Alpine wet meadows: soil properties’ effect on plant diversity

Madeline Castro1, Fidel Machado-Perez1, Rebecca Raven2

1University of California, Merced; 2University of California, Riverside

ABSTRACT

Alpine ecosystems are a harsh environment with little nutrients and the abiotic effect that the soil has on the plant community is relatively unknown. The focus of this study is to illuminate the role that soils play in the plant diversity of alpine wet meadows. In doing so we investigated the function of clay and root content, organic matter, pH and soil moisture in determining plant diversity in three meadows in the White Mountains, California. We found that water may key role in plant diversity and richness both among and within meadows. Other abiotic properties of soil had no effect on species diversity and richness. These findings have many implications in the further study of erosion and nutrient dynamics in mountainous and alpine ecosystems.

Keywords: alpine wet meadows, pH, soil composition, clay, plant community

INTRODUCTION composition, organic matter, and pH. Water is important for plants because they use it In ecosystems, biotic and abiotic factors for photosynthesis, transporting nutrients interact to determine the richness and and growth. diversity of plant communities. Chemical When water is scarce plant growth is and physical characteristics of soils play a limited (Duan 2008). Organic content in the role in driving the diversity and richness in an soil includes decomposing plant matter and ecosystem. As climate weathers rocks, roots. Plants roots allow plants to uptake different types of soils are deposited on a nutrients. In more nutrient-deprived soils, landscape. These soils have different plant roots become more abundant in order properties that allow for differential plant to better access nutrients from the soil growth. For example, clay accumulation can (Trejo et al. 2018). Organic matter plays a help plant communities grow. Due to clay’s direct role in soil carbon cycling, meaning the negatively charged ions, positively charged more productive the habitat the more acidic cations such as calcium (Ca2+), magnesium the soil pH becomes (Palozzi 2017). Likewise, (Mg2+) and potassium (K+) accumulate the dynamic relationship between pH and within clay substrates. Clay soil improves the organic matter also lends itself to uptake and exchange of these important understanding nutrient cycling within a macronutrients (Wolde et al. 2014). Other system (Palozzi 2017). important components of soil include water

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Equally, plants play a key role in the affects the regional climate increase in development of soils. Through organic temperature because of the release of weathering, plants release acids from their excess carbon (Jin et al. 2008; Wang et al. roots to decrease the pH within the soil, 2002; Xu et al. 2004; Schaefer et al. 2011). ultimately breaking down rock minerals to Some research has analyzed the effects of access more nutrients. (Drever et al. 1997) nutrients and biotic factors. For example, the The development of plant roots also allows effects of nitrogen on aboveground biomass for micropores to form within the soil (Wang et al. 2018; Yingfang et al. 2018) and profiles, increasing water velocity and mycorrhizal-plant interactions (Yongjun et mineral stabilization. (Angers, 1998) al. 2015) have been extensively studied. Understanding how and why these However, there has been little research of interactions take place is a key component of the effects of abiotic soil properties on plant soil science. While dictated by the soil diversity. properties, plant communities directly In this study we examined the relationship influence the habitat they live in to increase between soil properties and plant diversity their fitness (Watt 1947). in alpine wet meadows in the Inyo White In alpine ecosystems the living conditions Mountains. We suspect that there will be for plants are particularly difficult. These large differences between nearby alpine systems are characterized by the high meadows of this region, and that this may altitude, lack of trees, a short growing period have an effect on both the soil and the plant and low accessibility to nutrients (Bowman community at large. Similarly, we believe et al. 1993). Nutrients, such as nitrogen, tend plant communities may change substantially to be very limited in an alpine ecosystem, from the center to edge of a meadow. making it difficult for plants to grow (Yuan et Additionally, we had several predictions al. 2015). Even gaining access to more about how soil properties will directly affect developed soils can be a challenge for plants plant diversity. Areas with more clay will within the alpines low weathered soil have higher diversity because they are able horizons due to the low weathered parent to supply a higher abundance of nutrients to material (Retzer 1956). Soil is stratified into soil roots (Barber 1995). Higher availability horizons that have very distinct of soil moisture should increase plant characteristics. In an alpine ecosystem these diversity because it allows for more growth horizons are often undeveloped. With these potential (Deng 2016). Higher root content unique living conditions, the plants that can should lower plant diversity due to survive in these places become specialized competition between plant species (Aerts to the area (Körner 2003). Alpine meadows 1998). Conversely, higher organic content in are an especially interesting habitat due to the soil should have a positive effect on plant their unique characteristics. For example, communities because of resources from horizon depths tend to be larger in alpine decomposing plants (Fu et al. 2004). meadows versus other alpine habitats and Increasing soil pH may decrease species the soils have more carbon overall (You richness due to a decrease in seed viability 2014). Alpine meadows take a long time to (Ma 2017). recover from degradation and this directly

