Phosphorus supply enhances the response of legumes to elevated CO2 (FACE) in a phosphorus-deficient vertisol

Background & aims

Understanding the mechanism of how phosphorus (P) regulates the response of legumes to elevated CO₂ (eCO₂) is important for developing P management strategies to cope with increasing atmospheric CO₂ concentration. This study aimed to explore this mechanism by investigating interactive effects of CO₂ and P supply on root morphology, nodulation and soil P fractions in the rhizosphere.

Methods

A column experiment was conducted under ambient (350?ppm) (aCO₂) and eCO₂ (550?ppm) in a free air CO₂ enrichment (FACE) system. Chickpea and field pea were grown in a P-deficient Vertisol with P addition of 0–16?mg?P?kg^?1.

Results

Increasing P supply increased plant growth and total P uptake with the increase being greater under eCO₂ than under aCO₂. Elevated CO₂ increased root biomass and length, on average, by 16?% and 14?%, respectively. Nodule biomass increased by 46?% in response to eCO₂ at 16?mg P kg^?1, but was not affected by eCO₂ at no P supply. Total P uptake was correlated with root length while N uptake correlated with nodule number and biomass regardless of CO₂ level. Elevated CO₂ increased the NaOH-extractable organic P by 92?% when 16?mg P kg^?1 was applied.

Conclusion

The increase in P and N uptake and nodule number under eCO₂ resulted from the increased biomass production, rather than from changes in specific root-absorbing capability or specific nodule function. Elevated CO₂ appears to enhance P immobilization in the rhizosphere.     

The plasticity of the growth and proliferation of wheat root system under elevated CO2

Background and Aims

Understanding crop responses to increasing atmospheric CO₂ requires knowledge of how their root systems grow, proliferate and function. The effect of elevated CO₂ on the growth and proliferation of wheat root system (Triticum aestivum L.), was examined.

Methods

Two pairs of sister lines of wheat contrasting in vigour (CV97 and CV207) and tillering (7750N and 7750PF) were grown in rhizo-boxes under ambient (380 μl L^?1) and elevated CO₂ (700 μl L^?1), and the root growth and proliferation mapped.

Results

Elevated CO₂ effects on shoot and root biomass were observed in the lines contrasting for vigour, but not in the lines contrasting for tillering. Root biomass was reduced by 67 % in the high vigour line CV97, reducing total plant biomass by 26 % compared to the low vigour line, CV207. This was due to a reduction in root length down the 1 m soil profile and root proliferation in the top 0.2 m layer. The reduction in root biomass was not compensated by an increase in shoot biomass.

Conclusions

The reduction in root biomass under elevated CO₂ in the vigour line CV97 can be explained through its inability to increase the sink strength due to the failure to increase tiller number to which the plant presumably responded by increasing losses of the newly assimilated carbon by respiration.     

Arbuscular mycorrhizas and their role in plant growth, nitrogen interception and soil gas efflux in an organic production system

Background and aims

Roots and mycorrhizas play an important role in not only plant nutrient acquisition, but also ecosystem nutrient cycling.

Methods

A field experiment was undertaken in which the role of arbuscular mycorrhizas (AM) in the growth and nutrient acquisition of tomato plants was investigated. A mycorrhiza defective mutant of tomato (Solanum lycopersicum L.) (named rmc) and its mycorrhizal wild type progenitor (named 76R) were used to control for the formation of AM. The role of roots and AM in soil N cycling was studied by injecting a ¹⁵N-labelled nitrate solution into surface soil at different distances from the 76R and rmc genotypes of tomato, or in plant free soil. The impacts of mycorrhizal and non-mycorrhizal root systems on soil greenhouse gas (CO₂ and ¹⁴⁺¹⁵N₂O and ¹⁵N₂O) emissions, relative to root free soils, were also studied.

Results

The formation of AM significantly enhanced plant growth and nutrient acquisition, including interception of recently applied NO ₃ ^? . Whereas roots caused a small but significant decrease in ¹⁵N₂O emissions from soils at 23?h after labeling, compared to the root-free treatment, arbuscular mycorrhizal fungi (AMF) had little effect on N₂O emissions. In contrast soil CO₂ emissions were higher in plots containing mycorrhizal root systems, where root biomass was also greater.

