CO2 Exchange Rate Research Articles

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 < 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.

Soil pore-water environment and CO2 emission in a Luvisol as influenced by contrasting tillage

Little is known how contrasting tillage (deep ploughing, top- and sub-soil loosening with straight or bent leg cultivator [BLC], direct drilling [DD]) affect important soil physical properties (total porosity [TP], pore size distribution [PSD], water release characteristics [WRC]) and CO2 emissions from a Luvisol. The study was aimed to alleviate compaction on land that had been under reduced tillage for 4 successive years. Undisturbed core samples were collected from 5–10, 15–20 and 25–30 cm depths for soil WRCs, TP and pore-size distribution determination. A closed chamber method was used to quantify the CO2 emissions from the soil. Soil loosening with straight or BLC produced the highest total soil porosity (on average 0.48 m3 m−3) within 5–30 cm soil layer, while conventional tillage (CT) gave 6%, DD up to 25% reduction. Sub-surface loosening with a BLC was the most effective tool to increase the amount of macro- and mesopores in the top- and sub-soil layers. It produced 21% more macro- and mesopores within 25–30 cm soil layer as compared to the soil loosened with a straight leg cultivator. Plant available water content under CT and DD was lower as compared to that under deep loosening with straight or BLC (23% and 18%, respectively). DD produced 12% lower soil surface net carbon dioxide exchange rate than CT and by 25–28% lower than deep soil loosening with straight or BLC. The increase in micropores within 25–30 cm soil layer caused net carbon dioxide exchange rate reduction. The amount of mesopores within the whole 5–30 cm soil layer acted as a direct dominant factor influencing net CO2 exchange rate (NCER) (Pxy = −3.063; r = 0.86).

Benefits for agriculture and the environment from urban waste

Soluble bio-based substances (SBO) that have been isolated from urban biowaste have recently been reported to enhance plant leaf chlorophyll content and growth. The same SBO have also been shown to enhance the photochemical degradation of organic pollutants in industrial effluent. These findings suggest that SBO may promote either C fixation or mineralization, according to operating conditions. The present work aims to investigate SBO performance, as a function of source material. Thus, three materials have been sampled from a municipal waste treatment plant: (i) the digestate of the anaerobic fermentation of a humid organic fraction, (ii) a whole vegetable compost made from gardening residues and (iii) compost made from a mixture of digestate, gardening residues and sewage sludge. These materials were hydrolyzed at pH13 and 60°C to yield SBO that display different chemical compositions. These products were applied to soil at 30, 145 and 500kgha−1 doses for tomato cultivation. Soil and plant leaf chemical composition, plant growth, leaf chlorophyll content and CO2 exchange rate as well as fruit quality and production rate were measured. Although it did not affect the soil's chemical composition, SBO were found to significantly increase plant photosynthetic activity, growth and productivity up to the maximum value achieved at 145kgha−1. The effects were analyzed as a function of SBO chemical composition and applied dose. The results of this work, compared with those of previous works, indicate that urban biowaste, if properly exploited, may furnish conjugate economic and environmental benefits, within a friendly sustainable ecosystem.

Concomitant CAM and C3 Photosynthetic Pathways in Dendrobium officinale Plants

Dendrobium officinale, endemic to China, is a rare and endangered medicinal herb. As a result of its high economic value, slow growth, and diminishing wild population, protected cultivation is preferred. However, little information is available on its growing environment and photosynthetic characteristics. In this study, the photosynthetic patterns of D. officinale were investigated under various environmental conditions by measuring the net CO2 exchange rates continuously for several days or weeks. Under non-stressed growth chamber conditions with 12-hour light and 12-hour dark periods, D. officinale had concomitance of C3 and crassulacean acid metabolism (CAM) photosynthesis patterns. Different degrees of CAM in D. officinale, expressed as the percentage of CO2 exchanges in the dark period to the daily amount of CO2 exchanges, were observed depending on environmental conditions. With decreasing substrate water content, a typical CAM pattern was found, and concomitance of C3 and CAM patterns was found again when plants were rewatered. The accumulation of leaf titratable acidity during a dark period increased as substrate dried out but decreased again as plants were rewatered. A shorter light–dark cycle (4-hour light and 4-hour dark periods) led to a C3 pattern alone. The substrate moisture and light–dark cycle were inducible factors for switching between C3 and CAM patterns in D. officinale. These results indicate that D. officinale is a facultative CAM plant and the C3 pathway can be induced by controlling the growing environment. Further studies are needed to identify the optimal environmental conditions to enhance the growth of D. officinale.

