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

Quantitative study on reducing arsenic concentration in rice by sulfur fertilizer based on meta-analysis

Arsenic (As), a toxic metalloid, is absorbed by rice and subsequently enters the human body through the food chain. Sulfur (S) possesses the capacity to reduce As accumulation in rice tissues and has been widely researched for its contributions to enhancing soil quality. However, a clear quantitative consensus regarding the impact of S application on As bioaccumulation and bioavailability has yet to be established. To gain a more nuanced understanding of the interaction between S and As, a comprehensive analysis was conducted on 318 data sets extracted from 23 articles. Both meta-regression and subgroup analyses were employed to investigate the effect of diverse variables on As accumulation in rice. The results indicated that S had a significant dose-dependent effect on reducing As accumulation in rice. The exogenous S significantly reduced the As concentration in rice by 8.95% and the optimal S/As ratio for inhibiting As accumulation was 1-20. Apart from sulfate S, the incorporation of elemental S, persulfate, thiosulfate, and gypsum has been demonstrated to significantly reduce As accumulation in rice. The exogenous S resulted in a significant reduction in TFroot to shoot content in rice, indicating that S application may impede the physiological process of As transfer from soil to the shoot of rice. Consequently, the exogenous S can effectively mitigate the As accumulation in rice, thereby offering a novel approach to reduce the As content in rice and minimize its detrimental impact on human health.

Assessing impact of elevated CO2 on heavy metal accumulation in crops: meta-analysis and implications for food security

Human activities led to elevation in carbon dioxide (CO2) concentrations in atmosphere. While such increase per se may be beneficial for the growth of some crops, it comes with a caveat of affecting crop nutritional status. Here, we present a comprehensive analysis of changes in concentration of essential (Cu, Fe, Mn, Zn, Mo, Ni) and non-essential (Ba, Cd, Cr, Hg, Pb, and Sr) heavy metals in response to elevated CO2, drawing on a meta-analysis of 1216 paired observations. The major findings are as follows: (1) Elevated CO2 leads to reduced concentrations of Cu, Fe, Mn, and Zn in crops; (2) the extent of above reduction varies among plants species and is most pronounced in cereals and then in legumes and vegetables; (3) reduction in accumulation of non-essential (toxic) metals is less pronounced, potentially leading to an unfavorable essential/non-essential metal ratio in plants; (4) the above effects will come with significant implication to human health, exacerbating effects of the "hidden hunger" caused by the lack of Fe and Zn in the human diets. The paper also analyses the mechanistic basis of nutrient acquisition (both at physiological and molecular levels) and calls for the changes in the governmental policies to increase efforts of plant breeders to create genotypes with improved nutrient use efficiency for essential micronutrients while uncoupling their transport from non-essential (toxic) heavy metals.

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.

Effect of warming on ground vegetation in Carpathian Norway spruce stands, exemplified by European blueberry (Vaccinium myrtillus L.) nutrient stoichiometry

Despite its small share of total forest biomass, ground vegetation plays an important role in biogeochemical cycles, being able to modify carbon (C) and nutrients fluxes. Global climate warming may affect plant nutrient uptake and the carbon:nitrogen:phosphorus (C:N:P) stoichiometry, the release of nutrients from the soil and soil organic matter, as well as significantly influence the tree stand nutrient supply. In this context, the response of Norway spruce (Picea abies (L.) H.Karst) stands' ground vegetation to warming is uncertain. An open-top chamber soil-warming simulation, lasting two growing seasons, was conducted in a spruce forest. At the end of each of the two growing seasons, before leaf senescence, European blueberry (Vaccinium myrtillus L.) aboveground biomass (leaves and stems) and mineral topsoil samples were collected from the plots. The C, N, P, micronutrient, and macronutrient concentrations were estimated in the samples. Warming caused significant decreases in C, N, and P in the soil. Warming also decreased the C:P and N:P stoichiometric ratios in the soil and increased the C:P ratio in plant stems. Significant increase in foliar C and decrease in foliar P in warmed plots were observed. The most evident effect was reduction of N and P in the soil, which directly affected the plant C:P and soil N:P stoichiometry. Our results show that warming has caused a significant decrease in the content of some nutrients in the aboveground plant tissues of blueberries. Given that N is a limiting factor of ecosystems productivity, its reduction in the soil caused by warming may be a serious threat to proper nutrient uptake and cause disruption of biogeochemical cycles. The decrease in nutrient content in aboveground tissues due to warming can result in disruptions to physiological processes.

