Modeling temperature- and radiation-driven leaf area expansion in the contrasting crops potato and wheat

The performance of a model for simulating increase in leaf area index (L) w as evaluated for potato (Solanum tuberosum L.) and wheat (Triticum aestivum L.) cultivars across environments (years and sites). Rate of L expansion j ust after emergence was assumed to depend on temperature. After a predefine d L, L-s, expansion was assumed to increase in proportion to leaf dry weigh t increase that depended on intercepted radiation, henceforward: radiation- limited expansion. The L-s value at which the model performed best was cons idered to be the most realistic L at which expansion shifts from temperatur e to radiation-limitation. An L-s value of zero leads to solely radiation-l imited expansion, whereas a value larger than maximum L leads to solely tem perature-limited expansion. The criteria used to evaluate the model were co nstancy of calibrated model parameters across environments, and predictive ability. For potato and wheat, parameters were most robust across environme nts, when L-s was neither zero nor at maximum L. Model parameters did not v ary with genotype. The model's predictions were best at an L-s of 1.0 for p otato and 1.5 for wheat. Using these L-s values, the coefficient of determi nation between observed and predicted values was 91% for potato and 88% for wheat. Sensitivity analysis revealed that smaller L-s values led to larger changes in rate of leaf area expansion and crop dry weight than larger val ues did. Crop dry weight was hardly affected by an increase in L-s. Implica tions of the results for modeling are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.