Published online January 30, 2023
Journal of Ecology and Environment (2023) 47:01
Department of Science Education, Dankook University, Yongin 16890, Republic of Korea
Correspondence to:Deokjoo Son
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background: The positive effects of Arctic plants on the soil environment and plant-species co-occurrence patterns are known to be particularly important in physically harsh environments. Although three dominant plants (Cassiope tetragona, Dryas octopetala, and Silene acaulis) are abundant in the Arctic ecosystem at Ny-Ålesund, Svalbard, few studies have examined their occurrence patterns with other species and their buffering effect on soil-temperature and soil-moisture fluctuation. To quantify the plant-species co-occurrence patterns and their positive effects on soil environments, I surveyed the vegetation cover, analyzed the soil-chemical properties (total carbon, total nitrogen, pH, and soil organic matter) from 101 open plots, and measured the daily soil-temperature and soil-moisture content under three dominant plant patches and bare soil.
Results: The Cassiope tetragona and Dryas octopetala communities increased the soil-temperature stability; however, the three dominant plant communities did not significantly affect the soil-moisture stability. Non-metric multidimensional scaling separated the sampling sites into three groups based on the different vegetation compositions. The three dominant plants occurred randomly with other species; however, the vegetation composition of two positive co-occurring species pairs (Oxyria digyna-Cerastium acrticum and Luzula confusa-Salix polaris) was examined. The plant species richness did not significantly differ in the three plant communities.
Conclusions: The three plant communities showed distinctive vegetation compositions; however, the three dominant plants were randomly and widely distributed throughout the study sites. Although the facilitative effects of the three Arctic plants on increases in the soil-moisture fluctuation and richness were not quantified, this research enables a deeper understanding of plant co-occurrence patterns in Arctic ecosystems and thereby contributes to predicting the shift in vegetation composition and coexistence in response to climate warming. This research highlights the need to better understand plant–plant interactions within tundra communities.
Keywords: Arctic ecosystem, Cassiope tetragona, Dryas octopetala, Ny-Ålesund, Silene acaulis, Soil temperature stability
Alpine, sub-Arctic, and Arctic ecosystems are well known for their harsh and stressful environmental conditions, characterized by low temperatures, strong winds, and desiccation (Klanderud and Totland 2004). In the high Arctic, Ny-Ålesund of Svalbard (lying at 78° 55’ N, 11° 56’ E) is the world’s northernmost settlement and, given its location, is an area of special environmental interest (i.e., bare soil, stones, crusts, mosses, and vegetation) (Chae et al. 2016; Dowdall et al. 2004). Svalbard is one of the places in the high Arctic where rapid changes in landscape forms have occurred due to deglaciation, early snowmelt, enhanced growing season length, and drying of shallow ponds, all of which have resulted from climate warming (Kwon et al. 2015; Mallik et al. 2011; Thomas et al. 2020). Contrarily, some research argue that rises in winter temperatures and increases in winter precipitation (snowfall) and snow depth may lead to shorter growing seasons (Buus-Hinkler et al. 2006; Cooper et al. 2011; Mallik et al. 2011). Obviously, vegetation productivity in Arctic ecosystems has increased over the past few decades, resulting in a trend of greening that coincides with increases in the air temperature (which has climbed about 2°C per decade over the last 30 years) (Pearson et al. 2013; Tape et al. 2006). Similarly, the increase in the growth and abundance of tundra shrubs has been expected in the circumpolar region over the last half-century (Angers-Blondin et al. 2018; Myers-Smith et al. 2015).
The plant species distribution and community characteristics are influenced by both biotic interactions and abiotic conditions, where the relative importance of each can depend on the spatial scale and environmental conditions (Bruno et al. 2003; Gouws et al. 2021). Arctic plant communities are determined by large-scale climatic variations or by local environmental conditions (Nabe-Nielsen et al. 2017). However, from early studies of plant community ecology, there have been debating views concerning the processes that assemble plant communities (Götzenberger et al. 2012). A biological community may contain either a random set of species or be structured by certain assembly rules (positive or negative relationship) (Vinarski et al. 2020). Plant-plant interactions in communities strongly affect the community structure and dynamics and can thereby determine which species can coexist (Padilla and Pugnaire 2006). Such interactions can be positive (facilitative), negative (competitive), or neutral (Lu et al. 2018). Facilitation and competition often co-occur in plant communities and are difficult to understand separately (Callaway and Walker 1997; Río et al. 2014). Besides, plant-plant interacions are driven by environmental conditions, functional traits, and evolutionary relatedness among interacting species, all of which are strongly related to each other (Soliveres et al. 2014; Webb et al. 2002).
