One major effect of global climate change will be altered precipitation patterns in many regions of the world. This will cause a higher probability of long‐term waterlogging in winter/spring and ...flash floods in summer because of extreme rainfall events. Particularly, trees not adapted at their natural site to such waterlogging stress can be impaired. Despite the enormous economic, ecological and social importance of forest ecosystems, the effect of waterlogging on trees is far less understood than the effect on many crops or the model plant Arabidopsis. There is only a handful of studies available investigating the transcriptome and metabolome of waterlogged trees. Main physiological responses of trees to waterlogging include the stimulation of fermentative pathways and an accelerated glycolytic flux. Many energy‐consuming, anabolic processes are slowed down to overcome the energy crisis mediated by waterlogging. A crucial feature of waterlogging tolerance is the steady supply of glycolysis with carbohydrates, particularly in the roots; stress‐sensitive trees fail to maintain sufficient carbohydrate availability resulting in the dieback of the stressed tissues. The present review summarizes physiological and molecular features of waterlogging tolerance of trees; the focus is on carbon metabolism in both, leaves and roots of trees.
Heavy metal (HM)-accumulating herbaceous and woody plants are employed for phytoremediation. To develop improved strategies for enhancing phytoremediation efficiency, knowledge of the ...microstructural, physiological and molecular responses underlying HM-accumulation is required. Here we review the progress in understanding the structural, physiological and molecular mechanisms underlying HM uptake, transport, sequestration and detoxification, as well as the regulation of these processes by signal transduction in response to HM exposure. The significance of genetic engineering for enhancing phytoremediation efficiency is also discussed. In herbaceous plants, HMs are taken up by roots and transported into the root cells via transmembrane carriers for nutritional ions. The HMs absorbed by root cells can be further translocated to the xylem vessels and unloaded into the xylem sap, thereby reaching the aerial parts of plants. HMs can be sequestered in the cell walls, vacuoles and the Golgi apparatuses. Plant roots initially perceive HM stress and trigger the signal transduction, thereby mediating changes at the molecular, physiological, and microstructural level. Signaling molecules such as phytohormones, reactive oxygen species (ROS) and nitric oxide (NO), modulate plant responses to HMs via differentially expressed genes, activation of the antioxidative system and coordinated cross talk among different signaling molecules. A number of genes participated in HM uptake, transport, sequestration and detoxification have been functionally characterized and transformed to target plants for enhancing phytoremediation efficiency. Fast growing woody plants hold an advantage over herbaceous plants for phytoremediation in terms of accumulation of high HM-amounts in their large biomass. Presumably, woody plants accumulate HMs using similar mechanisms as herbaceous counterparts, but the processes of HM accumulation and signal transduction can be more complex in woody plants.
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•Phosphorus nutrition was characterized during the annual growth of Fagus sylvatica.•Organic phosphorus storage and intense P re-cycling are hallmarks of P nutrition.•Phosphorus ...storage differs between adult beech trees and their offspring.•Soil phosphorus is not reflected by phosphorus contents of twig tissues and leaves.
Forest ecosystems have often developed on phosphorus (P) −limited soils and, thus, are thought to require an efficient P-nutrition strategy during annual growth to sustain sufficient P-supply for growth and development. The present study was aimed at characterizing seasonal changes in P-composition and concentrations in different organs and transport tissues of mature and young European beech (Fagus sylvatica L.) trees growing at different soil-P availability. From these changes, a model of tree internal P-cycling strategy as dependent on tree age and P-availability was developed. For this purpose, leaves, stem tissues and roots, as well as xylem sap and phloem exudate were collected from adult trees and their progeny at two field sites in southern Germany, one with low but sufficient (Conventwald field site), and one with extremely low (Tuttlingen field site) P-availability in the soil. P-cycling during annual growth with bark and wood as the main P-storage tissues in winter is strongly indicated and was much more pronounced in adult beeches compared to its progeny, and of higher significance at extremely low soil-P. The re-use of stored organic phosphorus containing compounds (Porg) from bark and wood during spring and the resorption of Porg from senescing leaves can be seen as a strategy to enhance tree internal P-cycling efficiency, especially in adult trees growing at extremely low P-availability. The consequences of tree internal P-cycling for ecosystem P-losses and its dependency on tree age and soil P-availability are discussed.
