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1.
CO2 concentrations in different plant communities (larch, birch, lilac, and grassland) were measured during the growing season in the Heilongjiang Forest Botanical Garden to study diurnal variation, seasonal and annual dynamics and factors that impact CO2 concentration in different spaces. CO2 concentration in different communities in green lands had an obvious diurnal variation, chronically decreasing, and temperature influenced the lilac area and the grassland. Seasonally, CO2 was lowest in the larch green land (344.03 ± 23.03 μmol/mol) and highest in the grassland (360.13 ± 22.43 μmol/mol). The overall trend in CO2 concentration was autumn > spring > summer; temperature is the main factor controlling variation in CO2 concentrations during the growing season; the CO2 concentration at the larch, birch, lilac, and grassland types of sites was negatively correlated with land surface temperature and air temperature, and the CO2 concentration at the larch and birch sites was positively correlated with atmospheric pressure. Without any obvious annual change law, further study and observation are needed.  相似文献   

2.
The influence of forest ageing on fine-root morphology and relations between fine-root and leaf characteristics is poorly studied. The aim of this study was to analyse age-driven changes in ectomycorrhizal roots (EcM roots) and leaf morphology in a chronosequence of silver birch (Betula pendula Roth.), which would provide a better understanding of adaptation responses and acclimation capacity of tree roots and leaves. The chronosequence included six age classes (3, 6, 14, 32, 45, and 60 years.). All stands had regenerated naturally and grew in a highly productive Oxalis forest site type in Estonia. Most changes in the morphology of EcM roots and leaves of silver birch occur faster at a young age. The functional parameters—mean specific area of EcM root (SRA) and leaf specific area (SLA) as well as leaf N—decreased with age. EcM root SRA and specific root length (SRL) decreased with stand age as a result of increased mean diameter and tissue density. In age classes of 6, 14, and 32 years, the total number of dominating EcM taxa was 34, and the distribution of four different dominating EcM exploration types (contact-, short-, medium-, long-distance) was similar. We conclude that high values of SRA, SLA, and leaf N measured in young silver birch stands indicate high activity of physiological processes necessary for fast-growing young trees. A decrease of SLA and SRA and N in the chronosequence of fertile stands of silver birch is most probably caused by down-regulation of growth, affecting simultaneously leaves and fine roots.  相似文献   

3.
Allometric equations are routinely used in the estimation of biomass stocks for carbon accounting within forest ecosystems. However, generic equations may not reflect the growth trajectories of afforestation species that are introduced to degraded farmland characterized by water and nutrient limitations. Using sequential measurements of the height, basal diameter, and above- and belowground biomass of juvenile trees, we developed allometric equations for five woody species (Moringa oleifera Lam., Leucaena leucocephala Lam., Jatropha curcas L., Anacardium occidentale L. and Parkia biglobosa Jacq.) subjected to a gradient of water and nutrient availability in an afforestation trial on degraded cropland in the semi-arid zone of Benin, West Africa. For three of the species studied, the allometric relationships between basal diameter and biomass components (i.e. leaves, stems and roots) were described best by a simple power-law model (R2 > 0.93). The incorporation of species-specific height–diameter relationships and total height as additional predictors in the power-law function also produced reasonable estimates of biomass. Fifteen months after planting, roots accounted for 10–58% of the total biomass while the root-to-shoot ratio ranged between 0.16 and 0.73. The total biomass of the saplings ranged between 1.4 and 10.3 Mg ha?1, yielding 0.6–4.3 Mg C ha?1, far exceeding the biomass in the traditional fallow system. The rate of stem carbon sequestration measured ca. 0.62 Mg C ha?1 year?1. Overall, the allometric equations developed in this study are generally useful for assessing the standing shoot and root biomass of the five afforestation species during the juvenile growth stage and can help in reporting and verifying carbon stocks in young forests.  相似文献   

