Growth and desiccation of Themeda triandra and Sporobolus fimbriatus in relation to diminishing moisture availability

Abstract

Water was withheld from individual plants of Themeda triandra and Sporobolus fimbriatus growing in pots in a greenhouse. Leaf extension growth, followed by successive degrees of tiller desiccation, were monitored on a daily basis and related to diminishing moisture availability. Leaf extension growth ceased after about 40 % soil water depletion in both species on the sandy clay loam used in the trial. Thereafter, leaves and growing points senesced progressively with increasing evaporative demand, despite a relatively small drop in soil moisture content. The tentative conclusion is that active leaf growth in semi‐arid grassveld takes place in short sporadic spells subsequent to each effective rainfall event. It seems, for example, that after a rain of 50 mm in midsummer, the duration of active leaf growth could be no more than a week.

Uittreksel

Water is van Themeda triandra en Sporobolus fimbriatus plante wat in ‘n gekontroleerde omgewing gegroei het, weerhou. Blaarverlengingsgroei, gevolg deur opeenvolgende grade van halm uitdroging is op ‘n daaglikse basis gemonitor en in verband gebring met vog beskikbaarheid. Na ongeveer 40 % grondvog vermindering van die sanderige kleileem grond wat in die proef gebruik is, is groei in albei grassoorte gestaak. Daarna het blare en groeipunte progressief verouder met toenemende verdampings‐aanvraag ten spyte van relatiewe klein vermindering in grondvog. Die voorlopige gevolgtrekking dui daarop dat aktiewe blaargroei, in die praktyk, in semi‐ariede grasveld met kort, onderbroke periodes na elke effektiewe neerslag plaasvind. Dit blyk byvoorbeeld dat na ‘n reën van 50 mm in midsomer, aktiewe groei niks langer as ‘n week sal duur nie.

Additional index words:

• leaves
• mortality
• semi‐arid grass‐veld
• shoot apices