Influence of Mycorrhiza on C:N:P Stoichiometry in Senesced Leaves

Senesced leaves play a vital role in nutrient cycles in the terrestrial ecosystem. The carbon (C), nitrogen (N) and phosphorus (P) stoichiometries in senesced leaves have been reported, which are influenced by biotic and abiotic factors, such as climate variables and plant functional groups. It is well known that mycorrhizal types are one of the most important functional characteristics of plants that affect leaf C:N:P stoichiometry. While green leaves' traits have been widely reported based on the different mycorrhiza types, the senesced leaves' C:N:P stoichiometries among mycorrhizal types are rarely investigated. Here, the patterns in senesced leaves' C:N:P stoichiometry among plants associated with arbuscular mycorrhizal (AM), ectomycorrhizal (ECM), or AM + ECM fungi were explored. Overall, the senesced leaves' C, with 446.8 mg/g in AM plants, was significantly lower than that in AM + ECM and ECM species, being 493.1 and 501.4 mg/g, respectively, which was mainly caused by boreal biomes. The 8.9 mg/g senesced leaves' N in ECM plants was significantly lower than in AM (10.4 mg/g) or AM + ECM taxa (10.9 mg/g). Meanwhile, the senesced leaves' P presented no difference in plant associations with AM, AM + ECM and ECM. The senesced leaves' C and N presented contrary trends with the changes in mean annual temperature (MAT) and mean annual precipitation (MAP) in ECM or AM + ECM plants. The differences in senesced leaves' C and N may be more easily influenced by the plant mycorrhizal types, but not P and stoichiometric ratios of C, N and P. Our results suggest that senesced leaves' C:N:P stoichiometries depend on mycorrhizal types, which supports the hypothesis that mycorrhizal type is linked to the evolution of carbon-nutrient cycle interactions in the ecosystem.

Global patterns of plant and microbial biomass in response to CO2 fumigation

Introduction

The stimulation of plant and microbial growth has been widely observed as a result of elevated CO₂ concentrations (eCO₂), however, this stimulation could be influenced by various factors and their relative importance remains unclear.

Methods

A global meta-analysis was performed using 884 lines of observations collected from published papers, which analyzed the eCO₂ impact on plant and microbial biomass.

Results

A significant positive impact of eCO₂ was observed on various biomass measures, including aboveground biomass (20.5%), belowground biomass (42.6%), soil microbial biomass (10.4%), fungal biomass (11.0%), and bacterial biomass (9.2%). It was found that eCO₂ levels above 200 ppm had a greater impact on plant biomass compared to concentrations at or below 200 ppm. On the other hand, studies showed that positive effects on microbial biomass were more prominent at lower eCO₂ levels (≤200 ppm) than at higher levels (>200 ppm), which could be explained by soil nitrogen limitations. Importantly, our results indicated that aboveground biomass was controlled more by climatic and experimental conditions, while soil properties strongly impacted the stimulation of belowground and microbial biomass.

Discussion

Our results provided evidence of the eCO₂ fertilization effect across various ecosystem types, experimental methods, and climates, and provided a quantitative estimate of plant and soil microbial biomass sensitivity to eCO₂. The results obtained in this study suggest that ecosystem models should consider climatic and edaphic factors to more accurately predict the effects of global climate change and their impact on ecosystem functions.

Influence of arbuscular mycorrhizal fungi on bioaccumulation and bioavailability of As and Cd: A meta-analysis

Increasing industrial activity has led to a growing risk of arsenic (As) and cadmium (Cd) accumulations and biomagnifications in plants and humans. Arbuscular mycorrhizal fungi (AMF) have been extensively studied as a soil amendment owing to their capability to reduce the accumulation of As and Cd in plant tissues. However, a quantitative and data-based consensus has yet to be reached on the effect of AMF on As and Cd bioaccumulation and bioavailability. Here, a meta-analysis was conducted to quantitatively evaluate the impact of AMF using 1430 individual observations from 194 articles. The results showed that AMF inoculation caused a decrease in shoot and root As and Cd accumulation compared to control, and the reduction rates were affected by experimental duration, P fertilizer, AMF species, plant family, plant lifecycle, and soil properties. Intermediate experimental duration (lasting 56-112 days) and no P fertilizer favored AMF to reduce the shoot As and root Cd accumulation. Compared to other plant families, the reduction in As and Cd accumulation in legumes was the greatest, following AMF inoculation. The soils with alkaline, high organic carbon (OC), and low available phosphorus (AP) appeared to be more favorable for AMF to reduce As accumulation in plant tissues, while soils with low AP were more conducive to reducing the Cd accumulation in plant tissues. In addition, AMF inoculation increased pH (1.92%), OC (6.27%), easily-extractable glomalin-related soil protein (EE-GRSP) (29.36%), and total glomalin-related soil protein (T-GRSP) (29.99%), and reduced bioavailable As (0.52%) and Cd (2.35%) in soils compared to control. Overall, the meta-analysis provides valuable guidelines for the optimal use of AMF in different plant-soil systems.

