Browsing by Author "Cocks, Martin"

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    The ecology and nitrogen-fixing ability of selected Aspalathus spp. in fynbos ecosystems
    (1994) Cocks, Martin; Stock, WD
    Aspects of the ecology of selected species of Aspalathus spp. (Fabaceae) were investigated to elucidate the role that this genus may play in the nitrogen economy and ecology of fynbos ecosystems. From the literature it is argued that fire plays a pivotal role in these ecosystems as decomposition is very slow. Decomposition returns nutrients trapped in the vegetation back to the soil. However, nitrogen is lost via volatilisation during fires and as deposition of nitrogen in precipitation is low, symbiotic and non-symbiotic nitrogen-fixation may be of importance in replacing lost nitrogen. The influence of soil total nitrogen and phosphorus on the occurrence of dense stands of Aspalathus plants in vegetation of different ages was investigated. Soil of young vegetation containing stands of Aspalathus plants had the same or higher concentration of phosphorus as nearby older vegetation which lacked stands of Aspalathus. Total nitrogen however showed no trends. Nodulation of 15 Aspalathus spp. at 11 study sites showed varying amounts of nodulation although all these species nodulated well under pot culture. Nodulation of three Aspalathus spp. at three seasonal study sites was followed over the course of one year. A. carnosa showed peak nodulation in the late winter months but A. retroflexa and A. abietina displayed no similar trends. Across the three seasonal sites, which had very similar soil, nodulation was positively correlated with soil total phosphorus and negatively correlated with soil total nitrogen in a multiple regression analysis. The ratio of soil total nitrogen to phosphorus was negatively correlated with nodulation. The opposite correlations for soil total nitrogen and phosphorus were found across all 11 study sites. Differences in soil types and organic content may be responsible for this apparent contradiction. Other soil factors such as pH, temperature and moisture were not correlated with nodulation. Total organic content, however, was negatively correlated with nodulation across the geographic survey study sites.
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