Effects of potassium carbonate as an alternative de-icer on ground vegetation and soil

The effects of the new de‐icer potassium carbonate on the growth and species composition of a mixed sward and on the pH and electrical conductivity of the soil were examined in a four‐year field trial and compared with sodium chloride. There were small positive effects of K₂CO₃ on the biomass yield of the sward at application rates up to 200 g m^?2 yr^?1, while effects were less negative than those of NaCl at annual application rates of 200 – 400 g m^?2 yr^?1. The species composition of the sward changed considerably with K₂CO₃ application, Agropyron repens becoming the dominant species. The pH was elevated slightly more by K₂CO₃ than by NaCl application. Electrical conductivity as an index of soil salinity was increased by both de‐icers. K₂CO₃ was more adsorbed to soil colloids than NaCl, so that the rise in E.C. resulting from application of the former was restricted to the uppermost 10 cm of soil.     

Seasonal soil‐surface carbon fluxes from the root systems of young Pinus radiata trees growing at ambient and elevated CO2 concentration

Elevated atmospheric CO₂ concentration may result in increased below‐ground carbon allocation by trees, thereby altering soil carbon cycling. Seasonal estimates of soil surface carbon flux were made to determine whether carbon losses from Pinus radiata trees growing at elevated CO₂ concentration were higher than those at ambient CO₂ concentration, and whether this was related to increased fine root growth. Monthly soil surface carbon flux density (f) measurements were made on plots with trees growing at ambient (350) and elevated (650 μmol mol^?1) CO₂ concentration in large open‐top chambers. Prior to planting the soil carbon concentration (0.1%) and f (0.28 μmol m^?2 s^?1 at 15 °C) were low. A function describing the radial pattern of f with distance from tree stems was used to estimate the annual carbon flux from tree plots. Seasonal estimates of fine root production were made from minirhizotrons and the radial distribution of roots compared with radial measurements of f. A one‐dimensional gas diffusion model was used to estimate f from soil CO₂ concentrations at four depths. For the second year of growth, the annual carbon flux from the plots was 1671 g y^?1 and 1895 g y^?1 at ambient and elevated CO₂ concentrations, respectively, although this was not a significant difference. Higher f at elevated CO₂ concentration was largely explained by increased fine root biomass. Fine root biomass and stem production were both positively related to f. Both root length density and f declined exponentially with distance from the stem, and had similar length scales. Diurnal changes in f were largely explained by changes in soil temperature at a depth of 0.05 m. Ignoring the change of f with increasing distance from tree stems when scaling to a unit ground area basis from measurements with individual trees could result in under‐ or overestimates of soil‐surface carbon fluxes, especially in young stands when fine roots are unevenly distributed.     

Acclimation of leaf hydraulic conductance and stomatal conductance of Pinus taeda (loblolly pine) to long-term growth in elevated CO2 (free-air CO2 enrichment) and N-fertilization

We investigated how leaf hydraulic conductance (K_leaf) of loblolly pine trees is influenced by soil nitrogen amendment (N) in stands subjected to ambient or elevated CO₂ concentrations (CO₂^a and CO₂^e, respectively). We also examined how K_leaf varies with changes in reference leaf water potential (Ψ_leaf‐ref) and stomatal conductance (g_s‐ref) calculated at vapour pressure deficit, D of 1 kPa. We detected significant reductions in K_leaf caused by N and CO₂^e, but neither treatment affected pre‐dawn or midday Ψ_leaf. We also detected a significant CO₂^e‐induced reduction in g_s‐ref and Ψ_leaf‐ref. Among treatments, the sensitivity of K_leaf to Ψ_leaf was directly related to a reference K_leaf (K_leaf‐ref computed at Ψ_leaf‐ref). This liquid‐phase response was reflected in a similar gas‐phase response, with g_s sensitivity to D proportional to g_s‐ref. Because leaves represented a substantial component of the whole‐tree conductance, reduction in K_leaf under CO₂^e affected whole‐tree water use by inducing a decline in g_s‐ref. The consequences of the acclimation of leaves to the treatments were: (1) trees growing under CO₂^e controlled morning leaf water status less than CO₂^a trees resulting in a higher diurnal loss of K_leaf; (2) the effect of CO₂^e on g_s‐ref was manifested only during times of high soil moisture.     

