Metabolite and transcript profiling of Guinea grass (Panicum maximum Jacq) response to elevated [CO2] and temperature

Balancing trade-offs: Enhanced carbon assimilation and productivity with reduced nutritional value in a well-watered C4 pasture under a warmer CO2-enriched atmosphere

The concentration of atmospheric CO2 and temperature are pivotal components of ecosystem productivity, carbon balance, and food security. In this study, we investigated the impacts of a warmer climate (+2 °C above ambient temperature) and an atmosphere enriched with CO2 (600 ppm) on gas exchange, antioxidant enzymatic system, growth, nutritive value, and digestibility of a well-watered, managed pasture of Megathyrsus maximus, a tropical C4 forage grass, under field conditions. Elevated [CO2] (eC) improved photosynthesis and reduced stomatal conductance, resulting in increased water use efficiency and plant C content. Under eC, stem biomass production increased without a corresponding increase in leaf biomass, leading to a smaller leaf/stem ratio. Additionally, eC had negative impacts on forage nutritive value and digestibility. Elevated temperature (eT) increased photosynthetic gains, as well as stem and leaf biomass production. However, it reduced P and K concentration, forage nutritive value, and digestibility. Under the combined conditions of eC and eT (eCeT), eT completely offset the effects of eC on the leaf/stem ratio. However, eT intensified the effects of eC on photosynthesis, leaf C concentration, biomass accumulation, and nutritive value. This resulted in a forage with 12% more acid detergent fiber content and 28% more lignin. Additionally, there was a decrease of 19% in crude protein leading to a 15% decrease in forage digestibility. These changes could potentially affect animal feeding efficiency and feedback climate change, as ruminants may experience an amplification in methane emissions. Our results highlight the critical significance of conducting multifactorial field studies when evaluating plant responses to climate change variables.

Revisiting Changes in Growth, Physiology and Stress Responses of Plants under the Effect of Enhanced CO2 and Temperature

Climate change has universally affected the whole ecosystem in a unified manner and is known to have improbable effects on agricultural productivity and food security. Carbon dioxide (CO2) and temperature are the major environmental factors that have been shown to increase sharply during the last century and are directly responsible for affecting plant growth and development. A number of previous investigations have deliberated the positive effects of elevated CO2 on plant growth and development of various C3 crops, while detrimental effects of enhanced temperature on different crop plants like rice, wheat, maize and legumes are generally observed. A combined effect of elevated CO2 and temperature has yet to be studied in great detail; therefore, this review attempts to delineate the interactive effects of enhanced CO2 and temperature on plant growth, development, physiological and molecular responses. Elevated CO2 maintains leaf photosynthesis rate, respiration, transpiration and stomatal conductance in the presence of elevated temperature and sustains plant growth and productivity in the presence of both these environmental factors. Concomitantly, their interaction also affects the nutritional quality of seeds and leads to alterations in the composition of secondary metabolites. Elevated CO2 and temperature modulate phytohormone concentration in plants, and due to this fact, both environmental factors have substantial effects on abiotic and biotic stresses. Elevated CO2 and temperature have been shown to have mitigating effects on plants in the presence of other abiotic stress agents like drought and salinity, while no such pattern has been observed in the presence of biotic stress agents. This review focuses on the interactive effects of enhanced CO2 and temperature on different plants and is the first of its kind to deliver their combined responses in such detail.

Cytochrome P450 Gene Families: Role in Plant Secondary Metabolites Production and Plant Defense

Cytochrome P450s (CYPs) are the most prominent family of enzymes involved in NADPH- and O2-dependent hydroxylation processes throughout all spheres of life. CYPs are crucial for the detoxification of xenobiotics in plants, insects, and other organisms. In addition to performing this function, CYPs serve as flexible catalysts and are essential for producing secondary metabolites, antioxidants, and phytohormones in higher plants. Numerous biotic and abiotic stresses frequently affect the growth and development of plants. They cause a dramatic decrease in crop yield and a deterioration in crop quality. Plants protect themselves against these stresses through different mechanisms, which are accomplished by the active participation of CYPs in several biosynthetic and detoxifying pathways. There are immense potentialities for using CYPs as a candidate for developing agricultural crop species resistant to biotic and abiotic stressors. This review provides an overview of the plant CYP families and their functions to plant secondary metabolite production and defense against different biotic and abiotic stresses.

