Root Phytomass Research Articles

Root systems reserve under humid conditions of floodplain meadows of the Ob River in the subzone of the southern taiga

The results of the study of the underground phytomass of the floodplain meadow communities in the Middle Ob obtained from three permanent sample plots in the area of the Kaibasovo research station of Tomsk University (Kri-vosheinsky district of the Tomsk region) are presented. The functioning and productivity of grassland ecosystems should be carefully studied, especially in the light of ongoing climate change, as they are actively involved in the carbon cycle. However, the belowground phytomass is given much less attention in the literature than the aboveground part, despite the fact that they are equally important for the study of the cycle. The study of vegetation cover in order to analyze the biological cycle of flood-plain ecosystems, the production and destruction of plant matter in this area was practically not carried out. The goal was to assess the structure and stock of root phytomass in the meadows of the Ob floodplain. In the course of the work, the hydro-climatic conditions of the growing season of the current and previous years were characterized in order to assess their impact on root development. The reserves of underground organs in the 0-20 cm soil layer were determined, the limits of fluctuations of the total reserves of roots in the 0-20 cm layer between the sampling periods in June and August were established.
 Key words. Belowground biomass, flood, floodplain meadows, productivity, roots, Western Siberia.

Kenaf (Hibiscus cannabinus L.) as a remedy to oxisol contaminated with different mercury (Hg2+) concentrations

We evaluated Hibiscus cannabinus (kenaf) to remedy oxisol contaminated with Hg2 + potential. The study was conducted in a controlled environment in pots with soil contaminated with HgCl2 solution, in a completely randomized design with 4 treatments: control (without Hg2+) and treatments with 5, 24 and 36 mg Hg2+ kg-1 of soil and 5 replicates / treatment. The quantification of total Hg in plant and soil samples was performed by atomic absorption spectrometry. Kenaf grown in contaminated pots did not show visual symptoms of toxicity. Plant height did not differ among treatments, but the dry shoot phytomass was 21.65% higher in control than the average of treatments with Hg. Treatment with 24 mg kg-1 showed dry root phytomass greater than control and the others. In general, oxisol was responsible for retaining greater amount of Hg than plants. Hg accumulated in greater proportion in roots than in shoots. In pots that received 36 mg kg-1, plants accumulated average of 2.57 mg kg-1 of Hg / pot, differing from the other treatments and the Hg transfer factor (TF) in plants was also calculated as the ratio of the concentration in shoots and in roots. The values were as follows: 3.11 for T1, 1.26 for T2, 0.05 for T3 and 0.02 for T4. Treatments showed no difference between T3 and T4 and TF decreased with increasing Hg dose. It could be concluded that Hg was more adsorbed by oxisol than by plants. Plants showed resistance to different soil Hg concentrations and can be considered as potential Hg2+ stabilizer

Fertilização orgânica e regimes hídricos em mudas de maracujazeiro amarelo desenvolvidas na região semiárida

The objective of this study was to evaluate the effects of doses of biofertilizer with different water regimes on the growth and phytomass of yellow passion fruit seedlings. The experiment was carried out using a material or substrate of the first 20 cm of a Eutrophic Floss Neossol. The design used was completely randomized (DIC), with a 5x2x2 factorial arrangement, referring to the doses of bovine biofertilizer (0; 200; 400; 600 and 800 mL) diluted in ratio of 1:2, S1- substrate levels 70% soil (1400 mL) + 30% bovine manure (600 mL); S2 - 30% soil (600 mL) + 70% bovine manure (1400 mL) and two water levels in the soil (ADS): L1 = 100% of the water available in the substrate (ADS) and L2 = 60% water available on the substrate, with 4 repetitions, totaling 80 experimental units. After sowing at 110 (DAS), the leaf area (AF) was evaluated; Dry shoot phytomass (FSPA); Dry root phytomass (FSR); Total dry phytomass (FST); Root part shoot (RRPA); Root length (CR) and Pearson's correlation. Passion fruit seedlings under water stress conditions inhibit their growth, but with biofertilizer and cattle manure they result in plants with greater vegetative potential.

