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1.
The belowground effects of Phytophthora cinnamomi on 1‐year‐old saplings of two common oak species in mid‐Atlantic US forests, white ( Quercus alba) and red oak ( Q. rubra), were examined after incubation in pathogen‐infested soilless potting mix. Fine root lengths (0–1.5 mm in diameter) of both oak species were quantified after incubation at successive 30‐day intervals up to 300 days, for a total of 10 incubation periods. In addition, colony‐forming units (CFU) of P. cinnamomi were quantified after white oak saplings were incubated in infested soilless potting mix at different temperature/duration combinations that reflect soil conditions present in the mid‐Atlantic United States. Impact of P. cinnamomi on fine root lengths of red and white oak saplings varied considerably over time. Significant periods of fine root loss occurred primarily during spring, when bud break and leaf flush began for both oak species. Red oaks had 17% fine root loss on average, while white oaks appeared more resistant to P. cinnamomi infection with a 2% decrease in fine roots over the course of the experiment. Phytophthora cinnamomi CFU declined significantly with exposure to all incubation temperatures except 8°C. This was in contrast to in vitro experiments, where the optimum temperature for mycelial growth was determined to be 21°C and above. Significant fine root loss caused by P. cinnamomi depended on plant phenology and the oak species tested. Extreme soil temperatures have a significant adverse impact on temporal changes of P. cinnamomi population. 相似文献
2.
Aboveground and belowground biomass of 15-year-old under-planted European beech seedlings ( Fagus sylvatica L.) in Norway spruce stand were studied along a light gradient in three plots, in the northern part of Slovenia. Differences
in soil water content, aboveground and fine root biomass distribution were confirmed between studied plots. Light had significant
effect on the total biomass, root-shoot ratio (0.388 ± 0.076 under canopy, 0.549 ± 0.042 in the edge, 0.656 ± 0.047 in the
open), specific root length (SRL) of fine beech roots (561.9 ± 42.2 under canopy, 664.3 ± 51.2 in the edge, 618.2 ± 72.8 in
the open) and specific leaf area in beech, indicating morphological adjustment to shade. However, SRL of beech fine roots
indicated no change between plots. The correlation between total aboveground and root biomass and light below the mature stand
canopy was higher in the case of diffuse light intensity. Most fine roots of spruce were concentrated in the top (0–20 cm)
soil layer. Beech fine roots under canopy and edge conditions were also concentrated in top (0–20 cm) soil layer and exhibited
shift downwards to deeper soil horizons in open plot. Root proportion between beech and spruce changed with light toward beech
with increasing light intensity for both fine and coarse roots. 相似文献
3.
Oak decline has been a serious problem in Europe since the beginning of the twentieth century. In south‐west Spain, Quercus ilex and Q. suber are the main affected species, and their decline has been associated with Phytophthora cinnamomi. During the last 10 years, a severe decline of Q. ilex and Q. faginea accompanied by a significant decrease in the production of acorns affecting natural regeneration was observed in the eastern part of the Iberian Peninsula. Therefore, the aim of this study was to investigate the possible involvement of Phytophthora spp. in the decline. A forest in the Natural Park ‘Carrascar de la Font Roja’ in Comunidad Valenciana (eastern Spain), which is dominated by Q. ilex and Q. faginea, was surveyed during 2010–2011. Symptomatic trees showed thinning and dieback of the crown, withering of leaves and death. An extensive loss of both lateral small woody roots and fine roots and callusing or open cankers on suberized roots were observed. Soil samples containing fine roots were baited using both Q. robur leaves and apple fruits. Six Phytophthora species were isolated: P. cryptogea, P. gonapodyides, P. megasperma, P. quercina, P. psychrophila and P. syringae. These are the first records of P. quercina and P. psychrophila on Q. faginea, of P. quercina in Spain and of P. psychrophila in mainland Spain. A soil infestation trial was conducted for 6 months under controlled conditions with 1‐year‐old seedlings of Q. ilex and Q. faginea. Phytophthora cinnamomi was included in the pathogenicity test for comparison. The results showed that Q. ilex seedlings were generally more susceptible to infection than Q. faginea with P. cinnamomi being the most aggressive pathogen to both oak species. The two most commonly isolated Phytophthora species, P. quercina and P. psychrophila, also proved their pathogenicity towards both Q. ilex and Q. faginea. 相似文献
4.
