杉木人工林C库与C吸存的动态研究

对湖南会同10年生、14年生杉木人工林C库和C吸存的动态研究结果表明,杉木人工林生态系统的C库主要由植被层、死地被物层、土壤层组成的,按其C库大小顺序排列为土壤层>植被层>死地被物层。10年生、14年生杉木林生态系统的C库分别为120.52和171.40t.hm-2,具有一定的年龄阶段和地带性特点。随着杉木林年龄的增长,乔木层C贮量的优势逐渐加强,从10年生的30.38t.hm-2增加到14年生的61.24t.hm-2,分别占总C库的25.21%和38.50%,树干C贮量占林分C贮量的比例最大,可达47.17%以上,并随杉木林年龄的增长而明显增强,分布在枝、叶、皮和根中的C贮量占48.11%以上,地上部分的C贮量占总C贮量的84.73%以上。10年生和14年生林地土壤层(0~60cm)的C库分别为88.21和108.20t.hm-2,占生态系统总C库的63.13%以上,土壤表层(0~15cm)的C储量分别占土壤总C库的36.57%和34.26%,土壤0~30cm层中的C储量分别占土壤总C库的63.44%和61.05%。地上部分C贮量与地下部分C贮量之比为10年生时为1∶3.53,14年生时为1∶2.22。10年生和14年生杉木人工林生态系统的年净固定C量分别为5.488和9.285t.hm-2.a-1。湖南省现有杉木林植被C库为0.1916×108t,潜在C库为1.4710×108t,C吸存潜力为1.2794×108t,湖南省现有杉木林植被的C库仅为其潜在C库的13.03%,低于全国水平26.46%。     

关帝山林区退化灌木林转变为华北落叶松林对生态系统碳储量的影响

针对我国大量灌木林出现退化而宜林地又日益减少的现状,在适宜种植乔木的地区,将退化灌木林转变为乔木林被认为是一种可行的植被恢复方式。以关帝山林区退化灌木次生林转变而成的不同林龄（10、18、23、27年和35年）华北落叶松（Larix principis-rupprechtii Mayr.）林为研究对象,并以相邻的退化灌木次生林为对照,探究这种转变对生态系统碳储量及其组分的影响,将为我国开展造林/再造林、林业碳汇项目等工作提供科学依据和数据支撑。与灌木林相比,造林初期的生态系统碳储量及其组分均出现不同程度的下降。10年生华北落叶松林的生态系统碳储量相对于灌木林显著下降了32.9%（P < 0.05）,但并非所有组分的下降都显著（P < 0.05）。植被碳储量下降34.7%,其植被地上和地下碳储量分别下降5.4%和70.9%,但只有植被地下碳储量是显著减少的（P < 0.05）;凋落物碳储量下降42.8%,但并不显著（P=0.71）;土壤有机碳储量（0-50 cm）显著下降32.6%（P < 0.05）,其不同土层（0-10、10-30 cm和30-50 cm）的碳储量也都出现显著减少（P < 0.05）。林龄从10年到35年,华北落叶松林生态系统碳储量增加了1.6倍,植被及其组成（地上和地下）、凋落物、土壤有机碳及其不同土层（0-10、10-30 cm和30-50 cm）等的碳储量也随之不断增加,从而使得生态系统碳储量及其组分逐渐达到并全面超过灌木林。但是,不同组分要达到灌木林的碳储量水平,需要的时间存在较大差异：土壤有机碳库 > 植被地下碳库 > 植被地上碳库,其中深层土壤有机碳 > 表层土壤有机碳（0-10 cm）。     

太行山东坡不同林龄杏树林碳储量及其分配特征

在生物量调查的基础上,对太行山东坡4、8、12年生和16年生杏树林生态系统碳储量及其分配特征进行了研究。结果表明:杏树各器官碳含量在447.3—488.1 g/kg;树干碳含量随林龄的增长而显著降低(P0.05),不同林龄间树根、树枝和树叶碳含量无显著差异;土壤层(0—100 cm)碳含量随林龄的增长而增大;随土层深度的增加而降低。林龄对杏树林乔木层、土壤层和生态系统碳储量均有显著影响。4、8、12年生和16年生杏树林生态系统碳储量分别为27.810、72.647、82.450 Mg/hm2和102.336Mg/hm2;土壤层碳储量占总碳储量的90.1%—99.6%,且主要集中于0—40 cm。乔木层碳储量分配随着林龄的增长而增加,土壤碳储量分配则减小。结果揭示了土壤层是杏树林生态系统的主要碳库;杏树人工林生态系统在生长过程中能显著地积累有机碳。研究结果可为经济林经营管理及碳汇功能评价提供参考。     