Desempenho de plantas de coentro (Coriandrum sativum L.) adubadas com diferentes doses de esterco caprino

O coentro (Coriandrum sativum L.) é uma olerícola que necessita de deposição de nutrientes, visto que os pré-existentes no solo são insuficientes para impulsionar o crescimento da mesma. Nesse contexto, objetivou-se, com este trabalho, avaliar a eficiência da adubação orgânica com esterco caprino no cultivo do coentro. O experimento foi realizado em casa de vegetação da Universidade Federal de Alagoas - Campus de Arapiraca. O delineamento experimental foi em cinco blocos ao acaso, com cinco tratamentos, que consistiram na adubação orgânica com esterco caprino associado ao solo em diferentes proporções: T1 = 20%; T2 = 40%; T3 = 60%; T4 = 80%; T5 = 0% da proporção solo/esterco. As variáveis analisadas foram altura de planta, comprimento de raizes, fitomassa fresca total, fitomassa seca da parte aérea, fitomassa seca de raízes, fitomassa seca total, relação raiz/parte aérea, taxa de crescimento absoluto e taxa de crescimento relativo em altura de planta. A adição de 60% de esterco caprino no substrato promove resultados positivos na maioria das variáveis investigadas, tendo prevalecido uma significância da ordem de 78% das variáveis investigadas. A proporção de 60% esterco caprino e 40% de solo é a mais indicada para obtenção de plantas de coentro de melhor qualidade.

SHADING LEVELS AND PLANT GROWTH REGULATOR FOR FORMATION OF SCHIZOLOBIUM AMAZONICUM COMPACT SEEDLINGS

Paricá (Schizolobium amazonicum) can be used for rehabilitation of degraded lands, timber manufacturing markets. However, for its planting, high-quality seedlings should be used. Thus, this study aimed to evaluate the effect of different types of paclobutrazol (PBZ) application and two shading levels on high-quality seedling production. As there was no replication of cultivation environments, we considered each one of them as an experiment. For each environment (35 and 50% shading screen), a completely randomized design was adopted, testing combinations of two types of PBZ application (direct seed immersion in 0.005% PBZ solution; substrate hydration with 0.005% PBZ solution; and 50% seed hydration and 50% substrate hydration; plus, a control), with five replications and five seedlings per plot. The environments were evaluated by analysis of groups of experiments. Seedling growth was evaluated. Under 50% shading, Paricá seedlings had better growth conditions. Application of 100% PBZ in substrate provided compact seedlings with larger dry root phytomass, besides being more practical.

Behavior of Sunflower Irrigated With Salt Water and Nitrogen Fertigation

The sunflower (Helianthus annus L.) crop has been gaining prominence in wastewater research due to its relevance to the production of edible oil, biodiesel and ornamental and decorative material. In the field of floriculture, the crop has been emerging as an alternative offer of a short-cycle product, with contrasting colors and easy identification by the consumer. The objective of this work was to evaluate the different electrical conductivities of water associated with nitrogen fertigation rates on the vegetative, physiological and productive behavior of ornamental sunflower. The experimental design was completely randomized, in a factorial scheme 6x4, referring to six levels of electrical conductivity of water (ECa of 0.5, 1.5, 2.5, 3.5, 4.5 and 5.5 dS m-1) and four nitrogen fertigation rates, with one control and the other three applications performed every 10, 20 and 30 days after emergence (DAE), with five replications, totaling 120 experimental units. The variables analyzed were: stem diameter, root length, chlorophyll a, b and total chlorophyll content, fresh and dry phytomass of shoots, roots and total phytomass, seed mass and capitulum mass. The salinity negatively affected the physiological variables, growth and productivity evaluated, decreasing with increasing electrical conductivity of irrigation water (dS m-1). Nitrogen fertigation at 10 days after emergence resulted in an increase in the stem diameter of sunflower plants.

