Soil Carbon Respiration

Soil respiration is an important component of the net carbon dioxide exchange between agricultural ecosystems and the atmosphere, and reliable estimates of soil respiration are required in carbon balance studies. Most of the field measurements of soil respiration reported in the literature have been made using alkali traps. The use of portable CO2 analysers in dynamic closed chamber systems is recent. The introduction of this new technique requires its evaluation against existing methods in order to compare new information with older data. Nine intercomparisons between dynamic systems and alkali traps were made. Measurements of Fc,s obtained by both chambers showed a good agreement in all but two comparisons in which alkali trap measurements were lower than the dynamic chamber by about 22%. This first report of agreement between both techniques suggests that many measurements made in the past using alkali traps may be comparable to the measurements made more recently using the dynamic chambers. Analysis of the soil temperature and CO2 concentration inside the alkali traps failed to explain why the alkali traps occasionally underestimated the fluxes. Soil respiration measured with a dynamic closed chamber were also compared to eddycorrelation measurements. The results did not reveal any consistent bias between techniques but the scattering was large. This dispersion is likely the result of the difference between the areas measured by the two techniques.

Carbon dioxide concentration in atmosphere is actively increasing since industrial revolution (1800) from 285 ppmv to 378 ppmv in 2005. Carbon dioxide efflux from soil due to floral and faunal respiration in soil, called soil respiration, is the second largest source of increasing concentration of CO2 in atmosphere. Soil respiration produces almost 11 times more carbon dioxide in atmosphere than that produced due to fossil fuel burning [18]. Microorganisms are the most abundant biotic group in soil and huge amount of CO2 is evolved from soil due to bacterial and fungal respiration. The present study investigated soil respiration and distribution of bacteria and fungi in the soil. The study was conducted in semi arid (subtropical) climate around New Delhi in India. Two different sites (Aravali Biodiversity Park and Yamuna Biodiversity Park) with ecologically different soil and vegetation conditions were studied. Three different locations were selected at each site and at each location CO2 efflux and microbial population were measured at three depths, topsoil (0–5 cm depth), midsoil (15–20 cm depth) and Deep soil (40–45 cm depth). Higher soil activity was found at Yamuna Biodiversity Park (YBP) having profuse ground vegetation, sandy soil with high organic matter and moisture content than Aravali Biodiversity Park (ABP) having scares vegetation, rocky area and dry soil with low organic matter content. Higher soil respiration is recorded in the surface and mid soil at YBP than ABP. However the soil respiration rate was slightly more in deep soil at ABP. In most of the cases soil respiration was found increasing from surface soil to deeper soil till 50 cm depth. Rate of soil respiration is highly correlated (R 2 = 0.7) to fungal population. Our study suggests that soil respiration process is a function of bacterial and fungal abundance in the soil. However, fungal population is more responsible for CO2 evolution in atmosphere from soil than bacterial population. Better understanding of soil respiration process can help in reducing CO2 emission and carbon sequestration process.

Soil respiration is a major component of the global carbon budget and Mediterranean ecosystems have usually been studied in locations with shallow soils, mild temperatures, and a prolonged dry season. This study investigates seasonal soil respiration rates and underlying mechanisms under wetter, warmer, and more fertile conditions in a Mediterranean cork oak forest of Northern Tunisia (Africa), acknowledged as one of the most productive forests in the Mediterranean basin. We applied a soil respiration model based on soil temperature and relative water content and investigated how ecosystem functioning under these favorable conditions affected soil carbon storage through carbon inputs to the soil litter. Annual soil respiration rates varied between 1774 gC m −2 year −1 and 2227 gC m −2 year −1 , which is on the highest range of observations under Mediterranean climate conditions. We attributed this high soil carbon flux as a response to favorable temperatures and soil water content, but this could be sustained only by a small carbon allocation to roots (root/shoot ratio = 0.31–0.41) leading to a large allocation to OPEN ACCESS

