Phosphorus Stoichiometry Research Articles

Nutrient conditions mediate mycorrhizal effects on biomass production and cell wall chemistry in poplar.

Large scale biofuel production from lignocellulosic feedstock is limited by the financial and environmental costs associated with growing and processing lignocellulosic material and the resilience of these plants to environmental stress. Symbiotic associations with arbuscular (AM) and ectomycorrhizal (EM) fungi represent a potential strategy for expanding feedstock production while reducing nutrient inputs. Comparing AM and EM effects on wood production and chemical composition is a necessary step in developing biofuel feedstocks. Here, we assessed the productivity, biomass allocation, and secondary cell wall composition of greenhouse grown Populus tremuloides inoculated with either AM or EM fungi. Given the long-term goal of reducing nutrient inputs for biofuel production, we further tested the effects of nutrient availability and nitrogen:phosphorus stoichiometry on mycorrhizal responses. Associations with both AM and EM fungi increased plant biomass by 14% to 74% depending on the nutrient conditions but had minimal effects on secondary cell wall composition. Mycorrhizal plants, especially those inoculated with EM fungi, also allocated a greater portion of their biomass to roots, which could be beneficial in the field where plants are likely to experience both water and nutrient stress. Leaf nutrient content was weakly, but positively correlated with wood production in mycorrhizal plants. Surprisingly, phosphorus played a larger role in EM plants compared to AM plants. Relative nitrogen and phosphorus availability was correlated with shifts in secondary cell wall composition. For AM associations the benefit of increased wood biomass may be partially offset by increased lignin content, a trait that affects downstream processing of lignocellulosic tissue for biofuels. By comparing AM and EM effects on the productivity and chemical composition of lignocellulosic tissue, this work links broad functional diversity in mycorrhizal associations to key biofuels traits and highlights the importance of considering both biotic and abiotic factors when developing strategies for sustainable biofuel production.

Long-term successive rotation affects soil microbial resource limitation and carbon use efficiency in Chinese fir (Cunninghamia lanceolata) monoculture plantations

Long-term successive rotation has resulted in negative effects on stand productivity, soil nutrient pool and microbial diversity and function in monoculture tree plantations. However, how successive rotation influences soil microbial nutrient limitation and carbon use efficiency (CUE) and their linkage with resource carbon (C): nitrogen (N): phosphorus (P) stoichiometry remain largely unknown. To solve this puzzle, we compared the C:N:P stoichiometries of leaf litter, fine root and soil, as well as microbial biomass and enzyme activities among three Chinese fir (Cunninghamia lanceolata) plantations with first (FRP), second (SRP) and third (TRP) generations and a natural broad-leaved forest (BL). We found that long-term successive rotation of Chinese fir decreased litter biomass by 64.7% ∼ 80.9% and enhanced litter C:N ratio by 2.7% ∼ 36.0% compared to the BL. Successive rotation decreased the contents of dissolved organic C, total N, and soil C:P and N:P ratios, and resulted in an increased C:N imbalance between soil microorganisms and nutrients in the TRP generation. Long-term successive rotation increased microbial C limitation by 1.5% ∼ 11.1% but decreased N and P limitations by 127.3% ∼ 160.9% and 15.3% ∼ 37.5%, compared with the BL, and resulted in significant increases in microbial CUE and substrate-induced respiration rate of C to N sources in the TRP generation. Structural equation modeling suggested that successive rotation indirectly affected microbial CUE and SIR by changing litter C:N, enzyme C:N and soil C:N imbalance. Collectively, these findings indicated that long-term successive rotation aggravated soil microbial C (energy) limitation and affected microbial CUE and capacity due to the increased stoichiometric imbalance between their resources. Future management practices that could increase litter and soil quality could be helpful to decrease microbial C limitation and maintain microbial functionality for sustainable monoculture plantations.

