Plant ecological stoichiometry, as a branch of ecological stoichiometry, focuses on the study of elemental content, ratios and relationships within and across plant organs, and the underlying biotic and abiotic drivers. In the 19th century, chemists detected the elemental contents in plant organs via laboratory experiments, sprouting the exploration of plant stoichiometric characteristics. Nowadays, ecologists have explored plant ecological stoichiometric characteristics and their responses to global changes and relationships with plant functional traits, using both field investigation and manipulative experiments. These sustained efforts have largely enriched the knowledge and understanding of plant ecological stoichiometry. In this paper, we briefly introduced the history and reviewed the research progresses of plant stoichiometry since the 19th century. Firstly, we proposed the developmental history of plant ecological stoichiometry as three main periods: sprouting, hypothesis foundation, and theoretical construction periods, and introduced some representative works for each period. Secondly, we overviewed plant ecological stoichiometric characteristics across organs, life forms and environmental gradients. The geometric mean values of leaf nitrogen (N) and phosphorus (P) contents and N:P mass ratios in global terrestrial plants are 18.74 mg∙g^-1, 1.21 mg∙g^-1 and 15.55 (i.e. similar to the Redfield ratio of 16:1), respectively. Leaf N and P contents at either species or community level generally show a decreasing trend with increasing temperature and precipitation, and have large variations among life forms, with higher values in herbaceous than woody plants, and deciduous broad-leaved than evergreen broad-leaved and coniferous woody plants. Compared with leaves, the stoichiometric characteristics of fine roots and other organs in plants remain poorly documented. Thirdly, we reviewed the effects of nutrient addition on plant ecological stoichiometric characteristics. In general, N addition increases soil N availability, then the N content and N:P in plants, thus leading to an increase in plant productivity to some extents. P addition might alleviate the N and P imbalance induced by excessive N inputs, and then increase plant P content. However, long-term nutrient fertilization could perturb the intrinsic stoichiometric characteristics in plants, resulting in the deteriorated nutrient imbalance in tissues and then the subsequent decline in plant productivity. Fourthly, we introduced the main hypotheses of plant ecological stoichiometry. These hypotheses include function-associated hypotheses, environment-associated hypotheses and evolution-associated hypotheses, which delineate the relationships of stoichiometric characteristics with plant growth functions, environmental factors and plant evolutionary history, respectively. Finally, we made an outlook on future research in the area of plant ecological stoichiometry, and highlighted ten potential and important research themes.

Changes in soil nutrient availability and primary succession of vegetation often co-occur during the processes of natural soil development. A low availability of nitrogen (N) and phosphorus (P) resources is common in the very early and late stage of soil development, respectively. Plants have evolved different nutrient-acquisition strategies (NASs) in response to low nutrient availability. Although the changes and responses of plant NASs to soil nutrients may affect primary succession and species diversity, the temporal trends and underlying mechanisms of plant NASs with soil development remain unknown. We reviewed 104 studies mainly carried out on soil chronosequences to clarify changes in plant NASs with soil age and its ecological significance. We classify plant NASs into Fine root, Microbial, Specialized root, Carnivorous and Parasitic strategies. We argue that the diversity of plant NASs changes with increasing soil age following a dumbbell-pattern, while reaching the maximum in the late stage of soil development. The role of Microbial and Fine root strategies in plants acquiring nutrients gradually decreases with increasing soil age, while the minimum and maximum role of Specialized root strategies in plants acquiring P is in the intermediate and late stages of soil development, respectively. The effects of NASs on interspecific relationships of plants vary with soil age. Specifically, pioneer plants with biological N fixation and specialized root strategies usually increase available soil N and regolith-derived nutrients to facilitate the colonization of subsequent plants in the early stage of soil development. During the early-intermediate stage, NASs mainly affect plant competitiveness in acquiring relatively abundantly available nutrients from soil. The facilitation and competition affected by NASs contribute to plant species turnover in the first two stages. In the late stage, diverse NASs enable plants to acquire distinct forms of nutrients from different soil spaces and complementary NASs enable plants to take up soil nutrients mobilized by their neighbors. Together with the interactions between NASs and soil pathogens, these processes contribute the coexistence and diversity of plant species in this stage when most soil nutrients have a very low availability. We propose that it is necessary to quantify the relationships between changes in soil nutrient availability (including concentrations and fractions) and plant NASs with soil age. More studies are also needed to quantify contributions of NASs to primary succession, diversity of plant species and soil development.

Aims Plants absorb mineral nutrients such as nitrogen (N) mainly through their roots. The nutrient uptake of plants with different root morphologies differs. Many studies have shown that arbuscular mycorrhizal fungi (AMF) can help their symbiotic associates absorb mineral N. However, there is little research on whether the effect of AMF on nutrient uptake of plant roots is affected by root morphology.

