title: Simplification of a light-based model for estimating final internode length in greenhouse cucumber canopies.
abstract: OBJECTIVE
  Light quantity and quality affect internode lengths in cucumber (Cucumis sativus), whereby leaf area and the optical properties of the leaves mainly control light quality within a cucumber plant community. This modelling study aimed at providing a simple, non-destructive method to predict final internode lengths (FILs) using light quantity and leaf area data.
  
  
  METHODS
  Several simplifications of a light quantity and quality sensitive model for estimating FILs in cucumber have been tested. The direct simplifications substitute the term for the red : far-red (R : FR) ratios, by a term for (a) the leaf area index (LAI, m(2) m(-2)) or (b) partial LAI, the cumulative leaf area per m(2) ground, where leaf area per m(2) ground is accumulated from the top of each plant until a number, n, of leaves per plant is reached. The indirect simplifications estimate the input R : FR ratio based on partial leaf area and plant density.
  
  
  RESULTS
  In all models, simulated FILs were in line with the measured FILs over various canopy architectures and light conditions, but the prediction quality varied. The indirect simplification based on leaf area of ten leaves revealed the best fit with measured data. Its prediction quality was even higher than of the original model.
  
  
  CONCLUSIONS
  This study showed that for vertically trained cucumber plants, leaf area data can substitute local light quality data for estimating FIL data. In unstressed canopies, leaf area over the upper ten ranks seems to represent the feedback of the growing architecture on internode elongation with respect to light quality. This highlights the role of this domain of leaves as the primary source for the specific R : FR signal controlling the final length of an internode and could therefore guide future research on up-scaling local processes to the crop level.
authors.affiliation: Institute of Biological Production Systems, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany. kahlen@gem.uni-hannover.de
authors.forename: Katrin
authors.initials: K
authors.lastname: Kahlen
authors.forename: Hartmut
authors.initials: H
authors.lastname: Stützel
mesh_terms: D003198:Computer Simulation; D018553:Cucumis sativus / Q000254:growth & development* / Q000502:physiology / Q000528:radiation effects; D008027:Light; D008954:Models, Biological; D010788:Photosynthesis; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects*; D018547:Plant Stems / Q000254:growth & development* / Q000502:physiology / Q000528:radiation effects; D013997:Time Factors