Untangling the influence of abiotic and biotic factors on leaf C, N, and P stoichiometry along a desert-grassland transition zone in northern China

Plant elemental composition and stoichiometry are useful tools for understanding plant nutrient strategy and biogeochemical cycling in terrestrial ecosystems. However, no studies have examined how plant leaf carbon (C), nitrogen (N), and phosphorus (P) stoichiometry responds to abiotic and biotic factors in the fragile desert-grassland ecological transition zone in northern China. Then a systematically designed 400 km transect was established to investigate the C, N, and P stoichiometry of 870 leaf samples of 61 species from 47 plant communities in the desert-grassland transition zone. At the individual level, plant taxonomic groups and life forms rather than climate or soil factors determined the leaf C, N, and P stoichiometry. In addition, leaf C, N, and P stoichiometry (except leaf C) was significantly influenced by soil moisture content in the desert-grassland transition zone. At the community level, leaf C content showed a considerable interspecific variation (73.41 %); however, the variation in leaf N and P content, as well as C:N and C:P ratios, was mainly due to intraspecific variation, which was in turn driven by soil moisture. We suggested that intraspecific trait variation played a key role in regulating community structure and function to enhance the resistance and resilience of plant communities to climate change in the desert-grassland transition zone. Our results highlighted the role of soil moisture content as a critical parameter for modeling the biogeochemical cycling in dryland plant-soil systems.

Ecological stoichiometry of soil and microbial biomass carbon, nitrogen and phosphorus in tea plantations with different ages.

The implementation of ecological engineering projects such as "Green for Grain" causes great changes in the cycling and stoichiometry of soil carbon (C), nitrogen (N), and phosphorus (P), with consequences on soil microbial biomass stoichiometric characteristics. However, the temporal dynamics and coordination of soil-microbial C:N:P stoichiometry are still unclear. In this study, we examined the variations of soil-microbial biomass C, N, and P with the tea plantation ages (<5 a, 5-10 a, 10-20 a, 20-30 a, and >30 a) in a small watershed in the Three Gorges Reservoir Area. We analyzed the relationships between their stoichiometric ratios, microbial entropy (qMBC, qMBN, qMBP), and stoichiometric imbalance (ratios of soil C, N, P stoichiometry to microbial biomass C, N, P stoichiometry). The results showed that with the increases of tea plantation ages, soil and microbial biomass C, N, P contents, soil C:N and C:P significantly increased, while soil N:P declined; the microbial biomass C:P and N:P increased first and then decreased, but microbial biomass C:N did not change. Tea plantation ages significantly affected soil microbial entropy and soil-microbial stoichiometry imbalance (C:Nimb, C:Pimb, N:Pimb). With the increases of tea plantation ages, qMBC first decreased and then increased, while qMBN and qMBP went up in a fluctuating pattern. The C-N stoichiometry imbalance (C:Nimb) and C-P stoichiometry imbalance (C:Pimb) increased significantly, while the N-P stoichiometry imbalance (N:Pimb) showed a fluctuating rise. Results of the redundancy analysis showed that qMBC was positively correlated with soil N:P and microbial biomass C:N:P, but negatively correlated with microbial stoichiometric imbalance and soil C:N, C:P; whereas qMBN and qMBP showed the opposite situation. The microbial biomass C:P was most closely related to qMBC, while C:Nimb and C:Pimb had greater effects on qMBN and qMBP.

Soil Carbon, Nitrogen, and Phosphorus Stoichiometry and Fractions in Blue Carbon Ecosystems: Implications for Carbon Accumulation in Allochthonous-Dominated Habitats.

Blue carbon ecosystems (BCEs) including mangroves, saltmarshes, and seagrasses are highly efficient for organic carbon (OC) accumulation due to their unique ability to trap high rates of allochthonous substrates. It has been suggested that the magnitude of OC preservation is constrained by nitrogen (N) and phosphorus (P) limitation in response to climate and anthropogenic changes. However, little is known about the connection of soil OC with N-P and their forms in response to allochthonous inputs in BCEs. By analyzing soil OC, N, and P densities of BCEs from 797 sites globally, we find that, in China, where allochthonous OC provides 50-75% of total OC, soil C/P and N/P ratios are 4- to 8-fold lower than their global means, and 23%, 29%, and 20% of buried OC, N, and P are oxidation-resistant fractions that linked with minerals. We estimate that the OC stocks in China should double over the next 40 years under high allochthonous inputs and elevated N/P ratio scenarios during BCE restoration. Allochthonous-dominated BCEs thus have the capacity to enhance refractory and mineral bound organic matter accumulation. Protection and restoration of such BCEs will provide long-term mitigating benefits against sea level rise and greenhouse gas emissions.

