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1.
2.
It is known that soil property varies along the slope. It suggests that soil solution chemistry also differs topographically.
To determine the variation in soil solution chemistry within one watershed, soil solution chemistry at the different positions
of the slope was investigated. Soil N transformation changed along the slope. NH4
+ ratio to inorganic N (NH4
+ + NO3
−) increased upslope. The tendency was verified by laboratory incubation. After incubation most of the mineralized N was nitrified
at the lower part of the slope, while little nitrification occurred at the upper part of the slope. At the ridge and the backslope
inorganic N form in soil solution was concomitant with inorganic N form by incubation. At the ridge NH4
+ was predominant form in soil solution, at that time major anion was sea salt originated Cl−. From this, soil solution chemistry seems to be regulated by the external nutrient source at the ridge. In the second year
of lysimeter installation NO3
− concentration increased in both sites and the ratio of NH4
+ to inorganic N decreased. It was considered due to the effect of lysimeter installation. The lag time and the magnitude of
NO3
− increase were different between the ridge and the backslope. It would be related with soil N transformation in pre-disturbance.
The influence of disturbance were shown in other solute concentrations of soil solution. 相似文献
3.
林木氮素吸收偏好性及其形成机制研究进展 总被引：1，自引：1，他引：0
森林土壤中可被林木吸收利用的氮（N）素主要以铵态氮（NH4+-N）和硝态氮（NO3--N）的形态存在。受全球气候变暖、氮沉降和人类活动等因素的影响，NH4+和NO3-的分布存在很大的时间波动性和空间异质性，且NH4+-N和NO3--N亏缺已成为限制林地生产力的主要因素。在森林土壤N亏缺和N异质分布的逆境中，在林木长期进化过程中形成了对不同形态N素的吸收偏好，且这种吸收偏好会随生长环境条件而发生改变。特别是对于NH4+和NO3-这2种主要形态的偏好选择性已被证明是决定林木生产力、竞争、共存和生态演替的重要因素之一。对不同树种在N异质分布环境下的N吸收偏好和形成机制的研究，是揭示林木N素营养遗传特性和提高林地N素利用效率的关键。文中从森林土壤中N的主要形态及其分布特征、林木对不同形态N素的吸收偏好和形成机制、林木N吸收偏好的影响因素3个方面进行总结阐述，并对未来研究方向进行展望，以期为我国人工林培育中不同树种的造林配置和合理N素施肥技术提供理论依据和参考。 相似文献
4.
Current uptake of 15N-labeled ammonium and nitrate in flooded and non-flooded black spruce and tamarack seedlings 总被引：1，自引：0，他引：1
5.
Virginia Sanz Pérez Pilar Castro Díez Fernando Valladares 《Annals of Forest Science》2007,64(2):201-210
We compare dry mass (DM) and storage of starch (St) and nitrogen (N) in seedlings of three Mediterranean oaks, two evergreens (Quercus coccifera L. and Q. ilex L. subsp. ballota (Desf.) Samp) and one deciduous (Q. faginea Lam.), across different scenarios of nutrient and water availabilities. Three fertilization (5, 50 and 200 mg of N per plant and growing period) and watering (28–39, 55–71 and 70–85 g H2O 100 g soil ?1 gravimetric soil water) treatments were applied to current-year seedlings between May and October 2002 in two independent experiments. The three species showed a similar response to fertilization, storing nitrogen instead of increasing biomass, in agreement with adaptations to nutrient-poor habitats. However, they differed in their responses to water, reflecting the different water requirements in the field: Q. coccifera, from arid zones, showed no response to water regarding DM and St; Q. faginea, from humid zones, required higher water availability to simultaneously increase growth and storage; while Q. ilex, spanning over most of the water availability range, exhibited a balanced increase of both functions when water increased moderately. In the two evergreen species, N concentration increased with water supply, whereas the reverse occurred in Q. faginea. The latter species favoured growth over storage at moderate water supply (according to its more competitive strategy), although it was the species which accumulated more St and N at the end of the experiments (autumn). 相似文献
6.
