Rock-eating mycorrhizas: their role in plant nutrition and biogeochemical cycles

Rates of water uptake by individual trees in a native Australian forest were measured on the Liverpool Plains, New South Wales, Australia, using sapflow sensors. These rates were up-scaled to stand transpiration rate (expressed per unit ground area) using sapwood area as the scalar, and these estimates were compared with modelled stand transpiration. A modified Jarvis-Stewart modelling approach (Jarvis 1976), previously used to calculate canopy conductance, was used to calculate stand transpiration rate. Three environmental variables, namely solar radiation, vapour pressure deficit and soil moisture content, plus leaf area index, were used to calculate stand transpiration, using measured rates of tree water use to parameterise the model. Functional forms for the model were derived by use of a weighted non-linear least squares fitting procedure. The model was able to give comparable estimates of stand transpiration to those derived from a second set of sapflow measurements. It is suggested that short-term, intensive field campaigns where sapflow, weather and soil water content variables are measured could be used to estimate annual patterns of stand transpiration using daily variation in these three environmental variables. Such a methodology will find application in the forestry, mining and water resource management industries where long-term intensive data sets are frequently unavailable.     

Transpiration of trees and forest stands: short and long-term monitoring using sapflow methods

We show that sapflow is a useful tool for studies of water fluxes in forest ecosystems, because (i) it gives access to the spatial variability within a forest stand, (ii) it can be used even on steep slopes, and (iii) when combined with eddy correlation measurements over forests, it allows separation of individual tree transpiration from the total water loss of the stand. Moreover, sapflow techniques are quite easy to implement. Four sapflow techniques currently coexist, all based on heat diffusion in the xylem. We found a good agreement between three of these techniques. Most results presented here were obtained using the radial flow meter (Granier 1985). Tree sapflow is computed as sap flux density times sapwood area. To scale up from trees to a stand, measurements have to be made on a representative sample of trees. Thus, a number of trees in each circumference class is selected according to the fraction of sapwood they represent in the total sapwood area of the stand. The variability of sap flux density among trees is usually low (CV. 10–15%) in close stands of temperate coniferous or deciduous forests, but is much higher (35–50%) in a tropical rain forest. It also increases after thinning or during a dry spell. A set of 5–10 sapflow sensors usually provides an accurate estimate of stand transpiration. Transpiration measured on two dense spruce stands in the Vosges mountains (France) and one Scot's pine plantation in the Rhine valley (Germany) showed that maximum rate was related to stand LAI and to local climate. Preliminary results comparing the sapflow of a stand of Pinus banksiana to the transpiration of large branches, as part of the BOREAS programme in Saskachewan, Canada showed a similar trend. For modelling purposes, tree canopy conductance (g_c) was calculated from Penman-Monteith equation. In most experiments, calculated canopy conductance was dependent on global radiation (positive effect) and on vapour pressure deficit (negative effect) in the absence of other limiting factors. A comparison of the vapour pressure deficit response curves of g_c for several tree species and sites showed only small differences among spruce, oak and pine forests when including understorey. Tropical rainforests exhibited a similar behaviour.     

