Effect of CO2 enrichment on biomass production,photosynthesis, and sink activity in Soybean cv. Bragg and its supernodulating mutant nts 1007

Soybean (Glycine max L. Merr.) cv. Bragg and its supernodulating mutant nts 1007 were grown in pots containing vermiculite with a N-free nutrient solution in order to examine the effect of elevated CO₂ concentration (100+20 Pa CO₂ ) on biomass production, photosynthesis, and biological nitrogen fixation. The whole plant weight increase in Bragg was higher than in the mutant at a high CO₂ concentration. Apparent photosynthetic activities of the upper leaves in both Bragg and the mutant increased up to 14 d after treatment initiation by the CO₂ enrichment and thereafter decreased to some extent. Both leaf area and leaf thickness of Bragg increased more than in nts 1007. With the elevated CO₂ concentration, biological nitrogen fixation (BNF) also responded in the same manner as biomass production in both Bragg and nts 1007. The increase of BNF in Bragg was largely due to an increase in nodule weight. Starch contents in the leaves of both Bragg and the mutant increased significantly by CO₂ enrichment, with a higher increase in Bragg than in its mutant. Sugar content in leaf differed only slightly in both Bragg and the mutant. N content in leaf decreased in both Bragg and its mutant, with the decrease being more pronounced in Bragg. However, in other plant parts (roots, stem, and petiole + pods), N content increased in the mutant while in Bragg, it decreased in the pod. N accumulation rate was higher in Bragg than in the mutant and increased more in Bragg than in the mutant by CO₂ enrichment. The ureide content in leaf decreased in Bragg but increased in the mutant by elevated CO₂ concentration. In the nodules, ureide content increased in both Bragg and the mutant by CO₂ enrichment. Based on these results, it is suggested that in terms of biomass production and photosynthetic rate, Bragg responded more to elevated CO₂ concentration than its mutant nts 1007. The alleviation of the stunted vegetative growth of the mutant by CO₂ enrichment was limited despite the significant increase in the photosynthetic activity, presumably due to the limitation of sink activity in the growing parts and not to insufficient supply of N through BNF.     

硼对砀山酥梨营养生长和果实品质的影响

为改善砀山酥梨树体营养状况,提高果实品质,在其新梢生长期（3～7月份）,叶面喷施不同浓度水平（0.2%,0.3%,0.4%）的硼肥（硼砂）,研究不同处理对砀山酥梨叶片硼含量及其变化动态、砀山酥梨营养生长和果实品质的影响。结果表明:砀山酥梨叶片硼含量随新梢生长而上升,在新梢停长期含量最高,之后开始下降,呈现低高低的变化趋势;叶面喷施不同浓度水平的硼肥后,在0.2%～0.3%范围内,叶片含硼量随喷施浓度的提高而增加;适量施硼促进了砀山酥梨的新梢生长,显著增加了单叶面积、百叶重、叶片叶绿素含量;提高了砀山酥梨果实的可溶性糖、可溶性固形物含量和果肉硬度,降低了果实含酸量。综合果树生长状况、果实品质和生产成本等因素,砀山酥梨树体缺硼时,在新梢生长期的3～7月份,叶面喷施2～3次0.3% 的硼肥效果最好。     

Biomass allocation and organs growth of cucumber (Cucumis sativus L.) under elevated CO2 and different N supply

This article studied the effects of nitrogen (N) and CO₂ enrichment on biomass and N accumulation and partitioning of cucumber grown in open top chambers. At the seedling stage, elevated CO₂ increased the biomass and N content of the entire plant. The root had the largest increase in biomass and N content among the organs and more biomass allocation. The largest drops of N concentration showed in root at moderate and high N, in leaf at low N, respectively. Elevated CO₂ increased stem biomass allocation at moderate and high N, but decreased leaf biomass allocation at all N levels. At the initial fruit stage, the response to elevated CO₂ of biomass and N content decreased. Elevated CO₂ increased biomass allocation to leaf and resulted in the largest drop of leaf N concentration at low and moderate N supply. High N supply promoted biomass production and N reallocation from the leaf to fruit, but decreased leaf biomass allocation. Thus, biomass allocation is initially affected by root–shoot growth balance to adapt to enriched CO₂, leading to the largest root growth, then biomass allocates to another sink (stem). Long exposure of elevated CO₂ results in photosynthetic acclimation in deficient N supply, which probably attributes to excessive stem and leaf biomass allocation and shortage of fruit storage. But high N shifts biomass allocation from leaf to fruit. Practically, sufficient N supply is needed for an efficient transport of carbohydrates to fruits and increases the yields under elevated CO₂.     

