Mountain biodiversity and ecosystem functions: interplay between geology and contemporary environments

The study aims to understand the interplay between contemporary and geological processes in shaping mountain biodiversity and ecosystem functions. While contemporary factors like climate and biotic/abiotic attributes are known drivers, the role of long-term geological processes, particularly in mountain regions, remains understudied. Mountains, formed by tectonic processes, exhibit strong elevational gradients in climate and abiotic factors, leading to distinct plant and animal zonation. The Himalayan-Tibetan orogeny, resulting from the collision of tectonic plates, provides an ideal setting for this research, harboring diverse ecosystems and major faults. This study proposes a framework integrating biological and earth science perspectives, incorporating both contemporary and long-term geological factors to investigate their effects on biodiversity and ecosystem functions along an elevational gradient. The research questions focus on how biodiversity and ecosystem functions vary along the elevational gradient, the primary drivers of these patterns (contemporary vs. geological), and how geological processes directly and indirectly influence these factors. Previous research has highlighted the importance of contemporary environments, but the incorporation of geological history adds a crucial temporal dimension to understanding biodiversity patterns and the stability of ecosystem services.

Existing literature establishes that biodiversity and ecosystem functions are influenced by contemporary environmental factors such as climate, biotic, and abiotic attributes. However, the long-term influence of geological processes, especially their lasting legacies on contemporary environments, has received less attention, particularly concerning their impact on microbial communities and ecosystem functions. While studies have shown the effects of erosion and soil heterogeneity on terrestrial tetrapod biodiversity, a comprehensive understanding of the interplay between contemporary and geological processes in shaping biological communities and ecosystem functions remains limited. This research seeks to address this gap by integrating geological and biological perspectives.

The study utilized a 3000-m elevational gradient on Galongla Mountain in Southeast Tibet, crossing the Indus-Yalu suture zone fault. 180 plots across 18 sites spanning six vegetation zones (from tropical rainforests to frigid shrub meadows) were surveyed. Data collected included plant community composition (abundance, diversity, and community structure), soil bacterial community composition (PLFAs, GDGTs, 16S rRNA gene sequencing), soil physiochemical properties, and 38 ecosystem functions (categorized into soil nutrients, plant biomass, microbial biomass, and carbon cycling). Geological variables such as soil parent rock composition (minerals), weathering indices (CIA, Ti/Fe, etc.), and metal element concentrations were measured. Statistical analyses, including piecewise linear regression to identify elevational breakpoints and multivariate models to assess the relative influence of contemporary and geological factors on biodiversity and ecosystem functions, were employed. The results were compared to data from Gongga Mountain to test the consistency of elevational patterns in bacterial communities. The study used various methods for assessing biodiversity including calculating species richness, using Detrended Correspondence Analysis (DCA) for community composition, and creating a multidiversity index (MD). Ecosystem functions were assessed through individual function analysis, ecosystem multi-functionality (EMF) calculations, and DCA for functional composition.

The study revealed consistent elevational breakpoints in biodiversity and ecosystem functions at 2000-2800 m, coinciding with the Indus-Yalu suture zone fault. This breakpoint was also observed in bacterial community data from Gongga Mountain, suggesting a widespread pattern. Mean annual temperature, soil pH, and moisture were identified as primary contemporary drivers. However, incorporating geological factors (parent rock and weathering) substantially improved model predictions. Specifically, the inclusion of geological effects increased the explained variation in plant communities by 67.9%, bacterial communities by 35.9%, and ecosystem functions by 27.6%. Parent rock and weathering had considerable direct effects on biodiversity but indirectly influenced ecosystem functions through interactions with biodiversity and contemporary environments. The results highlight the significant and distinct influence of geological processes on both biodiversity and ecosystem functions along elevational gradients.

The findings demonstrate the significant contribution of geological processes, alongside contemporary environmental factors, in shaping mountain biodiversity and ecosystem functions. The consistent elevational breakpoints across different mountain ranges suggest a broad-scale influence of geological features. The study's integration of geological and ecological perspectives provides a more comprehensive understanding of biodiversity patterns and ecosystem functioning. The strong influence of geological factors highlights the need for incorporating long-term geological history into ecological models. The study's results have important implications for biodiversity conservation and ecosystem management in mountain regions, particularly under the context of ongoing climate change and anthropogenic disturbances. Future studies should explore the mechanisms linking parent rock and weathering to specific aspects of biodiversity and ecosystem functions.

This study underscores the crucial role of geological processes in shaping mountain biodiversity and ecosystem function. By integrating geological and environmental factors, the research enhances our understanding of elevational patterns and their underlying drivers. The consistent breakpoints identified highlight the importance of geological features in influencing biodiversity and ecosystem functions across large spatial scales. Future research should focus on mechanistic studies investigating the specific pathways through which geological processes influence biodiversity and ecosystem function, and the implications of these findings for predicting responses to global change.

While this study provides a comprehensive analysis, certain limitations exist. The study is geographically focused on two mountain ranges in the Tibetan Plateau, limiting the generalizability of findings to other mountain systems. Some important ecosystem functions, such as plant-available phosphorus, carbon fixation, and nitrogen fixation, were not measured, potentially influencing the overall interpretation of ecosystem multifunctionality. Further, while rarefaction was used to account for variation in sampling intensity, future studies could explore alternative approaches to confirm these results. Finally, the study mainly focuses on the effects of geological history on plant and soil microbial communities, and future work may consider extending it to more complex food webs.