Interaction of Epiphytic Bacteria and Activated Carbon on Root Growth

The influence of activated carbon and aseptic conditions has been studied on the growth of the primary root of wheat seedlings in order to ascertain whether or not the growth effect of activated carbon is connected with the occurrence of epiphytic bacteria. Growth was measured as mitotic activity, rate of cell elongation and duration of cell elongation. The surface infection of the septic roots probably consisted of common airborn and waterborn bacteria. Aseptic conditions increased the rate of cell elongation by ca 70 % but had no effect on the meristem activity. Activated carbon increased mitoses in the meristem and slightly augmented the duration of cell elongation but had no effect on the rate of elongation. The effects of sepsis and carbon were independent and appeared additative. Activated carbon removed inhibitors produced by the root tip itself but not those formed by the bacteria. In these experiments neither group of inhibitors seemed to contain IAA-like substances.     

Measuring Fine Root Turnover in Forest Ecosystems

Development of direct and indirect methods for measuring root turnover and the status of knowledge on fine root turnover in forest ecosystems are discussed. While soil and ingrowth cores give estimates of standing root biomass and relative growth, respectively, minirhizotrons provide estimates of median root longevity (turnover time) i.e., the time by which 50% of the roots are dead. Advanced minirhizotron and carbon tracer studies combined with demographic statistical methods and new models hold the promise of improving our fundamental understanding of the factors controlling root turnover. Using minirhizotron data, fine root turnover (y⁻¹) can be estimated in two ways: as the ratio of annual root length production to average live root length observed and as the inverse of median root longevity. Fine root production and mortality can be estimated by combining data from minirhizotrons and soil cores, provided that these data are based on roots of the same diameter class (e.g., < 1 mm in diameter) and changes in the same time steps. Fluxes of carbon and nutrients via fine root mortality can then be estimated by multiplying the amount of carbon and nutrients in fine root biomass by fine root turnover. It is suggested that the minirhizotron method is suitable for estimating median fine root longevity. In comparison to the minirhizotron method, the radio carbon technique favor larger fine roots that are less dynamics. We need to reconcile and improve both methods to develop a more complete understanding of root turnover.     

A Model of Shoot: Root Partitioning with Optimal Growth

A shoot: root partitioning model is presented, which is a developmentof previous approaches in the area. The model incorporates asa physiologically reasonable apparent ‘goal’ forthe plant, the assumption that the partitioning of growth betweenthe shoot and root maximizes the plant specific growth ratein balanced exponential growth. The analysis is concerned principallywith plant growth being a function of carbon and nitrogen only,although it is indicated how other nutrients, or growth factors,may be incorporated. Plant growth is driven by the environmentalconditions, and partitioning is defined entirely in terms ofthe shoot: root ratio and carbon and nitrogen status of theplant. In its basic form the model requires the definition ofa single plant growth parameter, along with the shoot and rootspecific activities and structural composition. Shoot: root partitioning, specific growth rate, vegetative phase     

Transpiration and Carbon Acquisition in Root Hemiparasitic Angiosperms

Press, M. C. Graves, J. D. and Stewart, G. R. 1988. Transpirationand carbon acquistion in root hemiparastic angiosperms.—J.exp. Bot. 39: 1009–1014. Field measurements of carbon dioxide and water vapour exchangewere made on eight species of root hemiparasite at sites insouthern England, Scotland and northern Sweden. Rates of light-saturatedphotosynthesis and night-time respiration were of the same orderof magnitude, ranging from 2.10 to 7.53 and – 2.76 to– 7.82 µmol m^–2 s^–1 respectively. Wesuggest that autotrophic carbon must be supplemented by a heterotrophic,host-derived supply. Day- and night-time transpiration rateswere very high, ranging from 6.12 to 9.22 and 2.58 to 8.69 mmolm^–25^–1 respectively. High transpiration rates, dayand night, will facilitate movement of water, inorganic andorganic solutes from host to parasite. Whereas in autotrophicplants stomata function to minimize water loss and maximizecarbon gain, in hemiparasites the reverse is the case, wherebywater loss is maximized in order to maximize carbon gain. Key words: Transpiration, photosynthesis, respiration, parasitic angiosperm     

Long-Term Simulated Atmospheric Nitrogen Deposition Alters Leaf and Fine Root Decomposition