Effect of elevated carbon dioxide on growth and nitrogen fixation of two soybean cultivars in northern China

The effect of elevated carbon dioxide (CO₂) concentration on symbiotic nitrogen fixation in soybean under open-air conditions has not been reported. Two soybean cultivars (Glycine max (L.) Merr. cv. Zhonghuang 13 and cv. Zhonghuang 35) were grown to maturity under ambient (415?±?16?μmol?mol^?1) and elevated (550?±?17?μmol?mol^?1) [CO₂] at the free-air carbon dioxide enrichment experimental facility in northern China. Elevated [CO₂] increased above- and below-ground biomass by 16–18% and 11–20%, respectively, but had no significant effect on the tissue C/N ratio at maturity. Elevated [CO₂] increased the percentage of N derived from the atmosphere (%Ndfa, estimated by natural abundance) from 59% to 79% for Zhonghuang 13, and the amount of N fixed from 166 to 275?kg N ha^?1, but had no significant effect on either parameter for Zhonghuang 35. These results suggest that variation in N₂ fixation ability in response to elevated [CO₂] should be used as key trait for selecting cultivars for future climate with respect to meeting the higher N demand driven by a carbon-rich atmosphere.     

PHOTOSYNTHETIC ACCLIMATION AND DECREASED CHLOROPHYLL(A + B) CONCENTRATIONS OCCUR IN NITROGEN-SUFFICIENT TOBACCO LEAVES IN RESPONSE TO CARBON DIOXIDE ENRICHMENT

Effects of carbon dioxide (CO₂) enrichment on plant growth and on nitrogen partitioning were examined in tobacco (Nicotiana tabacum L. cv. ‘Samsun’). Dry matter, leaf area and specific leaf weight were unchanged (P > 0.05) by CO₂ enrichment. Total soluble protein, soluble amino acids and inorganic nitrate also were unaffected by CO₂ enrichment (P > 0.05). Leaf chlorophyll (a + b) levels decreased 13% (P ≤ 0.05) in response to CO₂ enrichment. The diurnal accumulation of soluble amino acids was delayed and the initial slope of the A/C _i response curve was decreased 14% in the elevated compared to the ambient CO₂ treatment. The above findings showed that CO₂ enrichment affected leaf chlorophyll levels, diurnal soluble amino acid metabolism and photosynthetic responses to low intercellular CO₂ concentrations even though the plants were nitrogen sufficient. Inadequate nitrogen fertility cannot explain all of the effects of CO₂ enrichment on photosynthesis by tobacco leaves.     

The influence of carbon dioxide on the growth,pigment, protein,carbohydrate, and mineral status of lettuce

Lettuce plants (Lactuca sativa L. cv. Grand Rapids) were grown in nutrient solution in controlled environment plant growth chambers to characterize certain qualitative responses to above ambient levels of CO₂. Increased plant material produced under high CO₂ levels did not differ nutritionally from plants grown under ambient levels. No differences were found in chloroplast pigment content, protein content, or in carbohydrate content on a weight basis. Sequential harvests did reveal, however, that there is a greater accumulation of carbohydrate, under high CO₂ conditions, prior to an increased growth rate as the plants reach maturity.     

Effects of Plant Growth Promoting Rhizobacteria on Yield and Some Fruit Properties of Strawberry

Effects of plant growth promoting rhizobacteria (PGPR) [(Pseudomonas BA-8 (biological control agent), Bacillus OSU-142 (N₂-fixing), and Bacillus M-3 (N₂-fixing and phosphate solubilizing)] on yield and some fruit properties of strawberry cultivar ‘Selva’ in the province of Erzurum, Turkey in 2002–2003. Foliar + root application of PGPR strains significantly increased yield per plant as compared with the control. Root application of PGPR strains significantly increased total soluble solids, total sugar and reduced sugar, but decreased titratable acidity. It was also determined that bacteria applications have no important effect on the average fruit weight and pH. The results of this study suggested that Pseudomonas BA-8, Bacillus OSU-142 and Bacillus M-3 have potential for increasing yield in strawberry plant.     