Conclusions

Taken together, these data indicate that roots and AMF have an important role to play in plant nutrient acquisition and ecosystem N cycling.     

Elevated CO2 improves root growth and cadmium accumulation in the hyperaccumulator Sedum alfredii

Aims

This study examined the effect of elevated CO₂ on plant growth, root morphology and Cd accumulation in S. alfredii, and assessed the possibility of using elevated CO₂ as fertilizer to enhance phytoremediation efficiency of Cd-contaminated soil by S. alfredii.

Methods

Both soil pot culture and hydroponic experiments were carried out to characterize plant biomass, root morphological parameters, and cadmium uptake in S. alfredii grown under ambient (350 μL L^?1) or elevated (800 μL L^?1) CO₂.

Results

Elevated CO₂ prompted the growth of S. alfredii, shoot and root biomass were increased by 24.6–36.7% and 35.0–52.1%, respectively, as compared with plants grown in ambient CO₂. After 10 days growth in medium containing 50 μM Cd under elevated CO₂, the development of lateral roots and root hairs were stimulated, additionally, root length, surface area, root volume and tip number were increased significantly, especially for the finest diameter roots. The total Cd uptake per pot was significantly greater under elevated CO₂ than under ambient CO₂. After 60 d growth, Cd phytoextraction efficiency was increased significantly in the elevated CO₂ treatment.

Conclusions

Results suggested that the use of elevated CO₂ may be a useful way to improve phytoremediation efficiency of Cd-contaminated soil by S. alfredii.     

Net root growth and nutrient acquisition in response to predicted climate change in two contrasting heathland species

Background and aims

Accurate predictions of nutrient acquisition by plant roots and mycorrhizas are critical in modelling plant responses to climate change.

Methods

We conducted a field experiment with the aim to investigate root nutrient uptake in a future climate and studied root production by ingrowth cores, mycorrhizal colonization, and fine root N and P uptake by root assay of Deschampsia flexuosa and Calluna vulgaris.

Results

Net root growth increased under elevated CO₂, warming and drought, with additive effects among the factors. Arbuscular mycorrhizal colonization increased in response to elevated CO₂, while ericoid mycorrhizal colonization was unchanged. The uptake of N and P was not increased proportionally with root growth after 5 years of treatment.

Conclusions

While aboveground biomass was unchanged, the root growth was increased under elevated CO₂. The results suggest that plant production may be limited by N (but not P) when exposed to elevated CO₂. The species-specific response to the treatments suggests different sensitivity to global change factors, which could result in changed plant competitive interactions and belowground nutrient pool sizes in response to future climate change.     

N2 fixation of pea hypernodulating mutants is more tolerant to root pruning than that of wild type

Background and aims

As a legume, pea plant has the ability to symbiotically fix N₂. However, symbiotic N₂ fixation is very sensitive to environmental stresses that affect plant growth, and there is little knowledge on the impact of root pruning on N₂ fixation and plant growth.

Methods

In this study, we removed half of the nodulated roots of pea wild-type Frisson and hypernodulating mutants P64, P118, and P121. Dinitrogen fixation was measured using ¹⁵N labeling and carbon assimilation and partitioning between plant organs using ¹³C labeling.

Results

Root pruning decreased N₂ fixation by ?46 to ?79 % in wild-type and mutants. Pea mutant P118 had a lower decrease of specific activity of N₂ fixation (?17 %) than both wild-type and other mutants (?36 to ?62 %). For all genotypes, root pruning increased root and nodule sinks strengths for carbon. For P118 and for P121, this was associated to higher nodule growth than for control plants, as measured 8 days after root pruning.

Conclusion

This is the first analysis of N₂-fixing plant response to root pruning. Importantly, we showed that some hypernodulating mutant pea lines (P118 and to a lesser extent P121) withstood this stress better than wild-type did.     