Variation in biomass and carbon storage by stand age in pine (Pinus tabulaeformis) planted ecosystem in Mt. Taiyue,Shanxi, China

Forest ecosystems play dominant roles in global carbon budget because of the large quantities stored in live biomass, detritus, and soil organic matter. Researchers in various countries have investigated regional and continental scale patterns of carbon (C) stocks in forest ecosystems; however, the relationship between stand age in different components (vegetation, forest floor detritus, and mineral soil) and C storage and sequestration remains poorly understood. In this paper, we assessed an age sequence of 18-, 20-, 25-, 38-, and 42-year-old Pinus tabulaeformis planted by analyzing the vertical distribution of different components biomass with similar site conditions on Mt. Taiyue, Shanxi, China. The results showed that biomass of P. tabulaeformis planted stands was ranged from 88.59 Mg ha^?1 for the 25-year-old stand to 231.05 Mg ha^?1 for the 42-year-old stand and the major biomass was in the stems. Biomass of the ground vegetation varied from 0.51 to 1.35 Mg C ha^?1 between the five stands. The forest floor biomass increased with increasing stand age. The mean C concentration of total tree was 49.94%, which was higher than C concentrations of ground vegetation and forest floor. Different organs of trees C concentration were between 54.14% and 47.74%. C concentrations stored in the mineral soil for each stand experienced decline with increasing soil depth, but were age-independent. Total C storage of five planted forests ranged from 122.15 to 229.85 Mg C ha^?1, of which 51.44–68.38% of C storage was in the soil and 28.46–45.21% in vegetation. The study provided not only with an estimation biomass of P. tabulaeformis planted forest in Mt. Taiyue, Shanxi, China, but also with accurately estimating forest C storage at ecosystem scale.     

Fine root dynamics and soil carbon accretion under thinned and un-thinned Cupressus lusitanica stands in, Southern Ethiopia

Background and aims

Forest management activities influences stand nutrient budgets, belowground carbon allocation and storage in the soil. A field experiment was carried out in Southern Ethiopia to investigate the effect of thinning on fine root dynamics and associated soil carbon accretion of 6-year old C. lusitanica stands.

Methods

Fine roots (≤2 mm in diameter) were sampled seasonally to a depth of 40 cm using sequential root coring method. Fine root biomass and necromass, vertical distribution, seasonal dynamics, annual turnover and soil carbon accretion were quantified.

Results

Fine root biomass and necromass showed vertical and temporal variations. More than 70 % of the fine root mass was concentrated in the top 20 cm soil depth. Fine root biomass showed significant seasonal variation with peaks at the end of the major rainy season and short rainy season. Thinning significantly increased fine root necromass, annual fine root production and turnover. Mean annual soil carbon accretion, through fine root necromass, in the thinned stand was 63 % higher than that in the un-thinned stand.

Conclusions

The temporal dynamics in fine roots is driven by the seasonality in precipitation. Thinning of C. lusitanica plantation would increase soil C accretion considerably through increased fine root necromass and turnover.     

The legacy of harvest and fire on ecosystem carbon storage in a north temperate forest

