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1.
The objectives of this study were to clarify the influences of nitrogen (N) load on the growth and photosynthetic responses
of Quercus serrata seedlings to O 3 and to obtain basic data for evaluating the critical levels of O 3 for protecting Q. serrata forests in Japan. The effects of O 3 and/or N load on growth and photosynthetic activity of Q. serrata seedlings were investigated during the two growing seasons. Two-year-old seedlings were assigned to 12 experimental treatments,
which were comprised of the combination of four gas treatments (charcoal-filtered air and three levels of O 3 at 1.0, 1.5 and 2.0 times ambient concentration) and three N treatments (0, 20 and 50 kg ha −1 year −1). During the second growing season, no significant interactive effects of O 3 and N load on the growth and net photosynthetic rate of the seedlings were detected. Threrfore, we concluded that N supply
to the soil at ≤50 kg ha −1 year −1 does not significantly influence the growth and photosynthetic responses of Q. serrata seedlings to O 3. Based on the O 3 exposure-response relationships for the whole-plant growth of the seedlings, the critical level of O 3 for Q. serrata was estimated to be approximately 36 nmol mol −1 as the average 15-h O 3 concentration during the one growing season. 相似文献
2.
To clarify the effects of ozone (O 3) on nitrogen (N) metabolism in the leaves of Fagus crenata seedlings under different N loads, the combined effects of O 3 and N load on N enzyme activity, amino acid profiles and soluble protein concentrations were investigated. The seedlings
were grown in potted andisol supplied with N at 0 (N0), 20 (N20) and 50 kg ha −1 year −1 (N50) and were exposed to charcoal-filtered air or O 3 at 1.0, 1.5 and 2.0 times the ambient concentration in open-top chambers from April 2004 to October 2005. The average 24-h
concentrations of O 3 during the two growing seasons were 11.8, 42.7, 63.3 and 83.7 ppb, respectively. In July 2005, exposure to O 3 did not significantly affect the concentration of total free amino acids and activities of nitrite reductase and glutamine
synthetase in any N treatment. Exposure to O 3 significantly increased the relative content of acidic amino acids in all N treatments while it significantly reduced concentration
of total soluble protein (TSP) and ratio of TSP concentration to leaf N concentration in the N50 treatment, but not in the
N0 and N20 treatments. Based on the results obtained in the present study, we concluded that exposure to O 3 reduces the allocation of N to soluble protein in addition to O 3-induced degradation of protein in the leaves of seedlings grown under a relatively high N load, with the result that the
degree of O 3-induced reduction in the soluble protein was greater under a relatively high N load than under a relatively low N load. 相似文献
3.
To obtain the basic data for evaluating the critical level of ozone (O 3) to protect Japanese deciduous broad-leaved forest tree species, the growth and photosynthetic responses of Fagus crenata seedlings to O 3 under different nitrogen (N) loads were investigated. The seedlings were grown in potted andisol supplied with N as NH 4NO 3 solution at 0, 20 or 50 kg ha −1 year −1 and were exposed to charcoal-filtered air or O 3 at 1.0, 1.5 and 2.0 times the ambient concentration for two growing seasons. The interactive effect of O 3 and N load on the whole-plant dry mass of the seedlings at the end of the second growing season was significant. The O 3-induced reduction in the whole-plant dry mass of the seedlings was greater in the relatively high N treatment than that in
the low N treatment. This interactive effect was mainly due to the difference in the degree of O 3-induced reduction in net photosynthesis among the N treatments. The degree of O 3-induced reduction in N availability to photosynthesis was greater in the relatively high N treatment than that in the low
N treatment. In conclusion, the sensitivity of growth and photosynthetic parameters of F. crenata seedlings to O 3 become high with increasing amounts of N added to the soil. Therefore, N deposition from the atmosphere should be taken into
account to evaluate the critical level of O 3 to protect Japanese deciduous broad-leaved forest tree species. 相似文献
4.