The influence of free-air CO2 enrichment on microorganisms of a paddy soil in the rice-growing season

The atmospheric CO₂ concentration is dramatically rising, and this rise may affect soil methanogens, methanotrophs, nitrifiers, and denitrifiers, which are important microorganisms for the processes of carbon and nitrogen turnover. An experimental platform of free-air CO₂ enrichment (FACE) was established in mid-June of 2001 over a rice–wheat rotation ecosystem located in a suburb of Wuxi, China, and its CO₂ fumigation was continued until mid-February of 2004. Using the most probable number (MPN) method, we measured the numbers of methanogens, methanotrophs, nitrifiers, and denitrifiers by sampling fresh soils from the fields exposed to the elevated and ambient CO₂ during the rice-growing season in 2002. Our results show that the elevated CO₂ significantly increased methanogen populations of the cultivated soil layers during the entire rice-growing season. This positive effect of elevated CO₂ may be attributed to stimulated rice growth, which may provide more substrates for methanogens. The methanotroph population was decreased by elevated CO₂ in the upper soil layer (0–5 cm) but was increased in the lower one (5–10 cm) in most rice-growing stages, and the effect of CO₂ elevation was reversed at rice maturity. Elevated CO₂ increased nitrifier and denitrifier populations in most rice stages, but it occasionally decreased the number of nitrifiers late in the growing season and that of denitrifiers early. The methanogen population gradually increased until the filling stage of rice growth but then declined under either elevated or ambient CO₂. Meanwhile the numbers of methanotrophs and nitrifiers gradually decreased during the entire rice season. The number of denitrifiers in the wet/flooded soil during the growing season was also decreased as compared to the dry soil before rice season.     

Factors Affecting on Response of Broad Bean and Corn to Air Quality and Soil CO2 Flux Rates in Egypt

In response to worldwide increases in the burning of fossil fuels to meet energy demands for electric power generation and transportation, atmospheric CO₂ concentrations are currently rising at approximately 0.5% per year and ground-level O₃ values are increasing at a rate of 0.32% per year. Some plants showed positive increases in response to elevated atmospheric CO₂ concentrations, but are depressed when exposed to enhanced O₃ air pollution. The objective of this research was to examine relationships between alterations in leaf plant characteristics in response to air quality treatments and soil CO₂ flux activities during the growing season. Field studies were conducted in 2-m diameter?×?2-m height open-top chambers (OTC’s) at Sharkia Province during 2004 and 2005 involving the growth of broad bean (Vicia faba L. cv. Giza 40) and corn (Zea mays L. cv. 30 K8) in rotations using no-till management while being subjected full-season to five air quality treatments: charcoal-filtered (CF) air; CF + 150 µL CO₂ L^?1; non-filtered (NF) air; NF + 150 µL CO₂ L^?1 and ambient air (AA). Leaf photosynthesis (P_s), leaf area index (LAI), and vegetative carbohydrate contents were determined during pre- and post-anthesis in the two crops and soil CO₂ flux rates were monitored monthly during two growing seasons (2004–2005). Multiple and stepwise regression analyses were performed to establish linkages between plant canopy characteristics and soil CO₂ flux rates with results combined over growth stages and year for each crop. Increasing the atmospheric CO₂ concentration typically stimulated leaf P_s, soluble and total leaf carbohydrate contents, LAI values, and soil CO₂ flux rates throughout the growing season in both crop; however, the elevated O₃ treatments in NF air tended to lower these values compared to CF air. Soil CO₂ flux rates were significantly correlated with LAI, soluble and total sugar contents at P?≤?0.01 and with P_s rates at P?≤?0.05 in broad bean leaves, but with soluble and total sugar contents of leaves in corns at P?≤?0.01 only. Results of this study provided solid evidences linking the impact of changing air quality on plants factors processes and possible indirect effects on soil CO₂ flux activities throughout the growing season.     

Tomato yield and water use efficiency – coupling effects between growth stage specific soil water deficits

To investigate the sensitivity of tomato yield and water use efficiency (WUE) to soil water content at different growth stages, the central composite rotatable design (CCRD) was employed in a five-factor-five-level pot experiment under regulated deficit irrigation. Two regression models concerning the effects of stage-specific soil water content on tomato yield and WUE were established. The results showed that the lowest available soil water (ASW) content (around 28%) during vegetative growth stage (here denoted θ₁) resulted in high yield and WUE. Moderate (around 69% ASW) during blooming and fruit setting stage (θ₂), and the highest ASW (around 92%) during early fruit growth stage (θ₃), fruit development (θ₄) and fruit maturity (θ₅) contributed positively to tomato yield, whereas high WUE was achieved at lower θ₂ and θ₃ ( around 44% ASW) and higher θ₄ and θ₅ (around 76% ASW). The strongest coupling effects of ASW in two growth stages were between θ₂ and θ₅, θ₃. In both cases a moderate θ₂ was a precondition for maximum yield response to increasing θ₅ and θ₃. Sensitivity analysis revealed that yield was most sensitive to soil water content at fruit maturity (θ₅). Numerical inspection of the regression model showed that the maximum yield, 1166 g per plant, was obtained by the combination of θ₁ (c. 28% ASW), θ₂ (c. 82% ASW), θ₃ (c. 92% ASW), θ₄ (c. 92% ASW), and θ₅ (c. 92% ASW). This result may guide irrigation scheduling to achieve higher tomato yield and WUE based on specific soil water contents at different growth stages.     

