Effects of Atmospheric CO(2) Enrichment on Photosynthesis, Respiration, and Growth of Sour Orange Trees

Numerous net photosynthetic and dark respiratory measurements were made over a period of 4 years on leaves of 24 sour orange (Citrus aurantium) trees; 8 of them growing in ambient air at a mean CO₂ concentration of 400 microliters per liter, and 16 growing in air enriched with CO₂ to concentrations approaching 1000 microliters per liter. Over this CO₂ concentration range, net photosynthesis increased linearly with CO₂ by more than 200%, whereas dark respiration decreased linearly to only 20% of its initial value. These results, together with those of a comprehensive fine-root biomass determination and two independent aboveground trunk and branch volume inventories, suggest that a doubling of the air's current mean CO₂ concentration of 360 microliters per liter would enhance the growth of the trees by a factor of 3.8.     

Free Atmospheric CO2 Enrichment (FACE) Increased Labile and Total Carbon in the Mineral Soil of a Short Rotation Poplar Plantation

The global net terrestrial carbon sink was estimated to range between 0.5 and 0.7 Pg C y⁻¹ for the early 1990s. FACE (free atmospheric CO₂ enrichment) studies conducted at the whole-tree and community scale indicate that there is a marked increase of primary production, mainly allocated into below-ground biomass. The enhanced carbon transfer to the root system may result in enhanced rhizodeposition and subsequent transfer to soil C pools. During the first rotation of the POP/EuroFACE experiment in a short-rotation Poplar plantation, total soil C content increased more under ambient CO₂ treatment than under FACE, while under FACE more new C was incorporated than under ambient CO₂. These unexpected and opposite effects may have been caused by a priming effect, where priming effect is defined as the stimulation of SOM decomposition caused by the addition of labile substrates. In order to gain insight into these processes affecting SOM decomposition, we obtained the labile, refractory and stable pools of soil C and N by chemical fractionation (acid hydrolysis) and measured rates of N-mineralization. Results of the first 2 years of the second rotation show a larger increase of total soil C% under FACE than under ambient CO₂. In contrast to the first rotation, total C% is now increasing faster under FACE than under ambient CO₂. Based on these observations we infer that the priming effect ceased during the second rotation. FACE treatment increased the labile C fraction at 0–10 cm depth, which is in agreement with the larger input of plant litter and root exudates under FACE. N-mineralization rates were not affected by FACE. We infer that the system switched from a state where extra labile C and sufficient N-availability (due to the former agricultural use of the soil) caused a priming effect (first rotation), to a state where extra C input is accumulating due to limited N-availability (second rotation). Our results on N-mineralization (second rotation) are in agreement with observations made at three forest FACE sites (Duke Forest, Oak Ridge, and Rhinelander), but our finding of increasing mineral soil C content contrasted with results at the Duke Forest where no significant increase in C content of the mineral soil occurred. However, the FACE induced increase in total C content occurred within the fraction with the shortest turnover time, i.e. the labile fraction. The refractory and stable fractions were not affected. The question remains whether the currently observed larger increase of total soil C and the increase of labile C under FACE will eventually result in long-term C storage in refractory and stable organic matter fractions.     

Ethylene Contamination of CO(2) Cylinders: Effects on Plant Growth in CO(2) Enrichment Studies

The mechanical extensibilities of stage IVb Phycomyces were measured before and after a humidified wind stimulus. We find that when the humidity of the wind is greater than that of the ambient air, there is an increase in the mechanical extensibility of the cell wall. We also find that a step decrease in wind humidity results in a decrease in the mechanical extensibility of the cell wall.     

