High Soil CO2 Research Articles

Soil CO2 dynamics and fluxes as affected by tree harvest in an experimental sand ecosystem

Soil CO2 production is a key process in ecosystem C exchange, and global change predictions require understanding of how ecosystem disturbance affects this process. We monitored CO2 levels in soil gas and as bicarbonate in drainage from an experimental red pine ecosystem, for 1 year before and 3 years after its aboveground biomass was removed. Lack of physical disturbance, strict prevention of plant regrowth, and a comparison ecosystem without rooted plants facilitated isolation of the microclimatic and biochemical effects of instantaneous canopy removal and cessation of photosynthesis. Preharvest gas‐phase CO2 levels fluctuated with growing‐season soil temperature but reached their greatest levels (up to 10,000 ppmV) during late winter beneath snow and ice cover. This pattern, and the annual CO2 efflux of ∼500 g C m−2 yr−1, continued for 2 years following harvest; the efflux declined by half in the third year. The surprising continuity of preharvest and postharvest rates of soil CO2 production reflects the replacement of root respiration with microbial respiration of root and litter substrates of declining lability, but boosted by soil temperature increases. Mass balance is consistent with a bulk root+litter exponential decay time (−1/k) of 4–6 years, such that most of the subsurface biomass accumulated over 15 years of tree growth would be lost in a decade after the harvest. The preharvest bicarbonate C efflux, which was less than 0.1% of the gas‐phase efflux, trebled after the harvest owing to elimination of evapotranspiration and consequent increases in drainage while soil CO2 levels remained high. A large fraction of this “hydrospheric” sink for atmospheric CO2 is attributed to weathering under high soil CO2 levels before spring snowmelt and soil‐water flushing. These observations suggest that disturbance may enhance long‐term chemical‐weathering CO2 sinks.

Relationships between soil CO2 concentration and CO2 production, temperature, water content, and gas diffusivity: implications for field studies through sensitivity analyses

Soil CO2 levels reflect CO2 production and transport in soil and provide valuable information about soil CO2 dynamics. However, extracting information from soil CO2 profiles is often difficult because of the complexity of these profiles. In this study, we constructed a simple numerical model that simulated soil CO2 dynamics and performed sensitivity analyses for CO2 production rates, soil water content and temperature, and gas diffusivity at the soil surface to clarify the relationships among these parameters. Increased soil surface CO2 flux did not always coincide with higher soil CO2 concentrations; increased CO2 production at shallow depths had little effect on soil CO2 concentrations, while the opposite may be true for high levels of soil water content. Higher soil CO2 concentration did not always coincide with greater soil surface CO2 flux; under high soil water conditions, soil surface CO2 flux sometimes decreased despite increased soil CO2 concentration. Increases in soil water content did not always enhance both soil surface CO2 flux and soil CO2 concentration. Under high soil water conditions, increases in soil water content could lower soil surface CO2 flux and increase soil CO2 concentration. Increases in soil temperature resulted in greater soil surface CO2 flux and higher soil CO2 concentration in our simulation (extremely high temperatures were not assumed in this study). Gas diffusivity in very shallow layers did affect, albeit weakly, soil CO2 concentration. The findings of this study may help direct future observations and aid in the interpretation of their results.

Soil CO2 Concentration Effects on Creeping Bentgrass Grown under Various Soil Moisture and Temperature Conditions

Use of creeping bentgrass [Agrostis stoloniferous L. var. palustris (Huds.)] on golf greens has expanded into the hotter, more humid regions of the United States where its quality is often low during summer months. The summer decline in bentgrass quality may be partially attributed to respiration rates exceeding photosynthesis during periods of supraoptimal temperatures and adverse soil conditions, such as excessive CO2 and inadequate O2 levels. The objectives of this study were to examine the effects of high temperature, high soil CO2, and irrigation scheduling on creeping bentgrass growth. A growth chamber study was conducted using `A-1' creeping bentgrass. Treatments included all combinations of three day/night temperature regimes (26.5/21 °C, 29.5/24 °C, and 32/26.5 °C), three irrigation schedules (field capacity daily, field capacity every two d, and half field capacity daily), and four soil CO2 injection levels (10%, 5%, 0.03%, and a noinjection control). Creeping bentgrass shoot and root dry weights and net photosynthetic rates were greater for day/night temperatures <32/26.5 °C. High temperatures (32/26.5 °C) and 10% CO2 reduced bentgrass net photosynthesis by 37.5 μmol CO2/m2/s. Shoot and root total nonstructural carbohydrates also were lowest for highest temperature regime. Respiration exceeded gross photosynthesis at 32/26.5 °C when 5% and 10% CO2 injection levels were used, indicating a carbon deficit occurred for these conditions. Irrigation volume and frequency did not affect bentgrass growth. High temperatures combined with high soil CO2 levels produced poorest turf quality.

