Nutrient contents and efficiencies of beech and spruce saplings as influenced by competition and O<Subscript>3</Subscript>/CO<Subscript>2</Subscript> regime

Saplings of Fagus sylvatica and Picea abies were grown under conditions of intra and interspecific competition in a 2-year phytotron study under combinations of ambient and elevated ozone (+O₃ which is 2 × O₃, but <150 nl l⁻¹) as well as carbon dioxide concentrations (+CO₂ which is amb. CO₂ + 300 μl CO₂ l⁻¹) in a full factorial design. Saplings were analysed for various mineral nutrients in different plant organs as well as biomass production and crown development. The study was based on the assumption that nutritional parameters important for growth and competitiveness are affected by stress defence under limiting nutrient supply. The hypotheses tested were (1) that nutrient uptake-related parameters (a) as well as efficiencies in nutrient use for above-ground competition (b) of beech rather than spruce are impaired by the exposure to elevated O₃ concentrations, (2) that the efficiency in nutrient uptake of spruce is enhanced by elevated CO₂ concentrations in mixed culture, and (3) that the ability to occupy above-ground space at low nutrient cost is co-determinant for the competitive success in mixed culture. Clear nitrogen deficiencies were indicated for both species during the 2-year phytotron study, although foliar nitrogen-biomass relationships were not so close for spruce than for beech. O₃ stress did not impair nutrient uptake-related parameters of beech; thus hypothesis (1a). was not supported. A negative effect of elevated O₃ (under amb. CO₂) on the N and P based efficiencies in above-ground space occupation (i.e. lower crown volume per unit of N or P invested in stems, limbs and foliage) of beech supported hypothesis (1b). It appeared that ozone stress triggered a nutrient demand for stress defence and tolerance at the expense of above-ground competition (trade-off). Crown volume of beech under O₃ stress was stabilized in monoculture by increased nutrient uptake. In general, the +CO₂-treatment was able to counteract the impacts of 2 × O₃. Elevated CO₂ caused lower N and S concentrations in current-year foliage of both tree species, slightly higher macronutrient amounts in the root biomass of spruce, but did not increase the efficiencies in nutrient uptake of spruce in mixed culture. Therefore hypothesis (2) was not supported. At the end of the experiment spruce turned out to be the stronger competitor in mixed culture as displayed by its higher total shoot biomass and crown volume. The amounts of macronutrients in the above-ground biomass of spruce individuals in mixed culture distinctly exceeded those of beech, which had been strongly reduced by interspecific competition. The superior competitiveness of spruce was related to higher N and P-based efficiencies in above-ground space occupation as suggested in hypothesis (3). This article belongs to the special issue “Growth and defence of Norway spruce and European beech in pure and mixed stands”.     

Positive nitrogen balance of <Emphasis Type="Italic">Acacia mangium</Emphasis> woodlots as fallows in the Philippines based on <Superscript>15</Superscript>N natural abundance data of N<Subscript>2</Subscript> fixation

Nitrogen inputs from biological nitrogen fixation contribute to productivity and sustainability of agroforestry systems but they need to be able to offset export of N when trees are harvested. This study assessed magnitudes of biological nitrogen fixation (natural ¹⁵N abundance) and N balance of Acacia mangium woodlots grown in farmer’s fields, and determined if N₂ fixation capacity was affected by tree age. Tree biomass, standing litter, understory vegetation and soil samplings were conducted in 15 farmer’s fields growing A. mangium as a form of sequential agroforestry in Claveria, Misamis Oriental, Philippines. The trees corresponded to ages of 4, 6, 8, 10 and 12 years, and were replicated three times. Samples from different plant parts and soils (0–100 cm) were collected and analyzed for δ¹⁵N and nutrients. The B-value, needed as a reference of isotopic discrimination when fully reliant on atmospheric N, was generated by growing A. mangium in an N₂-free sand culture in the glasshouse. Isotopic discrimination occurring during N₂ fixation and metabolic processes indicated variation of δ¹⁵N values in the order of nodules > old leaves > young leaves > stems > litterfall and roots of the trees grown in the field, with values ranging from −0.8 to 3.5‰ except nodules which were enriched and significantly different from other plant parts (P < 0.0001). Isotopic discrimination was not affected by tree age (P > 0.05). Plants grown in N free sand culture exhibited the same pattern of isotopic discrimination as plants grown in the field. The estimated B-value for the whole plant of A. mangium was −0.86‰. Mature tree stands of 12 years accumulated up to 1994 kg N ha⁻¹ in aboveground biomass. Average proportion of N derived from N₂ fixation of A. mangium was 54% (±22) and was not affected by age (P > 0.05). Average yearly quantities of N₂ fixed were 128 kg N ha⁻¹ in above-ground biomass amounting to 1208 kg N fixed ha⁻¹ over 12 years. Harvest of 12-year old trees removed approximately 91% of standing aboveground biomass from the site as timber and fuel wood. The resulting net N balance was +151 kg N ha⁻¹ derived from remaining leaves, twigs, standing litter, and +562 kg N ha⁻¹ when tree roots were included in the calculation. The fast growing A. mangium appears to be a viable fallow option for managing N in these systems. However, other nutrients have to be replaced by using part of the timber and fuel wood sales to compensate for large amounts of nutrient removed in order for the system to be sustainable.     

