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1.
We examined soil nitrogen (N) mineralization and nitrification rates, and soil and forest floor properties in one native forest:
evergreen broad-leaved forest (EBLF), one secondary shrubs (SS), and three adjacent plantation forests: Chinese fir plantation
(CFP), bamboo plantation (BP) and waxberry groves (WG) in Tiantong National Forest Park, Eastern China. All forests showed
seasonal dynamics of N mineralization and nitrification rates. Soil N mineralization rate was highest in EBLF (1.6 ± 0.3 mg-N kg−1 yr−1) and lowest in CFP (0.4 ± 0.1 mg-N kg−1 yr−1). Soil nitrification rate was also highest in EBLF (0.6 ± 0.1 mg-N kg−1 yr−1), but lowest in SS (0.02 ± 0.01 mg-N kg−1 yr−1). During forest conversion of EBLF to SS, CFP, BP and WG, soil N mineralization rate (10.7%, 73%, 40.3% and 69.8%, respectively),
soil nitrification rate (94.9%, 32.2%, 33.9% and 39%, respectively), and soil N concentration (50%, 65.4%, 78.9% and 51.9%,
respectively) declined significantly. Annual soil N mineralization was positively correlated with total C and N concentrations
of surface soil and total N concentration of forest floor, and negatively correlated with soil bulk density, soil pH and C:N
ratio of forest floor across the five forests. Annual soil nitrification was positively correlated with total C concentration
of surface soil and N concentration of forest floor, and negatively correlated with soil bulk density and forest floor mass.
In contrast, annual soil nitrification was not correlated to pH value, total N concentration, C:N ratio of surface soil and
total C concentration and C:N ratio of forest floor. 相似文献
2.
De Schrijver A Geudens G Augusto L Staelens J Mertens J Wuyts K Gielis L Verheyen K 《Oecologia》2007,153(3):663-674
Converting deciduous forests to coniferous plantations and vice versa causes environmental changes, but till now insight into
the overall effect is lacking. This review, based on 38 case studies, aims to find out how coniferous and deciduous forests
differ in terms of throughfall (+stemflow) deposition and seepage flux to groundwater. From the comparison of coniferous and
deciduous stands at comparable sites, it can be inferred that deciduous forests receive less N and S via throughfall (+stemflow)
deposition on the forest floor. In regions with relatively low open field deposition of atmospheric N (<10 kg N ha−1 year−1), lower NH4+ mean throughfall (+stemflow) deposition was, however, reported under conifers compared to deciduous forest, while in regions
with high atmospheric N pollution (>10 kg N ha−1 year−1), the opposite could be concluded. The higher the open field deposition of NH4+, the bigger the difference between the coniferous and deciduous throughfall (+stemflow) deposition. Furthermore, it can be
concluded that canopy exchange of K+, Ca2+ and Mg2+ is on average higher in deciduous stands. The significantly higher stand deposition flux of N and S in coniferous forests
is reflected in a higher soil seepage flux of NO3−, SO42−, K+, Ca2+, Mg2+ and Al(III). Considering a subset of papers for which all necessary data were available, a close relationship between throughfall
(+stemflow) deposition and seepage was found for N, irrespective of the forest type, while this was not the case for S. This
review shows that the higher input flux of N and S in coniferous forests clearly involves a higher seepage of NO3− and SO42− and accompanying cations K+, Ca2+, Mg2+ and Al(III) into the groundwater, making this forest type more vulnerable to acidification and eutrophication compared to
the deciduous forest type. 相似文献
3.
Peter M. Groffman Janet P. Hardy Melany C. Fisk Timothy J. Fahey Charles T. Driscoll 《Ecosystems》2009,12(6):927-943
We exploited the natural climate gradient in the northern hardwood forest at the Hubbard Brook Experimental Forest (HBEF)
to evaluate the effects of climate variation similar to what is predicted to occur with global warming over the next 50–100 years
for northeastern North America on soil carbon (C) and nitrogen (N) cycle processes. Our objectives were to (1) characterize
differences in soil temperature, moisture and frost associated with elevation at the HBEF and (2) evaluate variation in total
soil (TSR) and microbial respiration, N mineralization, nitrification, denitrification, nitrous oxide (N2O) flux, and methane (CH4) uptake along this gradient. Low elevation sites were consistently warmer (1.5–2.5°C) and drier than high elevation sites.
