CO2 Exchange Rate Research Articles

Physical and chemical mutagenesis in Stevia rebaudiana: variant generation with higher UGT expression and glycosidic profile but with low photosynthetic capabilities

The leaf explants of Stevia rebaudiana were exposed to a range of EMS (chemical mutagen) and gamma radiation (physical mutagen) doses. Among all the treatments, doses of 0.4 % v/v EMS and 0.95 KR gamma radiation were found to be most effective treatment for selection of variants via direct shoot bud induction. The field-established plants designated as EMS (E), gamma (G), and control (C) plants were subjected to photosynthetic parameter studies where E and G plants showed lower chlorophyll content, transpiration rate, CO2 exchange rate, and stomatal conductance. The implanted field soil at the time of harvesting of plants showed reduction in organic carbon (OC), electrical conductivity (EC), phosphorus (P)/potassium (K), and total Kjeldahl nitrogen (TKN). The ISSR profiling of E, G, and C scored total of 107 bands out of which 63 % were polymorphic bands, and plant E was found to be more distant from the C plant phylogenetically. On phytochemical analysis, the G plant registered twofold enhanced rebaudioside A with lower stevioside (3.2 ± 0.22 % dry wt.) content, whereas E plant showed more than 1.5- and 2.0-fold increase in stevioside and rebaudioside A as compared to control plants. Both the E (3.1 ± 0.15 % dry wt.) and G (2.3 ± 0.21 % dry wt.) plants registered lower steviol. The enhanced steviol glycoside profile was supported by the RT-PCR analysis of UGT74G1 and UGT76G1 that corresponds to stevioside and rebaudioside A biosynthesis, respectively. While the E plant showed 5–6-fold increase in the UGT74G1 (RQ = 5.51 ± 0.5) and UGT76G1 (RQ = 6.61 ± 0.5) gene expression, the G plant showed 5-fold increase in UGT76G1 (RQ = 5.29 ± 0.2) gene expression.

Polyethylene glycol acrylate-grafted polysulphone membrane for artificial lungs: plasma modification and haemocompatibility improvement

In this study, polyethylene glycol acrylate (PEGA) was introduced onto the surface of polysulphone (PSF) membrane to prepare PSF–PEGA membranes through low-temperature plasma technology for haemocompatibility improvement of artificial lungs. The effects of plasma power, PEGA solution concentration and dipcoating temperature on surface modification were systematically investigated. Results of Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and PEGA grafting degree confirmed that PEGA was successfully grafted onto the PSF membranes. Contact angle values showed that the hydrophilicity of the PSF–PEGA membrane surface increased by 21.5%. The results of the protein adsorption, platelet adhesion and coagulation tests further showed the excellent haemocompatibility of the modified membrane. Gas exchange tests also revealed that at a porcine blood flow rate of 5 l min−1, O2 and CO2 exchange rates through the PSF–PEGA membrane were 198.6 and 170.9 ml min−1, respectively; approximately this is the gas exchange capacity of commercial respiratory assistance devices.

Multigas Leakage Correction in Static Environmental Chambers Using Sulfur Hexafluoride and Raman Spectroscopy.

In static environmental chamber experiments, the precision of gas flux measurements can be significantly improved by a thorough gas leakage correction to avoid under- or overestimation of biological activity such as respiration or photosynthesis. Especially in the case of small biological net gas exchange rates or gas accumulation phases during long environmental monitoring experiments, gas leakage fluxes could distort the analysis of the biogenic gas kinetics. Here we propose and demonstrate a general protocol for online correction of diffusion-driven gas leakage in plant chambers by simultaneous quantification of the inert tracer sulfur hexafluoride (SF6) and the investigated biogenic gases using enhanced Raman spectroscopy. By quantifying the leakage rates of carbon dioxide (CO2), methane (CH4), and hydrogen (H2) simultaneously with SF6 in the test chamber, their effective diffusivity ratios of approximately 1.60, 1.96, and 5.65 were determined, each related to SF6. Because our experiments suggest that the effective diffusivity ratios are reproducible for an individual static environmental chamber, even under varying concentration gradients and slight changes of the chamber sealing, an experimental method to quantify gas leakage fluxes by using effective diffusivity ratios and SF6 leakage fluxes is proposed. The method is demonstrated by quantifying the CO2 net exchange rate of a plant-soil ecosystem (Mirabilis jalapa). By knowing the effective chamber diffusivity ratio CO2/SF6 and the measured SF6 leakage rate during the experiment, the leakage contribution to the total CO2 exchange rate could be calculated and the biological net CO2 concentration change within the chamber atmosphere determined.

