Species identity and neighbor size surpass the impact of tree species diversity on productivity in experimental broad-leaved tree sapling assemblages under dry and moist conditions

Species diversity may increase the productivity of tree communities through complementarity and/or selection effects, but it is not well known how this relationship changes under water limitation. We tested the stress-gradient hypothesis, which predicts that resource use complementarity and facilitation are more important under water-limited conditions. We conducted a growth experiment with saplings of five temperate broad-leaved tree species that were grown in assemblages of variable diversity (1, 3 or 5 species) and species composition under ample and limited water supply to examine effects of species richness and species identity on stand and tree-level productivity. Special attention was paid to effects of neighbor identity on the growth of target trees in mixture as compared to growth in monoculture. Stand productivity was strongly influenced by species identity while a net biodiversity effect was significant in the moist treatment (mostly assignable to a complementarity effect) but of minor importance. The growth performance of some of the species in the mixtures was affected by tree neighborhood characteristics with neighbor size likely being more important than neighbor species identity. Diversity and neighbor identity effects visible in the moist treatment mostly disappeared in the dry treatment, disproving the stress-gradient hypothesis. The mixtures were similarly sensitive to drought-induced growth reduction as the monocultures, which may relate to the decreased complementarity effect on growth upon drought in the mixtures

Data from: De novo transcriptome assembly and analysis of differential gene expression in response to drought in European beech

Despite the ecological and economic importance of European beech (Fagus sylvatica L.) genomic resources of this species are still limited. This hampers an understanding of the molecular basis of adaptation to stress. Since beech will most likely be threatened by the consequences of climate change, an understanding of adaptive processes to climate change-related drought stress is of major importance. Here, we used RNA-seq to provide the first drought stress-related transcriptome of beech. In a drought stress trial with beech saplings, 50 samples were taken for RNA extraction at five points in time during a soil desiccation experiment. De novo transcriptome assembly and analysis of differential gene expression revealed 44,335 contigs, and 662 differentially expressed genes between the stress and normally watered control group. Gene expression was specific to the different time points, and only five genes were significantly differentially expressed between the stress and control group on all five sampling days. GO term enrichment showed that mostly genes involved in lipid- and homeostasis-related processes were upregulated, whereas genes involved in oxidative stress response were downregulated in the stressed seedlings. This study gives first insights into the genomic drought stress response of European beech, and provides new genetic resources for adaptation research in this species

De novo transcriptome assembly of European beech

De novo assembly of a drought-related transcriptome of European beech

<i>De novo</i> transcriptome assembly and analysis of differential gene expression in response to drought in European beech

<div><p>Despite the ecological and economic importance of European beech (<i>Fagus sylvatica</i> L.) genomic resources of this species are still limited. This hampers an understanding of the molecular basis of adaptation to stress. Since beech will most likely be threatened by the consequences of climate change, an understanding of adaptive processes to climate change-related drought stress is of major importance. Here, we used RNA-seq to provide the first drought stress-related transcriptome of beech. In a drought stress trial with beech saplings, 50 samples were taken for RNA extraction at five points in time during a soil desiccation experiment. <i>De novo</i> transcriptome assembly and analysis of differential gene expression revealed 44,335 contigs, and 662 differentially expressed genes between the stress and normally watered control group. Gene expression was specific to the different time points, and only five genes were significantly differentially expressed between the stress and control group on all five sampling days. GO term enrichment showed that mostly genes involved in lipid- and homeostasis-related processes were upregulated, whereas genes involved in oxidative stress response were downregulated in the stressed seedlings. This study gives first insights into the genomic drought stress response of European beech, and provides new genetic resources for adaptation research in this species.</p></div

High variation in hydraulic efficiency but not xylem safety between roots and branches in four temperate broad‐leaved tree species

International audience1. Xylem hydraulic safety and efficiency are key traits determining tree fitness in a warmer and drier world. While numerous plant hydraulic studies have focused on branches, our understanding of root hydraulic functioning remains limited, although roots control water uptake, influence stomatal regulation and have commonly been considered as the most vulnerable organ along the hydraulic pathway.2. We investigated 11 traits related to xylem safety and efficiency along the hydraulic pathway in four temperate broad-leaved tree species.3. Continuous vessel tapering from coarse roots to stems and branches caused considerable reduction in hydraulic efficiency. Wood density was always lowest in roots, but did not decline linearly along the flow path. In contrast, xylem embolism resistance (P-50) did not differ significantly between roots and branches, except for one species. The limited variation in xylem safety between organs did not adequately reflect the corresponding reductions in vessel diameter (by similar to 70%) and hydraulic efficiency (by similar to 85%). Although we did not observe any trade-off between xylem safety and specific conductivity, vessel diameter, vessel lumen fraction and wood density were related to embolism resistance, both across and partly within organs.4. We conclude that coarse roots are not highly vulnerable to xylem embolism as commonly believed, indicating that hydraulic failure during soil drying might be restricted to fine roots. A free Plain Language Summary can be found within the Supporting Information of this article

GO terms significantly enriched in downregulated DEGs compared to the reference gene set (total set of sequences with assigned GO terms) over all sampling days.

<p>GO terms significantly enriched in downregulated DEGs compared to the reference gene set (total set of sequences with assigned GO terms) over all sampling days.</p

GO slim term distribution in the transcriptome.

<p>GO slim term distribution in the transcriptome.</p

Venn diagrams for DEGs over all sampling days.

<p>The Venn diagram was prepared using the online tool provided by VIB and Ghent University (<a href="http://bioinformatics.psb.ugent.be/webtools/Venn/" target="_blank">http://bioinformatics.psb.ugent.be/webtools/Venn/</a>).</p

GO terms significantly enriched in upregulated DEGs compared to the reference gene set (total set of sequences with assigned GO terms) over all sampling days.

<p>GO terms significantly enriched in upregulated DEGs compared to the reference gene set (total set of sequences with assigned GO terms) over all sampling days.</p