According to the stress-gradient hypothesis, positive interactions are expected to be more frequent and more intense in more severe habitats (alpine, Arctic, Antarctic, and arid regions) (Bonanomi et al. 2016; Haussmann et al. 2010; Hupp et al. 2017; Pueyo et al. 2016; Soliveres and Maestre 2014), resulting in a stronger impact on individual species and communities in stressful environments (Gouws et al. 2021; He et al. 2013). An important type of positive plant interaction arises from nurse plants (e.g.,
Several studies on the plant ecology in Ny-Ålesund have examined vegetation development (Yoshitake et al. 2011), the photosynthetic characteristics of dominant plant species (Muraoka et al. 2008), colonization characteristics of
Despite the importance of Arctic vegetation for biodiversity and conservation in the tundra biome against climate warming, few attempts have been made to compare the vegetation composition including dominant plants and their positive effect on the soil-environment in the high Arctic (Grau et al. 2014). To recognize the changes in Arctic plant composition for climate change adaptation, it is crucial to describe the co-occurrence patterns of Arctic plants and their diversity, which are centered on three dominant plants (
The data were collected in July 2015 in Ny-Ålesund (78°55’ N, 11°55’ E) on Spitsbergen, the largest island of the Svalbard archipelago. This area was deglaciated ca. 11,000–13,000 years ago (Cannone et al. 2004), and mature vegetation is dominant in a portion of the study area (Park et al. 2018). The mean temperature is –3.2°C, and the average total annual precipitation of rain or snow was 490.5 mm for the period from 2011 to 2015 (Son and Lee 2022). For July 2015, the mean temperature and total precipitation equaled 6.6°C (maximum 14.8°C and minimum 2.3°C) and 13.2 mm, respectively (https://www.yr.no). Each year, the snow-free period lasts from June to August; at other times during the year, the study area is snow-covered (Blaud et al. 2015). The vegetation’s growing season only lasts from June to September each year due to the high latitude of Svalbard, and vigorous growth occurs only in July and August (Ren et al. 2021).
The vegetation in the study site was dominated by
The vegetation composition at a total of 101 sampling sites (area: about 220 m × 320 m) (Fig. 1) was investigated during July 2015. At each sampling site, I randomly placed a 1 m × 1 m quadrat at least 10 m away from the other quadrats to visually estimate species cover (%). Seventeen bare-soil quadrats without vascular plants were also included as a control. While simultaneously considering cover and frequency, the plots of the sampling sites named after the most abundant plant species with highest cover in each quadrat were divided into three groups:
To monitor the soil-environmental conditions, soil-temperature and soil-moisture were measured at intervals of 1 hour from 12 July 2015 to 18 July 2015 (5TM sensor; Decagon Devices Inc., Pullman, WA, USA) (Tables S1 and S2). For recording the soil-temperature, two measurement devices, each comprising four probes, were located 25 m apart. In each measurement group, the four probes were placed at a depth of 5 cm beneath the three plant species
Simultaneously with the vegetation survey, I collected soil samples beneath the three plants or from the bare soil at each of the 101 sampling sites to quantify the local soil-chemical properties. Soil was taken from three locations per sampling site using a soil auger (corer dimensions: 5 cm diameter and 5 cm depth). Separately for each sampling site, the collected soil was mixed thoroughly to produce a composite sample. Soil analysis included the quantification of total carbon and total nitrogen using an element analyzer (EA1110; CE Instruments, Wigan, England) at the National Instrumentation Center for Environmental Management of Seoul National University. The soil EC and pH were measured with a glass electrode in an 1:5 soil-to-distilled-water slurry (Eutech PC 2700; EUTECH Instrument, Singapore). The soil organic matter was determined by measuring the amount of weight lost after drying the samples in a furnace at 550°C for 4 hours (Achat et al. 2012).
Statistical analyses were performed using the R software (R Core Team 2022). First, species-cover values were log-transformed (ln[cover + 1]) to reduce the influence of outliers. The significance of the distinctiveness in the vegetation composition between the three dominant plants was tested using the “adonis” function in the ‘vegan’ R package (Oksanen et al. 2018) to perform a permutation test with the F statistic (McGranahan et al. 2013). To describe the relationships between soil-chemical properties and plant-community compositions, I performed a NMDS based on the Bray-Curtis dissimilarities (species cover data) using the ‘metaMDS’ function of the ‘vegan’ R package (Oksanen et al. 2020). The environmental factors were fit a posteriori to the NMDS ordination, with the significant factors (
Second, to compare the buffering effect on daily soil- temperature differences and daily soil-moisture differences related to the three dominant plants, I used a Kruskal-Wallis test with Bonferroni correction due to the unequal
Third, the plant co-occurrence frequency was analyzed using the presence/absence data of the plant pairwise and “coocur” package in R software (Griffith et al. 2016) to detect positive and negative co-occurrences between species. This package employs a probabilistic approach to determine which species pairs co-occur less often (negative co-occurrence) or more often (positive co-occurrence) than is likely by chance (Brazeau and Schamp 2019).