Jaime Puértolas Juan A. Oliet Douglass F. Jacobs Luis F. Benito Juan L. Peñuelas 《Forest Ecology and Management》2010
Tube shelters were designed to protect against browsing, but they improve seedling survival in Mediterranean dry climates. Mechanisms for this response, however, are not fully understood and this knowledge can be useful to help design optimal tube shelters for Mediterranean species and climates. Our objective in this study was to determine if the positive effect of tube shelters is due to enhanced growth during the wet season or to reduced light stress during the dry season. We performed two independent experiments. In the first, we assessed root growth during the wet season in two Mediterranean species with contrasting light tolerance (Quercus ilex L. and Pinus halepensis Mill.) growing in tubes with varying light transmissivity. In the second experiment, we studied the response of a Quercus ilex plantation to different shelter treatments. Root growth during the wet season was reduced with decreasing light transmissivity in the shade intolerant P. halepensis, but not in the shade tolerant Quercus ilex. Survival of Q. ilex shaded by a mesh shelter only during summer was higher than in unsheltered seedlings and similar to the survival in tube and mesh shelters during the whole season. This suggests that shade during the dry period was the main factor explaining survival in this species. This effect could be related to the lower leaf temperature recorded in sheltered seedlings. We conclude that Q. ilex (and perhaps other late successional, shade tolerant Mediterranean species) should be planted in tubes with the currently used light transmissivity because these shelters reduce light stress in summer without impairing root growth in the wet season. However, current tubes impair root growth in P. halepensis (and likely other pioneer, shade intolerant Mediterranean species), so higher transmissivity tubes may be necessary. Optimal transmissivity for tube shelter in Mediterranean climates is species-specific and identifiable as the point that minimizes light stress during summer without impairing root growth in the wet season. 相似文献
7.
Athina A. Pappa Nikolaos E. Tzamtzis Sofia E. Koufopoulou 《Annals of Forest Science》2008,65(2):210-210
The application of Long Term fire Retardants (LTRs) for forest fire prevention and/or suppression purposes can result in chemicals leaching, from soil to the drainage water, during the annual rain fall period. In leachates, large concentrations of nitrogen (N), one of the major components of LTRs, could affect the groundwater quality. N leaching due to the application of a nitrogen phosphate based LTR was studied in laboratory microcosms. The concentrations of nitrate (NO 3 ? -N) and ammonium nitrogen (NH 4 + -N) were measured in the resulting leachates from pots with forest soil and pine seedlings (Pinus halepensis) alone and in combination with fire. Up to 30% of the total N in the retardant was lost to leaching, primarily as NO 3 ? -N. The vegetation seems to decrease to some extent the N leaching. The N leaching from treated pots with a burnt tree is lower compared with that from treated pots with a living tree, due to the partial N volatilization during the fire. Although this is a laboratory study, these results may be considered as rough indications of LTR environmental implications, due to the leaching of a significant part of the retardant’s N into groundwater. 相似文献
8.
Wei-Xing Zhu 《Forest Ecology and Management》2011,261(3):675-682
Human activities have fundamentally changed global nitrogen (N) cycling, leading to elevated N deposition in most parts of the world. The fate of deposited N, whether being retained to sustain plant growth or causing ecosystem N saturation, is critical to the global carbon (C) cycling and local environment. In a short-term laboratory experiment, we used 15N-labeled NH4+ and NO3− to study the fate of N inputs in forest soils and what regulates N retention. Soils with a wide range of organic matter content and other attributes were collected from a 70-year-old plantation containing monotypic stands of Norway spruce (Picea abies), red pine (Pinus resinosa), sugar maple (Acer saccharum), and red oak (Quercus rubra), and separated into 0-5 cm and 5-15 cm layers. Nitrogen added to the soil was either immediately extracted (Time 0: T0) with K2SO4 solution, or incubated for 7 d (T7) and then extracted. Retention of 15N into the non-extractable soil pool at T0 was limited; but after the 7-d incubation, between 20 and 70% of the 15NH4+ was retained. Nitrification transformed on average 50% of the 15NH4+ into 15NO3− during the incubation while retention of 15NO3− at T7 remained low (7.40 ± 1.08%). Retention of 15NH4+ into non-extractable soil at T7 was positively correlated to the percentage of soil organic matter (SOM) (r2 = 0.323, P < 0.001), and was significantly higher (P < 0.001) in the high-SOM 0-5 cm layer than in the low-SOM 5-15 cm layer. Conversion of 15NH4+ to 15NO3− during incubation significantly reduced the 15NH4+ retention (P < 0.001). Our results suggest that the variations of SOM and other soil attributes play strong roles in the retention of newly deposited inorganic N and could affect forest ecosystem responses to chronic N deposition. 相似文献
9.
