Standing fine root mass and production in four Chinese subtropical forests along a succession and species diversity gradient

Background and aims

The influences of succession and species diversity on fine root production are not well known in forests. This study aimed to investigate: (i) whether fine root biomass and production increased with successional stage and increasing tree species diversity; (ii) how forest type affected seasonal variation and regrowth of fine roots.

Methods

Sequential coring and ingrowth core methods were used to measure fine root production in four Chinese subtropical forests differing in successional stages and species diversity.

Results

Fine root biomass increased from 262 g·m^?2 to 626 g·m^?2 with increasing successional stage and species diversity. A similar trend was also found for fine root production, which increased from 86 to 114 g·m^?2 yr ^?1 for Cunninghamia lanceolata plantation to 211–240 g·m^?2 yr ^?1 for Choerospondias axillaries forest when estimated with sequential coring data. Fine root production calculated using the ingrowth core data ranged from 186 g·m^?2 yr ^?1 for C. lanceolata plantation to 513 g·m^?2 yr ^?1 for Lithocarpus glaber – Cyclobalanopsis glauca forest.

Conclusions

Fine root biomass and production increased along a successional gradient and increasing tree species diversity in subtropical forests. Fine roots in forests with higher species diversity exhibited higher seasonal variation and regrowth rate.     

Fine root dynamics along a 2,000-m elevation transect in South Ecuadorian mountain rainforests

Fine root turnover plays an important role in the cycling of carbon and nutrients in ecosystems. Not much is known about fine root dynamics in tropical montane rainforests, which are characterized by steep temperature gradients over short distances. We applied the minirhizotron technique in five forest stands along an elevational transect between 1,050 and 3,060 m above sea level in a South Ecuadorian montane rainforest in order to test the influence of climate and soil parameters on fine root turnover. Turnover of roots with diameter <?2.0 mm was significantly higher in the lowermost and the uppermost stand (0.9 cm cm^?1 year^?1) than in the three mid-elevation stands (0.6 cm cm^?1 year^?1). Root turnover of finest roots (d?<?0.5 mm) was higher compared to the root cohort with d?<?2.0 mm, and exceeded 1.0 cm cm^?1 year^?1 at the lower and upper elevations of the transect. We propose that the non linear altitudinal trend of fine root turnover originates from an overlapping of a temperature effect with other environmental gradients (e.g. adverse soil conditions) in the upper part of the transect and that the fast replacement of fine roots is used as an adaptive mechanism by trees to cope with limiting environmental conditions.     

Fine root dynamics in a Norway spruce forest (Picea abies (L.) Karst) in eastern Sweden

The annual dynamics of live and dead fine roots for trees and the field layer species and live/dead ratios were investigated at a coniferous fern forest (Picea abies L. Karts) in Sweden. Our methods of estimating the average amount of fine roots involved the periodic sampling of fine roots in sequential cores on four sampling occasions. The highest live/dead ratio was found in the upper part of the humus layer for both tree and field-layer species and decreased with depth. Most tree fine roots on the four sampling occasions were found in the mineral soil horizon, where 86, 81, 85 and 89% of <1 mm and 89, 88, 89 and 92% of <2 mm diameter of the total amounts of live fine roots in the soil profile were found. The mean amounts of live fine roots of tree species for the total soil profile on the four sampling occasions was 317, 150, 139 and 248 g m^?2 for <1 mm and 410, 225, 224 and 351 g m^?2 for <2 mm diameter fine roots. The related amount of dead fine roots was 226, 321, 176 and 299 g m^?2 and 294, 424, 282 and 381 g m^?2, respectively. Average amounts of live and dead fine-roots and live/dead ratios from other Picea abies forest ecosystems were within the range of our estimates. The production of fine roots, <1 and <2 mm in diameter, estimated from the annual increments in live fine roots, was 207 and 303 g m^?2. The related accumulation of dead fine roots was 257 and 345 g m^?2, The turnover rate of tree fine roots <1 mm in diameter in the total soil profile amounted to 0.7 yr^?1 for live and 0.8 yr^?1 for dead fine roots. The related turnover rates for tree fine roots <2 mm were 0.4 yr^?1 and 0.7 yr^?1. Our data, although based on minimum estimates of the annual fluxes of live and dead fine roots, suggests a carbon flow to the forest soil from dead fine-roots even more substantial than from the needle litter fall. Fine-root data from several Picea abies forest ecosystems, suggest high turnover rates of both live and dead tree fine-roots.     