Soil sustainability changes in organic crop rotations with diverse crop species and the share of legumes

There have been few long-term field studies on greenhouse gases measurement in organic crop rotations under temperate climatic conditions. Little is known about the extent to which the share of legumes in a crop rotation of organic farming affects the potentials for CO2 emission and soil organic carbon sequestration. The current study was aimed to investigate soil physicochemical state and soil net CO2 exchange rate in diverse organic crop rotations with different crop species and proportions of legumes. Four 5-year duration crop rotations were investigated. The best soil sustainability of the arable layer was found in a crop rotation enriched with red clover (Trifolium pratense L.). This rotation resulted in the highest soil mesoporosity and the lowest microporosity, ensured the best supply of plant-available water and revealed high soil resistance to dry conditions. Red clover secured the highest soil organic C sequestration, caused the increase in reserves of total N and available K, and slackened the decrease of soil-available P sources. Red clover-based cropping system exhibited the highest soil net CO2 exchange rate during five experimental years. The effect of crop rotation, consisting of phacelia (Phacelia tanacetifolia Benth.), peas (Pisum sativum L.) and yellow lupin (Lupinus luteus L.), on soil sustainability was weaker than the effect of rotation with red clover. Non-legume rotations, i.e. binary (two-crop) rotation and the crop rotation involving four spring and one winter species, can be regarded as miners of soil nutrient resources rather than contributors. These rotations did not promote soil sustainability because the soil lost large amounts of macronutrients and caused 26–33% lower soil net CO2 exchange rate, compared with leguminous rotations. For future, it could be recommended for ecological farming to rely more on crop rotations with red clover to improve ecosystems functioning.

Storage of grafted-tomato seedling under low-light conditions with light-emitting diodes and an electroluminescent sheet

We investigated the effects of photosynthetic active radiation generated by blue (465 nm peak wavelength) light-emitting diodes (LEDs), red (625 nm peak wavelength) LEDs, or an electroluminescent sheet (EL) (two peak wavelengths: 454 and 565 nm), and dark conditions on the quality preservation of tomato (Solanum lycopersicum) seedlings during low-light irradiation (LLI) storage. The photosynthetic photon flux density (PPFD) at the plant canopy level was automatically controlled using a proportional-integral-derivative (PID) controller to maintain the CO2 exchange rate of the seedlings at zero. Nine seedlings were stored for 21 d in a storage case at 10 ± 0.5°C and at greater than 95% RH. The total dry weight of the tomato seedlings after storage under any LLI was significantly greater compared to that before storage and during dark storage. The PPFD required for maintaining the CO2 exchange rate of the seedlings at zero under all LLI treatments over a 21 d storage period gradually decreased due to the low-light adaptation of the plant. The mean PPFDs to maintain a light compensation point under the blue LED-, red LED-, and EL-LLI for the last week of storage were 5.15, 5.03, and 5.20 µmol·m−2·s−1, respectively. The spectral distribution of the EL light may help preserve seedling quality better than that of the blue or red LED lights and the dark condition, providing a vigorous seedlings with upright morphology and significantly lower specific leaf area (cm2·g−1 DW), which reflects a thick leaf. For green plant storage, an EL or other kind of mixed light is able to control PPFD automatically, which may help maintain seedling quality for more than 3 weeks longer than with blue or red monochromatic light.

