Distribution patterns of desert plant diversity and relationship to soil properties in the Heihe River Basin, China SHANJIA LI,1,2 PEIXI SU,1, HAINA ZHANG,1 ZIJUAN ZHOU,1 TINGTING XIE,1 RUI SHI,1 AND WEI GOU2 1
Key Laboratory of Land Surface Process and Climate Change in Cold and Arid Regions, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000 China 2 School of Life Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 China Citation: Li, S., P. Su, H. Zhang, Z. Zhou, T. Xie, R. Shi, and W. Gou. 2018. Distribution patterns of desert plant diversity and relationship to soil properties in the Heihe River Basin, China. Ecosphere 9(7):e02355. 10.1002/ecs2.2355
Abstract. The study on the patterns of plant species diversity and the factors influencing these patterns forms the basis of ecology and is fundamental to conservation biology. In this paper, desert plant species diversity and soil properties (nutrient and texture) were investigated along desert region of the Heihe River Basin (HRB) to determine whether soil environmental factors influenced desert plant species diversity. We found a total of 44 shrub and herb species belonging to 40 genera of 17 families. The largest family was the Compositae, accounting for 25.0% of the total. Twenty-four survey plots were clustered into eight plant community types. The Margalef richness (D), Simpson dominance (C), Pielou evenness (Jsw), and Shannonwiener (H) index differed significantly among community types. Redundancy analysis (RDA) revealed a relatively strong relationship between the species diversity and soil environmental factors. The first RDA axis accounted for 80.5% and 81.8% of the variation in soil nutrient and texture properties, respectively, but was not statistically significant. RDA suggested that total phosphorus (TP) and medium sand (0.25– 0.5 mm) content were the only two statistically significant factors in the study area. Both classification and ordination resulted in a clear demonstration of the spatial variability of community and soil properties. In general, the distribution pattern of desert plant community was mainly related to soil nutrient and texture properties factors, but the relation was not strong. This study provides insights into desert plant diversity and community conservation of Inland HRB in arid desert ecosystems. Key words: desert community; distribution pattern; Heihe River Basin; plant species diversity; soil properties. Received 5 December 2017; revised 19 April 2018; accepted 20 April 2018. Corresponding Editor: Theresa M. Crimmins. Copyright: © 2018 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. E-mail:
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INTRODUCTION
has attracted particular attention because of its applicability in assessing current species performance and predicting future community composition (Wang et al. 2008). Environmental factors play key roles in determining the spatial variation of biodiversity across broad geographic extents. Quantitative classification and ordination have been widely used to analyze the community structures and understand the relationships between communities and their environment in the study of community ecology (Leps and Smilauer 2003, Zhang et al. 2008, Zhu et al. 2012).
Since the 1980s, the development of ecological theory and application has led community ecology research to gradually focus on community patterns (Burke 2001). The distribution pattern of community species diversity is the synthetic reflection of all types of ecological gradients, and the spatial variation pattern of biodiversity along environmental gradients is one of the basic issues and important properties in biodiversity research (Kratochwil 1999, Stohlgren 2007, Tom as et al. 2013). Plant species diversity ❖ www.esajournals.org
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environmental impacts on desert plant community diversity throughout the whole basin. In this study, we investigated plant species diversity patterns and their relationships with soil environmental factors in the HRB. In order to characterize these patterns and relationships, we (1) described and classified the species compositions of HRB plant communities; (2) quantified variation in species diversity indices among the different community types; and (3) determined the main soil factors affecting the distribution patterns of species diversity throughout the basin. Studying these patterns of diversity and relationships with soil properties will improve plant biodiversity conservation in fragile arid and semi-arid ecosystems by furthering our understanding of desert ecosystem structure and function and improving our ability to recover and protect desert ecosystems and species.
