共查询到20条相似文献,搜索用时 15 毫秒
1.
Sands Roger Nugroho Putranto B. Leung David W.M. Sun Osbert J. Clinton Peter W. 《Plant and Soil》2000,225(1-2):213-225
This study examined the reciprocal effects of growing ryegrass, lotus and other weed species in competition with radiata pine
on soil CO2 and O2 concentrations and on the growth and root respiration of the radiata pine. Soil O2 concentrations decreased and soil CO2 concentrations increased with increasing soil depth. Radiata pine plus competing species slightly reduced soil O2 concentrations and markedly increased soil CO2 concentrations (up to 40 mmol mol−1) compared with radiata pine alone. The dry weights of shoots and roots, and the root respiration rates of radiata pine grown
with competing vegetation were much less than those for radiata pine alone. This probably was not solely caused by competition
for nutrients water or light since adequate water and nutrients were supplied to all treatments and the radiata pine overtopped
the competing vegetation. When radiata pine roots were raised in NaHCO3 solutions equivalent to a range of CO2 concentrations, succinate dehydrogenase activity (a metabolic indicator of mitochondrial respiration) and elongation rates
of roots decreased as CO2 concentrations increased from 0 to 40 mmol mol−1. This suggests that the elevated CO2 concentrations found in the experiments in soil was the cause, at least in part, of the reduced growth of radiata pine in
competition with other species.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Richard T. Conant Jeffery M. Klopatek Robert C. Malin Carole C. Klopatek 《Biogeochemistry》1998,43(1):43-61
Carbon pools and fluxes were quantified along an environmentalgradient in northern Arizona. Data are presented on vegetation, litter, andsoil C pools and soil CO2 fluxesfrom ecosystems ranging from shrub-steppe through woodlands to coniferousforest and the ecotones in between. Carbon pool sizes and fluxes in thesesemiarid ecosystems vary with temperature and precipitation and are stronglyinfluenced by canopy cover. Ecosystem respiration is approximately 50percent greater in the more mesic, forest environment than in the dryshrub-steppe environment. Soil respiration rates within a site varyseasonally with temperature but appear to be constrained by low soilmoisture during dry summer months, when approximately 75% of totalannual soil respiration occurs. Total annual amount of CO2 respired across all sites ispositively correlated with annual precipitation and negatively correlatedwith temperature. Results suggest that changes in the amount and periodicityof precipitation will have a greater effect on C pools and fluxes than willchanges in temperature in the semiarid Southwestern United States. 相似文献
3.
C. I. Salimon E. A. Davidson† R. L. Victoria A. W. F. Melo 《Global Change Biology》2004,10(5):833-843
Stocks of carbon in Amazonian forest biomass and soils have received considerable research attention because of their potential as sources and sinks of atmospheric CO2. Fluxes of CO2 from soil to the atmosphere, on the other hand, have not been addressed comprehensively in regard to temporal and spatial variations and to land cover change, and have been measured directly only in a few locations in Amazonia. Considerable variation exists across the Amazon Basin in soil properties, climate, and management practices in forests and cattle pastures that might affect soil CO2 fluxes. Here we report soil CO2 fluxes from an area of rapid deforestation in the southwestern Amazonian state of Acre. Specifically we addressed (1) the seasonal variation of soil CO2 fluxes, soil moisture, and soil temperature; (2) the effects of land cover (pastures, mature, and secondary forests) on these fluxes; (3) annual estimates of soil respiration; and (4) the relative contributions of grass‐derived and forest‐derived C as indicated by δ13CO2. Fluxes were greatest during the wet season and declined during the dry season in all land covers. Soil respiration was significantly correlated with soil water‐filled pore space but not correlated with temperature. Annual fluxes were higher in pastures compared with mature and secondary forests, and some of the pastures also had higher soil C stocks. The δ13C of CO2 respired in pasture soils showed that high respiration rates in pastures were derived almost entirely from grass root respiration and decomposition of grass residues. These results indicate that the pastures are very productive and that the larger flux of C cycling through pasture soils compared with forest soils is probably due to greater allocation of C belowground. Secondary forests had soil respiration rates similar to mature forests, and there was no correlation between soil respiration and either forest age or forest biomass. Hence, belowground allocation of C does not appear to be directly related to the stature of vegetation in this region. Variation in seasonal and annual rates of soil respiration of these forests and pastures is more indicative of flux of C through the soil rather than major net changes in ecosystem C stocks. 相似文献
4.