In vitro Growth and Shoot Multiplication of Achras zapota in a Controlled Carbon Dioxide Environment

The culture vessels with multiplying shoots of Achras zapota L. on Schenk and Hildebrandt (SH) medium containing 8.88 M 6-benzylaminopurine (BAP) with or without sucrose were kept under varied CO₂ concentrations ranging from 0.6 to 40.0 g m^–3 using different concentrations of sodium bicarbonate (NaHCO₃), sodium carbonate (Na₂CO₃), potassium bicarbonate (KHCO₃), and potassium carbonate (K₂CO₃) in small acrylic chambers. Complete absence of carbon source caused death of shoots within 20 d. Under elevated concentrations of CO₂ (10.0 and 40.0 g m^–3) the shoots grew photoautotrophically on sucrose-free medium. The growth of cultures was better at 40.0 g (CO₂) m^–3 than on 3.0 % sucrose under ambient air of growth room. However, the best response was obtained at 10.0 g (CO₂) m^–3 and 3.0 % sucrose where maximum number of shoots, shoot length, fresh and dry mass, total number of leaves and leaf area was observed.     

Interannual variability in global soil respiration, 1980–94

We used a climate‐driven regression model to develop spatially resolved estimates of soil‐CO₂ emissions from the terrestrial land surface for each month from January 1980 to December 1994, to evaluate the effects of interannual variations in climate on global soil‐to‐atmosphere CO₂ fluxes. The mean annual global soil‐CO₂ flux over this 15‐y period was estimated to be 80.4 (range 79.3–81.8) Pg C. Monthly variations in global soil‐CO₂ emissions followed closely the mean temperature cycle of the Northern Hemisphere. Globally, soil‐CO₂ emissions reached their minima in February and peaked in July and August. Tropical and subtropical evergreen broad‐leaved forests contributed more soil‐derived CO₂ to the atmosphere than did any other vegetation type (～30% of the total) and exhibited a biannual cycle in their emissions. Soil‐CO₂ emissions in other biomes exhibited a single annual cycle that paralleled the seasonal temperature cycle. Interannual variability in estimated global soil‐CO₂ production is substantially less than is variability in net carbon uptake by plants (i.e., net primary productivity). Thus, soils appear to buffer atmospheric CO₂ concentrations against far more dramatic seasonal and interannual differences in plant growth. Within seasonally dry biomes (savannas, bushlands and deserts), interannual variability in soil‐CO₂ emissions correlated significantly with interannual differences in precipitation. At the global scale, however, annual soil‐CO₂ fluxes correlated with mean annual temperature, with a slope of 3.3 Pg C y^?1 per °C. Although the distribution of precipitation influences seasonal and spatial patterns of soil‐CO₂ emissions, global warming is likely to stimulate CO₂ emissions from soils.     

Fine root dynamics in a loblolly pine forest are influenced by free-air-CO2-enrichment: a six-year-minirhizotron study

Efforts to characterize carbon (C) cycling among atmosphere, forest canopy, and soil C pools are hindered by poorly quantified fine root dynamics. We characterized the influence of free‐air‐CO₂‐enrichment (ambient +200 ppm) on fine roots for a period of 6 years (Autumn 1998 through Autumn 2004) in an 18‐year‐old loblolly pine (Pinus taeda) plantation near Durham, NC, USA using minirhizotrons. Root production and mortality were synchronous processes that peaked most years during spring and early summer. Seasonality of fine root production and mortality was not influenced by atmospheric CO₂ availability. Averaged over all 6 years of the study, CO₂ enrichment increased average fine root standing crop (+23%), annual root length production (+25%), and annual root length mortality (+36%). Larger increase in mortality compared with production with CO₂ enrichment is explained by shorter average fine root lifespans in elevated plots (500 days) compared with controls (574 days). The effects of CO₂‐enrichment on fine root proliferation tended to shift from shallow (0–15 cm) to deeper soil depths (15–30) with increasing duration of the study. Diameters of fine roots were initially increased by CO₂‐enrichment but this effect diminished over time. Averaged over 6 years, annual fine root NPP was estimated to be 163 g dw m^?2 yr^?1 in CO₂‐enriched plots and 130 g dw m^?2 yr^?1 in control plots (P= 0.13) corresponding to an average annual additional input of fine root biomass to soil of 33 g m^?2 yr^?1 in CO₂‐enriched plots. A lack of consistent CO₂× year effects suggest that the positive effects of CO₂ enrichment on fine root growth persisted 6 years following minirhizotron tube installation (8 years following initiation of the CO₂ fumigation). Although CO₂‐enrichment contributed to extra flow of C into soil in this experiment, the magnitude of the effect was small suggesting only modest potential for fine root processes to directly contribute to soil C storage in south‐eastern pine forests.     