Root mat method described by Kuchenbuch and Jungk was used to study the rhizosphere processes. The experiment was carried
out on two years oldPinus koraiensis seedlings. Soil samples collected from the upper 20-cm soil layer in Changbai Mountain were treated with three different
forms of nitrogen fertilizers: NO3
−−N, NH4
+−N and NH4NO3. The results showed that the soil pH and available P near the roots were all lower than in the bulk soil in control treatment.
NH4
+−N application greatly decreased the soil pH near the roots compared to the control treatment and promoted the absorption
of phosphorus, which led to a more remarkable depletion region of available P. On the contrary, the rhizosphere soil pH was
higher than in the bulk soil in treatments with NO3
−−N and retarded the P absorption, which led to a nearly equal available P contents to the bulk soil. In treatment with NH4NO3, the rhizosphere soil pH was only a little lower than that in the control treatment and its effects on P absorption is mediate
between the treatments with NH4
+−N and NO3
−−N.
Foundation item: This paper was supported by National Natural Science Foundation of China (Grant No. 30170167).
Biography: Chen Yong-liang (1969-), male, Ph. Doctor, lecture of Northeast Forestry University, Harbin 150040, Post-doctor in Institute
of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P.R. China. E-mail: ylchin@sohu.com
Responsible editor: Seng Funan 相似文献
10.
Seedlings of Quercus ilex and Q. cerrioides, an evergreen and a winter-deciduous oak co-occurring in western-Mediterranean forests, were grown at two light regimes (8 and 36% of photosynthetically active radiation), at two water regimes (500 and 800 mm) and with two nutrient availabilities (standard substrate and 7% increase in soil N). The concentrations of soluble condensed tannins (CT) and nitrogen in the leaves were analyzed to test the phenotypic plasticity of these commonly related parameters in two con-generic species with contrasting leaf habit. Q. ilex contains seven times more CT and a few less N than Q. cerrioides. Light increased CT, whereas neither fertilization nor water had an effect on CT. N concentration was decreased by light, increased by fertilization and not affected by water treatment. Plant growth was increased by light but not affected by fertilization or water treatment. CT were negatively correlated with N concentration. CT of the evergreen species exhibited greater plasticity than the deciduous one as reflected by a steeper negative correlation among nitrogen and CT concentrations in Q. ilex. Given the antiherbivory activity of CT, this implies that in less shaded environments, e.g. canopy aperture by disturbances, leaf tissue quality for herbivores will be much more reduced in Q. ilex than in Q. cerrioides. Higher leaf CT in Q. ilex and its higher plasticity to light availability may explain the higher browsing by sheep in Q. cerrioides than in Q. ilex resprouts, as well as the low recruitment rates of seedlings of the former species, reported in other studies. 相似文献
11.
The fate of high and equally distributed ammonium and nitrate deposition was followed in a 72-year-old roofed Norway spruce forest at Solling in central Germany by separately adding 15NH4+ and 15NO3− to throughfall water since November 2001. The objective was to quantify the retention of atmospheric ammonium and nitrate in different ecosystem compartments as well as the leaching loss from the forest ecosystem. δ15N excess in tree tissues (needles, twigs, branches and bole woods) decreased with increased tissue age. Clear 15N signals in old tree tissues indicated that the added 15N was not only assimilated to newly produced tree tissues but also retranslocated to old ones. During a period of over 3-year 15N addition, 30% of 15NH4+ and 36% of 15NO3− were found in tree compartments. For both 15N tracers, 15% of added 15N was found in needles, followed by woody tissues (twigs, branches and boles, 7–13%) and live fine roots (7%). The recovery of 15NH4+ and 15NO3− in the live fine roots differed with soil depth. The recovery of 15NH4+ tended to be higher in the live fine roots in the organic layer than in the upper mineral soil. In the live fine roots in deeper soil, the recovery of 15NO3− tended to be higher than that of 15NH4+. Soil retained the largest proportion of 15N, accounting for 71% of 15NH4+ and 42% of 15NO3−. Most of 15NH4+ was recovered in the organic layer (65%) and the recovery decreased with soil depth. Conversely, only 8% of 15NO3− was found in the organic layer and 34% of 15NO3− was evenly distributed throughout the mineral soil layers. Nitrate leaching accounted for 3% of 15NH4+ and 19% of 15NO3−. Only less than 1% of the both added 15N was leached as DON. These results suggested that trees had a high contribution to the retention of atmospheric N and soil retention capacity determined the loss of atmospheric N by nitrate leaching. 相似文献
12.