Soil Carbon Dioxide Evolution, Litter Decomposition, and Nitrogen Availability Four Years after Thinning in a Japanese Larch Plantation

Soil carbon dioxide (CO2) evolution, litter decomposition, and nitrogen availability was measured four years after thinning in a 19-year-old Japanese larch (Larix leptolepis Gord.) plantation of central Korea. Four different thinning intensities [control (C), 10% (T10), 20% (T20), and 40% (T40)] were applied. There were significant differences in seasonal mean soil temperature, moisture, and CO2 evolution among the thinning intensities. Annual soil CO2 evolution (Mg CO2 ha−1) was 29.8 for C, 27.0 for T10, 24.2 for T20, and 23.8 for T40, respectively, and decreased with the thinning intensity. High soil CO2 evolution in the control and light thinning plots might be related to root respiration from high stand densities. After decomposing for four years, 30 and 23%, 30 and 27%, 21 and 10%, and 28 and 30% of the original needle litter dry mass and nitrogen mass remained for control, T10, T20, and T40, respectively. However, there were no significant trends with the thinning intensity. Needle litter acted as a net source for nitrogen during its 4th year of decomposition in this site. Thinning did not increase or decrease , , or total inorganic nitrogen concentrations, measured using the ion exchange resin bag method. Growing season sum resin inorganic nitrogen concentration (mg N bag−1) was 8.7 for C, 9.6 for T10, 8.6 for T20, and 9.2 for T40, respectively.

Goethite, calcite, and organic matter from Permian and Triassic soils: carbon isotopes and CO2 concentrations

Pedogenic goethites in each of two Early Permian paleosols appear to record mixing of two isotopically distinct CO2 components—atmospheric CO2 and CO2 from in situ oxidation of organic matter. The δ13C values measured for the Fe(CO3)OH component in solid solution in these Permian goethites are −13.5‰ for the Lower Leonardian (∼283 Ma BP) paleosol (MCGoeth) and −13.9‰ for the Upper Leonardian (∼270 Ma BP) paleosol (SAP). These goethites contain the most 13C-rich Fe(CO3)OH measured to date for pedogenic goethites crystallized in soils exhibiting mixing of the two aforementioned CO2 components. δ13C measured for 43 organic matter samples in the Lower Leonardian (Waggoner Ranch Fm.) has an average value of −20.3 ± 1.1‰ (1s). The average value yields a calculated Early Permian atmospheric Pco2 value of about 1 × PAL, but the scatter in the measured δ13C values of organic matter permits a calculated maximum Pco2 of 11 × PAL (PAL = present atmospheric level). Measured values of the mole fraction of Fe(CO3)OH in MCGoeth and SAP correspond to soil CO2 concentrations in the Early Permian paleosol profiles of 54,000 and 50,000 ppmV, respectively. Such high soil CO2 concentrations are similar to modern soils in warm, wet environments.The average δ13C values of pedogenic calcite from 9 paleosol profiles stratigraphically associated with MCGoeth (Waggoner Ranch Fm.) range from −6.5‰ to −4.4‰, with a mean δ13C value for all profiles of −5.4‰. Thus, the value of Δ13C between the pedogenic calcite data set and MCGoeth is 8.1 (±0.9)‰, which is in reasonable accord with the value of 7.7‰ expected if atmospheric Pco2 and organic matter δ13C values were the same for both paleosol types. Furthermore, the atmospheric Pco2 calculated for the Early Permian from the average measured carbon isotopic compositions of the paleosol calcite and organic matter is also analytically indistinguishable from 1 × PAL, with a maximum calculated atmospheric Pco2 (permitted by one standard deviation of the organic matter δ13C value) of ∼5 × PAL.If, however, measured average δ13C values of the plant organic matter are more positive than the original soil organic matter as a result of diagenetic loss of 13C-depleted, labile organic compounds, calculated Permian atmospheric Pco2 using these 13C-enriched organic values would underestimate the actual atmospheric Pco2 using either goethite or calcite. This is the first stratigraphically constrained, intrabasinal study to compare ancient atmospheric CO2 concentrations calculated from pedogenic goethite and calcite. These results demonstrate that the two different proxies record the same information about atmospheric CO2.The Fe(CO3)OH component in pedogenic goethite from a Triassic paleosol in Utah is significantly enriched in 13C relative to Fe(CO3)OH in goethites from soils in which there are mixtures of two isotopic CO2 components. Field-relationships and the δ13C value (−1.9‰) of the Triassic goethite indicate that this ancient paleosol profile experienced mixing of three isotopically distinct CO2 components at the time of goethite crystallization. The three components were probably atmospheric CO2, CO2 from in situ oxidation of organic matter and CO2 from in situ dissolution of preexisting calcite. Although mixing of three isotopically distinct CO2 components, as recorded by Fe(CO3)OH in goethite, has been described in modern soil, this is the first example from a documented paleosol. Its preservation affirms the need for careful, case-by-case assessment of ancient paleosols to establish that goethite in any particular soil is likely to be a valid proxy of atmospheric Pco2.

