The snowmelt niche differentiates three microbial life strategies that influence soil nitrogen availability during and after winter

Abstract

28Soil microbial biomass can reach its annual maximum pool size beneath the winter 29 snowpack and is known to decline abruptly following snowmelt in seasonally snow-covered 30 ecosystems. Observed differences in winter versus summer microbial taxonomic composition 31 also suggests that phylogenetically conserved traits may permit winter-versus summer-adapted 32 microorganisms to occupy distinct niches. In this study, we sought to identify archaea, bacteria, 33 and fungi that are associated with the soil microbial bloom overwinter and the subsequent 34 biomass collapse following snowmelt at a high-altitude watershed in central Colorado, USA. 35 Archaea, bacteria, and fungi were categorized into three life strategies (Winter-Adapted, 36 Snowmelt-Specialist, Spring-Adapted) based on changes in abundance during winter, the 37 snowmelt period, and after snowmelt in spring. We calculated indices of phylogenetic 38 relatedness (archaea and bacteria) or assigned functional attributes (fungi) to organisms within 39 life strategies to infer whether phylogenetically conserved traits differentiate Winter-Adapted, 40 Snowmelt-Specialist, and Spring-Adapted groups. We observed that the soil microbial bloom 41 was correlated in time with a pulse of snowmelt infiltration, which commenced 65 days prior to 42 soils becoming snow-free. A pulse of nitrogen (N, as nitrate) occurred after snowmelt, along 43 with a collapse in the microbial biomass pool size, and an increased abundance of nitrifying 44 archaea and bacteria (e.g., Thaumarchaeota, Nitrospirae). Winter-and Spring-Adapted archaea 45 and bacteria were phylogenetically clustered, suggesting that phylogenetically conserved traits 46 allow Winter-and Spring-Adapted archaea and bacteria to occupy distinct niches. In contrast, 47Snowmelt-Specialist archaea and bacteria were phylogenetically overdispersed, suggesting that 48 the key mechanism(s) of the microbial biomass crash are likely to be density-dependent (e.g., 49trophic interactions, competitive exclusion) and affect organisms across a broad phylogenetic 50 3 spectrum. Saprotrophic fungi were the dominant functional group across fungal life strategies, 51 however, ectomycorrhizal fungi experienced a large increase in abundance in spring. If well-52 coupled plant-mycorrhizal phenology currently buffers ecosystem N losses in spring, then 53 changes in snowmelt timing may alter ecosystem N retention potential. Overall, we observed that 54 the snowmelt separates three distinct soil niches that are occupied by ecologically distinct groups 55 of microorganisms. This ecological differentiation is of biogeochemical importance, particularly 56 with respect to the mobilization of nitrogen during winter, before and after snowmelt. 57 58 59

Integrating airborne remote sensing and field campaigns for ecology and Earth system science

“…The timing of these collections was particularly important due to the rapid phenological change throughout the season, and well‐calibrated models were therefore dependent on both spatial and temporal alignment of field and airborne data. In addition, datasets such as microbial composition, soil moisture and soil nutrient status change at different and sometimes unknown rates within and across seasons (Schmidt et al., 2007; Sorensen et al., 2020), so we planned to sample contemporaneously with the AOP survey to avoid temporal mismatch. This too may present a challenge to other groups depending on the characteristics of interest, but whenever possible, we recommend collecting and stabilizing co‐aligned samples of characteristics that may change rapidly (i.e.…”

“…Based on this input, we designed an integrated sampling campaign to collect vegetation, soil physical/chemical, microbial and geophysical data at co‐located sampling sites to coincide with the timing of the AOP survey. We planned to collect samples within 72 hr of overflight, and without intervening rainfall, to the extent possible, given the rapid and sometimes unknown rates of change in processes of interest (Schmidt et al., 2007; Sorensen et al., 2020).…”

Early Spring Snowmelt and Summer Droughts Strongly Impair the Resilience of Key Microbial Communities in Subalpine Grassland Ecosystems

“…This confirmed a strong influence of droughts and associated soil moisture deficits on DEA (Di et al, 2020; Philippot et al, 2009), which was especially pronounced for SR+D indicating the cascading effect of SR and declined nitrification upon snowmelt. The collapse in microbial pool size upon snowmelt has also been observed while studying the niche differentiation perspectives in soils (Sorensen et al, 2020). A strong turnover by these nitrifying and denitrifying microbial communities was previously shown for similar subalpine grasslands upon natural variations in snowpack depth (Jusselme et al, 2016).…”

Microbial contribution to post-fire tundra ecosystem recovery over the 21st century

“…Second, modeled abrupt deepening of the ALD after 2060 exposed ancient organic matter previously sequestered in permafrost, which can be rapidly mineralized, yielding nutrients that are available for plant uptake 55 . Third, the model predicts an increasing snowpack depth over the century, and the resulting higher winter soil temperatures (from ~ -9℃ in 2000 to ~ 0℃ in 2080) encourage microbial growth and activity throughout the winter time, which has previously been shown to be an important time period for the release of nutrients 87,88 and uptake by plants 89 . In addition to faster, more open nutrient cycles in the late st Century, a notable relative decline in soil moisture occurs ~3 years following fire, which permits further oxygenation of the soil, thereby increasing microbial activity 90 .…”