Despite higher temperatures, low elevation plots had less snow and more soil frost than high elevation plots. Net N mineralization
and nitrification were slower in warmer, low elevation plots, in both summer and winter. In summer, this pattern was driven
by lower soil moisture in warmer soils and in winter the pattern was linked to less snow and more soil freezing in warmer
soils. These data suggest that N cycling and supply to plants in northern hardwood ecosystems will be reduced in a warmer
climate due to changes in both winter and summer conditions. TSR was consistently faster in the warmer, low elevation plots.
N cycling processes appeared to be more sensitive to variation in soil moisture induced by climate variation, whereas C cycling
processes appeared to be more strongly influenced by temperature. 相似文献
4.
Soil Inorganic N Leaching in Edges of Different Forest Types Subject to High N Deposition Loads 总被引:2,自引:0,他引:2
Karen Wuyts An De Schrijver Jeroen Staelens Lotte Van Nevel Sandy Adriaenssens Kris Verheyen 《Ecosystems》2011,14(5):818-834
We report on soil leaching of dissolved inorganic nitrogen (DIN) along transects across exposed edges of four coniferous and
four deciduous forest stands. In a 64-m edge zone, DIN leaching below the main rooting zone was enhanced relative to the interior
(at 128 m from the edge) by 21 and 14 kg N ha−1 y−1 in the coniferous and deciduous forest stands, respectively. However, the patterns of DIN leaching did not univocally reflect
those of DIN throughfall deposition. DIN leaching in the first 20 m of the edges was lower than at 32–64 m from the edge (17
vs. 36 kg N ha−1 y−1 and 15 vs. 24 kg N ha−1 y−1 in the coniferous and deciduous forests, respectively). Nitrogen stocks in the mineral topsoil (0–30 cm) were, on average,
943 kg N ha−1 higher at the outer edges than in the interior, indicating that N retention in the soil is probably one of the processes
involved in the relatively low DIN leaching in the outer edges. We suggest that a complex of edge effects on biogeochemical
processes occurs at the forest edges as a result of the interaction between microclimate, tree dynamics (growth and litterfall),
and atmospheric deposition of N and base cations. 相似文献
5.
Dissolved organic carbon affects soil microbial activity and nitrogen dynamics in a Mexican tropical deciduous forest 总被引:1,自引:0,他引:1
Seasonal variation of dissolved organic C (DOC) and its effects on microbial activity and N dynamics were studied during two
consecutive years in soils with different organic C concentrations (hilltop and hillslope) in a tropical deciduous forest
of Mexico. We found that DOC concentrations were higher at the hilltop than at the hillslope soils, and in both soils generally
decreased from the dry to the rainy season during the two study years. Microbial biomass and potential C mineralization rates,
as well as dissolved organic N (DON) and NH4+ concentrations and net N immobilization were higher in soils with higher DOC than in soils with lower DOC. In contrast, net
N immobilization and NH4+ concentration were depleted in the soil with lowest DOC, whereas NO3− concentrations and net nitrification increased. Negative correlations between net nitrification and DOC concentration suggested
that NH4+ was transformed to NO3− by nitrifiers when the C availability was depleted. Taken together, our results suggest that available C appears to control
soil microbial activity and N dynamics, and that microbial N immobilization is facilitated by active heterotrophic microorganisms
stimulated by high C availability. Soil autotrophic nitrification is magnified by decreases in C availability for heterotrophic
microbial activity. This study provides an experimental data set that supports the conceptual model to show and highlight
that microbial dynamics and N transformations could be functionally coupled with DOC availability in the tropical deciduous
forest soils.
Responsible Editor: Chris Neill 相似文献
6.
