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AOBPreview originally published online on July 25, 2006
Annals of Botany 2006 98(4):827-834; doi:10.1093/aob/mcl163
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Published by Oxford University Press on behalf of the Annals of Botany Company 2006 For Permissions, please email: journals.permissions@oxfordjournals.org

Predicting Germination Response to Temperature. III. Model Validation Under Field-variable Temperature Conditions

STUART P. HARDEGREE*

USDA Agricultural Research Service, Northwest Watershed Research Center, 800 Park Blvd, Suite 105, Boise, ID 83712, USA

* E-mail shardegr{at}nwrc.ars.usda.gov

Received: 4 May 2006    Returned for revision: 2 June 2006    Accepted: 8 June 2006    Published electronically: 25 July 2006

•Background and Aims Two previous papers in this series evaluated model fit of eight thermal-germination models parameterized from constant-temperature germination data. The previous studies determined that model formulations with the fewest shape assumptions provided the best estimates of both germination rate and germination time. The purpose of this latest study was to evaluate the accuracy and efficiency of these same models in predicting germination time and relative seedlot performance under field-variable temperature scenarios.

•Methods The seeds of four rangeland grass species were germinated under 104 variable-temperature treatments simulating six planting dates at three field sites in south-western Idaho. Measured and estimated germination times for all subpopulations were compared for all models, species and temperature treatments.

•Key Results All models showed similar, and relatively high, predictive accuracy for field-temperature simulations except for the iterative-probit-optimization (IPO) model, which exhibited systematic errors as a function of subpopulation. Highest efficiency was obtained with the statistical-gridding (SG) model, which could be directly parameterized by measured subpopulation rate data. Relative seedlot response predicted by thermal time coefficients was somewhat different from that estimated from mean field-variable temperature response as a function of subpopulation.

•Conclusions All germination response models tested performed relatively well in estimating field-variable temperature response. IPO caused systematic errors in predictions of germination time, and may have degraded the physiological relevance of resultant cardinal-temperature parameters. Comparative indices based on expected field performance may be more ecologically relevant than indices derived from a broader range of potential thermal conditions.

Key words: Temperature, germination, model, Elymus elymoides, Elymus lanceolatus, Poa secunda, Pseudoroegneria spicata


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