人工林碳汇和植物根系呼吸研究进展

中国科学家对华南地区大面积种植的人工林树种尾叶桉和厚荚相思的根系呼吸进行研究,发现尾叶桉人工林是很强的碳汇,华南人工桉所截获的碳可以抵消全球失踪碳的2％。而长期以来一直受到忽略的粗根的呼吸则占根系呼吸总量的50左右,粗根的呼吸作用并不可忽视。同时,对两种树种的根系呼吸情况进行观测及统计后发现,     

不同树龄杨树人工林的根系呼吸季节动态

根系呼吸是准确评估森林生态系统土壤碳收支的一个重要依据。基于LI-COR-6400-09土壤呼吸系统连续2a测定的3个生长阶段杨树人工林的根系呼吸数据,分析了根系呼吸的季节变化规律及树龄、土壤水热因子和细根生物量对它的影响。结果表明:3个不同树龄人工林的根系呼吸速率均呈明显的季节变化,最大值出现在夏初,最小值出现在秋末,基本上与表层土壤温度的季节变化相一致。根系呼吸的峰值早于土壤温度和细根生物量的峰值,说明林木根系的季节生长节律、地下碳分配模式都可能影响根系呼吸的季节变化。2年生人工林的根系呼吸速率最高,平均为3.78μmolCO2m-2s-1,并随树龄增长呈下降趋势。3个树龄人工林根系呼吸占土壤呼吸的比例介于38.6%-58.0%之间,且2年生人工林最大。不同林龄之间根系呼吸的差异主要与根系的生长周转速率及代谢活性随生长阶段的变化有关。总的来说,表层土壤温度和细根生物量的协同作用可解释根系呼吸速率变化的76%。此外在评估一个轮伐期内的根系呼吸强度时,应考虑不同生长阶段对它的影响。     

镉和双酚A对根系微生态效应研究进展

近年关于镉（Cd）单一污染对植株伤害的报道比较多,但是自然背景下,污染多呈复合型,而双酚A（BPA）是一种新兴的环境激激素,故研究二者复合污染具有一定理论价值和实践意义。本研究综述了Cd和BPA胁迫下植物根系的形态学变化及生理生化改变,以及镉和双酚A在植物体内的代谢过程和其对植物毒性机制的研究进展,并提出有待进一步研究的内容。研究表明Cd和BPA对根系生长的影响可能与其影响植物根系活力,矿质代谢和根系保护酶有关,低浓度的Cd和BPA对植株干质量、根系总长度、根系表面积、根体积和根系活力都有促进作用,高浓度则可能存在抑制效应。     

根系分泌物生态学研究

在植物生长过程中 ,由根系的不同部位分泌或溢泌一些无机离子及有机化合物 ,这些物质统称为根系分泌物。植物在其生长过程中不断地分泌无机离子及有机化合物 ,这是植物长期适应外界环境而形成的一种适应机制。早在 2 0世纪 5 0年代就有人对植物根系分泌物进行了研究 ,Ｒｏｖｉｒａ等[4 3] 和Ｖａｎｃｕｒａ等[4 7] 对根土界面根系分泌物进行了系统的研究 ,切尔诺布里维卡[2 6 ] 研究了植物根系分泌物的生物学作用 ,揭示了其在间作中的作用 ,直到 70年代对根系分泌物的研究才出现了蓬勃发展的趋势。近年来的研究表明 ,根系分泌物是保持根际微…     

