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Journal of Resources and Ecology >

2023 , Vol. 14 >Issue 4: 816 - 821

DOI: https://doi.org/10.5814/j.issn.1674-764x.2023.04.014

Evaluation and Improvement of Mine Site Quality

Spatial Variations in Soil Physicochemical Properties and Enzyme Activities in the Low Mountain Area of Helan Mountain

  • LI Guoqi , 1, 2, 3, * ,
  • WANG Yafang 1, 2, 3 ,
  • LIU Xing 1, 2, 3 ,
  • SHI Yun 4 ,
  • YUE Liling 5 ,
  • GU Qingmin 6
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  • 1. Breeding Base for State Key Laboratory of Land Degradation and Ecological Restoration in Northwest China, Ningxia University, Yinchuan 750021, China
  • 2. Key Laboratory for Recovery and Restoration of Degraded Ecosystems in Northwestern China of Ministry of Education, Ningxia University, Yinchuan 750021, China
  • 3. School of Ecology and Environment, Ningxia University, Yinchuan 750021, China
  • 4. School of Geography and Planning, Ningxia University, Yinchuan 750021, China
  • 5. Zaoquan Coal Mine of Ningxia Coal Industry Co., Ltd., China Energy Group, Lingwu, Ningxia 751411, China
  • 6. Yangchangwan Coal Mine of Ningxia Coal Industry Co., Ltd., China Energy Group, Lingwu, Ningxia 751411, China
*LI Guoqi, E-mail:

Received date: 2022-11-10

  Accepted date: 2023-04-20

  Online published: 2023-07-14

Supported by

Key Research and Development Program of China(2017YFC0504406)

The Key Research and Development Program of Ningxia Hui Autonomous Region(2022BEG03066)

The Major Strategic Consulting Research Project of Chinese Academy of Engineering(2021NXZD5)

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Abstract

The low mountainous area of Helan Mountain has sparse vegetation, severe surface erosion and a fragile ecological environment. In this study, we analyzed surface soils at five different altitudes in the low mountainous area of Helan Mountain to determine their basic physical and chemical properties. the activities of four common soil enzymes and their correlations. The results showed that with increasing altitude, the soil moisture content and total porosity showed upward trends, while bulk density, organic matter and available phosphorus showed downward trends, and TC, TN and alkali-hydrolyzed nitrogen showed trends that were first decreasing and then increasing. As the altitude increased, the carbon-nitrogen ratio increased and showed a trend of first increasing and then decreasing, while soil urease and alkaline phosphatase activities showed the opposite trends that were first decreasing and then increasing, and sucrase and catalase showed steadily increasing trends. Urease activity and phosphatase activity were significantly positively correlated with soil total nitrogen. Previous studies had also found differences in various physical and chemical property indexes and enzyme activities of surface soil at different altitudes, and that the physical and chemical properties of soil and enzyme activities affect each other.

Key words： Helan Mountain; altitude; soil enzyme activity

Cite this article

LI Guoqi , WANG Yafang , LIU Xing , SHI Yun , YUE Liling , GU Qingmin . Spatial Variations in Soil Physicochemical Properties and Enzyme Activities in the Low Mountain Area of Helan Mountain[J]. Journal of Resources and Ecology, 2023 , 14(4) : 816 -821 . DOI: 10.5814/j.issn.1674-764x.2023.04.014

