Contribution Of Root Respiration Research Articles

Characterization of farmland soil respiration and modeling analysis of contribution of root respiration

Characterization of farmland soil respiration and modeling analysis of contribution of root respiration

Integration of Process-based Soil Respiration Models with Whole-Ecosystem CO2 Measurements

We integrated soil models with an established ecosystem process model (SIPNET, simplified photosynthesis and evapotranspiration model) to investigate the influence of soil processes on modelled values of soil CO2 fluxes (RSoil). Model parameters were determined from literature values and a data assimilation routine that used a 7-year record of the net ecosystem exchange of CO2 and environmental variables collected at a high-elevation subalpine forest (the Niwot Ridge AmeriFlux site). These soil models were subsequently evaluated in how they estimated the seasonal contribution of RSoil to total ecosystem respiration (TER) and the seasonal contribution of root respiration (RRoot) to RSoil. Additionally, these soil models were compared to data assimilation output of linear models of soil heterotrophic respiration. Explicit modelling of root dynamics led to better agreement with literature values of the contribution of RSoil to TER. Estimates of RSoil/TER when root dynamics were considered ranged from 0.3 to 0.6; without modelling root biomass dynamics these values were 0.1–0.3. Hence, we conclude that modelling of root biomass dynamics is critically important to model the RSoil/TER ratio correctly. When soil heterotrophic respiration was dependent on linear functions of temperature and moisture independent of soil carbon pool size, worse model-data fits were produced. Adding additional complexity to the soil pool marginally improved the model-data fit from the base model, but issues remained. The soil models were not successful in modelling RRoot/RSoil. This is partially attributable to estimated turnover parameters of soil carbon pools not agreeing with expected values from literature and being poorly constrained by the parameter estimation routine. We conclude that net ecosystem exchange of CO2 alone cannot constrain specific rhizospheric and microbial components of soil respiration. Reasons for this include inability of the data assimilation routine to constrain soil parameters using ecosystem CO2 flux measurements and not considering the effect of other resource limitations (for example, nitrogen) on the microbe biomass. Future data assimilation studies with these models should include ecosystem-scale measurements of RSoil in the parameter estimation routine and experimentally determine soil model parameters not constrained by the parameter estimation routine.

Soil and Root Respiration Under Elevated CO 2 Concentrations During Seedling Growth of P inus sylvestris var. sylvestriformis

The objectives of this study were to investigate the effect of higher CO 2 concentrations (500 and 700 μmol mol −1) in atmosphere on total soil respiration and the contribution of root respiration to total soil respiration during seedling growth of Pinus sylvestris var. sylvestriformis. During the four growing seasons (May-October) from 1999 to 2003, the seedlings were exposed to elevated concentrations of CO 2 in open-top chambers. The total soil respiration and contribution of root respiration were measured using an LI-6400-09 soil CO 2 flux chamber on June 15 and October 8, 2003. To separate root respiration from total soil respiration, three PVC cylinders were inserted approximately 30 cm deep into the soil in each chamber. There were marked diurnal changes in air and soil temperatures on June 15. Both the total soil respiration and the soil respiration without roots showed a strong diurnal pattern, increasing from before sunrise to about 14:00 in the afternoon and then decreasing before the next sunrise. No increase in the mean total soil respiration and mean soil respiration with roots severed was observed under the elevated CO 2 treatments on June 15, 2003, as compared to the open field and control chamber with ambient CO 2. However, on October 8, 2003, the total soil respiration and soil respiration with roots severed in the open field were lower than those in the control and elevated CO 2 chambers. The mean contribution of root respiration measured on June 15, 2003, ranged from 8.3% to 30.5% and on October 8, 2003, from 20.6% to 48.6%.