Vertical transport of dissolved organic C and N under long-term N amendments in pine and hardwood forests 总被引:32,自引:3,他引:29
William S. Currie John D. Aber William H. McDowell Richard D. Boone Alison H. Magill 《Biogeochemistry》1996,35(3):471-505
At the Harvard Forest, Massachusetts, a long-term effort is under way to study responses in ecosystem biogeochemistry to chronic inputs of N in atmospheric deposition in the region. Since 1988, experimental additions of NH4NO3 (0, 5 and 15 g N m–2 yr–1) have been made in two forest stands:Pinus resinosa (red pine) and mixed hardwood. In the seventh year of the study, we measured solute concentrations and estimated solute fluxes in throughfall and at two soil depths, beneath the forest floors (Oa) and beneath the B horizons.Beneath the Oa, concentrations and fluxes of dissolved organic C and N (DOC and DON) were higher in the coniferous stand than in the hardwood stand. The mineral soil exerted a strong homogenizing effect on concentrations beneath the B horizons. In reference plots (no N additions), DON composed 56% (pine) and 67% (hardwood) of the total dissolved nitrogen (TDN) transported downward from the forest floor to the mineral soil, and 98% of the TDN exported from the solums. Under N amendments, fluxes of DON from the forest floor correlated positively with rates of N addition, but fluxes of inorganic N from the Oa exceeded those of DON. Export of DON from the solums appeared unaffected by 7 years of N amendments, but as in the Oa, DON composed smaller fractions of TDN exports under N amendments. DOC fluxes were not strongly related to N amendment rates, but ratios of DOC:DON often decreased.The hardwood forest floor exhibited a much stronger sink for inorganic N than did the pine forest floor, making the inputs of dissolved N to mineral soil much greater in the pine stand. Under the high-N treatment, exports of inorganic N from the solum of the pine stand were increased >500-fold over reference (5.2 vs. 0.01 g N m–2 yr–1), consistent with other manifestations of nitrogen saturation. Exports of N from the solum in the pine forest decreased in the order NO3-N> NH4-N> DON, with exports of inorganic N 14-fold higher than exports of DON. In the hardwood forest, in contrast, increased sinks for inorganic N under N amendments resulted in exports of inorganic N that remained lower than DON exports in N-amended plots as well as the reference plot. 相似文献
5.
Plantations of radiata pine (P. radiata D.Don) on soils previously under legume based pastures have a high incidence of stem deformity compared with forest soils.
A comparison of soil properties and tree nutrition of 5 to 7 year-old radiata pine on former pastures in the first part of
the study showed that stem deformity was strongly correlated with mineralisation of soil N and in particular with nitrification.
Other soil properties that have changed as a result of pasture improvement, e.g. pH, available P and Mn, were only partially
correlated with stem deformity. In the second part of the study, the role of N availability and other soil properties in the
expression of deformity was further investigated in a separate field experiment on soils formerly under native eucalypt forest,
tobacco cropping, and improved pasture. Young radiata pine plantings were treated with lime, phosphorus, and nitrogen applied
as urea and sodium nitrate. Liming increased soil pH by around 1.5 units, raised exchangeable Ca2+ and decreased available Mn. Soil mineral N content was only marginally affected by liming. Superphosphate increased soil
available P and raised levels of P in foliage. Changes in soil pH, availability of P, Mn, and B did not affect growth or stem
deformity at any of the sites. In contrast, application of N fertilisers at 200 and 600 kg N ha-1 increased mineral N content and stimulated nitrification, particularly at the forest site. The high rate of N fertiliser
increased basal area at the forest site by 45%, but also raised the level of stem deformity from 12% to 56%. At the tobacco
and pasture sites, this treatment did not increase growth and did not significantly raise stem deformity above the already
high basic level of deformity (63%). Implications of stem deformity in young plantations of radiata pine on potential utilisation
later in the rotation are discussed. 相似文献
6.