Elevated CO2 and biochar differentially affect plant C:N:P stoichiometry and soil microbiota in the rhizosphere of white lupin (Lupinus albus L.)

Biochar application is a potent climate change mitigation strategy in agroecosystems. However, little is known about the interactive effects of elevated CO₂ (eCO₂) and biochar on plant nutrient uptake and soil microbial processes. A pot experiment was conducted to investigate the effects of eCO₂ and biochar addition on plant C:N:P stoichiometry and rhizobacterial community for better management of nutrient balance and use efficiency in a future climate scenario. White lupin (Lupinus albus L.) was grown for 30 days in topsoil and subsoil with or without 2% corn-stubble biochar under ambient CO₂ (aCO₂: 390 ppm) or eCO₂ (550 ppm). Elevated CO₂ increased, but biochar decreased, plant biomass and shoot N and P uptake, with no interactions in either soil layer. Elevated CO₂ decreased shoot N concentration by 16% and biochar decreased shoot P concentration by 11%. As a result, eCO₂ increased shoot C:N ratio by 20% and decreased the N:P ratio by 11%. Biochar decreased shoot C:N ratio by 8% in the subsoil under eCO₂. However, biochar increased shoot C:P ratio by an average of 13% and N:P ratio by 23% in the subsoil. Moreover, plants grown in the subsoil showed lower shoot N (35%) and P (70%) uptake compared to the topsoil. The results indicate that N and P are the more limiting factors that regulate plant growth under eCO₂ and biochar application, respectively. Elevated CO₂ and biochar oppositely affected dominant rhizobacterial community composition, with the eCO₂ effect being greater. The microbiota in the subsoil held a greater diversity of contrasting species than the topsoil, which were associated with nutrient cycling, hydrocarbon degradation and plant productivity. These results enrich our understanding of potential soil nutrient cycling and plant nutrient balance in future agroecosystems.

Three Decades of Changing Nutrient Stoichiometry from Source to Sea on the Swedish West Coast

European ecosystems have been subject to extensive shifts in anthropogenic disturbance, primarily through atmospheric deposition, climate change, and land management. These changes have altered the macronutrient composition of aquatic systems, with widespread increases in organic carbon (C), and declines in nitrogen (N) and phosphorus (P). Less well known is how these disturbances have affected nutrient stoichiometry, which may be a more useful metric to evaluate the health of aquatic ecosystems than individual nutrient concentrations. The Swedish west coast has historically experienced moderate to high levels of atmospheric deposition of sulfate and N, and eutrophication. In addition, coastal waters have been darkening with damaging effects on marine flora and fauna. Here, we present three decades of macronutrient data from twenty lakes and watercourses along the Swedish west coast, extending from headwaters to river mouths, across a range of land covers, and with catchments ranging 0.037–40,000 km2. We find a high degree of consistency between these diverse sites, with widespread increasing trends in organic C, and declines in inorganic N and total P. These trends in individual macronutrients translate into large stoichiometric changes, with a doubling in C:P, and increases in C:N and N:P by 50% and 30%, showing that freshwaters are moving further away from the Redfield Ratio, and becoming even more C rich, and depleted in N and P. Although recovery from atmospheric deposition is linked to some of these changes, land cover also appears to have an effect; lakes buffer against C increases, and decreases in inorganic N have been greatest under arable land cover. Our analysis also detects coherently declining P concentrations in small forest lakes; so called (and unexplained) “oligotrophication.” Taken together, our findings show that freshwater macronutrient concentrations and stoichiometry have undergone substantial shifts during the last three decades, and these shifts can potentially explain some of the detrimental changes that adjacent coastal ecosystems are undergoing. Our findings are relevant for all European and North American waters that have experienced historically high levels of atmospheric deposition, and provide a starting point for understanding and mitigating against the trajectories of long-term change in aquatic systems.