疏伐对黄土丘陵区刺槐林蒸腾的影响

黄土高原地区植被建设已达到土壤水分承载力的阈值,需要对现有林分进行结构优化并提升其生态功能。不合理的林分密度是导致黄土丘陵区刺槐林土壤干化、生长衰退的主要原因之一。疏伐可以优化林分结构,并能够通过控制蒸腾耗水来调控土壤水分,是促进刺槐林可持续生长的有效手段。疏伐对黄土丘陵区刺槐林蒸腾有何影响,目前并不清楚。研究基于树干液流法估算了4个不同疏伐强度（样地1：52%、样地2：48%、样地3：35%、样地4：未疏伐）下刺槐单株尺度的液流速率与林分尺度的日平均蒸腾量,并分析了不同时间尺度下液流速率与环境因子的关系,以阐明疏伐对黄土丘陵区刺槐林蒸腾的影响。结果表明：（1） 单株尺度刺槐蒸腾速率（即液流速率）随疏伐强度减小（林分密度增大）呈现下降趋势（样地1：0.53 kg cm^-2 d^-1、样地2：0.41 kg cm^-2 d^-1、样地3：0.31 kg cm^-2 d^-1、样地4：0.33 kg cm^-2 d^-1）;（2） 观测期林分尺度日平均蒸腾量随疏伐强度减小呈现上升趋势（样地1：0.90 mm/d、样地2：1.18 mm/d、样地3：1.04 mm/d、样地4：1.44 mm/d）;（3） 在半小时尺度与日尺度上,各样地液流速率与环境因子的关系没有显著差异,半小时尺度单株液流速率均与太阳辐射相关性最高（相关系数0.883-0.908）,液流速率日变化过程与环境因子日变化过程存在时滞现象;日尺度单株液流速率与饱和水汽压亏缺相关性最高（相关系数0.843-0.913）,样地间日尺度单株液流速率的差异性随着饱和水汽压亏缺增大而增大。研究结果初步反映了疏伐导致的林分密度变化对刺槐蒸腾的影响,将为黄土丘陵区刺槐林的结构改造、功能提升和土壤水分调控提供理论支持。     

Water relations of ponderosa pines in Patagonia Argentina: implications for local water resources and individual growth

Replacement of grasslands by forests may result in increased water consumption, and the magnitude of this will depend on stand density. To test this hypotheses and evaluate the impact of pine plantations on hydric resources in Patagonia Argentina, we measured over two seasons (1999–2000 and 2000–2001) and at two densities of ponderosa pine plantations (350 and 500 trees ha^?1) the following variables: soil water content, leaf water potential (ψ), individual tree growth, individual sap flow, and response of sap flow density (u) to vapor pressure deficit (VPD). Stand transpiration (T) and whole-plant liquid-phase hydraulic conductance (L) were also estimated. Pre-dawn ψ varied from about –0.5 to –1.0 MPa. No differences were found in midday maximum u (1100–1800 hours) on clear days between the 2 measurement years, throughout each season, or between different densities of plantation. Sapflow density was also not correlated with soil water storage up to 1.4 m soil depth. Sapflow increased until VPD of about 2.3 kPa, and decreased at VPD >4 kPa, describing a hysteresis in the afternoon. Values of L in Patagonian trees were similar to those recalculated from published data for pines of the same height in the USA. Average stand transpiration increased with increased density (2.07 and 3.08 mm day^-1 for 350 and 500 pines ha^-1, respectively) and size of the trees. We conclude that ponderosa pines in Patagonia Argentina use more water, in a magnitude depending on the density of the trees, than native grasslands. Accordingly, ponderosa pines use deep water to maintain high water potential and transpiration rates even during the dry season.     

Canopy transpiration in a chronosequence of Central Siberian pine forests

Tree transpiration was measured in 28, 67, 204 and 383‐y‐old uniform stands and in a multicohort stand (140–430 y) of Pinus sylvestris ssp. sibirica Lebed. in Central Siberia during August 1995. In addition transpiration of three codominant trees was monitored for two years in a 130‐y‐old stand. All stands established after fire. Leaf area index (LAI) ranged between 0.6 (28‐y‐old stand) and 1.6 for stands older than 67‐y. Stand xylem area at 1.3 m height increased from 4 cm² m^?2 (28‐y) to 11.5 cm² m^?2 (67‐y) and decreased again to 7 cm² m^?2 in old stands. Above‐ground living biomass increased from 1.5 kg dry weight m^?2 (28‐y) to 14 kg dry weight m^?2 (383‐y). Day‐to‐day variation of tree transpiration in summer was dependent on net radiation, vapour pressure deficit, and soil water stress. Tree‐to‐tree variation of xylem flux was small and increased with heterogeneity in canopy structure. Maximum rates of xylem flux density followed the course of net radiation from mid April when a constant level of maximum rates was reached until mid September when low temperatures and light strongly reduced flux density. Maximum sap flux density (60 g m^?2 s^?1) and canopy transpiration (1.5 mm d^?1) were reached in the 67‐y stand. Average canopy transpiration of all age classes was 0.72 ± 0.3 mm d^?1. Canopy transpiration (E) was not correlated with LAI but related to stand sapwood area SA (E = ? 0.02 + 1.15SA R²) which was determined by stand density and tree sapwood area.     