Cytokinins affect the stomatal conductance and CO2 exchange of in vitro apple leaves

Effects of different cytokinin supplies including two types of aromatic cytokinins, such as benzyl-adenine, and 3-hydroxybenzyladenine applied at two different concentrations (2.0 and 6.0 μM) were studied on water and gas exchange parameters in in vitro apple leaves of ‘Royal Gala’ and ‘Freedom’ scions after 3 weeks of culture. Cytokinin supply affected the stomatal conductance of water vapour, transpiration rate and the sub-stomatal CO2 concentration of leaves. Effect of cytokinin depended on its applied type and concentration, moreover on the apple scion. According to the results, the rate of CO2 exchange itself is not usable for characterization of function of photosynthetic apparatus of in vitro leaves. However, measurements of stomatal conductance of water vapour and transpiration rate seemed to be good indicators for stomatal behaviour of in vitro apple leaves.

Nitrogen-addition effects on leaf traits and photosynthetic carbon gain of boreal forest understory shrubs

Boreal coniferous forests are characterized by fairly open canopies where understory vegetation is an important component of ecosystem C and N cycling. We used an ecophysiological approach to study the effects of N additions on uptake and partitioning of C and N in two dominant understory shrubs: deciduous Vaccinium myrtillus in a Picea abies stand and evergreen Vaccinium vitis-idaea in a Pinus sylvestris stand in northern Sweden. N was added to these stands for 16 and 8 years, respectively, at rates of 0, 12.5, and 50 kg N ha(-1) year(-1). N addition at the highest rate increased foliar N and chlorophyll concentrations in both understory species. Canopy cover of P. abies also increased, decreasing light availability and leaf mass per area of V. myrtillus. Among leaves of either shrub, foliar N content did not explain variation in light-saturated CO2 exchange rates. Instead photosynthetic capacity varied with stomatal conductance possibly reflecting plant hydraulic properties and within-site variation in water availability. Moreover, likely due to increased shading under P. abies and due to water limitations in the sandy soil under P. sylvestris, individuals of the two shrubs did not increase their biomass or shift their allocation between above- and belowground parts in response to N additions. Altogether, our results indicate that the understory shrubs in these systems show little response to N additions in terms of photosynthetic physiology or growth and that changes in their performance are mostly associated with responses of the tree canopy.

Daily, biweekly, and seasonal temporal scales ofpCO2variability in two stratified Mediterranean reservoirs

Temporal scales of variability for the partial pressure of CO2 (pCO2) in the surface waters of two stratified Mediterranean reservoirs were examined through the temporal decomposition of 5 month time series with hourly sampling frequency. pCO2 time series included similar patterns of variability at daily, biweekly, and seasonal scales regardless of the difference in amplitude of the pCO2 variation in the two reservoirs studied. Daily variability was strongly related to the day-night cycles of metabolic activity, accounting for about one third of the total amplitude in pCO2 variation. At a biweekly scale, wind forcing led to higher rates of air-water CO2 exchange and subsequently temporary partial mixing events associated to relevant increase of CO2 concentration in surface waters. Seasonal variability accounted for one third of the amplitude of the pCO2 variability and was coupled to the seasonal dynamics of water temperature and thermal stratification of the water column. Our results provide evidence that CO2 emission from stratified water bodies shows significant variability at daily, biweekly, and seasonal scales; all of which should be taken into consideration in the analyses of the carbon fluxes. The wind-induced mixing events, operating at temporal scales between daily and seasonal cycles, may become a major factor controlling the pCO2 dynamics. Hence, some of the most common models for computing CO2 fluxes from pCO2 were not able to reproduce the biweekly response patterns of CO2 emissions to wind forcing.

