Carbon isotope fractionation in tree ring early and late wood in relation to intra-growing season water balance

We determined the stable carbon isotope composition (δ^1.3C) of cellulose extracted from early and late wood in Douglas fir [Pseudotsuga menziexii (Mirb.) Franco] tree rings. Data were obtained for the period 1962 to 1981, at the start of which the trees were 20 years old. A water balance model was used to calculate daily stand transpiration and water deficit. The model incorporates site factors (soil water availability, slope and aspect) and environmental variables (solar radiation, air temperature and rainfall). There was far greater variability in late wood than in early wood δ^1.3C. In wet years, late wood δ^1.3C was significantly lighter (by as much as 2δ) than early wood δ^1.3C but in dry years this difference was reversed. Differences between spring and summer cumulative transpiration accounted for almost 60δ of the variability in differences between early and late wood δ^1.3C. We found excellent correspondence between summer cumulative transpiration and late wood δ^1.3C, with estimates of transpiration accounting for up to 93% of the variability in δ^1.3C. Correlations between early wood δ^1.3C and spring transpiration were generally poor (r2<0.4), but we were able to identify those exceptional years in which there had been a very dry spring. Our results indicate that, while tree ring δ^1.3C correlates reasonably well with basal area increment, it is a far better indicator of inter- and intra-annual variability in water availability than radial growth.     

Physiological aspects of Taxus brevifolia seeds in relation to seed storage characteristics

Water relations, desiccation tolerance and longevity of Taxus brevifolia (Nutt.) seeds were studied to determine the optimal stage of development and storage conditions for seeds of this species. Seeds equilibrated to a range of relative humidities (RHs) had unusually low water contents which can be accounted for by the high lipid content of gametophyte tissues (71% of the dry mass). Water relations of embryonic tissue were more typical of those reported for other seed species. The water content below which freezing transitions were not observable in the embryo was ca 0.24 g H₂O (g dry weight)⁻¹ (g g⁻¹) for all maturity classes studied. Embryos did not achieve significant levels of desiccation tolerance (survival to water contents less than 0.5 g g⁻¹) until the latter stages of development when dry matter was maximal. Mature embryos could be dried to 0.025 g g⁻¹ (seed water content of 0.010 g g⁻¹) with no loss of viability. Thus, at the latter stages of development, embryo water content could be optimized to avoid both desiccation and freezing damage. Survival of mature seeds declined over a 2-year period when seeds were stored at temperatures between 5 and 35°C and RHs between 14 and 75%, corresponding to seed water contents between 0.015 and 0.07 g g⁻¹. The deterioration rate was slowest for seeds stored at the lowest RH and temperature. Our data indicate that seeds of Taxus brevifolia show orthodox rather than recalcitrant storage characteristics, but that the optimum water content for storage was extremely low. The results suggest that even if stored at optimal water contents and low temperatures, T. brevifolia seeds will be relatively short lived. The high quantity of lipids or reducing sugars may be contributing factors in the poor storage characteristics.     

The effects of soil warming on plant recruitment

We demonstrate, using a simple field experiment, that soil warming is sufficient, independent of other cues, to potentially alter the recruitment of Betula pendula seedlings. This study suggests that changing temperature, and correlated changes in edaphic factors, can alter patterns in plant recruitment via differential effects on seed dormancy. Increased soil temperatures (of less than 5 °C) throughout the year led to a significant increase in the number of birch seedlings that emerged from soil samples collected in the spring. No concomitant changes in the emergence of other species was observed. Such temperature induced changes in seedbank dynamics and their subsequent effects on the competitive interactions within a plant community suggest far reaching ecological consequences of current increases in global temperature.     

Stimulation of the growth and solamargine production by Solanum paludosum multiple shoot cultures using a new culture medium

Organogenic callus cultures of Solanum paludosum were obtained from root, hypocotyle and cotyledon explants of plantlets cultured in sterile conditions. These callus cultures developed multiple shoots which proliferated in Murashige and Skoog basal liquid medium. These multiple shoots produced solamargine, the main steroidal glycoalkaloid present in the unripe fruits.The optimization of the macronutrient composition of the liquid medium was performed by a method derived from the plant composition. This approach results in the establishment of an appropriate medium (SPOM medium) suitable for the improvement of both growth and solamargine production by multiple shoot cultures of S. paludosum.     