The water balance and water sources of a Eucalyptus plantation over shallow saline groundwater

Eucalypt plantations have been trialled in recent years as a control measure for shallow groundwater associated with secondary salinity. Uncertainty still remains as to the potential growth and water use of these plantations; these relate mainly to the problems associated with drought stress and accumulated solutes in the root zone resulting from saline groundwater uptake. This study investigates the water balance and identifies water sources of a 21 year old unirrigated Eucalyptus grandis W. Hill ex Maiden (flooded or rose gum) and E. camaldulensis Dehnh. (river red gum) plantation over shallow saline groundwater in the Shepparton Irrigation Region of northern Victoria, Australia. Water sources used by the plantation were identified using a monthly water balance approach, together with investigations of stable isotopes of water (deuterium and oxygen-18), soil water and chloride. We found these trees to be heavily reliant on rainwater, and derive approximately 15% of their transpiration requirements from saline (10,000 mg l^?1) groundwater at the capillary fringe. Rainfall at the site is relatively low (465 mm year^?1 on average) and groundwater uptake provides a stable water source that leads to a slight extension of the growing period of these trees. There is little potential for recharge, with subsurface water moving into the groundwater depression created by tree water uptake.     

Groundwater Capture Using Hybrid Poplar Trees: Evaluation of a System in Ogden,Utah

A phytoremediation system was installed in 1996 in Ogden, Utah, with the objective of controlling groundwater containing petroleum hydrocarbons. Hybrid poplar trees were deeply and densely planted in rows oriented perpendicular to the direction of groundwater flow, and the stand was never irrigated. Piezometers were installed to measure water table elevation and contaminant levels upgradient, within, and down-gradient of the trees. In 1998, an analysis of the root structure of a representative tree indicated that roots had extended down to the saturated zone, approximately 6 ft below ground surface. The rate of water use by the stand during 1998 was estimated from reference evapotranspiration (ET_o), leaf area, and a water use multiplication factor ($tH) specific to poplar trees. Sap velocity data were collected to measure actual water use by the stand in late summer of 1998. Estimated and measured values compared favorably, with measured values averaging 2.8 gallons day^-1 tree^-1 (1.7 mm day^-1 tree^-1). Water use by the stand in 1999 averaged an estimated 445 gallons day^-1 (6.9 mm day^-1 for the stand). Although the trees transpired a volume of water equivalent to a 10-ft thickness of the saturated zone, water table elevation data collected in 1999 did not indicate a depression in the water table.     

Seasonal photosynthesis and water relations of juvenile loblolly pine relative to stand density and canopy position

To assess the effects of stand density and canopy environment on tree physiology, we measured gas exchange responses of the same needle age class of 16-year-old loblolly pines ( Pinus taeda L.) in thinned (512 trees ha ^-1) and non-thinned treatment plots (2,863 trees ha ^-1) in central Louisiana. Physiological data were collected in the upper and lower canopy positions on 26 sunny days between July 1996 and June 1997 (one-half of the leaf life span). Mean net photosynthesis was highest (4.3 µmol m ^-2 s ^-1) in the spring and closely corresponded with light intensity in the canopy. Photosynthesis in the winter was nearly 3.0 µmol m ^-2 s ^-1, indicating that loblolly pine enables substantial carbon fixation all year around in the Gulf Coastal Plain region. Mean transpiration and stomatal conductance were highest in the summer and lowest in the winter. With increased light availability after thinning, needle photosynthesis, transpiration and stomatal conductance rose 84, 40 and 23%, respectively, in the lower canopy of the thinned-treatment trees. Light-saturated photosynthetic capacity of the lower canopy needles was 5.2 µmol m ^-2 s ^-1 for the thinned treatment and 4.2 µmol m ^-2 s ^-1 for the non-thinned treatment. It is concluded that thinning-induced light penetration through the canopy enhances physiological activities in the lower canopy foliage of residual trees, and that light availability is the only significant variable for predicting needle-level photosynthesis rates.     