Atmospheric nitrogen deposition increases forest carbon sequestration across broad parts of the Northern Hemisphere. Slower organic matter decomposition and greater soil carbon accumulation could contribute to this increase in carbon sequestration. We investigated the effects of chronic simulated nitrogen deposition on leaf litter and fine root decomposition at four sugar maple (Acer saccharum)-dominated northern hardwood forests. At these sites, we previously observed that nitrogen additions increased soil organic carbon and altered litter chemistry. We conducted a 3-year decomposition study with litter bags. Litter production of leaves and fine roots were combined with decomposition dynamics to estimate how fine roots and leaf litter contribute to soil organic carbon. We found that nitrogen additions marginally stimulated early-stage decomposition of leaf litter, an effect associated with previously documented changes in litter chemistry. In contrast, nitrogen additions inhibited the later stages of fine root decomposition, which is consistent with observed decreases in lignin-degrading enzyme activities with nitrogen additions at these sites. At the ecosystem scale, slower fine root decomposition led to additional root mass retention (g m^?2), and this greater retention of root residues was estimated to explain 5–51% of previously documented carbon accumulation in the surface soil due to nitrogen additions. Our results demonstrated that simulated nitrogen deposition created contrasting effects on the decomposition of leaf litter and fine roots. Although previous nitrogen deposition studies have focused on leaf litter, this work suggests that slower fine root decomposition is a major driver of soil organic carbon accumulation under elevated nitrogen deposition.     

A Shoot:Root Partitioning Model

A model for partitioning newly-synthesized structural dry matterbetween shoot and root is developed. It is based on a postulatedpartitioning function, which depends upon the relative levelsof carbon and nitrogen substrates, with parameters determiningthe control point and also the degree of control. The modelis used to investigate the relationships between plant specificgrowth rate, shoot:root ratio, and the specific activities ofshoot and root (which depend upon environment), during steady-stateexponential growth; the transient behaviour of the model isalso explored and oscillations in these quantities are obtained. Shoot:root ratio, specific growth rate, mathematical model, partition of assimilates     

The Effect of Carbon Dioxide on the Absorption of Manganese by Root Tissues of Red Beet

The absorption of manganese by beetroot tissue is shown to bepartially inhibited by the presence of carbon dioxide. Preliminarytreatment of well-washed tissue slices with carbon dioxide alsoproduces, after placing them in manganese solutions, an inhibitionof absorption for a time similar to that shown by tissue sliceswhen first excised from stored roots. It is suggested that aninhibitory substance is formed in bulky storage roots and tubersby dark fixation of accumulated respiratory carbon dixoide.On cutting thin slices from such organs, the removal of inhibitormay take place by diffusion into water during washing, by reversalof the fixation reaction when the partial pressure of carbondioxide is reduced, and possibly also by oxidation to form asubstance capable of stimulating manganese absorption when sufficientlyhigh oxygen concentrations are available.     

森林生态系统细根周转规律及影响因素

根系周转是陆地生态系统碳循环的关键过程, 对研究土壤碳库变化及全球气候变化均具有重要意义。然而由于根系周转率的测量计算方法较多, 不同方法得出的结果差异较大, 且目前对全球区域尺度上森林生态系统根系周转的研究还不够充分, 使得全球森林生态系统根系周转变化规律仍不清楚。该研究通过收集文献数据并统一周转率计算方法, 对全球5种森林类型的细根周转空间格局进行整合, 同时结合土壤理化性质和气候数据, 得出影响森林生态系统细根周转的因子。结果表明, 不同森林类型细根周转率存在显著差异, 且随着纬度的升高逐渐降低; 森林生态系统细根周转率与年平均温度和年平均降水量呈正相关; 森林生态系统细根周转率与土壤有机碳含量呈正相关但与土壤pH值呈负相关。该研究为揭示森林生态系统细根周转规律及机制提供了科学依据。     