Adjustments in photosynthetic pigments, PS II photochemistry and photoprotection in a tropical C4 forage plant exposed to warming and elevated [CO2]

Global climate change will impact crops and grasslands, affecting growth and yield. However, is not clear how the combination of warming and increased atmospheric carbon dioxide concentrations ([CO₂]) will affect the photosystem II (PSII) photochemistry and the photosynthetic tissue photoinhibition and photoprotection on tropical forages. Here, we evaluated the effects of elevated [CO₂] (∼600 μmol mol^-1) and warming (+2 °C increase temperature) on the photochemistry of photosystem II and the photoprotection strategies of a tropical C4 forage Panicum maximum Jacq. grown in a Trop-T-FACE facility under well-watered conditions without nutrient limitation. Analysis of the maximum photochemical efficiency of PSII (F_v/F_m), the effective PSII quantum yield Y(II), the quantum yield of regulated energy dissipation Y(NPQ), the quantum yield of non-regulated energy dissipation Y(NO), and the malondialdehyde (MDA) contents in leaves revealed that the photosynthetic apparatus of plants did not suffer photoinhibitory damage, and plants did not increase lipid peroxidation in response to warming and [CO₂] enrichment. Plants under warming treatment showed a 12% higher chlorophyll contents and a 58% decrease in α-tocopherol contents. In contrast, carotenoid composition (zeaxanthin and β-carotene) and ascorbate levels were not altered by elevated [CO₂] and warming. The elevated temperature increased both net photosynthesis rate and aboveground biomass but elevated [CO₂] increased only net photosynthesis. Adjustments in chlorophyll, de-epoxidation state of the xanthophylls cycle, and tocopherol contents suggest leaves of P. maximum can acclimate to 2 °C warmer temperature and elevated [CO₂] when plants are grown with enough water and nutrients during tropical autumn-winter season.

Warming offsets the benefits of elevated CO2 in water relations while amplifies elevated CO2-induced reduction in forage nutritional value in the C4 grass Megathyrsus maximus

Tropical grasslands are very important to global carbon and water cycles. C4 plants have increased heat tolerance and a CO2 concentrating mechanism that often reduces responses to elevated concentrations of CO2 ([CO2]). Despite the importance of tropical grasslands, there is a scarcity of studies that elucidate how managed tropical grasslands will be affected by elevated [CO2] and warming. In our study, we used a combination of a temperature-free air-controlled enhancement (T-FACE) and a free-air carbon dioxide enrichment (FACE) systems to increase canopy temperature and [CO2] under field conditions, respectively. We warmed a field-grown pasture dominated by the C4 tropical forage grass Megathyrsus maximus by 2°C above ambient under two levels of [CO2] (ambient (aC) and elevated (eC - 600 ppm) to investigate how these two factors isolated or combined regulate water relations through stomatal regulation, and how this combination affects PSII functioning, biochemistry, forage nutritive value, and digestibility. We demonstrated that the effects of warming negated the effects of eC in plant transpiration, water potential, proline content, and soil moisture conservation, resulting in warming canceling the eCO2-induced improvement in these parameters. Furthermore, there were additive effects between eC and warming for chlorophyll fluorescence parameters and aboveground nutritive value. Warming sharply intensified the eCO2-induced decrease in crude protein content and increases in forage fibrous fraction and lignin, resulting in a smaller forage digestibility under a warmer CO2-enriched atmosphere. Our results highlight the importance of multifactorial studies when investigating global change impacts on managed ecosystems and the potential consequences for the global carbon cycle like amplification in methane emissions by ruminants and feeding a positive climate feedback system.

Genome-Wide Association Mapping Reveals Novel Putative Gene Candidates Governing Reproductive Stage Heat Stress Tolerance in Rice

Temperature rise predicted for the future will severely affect rice productivity because the crop is highly sensitive to heat stress at the reproductive stage. Breeding tolerant varieties is an economically viable option to combat heat stress, for which the knowledge of target genomic regions associated with the reproductive stage heat stress tolerance (RSHT) is essential. A set of 192 rice genotypes of diverse origins were evaluated under natural field conditions through staggered sowings for RSHT using two surrogate traits, spikelet fertility and grain yield, which showed significant reduction under heat stress. These genotypes were genotyped using a 50 k SNP array, and the association analysis identified 10 quantitative trait nucleotides (QTNs) for grain yield, of which one QTN (qHTGY8.1) was consistent across the different models used. Only two out of 10 MTAs coincided with the previously reported QTLs, making the remaing eight novel. A total of 22 QTNs were observed for spikelet fertility, among which qHTSF5.1 was consistently found across three models. Of the QTNs identified, seven coincided with previous reports, while the remaining QTNs were new. The genes near the QTNs were found associated with the protein–protein interaction, protein ubiquitination, stress signal transduction, and so forth, qualifying them to be putative for RSHT. An in silico expression analysis revealed the predominant expression of genes identified for spikelet fertility in reproductive organs. Further validation of the biological relevance of QTNs in conferring heat stress tolerance will enable their utilization in improving the reproductive stage heat stress tolerance in rice.

