1 INTRODUCTION
Changes in land use, and its main vegetation cover, modify soil physico-chemical properties, including soil organic carbon content (Guillaume et al., 2015), phosphorous content and fractions (Maranguit et al., 2017). Land use change is a major driver of soil bacterial and fungal communities (Szoboszlay et al., 2017; Tian et al., 2017; Meng et al., 2019), leading to changes in microbial community composition. These changes are likely to influence ecosystem functioning (Sala et al., 2000; Lauber et al., 2008; Zhu et al., 2011; Xue et al., 2017). Increased land-use intensity, such as conversion of natural vegetation to arable agriculture, hampers disturbance-sensitive species, thereby selecting for species tolerant of such disturbance (Balmford, 1996; Williams et al., 2017). It leads to decreased populations and often to reduced soil microbial diversity (De Vries et al., 2012; Tsiafouli et al., 2015; Williams et al., 2017; Delgado-Baquerizo et al., 2017a; Newbold et al., 2018) as well as homogenization of microbial assemblage biodiversity across space (McKinney et al., 1999; Newbold et al., 2018; Tian et al., 2018). This effect have been consistently observed across the continental scale (Szoboszlay et al., 2017).
The effects of land use change on soil microbial communities has the potential to affect soil ecosystem multifunctionality and stability (Naeem & Li, 1997; Lefcheck et al., 2015; Maestre et al., 2015). Ecological stability consists of two components: resistance (the amount of change caused by a disturbance), and resilience (the speed with which a system returns to its pre-disturbance level) (Pimm, 1984).Recent studies have shown that changes in microbial properties, such as bacterial ⍺-diversity (Jing et al., 2015) affected multifunctional resistance of ecosystem(De Vries & Shade, 2013; Luo et al., 2019). At the same time, microbial communities can regulate the multifunctional resistance of ecosystems to global change (Delgado-Baquerizov et al., 2017b). Microbial diversity is a strong predictor of ecosystem multifunctionality (Luo et al., 2017). Soil microbial communities drive biogeochemical processes, including carbon dynamics and nutrient transformation (Camenzind et al., 2018), litter decomposition (Delgado-Baquerizov et al., 2016), and plant productivity (Creamer et al., 2010). Increased bacterial abundance raises the protozoa abundance (Valencia et al., 2018) and conversely, reduces bacterial abundance is related to multifunctionality (Wagg et al., 2014). As a result, microbial function has a positive linear relationship with the multifunctional resistance of ecosystems (Luo et al., 2019).
Karst ecosystems account for 15-20% of global ice-free surface area (Hu et al., 2016). The karst area in southwestern China is one of the largest in the world (Liang et al., 2015). Widespread soil degradation observed in the southwest Chinese karst has been driven by rapid population growth, intensive agriculture and urbanization over the last 50 years (Huang & Cai,2006; Chen et al., 2011; Gao et al., 2013). Increasing land use intensity in the region has caused increased exposure of carbonate rock outcrops leading to loss and limitation of nitrogen and phosphorus nutrients (Zhang et al., 2015), decreasing soil organic carbon and microbial biomass carbon concentration in aggregates (Xiao et al., 2017). Recent studies have reported effects of land use change on soil microbial communities in the Chinese karst (Yun et al., 2016; Xiao et al., 2017; Wang et al., 2017; Li et al., 2018). However, direct evidence on how microbial communities regulate the multifunctional resistance of ecosystems following land-use change in karst areas is still lacking, particularly on the quantifiable impact of microbial communities on multifunctional resistance of ecosystems and the key bacterial taxa involved.
We hypothesize that (1) changes in land use reduces multifunctional resistance of ecosystems by affecting microbial communities; (2) the composition of microbial communities are a significant driver of ecosystem multifunctional resistance. A specific aspect is that oligotrophic bacteria have high resistance with increasing land use disturbance because they are well adapted to soils with low substrate availability (Fierer et al., 2007; Tian et al., 2017). To test our hypotheses, the present study focused on the link between bacterial community structure and ecosystem multifunctionality along a land-use change gradient in the karst region. We (1) evaluated multifunctional resistance of the soil ecosystems and the resistance of major bacterial taxa and (2) determined the main predictors of multifunctional resistance of ecosystems and quantified the ability of specific bacterial groups to predict both multifunctional and single function resistance of ecosystems including carbon, nitrogen, and phosphorus cycling.