Land-Use Change and Biogeochemical Controls of Methane Fluxes in Soils of Eastern Amazonia 总被引:3,自引:0,他引:3
Tropical soils account for 10%–20% of the 15–35 Tg of atmospheric methane (CH4) consumed annually by soils, although tropical deforestation could be changing the soil sink. The objectives of this study
were (a) to quantify differences in soil CH4 fluxes among primary forest, secondary forest, active pasture, and degraded pasture in eastern Amazonia; and (b) to investigate
controlling mechanisms of CH4 fluxes, including N availability, gas-phase transport, and soil respiration. At one ranch, Fazenda Vitória, annual uptake
estimates (kg CH4ha−1 y−1) based on monthly measurements were: primary forest, 2.1; secondary forest, 1.0; active pasture, 1.3; degraded pasture, 3.1.
The lower annual uptake in the active pasture compared with the primary forest was due to CH4 production during the wet season in the pasture soils, which is consistent with findings from other studies. In contrast,
the degraded pasture was never a CH4 source. Expressing uptake as a negative flux and emission as a positive flux, CH4 fluxes were positively correlated with CO2 fluxes, indicating that root and microbial respiration in the productive pastures, and to a lesser extent in the primary
forest, contributed to the formation of anaerobic microsites where CH4 was produced, whereas this productivity was absent in the degraded pasture. In all land uses, uptake rates of atmospheric
CH4 were greater in the dry season than in the wet season, indicating the importance of soil water content and gas transport
on CH4 fluxes. These clay soils had low annual uptake rates relative to reported rates on sandy soils, which also is consistent
with gas transport within the soil being a limiting factor. Nitrogen availability indices did not correlate with CH4 fluxes, indicating that inhibition of CH4 oxidation was not an important mechanism explaining differences among land uses. At another ranch, Fazenda Agua Parada, no
significant effect of pasture age was observed along a chronosequence of pasture ages. We conclude that land-use change can
either increase or decrease the soil sink of CH4, depending on the duration of wet and dry seasons, the effects of seasonal precipitation on gas-phase transport, and the
phenology and relative productivity of the vegetation in each land use. 相似文献
7.
The net ecosystem exchange (NEE) of forests represents the balance of gross primary productivity (GPP) and respiration (R). Methods to estimate these two components from eddy covariance flux measurements are usually based on a functional relationship between respiration and temperature that is calibrated for night‐time (respiration) fluxes and subsequently extrapolated using daytime temperature measurements. However, respiration fluxes originate from different parts of the ecosystem, each of which experiences its own course of temperature. Moreover, if the temperature–respiration function is fitted to combined data from different stages of biological development or seasons, a spurious temperature effect may be included that will lead to overestimation of the direct effect of temperature and therefore to overestimates of daytime respiration. We used the EUROFLUX eddy covariance data set for 15 European forests and pooled data per site, month and for conditions of low and sufficient soil moisture, respectively. We found that using air temperature (measured above the canopy) rather than soil temperature (measured 5 cm below the surface) yielded the most reliable and consistent exponential (Q10) temperature–respiration relationship. A fundamental difference in air temperature‐based Q10 values for different sites, times of year or soil moisture conditions could not be established; all were in the range 1.6–2.5. However, base respiration (R0, i.e. respiration rate scaled to 0°C) did vary significantly among sites and over the course of the year, with increased base respiration rates during the growing season. We used the overall mean Q10 of 2.0 to estimate annual GPP and R. Testing suggested that the uncertainty in total GPP and R associated with the method of separation was generally well within 15%. For the sites investigated, we found a positive relationship between GPP and R, indicating that there is a latitudinal trend in NEE because the absolute decrease in GPP towards the pole is greater than in R. 相似文献
8.
