Nutrient remobilization and C:N:P stoichiometry in response to elevated CO2 and low phosphorus availability in rice cultivars introgressed with and without Pup1

The continuously rising atmospheric CO2 concentration potentially increase plant growth through stimulating C metabolism; however, plant C:N:P stoichiometry in response to elevated CO2 (eCO2) under low P stress remains largely unknown. We investigated the combined effect of eCO2 and low phosphorus on growth, yield, C:N:P stoichiometry, and remobilization in rice cv. Kasalath (aus type), IR64 (a mega rice variety), and IR64-Pup1 (Pup1 QTL introgressed IR64). In response to eCO2 and low P, the C accumulation increased significantly (particularly at anthesis stage) while N and P concentration decreased leading to higher C:N and C:P ratios in all plant components (leaf, sheath, stem, and grain) than ambient CO2. The remobilization efficiencies of N and P were also reduced under low P with eCO2 as compared to control conditions. Among cultivars, the combined effect of eCO2 and low P was greater in IR64-Pup1 and produced higher biomass and grain yield as compared to IR64. However, IR64-Pup1 exhibited a lower N but higher P concentration than IR64, indicating that the Pup1 QTL improved P uptake but did not influence N uptake. Our study suggests that the P availability along with eCO2 would alter the C:N:P ratios due to their differential partitioning, thereby affecting growth and yield.

Plant biomass responses to elevated CO2 are mediated by phosphorus uptake

Elevated atmospheric CO₂ concentrations [CO₂] potentially alter carbon (C) and phosphorus (P) cycles in terrestrial ecosystems. Although numerous field experiments and a few meta-analyses have been conducted, it is still largely unclear how the P cycle affects plant biomass responses under elevated [CO₂] globally. Here, we conducted a global synthesis by analyzing 111 studies on the responses of above- and belowground P cycling to elevated [CO₂], to examine how changes in the P cycle affect the plant biomass response to elevated [CO₂]. Our results show that elevated [CO₂] significantly increased plant aboveground biomass (+13 %), stem biomass (+4 %), leaf biomass (+11 %), belowground biomass (+12 %), and the root: shoot ratio (+7 %). Effects of elevated [CO₂] on aboveground biomass, belowground biomass, and root: shoot ratio were best explained by plant P uptake. In addition, elevated [CO₂]-induced changes in the aboveground P pool, leaf P pool, and leaf P concentration were modulated by ecological drivers, such as ΔCO₂, experimental duration, and aridity index. Our findings highlight the importance of plant P uptake for both above- and belowground plant biomass responses under elevated [CO₂], which should be considered in future biosphere models to improve predictions of terrestrial carbon-climate feedbacks.

Long-term leaf C:N ratio change under elevated CO2 and nitrogen deposition in China: Evidence from observations and process-based modeling

Climate change, elevating atmosphere CO₂ (eCO₂) and increased nitrogen deposition (iNDEP) are altering the biogeochemical interactions between plants, microbes and soils, which further modify plant leaf carbon‑nitrogen (C:N) stoichiometry and their carbon assimilation capability. Many field experiments have observed large sensitivity of leaf C:N ratio to eCO₂ and iNDEP. However, the large-scale pattern of this sensitivity is still unclear, because eCO₂ and iNDEP drive leaf C:N ratio toward opposite directions, which are further compounded by the complex processes of nitrogen acquisition and plant-and-microbial nitrogen competition. Here, we attempt to map the leaf C:N ratio spatial variation in the past 5 decades in China with a combination of data-driven model and process-based modeling. These two approaches showed consistent results. Over different regions, we found that leaf C:N ratio had significant but uneven changes between 2 time periods (1960-1989 and 1990-2015): a 5% ± 8% increase for temperate grasslands in northern China, a 3% ± 6% increase for boreal grasslands in western China, and by contrast, a 7% ± 6% decrease for temperate forests in southern China, and a 3% ± 5% decrease for boreal forests in northeastern China. Additionally, the structural equation models indicated that the leaf C:N change was sensitive to ΔNDEP, ΔCO₂ and ΔMAT rather than ΔMAP and ecosystem types. Process-based modeling suggested that iNDEP was the main source of soil mineral nitrogen change, dominating leaf C:N ratio change in most areas in China, while eCO₂ led to leaf C:N ratio increase in low iNDEP area. This study also indicates that the long-term leaf C:N ratio acclimation was dominated by climate constraint, especially temperature, but was constrained by soil N availability over decade scale.