Modelling the growth of floodplain grasslands to explore the impact of changing hydrological conditions on vegetation productivity

This study (i) presents a coupled vegetation-soil model adapted to perennial C4 seasonally flooded semi-arid grasslands; and (ii) applies the model to evaluate changes in the annual productivity of the grasslands of the Tana River Delta, Kenya, under changing flooding conditions. Main plant growth processes are modelled within coupled plant carbon balance and soil water budget modules: photosynthesis, allocation of photosynthates, respiration, translocation of root phytomass to aerial phytomass, senescence and litter production. Aerial phytomass can also be subtracted from the system, to simulate grazing or cutting. New features concern the inclusion of effects of floods on energy conversion efficiency, photosynthate allocation, senescence and litter production. The vegetation model, composed of four phytomass compartments (leaves, stems, roots, aerial dead matter), simulates three main growth phases related to flooding: floods, a post-flood phase and a non-flooded phase. It was designed to be used with limited climatic data. Data collected during a 14-month experiment (2010–2012) in the Tana River Delta, Kenya, in which different irrigation and cutting treatments and flood events were recorded, were used for calibration and validation purposes. Fourteen parameters, selected through a sensitivity analysis, were calibrated on half of these treatments. Uncertainty in parameter estimation was expressed through a stochastic ensemble of simulations. The remaining independent data were used for model validation. Overall, the model predictions are in good agreement with the experimental data. This model can be used to assess the impact of rain variability, grazing or flooding patterns on the annual primary productivity of Sub-Saharan floodplain grasslands composed mainly of Echinochloa stagnina (Retz) P. Beauv. In particular, simulations for the Tana River Delta suggest that past changes in the hydrological regime of the river, as well as future changes due to the construction of hydroelectric infrastructure, have led and will certainly lead to an important decrease of the floodplain grassland productivity. As local and regional livestock keeping activities rely heavily on the dry seasons’ grazing resources available within the wetland, future development plans should seriously consider the negative effects of these changes on local activities and livelihoods.

Modeling Production Processes in Forest Stands: An Adaptation of the Solow Growth Model

The model of forest stand growth proposed in this study is based on R. Solow’s model of economic growth. The variables introduced into the model are the “capital” (the phytomass of the non-synthesizing tree components in the stand—the stem, roots, and branches) and the “labor” (the phytomass of the photosynthesizing tree components in the stand—leaves or needles). Root phytomass is calculated with a special independent model. The process of energy production by the trees is described with the Cobb-Douglas equation. The proposed approach is used to describe growth processes in the forest stands comprising various species in Siberia and the age dynamics of net primary production. The model can explain a number of effects (such as death of the forest stand after the needles have been consumed by defoliating insects) that cannot be explained by standard logistic models.

STRUCTURE OF THE VEGETABLE BIOMASS OF BIRCH FORESTS IN CHERNIGIV REGION

Проведено дослідження фітомаси та мортмаси березових лісів. Опрацьовано методичні підходи для комплексного оцінювання кількісних показників органічної речовини живих та відмерлих деревних рослин. Здійснено аналіз структури фітомаси та мортмаси за їх компонентами. На основі емпіричних дослідних даних встановлено особливості розподілу компонентів у структурі біомаси. Досліджено, що фітомаса стовбурів у корі 10-річного березового насадження може становити 48 %, фітомаса крон – 9 %, фітомаса коренів дерев – 13 %, живий надґрунтовий покрив (з корінням) – 7 %. Мортмаса сухостою становить 4 %, мортмаса підстилки у структурі загальної рослинної біомаси становить 16 %, а мортмаса коренів дерев берези – 3 %. Встановлено, що у дослідному 53-річному березняку фітомаса стовбурів у корі становить 69 %, фітомаса крон – 6 %, фітомаса коренів дерев – 15 % та фітомаса живого надґрунтового покриву (з корінням) – 1 %. Мортмаса в структурі 53-річного березового насадження становить 9 %, зокрема 5 % припадає на сухостій, 1 % – на деревну ламань, менше 1 % – на опад грубих гілок та 2 % – на підстилку. Виявлено, що структурі загальної біомаси березняків характерне зменшення частки мортмаси з віком. Встановлено обсяг живої та відмерлої рослинної органічної речовини та виявлено, що у структурі рослинної біомаси (абсолютно сухий стан) березових лісів Чернігівщини загальна мортмаса становить 23 % у молодняках та 9 % у стиглих насадженнях.