Recent advances in soil C saturation concepts have increased our understanding of soil C storage and mineralization without
explicit links to N retention and saturation theories. Here, we exploit soil texture and organic matter (OM) gradients in
a Maryland, USA hardwood forest to test hypotheses that link soil organic C saturation with soil 15N retention and nitrification. At our site, mineral-associated OM (MAOM) N concentrations in the silt + clay particle fraction
(g MAOM-N g silt + clay−1) were negatively correlated with the fraction of NH4-N transferred to MAOM during a 3-day in situ incubation (R = −0.85), but positively correlated with potential net nitrification (R = 0.76). Moreover, the fraction of NH4-N transferred to MAOM was negatively correlated with potential net nitrification (R = −0.76). Due to physico-chemical stabilization mechanisms, MAOM is considered to be resistant to mineralization. Carbon
saturation theory suggests that the proportion of new C inputs that can be stabilized in MAOM decreases in proportion to the
amount of C already present in the fraction; C inputs not stabilized in MAOM are susceptible to rapid mineralization. We demonstrate
that NH4-N stabilization in MAOM is similar to C stabilization in MAOM and associated with nitrification, thereby extending soil C
saturation theory to mineral N and linking it with N retention and saturation theories. These data and concepts complement
N saturation models that emphasize vegetation type, N input levels, and microbial turnover. Incorporating the OM retention
capacity of fine mineral particles into N saturation theory can improve predictions of N saturation rates and resolve inconsistent
relationships between soil organic matter, texture, N mineralization, and N retention. 相似文献
7.
雪被斑块对川西亚高山两个森林群落冬季土壤氮转化的影响 总被引:2,自引:0,他引:2
为了解气候变暖情景下雪况变化对高寒森林冬季土壤氮转化的影响,测定了川西亚高山冷杉(Abies faxoniana)+红桦(Betula albo-sinensis)混交林(MF)和冷杉次生林(SF)三类雪被斑块(浅雪被、中厚度雪被和厚雪被)内冬季土壤氮矿化特征。结果表明:经过一个冬季(2011-2012),两个森林群落土壤净氮氨化量都为负值,净氮硝化量都为正值,且净氮硝化量显著高于净氮氨化量;冬季土壤氮氨化、硝化、矿化和固持量都是中度雪被厚度最高,但各雪被斑块之间都未达到显著水平。各雪被斑块下,冷杉次生林土壤氮矿化参数都显著高于针阔混交林,但雪被斑块和林型交互作用对冬季土壤氮矿化无显著影响。这表明,该区冬季土壤氮矿化以硝化过程为主,硝化和氨化过程可能受不同微生物群落调控;短时期内,未来气候变化所导致的雪被减少对该区森林冬季土壤氮转化影响可能不明显。 相似文献
8.
Jeroen Staelens Tobias Rütting Dries Huygens An De Schrijver Christoph Müller Kris Verheyen Pascal Boeckx 《Biogeochemistry》2012,108(1-3):259-277
Despite long-term enhanced nitrogen (N) inputs, forests can retain considerable amounts of N. While rates of N inputs via throughfall and N leaching are increased in coniferous stands relative to deciduous stands at comparable sites, N leaching below coniferous stands is disproportionally enhanced relative to the N input. A better understanding of factors affecting N retention is needed to assess the impact of changing N deposition on N cycling and N loss of forests. Therefore, gross N transformation pathways were quantified in undisturbed well-drained sandy soils of adjacent equal-aged deciduous (pedunculate oak (Quercus robur L.)) and coniferous (Scots pine (Pinus sylvestris L.)) planted forest stands located in a region with high N deposition (north Belgium). In situ inorganic 15N labelling of the mineral topsoil (0–10?cm) combined with numerical data analysis demonstrated that (i) all gross N transformations differed significantly (p?<?0.05) between the two forest soils, (ii) gross N mineralization in the pine soil was less than half the rate in the oak soil, (iii) meaningful N immobilization was only observed for ammonium, (iv) nitrate production via oxidation of organic N occurred three times faster in the pine soil while ammonium oxidation was similar in both soils, and (v) dissimilatory nitrate reduction to ammonium was detected in both soils but was higher in the oak soil. We conclude that the higher gross nitrification (including oxidation of organic N) in the pine soil compared to the oak soil, combined with negligible nitrate immobilization, is in line with the observed higher nitrate leaching under the pine forest. 相似文献
9.
