Microbial phenology in high-alpine environments: the influence of plant dynamics and physiological stress in a changing climate.

Alpine biomes experience harsh environmental conditions and short growing seasons, which necessitate interspecific and intraspecific interactions among plants and soil microbes to ensure the stability of diversity and ecosystem multifunctionality. With strong seasonal dynamics in alpine regions, including snow cover, snowmelt, and drought, “hot moments” of biogeochemical activity occur when pulses of nutrients dictate microbial processes across the biome. However, within the rhizosphere, microbial processes are promoted or deterred during phases of plant growth, senescence, and nutrient allocation, leading to a more nuanced seasonal pattern of soil microbes. Indeed, these factors lead to a general microbial phenology of soil processes and community composition. Yet, shifted climatic regimes due to warming likely cause these relationships to be strained, potentially resulting in physiological stress among plants and microbes. Therefore, our research focuses on the coupling or decoupling of plant and microbial parameters across seasonal changes in the Austrian Alps by assessing stoichiometric ratios of shared nutrients such as carbon (C), nitrogen (N) and phosphorus (P), along with microbial diversity. 

Using elevation gradients, the corresponding influence of plants, soil chemistry, and environmental conditions upon microbial phenology can be assessed in two different biomes: undeveloped subnival zones and nutrient-rich alpine meadows.  Furthermore, by combining methods for assessing biological soil parameters, such as chloroform fumigation extraction, enzymatic assays, and respiration measurements, with amplicon DNA sequencing, we can observe broad microbial community responses such as increased biomass (C_mic) in different seasons related to plant-specific interactions while identifying microbial taxa (fungal and bacterial) that indicate nutrient limitations in conjunction with ratios of enzymatic activity. Additionally, by measuring plant nutrient concentrations in distinct plant organs, we can infer which physiological processes among plant species most closely correspond with changes in broad microbial parameters and rhizosphere diversity.

Therefore, we propose that certain aspects of microbial phenology are generalizable, such as increased N cycling during winter and spring months, while the temporal optima for C cycling is more plant-specific. Furthermore, we present results from the rarely studied snow-covered winter months, in which the mineralization of C, P, and chitin degradation are highest. In total, these studies demonstrate a thorough analysis of plant-microbial interactions in alpine ecosystems which are subject to significant change within the coming decades.