Long-term Effects of Free Air CO2 Enrichment (FACE) on Soil Respiration

Emissions of CO₂ from soils make up one of the largest fluxes in the global C cycle, thus small changes in soil respiration may have large impacts on global C cycling. Anthropogenic additions of CO₂ to the atmosphere are expected to alter soil carbon cycling, an important component of the global carbon budget. As part of the Duke Forest Free-Air CO₂ Enrichment (FACE) experiment, we examined how forest growth at elevated (+200 ppmv) atmospheric CO₂ concentration affects soil CO₂ dynamics over 7 years of continuous enrichment. Soil respiration, soil CO₂ concentrations, and the isotopic signature of soil CO₂ were measured monthly throughout the 7 years of treatment. Estimated annual rates of soil CO₂ efflux have been significantly higher in the elevated plots in every year of the study, but over the last 5 years the magnitude of the CO₂ enrichment effect on soil CO₂ efflux has declined. Gas well samples indicate that over 7 years fumigation has led to sustained increases in soil CO₂ concentrations and depletion in the δ¹³C of soil CO₂ at all but the shallowest soil depths.     

Three Phases of Plant Response to Atmospheric CO(2) Enrichment

Several years of research on seven different plants (five terrestrial and two aquatic species) suggest that the beneficial effects of atmospheric CO₂ enrichment may be divided into three distinct growth response phases. First is a well-watered optimum-growth-rate phase where a 300 parts per million increase in the CO₂ content of the air generally increases plant productivity by approximately 30%. Next comes a nonlethal water-stressed phase where the same increase in atmospheric CO₂ is more than half again as effective in increasing plant productivity. Finally, there is a water-stressed phase normally indicative of impending death, where atmospheric CO₂ enrichment may actually prevent plants from succumbing to the rigors of the environment and enable them to maintain essential life processes, as life ebbs from corresponding ambient-treatment plants.     

Growth and maintenance respiration in stems of Quercus alba after four years of CO2 enrichment

Atmospheric CO₂ enrichment is increasingly being reported to inhibit leaf and whole-plant respiration. It is not known, however, whether this response is unique to foliage or whether woody-tissue respiration might be affected as well. This was examined for mid-canopy stem segments of white oak (Quercus alba L.) trees that had been grown in open-top field chambers and exposed to either ambient or ambient + 300 µmol mol^?1 CO₂ over a 4-year period. Stem respiration measurements were made throughout 1992 by using an infrared gas analyzer and a specially designed in situ cuvette. Rates of woody-tissue respiration were similar between CO₂ treatments prior to leaf initiation and after leaf senescence, but were several fold greater for saplings grown at elevated concentrations of CO₂ during much of the growing season. These effects were most evident on 7 July when stem respiration rates for trees exposed to elevated CO₂ concentrations were 7.25 compared to 3.44 µmol CO₂ m^?2 s^?1 for ambient-grown saplings. While other explanations must be explored, greater rates of stem respiration for saplings grown at elevated CO₂ concentrations were consistent with greater rates of stem growth and more stem-wood volume present at the time of measurement. When rates of stem growth were at their maximum (7 July to 3 August), growth respiration accounted for about 80 to 85% of the total respiratory costs of stems at both CO₂ treatments, while 15 to 20% supported the costs of stem-wood maintenance. Integrating growth and maintenance respiration throughout the season, taking into account treatment differences in stem growth and volume, indicated that there were no significant effects of elevated CO₂ concentration on either respiratory process. Quantitative estimates that could be used in modeling the costs of woody-tissue growth and maintenance respiration are provided.     

Effect of Atmospheric CO(2) Enrichment on Growth, Nonstructural Carbohydrate Content, and Root Nodule Activity in Soybean

The objective of this study was to determine whether the supply of current photosynthate was limiting root nodule activity. Both short-term (36 hours) and long-term (16 days) periods of CO₂ enrichment were imposed on vegetative, growth chamber-grown soybean plants (Glycine max. [L.] Merr. cv. `Clay') to increase the supply of current photosynthate and to observe the effects on photosynthate partitioning in the plants, plant growth, and root nodule activity.     