Optimization and quality assessment of adventitious roots culture in Panax quinquefolium L.

In this study, adventitious roots of Panax quinquefolium L. have been successfully established. The highest induction rate of roots was obtained in MS medium containing 3 mg L^?1 IBA after 4 weeks of culture. The culture conditions of adventitious root were optimized and evaluated with response surface methodology. The best culture conditions for root growth seemed to be 0.75 salt strength MS medium, 4.70 g L^?1 inoculum size and 40 days of culture. The active component contents of adventitious roots were compared with those of native roots. The total saponins content was found to be 16.28 mg g^?1 in native root and 4.64 mg g^?1 in adventitious root. The polysaccharide content of the adventitious root was 1.5 times higher than that in the native P. quinquefolium (30.54 vs. 20.28 mg g^?1).     

Effect of sugar concentration on ginsenoside biosynthesis in hairy root cultures of Panax quinquefolium cultivated in shake flasks and nutrient sprinkle bioreactor

The study assessed the influence of sugar concentration (10, 20, 30, 50, 70, 100, 120 g l^?1) on growth and ginsenoside biosynthesis in Panax quinquefolium hairy roots cultivated in shake flasks and a nutrient sprinkle bioreactor. The highest growth rate was achieved in medium containing 3–5 % sucrose. More than 70 g l^?1 or less than 20 g l^?1 sugar content in the medium induces significant inhibition of root growth when cultivated in shake flasks. The saponin content was determined using HPLC. The maximum yield (above 9 mg g^?1 d.w.) of the sum of six examined ginsenosides (Rb₁, Rb₂, Rc, Rd, Re and Rg₁) in hairy roots cultivated in shake flasks was obtained with 30 g l^?1 sucrose in the medium. The sucrose concentration in the medium was found to correlate with saponin content in bioreactor-cultured specimens. A higher level of protopanaxadiol derivatives was found for lower (20 and 30 g l^?1) sucrose concentrations; higher sucrose concentrations (50 and 70 g l^?1) in the medium stimulated a higher level of Rg group saponins.     

AM真菌对紫花苜蓿细根生长及其生物量动态特征的影响

细根对植物功能的发挥和土壤碳库及全球碳循环具有重要意义。采用容器法和微根管法于2013年6~10月整个生长季内对紫花苜蓿的细根生物量、生产以及周转规律进行研究。结果表明:(1)紫花苜蓿活细根现存生物量平均值以接种摩西球囊霉(Gm)处理最高(12.46g·m-2),未接种对照最低(7.31g·m-2),并且活细根现存量在9月中旬达到峰值;死细根现存生物量呈先增加后降低再增加的变化趋势,在整个生长过程中未接种处理高于接种处理,接种根内球囊霉(Gi)处理死细根现存平均生物量(3.11g·m-2)又较接种组其他处理低。(2)苜蓿植株细根生长量以接种幼套球囊霉(Ge)处理最大(0.045 mm·cm-2·d-1),接种Gm处理和未接种对照最低(均为0.027mm·cm-2·d-1);而未接菌植株细根死亡量(0.044mm·cm-2·d-1)显著高于接种植株,接种组又以Gi处理最低(0.021mm·cm-2·d-1)。(3)紫花苜蓿在生长季节内细根生产和死亡的高峰分别出现在8月底和10月份,低谷出现在9月底到10月中旬和6月底到8月;接种地表球囊霉(Gv)后细根现存量和年生长量显著高于对照和接种其他菌种处理,细根的周转以对照组最大,而接种Gv和Gm处理较低。研究发现,通过接种丛植菌根真菌可以提高苜蓿细根生物量,降低细根的死亡,增加细根寿命。     

Toxicity of Cd to signal grass (Brachiaria decumbens Stapf.) and Rhodes grass (Chloris gayana Kunth.)