Productivity and Carbon Dioxide Exchange of Leguminous Crops: Estimates from Flux Tower Measurements

Net CO2 exchange data of legume crops at 17 flux tower sites in North America and three sites in Europe representing 29 site‐years of measurements were partitioned into gross photosynthesis and ecosystem respiration by using the nonrectangular hyperbolic light‐response function method. The analyses produced net CO2 exchange data and new ecosystem‐scale ecophysiological parameter estimates for legume crops determined at diurnal and weekly time steps. Dynamics and annual totals of gross photosynthesis, ecosystem respiration, and net ecosystem production were calculated by gap filling with multivariate nonlinear regression. Comparison with the data from grain crops obtained with the same method demonstrated that CO2 exchange rates and ecophysiological parameters of legumes were lower than those of maize (Zea mays L.) but higher than for wheat (Triticum aestivum L.) crops. Year‐round annual legume crops demonstrated a broad range of net ecosystem production, from sinks of 760 g CO2 m−2 yr−1 to sources of –2100 g CO2 m−2 yr−1, with an average of –330 g CO2 m−2 yr−1, indicating overall moderate CO2–source activity related to a shorter period of photosynthetic uptake and metabolic costs of N2 fixation. Perennial legumes (alfalfa, Medicago sativa L.) were strong sinks for atmospheric CO2, with an average net ecosystem production of 980 (range 550–1200) g CO2 m−2 yr−1.

PHOTOSYNTHETIC CHARACTERISTICS AND DEVELOPMENT OF LONGAN LEAF

Changes in longan (Dimocarpus longan Linn.) leaf photosynthetic characteristics with leaf age, growth and development were determined. The experiment was conducted at the Agricultural Technology Research Institute, Rajamangala University of Technology Lanna, Lampang. Ten longan trees were pruned on June 1, 2010. The result showed that longan trees began flushing about 22 days after pruning, leaf width and leaf length parameters increased during leaf development and leaf photosynthesis also increased. Leaf expansion parameter correlated with SPAD unit, chlorophyll fluorescence, the net CO2 exchange rate (NCER), transpiration rate and stomata conductance. The longan leaves fully expanded 21 days after terminal bud break (DATBB). Chlorophyll content (SPAD unit) and chlorophyll fluorescence (Fv/Fm) increased from 19.06 to 45.46 between 7 and 28 DATBB and 0.58 to 0.78 between 7 and 21 DATBB, for chlorophyll content and chlorophyll fluorescence, respectively. Moreover, the net CO2 exchange rate, transpiration rate and stomata conductance increased from -1.44 to 9.53 µmol m-2 s-1, 0.62 to 2.46 mmol m-2 s-1 and 0.02 to 0.34 mol m-2 s-1 between 7 and 35 DATBB, for net CO2 exchange, transpiration and stomata conductance, respectively.

Carbon exchange rates in Polytrichum juniperinum moss of burned black spruce forest in interior Alaska

The Boreal black spruce forest is highly susceptible to wildfire, and postfire changes in soil temperature and substrates have the potential to shift large areas of such an ecosystem from a net sink to a net source of carbon. In this paper, we examine CO2 exchange rates (e.g., NPP and Re) in juniper haircap moss (Polytrichum juniperinum) and microbial respiration in no-vegetation conditions using an automated chamber system in a five-year burned black spruce forest in interior Alaska during the fall season of 2009. Mean ± standard deviation microbial respiration and NEP (net ecosystem productivity) of juniper haircap moss were 0.27 ± 0.13 and 0.28 ± 0.38 gCO2/m2/hr, respectively. CO2 exchange rates and microbial respiration showed temporal variations following fluctuation in air temperature during the fall season, suggesting the temperature sensitivity of juniper haircap moss and soil microbes after fire. During the 45-day fall period, mean NEP of P. juniperinum moss was 0.49 ± 0.28 MgC/ha following the five-year-old forest fire. On the other hand, simulated microbial respiration normalized to a 10 °C temperature might be stimulated by as much as 0.40 ± 0.23 MgC/ha. These findings demonstrate that the fire-pioneer species juniper haircap moss is a net C sink in the burned black spruce forest of interior Alaska.