Natural abundance of <Superscript>15</Superscript>N in two cacao plantations with legume and non-legume shade trees

Natural abundance of ¹⁵N was sampled in young and mature leaves, branches, stem, and coarse roots of trees in a cacao (Theobroma cacao) plantation shaded by legume tree Inga edulis and scattered non-legumes, in a cacao plantation with mixed-species shade (legume Gliricidia sepium and several non-legumes), and in a tree hedgerow bordering the plantations in Guácimo, in the humid Caribbean lowlands of Costa Rica. The deviation of the sample ¹⁵N proportion from that of atmosphere (δ¹⁵N) was similar in non-legumes Cordia alliodora, Posoqueria latifolia, Rollinia pittieri, and T. cacao. Deep-rooted Hieronyma alchorneoides had lower δ¹⁵N than other non-N₂-fixers, which probably reflected uptake from a partially different soil N pool. Gliricidia sepium had low δ¹⁵N. Inga edulis had high δ¹⁵N in leaves and branches but low in stem and coarse roots. The percentage of N fixed from atmosphere out of total tree N (%N_f) in G. sepium varied 56–74%; N₂ fixation was more active in July (the rainiest season) than in March (the relatively dry season). The variation of δ¹⁵N between organs in I. edulis was probably associated to ¹⁵N fractionation in leaves. Stem and coarse root δ¹⁵N was assumed to reflect the actual ratio of N₂ fixation to soil N uptake; stem-based estimates of %N_f in I. edulis were 48–63%. Theobroma cacao below I. edulis had lower δ¹⁵N than T. cacao below mixed-species shade, which may indicate direct N transfer from I. edulis to T. cacao but results so far were inconclusive. Further research should address the ¹⁵N fractionation in the studied species for improving the accuracy of the N transfer estimates. The δ¹⁵N appeared to vary according to ecophysiological characteristics of the trees.     

Crop residue effect on crop performance,soil N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions in alley cropping systems in subtropical China

