Root growth and Zn uptake of three common crop plants in response to heterogeneity in soil texture and Zn distribution

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The responses of root growth to non-uniformities in soil conditions can be of great importance for the acquisition of soil nutrients by plants. Here we monitored the root growth response of white lupin, cucumber and spring wheat to constructed horizontal heterogeneity in soil texture (and thereby also soil moisture) and zinc (Zn) distribution in rhizoboxes filled with sandy low-Zn soil using neutron radiography imaging. We investigated how the position of Zn-enriched soil relative to the heterogeneity in soil texture and moisture distribution affected Zn uptake, as compared to a control treatment with homogeneous texture. In all treatments the same total amount of water was added to the rhizoboxes. In cucumber heterogeneity in texture and moisture increased root length, root biomass and, independent of the position of Zn enrichment, also Zn uptake. In lupin it decreased cluster root formation and root biomass and in wheat specific root length, but in both of them it had no effect on total root length and shoot Zn uptake. The effects on root traits were associated with increased shoot biomass in wheat and cucumber, but not in lupin. Spatial differences in root growth between opposite sections in the heterogeneous packings were limited to the treatment in which coarse texture was combined with Zn enrichment. The results indicate that the responses in root system development were dominated by systemic factors with little modification by local responses and that the morphological root traits studied here were not limiting plant Zn uptake.