Allometric Biomass,Biomass Expansion Factor and Wood Density Models for the OP42 Hybrid Poplar in Southern Scandinavia

Biomass and biomass expansion factor functions are important in wood resource assessment, especially with regards to bioenergy feedstocks and carbon pools. We sampled 48 poplar trees in seven stands with the purpose of estimating allometric models for predicting biomass of individual tree components, stem-to-aboveground biomass expansion factors (BEF) and stem basic densities of the OP42 hybrid poplar clone in southern Scandinavia. Stand age ranged from 3 to 31 years, individual tree diameter at breast height (dbh) from 1.2 to 41 cm and aboveground tree biomass from 0.39 to 670 kg. Models for predicting total aboveground leafless, stem and branch biomass included dbh and tree height as predictor variables and explained more than 97 % of the total variation. The BEF was approaching 2.0 for the smallest trees but declined with increasing tree size and stabilized around 1.2 for trees with dbh >10 cm. Average stem basic density was more than 400 kg m^?3 for the smallest trees but declined with increasing tree height and stabilized around 355 kg m^?3, at a tree height of about 20 m. Existing biomass functions from the literature all underestimated the measured sample tree biomass. Possible explanations include not only differences in competition among trees in the examined stands and site conditions but also differences in sampling procedures. We observed that basic density increased with height above the ground. This trend may have led to the observed underestimation by existing biomass functions including only few samples from the lower end of the stems.     

Root biomass distribution and soil properties of an open woodland on a duplex soil

Data on the distribution of root biomass are critical to understanding the ecophysiology of vegetation communities. This is particularly true when models are applied to describe ecohydrology and vegetation function. However, there is a paucity of such information across continental Australia. We quantified vertical and horizontal root biomass distribution in a woodland dominated by Angophora bakeri and Eucalyptus sclerophylla on the Cumberland Plains near Richmond, New South Wales. The site was characterised by a duplex (texture contrast) soil with the A horizon (to 70 cm) consisting of loamy sand and the B horizon (to > 10 m) consisting of sandy clay. The topsoil had a smaller bulk density, a smaller water holding capacity but a larger organic component and a larger hydraulic conductivity in comparison to the subsoil. Root biomass was sampled to 1.5 m depth and declined through the soil profile. Whilst total biomass in the B horizon was relatively small, its contribution to the function of the trees was highly significant. Coarse roots accounted for approximately 82% of the root mass recovered. Lateral distribution of fine roots was generally even but coarse roots were more likely to occur closer to tree stems. Variation in tree diameter explained 75% of the variation in total below-ground biomass. The trench method suggested the belowground biomass was 6.03?±?1.21 kg m^?2 but this method created bias towards sampling close to tree stems. We found that approximately 68% of root material was within a 2 m radius of tree stems and this made up 54% of the total number of samples but in reality, only approximately 5 to 10% of the site is within a 2 m radius of tree stems. Based on these proportions, our recalculated belowground biomass was 2.93?±?0.59 kg m^?2. These measurements provide valuable data for modeling of ecosystem water use and productivity.     

Tree Species Composition, Structure, and Aboveground Wood Biomass of a Riparian Forest of the Lower Miranda River, Southern Pantanal, Brazil

