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1.
We examined whether N-fertilization and soil origin of Douglas-fir [ Psuedotsuga menziesii (Mirb.) Franco] stands in western Washington state could affect C sequestration in both the tree biomass and in soils, as well as the flux of dissolved organic carbon (DOC) through the soil profile. This study utilized four forest sites that were initially established between 1972 and 1980 as part of Regional Forest Nutrition Research Project (RFNRP). Two of the soils were derived from coarse-textured glacial outwash and two from finer-textured volcanic-source material, primarily tephra, both common soil types for forestry in the region. Between 1972 and 1996 fertilized sites received either three or four additions of 224 kg N ha −1 as urea (672–896 kg N ha −1 total). Due to enhanced tree growth, the N-fertilized sites (161 Mg C ha −1) had an average of 20% more C in the tree biomass compared to unfertilized sites (135 Mg C ha −1). Overall, N-fertilized soils (260 Mg C ha −1) had 48% more soil C compared to unfertilized soils (175 Mg C ha −1). The finer-textured volcanic-origin soils (348 Mg C ha −1) had 299% more C than glacial outwash soils (87.2 Mg C ha −1), independent of N-fertilization. Soil-solution DOC collected by lysimeters also appeared to be higher in N-fertilized, upper soil horizons compared to unfertilized controls but it was unclear what fraction of the difference was lost from decomposition or contributed to deep-profile soil C by leaching and adsorption. When soil, understory vegetation and live-tree C compartments are pooled and compared by treatment, N-fertilized plots had an average of 110 Mg C ha −1 more than unfertilized controls. These results indicate these sites generally responded to N-fertilization with increased C sequestration, but differences in stand and soil response to N-fertilization might be partially explained by soil origin and texture. 相似文献
2.
Annual litter fall of Acacia mangium in the period of September 1995 to August 1996 was estimated at 5939 kg ha −1 year −1 and from September 1995 to August 1996 at 6048 kg ha −1 year −1, with the highest seasonal production in the dry season. The litter fall was dominated mainly by leaves, 4446 kg (75%) and 4137 kg (68%), respectively. Seed production in the litter fall was estimated at 42.4 kg ha −1 year −1 (4.1 million seeds ha −1) and 39 kg ha −1 year −1 (3.8 million seeds ha −1), with the highest in the dry season from June to October. The accumulated litter fall in the forest floor together with shrubs and grass provide a high fuel load, increasing fire risk. 相似文献
3.
Ammonification and nitrification rates and nitrogen uptake were measured using the buried-bag technique in irrigated mixed plantations of shisham ( Dalbergia sissoo Roxb. ex DC.) and mulberry ( Morus alba L.). Nitrogen transformations were rapid in these stands, particularly following thinning to reduce stand density. In young stands, net N mineralization was 26.72 mg N kg −1 soil month −1 (approximately 480 kg ha −1 month −1), but, as the end of the 22-year rotation approached, nitrification slowed to 13.41 mg N kg −1 soil month −1 (approximately 241 kg ha −1 month −1). N 2-fixing shisham appeared to respond after thinning only to the increased space and temporarily reduced competition for light and moisture, but mulberry appeared to benefit greatly from the nitrogen released through mineralization following thinning. 相似文献
4.
Periodic variations in the concentration, deposition and canopy impact of different forms of N on annual N deposition through rainfall, throughfall and stemflow in 5 and 8 year old stands of Casuarina equisetifolia were studied. Throughfall and stemflow ranged from 70 to 76% and 5–6% of annual precipitation respectively. The total N deposition by rainfall was 11.1 kg ha −1 year −1, and by throughfall was 13.6 kg ha −1 year −1 and 16.5 kg ha −1 year −1 in 5-year-old and 8-year old plantations, respectively. The quantities of N deposited through stemflow in the two plantations were nearly identical, accounting for 1.6 kg ha −1 year −1. Observations of the monthly deposition of NH 4,N, NO 3-N, Kjeldahl-N and organic-N revealed that maximum deposition occurred in July and the minimum in September. Organic-N deposition was 17% less (5-year) than the rainwater content. Net deposition of N, as an effect of canopy, was 7–8.7 kg ha −1 year −1, which was added directly to the available nutrient pool of soil. 相似文献
5.