Warming reduces the production of a major annual forage crop on the Tibetan Plateau

Climate warming has been proposed to increase primary production of natural grasslands in cold regions. However, how climate warming affects the production of artificial pastures in cold regions remains unknown. To address this question, we used open-top chambers to simulate warming in a major artificial pasture (forage oat) on the cold Tibetan Plateau for three consecutive years. Surprisingly, climate warming decreased aboveground and belowground biomass production by 23.1%-44.8% and 35.0%-46.5%, respectively, without a significant impact on their ratio. The adverse effects on biomass production could be attributed to the adverse effects of high-temperatures on leaf photosynthesis through increases in water vapor pressure deficit (by 0.05-0.10 kPa), damages to the leaf oxidant system, as indicated by a 46.6% increase in leaf malondialdehyde content, as well as reductions in growth duration (by 4.7-6.7 days). The adverse effects were also related to exacerbated phosphorus limitation, as indicated by decreases in soil available phosphorus and plant phosphorus concentrations by 31.9%-40.7% and 14.3%-49.4%, respectively, and increases in the plant nitrogen: phosphorus ratio by 19.2%-108.3%. The decrease in soil available phosphorus concentration could be attributed to reductions in soil phosphatase activities (by 9.6%-18.5%). The findings of this study suggest an urgent need to advance agronomic techniques and cultivate more resilient forage genotypes to meet the increasing demand of forage for feeding livestock and to reduce grazing damage to natural grasslands on the warming-sensitive Tibetan Plateau.

Management of phosphorus nutrient amid climate change for sustainable agriculture

Nutrients are essential for plant growth and development and influence overall agricultural production. Phosphorus (P) is a major nutrient required for many physiological and biochemical functions of a plant. Phosphate rock is the major source of phosphate fertilizer but is becoming increasingly limited in both developing and developed countries. The resources of phosphate rock need to be conserved, and import dependency on phosphate fertilizer needs to be minimized; this will help increase the availability of phosphate fertilizer over the next 300 yr. Climate change creates new challenges in the management of nutrients including P, affecting the overall production of crops. The availability, acquisition, and translocation of P are influenced by the fluctuation of temperatures, pH, drought, and elevated CO₂ . Both lower and higher soil temperatures reduce uptake and translocation of P. High soil pH affects P concentration and decreases the rate of plant P uptake. Low soil pH decreases the activity of soil microorganisms, the rate of transpiration, and P uptake and utilization. Elevated CO₂ decreases P uptake from soil by the plants. Future research is needed on chemical, molecular, microbiological, and physiological aspects to improve the understanding on how temperature, pH, drought, and elevated CO₂ affect the availability, acquisition, and transport of P by plants. Better P management strategies are required to secure the P supply to ensure long-term protection of soil fertility and to avoid environmental impacts such as eutrophication and water pollution, ensuring sustainable food production.

Elevated atmospheric CO2 concentration triggers redistribution of nitrogen to promote tillering in rice