Land management practices that simultaneously improve soil properties are crucial to high crop production and minimize detrimental impact on the environment. We examined the effects of crop residues on crop performance, the fluxes of soil N₂O and CO₂ under wheat-maize (WM) and/or faba bean-maize (FM) rotations in Amorpha fruticosa (A) and Vetiveria zizanioides (V) intercropping systems on a loamy clay soil, in subtropical China. Crop performance, soil N₂O and CO₂ as well as some potential factors such as soil water content, soil carbon, soil nitrogen, microbial biomass and N mineralization were recorded during 2006 maize crop cultivation. Soil N₂O and CO₂ fluxes are determined using a closed-based chamber. Maize yield was greater after faba bean than after wheat may be due to differences in supply of N from residues. The presence of hedgerow significantly improved maize grain yields. N₂O emissions from soils with maize were considerably greater after faba bean (345 g N₂O–N ha⁻¹) than after wheat (289 g N₂O–N ha⁻¹). However, the cumulated N₂O emissions did not differ significantly between WM and FM. The difference in N₂O emissions between WM and FM was mostly due to the amounts of crop residues. Hedgerow alley cropping tended to emit more N₂O than WM and FM, in particular A. fruticosa intercropping systems. Over the entire 118 days of measurement, the N₂O fluxes represented 534 g N₂O–N ha⁻¹ (AWM) and 512 g N₂O–N ha⁻¹ (AFM) under A. fruticosa species, 403 g N₂O–N ha⁻¹ (VWM) and 423 g N₂O–N ha⁻¹ (VFM) under Vetiver grass. We observed significantly higher CO₂ emission in AFM (5,335 kg CO₂–C ha⁻¹) from June to October, whereas no significant difference was observed among WM (3,480 kg CO₂–C ha⁻¹), FM (3,302 kg CO₂–C ha⁻¹), AWM (3,877 kg CO₂–C ha⁻¹), VWM (3,124 kg CO₂–C ha⁻¹) and VFM (3,309 kg CO₂–C ha⁻¹), indicating the importance of A. fruticosa along with faba bean residue on CO₂ fluxes. As a result, crop residues and land conversion from agricultural to agroforestry can, in turn, influence microbial biomass, N mineralization, soil C and N content, which can further alter the magnitude of crop growth, soil N₂O and CO₂ emissions in the present environmental conditions.     

Characterization of sp<Superscript>2</Superscript>- and sp<Superscript>3</Superscript>-bonded carbon in wood charcoal

Japanese cedar (Cryptomeria japonica) preheated at 700°C was subsequently heated to 1800°C and characterized by electron microscopy, X-ray diffraction, and micro-Raman spectroscopy. The degree of disorder of carbon crystallites and the amount of amorphous phase decreased considerably with an increase in heat treatment temperature to 1400°C, while carbon crystallites clearly developed above this temperature, showing that the microstructure of carbonized wood undergoes drastic changes around 1400°C. Besides showing the bands for sp²-bonded carbon, the Raman spectra showed a shoulder near 1100 cm⁻¹ assigned to sp³-bonded carbon. With an increase of heat treatment temperature, the peak position of the Raman sp³ band shifted to a lower frequency from 1190 to 1120 cm⁻¹, which is due to the transformation of sp³-bonded carbon from an amorphous phase to a nanocrystalline phase. These data showed that the microstructure of carbonized wood from 700° to 1800°C consisted of the combination of sp²- and sp³-bonded carbon, which is probably due to the disordered microstructure of carbonized wood. It is suggested that the sp³-bonded carbon is transformed from an amorphous structure to a nanocrystalline structure with the growth of polyaromatic stacks at temperatures above 1400°C.     

Seasonal change in N<Subscript>2</Subscript>O flux from forest soils in a forest catchment in Japan

Temperate forest soils are one source of nitrous oxide (N₂O), which is an important greenhouse gas and the most important ozone-depleting substance. To clarify N₂O flux mechanisms in relation to soil temperature, moisture, and nitrification activity, we measured N₂O fluxes and net nitrification rates over 3 years at the lower (Japanese cedar) and upper (deciduous broad-leaved trees) parts of a hill slope in a small forest catchment in the northern Kanto region of Japan. The N₂O flux was measured by the closed-chamber technique every month, along with soil temperature and water-filled pore space (WFPS). At the lower slope, the N₂O flux increased with increasing soil temperature (r ² = 0.383, P < 0.01) owing to an increase in the nitrification rate. At the upper slope, no positive linear correlation of N₂O flux with soil temperature, WFPS, or nitrification rate was observed. The low N₂O flux at the upper slope during summer was caused by the low summertime WFPS there. We attributed the higher mean N₂O fluxes observed at the lower slope (median 2.36 μg N m⁻² h⁻¹) than at the upper slope (median 1.10 μg N m⁻² h⁻¹) to a high soil moisture during summer season in the surface soil of the lower slope.     

