Effect of pH on sulphur isotope variation on a landscape

I recently ran a forest regression model, this model showed me that increasing soil pH increases sulphur isotope variation across the landscape. I am not how this is possible and if it makes sense




Sulfur has a natural variation in the proportions of its isotopes (consider [volcanoes, for example, which act as natural isotope fractionators](https://www.sciencedirect.com/science/article/abs/pii/0016703758900073)). So the variation due to biochemical action is expected.


The [United States Geological Survey (USGS) discusses](https://wwwrcamnl.wr.usgs.gov/isoig/period/s_iig.html) the use of sulfur (and oxygen) isotope ratio to determine the source of sulfur, temperature and pH in forests.


The [National Center for Biotechnology Information (NCBI) discuses](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5570529/) the fractionation of sulfur isotopes in beech forests: "The investigation of the **fractionation of S compounds in forest soils** is a powerful tool for interpreting S dynamics and S biogeochemistry in forest ecosystems. Beech stands on **high pH (nutrient-rich)** sites on Flysch and on **low pH (nutrient-poor)** sites on Molasse were selected for testing the influence of stemflow, which represents a high input of water and dissolved elements to the soil, on spatial patterns of sulfur (S) fractions." This seems to me to explain the results of your tests.


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