Stoichiometric Shifts in Soil C:N:P Promote Bacterial Taxa Dominance, Maintain Biodiversity, and Deconstruct Community Assemblages

Abstract

Imbalances in C:N:P supply ratios may cause bacterial resource limitations and constrain biogeochemical processes, but the importance of shifts in soil stoichiometry are complicated by the nearly limitless interactions between an immensely rich species pool and a multiple chemical resource forms. To more clearly identify the impact of soil C:N:P on bacteria, we evaluated the cumulative effects of single and coupled long-term nutrient additions (i.e., C as mannitol, N as equal concentrations NH4+ and NO3−, and P as Na3PO4) and water on communities in an Antarctic polar desert, Taylor Valley. Untreated soils possessed relatively low bacterial diversity, simplified organic C sources due to the absence of plants, limited inorganic N, and excess soil P potentially attenuating links between C:N:P. After 6 years of adding resources, an alleviation of C and N colimitation allowed one rare Micrococcaceae, an Arthrobacter species, to dominate, comprising 47% of the total community abundance and elevating soil respiration by 136% relative to untreated soils. The addition of N alone reduced C:N ratios, elevated bacterial richness and diversity, and allowed rare taxa relying on ammonium and nitrite for metabolism to become more abundant [e.g., nitrite oxidizing Nitrospira species (Nitrosomonadaceae), denitrifiers utilizing nitrite (Gemmatimonadaceae) and members of Rhodobacteraceae with a high affinity for ammonium]. Based on community co-occurrence networks, lower C:P ratios in soils following P and CP additions created more diffuse and less connected communities by disrupting 73% of species interactions and selecting for taxa potentially exploiting abundant P. Unlike amended nutrients, water additions alone elicited no lasting impact on communities. Our results suggest that as soils become nutrient rich a wide array of outcomes are possible from species dominance and the deconstruction of species interconnectedness to the maintenance of biodiversity.

Rapid Microbial Dynamics in Response to an Induced Wetting Event in Antarctic Dry Valley Soils

“…McKnight et al (2007) also demonstrated a rapid increase in cyanobacterial mat biomass and biological activity after introduction of water to a relic stream, showing that biological communities maintain the potential to respond quickly to renewed flow (McKnight et al, 2007). While these experiments differed substantially from the wetting experiment described here, results of these and other studies (e.g., Schwartz et al, 2014; Aanderud et al, 2018) demonstrate that endemic communities in the MDV can respond within timeframes considerably shorter than previously hypothesized, thereby challenging long-held perceptions regarding the MDV of extremely slow response rates (Burkins et al, 2001; Elberling et al, 2006; Barrett et al, 2007).…”

Anthropogenic global shifts in biospheric N and P concentrations and ratios and their impacts on biodiversity, ecosystem productivity, food security, and human health

“…Changes in media (water or soil) N:P ratios affect the structure of terrestrial (Fanin et al, ; Scharler et al, ; Zechmeister‐Bolstenstren et al, ) and aquatic (Sitters, Atkinson, Guelzow, Kelly, & Sullivan, ) food webs, but associated impacts on community diversity are unclear. For example, some studies have reported increases in N:P ratios due to N deposition or land‐use change associated with reduced diversity of microbes (Zhang, Chen, & Ruan, ), plants (DeMalach, ; Güsewell, Bailey, Roem, & Bedford, ), and animals (Vogels, Verbek, Lamers, & Siepel, ; Wei et al, ), but other studies have found increases in microbial (Aanderud et al, ; Ren et al, ; ) and plant (Laliberté et al, ; Pekin, Boer, Wittkuhn, Macfarlane, & Grieson, ; Wassen et al, ; Yang et al, ) diversity. The diversity of plant species has been associated with an optimum plant N:P mass ratio near 20 (Sasaki et al, ), but the tendency for biodiversity to depend on concentrations of N and P in soil hinders the establishment of a generalized hypothesis for the relationship between N:P ratios and diversity for all components of terrestrial communities (DeMalach, ).…”

Aggregation of nontuberculous mycobacteria is regulated by carbon:nitrogen balance

“…The ratio of C:N in natural environments such as soil affects bacterial diversity and growth and is often tuned in order to favor desired bacterial metabolisms in industrial settings (42, 43). It is therefore notable that even when grown in pyruvate defined medium with no ammonium (117 mM carbon, 5.5 mM nitrogen, C:N of the medium = 21.4, equal to glycerol defined medium), M. smegmatis had a relatively low cellular C:N ratio of 5.23 (stdev 0.38, p = 0.01 compared to glycerol grown cells) and grew as mostly planktonic cells (Fig.…”