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METHODS the edge pit (pit E) and the highland pit (pit H). Pit C is located at the center of the 2.1 Natural History meadow where meadow plant abundance is the highest. Pit E is located on the outskirts This study consisted of the analysis of of the meadow where the vegetation begins three meadows within Barcroft Field Station to change from wetland affinity plant species in the White Mountains, California. The to drought-tolerant plant species. Pit H was meadows include Barcroft Gate (37 33.560N, located 30 meters upslope from the pit E, 118 14.091W), East Shield (37 34.478N, 118 outside of the meadow. The pits were dug 13.499W), and Marmot Meadow (37 along a transect that went up the highest 34.164N, 118 13.945W). The meadows were slope of the meadow. Each pit was dug down chosen for the differences in elevation. to the C soil horizon if possible. Large rocks Barcroft Gate’s elevation was 3530 m, East were encountered in some pits making it Shield was at 3690 m, and Marmot Meadow impossible to continue digging. (Figure 1). was at 3645 m. The boundaries for each meadow was defined by the absence of drought-tolerant vegetation and presence the wetland affinity vegetation. Each meadow’s edge was established by the transition line between the two vegetation types. Barcroft Gate meadow is 90 m long and 27 m wide. East Shield meadow is 45 m long and 68 m wide. Marmot Meadow is 62 m long and 71 m wide. All lengths are facing approximately north. Figure 1: Diagram of study site. Meadow was 2.2 Transect Location surveyed using a transect from the center of the meadow to 30 m beyond the meadow edge. 0.5 m by For each meadow a transect was laid out 0.5 m pits were dug in the highland, edge and center from the center of the meadow to 30 meters of each meadow. Soil cores were taken every 5 m past the edge of the meadow along the along the transect. Blue squares represents the pits, x steepest upward slope. The center of the in the circle is the cores, the green field is the meadow boundary, the yellow field is the highland boundary, meadow is defined by the high abundance of and the vectors are the aspect. wetland affinity plant species and the edge of the meadow is defined by the vegetation 2.3 Soil Type change from meadow species to drought- tolerant plant species. At each pit, the soil horizons were identified and classified into A, B, B+, C and 2.3 Soil Pits Cr. Depths of each horizon were measured. Soil samples were collected from each Pits were about 0.3 by 0.3 m and about 1 horizon for further analysis of soil moisture, m deep. Three pits were dug within each of and particle size. the three meadows; the center pit (pit C),

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2.3 Soil Moisture oven reached ~248.89-260 ˚C. For pH analysis, a 1:1 solution of soil and neutral tap Soil moisture was determined by water was made and then using litmus paper measuring the weight of the collected wet the pH was measured. soil samples and placing them in an oven at approximately 53.34 ˚C. After being baked 2.3 Plant Diversity and Richness for approximately 3 hours, the mass of the dried samples was taken to calculate soil Plant diversity was measured by moisture. To measure the soil moisture, we estimating the percent cover of each plant took the mass of the dried soil, subtracted it species within quadrats along the transect. from the mass of the wet soil and then The quadrat has a dimension of 0.5 m by 0.5 divided that vault from the mass of the wet m. Measurements were taken every 5 soil. meters. We calculated plant diversity in each quadrat using the Shannon-H index. 2.3 Soil Sieving 2.3 Statistical Methods Before conducting moisture analysis dried soil was sieved through a soil sieve We used JMP 14 statistical software for all containing 120 and 230 mesh layers, which statistical analyses. Soil pit data was used to collected the clay content. Clay content and analyze clay content, root content, and soil root content was weighed and measured as moisture. Soil core data was used to analyze percent of total weight. pH and organic content. To test the effect of meadow identity on clay content, root 2.3 pH and Organic Content content, and soil moisture we ran ANOVAs. To analyze how position within the meadow The transect line was broken into two (center, edge, highland) affected the same parts at pit E, categorized into the highland soil properties we ran ANOVAs. To analyze part of the transect above pit E and the how different meadows, meadow position, central part of the transect below pit E. Two and different horizons affected plant soil cores were taken every 5 meters along diversity we ran ANOVAs. We used linear this transect to examine the A and B horizon. regressions to quantify the relationship The soil auger used was able to go down 12 between plant diversity and clay content, inches into the ground to examine the entire root content, and soil moisture. A horizon and the top of the B horizon. Two samples from each horizon were collected to RESULTS examine soil pH and organic matter of the A and B horizon. To get the organic matter 3.1 Analysis of Soil Properties percentage, the mass of dried soils where taken and then the samples were placed in The pH was the only soil property that aluminum foil and folded to attempt to differed between meadows with pH the create anaerobic conditions to minimize highest at East Shield and the lowest at smoke. Then the packets where labeled and Barcroft Gate (pH: N = 60, f = 4.46, p = 0.02; placed into an oven at max temperature; our Figure 2; clay content: N = 32, f = 0.42, p =