The contribution of bryophytes to the carbon exchange for a temperate rainforest

Bryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp‐broadleaved forest in New Zealand, dominated by 100–400‐year‐old rimu (Dacrydium cupressimum) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth <30 mm), but dense, canopy that experienced elevated CO₂ partial pressures (median 46.6 Pa immediately below the bryophyte canopy) relative to the surrounding air (median 37.6 Pa at 100 mm above the canopy). Light‐saturated rates of net CO₂ exchange from 14 microcosms collected from the forest floor were highly variable; the maximum rate of net uptake (bryophyte photosynthesis – whole‐plant respiration) per unit ground area at saturating irradiance was 1.9 μmol m^?2 s^?1 and in one microcosm, the net rate of CO₂ exchange was negative (respiration). CO₂ exchange for all microcosms was strongly dependent on water content. The average water content in the microcosms ranged from 1375% when fully saturated to 250% when air‐dried. Reduction in water content across this range resulted in an average decrease of 85% in net CO₂ uptake per unit ground area. The results from the microcosms were used in a model to estimate annual carbon exchange for the forest floor. This model incorporated hourly variability in average irradiance reaching the forest floor, water content of the bryophyte layer, and air and soil temperature. The annual net carbon uptake by forest floor bryophytes was 103 g m^?2, compared to annual carbon efflux from the forest floor (bryophyte and soil respiration) of ?1010 g m^?2. To put this in perspective of the magnitude of the components of CO₂ exchange for the forest floor, the bryophyte layer reclaimed an amount of CO₂ equivalent to only about 10% of forest floor respiration (bryophyte plus soil) or ～11% of soil respiration. The contribution of forest floor bryophytes to productivity in this temperate rainforest was much smaller than in boreal forests, possibly because of differences in species composition and environmental limitations to photosynthesis. Because of their close dependence on water table depth, the contribution of the bryophyte community to ecosystem CO₂ exchange may be highly responsive to rapid changes in climate.     

钾肥及与秸秆配施对紫色土作物产量和微生物群落结构的影响

基于紫色菜园土壤莴笋-白菜-甜玉米轮作4年12季连续定位施钾肥试验,研究不同种类钾肥及用量对重庆地区紫色菜园土上作物产量和土壤微生物群落结构的影响,为该地区作物生产确定合理的施钾技术提供科学依据。结果表明,在施用氮磷肥基础上,不同钾肥处理莴笋、白菜、甜玉米产量均显著提高;从3种作物4年平均产量和钾肥效益看,以单施适量化学钾(K_2)、单施适量秸秆钾(M_2)和秸秆还田配施少量化学钾(K_1+M_1)的施钾肥模式对白菜的增产效果好,增产28.05%—30.27%;M_2和K_1+M_1施钾肥模式对莴笋的增产效果较好,增产13.89%和13.81%;K_1+M_1施钾肥模式对甜玉米的增产效果最好,增产15.10%,表明秸秆还田配施少量化学钾(K_1+M_1)模式在供试3种作物生产中具有很好的应用前景。不同施钾处理对土壤微生物群落结构及丰度均会产生一定影响,以秸秆还田配施少量化学钾肥(K_1+M_1)对提高土壤细菌、真菌、革兰氏阳性菌的作用较好,并显著增加土壤微生物总PLFA含量,缓解对土壤微生物生存环境的胁迫,说明K_1+M_1能为土壤微生物的生长繁育创造有利环境。莴笋、白菜、甜玉米3种作物4年平均产量与土壤细菌、真菌、革兰氏阳性菌和革兰氏阴性菌数量间存在显著相关性(P0.05),而不同钾肥处理对土壤微生物特征具有一定影响,说明施钾肥可能会调节土壤微生物特征,从而促进作物增产。     

Sources of increased N uptake in forest trees growing under elevated CO2: results of a large‐scale 15N study