Biomass and aboveground net primary production (ANPP) in a monospecific pioneer stand of a mangrove Kandelia obovata (S., L.) Yong were quantified. The estimated biomasses in leaves, branches, stems, roots, aboveground and total were 5.61
(3.68%), 28.8 (18.9%), 46.1 (30.2%), 71.8 (47.2%), 80.5 (52.8%) and 152 Mg ha −1 (100%), respectively. Stem phytomass increment per tree was estimated using allometric relationships and stem analysis. Stem
volume without bark of harvested trees showed a strong allometric relationship with D
0.12
H ( D
0.1, diameter at a height of one-tenth of tree height H) ( R
2 = 0.924). Annual stem volume increment per tree showed a strong allometric relationship with D
0.12
H ( R
2 = 0.860). Litterfall rate ranges from 3.87 to 56.1 kg ha −1 day −1 for leaves and 0.177 to 46.2 kg ha −1 day −1 for branches. Seasonal changes of litterfall rate were observed, which showed a peak during wet season (August–September).
Total annual litterfall was estimated as 10.6 Mg ha −1 year −1, in which 68.2% was contributed by the leaves. The ANPP in the K. obovata stand was 29.9–32.1 Mg ha −1 year −1, which is ca. 2.8–3.0 times of annual litterfall. The growth efficiency (aboveground biomass increment/LAI) was 5.35–5.98 Mg ha −1 year −1. The low leaf longevity (9.3 months) and high growth efficiency of K. obovata makes it a highly productive mangrove species. 相似文献
5.
The aim of this study was to quantify the effects of fertiliser N on C stocks in trees (stems, stumps, branches, needles,
and coarse roots) and soils (organic layer +0–10 cm mineral soil) by analysing data from 15 long-term (14–30 years) experiments
in Picea abies and Pinus sylvestris stands in Sweden and Finland. Low application rates (30–50 kg N ha −1 year −1) were always more efficient per unit of N than high application rates (50–200 kg N ha −1 year −1). Addition of a cumulative amount of N of 600–1800 kg N ha −1 resulted in a mean increase in tree and soil C stock of 25 and 11 kg (C sequestered) kg −1 (N added) (“N-use efficiency”), respectively. The corresponding estimates for NPK addition were 38 and 11 kg (C) kg −1 (N). N-use efficiency for C sequestration in trees strongly depended on soil N status and increased from close to zero at
C/N 25 in the humus layer up to 40 kg (C) kg −1 (N) at C/N 35 and decreased again to about 20 kg (C) kg −1 (N) at C/N 50 when N only was added. In contrast, addition of NPK resulted in high (40–50 kg (C) kg −1 (N)) N-use efficiency also at N-rich (C/N 25) sites. The great difference in N-use efficiency between addition of NPK and
N at N-rich sites reflects a limitation of P and K for tree growth at these sites. N-use efficiency for soil organic carbon
(SOC) sequestration was, on average, 3–4 times lower than for tree C sequestration. However, SOC sequestration was about twice
as high at P. abies as at P. sylvestris sites and averaged 13 and 7 kg (C) kg −1 (N), respectively. The strong relation between N-use efficiency and humus C/N ratio was used to evaluate the impact of N
deposition on C sequestration. The data imply that the 10 kg N ha −1 year −1 higher deposition in southern Sweden than in northern Sweden for a whole century should have resulted in 2.0 ± 1.0 (95% confidence
interval) kg m −2 more tree C and 1.3 ± 0.5 kg m −2 more SOC at P. abies sites in the south than in the north for a 100-year period. These estimates are consistent with differences between south
and north in tree C and SOC found by other studies, and 70–80% of the difference in SOC can be explained by different N deposition. 相似文献
6.
In the present study we analysed whether airborne N pollution may constitute one important driver for the encroachment of
Molinia caerulea in dry heathland ecosystems. Based on full-factorial field experiments (in 2006 and 2008) and complementary greenhouse experiments
(in 2008), we quantified growth responses of Molinia caerulea to N and P fertilisation (50 kg N ha −1 year −1, 20 kg P ha −1 year −1). Aboveground biomass production of Molinia
caerulea was limited by P in 2006, but by N in both experiments in 2008. In the greenhouse experiment, N addition caused a sixfold
increase of the biomass of vegetative tillers, and in all experiments the biomass and numbers of flowering tillers showed
a significant increase due to fertilisation. Our experiments indicated that growth of Molinia caerulea was primarily limited by N, but in dry heaths the kind of nutrient limitation may be mediated by other factors such as water
availability during the vegetative period. Shifts in biomass allocation patterns resulting from N fertilisation showed that
Molinia
caerulea encroachment in dry heaths is not only attributable to increased leaf biomass, but also due to higher investments in reproductive
tissue that allow for increased seed production and thus accelerated encroachment of seedlings in places where the dwarf shrub
canopy has been opened after disturbance. 相似文献
7.