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0.68; root content: N = 32, f = 0.32, p = 0.73; soil moisture: N = 32, f = 1.08, p = 0.35; organic content: N = 58, f = 1.21, p = 0.31). Clay and root content differed within meadows with higher content closer to the highland (clay content: N = 32, f = 5.68, p = 0.0085; root content: N = 32, f = 5.21, p = 0.0119; Figure 3). Other soil properties did not differ within meadows (soil moisture: N = 32, f = 1.41, p = 0.26; pH: N = 60, t = 1.48, p = 0.14; organic content: N = 58, t = 0.24, p = 0.81).

Figure 3: Percent clay and root content within the center, edge, and highland of each meadow. Clay and root content differed within meadows with higher content closer to the highland. Representing clay is the light grey bar. Representing the root content is the dark grey bar. x-axis displays the location within the meadow, y-axis displays the percent of clays and root content, vertical lines represent a standard error.

3.2 Analysis of Plant Diversity and Richness

Plant diversity was highest in Marmot Meadow, intermediate in East Shield and Figure 2: Soil pH across three alpine meadows. Bars lowest in Barcroft Gate (N = 32, f = 37.1, p < represent mean pH per meadow + 1 S.E. East Shield 0.0001; Figure 4). Plant diversity marginally Meadow showed a higher pH value compared to increased with soil moisture (N = 32, r2 = Barcroft Gate and Marmot Meadow. Barcroft Gate 0.09, p = 0.09; Figure 5). Diversity was not and Marmot Meadow did not have a difference in pH values. x-axis displays meadows analyzed, y-axis affected by any other measured soil displays pH values, vertical lines represent a standard properties (clay content: N = 32, r2 = 0.007, error. yellow field is the highland boundary, and the p = 0.66; root content: N = 32, r2 = 0.002, p vectors are the aspect. = 0.79). Plant richness increased as distance from the center of the meadow increased (N = 46, r2 = 0.10, p = 0.03; Figure 6). There was no effect of pH and organic content on plant richness (pH: N = 46, r2 = 0.02, p = 0.38; organic content: N = 44, r2 = 0.002, p = 0.77).

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Figure 4: Plant diversity across three alpine Figure 6: Change of plant diversity within increasing meadows. Plant diversity was highest in Marmot distance from meadow’s center. Plant richness Meadow, intermediate in East Shield and lowest in increases as distance from the center of the meadow Barcroft Gate. x-axis displays the meadows being increases. x-axis displays the distance from the center analyzed, y-axis displays the value of plant species of the meadow, y-axis displays the number of plant diversity, vertical lines represent a standard error. species found in the meadow.

DISCUSSION

Overall, we found less differences in soil between the meadows than expected, and fewer effects of plant diversity on soil. However, there were some interesting differences in soil and plant diversity both within and among meadows. In accordance with our hypothesis, soil pH changed between meadows. The pH was highest at East Shield and lowest at Barcroft Gate meadow. These differences could indicate the relative resilience or fragility of the Figure 5: Change of plant diversity with soil moisture habitat locally due to the adaptations of within three alpine meadows: Plant diversity wetland species (Rusek 1993). The marginally increased with soil moisture. It was found differences in pH could be because wetland that Marmot Meadow had two samples that drove habitats have acidic soils due to deposition the trend for plant diversity with soil moisture. X-axis displays the soil moisture measured (mL), y-axis and leaching; therefore, as the wet displays the plant species diversity. meadows recede, it would be interesting to investigate the encroachment of highland species and the shift from acidic to neutral soils if that is the case (Gunnarsson et al. 2000). In our study we found no change in