The aboveground wood biomass (AWB) of tropical forests plays an important role in the global carbon cycle, and local AWB estimates provide essential data that enable the extrapolation of biomass stocks to ecosystem or biome-wide carbon cycle modelling. Few AWB estimates exist in Neotropical freshwater floodplains, where tree species distribution and forest structure depend on the height and duration of periodic inundations. We investigated tree species composition, forest structure, wood specific gravity, and AWB of trees ≥10 cm dbh in 16 plots totalling an area of 1 ha in a seasonally inundated riparian forest of the lower Miranda River, southern Pantanal, Brazil. The 443 tree individuals belonged to 46 species. Four species (Inga vera, Ocotea suaveolens, Tabebuia heptaphylla and Cecropia pachystachya) comprised more than 50% of the Total Importance Values (TIV), and floristic similarities between the plots averaged 38%. Although we detected an overall increase in species diversity correlated with decreasing flood levels, the most important tree species had almost identical distribution patterns along the flooding gradient. The stand basal area per plot (±?s.d.) amounted to 3.0?±?1.1 m² (47.8?±?18.1 m²/ha), and the tree heights averaged 10.9?±?1.4 m. Multiplying the individual basal areas by individual tree heights and a form factor of 0.6, we estimated the aboveground wood volume (AWV) for each individual, and for each plot (24.4?±?11.7 m³, 391.1?±?188 m³/ha). Wood specific gravity (SG) varied between 0.39 g/cm³ (Cecropia pachystachya) and 0.87 g/cm³ (Tabebuia heptaphylla), with a stand level average of 0.63?±?0.12 g/cm³. Multiplying the individual AWV with species SG, we estimated the plot AWB to be 16.2?±?6.4 Mg (259.4?±?102 Mg/ha). This value is comparable to that reported for late-successional forest stands of Amazonian floodplain forests, and it is close to the worldwide tropical average AWB. Because tree heights in the present forest were comparatively low when compared to other Neotropical forests, we found that resprouting of stems accounted for comparatively high basal areas. We argue that stem resprouting is an adaptation of tree species originating in non-flooded Cerrado to the seasonal inundations of riparian forests.     

Coarse root biomass for eucalypt plantations in Tasmania,Australia: sources of variation and methods for assessment

This study develops a feasible method for evaluating coarse root biomass (roots >2 mm diameter) of well established plantations of eucalypts and then examines coarse root biomass variability across tree age and size, fertilization treatment, species and site for Eucalyptus globulus and E. nitens in Tasmania, Australia. The most efficient sampling protocol consisted of rootball excavation and soil coring for bulk coarse roots, which when compared with total tree excavation estimated total coarse root biomass contained inside the sampled area to within 10%. Across all treatments, an average of 76% of the coarse root biomass was located within the rootball. The majority (>65%) of the coarse roots outside the rootball were located in the surface 20 cm of soil. When size class distribution was examined, 75% of coarse root biomass was found to occur in the larger (20+ mm) diameter size class, a size class that displayed considerable spatial heterogeneity. At the stand level, coarse root biomass ranged from 2.18 to 7.38 kg m ^-2 depending primarily on tree size but also on fertilization treatment, species and site. It is estimated that allocation to coarse root biomass production was around 0.2 kg m ^-2 year ^-1 (around 6% of estimated NPP) for the E. nitens stands examined in this study and around 1 kg m ^-2 year ^-1 (around 20% of estimated NPP) for the E. globulus stand examined. Robust relationships using above-ground parameters could be used to predict coarse root biomass regardless of fertilization or site, but species changed the relationship.     

Soil nutrients affect spatial patterns of aboveground biomass and emergent tree density in southwestern Borneo

Studies on the relationship between soil fertility and aboveground biomass in lowland tropical forests have yielded conflicting results, reporting positive, negative and no effect of soil nutrients on aboveground biomass. Here, we quantify the impact of soil variation on the stand structure of mature Bornean forest throughout a lowland watershed (8–196 m a.s.l.) with uniform climate and heterogeneous soils. Categorical and bivariate methods were used to quantify the effects of (1) parent material differing in nutrient content (alluvium > sedimentary > granite) and (2) 27 soil parameters on tree density, size distribution, basal area and aboveground biomass. Trees ≥10 cm (diameter at breast height, dbh) were enumerated in 30 (0.16 ha) plots (sample area = 4.8 ha). Six soil samples (0–20 cm) per plot were analyzed for physiochemical properties. Aboveground biomass was estimated using allometric equations. Across all plots, stem density averaged 521 ± 13 stems ha⁻¹, basal area 39.6 ± 1.4 m² ha⁻¹ and aboveground biomass 518 ± 28 Mg ha⁻¹ (mean ± SE). Adjusted forest-wide aboveground biomass to account for apparent overestimation of large tree density (based on 69 0.3-ha transects; sample area = 20.7 ha) was 430 ± 25 Mg ha⁻¹. Stand structure did not vary significantly among substrates, but it did show a clear trend toward larger stature on nutrient-rich alluvium, with a higher density and larger maximum size of emergent trees. Across all plots, surface soil phosphorus (P), potassium, magnesium and percentage sand content were significantly related to stem density and/or aboveground biomass (R _Pearson = 0.368–0.416). In multiple linear regression, extractable P and percentage sand combined explained 31% of the aboveground biomass variance. Regression analyses on size classes showed that the abundance of emergent trees >120 cm dbh was positively related to soil P and exchangeable bases, whereas trees 60–90 cm dbh were negatively related to these factors. Soil fertility thus had a significant effect on both total aboveground biomass and its distribution among size classes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Phosphatase and phytase activities in nodules of common bean genotypes at different levels of phosphorus supply