1 Introduction

Soil moisture content, bulk density and total porosity are the basic physical properties of soil, and they are closely related to the decomposition of litter on the soil surface and the growth and development of above-ground plants (Ma et al., 2006; Yao et al., 2006; Geng et al., 2014). Enzymes in soil are mainly derived from the secreted substances of above-ground vegetation roots, the life activities of soil microorganisms and the decomposition of organic matter such as plant and animal residues in soil; and their activities are affected by soil hydrothermal conditions, soil nutrient content and surface litter (Allwason and Treseder, 2008; Wang et al., 2014). Soil enzymes participate in the transformation and cycling process of soil nutrients by catalyzing the decomposition of organic matter in soil, and they are closely related to changes in soil nutrients. They are commonly used indicators for measuring soil quality and soil fertility (Boerner et al., 2005; Liu et al., 2011; Hewins et al., 2015). Slope direction and elevation are two important factors that affect the formation of spatial heterogeneity in a mountain environment. At different altitudes, climatic conditions such as temperature and precipitation, soil types and above-ground vegetation communities may vary, resulting in differences in soil moisture content, bulk density, porosity and other key physical and chemical properties, while the spatial differences in soil properties may directly or indirectly affect the activities of enzymes in the soil (Margesin et al., 2010). In recent years, many studies at home and abroad have investigated the soil physical and chemical properties and soil enzyme activities in mountain ecosystems. These studies have shown that soil physical and chemical factors and enzyme activities vary between altitudes, but the trends of changes in the soil physical and chemical factors and enzyme activities with increasing altitude are inconsistent (Liu et al., 2013; Gonzalez et al., 2014). For example, the oil organic matter content and available phosphorus content decreased with increasing altitude in the Wumeng Mountain area of Yunnan Province (Xie et al., 2019), while these indicators increased with increasing altitude in karst evergreen deciduous broad-leaved mixed forest (Wang et al., 2017). Furthermore, soil urease activity and alkaline phosphatase activity showed decreasing trends with increasing altitude in Nyenchen Tanglha Mountain swamp (Si et al., 2014), while the activities of sucrase and urease in soil showed increasing-decreasing-increasing trends with increasing altitude in the alpine canyon area of western Sichuan (Cao et al., 2016).
The ecological restoration of Helan Mountain directly affects the ecological security of Northwestern China, Northern China and even the whole of China because Helan Mountain is a key shelter zone in the Chinese “two barriers and three belts” pattern. Moreover, it is one of the eight major centers of biodiversity in China (Jin, 2009; Wang, 2011). Helan Mountain is located in the Northern farming-pastoral transitional zone, and its ecological environment in the low mountainous area is relatively fragile, with low and sparse vegetation (Jiang, 2004; Liang et al., 2004; Gu et al., 2016). Recent studies on Helan Mountain mainly focus on biodiversity, above-ground vegetation community characteristics, and similar topics. However, there is limited research on the spatial heterogeneity of soil physical and chemical properties and enzyme activities, and their correlations. In this study, the surface soil at five elevations in the lower mountain area of Helan Mountain was selected as the research object to explore the response of soil physicochemical indexes to the elevation gradient, the response of soil enzyme activity to the elevation gradient and the correlations between soil enzyme activities and soil physicochemical indexes. These findings provide a theoretical basis for the scientific evaluation of soil quality and the policy-decisions related to ecological restoration measures in Helan Mountains.

2 Study area

The study area is located in the Rujigou of Helan Mountain National Nature Reserve, Ningxia Hui Autonomous Region, which has a typical temperate continental climate and mountain climate. The geographical coordinates are 105°49°-106°41°E, 38°19°-39°22°N. It is located in an ecotone of agriculture and husbandry (Jin, 2009; Wang, 2011). In the low mountainous area of Helan Mountain, the temperature changes dramatically, and this area is characterized by drought with limited rain that is mainly concentrated from July to September (Gu et al., 2016). The average annual precipitation is approximately 420 mm, with 70%-80% of it occurring in July to September, but the annual evaporation is 2000 mm. The average annual temperature is -0.8 ℃, the annual minimum temperature can reach -23.5 ℃, and the annual maximum temperature can reach 35.1 ℃. The frost-free period is 229 days. In spring and winter, the weather is windy, often accompanied by sandstorms, and the main wind direction is from the northwest (Wang et al., 2021). The vegetation and soil have obvious regularity in their spatial differentiation from the foot to the top of the mountain. The vegetation can be divided into four vertical zones according to elevation: piedmont desert and desert steppe zone below 1600 m; foothills and low mountain prairie belt from 1600 to 1800 m; low mountain steppe zone, middle mountain and subalpine coniferous forest zone from 1800 to 3100 m; and alpine subalpine shrub and meadow zone above 3100 m. The soil can be divided into three vertical zones: brown calcic soil zone, grey brown soil zone, alpine subalpine shrub zone and meadow soil zone (Liang et al., 2004).

3 Data and methods

3.1 Sample site design and sample collection

At elevations from 1200 m to 2000 m, a sampling site was set every 200 m, and three 5 m×5 m plots were set in each area where the above-ground vegetation community habitat was relatively uniform. All five sampling sites were located on a sunny slope. Three 1 m×1 m small plots were arranged diagonally within each large plot, and a five-point sampling method was used to collect soil samples in each small plot (the sampler was 20 cm×20 cm×10 cm in size).

