Effects of grazing exclusion on soil properties, fungal community structure and diversity in different grassland types11Fund Project: Supported the 2022 National Natural Science Foundation(32260355).* Corresponding author: DONG Yiqiang (1989-), male, native of Pizhou, Jiangsu, lecturer, master supervisor, doctor, mainly engaged in grassland resources and ecological research, E-mail: xjdyq1210@163.com
Zhou Shijie a, Dong Yiqiang a,b,c, *, Yang Helong a,b,c, Yang Suwena,b,c,, Asitaiken·Julihaiti a, Liu Zeyu a, Nie Tingting a, Jiang Anjinga, Wu Yue a, An Shazhoua,b,c
a School of Grassland, Xinjiang Agricultural University, Urumqi, 830052;
b Key Laboratory of Grassland Resources and Ecology Autonomous Region, Xinjiang, Urumqi, 830052;
c Key Laboratory of Grassland Resources and Ecology, Ministry of Education, Western Arid Region, Urumqi, 830052
Abstract: Soil fungi are involved in the decomposition of organic matter, and they alter soil structure and physicochemical properties and drive the material cycle and energy flow in terrestrial ecosystems. Grazing exclusion is one of the most common measures used to restore degraded grasslands worldwide. However, changes in soil fungal community characteristics during grazing exclusion in different types of grasslands are unknown. Here, we investigated the effects of a 9-year grazing exclusion on soil properties, fungal community composition and diversity in three grassland types (temperate desert, temperate steppe and mountain meadow). The results showed that in the 0-5 cm soil layer, grazing exclusion significantly affected the physicochemical parameters of all three studied grassland types. In the 5-10 cm soil layer, grazing exclusion significantly increased total phosphorus (TP) in temperate deserts by 34.1%, while significantly decreasing bulk density (BD) by 9.8% and the nitrogen: phosphorus ratio (N:P) by 47.1%. The soil fungal community composition differed among the grassland types, For example, significant differences were found among the three grassland types for the Glomeromycota and Mucoromycota , Grazing exclusion, grassland type, and the interaction between the two did not significantly affect soil fungal α-diversity or community composition(P > 0.05), but significantly altered fungal β-diversity (P < 0.05). Overall, our results highlight the importance of soil nutrient content, especially soil Kjeldahl nitrogen, total phosphorus and organic carbon on fungal diversity, and the results provide key insights into how soil fungi respond to grazing exclusion in different grassland types.
Keywords: Grazing exclusion; Soil properties; Soil fungi; Diversity; Driving factor; Grassland type
Introduction
Grasslands cover 20% of the land surface and play an important role in preventing soil erosion and supporting livestock farming in semiarid areas (Jing et al., 2013; Jing et al., 2014). In recent decades, grassland degradation has become widespread globally due to increased human activity and climate change (O’Mara, 2012; Jalaludin et al., 2020). China has approximately 400 million hectares of grasslands of various types, accounting for approximately 41.7% of the country’s land area (Xu et al., 2016), and more than 90% of the grasslands are in a degraded state (Wang et al., 2020). The low quality of grasslands leads to a severe weakening of grassland ecological functions, the degradation of soil nutrients (Jing et al., 2014), and disruption in the original balance of the system, transforming them into a fragile ecosystems (Zheng et al., 2012). How to effectively rehabilitate degraded grasslands is an enormous scientific and technical challenge (Wang et al., 2020). The most widely used measure for the ecological management of degraded grasslands is grazing exclusion, which can restore vegetation biomass (Su et al., 2005), improve soil fertility (Mekuria et al., 2007) and increase grassland use efficiency (Yang et al., 2005). Previous studies have focused on the effects of grazing exclusion on plant communities and soil properties (Wu, 2021; Dong et al., 2016), while research on the effects on soil fungal communities has been limited.
