Evaluation in field conditions of a three-dimensional architectural model of the maize root system: Comparison of simulated and observed horizontal root maps

Abstract

Most existing water and nutrient uptake models are based on the assumption that roots are evenly distributed in the soil volume. This assumption is not realistic for field conditions, and significantly alters water or nutrient uptake calculations. Therefore, development of models of root system growth that account for the spatial distribution of roots is necessary.The objective of this work was to test a three dimensional architectural model of the maize root system by comparing simulated horizontal root maps with observed root maps obtained from the field. The model was built using the current knowledge on maize root system morphogenesis and parameters obtained under field conditions. Simulated root maps (0.45 × 0.75 m) of horizontal cross sections at 3 depths and 3 dates were obtained by using the model for a plant population. Actual root maps were obtained in a deep, bamer-free clay-loamy soil by digging pits, preparing selected horizontal planes and recording root contacts on plastic sheets.Results showed that both the number of cross-sections of axile roots, and their spatial distribution characterized with the R-index value of Clark and Evans (1954), were correctly accounted for by the model at all dates and depths. The number of cross-sections of laterals was also correctly predicted. However, laterals were more clustered around axile roots on simulated root maps than on observed root maps. Although slight discrepancies appeared between simulated and observed root maps in this respect, it was concluded that the model correctly accounted for the general colonization pattern of the soil volume by roots under a maize crop.

A mathematical model of plant nutrient uptake

“…The same group of authors have also found that the distance between the sub-branches can vary along the zero order root [100], [98], [101], [123], [132], but in general the diameter of sub-branches is at least an order of magnitude smaller than the distance between them. Experimental measurements of distance between different maize roots in field conditions were conducted by Tardieu [119] and Varney et al [132].…”

“…However, all this work relies heavily on large scale numerical computations making it less transparent for spotting the mechanisms controlling the behaviour of the system. Pagès et al have conducted three dimensional simulations of root development for maize [49], [97], [98], [100], [101]. For example in [49] they calculate root length density profiles using a 3 dimensional branching model.…”

“…For the discrete set of branching points ψ 1 (r) = i δ(r −r i ), with r i = l b,0 +il n,0 , where l b,0 is the length of zero order root basal non-branching zone, and l n,0 is the inter-branch distance 1 . Some of the measurements of root branching density indicate that there are more sub-branches per cm of root length near the base of the root than near the tip [100], [98], [101]. However, for simplicity we will use in this chapter a piecewise continuous distribution as used by Pagés et al [97] and take the branching points to be distributed uniformly in the branching zone, i.e., we take ψ 1 (r) = 1/l n,0 for l b,0 < r < l 0 (t) − l a,0 , and ψ 1 (r) = 0 for 0 < r < l b,0 and r > l 0 (t) − l a,0 , where l 0 (t) is the length of zero order root at time t given by equation (6.2) and l n,0 is the inter-branch distance.…”

An introduction on below-ground environment and resource acquisition, with special reference on trees. Simulation models should include plant structure and function

“…Roots tend to be clustered in space (e.g. [22]), and young root tips especially tend to be located at particular sites within the whole architecture. Conversely, it is clear that roots that are either woody or old tend to be grouped near the stem, making the stump structure.…”

Clustered root distribution in mature stands of Fagus sylvatica and Picea abies

“…This assumption has been rejected in recent studies in natural ecosystems for fine roots Pellerin and Pages 1996;Ryel et al 1996;Ho¨lscher et al 2002). Spatial heterogeneity in root distribution is governed by patchiness in soil resources such as water and nutrients that may not always follow the vertical root distribution function.…”