## 4 Discussion  
Explaining Variance in Soil Physicochemical Properties in Sand vs. a Mix of Sand and Feldspathic Sandstone  
Soil texture is of great significance for regional soil improvement because it affects various soil traits, such as permeability, water holding capacity, arability, and nutrient migration, and the distribution and utilization efficiency in soil [34]. Our results showed that after 10 months of feldspathic sandstone and sand mixing, the soil texture transformed from sand to sandy loam, thus transforming the aeolian sandy soil (the sand soil) that was prone to leaking water and nutrients, severe wind and water erosion, and oligotrophs into a relatively stable soil with higher porosity and better field capacity. To some extent, the mixed soil appropriately made up the shortage of aeolian sandy soil, indicating that adding feldspathic sandstone into sand can improve the soil conditions. Organic matter is an important cementing material in the formation of soil aggregates, and its content is positively correlated with the stability and quantity of soil water-stable aggregates [35]. In our study, STC, SOC, SWC, and field capacity significantly increased, while SIC decreased in mixed soil, which not only indicated that mixing feldspathic sandstone and sand has obvious effects on carbon sequestration and water and fertility preservation, but also further indicated the soil structure was more stable in mixed soil. In general, mixing feldspathic sandstone and sand can reduce or prevent the leakage of water in the aeolian sandy soil, improve fertility, and weaken the hardening of feldspathic sandstone, thus achieving the dual purposes of controlling sand and improving feldspathic sandstone. Explaining Variance in Soil Microbial Biomass Indices in Sand vs. a Mix of Sand and Feldspathic Sandstone  
In our study, the microbial biomass of sand soil was consistent with that of desert biomes reported by [PERSON] et al. [36]. However, the soil microbial biomass significantly increased in mixed soil (Figure 2). This is because that adding feldspathic sandstone into sand for 10 months significantly improved soil physiochemical properties, provided abundant nutrients such as carbon, nitrogen, and phosphorus for microbes, promoted microbial reproduction, and thus helped to increase soil microbial biomass C, N, and P [37]. The increase in microbial biomass also indicates that soil microbes have a significant improve in the ability to fix soil carbon, nitrogen, and phosphorus [38]. At the same time, the addition of feldspathic sandstone increases the porosity of the original sandy soil, meaning better soil aeration, which further enhances soil microbial growth and activity [39]. Moreover, we found a significant positive correlation between microbial biomass C, N, P and SWC, STC, SOC, field capacity (Figure 3, Table S2), which is consistent with previous studies [40; 41; 42; 43], indicating that microbial biomass can characterize soil fertility status and water capacity. We also observed that soil MBN and MBP were  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**(b)**} & \multicolumn{6}{c}{**Edapibic Biotic Factors**} \\ \cline{2-7}  & **MBC** & **MBN** & **MBP** & **MBCMBN** & **MBCMBP** & **MBN-MBP** & **MBCSOC** \\ \hline BG & 0.996 \(  
significantly positively correlated with MBC, indicating that MBC accumulation promoted the fixation of microbial to N and P nutrients, while the biomineralization and consumption of N and P in soil depended on the transformation and decomposition of organic matter by soil microbes [31]. These results also indicated that there was a good mutual constraint between the microbial biomass C, N, and P [36; 44]. In addition, the ecological stoichiometry of soil microbial biomass is of great significance for exploring the restricted nutrients of soil ecosystems. [PERSON] et al. [36] reported that the global average soil MBC:MBN, MBC:MBP, and MBN:MBP ratios were 7.6, 42.4, and 5.6, respectively.