Forest harvesting and wildfire were widespread in the upper Great Lakes region of North America during the early 20th century. We examined how long this legacy of disturbance constrains forest carbon (C) storage rates by quantifying C pools and fluxes after harvest and fire in a mixed deciduous forest chronosequence in northern lower Michigan, USA. Study plots ranged in age from 6 to 68 years and were created following experimental clear‐cut harvesting and fire disturbance. Annual C storage was estimated biometrically from measurements of wood, leaf, fine root, and woody debris mass, mass losses to herbivory, soil C content, and soil respiration. Maximum annual C storage in stands that were disturbed by harvest and fire twice was 26% less than a reference stand receiving the same disturbance only once. The mechanism for this reduction in annual C storage was a long‐lasting decrease in site quality that endured over the 62‐year timeframe examined. However, during regrowth the harvested and burned forest rapidly became a net C sink, storing 0.53 Mg C ha⁻¹ yr⁻¹ after 6 years. Maximum net ecosystem production (1.35 Mg C ha⁻¹ yr⁻¹) and annual C increment (0.95 Mg C ha⁻¹ yr⁻¹) were recorded in the 24‐ and 50‐year‐old stands, respectively. Net primary production averaged 5.19 Mg C ha⁻¹ yr⁻¹ in experimental stands, increasing by < 10% from 6 to 50 years. Soil heterotrophic respiration was more variable across stand ages, ranging from 3.85 Mg C ha⁻¹ yr⁻¹ in the 6‐year‐old stand to 4.56 Mg C ha⁻¹ yr⁻¹ in the 68‐year‐old stand. These results suggest that harvesting and fire disturbances broadly distributed across the region decades ago caused changes in site quality and successional status that continue to limit forest C storage rates.     

Carbon storage and fluxes in ponderosa pine forests at different developmental stages

We compared carbon storage and fluxes in young and old ponderosa pine stands in Oregon, including plant and soil storage, net primary productivity, respiration fluxes, eddy flux estimates of net ecosystem exchange (NEE), and Biome‐BGC simulations of fluxes. The young forest (Y site) was previously an old‐growth ponderosa pine forest that had been clearcut in 1978, and the old forest (O site), which has never been logged, consists of two primary age classes (50 and 250 years old). Total ecosystem carbon content (vegetation, detritus and soil) of the O forest was about twice that of the Y site (21 vs. 10 kg C m^?2 ground), and significantly more of the total is stored in living vegetation at the O site (61% vs. 15%). Ecosystem respiration (R_e) was higher at the O site (1014 vs. 835 g C m^?2 year^?1), and it was largely from soils at both sites (77% of R_e). The biological data show that above‐ground net primary productivity (ANPP), NPP and net ecosystem production (NEP) were greater at the O site than the Y site. Monte Carlo estimates of NEP show that the young site is a source of CO₂ to the atmosphere, and is significantly lower than NEP(O) by c. 100 g C m^?2 year^?1. Eddy covariance measurements also show that the O site was a stronger sink for CO₂ than the Y site. Across a 15‐km swath in the region, ANPP ranged from 76 g C m^?2 year^?1 at the Y site to 236 g C m^?2 year^?1 (overall mean 158 ± 14 g C m^?2 year^?1). The lowest ANPP values were for the youngest and oldest stands, but there was a large range of ANPP for mature stands. Carbon, water and nitrogen cycle simulations with the Biome‐BGC model suggest that disturbance type and frequency, time since disturbance, age‐dependent changes in below‐ground allocation, and increasing atmospheric concentration of CO₂ all exert significant control on the net ecosystem exchange of carbon at the two sites. Model estimates of major carbon flux components agree with budget‐based observations to within ± 20%, with larger differences for NEP and for several storage terms. Simulations showed the period of regrowth required to replace carbon lost during and after a stand‐replacing fire (O) or a clearcut (Y) to be between 50 and 100 years. In both cases, simulations showed a shift from net carbon source to net sink (on an annual basis) 10–20 years after disturbance. These results suggest that the net ecosystem production of young stands may be low because heterotrophic respiration, particularly from soils, is higher than the NPP of the regrowth. The amount of carbon stored in long‐term pools (biomass and soils) in addition to short‐term fluxes has important implications for management of forests in the Pacific North‐west for carbon sequestration.     

Post-logging organic matter recovery in forest ecosystems of eastern Baikal region

The dynamics of organic matter accumulated in the soil and main vegetation elements was analyzed for post-logging forest ecosystem succession series in eastern Baikal region. The phytomass was found to allocate up 63 and 50% of carbon in undisturbed Scots pine and fir stands, respectively. The post-logging phytomass contribution to the total carbon pool appeared to decrease down to 16% in Scots pine and 6% in fir stands. In Scots pine stands, carbon storage was determined to account for almost 70% of the initial carbon 60 years after logging. In 50- to 55-year-old fir stands, carbon recovered its initial pool only by 10%. Soil carbon recorded in recently logged Scots pine and fir sites appeared to be 5 and 16 times that accumulated in the phytomass, respectively. The ratio between phytomass carbon and soil organic matter recovered back to the prelogging level in Scots pine stands by the age of 50–60 years. While phytomass carbon also increased in fir stand of the same age, it did not reach the level of the control stand.     