Serpentine ecosystem responses to varying water availability and prescribed fire in the U.S. Mid‐Atlantic region

Grasslands growing atop serpentine bedrock are subject to edaphic stresses and, as a result, are low productivity ecosystems. Nutrient limitations are so severe in some serpentine grasslands that plant growth is unaffected by increased water availability. However, little is known of how serpentine grasslands in eastern North America function and respond to environmental changes, including variation in water availability. Serpentine barrens of the U.S. Mid‐Atlantic region are globally rare ecosystems currently threatened by forest encroachment. Prescribed fire has been applied to maintain these ecosystems, although ecosystem responses to prescribed fire remain unquantified. Monthly measurements of CO2 exchange and leaf area index (LAI) were made at managed and unmanaged sites over two years. Environmental factors influencing CO2 exchange rates were monitored, and soil composition was also assessed. Unusually dry conditions in 2012 led to suppressed CO2 exchange rates and LAI across sites, while wet conditions in 2013 resulted in higher CO2 exchange rates and LAI. Seasonal maxima for net ecosystem production (NEP), ecosystem respiration (ER), and gross ecosystem production occurred in the late summer in 2012 and mid‐summer in 2013. Over the study period, maximum NEP and ER were 13.68 and −9.40 μmol CO2 m−2 s−1, respectively, while LAI reached 2.18 m2 m−2. Across sites, carbon storage in the top 10 cm of soil was 33.1–41.3 Mg C ha−1. Prescribed fire did not affect CO2 exchange, LAI, or soil carbon storage in the four to six years following a fire. In contrast to prior studies, Mid‐Atlantic serpentine barrens responded positively to increased soil water availability and were more productive than expected. These ecosystems were functionally similar to tallgrass prairie, suggesting that fire management practices from prairies may be applicable in Mid‐Atlantic serpentine barrens. Increased frequency of prescribed fire would likely reduce litter inputs to the soil and maintain the ecosystem's natural edaphic stessors, thereby combating forest encroachment.

Reproducing CO2 exchange rates of a crop rotation at contrasting terrain positions using two different modelling approaches

In undulating landscapes erosion is largely responsible for the spatial distribution of C stocks in agricultural soils. Whether these stocks contribute to global atmospheric CO2 concentrations as source or sink of CO2 is under constant debate. Periodic CO2 measurements were carried out at a hummocky ground moraine site grown with maize, fodder rye and sorghum using dynamic non-steady-state transparent and opaque chambers. Flux calculation for CO2 was conducted using the empirical gap-filling model of Hoffmann et al. (2015b), which uses temperature and radiation to simulate ecosystem respiration (Reco) and gross primary production (GPP) and to calculate net ecosystem CO2 exchange (NEE). This model was compared with a process-based agro-ecosystem simulation model, MONICA, which was tested for its ability to simulate Reco, GPP and NEE, using the empirical model as benchmark. Both models simulated GPP and Reco in the same order of magnitude, with MONICA simulating a considerably higher amount of CO2 produced by photosynthesis for maize and less deviating CO2 produced by photosynthesis for the other crops and CO2 consumed by respiration for all crops as compared to the empirical model. Both models largely agree in CO2 flux patterns, but show considerable differences directly after harvest and during bare soil periods. Strengths and weaknesses of both approaches were discussed and synergies of applying both approaches in conjunction were identified in a way that (i) MONICA may act as an independent method to identify significant deviations from the optimum crop growth pattern and thus point at times during which assumptions of the empirical model for simulating NEE may be violated and that (ii) the empirical model may act as a calibration benchmark for MONICA flux simulations.

Effect of open water pools on ecosystem scale surface-atmosphere carbon dioxide exchange in a boreal peatland

Peatland carbon dioxide (CO2) exchange can vary spatially over a few meters because of the heterogeneity in plant communities, differing responses to environmental conditions, and the presence of pools in patterned peatlands. In contrast to the plant communities comprising a peatland’s vegetated surface, permanent pools that are characteristic of peatlands in temperate to subarctic regions are net sources of CO2 to the atmosphere. Measurements of net ecosystem CO2 exchange using the eddy covariance (EC) technique over peatlands without permanent pools do not show the smaller plant scale spatial heterogeneity in fluxes because the atmosphere mixes the variations in fluxes over the EC tower source area. However, if different vegetation communities and pools approach the spatial scale that they form a significant proportion of an EC tower’s source area, such as might be the case in peatlands with pools, they should be able to be discriminated if the surface fluxes by cover type are significantly different. In the present study, we evaluate if the observed variability in peatland surface CO2 exchange can be identified from 30-min net ecosystem CO2 exchange measurements using the proportion of the different plant communities or pools within the eddy covariance tower source area. Our results show that the variability in CO2 exchange at the local scale across the peatland surface has a measureable impact on the ecosystem level measurement, primarily when open water pools are present within the tower source area. Our results also suggest that large CO2 exchange rates measured above Sphagnum spp. hummocks with Picea mariana, combined with their large fractional contribution to the source area, counterbalanced the CO2 loss from the open water pools, explaining why the ecosystem as a whole was a net CO2 sink during the measurement period.

