Distribution of roots in the wet and dry regions of the Kalahari

Distribution of roots in the wet and dry regions of the Kalahari

Introduction

Although roots play a vital role in the soil-plant-atmosphere interactions, they still remain poorly investigated compared to aboveground biomass in arid and semi-arid environments. Ecological interactions in arid ecosystems such as competition for nutrients and hydrological processes of soil that affect plant survivorship primarily occur belowground or near the soil surface (Casper & Jackson 1997). Observations have indicated that plants that are able to utilize available belowground space efficiently tend to have greater aboveground biomass (Brisson & Reynolds 1997) in contrast to ones with limited ability to utilize the available space.

Another adaptation mechanism involves the growing of roots into deeper depths of the soil profile. Canadell et al. (1996) found that Boscia albitrunca and Acacia erioloba have the ability to grow and extend their roots as deep as 68 m and 60 m, respectively, in the central Kalahari, Botswana. Acacia tortilis and A. nigrescens have been found at depths of 30m and 50m respectively in the exploration shafts (Cole 1986) in eastern Botswana. Canadell et al. (1996) reported a case in which mesquite roots were found at a depth of 53 m in the Sonoran Desert, United States, whereas Stone & Kalisz (1991) reported 11 tree species that were rooted below 20 m depth. Based on field observations from various parts of the world, Canadell et al. (1996) deduced that survivorship of some species in arid systems depend completely on a plant's ability to tap water from permanent water tables, which are sometimes located at depths of 18 m or more (de Vries, Selaolo, & Beekman 2000).
Statement of Problem

Due to the limited amount of detailed and accurate information on roots dynamics, researchers and modelers tend to use the aboveground data for estimating and modeling the functions of belowground biomass. Hartle et al. (2006) has cautioned that the use of aboveground observations in estimation the belowground functions might be misleading as in most cases the two functions are not dependent on each other. Palacio & Montserrat-Martí (2007) shared the same sentiments, stating that only studying the aboveground phenology a lot of root information is missed, which have relevance to the nutrient and carbon cycling of the ecosystem. Casper et al. ( 2003) noted that the zones of influence for both below and aboveground biomass for a tree are not likely to be the same because the two phenotypes are delimited by different factors.


Although it is well established that roots play a vital role in absorption and transportation of nutrients and water into the plant, these interactions have not yet been intensively investigated. This may be due to the amount of labor and time required to obtain the samples. For example, soil pits for sampling roots at 3 meter depths may take one or two days to dig. The samples, which come from beneath the surface, are soiled and often require pre-treatment before analysis can be done. Another challenge is that roots of different species sometimes intertwine and make it very difficult to make distinctions.
Study Area

The study will be along the Kalahari Transect (KT) in the Kalahari Desert. Kalahari Transect is one of the International Geosphere-Biosphere Programme (IGBP) mega transects that had been set in early 1990s by the Global Change and Terrestrial Ecosystems (GCTE) project (Canadell et al. 2002). The IGBP transects were set and run for more than 1000km in critical and highly sensitive regions and cover diverse environmental conditions and gradients (Koch et al. 1995) such as high altitude, tropical regions and various land uses. Kalahari Transect is located along a north-south striking moisture gradient (from about 200 mm to more than 1000 mm of mean annual precipitation (Wang et al. (2007). Data from two sites will be analyzed to determine the distribution of roots. The two sites are in different rainfall regime; one is a very dry place while the other one is relatively humid.
Aim, goals and objective (Purpose)
This study will aim to investigate the below ground biomass along the Kalahari Transect. Specifically, this will involve mapping the distribution of roots and determining the distribution both laterally and vertically.




Reference:
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