Efflux of carbon dioxide from snow-covered forest floors 总被引:1,自引:0,他引:1
The release of CO2 from the snow surface in winter and the soil surface in summer was directly or indirectly measured in four cool-temperate
deciduous broadleaved and evergreen needle forests. The closed chamber method (CC-method) and Fick's diffusion model (DM-method)
were used for the direct and indirect measurements, respectively. The winter soil temperatures from the soil surface to 10
cm depth were between 0 and 2°C. The concentration of CO2 within snowpack increased linearly with increasing snow depth. The average effluxes of CO2 calculated from the gradients of CO2 concentration in the snow using the DM-method ranged from 20 to 75 mg CO2 m−2 h−1, while the CC-method showed the average effluxes of 20 to 50 mg CO2m−2h−1. These results reveal that the snow thermally insulates the soil, allowing CO2 production to continue at soil temperatures a little above freezing throughout the winter. Carbon dioxide formed in the soil
can move across snowpack up to the atmosphere. The winter/summer ratio of CO2 emission was estimated to be higher than 7%. Therefore, the snow-covered soil served as a source of CO2 in the winter and the effluxes represent an important part of the annual CO2 budget in snowy regions. 相似文献
10.
Effects of long-term nitrogen addition on phosphorus cycling in organic soil horizons of temperate forests 总被引:1,自引:0,他引:1
Christine Heuck Georg Smolka Emily D. Whalen Serita Frey Per Gundersen Filip Moldan Ivan J. Fernandez Marie Spohn 《Biogeochemistry》2018,141(2):167-181
High atmospheric nitrogen (N) deposition is expected to impair phosphorus (P) nutrition of temperate forest ecosystems. We examined N and P cycling in organic soil horizons of temperate forests exposed to long-term N addition in the northeastern USA and Scandinavia. We determined N and P concentrations, enzyme activities and net N and P mineralization rates in organic soil horizons of two deciduous (Harvard Forest, Bear Brook) and two coniferous (Klosterhede, Gårdsjön) forests which had received experimental inorganic N addition between 25 and 150 kg N ha?1 year?1 for more than 25 years. Long-term N addition increased the activity of phosphatase (+?180%) and the activity of carbon (C)- and N-acquiring enzymes (cellobiohydrolase: +?70%, chitinase: +?25%). Soil N enrichment increased the N:P ratio of organic soil horizons by up to 150%. In coniferous organic soil horizons, net N and P mineralization were small and unaffected by N addition. In deciduous organic soil horizons, net N and P mineralization rates were significantly higher than at the coniferous sites, and N addition increased net N mineralization by up to 290%. High phosphatase activities concomitant with a 40% decline in P stocks of deciduous organic soil horizons indicate increased plant P demand. In summary, projected future global increases in atmospheric N deposition may induce P limitation in deciduous forests, impairing temperate forest growth. 相似文献
11.
Net nitrogen mineralization and net nitrification along a tropical forest-to-pasture chronosequence 总被引:8,自引:0,他引:8
Soil inorganic nitrogen pools, net mineralization and net nitrification rates were compared during the dry season along a chronosequence of upland (terra firme) forest, 3-, 9- and 20-year-old pastures in the western Brazilian Amazon Basin state of Rondônia to investigate the influence of forest conversion to pasture on soil nitrogen cycles. Surface soil (0 to 10 cm) from forest had larger extractable inorganic nitrogen pools than pasture soils. In the forest, NO
3
–
pools equaled or exceeded NH
4
+
pools, while pasture inorganic N pools consisted almost exclusively of NH
4
+
. Rates of net N mineralization and net nitrification in seven -day laboratory incubations were higher in the seven - day forest than in the pastures. Net N mineralization rates did not differ significantly among different-aged pastures, but net nitrification rates were significantly lower in the 20-year-old pasture. Higher net N mineralization and net nitrification rates were measured in laboratory and in situ incubations of sieved soil, compared with in situ incubations of intact soil cores. Rates calculated in seven-day incubations were higher than determined by longer incubations. Sieving may increase N mineralization and/or decrease N immobilization compared with intact cores. We concluded that 7-day laboratory incubation of sieved soil was the most useful index for comparing N availability across the chronosequence of forest and pasture sites. High net nitrification rates in forest soils suggest a potential for NO
3
–
losses either through leaching or gaseous emissions. 相似文献
12.