Ecosystem resistance in the face of climate change: a case study from the freshwater marshes of the Florida Everglades

Shaped by the hydrology of the Kissimmee‐Okeechobee‐Everglades watershed, the Florida Everglades is composed of a conglomerate of wetland ecosystems that have varying capacities to sequester and store carbon. Hydrology, which is a product of the region's precipitation and temperature patterns combined with water management policy, drives community composition and productivity. As shifts in both precipitation and air temperature are expected over the next 100 years as a consequence of climate change, CO2 dynamics in the greater Everglades are expected to change. To reduce uncertainties associated with climate change and to explore how projected changes in atmospheric CO2 concentration and climate can alter current CO2 exchange rates in Everglades freshwater marsh ecosystems, we simulated fluxes of carbon among the atmosphere, vegetation, and soil using the DAYCENT model. We explored the effects of low, moderate, and high scenarios for atmospheric CO2 (550, 850, and 950 ppm), mean annual air temperature (+1, +2.5, and +4.2°C) and precipitation (−2, +7, and +14%), as predicted by the IPCC for the year 2100 for the region, on CO2 exchange rates in short‐ and long‐hydroperiod wetland ecosystems. Under 100 years of current climate and atmospheric CO2 concentration, Everglades freshwater marsh ecosystems were estimated to be CO2‐neutral. As atmospheric CO2 concentration increased and under climate change projections, there were slight shifts in the start and length of the wet season (−1 to +7 days) and a small enhancement in the sink capacity (by −169 to −573 g C m−2 century−1) occurred at both short‐ and long‐ hydroperiod ecosystems compared to CO2 dynamics under the current climate regime. Over 100 years, rising temperatures increased net CO2 exchange rates (+1 to 13 g C m−2 century−1) and shifts in precipitation patterns altered cumulative net carbon uptake by +13 to −46 g C m−2 century−1. While changes in ecosystem structure, species composition, and disturbance regimes were beyond the scope of this research, results do indicate that climate change will produce small changes in CO2 dynamics in Everglades freshwater marsh ecosystems and suggest that the hydrologic regime and oligotrophic conditions of Everglades freshwater marshes lowers the ecosystem sensitivity to climate change.

POD NUMBER AND PHOTOSYNTHESIS AS PHYSIOLOGICAL SELECTION CRITERIA IN SOYBEAN (Glycine max L. Merrill) BREEDING FOR HIGH YIELD

Field studies were conducted in two years using 638 F2 and 1185 F3 lines of selected 16 F1 and 15 F2 parent lines (³80 pods plant -1 ) to evaluate pod number and CO 2 exchange rate (CER) as selection criteria. Pod and seed number, and seed weight of individual lines were observed during harvesting time, and CER of randomly selected 32 F2 and 30 F3 lines was measured at initial seed filling stage. The selection of F2 lines based on pod number to generate F3 lines increased the average of seed yield by 39%, and pod number by 77% in F3 lines compared with F2 lines. A close relationships was found between seed weight and pod or seed number per plant. Net CER responded sensitively to a reduction of light in a short-term and showed 78% of F2 lines and all F3 lines with maximum CER (Pmax)³20 mmolCO 2 .m -2 .s -1 . The ratio of pod number per plant and Pmax varied between lines and were used to group lines resulting in close relationships between Pmax and pod number. It is concluded that the use of pod number and CER (Pmax) as selection criteria offers an alternative approach in soybean breeding for high yield.

Vegetation exerts a greater control on litter decomposition than climate warming in peatlands.