Creeping Bentgrass Growth Response to Elevated Soil Carbon Dioxide

Increased soil moisture and temperature along with increased soil microbial and root activity during summer months elevate soil CO2 levels. Although previous research has demonstrated negative effects of high soil CO2 on growth of some plants, little is known concerning the impact high CO2 levels on creeping bentgrass (Agrostis palustris Huds.). The objective of this study was to investigate effects of varying levels of CO2 on the growth of creeping bentgrass. Growth cells were constructed to U.S. Golf Association (USGA) greens specification and creeping bentgrass was grown in the greenhouse. Three different levels of CO2 (2.5%, 5.0%, and 10.0%) were injected (for 1 minute every 2 hours) into the growth cells at a rate of 550 cm3·min-1. An untreated check, which did not have a gas mixture injected, maintained a CO2 concentration <1%. Gas injection occurred for 20 days to represent a run. Two runs were performed during the summer of 1999 on different growth cells. Visual turf quality ratings, encompassing turf color, health, density, and uniformity, were evaluated every 4 days on a 1-9 scale, with 9 = best turf and <7 being unacceptable. Soil cores were taken at the end of each run. Roots were separated from soil to measure root depth and mass. Turf quality was reduced to unacceptable levels with 10% CO2, but was unaffected at lower levels over the 20-day treatment period. Soil CO2 ≥2.5% reduced root mass and depth by 40% and 10%, respectively.

CO2 efflux from a Mediterranean semi-arid forest soil. I. Seasonality and effects of stoniness

We studied the seasonality of total soil CO2efflux and labeled C-CO2 released from 14Clabeled straw incubated in the H horizon of asemi-arid Mediterranean forest soil. Fieldmeasurements were carried out over 520 days in aseries of reconstructed soil profiles with and withouta gravel layer below the H horizon. We monitored soilclimate and related this to soil CO2 efflux.Seasonal variations in soil CO2 efflux in asemiarid Mediterranean forest were mainly related tochanges in soil temperature. In spite of drought, highrespiration rates were observed in mid summer. Highsoil CO2 efflux in hot and dry episodes wasattributed to increases in soil biological activity.The minimum soil CO2 efflux occurred in latesummer also under dry conditions, probably related toa decrease in soil biological activity in deephorizons. Biological activity in organic layers waslimited by water potential (Ψ) in summer and bytemperature in winter. Rewetting a dry soil resultedin large increases in soil CO2 efflux only at hightemperatures. These large increases represented asignificant contribution to the decomposition oforganic matter in the uppermost horizons. Soilbiological activity in the uppermost horizons was moresensitive to changes in soil Ψ and hence tosummer rainstorms than the bulk soil microbialactivity. The presence of a layer of gravel improvedboth moisture and temperature conditions for thedecomposition of organic matter. As a result, soilCO2 efflux increased in soils containing rockfragments. These effects were especially large for theorganic layers.

EXAMINATION OF TREE AND ROOT PERFORMANCE ON CLOSED LANDFILLS IN MERSEYSIDE

Summary A study of the above ground and below ground growth of alder, willow and poplar on four poorly restored landfill sites in Merseyside has been carried out, in conjunction with measurements of physical site characteristics. Soil gas analysis identified the incidence of high methane (CH4) and carbon dioxide (CO2) and low oxygen (O2) concentrations in the root zone at some sites. Statistical analysis revealed that tree roots were inhibited by high soil bulk density. Height growth was also inhibited by soil compaction, and high soil CO2 and low oxygen concentrations. The results demonstrate that satisfactory woodland can only be achieved if adequate physical soil conditions are obtained. However, the study also shows that useful woodlands may develop without a detailed and expensive restoration prescription.

Geochemical investigations applied to active fault detection in a volcanic area: the North‐East Rift on Mt. Etna (Sicily, Italy)

Geochemical investigations were performed on the Northeast Rift of Mt. Etna, a prominent volcanic structure of this volcano. Low‐temperature fumaroles were found on the upper part of this area and the isotopic compositions of C(CO2) and He suggest a likely magmatic origin of the emitted gases. On the contrary, very low degassing was found in the lower part of the NE‐Rift, with CO2 concentrations generally very close to those in air. This pattern is probably due to sealing of the eruptive fissures by the repeated injections of magma solidified into dikes and by consequent shallow hydrothermal alteration of the fissured rocks due to residual magma degassing. High soil CO2 concentrations were also found in an elongated area parallel to the NE‐Rift and located immediately to the east of it. The geometry of these anomalies suggests the existence of several hidden faults, sub‐parallel to the NE‐Rift and likely connected to the Pernicana fault system. This latter structure seems to merge with the NE‐Rift at the altitude where the fumarole emissions are located. The hidden structures, together with the Pernicana system and the NE‐Rift, represent the western and northern boundaries of a large eastward collapsing sector of Mt. Etna.