Effect of different water supply on plant growth and fruit quality of Lycopersicon esculentum

It is well known from earlier work that water stress and salinity results in depressed plant growth and high fruit quality of tomato (e.g. increased sugar and acid levels), but generally is associated with a low marketable fruit yield. In the present work we investigated whether even a small reduction in water supply (without visible symptoms of water stress) also results in a high fruit quality together with high marketable fruit proportions. To characterize fruit quality sugars (glucose and fructose), titratable acids, odour-active aroma volatiles and vitamin C were investigated. Tomato plants (Lycopersicon esculentum Mill. cv Vanessa) were grown in soil and with the onset of fruit development water supply was varied (70% and 50% water capacity). In the treatment with lower water supply plant growth, and in particular the number of fruit settings were depressed and the sugar and vitamin C concentrations in the fruits were significantly increased, especially during fruit ripening. Furthermore, with lower water supply the concentrations of titratable acids and of C₆ aldehydes (hexanal, (Z)-3-hexenal and (E)-2-hexenal) were significantly increased in the red fruits. Fruit growth was identical in both treatments. The higher levels of sugars, titratable acids, aroma volatiles and vitamin C are responsible for the higher fruit quality under conditions of lower water supply. Since not all fruits of the well watered plants became mature, the marketable yield in both treatments was rather similar and hence, together with a higher fruit quality in the treatment with lower water supply, high proportions of marketable fruits can be harvested.     

Treatment of Pistachio Trees with Zinc and Copper in Time of Swollen Bud in Two Consecutive Years

This study was done to investigate the effects of foliar sprays of zinc (Zn) and copper (Cu) on fruit set, yield, yield components, vegetative growth, and leaf nutrient concentrations of pistachio trees (cv. Owhadi), over two consecutive seasons 2010 (ON) and 2011 (OFF). Tests were done at a commercial orchard in the region of Rafsanjan in Iran. Tests were designed as a 3 × 2 factorial experiment in a randomized complete block with four replications. Treatments tested in the study were three concentration levels of zinc sulfate (0, 1000, and 2000 mg L^?1) and two concentration levels of copper sulfate (0 and 200 mg L^?1). Results showed that Zn foliar application increased first fruit set, final fruit set, fresh yield, and dry yield. Nut weight was increased by Zn spray by 3 and 4% at the second and third levels of Zn, respectively, compared with the control. However, Cu application increased splitting and vegetative growth. Vegetative growth in the OFF year was greater than that of the ON year. Phosphorus, sodium, and Cu concentrations in leaf were greater in the ON year than in the OFF year, but concentrations of Zn and potassium in leaf were lower in the ON year than they were in the OFF year. These results show that Zn and Cu applications can affect growth and yield of pistachio, especially when the plant is grown in calcareous soils. However, the alternate bearing pattern had a significant effect on vegetative growth and some leaf nutrient concentrations.     

The Influence of Carbon Dioxide or Ozone Concentration on Growth and Assimilate Partitioning in Seedlings of Nine Conifers

Abstract

Seedlings of nine different conifers were exposed to 355 and 730 μmol mol-1 CO₂, or low (> 15 nmol mol^?1) and elevated 0₃ concentration (70 nmol mol^?1) for 81–116 days. The experiments were conducted in growth chambers placed in a greenhouse. Increased CO₂ concentration enhanced the mean relative growth rate (RGR) and total plant dry weight by 4 and 33% in Larix leptolepis, by 4 and 38% in Larix sibirica, by 7 and 47% in Picea glauca and by 3 and 16% in Picea sitchensis, respectively. The growth rates and dry weights of Pimis contorta, Pinus mugo and Pseudotsuga menziesii were not significantly affected. Carbon dioxide enrichment enhanced RGR of two provenances of Picea abies by 4 and 6%, respectively, while a third provenance was unaffected. In Pimis sylvestris, only the RGR of one of three provenances was stimulated by CO₂ enrichment (4%).