Soil CO<Subscript>2</Subscript> emissions in agricultural watersheds with agroforestry and grass contour buffer strips

The potential for agricultural soils to act as a sink and sequester carbon (C) or a source and emit carbon dioxide (CO₂) is largely dependent upon the agricultural management system. The establishment of permanent vegetation, such as trees and grass contour buffer strips, may cause accumulation of above- and below-ground C over time, thereby acting as a sink for tropospheric CO₂. However, the effects of contour grass strips and grass-tree strips (agroforestry) on soil CO₂ emissions have not been extensively studied in row-crop watersheds in the temperate regions. The objective of this study was to determine the effects of agroforestry and grass contour buffer strips and landscape position on soil surface efflux rate of CO₂ in three adjacent agricultural watersheds with claypan soils in northeast Missouri. The three watersheds were in a corn-soybean rotation, and contained (1) cropped only (CR), (2) cropped with grass contour strips (GR), or (3) cropped with tree-grass contour strips (AF) management systems. Soil surface CO₂ efflux was measured throughout the 2004 growing season at the upper (UBS), middle (MBS), and lower (LBS) backslope landscape positions within the three watersheds. The cumulative soil CO₂ production was lowest in the CR (0.9 kg CO₂-C m⁻²) compared to the AF (1.5 kg CO₂-C m⁻²) and GR watersheds (1.5 kg CO₂-C m⁻²). The lower backslope position (1.6 kg CO₂-C m⁻²) across all three watersheds produced 32 and 40% greater cumulative soil CO₂ than the upper and middle backslope positions, respectively. A 72-day incubation study determined the effects of 40, 60, 80, and 100% soil water-filled pore space (WFPS) and N rate (0 and 1.39 g KNO₃ kg soil⁻¹) on soil CO₂ efflux from bulk soil collected under each management system. The cumulative CO₂ production was highest in the grass soil (1,279 mg CO₂-C kg soil⁻¹) compared to the agroforestry (661 mg CO₂-C kg soil⁻¹) and cropped (483 mg CO₂-C kg soil⁻¹) soils regardless of WFPS and N rate. The highest cumulative CO₂ production for the grass soil (1,279 mg CO₂-C kg soil⁻¹) occurred at 80% WFPS, and was approximately 2 to 2.6 times greater than the agroforestry and cropped soils at 80% WFPS. The results of this study indicate that conservation management practices, such as grass and grass-tree contour buffer strips, and landscape position affect soil surface CO₂ production and accumulation of soil organic C that may influence soil C sequestration.     

Consumption of O<Subscript>2</Subscript>, evolution of CO<Subscript>2</Subscript> and reduction of Cr(VI) during fixation of chromium based wood preservatives in wood

Norway spruce dust was impregnated with aqueous solutions of chromated copper wood preservatives. Immediately after treatment, observation of CO₂ evolution and O₂ consumption were performed. Significant quantities of CO₂ were released during reaction of chromium (K₂Cr₂O₇) containing solutions with wood or brown rotted wood. Nevertheless, during reaction of cellulose with these preservatives we did not observe evolution of CO₂. The presence of copper did not influence on concentration of CO₂. Opposite to CO₂ evolution, treatment of wood and brown rotted wood resulted in O₂ consumption. The oxygen concentration decrease in the measuring chamber was approximately 5 times greater than increase of concentration of carbon dioxide. Electron paramagnetic resonance (EPR) observations of chromium fixation showed that chromium is reduced from Cr(VI) to Cr(III) with Cr(V) as an intermediate on wood, brown rotted wood and cellulose. However, the reduction on wood and brown rotted wood was faster than the reduction on cellulose, as determined from changes of Cr signals in EPR spectra. So, evolution of CO₂ and consumption of O₂ as well as EPR signals of Cr species thus indicate that brown rotted wood, consisting of lignin and hemicelluloses in contact with Cr(VI) reacts more intensively than cellulose, and possibly, oxidation mechanisms of lignin and cellulose with Cr(VI) are different. Received: 20 July 2000     

TCF bleaching of <Emphasis Type="Italic">Populus tomentosa</Emphasis> kraft pulps with H<Subscript>2</Subscript>O<Subscript>2</Subscript> pretreatment under acid condition