Elevated atmospheric CO₂ concentration (eCO₂) often reduces nitrogen (N) content in rice plants and stimulates tillering. However, there is a general consensus that reduced N would constrain rice tillering. To resolve this contradiction, we investigated N distribution and transcriptomic changes in different rice plant organs after subjecting them to eCO₂ and different N application rates. Our results showed that eCO₂ significantly promoted rice tillers (by 0.6, 1.1, 1.7, and 2.1 tillers/plant at 0, 75, 150, and 225 kg N ha^-1 N application rates, respectively) and more tillers were produced under higher N application rates, confirming that N availability constrained tillering in the early stages of growth. Although N content declined in the leaves (-11.0 to -20.7 mg g^-1) and sheaths (-9.8 to -28.8 mg g^-1) of rice plants exposed to eCO₂, the N content of newly emerged tillers on plants exposed to eCO₂ equaled or exceeded the N content of tillers produced under ambient CO₂ conditions. Apparently, the redistribution of N within the plant per se was a critical adaptation strategy to the eCO₂ condition. Transcriptomic analysis revealed that eCO₂ induced less extensive alteration of gene expression than did N application. Most importantly, the expression levels of multiple N-related transporters and receptors such as nitrate transporter NRT2.3a/b and NRT1.1a/b were differentially regulated in leaf and shoot apical meristem, suggesting that multiple genes were involved in sensing the N signal and transporting N metabolites to adapt to eCO₂. The redistribution of N in different organs could be a universal adaptation strategy of terrestrial plants to eCO₂.

Spatially divergent trends of nitrogen versus phosphorus limitation across European forests

Nitrogen (N) and phosphorus (P) are essential nutrients that widely limit plant growth in global terrestrial ecosystems. Rising atmospheric CO₂ concentration generally stimulates terrestrial net primary productivity and consequently may cause or aggravate N and P limitation due to a dilution effect, but the spatial variation of temporal trends in N versus P limitation and its key regulating factors is poorly understood. Using the leaf N:P ratio of 15 dominant tree species as an indicator, we analysed the spatial variation of plot-level shift towards N or P limitation across 163 European forest plots during 1995-2017. Phosphorus limitation increased from 25% to 33% of the studied plots between 1995-1997 and 2015-2017, while N limitation occurred in a negligible number of plots. A major proportion (56%) of the plots showed no significant trend in leaf N:P ratio, implying no shifts in N versus P limitation status. In the remaining plots, 38% of the plots showed a significant increase of leaf N:P ratio and only 6% of the plots showed a significant decrease of leaf N:P ratio. The spatial variation in the rate of decrease in leaf N:P ratio was associated with a significant decrease in leaf N concentration and mainly explained by the rate of decrease in N deposition. In contrast, the spatial variation in the rate of increase in leaf N:P ratio was associated with a significant decrease in leaf P concentration and mainly explained by forest category (broadleaf vs. conifer), mean annual temperature and soil C:N ratio. Our findings highlight a remarkable spatial divergence in temporal trends of nutrient limitation status across European forests over the past two decades, but overall, P is becoming more limiting versus N, especially in broadleaved forests.

Anthropogenic global shifts in biospheric N and P concentrations and ratios and their impacts on biodiversity, ecosystem productivity, food security, and human health

The availability of carbon (C) from high levels of atmospheric carbon dioxide (CO2 ) and anthropogenic release of nitrogen (N) is increasing, but these increases are not paralleled by increases in levels of phosphorus (P). The current unstoppable changes in the stoichiometries of C and N relative to P have no historical precedent. We describe changes in P and N fluxes over the last five decades that have led to asymmetrical increases in P and N inputs to the biosphere. We identified widespread and rapid changes in N:P ratios in air, soil, water, and organisms and important consequences to the structure, function, and biodiversity of ecosystems. A mass-balance approach found that the combined limited availability of P and N was likely to reduce C storage by natural ecosystems during the remainder of the 21st Century, and projected crop yields of the Millennium Ecosystem Assessment indicated an increase in nutrient deficiency in developing regions if access to P fertilizer is limited. Imbalances of the N:P ratio would likely negatively affect human health, food security, and global economic and geopolitical stability, with feedbacks and synergistic effects on drivers of global environmental change, such as increasing levels of CO2 , climatic warming, and increasing pollution. We summarize potential solutions for avoiding the negative impacts of global imbalances of N:P ratios on the environment, biodiversity, climate change, food security, and human health.