Litterfall was collected over a 12-month period with littertraps in hoop pine ( Araucaria cunninghamii) plantations aged 10, 14 and 62 years in southeast Queensland, Australia. The bulk of litterfall occurred during spring, mainly as hoop pine foliage with the annual litterfall ranging between 6.0 and 10.9 t ha −1, respectively, for the younger stands (10 and 14 years) and the mature 62-year old stand. The amount of nitrogen (N) and phosphorous (P) recycled annually through litterfall was lower in the younger stands (28–37 kg N ha −1 and 4.4–5.3 kg P ha −1) compared with that of the mature stand (85 N ha −1 and 6.2 kg P ha −1). The N and P retranslocated during senescence varied across the three stands studied with a trend for N and P retranslocation to increase as availability of soil mineral-N decreased. Decomposition of the hoop pine foliage component of litter was also studied in the same stands using a litterbag technique and mass-balance analysis. The estimated half-life of hoop pine foliage mass ranged between 1.5 and 1.8 years. Litter-mass loss was strongly correlated with litter substrate quality indicators of N, C, P, C/N ratio, lignin, lignin/N ratio and polyphenols. During the course of the study, there was no difference in litter-mass loss between the stands of different ages. During the 15-month period, the order of element release from the hoop pine litter was K>Na>C>Mg>P, with N, Ca and Mn generally demonstrating varying degrees of net accumulation. During the course of the study, the lignin/C ratio of the hoop pine litter increased from 0.61 to 0.96. This suggested that the litter-C was predominantly in a recalcitrant form and, therefore, the associated N was unlikely to be rapidly released in the hoop pine litter layer. 相似文献
6.
Following the tree harvest, the biogeochemistry of a catchment is modified by changes in soil temperature and moisture, and nutrient cycling. We monitored soil-solution and stream-water chemistry, and soil properties in a Pinus radiata D. Don plantation in New Zealand before and after clear-cutting and replanting in 1997. The annual rainfall during the study was 1440–1860 mm. The soil was a 1800-year-old pumice soil of high natural N status; the catchment had received large inputs of volcanic N in rain, probably over the 1800 years since the pumice had been deposited. The leaching loss of nitrate-N was 28 kg ha −1 yr −1 in 1996, and then decreased sharply after clear-cutting to 3 kg ha −1 yr −1 in 1998 and <1 kg ha −1 yr −1 in 1999. Weed growth and soil microbial biomass increased during this time, and would have removed much of the N from soil solution in the upper soil layers. Although the catchment was small (8.7 ha), there was a 2-year lag until N decreased in stream-water; the losses of dissolved organic N to stream-water were low. There was no change in soil pH over the 4 years, but spring-water pH appeared to increase, which was consistent with the increase in bicarbonate that accompanied grass/weed growth. The export of cations (mmol c l −1) in the spring-water was Na>Ca>Mg=K as expected for rhyolitic pumice, and the total concentration was probably controlled by the accompanying anions. The export of anions was NO 3=Cl>SO 4=HCO 3 before harvest and HCO 3=Cl>SO 4=NO 3 after harvest. 相似文献
7.