3.2 Test methods

The determination of soil physical and chemical properties followed a conventional analysis (Guckert et al., 1986). For determining soil enzyme activities, each naturally air-dried soil sample was screened to 1 mm, and the enzyme activity was determined with a spectrophotometer (Table 1).
Table 1 Determination methods of soil enzyme activities
Measured metric Method
Urease (UE) Colorimetric method of sodium phenol-sodium hypochlorite
Alkaline phosphatase
(ALP)		 Benzene disodium phosphate colorimetric method
Sucrase (SR) 3, 5-Dinitrosalicylic acid by colorimetric method
Catalase enzyme (CAT) Potassium hypermangante volumetric method

3.3 Data statistics and analysis

The calculation formula for the soil bulk density was:
$\text{ }\!\!~\!\!\text{ }S\text{ }\!\!~\!\!\text{ }=\frac{g\times 100}{V\times (100+W)}$
where S represents the soil bulk density; g represents the wet weight inside the cutting ring; V represents the volume of the cutting ring; and W represents the water percentage of the sample. The unit of soil bulk density is g cm-3.
The formula for calculating the fractal dimension of soil particle size was:
$\frac{V\left( r<{{R}_{i}} \right)}{{{V}_{T}}}={{\left( \frac{{{R}_{i}}}{{{R}_{\max }}} \right)}^{3}}-D$
where D represents the fractal dimension of soil particles; r stands for soil particle size (μm); Ri is the soil particle size of particle size class i (μm); VT represents the total volume of soil particles (%); Rmax is the maximum value of the soil particle size (μm); and V represents the volume fraction of soil with soil particle size less than Ri. When the particle size is less than 2 μm, Ri is 1 μm.
The experimental data were preliminarily processed, data were collated and charts were made in Excel, and the statistical analysis and correlation analysis were carried out with SPSS 17.0. The single factor variance analysis and LSD method were used to make multiple comparisons of the soil
properties at different altitudes, and the Pearson correlation coefficient method was used for correlation analysis

4 Results

4.1 Soil physical and chemical properties at different altitudes

It is well known that with an increase in altitude, the temperature on the mountain decreases and precipitation increases. As shown in Table 2, the soil moisture content showed an increasing trend with elevation, with the highest value of 5.14% at 2000 m and the lowest value of 1.29% at 1200 m. The soil bulk density decreased with increasing altitude, and was the highest at 1200 m (1.69 g cm-3) and the lowest at 2000 m (1.50 g cm-3). The total soil porosity was enhanced with increasing elevation, and was the highest (43.25%) at 2000 m and the lowest (36.35%) at 1200 m, which indicated that soil aeration and permeability increased with the elevation.
Table 2 Soil physical and chemical properties at different altitudes
Altitude (m) 1200 1400 1600 1800 2000
Soil moisture content (%) 1.29±0.04C 1.49±0.10C 2.25±0.21B 4.73±0.57A 5.14±0.44A
Soil bulk density (g cm-3) 1.69±0.03A 1.57±0.05B 1.53±0.04B 1.52±0.04B 1.50±0.04B
Total porosity (%) 36.35±1.30B 40.84±1.70A 42.40±1.49A 42.50±1.56A 43.25±1.68A
pH 8.56±0.06A 8.13±0.05B 8.19±0.04B 8.27±0.0.03B 8.46±0.07A
Electric conductivity (mS (10 cm)-1) 9.04±0.71B 16.90±1.84A 5.86±0.42C 6.83±0.37C 6.66±0.27C
Soil organic matter, SOM (g kg-1) 4.89±0.01A 4.28±0.02B 1.21±0.04E 1.54±0.08D 2.22±0.03C
Total carbon, TC (g kg-1) 26.85±1.92A 12.84±0.48C 13.56±0.52C 16.23±0.36BC 17.78±0.64B
Total nitrogen, TN (g kg-1) 0.64±0.09A 0.28±0.04B 0.30±0.02B 0.54±0.03A 0.60±0.05A
Alkali-hydrolyzed nitrogen, AN (mg kg-1) 71.58±9.68A 68.43±6.88A 36.75±0.35B 69.13±4.89A 74.20±5.28A
Available phosphorus, AP (mg kg-1) 20.26±0.49A 11.78±0.27B 9.11±0.47C 7.38±0.35D 3.62±0.16E

Note: Different letters indicate significant differences between the altitudes (P<0.05).

As shown in Table 2, there are differences in the various indexes of soil surface nutrients at the different elevations. Among them, organic matter and available phosphorus were negatively correlated with altitude, with their highest values at 1200 m. Organic matter and available phosphorus gradually decreased with increasing altitude, and the difference was significant among the various altitudes (P<0.05). TC, TN and alkali-hydrolyzed nitrogen decreased at first and then increased with increasing altitude, and the differences were significant at the different altitudes (P<0.05). TC and TN were the highest at 1200 m and the lowest at 1400 m. Alkali-hydrolyzed nitrogen was highest at 2000 m and lowest at 1600 m.