Historically, slow decomposition rates have resulted in the accumulation of large amounts of carbon in northern peatlands. Both climate warming and vegetation change can alter rates of decomposition, and hence affect rates of atmospheric CO2 exchange, with consequences for climate change feedbacks. Although warming and vegetation change are happening concurrently, little is known about their relative and interactive effects on decomposition processes. To test the effects of warming and vegetation change on decomposition rates, we placed litter of three dominant species (Calluna vulgaris, Eriophorum vaginatum, Hypnum jutlandicum) into a peatland field experiment that combined warming.with plant functional group removals, and measured mass loss over two years. To identify potential mechanisms behind effects, we also measured nutrient cycling and soil biota. We found that plant functional group removals exerted a stronger control over short-term litter decomposition than did approximately 1 degrees C warming, and that the plant removal effect depended on litter species identity. Specifically, rates of litter decomposition were faster when shrubs were removed from the plant community, and these effects were strongest for graminoid and bryophyte litter. Plant functional group removals also had strong effects on soil biota and nutrient cycling associated with decomposition, whereby shrub removal had cascading effects on soil fungal community composition, increased enchytraeid abundance, and increased rates of N mineralization. Our findings demonstrate that, in addition to litter quality, changes in vegetation composition play a significant role in regulating short-term litter decomposition and belowground communities in peatland, and that these impacts can be greater than moderate warming effects. Our findings, albeit from a relatively short-term study, highlight the need to consider both vegetation change and its impacts below ground alongside climatic effects when predicting future decomposition rates and carbon storage in peatlands.

Substitution of Co(2+) ions into CdS-based molecular clusters.

We report on the metal ion exchange between Co(2+) and CdS-based molecular clusters. These studies demonstrate that exchange into the smaller [Cd4(SPh)10](2-) clusters is facile compared to the larger [Cd10S4(SPh)16](4-) and [Cd17S4(SPh)28](2-) clusters. This trend correlates with the rate of benzenethiolate interconversion and μ-S(2-) and μ-SPh(-) content among the clusters.

Climate Change Effects on Long-term World-crop Production: Incorporating a Crop Model into Long-term Yield Estimates

Annual crop yield forecasts are necessary for analysis because evaluating climate–change impacts on world food markets requires supply–response functions, including output prices of the prior year. This research was undertaken to develop yield–response functions of the world food model to evaluate climate–change effects by incorporating a crop model into the yield–trend function. Yield–trend functions of rice, wheat, maize, and soybeans were obtained by estimating logistic functions or linear functions with a logarithmic time–trend term and climate variables. Furthermore, temperature and solar–radiation elasticities of yields were calculated using a crop model of the FAO and IIASA. The functions of the maximum rate of gross biomass production and the maximum net rate of CO2 exchange of leaves in the crop model were modified by introducing cubic spline interpolation and logistic functions. Smoothing these two functions alleviates drastic changes, but reveals small changes in the elasticities of crop yields compared to the kinked functions and these more realistic elasticities can improve the evaluation accuracy of climate–change impacts on crop supply and demand. These variable elasticities of temperature and solar–radiation were inserted into the yield–trend functions, whereupon the global effects of changes in climate variables, including rainfall, were analyzed. The changes in yields obtained using climate variables of two of the four RCP scenarios were compared with the baseline, for which climate variables were fixed. Results of trend analyses show that yields of rice, wheat, maize, and soybeans under RCP8.5 are lower than those under RCP2.6, except for wheat in China. Results of geographical analysis show that climate change can be expected to affect wheat and maize productions in low–latitude countries. Furthermore, results suggest that climate change will depress rice production in sub–Saharan African countries in the 2040s.

High Light Intensity Increases the CAM Expression in “MD-2” Micro-Propagated Pineapple Plants at the End of the Acclimatization Stage