Fast growth tree plantations and secondary forests are considered highly efficient carbon sinks. In northwest Patagonia, more than 2 million ha of rangelands are suitable for forestry, and tree plantation or native forest restoration could largely contribute to climate change mitigation. The commonest baseline is the heavily grazed gramineous steppe of Festuca pallescens (St. Yves) Parodi. To assess the carbon sequestration potential of ponderosa pine ( Pinus ponderosa (Dougl.) Laws) plantations and native cypress ( Austrocedrus chilensis (Don) Flor. et Boutl.), individual above and below ground biomass models were developed, and scaled to stand level in forests between 600 and 1500 annual rainfall. To calculate the carbon sequestration baseline, the pasture biomass was simulated. Also, soil carbon at two depths was assessed in paired pine-cypress-pasture sample plots, the same as the litter carbon content of both forest types. Individual stem, foliage, branch and root log linear equations adjusted for pine and cypress trees presented similar slopes ( P>0.05), although some differed in the elevations. Biomass carbon was 52.3 Mg ha −1 (S.D.=30.6) for pine stands and 73.2 Mg ha −1 (S.D.=95.4) for cypress forests, given stand volumes of 148.1 and 168.4 m 3 ha −1, respectively. Soil carbon (litter included) was 86.3 Mg ha −1 (S.D.=46.5) for pine stands and 116.5 Mg ha −1 (S.D.=38.5) for cypress. Root/shoot ratio was 19.5 and 11.4%, respectively. The low r/s value for cypress may account for differences in nutrient cycling and water uptake potential. At stand level, differences in foliage, taproot and soil carbon compartments were highly significative ( P<0.01) between both forest types. In pine stands, both biomass and soil carbon were highly explained by the rainfall gradient ( r2=0.94). Nevertheless, such a relationship was not found for cypress, possibly due to stand and soil disturbances in sample plots. The carbon baseline estimated in pasture biomass, including litter, was 2.6 Mg ha −1 (S.D.=0.8). Since no differences in soil carbon were found between pasture and both forest types, additionality should be accounted only by biomass. However, the replacement of pasture by pine plantations may decrease the soil carbon storage, at least during the first years. On the other hand, the soil may be a more relevant compartment of sequestered carbon in cypress forests, and if pine plantation replaces cypress forests, soil carbon losses could cause a negative balance. 相似文献
8.
Deposition of N and S has increased since the 1950s in most European countries and N accumulates in ecosystems that are not N saturated. This study shows long-term effects of a (modelled) N deposition of 7–17 kg N ha −1 per year on biological and chemical processes in soil, vegetation composition, and functional types of field-layer plant species in deciduous forests. Soil pH largely determined the response of the soil processes, emphasising the importance to compare soils of similar acidity regarding the effects of N deposition. The most pronounced effects were demonstrated for the most acid study plots. When we compared regions with a deposition of 7 and 17 kg N ha −1 per year we found a 40–80% higher soil N mineralisation rate, 2–90% higher nitrification rate and 10–25% lower C:N ratio in the region with the highest deposition. Similar but smaller differences were indicated when regions with a deposition of 7 and 10 kg N ha −1 per year were compared. Number of species was lower in the regions with the highest deposition. Literature data for plants on N concentration, nitrate reductase activity (NRA), growth rates, morphology and height were calculated on a site basis. They varied to different extent between the regions. The N concentration was 7–24% higher in the regions with the highest N deposition. We argue that the effect-related critical load based on our results should be set to a N deposition of 7–10 kg N ha −1 per year. Critical loads for a subdivision of deciduous forests would give lower critical loads for the most acid soils compared to less acid soil. 相似文献
9.
We quantified structural features and the aboveground biomass of the deciduous conifer, Metasequoia glyptostroboides (Hu and Cheng) in six plantations in central Japan. In order to derive biomass estimates we dissected 14 M. glyptostroboides trees into three structural components (stem wood, branch wood and foliage) to develop allometric equations relating the mass of these components and of the whole tree to diameter at breast height (DBH). We found robust relationships at the branch and whole tree level that allow accurate prediction of component and whole tree biomass. Dominant tree height was similar within five older (>40 years) plantations (27–33 m) and shorter in a 20-year-old plantation (18 m). Average stem diameter varied from 12.8 cm in the youngest stand to greater than 35 cm in the oldest stand. Metasequoia have relatively compact crowns distributed over the top 30% of the tree although the youngest stand had the deepest crown relative to tree height (up to 38%). At the individual tree level in older stands, 87% of the aboveground biomass was allocated to the stem, 9% to branch wood and 4% to foliage. We found little difference in the relative distribution of above ground biomass among the stands with the exception of lower foliage biomass in larger diameter trees. Total aboveground biomass of the older stands varied twofold, ranging from a maximum of 450 Mg ha−1 in a 42-year-old stand to a minimum of 196 Mg ha−1 in a 48-year-old stand. Total above ground biomass of the 20-year-old stand was 176 Mg ha−1. 相似文献
10.
