Modelling the carbon balance in bryophytes and lichens: Presentation of PoiCarb 1.0, a new model for explaining distribution patterns and predicting climate‐change effects

Abstract

PremiseBryophytes and lichens have important functional roles in many ecosystems. Insight into how their CO2 exchange responds to climatic conditions is essential for understanding current and predicting future productivity and biomass patterns, but responses are hard to quantify at time‐scales beyond instantaneous measurements. We present PoiCarb 1.0, a model to study how CO2 exchange rates of these poikilohydric organisms change through time as a function of weather conditions.MethodsPoiCarb simulates diel fluctuations of CO2 exchange and estimates long‐term carbon balances, identifying optimal and limiting climatic patterns. Modelled processes are net photosynthesis, dark respiration, evaporation and water uptake. Measured CO2‐exchange responses to light, temperature, atmospheric CO2 concentration, and thallus water content (calculated in a separate module) are used to parameterise the model's carbon module. We validated the model by comparing modelled diel courses of net CO2 exchange to such courses from field measurements on the tropical lichen Crocodia aurata. To demonstrate the model's usefulness, we simulated potential climate‐change effects.ResultsDiel patterns were reproduced well and modelled and observed diel carbon balances were strongly positively correlated. Simulated warming effects via changes in metabolic rates were consistently negative, while effects via faster drying were variable, depending on the timing of hydration.ConclusionsBeing able to reproduce the weather‐dependent variation in diel carbon balances is a clear improvement compared to simple extrapolations of short‐term measurements or potential photosynthetic rates. Apart from predicting climate‐change effects, future uses of PoiCarb include testing hypotheses about distribution patterns of poikilohydric organisms and guiding species’ conservation.This article is protected by copyright. All rights reserved.