The effects of tree establishment on water and salt dynamics in naturally salt-affected grasslands

Plants, by influencing water fluxes across the ecosystem–vadose zone–aquifer continuum, can leave an imprint on salt accumulation and distribution patterns. We explored how the conversion of native grasslands to oak plantations affected the abundance and distribution of salts on soils and groundwater through changes in the water balance in naturally salt-affected landscapes of Hortobagy (Hungary), a region where artificial drainage performed ∼150 years ago lowered the water table (from −2 to −5 m) decoupling it from the surface ecosystem. Paired soil sampling and detailed soil conductivity transects revealed consistently different salt distribution patterns between grasslands and plantations, with shallow salinity losses and deep salinity gains accompanying tree establishment. Salts accumulated in the upper soil layers during pre-drainage times have remained in drained grasslands but have been flushed away under tree plantations (65 and 83% loss of chloride and sodium, respectively, in the 0 to −0.5 m depth range) as a result of a five- to 25-fold increase in infiltration rates detected under plantations. At greater depth, closer to the current water table level, the salt balance was reversed, with tree plantations gaining 2.5 kg sodium chloride m⁻² down to 6 m depth, resulting from groundwater uptake and salt exclusion by tree roots in the capillary fringe. Diurnal water table fluctuations, detected in a plantation stand but not in the neighbouring grasslands, together with salt mass balances suggest that trees consumed ∼380 mm groundwater per year, re-establishing the discharge regime and leading to higher salt accumulation rates than those interrupted by regional drainage practices more than a century ago. The strong influences of vegetation changes on water dynamics can have cascading consequences on salt accumulation and distribution, and a broad ecohydrological perspective that explicitly considers vegetation–groundwater links is needed to anticipate and manage them.     

半干旱区城市环境下油松林分蒸腾特征及其影响因子

在城市环境下,由于不透水地面面积的增加,土壤-植物-大气之间水汽循环减弱,水汽调节能力差,因而研究城市树木蒸腾对环境因子的响应对于城市进行合理的水汽调节具有重要意义。于2017年生长季,在内蒙古呼和浩特市区树木园内选择58年生油松(Pinus tabulaeformis Carr.)作为研究树种,采用热扩散法测定其树干液流,并同步监测气象因子和土壤含水量变化,利用彭曼公式计算冠层气孔导度。结果表明:(1)生长季内,油松林分蒸腾存在明显日、月变化,晴天天气下林分蒸腾日变化呈单峰曲线,月林分蒸腾量5月最大,其次是7月、8月、6月和9月,分别为20.96、19.89、18.09、17.25 mm和7.49 mm。(2)油松林分蒸腾与饱和水汽压差、太阳总辐射、土壤含水量和风速均存在极显著相关关系(P0.01),太阳总辐射、饱和水汽压差和土壤含水量是影响林分蒸腾的主要环境因子(R~2=0.47、R~2=0.31和R~2=0.16),风速对林分蒸腾的影响程度最小(R~2=0.12);不同降雨量对林分蒸腾的影响作用不同,10 mm以上的日降雨量对油松林分蒸腾作用明显。(3)除环境因子外,油松叶片气孔通过响应环境变化控制蒸腾作用,当饱和水汽压差1.5 kPa时,叶片气孔对饱和水汽压差的响应更敏感;当太阳总辐射250 W/m~2时,叶片气孔对蒸腾起促进作用,超过该阈值,叶片气孔关闭从而抑制树木蒸腾。     

Changes in Biomass Carbon and Soil Organic Carbon Stocks following the Conversion from a Secondary Coniferous Forest to a Pine Plantation