C, N, and P Stoichiometry Characteristics of Fresh and Weathered Sandstones in Longhushan Area, SE China

Carbon (C), nitrogen (N), and phosphorus (P) stoichiometry and their allometric relationships in soil and plants are hot topics that attract a lot of attention, while those rocks that form soils are often neglected. Weathering is a common geological phenomenon that may significantly influence the nutrient composition and release of nutrients from rock and its inherent soils. This study presents C, N, and P concentrations data as well as microscope petrological photographs of fresh and weathered sandstones from Longhushan World Geopark in SE China, in an attempt to investigate C, N, and P stoichiometry of rocks before and after weathering and discuss the driving mechanisms. The results show that weathering significantly decreased rock C, C/N, and C/P concentrations, slightly decreased N and N/P concentrations, and slightly increased P concentration. Microscope observations show that fresh sandstones contain calcite, apatite, microplagioclase, and organic matter, while weathered sandstones feature apatite and organic matter. The flexible allometric relationships and mineral changes before and after rock weathering indicate that chemical mechanisms, such as dissolution of carbonate and hydration of microplagioclase, have changed the existence form of C, N, P and, thus, significantly influence rock C, N, and P stoichiometry. This stoichiometry feature can be in turn used to reflect the regulation effect of rock weathering.

Ecological Stoichiometry of Soil Carbon, Nitrogen and Phosphorus in Reclaimed Farmland in Coal Mining Subsidence Area

Ecological Stoichiometry of Soil Carbon, Nitrogen and Phosphorus in Reclaimed Farmland in Coal Mining Subsidence Area

Mixed planting improves soil aggregate stability and aggregate-associated C-N-P accumulation in subtropical China

Research on the variations in soil aggregate stability and ecological stoichiometry at aggregate scales by stand type is of great significance in investigating the distribution, limitation, balance, and cycling of organic carbon, nitrogen, and phosphorus (C-N-P). However, the effect of pure and mixed Chinese fir plantations on soil aggregate stability, organic carbon (OC), total nitrogen (TN), and total phosphorus (TP) stoichiometry characteristics at aggregate scales is still unclear. In this research, we explored the variations in soil aggregate mean weight diameter (MWD) and geometric mean diameter (GMD); soil OC, TN, and TP contents and stocks and the C:N:P ratios as affected by different stand types (mixed stands of Chinese fir and Mytilaria laosensis, mixed stands of Chinese fir and Michelia macclurei, and pure stand of Chinese fir); and aggregate size (&amp;lt;0.25, 0.25–1, 1–2, and &amp;gt;2 mm) at 0–20 and 20–40 cm depths in subtropical China. The soil OC and TN contents, as well as C:N:P ratios declined as aggregate size increased, whereas the C-N-P stocks showed the opposite tendencies, which were more distributed in &amp;gt;2 mm aggregates. Mixed stands of Chinese fir and M. laosensis with Chinese fir and M. macclurei displayed significantly higher soil aggregate stability, aggregate-associated TP content, OC and TN contents and stocks, and C:N and C:P ratios than did pure stands of Chinese fir. Soil aggregate stability was significantly positively correlated with the C-N-P contents and stocks as well as the C:N and C:P ratios, especially the C:N ratio and TN content. Overall, this work offers further information for scientific management and sustainable development of Chinese fir plantations, soil OC and nutrient cycling with ecological stoichiometry in the global terrestrial ecosystem.