Seed viability of Dimorphandra gardneriana subject to water stress in different temperatures

ABSTRACT: The forest species Dimorphandra gardneriana Tul. is widely used for various pharmacological products, yet few basic studies have been undertaken to understand their ecological and physiological attributes under stress conditions. The goal of this research was to evaluate the seed germination and vigor when subjected to different osmotic potentials and temperatures. Water restriction was simulated with polyethylene glycol 6000 solution (PEG 6000) with osmotic potentials of 0; -0,2; -0,4; -0,6; -0,8, and -1,0MPa at temperatures of 20, 25, 30, and 35°C. The effect of the treatment was determined by the germination and vigor (germination speed index, length and phytomass of dry shoot and roots) of the seeds, in an entirely random design with four repetitions. From-0, 4MPa it occurs a drastic reduction in germination and vigor of seeds although these factors were less affected at temperature of 25°C up to -0, 2MPa.

English

The objective of this work was to evaluate the interference resulting from the use of different phytomass quantities of Uroclhoa brizantha cv. Marandu and the management of straw to control beggar-ticks (Bidens subalternans). The experiment was performed under greenhouse from May to August, 2014, using a randomized block experimental design with four replicates, in a factorial scheme (3 × 4) + 1, with Factor A constituted by three management methods (incorporated, incorporated+surface and surface), and Factor B constituted by five straw levels (3; 6; 9 and 12 t ha-1), plus one treatment without the usage of any cover plant (control treatment). The variables evaluated were the total number of plants emerged, the index of emergence velocity, dry phytomass of the aerial plant portion, leaf area, dry phytomass of roots and the volume of roots. Different management methods at different straw levels were efficient, with an emphasis to the surface management in the suppression of beggar-ticks (B. subalternans).          Key words: Allelopathy, beggar-tick, Brachiaria brizantha, weed

Irrigation with wastewater on a Canavalia ensiformis cultivation in substrate treated with coffee dregs vermicompost

Taking into account the necessity of creating alternatives to minimize the environmental impacts caused by solid and liquid residues, this study aimed at examining the feasibility of Canavalia ensiformis (jack bean) cultivation in substrates treated with coffee dregs vermicompost and fertirrigated with wastewater. Initially, the vermicompost was prepared using Eisenia foetida worms and different percentages of coffee dregs. To study the C. ensiformis development, experimental units were established, organized in a completely randomized design, with four treatments and eight repetitions. The following parameters were obtained: average number of leaves per plant; height of the aerial part; fresh and dry phytomass of aerial parts and roots, and length of roots. Chemical analyses of irrigation water and cultivation soil were carried out. The results showed that the substrates treated with a compost made of 25% coffee dregs and 75% cattle manure provided the most favorable conditions for E. foetida to grow, and it is suggested as an alternative to vermicomposting. The groups cultivated with the application of coffee dregs vermicompost and irrigated with wastewater presented the best results in terms of the variables chosen to assess plant development. This has possibly resulted from the higher concentrations of N, P and K present in the wastewater and in the substrate treated with the coffee dregs vermicompost. This study points to the potential use of irrigation with wastewater, combined with a substrate treated with coffee dregs vermicompost, in C. ensiformis cultivation.