The objectives of this study were to estimate changes of tree carbon (C) and soil organic carbon (SOC) stock following a conversion in land use, an issue that has been only insufficiently addressed. For this study, we examined a chronosequence of 2 to 54-year-old Pinus kesiya var. langbianensis plantations that replaced the original secondary coniferous forest (SCF) in Southwest China due to clearing. C stocks considered here consisted of tree, understory, litter, and SOC (0–1 m). The results showed that tree C stocks ranged from 0.02±0.001 Mg C ha^-1 to 141.43±5.29 Mg C ha^-1, and increased gradually with the stand age. Accumulation of tree C stocks occurred in 20 years after reforestaion and C stock level recoverd to SCF. The maximum of understory C stock was found in a 5-year-old stand (6.74±0.7 Mg C ha^-1) with 5.8 times that of SCF, thereafter, understory C stock decreased with the growth of plantation. Litter C stock had no difference excluding effects of prescribed burning. Tree C stock exhibited a significant decline in the 2, 5-year-old stand following the conversion to plantation, but later, increased until a steady state-level in the 20, 26-year-old stand. The SOC stocks ranged from 81.08±10.13 Mg C ha^-1 to 160.38±17.96 Mg C ha^-1. Reforestation significantly decreased SOC stocks of plantation in the 2-year-old stand which lost 42.29 Mg C ha^-1 in the 1 m soil depth compared with SCF by reason of soil disturbance from sites preparation, but then subsequently recovered to SCF level. SOC stocks of SCF had no significant difference with other plantation. The surface profile (0–0.1 m) contained s higher SOC stocks than deeper soil depth. C stock associated with tree biomass represented a higher proportion than SOC stocks as stand development proceeded.     

Contribution of vines to the evapotranspiration of a secondary forest in eastern Amazonia

The contribution of vines to the evapotranspiration (ET) of a secondary forest in eastern Amazonia was estimated based on field measurements of vine and tree transpiration, and seasonal changes in soil water content to 12 meters depth. Transpiration of vines and trees was measured with sapflow gauges placed around stems or branches. Total ET of the secondary forest was estimated as the sum of rainfall and reductions in soil moisture measured using Time Domain Reflectometry sensors installed in the walls of soil shafts. Our results suggest that vines transpire more than trees with stems of similar diameter, and with similar leaf crown exposure to sunlight. Trees experienced a smaller reduction in transpiration from the wet to the dry season than did vines. During the dry season, vines represented 8% (0.4 mm d^–1) of total secondary forest ET (5.4 mm d^–1), but they represented only 5.5% (0.5 m² ha^–1) of total secondary forest basal area (9.6 m² ha^–1). Considering that transpiration corresponds to 66–90% of forest ET, vines may contribute 9–12% to the transpiration of the forest. Hence, vine cutting, which is a commonly recommended management practice to favor the growth of tropical timber trees, may result in a proportionally larger reduction in evapotranspiration than in forest basal area.     

树干液流对环境变化响应研究进展

随着大气中CO2浓度和其它温室气体的上升,预计全球和区域尺度的温度会增加,由于增温导致地球上一些地区降水增加,一些地区可能面临干旱的加剧.要分析气候、环境变化对植被的影响,需要深入了解植被和大气之间能量、水汽和CO2交换,蒸腾是这个交换过程的一个重要组成部分,是水分和能量离开森林生态系统的主要途径.目前,树干液流测定技术已经发展得比较成熟,能比较可靠的估计整树蒸腾,逐步被应用于研究树木水分利用对环境变化的响应.介绍比较成熟的树木(林分)蒸腾估算方法,就树木(林分)水分利用对环境变化响应研究中的几个热点问题进行了总结:(1) 大气中CO2浓度升高对树木水分利用、气孔导度和冠层结构的影响,环境条件决定树木水分利用对CO2的响应幅度.(2) 树木蒸腾对降雨的响应类型,降雨格局改变导致的土壤干旱对林分蒸腾的影响.(3) 树体储存水的生理意义.随着液流技术的发展和推广,其作为一种科学研究的技术与手段将会受到更多学者的重视,也必将推进树木水分利用对环境变化响应的研究.     

Effects of P fertilisation and ectomycorrhizal fungal inoculation on early growth of eucalypt plantations in southern China