Root dynamics and global change: seeking an ecosystem perspective

Changes in the production and turnover of roots in forests and grasslands in response to rising atmospheric CO₂ concentrations, elevated temperatures, altered precipitation, or nitrogen deposition could be a key link between plant responses and longer-term changes in soil organic matter and ecosystem carbon balance. Here we summarize the experimental observations, ideas, and new hypotheses developed in this area in the rest of this volume. Three central questions are posed. Do elevated atmospheric CO₂, nitrogen deposition, and climatic change alter the dynamics of root production and mortality? What are the consequences of root responses to plant physiological processes? What are the implications of root dynamics to soil microbial communities and the fate of carbon in soil? Ecosystem-level observations of root production and mortality in response to global change parameters are just starting to emerge. The challenge to root biologists is to overcome the profound methodological and analytical problems and assemble a more comprehensive data set with sufficient ancillary data that differences between ecosystems can be explained. The assemblage of information reported herein on global patterns of root turnover, basic root biology that controls responses to environmental variables, and new observations of root and associated microbial responses to atmospheric and climatic change helps to sharpen our questions and stimulate new research approaches. New hypotheses have been developed to explain why responses of root turnover might differ in contrasting systems, how carbon allocation to roots is controlled, and how species differences in root chemistry might explain the ultimate fate of carbon in soil. These hypotheses and the enthusiasm for pursuing them are based on the firm belief that a deeper understanding of root dynamics is critical to describing the integrated response of ecosystems to global change.     

Root production and mortality under elevated atmospheric carbon dioxide

An essential component of an understanding of carbon flux is the quantification of movement through the root carbon pool. Although estimates have been made using radiocarbon, the use of minirhizotrons provides a direct measurement of rates of root birth and death. We have measured root demographic parameters under a semi-natural grassland and for wheat. The grassland was studied along a natural altitudinal gradient in northern England, and similar turf from the site was grown in elevated CO₂ in solardomes. Root biomass was enhanced under elevated CO₂. Root birth and death rates were both increased to a similar extent in elevated CO₂, so that the throughput of carbon was greater than in ambient CO₂, but root half-lives were shorter under elevated CO₂ only under a Juncus/Nardus sward on a peaty gley soil, and not under a Festuca turf on a brown earth soil. In a separate experiment, wheat also responded to elevated CO₂ by increased root production, and there was a marked shift towards surface rooting: root development at a depth of 80–85 cm was both reduced and delayed. In conjunction with published results for trees, these data suggest that the impact of elevated CO₂ will be system-dependent, affecting the spatio-temporal pattern of root growth in some ecosystems and the rate of turnover in others. Turrnover is also sensitive to temperature, soil fertility and other environmental variables, all of which are likely to change in tandem with atmospheric CO₂ concentrations. Differences in turnover and time and location of rhizodeposition may have a large effect on rates of carbon cycling.     

Shoot and Root Activities During Steady-state Plant Growth

A simple model for steady-state plant growth is described. Thegrowth constant, measured during steady-state exponential growth,is related to the specific activities of the shoot and the root,enabling the effects of certain environmental variables (light,carbon dioxide and nitrogen) on the growth constant to be examined.The model is used to interpret data on the growth kinetics ofwheat (Macdowall, 1972a, b, c).     

秦岭北坡几种人工林根系及土壤有机碳剖面分布特征的研究

对秦岭北坡浅山区刺槐、油松、侧柏人工林根系生物量、土壤有机碳含量以及土壤氮素进行了测定分析.结果表明,3种人工林之间的根系生物量存在差异,变异系数达到27.75%;土壤有机碳含量差异不明显,变异系数只有3.36%;在土壤剖面上,3种人工林根系生物量的垂直分布有明显差异,但土壤有机碳含量的层次变化基本一致,土壤有机碳主要集中在0~10 cm土层中,其含量超过0~60 cm土层总量的40%;3种人工林土壤全氮与土壤有机碳含量之间都呈显著的线性正相关.     

Sugar-Starvation-Induced Changes of Carbon Metabolism in Excised Maize Root Tips

Excised maize (Zea mays L.) root tips were used to study the early metabolic effects of glucose (Glc) starvation. Root tips were prelabeled with [1-13C]Glc so that carbohydrates and metabolic intermediates were close to steady-state labeling, but lipids and proteins were scarcely labeled. They were then incubated in a sugar-deprived medium for carbon starvation. Changes in the level of soluble sugars, the respiratory quotient, and the 13C enrichment of intermediates, as measured by 13C and 1H nuclear magnetic resonance, were studied to detect changes in carbon fluxes through glycolysis and the tricarboxylic acid cycle. Labeling of glutamate carbons revealed two major changes in carbon input into the tricarboxylic acid cycle: (a) the phosphoenolpyruvate carboxylase flux stopped early after the start of Glc starvation, and (b) the contribution of glycolysis as the source of acetyl-coenzyme A for respiration decreased progressively, indicating an increasing contribution of the catabolism of protein amino acids, fatty acids, or both. The enrichment of glutamate carbons gave no evidence for proteolysis in the early steps of starvation, indicating that the catabolism of proteins was delayed compared with that of fatty acids. Labeling of carbohydrates showed that sucrose turnover continues during sugar starvation, but gave no indication for any significant flux through gluconeogenesis.     