Increasing atmospheric CO2 concentrations correlate with declining nutritional status of European forests

The drivers of global change, including increases in atmospheric CO₂ concentrations, N and S deposition, and climate change, likely affect the nutritional status of forests. Here we show forest foliar concentrations of N, P, K, S and Mg decreased significantly in Europe by 5%, 11%, 8%, 6% and 7%, respectively during the last three decades. The decrease in nutritional status was especially large in Mediterranean and temperate forests. Increasing atmospheric CO₂ concentration was well correlated with the decreases in N, P, K, Mg, S concentrations and the increase of N:P ratio. Regional analyses indicated that increases in some foliar nutrient concentrations such as N, S and Ca in northern Europe occurred associated with increasingly favourable conditions of mean annual precipitation and temperature. Crucial changes in forest health, structure, functioning and services, including negative feedbacks on C capture can be expected if these trends are not reversed.

Emerging concepts of potassium homeostasis in plants

Potassium (K+) is an essential cation in all organisms that influences crop production and ecosystem stability. Although most soils are rich in K minerals, relatively little K+ is present in forms that are available to plants. Moreover, leaching and run-off from the upper soil layers contribute to K+ deficiencies in agricultural soils. Hence, the demand for K fertilizer is increasing worldwide. K+ regulates multiple processes in cells and organs, with K+ deficiency resulting in decreased plant growth and productivity. Here, we discuss the complexity of the reactive oxygen species-calcium-hormone signalling network that is responsible for the sensing of K+ deficiency in plants, together with genetic approaches using K+ transporters that have been used to increase K+ use efficiency (KUE) in plants, particularly under environmental stress conditions such as salinity and heavy metal contamination. Publicly available rice transcriptome data are used to demonstrate the two-way relationship between K+ and nitrogen nutrition, highlighting how each nutrient can regulate the uptake and root to shoot translocation of the other. Future research directions are discussed in terms of this relationship, as well as prospects for molecular approaches for the generation of improved varieties and the implementation of new agronomic practices. An increased knowledge of the systems that sense and take up K+, and their regulation, will not only improve current understanding of plant K+ homeostasis but also facilitate new research and the implementation of measures to improve plant KUE for sustainable food production.

Impact of elevated CO2 on C:N:P ratio among soybean cultivars

Elevated atmospheric CO2 concentration (eCO2) exerts significant influence on nutrient requirement in plant. The investigation of C:N:P ratios in major cropping soils is important for managing nutrient balance and maximizing their use efficiency in future farming systems. This study aimed to examine the effect of eCO2 on the C:N:P ratios in different plant parts among soybean cultivars. Twenty-four soybean cultivars were planted in open top chambers at two CO2 concentrations (390 and 550 ppm) and sampled at the initial pod filling stage (R5) and the full maturity stage (R8). The C, N and P concentrations in root, stem, leaf and seed were determined. Elevated CO2 decreased the N concentrations in stem (-5.1%) and leaf (-3.2%) at R5, and in root (-24%), stem (-25%) and seed (-6.2%) at R8, resulting in a significant decrease of C:N ratio in the corresponding parts. The P concentration was significantly increased in root (6.0%), stem (7.9%) and leaf (16%) at R5, and in root (2.6%), stem (29%) and seed (16%) at R8 across 24 cultivars, leading to a decrease in the C:P ratio. Elevated CO2 significantly decreased the N:P ratio in root (-4.5%), stem (-12%) and leaf (-17%) at R5, and in root (-26%), stem (-57%) and seed (-22%) at R8. Furthermore, the response of C:N:P ratios to eCO2 varied greatly among soybean cultivars leading to significant CO2 × cultivar interactions. Nitrogen, but not P was the limiting factor for the soybean plants grown in Mollisols under eCO2. The considerable variation in the C:N:P ratios among cultivars in response to eCO2 indicates a potential improvement in soybean adaptability to climate change via selection new cultivars. Cultivars SN22 and ZH4 that did not considerably altered the C:N and C:P ratios in response to eCO2 are likely the optimal genomes in soybean breeding programs for eCO2 adaption.