Nitrogen availability in terrestrial ecosystems strongly influences plant productivity and nutrient cycling in response to increasing atmospheric carbon dioxide (CO₂). Elevated CO₂ has consistently stimulated forest productivity at the Duke Forest free‐air CO₂ enrichment experiment throughout the decade‐long experiment. It remains unclear how the N cycle has changed with elevated CO₂ to support this increased productivity. Using natural‐abundance measures of N isotopes together with an ecosystem‐scale ¹⁵N tracer experiment, we quantified the cycling of ¹⁵N in plant and soil pools under ambient and elevated CO₂ over three growing seasons to determine how elevated CO₂ changed N cycling between plants, soil, and microorganisms. After measuring natural‐abundance ¹⁵N differences in ambient and CO₂‐fumigated plots, we applied inorganic ¹⁵N tracers and quantified the redistribution of ¹⁵N for three subsequent growing seasons. The natural abundance of leaf litter was enriched under elevated compared to ambient CO₂, consistent with deeper rooting and enhanced N mineralization. After tracer application, ¹⁵N was initially retained in the organic and mineral soil horizons. Recovery of ¹⁵N in plant biomass was 3.5 ± 0.5% in the canopy, 1.7 ± 0.2% in roots and 1.7 ± 0.2% in branches. After two growing seasons, ¹⁵N recoveries in biomass and soil pools were not significantly different between CO₂ treatments, despite greater total N uptake under elevated CO₂. After the third growing season, ¹⁵N recovery in trees was significantly higher in elevated compared to ambient CO₂. Natural‐abundance ¹⁵N and tracer results, taken together, suggest that trees growing under elevated CO₂ acquired additional soil N resources to support increased plant growth. Our study provides an integrated understanding of elevated CO₂ effects on N cycling in the Duke Forest and provides a basis for inferring how C and N cycling in this forest may respond to elevated CO₂ beyond the decadal time scale.     

The timber and energy biomass potential of intensively managed cloned Norway spruce stands

We used ecosystem model simulations to study the timber and energy biomass potential offered by intensively managed cloned Norway spruce stands. More specifically, we analysed how the use of cloned trees compared with non‐cloned trees, together with thinning, nitrogen (N) fertilisation and rotation length (from 60 to 100 years), affects the annual mean production of timber (i.e., saw logs, pulpwood) and energy biomass (i.e., stumps and harvesting residuals in the final felling) and its economic profitability [annual mean of net present value (NPV) with a 2% interest rate]. Furthermore, we employed a life cycle analysis/emission calculation tool to assess the total net CO₂ emissions per unit of energy (kg CO₂ MW h^?1) produced based on energy biomass. We found that both the annual mean production of timber and the NPV increased substantially, regardless of the management regime, if cloned trees with an annual growth increase of up to 30% compared with non‐cloned trees were used in regeneration. In general, the use of a short rotation with N fertilisation clearly increased the annual mean of the NPV. Consequently, the use of cloned trees also clearly increased the annual mean production of energy biomass and decreased the total net CO₂ emissions per unit of energy produced based on energy biomass. However, the total annual net CO₂ emissions were the lowest if a long rotation was used with N fertilisation. To conclude, the use of cloned trees together with intensive management could potentially be highly beneficial for the cost‐efficient and sustainable production of timber and energy biomass in an integrated way.     

Characterization of crystalline structures in Opuntia ficus-indica

This research studies the crystalline compounds present in nopal (Opuntia ficus-indica) cladodes. The identification of the crystalline structures was performed using X-ray diffraction, scanning electron microscopy, mass spectrometry, and Fourier transform infrared spectroscopy. The crystalline structures identified were calcium carbonate (calcite) [CaCO₃], calcium-magnesium bicarbonate [CaMg(CO₃)₂], magnesium oxide [MgO], calcium oxalate monohydrate [Ca(C₂O₄)•(H₂O)], potassium peroxydiphosphate [K₄P₂O₈] and potassium chloride [KCl]. The SEM images indicate that calcite crystals grow to dipyramidal, octahedral-like, prismatic, and flower-like structures; meanwhile, calcium-magnesium bicarbonate structures show rhombohedral exfoliation and calcium oxalate monohydrate is present in a drusenoid morphology. These calcium carbonate compounds have a great importance for humans because their bioavailability. This is the first report about the identification and structural analysis of calcium carbonate and calcium-magnesium bicarbonate in nopal cladodes, as well as the presence of magnesium oxide, potassium peroxydiphosphate and potassium chloride in these plants. The significance of the study of the inorganic components of these cactus plants is related with the increasing interest in the potential use of Opuntia as a raw material of products for the food, pharmaceutical, and cosmetic industries.     