An Improved Multichamber Gas Exchange System for Determining Whole-Canopy Water-Use Efficiency in Grapevine

A multichamber whole-canopy gas exchange system coupled with an automatic pot weighing device was tested for continuous 24 hr recording over 50 days in a trial comparing cv. Sangiovese vines subjected to progressive reduction of total transpiration water supply to well-watered vines. The system ran smoothly under regular maintenance for the entire period and gravimetric vine water loss was highly correlated with chamber-derived vine transpiration (r = 0.95) for data pooled over treatments. Seasonal and diurnal whole-canopy net CO2 exchange rate (NCER) and transpiration (Tc) showed that supplying 50% and 30% of daily gravimetric vine water loss (Tg) consistently corresponded to a NCER more than proportionally limited as compared to Tc, hence leading to lower canopy water-use efficiency (WUE) expressed as NCER/Tc ratio. Conversely, canopy WUE did not differ between treatments at 70% Tg restitution and rewatering. Similarly, during the most limiting water supply periods, the WUE difference between treatments was greatly reduced during cloudy days with lower vapor pressure deficit and higher diffuse-to-direct light intensity ratio. Data sets taken over different time frames on whole-canopy WUE provide a scenario different from that which might derive from traditional single-leaf assessment, reporting in almost all cases that intrinsic WUE increases under stress and suggests that the methodology used can mask or alter conclusions about adaptive response of grapevine cultivars to water stress.

How does carbon dioxide permeate cell membranes? A discussion of concepts, results and methods

We review briefly how the thinking about the permeation of gases, especially CO2, across cell and artificial lipid membranes has evolved during the last 100 years. We then describe how the recent finding of a drastic effect of cholesterol on CO2 permeability of both biological and artificial membranes fundamentally alters the long-standing idea that CO2—as well as other gases—permeates all membranes with great ease. This requires revision of the widely accepted paradigm that membranes never offer a serious diffusion resistance to CO2 or other gases. Earlier observations of “CO2-impermeable membranes” can now be explained by the high cholesterol content of some membranes. Thus, cholesterol is a membrane component that nature can use to adapt membrane CO2 permeability to the functional needs of the cell. Since cholesterol serves many other cellular functions, it cannot be reduced indefinitely. We show, however, that cells that possess a high metabolic rate and/or a high rate of O2 and CO2 exchange, do require very high CO2 permeabilities that may not be achievable merely by reduction of membrane cholesterol. The article then discusses the alternative possibility of raising the CO2 permeability of a membrane by incorporating protein CO2 channels. The highly controversial issue of gas and CO2 channels is systematically and critically reviewed. It is concluded that a majority of the results considered to be reliable, is in favor of the concept of existence and functional relevance of protein gas channels. The effect of intracellular carbonic anhydrase, which has recently been proposed as an alternative mechanism to a membrane CO2 channel, is analysed quantitatively and the idea considered untenable. After a brief review of the knowledge on permeation of O2 and NO through membranes, we present a summary of the 18O method used to measure the CO2 permeability of membranes and discuss quantitatively critical questions that may be addressed to this method.

Carbon dioxide flux in the ablation area of Koxkar glacier, western Tien Shan, China

AbstractAccelerating loss of glacial mass caused by rising global temperatures has significant implications. The global cycle of the greenhouse gas CO2 is also associated with mineral weathering and glaciation. In glaciated areas, most estimates of atmospheric CO2 consumption are confined to chemical ionic mass balance or analog modeling methods. We applied the gradient method to the surface of Koxkar glacier, western Tien Shan, China, for a 5 month period during 2012. The overall net glacier-system CO2 exchange (NGE) rate was measured as -0.05 and -0.07mmol m–2 s–1 for regions of exposed ice and supraglacial moraine, respectively. This suggests that atmospheric CO2 drawdown may occur during ice melting because of consumption of H+ by CO2 hydrolysis that occurs in solutions. Using the degree-day model to calculate glacier ablation in bare-ice regions and considering characteristics of the NGE rate in the supraglacial debris region with the support of GIS, the daily NGE rate was estimated to be -1.23 ± 0.17μmmol m–2 d–1 between Julian days 125 and 268 of 2012. These findings present a new approach for modeling the dynamics of glacial CO2 sinks undergoing melting, and develop an understanding of the mechanism of atmospheric CO2 exchange.

