Adaptation and Functional Balance Between Shoot and Root Activity of Sunflower Plants Grown at Different Root Temperatures

Helianthus annuus L. plants were grown with the shoots at normalair temperature and with the roots in nutrient solution at 10,20 or 30 °C. The higher the root temperature the greaterthe growth of the leaves, resulting in higher production ofphotosynthates. Irrespective of growth conditions an equilibriumwas established between the maintenance respiratory activityof shoot and roots. A constant proportion of the photosynthateproduced was used in respiration. The results are discussedin relation to a thermodynamic theory of stability of biologicalsystems. It is suggested that changes in energy partition betweenmaintenance and growth, and then in relative growth rates ofshoots and roots during an adaptation period, represent a majorhomeostatic mechanism. shoots, roots, maintenance respiration, growth, relative growth rate, respiration, adaptation, sunflower, Helianthus annuus L.     

Efficiency of Root Respiration in Relation to Growth Rate, Morphology and Soil Composition

Root growth respiration and root maintenance respiration rate of the following species were determined: Hypochaeris radicata L. ssp. radicata L., H. radicata ssp. ericetorum Van Soest, Plantago lanceolata L., P. major L. ssp. major, P. major ssp. pleiosperma Pilgcr, P. maritime L., Senecio viscosus L., S. vulgaris L. and Urtica dioica L. A high root growth respiration (i.e. the amount of oxygen consumed for synthesis of a given weight of root material) implied a high maintenance respiration rate (i.e. the amount of oxygen consumed per unit of time and dry weight, but not connected with growth). High values of both components reflect a low efficiency of root respiratory processes. The efficiency of root respiration, as determined by the values for root growth respiration and root maintenance respiration rate could not be demonstrated to be of advantage in adaptation to soil conditions, as e.g. nitrogen content, moisture content and pH. It is concluded that (he degree of ‘wasteful utilization of sugars’ in roots, i.e. such consumption of sugars as cannot be related to structural growth, storage of carbohydrates or maintenance processes, depends on imbalance of transport of sugars from the shoot to the roots with utilization of sugars for synthesis of root material. The results are discussed in relation to Brouwer's explanation for the equilibrium between the growth of shoots and of roots. Root growth rate in the present species appears limited by a factor produced in the shoot under light conditions, and which factor is distinct from carbohydrates. The evidence presented shows that relatively inefficient root respiration does not imply a low growth rate. In regulation of plant growth the growth rate itself and also the shoot to-root ratio may be more important than the regulation of the efficiency of energy metabolism.     

磷有效性对大豆根冠中碳分配的影响

在水培条件下,研究不同浓度磷影响大豆根冠中碳分配的结果表明：磷有效性对大豆根冠中碳分配的影响依赖于磷浓度与胁迫时间。磷浓度高于0．125mmol．L^-1或低磷胁迫7d以内,大豆根冠中碳分配受到的影响不显著。低磷胁迫14d的大豆的净光合速率和根呼吸速率均显著下降,根冠比显著提高。这显示长期低磷胁迫下大豆碳同化总量和根呼吸消耗的碳量虽然减少,但根系生长的碳消耗则增加,光合碳同化形成的碳水化合物向根部的分配是受到促进的。     

Regrowth of western wheatgrass utilizing 14C-labeled assimilates stored in belowground parts

Summary Results of this study showed that carbohydrates stored in the roots of western wheatgrass are utilized for regrowth following clipping of the aboveground foliage. Shoots remained dependent on carbohydrates stored in roots until sufficient photosynthetic leaf surface was developed to supply carbon to the shoots. During early phenophases, the partitioning of carbohydrates between shoots and roots was identical, indicating equal metabolic demands for carbon from both the shoot and root systems. Subsequent fluctuations in root and shoot carbohydrates may be caused by selected pressure imposed on either the root or shoot systems by physiological changes in these organs.Respiratory losses of ¹⁴C were slower during the early phenophases which may indicate that either the rate of respiration was slower or that recently assimilated nonlabeled carbon sources were utilized for respiration instead of the endogenous sources assimilated earlier in the growth period. re]19760427     

Temperature and Time-course of the Carbon Balance of Vegetative Tomato Plants During Prolonged Darkness: Examination of a Method of Estimating Maintenance Respiration