Effects of fly ash application on plant biomass and element accumulations: a meta-analysis

Fly ash generated from coal-fired power plants is a source of potential pollutants, but can be used as a soil ameliorant to increase plant biomass and yield in agriculture. However, the effects of fly ash soil application on plant biomass and the accumulation of both nutrient and toxic elements in plants remain unclear. Based on 85 articles, we conducted a comprehensive meta-analysis to evaluate changes in plant biomass and concentrations of 21 elements in plants in response to fly ash application. These elements included macro-nutrients (N, P, K, Ca, and S), micro-nutrients (B, Co, Cu, Fe, Mn, Mo, Ni, and Zn), and metal(loid)s (Al, As, Cd, Cr, Pb, and Se). Overall, fly ash application decreased plant biomass by 15.2%. However, plant biomass was enhanced by fly ash application by 11.6-29.2% at lower application rates (i.e. <25% of soil mass), and decreased by 45.8% at higher application rates (i.e. 50-100%). Belowground biomass was significantly reduced while yield was enhanced by fly ash application. Most of the element concentrations in plants were enhanced by fly ash application, and followed a descending order with metal(loid)s > micro-nutrients > macro-nutrients. Concentrations of elements tended to increase with an increase in fly ash application rate. Our syntheses indicated that fly ash should be applied at less than 25% in order to enhance plant biomass and yield but avoid high accumulations of metal(loid)s.

Nitrogen and Phosphorus Retranslocation of Leaves and Stemwood in a Mature Eucalyptus Forest Exposed to 5 Years of Elevated CO2

Elevated CO2 affects C cycling processes which in turn can influence the nitrogen (N) and phosphorus (P) concentrations of plant tissues. Given differences in how N and P are used by plants, we asked if their stoichiometry in leaves and wood was maintained or altered in a long-term elevated CO2 experiment in a mature Eucalyptus forest on a low P soil (EucFACE). We measured N and P concentrations in green leaves at different ages at the top of mature trees across 6 years including 5 years in elevated CO2. N and P concentrations in green and senesced leaves and wood were determined to evaluate both spatial and temporal variation of leaf N and P concentrations, including the N and P retranslocation in leaves and wood. Leaf P concentrations were 32% lower in old mature leaves compared to newly flushed leaves with no effect of elevated CO2 on leaf P. By contrast, elevated CO2 significantly decreased leaf N concentrations in newly flushed leaves but this effect disappeared as leaves matured. As such, newly flushed leaves had 9% lower N:P ratios in elevated CO2 and N:P ratios were not different in mature green leaves (CO2 by Age effect, P = 0.02). Over time, leaf N and P concentrations in the upper canopy slightly declined in both CO2 treatments compared to before the start of the experiment. P retranslocation in leaves was 50%, almost double that of N retranslocation (29%), indicating that this site was P-limited and that P retranslocation was an important mechanism in this ecosystem to retain P in plants. As P-limited trees tend to store relatively more N than P, we found an increased N:P ratio in sapwood in response to elevated CO2 (P < 0.01), implying N accumulation in live wood. The flexible stoichiometric ratios we observed can have important implications for how plants adjust to variable environmental conditions including climate change. Hence, variable nutrient stoichiometry should be accounted for in large-scale Earth Systems models invoking biogeochemical processes.

Changes in plant C, N and P ratios under elevated [CO2] and canopy warming in a rice-winter wheat rotation system