ZHAO Qiong ZENG De-hui FAN Zhi-ping 《林业研究》2008,19(1):44-48
A laboratory simulated freeze-thaw was conducted to determine the effects of freeze-thaw on soil nutrient availability in temperate semi-arid regions. Soil samples were collected from sandy soils （0-20 cm） of three typical ecosystems （grassland, Mongolian pine plantation and poplar plantation） in southeastern Keerqin Sandy Lands of China and subjected to freeze-thaw treatment （-12℃ for 10 days, then r 20℃ for 10 days） or incubated at constant temperature （20℃ for 20 days）. Concentrations of the soil NO3^--N, NH4^＋-N, NaHCO3 extractable inorganic P （LPi） and microbial biomass P （MBP） were determined on three occasions： at the start of the incubation, immediate post-thawing and at the 10th day post-thawing. The results showed that soil net nitrification and N mineralization rates at three sites were negatively affected by freeze-thaw treatment, and decreased by 50%-85% as compared to the control, of which the greatest decline occurred in the soil collected from poplar plantation. In contrast, the concentration of soil NH4^＋-N, NaHCO3 extractable inorganic P （LPi） and microbial biomass P were insignificantly influenced by freeze-thaw except that LPi and NH4^＋-N showed a slight increase immediate post-thawing. The effects of freeze-thaw on soil N transformation were related to soil biological processes and the relatively constant available P was ascribed to severe soil aridity. 相似文献
13.
Intensification of coffee (Coffea arabica) production is associated with increases in inorganic fertilizer application and decreases in species diversity. Both the use of organic fertilizers and the incorporation of trees on farms can, in theory, reduce nutrient loss in comparison with intensified practices. To test this, we measured nutrient concentrations in leachate at 15 and 100 cm depths on working farms. We examined (1) organically managed coffee agroforests (38 kg N ha?1 year?1; n = 4), (2) conventionally managed coffee agroforests (96 kg N ha?1 year?1; n = 4), and (3) one conventionally managed monoculture coffee farm in Costa Rica (300 kg N ha?1 year?1). Concentrations of nitrate (NO3 ?-N) and phosphate (PO4 3?-P) were higher in the monoculture compared to agroforests at both depths. Nitrate concentrations were higher in conventional than organic agroforests at 15 cm only. Soil solutions collected under nitrogen (N)-fixing Erythrina poeppigiana had elevated NO3 ?-N concentrations at 15 cm compared to Musa acuminata (banana) or Coffea. Total soil N and carbon (C) were also higher under Erythrina. This research shows that both fertilizer type and species affect concentrations of N and P in leachate in coffee agroecosystems. 相似文献
14.
Allocation of biomass and nutrient elements including Nitrogen to above and belowground compartments of beech seedlings (Fagus sylvatica L.) treated by labeled nitrogen fertilizer in the form of 15NH4 and 15NO3 were investigated at the end of two successive growing seasons. Pot cultured beech seedlings were grown at a green house on intact soil cores sampled from three adjacent stands including beech, Norway spruce and mixed beech-spruce cultures of Solling forest, Germany. Comparing biomass allocation and nutrients concentrations of the seedlings between the control and 15N-fertilized treatments revealed no significant effect of N fertilization on nutrients uptake by seedlings over the experiment. The form of N input influenced its movement into plant pools. It was demonstrated that beech seedlings take up nitrogen mainly in the form of nitrate, which is then reduced in the leaves, although the differences between the retention of NO3 ?-N and NH4 +-N in plants were not statistically significant. Percent recoveries of 15N in trees were typically greater after 15NO3 than after 15NH4 additions. It was indicated that immobilization of 15N tracer in fine roots was a slower process comparing other plant compartments such as stem and coarse roots, but a powerful sink for N during the course of study. 相似文献
15.