Given that Cd accumulates within plant tissues to levels that are toxic to animals, it is necessary to understand the role of plants in highly Cd-contaminated systems and their subsequent impact on the health of animals. A solution culture experiment was conducted to elucidate the effects of increasing Cd²⁺ activity ({Cd²⁺}) on growth of Rhodes grass (Chloris gayana Kunth.) and signal grass (Brachiaria decumbens Stapf.). The shoot and root fresh mass of both Rhodes grass and signal grass was reduced by 50% at ca. 0.5 µM {Cd²⁺}. Elevated {Cd²⁺} resulted in a significant decrease in the tissue Mn concentration for both the shoots and roots, and caused a chlorosis of the veins in the shoots. Root hair growth was prolific even at high {Cd²⁺}, thus root hair growth appeared to be less sensitive to elevated Cd than was root growth per se. The critical shoot tissue concentrations (50% reduction in growth), 230 µg g^?1 for Rhodes grass and 80 µg g^?1 for signal grass, exceeded the maximum level of Cd tolerated in the diet of animals (ca. 5 µg g^?1). When assessing the risk associated with the revegetation of Cd-contaminated sites with Rhodes grass or signal grass, careful consideration must be given, therefore, to the transfer of toxic concentrations of Cd to grazing animals and through the wider food chain.     

Fine root morphological and functional traits in Fagus sylvatica and Fraxinus excelsior saplings as dependent on species, root order and competition

Aims

The mechanisms of belowground competition are not well understood. Addressing literature reports on competition-induced changes in tree fine root morphology, we conducted a growth experiment with tree saplings to investigate competition effects on important root morphological and functional traits in a root order-focused analysis.

Methods

European beech and European ash saplings were grown for 34 months in containers under greenhouse conditions in monoculture (2 conspecific plants), in mixture (1 beech and 1 ash) or as single plants. The root system was fractionated according to root orders and eight morphological and functional properties were determined.

Results

Root order was the most influential factor affecting the fine root traits (except for root diameter and δ¹³C); a significant species identity effect was found for root diameter, tissue density, N concentration and δ¹³C. Ash fine roots were thicker, but had lower tissue densities, contained more N and had systematically higher δ¹³C values than beech roots. The competition treatments had no significant effect on morphological root traits but altered δ¹³C in the 2nd root order.

Conclusion

Neither intra- nor interspecific root competition affected fine root morphology significantly suggesting that competition-induced root modification may not be a universal phenomenon in temperate trees.     

Vertical distribution, biomass, production and turnover of fine roots along a topographical gradient in a sandy shrubland

In an artificial Salix gordejevii Chang et Skv. plantation of the Horqin sandy land, we investigated vertical distribution (in 0–100 cm depth), biomass (FRD), fine root production (FRP), fine root length density (FRLD) and turnover of fine roots (<2 mm diameter) at three sites (dune top, midslope and bottom of dune) along leeward slopes. Meanwhile, the correlation between FRP and soil available resources was analyzed. Our results indicate that more than 65% of total fine root biomass is distributed in 0–40 cm depth, and the patterns are different at three sites. The mean monthly FRD ranges from 227 to 324 g·m^?2, and they follows the order: dune top > midslope > bottom of dune. Ingrowth cores were harvested after 2, 3, 4, 5, 6 and 8 months of installation. At the first five sampling times, FRP and FRLD (0–40 cm) follows the same order with FRD along the topographical gradient, while FRP harvested after 8 months does not follow the same tendency, they are 348, 402 and 356 g·cm^?2 in dune top, midslope and bottom of dune, respectively. Fine root turnover ranges from 1.04–1.92 year^?1, and fine root turnover (20–40 cm) increases from dune top to bottom of dune along the topographical gradient. Correlation analysis between FRP and soil available resources indicates that only mean soil volumetric water content significantly correlates with annual FRP, which suggests that soil water content might be more crucial for shrub growth than fertility along the topographical gradient.     

Interspecific differences in root architecture among maize and triticale genotypes grown under drought,waterlogging and soil compaction