Eucalypt plantations in China have largely been established on soils that are low in phosphorus (P) and have few eucalypt-compatible ectomycorrhizal fungi. Effects of P application and ectomycorrhizal fungal inoculation on early tree growth in plantations of Eucalyptus urophylla Blake in Guangdong (Gaoyao) and E. globulus Labill. in Yunnan (Chuxiong) in southern China were investigated as part of a larger study. Application of superphosphate at establishment, in the presence of a basal fertiliser, increased early growth of E. urophylla and E. globulus. The optimum treatments for maximum stand volume at year 3 were 200 kg P ha^–1 which increased stand volume by 750% on the strongly acidic, P-deficient lateritic red oxisol at Gaoyao, and 40 kg P ha^–1 which increased stand volume by 55% on the mildly P-deficient red ultisol at Chuxiong, at 3 years. Superphosphate increased tree survival at Gaoyao as well as at Chuxiong. Nursery inoculation of eucalypt seedlings with ectomycorrhizal fungi significantly affected tree height and stand volume of the E. urophylla plantation, but the effect (positive or negative) was isolate-dependent and related to tree survival rate. A Laccaria isolate (CSIRO E4728) significantly increased stand volume by 27% at Gaoyao and a Scleroderma (MURU LH041) increased growth by 15% at Chuxiong at age 3 years. All isolates increased tree growth under P-limited soil conditions and only one isolate increased tree growth at marginal soil P. The results suggest that tree growth should be able to be optimised in plantations by the use of effective ectomycorrhizal fungi combined with a judicious fertilisation program at establishment.     

Growth and maintenance respiration in leaves of northern red oak seedlings and mature trees after 3 years of ozone exposure

A two-component model of growth and maintenance respiration is used to study the response of northern red oak (Quercus rubra L.) seedlings and 32-year-old trees to sub-ambient (10 μmol h; cumulative dose based on 7 h daily mean), ambient (43 μmol h), and twice-ambient (85 μmolh) ozone. The relative growth rates (RGR) of leaves sampled from seedlings and trees were similar across treatments, as were specific leaf respiration rates (SRR). Growth coefficients estimated from the SRR versus RGR relationship averaged 25-3 mol CO2 kg^?1 leaf dry mass produced for seedlings and 21-5 mol kg^?1 for trees. Maintenance coefficients ranged from 0-89 to 1-07 mol CO₂ kg^?1 leaf dry mass d^?1 for seedlings and from 0-64 to 0-84 mol kg-1 d^?1 for trees. Neither coefficient was affected by ozone. Leaves sampled throughout the growing season also showed little response of respiration to ozone. This occurred despite a 30% reduction in net photosynthesis for trees grown at twice-ambient ozone. These results suggest that growth and maintenance respiration in young northern red oak leaves are not affected by ozone and that in older leaves injury can occur without a parallel increase in so-called ‘maintenance’ respiration.     

Density-dependent shift from facilitation to competition in a dwarf <Emphasis Type="Italic">Avicennia germinans</Emphasis> forest

The global effort to rehabilitate and restore destroyed mangrove forests is unable to keep up with the high mangrove deforestation rates, which exceed the average pace of global deforestation. Although facilitation theory presents new possibilities for the restoration of heavily degraded mangrove sites, knowledge of tree–tree interactions in stressed mangrove forest ecosystems is too limited to utilize facilitation appropriately. The aim was to determine the mode of local interaction among stressed mangrove trees by investigating the effect of clustering on tree size and crown morphology under contrasting stand densities. The study was conducted in a dwarf Avicennia germinans forest in Northern Brazil, in which tree growth is limited by infrequent inundation and high pore-water salinity. Autoregressive regression, Voronoi tessellation and spatial point pattern statistics were used to address the spatial processes underlying tree interaction. Under low stand density (1.2 trees m^?2) dwarf trees which grew in clustered cohorts of A. germinans had a less stunted crown morphology revealing the dominance of a positive neighborhood influence among plants. In contrast, dwarf trees in the denser forest stand (2.7 trees m^?2) were interacting competitively as indicated by the more negative effect of neighbors on crown morphology and size. The shift from facilitative to competitive interactions is an important feature of mangrove forest regeneration under harsh environmental conditions. If mangrove trees are unable to regenerate naturally on severely degraded sites, intraspecific facilitation could be used to assist regeneration by planting seedlings in clusters and not evenly spaced.     