Winter climate change is an important environmental driver that alters the biogeochemical processes of forest soils. The decrease in snowpack amplifies soil freeze–thaw cycles and decreases the snowmelt water supply to soil. This study examined how snow decrease affects nitrogen (N) mineralization and nitrification in forest soil in northern Japan by conducting an in situ experimental snowpack manipulation experiment and a laboratory incubation of soil with different moisture, temperature and freeze–thaw magnitudes. For the incubation studies, surface mineral soil (0–10 cm) was collected from a cool-temperate natural mixed forest and incubated using the resin core method during the winter. In the field, there were two treatments: 50 and 100 % snow removal and control plots. The increase in the soil freeze–thaw cycle increased net N mineralization and marginally decreased the net nitrification in soil. The dissolved organic carbon (DOC) and DOC/DON ratio in soil increased with the decrease in snowpack especially during the snow melt period. These results suggested that the change in substrate quality by the increase in freeze–thaw cycles caused the significant enhancement of microbial ammonium production in soil. The lower soil moisture and higher gross immobilization of inorganic N by soil microbes may be maintaining the slow net nitrification and low nitrate leaching in freeze–thaw cycles with less snowpack. The results indicate that winter climate change would strongly impact N biogeochemistry through the increase in ammonium availability in soil for plants and microbes, whereas it would be unlikely that nitrate loss from surface soil would be enhanced. 相似文献
13.
Nitrate and dissolved organic carbon mobilization in response to soil freezing variability 总被引:1,自引:0,他引:1
Colin B. Fuss Charles T. Driscoll Peter M. Groffman John L. Campbell Lynn M. Christenson Timothy J. Fahey Melany C. Fisk Myron J. Mitchell Pamela H. Templer Jorge Durán Jennifer L. Morse 《Biogeochemistry》2016,128(1-2):35-49
Reduced snowpack and associated increases in soil freezing severity resulting from winter climate change have the potential to disrupt carbon (C) and nitrogen (N) cycling in soils. We used a natural winter climate gradient based on elevation and aspect in a northern hardwood forest to examine the effects of variability in soil freezing depth, duration, and frequency on the mobilization of dissolved organic carbon (DOC) and nitrate (NO3 ?) in soils over the course of 2 years. During a winter with a relatively thin snowpack, soils at lower elevation sites experienced greater freezing and especially variable freeze/thaw cycles, which in turn led to greater leaching of DOC from the organic horizon during the following growing season. In contrast to several previous field manipulation studies, we did not find changes in soil solution NO3 ? concentrations related to soil freezing variables. Our results are consistent with a soil matrix disturbance from freezing and thawing which increases leachable C. These results build upon previous laboratory experiments and field manipulations that found differing responses of DOC and NO3 ? following soil freezing, suggesting that mobilization of labile C may suppress NO3 ? losses through microbial immobilization of N. This research highlights the importance of studying natural variation in winter climate and soil freezing and how they impact soil C and N retention, with implications for surface water runoff quality. 相似文献
14.