Winter soil respiration from an Austrian mountain forest

We measured soil respiration in a mountain forest in the Province of Tyrol, Austria, during winter. Although soil respiration constitutes a major part of total carbon (C) flux, direct measurements are often restricted to the growing season. In this study, we present data on winter soil respiration measured as CO 2 efflux through the snow cover and the fraction of root respiration through trenching. We compared three methods: (1) a closed dynamic chamber on the snow surface ( F Chamb), (2) diffusional flux calculation based on the conductance properties of the snow pack and the CO 2 concentration gradient between the soil surface and the snow surface ( F 2Point), (3) diffusional flux calculated on the basis of incrementally measured CO 2 concentration profiles through the snow pack ( F Probe). Lateral diffusion and retention of CO 2 within the snow pack accounted for an average 38% flux underestimation by F Chamb. F 2Point and F Probe yielded similar C flux estimates, except where ice layers within the snow profile partially blocked CO 2 diffusion and led to a non-linear CO 2 gradient and an overestimation of the C flux by the F 2Point method. The insulating effect of the snow cover kept soil temperatures above freezing, even where air temperatures were far below 0 °C. CO 2 efflux was highest in early winter (0.64 ± 0.05 μmol CO 2-C m −2 s −1) and decreased until the end of snow cover. Accumulated CO 2 efflux from snow-covered soils was 62 g C m −2 or approximately 12% of total annual soil respiration. The contribution of root respiration to total soil respiration varied between 13% and 50% throughout the winter.

Contribution of root to soil respiration and carbon balance in disturbed and undisturbed grassland communities, northeast China

Changes in the composition of plant species induced by grassland degradation may alter soil respiration rates and decrease carbon sequestration; however, few studies in this area have been conducted. We used net primary productivity (NPP),microbial biomass carbon (MBC), and soil organic carbon (SOC)to examine the changes in soil respiration and carbon balance in two Chinese temperate grassland communities dominated by Leymus chinensis (undisturbed community; Community 1)and Puccinellia tenuiflora (degraded community; Community 2), respectively. Soil respiration varied from 2.5 to 11.9 g CO 2 m ;-2 d;-1 and from 1.5 to 9.3 g CO2 m;-2 d;-1, and the contribution of root respiration to total soil respiration from 38% to 76% and from 25% to 72% in Communities 1 and 2,respectively. During the growing season (May-September), soil respiration, shoot biomass, live root biomass, MBC and SOC in Community 2 decreased by 28%,39%,45%,55% and 29%,respectively, compared to those in Community 1.The considerably lower net ecosystem productivity in Community 2 than in Community 1 (104.56 vs. 224.73 g C m;-2 yr;-1) suggests that the degradation has significantly decreased carbon sequestration of the ecosystems.

Soil respiration and carbon balance in a subtropical native forest and two managed plantations

From 1999 to 2003, a range of carbon fluxes was measured and integrated to establish a carbon balance for a natural evergreen forest of Castanopsis kawakamii (NF) and adjacent monoculture evergreen plantations of C. kawakamii (CK) and Chinese fir (Cunninghamia lanceolata, CF) in Sanming Nature Reserve, Fujian, China. Biomass carbon increment of aboveground parts and coarse roots were measured by the allometric method. Above- and belowground litter C inputs were assessed by litter traps and sequential cores, respectively. Soil respiration (SR) was determined by the alkaline absorbance method, and the contribution from roots, above- and belowground litters was separated by the DIRT plots. Annual SR averaged 13.742 t C ha−1 a−1 in the NF, 9.439 t C ha−1 a−1 in the CK, and 4.543 t C ha−1 a−1 in the CF. For all forests, SR generally peaked in later spring or early summer (May or June). The contribution of root respiration ranged from 47.8% in the NF to 40.3% in the CF. On average, soil heterotrophic respiration (HR) was evenly distributed between below- (47.3∼54.5%) and aboveground litter (45.5%–52.7%). Annual C inputs (t C ha−1 a−1) from litterfall and root turnover averaged 4.452 and 4.295, 4.548 and 2.313, and 2.220 and 1.265, respectively, in the NF, CK, and CF. As compared to HR, annual net primary production (NPP) of 11.228, 13.264, and 6.491 t C ha−1 a−1 in the NF, CK, and CF brought a positive net ecosystem production (NEP) of 4.144, 7.514, and 3.677 t C ha−1 a−1, respectively. It suggests that native forest in subtropical China currently acts as an important carbon sink just as the timber plantation does, and converting native forest to tree plantations locally during last decades might have caused a high landscape carbon loss to the atmosphere.

Contribution of plant root respiration to the CO2 emission from soil

The respiration activity of roots was studied in field experiments on gray forest and soddy-podzolic soils and under cropland and natural vegetation. It was shown that the contribution of roots to the CO2 emission from the soil surface depends significantly on the method of determination. The contributions of fine and coarse roots to the total root respiration were approximately similar in forest ecosystems. The use of the method of substrate-induced respiration made it possible to obtain the best estimates of the contributions of root respiration and respiration of microorganisms. The application of glucose in the form of a dry mixture with sand or talc instead of in the water-soluble form appeared to be the optimal procedure for determining the root respiration under field moisture conditions.