淹水胁迫对不结球白菜根系生长与呼吸酶活性的影响

采用双套盆法,以不结球白菜‘新矮青’和‘新夏青2号’品种为材料,研究了不同时间(1、3、5、恢复7d后)和不同程度淹水处理(根淹、半淹)后不结球白菜根系生长及呼吸代谢的变化规律。结果显示:(1)与对照相比,淹水胁迫下,不结球白菜幼苗根系鲜重、根系长度、根系活力显著下降,且半淹处理的下降幅度大于根淹处理。(2)淹水胁迫下,乳酸脱氢酶(LDH)、乙醇脱氢酶(ADH)活性较对照显著升高,而苹果脱氢酶(MDH)、琥珀酸脱氢酶(SDH)活性显著降低,且半淹处理的降幅大于根淹,淹水5d后与淹水1d后有显著性差异。(3)淹水胁迫下,‘新矮青’乳酸发酵途径弱于‘新夏青2号’,乙醇发酵则相反,导致后者根系中乳酸积累多于前者,细胞质酸化较严重,降低了对淹水胁迫的耐性。研究表明,不结球白菜幼苗期受到淹水胁迫时,其有氧呼吸明显受阻,无氧呼吸代谢被促进,而且随着淹水时间的延长及淹水深度的加深,根系呼吸代谢受到的抑制程度越严重,最终导致根系生长受到抑制。     

湿地植物根系泌氧及其在自然基质中的扩散效应研究进展

湿地植物根系径向泌氧(ROL)是构造根际氧化-还原异质微生态系统的核心要素,其扩散层为好氧、厌氧微生物提供了良好生境并促进其代谢活动,使湿地植物根际成为有机物降解、物质循环及生命活动最为强烈的场所,已有成果证明湿地植物根系ROL的强弱与污染物的去除效果密切相关。因此,开展湿地植物根系ROL及其在自然基质中的扩散效应研究,对于了解湿地植物根系ROL机理及其根际氧环境特征,进而发挥湿地植物的污染去除功能具有十分重要的意义。基于此,首先归纳了湿地植物根系ROL特征及其受影响机制的研究现状,而后从种属差异、时空分布及对微生物的影响等方面对根系ROL在自然基质中的扩散效应国内外研究成果进行了总结,最终根据研究现状与不足对今后的研究方向进行了简要展望。创新之处在于:1)提出影响根系氧供给及氧输送释放通道的环境、生物等因素,阐述了其对根系ROL的影响机制;2)着重阐述了目前研究较少提及的根系ROL扩散效应测定方法。     

根系分泌物及其在植物修复中的作用

 近年来环境污染日益严重,污染物在土壤植物中的行为引起了人们的高度关注。利用植物去除土壤水体等介质中污染物的植物修复是近10年来兴起的一项安全、廉价的技术,已成为污染生态学和环境生态学的研究热点,它通过植物吸收、根滤、稳定、挥发等方式清除环境中的重金属和有机污染物。国内外有关植物修复的研究报道和概述很多, 但对植物根系分泌物在植物修复中所起的作用及其机理少有述评。 本文从根系分泌物对土壤重金属和土壤有机污染物的去除作用出发,对根系分泌物的种类、数量及其在去除环境污染物中的作用机理和功能地位进行了总结,并借助研究事例对影响植物根系分泌的内外因子,如植物种类、营养胁迫、重金属胁迫、根际环境的理化性质、土壤微生物及其它环境因子进行了讨论。概言之,根系分泌物在修复污染土壤中的重金属途径是多种多样的,主要是通过调节根际pH值、与重金属形成螯合物、络合反应、沉淀、提高土壤微生物数量和活性来改变重金属在根际中的存在形态以及提高重金属的生物有效性,从而减轻它对环境的危害。在清除有机污染物时,根系分泌物中的酶可以对有机污染物进行直接降解,根系分泌物影响下的微生物也可以对有机污染物进行间接降解,且被认为是主要的降解途径。根系分泌物在植物修复过程中确实起着某些重要作用,今后应将这方面的研究重点放在某些特异性根系分泌物植物,尤其是某些重金属超富集植物资源的寻找、筛选上,通过室内实验和野外研究确定其根系分泌物对清除重金属和有机污染物的效率,证实超富集植物根系分泌物的特异性与污染物超富集的内在联系,找到污染土壤生态恢复和治理的有效方法并加以推广应用,如针对性地在被污染地大面积种植此类具特异性根分泌物植物,并辅以营林措施如修剪等,加快生物修复进程,提高修复效率。植物根系分泌物在植物修复过程中所具有的重要生态意义和可能应用前景,为污染生态学和化学生态学之间的联合研究开拓了全新的领域,今后将取得新的突破和重要进展。     