Chen C. R. Condron L. M. Sinaj S. Davis M. R. Sherlock R. R. Frossard E. 《Plant and Soil》2003,256(1):115-130
Vegetative conversion from grass to forest may influence soil nutrient dynamics and availability. A short-term (40 weeks) glasshouse experiment was carried out to investigate the impacts of ryegrass (Lolium perenne) and radiata pine (Pinus radiata) on soil phosphorus (P) availability in 15 grassland soils collected across New Zealand using 33P isotopic exchange kinetics (IEK) and chemical extraction methods. Results from this study showed that radiata pine took up more P (4.5–33.5 mg P pot–1) than ryegrass (1.1–15.6 mg pot–1) from the soil except in the Temuka soil in which the level of available P (e.g., E
1min Pi, bicarbonate extractable Pi) was very high. Radiata pine tended to be better able to access different forms of soil P, compared with ryegrass. There were no significant differences in the level of water soluble P (Cp, intensity factor) between soils under ryegrass and radiata pine, but the levels of Cp were generally lower compared with original soils due to plant uptake. The growth of both ryegrass and radiata pine resulted in the redistribution of soil P from the slowly exchangeable Pi pool (E
> 10m Pi, reduced by 31.8% on the average) to the rapidly exchangeable Pi (E
1min-1d Pi, E
1d-10m Pi) pools in most soils. The values of R/r
1 (the capacity factor) were also generally greater in most soils under radiata pine compared with ryegrass. Specific P mineralisation rates were significantly greater for soils under radiata pine (8.4–21.9%) compared with ryegrass (0.5–10.8%), indicating that the growth of radiata pine enhanced mineralisation of soil organic P. This may partly be ascribed to greater root phosphatase activity for radiata pine than for ryegrass. Plant species × soil type interactions for most soil variables measured indicate that the impacts of plant species on soil P dynamics was strongly influenced by soil properties. 相似文献
9.
Changes in seasonal soil respiration with pasture conversion to forest in Atlantic Canada 总被引:2,自引:0,他引:2
This study compares approximately weekly soil respiration across two forest–pasture pairs with similar soil, topography and
climate to document how conversion of pasture to forest alters net soil CO2 respiration. Over the 2.5 year period of the study, we found that soil respiration was reduced by an average of 41% with
conversion of pasture to forest on an annual basis. Both pastured sites showed similar annual soil respiration rates. Comparisons
of the paired forests, one coniferous and the other broadleaf, only showed a significant difference over one annual cycle.
Enhanced soil respiration in pastures may be the result of either enhanced root respiration and/or microbial respiration.
Differences in pasture–forest soil respiration were primarily observed during the July through September summer period at
all sites, suggesting that this is the critical period for observing and documenting differences. Evaluation of the soil microclimatic
controls on soil respiration suggest that soil temperature exerts a major control on this process, and that examining these
relationships on a seasonal rather than weekly basis provides the strongest relationships in poorly drained soils. Consistently
greater pastured site Q
10s (2.52;2.42) than forested site Q
10s (2.27; 2.17) were observed, with paired-site differences of 0.25. 相似文献
10.