After two growth seasons CO₂ enrichment enhanced RGR and total plant dry weight by 11 and 35% in Picea abies and by 12 and 36% in Pinus sylvestris, respectively. Elevated CO₂ decreased the shoot:root ratio in Larix leptolepis, and decreased the needlerstem ratio in Picea glauca, but increased it in Pseudotsuga menziesii.

Elevated O₃ significantly decreased the plant dry weight in Picea sitchensis, Pseudotsuga menziesii and in one of three provenances of Pinus sylvestris, while the other species and provenances were unaffected. Increased O₃ concentration increased the shoot:root dry weight ratio in one of three Picea abies provenances, in all three Pinus sylvestris provenances and in Pinus contorta. The needle:stem ratio was enhanced by O₃ in seven of the nine species. The O₃ exposure caused chlorosis of needles in all species except Pseudotsuga menziesii.     

园艺地布和秸秆覆盖对枣园土壤温湿度与枣树生长的影响

为比较不同覆盖材料对枣园土壤温湿度及灵武长枣果实品质的影响,以灵武长枣为试验对象,采用园艺地布、秸秆进行全园覆盖,并以清耕为对照(CK),定期测定土壤温湿度变化,枣吊生长和果实有机酸含量、可溶性糖含量、Vc含量等。结果表明,与CK相比,园艺地布覆盖处理枣园日平均土壤温度提高0.7℃,而秸秆覆盖处理的土壤温度降低了2.0℃;2种材料覆盖处理均明显提高枣园日平均土壤湿度,其中园艺地布覆盖处理较CK提高了3.1%,秸秆覆盖处理较CK提高了2.8%;2种材料覆盖处理均对灵武长枣营养生长和果实品质有显著影响,其中秸秆覆盖处理果实的可溶性糖含量较CK提高了33.7%,可溶性固形物含量提高了20.0%。园艺地布覆盖处理果实Vc含量较CK提高了14.8%,可溶性糖含量提高了24.1%。因此,园艺地布、秸秆覆盖能够促进灵武长枣营养生长,提高果实品质。本研究为西北干旱、半干旱地区枣园生产提供了参考。     

Effects of Salinity Stress at Different Growth Stages on Tomato Growth,Yield, and Water-Use Efficiency

This study investigated the effects of salinity stress at different growth stages on the growth, yield, fruit quality, and water-use efficiency (WUE) of tomato (Solanum lycopersicum) plants cultivated under soilless conditions. Six different growth stages were exposed to the same salinity stress treatments using a completely randomized design, with three pots (six plants) per treatment. It was found that short-term (<21 days) salinity stress during any of the growth stages did not affect tomato growth or WUE, and during the vegetative stage did not affect yield. Salinity stress during the flowering and fruiting stages caused a reduction in tomato yield, which was due to a reduction in the number of fruit produced rather than the fruit size. However, salt exposure at the fruiting stage also improved fruit quality. The effect of salinity stress on the yield and fruit quality of the frontal and later truss depended on the developmental stage of the truss at the time when the stress occurred.     

氮钾化肥配合追施对日光温室番茄越冬长季节栽培产量与品质的影响

采用有机基质进行番茄越冬长季节栽培试验,研究尿素和硫酸钾不同追施比例对番茄产量与品质的影响。结果表明,氮钾肥合理配施可维持番茄植株营养生长与生殖生长的平衡,促进植株生长;氮钾肥适宜配比可增加番茄座果数与单果重,提高番茄产量;并增加番茄果实中Vc、还原糖与有机酸的含量,改善果实品质。整体而言,番茄越冬长季节栽培过程中,氮钾(N∶K2O)的追施比例以1∶1.2～1.3为宜;但不同生长时期番茄对氮钾养分的需求比例不同。因此,番茄越冬长季节栽培的生长期肥料供给应采用分段式管理,前期营养生长与生殖生长均旺盛,氮钾(N∶K2O)适宜追施比例为1∶1左右;中期大量钾素随果实采收而移走,应增加钾肥施用量,氮钾(N∶K2O)追施比例宜为1∶1.2～1∶1.4;后期番茄植株营养生长下降,应重视氮钾肥平衡施用,氮钾(N∶K2O)追施比例应为1∶1.2左右。     

Nitrogen supply determines responses of yield and biomass partitioning of perennial ryegrass to elevated atmospheric carbon dioxide concentrations