Bernard Prévosto Yogan Monnier Christian RipertCatherine Fernandez 《Forest Ecology and Management》2011,262(8):1426-1433
The use of shelterwoods to favour the development of natural or underplanted seedlings is common in temperate forests but rare in the pine forests of the Mediterranean area. Our aim was to assess the use of shelterwoods in Aleppo pine (Pinus halepensis) woodlands in southern France to promote the survival and growth of two co-occurring oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex.Twelve Aleppo pine stands were selected and differentially thinned to create a light shelterwood (basal area = 10 m2/ha, irradiance 52%), a medium shelterwood (basal area = 19 m2/ha, irradiance 33%) and a dense shelterwood (basal area = 32 m2/ha, irradiance 13%). A total of 1248 sowing points, half composed of Q. pubescens and half of Q. ilex, were then set up in these three conditions. Seedling survival and growth were monitored for 3 years. Plant stress was assessed by measuring predawn leaf potential and photosynthetic performance through the Fv/Fm ratio. Soil moisture was also recorded at two depths during two growing seasons.Survival was high for both species in all three conditions due to three consecutive wet years. The lowest survival was recorded for Q. pubescens in the dense shelterwoods. Growth in diameter and height increased from the dense to the light shelterwoods. Shrubs developed more strongly in the light shelterwood, and increasing shrub cover enhanced height growth. Photosynthetic performance was lowest for Q. pubescens in dense shelterwoods and highest in light shelterwoods, whereas the reverse was true for Q. ilex. The lowest predawn potentials were recorded in the dense shelterwoods even though higher soil water content values were measured in this treatment during the summer drought.We show that light shelterwoods were more beneficial to growth than denser ones, indicating control mainly by light availability during the 3 years of the study. However, as lower soil moisture at 30-50 cm depth and faster understorey development were also recorded in this condition, more extended observation is needed to determine whether this benefit persists in subsequent years. 相似文献
16.
Megumi Kuroiwa Keisuke Koba Kazuo Isobe Ryunosuke Tateno Asami Nakanishi Yoshiyuki Inagaki Hiroto Toda Shigeto Otsuka Keishi Senoo Yuichi Suwa Muneoki Yoh Rieko Urakawa Hideaki Shibata 《Journal of Forest Research》2011,16(5):363-373
Measurements of gross NH 4 + and NO 3 ? production in forest soils were conducted using the 15N pool dilution method. Mineral topsoils (0?C10?cm depth) were collected from four forests from northern to southern Japan with a natural climate gradient to elucidate the mechanisms regulating gross nitrification rates in forest soils. Additionally, we attempted to evaluate the relative importance of heterotrophic nitrification in gross total nitrification using acetylene as a specific inhibitor of autotrophic nitrification. Distinct differences were found among sites in the gross rates of NH 4 + production (3.1?C11.4?mg?N?kg?1?day?1) and gross total nitrification (0.0?C6.1?mg?N?kg?1?day?1). The rates of gross heterotrophic nitrification were low in this study, indicating that heterotrophic nitrification is of minor importance in most forest mineral topsoils in Japan. Significant relations were found between gross autotrophic nitrification and gross NH 4 + production, soil N, and soil C concentrations, but none was found between gross autotrophic nitrification and soil pH. We determined the critical value of the gross NH 4 + production rates for gross autotrophic nitrification under which no gross autotrophic nitrification occurred, as well as the critical soil C/N ratio above which gross autotrophic nitrification ceased. Results show that tight coupling of production and consumption of NH 4 + prevents autotrophic nitrifiers from utilizing NH 4 + as long as NH 4 + availability is low. 相似文献
17.
