Springer Science and Business Media LLC

Australia has a large endemic tree flora with many of the genera largely confined to the southern hemisphere. The two dominant genera are Eucalyptus and Acacia. Isozyme studies of patterns of genetic diversity in populations of these species are reviewed. Generally, Australian tree species have high levels of allozyme variation with most of this variation within rather than between populations. The species with the most genetic differentiation between populations are those with regional distributions but with small disjunct populations. Many of the species show no discernible relationship between current population sizes and genetic diversity. A number of species with widespread distributions exhibit similar clusters of populations both on isozymes and other traits. Such clusters often correspond to large geographic regions. This pattern suggests that preliminary low intensity isozyme surveys could help to define more efficient sampling strategies for intensive seed collections and subsequent field trials of many tree species.

The East Indian sandalwood (Santalum album L), one among the valued timber species in the global market due to its sweet-scented heartwood, is facing a drastic decline of its natural populations over the past three decades. The major constraint in the regeneration of sandal is the slow, staggered, and poor germination of the seeds. The germination may continue even up to one year. The present investigation focused on the impact of biopriming on the germination and seedling performance in sandal. Fresh mature seeds of sandal were procured from the Nachivayal Reserve Forest, Marayur Sandal Division. The seeds were subjected to 16 biopriming treatments using Pseudomonas fluorescens at 4 concentrations (25, 50, 75 and 100%) and 4 durations (2, 4, 6, and 8 days). The results revealed that the biopriming at 100% for 8 days recorded the highest germination percentage (88%) within 21 days with lowest energy period (15 days) and highest germination energy (62.98%). Biopriming at 50% concentration for 8 days was the next best treatment which improved the germination of sandal seeds and the lowest germination percentage was recorded in control seeds (46%). With regard to the seedling growth, the biopriming treatment contributed a significant increase in growth attributes of the seedlings. We recommend the biopriming with Pseudomonas fluorescens at 100% for 8 days as a potential technique to enhance seed germination and seedling growth in sandal.

Provenance/family trials of Eucalyptus pellita F. Muell were established at three seasonally-dry tropical sites in northern Australia (two in north Queensland and one on Melville Island in the Northern Territory), and at Luasong, a tropical site with year-round high rainfall and humidity in Sabah, Malaysia. After 2–3 years, it was clear that New Guinea provenances outperformed Queensland provenances in their survival, growth and form, and in their crown health, in the humid tropical environment of Luasong. New Guinea provenances were also clearly superior to Queensland provenances in their growth and form at Melville Island, but less clearly so at Cardwell, Queensland. Among Queensland provenances, Helenvale and Kuranda were superior to the more northerly Cape York provenances, Tozers Gap and Lankelly Creek, while there was little difference between the two New Guinea provenances tested, Bupul-Muting (Irian Jaya) and Keru (Papua New Guinea). Significant differences in growth traits, form and survival were demonstrated between families within provenances. In a species/provenance trial at Luasong, E. pellita displayed better growth and survival than tropical provenances of E. grandis and E. urophylla, but was inferior in growth and crown health to Acacia mangium.

The impact of seed size and successional status on seedling growth under elevated CO2 was studied for five dry tropical tree species viz. Albizia procera, Acacia nilotica, Phyllanthus emblica, Terminalia arjuna and Terminalia chebula. Seedlings from large (LS) and small seeds (SS) were grown at two CO2 levels (ambient and elevated, 700–750 ppm). CO2 assimilation rate, stomatal conductance, water use efficiency and foliar N were determined after 30 d exposure to elevated CO2. Seedlings were harvested after 30 d and 60 d exposure periods. Height, diameter, leaf area, biomass and other growth traits (RGR, NAR, SLA, R:S) were determined. Seedling biomass across species was positively related with seed mass. Within species, LS seedlings exhibited greater biomass than SS seedlings. Elevated CO2 enhanced plant biomass for all the species. The relative growth rate (RGR), net assimilation rate (NAR), CO2 assimilation rate, R:S ratio and water use efficiency increased under elevated CO2. However, the positive impact of elevated CO2 was down regulated beyond 30 d exposure. Specific leaf area (SLA), transpiration rate, stomatal conductance declined due to exposure to elevated CO2. Fast growing, early successional species exhibited greater RGR, NAR and CO2 assimilation rate. Per cent enhancement in such traits was greater for slow growing species. The responses of individual species did not follow functional types (viz. legumes, non-legumes). The enhancement in biomass and RGR was greater for large-seeded species and LS seedlings within species. This study revealed that elevated CO2 could cause large seeded, slow growing and late successional species to grow more vigorously.