Root navigation by self inhibition

Circumventing physical obstacles is critical for a plant's survival and performance. Although the ability of roots to circumvent obstacles has been known for over 100 years, the phenomena and its mechanisms have received relatively little attention. In this study it is demonstrated that roots of Pisum sativum are able to detect and avoid growth towards inanimate obstacles and the hypothesis that this behaviour is based on the sensitivity of roots to their own allelopathic exudates that accumulate in the vicinity of physical obstacles is tested. The development of lateral roots of Pisum sativum towards an obstacle (a piece of nylon string, similar in dimensions to a plant root) was followed. Lateral roots were similar in number, but significantly shorter in the direction of the nylon string. In addition, up to half of the lateral roots that developed towards the nylon string withered, whereas no withering was observed in the absence of the nylon string. These avoidance growth patterns were suppressed in the presence of potassium permanganate or activated carbon, indicating a role of allelopathic exudates in promoting obstacle avoidance. The demonstrated obstacle avoidance by self inhibition could increase plant performance by limiting resource allocation to less promising parts of the root system.     

Variation of the Linkage of Root Function with Root Branch Order

Mounting evidence has shown strong linkage of root function with root branch order. However, it is not known whether this linkage is consistent in different species. Here, root anatomic traits of the first five branch order were examined in five species differing in plant phylogeny and growth form in tropical and subtropical forests of south China. In Paramichelia baillonii, one tree species in Magnoliaceae, the intact cortex as well as mycorrhizal colonization existed even in the fifth-order root suggesting the preservation of absorption function in the higher-order roots. In contrast, dramatic decreases of cortex thickness and mycorrhizal colonization were observed from lower- to higher-order roots in three other tree species, Cunninghamia lanceolata, Acacia auriculiformis and Gordonia axillaries, which indicate the loss of absorption function. In a fern, Dicranopteris dichotoma, there were several cortex layers with prominently thickened cell wall and no mycorrhizal colonization in the third- and fourth-order roots, also demonstrating the loss of absorptive function in higher-order roots. Cluster analysis using these anatomic traits showed a different classification of root branch order in P. baillonii from other four species. As for the conduit diameter-density relationship in higher-order roots, the mechanism underpinning this relationship in P. baillonii was different from that in other species. In lower-order roots, different patterns of coefficient of variance for conduit diameter and density provided further evidence for the two types of linkage of root function with root branch order. These linkages corresponding to two types of ephemeral root modules have important implication in the prediction of terrestrial carbon cycling, although we caution that this study was pseudo-replicated. Future studies by sampling more species can test the generality of these two types of linkage.     

Root carbon and protein metabolism associated with heat tolerance

Extensive past efforts have been taken toward understanding heat tolerance mechanisms of the aboveground organs. Root systems play critical roles in whole-plant adaptation to heat stress, but are less studied. This review discusses recent research results revealing some critical physiological and metabolic factors underlying root thermotolerance, with a focus on temperate perennial grass species. Comparative analysis of differential root responses to supraoptimal temperatures by a heat-adapted temperate C3 species, Agrostis scabra, which can survive high soil temperatures up to 45 °C in geothermal areas in Yellow Stone National Park, and a heat-sensitive cogeneric species, Agrostis stolonifera, suggested that efficient carbon and protein metabolism is critical for root thermotolerance. Superior root thermotolerance in a perennial grass was associated with a greater capacity to control respiratory costs through respiratory acclimation, lowering carbon investment in maintenance for protein turnover, and efficiently partitioning carbon into different metabolic pools and alternative respiration pathways. Proteomic analysis demonstrated that root thermotolerance was associated with an increased maintenance of stability and less degradation of proteins, particularly those important for metabolism and energy production. In addition, thermotolerant roots are better able to maintain growth and activity during heat stress by activating stress defence proteins such as those participating in antioxidant defence (i.e. superoxide dismutase, peroxidase, glutathione S-transferase) and chaperoning protection (i.e. heat shock protein).     

