In temperate regions, warming temperatures due to climate change have shortened winters and altered the seasonal timing of events including plant leaf out, flowering, and species migrations. Each species and assemblage may respond to new temperature regimes differently, resulting in phenological disconnects between organisms where activity levels were previously temporally synchronous. In the northeast United States, snow melt and last frost date have advanced, leading to warmer vernal soils initiating earlier soil microbial activity. Plant phenology has also advanced, but at a slower rate than snowmelt. The result is an extended spring period with active soils and dormant vegetation. Microbial mineralization during this plant-microbe activity asynchrony can result in a soil nutrient pool vulnerable to leaching with important consequences for water quality and ecosystem productivity that may vary across soils with different chemical and physical characteristics. We conducted a replicated climate change mesocosm experiment to examine the following questions: (1) Is the length of phenological disconnects affected by reduced snowpack and increased temperature? (2) Are carbon and nutrient losses increased during lengthened phenological disconnects? (3) Do soil characteristics affect the length of disconnects and the magnitude of carbon and nutrient losses?
Results/Conclusions
We found the length of asynchronies to vary with climate treatment, and to significantly affect both carbon and nitrogen losses in soil water. In year one, aboveground heating resulted in 4 additional days with soils warm enough to foster rapid biological activity in the period before plants had leafed out (p = 0.03). This was driven by heated soils warming earlier than controls (p = 0.001). The asynchrony length was amplified in the second year of the study, when heating resulted in 8 additional days with soils warm enough for microbial activity prior to initiation of plant transpiration (p < 0.001). Again, this was driven by soils warming earlier in the spring. However, soil texture affected the date that soils warmed such that heated fine and coarse soils warmed enough to support microbial activity on average 11 and 3 days, respectively, before controls (p = 0.01). We found longer asynchronies to be associated with greater leachate losses of carbon (p = 0.05) and nitrate (p = 0.03). Collectively, these results provide evidence that as the climate changes in seasonally snow-covered ecosystems, warming temperatures can cause temporal disconnects in soil and plant activity that amplify ecosystem losses of carbon and nitrogen.