Spatial distribution and turnover of root-derived carbon in alfalfa rhizosphere depending on top- and subsoil properties and mycorrhization

Aims

This study analyzed the extent to which root exudates diffuse from the root surface towards the soil depending on topsoil and subsoil properties and the effect of arbuscular mycorrhizal fungal hyphae on root-derived C distribution in the rhizosphere.

Methods

Alfalfa was grown in three-compartment pots. Nylon gauze prevented either roots alone or roots and arbuscular mycorrhizal fungal hyphae from penetrating into the rhizosphere compartments. ¹⁴CO₂ pulse labeling enabled the measurement of ¹⁴C-labeled exudates in dissolved (DOC) and total organic carbon (TOC) in the rhizosphere, distributed either by diffusion alone or by diffusion, root hair and hyphal transport.

Results

Root exudation and microbial decomposition of exudates was higher in the rhizosphere with topsoil compared to subsoil properties. Exudates extended over 28 mm (DOC) and 20 mm (TOC). Different soil properties and mycorrhization, likely caused by the low arbuscular mycorrhizal colonization of roots (13?±?4 % (topsoil properties) and 18?±?5 % (subsoil properties)), had no effect.

Conclusions

Higher microbial decomposition compensated for higher root exudation into the rhizosphere with topsoil properties, which resulted in equal exudate extent when compared to the rhizosphere with subsoil properties. Higher ¹⁴C activity used for labeling compared with previous studies enabled the detection of low exudate concentrations at longer distances from the root surface.     

Genetic variation in plant below-ground response to elevated CO2 and two herbivore species

Aims

It is unclear how changing atmospheric conditions, including rising carbon dioxide concentration, influence interactions between above and below-ground systems and if intraspecific variation exists in this response.

Methods

We assessed interactive effects of atmospheric CO₂ concentration, above-ground herbivory, and plant genotype on root traits and mycorrhizal associations. Plants from five families of Asclepias syriaca, a perennial forb, were grown under ambient and elevated atmospheric CO₂ concentrations. Foliar herbivory by either lepidopteran caterpillars or phloem-feeding aphids was imposed. Mycorrhizal colonization, below-ground biomass, root biomass, and secondary defensive chemistry in roots were quantified.

Results

We observed substantial genetic variation among A. syriaca families in their mycorrhizal colonization levels in response to elevated CO₂ and herbivory treatments. Elevated CO₂ treatment increased root biomass in all genetic families, whereas foliar herbivory tended to decrease root biomass. Root cardenolide concentration and composition varied greatly among plant families, and elevated CO₂ treatment increased root cardenolides in two of the five plant families. Moreover, herbivores differentially affected the composition of cardenolides expressed below ground.

Conclusions

Increased atmospheric CO₂ has the potential to influence interactions among plants, herbivores and mycorrhizal fungi and intraspecific variation suggests that such interactions can evolve.     

Conservation agriculture, increased organic carbon in the top-soil macro-aggregates and reduced soil CO2 emissions

Background and aims

Conservation agriculture, the combination of minimal soil movement (zero or reduced tillage), crop residue retention and crop rotation, might have the potential to increase soil organic C content and reduce emissions of CO₂.

Methods

Three management factors were analyzed: (1) tillage (zero tillage (ZT) or conventional tillage (CT)), (2) crop rotation (wheat monoculture (W), maize monoculture (M) and maize-wheat rotation (R)), and (3) residue management (with (+r), or without (?r) crop residues). Samples were taken from the 0–5 and 5–10?cm soil layers and separated in micro-aggregates (< 0.25?mm), small macro-aggregates (0.25 to 1?mm) and large macro-aggregates (1 to 8?mm). The carbon content of each aggregate fraction was determined.

Results

Zero tillage combined with crop rotation and crop residues retention resulted in a higher proportion of macro-aggregates. In the 0–5?cm layer, plots with a crop rotation and monoculture of maize and wheat in ZT+r had the greatest proportion of large stable macro-aggregates (40%) and highest mean weighted diameter (MWD) (1.7?mm). The plots with CT had the largest proportion of micro-aggregates (27%). In the 5–10?cm layer, plots with residue retention in both CT and ZT (maize 1?mm and wheat 1.5?mm) or with monoculture of wheat in plots under ZT without residues (1.4?mm) had the greatest MWD. The 0–10?cm soil layer had a greater proportion of small macroaggregates compared to large macro-aggregates and micro-aggregates. In the 0–10?cm layer of soil with residues retention and maize or wheat, the greatest C content was found in the small and large macro-aggregates. The small macro-aggregates contributed most C to the organic C of the sample. For soil cultivated with maize, the CT treatments had significantly higher CO₂ emissions than the ZT treatments. For soil cultivated with wheat, CTR-r had significantly higher CO₂ emissions than all other treatments.

