%X The perfect storm. That is the term used by Gerald C. Nelson to describe the triple challenge of increasing food production while adapting to climate change and reducing the environmental impact of agricultural systems. Nowadays, conventional farming systems are showing some limitations, such as low resources use efficiency and poor ecosystems services that appear to be associated to the loss of plant diversity and perenniality in crop rotations. In addition, water, the most important yield limiting factor worldwide, will increasingly restrict food production in the future due to rainfall shortage and increase in human consumption. In such context, perennial crops, with denser and deeper root system could use resources in deep soil layers that are logically inaccessible to crops with shallower root system. The goal of this thesis was therefore to investigate the root growth and water uptake capacity of intermediate wheatgrass (Kernza®) and alfalfa, two deep rooted perennial crops, under field conditions and at great soil depth (i.e. 1.0-2.5 m).
	Maintaining hydraulic continuity along the soil-plant-atmosphere continuum is a prerequisite for deep water uptake. At the plant level, hydraulic conductivity depends on complex anatomical and physiological processes among which the root system constitutes the second largest resistance to water flow. Therefore, in depth characterisation of root and xylem anatomy was done to understand the hydraulic properties of the crop root systems, with a focus on their evolution with soil depth. Crops were grown in the field, rhizoboxes, mesocosms and solution culture to take into account the variability of root type and soil depth as well as growing environment. For both crops, axial hydraulic conductance decreased with soil depth and along individual root segment. Alfalfa roots had greater axial hydraulic conductance in comparison to intermediate wheatgrass roots, especially at depth. Root and xylem anatomy were highly variable across crop species, root types and growing environments. In parallel, a combination of imaging and sensor technology, stable isotope techniques and a modelling approach was used to study root growth and water uptake under field conditions during the 2018-2019 seasons. Both crops presented roots down to 2.0 m soil depth that were active in terms of water uptake. Alfalfa had greater root length at depth and absorbed twice as much water below 1 m soil depth, than intermediate wheatgrass. For both crops, model simulations predicted that water uptake in deep soil layers (i.e. 1.5 – 2.0 m) increase (i.e.>30%) under dry conditions.
	This thesis brings insights into the understudied field of root growth and water uptake at great soil depth. Particular efforts were put in understanding the environmental and agricultural contexts in which deep root growth, deep water uptake and the development of perennial cropping systems would be possible and favourable.
%I University of Copenhagen
%L orgprints39730
%A Corentin Clement
%T Deep water uptake of perennial crops. A case study on intermediate wheatgrass and alfalfa.
%D 2021
%K Deep roots, Water Uptake, Perennial crop, Stable isotopes, Hydrus-1D, Minirhizotrons, Alfalfa, Intermediate wheatgrass, Kernza, Root anatomy, Xylem anatomy, TDR sensors
%P 1-151