부산대학교 도서관

• We estimated the age of four geoxylic taxa by 14C dating B. insignis, C. laureola, P. simplex and T. kraussiana xylopodia. • The relatively medium to large xylopodia of all forbs tested were older than a decade, and up to five decades old. • Xylopodia showed no ring structure or unclear structures only visible at 7X magnification, which did not match 14C dates. • We recommend Radiocarbon dating using AMS, with sample treatment improvements, to calculate geoxyle age. Annual growth rings are absent in many long-lived grassland geoxyles. Thus, estimates of age for individuals are largely based on non-benchmarked assessments by experienced botanists. We wished to obtain a more precise estimate of age from the xylopodia of four geoxylic taxa (i.e. Berkheya insignis, Callilepis laureola, Protea simplex and Tephrosia kraussiana) growing in a Pondoland grassland, using both the gas proportional counting and Accelerated Mass Spectroscopy radiocarbon dating techniques. Plants sampled in 2008 fell within modern concentrations of carbon 14; therefore, radiocarbon dating generally yielded two ages for each plant, an older age (range: 45–51 years, mean=49, CV=3.6%) corresponding with the nuclear testing period, and a younger age (range: 10–29 years, mean=18, CV=35%), corresponding to the period after the Partial Nuclear Test Ban Treaty. Hence the older ages are much less variable than the younger ages. All plants had the older age estimate, and all but two had the younger age estimate. In addition, two plants each, had two similar older age estimates. P. simplex plants were 16, 24, 27 and 29, or 45, 46–49, 47 and 49 years, T. kraussiana 13, 15 and 16, or 50 and two of 51 years, C. laureola 12, 15 and 21, or 49–50 and two of 50 years and B. insignis were 10, or 49, 50 and 51 years old. Growth rings were not visible with the naked eye. However, using stereomicroscopy, ring-like patterns were visible to some extent at 7X magnification for B. insignis, P. simplex and T. kraussiana , but not C. laureola. Counts of these structures were much lower than the younger 14C dates, and hence are unlikely to be annual rings. Despite the ambiguity of multiple ages, these estimates are a useful starting point or benchmark for future empirical investigations of age for forbs with no clear annual rings. Most studies have used radiocarbon dating to estimate the age of woody tree stem tissue, whereas this study is one of few to measure the age of below-ground modern tissues of South African forbs. Suggestions for further refinement during collection and processing of geophytic sample material are made based on lessons learned from this investigation. [ABSTRACT FROM AUTHOR]