Environmental stresses (soil compaction, drought, waterlogging) cause changes in plants’ root system structure, also affecting the growth of above-ground parts. The aim of this study was to estimate phenotypic variation among maize and triticale genotypes in root penetration ability through petrolatum-wax-layer (RPA). Also, the effect of shortage or excess of soil water on dry matter of shoots and roots and morphological changes in root system structure in sensitive and resistant maize and triticale genotypes grown in low or high soil compaction level was evaluated. To estimate RPA index, the petrolatum-wax-layer method (PWL) was used. The strength of three petrolatum-wax concentrations 60, 50 and 40 % was 0.52, 1.07 and 1.58 MPa, respectively. High coefficients of variation (CV) were observed in 0.52 and 1.07 MPa and for maize were 19.2 and 21.7 %, and for triticale, 12.5 and 18.3 %, respectively. The data indicate that the use of PWL technique is an effective screening method, and makes it possible to divide the genotypes into resistant and sensitive groups. The second part of this study investigated a multistress effect of soil compaction combined with drought or waterlogging on root and shoot growth and morphological changes in root system structure of maize and triticale genotypes differing in susceptibility to environmental stresses. Seedlings were grown for 4 weeks in root-boxes under conditions of low (LSC 1.1 g cm^?3) or severe (SSC 1.6 g cm^?3) soil compaction. Drought or waterlogging stresses were applied for 2 weeks from 14th to 28th day. In comparison to LSC treatment, in SSC treatment the decrease in dry matter of shoots and roots was greater for sensitive genotypes of maize and triticale (Ancora, CHD-147). Soil drought or waterlogging caused greater decrease of dry matter of shoots and roots in seedlings grown in SSC in comparison to LSC. The root penetration index (RPI) was estimated as a ratio of root dry matter in 15–40 cm root-box layer to total root dry matter. On the basis of RPI it was possible to group the genotypes according to their ability to distribute roots in soil profile. In comparison to LSC, SSC exerted a strong influence on the length of seminal and seminal adventitious roots, as well as the number and length of L- and S-type lateral roots developed on seminal and nodal roots. In both species the restriction effect of soil compaction on number and length of roots was more severe in sensitive (Ankora, CHD-147) than in resistant (Tina, CHD-247) genotypes. The restriction in roots propagation was greater in triticale than in maize. Exposure to drought or waterlogging in the case of genotypes grown in LSC and SSC treatments caused a decrease in number and length of particular components of root system structure. In both species the decrease of root number and length in plants grown under waterlogging was greater than under drought. The observed changes in root system were greater in sensitive (Ankora, CHD147) than in resistant (Tina, CHD-247) genotypes. Statistically significant correlations were found between RPA and RPI and also between these indexes and soil compaction, drought and waterlogging susceptibility indexes. This indicates that genotypes resistant to soil compaction were resistant to drought or waterlogging and also that genotypes resistant to drought were resistant to waterlogging.     

Physiological responses and accumulation of pollutants in woody species under in situ polluted condition in Southern China

Physiological leaf traits and accumulation of pollutants of ten woody species in response to air pollution at seriously polluted site Sanguigang (SGG) and control site Maofengshan (MFS) in Southern China were studied. Net photosynthetic rates of most species at SGG were lower than those at MFS, but stomatal conductance (g_s) showed opposite trend. The specific leaf area of Aporusa dioica, Sapium discolor, Schefflera octophylla and Toxicodendron succedaneum were significantly, 46.77, 13.09, 55.11 and 23.51 %, higher in SGG than in MFS, while chlorophyll content being the opposite. A. dioica had the highest sulphur (S) content at both sites (11.74 mg g^?1 at SGG and 11.07 mg g^?1 at MFS). Heavy metals concentrations were generally higher in species at SGG than at MFS. S. octophylla showed significantly higher concentrations of Zn, Cd and Mn (341.81, 2.41 and 2,287.29 μg g^?1) than other species at SGG. Moreover, A. dioica had the highest Pb concentration (9.19 μg g^?1), and L. glutinosa showed the highest Cr concentration (3.40 μg g^?1). According to the integrated results, we infer that A. dioica, S. octophylla and L. glutinosa are the promising species for phytoremediation in the ceramic industry polluted environment.     

Microdistribution of major to trace elements between roots of Halimione portulacoides and host sediments (Tagus estuary marsh,Portugal)

Aim

This study presents a micrometre-scale map of the elemental distribution within roots and surrounding sediment of Halimione portulacoides of a contaminated salt marsh in the Tagus estuary.

Methods

Microprobe particle induced X-ray emission analysis was performed in sediment slices containing roots with tubular rhizoconcretions attached to host sediments.

Results

Strong concentration gradients were found particularly in the inner part of rhizoconcretions adjacent to the root wall. Local enrichment was observed in sediment interstices with Fe precipitates and other associated elements. A maximum of 55 % of Fe was measured near the concretion–root interface, with a decrease to <5 % in the host sediment. Maximum concentrations of P (3 %), As (1,200 μg g^?1) and Zn (3,000 μg g^?1) were registered in concretions, one order of magnitude above the values of the host sediment. The elemental concentration profiles across roots showed that the epidermis was an efficient selective barrier to the entrance of elements. Fe and As were retained in the epidermis. The highest Cu and Zn concentrations were also observed in the epidermis. However, the concentrations of Mn, Cu and Zn increased in the inner root.