Studies on the patterns of plant species diversity and the environmental factors influencing these patterns are the basis of much of ecology and also central to conservation biology (Noss 1990). Many studies have demonstrated that both local and regional community distribution patterns are controlled by environmental factors such as climate, topography, and soil physical and chemical properties (Wang et al. 2015). Among different environmental factors, soil is the basis of habitat heterogeneity, climate, organisms, and parent material (Levin 1981). Soil is the key ecological factor controlling ecological processes in ecosystem (Yang et al. 2011) and plays a key role in the distribution and characteristics of community (Wang et al. 2004, 2015), because soil properties affect rainwater redistribution, such as the dynamics of its runoff and infiltration (Le Houerou et al. 1988). Plant community and soil parameter dynamics cannot be separated, such that community distribution and diversity vary with chemical, physical, and microbiological properties of soils (Eskelinen et al. 2009, Xu et al. 2011). The limiting effect of soil moisture on plants is affected by soil properties; soil variability also strongly influences competitive and facilitative interactions among plants, particularly in environments with a high degree of water stress (Chapin et al. 1994), such as semi-arid and arid habitats (Fowler 1986, Wang et al. 2015). The Heihe River Basin (HRB) is an inland river located in extremely arid and fragile ecological environment, and the desert ecosystem stretching from the piedmont alluvial plain to the lower reaches, where has a unique ecological structure and plant communities dominated by shrub species (Li et al. 2009). Many studies have reported the relationships between community and the environment in the inland river basin. However, to the best of our knowledge, these studies have been limited to smaller or local scale research (Li et al. 2003, Zhang et al. 2005, Wang et al. 2007, Gui et al. 2010, Zhu et al. 2012), and there is no systematic knowledge of the interactions between the community structure and soil properties across the arid area of whole basin scale. Currently, the HRB Eco-Hydrological Process Integration Research Project of the National Natural Science Foundation of China is in progress. This large-scale project allows for the study of ❖ www.esajournals.org
MATERIALS AND METHODS Study area The HRB is the second-largest inland river located in the arid regions of northwestern China (Wang et al. 2009), and lies in 98°000 –101°300 E, 38°000 –42°300 N, covering an area of 13 9 104 km2 and length of 821 km. It flows from the southern Qilian Mountains in Qinghai Province through the Hexi Corridor in Gansu Province and terminates at East and West Juyanhai Lakes in the arid Ejina basin of the Inner Mongolia Autonomous Region (Chen 2006). The study was conducted on arid desert plant communities dominated by desert shrub and semi-shrub plants within the HRB (Fig. 1). We studied desert vegetation at the whole HRB scale, but desert plants are not distributed in the upper reaches of the river, because the upper reaches are located on the Qilian Mountain. Desert community distributed in arid region of piedmont alluvial plain, middle reaches, and lower reaches of the HRB. Located in the hinterland of the Asian continent, this stretch of the river is exposed to a continental climate, characterized by extremely hot summer and severely cold winter, with the majority of rainfall (about 60–70%) occurring from July to September (Zhang et al. 2009). The soil types throughout the HRB range include brown calcic, desert calcic, meadow, marsh, salty, and sandy (Li et al. 2
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Fig. 1. Geographical location of community plots in the study area of Heihe River Basin. The green areas signified vegetation, the yellow spot signified community plots, the text described the upper, middle, and lower reaches of Heihe River Basin.
2009). The community type had one feature in common: Xeric and super-xeric shrubs and subshrubs dominated the community. Due to the lack of precipitation and temperature data for each of study areas, we were not able to investigate the influences of these climatic factors on their communities.
of these sites, we randomly established three 20 9 20 m or 5 9 5 m plots to survey sparse and dense communities, respectively. We also established three 1 9 1 m plots to survey herbs, with these quadrats placed in the corners of the shrub plots. We established a total of 24 sample sites, including three shrubs plots and nine herb plots at each site. In each quadrat, we recorded the species of each plant, the total number of species, the height of each plant, the crown dimensions, the community cover (based on the sum of the crown areas). The above-ground biomass was estimated by digging the representative samples from the quadrat to the laboratory. The quadrat locations (elevation, longitude, and latitude) were recorded using navigation satellites timing and ranging global position system (GPS) GPS receiver.
Community surveys We established eight transects along the HRB to provide widespread geographic coverage of desert plants. The community surveys were conducted in September 2014, the period when desert plant biomass reached the maximum. Transects with flat to gently sloping topography were chosen for the study; we chose three sites in each transect, each site about 2500 m2 in size. At each ❖ www.esajournals.org
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Soil environmental data
Statistics analysis
The soil was sampled at 0–40 cm depth in each plot. Three random soil samples were taken from each surveyed community plot. To determine soil water content, samples were collected after 2–3 d without precipitation, to eliminate the influence of precipitation on soil water content. Wet and dry weights of all soil samples were used to calculate soil water content. Then, we mixed to form a composite sample at each plots. These soil samples were dried at 80°C for chemistry analyses. The soil samples were then passed through a 2-mm screen to remove roots and other debris. Soil organic matter was determined using the K2Cr2O7 method. Total nitrogen (TN, %) was determined using the micro-Kjeldahl procedure, which involves digestion with concentrated H2SO4 followed by measurement of NH3 on an autoanalyzer (KjeltecTM 2100, FOSS, Sweden) using the indophenol blue method (ISSCAS, 1978). Available nitrogen (AN, %) and total phosphorus (TP, %) were measured after extracted with 2 M KCl and HClO4-H2SO4, respectively. Available phosphorus (AP, %) was measured following the Olsen’s method with a 0.5 mol/L NaHCO3 solution at pH 8.5. Total potassium (TK, %) was measured using the NaOH fused flaming spectrum method (Digital Flame Analyzer, Model 2655-00, Cole-Parmer Instrument, Chicago, USA). Available potassium (AK, %) was quantified in 2 mol/L ammonium acetate at pH 7.0 (Sang 2009). The pH was determined in a 1:2.5 (w:v) suspension of soil in water using a SG2 glass-electrode potentiometer (Mettler-toledo Instrument, Shanghai, China). Electrical conductivity (EC) was measured using a DDS-307a portable conductivity meter (Leici Instrument, Shanghai, China) using methods described by Zhang and Gong (2012). Soil texture particle composition was measured by traditional pipette and sieve analysis, according to granulometric hierarchy of classification standard from USDA (ISSCAS (Institute of Soil Sciences, Chinese Academy of Sciences) 1978). It includes nine granulometric hierarchy on the basis of effective diameter of soil particle, gravel >2 mm, extremely coarse sand 1~2 mm, coarse sand 0.5~1 mm, middle sand 0.25~0.5 mm, fine sand 0.1~0.25 mm, extremely fine sand 0.05~0.1 mm, coarse silt 0.02~0.05 mm, fine silt 0.002~0.02 mm, clay