In order to examine the suitability of estimating maintenancerespiration in prolonged darkness, the variation of structuraldry matter (SDM) was calculated on vegetative tomato plantsduring 48 h of darkness. For that purpose, the time-coursesof respiration rate and carbohydrate content were recorded inshoots and roots at temperatures of 10, 15, 20, and 25 °C Two exponential declines of respiration rate, separated by ashort resumption, were observed in shoots and roots, differentcarbohydrate pools might be involved. Respiration rate was alwayshigher in roots than in shoots: the part played by energy costsof mineral absorption has to be investigated. After 14 h ofdarkness, a fall in respiration rate was associated with a progressiveexhaustion of sucrose and starch - which was quicker at highertemperatures - and a decrease in shoot to root carbon translccation.After 24 h of darkness, respiration stabilized at all temperatures.However, structural growth persisted throughout the dark periodat 10 °C, stopped after about 14 h darkness at. 15 and 20°C, and became negative beyond 24 h at 25 °C The hypothesis of maintenance of SDM after a period of darknesscan thus be invalidated. The simple observation of the time-courseof respiration rate does not allow complete inferences to bemade concerning biomass maintenance Lycopersicon esculentum Mill., tomato, respiration, maintenance respiration, carbohydrate reserves, translocation, structural dry matter, temperature     

Kinetin application to roots and its effect on uptake, translocation and distribution of nitrogen in wheat (Triticum aestivum) grown with a split root system

The root systems of wheat seedlings ( Triticum aestivum L. cv. SUN 9E) were pruned to two seminal roots. One of the roots was supplied with a suboptimal level of NO₃, the other was deprived of N. Different levels of kinetin were supplied to the NO₃-deprived roots. Root respiration and the increment of C and N in the roots were measured to determine the C/N ratio of the phloem sap feeding the NO₃-deprived roots. Thus, it was possible to determine retranslocation of N from the shoots to the roots, as affected by the rate of kinetin application. It was calculated that the C/N ratio of phloem sap feeding roots growing without kinetin was ca 61. Kinetin application increased this ratio to ca 75, partly due to decreased translocation of N from the shoots back to the roots. Kinetin application decreased the proportion of N that was retranslocated to the roots after translocation to the shoots. Kinetin increased the rate of NO₃ uptake per root and the rate of N incorporation in both roots and shoots by ca 60%, but had no effect on shoot dry matter production. In control plants at most 70% of the N incorporated in the NO₃-fed roots could have been imported from the shoots, whilst kinetin application reduced this value to ca 40%. Thus root growth was not fully dependent on a supply of N via the phloem.
It is concluded that cytokinins affect the pattern of N-translocation in wheat plants by increasing incorporation of N in dry matter of the shoot, thus leaving less for export. Cytokinins did not play a major role in the regulation of shoot growth and the shoot to root ratio of the present plants.     

Translocation and utilization of carbon in wheat (Triticum aestivum)

Wheat ( Triticum aestivum L. cv. SUN 9E) was grown in a growth chamber under conditions of low soil nitrogen. Translocation of carbon to the roots and the subsequent utilization of these carbohydrates was determined. In vegetative plants (22 days old), 21.5 mg C day⁻¹ were translocated to the roots. 29% of this was incorporated into dry matter, 32% was respired (28% via the cytochrome and 4% via a SHAM-sensitive, presumably the alternative nonphosphorylating, pathway) and 39% was translocated back to the shoots, mainly in the form of amino acids. – The rote of root maintenance respiration during the vegetative phase was estimated to be 0.7 mg O₂ h⁻¹ (g dry weight of roots)⁻¹ and the root growth respiration to be 0.41 g O₂ (g dry weight of roots)⁻¹. Total carbohydrate utilization due to root respiration via the alternative, nonphosphorylating pathway during the major part of the growth period was calculated to be only ca 6% of carbohydrate utilization for grain growth. The rate of specific mass transfer (SMT) of sugars in the sieve tubes was estimated from the data on C-translocation and data on the total area occupied by sieve tubes in a cross section of the root system. SMT was calculated to be 0.8 mg sucrose s⁻¹ cm⁻², which is very similar to the published value on SMT for other organs, except roots.     