Conclusions

As and Fe were mostly retained in the concretion, whereas P, Mn, Cu and Zn were mobilised by the root.     

Fine-root morphological and growth traits in a Turkey-oak stand in relation to seasonal changes in soil moisture in the Southern Apennines, Italy

We investigated the effects of seasonal changes in soil moisture on the morphological and growth traits of fine roots (<2?mm in diameter) in a mature Turkey-oak stand (Quercus cerris L.) in the Southern Apennines of Italy. Root samples (diameter:?<0.5, 0.5?C1.0, 1.0?C1.5, and 1.5?C2.0?mm) were collected with the Auger method. Mean annual fine-root mass and length on site was 443?g?m^?2 (oak fine roots 321?g?m^?2; other species 122?g?m^?2) and 3.18?km?m^?2 (oak fine roots 1.14?km?m^?2; other species 2.04?km?m^?2), respectively. Mean specific root length was 8.3?m?g^?1. All fine-root traits displayed a complex pattern that was significantly related to season. In the four diameter classes, both fine-root biomass and length peaked in summer when soil water content was the lowest and air temperature the highest of the season. Moreover, both fine-root biomass and length were inversely related with soil moisture (p?<?0.001). The finest roots (<0.5?mm in diameter) constituted an important fraction of total fine-root length (79?%), but only 21?% of biomass. Only in this root class, consequent to change in mean diameter, specific root length peaked when soil water content was lowest showing an inverse relationship (p?<?0.001). Furthermore, fine-root production and turnover decreased with increasing root diameter. These results suggest that changes in root length per unit mass, and pulses in root growth to exploit transient periods of low soil water content may enable trees to increase nutrient and water uptake under seasonal drought conditions.     

Comprehensive assessments of root biomass and production in a Kobresia humilis meadow on the Qinghai-Tibetan Plateau

Alpine meadow covers ca. 700,000 km² with an extreme altitude range from 3200 m to 5200 m. It is the most widely distributed vegetation on the vast Qinghai-Tibetan Plateau. Previous studies suggest that meadow ecosystems play the most important role in both uptake and storage of carbon in the plateau. The ecosystem has been considered currently as an active “CO₂ sink”, in which roots may contribute a very important part, because of the large root biomass, for storage and translocation of carbon to soil. To bridge the gap between the potential importance and few experimental data, root systems, root biomass, turnover rate, and net primary production were investigated in a Kobresia humilis meadow on the plateau during the growing season from May to September in 2008 and 2009. We hypothesized that BNPP/NPP of the alpine meadow would be more than 50%, and that small diameter roots sampled in ingrowth cores have a shorter lifespan than the lager diameter roots, moreover we expected that roots in surface soils would turn over more quickly than those in deeper soil layers. The mean root mass in the 0–20 cm soil layer, investigated by the sequential coring method, was 1995?±?479 g?m^?2 and 1595?±?254 g?m^?2 in growing season of 2008 and 2009, respectively. And the mean fine root biomass in ingrowth cores of the same soil layer was 119?±?37 g?m^?2 and 196?±?45 g?m^?2 in the 2 years. Annual total NPP was 12387 kg?ha^?1?year^?1, in which 53% was allocated to roots. In addition, fine roots accounted for 33% of belowground NPP and 18% of the total NPP, respectively. Root turnover rate was 0.52 year^?1 for bulk roots and 0.74 year^?1 for fine roots. Furthermore, roots turnover was faster in surface than in deeper soil layers. The results confirmed the important role of roots in carbon storage and turnover in the alpine meadow ecosystem. It also suggested the necessity of separating fine roots from the whole root system for a better understanding of root turnover rate and its response to environmental factors.     