Dry evergreen forest (DEF) and dry deciduous dipterocarp forest (DDF) are major forest types extensively distributed in northeastern
Thailand, exhibiting different nutrient cycling properties. This study aims to improve our understanding on the pattern of
mass loss and nitrogen release from two categories of roots (fine, <2 mm and small, 2–5 mm) of Hopea ferrea at DEF and fine roots of mixed trees and dwarf bamboo ( Arundinaria pusilla) at DDF sites. Decomposition experiment was performed for more than 12 months using buried litter bag technique. Initial
chemistry was significantly different among the four root litters; fine root of H. ferrea exhibited a low ratios of C:N and acid-insoluble:N. The fine root of dwarf bamboo was characterized by high contents of total
carbohydrate and ash. Decomposition rate constants (year −1) of ash-free weight remaining were 1.27 and 0.55 for fine and small roots of H. ferrea, and 0.73 and 0.66 for fine root of mixed trees and dwarf bamboo, respectively. At the end of the experiment, the N concentration
in fine and small roots of H. ferrea increased to 1.5 times the initial concentration. Whereas, N mass of dwarf bamboo decreased during the experiment. This suggests
a different pattern of root decomposition and N release in two forest ecosystems. Generally, the fine root decomposition was
faster in the DEF than in the DDF. The role of initial litter chemistry was more pronounced than the climatic seasonality
on the belowground decomposition pattern in our study. 相似文献
5.
The performance of laboratory X‐ray computed tomography (XCT) for the non‐destructive imaging of root wood was evaluated. Lateral roots of oriental cherry ( Prunus serrulata var. spontanea) and Japanese zelkova ( Zelkova serrata) were severed in spring and maintained in soil for 6 months. Without sectioning, XCT revealed the phloem, xylem and vascular cambium structures in the root wood. A virtual transverse section showed a ring of woundwood covering the severed, lateral root of the two trees. Different levels of X‐ray absorption were evident around the cut surfaces of P. serrulata; however, they were rarely detected in Z. serrata. More adventitious roots were observed on Z. serrata than on P. serrulata. Distinct white spots in the rays were only detected in Z. serrata. These results suggest that XCT has potential applications in forest pathology, providing virtual sections of wound closure, wood density distribution, organ redifferentiation, and mineral deposition in root wood. 相似文献
6.
We studied the biology of the ambrosia beetle Platypus quercivorus in the logs of five tree species to determine: (1) the relationship between the amount of frass produced by beetles and tunnel
length, (2) the relationship between frass shape and the morphological characteristics of P. quercivorus mouthparts, and (3) the suitability of five tree species for P. quercivorus reproduction. Five logs each from healthy Quercus crispula, Q. serrata, Castanea crenata, Sorbus japonica, and Cryptomeria japonica trees were used in this experiment. The results showed that there was a linear relationship between the amount of frass and
tunnel length. Whenever powdery frass was produced, larvae were found in the gallery in the log, while fibrous frass was present
only in galleries that contained just adults. The mouthparts of adults were completely sclerotized, which likely accounts
for the fibrous frass production. Host preference of P. quercivorus was examined at two stages using five tree species. The first stage is digging initiation, which concerns male preference
for digging a tunnel. More holes were made by males on S. japonica and Q. serrata logs, while fewer holes were made on C. japonica logs. The second stage is characterized by female orientation, mating, and progeny development. Platypus quercivorus could complete its lifecycle only in the two Quercus spp. 相似文献
7.
Establishment of native timber trees on deforested land may contribute to the livelihood of farmers, to improved ecosystem
services and to increased greenhouse gas uptake. Here, we present a new silvopastoral planting design to assess species performance
and interspecific competition or facilitation effects among native timber and multipurpose trees in Central America. Two timber
species, Tabebuia rosea and Cedrela odorata, were established in three low-density planting regimes allowing combined tree and future livestock production: (1) solitary
planting, (2) companion planting with Guazuma ulmifolia, and (3) companion planting with the nitrogen-fixing Gliricidia sepium. We quantified survival, growth and reforestation potential of the two timber species subjected to the different planting
regimes for the first 2 years after establishment. Nitrogen concentration as well as stable nitrogen and carbon isotope composition
(δ 15N, δ 13C) of leaves of the timber saplings were determined. T. rosea showed higher survival and better growth than C. odorata under varying environmental conditions (soil, concomitant vegetation). Performance of the timber saplings was unaffected
by either companion species. Planting regimes had no effect on foliar nitrogen concentration and δ 15N of the two timber species, although δ 15N values indicated nitrogen fixation activity in G. sepium trees. Planting regimes affected foliar δ 13C values in T. rosea. δ 13C values were significantly higher in solitarily growing individuals, suggesting lower exposition to water stress conditions
in saplings surrounded by companion species. As we found positively correlated growth traits among timber and multipurpose
trees, a combined planting may benefit farmers by providing additional goods and services. 相似文献
8.