Short-term effects of extensive fertilization on community composition and carbon uptake in a Pannonian loess grassland

Among the most extended ecosystems of the temperate zone, the seminatural, dry grasslands constitute a substantial proportion in the Carpathian Basin. The aim of our present study was to investigate the short-term effect of extensive fertilization on the species composition and CO2 exchange of loess grassland at community level. The in situ investigation of the latter parameter have not been yet carried out in Pannonian loess grasslands. Most of the parameters studied showed a considerable interannual variation both in the fertilized and in the control stands. As a result of the treatment, the average species number of the fertilized stand decreased by 22%, which was more significant in the autumn (26%) than in the spring. Diversity values, including Shannon index and species richness, increased by nearly 1.5 times in the year with adequate rainfall compared with the initial values. In general, species richness and the ratio of dicots decreased, while the ratio of therophytes, alien competitors, and C4 plants increased with the addition of fertilizers. Significant carbon sequestration potential was only detected during wet periods in the fertilized grass. The rate of CO2 uptake was found to be nearly five times higher in the fertilized stand and nearly three times higher in the control stand during the wet year compared with the previous, extremely dry year. The CO2 uptake potential of the fertilized grassland exceeded that of the control stand by 12% in the year with high rainfall, while the rate of CO2 exchange dropped by 50% in the dry year in the fertilized stand. Our study reinforced the idea that the decline in species richness was not necessarily followed by the reduction of stand level carbon uptake in a short period due to an insignificant change in ecophysiological functional groups.

Behind the scenes: the roles of reactive oxygen species in guard cells

Guard cells regulate stomatal pore size through integration of both endogenous and environmental signals; they are widely recognized as providing a key switching mechanism that maximizes both the efficient use of water and rates of CO₂ exchange for photosynthesis; this is essential for the adaptation of plants to water stress. Reactive oxygen species (ROS) are widely considered to be an important player in guard cell signalling. In this review, we focus on recent progress concerning the role of ROS as signal molecules in controlling stomatal movement, the interaction between ROS and intrinsic and environmental response pathways, the specificity of ROS signalling, and how ROS signals are sensed and relayed. However, the picture of ROS-mediated signalling is still fragmented and the issues of ROS sensing and the specificity of ROS signalling remain unclear. Here, we review some recent advances in our understanding of ROS signalling in guard cells, with an emphasis on the main players known to interact with abscisic acid signalling.

Diurnal Variation of Instantaneous CO<sub>2</sub> and H<sub>2</sub>O Gas-Exchange over Canopy and Leaf Level of Spring Maize in Arid Area

Information on the relationship between crop photosynthetic rate and water use efficiency at the leaf level and these at the canopy level is important on the study of theory and practice of high efficiency and water-saving agriculture. We simultaneous made instantaneous CO2 and H2O exchange rate, and instantaneous water use efficiency measurement at both leaf and canopy level in a rain-fed cropping system with spring corn during filling stage by Li-6400 infrared gas analysis meter and eddy correlation system. The results showed that in arid area water stress was the mainly factor influencing the net photosynthesis rate and water use efficiency. At the diurnal course, when soil relative moisture was about 40% at 0-100 cm soil layer, the maximum of net photosynthetic rate at leaf level occurred at about 10:00 under soil water stress, and at about 12:00 at canopy level on sunny days, the maximum leaf photosynthetic rate reached 1.3 mgm-2s-1 , almost close to those of irrigation corn at similar latitude area, and the maximum canopy assimilation rate were 0.9 mgm-2s-1 , reached 54.5% of those of irrigation corn at similar latitude area during filling stage, respectively;The maximum values of instantaneous water use efficiency at leaf and canopy level were 0.16 g (CO2)/ g (H2O) and 0.06 g (CO2)/ g (H2O), and ranged between 0.0055g (CO2)/ g (H2O) and 0.0123 g (CO2)/ g (H2O), 0.0113 g (CO2)/ g (H2O) and 0.0197 g (CO2)/ g (H2O) around noon, respectively. Instantaneous net photosynthetic rate and water use efficiency at leaf level were higher than those at canopy level after 10:00.

