degraded alpine grasslands on the Tibetan Plateau.

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