Combination of grazing exclusion and grassland type altered soil properties and fungal β-diversity but not α-diversity11Fund 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 Suwen^a,b,c,, Asitaiken·Julihaiti ^a, Liu Zeyu ^a, Nie Tingting ^a, Jiang Anjing^a, Wu Yue ^a, An Shazhou^a,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, 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 to restore degraded grasslands worldwide. However, changes in soil fungal community characteristics during grazing exclusion in different types of grasslands are unknown, and in particular, there is a lack of experimental evidence on the effects of grassland type and grazing exclusion on soil fungal diversity. Here, we investigate 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 soil fungal community composition differed between grassland types, and that grazing exclusion, grassland type and the interaction between the two did not significantly affect soil fungal α-diversity and composition, but significantly altered fungal β-diversity. Overall, our results highlight the importance of soil nutrient content on fungal diversity, particularly soil total nitrogen, total phosphorus and organic carbon, and provide key evidence to reveal the mechanisms by which soil fungi respond to grazing exclusion in different grassland types.

Keywords: Grazing exclusion; Grassland type; Fungal diversity; Fungal communities; Soil properties

Grasslands cover 20% of the land surface and play an important role in preventing soil erosion and supporting livestock farming in semi-arid 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 about 400 million hectares of grasslands of various types, accounting for about 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). This will lead to a severe weakening of grassland ecological functions, degradation of soil nutrients (Jing et al., 2014), and disruption of the original balance of the system, transforming it into a fragile ecosystem (Zheng et al., 2012). How to effectively rehabilitate degraded grasslands is a huge scientific and technical challenge for humans (Wang et al., 2020). The most widely used technical measure for 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 of soil fungal communities has been limited.

Soil fungal communities are sensitive to environmental change and have been recognised as early warning and important indicators of change in soil ecosystems (Kennedy et al., 1995; Somova et al., 2001) and 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 disintegrated and limited (Zhou et al., 2011). Therefore, rebuilding soil microbial communities is the primary task in restoring degraded grasslands. Furthermore, soil fungal communities play an essential role in reflecting environmental change (Chen et al., 2020). The composition and diversity of soil fungal communities have been extensively used as an important biological indicator for restoring soil quality and ecosystem function in degraded grasslands (Gao et al., 2021). Therefore, it is critical 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 environmental change.

Different types of grasslands have an integral part in maintaining the stability and diversity of grassland ecosystems (Yang et al., 2018). Numerous studies have shown that the response of soil microorganisms to grazing exclusion is not consistent across different grassland types. In alpine grasslands, soil microbial richness indices were significantly higher than in grazed samples, grazing changed the structure of soil microbial communities (Jing et al., 2021), while in alpine meadows, the total number of soil microorganisms was significantly lower after grazing (Xie et al., 2017). Sun et al. found that grazing exclusion had no significant effect on the overall numbers of soil bacteria and fungi (Sun et al., 2018). Hence, the response pattern of soil microorganisms to grazing exclusion still needs further study. Fungi can be closely associated with host plants through symbiosis or parasitism (García et al., 2014) and play a dominant role in soil nutrient cycling (Mcguire et al., 2010; Treseder et al., 2013). However, former studies have largely shown that grazing exclusion does not significantly affect the diversity of fungal communities, probably due to the greater stability of fungi compared to 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 highly controversial, which limits our understanding of the changes in soil fungal communities after grazing exclusion. The total area of natural grassland in Xinjiang is about 5.7×107 hm² , accounting for 34.4% of the land area (Xu et al., 1993), which is a valuable resource for the development of the livestock industry and national economy in Xinjiang. Among them, temperate desert, temperate steppe and mountain meadow grasslands account for 48.28% of the total grassland area in Xinjiang (Wang et al., 2006). Therefore, it is vital to understand the changes in soil fungal communities of different types of grassland in Xinjiang during grazing exclusion in order to assess the factors that influence the fungi communities’ characteristics in different grassland types of exclusion, this has great significance for grassland managers and policymakers.

Here, we conducted a regional field experiment to assess the effects of grazing exclusion, grassland type and their interaction on soil physicochemical properties, soil fungal community composition and diversity in combination with plant community characteristics and soil properties. We attempted to answer three questions: 1) Does fungal composition and diversity respond consistently to grazing exclusion in different grassland types? 2) Do grazing exclusion and grassland types alter fungal communities and diversity? 3) Is soil fungal diversity indirectly driven by plant and abiotic factors under the grazing exclusion and grassland type treatments? This study contributes to the understanding of changes in soil nutrients, especially soil fungi in different grassland types and provides new ideas for grassland management in the semi-arid zone.

2.1. Study area

The study area is located in Changji Hui Autonomous Prefecture (43.62°-44.39°N, 88.15°-90.25°E, 514-2611m elevation) in the eastern section of the northern slope of the Tianshan Mountains in Xinjiang. The region has a typical temperate continental 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. In the temperate desert zone(Fukang City), the main dominant plants are Haloxylon ammodendron and Seriphidium santolinum ; in the temperate steppe zone(Mubi County), the main dominant plants are Festuca ovina and Carex liparocarpos ; in the mountain meadow zone(Qitai County), the dominant plants are mostly grasses and weedy grasses.