The objective of this study was to evaluate the effect of N fertilization and the presence of N 2 fixing leguminous trees on soil fluxes of greenhouse gases. For a one year period, we measured soil fluxes of nitrous oxide
(N 2O), carbon dioxide (CO 2) and methane (CH 4), related soil parameters (temperature, water-filled pore space, mineral nitrogen content, N mineralization potential) and
litterfall in two highly fertilized (250 kg N ha −1 year −1) coffee cultivation: a monoculture (CM) and a culture shaded by the N 2 fixing legume species Inga densiflora (CIn). Nitrogen fertilizer addition significantly influenced N 2O emissions with 84% of the annual N 2O emitted during the post fertilization periods, and temporarily increased soil respiration and decreased CH 4 uptakes. The higher annual N 2O emissions from the shaded plantation (5.8 ± 0.3 kg N ha −1 year −1) when compared to that from the monoculture (4.3 ± 0.1 kg N ha −1 year −1) was related to the higher N input through litterfall (246 ± 16 kg N ha −1 year −1) and higher potential soil N mineralization rate (3.7 ± 0.2 mg N kg −1 d.w. d −1) in the shaded cultivation when compared to the monoculture (153 ± 6.8 kg N ha −1 year −1 and 2.2 ± 0.2 mg N kg −1 d.w. d −1). This confirms that the presence of N 2 fixing shade trees can increase N 2O emissions. Annual CO 2 and CH 4 fluxes of both systems were similar (8.4 ± 2.6 and 7.5 ± 2.3 t C-CO 2 ha −1 year −1, −1.1 ± 1.5 and 3.3 ± 1.1 kg C-CH 4 ha −1 year −1, respectively in the CIn and CM plantations) but, unexpectedly increased during the dry season. 相似文献
8.
Effects of inoculation of wheat ( Triticum aestivum L.) with the rhizobacterium Pseudomonas chlororaphis subsp. aurantiaca strain SR1 (termed SR1) were studied at an experimental field site in Río Cuarto, Argentina. Treatments involved SR1 inoculation
with or without nitrogen/phosphorus fertilization. Inoculation produced a significant increase in plant height and root length
in early growth stages. Inoculation plus fertilization with 40 kg ha −1 urea/30 kg ha −1 diamonic phosphate (“50% dose”) gave a yield increase of 636 kg ha −1 relative to control, and an increase of 472 kg ha −1 relative to fertilization with 80 kg ha −1 urea/60 kg ha −1 phosphate without inoculation. SR1 inoculation without fertilization, compared to control, produced increases of 6% in weight
of 1,000 grains, 13% in number of spikes per plant, and 30% in number of grains per spike. Inoculation plus 50% dose fertilization
also improved these parameters. Results of the study indicate that inoculation of wheat with SR1 improves various growth and
yield parameters, and allows reduced dosage of nitrogen/phosphorus fertilizers in the field. 相似文献
9.
We estimated net anthropogenic phosphorus inputs (NAPI) in the Chesapeake Bay region. NAPI is an index of phosphorus pollution
potential. NAPI was estimated by quantifying all phosphorus inputs and outputs for each county. Inputs include fertilizer
applications and non-food phosphorus uses, while trade of food and feed can be an input or an output. The average of 1987,
1992, 1997, and 2002 NAPI for individual counties ranged from 0.02 to 78.46 kg P ha −1 year −1. The overall area-weighted average NAPI for 266 counties in the region was 4.52 kg P ha −1 year −1, indicating a positive net phosphorus input that can accumulate in the landscape or can pollute the water. Large positive
NAPI values were associated with agricultural and developed land cover. County area-weighted NAPI increased from 4.43 to 4.94 kg P ha −1 year −1 between 1987 and 1997 but decreased slightly to 4.86 kg P ha −1 year −1 by 2002. Human population density, livestock unit density, and percent row crop land combined to explain 83% of the variability
in NAPI among counties. Around 10% of total NAPI entering the Chesapeake Bay watershed is discharged into Chesapeake Bay.