Conclusion

Reduction in soil disturbance combined with residue retention increased the C retained in the small and large macro-aggregates of the top soil due to greater aggregate stability and reduced the emissions of CO₂ compared with conventional tillage without residues retention and maize monoculture (a cultivation system normally used in the central highlands of Mexico).     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Carbon allocation in Larrea tridentata plant-soil systems as affected by elevated soil moisture and N availability

Background and Aims

Global change will likely express itself in southwestern United States arid lands through changes in amounts and timing of precipitation in response to elevated CO₂ concentrations. In addition, increased nitrogen (N) deposition may occur due to increased urban development. This study addressed the effects of water and N availability on C allocation in arid land soil-plant systems.

Methods

Columns filled with Mojave Desert topsoil containing Larrea tridentata seedlings with two treatment levels each of N and soil moisture were labeled by exposure to ¹³C-enriched CO₂.

Results

Increased soil moisture increased plant biomass, total ¹³C uptake, ¹³C levels in leaves, soil organic matter, and soil respiration, decreased relative C allocation to stems but increased allocation to soil organic matter. Increased soil N availability increased N uptake but decreased C allocation to soil respiration presumably due to decreased substrate supply for microbes. There was no detectable label in carbonate C, suggesting that this pool does not significantly contribute to ecosystem C fluxes.

Conclusions

Our study indicates that increased water availability causes increased C uptake with increased C allocation to soil organic matter in Larrea tridentata-dominated communities while increased N deposition will have a minimal impact on C sequestration.     

Soil carbon dioxide and methane fluxes as affected by tillage and N fertilization in dryland conditions

Background and aims

The effects of tillage and N fertilization on CO₂ and CH₄ emissions are a cause for concern worldwide. This paper quantifies these effects in a Mediterranean dryland area.

Methods

CO₂ and CH₄ fluxes were measured in two field experiments. A long-term experiment compared two types of tillage (NT, no-tillage, and CT, conventional intensive tillage) and three N fertilization rates (0, 60 and 120 kg N ha^?1). A short-term experiment compared NT and CT, three N fertilization doses (0, 75 and 150 kg N ha^?1) and two types of fertilizer (mineral N and organic N with pig slurry). Aboveground and root biomass C inputs, soil organic carbon stocks and grain yield were also quantified.

Results

The NT treatment showed a greater mean CO₂ flux than the CT treatment in both experiments. In the long-term experiment CH₄ oxidation was greater under NT, whereas in the short-term experiment it was greater under CT. The fertilization treatments also affected CO₂ emissions in the short-term experiment, with the greatest fluxes when 75 and 150 kg organic N ha^?1 was applied. Overall, the amount of CO₂ emitted ranged between 0.47 and 6.0 kg CO₂?equivalent kg grain^?1. NT lowered yield-scaled emissions in both experiments, but these treatment effects were largely driven by an increase in grain yield.

Conclusions

In dryland Mediterranean agroecosystems the combination of NT and medium rates of either mineral or organic N fertilization can be an appropriate strategy for optimizing CO₂ and CH₄ emissions and grain yield.     

Spatial distribution of rhizodeposit carbon of maize (Zea mays L.) in soil aggregates assessed by multiple pulse 13C labeling in the field

Background and aims

Rhizosphere effect is controlled by spatial distribution of rhizodeposits, which may be influenced by soil aggregation and soil moisture regime in relation to water uptake by roots. The objectives of this study were to measure soil organic carbon (SOC) concentration and its δ¹³C abundance by aggregate size in the rooted bulk soil and by distance in the root-free soil vertically and horizontally away from roots, and to measure DOC concentration and its δ¹³C abundance in pore water in the rooted bulk soil after a seasonal pulse labelings of ¹³CO₂ to maize (Zea mays L.).

