Soil microbial functional diversity along an elevation gradient in Northwestern Caucasus

In contrast to taxonomic diversity of soil microbiome, the distribution patterns of functional diversity for various ecosystems, including along an altitudinal gradient, is poorly understood. Consequently, the study focuses on finding out the spatial distribution features of microbial functional diversity in mountainous soils along elevation through forests and meadows ecosystems. We hypothesized that soil microbial functional diversity is increasing along the altitudinal gradient in conjunction with plant diversity. In Northwestern Caucasus (Karachay-Cherkess Republic, Russia) the north-eastern mountain slope was studied across mixed, fir and deciduous forests, subalpine and alpine meadows located from 1260 to 2480 m above sea level. Twelve plots (0.25 m² each) were randomly chosen within each ecosystem (total 60). Plant species composition and Shannon plant diversity index (H) were assessed for the plots. Topsoil samples (0-10 cm) were taken from the plots in August for assessment microbial functional diversity through community level physiological profile (CLPP). It was determined by microbial respiration response on amino, carboxylic, phenolic acids and carbohydrates (MicroResp). Shannon's functional diversity index based on the CLPP (H_CLPP) was calculated. Edaphic properties as moisture, temperature, pH, total carbon (C) and nitrogen (N) contents were determined as possible drivers of CLPP. As expected, plant diversity was increased along the elevation gradient with the lowest H value in the mixed forest (0.6) and the highest – in the alpine meadow (1.9). The H_CLPP did not differ among studied ecosystems and reached on average 2.4 for each. Microbial respiration response on amino acids was mainly contributed to dissimilarities between studied ecosystems and increased on average by 1.3 times with elevation from mixed to fir and deciduous forests. Along this elevation row, the soil N content was the most significant driver compared to other edaphic properties. Among subalpine and alpine meadows the differences between microbial responses on studied carbon substrates were not found.

Considering that elevation didn’t contribute to distribution patterns of soil H_CLPP at the inter-ecosystems level, consequently, the hypothesis of our study was rejected. Plant diversity was not related to H_CLPP as expected. Meanwhile, the distribution patterns of soil microbial community, utilizing amino acids, along the altitudinal gradient was found.

The current research was financially supported by RFBR No 20-34-70121