A meta-analysis highlights globally widespread potassium limitation in terrestrial ecosystems

Disguised Blessings: A Mechanistic Understanding of the Beneficial Outcomes Triggered by Partial K Replacement With Na in Two Eucalyptus Species Under Drought Stress

While not essential for most plants, sodium (Na+) can partially substitute for potassium (K+) in some metabolic functions. Thus, understanding the mechanisms underlying K+ and Na+ uptake, transport, utilization, and ion replacement is crucial to sustain forest production. A pot experiment was designed with 6 K/Na ratios (100/0, 85/15, 70/30, 55/45, 40/60, and 0/0%) and two water conditions (well-watered, W+; and water-stressed, W-) on two Eucalyptus species with contrasting drought tolerance. In a multi-level analysis, we measured morphological, nutritional, physiological, biochemical, molecular, and anatomical traits. Low to moderate K replacement with Na (85/15%-55/45%) provided partial and faster stomatal closure (lower δ13C), thereby enhancing plants' water status (WUE, RLWC, ΨPD, ΨMD), photosynthetic capacity (gs, E, A, Ci/Ca), photoprotection (NPQ, qP, ETR, Fv/FM, ΦPSII), and growth (height, collar diameter, LA, TDM) relative to exclusive K supply. The 70/30% K/Na replacement was defined as the ideal ratio, upregulating K+ and water uptake (overexpression of AKT1, PIP2;5, PIP2;7 and TIP1;3), maximizing enzymatic antioxidant performance and biomass production, and reducing oxidative stress. High K replacement with Na (40/60%) and K deficiency (0/0%) led to incomplete stomatal closure reduced water status, photosynthetic capacity, photoprotection, and growth, especially in the species with low drought tolerance.

Nutrient limitations on photosynthesis: from individual to combinational stresses

Liebig's law of the minimum states that increasing photosynthetic productivity on nutrient-impoverished soils depends on addressing the most limiting nutrient. Research has identified the roles of different mineral nutrients in photosynthetic processes. However, diffusional and biochemical regulation of photosynthesis both feature patterns of cumulative effects that jointly determine photosynthetic capacity. More importantly, responses to multiple nutrient stresses are not simply additive and require a comprehensive understanding of how these stresses interact and impact photosynthetic performance. In this review we highlight key macroelements for photosynthesis - nitrogen, phosphorus, potassium, and magnesium - focusing on their unique functions and interactions in regulating carbon fixation under multiple nutrient deficiencies, with the goal of enhancing crop productivity through balanced nutrient applications.

Alleviating Nitrogen and Phosphorus Limitation Does Not Amplify Potassium-Induced Increase in Terrestrial Biomass

Potassium (K) is the second most abundant nutrient element in plants after nitrogen (N), and has been shown to limit aboveground production in some contexts. However, the role of N and phosphorus (P) availability in mediating K limitation in terrestrial production remains poorly understood; and it is unknown whether K also limits belowground carbon (C) stocks, which contain at least three times more C than those aboveground stocks. By synthesizing 779 global paired observations (528, 125, and 126 for aboveground productivity, root biomass, and soil organic C [SOC], respectively), we found that K addition significantly increased aboveground production and SOC by 8% and 5%, respectively, but did not significantly affect root biomass (+9%). Moreover, enhanced N and/or P availability (through N and P addition) did not further amplify the positive effect of K on aboveground productivity. In other words, K had a positive effect on aboveground productivity only when N and/or P were limiting, indicating that K could somehow substitute for N or P when they were limiting. Climate variables mostly explained the variations in K effects; specifically, stronger positive responses of aboveground productivity and SOC to K were found in regions with high mean annual temperature and wetness. Our results suggest that K addition enhances C sequestration by increasing both aboveground productivity and SOC, contributing to climate mitigation, but the positive effects of K on terrestrial C stocks are not further amplified when N and P limitations are alleviated.

Growth and survival strategies of oilseed rape (Brassica napus L.) leaves under potassium deficiency stress: trade-offs in potassium ion distribution between vacuoles and chloroplasts

Potassium (K) is a prevalent limiting factor in terrestrial ecosystems, with approximately one-eighth of the world's soils undergoing K+ deficiency stress. Upon encountering K+ deficiency stress, leaf area (LA) declines before the net photosynthetic rate (An). The sequential alterations fundamentally represent the adaptive trade-off between survival and growth in plants subjected to K+ deficiency stress. This trade-off is hypothesized to be linked to the differences in the subcellular distribution of limited K+ resources. Thus, the K+ distribution and apparent concentration in subcellular compartments, along with the LA and An characteristics of rapeseed leaves at various developmental stages and K+ supply conditions were quantified to elucidate the mechanisms by which subcellular K+ regulates leaf growth and survival. The results revealed that during the early stages of K+ deficiency, leaves actively downregulate growth to sustain normal physiological functions. This is primarily accomplished by lowering the K+ distribution and apparent concentration in vacuoles, restricting LA expansion, and enhancing K+ distribution to chloroplasts to ensure An. Prolonged K+ deficiency decreased the apparent K+ concentration in chloroplasts below the critical threshold (37.8 mm), disrupting chloroplast structure and function, impairing An, and ultimately threatening the survival of rapeseed. Hence, sustaining an adequate concentration of K+ within chloroplasts is crucial for preserving leaf photosynthetic efficiency and ensuring survival under K+ deficiency stress. In conclusion, under K+ deficiency stress, leaves regulate LA and An by trade-offs in the K+ distribution between vacuoles and chloroplasts to coordinate growth and survival.