A meta-analysis of responses of C3 plants to atmospheric CO2 : dose-response curves for 85 traits ranging from the molecular to the whole-plant level

Generalised dose-response curves are essential to understand how plants acclimate to atmospheric CO₂ . We carried out a meta-analysis of 630 experiments in which C₃ plants were experimentally grown at different [CO₂ ] under relatively benign conditions, and derived dose-response curves for 85 phenotypic traits. These curves were characterised by form, plasticity, consistency and reliability. Considered over a range of 200-1200 µmol mol^-1 CO₂ , some traits more than doubled (e.g. area-based photosynthesis; intrinsic water-use efficiency), whereas others more than halved (area-based transpiration). At current atmospheric [CO₂ ], 64% of the total stimulation in biomass over the 200-1200 µmol mol^-1 range has already been realised. We also mapped the trait responses of plants to [CO₂ ] against those we have quantified before for light intensity. For most traits, CO₂ and light responses were of similar direction. However, some traits (such as reproductive effort) only responded to light, others (such as plant height) only to [CO₂ ], and some traits (such as area-based transpiration) responded in opposite directions. This synthesis provides a comprehensive picture of plant responses to [CO₂ ] at different integration levels and offers the quantitative dose-response curves that can be used to improve global change simulation models.

Calcium Regulates Growth and Nutrient Absorption in Poplar Seedlings

As a crucial element for plants, calcium (Ca) is involved in photosynthesis and nutrient absorption, and affects the growth of plants. Poplar is an important economic forest and shelter forest species in China. However, the optimum calcium concentration for its growth is still unclear. Herein, we investigated the growth, biomass, photosynthetic pigments, photosynthetic parameters and products, chlorophyll fluorescence parameters, water use efficiency (iWUE), and antioxidant enzyme activity of "Liao Hu NO.1" poplar (P. simonii × P. euphratica) seedlings at 0, 2.5, 5, 10, and 20 mmol·L^-1 concentrations of Ca²⁺, and further studied the absorption, distribution, and utilization of nutrient elements (C, N, P, K, and Ca) in plants. We found that with increasing calcium gradient, plant height and diameter; root, stem, leaf, and total biomasses; net photosynthetic rate (Pn); stomatal conductance (Gs); intercellular carbon dioxide (Ci) level; transpiration rate (Tr); Fv/Fm ratio; Fv/F0 ratio; chlorophyll-a; chlorophyll-b; soluble sugar and starch content; superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) levels; and long-term water use efficiency (iWUE) of poplar seedlings first increased and then decreased. These parameters attained maximum values when the calcium concentration was 5 mmol·L^-1, which was significantly different from the other treatments (P < 0.05). Moreover, a suitable Ca²⁺ level promoted the absorption of C, N, P, K, and Ca by various organs of poplar seedlings. The absorption of C, N, P, and K increased first and then decreased with the increased calcium concentration, but the optimum calcium concentrations for the absorption of different elements by different organs were different, and the calcium concentration in leaves, stems, and roots increased gradually. Furthermore, the increase in exogenous calcium content led to a decreasing trend in the C/N ratio in different organs of poplar seedlings. C/P and N/P ratios showed different results in different parts, and only the N/P ratio in leaves showed a significant positive correlation with Ca²⁺ concentration. In conclusion, the results of this study indicate that 5 mmol·L^-1 concentration of Ca²⁺ is the optimal level, as it increased growth by enhancing photosynthesis, stress resistance, and nutrient absorption.

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.

Incorporating carbon dioxide into a stoichiometric producer-grazer model

Climate change models predict increases in atmospheric carbon dioxide concentration. As ecosystems equilibrate with the atmosphere, stimulation of photosynthesis is expected to occur. However, growth limitation due to soil nutrients may potentially limit sequestration of carbon. Additionally, changes in producer nutritional quality may cause a decline in grazer populations. Here we extend the WKL model to allow for consideration of the impacts of elevated atmospheric carbon dioxide concentration on producer-grazer dynamics. We do so by explicitly tracking the free carbon in the medium and allowing the producer's growth rate to be limited by available carbon instead of light. This model is analyzed using primarily local bifurcation analysis. Overall, these analyses show that carbon sequestration due to increased atmospheric carbon dioxide can be limited by insufficient available phosphorus. Furthermore, increased atmospheric carbon dioxide will cause decreased stoichiometric quality of producers where available phosphorus is limiting.