In total, 17 plant species from 10 families were found (Table S3) at the three dominant plant communities (29
The two plants significantly reduced the daily soil-temperature fluctuations. This effect was especially pronounced for
The three dominant plants did not significantly stabilize the soil-moisture differences (Fig. 2B). Even though
There was a significant distinctiveness in the vegetation composition between the three dominant plant communities that explained 48.9% of the compositional variance (F = 38.8;
The vegetation composition was significantly correlated with the following soil-environmental variables: total carbon, pH, and SOM, according to the NMDS ordination (Fig. 3). While the total carbon and pH were positively correlated with the
The difference in EC between the dominant plant types and bare soil was significant from the results of Welch’s ANOVA (Table 1). Despite no significances, the total carbon from the S
A total of 45 species pair combinations, with 10 species having more than a 1% importance value, were analyzed based on species presence/absence. From the co-occurrence matrix, two positive co-occurrences are represented:
I have examined plant composition structures based on the three dominant plants (
In the particularly harsh physical environment of Ny-Ålesund, Svalbard, the two Arctic plants
Even though soil-temperatures were measured for only 1 week using two measurement devices, this research shows that
Previous studies have demonstrated that different kinds of Arctic plants keep soil-temperatures stable and warm. For example, Molenda et al. (2012) found that on a microclimatic scale,
The buffering effect of the daily soil-temperature fluctuation of
Unlike soil-temperature, there are no distinctive buffering effects of the three dominant plants on soil-moisture stabilization. This is consistent with the findings by Hupp et al. (2017), who showed that the nurse plant
Soil organic matter, total carbon, total nitrogen, and pH in soil are not associated with different dominant plant communities. Interestingly, the EC in bare soil without vegetation is significantly higher than that in the three dominant plant communities. At the study site, the presence of wild animals (e.g., Svalbard reindeer, Arctic fox) eating Arctic plants is frequent and animal feces can be found on the surface of bare soil (Hayashi et al. 2014; Son and Lee 2022). In particular, the impacts of Svalbard reindeer
In this study, the live plants and dead plant litter of the three dominant plants did not improve the soil nutrients. A similar finding has been reported by Badano et al. (2006), who investigated a nurse plant,
Based on the NMDS result, although there were significant relationships between the three plant community structures and soil-chemical properties, the blue arrow of the soil SOM was located between the
Regarding soil nutrients, the facilitative effects of plants are unlikely to prevail because limited nutrients are shared via competition or interference with other plants (Padilla and Pugnaire 2006). Additionally, plants compete with soil microbes for soil nitrogen in unproductive soil (Bardgett et al. 2003). In tundra, the carbon output to the soil and decomposition are too slow to detect due to poor litter quality, low temperatures, and frequent soil anoxia (De Deyn et al. 2008; Mack et al. 2004). Furthermore, patches or cushions of plants with different sizes and succession stages have different demands for soil nutrients and soil-moisture (Lu et al. 2018). These reasons contribute to explaining why the three plant communities here do not show distinctively higher soil-chemical nutrients compared to that of bare soil.
Three studied plants distributed widely and randomly with other plant species in Ny-Ålesund. Furthermore, species richness did not differ significantly between the three dominant plant communities. It was predicted that the
Based on the NMDS (Fig. 3) and species co-occurrence matrix (Fig. 6),
Previous research about plant-plant interactions (the nurse effect, in particular) have shown that certain plants favor the establishment and survival of the associated plant species by modifying the local environment (Nuñez et al. 1999). Nurse plants can provide facilitative effects on seedling establishment and survival within or under their canopies (Cavieres et al. 2007) by creating more favorable microhabitats for other plant species than what is offered by the surrounding environment (Chen et al. 2015).
On the other hand, Boulanger-Lapointe et al. (2016) suggested that
Kapfer and Grytnes (2017) reported that the climatic warming in the high Arctic has contributed to significant changes in the vegetation on Svalbard over the past 85 years. Dwarf shrubs, such as
Plant compositional patterns can be driven by both biotic and abiotic conditions in Arctic ecosystems. The soil- temperature under
Supplementary information accompanies this paper at https://doi.org/10.5141/jee.23.002.
Table S1. Soil-temperature from 12 July 2015 to 18 July 2015. Table S2. Soil-moisture content from 12 July 2015 to 18 July 2015. Table S3. The list of surveyed plants.
I especially thank Eun Ju Lee (Seoul National University) and Saeromi Mun (National Institute of Ecology) for the support to this paper. I also thank the anonymous reviewers.
ANOVA: Analysis of variance
Bare: Bare soil
C: Total carbon
EC: Electrical conductivity
HSD: Honest significant difference
N: Total nitrogen
NMDS: Non-metric multidimensional scaling
SOM: Soil organic matter
This study was supported by the National Research Foundation of Korea (NRF-2011-0021071).
The datasets are available from the corresponding author on reasonable request.
The author declares that they have no competing interests.