Below-ground respiratory responses of sugar maple and red maple saplings to atmospheric CO2 enrichment and elevated air temperature

The research described in this paper represents a part of a much broader research project with the general objective of describing the effects of elevated [CO2] and temperature on tree growth, physiological processes, and ecosystem-level processes. The specific objective of this research was to examine the below-ground respiratory responses of sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) seedlings to elevated atmospheric [CO2] and temperature. Red maple and sugar maple seedlings were planted in the ground in each of 12 open-top chambers and exposed from 1994 through 1997 to ambient air or air enriched with 30 Pa CO2,< in combination with ambient or elevated (+4 °C) air temperatures. Carbon dioxide efflux was measured around the base of the seedlings and from root-exclusion zones at intervals during 1995 and 1996 and early 1997. The CO2 efflux rates averaged 0.4 μmol CO2 m-2 s-1 in the root-exclusion zones and 0.75 μmol CO2 m-2 s-1 around the base of the seedlings. Mineral soil respiration in root-exclusion zones averaged 12% higher in the high temperature treatments than at ambient temperature, but was not affected by CO2 treatments. The fraction of total efflux attributable to root + rhizosphere respiration ranged from 14 to 61% in measurements made around red maple plants, and from 35 to 62% around sugar maple plants. Root respiration rates ranged from 0 to 0.94 μmol CO2 s-1 m-2 of soil surface in red maple and from 0 to 1.02 in sugar maple. In both 1995 and 1996 root respiration rates of red maple were highest in high-CO2 treatments and lowest in high temperature treatments. Specific red maple root respiration rates of excised roots from near the soil surface in 1996 were also highest under CO2 enrichment and lowest in high temperature treatments. In sugar maple the highest rates of CO2 efflux were from around the base of plants exposed to both high temperature and high-CO2, even though specific respiration rates were< lowest for this species under the high temperature and CO2 enrichment regime. In both species, patterns of response to treatments were similar in root respiration and root mass, indicating that the root respiration responses were due in part to differences in root mass. The results underscore the need for separating the processes occurring in the roots from those in the forest floor and mineral soil in order to increase our understanding of the effects of global climate change on carbon sequestration and cycling in the below-ground systems of forests.     

Analytical estimation of branchwood volume in sugar maple, linked to branchiness

 An analytical link is proposed between branchwood volume and branchiness. A segmented linear model with one parameter is used to describe the branch basal area density along the tree bole and integrated to find a function describing the cumulative branch basal area. It appears that the bases of insertion of the branches defining the base of the light crown correspond to the maximum branch basal area density along the bole. This function is then used together with an individual branch volume equation to find a model that estimates branchwood volume. This model is calibrated with data gathered in 15 stands dominated by sugar maple (Acer saccharum Marsh.) in southern Quebec. A comparison is made with other models of branchwood volume found in the literature. Received: 22 August 1997 / Accepted: 9 February 1998     

低温处理对糖槭（Acer saccharum）种子萌芽效应的研究

槭属某些种的种子具有休眠生物学特性,如糖槭(Acer saccharum)和茶条槭(Acer ginnala)。本试验采用低温处理糖槭种子,打破它的休眠,获得高达95%的种子萌芽率,并用这种已萌芽的种子播种,出苗速度快,缩短了播种管理时间。试验还表明,主要存在于糖槭种子子叶、种皮中抑制种子萌芽的调节物质,在0—8℃低温、相对湿度90—100%(遮光)的条件下,能够被逐渐转化、消失,使种子得以萌芽出苗。不经低温处理的种子则不能萌芽,而且低温处理只有伴随高湿的条件才会发生良好的效应。     