Perennial ryegrass (Lolium perenne L. cv. Parcour) grown at eight levels of nitrogen (N) fertilization (0–765 mg/pot) was exposed to ambient (390 ppm) and elevated (690 ppm) carbon dioxide (CO₂) concentrations for 83 days. Plants were cut three times and dry matter yields determined for each harvest. At final harvest, dry weight of root and stubble biomass was determined, as N concentrations of all plant fractions were determined. Carbon dioxide enrichment effects on yield and total plant biomass increased with increasing N fertilization. The weaker CO₂‐related yield enhancement at low N supply was due to the plants inability to increase tiller number. Root fraction of total plant biomass at final harvest was increased by high CO₂ and decreased by N supply. Root biomass was significantly increased by CO₂ enrichment and for both CO₂ treatments the N supply for maximum root mass coincided with the N supply for reaching maximum total plant biomass. A significant correlation between root fraction of total plant dry matter and N concentration of total plant biomass, which was not changed by CO₂ enrichment, indicates that biomass partitioning between shoot and root is controlled by the internal N status of the plant.     

Effects of Nitrogen Form and Concentration on Yield and Quality of Cucumbers Grown on Rockwool During Spring and Winter in Southern Greece

The influence of nitrogen concentration and the ratio of NO₃ to NH₄ on the marketable yield and fruit quality characteristics of cucumbers (Cucumis sativus L. cv. Palmera) grown on rockwool during spring and winter in southern Greece were studied. Nitrogen (N) was supplied at three N concentrations and four ratios of NO₃ to NH₄. During the spring, increasing total nitrogen or NH₄ concentration within the nutrient solution significantly decreased the mean total yield and fruit size. However, during the winter, the yield and number of fruits per plant were not affected by N concentration, but were reduced by increasing NH₄:NO₃ ratio. Fruits that were produced under low N concentrations were lighter in color, but only the color of the apical tissues of the fruit was affected by the NH₄:NO₃ ratio. Flesh firmness of the fruit was not affected by N source or concentration, except for the apical tissue, the firmness of which declined with increasing N concentration. On the basis of the present results, for highest yield and fruit quality during both the spring and winter seasons of southern Greece, 100 ppm N applied solely in the form of NO₃ is indicated.     

Effects of carbon dioxide enrichment on cotton nutrient dynamics

The rise in atmospheric carbon dioxide (CO₂) concentration is predicted to have positive effects on agro‐ecosystem productivity. However, an area which requires further study centers on nutrient dynamics of crops grown under elevated CO₂ in the field. In 1989 and 1990, cotton [Gossypium hirsutum (L.) ‘Deltapine 77'] was grown under two CO₂ levels [370 umol mol^‐1=ambient and 550 μmol mor^‐1=free‐air CO₂ enrichment (FACE)]. At physiological maturity, nutrient concentration and content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) were determined for whole plant and individual plant organs. While the effects of added CO₂ on whole plant nutrient concentrations and contents were consistent, some differences among plant organs were observed between years. FACE often decreased tissue nutrient concentration, but increased total nutrient accumulation. Results indicate that under elevated CO₂, field grown cotton was more nutrient efficient in terms of nutrient retrieval from the soil and nutrient utilization in the plant. This implies more efficient fertilizer utilization, better economic return for fertilizer expenditures, and reduced environmental impact from agricultural fertilization practices in the future.     

Assessment of 10 years of CO2 fumigation on soil microbial communities and function in a sweetgum plantation

Increased vegetative growth and soil carbon (C) storage under elevated carbon dioxide concentration ([CO₂]) has been demonstrated in a number of experiments. However, the ability of ecosystems, either above- or belowground, to maintain increased C storage relies on the response of soil processes, such as those that control nitrogen (N) mineralization, to climatic change. These soil processes are mediated by microbial communities whose activity and structure may also respond to increasing atmospheric [CO₂]. We took advantage of a long-term (ca 10 y) CO₂ enrichment experiment in a sweetgum plantation located in the southeastern United States to test the hypothesis that observed increases in root production in elevated relative to ambient CO₂ plots would alter microbial community structure, increase microbial activity, and increase soil nutrient cycling. We found that elevated [CO₂] had no detectable effect on microbial community structure using 16S rRNA gene clone libraries, on microbial activity measured with extracellular enzyme activity, or on potential soil N mineralization and nitrification rates. These results support findings at other forested Free Air [CO₂] Enrichment (FACE) sites.