4.2 Soil enzyme activities at different altitudes

The data in Fig. 1 show that soil enzyme activity is closely related to altitude. Soil enzyme activities were different at the various altitudes and for the different kinds of enzymes. With increasing altitude, soil urease activity decreased at first and then increased, varying from 1.14 mg g-1 h-1 to 2.09 mg g-1 h-1. Urease (UE) activity was significantly reduced at 1400 m altitude (P<0.05), but significantly higher at the 1600 m-2000 m altitudes (P<0.05). Soil sucrose (SR) activity was positively correlated with altitude. The SR activity ranged from 2.66 mg g-1 h-1 to 6.72 mg g-1 h-1, with the lowest activity at 1200 m (2.66 mg g-1 h-1) and the highest activity at 2000 m (6.72 mg g-1 h-1). With increasing altitude, the fluctuations of soil catalase activity (CAT) increased. The CAT activity varied from 0.69 mg g-1 h-1 to 1.14 mg g-1 h-1 (at 1800 m), and showed an increasing-decreasing-increasing-decreasing activity trend with the rising altitudes from 1200 m to 2000 m. CAT was significantly higher at 1400 m and 1800 m (P<0.05), but lower at 1600 m and 2000 m (P<0.05). With increasing altitude, soil alkaline phosphatase activity (ALP) first decreased and then increased. The activity of ALP varied from 0.86 mg g-1 h-1 (at 1400 m) to 1.43 mg g-1 h-1 (at 2000 m). The ALP was significantly lower from 1400 m to 1600 m (P<0.05), significantly higher at 1800 m to 2000 m (P<0.05), and the maximum ALP was at 1200 m, which represented an increase but without a significant difference (P>0.05).
Fig. 1 Soil enzyme activities at the different altitudes

4.3 Correlation analysis of soil enzymes and soil physicochemical properties

The correlations between soil physical and chemical factors and soil enzyme activities at different altitudes in the lower mountain area of Helan Mountain are shown in Table 3. Correlation analysis of the soil indexes showed that in the lower mountain area of Helan Mountain, soil bulk density (SBD) was very significantly negatively correlated with total porosity (TPS) (P<0.01), but very significantly positively correlated with the available phosphorus (AP) content (P<0.01). TPS was very significantly negatively correlated with AP. Also, pH was significantly positively correlated with total carbon content (TC) and total nitrogen content (TN) (P< 0.05), and very significantly positively correlated with urease activity (UE) (P<0.01). Total nitrogen content (TN) was significantly positively correlated with UE and Alkaline phosphatase (ALP) (P<0.05). There was a significant negative correlation between available phosphorus (AP) content and sucrase activity (SR) (P<0.05). The UE was significantly positively correlated with ALP (P<0.05). These results indicated that the soil sucrase (SR), urease (UE) and alkaline phosphatase (ALP) activities at different elevations in the low mountain area of Helan Mountain were greatly affected by soil pH, soil bulk density (SBD), total porosity (TPS), total nitrogen (TN) and available phosphorus content (AP).
Table 3 Correlation analysis of the soil indicators
Items SBD TPS pH EC SOM TC TN C/N AN AP UE SR CAT
Total porosity (TPS) -0.999**
pH 0.490 -0.513
Electric conductivity (EC) 0.294 -0.285 -0.393
Soil organic matter (SOM) 0.832 -0.834 0.341 0.692
Total carbon (TC) 0.774 -0.792 0.919* -0.215 0.546
Total nitrogen (TN) 0.276 -0.309 0.918* -0.468 0.148 0.804
Carbon nitrogen ratio (C/N) 0.266 -0.234 -0.657 0.693 0.350 -0.394 -0.849
Alkali-hydrolyzed nitrogen (AN) 0.220 -0.252 0.513 0.307 0.522 0.445 0.640 -0.454
Available phosphorus (AP) 0.982** -0.976** 0.331 0.333 0.783 0.661 0.121 0.405 0.082
Urease (UE) 0.283 -0.307 0.968** -0.59 0.098 0.817 0.928* -0.79 0.413 0.123
Sucrase (SR) -0.844 0.831 0.030 -0.462 -0.662 -0.359 0.188 -0.638 0.100 -0.928* 0.231
Catalase enzyme (CAT) -0.630 0.609 -0.331 0.095 -0.356 -0.465 0.040 -0.340 0.428 -0.635 -0.254 0.495
Alkaline phosphatase (ALP) 0.233 -0.256 0.860 -0.766 -0.111 0.765 0.896* -0.807 0.234 0.119 0.928* 0.161 -0.189

Note: * means significantly correlated at the 0.05 level (two-sided); ** means significantly correlated at the 0.01 level (two-sided).

