Phosphorus deficiency alters scaling relationships between leaf gas exchange and associated traits in a wide range of contrasting Eucalyptus species

Silicon attenuates nutritional disorder of phosphorus in seedlings of Eucalyptus grandis × Eucalyptus urophylla

BACKGROUND

Nutritional disorders of phosphorus (P), due to deficiency or toxicity, reduce the development of Eucalyptus spp. seedlings. Phosphorus deficiency often results in stunted growth and reduced vigor, while phosphorus toxicity can lead to nutrient imbalances and decreased physiological function. These sensitivities highlight the need for precise management of P levels in cultivation practices. The use of the beneficial element silicon (Si) has shown promising results under nutritional stress; nevertheless, comprehensive studies on its effects on Eucalyptus spp. seedlings are still emerging. To further elucidate the role of Si under varying P conditions, an experiment was conducted with clonal seedlings of a hybrid Eucalyptus spp. (Eucalyptus grandis × Eucalyptus urophylla, A207) in a soilless cultivation system. Seedlings were propagated using the minicutting method in vermiculite-filled tubes, followed by treatment with a nutrient solution at three P concentrations: a deficient dose (0.1 mM), an adequate dose (1.0 mM) and an excessive dose (10 mM), with and without the addition of Si (2mM). This study assessed P and Si concentration, nutritional efficiency, oxidative metabolism, photosynthetic parameters, and dry matter production.

RESULTS

Si supply increased phenolic compounds production and reduced electrolyte leakage in seedlings provided with 0.1 mM of P. On the other hand, Si favored quantum efficiency of photosystem II as well as chlorophyll a content in seedlings supplemented with 10 mM of P. In general, Si attenuates P nutritional disorder by reducing the oxidative stress, favoring the non-enzymatic antioxidant system and photosynthetic parameters in seedlings of Eucalyptus grandis × Eucalyptus urophylla.

CONCLUSION

The results of this study indicate that Eucalyptus grandis × Eucalyptus urophylla seedlings are sensitive to P deficiency and toxicity and Si has shown a beneficial effect, attenuating P nutritional disorder by reducing the oxidative stress, favoring the non-enzymatic antioxidant system and photosynthetic parameters.

A transcriptional activator from Rhizophagus irregularis regulates phosphate uptake and homeostasis in AM symbiosis during phosphorous starvation

Introduction

Phosphorus (P) is one of the most important nutrient elements for plant growth and development. Under P starvation, arbuscular mycorrhizal (AM) fungi can promote phosphate (Pi) uptake and homeostasis within host plants. However, the underlying mechanisms by which AM fungal symbiont regulates the AM symbiotic Pi acquisition from soil under P starvation are largely unknown. Here, we identify a HLH domain containing transcription factor RiPho4 from Rhizophagus irregularis.

Methods

To investigate the biological functions of the RiPho4, we combined the subcellular localization and Yeast One-Hybrid (Y1H) experiments in yeasts with gene expression and virus-induced gene silencing approach during AM symbiosis.

Results

The approach during AM symbiosis. The results indicated that RiPho4 encodes a conserved transcription factor among different fungi and is induced during the in planta phase. The transcription of RiPho4 is significantly up-regulated by P starvation. The subcellular localization analysis revealed that RiPho4 is located in the nuclei of yeast cells during P starvation. Moreover, knock-down of RiPho4 inhibits the arbuscule development and mycorrhizal Pi uptake under low Pi conditions. Importantly, RiPho4 can positively regulate the downstream components of the phosphate (PHO) pathway in R. irregularis.

Discussion

In summary, these new findings reveal that RiPho4 acts as a transcriptional activator in AM fungus to maintain arbuscule development and regulate Pi uptake and homeostasis in the AM symbiosis during Pi starvation.

Grazing rest during spring regreening period promotes the ecological restoration of degraded alpine meadow vegetation through enhanced plant photosynthesis and respiration

Grazing rest during the spring regreening period is the most economical and feasible measure for the ecological restoration of degraded alpine meadows and has been widely popularized and applied in China. The aim of the present study was to undertake a comparative analysis of the effects of grazing rest on the ecological restoration of degraded alpine meadows by plant photosynthesis and respiration. Coverage, height, ground biomass, belowground biomass of degraded alpine meadow vegetation, net photosynthetic rate, stomatal conductance, transpiration rate, intercellular CO₂ concentration, chlorophyll fluorescence parameters, relative chlorophyll content, respiration rate, metabolite content, leaf relative water content, and related mineral element content of the dominant grass Elymus nutans Griseb. were measured in degraded alpine grassland with different grazing rest years. The results show that grazing rest during the spring regreening period promoted the ecological restoration of degraded alpine meadows by enhancing the photosynthesis and respiration of the dominant grass E. nutans Griseb. Grazing rest enhanced photosynthesis in dominant grass by increasing metabolites related to the Calvin cycle, chlorophyll content, leaf relative water content, and related mineral element content. Grazing at rest enhanced the respiration of dominant grass by increasing metabolites related to the TCA cycle, leaf relative water content, and related mineral element content. This positive effect gradually became stable with increasing years of grazing rest. Our results provide a fundamental basis for the popularization and application of grazing rest during the spring regreening period on degraded Tibetan Plateau grasslands.