Effects of fire frequency on plant species composition of sandstone communities in the Sydney region: Inter-fire interval and time-since-fire

Abstract Fire frequency is the number of fires experienced by a particular community within a given time period. This concept can potentially be resolved into a number of interacting variables, including: time since the most recent fire, the length of the inter-fire intervals, and the variability of the length of the inter-fire intervals. We estimated the effects of these three variables on the floristic composition of 65 samples from dry sclerophyll vegetation with different fire histories in Brisbane Water, Ku-ring-gai Chase and Royal National Parks near Sydney. Our analyses suggest that fire frequency may account for about 60% of the floristic variation among our samples. They confirm the hypothesis that the recent (<30 years) fire frequency produces effects on floristic composition of fire-prone communities that can recognizably be attributed both to the time since the most recent fire and to the length of the intervals between fires. These effects are equal in magnitude but are different in the nature of the floristic variation they are associated with. Increasing time-since-fire is associated with a decline in the evenness of fire-tolerant species, indicating that fewer of these species come to dominate the community in the prolonged absence of fire. Herbs and small shrubs decrease in abundance, while larger shrubs increase in abundance. Inter-fire intervals of decreasing length are associated with a decrease in the evenness of the fire-sensitive species, particularly those large Proteaceae shrubs that often dominate the community biomass in dry sclerophyll shrublands of southeastern Australia. Furthermore, the variation associated with inter-fire intervals is not necessarily solely related to the shortest inter-fire interval, but is related to combinations of inter-fire intervals through time. Thus, increasing variability of the length of the inter-fire intervals is associated with an increase in the species richness of both fire-sensitive and fire-tolerant species, implying that it may be variation of the inter-fire intervals through time that is primarily responsible for maintaining the presence of a wide variety of plant species in a particular community. Our results also suggest that the floristic variation associated with different inter-fire intervals decreases with increasing time-since-fire.     

FLIGHT ACTIVITY AND FATTY ACID UTILIZATION IN MYTHIMNA SEPARATA (WALKER) MOTHS*

Abstract The fatty acid (FA) compositions for total lipids from fat body, hemolymph and flight muscle of the armyworm moths, Mythirnna separata, at rest and after tethered flight for 1 h were determined by GC and GC-MS. The composition in these tissues comprises myristic acid (1%-2%), palmitic acid (more than 35%1, palmitoleic acid (9%-11%), stearic acid (less than 1%), oleic acid (about 32%), linoleic acid (12%-17%) and linolenic acid (3%-6%). After flight, FA level in the fat body, compared to that at rest, shows a significant decline at about 20 μg/mg tissue.h^-1; the concentration of FAs in hemolymph rises evidently, but change of FA content in flight muscle appears to be small. From the changes of proportional composition of FAs in fat body, hemolymph and flight muscle, it is found that the FAs selectively utilized for flight in flight muscle are predominantly the palmitic acid and oleic acid.     

Changes in organic matter composition of forest soil treated with a large amount of urea to promote ammonia fungi and the abilities of these fungi to decompose organic matter

Organic matter composition (lignin, holocellulose, 50% (v/v) methanol extract, water-soluble carbohydrate (WSC) and phenolics (WSP), petroleum ether extract, and ash) of A₀ layer soil treated with 700 g/m² of urea to promote ammonia fungi was investigated in a Japanese red pine (Pinus densiflora) forest. Nine species of fungi were found during the study period of 18 months after the treatment. Of these, seven species belong to the ammonia fungi. WSC content of the treated soil was lower than that of the control. Methanol extract content increased initially after the treatment, then decreased to below the control level. There were no consistent differences in other components between the treated plot and the control. The abilities to decompose cellulose, lignin, chitin, protein and lipid in 18 strains in 10 species of the ammonia fungi were also screened. Cellulose was not lysed byPseudombrophila deerata, Hebeloma spp. andLaccaria bicolor. Strong lignolytic activity was shown byLyophyllum tylicolor, Coprinus echinosporus andP. deerata. Chitin was decomposed byAmblyosporium botrytis, L. tylicolor, C. echinosporus andHebeloma vinosophyllum. All strains possessed proteolytic and lipolytic activities. Supply of glucose to the culture media resulted in weaker enzyme activities except for lignolytic ability.     