5 Discussion

Soil moisture content, bulk density and total porosity are the basic physical properties of soil, which are closely related to the decomposition of litter on the soil surface and the growth and development of above-ground plants (Ma et al., 2006; Yao et al., 2006; Geng et al., 2014). Previous researchers have studied the soil of typical vegetation zones at different altitudes on Helan Mountain and found that the soil moisture content and total porosity in the low mountainous area of Helan Mountain increased with increasing elevation, while the soil bulk density decreased with the rise in elevation, which were consistent with the results of this study (Liu et al., 2013). However, another study of the soil of the Huangshan pine forest at different altitudes in Dayun Mountain, Fujian Province indicated that the soil water content decreased with increasing altitude. This inconsistency may be caused by different factors affecting the soil moisture contents in mountain ecosystems with different research scales (Zhao et al., 2019). For example, soil properties and topography have obvious effects on the soil moisture content at a small scale. However, on a large scale, the soil moisture content is closely related to meteorological factors such as precipitation and temperature (Li, 2019). Temperature, soil moisture content, microbial decomposition and conversion rate significantly affected the soil nutrient status. Previous research on soil nutrients both in karst evergreen deciduous broad-leaved mixed forest and in the small watershed of the Loess Plateau showed that organic matter and available phosphorus were negatively correlated with altitude, which was consistent with the results of this study (Yang et al., 2014; Wang et al., 2017). Some studies found that organic matter and available phosphorus were positively correlated with altitude, which may be due to the higher temperature in the low altitude area and the resulting higher decomposition and transformation efficiency of soil microorganisms (Wu et al., 2014; Xie et al., 2019).
Enzyme activities in soil are affected by soil hydrothermal conditions, soil nutrient content and surface litter (Allwason and Treseder, 2008; Wang et al., 2014). Cao et al. (2016), in an alpine canyon area, and Jin et al. (2011), in typical vegetation zones at different altitudes in Wuyi Mountain, both reported that the activities of soil urease and alkaline phosphatase first decreased and then increased with increasing altitude, while sucrase and catalase increased with increasing altitude, which are all consistent with the results of this study. Lei et al. (2017) found no obvious relationship between soil enzyme activities and altitude in the alpine soil of the Qinghai-Tibet Plateau. This may be due to the changes in regional climate, soil types and above- ground vegetation communities caused by altitude changes, which directly or indirectly affect soil enzyme activities.
In mountain ecosystems, climatic conditions such as temperature and precipitation, soil types and above-ground vegetation communities at different altitudes may be different, resulting in variations in soil moisture content, bulk density, porosity and other physical and chemical properties, while the spatial differences in soil properties may directly or indirectly affect soil enzyme activities. Sun et al. (2015) found a significant positive correlation between urease activity and soil total nitrogen, while alkaline phosphatase activity had no significant correlation with soil total nitrogen. However, the results of this study showed significant positive correlations between urease activity and alkaline phosphatase activity and soil total nitrogen. As the altitude increased, the soil urease activity first decreased and then increased at the altitude of 1400 m, while both the urease activity and alkaline phosphatase activity were significantly lower than at the other altitude areas, which may be due to the better hydrothermal conditions of the soil at this altitude, and to the higher decomposition and conversion efficiency of N-related substances by microorganisms.

6 Conclusions

The physical and chemical properties and enzyme activities of surface soil at five elevations in the lower mountain area of Helan Mountains varied, and the physical and chemical properties and enzyme activities influenced each other. The results of this study lead to three main conclusions. Firstly, with increasing altitude, the reductions in soil moisture content, porosity and soil bulk density indicated an improvement of the soil physical properties, and the increases in TC and TN indicated the enhancement of soil chemical properties. Secondly, the activities of urease, phosphatase, sucrase and catalase increased with elevation (1400-2000 m), except at 1200 m. Thirdly, the soil physicochemical properties and enzyme activities in the low mountainous area of Helan Mountain increase to varying degrees with increases in altitude, and there are positive correlations between the soil physicochemical properties and the enzyme activities.

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