Cold tolerance of Acacia karroo and A. nilotica, two tree species from South Africa, in Beijing

Fynbos plant communities developed under geographic and climatic conditions unique to South Africa. Acacia karroo is the most widespread tree species, well known for its drought tolerance. A. nilotica exudes a good quality gum which is edible and suitable for confectionery. The two species have been introduced to China but little is known about their adaptability under the new environmental conditions. For our present study, the growth potential and physiological and biochemical parameters of the two species in response to cold stress were investigated. The results, measured as seed qualities (purity, thousand seed weights, germination, etc.) show differences between A. karroo and A. nilotica. The seed germination rate was between 10% and 60%. Seedlings were established in fields, pots and plugs. Those in the field grew well during the growing season but completely died in the winter. Those in pots or plugs were moved to and managed in the greenhouse. The plants were green in winter. The electrical conductivity of cells, the contents of water soluble sugars, proteins, malondialdehyde (MDA) increased during eight hours of low temperature treatment at 4℃. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) decreased markedly during the eight hours of 4℃treatment. We conclude that A. karroo and A. nilotica have little adaptability to the cold winter weather and cannot survive in the outdoors in the Beijing area, but could grow well indoors as ornamentals.     

Research on planting stock and forest regeneration in South Africa

Unlike countries with substantial forest resources, South Africa has a limited area available for forestry development and timber production. This is mainly because of insufficient rainfall for a viable timber production in most of the country, and the priority to utilize land for other purposes such as food production, fundamental community needs and water harvesting. The timber production has steadily increased over the last years, mainly due to breeding strategies and intensive silviculture. The variety of sites and products, as well as the need for improved and product-specific timber properties, force the grower to utilize a multitude of species, hybrids and clones in a fairly uniform operational system. Research-derived plantation forestry in South Africa provides examples of successful biological technology, yet its optimization needs attention. A better integration of components in the `harvesting/processing-nursery-regeneration-tending-harvesting/processing' cycle offers a tremendous challenge for future research.     

Drought tolerance of Acacia karroo, a native tree species to South Africa, in Beijing

Acacia karroo is an indigenous, strong drought-tolerant and widely planted tree in South Africa. In order to match the plant with its adaptation to forest sites in China, it is important to know the drought-tolerance of this species under Chinese forest site conditions. Our study was carried out in cinnamon soils in Beijing and with Platycladus orientalis, the most drought-tolerant tree in Beijing, as control. Physiological parameters of young plants of the trees were measured and divided into three groups in response to soil drying. The first group included root activity, ABA content in roots and peroxidase (POD) activity in leaves. Their values changed similarly to those of P. orientalis and dramatically increased to maximum values when the soil water content (SWC) decreased from its normal level of 20% to 7.6% where the three indices decreased dramatically when SWC was reduced further from 7.6%. The second group of parameters included the contents of proline, soluble protein and malondialdehyde (MDA). Their values showed greater variation than those of P. orientalis and significantly increased when SWC decreased from 20% in response to soil drying. However, the proline and soluble protein contents fluctuated in A. karroo at a lower level than those in P. orientalis. In contrast, the content of MDA in A. karroo was much higher than that in P. orientalis which almost did not increase in the drying soil. The third group of parameters consisted of soluble sugar, superoxide dismutase (SOD) and catalase (CAT). These parameters showed greater diversity and fluctuations among the three varieties of A. karroo compared with the control in response to soil drying. These results suggest that A. karroo is characterized as a strong, drought tolerant species in most of physiological parameters but weaker than P. orientalis in membrane lipid antioxidation.     