Methods

Pulse labeling was conducted in the field once a week for 11 weeks. Soil cells (50 mm in diameter and 100 mm long) mimicking root-free soils were imbedded vertically and horizontally 25–50 mm away from the main root of a maize crop. The rooted bulk soils were sampled to extract soil pore water at different suctions and to fractionate aggregates by wet sieving. The root-free soil cells were sliced by 1 mm intervals from the root end to 20 mm away. All the sampling was 12 days after the last labeling after the crop was harvested.

Results and discussion

The δ¹³C abundance before and after the continuous labeling was ?24.20?±?0.05?‰ and ?23.80?±?0.05?‰ in the rooted bulk soil. The labeling caused increases in δ¹³C abundance in all the aggregates in the rooted bulk soil and down to 14 mm away from the roots in both the root-free cells. The δ¹³C abundance was enriched in the >2 mm and 1–2 mm aggregates (?23.17?±?0.12?‰ and ?23.26?±?0.05?‰) though the SOC concentration was not different among the >0.25 mm aggregates, indicating that rhizodeposits or their metabolites were protected and distributed widely in whole soil through soil aggregation. The δ¹³C abundance in pore water (?24.0?±?0.01?‰) was much lower than those soil aggregates and greatest from the >2 μm soil pores though the DOC concentration was greater from the <20 μm soil pores. The δ¹³C abundance was in general greater in the horizontal cell than in the vertical cell. The δ¹³C abundance decreased with the increasing distance to the roots in the vertical cell and peaked at the 5 and 6 mm distance to the roots in the horizontal cell (?23.66?±?0.11?‰ and ?23.5?±?0.10?‰), possibly due to the drier condition unfavorable to microbial decomposition in the horizontal cell. The higher δ¹³C abundance in the horizontal cell than in the vertical cell was accompanied by a lower SOC concentration and a lower C: N ratio within 3 mm away from the roots, suggesting a stronger priming effect due to the longer residence time of rhizodeposits in the horizontal cell than in the vertical cell.

Conclusions

Rhizodeposits or their metabolites were protected during soil aggregation and distributed to 14 mm beyond the rhizosphere in the natural soil-plant system. This extension is of significance in regulating the formation of soil structure and the priming of soil organic matter during the whole life cycle of plants, which needs further study.     

Effect of sand-stabilizing shrubs on soil respiration in a temperate desert

Aims

Explore how soil CO₂ efflux and its components change after moving sand dunes are stabilized with shrubs, and how abiotic factors affect those components at different scales.

Methods

Soil CO₂ efflux from a sand-stabilized area was compared to that from moving sand dunes in the Tengger Desert. To partition rhizosphere respiration (R_R) from soil basal respiration (R_B), a root-isolation plot was established.

Results

Compared to moving sand dunes, total soil respiration (R_T) in the sand-stabilized area increased 3.2 fold to 0.28?±?0.08 μmol CO₂ m^-2?s^-1, two thirds of which was from R_B. Shrub patchiness produced spatial variation in soil respiration, whereas temporal dynamics of soil respiration were affected mainly by soil water content. Shallow soil water content (0–20 cm) influenced R_T and R_B, whereas deep soil water content (30–210 cm) influenced R_R and the ratio R_R/R_T. During most of the year when soil water content was below field capacity, diurnal changes in soil respiration were partially decoupled from soil temperature but could be modeled using soil temperature and photosynthetic active radiation.

Conclusions

Sand-dune stabilization increased soil respiration, and increased R_B from biological soil crust and altered soil properties such as increased soil organic matter contributed more than increased R_R from increased shrubs.     

Elevated CO2 affects plant responses to variation in boron availability

Aim

Effects of elevated CO₂ on N relations are well studied, but effects on other nutrients, especially micronutrients, are not. We investigated effects of elevated CO₂ on response to variation in boron (B) availability in three unrelated species: seed geranium (Pelargonium x hortorum), barley (Hordeum vulgare), and water fern (Azolla caroliniana).