In terrestrial ecosystems, soil nutrient regimes at a plant’s living site generally represent the plant’s “nutrition habitat”.
Plant species frequently well adapt to their original “nutrition habitat” during a long process of evolution, and the apparent
preference for ammonium or nitrate nitrogen source (NH4
+ or NO3
−) might be an important aspect of the adaptation. Plants typically favor the nitrogen form most abundant in their natural
habitats. Nitrate has been recognized as the dominant mineral nitrogen form in most agricultural soils and the main nitrogen
source for crops, but it is not usually the case in forest ecosystems. A large number of studies show that the “nutrition
habitats” associated with primary forest soils are typically dominated by NH4
+ rather than NO3
−, generally with NO3
− content much lower than NH4
+. Low levels of NO3
− in these forest soils generally correspond to low net rates of nitrification. The probable reasons for this phenomenon include:
1) nitrification limitations and/or inhibitions caused by lower pH, lower NH4
+ availability (autotrophic nitrifiers cannot successfully compete for NH4
+ with heterotrophic organisms and plants), or allelopathic inhibitors (tannins or higher-molecular-weight proanthocyanidins)
in the soil; or 2) substantial microbial acquisition of nitrate in the soils, which makes net nitrification rates substantially
less than gross nitrification rates even though the latter are relatively high.
Many coniferous species (especially such late successional tree species as Tsuga heterophylla, Pinus banksiana, Picea glauca, Pseudotsuga meziesii, Picea abies, etc.) fully adapt to their original NH4
+-dominated “nutrition habitats” so that their capacities of absorbing and using non-reduced forms of nitrogen (e.g., NO3
−) substantially decrease. These conifers typically show distinct preference to NH4
+ and reduced growth due to nitrogen-metabolism disorder when NO3
− is the main nitrogen source. The physiological and biochemical mechanisms that account for the adaptation to NH4
+-dominated systems (or limited ability to use NO3
−) for the coniferous species include: i) distribution and activity of enzymes for catalyzing nitrogen reduction and assimilation,
generally characterized by lower nitrate reductase (NR); ii) greater tolerance to NH4
+ or rapid detoxification of ammonium nitrogen in the roots; iii) lower capacity of absorption to NO3
− by roots that might be controlled by feedback regulations of certain N-transport compounds, such as glutamine; iv) relations
and balance between nitrogen and other elements (such as Ca2+, Mg2+, and Zn2+ etc.). Some NH4
+-preferred conifers might be more adapted (tolerant) to lower base cation conditions; v) NO3
− nutrition, rather than NH4
+, that may lead to the loss of considerable quantities of organic and inorganic carbon to the surrounding media and mycorrhizal
symbiont and probably contribute to slower growth; and vi) the metabolic cost of reducing NO3
− to NH4
+ that may make shade-tolerant conifers favor the uptake of reduced nitrogen (NH4
+).
The adaptation of late successional conifers to NH4
+-dominated habitats has profound ecological implications. First, it might be an important prerequisite for the climax forest
communities dominated by these conifers to maintain long-term stability. Second, primary coniferous or coniferous-broadleaved
forests have been widely perturbed because of commercial exploitation, where the soil ammonium nitrogen pool tends to be largely
transformed to nitrate after disturbance. In such a situation, the coniferous species that were dominant in undisturbed ecosystems
may become poor competitors for nitrogen, and the site will be occupied by early successional (pioneer) plants better adapted
to nitrate utilization. In other words, the implicit adaptation of many conifers dominant in undisturbed communities to ammonium
nitrogen will cause difficulties in their regeneration on disturbed sites, which must be taken into account in the practical
restoration of degraded temperate forest ecosystems.
__________
Translated from Acta Ecologica Sinica, 2005, 25(11): 3,082–3,092 [译自: 生态学报] 相似文献
18.