Elevated atmospheric CO2 concentration ([CO2]) can stimulate plant growth through enhanced photosynthetic rate. However, plant C, N and P ratios in response to elevated [CO2] combined with canopy warming in rice-winter wheat rotation system remain largely unknown. Here we investigated the impacts of elevated [CO2] and warming on plant nutrient ratios under open-air conditions. Four treatments including the ambient condition (CK), elevated [CO2] (500 ppm, CE), canopy warming (+2 °C, WA), and the combination of elevated [CO2] and warming (CW) were used to investigate the responses of plant C, N and P ratios in a rice-winter wheat rotation system in southeast China. Results showed that elevated [CO2] increased C:N ratio in whole plant by 8.4-14.3% for both crops, and increased C:P ratio by 11.3% for rice. The changes in ratio were due to an increase in C concentration by 0.8-1.2% and a reduction in N concentration by 7.4-10.7% for both crops, and a reduction in P concentration by 10.0% for rice. Warming increased N allocation in rice leaf and N concentration by 12.4% for rice, resulting in increases in the ratios of N to C and P by 11.9% and 9.7% in rice, but not in wheat. However, CW had no effect on plant C:N ratio in rice, indicating the positive effect of elevated [CO2] could offset the negative impact of warming on C:N ratio. By contrast, CW significantly decreased plant C:P and N:P ratios by 16% due to the increase in P allocation in stem for wheat. These results suggest that impacts of climate change on plant nutrient balance occur through interactions between the effects of climate change on nutrient uptake and allocation, which is important for food quality and productivity under global climate change.

Effects of elevated CO2 on plant C-N-P stoichiometry in terrestrial ecosystems: A meta-analysis

A substantial number of experiments have so far been carried out to study the response of the C-N-P stoichiometry of terrestrial plants to the rising CO₂ level of the earth. However, there is a need of systematic evaluation for assessing the impact of the elevated CO₂ on plant C-N-P stoichiometry. In the present investigation, a comprehensive meta-analysis involving 386 published reports and including 4481 observations has been carried out. The goal of the research was to determine the response of plants to their C-N-P stoichiometry due to elevated levels of global atmospheric CO₂. The results showed that rising CO₂ altered the concentration of C (+2.19%, P < 0.05), N (-9.73%, P < 0.001) and P (-3.23%, P < 0.001) and C:N (+13.29%, P < 0.001) and N:P ratios (-7.32%, P < 0.0001). Overall, a slightly increasing trend in the C:P ratio (P > 0.05) in the plant was observed. However, plant leaf, shoot and herbaceous type of plants showed more sensitivity to rising CO₂. CO₂ magnitude exhibited a positive effect (P < 0.05) on C:N ratio. Additionally, "CO₂ acclimation" hypothesis as proposed by the authors of the current paper was also tested in the study. Results obtained, especially, show changes of C and N concentrations and C:P ratio to an obvious down-regulation for long-term CO₂ fumigation. At spatial scales, a reduction of plant N concentration was found to be higher in the southern hemisphere. The CO₂ enrichment methods affected the plant C-N-P stoichiometry. Compared to FACE (free-air CO₂ enrichment), OTC (open top chamber) showed larger changes of C, N, P, and N:P. The results of the present study should, therefore, become helpful to offer a better understanding towards the response of the terrestrial plant C-N-P stoichiometry to an elevated global atmospheric CO₂ in the future.

Individual and combined effects of multiple global change drivers on terrestrial phosphorus pools: A meta-analysis

Human activity-induced global change drivers have dramatically changed terrestrial phosphorus (P) dynamics. However, our understanding of the interactive effects of multiple global change drivers on terrestrial P pools remains elusive, limiting their incorporation into ecological and biogeochemical models. We conducted a meta-analysis using 1751 observations extracted from 283 published articles to evaluate the individual, combined, and interactive effects of elevated CO₂, warming, N addition, P addition, increased rainfall, and drought on P pools of plant (at both single-plant and plant-community levels), soil and microbial biomass. Our results suggested that (1) terrestrial P pools showed the most sensitive responses to the individual effects of warming and P addition; (2) P pools were consistently stimulated by P addition alone or in combination with simultaneous N addition; (3) environmental and experimental setting factors such as ecosystem type, climate, and latitude could significantly influence both the individual and combined effects; and (4) the interactive effects of two-driver pairs across multiple global change drivers are more likely to be additive rather than synergistic or antagonistic. Our findings highlighting the importance of additive interactive effects among multiple global change drivers on terrestrial P pools would be useful for incorporating P as controls on ecological processes such as photosynthesis and plant growth into ecosystem models used to analyze effects of multiple drivers under future global change.