中国寒温带不同林龄白桦林碳储量及分配特征

为了解中国寒温带地区不同林龄白桦林生态系统碳储量及固碳能力, 在样地调查基础上, 以大兴安岭地区25、40与61年白桦(Betula platyphylla)林生态系统为研究对象, 对其乔木层、林下地被物层(灌木层、草本层、凋落物层)、土壤层(0-100 cm)碳储量与分配特征进行调查研究。结果表明白桦林乔木层各器官碳含量在440.7-506.7 g·kg ^-1之间, 各器官碳含量随着林龄的增长而降低; 灌木层、草本层碳含量随林龄的增加呈先降后升的变化趋势; 凋落物层碳含量随林龄增加而降低; 土壤层(0-100 cm)碳含量随林龄增加而显著升高, 随着土层深度的增加而降低。白桦林生态系统各层次碳储量均随林龄的增加而明显升高。25、40与61年白桦林乔木层碳储量分别为11.9、19.1和34.2 t·hm ^-2, 各器官碳储量大小顺序表现为树干>树根>树枝>树叶, 树干碳储量分配比例随林龄增加而升高。25、40与61年白桦林生态系统碳储量分别为77.4、180.9和271.4 t·hm ^-2, 其中土壤层占生态系统总碳储量的81.6%、87.7%和85.9%, 是白桦林生态系统的主要碳库。随林龄增加, 白桦林年净生产力(2.0-4.4 t·hm ^-2·a ^-1)、年净固碳量(1.0-2.1 t·hm ^-2·a ^-1)均出现增长, 老龄白桦林仍具有较强的碳汇作用。     

桃江县毛竹林生态系统碳储量及其空间分布

采用标准地调查和生物量实测方法,研究了湖南省桃江县毛竹林生态系统生物量、碳含量、碳储量及空间分布格局。结果表明,不同年龄毛竹林生态系统总生物量分别为:28.147、30.889 t/hm~2和57.763 t/hm~2,其中竹林层生物量为20.254、25.036、55.685 t/hm~2,各器官生物量均以竹竿最高,占器官生物量的63.0%以上。不同年龄毛竹各器官碳平均含量为0.466—0.483 g C/g;灌木层碳含量为0.474—0.489 g C/g;草本层为0.472—0.490 g C/g;死地被物层为0.213—0.276 g C/g;土壤层有机碳含量为14.790—34.503 g C/g。各年龄毛竹林生态系统总碳储量分别为131.273、139.089 t/hm~2和167.817 t/hm~2,其中植被层碳储量为13.627—28.419 t/hm~2,占系统总碳储量的9.935%—16.935%;死地被物为0.307—0.420 t/hm~2,占0.234%—0.265%;土壤层为117.339—138.978 t/hm~2,占82.815%—89.799%。毛竹林生态系统碳储量分布格局为:土壤层植被层死地被物层。研究结果可为深入研究毛竹林的碳平衡提供基础数据。     

