Eckart Priesack

Agricultural Crop Models: Concepts of Resource Acquisition and Assimilate Partitioning

In this review, we analyze how the acquisition of resources, e.g. carbon (C) and nitrogen (N), and the distribution of assimilates between plant organs is described by common agricultural crop growth models. We consider agricultural crop growth models that are integrated into larger agro-ecosystem or agricultural soil- plant-atmosphere system models. These system models are developed to simulate not only plant growth processes but also energy and matter fluxes between atmosphere and soil including decomposition of plant residues and C- and N-turnover of soil organic matter. Within the crop models different approaches are used to up-scale eco-physiological processes from the plant-organ level to the plant and canopy level, they are discussed with respect to data requirement and adequate representation of resource acquisition. Considering mainly trees, basic concepts used to model assimi- late partitioning in plants have been classified as empirical, teleonomic, based on source-sink relations or based on transport and transformation processes. Application of these concepts in agricultural crop models are presented and examined. Moreover, a survey of modeling approaches is given that consider the impact of different kinds of biotic and abiotic stresses on partitioning in crop growth models.

PLATHO - A Dynamic Plant Growth Model Considering Competition between Individuals and Allocation to Carbon-Based Secondary Compounds

To explain patterns and variations in concentration of defence-related carbon-based secondary compounds in plant tissues, different complementary and in some parts contradictory plant-defence hypotheses were developed since several years. These conceptual hypotheses cannot be fully evaluated without a plant growth simulation model and consequently, the discussion about adequacy of plant-defence hypotheses neglects to a large extent the dynamics of plant growth. To get a more realistic view of the volatile dynamics of plant internal source and sink strengths of carbon and nitrogen during different phenological growth stages, a modelling approach for allocation of carbohydrates to a pool of carbon-based secondary compounds was integrated into the functional generic plant growth model PLATHO. In this paper, we explain the fundamental assumptions of our modelling approach and present the results of a simulation study for juvenile beech and spruce trees growing in mono- and mixed cultures under ambient and elevated atmospheric CO2.