Plants grown at limited P supply can increase the activity of phosphatases in roots to hydrolyse organic-P compounds in the soil thus improving plant P acquisition, but little information is available about the role of these enzymes for internal plant metabolism at limited-P conditions. This work intended to measure the activities of acid phosphatases and phytases in nodules of common bean (Phaseolus vulgaris) genotypes at different levels of P supply. The experiment was carried out in a 5?×?5 factorial design with four replicates, comprising five bean genotypes and five P levels (20, 40, 80, 160 and 320 μmol P plant^?1 week^?1) in nutrient solution. Root seedlings were inoculated with Rhizobium tropici and plants were grown in 1-l bottles. Nodule samples were detached from 39-day-old plants and enzyme activities were determined in crude extracts. Plants were harvested at the stage of pod setting. Polynomial models fitted to data indicated maximal values at the level of 194 μmol P for shoot mass, at 206 μmol P for nodule mass and at 221 μmol P for shoot N. Whereas shoot mass was 1.7 times lower at 20 than at 160 μmol P, nodule mass was 7.5 times lower. Concentration of P in nodules increased from 40 to 320 μmol P but remained stable between 20 and 40 μmol P, suggesting a minimal threshold concentration of 3 mg P g^?1 for nodule growth. Activities of phosphatases and phytases in nodules decreased strongly as P supply was raised from 20 to 80 μmol P, remaining almost stable at higher P levels. Phosphatase activity ranged from 1,154 to 406 nmol min^?1 g^?1 (nodule fresh mass) from 20 to 80 μmol P respectively, while the phytase activity ranged from 55 to 14 nmol min^?1 g^?1 from 20 to 80 μmol P. Bean genotypes differed in shoot and nodule mass at the levels of 80 and 160 μmol P, whilst they differed in nodule enzyme activities only at the lowest P level, the relationship between nodule enzyme activities and growth of different bean genotypes was not evident. It is concluded that bean plants at P-deficient conditions increase the activities of phosphatases and phytases in nodules. This may constitute an adaptive mechanism for N₂-fixing legumes to tolerate P deficiency, by increasing the utilisation of the scarce P within the nodules.     