Carbon dioxide measurements from soil surface may indicate the potential for soil respiration and carbon
consumption according to microbial biomass and root activity. These processes may be influenced by land
use and cover change, and abandonment especially in the upper soil organic layer. Seven environments
from cultivation to late abandonment, with the same soil type classified as Lithic Xerorthent, were tested
to ascertain the respiration capacity according to the current use and cover, and to establish the ability to preserve
and eventually increase the organic matter pools after abandonment. Given the importance of carbon
dioxide measurements at soil surface, a comparison between the classic soda lime method (SL) and a rapid
method based on infrared sensor analyzer (IR) was performed from autumn 2008 to autumn 2009 in the
field. The field measurements of CO2 proved significant correlations between the values from the two techniques
under the same natural conditions and along the period of observation. However, the values of CO2
measured by the soda lime method were always higher than those obtained by the infrared analyzer. This
pattern was attributed to the difference in time of measurement, larger in the former method, and type of
measurement technique. Despite that the trend of measured CO2 values was rather similar along the year.
On average, the highest values of CO2 emission in the field were recorded in the warmest periods of the
year and with soil surface moisture not lower than 3% independently on the method used. High soil surface
temperature with soil moisture below 3% decreased drastically the CO2 production from the dry soil. The cultivated
environments and soil under forests have resulted higher CO2 producers than abandoned soils
depending on the age of abandonment, climatic conditions, and within abandonment perturbations. Those
abandoned soils preserved by perturbations like wildfire showed a higher potential for accumulating organic
carbon, as indicated by the lowest emission of CO2 with respect to SOC content, during the period of observation.
Results demonstrated the reliability of the methods used to evaluate the soil carbon dioxide production
capacity and allowed to classify through environments with increasing potential for carbon
sequestration. The classification was rather similar by using both methods indicating a higher susceptibility
to carbon loss in the following order: soil under Vines (V)>under Olives (O)>under Pine trees (PI)
>under Cork Trees (S)>under Pasture (PR)>under Cistus scrub (MC)>under Erica scrub (MB) by using
the SL method and V>O>PI>S>MC>MB>PR by using the IR method. Indications about the need of management
of abandoned areas were also considered in order to recover the landscape heterogeneity.

•Recent studies have highlighted a direct, fast transfer of recently assimilated C from the tree canopy to the soil. However, the effect of environmental changes on this flux remains largely unknown.•We investigated the effects of drought on the translocation of recently assimilated C, by pulse-labelling 1.5-yr-old beech tree mesocosms with 13CO2. 13C signatures were then measured daily for 1 wk in leaves, twigs, coarse and fine root water-soluble and total organic matter, phloem organic matter, soil microbial biomass and soil CO2 efflux.•Drought reduced C assimilation and doubled the residence time of recently assimilated C in leaf biomass. In phloem organic matter, the 13C label peaked immediately after labelling then decayed exponentially in the control treatment, while under drought it peaked 4 d after labelling. In soil microbial biomass, the label peaked 1 d after labelling in the control treatment, whereas under drought no peak was measured. Two days after labelling, drought decreased the contribution of recently assimilated C to soil CO2 efflux by 33%.•Our study showed that drought reduced the coupling between canopy photosynthesis and belowground processes. This will probably affect soil biogeochemical cycling, with potential consequences including slower soil nitrogen cycling and changes in C-sequestration potential under future climate conditions.Recent studies have highlighted a direct, fast transfer of recently assimilated C from the tree canopy to the soil. However, the effect of environmental changes on this flux remains largely unknown.We investigated the effects of drought on the translocation of recently assimilated C, by pulse-labelling 1.5-yr-old beech tree mesocosms with 13CO2. 13C signatures were then measured daily for 1 wk in leaves, twigs, coarse and fine root water-soluble and total organic matter, phloem organic matter, soil microbial biomass and soil CO2 efflux.Drought reduced C assimilation and doubled the residence time of recently assimilated C in leaf biomass. In phloem organic matter, the 13C label peaked immediately after labelling then decayed exponentially in the control treatment, while under drought it peaked 4 d after labelling. In soil microbial biomass, the label peaked 1 d after labelling in the control treatment, whereas under drought no peak was measured. Two days after labelling, drought decreased the contribution of recently assimilated C to soil CO2 efflux by 33%.Our study showed that drought reduced the coupling between canopy photosynthesis and belowground processes. This will probably affect soil biogeochemical cycling, with potential consequences including slower soil nitrogen cycling and changes in C-sequestration potential under future climate conditions.