Within-crown plasticity of hydraulic properties influence branch dieback patterns of two woody plants under experimental drought conditions

Crown die-back of peri-urban forests after combined heatwave and drought was species-specific, size-dependent, and also related to tree neighbourhood characteristics

The Rhine River valley of Germany has been facing recurrent and intense spells of drought and heatwaves threatening the health of trees in peri-urban forests. Crown damage intensified by climate change accelerates tree mortality, threatening its ecological, economic, and social benefits; however, the pattern of crown die-back in peri-urban forests remained unclear. We performed a field inventory to estimate the crown die-back of 2578 trees of 51 species from 68 randomly selected peri-urban forest plots in Karlsruhe region on the right bank of the Rhine, after the catastrophic summer heatwave and drought of 2018. We related crown die-back to species-specific drought tolerance, wood anatomical traits, tree size, canopy surface temperature, tree density, Shannon's diversity and Gini coefficient for tree height. Regression results indicate that small-size trees were found to be more susceptible to canopy damage than large trees, with a 1-meter increase in tree height associated with a 0.8 % reduction in crown die-back. This size-dependent process is also species-specific. Among the 12 species with significant (p < 0.05) linear relationship between height and die-back, 9 species demonstrated negative correlations and 3 species showed positive relationships. Species tolerant to drought or cavitation (e.g., trees with diffuse porous xylem, 21 species) had significantly lower crown dieback. For example, with a 1-point-scale increase in drought tolerance crown die-back declined 14.35 %. Trees that experienced high canopy surface temperature and grew with high tree density and species diversity (Shannon's diversity) had more crown die-back. However, high structural diversity (Gini coefficient) was related to lower crown die-back. Our results suggested that future research should focus more on tree species-specific hydraulic and thermal traits and tree density and structure management to improve tree health and species selection in peri-urban forests under future climate change.

Comparative analysis and characterization of the chloroplast genome of Krascheninnikovia ceratoides (Amarathaceae): a xerophytic semi-shrub exhibiting drought resistance and high-quality traits

BACKGROUND

Krascheninnikovia ceratoides, a perennial halophytic semi-shrub belonging to the genus Krascheninnikovia (Amarathaceae), possesses noteworthy ecological, nutritional, and economic relevance. This species is primarily distributed across arid, semi-arid, and saline-alkaline regions of the Eurasian continent, encompassing Inner Mongolia, Xinjiang, Qinghai, Gansu, Ningxia, and Tibet.

RESULTS

We reported the comprehensive chloroplast (cp) genome of K. ceratoides, characterized by a circular conformation spanning 151,968 bp with a GC content of 36.60%. The cp genome encompassed a large single copy (LSC, 84,029 bp), a small single copy (SSC, 19,043 bp), and a pair of inverted repeats (IRs) regions (24,448 bp each). This genome harbored 128 genes and encompassed 150 simple sequence repeats (SSRs). Through comparative analyses involving cp genomes from other Cyclolobeae (Amarathaceae) taxa, we observed that the K. ceratoides cp genome exhibited high conservation, with minor divergence events in protein-coding genes (PCGs) accD, matK, ndhF, ndhK, ycf1, and ycf2. Phylogenetic reconstructions delineated K. ceratoides as the sister taxon to Atriplex, Chenopodium, Dysphania, and Suaeda, thus constituting a robust clade. Intriguingly, nucleotide substitution ratios (Ka/Ks) between K. ceratoides and Dysphania species for ycf1 and ycf2 genes surpassed 1.0, indicating the presence of positive selection pressure on these loci.

CONCLUSIONS

The findings of this study augment the genomic repository for the Amarathaceae family and furnish crucial molecular instruments for subsequent investigations into the ecological adaptation mechanisms of K. ceratoides within desert ecosystems.

Quantifying the effects of precipitation exclusion and groundwater drawdown on functional traits of Haloxylon ammodendron - How does this xeric shrub survive the drought?

The increasing frequency of drought and decline in groundwater levels are causing ecophysiological changes in woody plants, particularly in desert ecosystems in arid regions. However, the combined effects of meteorological and hydrological droughts on perennial desert plants, especially phreatophytes, remain poorly understood. To address this knowledge gap, we conducted a 5-year precipitation exclusion experiment at two sites with contrasting groundwater depths in the Gurbantunggut Desert located in northwest China. Our study aimed to investigate the impacts of precipitation exclusion and groundwater depth decline on multiple traits of H. ammodendron. We found that long-term precipitation exclusion enhanced midday leaf water potential, stomatal conductance, chlorophyll content, root nonstructural carbohydrates concentration, leaf starch concentration, but decreased water use efficiency. Groundwater drawdown decreased predawn and midday leaf water potentials, maximum net photosynthetic rate, stomatal conductance, Huber value, stem water δ18O, but enhanced water use efficiency and branch nonstructural carbohydrates concentration. A combination of precipitation exclusion and groundwater depth decline reduced Huber value, but did not show exacerbated effects. The findings demonstrate that hydrological drought induced by groundwater depth decline poses a greater threat to the survival of H. ammodendron than future changes in precipitation.