Seasonal variation in CO2 efflux of stems and branches of Norway spruce trees

BACKGROUND AND AIMS: Stem and branch respiration, important components of total forest ecosystem respiration, were measured on Norway spruce (Picea abies) trees from May to October in four consecutive years in order (1) to evaluate the influence of temperature on woody tissue CO2 efflux with special focus on variation in Q10 (change in respiration rate resulting from a 10 degrees C increase in temperature) within and between seasons, and (2) to quantify the contribution of above-ground woody tissue (stem and branch) respiration to the carbon balance of the forest ecosystem. METHODS: Stem and branch CO2 efflux were measured, using an IRGA and a closed gas exchange system, 3-4 times per month on 22-year-old trees under natural conditions. Measurements of ecosystem CO2 fluxes were also determined during the whole experiment by using the eddy covariance system. Stem and branch temperatures were monitored at 10-min intervals during the whole experiment. KEY RESULTS: The temperature of the woody tissue of stems and branches explained up to 68% of their CO2 efflux. The mean annual Q10 values ranged from 2.20 to 2.32 for stems and from 2.03 to 2.25 for branches. The mean annual normalized respiration rate, R10, for stems and branches ranged from 1.71 to 2.12 micromol CO2 m(-2)s (-1) and from 0.24 to 0.31 micromol CO2 m(-2) s(-1), respectively. The annual contribution of stem and branch CO2 efflux to total ecosystem respiration were, respectively, 8.9 and 8.1% in 1999, 9.2 and 9.2% in 2000, 7.6 and 8.6% in 2001, and 8.6 and 7.9% in 2002. Standard deviation for both components ranged from 3 to 8% of the mean. CONCLUSIONS: Stem and branch CO2 efflux varied diurnally and seasonally, and were related to the temperature of the woody tissue and to growth. The proportion of CO2 efflux from stems and branches is a significant component of the total forest ecosystem respiration, approx. 8% over the 4 years, and predictive models must take their contribution into account.     

广西不同林龄喀斯特森林生态系统碳储量及其分配格局

基于广西喀斯特地区45块1000 m²样地的调查,研究幼龄林、中龄林、近熟林、成熟林、过熟林5个林龄阶段喀斯特森林植被与土壤碳储量的分配格局.结果表明: 广西不同林龄喀斯特森林总碳储量表现为幼龄林(86.03 t·hm^-2)＜近熟林(110.63 t·hm^-2)＜中龄林(112.11 t·hm^-2)＜成熟林(149.1 t·hm^-2)＜过熟林(244.38 t·hm^-2);各林龄阶段植被不同层碳储量分配均不同,乔木层所占比例占绝对优势,达到92.3%～98.7%,随林龄的增加而增长,灌木层、草本层、凋落物层所占比例分别为0.3%～1.9%、0.3%～1.2%和0.3%～2.5%,细根所占比例为0.3%～3.3%.土壤有机碳密度随土层深度的增加而递减,土壤层碳储量为51.75～81.21 t·hm^-2,所占生态系统比例为33.2%～66.2%,其随林龄的增大呈减小趋势.生态系统地上、地下部分碳储量分别为22.80～141.72和62.30～102.66 t·hm^-2,除过熟林外均为地下部分＞地上部分,地上碳储量随林龄的增大呈逐渐增加的趋势,地下碳储量的变化规律与土壤碳储量变化趋势一致.土壤层和乔木层为生态系统的主要碳库,二者所占比例达到了96%以上.     

Culm recruitment,dry matter dynamics and carbon flux in recently harvested and mature bamboo savannas in the Indian dry tropics

Culm recruitment, standing crop biomass, net production and carbon flux were estimated in mature (5 years after last harvest) and recently harvested bamboo (Dendrocalamus strictus (Roxb.) Nees) savanna sites in the dry tropics. During the 2 study years bamboo shoot recruitment was 1711–3182 and 1432–1510 shoots ha⁻¹ in harvested and mature sites, respectively. Corresponding shoot mortality was 66–93% and 62–69%, respectively. Total biomass was 34.9 t ha⁻¹ at the harvested site and 47.4 t ha⁻¹ at the mature site. Harvesting increased the relative contribution of belowground bamboo biomass. Annual litter input to soil was 2.7 and 5.9 t ha⁻¹ year⁻¹ at the harvested and mature sites, respectively. The bulk of the annual litterfall (78–88%) occurred in the cool dry season (November to February). The mean litter mass on the savanna floor ranged from 3.1 to 3.3 t ha⁻¹; at the harvested site wood litter contributed 70% of the litter mass and at the mature site leaves formed 77% of the litter mass. The mean total net production (TNP) for the two annual cycles was 15.8 t ha⁻¹ year⁻¹ at the harvested site and 19.3 t ha⁻¹ year⁻¹ at the mature site. Nearly half (46–57%) of the TNP was allocated to the belowground parts. Short lived components (leaves and fine roots) contributed about four-fifths of the net production of bamboo. Total carbon storage in the system was 64.4 t ha⁻¹ at the harvested site and 75.4 t ha⁻¹ at the mature site, of which 23–28% was distributed in vegetation, 2% in litter and 70–75% in soil. Annual net carbon deposition was 6.3 and 8.7 t ha⁻¹ year⁻¹ at harvested and mature sites, respectively.     

