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Testing simulations of intra‐ and inter‐annual variation in the plant production response to elevated CO 2 against measurements from an 11‐year FACE experiment on grazed pasture
Author(s) -
Li Frank Yonghong,
Newton Paul C. D.,
Lieffering Mark
Publication year - 2014
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.12358
Subject(s) - environmental science , ecosystem , pasture , atmospheric sciences , legume , carbon dioxide in earth's atmosphere , stomatal conductance , climate change , ecosystem model , biomass (ecology) , simulation modeling , terrestrial ecosystem , agronomy , photosynthesis , ecology , biology , botany , mathematics , geology , mathematical economics
Ecosystem models play a crucial role in understanding and evaluating the combined impacts of rising atmospheric CO 2 concentration and changing climate on terrestrial ecosystems. However, we are not aware of any studies where the capacity of models to simulate intra‐ and inter‐annual variation in responses to elevated CO 2 has been tested against long‐term experimental data. Here we tested how well the ecosystem model APSIM/AgPasture was able to simulate the results from a free air carbon dioxide enrichment ( FACE ) experiment on grazed pasture. At this FACE site, during 11 years of CO 2 enrichment, a wide range in annual plant production response to CO 2 (−6 to +28%) was observed. As well as running the full model, which includes three plant CO 2 response functions (plant photosynthesis, nitrogen (N) demand and stomatal conductance), we also tested the influence of these three functions on model predictions. Model/data comparisons showed that: (i) overall the model over‐predicted the mean annual plant production response to CO 2 (18.5% cf 13.1%) largely because years with small or negative responses to CO 2 were not well simulated; (ii) in general seasonal and inter‐annual variation in plant production responses to elevated CO 2 were well represented by the model; (iii) the observed CO 2 enhancement in overall mean legume content was well simulated but year‐to‐year variation in legume content was poorly captured by the model; (iv) the best fit of the model to the data required all three CO 2 response functions to be invoked; (v) using actual legume content and reduced N fixation rate under elevated CO 2 in the model provided the best fit to the experimental data. We conclude that in temperate grasslands the N dynamics (particularly the legume content and N fixation activity) play a critical role in pasture production responses to elevated CO 2 , and are processes for model improvement.