Diffuse emission of carbon dioxide, methane, and helium‐3 from Teide Volcano, Tenerife, Canary Islands

Diffuse emission of CO2, CH4 and ³He was investigated in the summit crater of Teide volcano, Tenerife, Canary Islands. The results indicate that Teide volcano releases abundant CO2 not only from its active crater, but also from its flanks as diffuse soil emanations. The spatial distribution of these emanations correlates quite closely with that of geothermal anomalies and manifestations. Our flux measurements indicate a total output of 380 ton·day−1 of CO2 and 1.6 on·day−1 of CH4 by diffuse degassing. From the ³He/CO2 ratios and the CO2 flux we estimate a diffuse ³He flux of 0.052 mol·year−1. Isotopic analysis of carbon in soil gas samples from sites of high soil CO2 flux indicates a magmatic origin for the CO2, also reported by high ³He/ 4He ratios of 5.50 and 5.87 Ra. The origin of methane is more uncertain with low δ13C values suggesting a biogenic contribution.

Land-use effects on soil methane and carbon dioxide fluxes in forests near Ithaca, New York

:Consumption of atmospheric methane (CH4) and fluxes of carbon dioxide (CO2) were higher for soil in (i) mixed hardwood forest on historically unplowed land than in (ii) 80-year-old mixed hardwood forest and (iii) 80-year-old conifer plantations both established on post-agricultural land, whereas flux rates were lowest in (iv) adjoining agriculture sites, showing that past and present land-use in forest ecosystems affects fluxes of atmospheric CH4 and CO2. Site differences in CH4 fluxes were more pronounced in drier 1993 and 1995 than in wetter 1994, whereas site differences in CO2 fluxes disappeared during winter and during pronounced drought in summer 1995. Seasonal variation in CH4 fluxes in forest sites were related to soil moisture but not CH4 concentrations in soil air. Notably, all four sites occasionally exhibited CH4 efflux to the atmosphere, and studies confirmed the presence of anaerobic CH4-producing microorganisms (methanogens) in the soil, despite well-drained conditions. Seasonal variation in CO2 fluxes in forest sites were related to soil temperature and CO2 concentrations in soil air, but not in the agricultural site that maintained somewhat higher soil CO2 levels. Future studies of soil CH4 and CO2 dynamics should recognize the persistent effects of historical (and recent) changes in land use.

Influence of soil O2 and CO2 on root respiration for Agave deserti

Respiration measured as CO2 efflux was determined at various soil O2 and CO2 concentrations for individual, attached roots of a succulent perennial from the Sonoran Desert, Agave deserti Engelm. The respiration rate increased with increasing O2 concentration up to about 16% O2 for established roots and 5% O2 for rain roots (fine branch roots on established roots induced by wetting of the soil) and then remained fairly constant up to 21% O2. When O2 was decreased from 21 to 0%, the respiration rates were similar to those obtained with increasing O2 concentration. The CO2 concentration in the root zone, which for the shallow‐rooted A. deserti in the field was about 1 000 μl l‐1, did not affect root respiration at concentrations up to 2 000 μl l‐1, but higher concentrations reduced it, respiration being abolished at 20 000 μl l‐1 (2%) CO2 for both established and rain roots. Upon lowering CO2 to 1 000 μl l‐1 after exposure to concentrations up to 10000 μl l‐1 CO2, inhibition of respiration was reversible. Uptake of the vital stain neutral red by root cortical cells was reduced to zero, indicating cell death, in about 4 h at 2% CO2, substantiating the detrimental effects of high soil CO2 concentrations on roots of A. deserti. This CO2 response may explain why roots of desert succulents tend to occur in porous, well‐aerated soils.

Soil carbon dioxide and mineral accumulation in citrus seedlings (Citrus sinensis var. Bessie)

This experiment was conducted in a greenhouse to study the influence of soil CO2 differential treatments on plant response, concentrations of nutrients in soils and plants, and total nutrients per plant (Citrus sinensis var. Bessie). Higher levels of soil CO2, applied to the roots, significantly increased the amount of dry weight per seedling, the height of seedling, and decreased the concentrations of N, P, Ca, Mg, and Mn in the tops. The dry weight of roots supplied with high soil CO2 was decreased, while the concentrations of Mg and Mn were increased. Concentrations of N, P, K, and B in the roots were also reduced due to high level of soil CO2. Only total K and Mg per plant were increased with an increased soil CO2 supply. No significant interactions were found between the soil CO2 treatments and years of experiment.