Methods In this study, we selected three rice mutants and one wild type (root hairless (rhl1), lateral rootless (iaa11), adventitious rootless (arl1) and wild type (Kas)) to investigate the role of root morphology in plant nutrient uptake. Subsequently, we used the ¹⁵N isotope labeling method to explore the effects of arbuscular mycorrhizal fungi and N addition (low N: 20 mg·kg^-1 NH₄⁺-N; high N: 100 mg·kg^-1 NH₄⁺-N) on N uptake of rice mutants with different root morphologies.

Important findings The results show that the leaf ¹⁵N concentrations of rhl1,Kas, iaa11 and arl1 were increased by 60%, 72%, 128% and 118%, respectively, under the high N compared to the low N treatment. This result indicates that the addition of N significantly promoted rice N uptake with the most evident effect occurring in iaa11 and arl1. The average effect sizes of AMF on rhl1, Kas, iaa11 and arl1 were 17%, 31%, 42% and 51% under the low N level, indicating that root morphology can alter the effect of AMF on plant N uptake. Compared to the low N treatment, high N significantly downregulated the AMF effect on N uptake by rice plants with different root morphologies, indicating that N addition may mediate the complementary effect of AMF and root morphology on plant nutrient uptake. In conclusion, our data provide direct experimental evidence of funcitonal complementarity of mycrrohzal fungi and their associated roots with different root morphogy.

Aims Nutrient resorption in different organs of plants is important for plant nutrient use strategies and elemental biogeochemical cycles. Previous researches on nutrient resorption have focused on leaves, but neglected culms. Additionally, leaves of different species have been collected at the same time during the peak growth stage in previous studies, ignoring the different peak times of nutrient content of different species, which leads to the underestimation of nutrient resorption efficiency.

Methods In order to explore the seasonal variation of nutrients and nutrient resorption efficiency in the culms and leaves of herbaceous plants, 22 common plants in Hulun Buir grassland were chosen as the research objects to determine the temporal dynamics of nutrient content during the growing season, and the resorption efficiency of nitrogen (N) and phosphorus (P) in plant culms and leaves.

Important findings The content of N, P in plants had obvious temporal dynamics during the growing season, showing an increasing trend first and then a decreasing trend. For most of the 22 species, the maximum content occurred in the middle and late August, but the peak time differed among different species. The resorption efficiency of N in leaves was higher than in culms, but that of P did not differ between leaves and culms. Nutrient resorption efficiency of plants was closely related to the nutrient content at the senescence stage, but not to that at the growth stage. In previous studies, different plants were sampled at the same time during the growth stage, which led to underestimation of N and P resorption efficiency of culms and leaves. This study re-examined the sampling strategy in nutrient resorption studies, and showed that the sampling time of mature tissues in the growth stage could be determined according to the peak nutrient content time of different species.

Aims The content of carbon (C), nitrogen (N) and phosphorus (P) in different plant organs and their stoichiometric characteristics can reflect the nutrient allocation and balance within the plant. In this paper, the response of C, N and P in different organs of tea plants to three management modes was investigated by field experiment. The purpose was to explore the variation characteristics of C, N and P contents and their stoichiometric ratios in roots, stems and leaves of tea plant and its allometric growth relationship under different management modes.

Methods We set up three different management modes in Tieguanyin tea plantations in Anxi, Fujian: routine management mode (M1), intercropping mode (M2) and modern technology mode (M3). In this paper, we investigated C, N, and P contents in the roots, stems, and leaves and their stoichiometric characteristics, nutrient variations and the allometric relationships of tea plants under different management modes.

Important findings The results showed that the N and P contents in roots, stems and leaves of tea plants under M2 and M3 management mode were significantly higher than those under M1 management mode, but no significant differences were observed for the C contents; the order of C:N, C:P and N:P ratios in roots, stems and leaves of tea plants was M1 > M2 > M3. The contents of C, N, and P varied significantly among different organs of tea plants. According to the analysis of variation sources, the management mode factors showed significant impacts on the content variation of all the three elements. The allometric relationships of N and P in roots, stems and leaves (N-P^1.7456, p< 0.01; N-P^1.0987, p< 0.01; N-P^1.1993, p< 0.01) suggested that the nutrient requirements of different organs were similar. Soil pH and bulk density were important factors affecting C:N, C:P and N:P, while soil water content and salinity had great impacts on C content in roots and leaves of tea plants. In general, intercropping, as well as modern drip irrigation and fertilizer management technology, can improve the nutrient absorption efficiency of tea plants, and have positive effects on solving the problem of soil nutrient imbalance.

Aims Plants of the same life-form may utilize different forms of nitrogen to avoid or reduce the competition for resources, thus achieving co-existence. Studying on whether niche separation exists in nitrogen uptake by plants of the same life-form in desert ecosystems is helpful to understand the survival strategy of desert plants and the effect of nitrogen on the survival of desert plants.