Methods

Plants were grown at two levels of CO₂ (370, 700?ppm) and low, medium, and high B. Treatment effects were measured on biomass, net photosynthesis (P_n) and related variables, tissue nutrient concentrations, and B transporter protein BOR1.

Results

In geranium, there were interactive effects (P?<?0.05) of B and CO₂ on leaf, stem, and total plant mass, root:shoot ratio, leaf [B], B uptake rate, root [Zn], and P_n. Elevated CO₂ stimulated growth at 45?μM B, but decreased it at 450?μM B and did not affect it at 4.5?μM B. P_n was stimulated by elevated CO₂ only at 45?μM B and chlorophyll was enhanced only at 450?μM B. Soluble sugars increased with high CO₂ only at 4.5 and 45?μM B. High CO₂ decreased leaf [B] and B uptake rate, especially at 450?μM B. Though CO₂ and B individually affected the concentration of several other nutrients, B x CO₂ interactions were evident only for Zn in roots, wherein [Zn] decreased under elevated CO₂. Interactive effects of B and CO₂ on growth were confirmed in (1) barley grown at 0, 30, or 1,000?μM B, wherein growth at high CO₂ was stimulated more at 30?μM B, and (2) Azolla grown at 0, 10, and 1,000?μM B, wherein growth at high CO₂ was stimulated at 0 and 10?μM B.

Conclusion

Thus, low and high B both may limit growth stimulation under elevated vs. current [CO₂], and B deficiency and toxicity, already common, may increase in the future.     

Quantifying the effect of soil moisture content on segmenting root system architecture in X-ray computed tomography images

Aims

A commonly accepted challenge when visualising plant roots in X-ray micro Computed Tomography (μCT) images is the similar X-ray attenuation of plant roots and soil phases. Soil moisture content remains a recognised, yet currently uncharacterised source of segmentation error. This work sought to quantify the effect of soil moisture content on the ability to segment roots from soil in μCT images.

Methods

Rice (Oryza sativa) plants grown in contrasting soils (loamy sand and clay loam) were μCT scanned daily for nine days whilst drying from saturation. Root volumes were segmented from μCT images and compared with volumes derived by root washing.

Results

At saturation the overlapping attenuation values of root material, water-filled soil pores and soil organic matter significantly hindered segmentation. However, in dry soil (ca. six days of drying post-saturation) the air-filled pores increased image noise adjacent to roots and impeded accurate visualisation of root material. The root volume was most accurately segmented at field capacity.

Conclusions

Root volumes can be accurately segmented from μCT images of undisturbed soil without compromising the growth requirements of the plant providing soil moisture content is kept at field capacity. We propose all future studies in this area should consider the error associated with scanning at different soil moisture contents.     

Grassland root demography responses to multiple climate change drivers depend on root morphology

Aims

We examine how root system demography and morphology are affected by air warming and multiple, simultaneous climate change drivers.

Methods

Using minirhizotrons, we studied root growth, morphology, median longevity, risk of mortality and standing root pool in the upper soil horizon of a temperate grassland ecosystem for 3 years. Grassland monoliths were subjected to four climate treatments in a replicated additive design: control (C); elevated temperature (T); combined T and summer precipitation reduction (TD); combined TD and elevated atmospheric CO₂ (TDCO₂).

Results

Air warming (C vs T) and the combined climate change treatment (C vs TDCO₂) had a positive effect on root growth rate and standing root pool. However, root responses to climate treatment varied depending on diameter size class. For fine roots (≤ 0.1 mm), new root length and mortality increased under warming but decreased in response to elevated CO₂ (TD vs TDCO₂); for coarse roots (> 0.2 mm), length and mortality increased under both elevated CO₂ and combined climate change drivers.

Conclusions

Our data suggest that the standing roots pool in our grassland system may increase under future climatic conditions. Contrasted behaviour of fine and coarse roots may correspond to differential root activity of these extreme diameter classes in future climate.     