This work describes the evaluation of morpho-physiological and biochemical changes in “MD-2” micro-propagated pineapple plants (Ananas comosus (L.) Merr.) grown after 30 days under low light intensity (LL, greenhouse light conditions at 250 μmol·m-2·s-1) or high light intensity (HL, field light conditions at 800 μmol·m-2·s-1). Gas exchange, leaf pH, protein content and superoxide dismutase activity (SOD) (EC 1.15.1.1) were measured every 3 h during one day. Chlorophylls content and succulence index (SI) were determined at 9 h. Results showed significant differences in CO2 exchange rates, with a maximum occurring at 6 h (3.00 and 8.25 μmol CO2 m-2·s-1 for leaves under LL and HL conditions respectively). Plants under HL conditions had higher CO2 uptake and lower pH values between 0 h and 6 h respective to LL plants. The maximum pH value was attained 3 h before in HL plants. Leaf SI was increased and chlorophyll content decreased by HL conditions. SOD activity was higher in plants under HL conditions, near doubling those of LL plants at 18 h (2.8 versus 1.5 U·mg-1 Protein respectively). Both groups showed a typical CAM phenotype, but it was stronger in HL conditions, which may confer these plants with a better acclimation to transfer to the field.

El Niño Southern Oscillation (ENSO) enhances CO2 exchange rates in freshwater Marsh ecosystems in the Florida everglades.

This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009–2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (−11 to −110 g CO2 m−2 yr−1) compared to El Niño and neutral years (−5 to −43.5 g CO2 m−2 yr−1). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m−2 yr−1) except in one exceptionally wet year that was associated with an El Niño phase (−16 g CO2 m−2 yr−1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades.

Stocking Rate and Grazing Season Modify Soil Respiration on the Loess Plateau, China

The influence of sheep grazing on carbon cycling in the midarid steppe of the Loess Plateau, Gansu, China, was investigated by measuring the CO2 exchange rate in pastures with a 7-year history of zero, light, moderate, and heavy grazing. Farming systems in the area are characterized by heavy grazing pressure and low vegetation productivity. The effect of stocking rate on soil respiration (Rs) was determined using field trials to investigate factors influencing spatial and temporal variation in Rs in August 2008 on two sites: summer grazed and winter grazed. Soil respiration is an important component of the carbon cycle in rangeland. Measurements included daily Rs, soil temperature, soil moisture, and root biomass. Daily Rs was also measured in late April and middle December 2008. The response of Rs to increasing stocking rate in August 2008 differed with site; on the summer-grazed site increased stocking rates reduced Rs (P < 0.02), whereas on the winter-grazed site, stocking rate had little effect on Rs. Path analysis revealed that on the summer-grazed site, soil moisture had the greatest influence on Rs, whereas on the winter site soil temperature was the most important factor; stocking rate had the least influence on Rs at both sites. The results highlight the importance of environmental variability in determining the effects of grazing on Rs.

The assessment of the impact of oil palm and rubber plantations on the biotic and abiotic properties of tropical peat swamp soil in Indonesia

Current intensification of agricultural activities in Indonesia has led to increased use of tropical peat swamp forests for agriculture. Ideally, peat swamp ecosystems should not be disturbed as they provide essential services such as soil erosion control, ecosystem stabilization and moderation of climate and energy fluxes as well as reducing carbon emission and conserving biodiversity. In this study, agricultural land from Giam Siak Kecil–Bukit Batu Biosphere Reserve in Indonesia was evaluated to assess the impact of oil palm (burning and without burning) and rubber (5–10 and >40 years old) plantations on soil properties through comparisons with soils from a natural forest (NF). Substantial changes in the physico-chemical properties of soils from both plantations were observed including significant reductions in soil organic matter (4–18%) and water holding capacity (22–53%), but an increase in bulk density (ρb) (0.08–0.17 g cm−3). A significant increase in bacterial biomass was also observed following conversion of the NF to plantation (p<0.05). However, the oil palm plantation (OPP) (without burning) showed reduced microbial activities and the lowest Shannon diversity values (2.90) compared to other samples. Community-level physiological profiling showed impaired community function only in soils from the OPP but higher CO2 exchange rates in most plantation soils. Soils from the rubber plantation (RP) were less impaired in terms of their natural function and therefore RPs appeared to be more suitable for sustainable agricultural use than OPP.

