The fate of carbon in a mature forest under carbon dioxide enrichment

Atmospheric carbon dioxide enrichment (eCO2) can enhance plant carbon uptake and growth1 5, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration6. Although evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth3 5, it is unclear whether mature forests respond to eCO2 in a similar way. In mature trees and forest stands7 10, photosynthetic uptake has been found to increase under eCO2 without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO2 unclear4,5,7 11. Here using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO2 exposure. We show that, although the eCO2 treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO2, and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO2 fertilization as a driver of increased carbon sinks in global forests. © 2020, The Author(s), under exclusive licence to Springer Nature Limited

Oviposition responses of Anopheles gambiae s.s. (Diptera: Culicidae) and identification of volatiles from bacteria-containing solutions

In this study, a dual-choice oviposition bioassay was used to screen responses of gravid An. gambiae toward 17 bacterial species, previously isolated from Anopheles gambiae s.l. (Diptera: Culicidae) midguts or oviposition sites. The 10 isolates from oviposition sites have been identified by phylogenetic analyses of their 16S rRNA genes. Eight of the 10 isolates were gram-positive, out of which six belonged to the Bacilli class. Solid phase microextraction and gas chromatography coupled to mass spectrometry (GC-MS) were used to identify the volatiles emitted from the bacterial isolates. Aromatic and aliphatic alcohols, aliphatic ketones, alkylpyrazines, dimethyl oligosulfides, and indole were among the chemical compounds identified from the headspace above bacteria-containing saline. The mosquitoes laid significantly more eggs in six of the bacteria-containing solutions compared with the sterile solution. These six bacteria did not emit any compounds in common that could explain the positive oviposition response. Instead, the bacteria were grouped according to principal component analysis (PCA) based on the relative amounts of volatiles emitted. The PCA-plots facilitated the identification of 13 putative oviposition attractants for An. gambiae mosquitoe

Enhancement of wheat (<i>Triticum aestivum</i>) drought tolerance by <i>Bacillus thuringiensis</i> AZP2 and <i>Paenibacillus polymyxa</i> B in sand soil.

<p>Panel A demonstrates the effect of AZP2 and B priming on seedlings survival after a severe 10-day drought stress episode. Panel B shows the effect of AZP2 priming on whole plant dry mass after 8 days growth without watering. The statistical analysis in (A) is based on a three-way ANOVA (stress, strains (i.e. AZP2 and B) and stress exposure time). ANOVA was conducted on two plant groups with 16 replicates in each group. *** indicate highly significant effects for the tested factor at <i>P≤</i>0.01. In B, eight independent experiments were performed, and treatments labelled with the same letter are not significantly different at <i>P≤</i>0.01.</p

Temporal variations in the emission rates of some benzenoids and terpenoids emitted by wheat plants.

<p>Benzaldehyde (A), β-pinene (B) and geranyl acetone (C) emission rates from leaves of drought-stressed (0, 2, 5, 8 and 10 days without water) wheat plants after priming with <i>Bacillus thuringiensis</i> AZP2 are demonstrated. The error bars indicate +SE for three biological replicates. Statistical analysis and levels of significance as in Fig. 4.</p

Effect of priming by <i>Bacillus thuringiensis</i> AZP2 on wheat <i>(Triticum aestivum L. cv. Stava)</i> on average (±SD) growth characteristics, water use efficiency and antioxidant enzyme activities.

1<p>Analysis of plant root was conducted by Root Reader3D Imaging and Analysis System and manually <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0096086#pone.0096086-Niinemets1" target="_blank">[7]</a>.</p>2<p>Twelve plants per treatment were sampled. Roots with adhering soil (RAS) were carefully separated from bulk soil by shaking. Soil and root dry mass (RT) was recorded after drying the samples at 105°C, and RAS/RT ratio was calculated.</p>3<p>Twelve plants were carefully separated from soil by shaking followed by washing the roots in distilled water and left to drain in Petri dishes with water to maintain humidity. Root system characteristics were evaluated by Zeiss LSM 710 microscope.</p>4<p>Water use efficiency is defined as the ratio of total plant dry mass per total water used.</p>5<p>MDHAR - Monodehydroascorbate reductase, GR- Glutathione reductase, SOD- Superoxide dismutase, CAT-Catalase.</p><p>See Materials and Methods for enzyme extraction and activity measurements.</p><p>*Means followed by the same letter are not significantly different at p≤0.01. See Experimental procedures.</p

Net assimilation rate (A) and stomatal conductance (B) of <i>Bacillus thuringiensis</i> AZP2-primed wheat seedlings under drought stress.

<p>The data are shown for plants grown for 0, 2, 5, 8 and 10 days without water. The error bars indicate +SE for three biological replicates. Statistical analysis is based on three-way ANOVA with stress, strains (<i>Bacillus thuringiensis</i> AZP2 vs. <i>P. polymyxa</i> B) and stress exposure time as factors. ***, ** and ns, indicate highly significant, significant or non-significant effects for the tested factor at <i>P<</i>0.05.</p

Electrophysiological and behavioural responses of Ips typographus (L.) to trans-4-thujanol—a host tree volatile compound

International audienceAbstractKey messageSpruce trees emit significant amounts of trans-4-thujanol, but the amount of this compound in bark decreases with tree age. Trans-4-thujanol acts as an efficient repellent for the bark beetle Ips typographus.ContextThe spruce bark beetle, Ips typographus, is an economically significant pest of Norway spruce (Picea abies) that preferentially infests and kills old trees.AimsWe looked for spruce volatiles that were perceivable by I. typographus and that differed as the host tree aged.MethodsBark beetles were collected in the wild. Bark samples from spruce trees of different age were hydrodistilled. Gas chromatography–electroantennogram detection (GC-EAD) was used to identify which compounds induced beetle olfactory responses. These were identified by gas chromatography–mass spectrometry (GC-MS). Behavioural responses of bark beetles were tested using a Y-tube olfactometer.ResultsSeveral EAD peaks were recorded, of which trans-4-thujanol was consistently active and could be identified chemically unequivocally. The antennae of I. typographus females responded to a lower dosage of the compound than males, but both sexes were repelled by it. The bark of 10-year-old spruce trees contained 3 times more trans-4-thujanol than that of 35- 40-year-old trees, 27 times more than that of 70- to 80-year-old trees, and 200 times more than that of 120-year-old trees.ConclusionsTrans-4-thujanol is a bioactive compound in Norway spruce bark that varies in amount with tree age and affects spruce bark beetle behaviour under laboratory conditions. It is suggested that trans-4-thujanol might play a role in both spruce tree defence and tree choice by beetles