Effects of vesicular-arbuscular mycorrhizal infection and phosphate on Plantago major ssp. pleiosperma in relation to the internal phosphate concentration

Two experiments were carried out to study physiological effects of vesicular-arbuseular mycorrhizal infection on Plantago major L., ssp. pleiosperma (Pilger). In the first experiment, infection by the Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe increased growth, shoot to root ratio, P concentrations in both shoot and roots and total uptake of P per plant. The percentages of dry matter in both shoot and roots were lower in mycorrhizal plants.
In the second experiment different P treatments were applied to both mycorrhizal and non-mycorrhizal P. major plants to separate any effects of mycorrhizal infection from increased uptake of P. In addition to the effects found in the first experiment, mycorrhizal, P, and mycorrhizal x P interaction effects were found on root respiration rate and the concentration of soluble sugars in the roots. No clear effects on total dry weight, N and starch concentrations in shoot and roots and sugar concentraion in the shoot were found. Irrespective of the mycorrhizal treatment, increased P concentration in the shoot correlated with an increased shoot to root ratio and root respiration rate, and a decreased percentage dry matter and sugar concentration in the roots. However, the root respiration rate and the P concentration in the roots of mycorrhizal plants were enhanced more than expected from the increased P concentrations in the shoots of these plants.     

Respiration of the growing shoots of Scots pine

The respiratory CO₂ exchange and the growth of the annual shoots were followed in Scots pine (Pinus sylvestris L.) trees growing under extreme continental forest-steppe conditions near the lake Baikal. The temperature coefficient of dark respiration (Q₁₀) in growing shoots dropped down from 3.2–4.0 (in the temperature range of 10–20°C) to 1.5–2.0 (in the temperature range of 20–30°C). The changes in averaged daily respiration rates correlated with the changes in shoot growth increments and temperature (with the multiple determination coefficient of 0.94). Growth respiration of the axial shoots during the phenophase reached 80% of the total respiration costs, with the coefficients of growth respiration and maintenance respiration 0.32 and 0.021. In young crown shoots, the average value of CO₂ evolution in the light combined for the whole observation period (years 1976–2004) was about 1 kg/dm², that is 9% of CO₂ evolution from the trunk surface.     

Energy metabolism of Plantago major ssp. major as dependent on the supply of mineral nutrients

Plantago major L. ssp. major , a grassland species from a relatively nutrient-rich habitat, was grown in nutrient-rich and nutrient-poor culture solutions. Half of the plants were transferred from high to low or from low to high nutrient conditions. The rate of dry matter accumulation in both shoots and roots decreased slowly upon transfer of plants to low nutrient conditions and the shoot to root ratio was unaffected. The rate of structural growth of both roots and shoots increased upon transfer from low to high nutrient conditions and the shoot to root ratio, if calculated from non-structural-carbohydrate-free dry weights, increased.
Photosynthesis was largely independent of the nutrient supply. Root respiration, particularly the activity of the alternative oxidative pathway, decreased with increasing age. This decrease was ascribed to a decreased shoot to root ratio, which reduced the relative amount of carbohydrates translocated to the roots and thus the amount available for the alternative pathway. It is calculated that in young as well as in old plants grown in full nutrient solution 48% of the daily produced photosynthates was translocated to the roots.
This is at variance with data on P. lanceolata , where a decreasing proportion of the daily produced photosynthates was translocated to the roots when the plants grew older. It is concluded that shoot growth plus shoot respiration consumed a constant amount of the daily produced photosynthates in P. major and that the rest was left for translocation. It is further calculated that in P. major plants grown in full nutrient solution c . 25% and c . 2% of the daily produced photosynthates in young and old plants, respectively, was respired in a way that is not involved in production of energy that is utilized in growth and maintenance ('inefficient root respiration').
The results are discussed in comparison with those of P. lanceolata , a species from a relatively nutrient-poor habitat.     