Scale-up of adventitious root cultures of Echinacea angustifolia in a pilot-scale bioreactor for the production of biomass and caffeic acid derivatives

In an attempt to scale-up of adventitious root cultures of Echinacea angustifolia for the production of biomass and caffeic acid derivatives, i.e. echinacoside, chlorogenic acid, cichoric acid, caftaric acid, and cynarin, the effects of Murashige and Skoog (MS) medium dilutions, and initial sucrose concentrations were investigated in a 5-L airlift bioreactor. In addition, the kinetics of adventitious root growth and accumulation of secondary metabolites were also studied. The greatest root dry weight (6.50 g L^?l) and accumulation of total phenolics [22.06 mg g^?1 DW (dry weight)], total flavonoids (5.77 mg g^?1 DW) and total caffeic acid derivatives (10.63 mg g^?1 DW) were obtained at quarter-strength MS medium. Of the various gradients of sucrose tested, 5 % sucrose supplementation was regarded as an optimal concentration for enhancing productivity of biomass and bioactive compounds. Neither higher salt strength (3/4–2 MS) nor sucrose concentrations (7 and 9 %) showed promotive effect on root growth and metabolite production. The kinetic studies revealed that 4 weeks of culture period is the optimal time to achieve highest productivity of metabolites. Based on these results, a large-scale (20 L) and a pilot-scale (500 L) adventitious root culture system was established. In the pilot-scale bioreactor, adventitious roots were elicitor-treated with 100 μM methyl jasmonate (MJ) on day 28. After 1 week of elicitation, 1.75 kg dry root biomass was harvested containing 60.41 mg g^?1 DW of total phenolics, 16.45 mg g^?1 DW of total flavonoids, and 33.44 mg g^?1 DW of total caffeic acid derivatives. Among the caffeic acid derivatives, the accumulation of echinacoside (the major bioactive compound) in MJ-treated adventitious roots grown in the 500-L bioreactor was the highest (12.3 mg g^?1 DW), which is approximately threefold more than the non-MJ-treated roots cultured in 5- and 20-L bioreactors.     

Specific root length as an indicator of environmental change

Abstract

Specific root length (SRL, m g^?1) is probably the most frequently measured morphological parameter of fine roots. It is believed to characterize economic aspects of the root system and to be indicative of environmental changes. The main objectives of this paper were to review and summarize the published SRL data for different tree species throughout Europe and to assess SRL under varying environmental conditions. Meta-analysis was used to summarize the response of SRL to the following manipulated environmental conditions: fertilization, irrigation, elevated temperature, elevated CO₂, Al-stress, reduced light, heavy metal stress and physical disturbance of soil. SRL was found to be strongly dependent on the fine root classes, i.e. on the ectomycorrhizal short roots (ECM), and on the roots <0.5 mm, <1 mm, <2 mm and 1 – 2 mm in diameter SRL was largest for ECM and decreased with increasing diameter. Changes in soil factors influenced most strongly the SRL of ECM and roots <0.5 mm. The variation in the SRL components, root diameter and root tissue density, and their impact on the SRL value were computed. Meta-analyses showed that SRL decreased significantly under fertilization and Al-stress; it responded negatively to reduced light, elevated temperature and CO_2. We suggest that SRL can be used successfully as an indicator of nutrient availability to trees in experimental conditions.     

Growth and maintenance respiration of roots of clonal Eucalyptus cuttings: scaling to stand-level

Root respiration consumes an important part of the daily assimilated carbon but the magnitude of this component of forest net ecosystem exchange and its partitioning among the different energy demanding processes in roots are still poorly documented. 5-month old Eucalyptus cuttings were grown in a greenhouse in pot filled with coarse sand. They were fertilized with three different amounts of a slow-release fertilizer with the doses of 8, 24 and 48 g of nitrogen per plant. Root respiration was measured using an infrared gas analyser by perfusing air through the pot on 9 plants per treatment on three dates 14 days apart. Measure of root respiration of the three treatments over time was made in order to obtain a large range of growth and nutrient uptake. Root respiration normalized at 22°C ranged from 0.09 to 0.23 g_C d^?1 for the three treatments during all the experiment. It was well predicted with a model that includes root growth rate and root nitrogen content.The nitrogen related maintenance coefficient was negatively correlated to the root nitrogen concentration suggesting a decrease in protein turnover with increasing fertility. Growth rate of fine root in a virtual stand was simulated using age-related allometric equations and further used to estimate root respiration in the field. Simulated root respiration increased over time from 0.39 to 3.14 g_C m^?2 d^?1 between 6 and 126 months assuming a turnover of 2 yr^?1 for fine roots. The major fraction of simulated root respiration in the field (78–92%) was used for the maintenance of the existing biomass.     

