Soil nematodes are a foremost component of terrestrial biodiversity, they display the whole gamut of trophic guilds and life strategies, and by their activity, affect major ecosystem processes, such as organic matter degradation and carbon cycling. Based on nematodes’ functional types, nematode community indices have been developed and can be used to link variation in nematode community composition and ecosystem processes. Yet, the use of these indices has been mainly restricted to anthropogenic stresses. In this study, we propose to expand the use of nematodes’ derived ecological indices to link soil and climate properties with soil food webs, and ecosystem processes that all vary along steep elevation gradients. For this purpose, we explored how elevation affects the trophic and functional diversity of nematode communities sampled every 300 m, from about 1000 m to 3700 m above sea level, across four transects in the lesser Himalayan range of Jammu and Kashmir. We found that (1) the trophic and functional diversity of nematodes increases with elevation; (2) differences in nematodes communities generate habitat-specific functional diversity; (3) the sigma maturity index, the channel index, and the metabolic footprint of nematodes increase with elevation, indicating less mature and less productive ecosystems, enhanced fungal-based energy flow, and a predominant role of nematodes in generating carbon influxes at high elevation sites, respectively. We thus conclude that the functional contribution of soil nematodes to belowground ecosystem processes, including carbon and energy flow, is stronger at high elevation. Overall, this study highlights the central importance of nematodes in sustaining soil ecosystems and brings insights into their functional role, particularly in alpine and arctic soils.

Ecological gradients are expected to be associated with structural rewiring of species interaction networks. The study of network structures along geographic and ecological gradients, however, remains marginal because documenting species interactions at multiple sites is a methodological challenge. Using a standardized DNA metabarcoding method applied to feces, we examined how structural properties of plant--orthoptera networks reflecting specialization and resilience vary with elevation. We found an increase in levels of generality and nestedness with decreasing temperature, and the correlation was stronger than in null models. These relationships corresponded to greater robustness and reduced importance of keystone species in alpine habitats. In cold environments, plant--herbivore networks are wired in a way that may reinforce the resilience of the system to species extinction. Documenting ecological networks along ecological gradients allows a better understanding of the influence of climate on the structure of ecosystems.

Biologists still strive to identify the ecological and evolutionary drivers of phytochemical variation that mediates biotic interactions. We hypothesized that plant species growing at sites characterized by high herbivore pressure would converge to produce highly toxic blends of secondary metabolites, independently of phylogenetic constraints. To address the role of shared evolutionary history and ecological niches in driving variation in plant phytochemistry, we combined targeted metabolomics, with insect herbivore bioassays on Cardamine species growing along the entire elevational gradient of the Alps. We observed that plant species cluster according to similar habitat-mediated plant-growth forms and chemical profiles, independently of phylogenetic relationship. We also showed that novel indices summarizing functional phytochemical diversity better explain plant resistance against chewing and sap-feeding herbivores than classic diversity indices. We conclude that the functional axis of phytochemical diversity should be integrated with the functional axis of plant growth forms to address convergence along large-scale ecological gradients.