施肥对红豆树苗木生长、根系结瘤和矿质营养的影响

探讨几种市售肥料对红豆树(Ormosia hosiei)苗木各器官生长发育及养分含量的影响,为培育红豆树优质苗木选用肥料提供参考。以红豆树当年生大田苗为试材,采用3种常见肥料(复合肥、缓释肥和尿素)分3个施肥水平进行施肥试验,测定苗高、地径、根系指标、根系结瘤指标、各器官生物量及N、P、K含量,对不同施肥处理苗木质量进行综合评价。不同施肥处理对红豆树苗木生长、结瘤和矿质营养均有显著或极显著影响。施缓释肥和复合肥的处理表现为随施肥量的增加苗木的生长和生理指标均表现出先增后降趋势,施尿素则表现为随施肥量增加呈逐渐递减趋势。通过隶属函数对苗木质量进行综合评价,表明缓释肥30 g·m^-2为最佳施肥处理,其苗高增量、各根系质量指标、各生物量指标、结瘤数量以及根、茎、叶的N、P、K含量均为最大。红豆树当年生苗木密度为50 株·m-2时,施用缓释肥(N-P-K: 30-6-7) 30 g·m^-2可以有效提高红豆树的苗木质量。     

Effect of Atmospheric CO2 Enrichment on Root Growth and Carbohydrate Allocation of Phaseolus spp

A glasshouse experiment was conducted with plants of Phaseolus grown in liquid culture. Root growth parameters (biomass, diameter, length, growth rate, zone of cell division), root rheological components (wall extensibility, water potential yield threshold, water potential), shoot growth, carbon allocation, and abscisic acid (ABA) concentration were measured in Phaseolus acutifolius A. Gray at ambient (550 μmol mol-1) and elevated (700 μmol mol-1) atmospheric CO2 concentrations. For contrast, measurements of above- and belowground growth were conducted on Phaseolus vulgaris L. in the same treatments. Under nonlimiting conditions of water and nutrients, elevated CO2 increased root and shoot growth of P. acutifolius but not P. vulgaris. While root mass was increased by nearly 60% in P. acutifolius, there was no effect of atmospheric CO2 on any of the rheological components measured. In contrast, starch and ABA accumulated in roots of P. acutifolius. The concentration of starch in roots of P. acutifolius increased by 10-fold, while root concentrations of ABA doubled. From the data it is concluded that CO2 enrichment is favorable for root growth in some species in that more carbon is allocated to belowground growth. In addition, ABA may play a role in growth responses and/or allocation of photosynthates at elevated CO2 in P. acutifolius.     

Photosynthesis and Growth of Water Hyacinth under CO(2) Enrichment

Water hyacinth (Eichhornia crassipes [Mart.] Solms) plants were grown in environmental chambers at ambient and enriched CO₂ levels (330 and 600 microliters CO₂ per liter). Daughter plants (ramets) produced in the enriched CO₂ gained 39% greater dry weight than those at ambient CO₂, but the original mother plants did not. The CO₂ enrichment increased the number of leaves per ramet and leaf area index, but did not significantly increase leaf size or the number of ramets formed. Flower production was increased 147%. The elevated CO₂ increased the net photosynthetic rate of the mother plants by 40%, but this was not maintained as the plants acclimated to the higher CO₂ level. After 14 days at the elevated CO₂, leaf resistance increased and transpiration decreased, especially from the adaxial leaf surface. After 4 weeks in elevated as compared to ambient CO₂, ribulose bisphosphate carboxylase activity was 40% less, soluble protein content 49% less, and chlorophyll content 26% less; whereas starch content was 40% greater. Although at a given CO₂ level the enriched CO₂ plants had only half the net photosynthetic rate of their counterparts grown at ambient CO₂, they showed similar internal CO₂ concentrations. This suggested that the decreased supply of CO₂ to the mesophyll, as a result of the increased stomatal resistance, was counterbalanced by a decreased utilization of CO₂. Photorespiration and dark respiration were lower, such that the CO₂ compensation point was not altered. The photosynthetic light and CO₂ saturation points were not greatly changed, nor was the O₂ inhibition of photosynthesis (measured at 330 microliters CO₂ per liter). It appears that with CO₂ enrichment the temporary increase in net photosynthesis produced larger ramets. After acclimation, the greater total ramet leaf area more than compensated for the lower net photosynthetic rate on a unit leaf area basis, and resulted in a sustained improvement in dry weight gain.     

