Radiation-use efficiency of a forest exposed to elevated concentrations of atmospheric carbon dioxide

We compared radiation-use efficiency of growth (epsilon;), defined as rate of biomass accumulation per unit of absorbed photosynthetically active radiation, of forest plots exposed to ambient (approximately 360 micro l l-1) or elevated (approximately 560 micro l l-1) atmospheric CO2 concentration ([CO2]). Large plots (30-m diameter) in a loblolly pine (Pinus taeda L.) plantation, which contained several hardwood species in the understory, were fumigated with a free-air CO2 enrichment system. Biomass accumulation of the dominant loblolly pines was calculated from monthly measurements of tree growth and site-specific allometric equations. Depending on the species, leaf area index (L*) was estimated by three methods: optical, allometric and litterfall. Based on the relationship between tree height and diameter during the first 3 years of exposure, we conclude that elevated [CO2] did not alter the pattern of aboveground biomass allocation in loblolly pine. There was considerable variation in L* estimates by the different methods; total L* was 18-42% lower when estimated by the optical method compared with estimates from allometric calculations, and this discrepancy was reduced when optical measurements were corrected for the non-random distribution of loblolly pine foliage. The allometric + litterfall approach revealed a seasonal maximum total L* of 6.2-7.1 with about 1/3 of the total from hardwood foliage. Elevated [CO2] had only a slight effect on L* in the first 3 years of this study. Mean epsilon; (+/- SD), calculated for loblolly pine only, was 0.49 +/- 0.05 and 0.62 +/- 0.04 g MJ-1 for trees in the ambient and elevated [CO2] plots, respectively. The 27% increase in epsilon; in response to CO2 enrichment was caused primarily by the stimulation of biomass increment, as there was only a small effect of elevated [CO2] on L* during the initial years of fumigation. Long-term increases in atmospheric [CO2] can increase epsilon; in closed-canopy forests but the absolute magnitude and duration of this increase remain uncertain.     

The Chinese grass carp, Ctenopharyngodon idella, its biology,introduction, control of aquatic macrophytes and breeding in the Sudan

The paper describes the distribution and biology of the grass carp following its introduction into Sudan. It provides aspects on the culture of the grass carp and its breeding under Sudanese conditions with emphasis on future research.     

Protective and defensive roles of non-glandular trichomes against multiple stresses:structure-function coordination

As superficial structures,non-glandular trichomes,protect plant organs against multiple biotic and abiotic stresses.The protective and defensive roles of these epidermal appendages are crucial to developing organs and can be attributed to the excellent combination of suitable structural traits and chemical reinforcement in the form of phenolic compounds,primarily fl avonoids.Both the formation of trichomes and the accumulation of phenolics are interrelated at the molecular level.During the early stages of development,non-glandular trichomes show strong morphological similarities to glandular ones such as the balloon-like apical cells with numerous phenolics.At later developmental stages,and during secondary wall thickening,phenolics are transferred to the cell walls of the trichomes.Due to the diff use deposition of phenolics in the cell walls,trichomes provide protection against UV-B radiation by behaving as optical fi lters,screening out wavelengths that could damage sensitive tissues.Protection from strong visible radiation is also aff orded by increased surface light refl ectance.Moreover,the mixtures of trichome phenolics represent a superfi-cial chemical barrier that provides protection against biotic stress factors such as herbivores and pathogens.Although the cells of some trichomes die at maturity,they can modulate their quantitative and qualitative characteristics during development,depending on the prevailing conditions of the external biotic or abiotic environment.In fact,the structure and chemical constituents of trichomes may change due to the particular light regime,herbivore damage,wounding,water stress,salinity and the presence of heavy metals.Hence,trichomes represent dynamic protective structures that may greatly aff ect the outcome of many plant–environment interactions.     

Incorporating forage grasses in riparian buffers for bioremediation of atrazine, isoxaflutole and nitrate in Missouri

Multi-species tree-shrub-grass riparian buffer systems have been recognized as one of the most cost-effective bioremediation approaches to alleviate nonpoint source agricultural pollution in heavily fertilized systems. However, highly concentrated herbicides in surface and subsurface water and shade cast by trees along the stream bank usually compromise the effectiveness of these systems. Greenhouse trials and field lysimeter studies were conducted to evaluate the tolerance of orchard grass (Dactylis glomerata), smooth bromegrass (Bromus inermis), tall fescue (Festuca arundinacea), timothy (Phleum pratense), and switchgrass (Panicum virgatum) ground covers to atrazine and Balance™ (isoxaflutole) plus their capacity to sequester and degrade these herbicides and their metabolites. Their ability to remove soil nitrate was also quantified. Concentrations of atrazine, Balance™ and their metabolites in the leachate, soil and plant samples were determined by solid phase extraction followed by high performance liquid or gas chromatographic analyses. Distribution of the herbicides and metabolites in the system was calculated using a mass balance approach. Herbicide bioremediation capacity of each lysimeter treatment was determined by the ratio of metabolites to parent herbicide plus metabolites. Bioremediation of nitrate was quantified by comparing nitrate reduction rates in grass treatments to the bare ground control. Based on this herbicide tolerance, bioremediation data and shade tolerance determined in a previous study, it was established that switch grass, tall fescue and smooth bromegrass are good candidates for incorporation into tree-shrub-grass riparian buffer systems designed for the bioremediation of atrazine, Balance™ and nitrate.     