Applied potassium negates osmotic stress impacts on plant physiological processes: a meta-analysis

Potassium (K) availability in plant cells is critical for maintaining plant productivity across many terrestrial ecosystems. Yet, there is no comprehensive assessment of the mechanisms by which plants respond to potassium application in such conditions, despite the global challenge of escalating osmotic stress. Herein, we conducted a meta-analysis using data from 2381 paired observations to investigate plant responses to potassium application across various morphological, physiological, and biochemical parameters under both osmotic and nonosmotic stress. Globally, our results showed the significant effectiveness of potassium application in promoting plant productivity (e.g. +12%~30% in total dry weight), elevating photosynthesis (+12%~30%), and alleviating osmotic damage (e.g. -19%~26% in malonaldehyde), particularly under osmotic stress. Moreover, we found evidence of interactive effects between osmotic stress and potassium on plant traits, which were more pronounced under drought than salt stress, and more evident in C3 than C4 plants. Our synthesis verifies a global potassium control over osmotic stress, and further offers valuable insights into its management and utilization in agriculture and restoration efforts.

Whole-tree harvesting improves the ecosystem N, P and K cycling functions in secondary forests in the Qinling Mountains, China

Forest ecosystem nutrient cycling functions are the basis for the survival and development of organisms, and play an important role in maintaining the forest structural and functional stability. However, the response of forest nutrient cycling functions at the ecosystem level to whole-tree harvesting remains unclear. Herein, we calculated the ecosystem nitrogen (N), phosphorus (P), and potassium (K) absorption, utilization, retention, cycle, surplus, accumulation, productivity, turnover and return parameters and constructed N, P, and K cycling function indexes to identify the changes in ecosystem N, P, and K cycling functions in a secondary forest in the Qinling Mountains after 5 years of five different thinning intensities (0% (CK), 15%, 30%, 45%, and 60%). We showed that the ecosystem's N, P, and K cycling parameters varied significantly and responded differently to thinning treatments. As the thinning intensity increased, the N, P, and K cycling function indexes increased by 5%~232%, 32%~195%, and 104%~233% compared with CK. Whole-tree harvesting promoted ecosystem N and P cycling functions through two pathways: (a) directly regulated litter biomass, indirectly affected soil nutrient characteristics, and then regulated ecosystem N and P cycling functions; (b) directly regulated plant productivity, indirectly affected plant and soil nutrient characteristics, and then regulated ecosystem N and P cycling functions. In contrast, whole-tree harvesting mainly indirectly affected the plant and soil nutrient characteristics by directly adjusting the plant productivity, and promoting the ecosystem K cycling function. Furthermore, N and P cycling functions were mainly regulated by understory plant productivity while tree and herb nutrient characteristics were key driving factors for K cycling functions. These findings indicated that whole-tree harvesting significantly improved the ecosystem N, P and K cycling functions, and reveals varied regulatory mechanisms, which may aid in formulating effective measures for sustainable forest ecosystem nutrient management.

Nutrient allocation patterns in different aboveground organs at different reproductive stages of four introduced Calligonum species in a common garden in northwestern China

Introduction

The Calligonum species is a typical shrub with assimilative branches (ABs) in arid regions in Central Asia. The nutrient distribution patterns at different reproductive stages are of great significance for further understanding the ecological adaptation and survival strategies of plants.

Methods

In the present study, a common garden experiment was employed to avoid interference by environmental heterogeneity. Furthermore, the nitrogen (N), phosphorus (P), and potassium (K) allocation characteristics in the supporting organs (mature branches), photosynthetic organs (ABs), and reproductive organs (flowers and fruits) of Calligonum caput-medusae (CC), Calligonum arborescens (CA), Calligonum rubicundum (CR), and Calligonum klementzii (CK) during the flowering, unripe fruit, and ripe fruit phases were systematically analyzed.

Results

Aboveground organs were the main factors affecting the variation of N, P, and K concentrations and their stoichiometric ratios, and the reproductive stages were secondary factors affecting N, P, and the P:K ratio and species were secondary factors affecting K and the N:P and N:K ratios. Meanwhile, significant interactions were found for all three of the aforementioned factors. The N and P concentrations in the ABs of the four species were highest during the flowering phase, while the N:P ratio was lowest, which then gradually decreased and increased, respectively, during plant growth. This result supported the growth rate hypothesis, i.e., that the growth rate is highest during the early growth stage. In the growth period, the N, P, and K concentrations in each organ of the four Calligonum species followed the power law, with the allocation rates of N and P being generally higher than K. There were differences among the species as the N-P scaling exponent in the ABs of CR was only 0.256; according to the scaling exponent law, this species was the least stressed and had the strongest environmental adaptability. Overall, the adaptability of the four species could be ranked as CR > CA > CC > CK. In conclusion, there were significant differences in nutrient traits among different aboveground organs, species, and reproductive stages.