Partitioning soil respiration of temperate forest ecosystems in northeastern China

Abstract Quantifying soil respiration components and their relations to environmental controls are essential to estimate both local and regional carbon (C) budgets of forest ecosystems. In this study, we used the trenching-plot and infrared gas exchange analyzer approaches to determine heterotrophic ( R H ) and autotrophic respiration ( R A ) in the soil surface CO 2 flux for six major temperate forest ecosystems in northeastern China. The ecosystems were: Mongolian oak forest (dominated by Quercus mongolica), aspen-birch forest (dominated by Populous davidiana and Betula platyphylla), mixed wood forest (composed of P. davidiana, B. platyphylla, Fraxinus mandshurica, Tilia amurensis, Acer amono, etc.), hardwood forest (dominated by F. mandshurica, Juglans mandshurica, and Phellodendron amurense), Korean pine ( Pinus koraiensis), and Dahurian larch ( Larix gmelinii) plantations, representing the typical secondary forest ecosystems in this region. Our specific objectives were to: (1) quantify R H and its relationship with the environmental factors of the forest ecosystems, (2) characterize seasonal dynamics in the contribution of root respiration to total soil surface CO 2 flux ( RC), and (3) compare annual CO 2 fluxes from R H and R A among the six forest ecosystems. Soil temperature, water content, and their interactions significantly affected R H in the ecosystems and accounted for 46.5%–78.8% variations in R H . However, the environmental controlling factors of R H varied with ecosystem types: soil temperature in hardwood and Dahurian larch forest ecosystems, soil temperature, and water content in the others. The RC for hardwood, poplar-birch, mixed wood, Mongolian oak, Korean pine, and Dahurian larch forest ecosystems varied between 32.40%–51.44%, 39.72%–46.65%, 17.94%–47.74%, 34.31%–37.36%, 33.78%–37.02%, and 14.39%–35.75%, respectively. The annual CO 2 fluxes from R H were significantly greater than those from R A for all the ecosystems, ranging from 337–540 g C·m −2·a −1 and 88‐331 gC·m −2·a −1 for R H and R A , respectively. The annual CO 2 fluxes from R H and R A differed significantly among the six forest ecosystems.

Partitioning the components of soil respiration: a research challenge

Little is known about the respiratory components of CO2 emitted from soils and attaining a reliable quantification of the contribution of root respiration remains one of the major challenges facing ecosystem research. Resolving this would provide major advances in our ability to predict ecosystem responses to climate change. The merits and technical and theoretical difficulties associated with different approaches adopted for partitioning respiration components are discussed here. The way forward is suggested to be the development of non-invasive regression analysis validated by stable isotope approaches to increase the sensitivity of model functions to include components of rhizosphere microbial activity, changing root biomass and the dynamics of a wide range of soil C pools.

Contribution of Root Respiration to Total Soil Respiration in a Leymus chinensis (Trin.) Tzvel. Grassland of Northeast China

AbstractThe loss of carbon through root respiration is an important component of grassland carbon budgets. However, few data are available concerning the contribution of root respiration to total soil respiration in grasslands in China. We investigated seasonal variations of soil respiration rate, root biomass, microbial biomass C and organic C content of the soil in a semi‐arid Leymus chinensis (Trin.) Tzvel. grassland of northeast China during the 2002 growing season (from May to September). The linear regression relationship between soil respiration rate and root biomass was used to determine the contribution of root respiration to total soil respiration. Soil respiration rate ranged from 2.5 to 11.9 g C/m2 per d with the maximum in late June and minimum in September. The microbial biomass C and organic C content of the soil ranged from 0.3 to 1.5 g C/m2 and from 29 to 34 g C/kg respectively. Root biomass had two peaks, in early June (1.80 kg/m2) and mid‐August (1.73 kg/m2). Root respiration rate peaked in mid‐August (6.26 g C/m2 per d), whereas microbial respiration rate peaked in late June (7.43 g C/m2 per d). We estimated that the contribution of root respiration to total soil respiration during the growing season ranged from 38% to 76%.(Managing editor: Ya‐Qin Han)

