Landscape history influences the availability of nutrients, and thus the ecological stoichiometry of resident biota and their responses to changes in resource availability. In the McMurdo Dry Valleys of Antarctica nitrogen and phosphorus availability vary predictably among distinct glacial deposits. We established a multiple nutrient addition experiment to examine how biotic responses to changes in resource availability are constrained by biogeochemical stoichiometry, i.e., soil N:P. We manipulated C, N and P availability in long-term experimental plots in soils with high levels of bulk P and soluble phosphate (low N:P) and on soils with low P availability and high concentrations of nitrate (high N:P). Soil biota (microbial biomass and nematode populations) and CO2 flux have been examined for 10 yrs. We hypothesize that landscape history influences the response of soil communities to changes in resource availability because differences in soil N and P availability have influenced soil biota over evolutionary and pedogenic timescales.
Results/Conclusions
Responses of soil biota to resource additions were influenced by the biogeochemical stoichiometry of the local soils. For example, CN additions stimulated CO2 efflux and microbial biomass in low N:P soils (p<0.0001), and CP, CN, and P additions stimulated CO2 efflux in high N:P soils (p<0.0001) for the most recent year of data collection. Responses of soil biota data were analyzed with a 2-way ANOVA with time and treatment as the main effects. Inter-annual variability accounted for significant proportions of variation in soil conditions and nematode populations, but treatment effects were discernable for most major soil biota by the seventh year of the experiment. For example, populations of the dominant soil animal, a microbial feeding nematode Scottnema lindsayae were significantly affected by year of sample collection (F=4.69, p<0.001) and treatment (F=4.363, p<0.001). Inter-annual variation was associated with greater soil water content in years 2008, 2010 and 2014 when soil water explained 22% of the variation in Scottnema abundance. In low N:P soils CN additions stimulated Scottnema relative to the unamended (p=0.0001) and water-amended plots (p=0.0001); this effect of CN is largely associated with an increase in recruitment of juveniles (p<0. 0.0001). In contrast, in high N:P soils CP, C and P additions stimulated Scottnema populations relative to unamended plots (F=2.58 p=0.0190). These results suggest that local populations of soil organisms are adapted to local soil conditions and demonstrate that native soil geochemical stoichiometry constrains the response of soil communities to changes in resource availability.