Soil CO2 efflux in contrasting boreal deciduous and coniferous stands and its contribution to the ecosystem carbon balance

Similar nonsteady‐state automated chamber systems were used to measure and partition soil CO₂ efflux in contrasting deciduous (trembling aspen) and coniferous (black spruce and jack pine) stands located within 100 km of each other near the southern edge of the Boreal forest in Canada. The stands were exposed to similar climate forcing in 2003, including marked seasonal variations in soil water availability, which provided a unique opportunity to investigate the influence of climate and stand characteristics on soil CO₂ efflux and to quantify its contribution to the net ecosystem CO₂ exchange (NEE) as measured with the eddy‐covariance technique. Partitioning of soil CO₂ efflux between soil respiration (including forest‐floor vegetation) and forest‐floor photosynthesis showed that short‐ and long‐term temporal variations of soil CO₂ efflux were related to the influence of (1) soil temperature and water content on soil respiration and (2) below‐canopy light availability, plant water status and forest‐floor plant species composition on forest‐floor photosynthesis. Overall, the three stands were weak to moderate sinks for CO₂ in 2003 (NEE of ?103, ?80 and ?28 g C m^?2 yr^?1 for aspen, black spruce and jack pine, respectively). Forest‐floor respiration accounted for 86%, 73% and 75% of annual ecosystem respiration, in the three respective stands, while forest‐floor photosynthesis contributed to 11% and 14% of annual gross ecosystem photosynthesis in the black spruce and jack pine stands, respectively. The results emphasize the need to perform concomitant measurements of NEE and soil CO₂ efflux at longer time scales in different ecosystems in order to better understand the impacts of future interannual climate variability and vegetation dynamics associated with climate change on each component of the carbon balance.     

Effect of elevated [CO2] on stem wood properties of mature Norway spruce grown at different soil nutrient availability

The objective of the present study was to investigate the interactive effects of elevated [CO₂] and soil nutrient availability on secondary xylem structure and chemical composition of 41‐year‐old Norway spruce (Picea abies (L.) Karst.) trees. The nonfertilized and irrigated‐fertilized trees were, for 3 years, continuously exposed to elevated [CO₂] in whole‐tree chambers. Elevated [CO₂] decreased concentrations of soluble sugars, acid‐soluble lignin and nitrogen in stem wood, but the effects were not consistent between sampling height and/or fertilization. The effect of 2*ambient [CO₂] on wood structure depended on the exposure year and/or fertilization. Radial lumen diameter decreased and annual ring width increased in the second year of exposure (1999) in elevated [CO₂]. In the latter, the CO₂ effect was significant only in the nonfertilized trees. Stem wood chemistry and structure were significantly affected by fertilization. Fertilization increased the concentrations of nitrogen and gravimetric lignin, annual ring width, and radial lumen diameter. Fertilization decreased C/N ratio, mean ring density, earlywood density, latewood density, cell wall thickness, cell wall index, and latewood percentage. We conclude that elevated [CO₂] had only minor effects on wood properties while fertilization had more marked effects and thus may affect ecosystem processes and suitability of wood for different end‐use purposes.     

Nitrogen fertilization raises CO2 efflux from inorganic carbon: A global assessment

Nitrogen (N) fertilization is an indispensable agricultural practice worldwide, serving the survival of half of the global population. Nitrogen transformation (e.g., nitrification) in soil as well as plant N uptake releases protons and increases soil acidification. Neutralizing this acidity in carbonate‐containing soils (7.49 × 10⁹ ha; ca. 54% of the global land surface area) leads to a CO₂ release corresponding to 0.21 kg C per kg of applied N. We here for the first time raise this problem of acidification of carbonate‐containing soils and assess the global CO₂ release from pedogenic and geogenic carbonates in the upper 1 m soil depth. Based on a global N‐fertilization map and the distribution of soils containing CaCO₃, we calculated the CO₂ amount released annually from the acidification of such soils to be 7.48 × 10¹² g C/year. This level of continuous CO₂ release will remain constant at least until soils are fertilized by N. Moreover, we estimated that about 273 × 10¹² g CO₂‐C are released annually in the same process of CaCO₃ neutralization but involving liming of acid soils. These two CO₂ sources correspond to 3% of global CO₂ emissions by fossil fuel combustion or 30% of CO₂ by land‐use changes. Importantly, the duration of CO₂ release after land‐use changes usually lasts only 1–3 decades before a new C equilibrium is reached in soil. In contrast, the CO₂ released by CaCO₃ acidification cannot reach equilibrium, as long as N fertilizer is applied until it becomes completely neutralized. As the CaCO₃ amounts in soils, if present, are nearly unlimited, their complete dissolution and CO₂ release will take centuries or even millennia. This emphasizes the necessity of preventing soil acidification in N‐fertilized soils as an effective strategy to inhibit millennia of CO₂ efflux to the atmosphere. Hence, N fertilization should be strictly calculated based on plant‐demand, and overfertilization should be avoided not only because N is a source of local and regional eutrophication, but also because of the continuous CO₂ release by global acidification.     