4.
Young trees were harvested to explore non-destructive methodologies to estimate live branch dry weights in young fast-growing Eucalyptus species under different spacing and fertilizer treatments. Branch growth can vary with silvicultural management such as spacing, fertilizing and thinning, and over relatively short periods in response to environmental conditions. Many published regressions based on standard measurements of height and diameter are site, age and treatment specific. The aim of this study was to improve our capacity to predict woody crown dry weight, based on stem measurements, and to minimize (or eliminate) treatment effects on the resulting model. In young trees, branches are temporary support structures for foliage and are often discarded as the base of the green crown rises. As temporary structures they represent an investment of biomass and nutrient elements, and are subject to selection pressures to maximize the return on investment by the tree. Trees were harvested from existing plantation experiments located in south-eastern Queensland for E. grandis W. Hill ex Maiden (ranging from 0.28 to 15.85 m in height, to 5 years old) and south-western Australia for E. globulus Labill. (0.10–34.4 m in height, to 10.2 years) in order to examine the impact of spacing, nitrogen and phosphorus fertilization on early growth. Relationships to estimate crown woody biomass from non-destructive measurements were developed, and these relationships tended to have different slopes and intercepts for trees with predominantly juvenile foliage and those with intermediate or adult foliage. Dry weight of whole-crown live branch wood (Wbranch) was related to heights and/or diameter at breast height (DBH), but the regressions parameters were different, depending on treatment. The relationships became more generic (i.e. less dependent on treatment effects) between Wbranch and stem sectional area at the height of the base of the green crown (SACB), consistent with the pipe model theory (R2 > 0.91 for the two species for trees with intermediate/adult leaves). However, Wbranch was more closely related again to the stem volume above the base of the green crown and treatment effects were not significant (VCon,gc, R2 > 0.93). Branches exit the stem below the green crown, and for E. grandis the best relationship was on stem volume above the lowest live branch (VCon,llb, R2 0.94). Limited sampling from four other species with similar or contrasting crown characteristics indicated that the relationship could be applied quite generally. Individual E. grandis branch woody dry weight was closely related to the conical volume of the main (first order) branch (Vcon,br, R2 0.98). The whole crown equivalent, branch woody dry weight plus stem dry weight above the lowest live branch, was also closely related to the stem volume within the woody crown (VCon,llb, R2 0.97–0.99). While the slope of this relationship was still significantly different between trees with juvenile and intermediate/adult foliage, it had a similar form, suggesting that trees with juvenile foliage allocated a different proportion of their woody biomass within the crown to branches than older trees.  相似文献   

5.
The growth, aboveground biomass production and nutrient accumulation in black alder (Alnus glutinosa (L.) Gaertn.), silver birch (Betula pendula Roth.) and Scots pine (Pinus sylvestris L.) plantations during 7 years after planting were investigated on reclaimed oil shale mining areas in Northeast Estonia with the aim to assess the suitability of the studied species for the reclamation of post-mining areas. The present study revealed changes in soil properties with increasing stand age. Soil pH and P concentration decreased and soil N concentration increased with stand age. The largest height and diameter of trees, aboveground biomass and current annual production occurred in the black alder stands. In the 7-year-old stands the aboveground biomass of black alder (2100 trees ha−1) was 2563 kg ha−1, in silver birch (1017 trees ha−1) and Scots pine (3042 trees ha−1) stands respective figures were 161 and 1899 kg ha−1. The largest amounts of N, P, K accumulated in the aboveground part were in black alder stands. In the 7th year, the amount of N accumulated in the aboveground biomass of black alder stand was 36.1 kg ha−1, the amounts of P and K were 3.0 and 8.8 kg ha−1, respectively. The larger amounts of nutrients in black alder plantations are related to the larger biomass of stands. The studied species used N and P with different efficiency for the production of a unit of biomass. Black alder and silver birch needed more N and P for biomass production, and Scots pine used nutrients most efficiently. The present study showed that during 7 years after planting, the survival and productivity of black alder were high. Therefore black alder is a promising tree species for the reclamation of oil shale post-mining areas.  相似文献   