The developed land component of NAPI had a strong direct correlation with measured phosphorus discharges from major rivers
draining to the Bay ( R
2 = 0.81), however, the correlation with the simple percentage of developed land was equally strong. Our results help identify
the sources of P in the landscape and evaluate the utility of NAPI as a predictor of water quality. 相似文献
10.
It is critical for spring wheat (Triticum aestivum L.) production in the semi-arid Loess Plateau to understand the impact of nitrogen (N) fertilizer on changes in N metabolism, photosynthetic parameters, and their relationship with grain yield and quality. The photosynthetic capacity of flag leaves, dry matter accumulation, and N metabolite enzyme activities from anthesis to maturity were studied on a long-term fertilization trial under different N rates [0 kg ha?1(N1), 52.5 kg ha?1 (N2), 105 kg ha?1 (N3), 157.5 kg ha?1 (N4), and 210 kg ha?1 (N5)]. It was observed that N3 produced optimum total dry matter (5407 kg ha?1), 1000 grain weight (39.7 g), grain yield (2.64 t ha?1), and protein content (13.97%). Our results showed that N fertilization significantly increased photosynthetic parameters and N metabolite enzymes at all growth stages. Nitrogen harvest index, partial productivity factor, agronomic recovery efficiency, and nitrogen agronomic efficiency were decreased with increased N. Higher N rates (N3–N5) maintained higher photosynthetic capacity and dry matter accumulation and lower intercellular CO2 content. The N supply influenced NUE by improving photosynthetic properties. The N3 produced highest chlorophyll content, photosynthetic rate, stomatal conductance and transpiration rate, grain yield, grain protein, dry matter, grains weight, and N metabolite enzyme activities compared to the other rates (N1, N2, N4, and N5). Therefore, increasing N rates beyond the optimum quantity only promotes vegetative development and results in lower yields. 相似文献
11.
This study evaluated the sources, sinks, and factors controlling net export of nitrogen (N) from watersheds on the west coast
of the US. We calculated input of new N to 22 watersheds for 1992 and 2002. 1992 inputs ranged from 541 to 11,644 kg N km −2 year −1, with an overall area-weighted average of 1,870 kg N km −2 year −1. In 2002, the range of inputs was 490–10,875 kg N km −2 year −1, averaging 2,158 kg N km −2 year −1. Fertilizer was the most important source of new N, averaging 956 (1992) and 1,073 kg N km −2 year −1 (2002). Atmospheric deposition was the next most important input, averaging 833 (1992) and 717 kg N km −2 year −1 (2002), followed by biological N fixation in agricultural lands. Riverine N export, calculated based on measurements taken
at the furthest downstream USGS water quality monitoring station, averaged 165 (1992) and 196 kg N km −2 year −1 (2002), although data were available for only 7 watersheds at the latter time point. Downstream riverine N export was correlated
with variations in streamflow (export = 0.94 × streamflow − 5.65, R
2 = 0.66), with N inputs explaining an additional 16% of the variance (export = 1.06 × streamflow + 0.06 × input − 227.78,
R
2 = 0.82). The percentage of N input that is exported averaged 12%. Percent export was also related to streamflow (%export = 0.05 × streamflow − 2.61,
R
2 = 0.60). The correlations with streamflow are likely a result of its large dynamic range in these systems. However, the processes
that control watershed N export are not yet completely understood. 相似文献
12.