根际微生物调控植物根系构型研究进展

根系构型是最重要的植物形态特征之一,具有可塑性,既由遗传因素控制,又受到许多环境因子的调控。近年的大量研究表明,根际微生物能够调控植物的根系构型,进而影响植物的一系列生理与生态过程。综述丛枝菌根真菌(AMF)、根瘤菌、植物根际促生菌(PGPR)等重要根际微生物类群对植物根系构型的调控模式以及相应的调控机理,并对进一步的研究进行了展望,旨在为今后的相关研究和实际应用提供参考。     

植物根系分泌物的研究方法

根系分泌物是植物根系释放到根际环境中的有机物质的总称,对土壤结构形成、土壤养分转化、植物养分吸收、土壤微生物分布、环境胁迫缓解等方面都具有重要作用。但是,由于土壤中微生物对根系分泌物的降解以及根系分泌物本身含量低、成分复杂,根系分泌物的研究方法一直是植物营养学与土壤科学的研究热点和难点。近年来,一些新的实验技术和研究方法被应用到对植物根系分泌物的研究中。本文对目前在根系分泌物研究中应用较多的以及新发展起来的各种收集、分离和鉴定方法进行了综述,希望有助于相关研究者在针对不同的研究对象和目的时选择出可行、合适、高效的根系分泌物研究方法和技术。     

淹水对甜樱桃根系呼吸强度和呼吸酶活性的影响

以美早/东北山樱桃(Prunus serrulataG.Don)和美早/马哈利(P. mahaleb L.)为试材,研究了淹水对甜樱桃根系（生长根和褐色木质根）呼吸强度和呼吸酶活性的影响.结果表明：淹水过程中,两种甜樱桃砧木生长根和褐色木质根呼吸强度均呈下降趋势,生长根降幅更大;东北山樱桃生长根和褐色木质根呼吸强度降幅分别是马哈利的1.47和1.36倍.丙酮酸脱羧酶(PDC)、乳酸脱氢酶(LDH)活性在两类根系中均呈先升后降趋势,乙醇脱氢酶(ADH)活性在生长根中亦先升后降,而在褐色木质根中为上升趋势,3种酶活性变化幅度表现为生长根大于褐色木质根;东北山樱桃ADH和LDH活性增幅大于马哈利,但PDC活性则相反.两类根系苹果酸脱氢酶(MDH)活性均下降,且生长根降幅大于褐色木质根;东北山樱桃MDH活性降幅大于马哈利.说明生长根对淹水的敏感性强于褐色木质根;与马哈利相比,东北山樱桃对淹水更敏感.     

Respiration in postharvest sugarbeet roots is not limited by respiratory capacity or adenylates

Control of respiration has largely been studied with growing and/or photosynthetic tissues or organs, but has rarely been examined in harvested and stored plant products. As nongrowing, heterotrophic organs that are reliant on respiration to provide all of their metabolic needs, harvested plant products differ dramatically in their metabolism and respiratory needs from growing and photosynthetically active plant organs, and it cannot be assumed that the same mechanism controls respiration in both actively growing and harvested plant organs. To elucidate mechanisms of respiratory control for a harvested and stored plant product, sugarbeet (Beta vulgaris L.) root respiration was characterized with respect to respiratory capacity, adenylate levels and cellular energy status in roots whose respiration was altered by wounding or cold treatment (1 degrees C) and in response to potential effectors of respiration. Respiration rate was induced by wounding in roots stored at 10 degrees C and by cold temperature in roots stored at 1 degrees C for 11-13d. Alterations in respiration rate due to wounding or storage temperature were unrelated to changes in total respiratory capacity, the capacities of the cytochrome c oxidase (COX) or alternative oxidase (AOX) pathways, adenylate concentrations or cellular energy status, measured by the ATP:ADP ratio. In root tissue, respiration was induced by exogenous NADH indicating that respiratory capacity was capable of oxidizing additional electrons fed into the electron transport chain via an external NADH dehydrogenase. Respiration was not induced by addition of ADP or a respiratory uncoupler. These results suggest that respiration rate in stored sugarbeet roots is not limited by respiratory capacity, ADP availability or cellular energy status. Since respiration in plants can be regulated by substrate availability, respiratory capacity or energy status, it is likely that a substrate, other than ADP, limits respiration in stored sugarbeet roots.     