6.
Allometric models for dominant shade tree species and coffee plants (Coffea arabica) were developed for coffee agroforestry systems in Matagalpa, Nicaragua. The studied shade tree species were Cordia alliodora, Juglans olanchana, Inga tonduzzi and I. punctata. The models predict aboveground biomass based on diameter at breast height (for trees), and the stem diameter at a height of 15 cm and plant height (for coffee plants). In addition, the specific gravity of the studied species was determined.The total aboveground biomass of the shade trees varied between 3.5 and 386 kg per tree, and between 0.005 and 2.8 kg per plant for coffee. The aboveground biomass components (foliage, branch, and stem) are closely related with diameter at breast height (r > 0.75). The best-fit models for aboveground biomass of the shade trees were logarithmic, with adjusted R 2 between 0.71 and 0.97. In coffee plants, a high correlation was found (r = 0.84) with the stem diameter at 15 cm height, and the best-fit model was logarithmic, as well. The mean specific gravity was 0.52 (± 0.11) for trees and 0.82 (± 0.06) for coffee plants.  相似文献   

7.
A suite of regional allometric aboveground biomass functions were derived for Betula pubescens and Betula pendula for Norwegian conditions. The data consisted of 67 trees sampled throughout Norway. A total of 14 component functions were developed for total aboveground, total stem, stemwood, stem bark, live crown, live branch, leaf, and dead branch biomass using combinations of diameter at breast height and height as predictor variables. Application of the derived functions to existing local southern Norwegian mountain birch and regional Swedish biomass datasets indicated an overall good predictive ability of the developed functions. However, the functions produced slight underestimates, suggesting that the respective birch populations had differing biomass allocation patterns. When the developed functions were applied to Norwegian National Forest Inventory data, they produced slightly higher biomass stock and stock change estimates than what is obtained using existing Swedish functions. The higher estimates were evident in the north, central, and western part of Norway, while estimates were similar in southeastern Norway where growing conditions are most similar to Swedish conditions. The analysis indicates that the derived functions are the best available for regional birch biomass stock and stock change estimation in Norway.  相似文献   

8.

New silvicultural regimes with high within-stand competition require new functions for estimation of standing stock and growth of biomass components, since the allometry of trees is changed by light competition. This paper presents functions for estimation of the aboveground biomass dry weights for stem wood, stem bark, branches and leaves of young (diameter at breast height <10 cm) Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and birch (Betula pendula Roth. and Betula pubescens Ehrh.) trees growing in dense mixed stands. The functions were derived from a sample consisting of 84 Scots pine, 43 Norway spruce and 66 birch trees from six stands in northern Sweden with high stand densities (>10000 st ha-1). The logarithmically transformed power function displayed a good ability to stabilize the variance of dry weights and showed a good fit to the material (0.37< R 2 <0.99). A comparison with the most commonly used biomass functions in Sweden today showed that they overestimated the weight of stem wood and branches, while the weight of foliage was underestimated. The nature of these discrepancies suggested that the precision of biomass estimations might also be improved for young trees at wider spacing.  相似文献   

9.
This study aims to derive allometric functions to estimate the above- and belowground biomass components of the most important tree species in Latvia. The study material included a total of 81 Norway spruce (Picea abies [L.] Karst), 102 Scots pine (Pinus sylvestris L.), 105 birch spp. (mainly silver birch (Betula pendula Roth)) and 84 European aspen (Populus tremula L.) trees sampled in 124 forest stands. The suitability of three mathematical models for the prediction of total aboveground biomass, stem biomass, total live and dead branch biomass, belowground biomass and small root biomass was evaluated. Our analysis revealed that the use of the Intergovernmental Panel on Climate Change mean default values for the root-to-shoot ratio recommended for temperate and boreal ecological zones leads to the overestimation of root biomass of young trees, especially Scots pine and Norway spruce. Our findings indicate that biomass functions recommended for other Baltic Sea countries are not appropriate for the assessment of the biomass stock in Latvia’s forests because these lead to biased estimates. The biomass functions derived in our study are recommended for reporting the biomass stock in Latvia.  相似文献   