This study was conducted to examine the influences of soil-moisture conditions on soil nitrogen (N) dynamics, including in
situ soil N mineralization, N availability, and denitrification in a pure Alnus japonica forest located in Seoul, central Korea. The soil N mineralization, N availability, and denitrification were determined using
the buried bag incubation method, ion exchange resin bag method, and acetylene block method, respectively. The annual net
N mineralization rate (kg N ha −1 year −1) and annual N availability (mg N bag −1) were 40.26 and 80.65 in the relatively dry site, −5.43 and 45.39 in the moist site, and 7.09 and 39.17 in the wet site,
respectively. The annual net N mineralization rate and annual N availability in the dry site were significantly higher than
those in the moist and wet sites, whereas there was no significant difference between the moist and wet sites. The annual
mean denitrification rate (kg N ha −1 year −1) in the dry, moist, and wet sites was 2.37, 2.76, and 1.59, respectively. However, there was no significant difference among
sites due to the high spatial and temporal variations. Our results indicate that soil-moisture condition influenced the in
situ N mineralization and resin bag N availability in an A. japonica forest, and treatments of proper drainage for poorly drained sites would increase soil N mineralization and N availability
and consequently be useful to conserve and manage the A. japonica forest. 相似文献
13.
Increased N deposition in Europe has affected mire ecosystems. However, knowledge on the physiological responses is poor.
We measured photosynthetic responses to increasing N deposition in two peatmoss species ( Sphagnum balticum and Sphagnum fuscum) from a 3-year, north–south transplant experiment in northern Europe, covering a latitudinal N deposition gradient ranging
from 0.28 g N m −2 year −1 in the north, to 1.49 g N m −2 year −1 in the south. The maximum photosynthetic rate (NP max) increased southwards, and was mainly explained by tissue N concentration, secondly by allocation of N to the photosynthesis,
and to a lesser degree by modified photosystem II activity (variable fluorescence/maximum fluorescence yield). Although climatic
factors may have contributed, these results were most likely attributable to an increase in N deposition southwards. For S. fuscum, photosynthetic rate continued to increase up to a deposition level of 1.49 g N m −2 year −1, but for S. balticum it seemed to level out at 1.14 g N m −2 year −1. The results for S. balticum suggested that transplants from different origin (with low or intermediate N deposition) respond differently to high N deposition.
This indicates that Sphagnum species may be able to adapt or physiologically adjust to high N deposition. Our results also suggest that S. balticum might be more sensitive to N deposition than S. fuscum. Surprisingly, NP max was not ( S. balticum), or only weakly ( S. fuscum) correlated with biomass production, indicating that production is to a great extent is governed by factors other than the
photosynthetic capacity. 相似文献
14.
The modification of large areas of tropical forest to agricultural uses has consequences for the movement of inorganic nitrogen
(N) from land to water. Various biogeochemical pathways in soils and riparian zones can influence the movement and retention
of N within watersheds and affect the quantity exported in streams. We used the concentrations of NO 3
− and NH 4
+ in different hydrological flowpaths leading from upland soils to streams to investigate inorganic N transformations in adjacent
watersheds containing tropical forest and established cattle pasture in the southwestern Brazilian Amazon Basin. High NO 3
− concentrations in forest soil solution relative to groundwater indicated a large removal of N mostly as NO 3
− in flowpaths leading from soil to groundwater. Forest groundwater NO 3
− concentrations were lower than in other Amazon sites where riparian zones have been implicated as important N sinks. Based
on water budgets for these watersheds, we estimated that 7.3–10.3 kg N ha −1 y −1 was removed from flowpaths between 20 and 100 cm, and 7.1–10.2 kg N ha −1 y −1 was removed below 100 cm and the top of the groundwater. N removal from vertical flowpaths in forest exceeded previously
measured N 2O emissions of 3.0 kg N ha −1 y −1 and estimated emissions of NO of 1.4 kg N ha −1 y −1. Potential fates for this large amount of nitrate removal in forest soils include plant uptake, denitrification, and abiotic
N retention. Conversion to pasture shifted the system from dominance by processes producing and consuming NO 3
− to one dominated by NH 4
+, presumably the product of lower rates of net N mineralization and net nitrification in pasture compared with forest. In
pasture, no hydrological flowpaths contained substantial amounts of NO 3
− and estimated N removal from soil vertical flowpaths was 0.2 kg N ha −1 y −1 below the depth of 100 cm. This contrasts with the extent to which agricultural sources dominate N inputs to groundwater
and stream water in many temperate regions. This could change, however, if pasture agriculture in the tropics shifts toward
intensive crop cultivation. 相似文献
15.