The Effects of CO2 Enrichment and Nutrient Supply on Growth Morphology and Anatomy of Phaseolus vulgaris L. Seedlings

Plants of Phaseolus vulgaris were grown from seed in open-topgrowth chambers at the present (P, 350 µmol mol^–1)atmospheric CO₂ concentration and at an elevated (E, 700 µmolmol^–1) CO₂ concentration, and at low (L, without additionalnutrient solution) and high (H, with additional nutrient solution)nutrient supply for 28 d The effects of CO₂ and nutrient availabilitywere examined on growth, morphological and biochemical characteristics Leaf area and dry mass were significantly increased by CO₂ enrichmentand by high nutrient supply Stomatal density, stomatal indexand epidermal cell density were not affected by elevated CO₂concentration or by nutrient supply Leaf thickness respondedpositively to CO₂ increasing particularly in mesophyll areaas a result of cell enlargement Intercellular air spaces inthe mesophyll decreased slightly in plants grown in elevatedCO₂ Leaf chlorophyll content per unit area or dry mass was significantlylower in elevated CO₂ grown plants and increased significantlywith increasing nutrient availability The content of reducingcarbohydrates of leaves, stem, and roots was not affected byCO₂ but was significantly increased by nutrient addition inall plant parts Starch content in leaves and stem was significantlyincreased by elevated CO₂ concentration and by high nutrientsupply Phaseolus vulgaris, elevated atmospheric CO₂, CO₂-nutrient interaction, stomatal density, leaf anatomy, chlorophyll, carbohydrates, starch     

Combined Effects of CO2 Enrichment and Drought Stress on Growth and Energetic Properties in the Seedlings of a Potential Bioenergy Crop Jatropha curcas

The rapid growth of worldwide energy demands has led to mounting concerns about energy shortages and has promoted the development of biofuels, which are susceptible to climate change. To evaluate the effects of future environmental changes such as CO₂ enrichment and water stress on the growth and biodiesel production of bioenergy plants, we exposed Jatropha curcas to two levels of CO₂ concentration (ambient and elevated) and three watering regimes (well-watered, moderate drought, and severe drought) to study its biomass accumulation and allocation, energy cost-gain properties, and photosynthetic response. Elevated CO₂ enhanced biomass accumulation of J. curcas by 31.5, 25.9, and 14.4 % under well-watered, moderate drought, and severe drought treatments, respectively, indicating that the stimulating effect was greater under optimum water conditions than in water-deficit conditions. Drought stress significantly increased the biomass allocation to roots, especially the fine roots. CO₂ enrichment also increased the root mass fraction, though not significantly. CO₂ enrichment significantly enhanced the photosynthetic rate measured under growth CO₂ concentration (A _growth) and decreased foliar N content and therefore construction cost irrespective of watering conditions. Under elevated CO₂, J. curcas employed a quicker return energy use strategy indicated by the higher photosynthetic energy use efficiency and lower payback time. There was a pronounced downregulation in the light-saturated photosynthetic rate under the common CO₂ concentration (P _max) under long-term CO₂ exposure, due to a decrease in the initial and total ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities and partially lower foliar N content. The significant interaction of CO₂ enrichment and watering regimes implied that the stimulation of plant growth by CO₂ enrichment may be negated by soil drought in the future. Long-term field experiments manipulating multiple factors simultaneously are needed to explore how the ecophysiological traits measured for J. curcas translate into bioenergy production.     