Ratios of carbon mass in nodules to other plant tissues in chickpea

A quantitative measurement of the mass and carbon (C) of nodules in legume crops will provide more accurate estimate of total C entering to the soil. This study quantified the ratios of C in roots and nodules in relation to above-ground plant tissue (AG) for chickpea (Cicer arietinum L.). The cultivars ‘CDC-Anna’ and ‘CDC-Frontier’ were grown in continuously-cropped no-till wheat stubble and conventionally-tilled summer fallow systems under three rates (0, 28 and 84 kg N ha^?1) of N fertilizers in Swift Current and Shaunavon, Saskatchewan, Canada, in 2004, 2005 and 2006. The AG biomass ranged between 4,680 and 7,250 kg ha^?1 and increased with the application of N fertilizer ≥28 kg N ha^?1. The nodule mass measured at the early flowering stage ranged between 143 and 355 kg ha^?1, accounting for 2 to 6% of the total AG biomass. Nodule mass decreased significantly from the early flowering to the late-flowering stages (3 wk between). The C value averaged from 1,970 to 2,640 kg ha^?1 in the AG parts, 866 to 1,161 kg ha^?1 in roots and 82 to 184 kg ha^?1 in nodules. The C value in the nodules was 32% greater for chickpea grown in the no-till system than in the tilled-fallow system. CDC-Frontier had 34% greater C value in AG and roots, and 76% greater in nodules than CDC-Anna. Below-ground C (roots plus nodules) accounted for 50% that of the AG tissue at N?=?0 kg ha^?1, and decreased to 45% as N increased to 84 kg ha^?1. At N?=?0 kg ha^?1, the C allocation among plant parts was in the ratio of 67: 29: 4, respectively, in the above-ground tissues: roots: nodules; at N?=?84 kg ha^?1, this ratio was shifted to 69: 30: 1. The quantitative C allocation coefficients can be of great value to modellers in estimating total C contribution to the soil by annual legumes.     

Composition, Stand Structure, and Biomass Estimates of “Willow Rings” on the Canadian Prairies

Many small wetlands are scattered across the Canadian Prairies. These wetlands are often surrounded by a ring of phreatophytic shrubs, of which willows are the dominant genus. Even though many of these willow rings are currently degraded, due to the lack of disturbance factors such as prairie wild fires and bison herds, they are still of great value as a biomass resource without carbon debt. Our study had the objectives to (1) study the distribution of five native willows (Salix bebbiana, Salix discolor, Salix eriocephala, Salix interior, and Salix petiolaris) in 12 willow wetland communities in relation to a moisture gradient and (2)examine the effects of age of the willow ring on biomass potential, stand structure, and species distribution. Annual biomass production ranged from 1.9 to 16.2 odt ha^?1 year^?1 for the 12 sites that were between 9 and 34 years old. Current standing biomass for the 12 willow rings with a total area of 1.5 ha was estimated at 239.2 odt. With age, stand structure changed from multiple small-diameter stems to fewer large-diameter stems, and at the same time the species distribution shifted from one dominated by S. petiolaris to one being dominated by S. discolor. Additionally, the sympatric willows showed a distribution along a moisture gradient, with S. eriocephala, S. interior, and S. petiolaris in moist locations and S. bebbiana and S. discolor in drier locations.     

Growth and N2 fixation in an Alnus hirsuta (Turcz.) var. sibirica stand in Japan

To estimate the N₂ fixation ability of the alder (Alnus hirsuta (Turcz.) var. sibirica), we examined the seasonal variation in nitrogenase activity of nodules using the acetylene reduction method in an 18-year-old stand naturally regenerated after disturbance by road construction in Japan. To evaluate the contribution of N₂ fixation to the nitrogen (N) economy in this alder stand, we also measured the phenology of the alder, the litterfall, the decomposition rate of the leaf litter, and N accumulation in the soil. The acetylene reduction activity per unit nodule mass (ARA) under field conditions appeared after bud break, peaked the maximum in midsummer after full expansion of the leaves, and disappeared after all leaves had fallen. There was no consistent correlation between ARA and tree size (dbh). The amount of N₂ fixed in this alder stand was estimated at 56.4 kg ha^?1 year^?1 when a theoretical molar ratio of 3 was used to convert the amount of reduced acetylene to the amount of fixed N₂. This amount of N₂ fixation corresponded to the 66.4% of N in the leaf litter produced in a year. These results suggested that N₂ fixation still contributed to the large portion of N economy in this alder stand.     

Structural relationships between form factor,wood density,and biomass in African savanna woodlands

Key message

Variation in tree biomass among African savanna species of equal size is driven by a wide inter-specific variation in wood specific gravity.