Branch transpiration of pine and spruce scaled to tree and canopy using needle biomass distributions

Branch water exchange and total tree water uptake were measured in a mixed Norway spruce and Scots pine stand in central Sweden during the 1995 and 1996 growing seasons. Branch transpiration was scaled to canopy level on the basis of a branch conductance model, using vertical needle-area distributions obtained by destructive sampling. Comparison with total tree water uptake scaled to canopy level showed agreement within 10%, for periods when the canopy was not affected by climatically induced stress. Comparison of scaled fluxes on individual trees showed that measurements of transpiration at branch level provide information on the direct response of transpiration to variations in weather, and furthermore that the time-lag between transpiration and tree water uptake was as much as 3 h. The vertical needle-area distribution of Scots pine was similar to that found by other authors. Needle-area distribution on Norway spruce, which has not been described before, showed that it has its largest needle area at the top of the crown. Specific needle area varied considerably both within trees and between trees. For spruce, mean specific needle area (±SD) varied from 2.4±0.5 mm² mg^–1 at the top of the crown to 7.1±1.9 mm² mg^–1 at the base. Corresponding figures for Scots pine were 3.4±2.0 and 9.1±2.1. Received: 5 March 1999 / Accepted: 17 March 2000     

林龄和竞争对日本落叶松各组分生物量异速关系的影响

基于7-、17-、30-和40年生日本落叶松生物量测定数据,应用方差分析和多重比较分析了林龄和林分内树木竞争类型(优势木、平均木和被压木)对各组分生物量分配比例和异速关系的影响,构建了含林龄和树木竞争类型作为哑变量的生物量异速方程,为准确估算日本落叶松人工林生物量和碳储量提供依据。结果表明:(1)林龄显著影响生物量分配比例的异速关系。随林龄增加干生物量比例增大,枝叶生物量比例减小,根生物量逐渐稳定。加入林龄的干、枝和叶生物量方程显著改善。年龄效应在幼龄林阶段作用最显著,需单独构建生物量模型。(2)树木竞争类型对生物量分配的影响小于林龄。立地条件一致下,虽然相同胸径的优势木比劣势木积累更多的枝叶生物量和少的干生物量,但它们分配生物量到不同器官的比例和方式是基本相同的,林内竞争不会导致生物量分配规律由"异速关系理论"向"环境优先理论"转化。因此,常规采用平均木法估算各组分生物量是可行的。(3)在近成熟林分中不同竞争类型树木的根生物量分配比例均较为稳定,采用根茎比比值来估算根生物量是可行的。     

Carbon and nitrogen storage in an age-sequence of <Emphasis Type="Italic">Pinus densiflora</Emphasis> stands in Korea

The carbon (C) and nitrogen (N) storage capabilities of Pinus densiflora in six different stand ages (10, 27, 30, 32, 44, and 71 years old) were investigated in Korea. Thirty sample trees were destructively harvested and 12 were excavated. Samples from the above and belowground tree components, coarse woody debris (CWD), forest floor, and mineral soil (0–30 cm) were collected. Tree biomass was highest in the 71-year-old stand (202.8 t ha⁻¹) and lowest in the 10-year-old stand (18.4 t ha⁻¹). C and N storage in the mineral soil was higher in the 71-year-old stand than in the other stands, mainly due to higher soil C and N concentrations. Consequently, the total ecosystem C and N storage (tree+forest floor+CWD+soil) was positively correlated with stand age: increasing from a minimum in the 10 year old stand (18.8 t C ha⁻¹ and 1.3 t N ha⁻¹) to a maximum in the 71-year-old stand (201.4 t C ha⁻¹ and 8.5 t N ha⁻¹). The total ecosystem C storage showed a similar sigmoidal pattern to that of tree C storage as a function of the age-sequence, while N storage in the CWD, forest floor and mineral soil showed no significant temporal trends. Our results provide important insights that will increase our understanding of C and N storage in P. densiflora stands and our ability to predict changes according to stand age in the region.     

林龄对红松和落叶松人工林土壤温室气体通量的影响

探讨人工林发育过程中土壤温室气体排放及其机制,可为森林温室气体通量估算提供理论依据.采用室内培养方法研究了黑龙江省帽儿山地区不同林龄(15、30和50年生)红松(Pinus koraiensis)和落叶松(Larix gmelinii)人工林土壤温室气体排放/吸收速率及其调控因素.结果 表明:30年生红松和落叶松人工林...