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1.
Brenner RE  Boone RD  Jones JB  Lajtha K  Ruess RW 《Oecologia》2006,148(4):602-611
Floristic succession in the boreal forest can have a dramatic influence on ecosystem nutrient cycling. We predicted that a decrease in plant and microbial demand for nitrogen (N) during the transition from mid- to late-succession forests would induce an increase in the leaching of dissolved inorganic nitrogen (DIN), relative to dissolved organic nitrogen (DON). To test this, we examined the chemistry of the soil solution collected from within and below the main rooting zones of mid- and late-succession forests, located along the Tanana River in interior Alaska. We also used a combination of hydrological and chemical analyses to investigate a key assumption of our methodology: that patterns of soil water movement did not change during this transition. Between stands, there was no difference in the proportion of DIN below the rooting zone. 84–98% of DIN at both depths consisted of nitrate, which was significantly higher in the deeper mineral soil than at the soil surface (0.46±0.12 mg NO 3 –N l−1 vs 0.17±0.12 mg NO 3 –N l−1, respectively), and 79–92% of the total dissolved N consisted of DON. Contrary to our original assumption that nutrients were primarily leached downward, out of the rooting zone, we found much evidence to suggest that the glacially-fed Tanana River (>200 m from these stands) was contributing to the influx of water and nutrients into the soil active layer of both stands. Soil water potentials were positively correlated with river discharge; and ionic and isotopic (δ18O of H2O) values of the soil solution closely matched those of river water. Thus, our ability to elucidate biological control over ecosystem N retention was confounded by riverine nutrient inputs. Climatic warming is likely to extend the season of glacial melt and increase riverine nutrient inputs to forests along glacially-fed rivers.  相似文献   

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   

3.
Microbiological and physico-chemical characteristics of tropical forest, grassland and cropfield soils from India were investigated. The study revealed that the conversion of natural forest led to a reduction of soil organic C (26–36%), total N (26–35%), total P (33–44%), microfungal biomass (44–66%) and total microbial biomass C, N and P (25–60%) over a period of 30–50 years. Comparative analysis of microbial activity in terms of basal soil respiration revealed maximum activity in the forest and minimum in the cropfield soil. Analysis of microbial metabolic respiratory activity (qCO2) indicated relatively greater respiratory loss of CO2-C per unit microbial biomass in cropfield and grassland than in forest soil. Considering the importance of the microbial component in soil, we conclude that the conversion of the tropical forest to different land uses leads to the loss of biological stability of the soil.  相似文献   

4.
Wildfire effects on carbon and nitrogen in inland coniferous forests   总被引:6,自引:0,他引:6  
Baird  M.  Zabowski  D.  Everett  R. L. 《Plant and Soil》1999,209(2):233-243
A ponderosa pine/Douglas-fir forest (Pinus ponderosa Dougl., Pseudotsuga menziesii (Mirb.) Franco; PP/DF) and a lodgepole pine/Engelmann spruce forest (Pinus contorta Loud., Picea engelmannii Parry ex Engelm.; LP/ES) located on the eastern slopes of the Cascade Mountains in Washington state, USA, were examined following severe wildfire to compare total soil carbon and nitrogen capitals with unburned (control) forests. One year after fire, the average C content (60 cm depth) of PP/DF and LP/ES soil was 30% (25 Mg ha-1) and 10% (7 Mg ha-1) lower than control soil. Average N content on the burned PP/DF and LP/ES plots was 46% (3.0 Mg ha-1) and 13% (0.4 Mg ha-1) lower than control soil. The reduction in C and N in the PP/DF soil was largely the result of lower nutrient capitals in the burned Bw horizons (12–60 cm depth) relative to control plots. It is unlikely that the 1994 fire substantially affected nutrient capitals in the Bw horizons; however, natural variability or past fire history could be responsible for the varied nutrient capitals observed in the subsurface soils. Surface erosion (sheet plus rill) removed between 15 and 18 Mg ha-1 of soil from the burned plots. Nutrient losses through surface erosion were 280 kg C ha-1 and 14 kg N ha-1 in the PP/DF, whereas LP/ES losses were 640 and 22 kg ha-1 for C and N, respectively. In both forests, surface erosion of C and N was 1% to 2% of the A-horizon capital of these elements in unburned soil. A bioassay (with lettuce as an indicator plant) was used to compare soils from low-, moderate- and high-severity burn areas relative to control soil. In both forests, low-severity fire increased lettuce yield by 70–100% of controls. With more severe fire, yield decreased in the LP/ES relative to the low-intensity burn soil; however, only in the high-severity treatment was yield reduced (14%) from the control. Moderate- and high-severity burn areas in the PP/DF were fertilized with 56 kg ha-1 of N four months prior to soil sampling. In these soils, yield was 70–80% greater than the control. These results suggest that short-term site productivity can be stimulated by low-severity fire, but unaffected or reduced by more severe fire in the types of forests studied. Post-fire fertilization with N could increase soil productivity where other environmental factors do not limit growth. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

