TY  - THES
T1  - Drought-induced processes in the rhizosphere of maize (Zea mays L.)
A1  - Käsbauer,Lena
Y1  - 2023/07/12
N2  - Drought events are increasing due to climate change, resulting in significant yield losses. Many breeding strategies focus on drought resistance to avoid these yield losses or complete crop failure. Additionally, to improve drought resistance under soil desiccation, the soil and particularly rhizosphere processes are more and more in the focus of research. Specifically, linkages between the diverse and highly dynamic interactions of soil, plant, and microorganism community must be understood. This thesis thus aims to answer the following research questions: i) Are root hairs relevant for water uptake, and what role do they play under drought? ii) Does local drought in Zea mays result in distinguishable systemic and local metabolic and physiological responses, as well as compensatory water uptake? iii) Do the physico-chemical properties of Zea mays mucilage differ between two common collection systems? 
In the first part, published studies considering root hairs in nutrient and water uptake were summarized, and show a high plasticity of root hairs under different nutrient and water availability states. This plasticity was apparent through changes in root hair morphology and development. Furthermore, the role of root hairs in water uptake is under discussion due to variable results from different studies and crop species. Nevertheless, it seems that overall root hairs improve drought resilience. Furthermore, a better nutrient uptake and mucilage exudation by root hairs and thus an increased drought stability is discussed. This suggests a beneficial role of root hairs for drought stress robustness. 
In the second part, local and systemic drought responses of maize and their effect on rhizosphere processes were assessed in a split-root experiment. The root system of maize was separated into two differently watered (watered, drought stressed) rhizobox chambers. The local drought treatment was performed for 10 days. Under these conditions, the local drought led to a local and systemic response through osmotic adjustment. Osmolarity increased in the shoot, while increased proline concentrations and slight changes in root exudates indicated a local response in the drought stressed root compartment. This metabolic adjustment contributed to a hydraulic redistribution of water between the root halves and enhanced water availability. 
Comparing the physico-chemical properties of maize mucilage collected by two common collection systems emphasized the impact of mucilage collection when interpreting the role of mucilage in rhizosphere processes. The mucilage differed in terms of physico-chemical properties, which included contact angle, viscosity, surface tension (physical) and nutrient content, pH, polysaccharide polymer length, and neutral sugar composition (chemical). The mucilage was collected in two ways: 1) from primary and seminal roots of seedlings growing in a semi-sterile aeroponic system and 2) from airborne brace roots of maize growing on sandy soil. The two collection systems differed in terms of plant age, environment (sterility, light availability, air humidity), and root type. The higher viscosity of the brace root mucilage may have reflected the drier air humidity surrounding the root and therefore the need to enhance water holding capacity. Non-sterile conditions during brace root mucilage collection probably resulted in higher shares of hexoses, while semi-sterile conditions may explain the lack of mannose in the aeroponic mucilage. Brace root mucilage may therefore have a greater relevance during soil desiccation than aeroponic mucilage.
In summary, this work helps to fill knowledge gaps in understanding and linking rhizosphere processes by i) providing a state-of-the-art summary of root hair plasticity related to nutrient and water availability and concluding a beneficial role of root hairs in drought robustness, ii) showing local and systemic osmotic adjustment and hydraulic redistribution under local drought, and iii) emphasizing the role of the mucilage collection systems when interpreting the role of mucilage in rhizosphere processes

KW  - Trockenheit
KW  - Rhizosphäre
KW  - Mais
CY  - Hohenheim
PB  - Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
AD  - Garbenstr. 15, 70593 Stuttgart
UR  - http://opus.uni-hohenheim.de/volltexte/2023/2184
ER  -