Héctor A. Bahamonde P. L. Peri R. Alvarez A. Barneix A. Moretto G. Martínez Pastur 《Agroforestry Systems》2013,87(2):259-271
In most temperate forest, nitrogen (N) is considered a limiting factor. This becomes important in extreme environments, as Nothofagus antarctica forests, where the antecedents are scarce. Thinning practices in N. antarctica forests for silvopastoral uses may modify the soil N dynamics. Therefore, the objective of this work was to evaluate the temporal variation of soil N in these ecosystems. The mineral extractable soil N, net nitrification and net N mineralization were evaluated under different crown cover and two site quality stands. The mineral N extractable (NH4 +–N + NO3 ?–N) was measured periodically. Net nitrification and net N mineralization were estimated through the technique of incubation of intact samples with tubes. The total mineral extractable N concentration varied between crown cover and dates, with no differences among site classes. The lowest and highest values were found in the minimal and intermediate crown cover, respectively. In the higher site quality stand, the annual net N mineralization was lower in the minimal crown cover reaching 11 kg N ha?1 year?1, and higher in the maximal crown cover (54 kg N ha?1 year?1). In the lower site quality stand there was no differences among crown cover. The same pattern was found for net nitrification. Thinning practices for silvopastoral use of these forests, keeping intermediate crown cover values, did not affect both N mineralization and nitrification. However, the results suggest that total trees removal from the ecosystem may decrease N mineralization and nitrification. 相似文献
19.
《Forest Ecology and Management》1999,121(3):227-237
Forest fires are known to influence nutrient cycling, particularly soil nitrogen (N), as well as plant succession in northern forest ecosystems. However, few studies have addressed the dynamics of soil N and its relationship to vegetation composition after fire in these forests. To investigate soil N content and vegetation establishment after wildfire, 13 sites of varying age class were selected in the Sub-Boreal spruce zone of the central interior of British Columbia, Canada. Sites varied in time since the last forest fire and were grouped into three seral age classes: (a) early-seral (<14 years), (b) mid-seral (50–80 years) and (c) late-seral (>140 years). At each site, we estimated the percent cover occupied by trees, shrubs, herbs and mosses. In addition, the soil samples collected from the forest floor and mineral horizons were analyzed for the concentrations of total N, mineralizable N, available NO3−-N and available NH4+-N. Results indicated that soil N in both the forest floor and mineral horizons varied between the three seral age classes following wildfire. Significant differences in mineralizable N, available NO3−-N and available NH4+-N levels with respect to time indicated that available soil N content changes after forest fire. Percent tree and shrub cover was significantly correlated to the amount of available NH4+-N and mineralizable N contents in the forest floor. In the mineral horizons, percent tree cover was significantly correlated to the available NH4+-N, while herb cover was significantly correlated with available NO3−-N. Moss cover was significantly correlated with total N, available NO3−-N and mineralizable N in the forest floor and available NO3−-N in the mineral horizons. We identified several unique species of shrubs and herbs for each seral age class and suggest that plant species are most likely influencing the soil N levels by their contributions to the chemical composition and physical characteristics of the organic matter. 相似文献
20.
Effects of nursery shading on seedling quality and post-planting performance in two Mediterranean species with contrasting shade tolerance 总被引：1，自引：1，他引：0
In Mediterranean climates, seedlings are frequently shaded in the nursery to avoid heat damage and save water. However, the
impact of this shading on the seedling quality and transplanting performance of Mediterranean species is not well known. We
studied the effect of nursery shading on pre-planting features and post-planting performance of two Mediterranean tree species:
the shade-intolerant pioneer Pinus halepensis and the shade-tolerant late-successional Quercus ilex. We grew one-year-old seedlings of both species under 100, 40 and 5% full sunlight. Shade had a low impact on the morphology
and physiology of Q. ilex seedlings. In pines, only the deep shade treatment produced low quality seedlings with poor root development. In both species,
transference to high light at planting in autumn did not impose any additional stress than that caused by frosts, but initial
root growth was impaired in the two shaded treatments in pine. Post-planting growth and survival of oak seedlings showed no
difference between treatments. Pine seedlings grown in deep shade showed higher mortality and lower growth after planting
than those grown in full sun and intermediate light treatments, while intermediate light only reduced growth. For the nursery
culture of Q. ilex seedlings, we advise using low light levels during summer to save water without impairing field performance. In P. halepensis, seedlings should be cultured under full sunlight conditions to maximize post-planting growth, but they can be cultured under
intermediate light without impairing survival. 相似文献