Root cooling strongly affects diel leaf growth dynamics,water and carbohydrate relations in Ricinus communis

In laboratory and greenhouse experiments with potted plants, shoots and roots are exposed to temperature regimes throughout a 24 h (diel) cycle that can differ strongly from the regime under which these plants have evolved. In the field, roots are often exposed to lower temperatures than shoots. When the root‐zone temperature in Ricinus communis was decreased below a threshold value, leaf growth occurred preferentially at night and was strongly inhibited during the day. Overall, leaf expansion, shoot biomass growth, root elongation and ramification decreased rapidly, carbon fluxes from shoot to root were diminished and carbohydrate contents of both root and shoot increased. Further, transpiration rate was not affected, yet hydrostatic tensions in shoot xylem increased. When root temperature was increased again, xylem tension reduced, leaf growth recovered rapidly, carbon fluxes from shoot to root increased, and carbohydrate pools were depleted. We hypothesize that the decreased uptake of water in cool roots diminishes the growth potential of the entire plant – especially diurnally, when the growing leaf loses water via transpiration. As a consequence, leaf growth and metabolite concentrations can vary enormously, depending on root‐zone temperature and its heterogeneity inside pots.     

The effect of wheat seed presowing treatment with salicylic acid on its endogenous content,activities of respiratory pathways,and plant antioxidant status

We studied the effects of wheat (Triticum aestivum L.) seed presowing treatment with 0.05 mM salicylic acid (SA) on its endogenous content and the ratio of free to bound forms in seedling shoots and roots. During two-week-long seedling growth, we observed a gradual decrease in the total SA content in shoots but not in roots. In shoots, the content of conjugated SA increased and that of its free form reduced. Seed presowing treatment with SA reduced total content of endogenous SA in both seedling shoots and roots. The content of free SA reduced intensely in shoots and somewhat less in roots. Such reduction was supposed to occur due to the disturbance in SA biosynthesis. These were accompanied by the increases in the shoot and especially root biomass and length, stimulation of total dark respiration, and changes in the ratio between respiratory pathways. In the roots, we observed an increased proportion of cytochrome respiration, whereas in the shoots — alternative cyan-resistant respiration. We also observed changes in the plant antioxidant system. A degree of lipid peroxidation was stronger in shoots than in roots. Pretreatment with SA resulted in MDA 2.5-fold accumulation in shoots, whereas its content in roots reduced by 1.7 times. We concluded that the type and intensity of SA effects on plant growth, energetic balance, and antioxidant status were related to changes in its endogenous content and redistribution between free and conjugated forms.     

Growth Depression in Mycorrhizal Citrus at High-Phosphorus Supply (Analysis of Carbon Costs)

Mycorrhizal-induced growth depression of plants in high-P soil has been reported in many species. The carbon costs of factors contributing to this growth depression were analyzed in Volkamer lemon (Citrus volkameriana Tan. & Pasq.) colonized by the mycorrhizal (M) fungus Glomus intraradices Schenck and Smith. M and nonmycorrhizal (NM) plants were each grown at two P-supply rates. Carbon budgets of M and NM plants were determined by measuring whole-plant carbon assimilation and respiration rates using gas-exchange techniques. Biomass, M colonization, tissue-P concentration, and total fatty acid concentration in the fibrous roots were determined. Construction costs of the fibrous roots were estimated from heat of combustion, N, and ash content. Root-growth respiration was derived from daily root growth and root-construction cost. M and NM plants grown in high-P soil were similar in P concentration, daily shoot carbon assimilation, and daily shoot dark respiration. At 52 d after transplanting (DAT), however, combined daily root plus soil respiration was 37% higher for M than for NM plants, resulting in a 20% higher daily specific carbon gain (mmol CO2 [mmol carbon]-1 d-1) in NM than M plants. Estimates of specific carbon gain from specific growth rates indicated about a 10% difference between M and NM plants. Absolute values of specific carbon gain estimated by whole-plant gas exchange and by growth analysis were in general agreement. At 52 DAT, M and NM plants at high P had nearly identical whole-plant growth rates, but M plants had 19% higher root dry weight with 10% higher daily rates of root growth. These allocation differences at high P accounted for about 51% of the differences in root/soil respiration between M and NM plants. Significantly higher fatty acid concentrations in M than NM fibrous roots were correlated with differences in construction costs of the fibrous roots. Of the 37% difference in daily total root/soil respiration observed between high-P M and NM plants at 52 DAT, estimated daily growth respiration accounted for only about 16%, two-thirds of which was associated with construction of lipid-rich roots, and the remaining one-third with greater M root growth rates. Thus, of the 37% more root/soil respiration associated with M colonization of high-P plants, 10% was directly attributable to building lipid-rich roots, 51% to greater M root biomass allocation, and the remaining 39% could have been used for maintenance of the fungal tissue in the root and growth and maintenance of the extramatrical hyphae.     