The current emphasis on global climate studies has led the scientific community to set up a number of sites for measuring long‐term biospheric fluxes, and to develop a wide range of biosphere–atmosphere exchange models. This paper presents a new model of this type, which has been developed for a pine forest canopy. In most coniferous species the canopy layer is well separated from the understorey and several cohorts of needles coexist. It was therefore found necessary to distinguish several vegetation layers and, in each layer, several leaf classes defined not only by their light regime and wetness status but also by their age. This model, named MuSICA, is a multilayer, multileaf process‐based model. Each submodel is first independently parameterized using data collected at a EUROFLUX site near Bordeaux (Southwestern France). Particular care is brought to identify the seasonal variations in the various physiological parameters. The full model is then evaluated using a two‐year long data set, split up into 12 day‐type classes defined by the season, the weather type and the soil water status. Beyond the good overall agreement obtained between measured and modelled values at various time scales, several points of further improvement are identified. They concern the seasonal variations in the stomatal response of needles and the soil/litter respiration, as well as their interaction with soil or litter moisture. A sensitivity analysis to some of the model features (in‐canopy turbulent transfer scheme, leaf age classes, water retention, distinction between shaded and sunlit leaves, number of layers) is finally performed in order to evaluate whether significant simplifications can be brought to such a model with little loss in its predictive quality. The distinction between several leaf classes is crucial if one is to compute biospheric fluxes accurately. It is also evidenced that accounting for in‐canopy turbulent transfer leads to better estimates of the sensible heat flux. 相似文献
11.
Sustainable management of grassland ecosystems for improved productivity can enhance their potential to sequester atmospheric CO2 in the soil. However, land-use management influences the quantity and quality of carbon (C) inputs which may, in turn, affect microbial activity and soil C decomposition rates. Understanding the potential changes in magnitude of soil C loss through respiration is critical for a comprehensive assessment of land-use conversion and grassland management impacts on terrestrial C dynamics. Thus, this study was designed to assess the effect of land-use management intensification on soil respiration in subtropical grasslands. Experimental sites consisted of a gradient of management intensities ranging from native rangeland (lowest), silvopasture (intermediate), to sown pasture (highest). Increasing management intensity from native rangeland to sown pasture elevated soil respiration. There was a significant effect of ‘season vs. management’ interaction on total soil respiration (RS), with greater increases in RS from summer to winter in sown pasture (∼200%) compared to native rangeland and silvopasture (∼91%). The temperature sensitivity of RS and heterotrophic soil respiration (RH) increased with management intensification, with a highest Q10 of 1.55 and 2.29, in sown pasture, compared to Q10 values of 1.09 and 1.48 in native rangelands. These results suggested that potential increases in soil C stock with intensification may be susceptible to faster turnover under warming climate scenarios. Improved resilience (and longer residence) of additionally sequestered soil C after intensification may be crucial for long-term ecological resilience, especially with changing climatic conditions. These findings are relevant for sustainable grassland management, especially within subtropical ecoregions, and add to the understanding of changes that may occur in rates of soil C losses as native grasslands are converted to more productive grassland ecosystems. 相似文献
12.
Seasonal and annual respiration of a ponderosa pine ecosystem 总被引:2,自引:0,他引:2
The net ecosystem exchange of CO2 between forests and the atmosphere, measured by eddy covariance, is the small difference between two large fluxes of photosynthesis and respiration. Chamber measurements of soil surface CO2 efflux (Fs), wood respiration (Fw) and foliage respiration (Ff) help identify the contributions of these individual components to net ecosystem exchange. Models developed from the chamber data also provide independent estimates of respiration costs. We measured CO2 efflux with chambers periodically in 1996–97 in a ponderosa pine forest in Oregon, scaled these measurements to the ecosystem, and computed annual totals for respiration by component. We also compared estimated half-hourly ecosystem respiration at night (Fnc) with eddy covariance measurements. Mean foliage respiration normalized to 10 °C was 0.20 μmol m–2 (hemi-leaf surface area) s–1, and reached a maximum of 0.24 μmol m–2 HSA s–1 between days 162 and 208. Mean wood respiration normalized to 10 °C was 5.9 μmol m–3 sapwood s–1, with slightly higher rates in mid-summer, when growth occurs. There was no significant difference (P > 0.10) between wood respiration of young (45 years) and old trees (250 years). Soil surface respiration normalized to 10 °C ranged from 0.7 to 3.0 μmol m–2 (ground) s–1 from days 23 to 329, with the lowest rates in winter and highest rates in late spring. Annual CO2 flux from soil surface, foliage and wood was 683, 157, and 54 g C m–2 y–1, with soil fluxes responsible for 76% of ecosystem respiration. The ratio of net primary production to gross primary production was 0.45, consistent with values for conifer sites in Oregon and Australia, but higher than values reported for boreal coniferous forests. Below-ground carbon allocation (root turnover and respiration, estimated as Fs– litterfall carbon) consumed 61% of GPP; high ratios such as this are typical of sites with more water and nutrient constraints. The chamber estimates were moderately correlated with change in CO2 storage in the canopy (Fstor) on calm nights (friction velocity u* < 0.25 m s–1; R2 = 0.60); Fstor was not significantly different from summed chamber estimates. On windy nights (u* > 0.25 m s–1), the sum of turbulent flux measured above the canopy by eddy covariance and Fstor was only weakly correlated with summed chamber estimates (R2 = 0.14); the eddy covariance estimates were lower than chamber estimates by 50%. 相似文献
13.