Soil fungal communities are sensitive to environmental change. Changes in local fungal communities are recognized as an early warning of problems andan important indication of changes in soil ecosystems (Kennedy et al., 1995; Somova et al., 2001). Soil fungi also play a key role in regulating material cycling in terrestrial ecosystems (Bais et al., 2006). The structure and function of soil fungal communities in degraded grasslands are often limited (Zhou et al., 2011). Soil fungi can decompose macromolecules such as lignin and cellulose in plant residues, and play important roles in soil nutrient accumulation, transformation and cycling(Oriol et al., 2017). Rebuilding soil microbial communities is the primary task in restoring degraded grasslands. Therefore, it is necessary to assess changes in soil fungal communities under grazing exclusion conditions for soil and vegetation restoration and to predict changes in grassland ecosystem dynamics under conditions of environmental change.
Different types of grasslands have integral roles in maintaining the stability and diversity of grassland ecosystems (Yang et al., 2018). Numerous studies have shown that the response of soil bacteria and fungi to grazing exclusion are not consistent across different grassland types. Soil microbial richness indices in alpine grasslands under grazing exclusion were higher than those in grazed grasslands of the same type and grazing changed the structure of soil microbial communities (Jing et al., 2021). In alpine meadows, the total number of soil microorganisms was significantly lower after grazing exclusion (Xie et al., 2017). Sun et al. (2018) found that grazing exclusion had no significant effect on the overall numbers of soil bacteria and fungi in a Seriphidium transiliense desert. Therefore, the state of knowledge regarding the variation in grazing exclusion of soil bacteria and fungi in different grassland types is insufficient and further research is necessary. Fungi can be closely associated with host plants through symbiosis or parasitism (García-Guzmán and Heil., 2014; Zhu et al., 2017; Maron et al., 2011) and play a dominant role in soil nutrient cycling (Mcguire et al., 2010; Treseder and Holden., 2013). However, studies indicate that grazing exclusion does not significantly affect the diversity of fungal communities, probably due to the greater stability of fungi than that of bacteria (Cheng et al., 2016; Zhang et al., 2018). The results of studies on the effects of grazing exclusion on the characteristics of soil fungal communities in different grassland types are still unclear, which limits our knowledge of the changes in soil fungal communities after grazing exclusion.
The total area of natural grassland in Xinjiang is approximately 5.7×107 ha , accounting for 34.4% of the land area (Xu et al., 1993), and this area is a valuable resource for the development of the livestock industry and national economy in Xinjiang. Among the Xinjiang grasslands, temperate desert, temperate steppe and mountain meadow grasslands account for 48.28% of the total grassland area (Wang et al., 2006). Considering the importance of grasslands in Xinjiang, it is vital to understand the effects of grazing exclusion on soil fungal communities in different grassland types in the region. This knowledge will have great significance for grassland managers and policy-makers. Here, we conducted a regional field experiment to assess the effects of grazing exclusion, grassland type and their interaction on soil physicochemical properties, and soil fungal community composition and diversity in combination with plant community characteristics and soil properties. We attempted to answer three questions: 1) Do grazing exclusion and grassland types alter fungal communities and diversity? 2) Do fungal composition and diversity respond consistently to grazing exclusion in different grassland types? 3) What are the main drivers of changes in soil fungal diversity under grazing exclusion and grassland type treatments?
Materials and methods
2.1. Study area
The study area is located in Changji Hui Autonomous Prefecture (43.62°-44.39°N, 88.15°-90.25°E, 514-2611 m elevation) in the eastern section of the northern slope of the Tianshan Mountains in Xinjiang. The region has a typical temperate arid climate, with high temperatures and rainy summers and cold, dry winters, with an average annual precipitation of 150-300 mm and an average annual temperature of 5-6 °C (Zhou et al., 2012). In the temperate desert zone (Fukang city), the main dominant plants are Haloxylon ammodendron (C.A.Mey.) Bunge and Seriphidium santolinum (Schrenk) Poljakov ; in the temperate steppe zone (Mulei County), the main dominant plants species areFestuca ovina and Carex liparocarpos ; in the mountain meadow zone (Qitai County), the dominant plants are mostly grasses and weedy grasses(Astiken et al., 2023).