Can current moisture responses predict soil CO2 efflux under altered precipitation regimes? A synthesis of manipulation experiments

[摘要] As a key component of the carbon cycle, soil CO₂ efflux (SCE) is beingincreasingly studied to improve our mechanistic understanding of thisimportant carbon flux. Predicting ecosystem responses to climate changeoften depends on extrapolation of current relationships between ecosystemprocesses and their climatic drivers to conditions not yet experienced bythe ecosystem. This raises the question of to what extent these relationshipsremain unaltered beyond the current climatic window for which observationsare available to constrain the relationships. Here, we evaluate whethercurrent responses of SCE to fluctuations in soil temperature and soil watercontent can be used to predict SCE under altered rainfall patterns. Of the58 experiments for which we gathered SCE data, 20 were discarded becauseeither too few data were available or inconsistencies precluded theirincorporation in the analyses. The 38 remaining experiments were used totest the hypothesis that a model parameterized with data from the controlplots (using soil temperature and water content as predictor variables)could adequately predict SCE measured in the manipulated treatment. Only for7 of these 38 experiments was this hypothesis rejected. Importantly,these were the experiments with the most reliable data sets, i.e., thoseproviding high-frequency measurements of SCE. Regression tree analysisdemonstrated that our hypothesis could be rejected only for experiments withmeasurement intervals of less than 11 days, and was not rejected for any ofthe 24 experiments with larger measurement intervals. This highlights theimportance of high-frequency measurements when studying effects of alteredprecipitation on SCE, probably because infrequent measurement schemes haveinsufficient capacity to detect shifts in the climate dependencies of SCE.Hence, the most justified answer to the question of whether current moistureresponses of SCE can be extrapolated to predict SCE under alteredprecipitation regimes is "no" – as based on the most reliable data setsavailable. We strongly recommend that future experiments focus more stronglyon establishing response functions across a broader range of precipitationregimes and soil moisture conditions. Such experiments should make accuratemeasurements of water availability, should conduct high-frequency SCEmeasurements, and should consider both instantaneous responses and thepotential legacy effects of climate extremes. This is important, becausewith the novel approach presented here, we demonstrated that, at least forsome ecosystems, current moisture responses could not be extrapolated topredict SCE under altered rainfall conditions.

[学科分类] 地球化学与岩石