Annual soil respiration in broadleaf forests of northern Wisconsin: influence of moisture and site biological,chemical, and physical characteristics

Soil temperature and moisture influence soil respiration at a range of temporal and spatial scales. Although soil temperature and moisture may be seasonally correlated, intra and inter-annual variations in soil moisture do occur. There are few direct observations of the influence of local variation in species composition or other stand/site characteristics on seasonal and annual variations in soil moisture, and on cumulative annual soil carbon release. Soil climate and soil respiration from twelve sites in five different forest types were monitored over a 2-year period (1998–1999). Also measured were stand age, species composition, basal area, litter inputs, total above-ground wood production, leaf area index, forest floor mass, coarse and fine root mass, forest floor carbon and nitrogen concentration, root carbon and nitrogen concentration, soil carbon and nitrogen concentration, coarse fraction mass and volume, and soil texture. General soil respiration models were developed using soil temperature, daily soil moisture, and various site/soil characteristics. Of the site/soil characteristics, above-ground production, soil texture, roots + forest floor mass, roots + forest floor carbon:nitrogen, and soil carbon:nitrogen were significant predictors of soil respiration when used alone in respiration models; all of these site variables were weakly to moderately correlated with mean site soil moisture. Daily soil climate data were used to estimate the annual release of carbon (C) from soil respiration for the period 1998–1999. Mean annual soil temperature did not differ between the 2 years but mean annual soil moisture was approximately 9% lower in 1998 due to a summer drought. Soil C respired during 1998 ranged from 8.57 to 11.43 Mg C ha⁻¹ yr⁻¹ while the same sites released 10.13 and 13.57 Mg C ha⁻¹ yr⁻¹ in 1999; inter-annual differences of 15.41 and 15.73%, respectively. Among the 12 sites studied, we calculated that the depression of soil respiration linked to the drought caused annual differences of soil respiration from 11.00 to 15.78%. Annual estimates of respired soil C decreased with increasing site mean soil moisture. Similarly, the difference of respired carbon between the drought and the non-drought years generally decreased with increasing site mean soil moisture.     

南亚热带不同林龄红锥人工林碳贮量与碳固定特征

采用乡土珍贵阔叶树种改造大面积针叶人工纯林已经成为我国亚热带地区人工林近自然化经营的有效模式.采用样地调查与生物量实测方法,研究了我国南亚热带广西3个不同林龄红锥人工林(10、20和27年生)的不同器官、凋落物层和土壤层的碳含量,以及不同林龄红锥人工林的乔木层、凋落物层和土壤层碳贮量及其分配特征.结果表明:红锥不同器官碳含量为49.7％～57.9％;凋落物层碳含量为40.8％ ～ 50.5％,而且未分解层＞半分解层;土壤层(0～60 cm)碳含量随林龄增加而增大,随土层深度的增加而下降.10、20和27年生红锥人工林碳贮量分别为182.42、234.75和269.75 t·hm-2,其中,乔木层分别占19.8％、32.0％和32.8％,凋落物层分别占1.5％、1.6％和1.3％,土壤层分别占78.7％、66.4％和65.9％.3个红锥人工林的年净固碳量分别为4.70、5.64和5.18 t· hm-2.红锥具有较高的固碳能力,是发展多目标森林经营模式的理想树种.     