Annual net primary production (NPP) and N uptake were estimated for lysimeter-grown basket willows ( Salix viminalis L.) during 3 years after planting. The willows were grown in a stand structure and continuously supplied with water and liquid fertilizer through drip tubes. The lysimeters contained either clay from the site or washed quartz sand. Shoot growth and leaf litter were measured and fine-root dynamics observed in minirhizotrons. Destructive samples were taken annually in late autumn and entire root systems were washed out. Dry mass and N content of all plant parts were determined. Fine-root production was estimated by two methods, based on destructive samplings and observations in minirhizotrons. The proportion of biomass allocated below ground increased considerably when estimates based on accumulated NPP were compared with those based on standing dry mass. In the first year, 49 and 58% of annual NPP in willows grown in clay and sand, respectively, was belowground. In subsequent years the proportions were 36–38% and 33–40%. Most belowground production was fine roots. Relatively more N was used belowground in the first year than subsequently, but no substrate-induced differences were observed in the allocation pattern. Both annual NPP and N uptake was always higher in plants in clay than in those in sand: in the final 2 years, 21–22 tonnes DM ha−1 year−1 and 190 kg N ha−1 year−1 in clay, and 9–10 tonnes DM ha−1 year−1 and 100 kg N ha−1 year−1 in sand. 相似文献
11.
The aim of this study was to quantify 5-year growth, yield and mortality responses of 9- to 13-year-old naturally regenerated, even-aged paper birch ( Betula papyrifera Marsh.) stands to pre-commercial thinning in interior British Columbia. The study included four residual densities (9902–21,807 stems ha −1 (unthinned control), 3000, 1000 and 400 stems ha −1) and four sites with 3-fold within-site replication in a randomised block design. The largest, straightest, undamaged trees were selected to leave during thinning. Thinning reduced stand basal area from 5.90 m 2 ha −1 in the control to 2.50, 1.53 and 0.85 m 2 ha −1 in the three thinning treatments, representing 42, 26 and 15% of control basal area, respectively. After 5 years, total stand volume per plot remained lower in the three thinning treatments than the control (50.20, 30.07, 18.99 and 11.86 m 3 in the control, 3000, 1000 and 400 stems ha −1 treatments), whereas mean stand diameter, diameter increment, height, and height increment were increased by thinning, and top height (tallest 100 trees ha −1) was unaffected. When a select group of crop trees (largest 250 trees ha −1) in the thinning treatments was compared with the equivalent group in the control, there was a significant increase in mean diameter, diameter increment, basal area, basal area increment, and volume increment. Mean height, height increment, top height, and total volume were unaffected by thinning. Crop tree diameter increment was the greatest following thinning to 400 stems ha −1 for all diameter classes. Thinning to 1000 stems ha −1 resulted in lower diameter increment than thinning to 400 stems ha −1 but tended to have higher volume increment. Dominant trees responded similarly to subdominant trees at 400 stems ha −1, but showed the greatest response at 3000 stems ha −1. Results suggest that pre-commercial thinning of 9–13-year-old stands to 1000 stems ha −1 would improve growth of individual trees without seriously under-utilising site resources. 相似文献
12.
The effects of nitrogen fertilization (100, 200 kg N ha −1 per year) and soil properties on mycorrhizal formation on Salix viminalis were investigated at three short rotation plantations on Gleysols and Cambisols (Abbachhof (ABB) and Wildeshausen (WIL) in Germany, Ultuna (ULT) in Sweden). During 3 years the ectomycorrhizal colonization, the composition of ectomycorrhizal morphotypes and the VAM spore density in the soil were analyzed. The ectomycorrhizal colonization was significantly altered due to N-fertilization at all sites. The quality and magnitude of the fertilization effects on mycorrhizal formation on Salix viminalis varied due to the soil properties, i.e. soil texture, soil N content and pH. The WIL site was characterized by sandy soil (low pH, high soil N content), whereas the ABB site was characterized by clayey soil (high pH, low N content). The ULT site was characterized by clayey soil (high pH, high N content). In the unfertilized control plots (C), ectomycorrhizal colonization was higher at WIL than at ABB. Fertilization reduced the ectomycorrhizal colonization at WIL but increased it at ABB. The distribution of the ectomycorrhizal morphotypes was very heterogeneous within the treatments, therefore significant differences were rare. Sporocarps were collected at ABB during one growing period. The sporocarps were mostly from saprophytic species, with exception of the ectomycorrhizal species Inocybe glabripes. Significant effects of N-fertilization on VAM spore density were observed at two of the three plantations. The pattern in VAM spore density was similar to the pattern seen for ectomycorrhizal colonization. Thus, VAM spore density was increased by fertilization at ABB (low soil N) and decreased at ULT (high soil N). The soil properties have been shown to modify the effects of fertilization on ectomycorrhizal colonization and VAM spore density. Therefore, in management practice of short rotation plantations, the benefit of N-fertilization should be evaluated keeping secondary effects caused by changed mycorrhizal formations in mind. 相似文献
13.