Soil‐surface CO2 efflux and its spatial and temporal variations in a young ponderosa pine plantation in northern California

Soil‐surface CO₂ efflux and its spatial and temporal variations were examined in an 8‐y‐old ponderosa pine plantation in the Sierra Nevada Mountains in California from June 1998 to August 1999. Continuous measurements of soil CO₂ efflux, soil temperatures and moisture were conducted on two 20 × 20 m sampling plots. Microbial biomass, fine root biomass, and the physical and chemical properties of the soil were also measured at each of the 18 sampling locations on the plots. It was found that the mean soil CO₂ efflux in the plantation was 4.43 µmol m^?2 s^?1 in the growing season and 3.12 µmol m^?2 s^?1 in the nongrowing season. These values are in the upper part of the range of published soil‐surface CO₂ efflux data. The annual maximum and minimum CO₂ efflux were 5.87 and 1.67 µmol m^?2 s^?1, respectively, with the maximum occurring between the end of May and early June and the minimum in December. The diurnal fluctuation of CO₂ efflux was relatively small (< 20%) with the minimum appearing around 09.00 hours and the maximum around 14.00 hours. Using daytime measurements of soil CO₂ efflux tends to overestimate the daily mean soil CO₂ efflux by 4–6%. The measurements taken between 09.00 and 11.00 hours (local time) seem to better represent the daily mean with a reduced sampling error of 0.9–1.5%. The spatial variation of soil CO₂ efflux among the 18 sampling points was high, with a coefficient of variation of approximately 30%. Most (84%) of the spatial variation was explained by fine root biomass, microbial biomass, and soil physical and chemical properties. Although soil temperature and moisture explained most of the temporal variations (76–95%) of soil CO₂ efflux, the two variables together explained less than 34% of the spatial variation. Microbial biomass, fine root biomass, soil nitrogen content, organic matter content, and magnesium content were significantly and positively correlated with soil CO₂ efflux, whereas bulk density and pH value were negatively correlated with CO₂ efflux. The relationship between soil CO₂ efflux and soil temperature was significantly controlled by soil moisture with a Q₁₀ value of 1.4 when soil moisture was <14% and 1.8 when soil moisture was >14%. Understanding the spatial and temporal variations is essential to accurately assessment of carbon budget at whole ecosystem and landscape scales. Thus, this study bears important implications for the study of large‐scale ecosystem dynamics, particularly in response to climatic variations and management regimes.     

Seasonal patterns of soil CO2 efflux and soil air CO2 concentration in a Scots pine forest: comparison of two chamber techniques

A non‐vented non‐steady state flow‐through chamber and a non‐vented non‐steady state non‐flow‐through chamber technique were used to measure CO₂ efflux of a young Scots pine forest on a fertile till soil in southern Finland. Soil temperature, soil moisture and soil CO₂ concentration were measured concurrently with CO₂ efflux for two and a half successive years. The CO₂ efflux showed a seasonal pattern, effluxes ranging from low 0.0–0.1 g CO₂ m ^{? 2} h ^{? 1} in winter to peak values of 2.3 g CO₂ m ^{? 2} h ^{? 1} occurring in late June and in July. The daily average effluxes in July measured by flow through chambers were 1.23 and 0.98 g CO₂ m ^{? 2} h ^{? 1} in 1998 and 1999, respectively. The annual accumulated CO₂ efflux was 3117 and 3326 g CO₂ m ^{? 2} in 1998 and 1999, respectively. The spatial variation in CO₂ efflux was high (CV 0.18–0.45) and increased with increasing efflux. Soil air CO₂ concentration showed similar seasonal pattern the peak concentrations occurring in July–August. The CO₂ concentrations ranged from 580 to 780 µ mol mol ^{? 1} in the humus layer to 13 620–14 470 µ mol mol ^{? 1} in the C‐horizon. In winter the soil air CO₂ concentrations were lower, especially in deeper soil layers. Drought decreased CO₂ efflux and soil air CO₂ concentration. The in situ comparison on forest soil between the chamber methods showed the non‐flow‐through chamber to give ～～50% lower efflux values than that of the flow‐through chamber. When calibrated against known CO₂ efflux ranging from 0.4 to 0.8 g CO₂ m ^{? 2} h ^{? 1} generated with a diffusion box method developed by Widén and Lindroth [Acta Universitatis Agriculturae Suecia Silvestria, 2001], the flow‐through chamber gave equal effluxes at the lower end of the calibration range, but overestimated high effluxes by 20%. Non‐flow‐through chamber underestimated the CO₂ efflux by 30%.     