The contribution of root respiration to soil CO2 efflux in Puccinellia tenuiflora dominated community in a semi-arid meadow steppe

In this study, the linear regression between soil respiration rate and root biomass was adopted to estimate the contribution of root respiration to total soil respiration in Puccinellia tenuiflora dominated community of a semi-arid meadow steppe in northeast China. The soil respiration rate reached the maximum value 2.45 μmol·m−2·s−1 in late June and the minimum value 0.39 μmol·m−2·s−1 in late September. Soil temperature is the major environmental factor controlling the seasonal variation of soil respiration. The root biomass ranged from 0.54 to 0.97 kg·m−2, showing insignificant seasonal variation. Microbial biomass C reached the maximum value 0.50 g·m−2 in mid August, presenting the least within-site variation. The pattern of seasonal change in root respiration rate was different from that in microbial respiration. Root respiration rate ranged from 0.19 μmol·m−2·s−1 in May, to the maximum value 1.39 μmol·m−2·s−1 in late June, then down to 0.28 μmol·m−2·s−1 in late September; whereas, microbial respiration rate ranged from 0.61 μmol·m−2·s−1 in May, to the maximum value 1.27 μmol·m−2·s−1 in July, then down to 0.11 μmol·m−2·s−1 in late September. There was a significant exponential correlation between microbial respiration rate and soil temperature, whereas not so for root respiration rate. We estimated that the contribution of root respiration to total soil respiration ranged within 24%–57% in spring and summer, and increased to 73% in autumn.

京都府南部広葉樹林において短期間に測定された根呼吸量の土壌呼吸量に対する寄与の評価

Root respiration was separated from total soil respiration in this study. Experiments were carried out in September 2003 at Yamashiro Experimental Forest located in Kyoto Prefecture. It is a secondary forest of broad-leaf trees including some conifer species. The root system was dug out and divided into several classes by size. The respiration rate of each size was measured by the closed-chamber method consisting of an IRGA, a pump, and a chamber made of acrylic. Temperature in the chamber was measured by thermo couple. The results showed that the smaller the diameter of the root was, the higher the respiration rate per unit weight was. A Mmuch higher rate was found in fine roots in comparison with other classes. From the relationships between basal diameter and root mass of each size for sample trees, root mass of each size per area was estimated. By combining the respiration rate and root mass of each size per area, root respiration could be calculated at 0.0707 mg CO2 m-2 s-1 as a total. More than the half was occupied by fine root respiration. Mean total soil respiration was 0.19 mg CO2 m-2 s-1 during this experiments. Therefore, the contribution of root respiration to soil respiration was estimated at 37.2%.

The importance of root respiration in annual soil carbon fluxes in a cool-temperate deciduous forest

Annual carbon fluxes via soil and root respiration were estimated in a cool-temperate deciduous forest to evaluate the importance of root respiration in the forest's overall carbon balance. Total soil respiration rates were measured during the snow-free season in 2000 and 2001 using an open-flow gas-exchange system with an infrared gas analyzer. To determine the annual carbon emission from the soil, we constructed a polynomial multiple-regression model that included two variables (soil temperature and soil water content) and that used hourly data for soil respiration rates. To estimate root respiration, we used data on the seasonal changes in the contribution of root respiration to the soil respiration rate that were determined in a previous study. The annual root respiration rate was estimated to be 4.8 t C ha −1 year −1, which corresponds to 45% of the annual total soil respiration (10.6 t C ha −1 year −1). Thus, root respiration contributed about half of the total annual soil respiration in the cool-temperate forest. The importance of root respiration in determining a forest's carbon balance is discussed in relation to data on net ecosystem production by the same forest.

Contribution of root respiration to soil respiration in a C3/C4 mixed grassland

The spatial and temporal variations of soil respiration were studied from May 2004 to June 2005 in a C3/C4 mixed grassland of Japan. The linear regression relationship between soil respiration and root biomass was used to determine the contribution of root respiration to soil respiration. The highest soil respiration rate of 11.54 micro mol m-2 s-1 was found in August 2004 and the lowest soil respiration rate of 4.99 micro mol m-2 s-1 was found in April 2005. Within-site variation was smaller than seasonal change in soil respiration. Root biomass varied from 0.71 kg m-2 in August 2004 to 1.02 in May 2005. Within-site variation in root biomass was larger than seasonal variation. Root respiration rate was highest in August 2004 (5.7 micro mol m-2 s-1) and lowest in October 2004 (1.7 micro mol m-2 s-1 ). Microbial respiration rate was highest in August 2004 (5.8 micro mol m-2 s-1 ) and lowest in April 2005 (2.59 micro mol m-2 s-1 ). We estimated that the contribution of root respiration to soil respiration ranged from 31% in October to 51% in August of 2004, and from 45% to 49% from April to June 2005.