Key message
On calcareous soil, European beech roots prefer organic nitrogen, but only arginine and not glutamine or inorganic nitrogen.
Nitrogen (N) acquisition is a major factor determining the ...processes and mechanisms involved in tree productivity, development, and competitiveness. However, only few studies have investigated changes in N capturing with tree age. We conducted
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N incubation experiments to quantify inorganic (i.e. ammonium and nitrate) and organic (i.e. glutamine-N and arginine-N) net N acquisition capacity of beech trees of five age classes. Our results showed no general pattern, but that net N uptake capacity was rather N source-specific. Inorganic and glutamine-N uptake did not differ between age classes at all. Arginine-N uptake was highest in the youngest and oldest stands reflecting a high N demand by seedlings for root foraging and biomass production despite low internal N storage capacities and by older trees for storage and reproduction. Organic N was preferred over inorganic N regardless of tree age. Overall, our study shows the high significance of organic N sources for N acquisition in beech trees.
Nitrogen (N) is an essential nutrient that is highly abundant as N2 in the atmosphere and also as various mineral and organic forms in soils. However, soil N bioavailability often limits the net ...primary productivity of unperturbed temperate forests with low atmospheric N input. This is because most soil N is part of polymeric organic matter, which requires microbial depolymerization and mineralization to render bioavailable N forms such as monomeric organic or mineral N. Despite this N limitation, many unfertilized forest ecosystems on marginal soil show relatively high productivity and N uptake comparable to agricultural systems. The present review article addresses the question of how this high N demand is met in temperate forest ecosystems. For this purpose, current knowledge on the distribution and fluxes of N in marginal forest soil and the regulation of N acquisition and distribution in trees are summarized. The related processes and fluxes under N limitation are compared with those of forests exposed to high N loads, where chronic atmospheric N deposition has relieved N limitation and caused N saturation. We conclude that soil microbial biomass is of decisive importance for nutrient retention and provision to trees both in high and low N ecosystems.
Aims
Root exudates are known to shape microbial activities in the rhizosphere and to be of fundamental importance for plant-soil-microbe-carbon–nitrogen interactions. However, it remains unclear how ...and to what extent the amount and composition of root exudation affects rhizosphere denitrification.
Methods
In this study root exudation patterns and rhizosphere denitrification enzyme activity of three different grass species grown on two agricultural soils under two different soil water contents were investigated under controlled conditions.
Results
We found that root exudation of primary metabolites largely depends on plant species, soil type, soil moisture and root exudation medium. In dependence of soil properties and soil moisture levels, plants largely controlled amount and quality of root exudation. Exudates affected denitrification activity and plant–microbe competition for nitrate. Specifically, exudation of organic acids stimulated denitrifying activity while the sugar lyxose exhibited an inhibitory effect.
Conclusion
We show that interactive effects of physicochemical soil properties and species-specific effects of plant metabolism on root exudation act as a dominant control of rhizosphere denitrification, thereby explaining more than half of its variance.
Overexpression of bacterial γ‐glutamylcysteine synthetase in the cytosol of Populus tremula × P. alba produces higher glutathione (GSH) concentrations in leaves, thereby indicating the potential for ...cadmium (Cd) phytoremediation. However, the net Cd²⁺influx in association with H⁺/Ca²⁺, Cd tolerance, and the underlying molecular and physiological mechanisms are uncharacterized in these poplars. We assessed net Cd²⁺influx, Cd tolerance and the transcriptional regulation of several genes involved in Cd²⁺transport and detoxification in wild‐type and transgenic poplars. Poplars exhibited highest net Cd²⁺influxes into roots at pH 5.5 and 0.1 mM Ca²⁺. Transgenics had higher Cd²⁺uptake rates and elevated transcript levels of several genes involved in Cd²⁺transport and detoxification compared with wild‐type poplars. Transgenics exhibited greater Cd accumulation in the aerial parts than wild‐type plants in response to Cd²⁺exposure. Moreover, transgenic poplars had lower concentrations of O₂˙⁻and H₂O₂; higher concentrations of total thiols, GSH and oxidized GSH in roots and/or leaves; and stimulated foliar GSH reductase activity compared with wild‐type plants. These results indicate that transgenics are more tolerant of 100 μM Cd²⁺than wild‐type plants, probably due to the GSH‐mediated induction of the transcription of genes involved in Cd²⁺transport and detoxification.