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pH within meadows and pH had no effect on Root content did not differ between plant richness. In a study on a mire species meadows, despite our expectations. Similar succession Gunnarsson et al. (2000) found a to clay content, root content may differ strong correlation between pH and species more in a localized area but less over a larger richness. Our study contained meadows that gradient. Likewise, alpine plants have were much less wet than in Gunnarsson et immensely large root systems that may not al. (2000) and perhaps this attributed to our differ much over an ecosystem. Root 1.5 change in pH versus their ~2.5 change. content, however, changed within sites and Soil pH may have a drastic effect on plant was most abundant in the highland. This communities, however, a larger change in could be attributed to a lower availability of pH may be needed than we found in our nutrients in the highland and a more study to affect plant richness. extensive root system is needed for plants to Contrary to our expectations, clay content survive (Trejo et al. 2018). Root content had did not change between sites. This could be no impact on plant diversity. According due to our sites having similar characteristics Tilman (1988) plants in arid habitats of sample placement within the meadow compete less with each other in both inter- plots. Our study locations in each site were and intraspecies interaction, but rather they the same (the center, edge and highland). facilitate each other’s growth to further Our findings on clay content within nutrient cycling. This then explains the lack meadows suggests that aspect and slope, of correlation with root content and plant may be another chief factor in determining diversity. The differences in root content clay spatial distribution. Another study in an that was found could be explained by the alpine system also found that clay content shift in plant community from highland to was increased in the highest sloped region of wetland. These habitats are characterized by their study area (Miller & Birkeland 1992). different species which suggests that there Clay content, however, did not have an could be variance within the sites due to this. effect on species diversity. We believed that In line with root content, organic matter it would have an effect because clay did not differ between the different provides a sink of nutrients for plant meadows. This could be due to similar communities. According to Wan et al. (2018) decomposition rates between the alpine clay content in soil is a useful indicator of meadow ecosystems creating a plant diversity in an ecosystem. Further homogeneous spread of organic material replication of our study could provide across each meadow. This could also explain support for Wan et al. (2018)’s finding. Or, why organic matter did not differ within perhaps, clay content does not pose as a meadows. We found no correlation between useful indicator in an alpine meadow organic content and plant diversity. Similar ecosystem. In Zhang et al. (2018)’s study in organic matter content across our meadows an alpine meadow it was found that nitrogen could explain this effect. and phosphorus were important nutrients. We found no differences in soil moisture Perhaps, further study could indicate if between or within meadows. This is an elements such as these are more useful especially surprising find because indicators than clay. anecdotally, we noticed wetter soils in East

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Shield and Marmot Meadow and at the soils holding some of the most diverse plant center of each meadow. Less surprisingly, communities (Laliberté et al. 2013). we found that soil moisture had a positive Soil properties have a direct influence on effect on plant diversity. However, this trend the communities and habitats that utilize it. seems to be drawn from two data points Through the investigation of the alpine soils, from Marmot Meadow. These two points it was found that this is the case, but there had very high levels of plant diversity and soil are many other factors such as climate, local moisture and they may not be represented variation and species cycles that play into as a whole for the effect of soil moisture on the function of the habitat and the plant diversity. Continued replication of our ecosystem. As we found, pH and water study in alpine meadows could provide for or content have a large role to play in both the refute this trend. For example, we soil and the plant community. Likewise, soil conducted our study after days of rain. This texture such as clay and the root abundance most likely caused the soil to be also seemed to play a role in this abiotic and disproportionally saturated for the time of biotic system. All these key pieces play a role year. Further study during weeks after rain in the delicate system that is the alpine fall could provide better results. ecosystem. We found that plant diversity and richness Alpine meadows are a unique and were highest in the highland part of our uncommon habitat that may be particularly meadow. This effect could be attributed to a subject to climate change. Already, alpine convergence of wetland and non-wetland ecosystems are changing drastically species in the highland section of our study (Jägerbrand 2009). In a study in sub-arctic site. alpine meadows it was found that Our findings suggest that plant diversity temperature increases caused an immense and richness could be more affected by change on the plant community in just a five- spatial position and not on the soil year period. (Jägerbrand 2009). One can only properties that we studied in alpine imagine the impact over a longer time. More meadows. Moreover, other soil factors that research should be done on alpine meadows we did not study could affect plant diversity before further degradation occurs. This and richness. A study in an alpine meadow in would be a good baseline study of soil the Qinghai-Tibetan Plateau it was found nutrient dynamic. With the increase in that nitrogen and silicone addition to soils precipitation changes within the California increased plant richness (Xu et al. 2018). mountain ranges, there are many geological Perhaps, nitrogen, silicon and other and meteorological changes that come along nutrients like these affect plant communities with changing climate (Null et al., 2010). One more than the soil properties that we of which is the increased erosion of alpine investigated. In this study we did not ecosystems that are not adjusted to high investigate the parent material which could erosion watershed events. This is present in lead to a deeper understanding of the soil many mountain ranges across the state, but composition and the mineral and predominantly in the eastern Sierras (Null et compounds found within it. This can be al., 2017). Similarly, the investigation of soil substantiated by the example of ancient erosion would be good baseline study for

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