Contribution of root respiration to total soil respiration in a mixed C3 and C4 grassland in Japan

contribution of root respiration to total soil respiration in a mixed C3 and C4 grassland in Japan

Contribution of root respiration to soil surface CO2 flux in a boreal black spruce chronosequence.

We quantified the contributions of root respiration (RC) and heterotrophic respiration to soil surface CO2 flux (RS) by comparing trenched and untrenched plots in well-drained and poorly drained stands of a black spruce (Picea mariana (Mill.) BSP) fire chronosequence in northern Manitoba, Canada. Our objectives were to: (1) test different equations for modeling RS as a function of soil temperature; and (2) model annual RS and RC for the chronosequence from continuous soil temperature measurements. The choice of equation to model RS strongly affected annual RS and RC, with an Arrhenius-based model giving the best fit to the data, especially at low temperatures. Modeled values of annual RS were positively correlated with soil temperature at 2-cm depth and were affected by year of burn and trenching, but not by soil drainage. During the growing season, measured RC was low in May, peaked in late July and declined to low values by the end of the growing season. Annual RC was < 5% of RS in the recently burned stands, approximately 40% in the 21-year-old stands and 5-15% in the oldest (152-year-old) stands. Evidence suggests that RC may have been underestimated in the oldest stands, with residual root decay from trenching accounting for 5-10% of trenched plot RS at most sites.

Carbon dynamics and budget in a Miscanthus sinensis grassland in Japan

We investigated the carbon dynamics and budget in a grassland of Miscanthus sinensis, which is widely distributed in Japan, over a 2‐year period (2000–2001). Plant biomass began to increase from May and peaked in September, then decreased towards the end of the growing season (October). Soil respiration rates also exhibited seasonal fluctuations that reflected seasonal changes in soil temperature and root respiration. The contribution of root respiration to total soil respiration was 22–41% in spring and summer, but increased to 52–53% in September. To determine the net ecosystem production (carbon budget), we estimated annual net primary production, soil respiration, and root respiration. Net primary production was 1207 and 1140 g C m−2 in 2000 and 2001, respectively. Annual soil respiration was 1387 g C m−2 in 2000 and 1408 g C m−2 in 2001; root respiration was 649 and 695 g C m−2 in 2000 and 2001, respectively. Moreover, some of the carbon fixed as net production (457–459 g C m−2) is removed by mowing in autumn in this grassland. Therefore, the annual carbon budget was estimated to be −56 g C m−2 in 2000 and − 100 g C m−2 in 2001. These results suggest that the Miscanthus sinensis grassland in Japan can act as a source of CO2.

Seasonal changes in the contribution of root respiration to total soil respiration in a cool-temperate deciduous forest

A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (R trench) and in a control plot (R control) were measured from May 2000 to September 2001 by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (R D) was estimated by using a root-bag method to correct the soil respiration measured from the trenched plots for the additional decaying root biomass. The soil respiration rates in the control plot increased from May (240–320 mg CO2 m−2 h−1) to August (840–1150 mg CO2 m−2 h−1) and then decreased during autumn (200–650 mg CO2 m−2 h−1). The soil respiration rates in the trenched plot showed a similar pattern of seasonal change, but the rates were lower than in the control plot except during the 2 months following the trenching. Root respiration rate (R r) and heterotrophic respiration rate (R h) were estimated from R control, R trench, and R D. We estimated that the contribution of R r to total soil respiration in the growing season ranged from 27 to 71%. There was a significant relationship between Rh and soil temperature, whereas R r had no significant correlation with soil temperature. The results suggest that the factors controlling the seasonal change of respiration differ between the two components of soil respiration, R r and R h.