Leafminer ( Phyllonorycter, Gracillariidae, Lepidoptera) and aphid ( Tuberculatus, Aphididae, Hemiptera) composition were studied in three deciduous oak species, Quercus dentata, Q. crispula, and Q. serrata, and their hybrids in Tomakomai Experimental Forest of Hokkaido University, Hokkaido, northern Japan. Identification of trees
in this forest was done mainly on the basis of discriminant analysis on leaf morphology with reference to trees in pure Q. dentata and Q. crispula stands and a Q. serrata stand mixed with Q. crispula. The results suggested that hybridization occurred in all combinations (i.e. Q. dentata– Q. crispula, Q. crispula– Q. serrata, and Q. serrata– Q. dentata) and the frequency of hybrids was approximately 10%. The composition of Phyllonorycter and Tuberculatus species differed between Q. dentata and Q. crispula or Q. serrata, but did not differ between Q. crispula and Q. serrata. Thus, Q. dentata could differ from Q. crispula and Q. serrata in chemical properties that determine herbivore host selection, survival, and performance, possibly reflecting eco-physiological
differences or phylogenetic distances. The study insects were divided into three groups: species specialized to Q. dentata (three Phyllonorycter and one Tuberculatus species), those to Q. crispula and Q. serrata (six Phyllonorycter and two Tuberculatus species), and a species collected at least from Q. dentata and Q. crispula (one Tuberculatus species). Putative hybrid trees of Q. dentata and Q. crispula harbored both Q. dentata-specific and Q. crispula-specific insects. 相似文献
9.
Human activities accelerate global nitrogen (N) deposition, and elevated N availability may alter the stoichiometric balance of nutrients and then affect nutrient absorption by plants. The boreal forest is considered one of the world’s most N-limited ecosystems, and its response to N deposition is already a hot issue. In order to explore how long-term nitrogen addition influences nutrient uptake and distribution in Larix gmelinii in a boreal forest, four N treatment levels (0, 25, 50 and 75 kg N ha?1 yr?1) have been applied in a boreal forest since May 2011. Nitrogen addition significantly reduced the soil pH, significantly changed the soil N availability, increased the total N and N/P in needles and fine roots, and decreased the total P in needles and the C/N in soil. Nitrogen addition significantly reduced nitrogen resorption efficiency, and its impacts on P resorption efficiency were not significant. Nitrogen addition significantly increased the root length, surface area and diameter of 4th- and 5th-order transport fine roots. The N and N/P of needles showed seasonal variation. The needle N concentration and N/P were positively correlated with N addition, while the needle P was negatively correlated with nitrogen addition. With increase in nitrogen addition, Larix gmelinii increased its investment in its belowground parts, which may explain why Larix gmelinii tended to put more C in long-lived roots to improve its C utilization efficiency. Given the P deficiency caused by N addition, Larix gmelinii may be more likely to absorb P from the soil and adjust its C distribution to meet its P demand rather than relying on internal nutrient resorption. 相似文献
10.