Shoot biomass production was estimated in two Estonian short rotation forest (SRF) plantations during the first rotation cycle (1994–1997). The plantations were established with six clones of Salix viminalis and one clone of Salix dasyclados in 1993. The plantation, located on well-composed organic soil, was characterised by higher productivity (6.2 t DM ha −1 per year) compared with the plantation on poor mineral soil (5.2 t DM ha −1 per year). Fertilisation of the latter plantation increased its productivity to 11.0 t DM ha −1 per year, which is the value close to a predicted maximum for Swedish climatic conditions. In fertilised plots, clone 81090 of S. dasyclados was characterised by the highest productivity among all clones, but also by high stool mortality. Clones 78021 and 78183 of S. viminalis had the most stable and relatively high productivity and can therefore be recommended as promising planting material for SRF in Estonia. When estimating production, the use of proper allometric relations between shoot dry weight and diameter is of crucial importance. Additional measurements on 1-year-old shoots in 1998 showed that besides shoot age also clone and fertilisation are significant factors influencing allometric relations. The dry weight of fertilised shoots was about 10% lower than that of non-fertilised shoots of the same height and diameter. Older shoots were heavier than younger shoots with a similar diameter. 相似文献
14.
The dynamics of nutrients were compared over three years in a clonal Eucalyptus plantation and in a native savanna in Congo. This paper focuses on the changes in the chemical composition of solutions during their transfer through the soil in both ecosystems. The main characteristics of the soil (Ferralic Arenosol) were similar in the two ecosystems, and the low inter-stand variability allowed reliable comparisons of the influence of afforestation on the soil solution chemistry. Rainfall amounted to about 1400 mm per year during the experimental period. In both ecosystems, an enrichment was observed for most elements during the transfer of solutions through the foliage, but N uptake occurred. Concentrations of H+ and dissolved organic carbon (DOC) in solutions increased through the litter layer in both stands. In the Eucalyptus ecosystem, a quick uptake of nutrients by a dense root mat inside the forest floor likely explained why the concentrations of gravitational waters were not enhanced markedly for ‘base cations’, despite the mineralization of high amounts of nutrients during the litter decay. Soil solutions were collected by zero tension lysimeters (ZTL) at a depth of 15 cm, but these lysimeters were inefficient at collecting gravitational solutions beyond this depth. By contrast, tension lysimeters (TL) maintained at a suction of −60 kPa, collected soil solutions at the depths of 15, 50 cm, 1, 2, 3, 4 m in both ecosystems and 6 m in the plantation. In the topsoil of both stands, the nutrient concentration decreased sharply when the time of residence of solutions increased. This pattern highlighted the crucial role of the inputs by throughfall, stemflow and mineralization of the litter layer for the nutrition of these stands. A combination of high nutrient requirements of the stands and low availability of exchangeable cations in this highly weathered soil might account for the extremely low nutrient concentrations in solutions collected by TL, regardless of the depth. 相似文献
15.