The process of peroxide bleaching of Populus tomentosa kraft pulp with H₂O₂ pretreatment under acid condition was studied. The variations of pulp characteristics such as brightness, Kappa number and viscosity during the peroxide bleaching process were discussed and the concept of the A/B value was presented for the first time. The results show that acid pretreatment with H₂O₂ is essential to improve pulp brightness and avoid viscosity loss. The conclusion is reached that the A/B value has great influence on pulp properties when the total amount of peroxide used in the bleaching process is 2%–5%. Pulp with a high viscosity and brightness can be obtained when A/B is about 0.15. [Supported by the National “863” Project (Grant No. 2002AA241071)]     

Impacts of initial stand density and thinning regimes on energy wood production and management-related CO<Subscript>2</Subscript> emissions in boreal ecosystems

An ecosystem model (Sima) was utilised to investigate the impact of forest management (by changing both the initial stand density and basal area thinning thresholds from current recommendations) on energy wood production (at energy wood thinning and final felling) and management-related carbon dioxide (CO₂) emissions for the energy wood production in Finnish boreal conditions (62°39′ N, 29°37′ E). The simultaneous effects of energy wood, timber and C stocks in the forest ecosystem (live and dead biomass) were also assessed. The analyses were carried out at stand level during a rotation period of 80 years for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) growing in different fertility sites. Generally, the results showed that decreased basal area thinning thresholds, compared with current thinning, reduced energy wood (logging residues) and timber production, as well as carbon stocks in the forest ecosystem. Conversely, increased thinning thresholds increased energy wood production (ca. 1–27%) at both energy wood thinning and final felling and reduced CO₂ emissions (ca. 2–6%) related to the production chain (e.g. management operations), depending on the thinning threshold levels, initial stand density, species and site. Increased thinning thresholds also enhanced timber production and carbon stocks in the forest ecosystem. Additionally, increased initial stand density enhanced energy wood production for energy wood thinning for both species, but this reduced energy wood production at final felling for Scots pine and Norway spruce. This study concluded that increases in both initial stand density and thinning thresholds, compared with the current level, could be useful in energy wood, timber and carbon stocks enhancement, as well as reducing management-related CO₂ emissions for energy wood production. Only 2.4–3.3% of input of the produced energy (energy wood) was required during the whole production chain, depending on the management regime, species and sites. However, a comprehensive substitution analysis of wood-based energy, in respect to environmental benefits, would also require the inclusion of CO₂ emissions related to ecosystem processes (e.g. decomposition).     

Removal of Cu<Superscript>2+</Superscript> ions from aqueous solution by amino-functionalized magnetic sawdust composites

In this study, amino-functionalized magnetic γ-Fe₂O₃/sawdust composites (MSC-NH₂) were investigated as biological absorption materials for removing Cu²⁺ ions from aqueous solution. These composites were fabricated by precipitated γ-Fe₂O₃ nanoparticles on sawdust substrate and then functionalized with 1,6-hexanediamine. Characterization of MSC-NH₂ was performed by means of SEM, TEM, XRD, FTIR, BET, MPMS and XPS analysis to discuss the uptake mechanism. As a result, the amino groups are grafted upon the sawdust surfaces. The MSC-NH₂ could be effectively used to remove Cu²⁺ from aqueous solution and be separated conveniently from the solution with the help of an external magnet. Batch experiments show that the adsorption equilibrium is achieved in 150 min, and the adsorption capacity is 7.55 mg/g at pH 6 and room temperature. The isotherm analysis indicates that the sorption data could be represented by Langmuir isotherm models. The kinetics is evaluated utilizing the Lagergren pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models. Thermodynamic parameters reveal the spontaneous, endothermic and chemical nature of adsorption.     

Diversity and spatio-temporal dynamics of dead wood in a temperate near-natural beech forest (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>)