Spring ephemeral herbs and nitrogen cycling in a northern hardwood forest: an experimental test of the vernal dam hypothesis 总被引:3,自引:0,他引:3
D. E. Rothstein 《Oecologia》2000,124(3):446-453
In the late 1970s R.N. Muller and F.H. Bormann posited their ”vernal dam” hypothesis, stating that spring-ephemeral herbs
in deciduous forests serve as a temporary sink for N when overstory trees are dormant, and then release this N later, in the
summer, when the trees are active. This hypothesis has gained wide acceptance, yet two of its critical assumptions have never
been experimentally tested: (1) that N taken up by spring ephemerals would otherwise be lost from the ecosystem, and (2) that
N from senesced ephemeral tissues contributes to increased rates of summertime N mineralization. To test these assumptions,
I quantified patterns of N cycling and loss from a set of paired plots, half of which served as controls and from half of
which all spring-ephemeral plants were removed. There were no significant differences in NO3
– leaching between plots with and without spring ephemeral vegetation. These results are consistent with the relatively low
rates of N uptake by the dominant spring ephemeral, Allium tricoccum, and its apparent preference for NH4
+, which is far less mobile in soil than NO3
–. In addition, based on sequential sampling, I found that soil microorganisms took up 8 times as much N during the spring
than did spring-ephemeral herbs (microbial uptake=3.19 vs. plant uptake=0.41 g N m–2), suggesting that microbial immobilization of N is the dominant sink for N during this season. Removal of spring ephemeral
vegetation also had no effect on summertime rates of net N mineralization. Furthermore, the addition of spring ephemeral litter
to soil+forest floor microcosms did not significantly increase rates of N mineralization in a laboratory incubation. Instead,
this experiment demonstrated the overwhelming influence of forest floor litter in controlling the release of mineral N from
these soils. Overall, neither assumption of the vernal dam hypothesis holds true in this ecosystem, where patterns of N cycling
and loss appear to be dominated by microbial decomposition of forest floor material and soil organic matter.
Received: 24 August 1999 / Accepted: 23 March 2000 相似文献
15.
Carleton S. White 《Biogeochemistry》1991,12(1):43-68
The effects of select monoterpenes on nitrogen (N) mineralization and nitrification potentials were determined in four separate laboratory bioassays. The effect of increasing monoterpene addition was an initial reduction in NO3
–-N production (nitrification inhibition), followed by a reduction in the sum of NH4
+-N and NO3
–-N (inhibition of net N mineralization and net immobilization at high monoterpene additions. Monoterpenes could produce this pattern by inhibiting nitrification, reducing net N mineralization, enhancing immobilization of NO3
–-N relative to NH4
+-N, and/or stimulating overall net immobilization of N by carbon-rich material.Initial monoterpene concentrations in the assay soils were about 5% of the added amount and were below detection after incubation in most samples.Potential N mineralization-immobilization, nitrification, and soil monoterpene concentrations were determined by soil horizon for four collections from a ponderosa pine (Pinus ponderosa) stand in New Mexico. Concentrations of monoterpenes declined exponentially with soil depth and varied greatly within a horizon. Monoterpene content of the forest floor was not correlated with forest floor biomass. Net N mineralization was inversely correlated with total monoterpene content of all sampled horizons. Nitrification was greatest in the mineral soil, intermediate in the F-H horizon, and never occurred in the L horizon. Nitrification in the mineral soil was inversely correlated with the amount of monoterpenes in the L horizon that contain terminal unsaturated carbon-carbon bonds (r
2 = 0.37, P 0.01). This pattern in the field corresponded to the pattern shown in the laboratory assays with increasing monoterpene additions. 相似文献
16.
Effects of mild winter freezing on soil nitrogen and carbon dynamics in a northern hardwood forest 总被引:27,自引:5,他引:27
Peter M. Groffman Charles T. Driscoll Timothy J. Fahey Janet P. Hardy Ross D. Fitzhugh Geraldine L. Tierney 《Biogeochemistry》2001,56(2):191-213
Overwinter and snowmelt processes are thought to be critical to controllersof nitrogen (N) cycling and retention in northern forests. However, therehave been few measurements of basic N cycle processes (e.g.mineralization, nitrification, denitrification) during winter and littleanalysis of the influence of winter climate on growing season N dynamics.In this study, we manipulated snow cover to assess the effects of soilfreezing on in situ rates of N mineralization, nitrification and soilrespiration, denitrification (intact core, C2H2 – based method),microbial biomass C and N content and potential net N mineralization andnitrification in two sugar maple and two yellow birch stands with referenceand snow manipulation treatment plots over a two year period at theHubbard Brook Experimental Forest, New Hampshire, U.S.A. The snowmanipulation treatment, which simulated the late development of snowpackas may occur in a warmer climate, induced mild (temperatures >–5 °C) soil freezing that lasted until snowmelt. The treatmentcaused significant increases in soil nitrate (NO3
–)concentrations in sugar maple stands, but did not affect mineralization,nitrification, denitrification or microbial biomass, and had no significanteffects in yellow birch stands. Annual N mineralization and nitrificationrates varied significantly from year to year. Net mineralization increasedfrom 12.0 g N m–2 y–1 in 1998 to 22 g N m–2 y–1 in 1999 and nitrification increased from 8 g N m–2 y–1 in 1998 to 13 g N m–2 y–1 in 1999.Denitrification rates ranged from 0 to 0.65 g N m–2 y–1. Ourresults suggest that mild soil freezing must increase soil NO3
– levels by physical disruption of the soil ecosystem and not by direct stimulation of mineralization and nitrification. Physical disruption canincrease fine root mortality, reduce plant N uptake and reduce competitionfor inorganic N, allowing soil NO3
– levels to increase evenwith no increase in net mineralization or nitrification. 相似文献
17.