Future warming will change the chemical composition and leaf blade structure of tropical C3 and C4 forage species depending on soil moisture levels

Temperature and soil moisture strongly affect the nutritional value and digestibility of forage plants through changes in leaf chemical composition or the proportion of leaf blade tissues. In this study, we aimed to evaluate leaf blade anatomical modifications of two tropical forage species, Stylosanthes capitata (C₃) and Megathyrsus maximus (C₄) under warmed conditions (+2 °C) at well-watered and rainfed conditions and investigate the interactions between leaf anatomical alterations, leaf chemical composition, and leaf digestibility. Experiments were conducted under field conditions using a Temperature-free air-controlled enhancement (T-FACE) system. We observed that plants under elevated temperature produced leaves with smaller stomata and thinner mesophyll tissue and reduced total leaf thickness, potentially impacting gas exchange. On the other hand, reduced soil moisture increased stomatal density and thickness of the adaxial epidermis. In both species, leaf fibrous fractions concentration increased under warmed and non-irrigated conditions, while crude protein concentration and digestibility decreased. However, leaf digestibility was associated with leaf chemical composition rather than the proportion of different leaf blade tissues. We concluded that although both species developed leaf anatomical modifications to acclimate under future warming conditions, leaf nutritional value and digestibility will be reduced, potentially impacting future livestock production and methane emissions by ruminants.

Challenges of Biomass Utilization for Bioenergy in a Climate Change Scenario

The climate changes expected for the next decades will expose plants to increasing occurrences of combined abiotic stresses, including drought, higher temperatures, and elevated CO2 atmospheric concentrations. These abiotic stresses have significant consequences on photosynthesis and other plants' physiological processes and can lead to tolerance mechanisms that impact metabolism dynamics and limit plant productivity. Furthermore, due to the high carbohydrate content on the cell wall, plants represent a an essential source of lignocellulosic biomass for biofuels production. Thus, it is necessary to estimate their potential as feedstock for renewable energy production in future climate conditions since the synthesis of cell wall components seems to be affected by abiotic stresses. This review provides a brief overview of plant responses and the tolerance mechanisms applied in climate change scenarios that could impact its use as lignocellulosic biomass for bioenergy purposes. Important steps of biofuel production, which might influence the effects of climate change, besides biomass pretreatments and enzymatic biochemical conversions, are also discussed. We believe that this study may improve our understanding of the plant biological adaptations to combined abiotic stress and assist in the decision-making for selecting key agronomic crops that can be efficiently adapted to climate changes and applied in bioenergy production.

Dynamic Transcriptomic and Metabolomic Analyses of Madhuca pasquieri (Dubard) H. J. Lam During the Post-germination Stages

The wild population of Madhuca pasquieri (Dubard) H. J. Lam is currently dwindling; its understory seedlings are rare, and there is a lack of molecular studies, which impedes the conservation of this species. This study exploited second-generation sequencing and widely targeted metabolomics analysis to uncover the dynamic changes in differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) in five post-germination stages of M. pasquieri whole organism. Notably, the weighted gene co-expression network analysis (WGCNA), transcriptome, and metabolome association analyses all indicated significant enrichment of the flavonoid biosynthesis pathway in stage 4 (two-leaf), and an upregulation of the genes encoding flavonol biosynthesis in this stage. In stage 5 (nine-leaf), the flavonols were significantly accumulated, indicating that the changes in metabolites were driven at the transcript level. According to the significant changes in gene expression encoding auxin transport carriers and their correlation with flavonols during stage 5, the flavonols were speculated to have a direct inhibitory effect on the expression of PIN4 encoding gene, which may inhibit the process of polar auxin transport. The results provided important insights into the molecular network relationships between the transcription and metabolism of this rare and endangered species during the post-germination stages and explained the reasons for the slow growth of its seedlings at the molecular level.

