Waterbalans studies in geselekteerde subhabitatte van 'n Burkea-Savanna

[摘要] English: During this project the field-water balances in foursubhabitats of the Burkea savanna in Phase II of theSavanna Ecosystem Project at Nylsvley were studied.The project included a study of the water redistributionpatterns in the soil, the determination of the changesin soil moisture storaqe over depth as well as the determinationof evapotranspiration losses in the E. pallens,O. pulchra, G. flavescens and B. africana subhabitats.The water-use efficiencies in the E. pallens, O. pulchraand G. flavescens subhabitats in terms of mm Et (daily)/unit leaf area for the species E. pallens association(grasses), O. pulchra and G. flavescens, and for the subhabitatsas a whole, were calculated.Water is the basic driving force and limiting factor inthe Burkea-savanna, anq a basic knowledge of the naturalfield-water balances is essential for further plantphysiologicaland other research aimed at the understanding ofthe natural plantphysiological processes in the Burkeasavanna ecosystem.There is a high degree of root -integration in the Burkeasavanna, and the three subhabitats E. pallens, O. pulchraand G. flavescens were hydrologically isolated by means ofpoly-ethylene strips in order to interpretate the hydrologicalprocesses on a subhabitat basis.The soil-water balance, based on changes in soil moisturestorage, was used in calculating evapotranspiration losses.Soil-water content was, determined gravimetrically and bymeans of the neutron scattering technique. The neutronprobe used in this study was calibrated in the field forNylsvley conditions.Leaf area determination was necessary as a criterium againstwhich the water-use in the isolated subhabitats could beevaluated. Different methods and techniques were used indetermining the leaf area of grasses, 0.pulchra andG. flavescens.The results are given as soil-water redistribution curves,daily evapotranspiration losses (mm) and water-use efficiencyin terms of daily Et (mm)/unit leaf area. The redistributioncurves show that water-uptake occurs mainly in the top 60 cm of the soil profile in the E. pallens andO. pulchra subhabitats. Deeper in the soil profileswater was available for uptake even throughout the drymonths. In the G. flavescens and B. africana subhabitatswater-uptake took place throughout the soil profileand no water was available during the dry months.Redistribution of water in the soil profile was rapidand a shower of + 50 mm redistributed within + 12 hoursto a depth of 90 cm. No statistical meaningful differencesin evapotranspiration losses were fOund· between the four subhabitats. There were, however, some tendencies and itseemed that the evapotranspiration losses were the highestfrom G. flavescens subhabitats, followed by B. africanasubhabitats, E. pallens subhabitats and finally O. pulchrasubhabitats. This was found for periods from four toseven days after a shower. As far as water-use efficiencyis concerned, no statistical meaningful difference wasfound. It appeared, however, that G. flavescens used themost water per unit leaf area.Highly statistical meaningful differences were foundbetween water-losses from sites with a transpiring grasscover; sites with a non-transpiring (dead)_grass cover;and sites with no grass cover (bare).Unfavourable weather-conditions resulted in smallerdifferences than could be expected under conditions ofdesication.

[发布机构] University of the Free State