Discussion

The results of this study contribute to a deeper understanding of the nutrient allocation strategies of different Calligonum species and provide scientific evidence for the ex-situ conservation and fixation application of these species.

Carbonate weakens the interactions between potassium and calcareous soil

The ion interfacial transport driven by ion-surface interactions in calcareous soil has a profound impact on the nutrient storage and environmental buffer capacity of the main agricultural soils in dry and semi-arid areas. The roles that carbonate plays in preserving the soil's inorganic carbon pool and soil structure stability have been widely investigated, but its significance in the aforementioned microscopic processes, especially the influence of carbonate on the interfacial reaction kinetics of nutrient elements, is yet to be determined. In this study, potassium (K) was used as an indicator ion to investigate its affinity in carbonate-removed (CREM) and carbonate-reserved (CRES) calcareous soil using the general theory of ion diffusion in an external electric field. We discovered that (1) at a given initial K concentration, the carbonate in CRES soil retards the adsorption rate and diminishes the adsorption amount of K in calcareous soil, reducing the interfacial transport properties of nutrient ions at the solid-liquid interface of calcareous soils compared with CREM soil; and (2) this weakening of the interfacial transport effect on nutrient K originates from the soil carbonate, which prefers to weaken the electrostatic interaction intensity between K and the calcareous soil surface. Furthermore, this is due to the carbonate shielding effect on the surface adsorption sites of other soil components and the competitive relationship between K+ and cations released by carbonate dissolution. The influence of carbonate on the nutrient ion transport at the solid-liquid interface of calcareous soil has been investigated by soil electrochemistry theory-based ion adsorption kinetics, and the links between kinetic features and ion-surface binding energy have been clarified.

Potassium deficiency enhances imbalances in rice water relations under water deficit by decreasing leaf hydraulic conductance

Potassium (K+) is an essential macronutrient for appropriate plant development and physiology. However, little is known about the mechanisms involved in the regulation of leaf water relations by K under water deficit. A pot experiment with two K supplies of 0.45 and 0 g K2O per pot (3 kg soil per pot) and two watering conditions (well-watered and water-deficit) was conducted to explore the effects of K deficiency on canopy transpiration characteristics, leaf water status, photosynthesis, and hydraulic traits in two rice genotypes with contrasting resistance to drought. The results showed that K deficiency reduced canopy transpiration rate by decreasing stomatal conductance, which led to higher canopy temperatures, resulting in limited water deficit tolerance in rice. In addition, K deficiency led to further substantial reductions in leaf relative water content and water potential under water deficit, which increased the imbalance in leaf water relations under water deficit. Notably, K deficiency limited leaf gas exchange by reducing leaf hydraulic conductance, but decreased the intrinsic water use efficiency under water deficit, especially for the drought-resistant cultivar. Further analysis of the underlying process of leaf hydraulic resistance revealed that the key limiting factor of leaf hydraulic conductance under K deficiency was the outside-xylem hydraulic conductance rather than the xylem hydraulic conductance. Overall, our results provide a comprehensive perspective for assessing leaf water relations under K deficiency, water deficit, and their combined stresses, which will be useful for optimal rice fertilization strategies.

The Complex Interplay between Arbuscular Mycorrhizal Fungi and Strigolactone: Mechanisms, Sinergies, Applications and Future Directions

Plants, the cornerstone of life on Earth, are constantly struggling with a number of challenges arising from both biotic and abiotic stressors. To overcome these adverse factors, plants have evolved complex defense mechanisms involving both a number of cell signaling pathways and a complex network of interactions with microorganisms. Among these interactions, the relationship between symbiotic arbuscular mycorrhizal fungi (AMF) and strigolactones (SLs) stands as an important interplay that has a significant impact on increased resistance to environmental stresses and improved nutrient uptake and the subsequent enhanced plant growth. AMF establishes mutualistic partnerships with plants by colonizing root systems, and offers a range of benefits, such as increased nutrient absorption, improved water uptake and increased resistance to both biotic and abiotic stresses. SLs play a fundamental role in shaping root architecture, promoting the growth of lateral roots and regulating plant defense responses. AMF can promote the production and release of SLs by plants, which in turn promote symbiotic interactions due to their role as signaling molecules with the ability to attract beneficial microbes. The complete knowledge of this synergy has the potential to develop applications to optimize agricultural practices, improve nutrient use efficiency and ultimately increase crop yields. This review explores the roles played by AMF and SLs in plant development and stress tolerance, highlighting their individual contributions and the synergistic nature of their interaction.