Litterfall is an important ecological process in forest ecosystems, influencing the transfer of organic matter, carbon (C), nitrogen (N), phosphorous (P) and other nutrients from vegetation to the soil. We examined the production of different litterfall fractions as well as nutrient content and nutrient inputs by senesced and green leaf-litter in a semiarid forest from central Mexico. From September 2006 to August 2007, monthly litter sampling was carried out in monospecific and mixed stands of Quercus potosina and Pinus cembroides. Litterfall displayed a marked bimodal pattern with the largest annual amount (5993 ± 655 kg ha −1 yr −1) recorded in mixed stands, followed by Q. potosina (4869 ± 510 kg ha −1 yr −1), and P. cembroides (3023 ± 337 kg ha −1 yr −1). Leaves constituted the largest fraction of total litterfall reaching almost 60%, while small branches contributed with 20–30%. Overall, N content in leaf-litter was higher while lignin content was significantly lower for Q. potosina than for P. cembroides. Thus, greater litter quality together with higher litter production caused the largest C, N and P inputs to forest soils to occur in monospecific Q. potosina stands. Green leaf fall displayed significantly lower lignin:N and C:N ratios in Q. potosina than P. cembroides suggesting faster decomposition and nutrient return rates by the former. Although we recorded only two green leaf fall events, they accounted for 18% and 11% of the total N and P input, respectively, from leaf-litter during the study period. Apart, from the large spatiotemporal heterogeneity introduced by differences in litter quantity and quality of evergreen, deciduous and mixed stands, green litterfall appears to represent a much more important mechanism of nutrient input to semiarid forest ecosystems than previously considered. 相似文献
11.
The study analyses the effects of two different forms of nitrogen fertilisation (nitrate and ammonium) on root structure and
water uptake of two hybrid poplar ( Populus maximowiczii x P. balsamifera) clones in a field experiment. Water uptake was studied using sap flow gauges on individual proximal roots and coarse root
structure was examined by excavating 18 whole-root systems. Finer roots were scanned and analyzed for architecture. Nitrogen
forms did not affect coarse-root system development, but had a significant effect on fine-root development. Nitrate-treated
trees presented higher fine:coarse root ratios and higher specific root lengths than control or ammonium treated trees. These
allocation differences affected the water uptake capacity of the plants as reflected by the higher sapflow rate in the nitrate
treatment. The diameter of proximal roots at the tree base predicted well the total root biomass and length. The diameter
of smaller lateral roots also predicted the lateral root mass, length, surface area and the number of tips. The effect of
nitrogen fertilisation on the fine root structure translated into an effect on the functioning of the fine roots forming a
link between form (architecture) and function (water uptake). 相似文献
12.
To access the process of nitrogen mineralization in soil, the buried-bag technique was used among traditional agroforestry systems in the Bhabhar belt of Kumaun Himalaya. The present study, determined the relationship between various parameters of N-mineralization with agroforestry systems, seasons and soil depths. Season and soil depth have significantly (p?<?0.001) affected the process of ammonification, nitrification and net N-mineralization. The soil ammonium-N pool was comparatively higher than the nitrate-N pool. Highest amount of ammonium and nitrate-N were recorded in the agri-horticulture (AH) system, and lowest in the agri-horti-silviculture (AHS) system. Among the systems, highest amount of inorganic-N (ammonium?+?nitrate) was recorded during rainy season while, lowest during winter season. The highest ammonification rate (6.47?±?1.47 mg kg?1 month?1) was observed in agri-silviculture system and lowest (5.67?±?1.68 mg kg?1 month?1) in AHS system, while nitrification value was maximum (2.53?±?0.40 mg kg?1 month?1) in AH system and minimum (2.23?±?0.37 mg kg?1 month?1) in AHS system. The values of net N-mineralization were ranged from 4.03?±?0.53 to 13.29?±?0.44 mg kg?1 month?1. The values of inorganic-N and net N-mineralization were significantly more (P?<?0.01) in the surface soil layer (0–20 cm) than the subsurface layers (20–40 cm and 40–60 cm). Nitrogen mineralization was negatively correlated with the soil pH and positively correlated with soil organic carbon and total soil nitrogen. Higher rate of N-mineralization in AHS system indicated rapid turnover of nitrogen due to soil management practices and suggested that the changes in agroforestry based land-use systems alter the process of net N-mineralization, nitrification and ammonification. 相似文献
13.
