Significance of current weather conditions for foliar traits of old-growth sessile oak (Quercus petraea Liebl) trees

The aim of the present study was to elucidate the significance of current weather conditions for foliar traits of adult sessile oak (Quercus petraea), one of the most valuable forest tree species in Central Europe. For this purpose, structural and functional traits were analysed in fully expanded, sun exposed leaves collected in south-west Germany from five old-growth forest stands, representing the meteorological and pedospheric conditions in the growing region, but differing in aridity during the 12 days before harvest in two consecutive years. Across the forest stands, most foliar traits differed significantly between wet and dry weather conditions before harvest as indicated by partial least square discriminant analysis (PLS-DA). These traits included fresh weight/dry weight ratio, leaf hydration, leaf-C content, leaf-C/N ratio, structural N, soluble protein-N, total amino acid-N, cell wall composition, numerous specific amino acids as well as soluble sugar content. Structural biomass, δ13C signature, total N and total C as well as H2O2 contents were not affected by the weather before harvest. These results indicate a high plasticity of the foliar metabolism of drought-tolerant sessile oak to current weather conditions. They also suggest that sessile oak is characterized by a high potential to cope with the growth conditions expected as a consequence of future climate change

Detecting early signs of heat and drought stress in Phoenix dactylifera (date palm)

Plants adapt to the environment by either long-term genome evolution or by acclimatization processes where the cellular processes and metabolism of the plant are adjusted within the existing potential in the genome. Here we studied the adaptation strategies in date palm, Phoenix dactylifera, under mild heat, drought and combined heat and drought by transcriptomic and metabolomic profiling. In transcriptomics data, combined heat and drought resembled heat response, whereas in metabolomics data it was more similar to drought. In both conditions, soluble carbohydrates, such as fucose, and glucose derivatives, were increased, suggesting a switch to carbohydrate metabolism and cell wall biogenesis. This result is consistent with the evidence from transcriptomics and cis-motif analysis. In addition, transcriptomics data showed transcriptional activation of genes related to reactive oxygen species in all three conditions (drought, heat, and combined heat and drought), suggesting increased activity of enzymatic antioxidant systems in cytosol, chloroplast and peroxisome. Finally, the genes that were differentially expressed in heat and combined heat and drought stresses were significantly enriched for circadian and diurnal rhythm motifs, suggesting new stress avoidance strategies.Peer reviewe

Leaf-level metabolic changes in response to drought affect daytime CO2 emission and isoprenoid synthesis pathways

In the near future, climate change will cause enhanced frequency and/or severity of droughts in terrestrial ecosystems, including tropical forests. Drought responses by tropical trees may affect their carbon use, including production of volatile organic compounds (VOCs), with implications for carbon cycling and atmospheric chemistry that are challenging to predict. It remains unclear how metabolic adjustments by mature tropical trees in response to drought will affect their carbon fluxes associated with daytime CO2 production and VOC emission. To address this gap, we used position-specific 13C-pyruvate labeling to investigate leaf CO2 and VOC fluxes from four tropical species before and during a controlled drought in the enclosed rainforest of Biosphere 2 (B2). Overall, plants that were more drought-sensitive had greater reductions in daytime CO2 production. Although daytime CO2 production was always dominated by non-mitochondrial processes, the relative contribution of CO2 from the tricarboxylic acid cycle tended to increase under drought. A notable exception was the legume tree Clitoria fairchildiana R.A. Howard, which had less anabolic CO2 production than the other species even under pre-drought conditions, perhaps due to more efficient refixation of CO2 and anaplerotic use for amino acid synthesis. The C. fairchildiana was also the only species to allocate detectable amounts of 13C label to VOCs and was a major source of VOCs in B2. In C. fairchildiana leaves, our data indicate that intermediates from the mevalonic acid (MVA) pathway are used to produce the volatile monoterpene trans-β-ocimene, but not isoprene. This apparent crosstalk between the MVA and methylerythritol phosphate pathways for monoterpene synthesis declined with drought. Finally, although trans-β-ocimene emissions increased under drought, it was increasingly sourced from stored intermediates and not de novo synthesis. Unique metabolic responses of legumes may play a disproportionate role in the overall changes in daytime CO2 and VOC fluxes in tropical forests experiencing drought