Atmospheric turbulence triggers pronounced diel pattern in karst carbonate geochemistry

Abstract. CO2 exchange between terrestrial ecosystems and the atmosphere is key to understanding the feedbacks between climate change and the land surface. In regions with carbonaceous parent material, CO2 exchange patterns occur that cannot be explained by biological processes, such as disproportionate outgassing during the daytime or nighttime CO2 uptake during periods when all vegetation is senescent. Neither of these phenomena can be attributed to carbonate weathering reactions, since their CO2 exchange rates are too small. Soil ventilation induced by high atmospheric turbulence is found to explain atypical CO2 exchange between carbonaceous systems and the atmosphere. However, by strongly altering subsurface CO2 concentrations, ventilation can be expected to influence carbonate weathering rates. By imposing ventilation-driven CO2 outgassing in a carbonate weathering model, we show here that carbonate geochemistry is accelerated and does play a surprisingly large role in the observed CO2 exchange pattern of a semi-arid ecosystem. We found that by rapidly depleting soil CO2 during the daytime, ventilation disturbs soil carbonate equilibria and therefore strongly magnifies daytime carbonate precipitation and associated CO2 production. At night, ventilation ceases and the depleted CO2 concentrations increase steadily. Dissolution of carbonate is now enhanced, which consumes CO2 and largely compensates for the enhanced daytime carbonate precipitation. This is why only a relatively small effect on global carbonate weathering rates is to be expected. On the short term, however, ventilation has a drastic effect on synoptic carbonate weathering rates, resulting in a pronounced diel pattern that exacerbates the non-biological behavior of soil–atmosphere CO2 exchanges in dry regions \\mbox{with carbonate soils}.

Improving the MicroResp™ substrate-induced respiration method by a more complete description of CO2 behavior in closed incubation wells

The MicroResp™ method allows soil respiration and microbial community physiological profiles to be determined colorimetrically in microplates. This method, however, neglects CO2 storage in the agar gel carrying the colorimetric indicator, and calcite dissolution associated with CO2-induced change in soil solution pH. Our objective was to improve the method by taking into account CO2 in the gel in the calculation of microbial respiration, describing the effect of microbial CO2 on the pH of the soil solution and calcite dissolution, and checking whether CO2 distribution among calcite, soil solution, air and gel is near equilibrium after incubation. We propose a thermodynamic equilibrium model describing (a) distribution of CO2 among calcite, soil solution, gel and air, (b) dissociations of water, carbonic acid, cresol red, and substrates in the gel and soil solution, (c) exchange of adsorbed cations with H3O+ in the gel, and (d) calcite dissolution in soil. In-gel experiments were designed to calibrate the model, quantify the rate of CO2 exchange with air, and compare conservation procedures. On-soil experiments were designed to check whether calcite dissolution is near equilibrium and whether the model predicts the effect of CO2 on the pH of the solution. In-microplate experiments were designed to assess the effects of incubation period and soil quantity on estimated microbial respiration. The model can describe the distribution and speciation of CO2 in the gel, the soil solution and the air space of each microplate well. Initial properties of the gel vary with storage: soda lime partly extracts CO2 supplied as NaHCO3, and dries out the gel, which can skew the calibration. When incubation is over, the proportion of microbial CO2 in the gel is higher at lower microbial respiration. Incubations shorter than 4h underestimate microbial respiration due to the slow diffusion of CO2 in the gel. CO2 in the soil solution cannot be overlooked; it decreases the soil pH and may promote calcite dissolution in calcareous soil. It is important to precisely estimate initial CO2 air fraction and to control temperature, which affects both thermodynamic constants and microorganisms.