An assessment on the uncertainty of the nitrogen to phosphorus ratio as a threshold for nutrient limitation in plants

BACKGROUND AND AIMS

The nitrogen (N) to phosphorus (P) ratio (N:P) has been widely used as a threshold for identifying nutrient limitations in terrestrial plants; however, the associated reliability has not been well assessed.

METHODS

The uncertainty of nutrient limitations caused by the N:P threshold was evaluated using two approaches: fertilization experiments synthesized across multiple ecosystems; and random sampling simulation of the impacts of different nutrient sufficiencies and deficiencies.

KEY RESULTS

The fertilization experiment data indicated that the types of nutrient limitation determined via N:P thresholds were partly inconsistent with the growth responses observed under N and P additions, i.e. under N:P thresholds of 14 and 16 (or 10 and 20), 32.5 % (or 16.2 %) of the data were inconsistent between these two. The random sampling simulation suggested that N:P thresholds may indicate N (or P) limitations when leaf N (or P) content is sufficient, whereas these thresholds may not indicate N (or P) limitations when leaf N (or P) content is deficient. The error risks calculated from the sampling simulation presented large fluctuations at small sample sizes and decreased as the thresholds of nutrient content sufficiency (or deficiency) increased (or decreased). The N:P thresholds of 10 and 20 showed lower error risks than the thresholds of 14 and 16.

CONCLUSIONS

These findings highlight that canonical N:P thresholds have the potential to introduce a large uncertainty when used to detect plant nutrient limitations, suggesting that the error risks should be cautioned in future studies.

Changes in nutrient concentrations of leaves and roots in response to global change factors

Global change impacts on biogeochemical cycles have been widely studied, but our understanding of whether the responses of plant elemental composition to global change drivers differ between above- and belowground plant organs remains incomplete. We conducted a meta-analysis of 201 reports including 1,687 observations of studies that have analyzed simultaneously N and P concentrations changes in leaves and roots in the same plants in response to drought, elevated [CO₂ ], and N and P fertilization around the world, and contrasted the results within those obtained with a general database (838 reports and 14,772 observations) that analyzed the changes in N and P concentrations in leaves and/or roots of plants submitted to the commented global change drivers. At global level, elevated [CO₂ ] decreased N concentrations in leaves and roots and decreased N:P ratio in roots but no in leaves, but was not related to P concentration changes. However, the response differed among vegetation types. In temperate forests, elevated [CO₂ ] was related with lower N concentrations in leaves but not in roots, whereas in crops, the contrary patterns were observed. Elevated [CO₂ ] decreased N concentrations in leaves and roots in tundra plants, whereas not clear relationships were observed in temperate grasslands. However, when elevated [CO₂ ] and N fertilization coincided, leaves had lower N concentrations, whereas root had higher N concentrations suggesting that more nutrients will be allocated to roots to improve uptake of the soil resources not directly provided by the global change drivers. N fertilization and drought increased foliar and root N concentrations while the effects on P concentrations were less clear. The changes in N and P allocation to leaves and root, especially those occurring in opposite direction between them have the capacity to differentially affect above- and belowground ecosystem functions, such as litter mineralization and above- and belowground food webs.

Effects of three global change drivers on terrestrial C:N:P stoichiometry: a global synthesis

Over the last few decades, there has been an increasing number of controlled-manipulative experiments to investigate how plants and soils might respond to global change. These experiments typically examined the effects of each of three global change drivers [i.e., nitrogen (N) deposition, warming, and elevated CO₂ ] on primary productivity and on the biogeochemistry of carbon (C), N, and phosphorus (P) across different terrestrial ecosystems. Here, we capitalize on this large amount of information by performing a comprehensive meta-analysis (>2000 case studies worldwide) to address how C:N:P stoichiometry of plants, soils, and soil microbial biomass might respond to individual vs. combined effects of the three global change drivers. Our results show that (i) individual effects of N addition and elevated CO₂ on C:N:P stoichiometry are stronger than warming, (ii) combined effects of pairs of global change drivers (e.g., N addition + elevated CO₂ , warming + elevated CO₂ ) on C:N:P stoichiometry were generally weaker than the individual effects of each of these drivers, (iii) additive interactions (i.e., when combined effects are equal to or not significantly different from the sum of individual effects) were more common than synergistic or antagonistic interactions, (iv) C:N:P stoichiometry of soil and soil microbial biomass shows high homeostasis under global change manipulations, and (v) C:N:P responses to global change are strongly affected by ecosystem type, local climate, and experimental conditions. Our study is one of the first to compare individual vs. combined effects of the three global change drivers on terrestrial C:N:P ratios using a large set of data. To further improve our understanding of how ecosystems might respond to future global change, long-term ecosystem-scale studies testing multifactor effects on plants and soils are urgently required across different world regions.