Nitrogen mineralization drives the response of forest productivity to soil warming: Modelling in ecosys vs. measurements from the Harvard soil heating experiment

Effects of climate warming on ecosystem productivity are strongly influenced by those on mineralization and uptake of key soil nutrients, particularly N. Models used to project these effects must therefore include a comprehensive and fully coupled N cycle which has undergone rigorous testing. Key hypotheses governing the response of the N cycle to warming in the terrestrial ecosystem model ecosys were tested against changes in ecosystem C and N stocks measured during 7 years of 5°C soil heating in the Harvard soil heating experiment. These hypotheses enabled the model to simulate gains in plant C stocks that rose from 50 to 200gCm−2y−1 driven by increased N mineralization and uptake as the soil heating experiment progressed. However these gains were offset by continuing losses of soil C stocks from 125 to 250gCm−2y−1 driven by increased heterotrophic respiration, so that total C stocks changed little with soil heating. Both gains and losses in the model were consistent with those measured in the soil heating experiment. The changes in N cycling with soil heating on which these model results were based were further corroborated by comparing modelled vs. measured increases in soil N mineralization rates, foliar N contents and reductions in root phytomass, and by comparing modelled increases in CO2 fluxes and net primary productivity with those reported in meta-analyses of warming effects on ecosystem productivity. However when the model was run under gradual climate warming by 5°C per century, these modelled changes in N cycling drove gains in ecosystem C stocks that rose gradually to ca. 165gCm−2y−1 after 100 years. The greater gain in ecosystem C modelled under gradual climate warming vs. sudden soil heating was attributed to much smaller losses in soil C stocks.

The effects of different amendments on the mobility and toxicity of nickel and copper in polluted soils

The efficiency of different amendments for the remediation of acidic sandy soils contaminated with heavy metals was assessed in a model laboratory experiment with podzols from the Kola Peninsula. The addition of SLOVAKITE®, lime, and vermiculite leads to significant reduction of the acidity and mobility of nickel and copper in polluted soils, as well as an increase in the length and phytomass of shoots and roots of Festuca rubra. The application of superphosphate for the remediation of soils that were polluted with nickel and copper was less helpful, while the apatite and zeolite additives were inefficient.

Performance of rice seeds treated with zinc, boron, and molybdenum

The objective of this study was to assess physiological quality of seeds and the initial growth of lowland rice seedlings, cv. PUITA INTA-CL, treated with a product based on Zinc, Boron and Molybdenum. The following dosages of product were used: 0 (control), 50, 100, 150 and 200 mL.100 kg-1 seed. A completely randomized experimental design was used, with 10 treatments and four replications. Physiological quality of seeds was assessed by following tests: germination; first count of germination; and length and dry phytomass of seedlings. The initial growth was assessed at 7, 14, 21, 35, and 42 days after emergence (DAE) through plant height, leaf area and dry phytomass of aerial parts and roots. It was concluded that the treatment of rice seeds with the product containing Zinc, Boron and Molybdenum up to the dosage tested of 200 mL.100 kg-1 seed does not influence germination, first count of germination, and the dry phytomass of aerial parts and roots; however, negatively influences seedling length. In addition, it also promotes greater plant height, higher leaf area, higher production of dry phytomass of seedlings, and increase on the growth rate, until 42 DAE.

Posições das mudas de alface nas bandejas de poliestireno e efeitos na normalidade e homogeneidade dos erros na produção de plantas