Abstract

Tree form and taper is a fundamental component of tree structure and has been used for over a century in forestry to estimate timber yields and in ecological theories of scaling laws. Here, we investigate variation in form factor in the context of biomass in African savannas. Biomass is a fundamental metric of vegetation state, yet in African savannas it remains unclear whether variation in form factor F (taper) or wood specific gravity (G) is a more dominant driver of biomass differences between tree species of equal stem diameter and height. Improving our knowledge of vertical mass distribution in savanna trees provides insight into differences in life strategies, such as tradeoffs between production, disturbance avoidance, and water storage. Here, we destructively harvested 782 stems in a savanna woodland near Kruger National Park, South Africa, and measured whole tree wet mass, wood specific gravity, water content, and form factor. We found that three of four dominant species can vary in mass by over twofold, yet inter-specific variation in taper was low and taper did not vary significantly between common species (P > 0.05) (species-mean form factors ranged from F = 0.57 to 0.77, where cone F =  $0.\bar{3}$ , quadratic paraboloid F = 0.5, cylinder F = 1.0). Comparison of a general biomass allometry model to species-specific models supported the conclusion that the large difference in biomass between species of the same size was explained almost entirely (R ² = 0.97) by including species-mean G with D and H in a general allometric equation, where F was constant. Our results suggest that inter-specific variation in wood density, not form factor, is the primary driver of biomass differences between species of the same size. We also determined that a simple analytical volume-filling model accurately relates wood specific gravity of these species to their water and gas content (R ² = 0.68). These results indicate which species use a wide spectrum of water storage strategies in savanna woodlands, adhering to a trade-off between the benefits of denser wood or increased water storage.     

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Abstract

Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m^?2, and that of spruce and pine 297 g m^?2 and 277 g m^?2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.     

Interactive effects of elevated CO2, phosphorus deficiency, and soil drought on nodulation and nitrogenase activity in Alnus hirsuta and Alnus maximowiczii

We examined the interactive effects of elevated CO₂, soil phosphorus (P) availability, and soil drought on nodulation, nitrogenase activity, and biomass allocation in Alnus hirsuta and Alnus maximowiczii. Potted seedlings were grown in either ambient or elevated CO₂ (36 Pa and 72 Pa CO₂), with different levels of P (7.7 and 0.77 mgP pot^?1 week^?1 for high-P and low-P, respectively) and water supply in a natural daylight phytotron. Measurements of nitrogenase activity by an acetylene reduction assay failed to reveal significant effects of the treatments in any species. In high-P, nodule biomass increased under elevated CO₂ and decreased under drought. In low-P, nodule biomass decreased substantially compared to high-P, but the effect of elevated CO₂ on nodule biomass was unclear. Soil drought increased the partitioning of biomass into nodules, especially in A. hirsuta. These results suggest that with high P availability, elevated CO₂ could promote N₂ fixation by increasing nodule biomass even under drought. On the other hand, if soil P is limiting, elevated CO₂ may not enhance N₂ fixation because of the suppression of growth.     

Patterns of wood carbon dioxide efflux across a 2,000-m elevation transect in an Andean moist forest

During a 1-year measurement period, we recorded the CO₂ efflux from stems (R _S) and coarse woody roots (R _R) of 13–20 common tree species at three study sites at 1,050, 1,890 and 3,050 m a.s.l. in an Andean moist forest. The objective of this work was to study elevation changes of woody tissue CO₂ efflux and the relationship to climate variation, site characteristics and growth. Furthermore, we aim to provide insights into important respiration–productivity relationships of a little studied tropical vegetation type. We expected R _S and R _R to vary with dry and humid season conditions. We further expected R _S to vary more than R _R due to a more stable soil than air temperature regime. Seasonal variation in woody tissue CO₂ efflux was indeed mainly attributable to stems. At the same time, temperature played only a small role in triggering variations in R _S. At stand level, the ratio of C release (g C m^?2 ground area year^?1) between stems and roots varied from 4:1 at 1,050 m to 1:1 at 3,050 m, indicating the increasing prevalence of root activity at high elevations. The fraction of growth respiration from total respiration varied between 10 (3,050 m) and 14% (1,050 m) for stems and between 5 (1,050 m) and 30% (3,050 m) for roots. Our results show that respiratory activity and hence productivity is not driven by low temperatures towards higher elevations in this tropical montane forest. We suggest that future studies should examine the limitation of carbohydrate supply from leaves as a driver for the changes in respiratory activity with elevation.     