The processes driving primary productivity and its impacts on fish production were investigated in field trials in eight seasonal
earthen wetland ponds ‘Fingerponds’ (192 m 2) in Uganda between 2003 and 2005. The ponds were stocked by the seasonal flood with predominantly Oreochromis spp. at densities ranging from 0.1 to 0.5 fish m −2. Chicken manure (521, 833 or 1,563 kg ha −1) was applied fortnightly. Results showed that primary productivity was enhanced with maximum average net primary productivity
(±Standard Error) of 11.7 (±2.5) g O 2 m −2 day −1 at the Gaba site and 8.3 (±1.5) g O 2 m −2 day −1 at the Walukuba site. Net fish yields were higher in manured ponds with up to 2,670 kg ha −1 yield for a 310 day growth period compared to less than 700 kg ha −1 in unmanured ponds. Fish production was limited mainly by high recruitment, falling water levels, light limitation from high
suspended solids and turbidity, and low zooplankton biomass. It was concluded that Fingerponds have a high potential for sustainable
fish production and can contribute to the alleviation of protein shortages amongst the riparian communities around Lake Victoria.
Production can be enhanced further with improved stock management. 相似文献
16.
In a declining sugar maple (SM) stand, we tested the hypothesis that an increasing relative abundance of American beech (AB)
and yellow birch (YB) would improve litter quality by providing a higher proportion of litterfall richer in base cations and
lower in acidity. From 1989 to 2006, SM leaf fall diminished from 59% (1,718 kg ha −1 year −1) to 36% (915 kg ha −1 year −1) of the total leaf fall biomass. Overall, the increase in AB and YB litterfall compensated for the SM decrease, resulting
in constant annual leaf litterfall fluxes (2,803 kg ha −1 year −1) over the period studied. However, because the leaf litter for AB and YB had Ca and Mg concentrations 2–3 times higher than
did SM, Ca and Mg concentrations and fluxes in leaf litterfall significantly increased between 1989 and 2006. Leaf litterfall
of AB and YB also has a higher base/acid ratio than SM. Consequently, changes in forest composition following SM decline led
to a clear improvement in litterfall quality in terms of base cations content and fluxes and acid–base properties. 相似文献
17.
Chemical fertilizers have been used in the cultivation of plants due to their high solubility and effect on crops yield. Biofertilizers
with phosphate rock (PR) and potash rock (KR) plus sulfur inoculated with Acidithiobacillus may improve plant growth and contribute to addition of available P and K in soil. The effectiveness of biofertilizers from
phosphate and potash rocks mixed with sulfur and Acidithiobacillus was studied in a Typic Fragiuldult soil of the Brazilian Northeast Tableland. Cowpea (cv. “IPA 206”) was grown with and without
rhizobia inoculation. Treatments were: (a) phosphate rock (1000 kg ha −1); (b) Biofertilizers-B P (250 and 500 kg ha −1); (c) triple superphosphate-TSP (250 kg ha −1); (d) potash rock (1000 kg ha −1); (e) biofertilizer-B K (250; 500 and 750 kg ha −1); (f) potassium chloride-KCl (250 kg K 20 ha −1); (g) control without P or K fertilization (P 0K 0). The soil was maintained under water submersion covered with black plastic (solarization process) for a period of 30 days.
Biofertilizers (B p and B K) and soluble fertilizers increased plant growth and NPK uptake. Biofertilizers reduced soil pH, especially when applied in
highest rates. Biofertilizers and TSP+KCl showed the best values of available P and K in soil. Rhizobial inoculation was effective
on cowpea, but no nodules were formed by bacteria native from the soil, probably due to the effect of the solarization process.
From obtained PK biofertilizers could be used as alternative for cowpea fertilization in Tableland soils. 相似文献
18.