Response of heterotrophic respiration to vegetation restoration in a karst area of SW China

AbstractThe Grain‐for‐Green Program in China aims to restore sloping karst cropland severely degraded by intensive agriculture to secondary forest. Heterotrophic respiration (Rh) is a major process of carbon release from soils and is associated with the sequestration of soil organic carbon (SOC). However, we still do not have a comprehensive understanding of Rh and what drives it along soil profile horizons during the natural vegetative recovery process in typical karst soils. We investigated the responses of Rh (C release per gram of soil) and specific Rh (C release per gram of SOC) in soil horizons from the soil surface to bedrock at the different vegetation recovery stages in a karst region. Coincident soil microbial properties (e.g., bacterial and fungal abundance, total microbial biomass, potential enzyme activities) and physicochemical properties were quantified. Vegetation restoration after cropland abandonment significantly increased Rh rates due to increased soil nutrients and microbial biomass, bacterial abundances, and hydrolase activities (all, p &lt; 0.05). The rates of Rh enhanced in sloping cropland (SC) from the soil surface to bedrock but reduced in the recovering stages (ASC: abandoned sloping cropland and SF: secondary forest) and primary forest (PF). The specific Rh between SF (1.34 mg CO2‐C g−1 SOC d−1) and PF (1.32 mg CO2‐C g−1 SOC d−1) were not significantly different but both of them were greater than those in SC (0.79 mg CO2‐C g−1 SOC d−1) and ASC (0.8 mg CO2‐C g−1 SOC d−1). Soil physicochemical properties and microbial properties explained approximately 48% and 22% of the variations in Rh along vegetation recovery, respectively. Nitrogen to phosphorus stoichiometry exerted the most direct and positive effects on Rh, suggesting the importance of managing soil nutrient status to regulate carbon decomposition during vegetation recovery in karst soils. The increased microbial biomass was the most important microbial factor regulating Rh in later vegetation recovery phases. Our results provide scientific insight into the impact of vegetation restoration on Rh in degraded ecosystems, which is important for reducing carbon loss in karst soils.

Biochar amendments combined with organic fertilizer improve maize productivity and mitigate nutrient loss by regulating the C–N–P stoichiometry of soil, microbiome, and enzymes

Coupled amendments of biochar and organic fertilizers may be one of the effective practice to ensure high cropland productivity and resource use efficiency, but there is little field-based evidence for this. Herein, we employed a eight-years (2014–2021) field experiment to explore the effectiveness of biochar and organic fertilizer amendments on crop productivity and nutrient runoff losses, as well as to further explored their relationships with the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of soil, microbiome, and enzymes. Experiment treatments include No fertilizer (CK), chemical-only fertilizer (CF), CF + biochar (CF + B), 20% chemical N was replaced by organic fertilizer (OF), and OF + biochar (OF + B). Compared with the CF, the CF + B, OF, and OF + B treatments increased average yield by 11.5%, 13.2%, and 32%, average N use efficiency by 37.2%, 58.6%, and 81.4%, average P use efficiency by 44.8%, 55.1%, and 118.6%, average plant N uptake by 19.7%, 35.6%, and 44.3%, as well as average plant P uptake by 18.4%, 23.1%, and 44.3%, respectively (p ≤ 0.05). Compared with the CF, the CF + B, OF, and OF + B decreased average average total N losses by 65.2%, 97.4%, and 241.2%, and average total P losses by 52.9%, 77.1%, and 119.7%, respectively (p ≤ 0.05). Organic-amended treatments (CF + B, OF, and OF + B) significantly changed soil total and available C, N, and P content, soil microbial C, N, and P content, as well as the potential activities of soil C-, N-, and P-acquiring enzymes. Plant P uptake and P-acquiring enzyme activity were the main drivers of maize yield, which was influenced by the contents and stoichiometric ratios of soil available C, N, and P. These findings suggest that organic fertilizer applications combined with biochar have the potential to maintain high crop yields while reducing nutrient losses by regulating the stoichiometric balance of soil available C and nutrients.