Managed forests often differ substantially from undisturbed forests in terms of tree structure and diversity. By altering the forest structure, management may affect the C stored in biomass and soil. A survey of 58 natural stands located in the south-westernmost limit of European beech forests was carried out to assess how the C pools are affected by the changes in tree structural diversity resulting from past management. The mean tree density, basal area and the number of large trees found in unmanaged forests were similar to those corresponding to virgin beech forests in Central Europe, whereas large live trees were totally absent from partially cut stands. Analysis of the Evenness index and the Gini coefficient indicated high structural diversity in the three stand types. The results of the Kolmogorov–Smirnov test used to compare the diameter distributions of each group revealed significant differences between stand types in terms of distributions of total tree species and of Fagus sylvatica. The mean C stocks in the whole ecosystem – trees, litter layer and mineral soil – ranged from 220 to 770 Mg ha−1 (average 380 Mg ha−1). Tree biomass (above and belowground), which averaged 293 Mg C ha−1, constituted the main C pool of the system (50–97%). The statistical test (Kolmogorov–Smirnov) revealed differences in the distribution of C pools in tree biomass between unmanaged and partially cut stands. As a consequence of the presence of large trees, in some unmanaged stands the C stock in tree biomass was as high as 500–600 Mg C ha−1. In the partially cut stands, most of the C was mainly accumulated in trees smaller than 20 cm dbh, whereas in unmanaged stands the 30% of tree C pool was found in trees larger than 50 cm dbh. Furthermore, many unmanaged stands showed a larger C pool in the litter layer. The C content of mineral soils ranged from 40 to 260 Mg C ha−1 and it was especially high in umbrisols. In conclusion, the implementation of protective measures in these fragile ecosystems may help to maintain the highly heterogeneous tree structure and enhance the role of both soils and trees as long-term C sinks. 相似文献
16.
For 20 years, there has been 42,000 ha estate of clonal Eucalyptus plantations around Pointe-Noire in Congo on sandy soils that have very low reserves of available nutrients. These plantations have been based on a natural hybrid ( E. PF1). This hybrid is being replaced by E. urophylla × E. grandis (UG), a more productive hybrid developed by the breeding program of UR2PI. A study of biogeochemical cycles showed that nutrient removal by harvesting is the main nutrient output in the E. PF1 ecosystem. It is therefore important to quantify the nutrient content (NC) in both hybrids to compare corresponding nutrient removal values. The work dealt with four UG clones and the most planted clone of E. PF1. Twelve trees per clone were sampled at the logging age (8 years) in a clonal test for UG clones and in a nearby stand for E. PF1. Tables were established to predict, from girth at breast height (C1.30 m), the biomass and nutrient content of stemwood, bark, dead and living branches, leaves, and were applied to the inventory of the different stands to evaluate corresponding biomass, NC and nutrient use efficiency (NUE) on a per-hectare basis. Total biomass differed between the two hybrids and among UG clones: 109 t ha−1 for E. PF1 and 108–155 t ha−1 for UG clones. In E. PF1 trees, total NC was globally lower for N, K, and Mg, but greater for P and Ca. In stemwood, nitrogen content was similar for both hybrids. By contrast, in UG clones, NC was much lower for P (−72%) and Ca (−40% to −55%). The same trends were observed for NUE: equivalent for both hybrids for N, but higher in UG clones for P (+72%) and Ca (+43% to +59%). A marked variability among clones was observed for K and Mg. UG clones allocated proportionally more nutrients in leaves than E. PF1. These results show that clones should not be selected only on growth traits but also on NUE and on the concentration of nutrients in tree components removed by harvesting. It will be then possible to limit the cost of fertilising needed to maintain stand growth and soil fertility. 相似文献
17.
Two thinning and fertilization studies, the first in 1969 and the second in 1971, were established to evaluate the question of nutrient limitation to tree growth and the consequences of stand manipulation of soil moisture supply. Fertilizer was applied yearly for the first 5 years in both studies; growth response has been measured through 1987. Results indicate that thinning is necessary to obtain a growth response to fertilizer applied at the rate of 111 kg nitrogen ha −1. The response to fertilization after fertilization ended lasted for 4 years in plots thinned to 800 stems ha −1, while a significant response continued for only 2 years in plots thinned to 1600 stems ha −1. A soil water-balance model was calibrated for the control and treatment plots of these two studies. Soil water-deficits were estimated and correlated with yearly average basal-area growth per tree. Results indicated that there is a correlation between seasonal soil-moisture deficit and growth during the years when soil moisture was measured for the unthinned control plots (r2 = −0.787, P = 0.002) but not for the thinned and fertilized plots (r2 = −0.652, P = 0.057). 相似文献
18.