Funneliformis mosseae Improves Growth and Nutrient Accumulation in Wheat by Facilitating Soil Nutrient Uptake under Elevated CO2 at Daytime, Not Nighttime

The concurrent effect of elevated CO₂ (eCO₂) concentrations and arbuscular mycorrhizal fungi (AMF) on plant growth, carbon (C), nitrogen (N), phosphorus (P) and potassium (K) accumulations in plant and soil is largely unknown. To understand the mechanisms of eCO₂ and mycorrhization on wheat (Triticum aestivum) performance and soil fertility, wheat seedlings were grown under four different CO₂ environments for 12 weeks, including (1) ambient CO₂ (ACO₂, 410/460 ppm, daytime/nighttime), (2) sole daytime eCO₂ (DeCO₂, 550/460 ppm), (3) sole nighttime eCO₂ (NeCO₂, 410/610 ppm), and (4) dual or continuous daytime/nighttime eCO₂ ((D + N)eCO₂, 550/610 ppm), and with or without AMF (Funneliformis mosseae) colonization. DeCO₂, NeCO₂ and (D + N)eCO₂ generally significantly increased shoot and root biomass, plant C, N, P and K accumulation, soil invertase and urease activity, but decreased shoot and root N, P and K concentrations, and soil available N, P and K. Compared with non-AMF, AMF effects on above-mentioned characteristics were significantly positive under ACO₂, DeCO₂ and (D + N)eCO₂, but negative on plant biomass, C, N, P and K accumulation under NeCO₂. Overall, AMF colonization alleviated soil nutrient constraints on plant responses to DeCO₂, while NeCO₂ decreased AMF's beneficial effects on plants. These results demonstrated that an integration of AMF's benefits to plants under factual field DeCO₂ and/or NeCO₂ will be critical for managing the long-term consequence of future CO₂ rising on global cropping systems.

Arbuscular Mycorrhization Enhances Nitrogen, Phosphorus and Potassium Accumulation in Vicia faba by Modulating Soil Nutrient Balance under Elevated CO2

Effects of arbuscular mycorrhizal fungi (AMF), elevated carbon dioxide (eCO₂), and their interaction on nutrient accumulation of leguminous plants and soil fertility is unknown. Plant growth, concentrations of tissue nitrogen (N), phosphorus (P), and potassium (K) in 12-week-old nodulated faba bean (Vicia faba, inoculated with Rhizobium leguminosarum bv. NM353), and nutrient use efficiency were thus assessed under ambient CO₂ (410/460 ppm, daytime, 07:00 a.m.–19:00 p.m./nighttime, 19:00 p.m.–07:00 a.m.) and eCO₂ (550/610 ppm) for 12 weeks with or without AM fungus of Funneliformis mosseae inoculation. eCO₂ favored AMF root colonization and nodule biomass production. eCO₂ significantly decreased shoot N, P and K concentrations, but generally increased tissue N, P and K accumulation and their use efficiency with an increased biomass production. Meanwhile, eCO₂ enhanced C allocation into soil but showed no effects on soil available N, P, and K, while AM symbiosis increased accumulation of C, N, P, and K in both plant and soil though increased soil nutrient uptake under eCO₂. Moreover, plant acquisition of soil NO₃⁻–N and NH₄⁺–N respond differently to AMF and eCO₂ treatments. As a result, the interaction between AM symbiosis and eCO₂ did improve plant C accumulation and soil N, P, and K uptake, and an alternative fertilization for legume plantation should be therefore taken under upcoming atmosphere CO₂ rising. Future eCO₂ studies should employ multiple AMF species, with other beneficial fungal or bacterial species, to test their interactive effects on plant performance and soil nutrient availability in the field, under other global change events including warming and drought.

Light and competition alter leaf stoichiometry of introduced species and native mangrove species

Ecological stoichiometry is the study of the balance of ecosystem energy and nutrient cycling, especially carbon (C), nitrogen (N), and phosphorus (P). C, N, and P are the key elements for plant growth and metabolism. Systematic research on leaf stoichiometry in mangrove forest ecosystems is still lacking. To understand the leaf stoichiometry of introduced species and native species in mangrove forests, we selected four species (one introduced species, Sonneratia apetala, and three native species, Avicennia marina, Aegiceras corniculatum, and Kandelia obovate) and measured leaf C, N, and P contents under different light conditions. The results showed that there were significant negative scaling relationships of leaf C versus N and C versus P but positive scaling relationships of leaf N versus P in the four mangrove species. Light and competition had significant effects on leaf stoichiometry, especially under the full light condition. S. apetala influenced leaf elements in a mixture with native species. Interspecific competition reduced leaf N and P contents in A. corniculatum and K. obovate but increased leaf N and P contents in A. marina. Leaf N and P contents of the four species showed similar responses to both intraspecific and interspecific competition. The ratio of leaf C:N:P (108:11:1) in the mangrove forests was lower than that in other ecosystems, and species with a higher growth rate had a higher leaf P content and lower N:P ratio, supporting the growth rate hypothesis. Leaf N:P was 11.04, indicating that there was N limitation in the mangrove forests. This systematic research of leaf stoichiometry of mangrove forests improves our understanding of mangrove growth and nutrient use strategies in response to different environmental stresses.

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.