Can the nitrogenous composition of xylem sap be used to assess salinity stress in Casuarina glauca?

It is predicted that dryland salinity will affect up to 17 Mha of the Australian landscape by 2050, and therefore, monitoring the health of tree plantings and remnant native vegetation in saline areas is increasingly important. Casuarina glauca Sieber ex Spreng. has considerable salinity tolerance and is commonly planted in areas with a shallow, saline water table. To evaluate the potential of using the nitrogenous composition of xylem sap to assess salinity stress in C. glauca, the responses of trees grown with various soil salinities in a greenhouse were compared with those of trees growing in field plots with different water table depths and groundwater salinities. In the greenhouse, increasing soil salinity led to increased allocation of nitrogen (N) to proline and arginine in both stem and root xylem sap, with coincident decreases in citrulline and asparagine. Although the field plots were ranked as increasingly saline-based on ground water salinity and depth-only the allocation of N to citrulline differed significantly between the field plots. Within each plot, temporal variation in the composition of the xylem sap was related to rainfall, rainfall infiltration and soil salinity. Periods of low rainfall and infiltration and higher soil salinity corresponded with increased allocation of N to proline and arginine in the xylem sap. The allocation of N to citrulline and asparagine increased following rainfall events where rain was calculated to have infiltrated sufficiently to decrease soil salinity. The relationship between nitrogenous composition of the xylem sap of C. glauca and soil salinity indicates that the analysis of xylem sap is an effective method for assessing changes in salinity stress in trees at a particular site over time. However, the composition of the xylem sap proved less useful as a comparative index of salinity stress in trees growing at different sites.     

Photosynthetic characteristics of olive tree (Olea europaea) bark

Functional and structural characteristics of corticular photosynthesis of sun-exposed bark of olive tree (Olea europaea L.) were examined. Stomata are only sporadically present during stem primary growth. Light transmission through the phellem was age dependent, decreasing rapidly in stems older than five years of age. Light transmission was also low in pubescent 1-year-old stems. Light transmission was about 50% higher in wet phellem than in dry phellem. Photosynthetic capacity on a unit area basis (measured with an oxygen disc electrode at 27 degrees C and about 5% CO(2) on chlorophyllous tissue discs isolated from the stem) was higher in 1-, 20- and 30-year-old stems compared with 2-10-year-old stems. Low chlorophyll a/b ratio and light compensation points were recorded in olive stems with low phellem light transmission, in accordance with the shade acclimation hypothesis. The intrinsic photochemical efficiency of photosystem II of all stems, especially young stems, was less than that of the leaves. Our results show that olive tree bark possesses an efficient photosynthetic mechanism that may significantly contribute not only to the reduction in concentrations of CO(2) in the inner bark, but also to whole-tree carbon balance.     

Seasonal and interannual ecophysiological responses of beech (Fagus sylvatica) at its south-eastern distribution limit in Europe

Due to its wide European distribution and its drought-susceptibility, beech (Fagus sylvatica L.) received intensive attention recently in the light of global warming. Contrary to central European beech ecosystems, little is known about the ecophysiology of beech at its south-eastern European distribution limit. Here we tested whether climatic fluctuations during a three-year period affected the ecophysiology of a beech site in Greece. Attention was paid at comparing our findings to the intense effects the 2003 extreme drought had on beech forests in central Europe.     

Active root distribution pattern of <Emphasis Type="Italic">Hevea brasiliensis</Emphasis> determined by radioassay of latex serum

The active root distribution pattern of mature rubber (Hevea brasiliensis Muell. Arg.) up to a lateral distance of 250 cm from the tree and to a soil depth of 90 cm was studied in an oxisol by employing ³²P soil injection technique in Kerala, the state which accounts for 83% of rubber cultivation in India. The trees were aged 18 years and grown at a spacing of 4.9 × 4.9 m. The extent of absorption of applied ³²P by the tree from various placements was assessed by radio assay of leaf and latex serum. Latex serum registered higher counts and variability was less compared to leaf indicating the suitability of latex serum as a potential source for radio assay for ³²P studies in rubber. The results revealed that rubber is a surface feeder with 55% of the root activity confining to the top 10 cm of soil layer. Root activity declined with increasing depths and the concentration of physiologically active roots at 90 cm depth was only 6%. A more or less uniform distribution of root activity was noticed with respect to lateral distance indicating more extensive spread of lateral roots. Concentration of physiologically active roots in the surface layer suggests the possibility for competition under intercropped situation in mature plantations.