Exposure to warming and CO2 enrichment promotes greater above-ground biomass, nitrogen, phosphorus and arbuscular mycorrhizal colonization in newly established grasslands

Aims

In view of the projected increase in global air temperature and CO₂ concentration, the effects of climatic changes on biomass production, CO₂ fluxes and arbuscular mycorrhizal fungi (AMF) colonization in newly established grassland communities were investigated. We hypothesized that above- and below-ground biomass, gross primary productivity (GPP), AMF root colonization and nutrient acquisition would increase in response to the future climate conditions. Furthermore, we expected that increased below-ground C allocation would enhance soil respiration (R_soil).

Methods

Grassland communities were grown either at ambient temperatures with 375?ppm CO₂ (Amb) or at ambient temperatures +3°C with 620?ppm CO₂ (T+CO₂).

Results

Total biomass production and GPP were stimulated under T+CO₂. Above-ground biomass was increased under T+CO₂ while belowground biomass was similar under both climates. The significant increase in root colonization intensity under T+CO₂, and therefore the better contact between roots and AMF, probably determined the higher above-ground P and N content. R_soil was not significantly affected by the future climate conditions, only showing a tendency to increase under future climate at the end of the season.

Conclusions

Newly established grasslands benefited from the exposure to elevated CO₂ and temperature in terms of total biomass production; higher root AMF colonization may partly provide the nutrients required to sustain this growth response.     

Effects of elevated CO2 and nitrogen addition on soil organic carbon fractions in a subtropical forest

Aims

The aim of this study was to investigate the effects of elevated CO₂ concentration and nitrogen addition on soil organic carbon fractions in subtropical forests where the ambient N deposition was high.

Methods

Seedlings of typical subtropical forest ecosystems were transplanted in ten open-top chambers and grown under CO₂ and nitrogen treatments. The treatments included: 1) elevated CO₂ (700?μmol?mol^-1); 2) N addition of 100?kg NH₄NO₃ ha^-1?yr^-1; 3) combined elevated CO₂ and N addition; and 4) control. We measured soil total organic carbon (TOC), particulate organic carbon (POC), readily oxidizable organic carbon (ROC), and microbial biomass carbon (MBC).

Results

Results showed that elevated CO₂ alone did not significantly affect soil TOC, POC and ROC after 4?years of treatment, but increased soil MBC and soil respiration compared to the control. N addition alone had no significant effect neither on soil TOC, POC and ROC, but decreased MBC and soil respiration over time. However, the elevated CO₂ and N addition together significantly increased soil POC and ROC, and had no significant effect on soil MBC.

Conclusions

This study indicated that even in N-rich subtropical forest ecosystems, inputs of N are still needed in order to sustain soil C accumulation under elevated CO₂.     

Respiratory Motion Reduction in PET/CT Using Abdominal Compression for Lung Cancer Patients

Purpose

Respiratory motion causes substantial artifacts in reconstructed PET images when using helical CT as the attenuation map in PET/CT imaging. In this study, we aimed to reduce the respiratory artifacts in PET/CT images of patients with lung tumors using an abdominal compression device.

Methods

Twelve patients with lung cancer located in the middle or lower lobe of the lung were recruited. The patients were injected with 370 MBq of ¹⁸F-FDG. During PET, the patients assumed two bed positions for 1.5 min/bed. After conducting free-breathing imaging, we obtained images of the patients with abdominal compression by applying the same setup used in the free-breathing scan. The differences in the standardized uptake value (SUV)_max, SUV_mean, tumor volume, and the centroid of the tumors between PET and various CT schemes were measured.

Results

The SUV_max and SUV_mean derived from PET/CT imaging using an abdominal compression device increased for all the lesions, compared with those obtained using the conventional approach. The percentage increases were 18.1% ±14% and 17% ±16.8% for SUV_max and SUV_mean, respectively. PET/CT imaging combined with abdominal compression generally reduced the tumor mismatch between CT and the corresponding attenuation corrected PET images, with an average decrease of 1.9±1.7 mm over all the cases.

Conclusions

PET/CT imaging combined with abdominal compression reduces respiratory artifacts and PET/CT misregistration, and enhances quantitative SUV in tumor. Abdominal compression is easy to set up and is an effective method used in PET/CT imaging for clinical oncology, especially in the thoracic region.