Short-term increases in relative nitrification rates due to trenching in forest floor and mineral soil horizons of different forest types 总被引:1,自引:0,他引:1
The representation of NO3
– dynamics within forest growth simulation models could improve forest management. An extensive literature review revealed an 88% probability of measuring a higher relative nitrification index (i.e. RNI = [NO3
–] ÷ [NO3
– + NH4
+]) in mineral soil horizons than in forest floors, across a wide range of conifer and hardwood ecosystems. We then hypothesised that humus form and fine root density could be used as two crude variables to predict changes in in situ, potential and relative nitrification rates. Twenty-seven trench plots were established in 1999, across nine contrasting hardwood and coniferous stands in the Eastern Townships of Québec. Forest floor and mineral soil samples were collected from each plot, and from a 1 m radius surrounding each plot, on three dates during summer 2000. In situRNI values increased significantly in trench plots as the season progressed. Potential nitrification rates (i.e. NO3
– concentrations following incubation) were two orders of magnitude higher in forest floor than in mineral soil samples. RNI was significantly higher in mineral soil than in forest floor samples after incubations, but the relative increase in RNI due to trenching was higher in forest floor samples. Indices of available C were significantly higher in forest floor than mineral soil samples, and decreased only in forest floor samples during incubations. Likewise, trenching significantly reduced available C in forest floor samples only. Seasonal changes in soil temperature and fine root growth were the most plausible explanations for seasonal changes in NO3
– dynamics, whereas other factors such soil acidity and moisture appeared less important in determining NO3
– dynamics in this study. We conclude that crude assessments of humus form and fine root density have the potential to be used as calibration parameters for the simulation of NO3
– dynamics in forest growth and yield models. 相似文献
18.
Christopher Neill Marisa C. Piccolo Carlos C. Cerri Paul A. Steudler Jerry M. Melillo Marciano Brito 《Oecologia》1997,110(2):243-252
Previous studies of the effect of tropical forest conversion to cattle pasture on soil N dynamics showed that rates of net N mineralization and net nitrification were lower in pastures compared with the original forest. In this study, we sought to determine the generality of these patterns by examining soil inorganic N concentrations, net mineralization and nitrification rates in 6 forests and 11 pastures 3 years old or older on ultisols and oxisols that encompassed a wide variety of soil textures and spanned a 700-km geographical range in the southwestern Brazilian Amazon Basin state of Rondônia. We sampled each site during October-November and April-May. Forest soils had higher extractable NO3 ?-N and total inorganic N concentrations than pasture soils, but substantial NO3 ?-N occurred in both forest and pasture soils. Rates of net N mineralization and net nitrification were higher in forest soils. Greater concentrations of soil organic matter in finer textured soils were associated with greater rates of net N mineralization and net nitrification, but this relationship was true only under native forest vegetation; rates were uniformly low in pastures, regardless of soil type or texture. Net N mineralization and net nitrification rates per unit of total soil organic matter showed no pattern across the different forest sites, suggesting that controls of net N mineralization may be broadly similar across a wide range of soil types. Similar reductions in rates of net N transformations in pastures 3 years old or older across a range of textures on these soils suggest that changes to soil N cycling caused by deforestation for pasture may be Basin-wide in extent. Lower net N mineralization and net nitrification rates in established pastures suggest that annual N losses from largely deforested landscapes may be lower than losses from the original forest. Total ecosystem N losses since deforestation are likely to depend on the balance between lower N loss rates from established pastures and the magnitude and duration of N losses that occur in the years immediately following forest clearing. 相似文献
19.