Methods Two annual plants, Ceratocarpus arenarius and Suaeda glauca, are widely distributed in Gurbantünggüt Desert. ¹⁵N isotope tracer method was used to study the nitrogen uptake strategies of two desert annuals in different months and from different soil layers.

Important findings The results showed that the nitrogen absorption rates of the two plants in shallow soil were higher in July than those in June. Comparing the absorption rates of different nitrogen forms, plants preferred inorganic nitrogen to organic nitrogen. Ceratocarpus arenarius preferred nitrate nitrogen, and the highest nitrogen absorption rate was 3.81 μg·h^-1 per gram dry root, while S. glauca preferred ammonium nitrogen, and the highest nitrogen absorption rate was 4.74 μg·h^-1 per gram dry root. The contribution rates of nitrate nitrogen out of total nitrogen uptake ranged from 35.7% to 43.9% for C. arenarius; while the contribution rate of ammonium nitrogen out of total nitrogen uptake ranged from 40.0% to 48.3% for S. glauca. The two annual plants can not only utilize inorganic nitrogen, but also directly absorb organic nitrogen in soil. The findings showed that the nitrogen uptake capacity of annual plants in Gurbantünggüt desert was different and diversified, and all of them could absorb the soluble organic nitrogen sources in the soil.

Aims Non-structural carbohydrates (NSC) are available carbon in plants and can be utilized as an energy source during plant metabolism, so NSC are important components for plant growth and metabolic activities, particularly under environmental stress. Moreover, NSC in senescent leaves as litter-fall provide available carbon for soil microorganisms involving in soil organic matter formation and biogeochemical cycles in forests. Therefore, study on the variation in NSC between fresh and senescent leaves is of great significance for understanding the carbon metabolism during plant growth and carbon biogeochemical cycles during early decomposition of plant litter. The objective of this study was to determine the difference in NSC content between fresh and senescent leaves of 11 subtropical tree species and the variation between leaves with different plant functional types.

Methods A common garden was established in the stands with similar soil development, aspect, slope, and management history at the Sanming Research Station of Forest Ecosystem and Global Change in February 2012. A total of 13 representative subtropical tree species (2-year-old) were planted in the common garden, which were designed according to random blocks with 4 replicates for each tree species (a total of 52 plots with approximately 0.1 hm² for each plot). In this study, the fresh and senescent leaves of 11 tree species, including evergreen broadleaved species Schima superba, Lindera communis, Elaeocarpus decipiens, Michelia macclurei, Castanopsis carlesii and Cinnamomum camphora, deciduous broadleaved tree species Liriodendron chinense, Liquidambar formosana and Sapindus mukorossi, and coniferous tree species Cunninghamia lanceolata and Pinus massoniana were collected in August 2019. The contents of NSCs, including soluble sugars and starch, in fresh and senescent leaves of the 11 tree species were determined.

Important findings The NSC content was significantly higher in fresh leaves than that in senescent leaves for all of the studied tree species. The NSC contents in fresh leaves were 68.7-126.3 mg∙g^-1, while those in senescent leaves were 31.4-79.5 mg∙g^-1. Notably, the variation in soluble sugar between fresh leaves and senescent leaves was much greater than that of starch. Specifically, the average content of soluble sugar in fresh leaves was 3.3 times greater than that of senescent leaves, and the average starch content in fresh leaves was 1.2 times greater than that of senescent leaves. Moreover, the NSC contents in both fresh and senescent leaves varied significantly among trees with different plant functional types. For example, the NSC contents in both fresh and senescent leaves of evergreen and deciduous broad-leaved trees showed similar levels, while the NSC contents in evergreen coniferous trees were significantly lower than those in broad-leaved trees. In fresh leaves, the average NSC contents in evergreen and deciduous broad-leaved trees were 99.7 and 96.8 mg∙g^-1, respectively, while the average NSC content in evergreen coniferous trees was 75.4 mg∙g^-1; In senescent leaves, the average NSC contents in evergreen and deciduous broad-leaved trees were 47.2 and 50.7 mg∙g^-1, respectively, while the average NSC content in evergreen coniferous trees was 33.3 mg∙g^-1. These results suggest that NSC, an important carbon metabolic component for trees, could be transferred from senescent leaves to fresh leaves before senescence; this is a significant strategy for carbon storage during plant growth. However, the NSC content was significantly lower in subtropical coniferous trees (such as Cunninghamia lanceolata and Pinus massoniana) than in broad-leaved trees, regardless of fresh and senescent leaves, suggesting that the initial substrate quality is lower in these coniferous litters with less labile components following forest plantation in subtropical China. This difference in NSC content in foliar litter has significant influence for litter decomposition and soil organic matter formation mediated by microbial metabolism and turnover. These results are of great significance for improving the theory of carbon metabolism during plant growth and for understanding the dynamic changes of carbon components during the early decomposition of leaves litter in subtropical forests.