A qualidade de um experimento pode ser descrita por intermédio de estatísticas, sendo o erro experimental um dos parâmetros de avaliação dessa qualidade. O objetivo do trabalho foi verificar a interferência de diferentes posições de mudas de alface em bandeja de poliestireno sobre a normalidade e homogeneidade dos erros em experimentos realizados em estufa plástica e em campo. Foram conduzidos seis experimentos no Departamento de Fitotecnia da Universidade Federal de Santa Maria, sendo três no verão (2006-2007) e três no outono-inverno (2007) com a cultura da alface, cultivar Vera. Os tratamentos foram 12 diferentes posições das mudas na bandeja de produção. As variáveis analisadas na produção de mudas e após o transplante aos ambientes foram a fitomassa fresca e seca da parte aérea e raiz e fitomassa fresca e seca da parte aérea, respectivamente. Foram testadas as normalidade e homogeneidade dos erros sendo comparadas às médias de cada tratamento. Há atendimento da homogeneidade e normalidade dos erros para as fitomassas fresca da parte aérea e de raiz de alface nos experimentos com diferentes posições de mudas na bandeja de produção, nos diferentes ambientes e estações sazonais de cultivo. Para a fitomassa seca da parte aérea não há atendimento da homogeneidade e/ou normalidade dos erros nos experimentos no verão, com produção de mudas e de plantas na estufa plástica. Para a fitomassa seca de raiz não há atendimento da normalidade dos erros no experimento no outono-inverno com produção de mudas.

Cronograma de amostragem de plantas de alface hidropônica para ajuste de curvas de crescimento

O ajuste de curvas de crescimento de plantas de alface durante seu ciclo necessita de amostragens no tempo, o que restringe o número de efeitos de tratamentos estudados. Com o objetivo de determinar o cronograma de amostragem de plantas de alface em hidroponia para o ajuste de curvas de crescimento até a fase de maturação das sementes, foram realizados dois cultivos em casa de vegetação durante a primavera e o outono, em área pertencente ao Departamento de Fitotecnia, na UFSM, Santa Maria, RS. A partir do ajuste de um modelo de crescimento com amostragem diária, simularam-se diferentes cronogramas de amostragem para o ajuste do mesmo modelo. Para encontrar o cronograma de maior intervalo entre amostragens, ou seja, menor número de coletas, foi comparado o ajuste do modelo de amostragem diária com os ajustes dos modelos dos diferentes intervalos de amostragens simulados, dois a dois, pelo teste F. Foram realizadas simulações considerando desde a data de transplante até a produção de sementes, para variáveis de fitomassa seca da planta e de partes da planta e área foliar. Em experimentos realizados com alface hidropônica na primavera, para o ciclo completo, recomendam-se amostragens a cada 3, 8, 20 e 9 dias para fitomassa seca relativa total da planta de alface, de folhas, de raiz e área foliar, respectivamente; enquanto que, para experimentos realizados no outono, é recomendável utilizar intervalos de amostragens a cada 2, 11, 12 e 11 dias, respectivamente.

Prolonged Growth of Young Spruce (Picea koraiensis Nakai) Plants at Double Atmospheric CO2 Concentration Stimulates the Preferential Growth of Thick Roots

Two-year-old young spruce (Picea koraiensis Nakai) plants were grown in a climatic chamber during three summer months at double atmospheric CO2 concentration, sufficient content of soil inorganic nitrogen, and diurnal variation of temperature and illuminance, which simulate natural growth conditions. The control plants were grown in another climatic chamber under the same conditions, but at atmospheric CO2 concentration (350 ppm). CO2 exchange was measured with a Li-Cor 6400 infra-red gas analyzer in attached leaves placed in a climatic chamber in the morning under growth conditions and saturating light 1200 µE/(m2 s) in June, July, and August. In addition, dry weights of needles, leafless shoot parts of plant, fraction of thick (more than 0.5 mm in diameter) and thin (less than 0.5 mm in diameter) roots were recorded. The data were used to plot CO2 exchange rates as a function of carbon dioxide concentration and to calculate the increment of shoot and root phytomass. The maximum gas exchange rates in the treated and control plants similarly depended on CO2 concentration. The slope of the CO2 dependence curve, which corresponded to the kinetic characteristic Vm /KM of photosynthetic carboxylation, increased monotonically during the experiment. To the end of observation period, the proportion of thick roots in plant phytomass significantly increased in the plants grown at double atmospheric CO2 concentration, as compared to the control plants. Thus, the increase in the rate of photosynthetic gas exchange in plants grown for three months at double atmospheric CO2 concentration was only due to the increase in CO2, the substrate of Rubisco carboxylation activity. We found no differences in the CO2 characteristic for Rubisco between the treated and control plants. The ratio of needle to thin roots in the treated and control plants was similar and did not change during the experiment. The excess of photoassimilates in the treated, as compared to the control plants, was preferentially used for thick root growth. This result shows that photosynthesis in young spruce forests can deposit excess atmospheric CO2 in the soil horizon in the form of thick root phytomass.