Heat stress increases the use of cytosolic pyruvate for isoprene biosynthesis

Ana Maria Yáñez-Serrano fa constar el CREAF com a adreça de correspondènciaThe increasing occurrence of heatwaves has intensified temperature stress on terrestrial vegetation. Here, we investigate how two contrasting isoprene-emitting tropical species, Ficus benjamina and Pachira aquatica, cope with heat stress and assess the role of internal plant carbon sources for isoprene biosynthesis in relation to thermotolerance. To our knowledge, this is the first study to report isoprene emissions from P. aquatica. We exposed plants to two levels of heat stress and determined the temperature response curves for isoprene and photosynthesis. To assess the use of internal C sources in isoprene biosynthesis, plants were fed with C position-labelled pyruvate. F. benjamina was more heat tolerant with higher constitutive isoprene emissions and stronger acclimation to higher temperatures than P. aquatica, which showed higher induced isoprene emissions at elevated temperatures. Under heat stress, both isoprene emissions and the proportion of cytosolic pyruvate allocated into isoprene synthesis increased. This represents a mechanism that P. aquatica, and to a lesser extent F. benjamina, has adopted as an immediate response to sudden increase in heat stress. However, in the long run under prolonged heat, the species with constitutive emissions (F. benjamina) was better adapted, indicating that plants that invest more carbon into protective emissions of biogenic volatile organic compounds tend to suffer less from heat stress

N contents [mmol g^-1 DW] in poplar plants exposed to normoxia or hypoxia for 14 days.

<p>During harvest the trees were divided into leaf, petiole, bark, wood, fine roots and coarse roots. The shoot was separated into the top 40 cm, middle 40 cm and bottom 50 cm Data shown are means ± SD of 22–24 biological replicates. The differences between plants exposed to either hypoxia or normoxia were tested by Student’s <i>t-test</i> at p< 0.05; significant differences are indicated by bold.</p><p>N contents [mmol g^-1 DW] in poplar plants exposed to normoxia or hypoxia for 14 days.</p

Effect of soil O₂ deficiency on biomass accumulation and daily transpiration of young poplar trees.

<p>Four months old, hydroponically grown poplar trees were exposed to either normoxic or hypoxic conditions. After 14 days of treatment the plants were harvested, oven dried and the dry weights determined. Root-to-shoot ratios were calculated for each plant. In addition, daily transpiration rates were determined. Data shown are means ± SD of 10–12 biological replicates per treatment. Statistically significant differences at p< 0.05 between hypoxic and normoxic plants were calculated by Student’s t-test and are shown by asterisk.</p

Effect of soil O₂ deficiency (hypoxia) on biomass (g DW) of poplar plants.

<p>During harvest the trees were divided into leaf, petiole, bark, wood, fine roots and coarse roots. The shoot was separated into the top 40 cm, middle 40 cm and bottom 50 cm Data shown are means ± SD of 22–24 biological replicates. The differences between plants exposed to normal O₂ supply (normoxia) and reduced soil O₂ supply (hypoxia) were tested by Student’s t-test at p<0.05; significant differences are indicated by bold.</p><p>Effect of soil O₂ deficiency (hypoxia) on biomass (g DW) of poplar plants.</p

Effect of hypoxia on ¹⁵N allocation rates of ¹⁵N derived from ¹⁵NO₃^- in young poplar trees.

<p>Poplar plants were treated as described in legend of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136579#pone.0136579.g003" target="_blank">Fig 3</a>. ¹⁵N contents in all plant organs in different plant parts (top 40 cm, middle 40 cm, lowest 50 cm, fine and coarse roots) were determined and data used to calculate ¹⁵N allocation rates to these organs. The color codes indicate the magnitude of the allocation rates to the organs. Data shown are means ± SD of 10–12 biological replicates. Statistically significant differences between normoxic and hypoxic plants were tested by Student’s t-test and are indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136579#pone.0136579.s001" target="_blank">S1 Fig</a>.</p

Effect of hypoxia on ¹⁵N allocation rates of ¹⁵N derived from ¹⁵NH₄⁺ in young poplar trees.

<p>Poplar plants were treated as described in legend of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136579#pone.0136579.g003" target="_blank">Fig 3</a>. ¹⁵N contents in all plant organs in different plant parts (top 40 cm, middle 40 cm, lowest 50 cm, fine and coarse roots) were determined and data used to calculate ¹⁵N allocation rates to these organs. The color codes indicate the magnitude of the allocation rates to the organs. Data shown are means ± SD of 10–12 biological replicates. Statistically significant differences between plants exposed to normoxia or hypoxia were tested by Student’s t-test and are indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136579#pone.0136579.s001" target="_blank">S1 Fig</a>.</p