Community dynamics of Ogawa Forest Reserve,a species rich deciduous forest,central Japan

Forest community dynamics were studied for 4 years in a 6 ha permanent plot of species rich, old-growth, temperate deciduous forest in Ogawa Forest Reserve, central Japan. The gap formation rate, recruitment, mortality, gain and loss rate in basal area during 4 years were 42 m2 ha^–1 yr^–1, 1.74% yr^–1, 1.19% yr^–1, 1.12% yr^–1 and 0.88% yr^–1, respectively. The turnover time calculated from them ranged from 58 to 240 years. Both the mortality and mortality factors were size dependent; trees in middle size class had smallest mortality, and the proportion of the trees killed by disturbances increased with size. Gap creations were concentrated in a particular year, suggesting a large heterogeneity in time. Spatial distribution of recruited trees were biassed to the old gaps (older than 4 years), especially that of the species with Bell-shaped dbh distribution (shade intolerant) strongly associated with the gaps. Recruitment in tree stems and the loss of basal area, thus had the larger variability than mortality of stems and this forest, and the species with L-shaped dbh distribution seemed to going to increase the importance in the future if the present trend continues to be held. The turnover time of population is positively correlated with the maximum dbh size of the species, indicating the slow change of the population of large sized species.     

Allometric equations to predict the total aboveground biomass of tree species in a planted forest in Egypt

The aim of this study is to estimate the total above‐ground biomass (TAGB), stem height (H), diameter at breast height (dbh) and basal area of five tree species (ages 7‐8 years) irrigated by municipal sewage water in the Egyptian‐Chinese friendship forest, Sadat City, Egypt. From the biomass data that obtained through destructive sampling, models for predicting aboveground biomass were developed. The highest values for stem density and height were estimated for Eucalyptus citriodora, while the lowest value for density was obtained for Dalbergia sissoo and stem height for Khaya senegalensis. The highest values for basal area and dbh were obtained for Casuarina spp., while the lowest values were recorded for Dalbergia sissoo. Eucalyptus camaldulensis had the highest stand stem biomass and TAGB (55.5, 83.9 t DW ha^‐1, respectively). In addition, Casuarina spp. had the highest leafy branches biomass (32.5 t DW ha^‐1) while Dalbergia sissoo had the lowest values for all tree components. All the generated allometric equations had high correlation coefficients at high probability levels. Moreover, the results revealed that not only the dbh data can be used as independent variable for biomass determination, but also stem height and size index are recommended for biomass estimation (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Allometric estimation of the above-ground biomass components of Alnus incana (L.) Moench used for landslide stabilisation at Bad Goisern (Austria)

Biomass analyses were conducted to evaluate the growth performance of an Alnus incana (L.) Moench stand established for the restoration of a land slide site. The study aimed to pioneer the quantification of biomass accumulation of alders which were planted for soil bioengineering and stabilisation purposes under extreme soil conditions. For above-ground phytomass estimation, allometric functions on a tree component level were created using linear regression analyses after ln-transformation. Based on D₁₃₀-D₁₀-relations D₁₀-data were applied for function derivation. Best fits were computed using ln-transformed D₁₀ and height data. At 7,023 stems ha^?1 (all trees >20 cm height), the total stand biomass added up to 18,000 kg ha^?1, had an LAI of 1.5 and indicated a high productivity even under unfavourable soil conditions. In the light of the results, grey alders appear to be highly valuable for growing on slide prone sites, indicating that they also exert a positive influence on the soil water regime and thus on slope stability.     