5.
Dead wood can be an important component of the carbon pool in many forests, but few measurements have been made of this pool in tropical forests, To fill this gap, we determined the quantity of dead wood (downed and standing dead) in 25 long-term (up to 30 yr) permanent forest plots located in six different life zones of Venezuela. Downed wood was separated into fine (< 10 cm in diameter) and coarse (≥ 10 cm in diameter) classes, and three decomposition states (sound, intermediate, or rotten). The total quantity of dead wood, averaged by life zone, was lowest in the dry (2.43 Mg/ha), reached a peak in the moist (42.33 Mg/ha) and decreased slightly in the wet (34.50 Mg/ha) life zone. Most of the dead wood was in the standing dead category (about 42–76% of the total). The decomposition state of dead wood in all plots was mostly rotten (45%) or intermediate (44%); there was little sound wood (11%). Turnover rates of dead wood generally ranged between 0.03/yr to 0.52/yr with no clear trend with life zone. The large amount of dead wood in some plots was equivalent to about 20 percent or less of aboveground biomass, indicating that dead wood can represent a significant amount of carbon in these forests.  相似文献   

6.
张泰东  王传宽  张全智 《生态学杂志》2017,28(10):3135-3143
采用土壤分层取样法测定了帽儿山地区相同气候条件、不同立地条件下林龄相近的2种人工针叶林(红松林和兴安落叶松林)和3种天然落叶阔叶林(蒙古栎林、杨桦林、硬阔叶林)的土壤碳(C)、氮(N)、磷(P)元素含量,以及土壤容重、土壤厚度等,研究土壤C、N、P含量和密度及化学计量关系的垂直变化特征.结果表明: 不同林型间土壤C、N、P含量和密度差异显著,其中硬阔叶林土壤O层和A层的C、N含量和密度均显著高于其他林型.所有林型土壤的C、N含量均随土层加深而下降;落叶阔叶林土壤P含量随土层加深而显著下降,但针叶林各土层间P含量差异不显著.不同林型间A层土壤C/N、O层土壤N/P,以及A和B层土壤C/P均存在显著差异.不同林型间土壤C-N存在显著的线性关系,且其斜率和截距在林型间差异均不显著,但土壤N-P、C-P关系只在阔叶林中存在显著相关关系.这表明不同林型间土壤C-N耦联关系有趋同现象,而土壤N-P和C-P关系随林型而变.  相似文献   

7.
The response of decomposition of litter for the dominant tree species in disturbed (pine), rehabilitated (pine and broadleaf mixed) and mature (monsoon evergreen broadleaf) forests in subtropical China to simulated N deposition was studied to address the following hypothesis: (1) litter decomposition is faster in mature forest (high soil N availability) than in rehabilitated/disturbed forests (low soil N availability); (2) litter decomposition is stimulated by N addition in rehabilitated and disturbed forests due to their low soil N availability; (3) N addition has little effect on litter decomposition in mature forest due to its high soil N availability. The litterbag method (a total of 2880 litterbags) and N treatments: Control-no N addition, Low-N: −5 g N m−2 y−1, Medium-N: −10 g N m−2 y−1, and High-N: −15 g N m−2 y−1, were employed to evaluate decomposition. Results indicated that mature forest, which has likely been N saturated due to both long-term high N deposition in the region and the age of the ecosystem, had the highest litter decomposition rate, and exhibited no significant positive and even some negative response to nitrogen additions. However, both disturbed and rehabilitated forests, which are still N limited due to previous land use history, exhibited slower litter decomposition rates with significant positive effects from nitrogen additions. These results suggest that litter decomposition and its responses to N addition in subtropical forests of China vary depending on the nitrogen status of the ecosystem.  相似文献   