CO2浓度升高对森林土壤微生物呼吸与根（际）呼吸的影响

 根呼吸与微生物呼吸的作用底物不同,二者对高浓度CO₂的响应机理及敏感程度亦不同。在大气CO₂浓度升高的背景下,精确区分根呼吸与微生物呼吸是构建森林生态系统碳循环模型和预测森林生态系统碳源/汇关系所必需的。根（际）呼吸与微生物呼吸对高浓度CO₂的响应呈增加、降低或无明显变化等不同趋势,根（际）呼吸变化主要与根生物量明显相关,细根的作用大于粗根;土壤微生物呼吸变化存在较大的不确定性,微生物量和微生物活性与土壤微生物呼吸相关或不相关。根系统对高浓度CO₂的响应会潜在地影响微生物的代谢底物,进而影响微生物呼吸强度。凡影响土壤总呼吸的生物与非生物因子都会直接或间接地影响根呼吸与土壤微生物呼吸。     

Malate plays a central role in plant nutrition

Malate occupies a central role in plant metabolism. Its importance in plant mineral nutrition is reflected by the role it plays in symbiotic nitrogen fixation, phosphorus acquisition, and aluminum tolerance. In nitrogen-fixing root nodules, malate is the primary substrate for bacteroid respiration, thus fueling nitrogenase. Malate also provides the carbon skeletons for assimilation of fixed nitrogen into amino acids. During phosphorus deficiency, malate is frequently secreted from roots to release unavailable forms of phosphorus. Malate is also involved with plant adaptation to aluminum toxicity. To define the genetic and biochemical regulation of malate formation in plant nutrition we have isolated and characterized genes involved in malate metabolism from nitrogen-fixing root nodules of alfalfa and those involved in organic acid excretion from phosphorus-deficient proteoid roots of white lupin. Moreover, we have overexpressed malate dehydrogenase in alfalfa in attempts to improve nutrient acquisition. This report is an overview of our efforts to understand and modify malate metabolism, particularly in the legumes alfalfa and white lupin.     

Interpreting,measuring, and modeling soil respiration

This paper reviews the role of soil respiration in determining ecosystem carbon balance, and the conceptual basis for measuring and modeling soil respiration. We developed it to provide background and context for this special issue on soil respiration and to synthesize the presentations and discussions at the workshop. Soil respiration is the largest component of ecosystem respiration. Because autotrophic and heterotrophic activity belowground is controlled by substrate availability, soil respiration is strongly linked to plant metabolism, photosynthesis and litterfall. This link dominates both base rates and short-term fluctuations in soil respiration and suggests many roles for soil respiration as an indicator of ecosystem metabolism. However, the strong links between above and belowground processes complicate using soil respiration to understand changes in ecosystem carbon storage. Root and associated mycorrhizal respiration produce roughly half of soil respiration, with much of the remainder derived from decomposition of recently produced root and leaf litter. Changes in the carbon stored in the soil generally contribute little to soil respiration, but these changes, together with shifts in plant carbon allocation, determine ecosystem carbon storage belowground and its exchange with the atmosphere. Identifying the small signal from changes in large, slow carbon pools in flux dominated by decomposition of recent material and autotrophic and mycorrhizal respiration is a significant challenge. A mechanistic understanding of the belowground carbon cycle and of the response of different components to the environment will aid in identifying this signal. Our workshop identified information needs to help build that understanding: (1) the mechanisms that control the coupling of canopy and belowground processes; (2) the responses of root and heterotrophic respiration to environment; (3) plant carbon allocation patterns, particularly in different forest developmental stages, and in response to treatments (warming, CO₂, nitrogen additions); and (4) coupling measurements of soil respiration with aboveground processes and changes in soil carbon. Multi-factor experiments need to be sufficiently long to allow the systems to adjust to the treatments. New technologies will be necessary to reduce uncertainty in estimates of carbon allocation, soil carbon pool sizes, and different responses of roots and microbes to environmental conditions.     