잣나무 조림지의 탄소수지에 관한 연구

공주 근교의 15년 된 잣나무 조림지에서 물질생산을 통한 탄소고정량과 토양호흡을 통한 탄소 방출량을 조사하였다. 연 순생산량은 상대생장법에 의해 보고된 물질생산 식을 이용하여 측정하고 이것을 이산화탄소의 고정량(순 흡수량)으로 환산하였다. 토양호흡은 대조구, 뿌리제거구, 낙엽제거구로 구분하여 2001년 4월부터 2002년 4월까지 2주 간격으로 측정하였으며, 이때 토양온도, 토양수분함량도 함께 측정하였다. 이들 자료를 기준으로 잣나무 조림지의 탄소수지를 파악하였다. 조사지역 잣나무 조림지의 연 순생산량은 25.7t·ha/sup -1/·yr/sup -1/이었으며, 이를 CO₂량으로 환산한 결과 연간 CO₂ 고정량은 42.5 t CO₂·ha/sup -1/·yr/sup -1/이었다. 잣나무 조림지 대조구의 연간 총 호흡량은 5.0 t CO₂·ha/sup -1/·yr/sup -1/이었다. 연간 이 산화탄소 발생량 중 낙엽층의 기여도는 전체의 32.0%, 뿌리의 기여도는 46.0%이었다. 임목밀도에 따라 연 순생산량에 차이가 있지만 본 조사지역의 경우 CO₂순 흡수량과 토양호흡에 의한 방출량의 차이는 37.5 t CO₂·ha/sup -1/·yr/sup -1/로 삼림이 대기 중의 이산화탄소를 감소시킴을 알 수 있다. Amounts of CO₂ fixed by net primary production and released by soil respiration were determined on big-cone pine plantation. Net primary production, which was determined by allometric method, was converted into CO₂. CO₂ evolution in forest ecosystems are mainly through soil and root respiration. In order to separate root respiration from soil respiration, root-free sites were made in stand. Litter removal sites were prepared to estimate CO₂ evolution through litter layer. Respiration was measured at every two weeks intervals from April 2001 through April 2002, and soil temperature and soil moisture were measured at the same time. Net primary production of this big-cone pine plantation was 25.7 t·ha/sup -1/·yr/sup -1/. The amount of CO₂ fixed by this plantation was 42.5 t CO₂·ha/sup -1/·yr/sup -1/, The amount of CO₂ released by soil respiration was 5.0 t CO₂·ha/sup -1/·yr/sup -1/. The relative contribution of root respiration and litter layer respiration to total respiration was 46% and 32%, respectively. Net amount of fixed CO₂ was 37.5 t CO₂·ha/sup -1/·yr/sup -1/ in this big-cone pine plantation. From this result, this big-cone pine plantation play a carbon sink source from the atmosphere.

Carbon partitioning and below-ground translocation by Lolium perenne

Carbon (C) balance, rhizodeposition and root respiration during development of Lolium perenne were studied on a loamy Gleyic Cambisol by 14CO 2 pulse labeling of shoots in a two-compartment chamber under controlled laboratory conditions. The losses from shoot respiration were about 36% of the total assimilated C. The highest respiration intensity was measured in the first night after the labeling, and diminishes exponentially over time. Total 14CO 2 efflux from the soil (root respiration, microbial respiration of exudates and dead roots) in the first eight days after the 14C pulse labeling increased with plant development from 2.7 to 11% of the total 14C assimilated by plants. A model approach used for the partitioning of rhizosphere respiration showed that measured root respiration was between 1.4 and 3.5% of assimilated 14C, while microbial respiration of easily available rhizodeposits and dead root residues was between 0.9 and 6.8% of assimilated C. Both respiration processes increased during plant development. However, only the increase in root respiration was significant. The average contribution of root respiration to total 14CO 2 efflux from the soil was approximately 46%. Total CO 2 efflux from the soil was separated into plant-derived and soil-derived CO 2 using 14C labeling. Additional decomposition of soil organic matter (positive priming effects) in rhizosphere was calculated by subtracting the CO 2 efflux from bare soil from soil-derived CO 2 efflux from soil with plants. Priming effects due to plant rhizodeposition reach 60 kg of C ha −1 d −1. 14C incorporated in soil micro-organisms (extraction–fumigation) amounts to 0.8–3.2% of assimilated C. The total below-ground transfer of organic C by Lolium perenne was about 2800 kg of C ha −1. The C input into the soil consists of about 50% of easily available organic substances.