10.
The fine root (diameter ≤2.0 mm) biomass and morphology of Japanese red pines (Pinus densiflora) grown under different aboveground conditions (i.e., high and low competitive environments) were examined in a pine–cypress mixed forest. All P. densiflora subject trees were about 40 years old, and the aboveground condition (i.e., size) of red pines appeared to be influenced by the surrounding Japanese cypress (Chamaecyparis obtusa). Smaller P. densiflora exhibited lower fine root biomasses, shorter root lengths, and lower root tip densities, but longer specific root lengths and higher specific root tip densities relative to larger pines. These results suggest that P. densiflora may adjust the morphological traits of fine roots to the different conditions in biomass allocation to fine roots of individuals with different aboveground growth.  相似文献   

11.
Aboveground biomass and carbon stock in the largest sacred grove of Manipur was estimated for trees with diameter [10 cm at 1.37 m height.The aboveground biomass,carbon stock,tree density and basal area of the sacred grove ranged from 962.94 to 1130.79 Mg ha~(-1),481.47 to 565.40 Mg ha~(-1) C,1240 to 1320 stem ha~(-1) and79.43 to 90.64 m~2 ha~(-1),respectively.Trees in diameter class of 30–40 cm contributed the highest proportion of aboveground biomass(22.50–33.73%).The aboveground biomass and carbon stock in research area were higher than reported for many tropical and temperate forests,suggesting a role of spiritual forest conservation for carbon sink management.  相似文献   

12.
Leaf area is a key driver of growth models and leaf weight is important for studying carbon and nutrient cycling in forestry. Both can change over relatively short intervals in young plantations in response to silvicultural treatments and climatic conditions. Relationships to estimate leaf dry weight and leaf area of young Eucalyptus grandis W. Hill ex Maiden and Eucalyptus globulus (Labill.) were developed from harvested trees ranging from 0.28 to 15.85 m and 0.12 to 34.4 m in height respectively. Trees were harvested from existing experiments in south-eastern Queensland and south-west Western Australia in order to assess the effects of spacing and application of nitrogen and phosphorus fertilizer on early plantation growth. A range of tree measurements were taken to determine the most efficient way to monitor the performance of young plantation eucalyptus. Leaf weight (Wleaf, kg) and leaf area (m2) were related to stem cross sectional area at the height of the base of the green crown (SACB), but the slope and intercept of the relationship differed for trees with predominantly juvenile foliage and those with predominantly intermediate or adult foliage. Specific leaf area (m2 kg?2) changed as the trees aged and leaf area was more closely related to the size of the support structure, represented by the stem volume within the green crown, approximated by the volume of a cone above the base of the green crown (VC,gc). Significantly, the relationships also applied to individual branches, that is, leaf weight was related to sectional area near the base of the branch (SAb) and leaf area to the volume of the main (first order) branch (VC,br). Most of the published work has been directed at trees of commercial size or to small trees in pot experiments, much less to small trees in the establishment phase of growth of interest to experimenters and managers looking at early intervention. This study provides a mechanism to directly assess canopies of intermediate size trees which are of interest for assessing treatment effects or early intervention for managers.  相似文献   

13.

Key message

A new system of additive tree biomass equations was developed for juvenile white birch plantations based on tree diameter at breast height (DBH) and tree height (HT). Compared with previous equations developed for natural white birch forests, the new system included one more biomass component and provided more accurate predictions.

Context

Accurate estimates of tree component and total biomass are necessary for evaluating alternative forest management strategies for biomass feedstock, carbon sequestration, and products. Previous biomass equations developed for white birch trees in natural stands provided substantially biased predictions for white birch plantations.

Aims

A new system of additive tree biomass equations was developed for juvenile white birch plantations in the northeastern China.

Methods

With destructive biomass sampling data from 501 trees sampled from white birch provenance and family trails at ages 7, 9, 10, and 13 in three provinces, a system of nonlinear additive tree biomass equations based on DBH and tree height was developed using the nonlinear seemingly unrelated regressions (NSUR) approach.

Results

Compared with previously published equations developed for natural white birch forests, the new system provided more accurate predictions of white birch tree component and aboveground and total biomass, especially of branch, foliage, and root biomass.

