## 5 Discussions  
### Lithological Influences on the Enrichments and Fractionations of REEs in the Soils  
Micronutrient element concentrations in the soils developed in mountain terrain were primarily inherited from parent materials [16; 17; 18]. As mentioned, REE distribution patterns of soils developed in different habitats presented a genetic relationship with their corresponding parent materials. According to 1:250,000 reports of regional geologic survey and our field survey, the protolith of hornblende-genesis in NGHs was female volcanic rock, whose REEs concentrations were higher than those that developed in loess; therefore, soils developed from hornblende-genesis contained higher REEs concentrations (\(\Sigma\)REE = 174 ug\(\cdot\)g\({}^{-1}\)) than that from loess (\(\Sigma\)REE = 149 ug\(\cdot\)g\({}^{-1}\)), which is in agreement with the expectations from the different lithologies that soils originating from volcanic rock tend to have higher REE concentrations than soils developed from loess [28; 33; 34]. Weathering crust in hornblende-genesis showed great variation of REEs concentrations than loess, resulting in relatively homogeneous REEs concentrations in the soils developed from loess (CV = 6.84%) and notable heterogeneity of REEs concentrations in the soils developed from hornblende-genesis (CV = 33.9%). The weathering of parent materials profoundly impacted the migrations and enrichments of REEs. The REE concentrations distribution pattern in soils of loess was significantly similar to their parent materials since their weak weathering and indistinctive movement of clay particles. However, the complex mineral compositions and grain sizes in hornblende-genesis significantly influenced the weathering process, resulting in remarkable discrepancies in migrations and enrichments of REEs during weathering [35; 36]. Two weathering profiles in hornblende-genesis locations exhibited different evolution of REEs. In profile 1, REE concentrations decreased in the order of soils \(<\) bedrock \(<\) regoliths, while in profile 2, REE concentrations decreased followed the order regoliths \(<\) topsoil \(<\) bedrock (Figure 6a,b). It can be speculated that in profile 1, as eluviation proceeded, soluble components were greatly leached while sparingly soluble components, including REEs, showed relative enrichments, resulting in the overall REE enrichments of the regoliths [37; 38]. REEs in the topsoil penetrated downward to the lower part of the profile, which was accompanied with REE-containing clay minerals [39; 40], resulting in depletion in the topsoil compared with the lower parts. However, the minerals grain size in the bedrock of profile 2 was much smaller than that in profile 1. As the mineral grain size decreases and specific surface area increases, fine-grained rock offers a potentially increased area over which water penetration may occur [41; 42]. Therefore, the reaction with water in the regolith and soils causes releasing of REE from REE-containing minerals and the leaching of REE, especially LREE. It was observed in the field that the humus horizon was 10 cm thick with a higher content of organic materials in profile 2; therefore,