Impact of arbuscular mycorrhizal fungi (AMF) and atmospheric CO2 concentration on the biomass production and partitioning in the forage legume alfalfa

The influence of mycorrhizal symbiosis, atmospheric CO₂ concentration and the interaction between both factors on biomass production and partitioning were assessed in nodulated alfalfa (Medicago sativa L.) associated or not with arbuscular mycorrhizal fungi (AMF) and grown in greenhouse at either ambient (392 μmol?mol^?1) or elevated (700 μmol?mol^?1) CO₂ air concentrations. Measurements were performed at three stages of the vegetative period of plants. Shoot and root biomass achieved by plants at the end of their vegetative period were highly correlated to the photosynthetic rates reached at earlier stages, and there was a significant relationship between CO₂ exchange rates and total nodule biomass per plant. In non-mycorrhizal alfalfa, the production of leaves, stems and nodules biomass significantly increased when plants had been exposed to elevated CO₂ concentration in the atmosphere for 4 weeks. Regardless CO₂ concentration at which alfalfa were cultivated, mycorrhizal symbiosis improved photosynthetic rates and growth of alfalfa at early stages of the vegetative period and then photosynthesis decreased, which suggests that AMF shortened the vegetative period of the host plants. At final stages of the vegetative period, AMF enhanced both area and biomass of leaves as well as the leaves to stems ratio when alfalfa plants were cultivated at ambient CO₂. The interaction of AMF with elevated CO₂ improved root biomass and slightly increased the leaves to stems ratio at the end of the vegetative growth. Therefore, AMF may favor both the forage quality of alfalfa when grown at ambient CO₂ and its perennity for next cutting regrowth cycle when grown under elevated CO₂. Nevertheless, this hypothesis needs to be checked under natural conditions in field.     

Population structure and dynamics oi Juniperus excelsa in Balouchistan,Pakistan

Abstract. 60 monospecific stands of Juniperus excelsa were sampled at four locations in Balouchistan. Density, basal area and height of individuals were recorded. Soils were analysed for selected physical and chemical characteristics and the degree of disturbance due to logging and burning was noted. The density of juniper trees (> 6 cm dbh) ranged from 56 to 332 stems / ha (average 174 stems / ha). Higher densities were recorded for relatively undisturbed stands and on west facing slopes. Density of seedlings and saplings (< 6 cm dbh) was strongly correlated with tree density and tree basal area. Among the edaphic variables CaC0₃ was correlated with juniper density and basal area. Diameter distributions within stands were mostly skewed and unimodal with gaps appearing in large size classes. The male to female ratio was close to 1. Cross-sections of 16 trees were used to determine age and growth rate. Number of rings in trees with 20 to 30 cm dbh ranged from 95 to 221 (x = 160 ± 38). Diameter and age were not related. Mean annual diameter increment ranged from 6 to 16 yr / cm x = 10 ± 3 yr / cm). It is concluded that size class gaps and low seedling / sapling densities are the consequence of anthropogenic disturbance.     

Remote sensing of phytoplankton-macrophyte coexistence in shallow hypereutrophic fluvial lakes

We investigated with remote sensing (APEX images) the coexistence of phytoplankton and macrophytes in three interconnected shallow and hypereutrophic fluvial lakes (Mantua Lakes, Northern Italy). High concentrations of chlorophyll-a, up to 60 mg m^?3, were determined in the open water between well-developed stands of floating-leaved, submerged, and emergent macrophytes. Our data suggest a general inhibition of phytoplankton by macrophytes, evidenced by decreasing chlorophyll-a concentrations in proximity of macrophyte stands. Chlorophyll-a concentrations halved in the proximity of emergent stands (~6 mg m^?3 within 21 m from the stand border) when compared to the outer zones (~13 mg m^?3). Contrasting trends were observed for submerged stands, where concentrations decreased inwards from ~8 to ~3 mg m^?3. Floating leaved stands had a neutral effect, chlorophyll-a being nearly constant in both inner and outer zones. Overall, remotely-sensed data allow evaluation of quantitative and spatially defined interactions of macrophytes and phytoplankton at the whole ecosystem scale.