Effects of soil frost on nitrogen net mineralization, soil solution chemistry and seepage losses in a temperate forest soil 总被引:1,自引:0,他引:1
KERSTIN HENTSCHEL WERNER BORKEN TOBIAS ZUBER CHRISTINA BOGNER† BERND HUWE† EGBERT MATZNER 《Global Change Biology》2009,15(4):825-836
Freezing and thawing may alter element turnover and solute fluxes in soils by changing physical and biological soil properties. We simulated soil frost in replicated snow removal plots in a mountainous Norway spruce stand in the Fichtelgebirge area, Germany, and investigated N net mineralization, solute concentrations and fluxes of dissolved organic carbon (DOC) and of mineral ions (NH4 + , NO3 − , Na+ , K+ , Ca2+ , Mg2+ ). At the snow removal plots the minimum soil temperature was −5 °C at 5 cm depth, while the control plots were covered by snow and experienced no soil frost. The soil frost lasted for about 3 months and penetrated the soil to about 15 cm depth. In the 3 months after thawing, the in situ N net mineralization in the forest floor and upper mineral soil was not affected by soil frost. In late summer, NO3 − concentrations increased in forest floor percolates and soil solutions at 20 cm soil depth in the snow removal plots relative to the control. The increase lasted for about 2–4 months at a time of low seepage water fluxes. Soil frost did not affect DOC concentrations and radiocarbon signatures of DOC. No specific frost effect was observed for K+ , Ca2+ and Mg2+ in soil solutions, however, the Na+ concentrations in the upper mineral soil increased. In the 12 months following snowmelt, the solute fluxes of N, DOC, and mineral ions were not influenced by the previous soil frost at any depth. Our experiment did not support the hypothesis that moderate soil frost triggers solute losses of N, DOC, and mineral ions from temperate forest soils. 相似文献
14.
Contribution of trees to carbon storage in soils of silvopastoral systems in Florida, USA 总被引:1,自引:0,他引:1
Silvopastoral systems that integrate trees in pasture production systems are likely to enhance soil carbon (C) storage in lower soil layers due to the presence of deep tree roots. To quantify the relative soil C contribution from trees (C3 plants) and warm season grasses (C4 plants) in silvopastoral systems, soil samples were collected and analyzed from silvopastures of slash pine ( Pinus elliottii )+bahiagrass ( Paspalum notatum ), and adjacent open pasture (OP), at six depths down to 125 cm, at four sites representing two major soil orders (Spodosols and Ultisols) of Florida. The plant sources of C in whole (nonfractionated) and three soil fraction sizes (250–2000, 53–250, and <53 μm) were traced using stable C isotope signatures. The silvopasture sites contained higher amounts of C3-derived soil organic carbon (SOC) compared with OP sites, at all soil depths. Slash pine trees (C3 plants) seemed to have contributed more C in the silt+clay-sized (<53 μm) fractions than bahiagrass (C4 plants), particularly deeper in the soil profile. Spodosols sites contained more C in the <53 μm fraction at and below the spodic horizon (occurring between 15 and 50 cm) in silvopasture compared with OP. The results indicate that most of SOC in deeper soil profiles and the relatively stable <53 μm C fraction were derived from tree components (C3 plants) in all the sites, suggesting that the tree-based pasture system has greater potential to store more stable C in the soil compared with the treeless system. 相似文献
15.
