Date of Defense
18-11-2025 12:30 PM
Location
F3-223
Document Type
Thesis Defense
Degree Name
Master of Science in Horticulture
College
CVAM
Department
Integrative Agriculture
First Advisor
Dr. Elke Neumann
Keywords
Microbial inoculation, Rhizosheath, Arbuscular mycorrhizal fungi (AMF), Nutrient uptake, Sorghum bicolor, Cyperus conglomeratus
Abstract
Organic matter and other sources of plant nutritional elements typically enter the soil from its surface, resulting in topsoil having the highest microbial activity, concentration of nutritional elements, and rooting densities. In agricultural systems of the UAE, high ambient temperature triggers rapid evaporation and causes the topsoil to dry. Nutrient uptake from dry soil is very challenging for plants, and topsoil dryness can have a negative impact on plant performance.
Beneficial soil microorganisms mediate plant growth by inducing tolerance against abiotic stresses. Arbuscular mycorrhizal (AM) fungi extend a large network of hyphae that helps the plants to acquire water and nutrients from far distances. However, it has also been observed that AM non-host plant species are relatively more common in the most extreme environments like the hyper-arid deserts of the Gulf Region. The reasons for this are not yet well understood. The present study thus compared the response of an AM-host plant, Sorghum bicolor, and a non-host, Cyperus conglomeratus, to inoculation with soil microorganisms and exposure to dry soil. C. conglomeratus is native to the desert ecosystems of the UAE and known to form thick rhzosheaths rather than AM fungal symbioses. Plants of the present study were either or not exposed to dry topsoil for a period of 48 days, and either or not inoculated with soil microorganisms from natural and agricultural soils of the UAE. Two different experiments were conducted, one aiming at assessing P uptake from dry topsoil, and another aiming at quantifying uptake of N.
As a result, the present study cannot confirm a positive interaction of C. conglomeratus with soil microorganisms. On the contrary, microbial inoculation reduced the P and N nutritional status of these plants. Our results thus rather suggest that C. conglomeratus is a plant that relies on non-microbial nutrient and water acquisition strategies. This might align with its adaptation to disturbed habitats from which plants, organic matter, and microbial life are largely absent.
In both plant species, more than 85 % of root biomass was found in the topsoil, even after a long period of restricted water supply to this part of the soil. This indicates that plants invest new roots in the acquisition nutritional elements from topsoil rather than water from moist subsoil.
The present study further confirms the importance of AM fungal symbioses for crop P acquisition from dry topsoil. Previous studies had demonstrated such contributions for isolated and selected AM fungal strains and in rather artificial systems. Our study deployed natural microbial communities found in agricultural and roadside soils in Al Ain and demonstrated that these can increase P uptake from a dry topsoil by around 100 %. There was no contribution of microbial inoculation to N uptake, confirming that AM fungi are primarily a P acquisition strategy and that a contribution to N uptake might only occur in conjunction with symbiotic contribution to P uptake. Field-scale validations of these findings will be crucial to assessing their real-world applicability, solidifying this work's contribution to enhancing food security in challenging climatic regions by harnessing the power of plant-microbe symbioses.
Included in
EFFECT OF MICROBIAL INOCULATION ON PHOSPHATE AND NITROGEN UPTAKE FROM DRY SOIL BY TWO GRASSES WITH DIFFERENT NUTRIENT ACQUISITION STRATEGIES
F3-223
Organic matter and other sources of plant nutritional elements typically enter the soil from its surface, resulting in topsoil having the highest microbial activity, concentration of nutritional elements, and rooting densities. In agricultural systems of the UAE, high ambient temperature triggers rapid evaporation and causes the topsoil to dry. Nutrient uptake from dry soil is very challenging for plants, and topsoil dryness can have a negative impact on plant performance.
Beneficial soil microorganisms mediate plant growth by inducing tolerance against abiotic stresses. Arbuscular mycorrhizal (AM) fungi extend a large network of hyphae that helps the plants to acquire water and nutrients from far distances. However, it has also been observed that AM non-host plant species are relatively more common in the most extreme environments like the hyper-arid deserts of the Gulf Region. The reasons for this are not yet well understood. The present study thus compared the response of an AM-host plant, Sorghum bicolor, and a non-host, Cyperus conglomeratus, to inoculation with soil microorganisms and exposure to dry soil. C. conglomeratus is native to the desert ecosystems of the UAE and known to form thick rhzosheaths rather than AM fungal symbioses. Plants of the present study were either or not exposed to dry topsoil for a period of 48 days, and either or not inoculated with soil microorganisms from natural and agricultural soils of the UAE. Two different experiments were conducted, one aiming at assessing P uptake from dry topsoil, and another aiming at quantifying uptake of N.
As a result, the present study cannot confirm a positive interaction of C. conglomeratus with soil microorganisms. On the contrary, microbial inoculation reduced the P and N nutritional status of these plants. Our results thus rather suggest that C. conglomeratus is a plant that relies on non-microbial nutrient and water acquisition strategies. This might align with its adaptation to disturbed habitats from which plants, organic matter, and microbial life are largely absent.
In both plant species, more than 85 % of root biomass was found in the topsoil, even after a long period of restricted water supply to this part of the soil. This indicates that plants invest new roots in the acquisition nutritional elements from topsoil rather than water from moist subsoil.
The present study further confirms the importance of AM fungal symbioses for crop P acquisition from dry topsoil. Previous studies had demonstrated such contributions for isolated and selected AM fungal strains and in rather artificial systems. Our study deployed natural microbial communities found in agricultural and roadside soils in Al Ain and demonstrated that these can increase P uptake from a dry topsoil by around 100 %. There was no contribution of microbial inoculation to N uptake, confirming that AM fungi are primarily a P acquisition strategy and that a contribution to N uptake might only occur in conjunction with symbiotic contribution to P uptake. Field-scale validations of these findings will be crucial to assessing their real-world applicability, solidifying this work's contribution to enhancing food security in challenging climatic regions by harnessing the power of plant-microbe symbioses.