玉米农田土壤呼吸作用的空间异质性及其根系呼吸作用的贡献

基于4月底到9月底东北地区玉米农田土壤呼吸作用全生长季的观测,阐明了土壤呼吸作用的空间异质性特征,综合分析了水热因子、土壤性质、根系生物量及其测定位置对土壤呼吸作用空间异质性的影响,并对生长季中根系呼吸作用占土壤呼吸作用的比例进行了估算。结果表明,在植株尺度上,土壤呼吸作用存在着明显的空间异质性,较高的土壤呼吸速率通常出现在靠近玉米植株的地方。根系生物量的分布格局是影响土壤呼吸作用空间异质性的关键因素。在空间尺度上,土壤呼吸作用与根系生物量呈显著的线性关系,而土壤湿度、土壤有机质、全氮和碳氮比对土壤呼吸作用空间异质性的影响并不显著。通过建立土壤呼吸作用与玉米根系生物量的回归方程,对根系呼吸作用占土壤呼吸作用的比例进行了间接估算。玉米生长季中,根系呼吸作用占土壤呼吸作用的比例在43．1％～63．6％之间波动,均值为54．5％。     

Sites of action of sulphite and bisulphite in the photosynthetic apparatus of sugar maple leaves as studied by photo-acoustic and modulated fluorescence methods

The photosynthetic activity of intact sugar maple leaves has been assessed in the presence of exogenous sulphite, bisulphite and sulphate under varying light conditions using photo-acoustic and modulated fluorescence methods. In the light, bisulphite was found to be more toxic than the other two, sulphate being the least toxic of all. Interestingly, the vitality index, R_rd, measured as the ratio of the modulated fluorescence decrease (F_d) to the steady-state fluorescence (F_s), which indicates the efficiency of the whole photosynthetic activity, was more affected than the total photosynthetic energy storage (PES) of PSII and PSI during linear and cyclic electron transport, and F_v/F_m (PSII activity). The severity of the damage appeared to be a function of light intensity. Bisulphite treatment in darkness resulted in a dramatic decrease in R_rd, a moderate decrease in PES and a marginal decrease in F_v/F_m. As for sulphite, the effect was negligible with a tendency for enhanced activity. It is inferred that the Calvin cycle is a good candidate for the primary site of bisulphite and sulphite action. Recovery of activity, especially at the R_rd level, obtained in the presence of ascorbate, glutathione and L-cysteine, indicated a contribution of O₂ free radicals to the observed inhibition of the photosynthetic activity in the light.     

High-irradiance Stress and Photochemical Activities of Photosystems 1 and 2 in vivo

High-irradiance (HI) stress induced changes in the photosynthetic energy storage (ES) of photosystems 1 (ESPS1) and 2 (ESPS2) were studied with 650 nm modulated radiation in intact sugar maple (Acer saccharum Marsh.) leaves. HI-treatment (420 W m-2, 1 h) caused an inhibition of about 40 % in ESPS2 and an enhancement of about 60 % in ESPS1. The rate of PS1 cyclic electron transport, measured with 705 nm modulated radiation, also increased in HI-treated leaves. There was a clear state 1- state 2 transition in HI-treated leaves. ESPS1 increased significantly and ESPS2 decreased drastically in leaves preadapted to state 1 after HI (600 W m-2, 30 min) treatment. Thus, the increase in PS1 activity observed immediately after HI-treatment in leaves preadapted to state 1 can be due to the coupling of LHC2 to PS1 during the HI-treatment. Further, the dissociation of LHC2 from PS2 during the HI-treatment resulted in apparently (about 15 %) greater inhibition than the "true" inhibition of PS2 activity. The presence of LHC2 with PS2 (state 1) at the time of HI-treatment caused no additional damage to PS2 or its coupling to PS1 offered no apparent HI-treatment. Further, the dissociation of LHC2 from PS2 during the HI-treatment resulted in apparently (about 15 %) greater inhibition than the "true" inhibition of PS2 activity. The presence of LHC2 with PS2 (state 1) at the time of HI-treatment caused no additional damage to PS2 or its coupling to PS1 offered no apparent protection to the photosynthetic apparatus.     