A field study was conducted to investigate the fate of 15N-labelled nitrate applied at 20 kg N ha −1 in a wet summer to microplots installed in areas under different residue management regimes in second-rotation hoop pine ( Araucaria cunninghamii) plantations aged 1–3 years in south-east Queensland, Australia. PVC microplots of 235 mm diameter and 300 mm long were driven into 250 mm soil. There were three replications of each of eight treatments. These were areas just under and between 1-year-old windrows (ca. 2–3 m in width) of harvesting residues spaced 15 m apart, and with and without incorporated foliage residues (20 t DM ha −1); the areas just under and between 2- or 3-year-old windrows spaced 10 m apart. Only 7–29% of the added 15N was recovered from the top 750 mm of the soil profile with the leaching loss estimated to be 70–86% over the 34-day period. The 15N loss via denitrification was 3.7–6.3% by directly measuring the 15N gases emitted. The microplots with the incorporated residues at the 1-year-old site had the highest 15N loss (6.3%) as compared with the other treatments. The 15N mass balance method together with the use of bromide (Br) tracer applied at 100 kg Br ha −1 failed to obtain a reliable estimate of the denitrification loss. The microplots at the 1-year-old site had higher 15N immobilisation rate (7.5–24.7%) compared with those at 2- and 3-year-old sites (2.1–3.6%). Incorporating the residues resulted in an increase in 15N immobilisation rate (24.5–24.7%) compared with the control without the incorporated residues (8.4–14.3%). These findings suggest that climatic conditions played important roles in controlling the 15N transformations in the wet summer season and that the residue management regimes could also significantly influence the 15N transformations. Most of the 15N loss occurred through leaching, but a considerable amount of the 15N was lost through denitrification. Bromide proved to be an unsuitable tracer for monitoring the 15N leaching and movement under the wet summer conditions. 相似文献
19.
A model to project forest growth in the Terra Firme forests of the eastern Amazon is described. It is based on 12–17 years measurements from experimental plots at Jarí and Tapajós. Forest stands are represented by cohorts of species group, diameter, and defect. There are 54 species groups, with a robust diameter increment function fitted to each, tables of mortality by crown and defect status, and recruit lists by disturbance level and locality. Stand level functions partition trees by crown status, and modify growth for stand density. Recruitment is a function of basal-area losses. Evaluation compares model performance with two experiments involving heavy felling in Tapajos State Forest. At one site, total bole volume growth of all species over 45 cm DBH was 2.56 m 3 ha −1 year −1 over 17 years, whereas the model projected 3.13 m 3 ha −1 year −1. At the other site, actual growth over 12 years was 0.39 m 3 ha −1 year −1, with the model giving an identical result. Both felled and control plots are compared in the study and accurately simulated. Some weaknesses in the model are discussed. 相似文献
20.
Carbon (C) sequestration was studied in managed boreal forest stands and in wood products under current and changing climate in Finland. The C flows were simulated with a gap-type forest model interfaced with a wood product model. Sites in the simulations represented medium fertile southern and northern Finland sites, and stands were pure Scots pine and Norway spruce stands or mixtures of silver and pubescent birch. Changing climate increased C sequestration clearly in northern Finland, but in southern Finland sequestration even decreased. Temperature is currently the major factor limiting tree growth in northern Finland. In southern Finland, the total average C balance over the 150 year period increased slightly in Scots pine stands and wood products, from 0.78 Mg C ha−1 per year to 0.84 Mg C ha−1 per year, while in birch stands and wood products the increase was larger, from 0.64 Mg C ha−1 per year to 0.92 Mg C ha−1 per year. In Norway spruce stands and wood products, the total average balance decreased substantially, from 0.96 Mg C ha−1 per year to 0.32 Mg C ha−1 per year. In northern Finland, the total average C balance of the 150 year period increased under changing climate, regardless of tree species: in Scots pine stands and wood products from 1.10 Mg C ha−1 per year to 1.42 Mg C ha−1 per year, in Norway spruce stands and wood products from 0.69 Mg C ha−1 per year to 0.99 Mg C ha−1 per year, and in birch stands and wood products from 0.43 Mg C ha−1 per year to 0.60 Mg C ha−1 per year. C sequestration in unmanaged stands was larger than in managed systems, regardless of climate. However, wood products should be included in C sequestration assessments since 12–55% of the total 45–214 Mg C ha−1 after 150 years' simulation was in products, depending on tree species, climate and location. The largest C flow from managed system back into the atmosphere was from litter, 36–47% of the total flow, from vegetation 22–32%, from soil organic matter 25–30%. Emissions from the production process and burning of discarded products were 1–6% of the total flow, and emissions from landfills less than 1%. 相似文献
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