A study of the growth and distribution ofcolophospermum mopane(kirk ex benth.) Kirk Ex J. Leon: The interaction of nitrogen, phosphorus and soil moisture stress

Abstract

Abstract Eight sites representative of the full diversity of Colophospermum mopane woodland were chosen in Rhodesia, Botswana and South Africa. Mopane performance, as measured by S diameter at breast height times density, over six height classes, was highly correlated (69 per cent of the variation accounted for) with total N and NaHCO3‐extractable P in the surface soil (0–10 cm). Mopane seedlings grown in pots responded to increased N and P supply, though, not significantly, on two soils with over 20 per cent water at 0,33 bars matric suction. Fluctuations in the available water supply from 100 to 0 per cent had no effect on yield or evapotranspiration rate on these soils. On a third soil, with only seven per cent water at 0,33 bars suction, yield decreased significantly (P < 0,01) with increased N and decreasing available water supply. These effects were primarily due to increased soil osmotic suction. Mopane growth was reduced at osmotic suctions less than 3 bars. At higher suctions (6–8 bars) internal osmotic adjustment appeared to enable the plant to continue growing at a reduced rate. These results are discussed in terms of mopane's distribution, and its apparent competitive advantage when induced to grow in “'coppice” habit.