Spatial variability of soil total nitrogen (N), available N (KCl extractable NH4+ and NO3−), and spatial patterns of N mineralization and nitrification at a stand scale were characterized with geostatistical and
univariate analysis. Two extensive soil spatial samplings were conducted in an evergreen broadleaf forest in Sichuan province,
southwestern China in June and August 2000. In a study area of 90 × 105 m2, three soil samples were collected from each 5 × 5 m2 plot (n = 378) in June and August, and were analyzed for total N and available N contents. Net N mineralization and nitrification
were measured by in situ core incubation and the rates were estimated based on the difference of NH4+ and NO3− contents between the two sampling dates. Total N, NH4+, and NO3− were all spatially structured with different semivariogram ranges (from high to low: NH4+, NO3−, and total N). The semivariograms of mineralization and nitrification were not as spatially structured as available N. NH4+ was the dominant soil inorganic N form in the system. Both NH4+ and NO3− affected spatial patterns of soil available N, but their relative importance switched in August, probably due to high nitrification
as indicated by greatly increased soil NO3− content. High spatial auto-correlations (>0.7) were found between available N and NH4+, available N and NO3− on both sampling dates, as well as total N measurements between both sampling dates. Although significant, the spatial auto-correlation
between NH4+ and NO3− were generally low. Topography had significant but low correlations with mineralization (r = −0.16) and nitrification (r = −0.14), while soil moisture did not. The large nugget values of the calculated semivariograms and high-semivariance values,
particularly for mineralization and nitrification, indicate that some fine scale (<5 m) variability may lie below the threshold
for detection in this study. 相似文献
20.
Nitrogen Oxide Fluxes and Nitrogen Cycling during Postagricultural Succession and Forest Fertilization in the Humid Tropics 总被引:2,自引:0,他引:2
The effects of changes in tropical land use on soil emissions of nitrous oxide (N2O) and nitric oxide (NO) are not well understood. We examined emissions of N2O and NO and their relationships to land use and forest composition, litterfall, soil nitrogen (N) pools and turnover, soil
moisture, and patterns of carbon (C) cycling in a lower montane, subtropical wet region of Puerto Rico. Fluxes of N2O and NO were measured monthly for over 1 year in old (more than 60 years old) pastures, early- and mid-successional forests
previously in pasture, and late-successional forests not known to have been in pasture within the tabonuco (Dacryodes excelsa) forest zone. Additional, though less frequent, measures were also made in an experimentally fertilized tabonuco forest.
N2O fluxes exceeded NO fluxes at all sites, reflecting the consistently wet environment. The fertilized forest had the highest
N oxide emissions (22.0 kg N · ha−1· y−1). Among the unfertilized sites, the expected pattern of increasing emissions with stand age did not occur in all cases. The
mid-successional forest most dominated by leguminous trees had the highest emissions (9.0 kg N · ha−1· y−1), whereas the mid-successional forest lacking legumes had the lowest emissions (0.09 kg N · ha−1· y−1). N oxide fluxes from late-successional forests were higher than fluxes from pastures. Annual N oxide fluxes correlated positively
to leaf litter N, net nitrification, potential nitrification, soil nitrate, and net N mineralization and negatively to leaf
litter C:N ratio. Soil ammonium was not related to N oxide emissions. Forests with lower fluxes of N oxides had higher rates
of C mineralization than sites with higher N oxide emissions. We conclude that (a) N oxide fluxes were substantial where the
availability of inorganic N exceeded the requirements of competing biota; (b) species composition resulting from historical
land use or varying successional dynamics played an important role in determining N availability; and (c) the established
ecosystem models that predict N oxide loss from positive relationships with soil ammonium may need to be modified.
Received 22 February 2000; accepted 6 September 2000. 相似文献