Effects of 12 weeks of aerobic exercise plus dietary restriction on body composition, resting energy expenditure and aerobic fitness in mildly obese middle-aged women

This study investigated the effects of 12 weeks of aerobic exercise plus voluntary food restriction on the body composition, resting metabolic rate (RMR) and aerobic fitness of mildly obese middle-aged women. The subjects were randomly assigned to exercise/diet (n = 17) or control (n = 15) groups. The exercise/diet group participated in an aerobic training programme, 45–60 min · day ^–1 at 50%–60% of maximal oxygen uptake (VO_2max), 3–4 days · week^–1, and also adopted a self-regulated energy deficit relative to predicted energy requirements (–1.05 MJ · day ^–1 to –1.14 MJ · day ^–1 ). After the regimen had been followed for 12 weeks, the body mass of the subjects had decreased by an average of 4.5 kg, due mainly to fat loss, with little change of fat free mass (m _ff). The absolute RMR did not change, but the experimental group showed significant increases in the RMR per unit of body mass (10%) and the RMR per unit of m _ff (4%). The increase in RMR/m _ff was not correlated with any increase in VO_2max/m _ff. The resting heat production per unit of essential body mass increased by an average of 21%, but the resting heat production rate per unit of fat tissue mass remained unchanged. We concluded that aerobic exercise enhances the effect of moderate dietary restriction by augmenting the metabolic activity of lean tissue.     

Rotifers of Benin River,Nigeria

Plankton hauls were made with 55 m Hydrobios nets at one Jamieson and six Benin River stations at monthly intervals for 12 and 24 months during 1981/82 and 1986–1988, respectively. In all, a 100 km stretch of the Benin River and its tributary, the Jamieson, were covered. Fifty species of Rotifera were recorded. About 80% were cosmopolitan. The turbulent nature of the river is reflected in a diversity of Lecanidae found, although the dominant species were Keratella tropica (Apstein) and Keratella cochlearis (Gosse) (Brachionidae). Spatial investigations revealed the euryhaline nature of Brachionus plicatilis (O. F. Muller), and showed most Benin River rotifers to be freshwater inhabitants.     

Activity of the tetramer and octamer of glutamine synthetase isoforms during primary leaf ontogeny of sugar beet (Beta vulgaris L.)

In extracts from the primary leaf blade of sugar beet (Beta vulgaris L.) we separated a chloroplastic isoform (GS 2) of glutamine synthetase (GS, EC 6.3.1.2) and one or two (depending on leaf age) cytosolic isoforms (GS 1a and GS 1b). The latter were prominent in the early (GS 1a) and late stages of leaf ontogeny (GS 1a and GS 1b), whereas during leaf maturation GS 2 was the predominantly active GS isoform. The GS 1 isoforms were active exclusively in the octameric state although tetrameric GS 1 protein was detected immunologically. Their activity stayed at a relatively constant level during leaf ontogeny; an increase was observed only in the senescent leaf. The activity of GS 2, however, changed drastically during primary leaf ontogeny and was modulated by changes in the oligomeric state of the active enzyme. In the early and late stages of leaf ontogeny when GS 2 activity was low (lower than that of the GS 1 isoforms), GS 2 was active only in the octameric state. In the maturing leaf, when GS 2 activity had reached its maximum level (much higher than that of the GS 1 isoforms), 80 of total GS 2 activity was due the activity of the tetrameric form of the enzyme and 20 was due to octameric GS 2. Tetrameric GS 2 was a hetero-tetramer and thus not the unspecific dissociation product of homo-octameric GS 2. In addition, GS 2 activity was modulated by an activation/inactivation of the tetrameric GS 2 protein. Due to an activation of the GS 2 tetramer, the activity of tetrameric GS 2 increased during leaf maturation from zero level 23-fold compared with that of GS 1a and 18-fold compared with that of GS 1b. Possible activators of tetrameric GS 2 are thiol-reactive substances. During leaf senescence, GS 2 activity decreased to zero; this decrease was due to an inactivation of the tetrameric GS 2 protein probably caused by oxidation.Abbreviations FLL final lamina length - FPLC fast protein liquid chromatography - GS glutamine synthetase - GHA -glutamyl hydroxamate - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase Dr. Roger Wallsgrove's (Rothamsted Experimental Station, Harpenden, UK) generous gift of GS antiserum is greatly appreciated.