格氏栲天然林与人工林根系呼吸季节动态及影响因素

通过用挖壕沟 静态碱吸收法对福建三明格氏栲天然林及33年生格氏栲和杉木人工林的根系呼吸进行为期2a定位研究。不同森林根系呼吸速率季节变化均呈单峰曲线,最大值出现在春末或夏初,最小值出现在冬季。1年中格氏栲天然林、格氏栲人工林和杉木人工林根系呼吸速率变化范围分别在157.76~480.40mgCO2/(m2·h)、53.03~339.45mgCO2/(m2·h)和16.66~228.02mgCO2/(m2·h)之间。在近似正常气候状况的2002年,不同森林根系呼吸主要受土壤温度影响(R2=0.52~0.72);而土壤温度和土壤湿度共同则可解释根系呼吸速率季节变化的81%~90%。在极端干旱的2003年,根系呼吸受土壤温度或湿度的影响较小,土壤温度和土壤湿度共同仅能解释根系呼吸变化的24%~60%,这与根系在持续干旱期间长期处于近休眠状态有关。根系呼吸对土壤温度和土壤湿度的敏感性大小顺序均为杉木人工林>格氏栲人工林>格氏栲天然林。格氏栲天然林根系呼吸占土壤呼吸比例(47.6%)均高于格氏栲和杉木人工林的(42.5%和40.2%),不同森林根系呼吸占土壤呼吸比例均以冬季最低,而以5月或6月最高。格氏栲天然林、格氏栲人工林和杉木人工林根系呼吸年通量分别为6.537、4.013和1.828tC/(m2·h)。     

Galactose as an Inhibitor of the Expansion of Root Cells

The inhibition of the growth of cultured tomato roots by galactoseis due to an inhibition of cell expansion. Galactose is rapidlyabsorbed during the first 8 h following application and thefull inhibitory effect on extension growth of the roots is exertedwithin the first 24 h. At a concentration of 0·05 percent or less (50 per cent inhibition occurs at 0·035per cent) the galactose is not toxic and growth continues for7 days at the partially inhibited rate. The simultaneous presenceof glucose reduces galactose uptake but significant galactoseuptake continues at sites insensitive to a high concentrationof external glucose. In presence of an appropriate level ofglucose, although galactose uptake proceeds, the growth inhibitoryeffect of the galactose is fully reversed. Galactose reduces the content in the cell walls of the -cellulosefraction and during feeding with (I-¹⁴C) galactose all the cellwall fractions become labelled. The -cellulose fraction thenyields galactose of high specific activity. Glucose inhibitsthe incorporation of carbon from galactose into the -cellulosefraction and galactose inhibits the incorporation into thisfraction of the carbon of sucrose. The hypothesis is developedthat galactose inhibits cell expansion by a disruption of cellulosesynthesis which involves a direct incorporation of the externallyapplied galactose into the a-cellulose fraction of the cellwalls.     

Root growth and functioning under atmospheric CO2 enrichment

This paper examines the extent to which atmospheric CO₂ enrichment may influence growth of plant roots and function in terms of uptake of water and nutrients, and carbon allocation towards symbionts. It is concluded that changes in dry matter allocation greatly depend on the experimental conditions during the experiment, the growth phase of the plant, and its morphological characteristics. Under non-limiting conditions of water and nutrients for growth, dry matter partitioning to the root is not changed by CO₂ enrichment. The increase in root/shoot ratio, frequently observed under limiting conditions of water and/or nutrients, enables the plant to explore a greater soil volume, and hence acquire more water and nutrients. However, more data on changes in dry matter allocation within the root due to atmospheric CO₂ are needed. It is concluded that nitrogen fixation is favored by CO₂ enrichment since nodule mass is increased, concomitant with an increase in root length. The papers available so far on the influence of CO₂ enrichment on mycorrhizal functioning suggest that carbon allocation to the roots might be increased, but also here more experiments are needed.Abbreviations LAR leaf area ratio - LWR leaf weight ratio - SWR stem weight ratio - RGR relative growth rate - R/S root/shoot - RWR root weight ratio