The reaction of young beech ( Fagus sylvatica L.) and Douglas fir ( Pseudotsuga
menziesii (Mirb.) Franco) saplings on competition of two types of vegetation—(1) gramineous with mainly Agrostis capillaries, Calamagrostis epigejos, Deschampsia flexuosa, and (2) small shrubs with mainly Rubus fruticosus and R. idaeus—on clear cuts on two sites was studied for 2 years. Half the sample saplings were released from competing vegetation by repeated
herbicide applications. This treatment significantly raised the diameter increment in both species at the site with higher
competition intensity, and more strongly after the removal of small shrubs than after the removal of grasses. Sapling length
increment was not significantly affected. After being released from small shrubs, saplings of both species developed a smaller
specific fine root length (cm g −1 fine root biomass) than unreleased saplings during the second year which was characterized by low rainfall. Root nitrogen
concentration significantly increased after weed control in both vegetation types. Sapling foliar content of main nutritional
elements was negatively related to dry mass and total chemical content of surrounding ground vegetation. Based on these results,
a release from ground vegetation could be a useful tool to improve growth of planted beech and Douglas-fir saplings on sites
with well-developed small shrubs competition (mainly by Rubus fruticosus and R. idaeus), or under fairly dry conditions. 相似文献
14.
This study was conducted to compare the virulences of various isolates of Raffaelea quercivora—a fungus that causes Japanese oak wilt disease—towards Japanese oak trees. Five isolates were collected from a wide range of Japan and inoculated into Quercus serrata logs and Q. crispula saplings. The tangential length of the discolored sapwood in the Q. serrata logs differed significantly among the isolates. The trend in isolate virulence was similar for the Q. serrata logs and the Q. crispula saplings. This is the first report suggesting that there is variability in virulence among isolates of R. quercivora. 相似文献
15.
Phytophthora multivora is associated with the rhizosphere of declining Eucalyptus gomphocephala, Eucalyptus marginata and Agonis flexuosa. Two pathogenicity experiments were conducted. The first experiment examined the pathogenicity of five P. multivora isolates and one Phytophthora cinnamomi isolate on the root systems of E. gomphocephala and one P. multivora isolate on the root system of E. marginata. In the second experiment, the pathogenicity of P. multivora to E. gomphocephala and E. marginata saplings was measured using under‐bark stem inoculation. In Experiment 1, the P. cinnamomi isolate was more aggressive than all P. multivora isolates causing significant loss of fine roots and plant death. Two P. multivora isolates and the P. cinnamomi isolate caused significant losses of E. gomphocephala fine roots 0–2 mm in diameter and significantly reduced the surface area of roots 0–1 mm in diameter. One P. multivora and the P. cinnamomi isolate significantly reduced the surface area of roots 1–2 mm in diameter. Two of the P. multivora isolates significantly reduced the number of E. gomphocephala root tips. In E. marginata, the length and surface area of roots 0–1 mm in diameter and number of root tips were significantly reduced by P. multivora infestation. Rhizosphere infestation with the P. multivora isolates and P. cinnamomi isolate on E. gomphocephala, and one P. multivora isolate on E. marginata, did not significantly influence the foliar nutrient concentrations. In Experiment 2, under‐bark inoculation with P. multivora caused significant lesion extension in E. gomphocephala and E. marginata saplings, compared to the control. We propose that P. multivora is inciting E. gomphocephala and E. marginata decline by causing fine root loss and subsequently interfering with nutrient cycling throughout the plant. The impact of fine root loss on the physiology of plants in sites infested with P. multivora requires further research. 相似文献
16.
To clarify the effects of asynchronous seed production among tree species on the population of seed predators, we investigated
the relationship between the annual variation in production of mature acorns and the insect damage in those acorns of two
sympatric oak species, Quercus variabilis Blume and Quercus serrata Thunb. ex Murray, over 4 years at two study sites. The annual variation in acorn production was noticeable, with a coefficient
of variation (CV) at the two sites of 1.05 and 0.80 for Q. variabilis and 0.87 and 0.73 for Q. serrata. Annual fluctuation in acorn production by Q. serrata was synchronized between the two sites. Since annual fluctuation in acorn production was not synchronized between the two
species, the CVs for the total acorn production by both oak species (0.83 and 0.62 at the two sites) were lower than those
for Q. variabilis and Q. serrata alone. The rate of predation by the specialist predators ( Curculio weevils) on the acorns of both species was not related to the annual acorn crop size. Prolonged diapause of Curculio weevils might stabilize their populations. The rate of acorn predation by the generalist predators (tortricid moths) was
also not related to the annual crop size. Asynchronous acorn production by the two oak species would help to stabilize the
population. 相似文献
17.