How does the nature of living and dead roots affect the residence time of carbon in the root litter continuum?

Root litter transformation is an important determinant of the carbon cycle in grassland ecosystems. Litter quality and rhizosphere activity are species-dependent factors which depend on the attributes of the dead and living roots respectively. These factors were tested, using non-disturbed soil monoliths ofDactylis glomerata L. andLolium perenne L. monocultures.13C-labelled root litter from these monoliths was obtained from a first stand of each crop, cultivated under veryδ 13C-depleted atmospheric CO2 (S1). In a factorial design,13C-labelled root litter of each species was submitted to a second, non13C-labelled, living stand of each species (S2). Carbon derived from S1 and from S2 was measured during an 18-month incubation in the root phytomass and in three particulate organic matter fractions (POM). The decay rate of each particle size fraction was fitted to the experimental data in a mechanistic model of litter transformation, whose outputs were mineralisation and stabilisation of the litter-C. Few differences were found between species, in the amount and biochemical composition of the initial root litter, butDactylis roots showed a greater C:N ratio, a lower mean root diameter and a greater specific root length compared toLolium. A transient accumulation of litter residues arose successively in POM fractions of decreasing particle size. The litter-continuum hypothesis was validated, i.e. that the attributes of the compartments (C:N, chemical composition and residence time) depended mainly on their particle size. The S1 species influenced the rate of litter decay while the S2 species controlled the efficiency of litter-C stabilisation versus mineralisation:Dactylis litter decomposed faster andLolium rhizosphere allowed a greater proportion of litter C stabilisation. Discussions focus on the processes responsible of species strategy in relation with the morphological root traits, and the implication of strategy diversity for rich grassland communities.

Rhizosphere activity, grass species and N availability effects on the soil C and N cycles

We examined whether grass species and soil nitrogen (N) availability could enhance Carbon (C) and N turnover during root litter decay in grassland. Three species with increasing competitiveness ( Festuca ovina, Dactylis glomerata and Lolium perenne) were grown at two N fertiliser levels in an undisturbed grassland soil, in which soil organic fractions derived for the last 9 years from Lolium root litter which was 13C-depleted. During the subsequent experimental year, the C turnover was calculated using the respective δ 13C values of the old and new C in the root phytomass, in two Particulate Organic Matter (POM) fractions above 200 μm and in the lightest part of the aggregated soil fraction between 50 and 200 μm. Soil N availability was monitored during the regrowth periods with ion exchange resins (IER). The C decay rates of each particle size fraction were calculated with a simple mechanistic model of C dynamics. The N mineralisation immobilisation turnover (MIT) was characterised by dilution of 15N-labelled fertiliser in the N harvest The C:N ratio and the residence time of C in the fractions decreased with particle size. The presence of a grass rhizosphere increased the decay rate of old C. Accumulation of new C in particle size fractions increased with species competitiveness and with N supply. Species competitiveness increased C turnover in the aggregated fraction, as a result of greater accumulation of new C and faster decay of old C. Fertiliser N increased N turnover and C mineralisation in the SOM. Species competitiveness decreased soil NO 3 − -N exchanged with the IER and increased dissolved organic C (DOC) content. The nature of the current rhizosphere is thus an important factor driving C and N transformations of the old root litter, in relation with grass species strategy. Plant competitiveness may stimulate the C and N turnover in the more evolved SOM fractions in a similar way to the mineral N supply.