Root growth and belowground interactions and plasticity of field crops

Abstract

Understanding the growth of roots and belowground interactions of field crops constitutes a pathway to enhancing the performance of field crops. Global challenges related to climate change and a growing population are driving a more rational use of agricultural inputs to reduce soil and water ressources degradation. Roots play a central role in this process, as shown by research that has provided valuable insights into their development, functions, diversity, and adaptations to the environmental conditions. <br/> To contribute to this understanding, the present thesis aims to investigate the root growth and interactions occuring in intercropping systems as well as the effects of nutrient omission on root traits of field crops. <br/> For intercropping, a field experiment was conducted using one faba bean cultivar and two spring wheat cultivars sown at three sowing densities, defining three intercropping designs. Destructive root coring was conducted (0–100 cm) in the intercrops and sole crops at two development stages. FTIR spectroscopy was used to discriminate the species' root masses. In intercrops, sowing density affected more than the cultivar choice the root growth and belowground interactions. The highest sowing density led to a decrease of root biomass and more competitive interaction between faba bean and winter wheat. The lowest sowing densities promoted deeper root growth of wheat. Regarding the cultivar choice, the early root growth in depth and in density of one spring wheat cultivar lowered faba bean root growth. The findings highlight the importance of plant density and root co-occurrence in belowground interactions of intercrops. <br/> To investigate the nutrient availability's effects on root growth and plasticity, root and shoot sampling was conducted in 2019 for sugar beet, 2019/20 and 2020/21 for winter wheat and 2021/2022 for winter rye at the long-term fertilizer experiment (LTFE) Dikopshof. Various fertilizer treatments were chosen in the three studies including: fully fertilized including manure (m) and supplemental mineral fertilizer (s) (NPKCa+m+s), fully fertilized without manure (NPKCa), N omitted (_PKCa), and P omitted (N_KCa) for winter rye and additionally lime omitted (NPK_) and no fertilization for winter wheat and sugar beet. N availability affected root morphology and plasticity: N omission reduced root growth in winter rye and winter wheat, with stage-specific effects on root diameter, root length density and P omission significantly impacts root traits of field crops, demonstrating the plasticity of root systems in adapting to nutrient-limited conditions. Sustained Ca and K omission affected to a less extent root morphological traits. The Results found in this thesis suggest that nutrient availability as well as intercropping system may affect the root growth and plasticity of field crops. However, the responses are species specific, and affected by growth stage. The results provide valuable insights into potential root traits that can be considered in breeding programs and agronomically relevant insights that serve to design sustainable cropping systems.