The sustainability of plantation forests is closely dependent on soil nitrogen availability in short-rotation forests established on low-fertility soils. Planting an understorey of nitrogen-fixing trees might be an attractive option for maintaining the N fertility of soils. The development of mono-specific stands of Acacia mangium (100A:0E) and Eucalyptus grandis (0A:100E) was compared with mixed-species plantations, where A. mangium was planted in a mixture at a density of 50% of that of E. grandis (50A:100E). N 2 fixation by A. mangium was quantified in 100A:0E and 50A:100E at age 18 and 30 months by the 15N natural abundance method and in 50A:100E at age 30 months by the 15N dilution method. The consistency of results obtained by isotopic methods was checked against observations of nodulation, Specific Acetylene Reduction Activity (SARA), as well as the dynamics of N accumulation within both species. The different tree components (leaves, branches, stems, stumps, coarse roots, medium-sized roots and fine roots) were sampled on 5–10 trees per species for each age. Litter fall was assessed up to 30 months after planting and used to estimate fine root mortality. Higher N concentrations in A. mangium tree components than in E. grandis might be a result of N 2 fixation. However, no evidence of N transfer from A. mangium to E. grandis was found. SARA values were not significantly different in 100A:0E and 50A:100E but the biomass of nodules was 20–30 times higher in 100A:0E than in 50A:100E. At age 18 months, higher δ15N values found in A. mangium tree components than in E. grandis components prevented reliable estimations of the percentage of N derived from atmospheric fixation (%Ndfa). At age 30 months, %Ndfa estimated by natural abundance and by 15N dilution amounted to 10–20 and 60%, respectively. The amount of N derived from N 2 fixation in the standing biomass was estimated at 62 kg N ha −1 in 100A:0E and 3 kg N ha −1 in 50A:100E by the 15N natural abundance method, and 16 kg N ha −1 in 50A:100E by the 15N dilution method. The total amount of atmospheric N 2 fixed since planting (including fine root mortality and litter fall) was estimated at 66 kg N ha −1 in 100A:0E and 7 kg N ha −1 in 50A:100E by the 15N natural abundance method, and 31 kg N ha −1 in 50A:100E by the 15N dilution method. The most reliable estimation of N 2 fixation was likely to be achieved using the 15N dilution method and sampling the whole plant. 相似文献
18.
An investigation was conducted to quantify fine roots and roots nodules over the four seasons in forestry and agroforestry alder (Alnus rubra) stands in North Wales. Soil samples collected in each season were excavated at three sampling points (0.30 m, 0.57 m and 1.00 m distance from the base of each tree) from nine trees of the agroforestry and forestry plots. Result showed that the density of live fine root had significant differences in between seasons and treatments (P < 0.001). The mean weight density of live fine root over the four seasons in agroforestry and forestry was 0.27±0.01 kg·m-3 and 0.54±0.03 kg·m-3, respectively. Weight density of dead root in each system remained constant throughout the year. The mean weight density of dead root was also significantly different (P < 0.01) between forestry and agroforestry systems. Weight density of live and dead root nodule was both constant throughout the year and between the different sampling distances. The mean weight densities of live and dead root nodule over the four seasons were 0.09±0.03 kg·m-3 and 0.05±0.03 kg·m-3 in agroforestry and 0.08±0.02 kg·m-3 and 0.03±0.01 kg·m-3 in the forestry plots, respectively. 相似文献
19.
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 N 2 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 δ 15N 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 N 2-free sand culture in the glasshouse. Isotopic discrimination occurring during N 2 fixation and metabolic processes indicated variation of δ 15N 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 N 2 fixation of A. mangium was 54% (±22) and was not affected by age ( P > 0.05). Average yearly quantities of N 2 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
20.
The effects of simulated acid fog (SAF) and ozone (O 3) stress on the growth and physiology of beech ( Fagus crenata) saplings were investigated. Three-year-old beech saplings were exposed to SAFs of pH 3 and pH 5 (control) during May 2007
to July 2008. In each SAF treatment group, half of the saplings were exposed to 60 ppb of O 3 during September 2007 to July 2008. In comparison to the control saplings, those from the pH 3 treatment had lower total
plant biomasses, epicuticular wax amounts, Ca 2+ concentrations in their leaves, and lower starch concentrations in their leaves and roots. The effect of O 3 was significant only for the starch concentration in the roots, but the O 3 exposure also negatively affected the growth and physiology of beech saplings. Results show that acid fog exerts various
severe effects, and that both chronic acid fog and O 3 exposure suppressed the physiological functions of beech saplings. 相似文献
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