Low phosphorus induces differential metabolic responses in eucalyptus species improving nutrient use efficiency

Phosphorus (P) is a vital nutrient for plant growth. P availability is generally low in soils, and plant responses to low P availability need to be better understood. In a previous study, we studied the growth and physiological responses of 24 species to low P availability in the soil and verified of eucalypts, five (Eucalyptus acmenoides, E. grandis, E. globulus, E. tereticornis, and Corymbia maculata) contrasted regarding their efficiency and responsiveness to soil P availability. Here, we obtained the metabolomic and lipidomic profile of leaves, stems, and roots from these species growing under low (4.5 mg dm^-3) and sufficient (10.8 mg dm^-3) P in the soil. Disregarding the level of P in the soils, P allocation was always higher in the stems. However, when grown in the P-sufficient soil, the stems steadily were the largest compartment of the total plant P. Under low P, the relative contents of primary metabolites, such as amino acids, TCA cycle intermediates, organic acids and carbohydrates, changed differently depending on the species. Additionally, phosphorylated metabolites showed enhanced turnover or reductions. While photosynthetic efficiencies were not related to higher biomass production, A/Ci curves showed that reduced P availability increased the eucalypt species' Vcmax, Jmax and photosynthetic P-use efficiency. Plants of E. acmenoides increased galactolipids and sulfolipids in leaves more than other eucalypt species, suggesting that lipid remodelling can be a strategy to cope with the P shortage in this species. Our findings offer insights to understand genotypic efficiency among eucalypt species to accommodate primary metabolism under low soil P availability and eventually be used as biochemical markers for breeding programs.

Eucalypt species drive rhizosphere bacterial and fungal community assembly but soil phosphorus availability rearranges the microbiome

Soil phosphorus (P) availability may limit plant growth and alter root-soil interactions and rhizosphere microbial community composition. The composition of the rhizosphere microbial community can also be shaped by plant genotype. In this study, we examined the rhizosphere microbial communities of young plants of 24 species of eucalypts (22 Eucalyptus and two Corymbia species) under low or sufficient soil P availability. The taxonomic diversity of the rhizosphere bacterial and fungal communities was assessed by 16S and 18S rRNA gene amplicon sequencing. The taxonomic modifications in response to low P availability were evaluated by principal component analysis, and co-inertia analysis was performed to identify associations between bacterial and fungal community structures and parameters related to plant growth and nutritional status under low and sufficient soil P availability. The sequencing results showed that while both soil P availability and eucalypt species influenced the microbial community assembly, eucalypt species was the stronger determinant. However, when the plants are subjected to low P-availability, the rhizosphere selection became strongest. In response to low P, the bacterial and fungal communities in the rhizosphere of some species showed significant changes, whereas in others remained relatively constant under low and sufficient P. Co-inertia analyses revealed a significant co-dependence between plant nutrient contents and bacterial and fungal community composition only under sufficient P. By contrast, under low P, bacterial community composition was related to plant biomass production. In conclusion, our study shows that eucalypt species identity was the main factor modulating rhizosphere microbial community composition; significant shifts due to P availability were observed only for some eucalypt species.

Gas exchange characteristics and their influencing factors for halophytic plant communities on west coast of Bohai Sea

Water-salt stress and nutrient limitation may affect leaf economic spectrum of halophytes and confuse our understanding on plant physiological principles in a changing world. In this study, three halophytic plant communities of Phragmites australis, Suaeda salsa, and Tamarix chinensis, were selected in two sites (sites 1 and 2) on the west coast of Bohai Sea. The net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), leaf vapor pressure deficit (VPDleaf) and their influencing factors were studied to test the possible carbon assimilation strategies of the halophytes. P. australis had higher Pn, Tr, and Gs than S. salsa and T. chinensis in both sites. Similar trends were found for leaf P and photosynthetic N and P efficiency (PNUE and PPUE, respectively) in one or both sites. By contrast, the leaf dry mass per area (LMA) increased in the order of P. australis < S. salsa < T. chinensis in both sites. For identical species in different sites, Pn, leaf P, and PNUE were lower but Tr, VPDleaf, leaf N, leaf N:P, and PPUE were higher in site 1 than in site 2 for one or more halophytes. Although soil physicochemical properties in different sites explained several variations among the halophytes, two-way ANOVA indicated that the species can explain most of the leaf traits compared with the site. LMA also had significant nonlinear relationships with Pn, Tr, Gs, and VPDleaf. PNUE and PPUE showed positive correlation with Pn in both sites, but they decreased in the power-law function with increasing LMA. Overall, the redundancy analysis showed that the gas exchange capacity of the halophytic plant communities was significantly affected by PPUE (60.0% of explanation), PNUE (57.1%), LMA (35.0%), leaf P (22.0%), and soil N (15.8%).

Functional ecology of congeneric variation in the leaf economics spectrum

Variation in resource availability can lead to phenotypic plasticity in the traits comprising the world-wide leaf economics spectrum (LES), potentially impairing plant function and complicating the use of tabulated values for LES traits in ecological studies. We compared 14 Carex (Cyperaceae) species in a factorial experiment (unshaded/shaded × sufficient/insufficient P) to analyze how changes in the network of allometric scaling relationships among LES traits influenced growth under favorable and resource-limited conditions. Changes in leaf mass per area (LMA) shifted the scaling relationships among LES traits expressed per unit area vs mass in ways that helped to sustain growth under resource limitation. Increases in area-normalized photosynthetic capacity and foliar nitrogen (N) were correlated with increased growth, offsetting losses associated with mass-normalized dark respiration and foliar N. These shifts increased the contributions to growth associated with photosynthetic N-use efficiency and the N : P ratio. Plasticity in LMA is at the hub of the functional role of the LES as an integrated and resilient complex system that balances the relationships among area- and mass-based aspects of gas exchange and foliar nutrient traits to sustain at least some degree of plant growth under differing availabilities of above- and below-ground resources.