Variations in Rainfall Affect the Responses of Foliar Chemical Properties of Cunninghamia lanceolata Seedlings to Soil Warming

Climate warming is becoming an increasingly serious threat. Understanding plant stoichiometry changes under climate warming is crucial for predicting the effects of future warming on terrestrial ecosystem productivity. Nevertheless, how plant stoichiometry responds to warming when interannual rainfall variation is considered, remains poorly understood. We performed a field soil warming experiment (+5°C) using buried heating cables in subtropical areas of China from 2015 to 2018. Stoichiometric patterns of foliar C:N:P:K:Ca:Mg, non-structural carbohydrate, and stable isotope of Cunninghamia lanceolata seedlings were studied. Our results showed that soil warming decreased foliar P and K concentrations, C:Ca, P:Ca, and P:Mg ratios. However, soil warming increased foliar Ca concentration, δ15N value, C:P and N:P ratios. The response ratios of foliar N, C:N, and δ15N to soil warming were correlated with rainfall. Our findings indicate that there was non-homeostasis of N and C:N under warming conditions. Three possible reasons for this result are considered and include interannual variations in rainfall, increased loss of N, and N limitation in leaves. Piecewise structural equation models showed that stoichiometric non-homeostasis indirectly affected the growth of C. lanceolata seedlings in response to soil warming. Consequently, the growth of C. lanceolata seedlings remained unchanged under the warming treatment. Taken together, our results advance the understanding of how altered foliar stoichiometry relates to changes in plant growth in response to climate warming. Our results emphasize the importance of rainfall variations for modulating the responses of plant chemical properties to warming. This study provides a useful method for predicting the effects of climate warming on economically important timber species.

Metabolomics and Transcriptomics Analyses of Two Contrasting Cherry Rootstocks in Response to Drought Stress

Drought is one of the main factors affecting sweet cherry yields, and cherry rootstocks can provide a range of tree vigor levels to better match sweet cherries with the characteristics of the soil. To investigate the molecular events of the cherry to water deficiency, we performed transcriptomic and metabolomic analyses of Prunus mahaleb CDR-1 (drought-tolerant cherry rootstock (DT)) and P. cerasus × P. canescens Gisela 5 (drought-susceptible cherry rootstock (DS)), respectively. The results revealed 253 common drought-responsive genes in leaves and roots in DT and 17 in DS; 59 upregulated metabolites were explored in leaves in DT and 19 were explored in DS. Differentially expressed metabolites related to the cyanoamino acid metabolism pathway and phenylpropanoid biosynthesis pathway may be key factors in the difference in drought resistance in the two rootstocks. Moreover, six central metabolites-3-cyanoalanine, phenylalanine, quinic acid, asparagine, p-benzoquinone, and phytosphingosine-were identified as potential biological markers of drought response in cherries and may be key factors in the difference in drought resistance, along with caffeic acid and chlorogenic acid. We also selected 17 differentially expressed genes as core candidate genes and the mechanism of DT in response to drought is summarized.

Age-dependent increase in α-tocopherol and phytosterols in maize leaves exposed to elevated ozone pollution

Tropospheric ozone is a major air pollutant that significantly damages crop production. Crop metabolic responses to rising chronic ozone stress have not been well studied in the field, especially in C4 crops. In this study, we investigated the metabolomic profile of leaves from two diverse maize (Zea mays) inbred lines and the hybrid cross during exposure to season-long elevated ozone (~100 nl L-1) in the field using free air concentration enrichment (FACE) to identify key biochemical responses of maize to elevated ozone. Senescence, measured by loss of chlorophyll content, was accelerated in the hybrid line, B73 × Mo17, but not in either inbred line (B73 or Mo17). Untargeted metabolomic profiling further revealed that inbred and hybrid lines of maize differed in metabolic responses to ozone. A significant difference in the metabolite profile of hybrid leaves exposed to elevated ozone occurred as leaves aged, but no age-dependent difference in leaf metabolite profiles between ozone conditions was measured in the inbred lines. Phytosterols and α-tocopherol levels increased in B73 × Mo17 leaves as they aged, and to a significantly greater degree in elevated ozone stress. These metabolites are involved in membrane stabilization and chloroplast reactive oxygen species (ROS) quenching. The hybrid line also showed significant yield loss at elevated ozone, which the inbred lines did not. This suggests that the hybrid maize line was more sensitive to ozone exposure than the inbred lines, and up-regulated metabolic pathways to stabilize membranes and quench ROS in response to chronic ozone stress.