以长白山阔叶红松林为研究对象,利用Raupach提出的局地近场理论(localized near field, LNF)耦合垂直风速标准差σw(z)和拉格朗日时间尺度TL (z),建立林冠内CO2源汇强度和平均浓度廓线之间的关系.结果表明,拉格朗日模型能准确、稳定地模拟林冠与大气之间CO2的交换特征.模拟值比涡动相关系统实测值高出约15%,与实测值的相关性为89%,这种差异可能主要来自于输入的浓度廓线的波动以及大气稳定层结造成的涡动相关观测系统误差.在近地面层,由于土壤呼吸作用,整个时间段都为CO2源.林冠层的CO2源汇强度变化较为复杂,其日变化经历了源-汇-源的转变过程.林冠与大气间CO2通量交换明显受大气稳定度影响. 相似文献
16.
用密闭静态箱式法观测了长白山阔叶红松林生态系统生长季中的土壤呼吸作用。结果表明, 长白山阔叶红松林生态系统土壤呼吸作用日动态呈单峰曲线, 在 18∶0 0左右达到最大值。土壤呼吸作用在生长季中的动态呈单峰曲线, 7月最大。 6、7、8、9各月平均土壤呼吸作用分别为 0.2 2、0.32、0.2 3和 0.13gC·m-2 ·h-1。温度升高可以提高土壤呼吸作用强度, 地下 5cm的土壤温度比气温更能准确地反映土壤呼吸作用的动态变化 ;土壤水分含量在一定范围内增加可使土壤呼吸作用强度增加, 但水分过多也会对土壤呼吸产生抑制作用而导致土壤碳排放减少。 相似文献
17.
Scaling carbon dioxide and water vapour exchange from leaf to canopy in a deciduous forest. II. Model testing and application 总被引:3,自引:3,他引:3
The scaling of CO2 and water vapour transfer from leaf to canopy dimensions was achieved by integrating mechanistic models for physiological (photosynthesis, stomatal conductance and soil/root and bole respiration) and micrometeorological (radiative transfer, turbulent transfer and surface energy exchanges) processes. The main objectives of this paper are to describe a canopy photosynthesis and evaporation model for a temperate broadleaf forest and to test it against field measurements. The other goal of this paper is to use the validated model to address some contemporary ecological and physiological questions concerning the transfer of carbon and water between forest canopies and the atmosphere. In particular, we examine the role of simple versus complex radiative transfer models and the effect of environmental (solar radiation and CO2) and ecophysiological (photo-synthetic capacity) variables on canopy-scale carbon and water vapour fluxes. 相似文献
18.
The strength of coupling between canopy gas exchange and root respiration was examined in ~15-yr-old ponderosa pine (Pinus ponderosa Doug. Ex Laws.) growing under seasonally drought stressed conditions. By regularly watering part of the root system to reduce tree water stress and measuring soil CO2 efflux on the dry, distant side of the tree, we were able to determine the strength of the relationship between soil autotrophic (root and rhizosphere) respiration and changes in canopy carbon uptake and water loss by comparison with control trees (no watering). After ~40 days the soil CO2 efflux rate, relative to pre-treatment conditions, was twice that of the controls. This difference, attributable to root and rhizosphere respiration, was strongly correlated with differences in transpiration rates between treatments (r2 = 0.73, p<0.01). By the end of the period, transpiration of the irrigated treatment was twice that of controls. Periodic measurements of photosynthesis under non-light limited conditions paralleled the patterns of transpiration and were systematically higher in the irrigated treatment. We observed no evidence for a greater sensitivity of soil autotrophic respiration to temperature compared to the response of heterotrophic respiration to temperature; the Q10 for total soil respiration was 1.6 (p>0.99) for both treatments. At the ecosystem scale, daily soil CO2 efflux rate was linearly related to gross primary productivity (GPP) as measured by eddy-covariance technique (r2 = 0.55, p<0.01), suggesting patterns of soil CO2 release appear strongly correlated to recent carbon assimilation in this young pine stand. Collectively the observed relationships suggest some consideration should be given to the inclusion of canopy processes in future models of soil respiration. 相似文献
19.