The diversity, spatial patterns and temporal dynamics of dead wood were examined within the near-natural beech forests (Fagus sylvatica) of Serrahn (North-eastern Germany). Data were collected in an 8 ha sample plot and in two permanent plots (0.36 and 0.25 ha) that had been established at the end of the 1960s. The mean volume of dead wood was 94 m³ ha⁻¹, amounting to 14% of the total volume of all trees. The dead wood displayed a large variation in dead wood type, tree size and decay class. Standing dead wood accounted for about one-third of the total dead wood volume. The densities of standing dead trees were about 10% of the densities of the living trees over a wide range of diameters. The overall spatial distribution of dead trees exhibited a random pattern. Among the different dead wood types, standing entire dead trees and uprooted trees deviated from this pattern by displaying a significantly aggregated pattern. In the permanent plots a high mortality of overstorey trees was observed (1.3% year⁻¹) and the average amount of dead wood increased greatly from 2.9 to 111.6 m³ ha⁻¹ over the 35-year observation period. The near-natural beech forests of Serrahn have experienced a long period of low human interference. Nevertheless, our results suggest that the structure and dynamics of dead wood are strongly affected by the last major disturbance events that took place at the end of the Middle Ages. Information about the forest history is therefore a basic requirement when interpreting the results obtained in near-natural forests.     

Branch CO<Subscript>2</Subscript> efflux in vertical profile of Norway spruce tree

Branch CO₂ efflux of Norway spruce tree [Picea abies (L.) Karst.] was measured in ten branches at five different whorls during the growing season 2004 (from June till October) in campaigns of 3–4 times per month at the Beskydy Mts., the Czech Republic. Branch CO₂ efflux was measured using a portable infrared gas analyzer (LI-6250, LI-COR, Inc., USA), operating as a closed system. Branch woody-tissue temperature was measured continuously in 10-min intervals for each sample position during the whole experiment period. On the basis of relation between CO₂ efflux rate and woody-tissue temperature, a value of Q₁₀ and of normalized CO₂ efflux rate (E₁₀–CO₂ efflux rate at 10°C) was calculated for each sampled position. Estimated Q₁₀ values ranged from 2.12 to 2.89, and E₁₀ ranged from 0.41 to 1.19 μmolCO₂m⁻²s⁻¹. Differences in branch CO₂ efflux were found between orientations, east-side branches presented higher efflux rate than west-side branches. The highest branch CO₂ efflux rate values were measured in August and the lowest in October, which corresponds with woody-tissue temperature and growth processes during these periods. Branch CO₂ efflux was significantly and positively correlated with branch position within canopy and woody-tissue temperature. Branches from the upper whorls showed higher CO₂ efflux activity and seasonal dynamics than branches from the lower whorls.     

Effects of Ca^2＋concentrations on accumulations of mineral elements in the components of Pteroceltis tatarinowii

The bark ofPteroceltis tatarinowii is a raw material for manufacturing Xuan Paper. The effects of Ca²⁺ concentrations on the accumulation of mineral elements in the bark, leaf and root ofPteroceltis tatarinowii were studied under controlled conditions. The types of Hoagland nutrient solution with three Ca²⁺ concentrations levels (200, 400 and 600 μg·g⁻¹) and a control (without Ca²⁺ were designed to culturePteroceltis tatarinowii. After 6 months, contents of seven mineral elements including Ca, K, Mg, Mn, Zn, Cu and Na in the root, leaf and bark were analyzed. The results indicated that Ca accumulations content in the root, leaf and bark had positively relation with Ca²⁺ concentrations (200, 400, 600 μg·g⁻¹), and the order of the Ca content in the three components was root>leaf>bark. Ca content in the root treated with 600 μg·g⁻¹ Ca²⁺ concentrations was 5.5 times as high as that of the control, and about 1.4 times as high as that of the root treated in 200 and 400 μg/g Ca²⁺ concentrations respectively. On the contrary, K and Mg contents in the root, leaf and bark were negatively related to Ca²⁺ concentrations, especially in the bark, and their accumulation trend followed the order of leaf>root>bark. K content in the bark treated with 600 μg·g⁻¹ Ca²⁺ concentrations was 39.3% of that of the control, and was 79.0% and 91.8% of that of the bark treated with 200μg·g⁻¹ and 400μg·g⁻¹ Ca²⁺ concentrations respectively; Mg content in the bark treated with 600μg·g⁻¹ Ca²⁺ concentrations was 23.4% of that of the control, and was 27.1% and 35.4% of that of the bark treated with 200 and 400 μg·g⁻¹ Ca²⁺ concentrations respectively. Compared with the control, the general tendency of Mn, Zn and Cu content decreased with increasing of Ca²⁺ concentrations and their contents were in the order: root>leaf>bark. Based on the results of this study, the experiment has been useful for providing academic bases in improving the bark quality ofPteroceltis tatarinowii on non-limestone soil. Foundation item: This paper is supported by National Natural Science Foundation of China (No. 39970608). Biography: Fang Shengzun (1963), male, Professor in Stiiviculture, Nanjing Forestry University, Nanjing 210027, P.R. China. Responsible editor: Zhu Hong     