A theoretical model of hydraulic conductivity recovery from embolism with comparison to experimental data on Acer saccharum

A theoretical model of bubble dissolution in xylem conduits of stems was designed using the finite differential method and iterative calculations via computer. The model was based on Fick's, Henry's and Charles' laws and the capillary equation. The model predicted the tempo of recovery from embolism in small diameter branches of woody plants with various xylem structures under different xylem water pressures. The model predicted the time required to recover conductivity in any position in the stem. Repeated iterative solution of the model for different situations yielded an empirical formula to calculate the time for complete recovery of conductivity in stems from a fully embolised initial state. The time, t_p, is given by: where α is a temperature coefficient; D is the coefficient of diffusion of air in wood at 25°C; r_cs is the ratio of the area of total conduit cross section to the stem cross section; Ψ_xp is the stem xylem pressure potential (Pa, where 0 Pa equals atmospheric pressure); τ is solution surface tension (0.072 N m^?1); and D_c and D_s are diameters of the conduits and the stem, respectively (m). The equation is valid only when Ψ_xp > –4τ/D_c. The model predicts no recovery of conductivity when Ψ_xp≤–4τ/D_c. The model agreed with experiments.     

Nitrate uptake and respiration in roots and shoots: A model

Respiration in plants is often divided into growth and maintenance components. From the growth respiration it is possible to estimate the efficiency of conversion of substrate to plant material. Analysis of recent experimental data on this basis suggests that the conversion efficiency is considerably lower in roots than in shoots, which conflicts with biochemical analysis. The conventional method for describing respiration data is developed to incorporate root activity and is applied to a set of experimental data. The model provides a means for estimating the respiratory cost of nitrate uptake and also a possible explanation for the inconsistency between experimental observations and theoretical analysis.     

An open-air system for exposing forest-canopy branches to ozone pollution

We developed a chamberless system to expose branches to elevated concentrations of ozone with little alteration of micro-meteorological conditions. In a 35-year-old stand of sugar maple (Acer saccharum Marsh.), scaffolding and a platform (14 m in height) provided access to 10 branches and ten paired controls within the canopy. Ozone was delivered to the canopy through a manifold and an array of loops (38 cm in diameter) of teflon tubing individually fitted to each branch. Ozone-enriched air was discharged through numerous small holes in each loop positioned beneath the exposed foliage. A sampling system controlled by a microcomputer monitored ozone concentrations for each loop by means of composite air samples from 12 leaves, drawn through small teflon tubes (1.65 mm diameter) attached to the petioles. On average, coefficients of variation for ozone concentrations for the sample points within each branch loop were less than 50%. Between 0900 and 1700 h for 68 d of exposure, the mean hourly ozone concentrations among the branches averaged 95nmol mol⁻¹ (±13SD), about twice the ambient mean. Frequency distributions of mean hourly concentrations during exposure were unimodal and approximately log-normal, comparable to ambient ozone concentrations. The open-air loop system enables exposure of branches to gaseous pollutants under relatively natural conditions.     

锡林河流域一个羊草群落中土壤呼吸与生物量之间的相关性分析

采用根系生物量梯度上土壤呼吸变化趋势线外推法对锡林河流域一个羊草(Leymus chinensis (Trin.) Tzvel.)群落中根系呼吸占土壤总呼吸的比例进行了估计,对生物量各组分(地上、地下部分)之间以及它们与土壤呼吸间的相关性进行了分析.结果表明:在测定年度(1998年)整个生长季的不同月份,该群落中根系呼吸量占土壤呼吸总量的比例在14%～39%之间,平均为27%;地上总生物量及根系生物量与土壤呼吸间的相关性较差,但地上活生物量与土壤呼吸间存在着显著的乘幂关系.上述结果与国外同类研究结果相比,具有很好的一致性.     

Contribution of Root Respiration to Total Soil Respiration in a Leymus chinensis （Trin.） Tzvel, Grassland of Northeast China