Aims Nitrogen (N) availability is an important limiting factor for grassland ecosystem productivity, and soil microorganisms are the main driving factor on soil N transformation. With the increase of atmospheric N deposition, the response of soil microbial characteristics to different nitrogen input levels is still unclear especially in saline-alkaline grassland.

Methods The experiment was conducted in Youyu Loess Plateau Grassland Ecosystem Research Station, Shanxi Province. Eight different nitrogen addition levels were set, which were 0, 1, 2, 4, 8, 16, 24 and 32 g·m^-2·a^-1, respectively. The Ammonia-oxidizing microorganisms (i.e. ammonia-oxidizing bacteria (AOB) and ammonia- oxidizing archaea (AOA)) abundance, soil bacterial and fungal abundance, as well as soil microbial biomass carbon (MBC) and nitrogen (MBN) content were measured in the growing season (May to September) in 2020 to explore the effects of different levels of N addition on soil microbial characteristics.

Important findings Our results showed that: (1) Sampling month had a significant effect on soil AOB, bacteria, fungal abundance and MBC, MBN content due to the variation in soil temperature and soil water content in the growing season. (2) N addition had a significant effect on soil AOB abundance, while had no effects on soil MBC, MBN content, and bacterial and fungal composition. (3) Higher N addition (24 and 32 g·m^-2·a^-1) significantly increased the abundance of ammonia-oxidizing bacteria (AOB) on the early growth stage (May to August), while having no effect on late growth period (September). (4) Soil microorganisms were mainly regulated by soil cations concentrations and soil pH values, which explained the variation of soil microorganisms by 21.8% and 17.2%, respectively. We found that soil microorganisms were not sensitive to N addition in saline-alkaline grassland, while AOB showed a significant increase under higher N addition, indicating that higher N addition might promote soil N transformation.

Aims Soil nitrogen (N) plays a vital role in regulating the structure and function of ecosystems and is affected by N deposition. Most previous studies focus on the responses of the N content in bulk soil to N deposition, but the responses of the N content in different soil organic matter (SOM) fractions remain unclear. We aimed to investigate how long-term N addition influenced soil N of different SOM fractions in a semi-arid grassland.

Methods A manipulated N addition experiment with 4 levels of N addition (0, 8, 32 and 64 g·m^-2·a^-1) has been conducted for 13 years in Duolun country, Nei Mongol. SOM was separated to particulate organic matter (POM) and mineral associated organic matter (MAOM) by density fractionation. The plant and soil properties were also measured.

Important findings The results showed that N addition had no significant effect on the carbon (C) content in bulk soil, POM, or MAOM. With increasing levels of N addition, the N content in bulk soil and in POM increased significantly. Furthermore, we found that the increased N content of POM was mainly associated with greater aboveground biomass following N addition. The N content of MAOM is mainly correlated with soil texture, but was not affected by N addition. These results suggest that continuous N addition can increase the soil N in bulk soil, but the increased N is mostly distributed in labile POM pools, which can be vulnerable to land use and climate change.

Pollen record is an essential data for reconstructing paleovegetation and paleoclimate. It is important for the studies of paleoenvironmental evolution, characteristics of paleoclimate change and simulation of paleobiogeochemical cycles from site to regional and global scales. In this paper, we collected and sorted out the pollen data records from published and unpublished Chinese literature between 1960 to 2020. The records included sample numbers, sampling locations (latitude, longitude and altitude of sampling sites), sample types, data sources, data types, surrounding vegetation, references, and pollen taxa, their compositions as well. They were filtered and standardized to integrate a pollen dataset of China. This dataset consists of 4 497 modern pollen sampling sites, including 660 published data from the Chinese Quaternary Pollen Database, 1 763 from early published data and 2 074 from recently collected data, belonging to 772 pollen taxa. The samples were mainly from surface soils (3 332 sites), and the rest were from moss plosters, surface sediments from lakes and the ocean. The sampling sites are widely scattered around China representing different geographical regions and vegetation types: 24.91%. in the temperate desert region, 24.02% in the subtropical evergreen broad-leaved forest region, followed by the temperate grassland region (16.14%) and alpine vegetation region of Qingzang Plateau (15.83%). The data can be divided into the raw data (58%) and numerical data (42%) according to their sources, and grain count (59%) and calculated pollen percentage (41%) by data type as well. The database constructed from the samples over China during the past half-century+ period is, though by far from complete, good representation of most of the areas in China, which can be effective in the reconstruction of past vegetation and climates as modern verification.