AM fungi root colonization increases the production of essential isoprenoids vs. nonessential isoprenoids especially under drought stress conditions or after jasmonic acid application

Asensio D., Rapparini F., Peñuelas J. (2012) AM fungi root colonization increases the production of essential isoprenoids vs. nonessential isoprenoids especially under drought stress conditions or after jasmonic acid application. Phytochemistry. 77: 149-161.
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Doi: 10.1016/j.phytochem.2011.12.012

Resum:

Previous studies have shown that root colonization by arbuscular mycorrhiza (AM) fungi enhances plant resistance to abiotic and biotic stressors and finally plant growth. However, little is known about the effect of AM on isoprenoid foliar and root content. In this study we tested whether the AM symbiosis affects carbon resource allocation to different classes of isoprenoids such as the volatile nonessential isoprenoids (monoterpenes and sesquiterpenes) and the non-volatile essential isoprenoids (abscisic acid, chlorophylls and carotenoids). By subjecting the plants to stressors such as drought and to exogenous application of JA, we wanted to test their interaction with AM symbiosis in conditions where isoprenoids usually play a role in resistance to stress and in plant defence. Root colonization by AM fungi favoured the leaf production of essential isoprenoids rather than nonessential ones, especially under drought stress conditions or after JA application. The increased carbon demand brought on by AM fungi might thus influence not only the amount of carbon allocated to isoprenoids, but also the carbon partitioning between the different classes of isoprenoids, thus explaining the not previously shown decrease of root volatile isoprenoids in AM plants. We propose that since AM fungi are a nutrient source for the plant, other carbon sinks normally necessary to increase nutrient uptake can be avoided and therefore the plant can devote more resources to synthesize essential isoprenoids for plant growth. © 2011 Elsevier Ltd. All rights reserved.

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Litter VOCs induce changes in soil microbial biomass C and N and largely increase soil CO 2 efflux

Asensio D., Yuste J.C., Mattana S., Ribas À., Llusià J., Peñuelas J. (2012) Litter VOCs induce changes in soil microbial biomass C and N and largely increase soil CO 2 efflux. Plant and Soil. 360: 163-174.
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Doi: 10.1007/s11104-012-1220-9

Resum:

Aims: We investigated the effects of volatile organic compounds (VOCs) emitted by pine litter, specifically terpenes, on soil microbial biomass carbon and nitrogen and heterotrophic soil respiration under different microclimatic scenarios of water availability and temperature. Methods: Soil in glass jars (0.6 L headspace) was exposed to pine needle litter, avoiding any physical contact between soils and litter. Treatments were subjected to two moisture levels, control and drought (20 % and 10 % gravimetric soil water content respectively) and to different temperatures (temperature response curve from 5 °C to 45 °C). Results: In control soils, exposure to litter was associated with a significant decrease in microbial biomass carbon and ninhydrin extractable organic nitrogen, and with a significant increase in heterotrophic respiration (up to 46 %) under optimum temperature (25 °C). Drought, on the other hand, restricted the effects of litter exposure on heterotrophic respiration but exposure to litter was associated with a significant increase in microbial biomass nitrogen. We did not detect significant overall microbial consumption of terpenes in this study. Conclusions: These results suggest either that other VOCs not measured in the study were being consumed and/or that VOCs emissions were triggering strong changes in the composition and functioning of soil microbial communities. More studies under field conditions are needed to assess the magnitude of litter VOCs effects on carbon and nitrogen cycles. © 2012 Springer Science+Business Media B.V.

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