The cactus family (Cactaceae) has been reported to have evolved a minimal photosynthetic plastome size, with the loss of inverted-repeat (IR) regions and NDH gene suites. However, there are very ...limited genomic data on the family, especially Cereoideae, the largest subfamily of cacti.
In the present study, we assembled and annotated 35 plastomes, 33 of which were representatives of Cereoideae, alongside 2 previously published plastomes. We analyzed the organelle genomes of 35 genera in the subfamily. These plastomes have variations rarely observed in those of other angiosperms, including size differences (with ~ 30 kb between the shortest and longest), dramatic dynamic changes in IR boundaries, frequent plastome inversions, and rearrangements. These results suggested that cacti have the most complex plastome evolution among angiosperms.
These results provide unique insight into the dynamic evolutionary history of Cereoideae plastomes and refine current knowledge of the relationships within the subfamily.
Phosphorus is one of the major limiting factors of primary productivity in terrestrial ecosystems and, thus, the P demand of plants might be among the most important drivers of soil and ecosystem ...development. The P cycling in forest ecosystems seems an ideal example to illustrate the concept of ecosystem nutrition. Ecosystem nutrition combines and extents the traditional concepts of nutrient cycling and ecosystem ecology. The major extension is to consider also the loading and unloading of nutrient cycles and the impact of nutrient acquiring and recycling processes on overall ecosystem properties. Ecosystem nutrition aims to integrate nutrient related aspects at different scales and in different ecosystem compartments including all processes, interactions and feedbacks associated with the nutrition of an ecosystem. We review numerous previous studies dealing with P nutrition from this ecosystem nutrition perspective. The available information contributes to the description of basic ecosystem characteristics such as emergence, hierarchy, and robustness. In result, we were able to refine Odum's hypothesis on P nutrition strategies along ecosystem succession to substrate related ecosystem nutrition and development. We hypothesize that at sites rich in mineral‐bound P, plant and microbial communities tend to introduce P from primary minerals into the biogeochemical P cycle (acquiring systems), and hence the tightness of the P cycle is of minor relevance for ecosystem functioning. In contrast, tight P recycling is a crucial emergent property of forest ecosystems established at sites poor in mineral bound P (recycling systems). We conclude that the integration of knowledge on nutrient cycling, soil science, and ecosystem ecology into holistic ecosystem nutrition will provide an entirely new view on soil–plant–microbe interactions.
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•Methylators were dominating in rice rhizosphere, rather than the bulk soil.•Hg-promoted methylators are key taxa in the rhizosphere at the flowering stage.•In planta demethylation ...and methylation in rice roots are possible.•Desulfovibrionaceae may play an important role in Hg detoxification of rice.
The plant microbiota can affect plant health and fitness by promoting methylmercury (MeHg) production in paddy soil. Although most well-known mercury (Hg) methylators are observed in the soil, it remains unclear how rice rhizosphere assemblages alter MeHg production. Here, we used network analyses of microbial diversity to identify bulk soil (BS), rhizosphere (RS) and root bacterial networks during rice development at Hg gradients. Hg gradients greatly impacted the niche-sharing of taxa significantly relating to MeHg/THg, while plant development had little effect. In RS networks, Hg gradients increased the proportion of MeHg-related nodes in total nodes from 37.88% to 45.76%, but plant development enhanced from 48.59% to 50.41%. The module hub and connector in RS networks included taxa positively (Nitrososphaeracea, Vicinamibacteraceae and Oxalobacteraceae) and negatively (Gracilibacteraceae) correlating with MeHg/THg at the blooming stage. In BS networks, Deinococcaceae and Paludibacteraceae were positively related to MeHg/THg, and constituted the connector at the reviving stage and the module hub at the blooming stage. Soil with an Hg concentration of 30 mg kg−1 increased the complexity and connectivity of root microbial networks, although microbial community structure in roots was less affected by Hg gradients and plant development. As most frequent connector in root microbial networks, Desulfovibrionaceae did not significantly correlate with MeHg/THg, but was likely to play an important role in the response to Hg stress.
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