Conclusion

The new system extended the applicability of biomass equations to white birch plantations in the northeastern China.
  相似文献   

14.
Several studies have been conducted on the response of crops to greater concentrations of atmospheric CO2 (CO2 fertilization) as a result of climate change, but only few studies have evaluated this effect on multipurpose agroforestry tree species in tropical environments. The objectives of this study were to quantify differences in growth parameters and in leaf carbon (C) and nitrogen (N) concentrations of Cedrela odorata L. and Gliricidia sepium (Jacq.) Walp. seedlings under current ambient temperature (32°C daytime, 22°C night time) and CO2 (360 ppm) (AMB); CO2 fertilization (800 ppm, 32°C daytime, 22°C night time) (fCO2); elevated ambient temperature (360 ppm, 34°C daytime, 25°C night time) (TEMP); and a combination of elevated temperature (32°C daytime, 22°C night time) and CO2 fertilization (800 ppm) (TEMPxfCO2). Results showed significant differences (P < 0.05) in seedling growth parameters (seedling height, number of stem leaves, leaf area ratio, shoot and root biomass, and shoot/root ratio) between treatments for both tree species. The greatest increases in growth parameters occurred in the TEMP and TEMPxfCO2 treatments compared to the AMB treatment for both tree species. However, growth parameters were significantly lower (P < 0.05) in the fCO2 treatment compared to that of the AMB treatment. Leaf N concentration was 1.1 to 2.1 times lower (P < 0.05) in all treatments when compared to current ambient conditions (AMB) in both tree species, but no significant changes in leaf C concentrations were observed. Results from our study suggested that fCO2 had the greatest negative impact on tree growth parameters, and leaf N concentrations were affected negatively in all treatments compared to current ambient conditions. It is expected that such changes in growth parameters and plant N content may impact the long-term cycling of nutrients in agroforestry systems.  相似文献   

15.
The effect of tree canopy on the growth, productivity and forage quality of Megathyrsus maximus and changes in soil properties were evaluated over three seasonal periods. Four adjacent plots (15 m × 17 m each) in a tropical secondary deciduous forest having 12 years of growth and dominated by Gliricidia sepium were randomly assigned to two treatments: removal of trees (SCA) in two of the plots and leaving trees intact (COA) in the other two. In all plots, M. maximus was planted with 50 cm spacing among plants. Tree removal significantly increased the incident photosynthetically active radiation (PAR, P < 0.001) and grass size (12.5 % in height, P < 0.01, and 16.5 % in clump diameter, P < 0.05), but did not significantly affect any other variable. Season significantly affected grass height (P < 0.003), tiller number (P < 0.001), clump diameter (P < 0.001), net CO2 assimilation rate (P < 0.001), forage biomass production (P < 0.003), and acid detergent fiber content (P = 0.033). Primary soil changes after 1 year of establishment of the grass were the decline by 3 % in organic carbon (P = 0.03), and qualitative changes in soil structure, regardless of tree presence. Results are consistent with the ability of M. maximus to tolerate shade. We conclude that under the conditions of the study there was no evidence for a negative effect of tree canopy on M. maximus mediated by a reduction in PAR.  相似文献   

16.
The growth, technical quality and nutritional status of pure and mixed silver birch (Betula pendula Roth) and downy birch (Betula pubescens Ehrh.) plantations were studied 21 and 22 years after planting on afforested organic soil arable land and on upland forest soil. In mixtures, 50% of both birch species was planted. Silver birch trees grew better, but had higher mortality than downy birch trees on both sites. Mortality of both species was highest, and the difference in their growth smallest, on organic soil. In pure stands on organic soil, downy birch dominant height, diameter and mean volume were 96%, 92% and 82% of those of silver birch and on mineral soil 87%, 84% and 60%, correspondingly. On mineral soil, silver birch had a higher mean annual increment (MAI) (5.8 m3 ha?1a?1) than downy birch (3.9 m3 ha?1a?1), but on organic soil the MAI of both species was similar (3.3–3.4 m3 ha?1 a?1). Planting birches in mixture did not affect the growth of the trees on organic soil. On mineral soil, the mean diameter and mean volume of silver birch trees were higher in mixed than in pure plantations. The technical stem quality of both tree species was low. On mineral soils, pure silver birch is more productive than mixture, but on peat soil the higher growth of silver birch could contribute to increased productivity and downy birch would ensure sufficient survival for future timber production.  相似文献   