Energy metabolism of Plantago lanceolata, as affected by change in root temperature

The long and short term metabolic effects of a shift in root temperature was investigated in Plantago lanceolata L. with special reference to the role of the cyanide resistant alternative pathway in root respiration. After a 10-day period of growth at a 13°C root temperature, a decrease in root as well as shoot growth was observed, compared to control plants grown continuously at 21°C. Apart from an increase in shoot soluble and insoluble sugar level, no changes in metabolism were found, neither in root respiration, shoot photosynthesis, nor in root sugar and plant protein level.
Decreasing the root temperature from 21 to 13°C gave several clear short term changes in metabolism. Within one hour a decrease in cytochrome chain activity of the roots was found together with an increase in activity of the alternative chain. After 24 h a recovery to the initial level of both chains was observed. An increase in root temperature from 13 to 21°C gave an immediate increase in activity of both respiratory chains that was still present 24 h after the switch.
It is concluded that the activity of the alternative respiratory pathway in the root is strongly affected by a sudden temperature change in the root environment. This pathway acts in a way which is described by 'the energy overflow model'. The presence of the alternative electron transport pathway should be taken into account in determinations of the respiratory Q₁₀. Moreover, the length of time between the temperature change and respiration measurements is an important factor.     

Die apparente Photosynthese von Bohnenkeimpflanzen (Phaseolus vulgaris L.) unter dem Einfluss einer kurzzeitigen Hemmung des Wurzelgaswechsels

Apparent photosynthesis (P_n) and root respiration (R_n) of 8 to 10 d old intact bean plants were studied separately at different temperatures and oxygen concentrations acting on the roots using IRGA technique. P_n is reversibly decreasing during 3 h root cooling (+ 5 °C) in accord with bending down of the primary leaves, and closing of the stomata. Plants adapted to low root temperatures show no effect of increasing the latter on P_n. Even 3 h oxygen deficit in the root medium has no influence on P_n but is increasing R_r in consequence of alteration in ’ metabolism from respiration to fermentation. One must distinguish between short time reaction and long time adaptation of the plant on root stress.      

Effects of phosphorus availability and vesicular–arbuscular mycorrhizas on the carbon budget of common bean (Phaseolus vulgaris)

Low phosphorus availability is often a primary constraint to plant productivity in native soils. Here we test the hypothesis that root carbon costs are a primary limitation to plant growth in low P soils by assessing the effect of P availability and mycorrhizal infection on whole plant C budgets in common bean ( Phaseolus vulgaris L.). Plants were grown in solid-phase-buffered silica sand providing a constant supply of low (1 μ m ) or moderate (10 μ m ) P. Carbon budgets were determined weekly during the vegetative growth phase. Mycorrhizal infection in low-P plants increased the root specific P absorption rate, but a concurrent increase in root respiration consumed the increased net C gain resulting from greater P uptake. The energy content of mycorrhizal and non-mycorrhizal roots was similar. We propose that the increase in root respiration in mycorrhizal roots was mainly due to increased maintenance and growth respiration of the fungal tissue. Plants grown with low P availability expended a significantly larger fraction of their total daily C budget on below-ground respiration at days 21, 28 and 35 after planting (29–40%) compared with plants grown with moderate P supply (18–25%). Relatively greater below-ground respiration in low P plants was mainly a result of their increased root:shoot ratio, although specific assimilation rate was reduced significantly at days 21 and 28 after planting. Specific root respiration was reduced over time by low P availability, by up to 40%. This reduction in specific root respiration was due to a reduction in ion uptake respiration and growth respiration, whereas maintenance respiration was increased in low-P plants. Our results support the hypothesis that root C costs are a primary limitation to plant growth in low-P soils.     