Early growth responses from weed control and planting larger stock of Pinus radiata are greater than that obtained from mechanical soil cultivation

Early growth of two grades ofbare-root Pinus radiata D.Don seedlingswere studied in response to four soilcultivation treatments and two weed controltreatments.Soil cultivation treatments included (i) pitsmade by hand, (ii) pits made with an auger,(iii) ripping alone, and (iv) ripping plusdisking. Weed treatments included (i) manualrelease 1 year after planting or (ii) totalweed control for 1 year involving the use ofherbicides and additional hoeing. Bare-rootseedlings were separated into either medium(4.1-mm average root-collar diameter; height25–31 cm) or small (2.8-mm average root-collardiameter; height 14–20 cm) size classes.Growth on this site was excellent and 7 yearsafter treatment, trees in the least expensivetreatment averaged 12.8 m in height. Use ofmedium seedlings and extra weed controlincreased merchantable volume by20 m³ ha^{minus 1} and 19 m³ ha^{minus 1},respectively. When combined, the increase was39 m³ ha^{minus 1}. However, none of the soilcultivation treatments caused a significantincrease in merchantable volume. Disking onthis site proved to be of no benefit. Aboundary-line analysis was used to examine themarginal returns from investing in intensivesilviculture.     

Contents Volume 22 2001

Volume Contents

Contents Volume 22 2001     

Economic returns from enhancing loblolly pine establishment on two upland sites: Effects of seedling grade,fertilization, hexazinone,and intensive soil cultivation

On two well drained Coastal Plain sites, early (4-year) and mid-rotation (12-year) performance of loblolly pine (Pinus taeda L.) was examined in relation to mechanical site preparation, herbaceous weed control, and fertilization with diammonium phosphate (DAP). In addition, seedling grade as determined by groundline diameter (GLD) was a fourth factor evaluated. Of the four factors examined, seedling grade was the only factor to consistently improve fourth-year survival. In Alabama, seedlings with a 2.5 mm GLD averaged 62% survival while 5.1 mm seedlings averaged 83% survival. In Virginia, 1.3 mm seedlings had 73% survival and 5.1 mm seedlings had 79% survival. Calculated volume gains from increasing seedling grade suggest that a 1 mm increase in GLD could amount to an additional 7 to 12 m³/ha at age 12. Seedling size and mechanical site preparation were partly exchangeable in influencing survival and growth. Use of hexazinone on late planted seedlings increased mortality at both sites. Applications of hexazinone increased volume/ha when combined with DAP fertilization. Fertilization with DAP increased 12-year volume/ha only when weeds were controlled with hexazinone or disking.Alabama Agricultural Experiment Station Journal Series No. 9-933657.     

Inhibitive effects of some treatments on the browning rate during the in vitro culture of Acacia karroo Hayne

Acacia karroo Hayne is an arbor species widely distributed in South Africa with the characteristics of fast growth and drought resistance. The species was introduced to China recently. In vitro culture is an effective method to rapidly produce plants and a strategy to minimize somaclonal variation among regenerated plants. Browning, however, is a problem in establishing the in vitro culture system. The present study diminished the problem by selecting explants, using different browning inhibitors and chilling treatment. Results showed that the use of embryos as explants reduced the browning ratio to 46.7%, whilst stem segment explants were browned up to 56.7%. The adventitious buds were successfully induced in the modified tissue culture medium supplemented with 5.0 mg·L-1 6-BA and 0.1 mg·L-1 NAA. The proliferation coefficient of adventitious buds is 2.8.     

Transplant Stress Index: A proposed method of quantifying planting check

This paper demonstrates a simple way of estimating the intensity and duration of planting check by examining height growth patterns. A transplant stress index is determined by the relationship between initial seedling height and subsequent height growth. This index is defined as the slope of a linear relationship between initial height and height increment. If the slope is negative, the plants (as a population) are said to be experiencing planting check. When the slope is approximately zero, the stock is said to be recovering from planting check. A steep positive slope suggests the stock has recovered from planting check. TSI values were determined for several conifers including Pinus elliottii Engelm. var. elliottii, Pinus taeda L., Pinus radiata D. Don, Picea sitchensis (Bongard) Carrière, and Larix× eurolepis Henry.