不同坡位对琉球松人工林凋落物及其养分归还量的影响

对日本冲绳岛北部不同坡位的琉球松人工林凋落物量及其养分归还量进行了为期3年的观测研究,结果表明,琉球松成林年凋落物量为6．54～8．05Mg·hm^-2·年^-1,其凋落高峰出现在6、7月份．台风干扰对年凋落物量及其季节动态影响显著．凋落物不同组分的养分含量差异明显．年均养分归还总量为113．4～154．6kg·hm^-2·年^-1,其中氮素归还量最大,占42．2％;各养分归还量的大小依次为N>Ca>K>Mg>Na>P．两调查林分由于立地条件的显著差异,年均凋落物量及其相应的养分归还量亦存在明显差异．在立地条件较好的下坡,林分P1的年均凋落物量达8．05Mg·hm^-2·年^-1,高于立地条件相对较差的上坡的林分P2的23．1％;其相应的年养分归还量为：N66、04,P1.63,K17．42,Ca48.31,Mg14.65和N。6、57kg·hm^-2·年^-1,分别高于林分P2的39.7％、48.8％、39．4％、32.9％、24.8％和49.3％．两林分凋落物的养分利用效率分别是N为122和138,P为4934和5945,K为462和523,林分P1明显低于林分P2,这与林分P2的立地条件较差相关．可见,所调查的琉球松林是一种高效的养分利用系统。     

湖南会同不同年龄杉木人工林土壤磷素特征

对湖南会同不同年龄(7年生、17年生、25年生)杉木人工林土壤全磷、有效磷、无机磷组分和有机磷进行了研究,结果表明:3种不同林龄杉木林土壤全磷和有效磷的含量分别在317.06—398.56 mg/kg和0.82—1.38 mg/kg之间,土壤全磷和速效磷含量均属低水平;杉木林土壤全磷含量从7年生幼龄林到25a近熟林出现先升高后降低的规律,并且17年生和25年生林分比7年生林分分别增加了19.68%、15.75%,土壤有效磷含量17年生和25年生林分比7年生林分提高了45.55%左右;土壤磷素活化系数均小于2.0%,这表明本研究区土壤全磷向速效磷转化较难,土壤中磷素的有效性较低,但该值随着林分年龄的增加而出现增大的现象;无机磷含量分别为:7年生169.50 mg/kg、17年生182.03 mg/kg、25年生175.94 mg/kg,从幼龄林到中龄林增高,中龄林以后降低;土壤中无机磷组分以O-P含量最高,其次是Fe-P,Ca-P,Al-P最少;杉木不同生长发育阶段对无机磷形态的吸收是有选择性的,幼龄林到中龄林阶段林木以吸收Al-P为主,近熟林阶段林木以吸收Fe-P和Ca-P为主;有机磷含量在全磷所占比例随林龄的变化来看,杉木生长过程中有部分的有机磷矿化为无机磷。土壤不同形态磷的相关性分析结果显示,土壤有效磷与有机磷相关系数为0.667,呈极显著相关性,是研究区杉木人工林土壤有效磷的主要来源。     

Effects of stand age, wildfire and clearcut harvesting on forest floor in boreal mixedwood forests

Carbon (C) in the forest floor (FF) of the boreal region is an important reservoir of terrestrial C. We examined the effects of stand age and disturbance type (clearcutting vs. wildfire) on quantity and quality of organic C of FF in a boreal mixedwood forest of central Canada. Forest floor samples were collected from 6 post-fire (2- to 203-year-old) and 3 post-harvest age classes (2- to 28-year-old) on mesic sites, each randomly replicated three times. Samples were analyzed to determine the physical and chemical properties and the C quality was assessed by quantifying C fractions as easily labile, moderately labile and recalcitrant. Bulk density, total organic C concentration, N concentration and the cation exchange capacity increased with stand age and peaked at 85-year-old sites. Soil pH and concentration of P and K decreased with stand age. In post-fire stands, the depth of FF, total organic C, and labile C fractions increased with stand age in the 2- to 85-year-old stands, while recalcitrant C was lower in 2-year-old stands than older stands. In stands ≤28 years old, post-harvest sites had significantly higher concentration of total organic C and the three C fractions than post-fire sites in 2-year-old stands. No or marginal difference occurred between the two stand origins in 10- and 28-year-old stands. The relative proportions of C fractions did not differ with stand age or stand origin. Our results showed that the quantity of organic C in FF of boreal mixedwoods increased with stand development till 85 years and then slightly decreased in older stands, and post-harvest stands had a higher amount of organic C than post-fire stands immediately after disturbance, but the effect of two disturbances on C in FF converged shortly (within 10 years). The quality of organic C remains the same through stand development and between the two studied stand origins.     