Growth and mineral content of coriander (<Emphasis Type="Italic">Coriandrum sativum</Emphasis> L.) plants under mild salinity with different salts

Soil salinity is a complex issue in which various anions and cations contribute to have a general adverse effect on plant growth. In the present study, effects of salinity from various salts including sodium chloride (NaCl), potassium chloride?+?sodium chloride?+?calcium chloride (KCl?+?NaCl?+?CaCl₂), potassium sulfate?+?magnesium nitrate (K₂SO₄?+?Mg(NO₃)₂) at two electric conductivities (EC) of 2 and 4 dS m^?1 of irrigation water, and a distilled water control were evaluated on coriander plants (Coriandrum sativum L.). At EC?=?2, all salts increased plant yield (shoot fresh weight) than control. Most growth traits including plant height, shoot fresh and dry weight, leaf SPAD value and vitamin C, leaf K, Mg and P concentrations were increased by K₂SO₄?+?MgNO₃, and remained unchanged by KCl?+?NaCl?+?CaCl₂ treatment (except reduced plant height). Leaf’s zinc concentration reduced by either treatment. Even sodium chloride at EC?=?2 showed some beneficial effects on leaf chlorophyll index, root fresh weight, leaf’s calcium and phosphorus concentration; however, most traits remained unchanged than control. Treatment of plants with NaCl or KCl?+?NaCl?+?CaCl₂ at either EC increased the number of flowered shoots and leaf proline content than control. Most growth and quality traits including leaf minerals and vitamin C content were reduced by NaCl at EC?=?4; however, shoot fresh and dry weights remained unchanged than control. Plant root fresh weight increased by NaCl at EC?=?2 and decreased at EC?=?4 than control. At EC?=?4, shoot dry weight was increased and leaf Ca, P, Zn and Mn were decreased by KCl?+?NaCl?+?CaCl₂, whereas shoot dry weight, leaf SPAD value and vitamin C content, leaf Mg and P were increased and leaf Zn was decreased by K₂SO₄?+?MgNO₃ than control. The results indicate that in contrast to sodium chloride, the salinity effects of other salts can not be detrimental on coriander plant growth.     

Soil CO2 efflux of two silver birch clones exposed to elevated CO2 and O3 levels during three growing seasons

In the present open‐top chamber experiment, two silver birch clones (Betula pendula Roth, clone 4 and clone 80) were exposed to elevated levels of carbon dioxide (CO₂) and ozone (O₃), singly and in combination, and soil CO₂ efflux was measured 14 times during three consecutive growing seasons (1999–2001). In the beginning of the experiment, all experimental trees were 7 years old and during the experiment the trees were growing in sandy field soil and fertilized regularly. In general, elevated O₃ caused soil CO₂ efflux stimulation during most measurement days and this stimulation enhanced towards the end of the experiment. The overall soil respiration response to CO₂ was dependent on the genotype, as the soil CO₂ efflux below clone 80 trees was enhanced and below clone 4 trees was decreased under elevated CO₂ treatments. Like the O₃ impact, this clonal difference in soil respiration response to CO₂ increased as the experiment progressed. Although the O₃ impact did not differ significantly between clones, a significant time × clone × CO₂× O₃ interaction revealed that the O₃‐induced stimulation of soil respiration was counteracted by elevated CO₂ in clone 4 on most measurement days, whereas in clone 80, the effect of elevated CO₂ and O₃ in combination was almost constantly additive during the 3‐year experiment. Altogether, the root or above‐ground biomass results were only partly parallel with the observed soil CO₂ efflux responses. In conclusion, our data show that O₃ impacts may appear first in the below‐ground processes and that relatively long‐term O₃ exposure had a cumulative effect on soil CO₂ efflux. Although the soil respiration response to elevated CO₂ depended on the tree genotype as a result of which the O₃ stress response might vary considerably within a single tree species under elevated CO₂, the present experiment nonetheless indicates that O₃ stress is a significant factor affecting the carbon cycling in northern forest ecosystems.     