Global insights to drought stress perturbed genes in oat (Avena sativa L.) seedlings using RNA sequencing

Oat (Avena sativa L.) is an important crop in northwestern China. Drought stress is the most significant factor affecting oat yield. In the present study, we explored the changes that occur in oats under drought stress conditions at a global genomic level. RNA sequencing was performed using 15-day-old oat seedlings. The differentially expressed transcripts were identified, and their related functions and pathways were investigated. In total, 1,065 unigenes were differentially expressed in oats under drought stress conditions. Of these, 386 unigenes were upregulated and 679 were downregulated. The perturbed transcripts were closely related to the biosynthesis of secondary metabolites, plant hormone signal transduction, and biosynthesis of antibiotics. DN50483_c0_g1_i3, which was annotated as acetyl-CoA carboxylase, was a significant node in the protein-protein interaction network. Biosynthesis of antibiotics and secondary metabolites may be involved in the drought stress response mechanisms of oats. The perturbed transcripts may provide targets for improving plant stress responses.

Review: Metabolomics as a prediction tool for plants performance under environmental stress

Metabolomics as a diagnosis tool for plant performance has shown good features for breeding and crop improvement. Additionally, due to limitations in land area and the increasing climate changes, breeding projects focusing on abiotic stress tolerance are becoming essential. Nowadays no universal method is available to identify predictive metabolic markers. As a result, research aims must dictate the best method or combination of methods. To this end, we will introduce the key aspects to consider regarding growth scenarios and sampling strategies and discuss major analytical and data treatment approaches that are available to find metabolic markers of plant performance.

Ecometabolomics for a Better Understanding of Plant Responses and Acclimation to Abiotic Factors Linked to Global Change

The number of ecometabolomic studies, which use metabolomic analyses to disentangle organisms' metabolic responses and acclimation to a changing environment, has grown exponentially in recent years. Here, we review the results and conclusions of ecometabolomic studies on the impacts of four main drivers of global change (increasing frequencies of drought episodes, heat stress, increasing atmospheric carbon dioxide (CO2) concentrations and increasing nitrogen (N) loads) on plant metabolism. Ecometabolomic studies of drought effects confirmed findings of previous target studies, in which most changes in metabolism are characterized by increased concentrations of soluble sugars and carbohydrate derivatives and frequently also by elevated concentrations of free amino acids. Secondary metabolites, especially flavonoids and terpenes, also commonly exhibited increased concentrations when drought intensified. Under heat and increasing N loads, soluble amino acids derived from glutamate and glutamine were the most responsive metabolites. Foliar metabolic responses to elevated atmospheric CO2 concentrations were dominated by greater production of monosaccharides and associated synthesis of secondary metabolites, such as terpenes, rather than secondary metabolites synthesized along longer sugar pathways involving N-rich precursor molecules, such as those formed from cyclic amino acids and along the shikimate pathway. We suggest that breeding for crop genotypes tolerant to drought and heat stress should be based on their capacity to increase the concentrations of C-rich compounds more than the concentrations of smaller N-rich molecules, such as amino acids. This could facilitate rapid and efficient stress response by reducing protein catabolism without compromising enzymatic capacity or increasing the requirement for re-transcription and de novo biosynthesis of proteins.

Role of Cytochrome P450 Enzymes in Plant Stress Response

Cytochrome P450s (CYPs) are the largest enzyme family involved in NADPH- and/or O₂-dependent hydroxylation reactions across all the domains of life. In plants and animals, CYPs play a central role in the detoxification of xenobiotics. In addition to this function, CYPs act as versatile catalysts and play a crucial role in the biosynthesis of secondary metabolites, antioxidants, and phytohormones in higher plants. The molecular and biochemical processes catalyzed by CYPs have been well characterized, however, the relationship between the biochemical process catalyzed by CYPs and its effect on several plant functions was not well established. The advent of next-generation sequencing opened new avenues to unravel the involvement of CYPs in several plant functions such as plant stress response. The expression of several CYP genes are regulated in response to environmental stresses, and they also play a prominent role in the crosstalk between abiotic and biotic stress responses. CYPs have an enormous potential to be used as a candidate for engineering crop species resilient to biotic and abiotic stresses. The objective of this review is to summarize the latest research on the role of CYPs in plant stress response.