Site and temporal variation of soil respiration in European beech, Norway spruce, and Scots pine forests

Global warming and changes in rainfall amount and distribution may affect soil respiration as a major carbon flux between the biosphere and the atmosphere. The objectives of this study were to investigate the site to site and interannual variation in soil respiration of six temperate forest sites. Soil respiration was measured using closed chambers over 2 years under mature beech, spruce and pine stands at both Solling and Unterlüß, Germany, which have distinct climates and soils. Cumulative annual CO₂ fluxes varied from 4.9 to 5.4 Mg C ha^?1 yr^?1 at Solling with silty soils and from 4.0 to 5.9 Mg C ha^?1 yr^?1 at Unterlüß with sandy soils. With one exception soil respiration rates were not significantly different among the six forest sites (site to site variation) and between the years within the same forest site (interannual variation). Only the respiration rate in the spruce stand at Unterlüß was significant lower than the beech stand at Unterlüß in both years. Soil respiration rates of the sandy sites at Unterlüß were limited by soil moisture during the rather dry and warm summer 1999 while soil respiration at the silty Solling site tended to increase. We found a threshold of ?80 kPa at 10 cm depth below which soil respiration decreased with increasing drought. Subsequent wetting of sandy soils revealed high CO₂ effluxes in the stands at Unterlüß. However, dry periods were infrequent, and our results suggest that temporal variation in soil moisture generally had little effect on annual soil respiration rates. Soil temperature at 5 cm and 10 cm depth explained 83% of the temporal variation in soil respiration using the Arrhenius function. The correlations were weaker using temperature at 0 cm (r² = 0.63) and 2.5 cm depth (r² = 0.81). Mean Q₁₀ values for the range from 5 to 15 °C increased asymptotically with soil depth from 1.87 at 0 cm to 3.46 at 10 cm depth, indicating a large uncertainty in the prediction of the temperature dependency of soil respiration. Comparing the fitted Arrhenius curves for same tree species from Solling and Unterlüß revealed higher soil respiration rates for the stands at Solling than in the respective stands at Unterlüß at the same temperature. A significant positive correlation across all sites between predicted soil respiration rates at 10 °C and total phosphorus content and C‐to‐N ratio of the upper mineral soil indicate a possible effect of nutrients on soil respiration.     

立地类型对张广才岭天然白桦林生态系统碳储量的影响

运用相对生长方程与碳/氮分析方法,测定了我国温带张广才岭7种立地类型(阳坡上、中、下坡位和阴坡上、中、下坡位及谷地)天然白桦林的生态系统碳储量(植被与土壤)及植被净初级生产力与年净固碳量,揭示立地类型对温带天然白桦林生态系统碳库及其固碳能力的影响规律。结果表明:1白桦林植被碳储量((76.28±18.11)—(115.57±5.59)t C/hm~2)在阴、阳坡的上坡位和下坡位显著高于谷地35.1%—51.5%(P0.05),阴、阳坡中坡位高于谷地但差异性不显著(32.5%—33.6%,P0.05);2其土壤碳储量((81.53±6.15)—(181.90±21.62)t C/hm~2)在阳坡各坡位显著高于阴坡中、下部与谷地24.0%—123.1%(P0.05),阴坡上、中部显著高于阴坡下部和谷地36.0%—81.2%(P0.05);3其生态系统碳储量((174.57±20.27)—(282.96±17.92)t C/hm~2)在阳坡各坡位显著高于阴坡中、下坡位与谷地14.1%—62.1%(P0.05),阴坡上、中坡位显著高于阴坡下坡位与谷地19.5%—48.1%(P0.05);4其植被净初级生产力((6.98±1.60)—(9.59±0.69)t hm~(-2)a~(-1))在阴、阳坡上坡位显著高于阴坡中坡位34.2%—37.4%(P0.05),其他4个立地类型高于阴坡中坡位但差异性不显著(8.5%—20.6%,P0.05);5其年净固碳量((3.26±0.74)—(4.56±0.36)t C hm~(-2)a~(-1))在阳坡上坡位显著高于阴坡中坡位39.9%(P0.05),其他5个立地类型高于阴坡中坡位但差异性不显著(9.2%—30.4%,P0.05)。因此,张广才岭天然白桦林的生态系统碳储量及其固碳能力均存在着明显的立地分异规律性,故在评价与管理我国温带白桦林碳汇时应考虑立地类型影响。