Wetland‐type conversion drives the C, N and P stoichiometry change of soil in river plain of lower of the Yellow River

AbstractLand use conversion on river plain has profound impacts on soil characteristics and elemental stoichiometry. Four wetland types (Riparian lower‐beach wetland [RLW], Riparian higher‐beach wetland [RHW], Cultivated wetland [CW] and Mesophytic wetland [MW]) were selected in the lower Yellow River area to investigate the consequence of wetland type conversion on soil carbon (C), nitrogen (N) and phosphorus (P) stoichiometry. The results demonstrated that wetland conversion induced significant spatio‐temporal variations in soil C, N and P stoichiometry and physicochemical characteristics in soil. Frequent agricultural activities (fertilizer input) raised the nutrient content of natural wetland, particularly in surface soil (0–30 cm). Soil volumetric water content (VWC), soil bulk density (SBD), pH and soil enzyme activity varied significantly in different wetlands. Total carbon (TC) and total nitrogen (TN) contents in MW decreased with increasing soil depth (&lt;40 cm layers), as did TN and total phosphorus (TP) contents in CW. On the other hand, TC, TN and TP contents in RLW and RHW did not change significantly with soil depth. However, the contents of TOC, and Fe/Al‐P, etc., varied among soil layers and among wetland types. Furthermore, the stoichiometric characteristics changed significantly in some soil layers, with mean values being less than the Chinese average. Statistically, significant positive correlations were determined between TC and TN (r = .56), TDC and TP (r = .62), N:P and pH (r = .57) (p &lt; .05) and and pH (r = .66, p &lt; .01). VWC was negatively correlated with pH (r = −.56, p &lt; .05), while C/P was negatively associated with soil temperature (ST) and SBD (r = −.55, r = −.64, p &lt; .05). TDC, IP, TN, Fe/Al‐P and ST were identified as the dominant factors, with the percentage of variance 41%, 20%, 12%, 9% and 6% respectively. These findings have a great scientific significance for the ecological conservation of wetlands in the lower Yellow River area.

Leaf Nitrogen and Phosphorus Stoichiometry and Its Response to Geographical and Climatic Factors in a Tropical Region: Evidence from Hainan Island

Leaf stoichiometry effectively indicates the response and adaptation of plants to environmental changes. Although numerous studies on leaf stoichiometry patterns have focused on the mid-latitudes and specific species of plants, these patterns and the effect of the climate change on them across a broad range of plants have remained poorly characterized in hot and humid regions at low latitudes. In the present study, leaf N, P, N:P, C:N, and C:P ratios, were determined from 345 plant leaf samples of 268 species at four forest sites in Hainan Island, China. For all plants, leaf N (3.80 ± 0.20 mg g−1) and P (1.82 ± 0.07 mg g−1) were negatively correlated with latitude and mean annual temperature (MAT) but were positively correlated with longitude. Leaf N was found to be positively correlated with altitude (ALT), and leaf P was positively correlated with mean annual precipitation (MAP). The leaf C:N ratio (278.77 ± 15.86) was significantly correlated with longitude and ALT, leaf C:P ratio (390.69 ± 15.15) was significantly correlated with all factors except ALT, and leaf N:P ratio (2.25 ± 0.10) was significantly correlated with ALT, MAT, and MAP. Comparable results were observed for woody plants. The results suggest that leaf stoichiometry on Hainan Island is affected by changes in geographical and climatic factors. In addition, the low N:P ratio indicates that plant growth may be limited by N availability. Moreover, the significant correlation between leaf N and P implies a possible synergistic relationship between N and P uptake efficiency in the plants of this region. This study helps to reveal the spatial patterns of leaf stoichiometry and their response to global climate change in a variety of plants in tropical regions with hot and humid environments, which may provide an insight in nutrient management in tropical rainforest.

Patterns of carbon, nitrogen, and phosphorus stoichiometry of three life-form desert plants and responses to soil and microbial biomass factors in a hyper-arid desert ecosystem.