Effects of photosynthetic photon flux and carbon dioxide concentration on the photosynthesis and growth of grafted pepper transplants during healing and acclimatization

In the production of grafted transplants, healing and acclimatization are the most critical processes for survival. We investigated the influence of the photosynthetic photon flux (PPF) and the carbon dioxide (CO2) concentration during healing and acclimatization on the photosynthetic characteristics and growth of grafted pepper transplants to determine the optimum environmental conditions for healing and acclimatization in a healing chamber with artificial lighting source. Grafted pepper transplants were healed and acclimatized under two levels of CO2 (374 or 1,013 μmol·mol−1) and four levels of PPF (dark, 50, 98 or 147 μmol·m−2·s−1) for six days. The CO2 exchange rates of the grafted pepper transplants significantly increased with increasing PPF during healing and acclimatization. The CO2 exchange rates were higher under elevated CO2 concentrations than ambient CO2 concentration. The effect of CO2 enrichment was greater in low light intensity. The CO2 exchange rates at 50, 98 or 147 μmol·m−2·s−1 under elevated CO2 concentrations were 511, 261, and 172%, respectively, compared to the ambient CO2 concentrations. The increase of photosynthesis led to an improvement in growth. The SPAD value, dry weight and leaf area were greater under higher PPF and CO2 concentrations. PPF also influenced the anatomical structures of the leaves, and the palisade and spongy tissue cells of the leaves irradiated with higher PPF were aligned more densely, with more chloroplasts and small empty space. When compared to the tunnel in the greenhouse with natural light, healing and acclimatization under high CO2 (1,000 μmol·mol−1) and PPF (150 μmol·m−2·s−1) conditions in the healing chamber promoted the growth and graft union formation of grafted pepper transplants. The results suggested that high-quality grafted pepper seedlings could be achieved by healing and acclimatization in a healing chamber where optimal conditions such as high PPF and CO2 were maintained within the range evaluated in this experiment.

The influence of tillage, fertilization and meteorological conditions on the CO2 exchange rate in a loamy Cambisol

is no consensus worldwide concerning the effects of soil management practices on soil net CO 2 exchange rate (NCER). The main goal of the study was to determine soil NCER in different agricultural management systems under contrasting meteorological conditions. The evaluation of moisture and temperature (determined by frequency domain reflectometry (FDR) method) impact on total soil NCER was performed. A closed chamber (CC) method using an infra-red gas analyzer (IRGA) was applied. A two-factorial field experiment was established on an Endocalcari-Epihypogleyic Cambisol (CMg-p-w-can) at the Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry. A three-year (2009-2012) study revealed that rainy weather conditions suppressed NCER sharply: NCER was 15-fold lower under rainy meteorological conditions than under dry or normal conditions. Soil temperature in both unfertilized tillage systems (conventional tillage, no-tillage) was the main determinant for soil NCER, while this effect was suppressed by the total influence of soil water content, air temperature and amount of rainfall. Soil carbon dioxide flux was slightly (3%) higher under conventional tillage than under no-tillage during dry 2009 and normal 2012 years. In a wet year 2010, conventional tillage increased soil NCER by 70% compared to no-tillage. Fertilization with mineral NPK fertilizers increased soil NCER by on average 32% compared to unfertilized plots, but did not eliminate suppressive effects of meteorological conditions on soil NCER.

Phenology and its role in carbon dioxide exchange processes in northern peatlands

AbstractEcosystem phenology plays an important role in carbon exchange processes and can be derived from continuous records of carbon dioxide (CO2) exchange data. In this study we examined the potential use of phenological indices for characterizing cumulative annual CO2 exchange in four contrasting northern peatland ecosystems. We used the approach of Jonsson and Eklundh (2004) to derive a set of phenological indices based on the daily time series of gross primary production (GPP), ecosystem respiration (Re), and net ecosystem production (NEP) measured in the four peatland sites. The main objectives of this study were (a) to examine the variation in phenological indices across sites and (b) to determine the relationships among phenological indices, environmental conditions, and cumulative annual CO2 exchange. The phenological index used to define the “start of the growing season” showed good potential for differentiation among sites based on their average annual site GPP. Sites with earlier growing seasons had the highest average annual site GPP. The “peak CO2 exchange rate” phenological index performed best in reflecting variations among sites and for estimating annual values of GPP, Re, and NEP (Pearson correlation coefficients ranged between 0.77 and 0.99, p &lt; 0.05 for all.). The phenological indices and annual GPP, Re, and NEP were sensitive to winter (January–March) and summer (July–September) temperature and precipitation, but correlations, though significant, were weak.