Interactions between osmoregulation and the alternative respiratory pathway in Plantago coronopus as affected by salinity

Plantago coronopus L., a species from the coastal zone, was grown in culture solution with and without 50 mM NaCl. In addition it was transferred from a non-saline solution to a solution containing 50 mM NaCl. Short term effects of NaCl on growth and various aspects of energy metabolism, including photosynthesis, shoot dark respiration, root respiration and the contribution of the SHAM-sensitive alternative pathway to root respiration were investigated. The concentrations of soluble and insoluble non-structural carbohydrates and of sorbitol a compatible osmotic solute in Plantago, in both shoots and roots were also determined. Growth of shoots and roots was largely unaffected by addition of 50 mM NaCl. Net photosynthesis, shoot dark respiration and the concentration of non-structural carbohydrates in both shoots and roots were also unaffected by salinity. The rate of root respiration immediately decreased upon addition of 50 mM NaCl. This decrease was almost exclusively attributed to a decreased activity of the SHAM-sensitive alternative pathway. The concentration of sorbitol in the roots increased quickly after addition of 50 mM NaCl, whilst the increase in sorbitol concentration in the shoots started later. The time course of the increase of sorbitol concentration was similar to that of the decrease in activity of the alternative pathway. During the first 12 h after exposure to 50 mM NaCl, the amount of carbohydrates which was saved in respiration, due to the decreased activity of the alternative pathway, was the same as that used for sorbitol synthesis in the roots. It is concluded that the activity of the alternative pathway decreased due to increased utilization of carbohydrates for sorbitol synthesis, according to a proposed ‘energy overflow model’. After 24 h, the sorbitol concentration in the cytoplasm of the root cells of plants transferred to a saline solution reached a level that was sufficient to compensate for 50 mM NaCl, assuming a cytoplasmic volume of ca. 10% of the total cell volume. The sorbitol concentration in roots of plants grown in a saline environment for several weeks was lower than that in roots of plants transferred to a saline environment for c. 24 h. It is suggested that sorbitol accumulated in roots of Plantago coronopus as an immediate reaction upon salinity, whilst other adaptations may occur thereafter.     

The effect of mineral nutrition on the growth and maintenance components of respiration during heterotrophic growth of barley seedlings

Spring barley seedling were grown in the dark for 21 d and respiration rates of the whole plant (including the seed), of the shoots, and of the roots were determined. A function describing the growth and maintenance components of respiration was interpolated through the experimental points and its parameters in plants under different mineral nutrition were compared. The plants grown in a complete nutrient solution showed the highest growth rate in the initial phase of development and thus reached the maximum respiration rate earlier than plants in the other variants. The highest proportion of substrate was respired in the shoot. Plants grown under deficiency of phosphorus and magnesium had a slower respiration rate than plants grown in the complete nutrient solution (NP), whereas the amount of respired substrate in plant parts was similar to that recorded in the NP plants. Plants grown in distilled water showed the lowest growth efficiency and respirated the highest proportion of substrate in the root.     

Responses of tree fine roots to temperature

Soil temperature can influence the functioning of roots in many ways. If soil moisture and nutrient availability are adequate, rates of root length extension and root mortality increase with increasing soil temperature, at least up to an optimal temperature for root growth, which seems to vary among taxa. Root growth and root mortality are highly seasonal in perennial plants, with a flush of growth in spring and significant mortality in the fall. At present we do not understand whether root growth phenology responds to the same temperature cues that are known to control shoot growth. We also do not understand whether the flush of root growth in the spring depends on the utilization of stored nonstructural carbohydrates, or if it is fueled by current photosynthate. Root respiration increases exponentially with temperature, but Q ₁₀ values range widely from c . 1.5 to > 3.0. Significant questions yet to be resolved are: whether rates of root respiration acclimate to soil temperature, and what mechanisms control acclimation if it occurs. Limited data suggest that fine roots depend heavily on the import of new carbon (C) from the canopy during the growing season. We hypothesize that root growth and root respiration are tightly linked to whole-canopy assimilation through complex source–sink relationships within the plant. Our understanding of how the whole plant responds to dynamic changes in soil temperature, moisture and nutrient availability is poor, even though it is well known that multiple growth-limiting resources change simultaneously through time during a typical growing season. We review the interactions between soil temperature and other growth-limiting factors to illustrate how simple generalizations about temperature and root functioning can be misleading.     