Plant, soil, and microbial biomass ratios of carbon (C), nitrogen (N), and phosphorus (P) are crucial in maintaining stability of desert ecosystems. Nevertheless, variation in relations of elemental ratios between different life forms of plants and soil and microbial biomass in desert ecosystems remains unclear. In a hyper-arid desert ecosystem, C, N, and P concentrations and ratios were analyzed in the plant-soil-microbial biomass system of three perennial desert species (Alhagi sparsifolia Shap. [Herb, Fabaceae], Karelinia caspica Pall. [Herb, non-Fabaceae], and Tamarix ramosissima Ledeb. [Shrub]). Concentrations of N and P in Alhagi sparsifolia leaf, stem, and root were significantly greater than those in Karelinia caspica and Tamarix ramosissima, whereas plant C and soil organic C (SOC) were highest with Tamarix ramosissima. Alhagi sparsifolia and Tamarix ramosissima were P-limited, whereas Karelinia caspica was N-limited. According to correlation analysis, SOC rather than soil total P (STP) regulated plant N:P ratios, and microbial biomass C, N, and P rather than SOC, soil total N, and STP regulated plant C:N:P ratios. Soil water content also affected plant nutrient balance. Thus, in a hyper-arid desert ecosystem, the plant-soil-microbial biomass system and the balance of C, N, and P are closely related, and the role of soil microbial biomass in affecting plant nutrient balance should receive increased attention.

Imbalanced phytoplankton C, N, P and its relationship with seawater nutrients in Xiamen Bay, China

Anthropogenic activities dramatically alter biogeochemical cycling and stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) within coastal marine ecosystems. Long-term nutrient input has led to significant deviation of the C, N and P stoichiometry of phytoplankton (C167N28P1) and surface seawater (C1299N24P1) from the Redfield ratio (C106N16P1), and overall P-limitation in Xiamen Bay. The bio-P in phytoplankton was spatially consistent with that of inorganic P in seawater; and the phytoplankton bio-C:N:P shifted towards the same trend as the seawater under prolonged nutrient stress, as one of the cascade effects of the imbalanced seawater elemental stoichiometry on the species composition and abundance, and in turn on bio-elemental stoichiometry, of phytoplankton community. It is suggested that the significant deviations in elemental stoichiometry of primary producers might impair their capacity of nutrient supply for organisms at higher trophic-levels of the food chains in the local coastal ecosystem and thus damage its health.

Soil carbon, nitrogen, and phosphorus stoichiometry and its influencing factors in Chinese fir plantations across subtropical China

The crucial roles of soil carbon (C) and nutrients and their stoichiometric characteristics in indicating the soil interior nutrient cycling and plant nutrient supply of forest ecosystems have been widely verified, whereas it has been less explored when considering the influencing factors regionally, especially for the widely cultivated plantation tree species. In the current study, the patterns of soil organic C (SOC), total nitrogen (TN), and total phosphorus (TP) stoichiometry in Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantations across subtropical China were analyzed, and their influencing factors were also investigated. The results showed that the range of SOC: TN (C:N), SOC: TP (C:P), and TN: TP (N:P) ratios were 7.32–18.27, 20.15–230.48, and 2.11–15.05 with a mean value of 13.22, 83.50, and 6.05, respectively. Well-constrained correlations were found in SOC and TN, as well as in TN and TP. Soil TN and TP contents increased with increasing altitude, whereas soil C:N, C:P, and N:P ratios decreased. Soil TP content decreased, and the C:P ratio increased with increasing mean annual temperature (MAT) and annual total solar radiation (ATSR). Soil C:N, C:P, and N:P ratios increased with increased mean annual precipitation (MAP) and mean annual evaporation (MAE). Overall, our findings suggested that the soil nutrient supply is relatively adequate in Chinese fir plantations across subtropical China. Meanwhile, soil C, N, and P stoichiometric characteristics were affected by geographical and climatic variables to different degrees.

Predicting ecosystem productivity based on plant community traits.