The input of phosphorus (P) through mineral aerosol dust deposition may be an important component of nutrient dynamics in
tropical forest ecosystems. A new dust deposition calculation is used to construct a broad analysis of the importance of dust-derived
P to the P budget of a montane wet tropical forest in the Luquillo Mountains of Puerto Rico. The dust deposition calculation
used here takes advantage of an internal geochemical signal (Sr isotope mass balance) to provide a spatially integrated longer-term
average dust deposition flux. Dust inputs of P (0.23 ± 0.08 kg ha −1 year −1) are compared with watershed-average inputs of P to the soil through the conversion of underlying saprolite into soil (between
0.07 and 0.19 kg ha −1 year −1), and with watershed-average losses of soil P through leaching (between 0.02 and 0.14 kg ha −1 year −1) and erosion (between 0.04 and 1.38 kg ha −1 year −1). The similar magnitude of dust-derived P inputs to that of other fluxes indicates that dust is an important component of
the soil and biomass P budget in this ecosystem. Dust-derived inputs of P alone are capable of completely replacing the total
soil and biomass P pool on a timescale of between 2.8 ka and 7.0 ka, less than both the average soil residence time (~15 ka)
and the average landslide recurrence interval (~10 ka). 相似文献
19.
Sphagnum, the main genus which forms boreal peat, is strongly affected by N and S deposition and raised temperature, but the physiological
mechanisms behind the responses are largely unknown. We measured maximum photosynthetic rate (NP max), maximum efficiency of photosystem II [variable fluorescence ( F
v)/maximum fluorescence yield ( F
m)] and concentrations of N, C, chlorophyll and carotenoids as responses to N and S addition and increased temperature in Sphagnum balticum (a widespread species in the northern peatlands) in a 12-year factorial experiment. NP max did not differ between control (0.2 g N m −2 year −1) and high N (3.0 g N m −2 year −1), but was higher in the mid N treatment (1.5 g N m −2 year −1). N, C, carotenoids and chlorophyll concentration increased in shoot apices after N addition. F
v/ F
m did not differ between N treatments. Increased temperature (+3.6°C) had a small negative effect on N concentration, but had
no significant effect on NP max or F
v/ F
m. Addition of 2 g S m −2 year −1 showed a weak negative effect on NP max and F
v/ F
m. Our results suggest a unimodal response of NP max to N addition and tissue N concentration in S. balticum, with an optimum N concentration for photosynthetic rate of ~13 mg N g −1. In conclusion, high S deposition may reduce photosynthetic capacity in Sphagnum, but the negative effects may be relaxed under high N availability. We suggest that previously reported negative effects
on Sphagnum productivity under high N deposition are not related to negative effects on the photosynthetic apparatus, but differences
in optimum N concentration among Sphagnum species may affect their competitive ability under different N deposition regimes. 相似文献
20.
The objective of this study was to evaluate the nitrogen (N) biogeochemistry of an 18–22 year old forested watershed in western
Maryland. We hypothesized that this watershed should not exhibit symptoms of N saturation. This watershed was a strong source
of nitrate (NO 3
−) to the stream in all years, with a mean annual export of 9.5 kg N ha −1 year −1 and a range of 4.4–18.4 kg N ha −1 year −1. During the 2001 and 2002 water years, wet deposition of inorganic N was 9.0 kg N ha −1 year −1 and 6.3 kg N ha −1 year −1, respectively. Watershed N export rates in 2001 and 2002 water years were 4.2 kg N ha −1 year −1 and 5.3 kg N ha −1 year −1, respectively. During the wetter water years of 2003 and 2004, the watershed exported 15.0 kg N ha −1 year −1 and 18.4 kg N ha −1 year −1, rates that exceeded annual wet deposition of N by a factor of two (7.5 kg N ha −1 year −1 in 2003) and three (5.5 kg N ha −1 year −1 in 2004). Consistent with the high rates of N export, were high concentrations (2.1–3.3%) of N in foliage, wood (0.3%) and
fine roots, low C:N ratios in the forest floor (17–24) and mineral soil (14), high percentages (83–96%) of the amount of mineralized
N that was nitrified and elevated N concentrations (up to 3 mg N l −1) in soil solution. Although this watershed contained a young aggrading forest, it exhibited several symptoms of N saturation
commonly observed in more mature forests. 相似文献
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