Assessing savanna shrub roots deployment using radiogenic strontium isotopes in the North-Eastern Kalahari, Namibia
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Date
2024
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Publisher
University of Namibia
Abstract
The belowground interaction between trees and grasses in the savanna biome and
mechanisms of moisture and nutrient uptake are poorly understood due to
methodological challenges. To fill this gap, this study tested the robustness of the
radiogenic strontium isotope method to study plant roots. The study was carried out at
a landscape level, in Northeastern, Namibia. Plant leaves of four randomly selected
shrubs and their 16 nearest neighborhood shrubs were collected within a 20 m x 20 m
plot for isotopic analysis. This was done to assess the method’s performance. The study
characterised the belowground structure and roots deployment of 17 of the 20 shrubs,
sampled for isotopic analysis. It also assessed soil isotope, soil physicochemical
properties, and the distribution of root biomass and density. Soil isotopes and soil
physicochemical properties were analysed in the laboratory from 50 samples taken
from five soil cores (10 cm interval, down to 1 m depth). A total of 450 soil samples
were taken from 45 soil cores, spaced 2.5 m in 5 transects to determine root density
and biomass. Data analysis was done in R.4.2.1. Results showed a relatively poor soil
nutrient at the study site, but a high concentration of nutrients was recorded in the first
50 cm soil profile, where 75% of the root biomass is invested. Comparable strontium
ratios were recorded along the soil profile, which did not vary significantly with soil
depth (p = 0.44). Results indicated that plants’ isotopic ratios are neither attributed to
rooting depths, nor to plant species. This study concluded that the isotope method lacks
precision to establish shrubs’ rooting depths for ecological studies. However, an
overlap between sampled plants and soils’ Sr ratios was recorded at the site, which
makes the results precise for studies with interest in geographical variations of isotopes
such as archaeology.
Description
A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Arts in Geography
Keywords
Belowground biomass, Soil depth, Kruskal-Wallis test, Soil physicochemical properties, Plant canopy, Sr ratios, z-score, University of Namibia, Namibia