8.
为探讨森林演替过程中土壤C、N、P的变化,通过测定鼎湖山3种演替阶段的森林土壤有机碳(SOC)、总氮(TN)、总磷(TP)含量,对他们的化学计量进行分析。结果表明,鼎湖山3种森林土壤SOC和TN随演替阶段而增加,演替中后期表层土壤(0~20 cm)与演替初期的差异达到显著水平(P0.05),在土壤剖面上的分布都呈现显著的表层富集现象,且表层土壤与其他土层均有显著差异(P0.05)。土壤TP含量随演替阶段没有呈现出有规律的变化,不同演替阶段间也没有显著差异,但不同演替阶段土壤TP在土壤剖面上的分布表现不同,演替前期土壤TP含量随着土层深度增加而增加,演替后期土壤TP随土层深度的增加而降低,而演替中期土壤TP含量在各土层间没有显著差异。土壤C∶N不受土层深度和演替进程的影响,而土壤C∶P和N∶P均表现为随演替阶段而增加,随土层加深而降低。这些揭示了森林土壤SOC、TN和TP含量随演替进展及其在土壤剖面上的分布取决于土壤C、N、P的来源方式。  相似文献   

9.
阔叶红松林是我国东北重要的原生群落,其土壤团聚体在森林生态系统碳固定中具有重要作用.本研究采用空间代替时间的方法,选取白桦幼龄林、白桦中龄林、白桦成熟林、阔叶红松成熟林和阔叶红松过熟林5个不同演替序列,通过湿筛法研究长白山天然针阔混交林群落恢复演替中土壤团聚体粒径组成及有机碳含量的变化.结果表明: 土壤团聚体粒径组成受演替过程影响较大,不同演替阶段下土壤团聚体各粒级所占比例差异显著.团聚体平均质量直径随演替的进行表现为先升高再降低的单峰形式,且最高点出现在白桦成熟林阶段.土壤中不同粒级的团聚体内有机碳含量随着演替的进行呈先增加后略有下降的趋势,且团聚体内有机碳含量最大值出现在阔叶红松成熟林阶段.在同一演替阶段下,0~5和5~10 cm土层(除演替末期的阔叶红松过熟林外)中的各粒径团聚体内有机碳含量都随着粒径的减小而增加,而10~20 cm土层中的各粒径团聚体内有机碳含量都随着粒径的减小而减小.从演替初期的白桦幼龄林到演替末期的阔叶红松过熟林,每个样地内的同一粒径团聚体内有机碳含量均具有明显的垂直分布特性,均随着土层深度的增加而显著降低.  相似文献   

10.
Free air CO2 enrichment (FACE) experiments in aggrading temperate forests and plantations have been initiated to test whether temperate forest ecosystems act as sinks for anthropogenic emissions of CO2. These FACE experiments have demonstrated increases in net primary production and carbon (C) storage in forest vegetation due to increased atmospheric CO2 concentrations. However, the fate of this extra biomass in the forest floor or mineral soil is less clear. After 6 years of FACE treatment in a short-rotation poplar plantation, we observed an additional sink of 32 g C m−2 y−1 in the forest floor. Mineral soil C content increased equally under ambient and increased CO2 treatment during the 6-year experiment. However, during the first half of the experiment the increase in soil C was suppressed under FACE due to a priming effect, that is, the additional labile C increased the mineralization of older SOM, whereas during the second half of the experiment the increase in soil C was larger under FACE. An additional sink of 54 g C m−2 y−1 in the top 10 cm of the mineral soil was created under FACE during the second half of the experiment. Although, this FACE effect was not significant due to a combination of soil spatial variability and the low number of replicates that are inherent to the present generation of forest stand FACE experiments. Physical fractionation by wet sieving revealed an increase in the C and nitrogen (N) content of macro-aggregates due to FACE. Further fractionation by density showed that FACE increased C and N contents of the light iPOM and mineral associated intra-macro-aggregate fractions. Isolation of micro-aggregates from macro-aggregates and subsequent fractionation by density revealed that FACE increased C and N contents of the light iPOM, C content of the fine iPOM and C and N contents of the mineral associated intra-micro-aggregate fractions. From this we infer that the amount of stabilized C and N increased under FACE treatment. We compared our data with published results of other forest FACE experiments and infer that the type of vegetation and soil base saturation, as a proxy for bioturbation, are important factors related to the size of the additional C sinks of the forest floor–soil system under FACE. Author Contribution: MRH conceived of and designed the study, performed research, analyzed data, and wrote the paper; GES conceived of and designed the study and performed research.  相似文献   

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