Gas exchange responses of <Emphasis Type="Italic">Eucalyptus</Emphasis>, <Emphasis Type="Italic">C. africana</Emphasis> and <Emphasis Type="Italic">G. robusta</Emphasis> to varying soil moisture content in semi-arid (Thika) Kenya

A dramatic decline in forest cover in eastern Africa along with a growing population means that timber and poles for building and fuelwood are in short supply. To overcome this shortage, the region is increasingly turning to eucalyptus. But eucalyptus raises environmental concerns of its own. Fears that it will deplete water supply, affect wildlife and reduce associated crop yields have caused many countries in the region to discourage farmers from planting this exotic. This paper is part of a series of investigations on the growth and water use efficiency of faster growing eucalyptus hybrids, which was introduced from South Africa to Kenya. The hypothesis is that the new hybrids are more efficient in using water and more suitable for the semi-arid tropics than existing eucalyptus and two popular agroforestry species. Gas exchange characteristics of juvenile Eucalyptus grandis (W. Hill ex Maiden), two eucalyptus hybrids (E. grandis × Eucalyptus camaldulensis Dehnh.), Grevillea robusta (A. Cunn) and Cordia africana (Lam) was studied under field and pot conditions using an infrared gas analyzer was used to measure photosynthetic active radiation (PAR), net photosynthetic rate (A), stomatal conductance (g _s) and transpiration rate (E) at CO₂ concentrations of 360 μmol mol⁻¹ and ambient humidity and temperature. A, E and g _s varied between species, being highest in eucalyptus hybrid GC 15 (24.6 μmol m⁻² s⁻¹) compared to eucalyptus hybrid GC 584 (21.0 μmol m⁻² s⁻¹), E. grandis (19.2 μmol m⁻² s⁻¹), C. africana (17.7 μmol m⁻² s⁻¹) and G. robusta (11.1 μmol m⁻² s⁻¹). C. africana exhibited high E values (7.0 mmol m⁻² s⁻¹) at optimal soil moisture contents than G. robusta (3.9 mmol m⁻² s⁻¹) and eucalyptus (5.3 mmol m⁻² s⁻¹) in field experiment and G. robusta (3.2 mmol m⁻² s⁻¹) and eucalyptus (4.2 mmol m⁻² s⁻¹) in pot-grown trees. At very low soil moisture content, extremely small g _s values were recorded in GC 15 and E. grandis (8 mmol m⁻² s⁻¹) and G. robusta (14 mmol m⁻² s⁻¹) compared to GC 584 (46.9 mmol m⁻² s⁻¹) and C. africana (90.0 mmol m⁻² s⁻¹) indicating strong stomatal control by the species. Instantaneous water use efficiency ranged between 3 and 5 μmol mmol⁻¹ and generally decreased with decline in soil moisture in pot-grown trees but increased with declining soil moisture in field-grown trees.     

Partial characterization of stress-induced carboxylesterase from adults of <Emphasis Type="Italic">Stegobium paniceum</Emphasis> and <Emphasis Type="Italic">Lasioderma serricorne</Emphasis> (Coleoptera: Anobiidae) subjected to CO<Subscript>2</Subscript>-enriched atmosphere

The kinetics effects of carbon dioxide enriched atmosphere on carboxylesterase (CarE) activity from Stegobium paniceum and Lasioderma serricorne were comparatively investigated here. The results showed that L. serricorne had significantly greater specific activity of CarE than S. paniceum [0.399 vs. 0.358 mmol (min mg)⁻¹]. Moreover, CarE of L. serricorne expressed a higher affinity (i.e. lower K _m value) to the substrate α-naphthyl acetate than S. paniceum (0.1 vs. 0.8 mM). The in vitro kinetics of CarE showed that there were no significant effects of controlled atmosphere on the affinity of carboxylexterase to α-naphthyl acetate for both pests besides increased of V _max values. Such result draws attention to the higher tolerance of L. serricorne to CO₂-enriched atmosphere and the necessary care required for managing this species with such a control tactic. The information also suggests a potential effect of esterases in mitigating the toxic effect of controlled atmosphere in insect pest species.     