Analysis of Dry Matter Partitioning in Dactylis glomerata during Vegetative Growth Using a Carbon Budget Model

The dry matter partitioning in vegetative plants of Dactylisglomerata was studied from experiments performed in controlledenvironments. Plants were grown hydroponically in growth chambers,at two constant temperatures (17 and 25 °C). In both experimentsthe root fraction decreased regularly with time, an effect thatwas more accentuated in the higher temperature regime. In orderto explain the change in dry matter partitioning, the experimentalshoot and root growth were analysed using a carbon budget modelwhich includes shoot and root maintenance requirements. Themodel predicts a relationship between the root specific growthrate and the product of shoot specific growth rate and shootto root dry weight ratio. In the range of experimental accuracy,this relationship was found to be linear at both temperatures,which should indicate that the partitioning coefficients andthe root maintenance coefficient remained constant during vegetativegrowth. The effect of temperature on the value of these coefficientscan be specified from a linear regression analysis. Between17 and 25 °C, the root maintenance coefficient increasedby about a factor of two, whereas the partitioning coefficientsdid not vary significantly. On the basis of these results, itwas shown that the decrease in root fraction during vegetativegrowth should be mainly attributed to the decrease in net specificactivity of shoots.Copyright 1994, 1999 Academic Press Dactylis glomerata L., vegetative growth, model, partitioning, root:shoot ratio, shoot specific activity, maintenance requirements     

Periodic carbon flushing to roots of Quercus rubra saplings affects soil respiration and rhizosphere microbial biomass

Patterns of root/shoot carbon allocation within plants have been studied at length. The extent, however, to which patterns of carbon allocation from shoots to roots affect the timing and quantity of organic carbon release from roots to soil is not known. We employed a novel approach to study how natural short-term variation in the allocation of carbon to roots may affect rhizosphere soil biology. Taking advantage of the semi-determinate phenology of young northern red oak (Quercus rubra L.), we examined how pulsed delivery of carbon from shoots to roots affected dynamics of soil respiration as well as microbial biomass and net nitrogen mineralization in the rhizosphere. Young Q. rubra exhibit (1) clear switches in the amount of carbon allocated below-ground that are non-destructively detected simply by observing pulsed shoot growth above-ground, and (2) multiple switches in internal carbon allocation during a single growing season, ensuring our ability to detect short-term effects of plant carbon allocation on rhizosphere biology separate from longer-term seasonal effects. In both potted oaks and oaks rooted in soil, soil respiration varied inversely with shoot flush stage through several oak shoot flushes. In addition, upon destructive harvest of potted oaks, microbial biomass in the rhizosphere of saplings with actively flushing shoots was lower than microbial biomass in the rhizosphere of saplings with shoots that were not flushing. Given that plants have evolved with their roots in contact with soil microbes, known species-specific carbon allocation patterns within plants may provide insight into interactions among roots, symbionts, and free-living microbes in the dynamic soil arena.     

Growth, photosynthesis and respiration in Plantago coronopus as affected by salinity

Plantago coronopus was grown in a non-saline culture solution and in a culture solution containing 50 m M NaCl. The rates of dry matter accumulation in both roots and shoots were not affected by 50 m M NaCl. Photosynthesis, expressed per shoot, was also the same in both environments. Neither the rate of shoot respiration nor that of root respiration was affected by salinity. In both environments the alternative respiratory pathway contributed to the same extent in root respiration. The activity of the alternative pathway decreased with increasing age. Since the respiratory activities were the same in plants grown under both saline and non-saline conditions and since the alternative respiratory pathway was also equally active in roots under both environmental conditions, it is concluded that respiratory costs involved in growth in 50 m M NaCl are negligible in terms of the plant's total energy costings.