Elaine M. Birk 《Plant and Soil》1992,143(1):115-125
Studies of nitrogen availability were carried out in radiata pine (Pinus radiata D. Don) plantations on former pasture sites in N.S.W. in conjunction with studies of the effects of previous land use on tree form. Sites were selected on previously improved pastures (cleared with introduced legumes) and unimproved pastures (partially cleared without legumes) to form age sequences of stands which had been established for periods of up to fifteen years. Mineral-N pools in soils and forest floor samples were determined monthly for thirteen months and nitrification potentials were determined from periodic laboratory incubations.Nitrate and ammonium pools in 2-, 4-, 6-, 9- and 15-year-old radiata pine stands fluctuated seasonally, peaking in summer and autumn. Maximum total mineral-N concentrations of 20 to 40 g g–1 soil occurred in the youngest, ex-improved pastures with nitrate-N concentrations of up to 25 g g–1. In the 15-year-old stands, nitrate-N was only detected during autumn, at less than 5 g g–1 soil. Net N-mineralization and nitrification potentials were consistently higher in the ex-improved pasture soils compared with the ex-unimproved pastures. N availability decreased with increasing stand age in the ex-improved pasture soils, but the pattern was less clear for the unimproved pasture sites. Suppression of clover by pines and the accumulation of nitrogen in the standing biomass are thought to be the major factors controlling the decline of available N during stand development. 相似文献
20.
Soil Respiration in the Cold Desert Environment of the Colorado Plateau (USA): Abiotic Regulators and Thresholds 总被引:11,自引:0,他引:11
Daniel P. Fernandez Jason C. Neff Jayne Belnap Richard L. Reynolds 《Biogeochemistry》2006,78(3):247-265
Decomposition is central to understanding ecosystem carbon exchange and nutrient-release processes. Unlike mesic ecosystems,
which have been extensively studied, xeric landscapes have received little attention; as a result, abiotic soil-respiration
regulatory processes are poorly understood in xeric environments. To provide a more complete and quantitative understanding
about how abiotic factors influence soil respiration in xeric ecosystems, we conducted soil- respiration and decomposition-cloth
measurements in the cold desert of southeast Utah. Our study evaluated when and to what extent soil texture, moisture, temperature,
organic carbon, and nitrogen influence soil respiration and examined whether the inverse-texture hypothesis applies to decomposition.
Within our study site, the effect of texture on moisture, as described by the inverse texture hypothesis, was evident, but
its effect on decomposition was not. Our results show temperature and moisture to be the dominant abiotic controls of soil
respiration. Specifically, temporal offsets in temperature and moisture conditions appear to have a strong control on soil
respiration, with the highest fluxes occurring in spring when temperature and moisture were favorable. These temporal offsets
resulted in decomposition rates that were controlled by soil moisture and temperature thresholds. The highest fluxes of CO2 occurred when soil temperature was between 10 and 16 °C and volumetric soil moisture was greater than 10%. Decomposition-cloth
results, which integrate decomposition processes across several months, support the soil-respiration results and further illustrate
the seasonal patterns of high respiration rates during spring and low rates during summer and fall. Results from this study
suggest that the parameters used to predict soil respiration in mesic ecosystems likely do not apply in cold-desert environments. 相似文献