Amplified temperature dependence in ecosystems developing on the lava flows of Mauna Loa, Hawai'i

Abstract

Through its effect on individual metabolism, temperature drives biologically controlled fluxes and transformations of energy and materials in ecological systems. Because primary succession involves feedbacks among multiple biological and abiotic processes, we expected it to exhibit complex dynamics and unusual temperature dependence. We present a model based on first principles of chemical kinetics to explain how biologically mediated temperature dependence of "reactant" concentrations can inflate the effective temperature dependence of such processes. We then apply this model to test the hypothesis that the temperature dependence of early primary succession is amplified due to more rapid accumulation of reactants at higher temperatures. Using previously published data from the lava flows of Mauna Loa, HI, we show that rates of vegetation and soil accumulation as well as rates of community compositional change all display amplified temperature dependence (Q(10) values of approximately 7-50, compared with typical Q(10) values of 1.5-3 for the constituent biological processes). Additionally, in young ecosystems, resource concentrations increase with temperature, resulting in inflated temperature responses of biogeochemical fluxes. Mauna Loa's developing ecosystems exemplify how temperature-driven, biologically mediated gradients in resource availability can alter the effective temperature dependence of ecological processes. This mechanistic theory should contribute to understanding the complex effects of temperature on the structure and dynamics of ecological systems in a world where regional and global temperatures are changing rapidly.

Fig. 1.

Accumulation rates of aboveground biomass and soil mass, C, N, and P over the first century of primary succession on ‘a’a (triangles) and pāhoehoe (circles) flows along the elevation/temperature gradient on the wet (filled symbols; left axes) and dry (open symbols; right axes) sides of Mauna Loa. Note that the y axes differ. Solid and dashed lines indicate separate fits to wet- and dry-side data, respectively [supporting information (SI) Table 3].

Fig. 2.

Effects of mean annual temperature (plotted as inverse temperature, 1/kT, so that the slope is −ε) (A) and mean annual precipitation (Eq. 3) (B) on rates of primary succession on the lava flows of Mauna Loa. Plotted are partial residuals or the rate corrected for all variables but the one of interest. The full model (Table 1) accounts for process type, temperature, precipitation (Eq. 3) and lava type (‘a’a versus pāhoehoe).

Fig. 3.

Concentrations of key reactants (leaf biomass, leaf nutrients, and soil nutrients) in young sites (109–138 yr) spanning a temperature gradient.

Fig. 4.

Comparison of the average temperature dependence of primary succession on Mauna Loa (ml; ε = 1.8) (Table 1) with the rates typically observed for some of the constituent processes: nitrogen fixation by S. vulcani (n; E_a ≈ 0.95 eV), basalt weathering (w; E_a ≈ 0.4–0.5 eV), aerobic respiration rates (r; E_a ≈ 0.65 eV), and photosynthesis (p; E_a ≈ 0.3 eV). For display purposes, values are rescaled to normalize the rates to 1 at 7°C.