Carbon exchange of grazed pasture on a drained peat soil

Land‐use changes have contributed to increased atmospheric CO₂ concentrations. Conversion from natural peatlands to agricultural land has led to widespread subsidence of the peat surface caused by soil compaction and mineralization. To study the net ecosystem exchange of carbon (C) and the contribution of respiration to peat subsidence, eddy covariance measurements were made over pasture on a well‐developed, drained peat soil from 22 May 2002 to 21 May 2003. The depth to the water table fluctuated between 0.02 m in winter 2002 to 0.75 m during late summer and early autumn 2003. Peat soil moisture content varied between 0.6 and 0.7 m³ m^?3 until the water table dropped below 0.5 m, when moisture content reached 0.38 m³ m^?3. Neither depth to water table nor soil moisture was found to have an effect on the rate of night‐time respiration (ranging from 0.4–8.0 μmol CO₂ m^?2 s^?1 in winter and summer, respectively). Most of the variance in night‐time respiration was explained by changes in the 0.1 m soil temperature (r²=0.93). The highest values for daytime net ecosystem exchange were measured in September 2002, with a maximum of ?17.2 μmol CO₂ m^?2 s^?1. Grazing events and soil moisture deficiencies during a short period in summer reduced net CO₂ exchange. To establish an annual C balance for this ecosystem, non‐linear regression was used to model missing data. Annually integrated (CO₂) C exchange for this peat–pasture ecosystem was 45±500 kg C ha^?1 yr^?1. After including other C exchanges (methane emissions from cows and production of milk), the net annual C loss was 1061±500 kg C ha^?1 yr^?1.     

Greenhouse gas fluxes from an Australian subtropical cropland under long‐term contrasting management regimes

The long‐term effects of conservation management practices on greenhouse gas fluxes from tropical/subtropical croplands remain to be uncertain. Using both manual and automatic sampling chambers, we measured N₂O and CH₄ fluxes at a long‐term experimental site (1968–present) in Queensland, Australia from 2006 to 2009. Annual net greenhouse gas fluxes (NGGF) were calculated from the 3‐year mean N₂O and CH₄ fluxes and the long‐term soil organic carbon changes. N₂O emissions exhibited clear daily, seasonal and interannual variations, highlighting the importance of whole‐year measurement over multiple years for obtaining temporally representative annual emissions. Averaged over 3 years, annual N₂O emissions from the unfertilized and fertilized soils (90 kg N ha^?1 yr^?1 as urea) amounted to 138 and 902 g N ha^?1, respectively. The average annual N₂O emissions from the fertilized soil were 388 g N ha^?1 lower under no‐till (NT) than under conventional tillage (CT) and 259 g N ha^?1 higher under stubble retention (SR) than under stubble burning (SB). Annual N₂O emissions from the unfertilized soil were similar between the contrasting tillage and stubble management practices. The average emission factors of fertilizer N were 0.91%, 1.20%, 0.52% and 0.77% for the CT‐SB, CT‐SR, NT‐SB and NT‐SR treatments, respectively. Annual CH₄ fluxes from the soil were very small (?200–300 g CH₄ ha^?1 yr^?1) with no significant difference between treatments. The NGGF were 277–350 kg CO₂‐e ha^?1 yr^?1 for the unfertilized treatments and 401–710 kg CO₂‐e ha^?1 yr^?1 for the fertilized treatments. Among the fertilized treatments, N₂O emissions accounted for 52–97% of NGGF and NT‐SR resulted in the lowest NGGF (401 kg CO₂‐e ha^?1 yr^?1 or 140 kg CO₂‐e t^?1 grain). Therefore, NT‐SR with improved N fertilizer management practices was considered the most promising management regime for simultaneously achieving maximal yield and minimal NGGF.