Insecticidal efficacy of <Emphasis Type="Italic">Isaria farinosa</Emphasis> in different life stages of <Emphasis Type="Italic">Pissodes punctatus</Emphasis> (Coleoptera: Curculionidae)

The insecticidal activity of an entomopathogenic fungus, Isaria farinosa on pine bark-weevil (Pissodes punctatus) at different life stages underwent laboratory testing. Larvae, pupae and adults of Pissodes punctatus were exposed to a range of concentrations of fungal conidia in suspension for 5 s; mean mortality and LC₅₀ values were calculated. The results showed I. farinosa can effectively infect larvae, pupae and adult pine bark-weevils, and the highest mean mortalities at each life stage can exceed 88%. The mean mortalities increased with higher concentrations of I. farinosa. Larvae were most susceptible with LC₅₀ 1.2 × 10⁶ conidia ml⁻¹ (15 days), pupae (30 days) exhibited the second largest effects, and adults (15 days) with LC₅₀ 1.72 × 10⁶ and 1.99 × 10⁶ conidia ml⁻¹, respectively, at end of the experiments. This suggests that I. farinosa could be a potential bio-control agent against the pine bark-weevil.     

Seasonal variations in stem CO<Subscript>2</Subscript> efflux in the Neotropical rainforest of French Guiana

• Introduction  

Stem CO₂ efflux (E _s) is a significant component of total ecosystem respiration, but there is only scant information on seasonal variations in E _s in tropical rainforests and on the main factors explaining these variations.     

在长白山生态系统中长期的高浓度CO2熏蒸对土壤酶的影响

从1999年到2006年在中科院长白山森林生态系统定位站（42°24＇N,128°28＇E,海拔738m）对长期高浓度CO2熏蒸对土壤酶活性的影响进行了研究.采用开顶箱（OTC）的方式对红松和长白松进行高浓度CO2处理, CO2浓度分别受控于高浓度CO2箱（500 μmol·mol^-1）、对照箱（370 μmol·mol^-1））和裸地（370 μmol·mol^-1）.经高浓度CO2（500 μmol·mol^-1）熏蒸8年后,土壤样品分别在2006年春季、夏季和秋季进行采集和分析.结果表明：在高CO2浓度（500 μmol mol^-1）条件下,转化酶活性除了红松夏季样品之外都是显著降低的;而脱氢酶活性却是增加的,但只有部分结果显著;长白松的多酚氧化酶活性都显著降低;过氧化氢酶活性在春季增加,而在其他季节均降低.总而言之,在高CO2浓度条件下,土壤酶的活性与树种有关.     

Screening for condensed tannin-degrading fungi with a synthetic <Superscript>14</Superscript>C-labeled compound

To find fungi that are potent for degradation of condensed tannin, a two-step screening was used. This involved measurement of fungal growth rate on Japanese cedar (Cryptomeria japonica) bark, followed by determination of [¹⁴C]-labeled CO₂ generated from fungal degradation of synthetic [¹⁴C]-labeled condensed tannin model. In the first screening, 75 strains of wood rot fungi were tested, and 19 strains effectively decreased bark weight and/or the weight of the methanol-soluble fraction. For the second screening, [¹⁴C]-labeled condensed tannin model compound was synthesized in 11.8% yield based on radioactivity measurements. Over the incubation period, Coriolus hirsutus K-2671, Lentinus edodes Is, and Lampteromyces japonicus Nn showed higher cumulative [¹⁴C]-labeled CO₂ emissions than the other strains and mineralized the [¹⁴C]-labeled condensed tannin model compound by 3.7%, 3.0%, and 3.0%, respectively. Fractionation of the methanol extracts from the medium by gel permeation chromatography after fungal treatment suggested that fungi that can induce the emission of significant levels of [¹⁴C]-labeled CO₂ can extensively depolymerize condensed tannins.