With the rapid accumulation of plant trait data, major opportunities have arisen for the integration of these data into predicting ecosystem primary productivity across a range of spatial extents. Traditionally, traits have been used to explain physiological productivity at cell, organ, or plant scales, but scaling up to the ecosystem scale has remained challenging. Here, we show the need to combine measures of community-level traits and environmental factors to predict ecosystem productivity at landscape or biogeographic scales. We show how theory can extend the production ecology equation to enormous potential for integrating traits into ecological models that estimate productivity-related ecosystem functions across ecological scales and to anticipate the response of terrestrial ecosystems to global change.

Ecological stoichiometric comparison of plant-litter-soil system in mixed-species and monoculture plantations of Robinia pseudoacacia, Amygdalus davidiana, and Armeniaca sibirica in the Loess Hilly Region of China

We examined how afforestation patterns impact carbon (C), nitrogen (N), and phosphorus (P) stoichiometry in the plant-litter-soil system. Plant leaf, branch, stem, and root, litter, and soil samples were collected from mixed-species plantations of Robinia pseudoacacia with Amygdalus davidiana (RPAD), R. pseudoacacia with Armeniaca sibirica (RPAS), and monocultures of R. pseudoacacia (RP), A. davidiana (AD), and A. sibirica (AS) in the Loess Hilly Region. The results showed that in mixed-species plantations, R. pseudoacacia had lower leaf N and P concentrations than in monocultures, while both A. davidiana and A. sibirica had higher leaf N and P concentrations. Soil P limited tree growth in both afforestation models. Mixing R. pseudoacacia with A. davidiana or A. sibirica reduced N-limitation during litter decomposition. Average soil total N and P concentrations were higher in RPAS than in RPAD, and both were higher than the corresponding monocultures. The average soil C:N ratio was the smallest in RPAS, while the average soil C:P ratio was larger in RPAS than in RP. A positive correlation between N and P concentrations, and between C:N and C:P ratios, was found in litter and all plant organs of mono- and mixed-stands. Alternatively, for N concentration and C:N ratio, the correlations between plant (i.e., leaf, branch, root) and litter and between plant and soil were inverse between plantation types. RPAD has an increased litter decomposition rate to release N and P, while RPAS has a faster rate of soil N mineralization. RPAD was the best plantation (mixed) to improve biogeochemical cycling, as soil nutrient restrictions, particularly for P-limitation, on trees growth were alleviated. This study thus provides insights into suitable tree selection and management by revealing C:N:P stoichiometry in the plant-litter-soil system under different afforestation patterns.

Environmental drivers of the leaf nitrogen and phosphorus stoichiometry characteristics of critically endangered Acer catalpifolium.

Acer catalpifolium is a perennial deciduous broad-leaved woody plant, listed in the second-class protection program in China mainly distributed on the northwest edge of Chengdu plain. However, extensive anthropogenic disturbances and pollutants emissions (such as SO2, NH3 and NOX) in this area have created a heterogeneous habitat for this species and its impacts have not been systematically studied. In this study, we investigated the leaf nitrogen (N) and phosphorus (P) content of A. catalpifolium in the natural distribution areas, and a series of simulation experiments (e.g., various water and light supply regimes, different acid and N deposition levels, reintroduction management) were conducted to analyze responses of N and P stoichiometric characteristics to environmental changes. The results showed that leaf nitrogen content (LNC) was 14.49 ~ 25.44 mg g-1, leaf phosphorus content (LPC) was 1.29~3.81 mg g-1 and the N/P ratio of the leaf (L-N/P) was 4.87~13.93. As per the simulation experiments, LNC of A. catalpifolium is found to be relatively high at strong light conditions (80% of full light), high N deposition (100 and 150kg N ha-1), low acidity rainwater, reintroduction to understory area or N fertilizer applications. A high level of LPC was found when applied with 80% of full light and moderate N deposition (100kg N ha-1). L-N/P was high under severe shade (8% of full light), severe N deposition (200kg N ha-1), and reintroduction to gap and undergrowth habitat; however, low L-N/P was observed at low acidity rainwater or P fertilizer application. The nutrient supply facilitates corresponding elements uptake, shade tends to induce P limitation and soil acidification shows N limitation. Our results provide theoretical guidance for field management and nutrient supply regimes for future protection, population rejuvenation of this species and provide guidelines for conservation and nutrient management strategies for the endangered species.