Mass maturity (end of the seed-filling phase) occurred at about 72 days after flowering (DAF) in developing seeds of Mimusops elengi, at which time seed moisture content had declined to about 55%. The onset of ability to germinate was detected at 56 DAF and seeds showed 98% germination by 84 DAF. Tolerance of desiccation to 10% moisture content was first detected at 70 DAF and was maximal by 84 DAF. Delaying collection by a further 14 days to 98 DAF, when fruits began to be shed, reduced seed viability, particularly for seeds first dried to 10% moisture content. Hence the best time for seed collection appears to be about 14 days before fruits shed. In a separate investigation with six different seed lots, desiccation below about 8–12% moisture content reduced viability (considerably in some lots). The viability of dry seeds (below about 10% moisture content) stored hermetically was reduced at cool temperatures (5 °C and below), and none survived storage at sub-zero temperatures. The results suggest that Mimusops elengi shows intermediate seed storage behaviour and that the optimal hermetic seed storage environment is about 10% moisture content at 10 °C, while short-term, moist, aerated storage at high (40%) moisture content is also feasible.

With over 1.5 billion forest tree seedlings produced annually in the USA, seedling quality assessment is critical to ensure reforestation success. While height and root-collar diameter are the most common traits evaluated during seedling quality assessment, above-ground morphology is not always an accurate predictor of performance after outplanting. Root system morphology and physiological status may provide a more accurate indication of seedling potential. However, relatively few studies have attempted to quantitatively assess root system quality in relation to outplanting success. Large root volume, high root fibrosity, and an increased number of first-order lateral roots have shown some correlation to improved field performance. Physiological seedling quality assessment is commonly practiced through evaluation of root growth potential. Other tests, such as root electrolyte leakage, have also shown some potential as measures of seedling physiological quality. This review identifies current methods of assessing seedling root system quality and discusses potential shortcomings of these methods. An increased understanding of the suitability of current tests, coupled with the development of new tests and multiple parameter relationships, may foster the development of species and site-specific targets for seedling root system quality assessment. The production of seedlings with root systems that meet high morphological and physiological standards better enables seedlings to rapidly establish and thrive upon outplanting.

Greenhouse and field studies were conducted to determine the effects of indole3-butyric acid (IBA) and 2,4-dichlorophenoxyacetic acid (2,4-D) on root development and survival of 3+0 bareroot Pinus ponderosa (Dougl. ex Laws.) and 2+0 bareroot Celtis occidentalis (L) seedlings. In the greenhouse, 100 and 200 ppm. IBA and 10 and 50 ppm 2,4-D were applied to seedlings through a root dip in an auxin hygroscopic gel mix. A randomized complete block analysis of variance indicated that IBA gel treatments increased root volume and root dry weight in hackberry and had no effect on ponderosa pine; 2,4-D gel treatments had detrimental effects on both species. In the field, IBA gel treated ponderosa pine seedlings exhibited improved height and survival relative to the non-treated control seedlings. There was no detectable improvement in survival in the field for hackberry. However, diameter and stem dry weight were lower for hackberry seedlings treated with the gel dip alone.

Leucaena leucocephala is an introduced species, which has been widely used in mountain ecological restoration in southwestern China. To investigate the allelopathic effects of decomposing L. leucocephala leaf litter, the photosynthetic physiology of seedlings of two recipient plants, Cynodon dactylon and Medicago sativa, were measured in this controlled study. As the amount of decomposing L. leucocephala leaf litter increased, the net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) decreased continuously, and the intercellular CO2 concentration (Ci) increased continuously in both recipient plants. In M. sativa, all abovementioned indices differed significantly compared with the control group: Pn, Gs, and Tr decreased by 41.69, 59.35, and 48.02%, respectively, and Ci increased by 28.53%. In C. dactylon, Gs decreased significantly by 27.27%. Analysis of the photosynthesis–light response curve indicated that the maximum net photosynthetic rate (Pnmax) and dark respiration rate (Rd) of C. dactylon, as well as Pnmax and light saturation point (Lsp) of M. sativa, decreased significantly as the amount of decomposing L. leucocephala leaf litter increased. These results indicated that the photosynthetic traits, light adaptation ability and physiological metabolism of recipient plants were affected by the treatment. The decreased photosynthesis was caused by the changes in pigments and soluble sugar contents induced by L. leucocephala leaf litter and is therefore considered to be associated with non-stomatal limitations. In addition, as the amount of decomposing L. leucocephala leaf litter increased, M. sativa showed decreased chlorophyll (Chla) and carotenoid (Car) contents, while C. dactylon showed decreased Chla and Chl(a + b) contents. However, both recipient plants exhibited significantly increases in their soluble sugar content. Overall, M. sativa was more sensitive than C. dactylon to the allelopathic effects induced by decomposing L. leucocephala leaf litter.