Root Damage by Insects Reverses the Effects of Elevated Atmospheric CO2 on Eucalypt Seedlings

Predicted increases in atmospheric carbon dioxide (CO₂) are widely anticipated to increase biomass accumulation by accelerating rates of photosynthesis in many plant taxa. Little, however, is known about how soil-borne plant antagonists might modify the effects of elevated CO₂ (eCO₂), with root-feeding insects being particularly understudied. Root damage by insects often reduces rates of photosynthesis by disrupting root function and imposing water deficits. These insects therefore have considerable potential for modifying plant responses to eCO₂. We investigated how root damage by a soil-dwelling insect (Xylotrupes gideon australicus) modified the responses of Eucalyptus globulus to eCO₂. eCO₂ increased plant height when E. globulus were 14 weeks old and continued to do so at an accelerated rate compared to those grown at ambient CO₂ (aCO₂). Plants exposed to root-damaging insects showed a rapid decline in growth rates thereafter. In eCO₂, shoot and root biomass increased by 46 and 35%, respectively, in insect-free plants but these effects were arrested when soil-dwelling insects were present so that plants were the same size as those grown at aCO₂. Specific leaf mass increased by 29% under eCO₂, but at eCO₂ root damage caused it to decline by 16%, similar to values seen in plants at aCO₂ without root damage. Leaf C:N ratio increased by >30% at eCO₂ as a consequence of declining leaf N concentrations, but this change was also moderated by soil insects. Soil insects also reduced leaf water content by 9% at eCO₂, which potentially arose through impaired water uptake by the roots. We hypothesise that this may have impaired photosynthetic activity to the extent that observed plant responses to eCO₂ no longer occurred. In conclusion, soil-dwelling insects could modify plant responses to eCO₂ predicted by climate change plant growth models.     

Interactive Effects of CO(2) and O(2) in Soil on Root and Top Growth of Barley and Peas

Barley and pea plants were grown under several regimens of different compositions of soil atmosphere, the O₂ concentration varying from 0 to 21% and the CO₂ concentration from 0 to 8%. In absence of CO₂, the effect of O₂ on root length in barley was characterized by equal root lengths within the range of 21 to 7% O₂ and a steep decline between 7 and 0%. In peas, while showing the same general response, the decline occurred between 14 and 7% O₂. Root numbers of the seminal roots of barley decreased already with reduction in O₂ concentration from 21 to 14%. Dry matter production was affected somewhat differently by O₂ and CO₂ concentration. Dry matter production in barley was reduced at 14% O₂ while root length decreased between 7 and 0%. In peas, dry matter production was favored by low CO₂ concentrations except where there was no oxygen. At 21% O₂, increasing CO₂ concentrations did not seem to affect root length up to concentrations of 2% CO₂. At 8% CO₂, root length was decreased. The inter-active effects of CO₂ and O₂ are characterized by a reduced susceptibility to CO₂ at O₂ values below 7%, and a very deleterious effect of 8% CO₂ at 7% O₂.     

Effects of CO(2) Enrichment and Carbohydrate Content on the Dark Respiration of Soybeans

During the period of most active leaf expansion, the foliar dark respiration rate of soybeans (Glycine max cv Williams), grown for 2 weeks in 1000 microliters CO₂ per liter air, was 1.45 milligrams CO₂ evolved per hour leaf density thickness, and this was twice the rate displayed by leaves of control plants (350 microliters CO₂ per liter air). There was a higher foliar nonstructural carbohydrate level (e.g. sucrose and starch) in the CO₂ enriched compared with CO₂ normal plants. For example, leaves of enriched plants displayed levels of nonstructural carbohydrate equivalent to 174 milligrams glucose per gram dry weight compared to the 84 milligrams glucose per gram dry weight found in control plant leaves. As the leaves of CO₂ enriched plants approached full expansion, both the foliar respiration rate and carbohydrate content of the CO₂ enriched leaves decreased until they were equivalent with those same parameters in the leaves of control plants. A strong positive correlation between respiration rate and carbohydrate content was seen in high CO₂ adapted plants, but not in the control plants.

Mitochondria, isolated simultaneously from the leaves of CO₂ enriched and control plants, showed no difference in NADH or malate-glutamate dependent O₂ uptake, and there were no observed differences in the specific activities of NAD⁺ linked isocitrate dehydrogenase and cytochrome c oxidase. Since the mitochondrial O₂ uptake and total enzyme activities were not greater in young enriched leaves, the increase in leaf respiration rate was not caused by metabolic adaptations in the leaf mitochondria as a response to long term CO₂ enrichment. It was concluded, that the higher respiration rate in the enriched plant's foliage was attributable, in part, to a higher carbohydrate status.