Effects of Light Quality and Intensity on the Carbon Dioxide Exchange Rate, Growth, and Morphogenesis of Grafted Pepper Transplants during Healing and Acclimatization

This study evaluated the influence of light quality and intensity during healing and acclimatization on the CO₂ exchange rate, growth, and morphogenesis of grafted pepper (Capsicum annuum L.) transplants, using a system for the continuous measurement of the CO₂ exchange rate. C. annuum L. ‘Nokkwang’ and ‘Tantan’ were used as scions and rootstocks, respectively. Before grafting, the transplants were grown for four weeks in a growth chamber with artificial light, where the temperature was set at 25/18℃ (light/dark period) and the light period was 14 hours·d -1 . The grafted pepper transplants were then healed and acclimatized under different light quality conditions using fluorescent lamps (control) and red, blue, and red + blue light-emitting diodes (LEDs). All the transplants were irradiated for 12 hours per day, for six days, at a photosynthetic photon flux (PPF) of 50, 100, or 180 μmol·m -2 ·s -1 . The higher PPF levels increased the CO₂ exchange rate during the healing and acclimatization. A smaller increase in the CO₂ exchange rates was observed in the transplants under red LEDs. At a PPF of 180 μmol·m -2 ·s -1 , the CO₂ exchange rate of the transplants irradiated with red LEDs was lowest and it was 37% lower than those irradiated with fluorescent lamps. The CO₂ exchange rates of transplants irradiated with blue LEDs was the highest and 20% higher than those irradiated under fluorescent lamps. The graft take was not affected by the light quality. The grafted pepper transplants irradiated with red LEDs had a lower SPAD value, leaf dry weight, and dry matter content. The transplants irradiated with blue LEDs had longer shoot length and heavier stem fresh weight than those irradiated with the other treatments. Leaves irradiated with the red LED had the smallest leaf area and showed leaf epinasty. In addition, the palisade and spongy cells of the pepper leaves were dysplastic and exhibited hyperplasia. Grafted pepper transplants treated with red + blue LEDs showed similar growth and morphology to those transplants irradiated with fluorescent lamps. These results suggest that high-quality grafted pepper transplants can be obtained by healing and acclimatization under a combination of blue and red lights at a high PPF level.

Contrasting leaf trait scaling relationships in tropical and temperate wet forest species

Summary We investigated whether plants adapted to thermally contrasting environments (e.g. tropical‐temperate habitats) exhibit inherent differences in leaf trait scaling relationships. Thirteen tropical and 12 temperate species (all characteristic of wet forests) were grown in a glasshouse (25/20 °C day/night). A range of leaf traits were quantified, including mass‐based leaf nitrogen [N], mass per unit area (LMA), light‐saturated photosynthesis (A) and respiration (Rdark). Average area‐ and mass‐based rates of net CO2 exchange were higher in the temperate species, compared to their tropical counterparts. Average leaf [N] and LMA values were also higher in temperate species than in their tropical counterparts. The higher LMA in the metabolically more active temperate species was the most striking contrast to the patterns and predictions of the GLOPNET leaf trait data base, and was associated with different elevations (i.e. y‐axis intercepts) but not slopes of bivariate trait scaling relationships. As expected, mass‐based rates of A and Rdark scaled positively with increasing [N] and negatively with increasing LMA in both tropical and temperate species. No differences were found between temperate and tropical species groups in terms of log‐log scaling relationships linking A and Rdark to N. However, at any given LMA, mass‐based values of [N], A and Rdark were all higher in the temperate species than in their tropical counterparts. Underpinning higher A in temperate species was a higher capacity for carboxylation (Vcmax) and RuBP regeneration (Jmax), with Jmax:Vcmax being greater in temperate species. In conclusion, our results suggest that as a consequence of greater overall N investment as well as greater proportional N investment in metabolic capacity, cool‐adapted temperate wet forest species exhibit higher photosynthetic and respiration rates than their warm‐adapted tropical counterparts when compared in a common environment.