The loss of carbon through root respiration Is an Important component of grassland carbon budgets. However, few data are available concerning the contribution of root respiration to total soil respiration in grasslands in China. We Investigated seasonal variations of soil respiration rate, root blomaaa, microbial blomaaa C and organic C content of the soil In a semi-arid Leymus chinensis （Trin.） Tzvel. grassland of northeast China during the 2002 growing season （from May to September）. The linear regression relationship between soil respiration rate and root blomaaa was used to determine the contribution of root respiration to total soil respiration. Soil respiration rate ranged from 2.5 to 11.9 g C/m^2 per d with the maximum in late June and minimum In September. The microbial blomaaa C and organic C content of the soil ranged from 0.3 to 1.5 g C/m^2 and from 29 to 34 g C/kg respectively. Root blomaaa had two peaks, In early June （1.80 kg/m^2） and mid-August （1.73 kg/m^2）. Root respiration rate peaked In mid-August （6.26 g C/m^2 per d）, whereas microbial respiration rate peaked In late June （7.43 g C/m^2 per d）. We estimated that the contribution of root respiration to total soil respiration during the growing season ranged from 38% to 76%.     

锡林河流域一个羊草群落中土壤呼吸与生物量之间的相关性分析(英)

采用根系生物量梯度上土壤呼吸变化趋势线外推法对锡林河流域一个羊草 (Leymuschinensis (Trin .)Tzvel.)群落中根系呼吸占土壤总呼吸的比例进行了估计 ,对生物量各组分 (地上、地下部分 )之间以及它们与土壤呼吸间的相关性进行了分析。结果表明 :在测定年度 (1998年 )整个生长季的不同月份 ,该群落中根系呼吸量占土壤呼吸总量的比例在 14 %～ 39%之间 ,平均为 2 7% ;地上总生物量及根系生物量与土壤呼吸间的相关性较差 ,但地上活生物量与土壤呼吸间存在着显著的乘幂关系。上述结果与国外同类研究结果相比 ,具有很好的一致性。     

隔离降水对杉木幼苗细根生物量和功能特征的影响

在福建三明陈大国有采育场杉木幼苗小区,采用土钻法和内生长环法,以非隔离降水为对照,对隔离降水50%处理一年的杉木幼苗细根生物量和形态、化学计量学、比根呼吸、非结构性碳水化合物等功能特征进行研究.结果表明: 与对照相比,隔离降水处理0～1 mm细根生物量显著降低,1～2 mm细根生物量差异不显著;隔离降水导致细根在形态上发生了适应性变化,0～1 mm和1～2 mm细根比根长分别增加21.1%和30.5%,0～1 mm细根组织密度显著降低,而比表面积显著增加.隔离降水导致细根氮的富集,但限制了对磷的吸收,氮磷比升高,导致营养失衡;隔离降水没有显著改变细根比根呼吸和非结构性碳水化合物含量,但导致1～2 mm细根可溶性糖、糖淀比显著降低,淀粉含量增加33.3%,表明其通过增加非结构性碳水化合物贮存比例以应对降水减少.     

Relationships among cytokinins, ethylene and poly amines during the stratification-germination process in seeds of Acer saccharum

Relatively high levels of dihydrozeatin and trans-zeatin were detected in unstratified seeds of Acer saccharum Marsh. Both cytokinins increased substantially over the first 20 days of stratification at 5°C and then fell rapidly to values well below original levels by first germination on day 55. In seeds held at 20°C, a non-afterripening temperature, cytokinin levels remained constant for the first 10 days and then declined to their lowest levels by day 20. Levels of putrescine, spermidine and spermine in the radicles and cotyledons did not change during the full course of the afterripening process, but large increments were noted during radicle emergence. A large increase in ethylene production at germination suggests that competition for S-adenosyl-methionine by the ethylene and polyamine biosynthetic pathways did not inhibit synthesis of ethylene or polyamines during seedling emergence and establishment. In seeds stratified at 20°C, ethylene showed an exceptionally large peak early in the stratification period, but polyamine contents remained low throughout the test. The present results are consistent with the hypothesis that cytokinins play a significant role in overcoming the metabolic block present in dormant seeds. This conclusion is supported by data showing that high levels of cytokinins develop concurrently with the start of tissue differentiation and at the time when abscisic acid and phenolic inhibitors decline in stratifying seeds. Changes in ethylene and polyamine contents did not correlate with any events in the afterripening process; however, large increases in levels of these substances were closely associated with the germinative process and, in the case of polyamines, specifically with the start of cell division.