Source of nitrogen as a factor limiting saponin production by hairy root and suspension cultures of <Emphasis Type="Italic">Calendula officinalis</Emphasis> L.

Triterpenic saponins represented in Calendula officinalis L. by oleanolic acid (OA) glycosides are pentacyclic triterpene compounds with a wide range of biological and medicinal properties. This report demonstrates nitrogen source impact on growth, saponin accumulation, and secretion in hairy root and suspension cultures of marigold. Hairy roots preferred nitrate as a mineral source of nitrogen, but its impact on growth, OA glycosides accumulation, and secretion were line-dependent. The best productivity of OA glycosides was found in CC16 line (74.86 mg flask^?1) in ½ MS medium modified by 2.5× KNO₃ and ammonium elimination with 2.5 g l^?1 peptone. Organic nitrogen source at 27.5-g l^?1 impairs the growth rate of hairy roots. Its effect on saponin accumulation and secretion to the surrounding medium depended on line and media composition. Nitrate:ammonium ratio of 4:2 for CC16 resulted in 5.7-fold increment of saponin secretion comparing to the standard medium. Embryo roots, apical bud, and hypocotyls explants were crucial for induction of suspension culture synthesizing saponins; however, effect of mineral form of nitrogen in cultivating medium had to be considered. The highest OA glycosides level (171.97 μg g^?1 of dry weight) was recorded in the root derived culture with nitrate as a sole mineral form of nitrogen. Peptone from lactalbumin decidedly inhibited the saponin formation; however, it was essential for culture initiation, proliferation, and organ differentiation.     

Root morphology and architecture respond to N addition in Pinus tabuliformis, west China

Belowground dynamics of terrestrial ecosystems are responding to global increases in anthropogenic N deposition with important consequences for productivity and ecosystem health. We compared root characteristics across five root orders in Pinus tabuliformis plantations treated for 3 years to a gradient of N addition (0–15 g m^?2 year^?1). In reference plots, the roots of P. tabuliformis were finer and with higher specific root length than reported for other pine species, suggesting severe N limitation. Addition of N resulted in slightly reduced fine root biomass and significant changes in root morphology, responses that were associated primarily with first and second order roots. In particular, root number, cumulative root length, individual root length, and specific root length all declined with increasing N addition for first and second order roots, with most of the responses elicited at <9 g m^?2 year^?1 N addition. These responses (1) support the concept of ephemeral root modules consisting of first and second orders and (2) are consistent with a change in functional demand from uptake to transport with increasing soil resource availability. Traditionally, fine roots have been identified by a somewhat arbitrary diameter cut-off (e.g., 1 or 2 mm); as an index of fine root function, diameter would fail to reveal most of the functional response.     

Production of biomass and bioactive compounds by adventitious root suspension cultures of Morinda citrifolia (L.) in a liquid-phase airlift balloon-type bioreactor

To improve root growth and production of bioactive compounds such as anthraquinones (AQ), phenolics, and flavonoids by adventitious root cultures of Morinda citrifolia, the effects of aeration rate, inoculum density, and Murashige and Skoog (MS) medium salt strengths were investigated using a balloon-type bubble bioreactor. The possible mechanisms underlying changes in activities of enzymic (superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase) and nonenzymic (vitamin E) antioxidants, phenylalanine ammonia lyase, and stress levels (accumulation of hydrogen peroxide and proline, peroxidation of lipids) were also studied. Low aeration rate (0.05 vvm [air volume/culture volume/min]) accelerated accumulation of root fresh weight and dry weight (DW). High aeration rates (0.1 to 0.3 vvm) stimulated accumulation of AQ, phenolics, and flavonoids and reduced root growth. Low inoculum densities (5 and 10 g l^–1) increased accumulation of those metabolites but inhibited root growth. Culture of adventitious roots with high concentrations of MS salts (1× and 1.5× MS) resulted in induction of oxidative stress that strongly inhibited root growth. Overall, an aeration rate of 0.05 vvm, 15 g l^–1 inoculum density, and half-strength (0.5×) MS medium were optimal for enhancing accumulation of root dry biomass (4.38 g l^–1), AQ (103.08 mg g^–1 DW), phenolics (54.81 mg g^–1 DW), and flavonoids (49.27 mg g^–1 DW).