Influence of temperature and soil drying on respiration of individual roots in citrus: integrating greenhouse observations into a predictive model for the field

In citrus, the majority of fine roots are distributed near the soil surface – a region where conditions are frequently dry and temperatures fluctuate considerably. To develop a better understanding of the relationship between changes in soil conditions and a plant’s below‐ground respiratory costs, the effects of temperature and soil drying on citrus root respiration were quantified in controlled greenhouse experiments. Chambers designed for measuring the respiration of individual roots were used. Under moist soil conditions, root respiration in citrus increased exponentially with changes in soil temperature (Q₁₀ = 1·8–2·0), provided that the changes in temperature were short‐term. However, when temperatures were held constant, root respiration did not increase exponentially with increasing temperatures. Instead, the roots acclimated to controlled temperatures above 23 °C, thereby reducing their metabolism in warmer soils. Under drying soil conditions, root respiration decreased gradually beginning at 6% soil water content and reached a minimum at <2% soil water content in sandy soil. A model was constructed from greenhouse data to predict diurnal patterns of fine root respiration based on temperature and soil water content. The model was then validated in the field using data obtained by CO₂ trapping on root systems of mature citrus trees. The trees were grown at a site where the soil temperature and water content were manipulated. Respiration predicted by the model was in general agreement with observed rates, which indicates the model may be used to estimate entire root system respiration for citrus.     

Exaggerated root respiration accounts for growth retardation in a starchless mutant of Arabidopsis thaliana

The knock‐out mutation of plastidial phosphoglucomutase (pgm) causes a starchless phenotype in Arabidopsis thaliana, and results in a severe growth reduction of plants cultivated under diurnal conditions. It has been speculated that high soluble sugar levels accumulating during the light phase in leaf mesophyll might cause a reduction of photosynthetic activity or that shortage of reduced carbon during the night is the reason for the slow biomass gain of pgm. Separate simultaneous measurements of leaf net photosynthesis and root respiration demonstrate that photosynthetic activity per unit fresh weight is not reduced in pgm, whereas root respiration is strongly elevated. Comparison with a mutant defective in the dominating vacuolar invertase (AtβFruct4) revealed that high sucrose concentration in the cytosol, but not in the vacuole, of leaf cells is responsible for elevated assimilate transport to the root. Increased sugar supply to the root, as observed in pgm mutants, forces substantial respiratory losses. Because root respiration accounts for 80% of total plant respiration under long‐day conditions, this gives rise to retarded biomass formation. In contrast, reduced vacuolar invertase activity leads to reduced net photosynthesis in the shoot and lowered root respiration, and affords an increased root/shoot ratio. The results demonstrate that roots have very limited capacity for carbon storage but exert rigid control of supply for their maintenance metabolism.     

Initial burst of root development with decreasing respiratory carbon cost in Fagus crenata Blume seedlings

As terrestrial plants are rooted in one place, their metabolism must be acclimatized to continuously changing environmental conditions. This process is influenced by different metabolic traits of plant organs during ontogeny. However, direct measurement of organ-specific metabolic rates is particularly scarce, and little is known about their roles in whole-plant metabolism. In this study, we investigated size scaling of respiration rate, fresh mass and surface area of leaves, stems and roots in 65 seedlings of Fagus crenata Blume (2 weeks to 16 months old). With the increase in plant mass, the proportion of roots in whole plants increased from 20.8 to 87.3% in fresh mass and from 12.8 to 95.0% in surface area, whereas there was only a 15.6 to 60.2% increase in respiration rate. As a result, the fresh-mass-specific and surface-area-specific respiration rates in the roots decreased by 85% and 90%, respectively, and these decreases were significantly size dependent. However, such a size-dependent decrease was not observed for the surface-area-specific respiration rate in the leaves and stems. It is likely that this rapid root development is specific to the early growth stage after germination and would help plants acquire water and nutrients efficiently (i.e., at relatively low respiratory carbon costs). Overall, it is probable that the establishment of F. crenata forests and survival of F. crenata seedlings could be promoted by substantial root growth, with a reduction in respiratory carbon cost.