     

Effects of CO2 Enrichment on Four Poplar Clones. I. Growth and Leaf Anatomy

The poplar clones Columbia River, Beaupre, Robusta and Raspaljehave been investigated under the present (350 µmol mol^–1)and double the present (700 µmol mol^–1) atmosphericCO₂ concentration. Cuttings were planted in pots and were grownin open-top chambers inside a glasshouse for 92 d. The number of leaves, total length of stem, total leaf area,overall growth rate, total leaf, stem and root d. wt respondedpositively to increased CO₂ but the leaf size and biomass allocationshowed no change with CO₂ enrichment. Beaupre and Robusta showeda larger growth response than either Columbia River or Raspalje. The effects of CO₂ enrichment were restricted to the early phaseof growth at the beginning of the growth season. Leaf cell numbers in all the clones were not affected by CO₂enrichment. Leaf thickness was affected; this was mainly theresult of larger mesophyll cells and more extensive intercellularspaces. Poplar clones, CO₂ enrichment, growth, leaf anatomy, leaf cell number     

The Influence of Resaturation Method and Tissue 3Quercus alba L. Seedlings

Parker, W. C. and Pallardy, S. G. 1987. The influence of resaturationmethod and tissue type on pressure-volume analysis of Quercusalba L. seedlings.—J. exp. Bot. 38: 535–549. The effect of resaturation method and amount of woody tissueon pressure-volume analysis was investigated using materialcollected from Quercus alba L. seedlings. Leaves excised fromwell-irrigated, intact plants had lower initial xylem pressurepotentials than did leaves resaturated by two artificial methods.Differential capacity for tissue rehydration among the threemethods was linked to shifts in the relative position of pressure-volumecurves, and differences in the osmotic potential and relativewater content at which turgor loss occurred were observed. Pressure-volumecurves from leaves resaturated by all three methods contained‘plateaus’ near full turgor, where xylem pressurepotential declined only slightly with relative water content.These plateaus were apparently associated with apoplastic waterthat accumulated in intercellular spaces of the leaf near fullturgidity, and acted to buffer changes in leaf xylem pressurepotential as tissues dehydrated. The presence of this waterhas implications for derived water relations parameter estimates.Pressure-volume curves for excised shoots also exhibited plateaus,but the relationship between xylem pressure potential and relativewater content over this region was steeper than was found forleaves. Shoot osmotic potentials were somewhat lower than thosefor leaves. The slope of the linear portion of shoot pressure-volumecurves was more shallow than for single leaves, a response associatedwith comparatively lower values of the symplastic water fractionin shoots. Key words: Pressure-volume curve, tissue-water relations, elasticity     

Growth under elevated CO(2) ameliorates defenses against photo-oxidative stress in poplar (Populus alba x tremula)

To test the hypothesis that growth-CO(2) concentrations affect stress susceptibility, leaves of poplar trees (Populus alba x tremula) grown under ambient or about twofold ambient CO(2) concentrations were subjected to chilling temperatures at high light intensities or were exposed to paraquat. Photosynthesis was less diminished and electrolyte leakage was lower in stressed leaves from poplar trees grown under elevated [CO(2)] as compared with those from ambient [CO(2)]. Severe stress caused pigment and protein degradation but to a lower extent in leaves from elevated as compared with those from ambient [CO(2)]. The protection was accompanied by rapid induction of superoxide dismutase activities (EC 1.15.1.1). Ascorbate and glutathione-related detoxification systems as well as catalase (EC 1.11.1.6) activities were less resistant than superoxide dismutases and declined in stress-exposed leaves from poplars grown under elevated [CO(2)] to a similar extent as in those from trees grown under ambient [CO(2)]. These results suggest that the CO(2)-mediated amelioration of stress was confined to SOD and limited since the destruction of H(2)O(2)-degrading systems was not prevented.