Stem and crown growth of Japanese larch and its hybrid F1 grown in two soils and exposed to two free-air O3 regimes

Ozone (O₃) pollution and soil infertility may negatively affect boreal forests across the Northern Hemisphere. Impacts to economically and ecologically important larches (Larix sp., Pinacaeae) are particularly concerning. Using a free air O₃ enrichment (FACE) system, we investigated the effect of 2-year elevated O₃ exposure (≈66 nmol mol^-1) on Japanese larch (L. kaempferi) and its hybrid larch F₁ (L. gmelinii var. japonica × L. kaempferi) planted directly into either fertile brown forest soil (BF) or BF mixed with infertile volcanic ash soil (VA). Overall, photosynthetic pigmentation and the growth performance of the stem and crown were reduced in both taxa exposed to elevated O₃. Furthermore, hybrid larch, in both O₃ treatments, performed better than Japanese larch. This finding contradicts findings of prior experiments with potential experimental artifacts of O₃ exposure facilities and root restrictions. Elevated O₃ also disproportionately inhibited stem diameter growth and caused an imbalance in chlorophylls a/b and chlorophyll/carotenoid ratios. Hybrid and Japanese larches grown in BF and VA had a significantly lower drop of stem diameter over the run of stem height (from base to top) when exposed to elevated O₃, compared to ambient O₃. This finding indicates altered stem shape under elevated O₃. Among 11 response variables, there were no significant interactions between O₃ treatment and taxa. There was also no significant interaction of soil condition and taxa, suggesting that the two larches shared a similar response to O₃ and soil type. Understanding the performance of hybrid larch in relation to its parent species has ramifications for breeding success in a soil-degraded and O₃-polluted environment.

Reproductive organ and young tissues show constrained elemental composition in Arabidopsis thaliana

BACKGROUND AND AIMS

The identification of stoichiometric homeostasis is crucial for understanding plant adaptive strategies under a changing environment. However, current knowledge of plant stoichiometric homeostasis has mainly been obtained from mature leaves, with little from other organs across different developmental stages.

METHODS

We conducted a greenhouse nitrogen (N) and phosphorus (P) addition experiment to evaluate the strength of stoichiometric homeostasis across different organs and developmental stages of Arabidopsis thaliana.

KEY RESULTS

Homeostatic regulation coefficients (H) for N (HN), P (HP) and N : P ratio (HNP) were highest in reproductive tissue, followed by stem and leaf at the same stage. All H parameters in the same organ decreased significantly over the developmental stages. Leaf HN, HP and HNP were highest at stage 1, followed by stages 2 and 3. Both stem and silique at stage 2 relative to stage 3 had higher HN, HP and HNP. These results suggested that reproductive tissue relative to other organs and young tissue relative to old tissue showed more constrained elemental composition in response to nutrient availabilities, and such trends were also evidenced by stoichiometric scaling relationships.

CONCLUSIONS

Our findings highlight that stoichiometric homeostasis is tightly related to the ontogenesis of plant tissue. These results could have a strong implication for diagnosing relative availabilities of N and P in ecosystems, suggesting that the N and P stoichiometry of old tissues might be stronger indicators of nutrient status for plants, but further study is needed to test the generality across species with more distinguishable functional traits.