Characteristics of Carbon, Nitrogen and Phosphorus Stoichiometry and Nutrient Reabsorption in Alfalfa Leaves with Different Fall-Dormancy Levels in Northern Xinjiang, China

Alfalfa productivity and cold resistance in different regions are influenced by the fall-dormancy level of alfalfa. However, it is unclear whether the stoichiometric characteristics and nutrient resorption efficiency in alfalfa leaves also vary with the fall-dormancy level. In order to further understand the differences in nutrient absorption and requirements of different fall-dormant alfalfa, we conducted field trials on 30 different fall-dormancy alfalfa cultivars for 2 consecutive years in 2020 and 2021. We investigated the concentrations of carbon, nitrogen, and phosphorus in mature and senescent alfalfa leaves; nutrient stoichiometry ratios; and the coupling relationship between nutrient reabsorption efficiency and dry matter yield. The differences in nutrient reabsorption, fall dormancy, and dry matter yield of different fall-dormant alfalfa, and the correlation between indicators were utilized to further analyze the regulatory mechanisms of nutrient reabsorption in different fall-dormancy alfalfa varieties. The results demonstrated that the nitrogen reabsorption efficiency (NRE) and phosphorus reabsorption efficiency (PRE) of leaves increased first and then decreased with the increase in fall dormancy, whereas the carbon reabsorption efficiency (CRE) showed the reverse tendency. Different fall-dormancy alfalfa varieties significantly affected the dry matter yield and nutrient absorption in the first cut, while the last cut had the lowest variable coefficient and impact. There was a significant decrease in the over-winter survival rate of alfalfa as the fall-dormancy level increased, whereas the over-summer survival rate was less affected by the fall-dormancy level. As the growth year increased, there was a significant decrease in the over-winter survival rate. Among mature leaves, the NRE and PRE showed a significant positive correlation with the C concentration, while they showed a significant negative association with the N and P concentrations. In the same cut, the dry matter yield decreased with the increase in CRE but increased with the increases in NRE and PRE, while there was no significant trend in dry matter yield and nutrient resorption efficiency (NuRE) between different cuts. Taken together, the alfalfa survival rate and dry matter yield were relatively better in the moderate fall-dormancy (fall-dormancy level, FD = 4, 5) types and fall-dormancy (FD = 3) type, with a corresponding increase in the reabsorption requirements for nitrogen and phosphorus.

Interactive effects of plant density and nitrogen availability on the biomass production and leaf stoichiometry ofArabidopsis thaliana

AbstractPlant density and nitrogen (N) availability influence plant survival and nutrient use strategies, but the interaction between these two factors for plant growth and the balance of elements remains poorly addressed. Here, we conducted experimental manipulations using Arabidopsis thaliana, with the combination of four levels of plant density and four levels of N addition, and then examined the corresponding changes in plant biomass production (indicated by total plant biomass and biomass partitioning) and nutrient use strategies (indicated by leaf N and phosphorus (P) stoichiometry). The biomass–density relationship was regulated by N availability, with a negative pattern in low N availability but an asymptotic constant final yield pattern at high N availability. Excessive N addition reduced plant growth at low plant density, but this effect was alleviated by increasing plant density. The root to shoot biomass ratio increased with plant density at low N availability, but decreased at high N availability. N availability was more important than plant density in regulating leaf N and P stoichiometry, with the increasing leaf N concentration and decreasing leaf P concentration under increasing N addition, resulting in a negative scaling relationship between these two elemental concentrations. Our results show that N availability and plant density interactively regulate plant biomass production and leaf stoichiometry of A. thaliana, and highlight that the interactive effects of these two factors should be considered when predicting plant growth behaviour under intraspecific competitive environments in the context of nutrient changes.