Elevated CO2 and warming change the nutrient status and use efficiency of Panicum maximum Jacq

Panicum maximum Jacq. ‘Mombaça’ (Guinea grass) is a C₄ forage grass widely used in tropical pastures for cattle feeding. In this study, we evaluated the isolated and combined effects of warming and elevated CO₂ concentration [CO₂] during summer on nutrient content, nutrient accumulation, nutrient use efficiency and growth of P. maximum under field conditions. Field temperature and [CO₂] were controlled by temperature free-air controlled enhancement and free-air CO₂ enrichment systems, respectively. We tested two levels of canopy temperature: ambient temperature (aT) and 2°C above ambient temperature (eT), as well as two levels of atmospheric [CO₂]: ambient [CO₂] (aCO₂) and 200 ppm above ambient CO₂ (eCO₂). The experiment was established in a completely randomized design with four replications, in a 2×2 factorial scheme. After pasture establishment, plants were exposed to the treatments during 30 days, with evaluations at 9, 16, 23 and 30 days after the treatments started. Results were dependent on the time of the evaluation, but in the last evaluation (beginning of the grazing), contents of N, K, Mg and S did not change as a function of treatments. However, P decreased as a function of warming under both levels of [CO₂], and Ca increased under [eCO₂] combined with warming. There was an increase in root dry mass under warming treatment. Combined treatment increased N, Ca and S accumulation without a corresponding increase in the use efficiency of these same nutrients, indicating that the fertiliser dose should increase in the next decades due to climate change. Our short-term results in young and well fertilized pasture suggest that under the combination of [eCO₂] and eT conditions, P. maximum productivity will increase and the nutritional requirement for N, Ca and S will also increase.

A comparative metabolomics study on anadromous clupeid Tenualosa ilisha for better understanding the influence of habitat on nutritional composition

INTRODUCTION

Fish inhabiting different aquatic habitats adapts to the environment by metabolomic readjustments. Understanding the combined activities of all the metabolic pathways (metabolome) helps in better understanding the complex interactions between gene and environment.

OBJECTIVES

The anadromous migratory Tenualosa ilisha is a high value food fish comprising the dominant fishery of the rivers Padma and Hooghly. The present study aimed at understanding the influence of the two habitats on the nutritional composition of hilsa.

METHODS

Metabolite profiling was carried out by GC/MS. De novo assembly of hilsa liver transcriptome was generated under Illumina HiSeq platform and multivariate analysis was employed for correlation and comparison.

RESULTS

GC/MS fingerprinting showed C16:0, C18:1, C20:5 and C22:6 to be the predominant fatty acids present in hilsa liver, which were also found to be significantly higher in Hooghly hilsa. Comparative transcriptome analysis revealed that the differentially expressed genes were mainly associated with 'lipid metabolism' and 'amino acid metabolism' pathways. Multivariate analysis between the metabolites amino acid, fatty acid and corresponding gene expression showed that few genes of amino acid metabolism (EZH1, ALAS2 and ALDH4A1) positively correlated with individual amino acids (lysine, glycine and glutamate) in Hooghly hilsa. Similarly, the key genes for LC-PUFA biosynthesis (ELOVL5, FADS2, CPT1) showed positive correlation with individual LC-PUFAs (C18:3, C20:4, C20:5, C22:6), indicating higher LC-PUFA biosynthesis potential in Hooghly hilsa.

CONCLUSION

Comparative metabolomic study in hilsa from the two different habitats showed that the habitats influence the nutritional composition as evidenced by high abundance of amino acids lysine, leucine and arginine and LC-PUFAs C18:3, C20:4, C20:5, C22:6 in Hooghly hilsa.

Short-term warming and water stress affect Panicum maximum Jacq. stoichiometric homeostasis and biomass production

Climate changes affect the growth of forage species. However, information regarding the effects of global climate change on the stoichiometry of tropical pastures is lacking, especially under field conditions. Such information is crucial to understand how temperature conditions and water availability states are likely to affect the stoichiometric homeostasis and biomass production of Panicum maximum, an important C4 tropical forage species, under future climate change scenarios. Thus, we, conducted a field experiment using a temperature free-air controlled enhancement system and evaluated the effects of two temperature conditions, ambient temperature and moderate warming (2 °C above ambient canopy temperature), and two levels of water availability, irrigated and non-irrigated, on the stoichiometric patterns of C:N:P and leaf biomass production. The experiment was conducted using a randomized complete block design in a factorial arrangement with four replications over 3 weeks. Our findings revealed that the N and P leaf concentration greatly decreased in water-stressed plants, which increased the C:N and C:P ratios, while warming increased the N:P ratio. Leaf biomass production was impaired by up to 16% under water stress and ambient temperature conditions, but the biomass production was improved by 20% under warming and irrigated conditions. Our findings showed that homeostatic instability under rainfed conditions resulted in decreased leaf biomass production. Therefore, we concluded that warming is only beneficial for plant growth (i.e., a high homeostatic capacity was maintained) under well-irrigated conditions.