17.
We developed site-specific allometric models for Leucaena leucocephala × pallida var. KX2 trees in a shaded coffee agroecosystem in Hawaii to predict above- and belowground biomass and the regrowth potential of pollarded trees. Models were used to compare tree growth rates in an experimental agroforestry system with different pollarding frequencies and additions of tree pruning residues as mulch. For all allometric equations, a simple power model (Y = aXb) provided the optimal prediction of biomass or regrowth after pollarding. For aboveground biomass components (stem, branches, leaves, and seed and pods), stem diameter alone was the best predictor variable. Stump diameter provided the best prediction of coarse root biomass and aboveground regrowth after pollarding. Predictions of biomass from generalized allometric models often fell outside the 95% confidence intervals of our site-specific models, especially as biomass increased. The combination of pollarding trees once per year plus the addition of tree mulch resulted in the greatest aboveground regrowth rates as well as accumulation of biomass and C in the stump plus coarse roots. Although optimal prediction required the development of site-specific allometric relationships, a simple power model using stem or stump diameter alone can provide an accurate assessment of above- and belowground tree biomass, as well as regrowth potential under specific management scenarios.  相似文献   

18.
Planting hedgerows on farm field edges can help mitigate greenhouse gas (GHG) emissions from agricultural landscapes by sequestering carbon (C) in woody biomass and in soil. Sequestration rates however, must be assessed in terms of their overall global warming potential (GWP) which must also consider GHG emissions. The objectives of this study were to (1) compare carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions from two types of hedgerows and adjacent annual agricultural production fields, and 2) better understand how climate, soil properties and plant species configurations affect hedgerow GHG emissions. At eight study sites in the lower Fraser River delta of British Columbia, we measured emissions from soil in both planted (P-Hedgerow) and remnant hedgerows (R-Hedgerow), as well as in adjacent annual crop production fields over 1 year using a closed-static chamber method. CO2 emissions were 59 % higher in P-Hedgerow than R-Hedgerow, yet there were no significant differences of relative emissions of CH4 and N2O. The environmental variables that explained the variation in emissions differed for the three GHGs. CO2 emissions were significantly correlated with soil temperature. CH4 and N2O and emissions were marginally significantly correlated with soil organic carbon (SOC) and soil water-filled pore space (WFPS), respectively. Emissions were not significantly correlated with hedgerow plant species diversity. While hedgerows sequester carbon in their woody biomass, we demonstrated that it is critical to measure hedgerow emissions to accurately ascertain their overall GHG mitigation potential. Our results show that there are no CO2e emission differences between the management options that plant new diverse hedgerows or conserve existing hedgerows.  相似文献   

19.
Theobroma cacao seedlings were grown alone (TCA) or associated with saplings of N2-fixing shade trees Gliricidia sepium and Inga edulis in 200 l of 15N labelled soil within a physical root barrier for studying direct nitrogen transfer between the trees and cacao. Root:shoot partitioning ratio for sapling total N was lower than biomass root:shoot ratio in all species. Sapling total 15N was partitioned between root and shoot in about the same ratio as total N in cacao and inga but in gliricidia much higher proportion of 15N than total N was found in roots. Thus, whole plant harvesting should be used in 15N studies whenever possible. Average percentage of fixed N out of total tree N was 74 and 81% for inga estimated by a yield-independent and yield-dependent method, respectively, and 85% for gliricidia independently of estimation method. Strong isotopic evidence on direct N transfer from trees to cacao was observed in two cases out of ten with both tree species. Direct N transfer was not correlated with mycorrhizal colonisation of either donor or receiver plant roots. Direct N transfer from inga and gliricidia to cacao is conceivable but its prevalence and the transfer pathway via mycorrhizal connections or via reabsorption of N-rich legume root exudates by cacao require further study. Competition in the restricted soil space may also have limited the apparent transfer in this study because the trees accumulated more soil-derived N than cacao in spite of active N2 fixation.  相似文献   

20.
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.  相似文献   

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