Soil inorganic nitrogen (N) has long been recognized to play an important role in plant invasions. Whilst comparing the N use strategies of multiple invasive versus native plant congeners along an entire N gradient is key to understanding plant invasion success, there are few related studies.

We conducted a potted experiment with six invasive and native congeneric pairs, which were subjected to 11 nitrate/ammonium (NO₃−/NH₄+) ratios (i.e. 100% NO₃− at one end and 100% NH₄+ at the other end), each with low- and high-N levels. Each species–N combination was replicated eight times, and thus there were 2112 pots in total. We measured the following traits: the total biomass, growth advantage, biomass allocation, leaf chlorophyll content and low-N tolerance.

Invasive and native congeners grew well at any NO₃−/NH₄+ ratios, and their responses of growth, allocation and tolerance were approximately parallel along the 11 NO₃−/NH₄+ ratios across two N levels. Plant invaders grew larger and had greater chlorophyll contents, higher root biomass allocation and stronger low-N tolerance than their congeneric natives. These findings suggest that invasive and native plant congeners may utilize similar inorganic N forms (i.e. NO₃− and NH₄+) across an entire N composition gradient and that higher N use efficiencies could favor alien plants to invade new plant communities where congeneric natives are dominants.

Reforestation can enhance soil carbon (C) stability and promote soil C accumulation. Experimental results are, however, highly variable, and the efficacy of reforestation in enhancing soil C stability is still in debate. Consequently, it remains unclear how the different soil C pools respond to reforestation in forest ecosystems.

The response of different soil C fractions to reforestation was examined in five subtropical forests, including the plantations of Eucalyptus urophylla (EU), Acacia crassicarpa (AC), Castanopsis hystrix (CH) and 10 species mixed (MX), and a naturally recovered shrubland (NS). Soil labile C fractions (readily oxidized organic C by KMnO₄: ROC; dissolved organic C: DOC), distribution of aggregate-size classes and aggregate-associated C from different soil layers (0–10, 10–20, 20–40 and 40–60 cm) were evaluated.

We found that reforestation and forest type did not affect ROC concentration, yet the highest DOC concentration was detected in NS at four soil layers. Aggregate C concentration was the highest in all aggregate-size classes of CH at 0–10 cm depth. In addition, forest type did not alter the proportion of soil water-stable aggregates at four soil layers. However, soil depths significantly affected the distribution of soil aggregates with >0.25 mm aggregates dominating in the topsoils (0–20 cm), but 0.053–2 mm aggregates being dominant in the deep soils (20–60 cm). These results indicate that reforestation and forest type affected soil DOC (0–60 cm) and aggregate C (0–10 cm). Furthermore, soil DOC and aggregate C were more susceptive to reforestation than ROC. The findings suggest that plantations reduce soil DOC concentration, highlighting that C leaching loss may decrease compared with natural recovery. Moreover, C. hystrix plantation may enhance soil C stability by physical protection in topsoil. This study provides valuable information on tree species selection for reforestation concerning soil C sequestration in southern subtropical China.

Successful plant invaders usually exhibit three strategies: Jack-of-all-trades (more robust in stressful sites), Master-of-some (more responsive in favorable sites) and Jack-and-master (both robustness and responsiveness). To revisit these strategies, we examined how soil inorganic nitrogen (N) compositions and levels influence the success of native and invasive plant congeners in the context of plant communities.

We conducted an experiment involving three fixed factors: species origin, N composition and N level. Here, we selected 21 plant species (eight pairs of invasive and native congeners and five non-congeneric natives) to assemble plant communities, which were subject to nine N environments consisting of three N compositions (3:1, 2:2 and 1:3 NO₃−/NH₄+) and three N levels (low, medium and high N). We determined the following metrics: total biomass, relative biomass (a proxy of species success), mortality rate and mortality time.

Across nine N environments, native and invasive congeners exhibited similar total biomass, relative biomass and mortality time, but invaders had a marginally lower mortality rate than natives. Similar success between native and invasive congeners was linked to their similar growth and tolerance. N compositions influenced mortality time and N levels affected the total biomass and relative biomass. Importantly, species origin, N composition and N level interactively affected the total biomass, relative biomass and mortality time. These findings suggest that native and invasive plant congeners may be similarly successful across different N environments, and that inorganic N compositions and levels both contribute to plant invasion success.

Classical theory predicts that herbivores impact herb assemblages and soil nitrogen (N) cycling through selective plant consumption and the deposition of N-rich waste, with effects dependent upon ecosystem N availability. Herbivores are predicted to accelerate N cycling when N availability is high and decelerate cycling when availability is low. However, experimental tests of these theories in natural systems are limited and have yielded contradictory results. California’s widespread chaparral shrublands provide a tractable system in which to test these theories. They are prone to periodic crown fire, which temporarily removes living shrub cover, deposits mineral N on soils and allows diverse herbaceous assemblages to dominate the landscape for 3–5 years. Chaparral is also increasingly vulnerable to herbaceous invasion; mammalian herbivory may limit the establishment of non-native herbs in the shrub understory.

We implemented a 2-year herbivore-exclosure experiment (Hopland, CA) to assess the impact of mammalian herbivory during early post-fire chaparral succession, both on herbaceous plant assemblages and soil N and C cycling. We predicted that, in high-N post-fire conditions, mammalian herbivory would not demonstrate a strong preference for N-fixing herbs, would accelerate N cycling and would reduce the abundance of non-native herbs.

Excluding mammalian herbivores increased herb standing biomass by 54%, but changed neither the relative abundance of N-fixing vs. non-N-fixing herbs nor any measure of N or C cycling. Herbivore impacts on nutrient cycling may not be significant over the 2-year time scale of the experiment and physical effects of herbivore activity could have counteracted the influence of plant litter and animal dung/urine inputs. Mammalian herbivores concentrated their feeding on typical non-native herbs, slightly decreasing their relative abundance; however, mammalian herbivory was not sufficient to stem the invasion of chaparral by invasive herbs or alter C and N cycling over the first 2 years after fire.

Sexual dimorphism is a common trait in plants with sex separation, which could influence female and male functions differently. In a subdioecious population of Dasiphora glabra on the Qinghai-Tibet Plateau, we investigated sexual dimorphism of floral traits and their effects on pollinator visitation, pollen flow and seed production. We also examined differences in genome size of hermaphroditic and dioecious plants.

We examined sexual dimorphism in flower number, flower size, and pollen and ovule production in a subdioecious population of D. glabra. We compared pollinator visitation, pollen dispersal and seed production between sexes. We also examined the genome size of three sex morphs using flow cytometry.

The number of hermaphroditic plants was significantly more than that of male and female plants, and dioecious plants accounted for ca. 40% in the study population. Hermaphroditic plants produced significantly more flowers than male and female plants. Flower size of male flowers was significantly larger than that of female and hermaphroditic flowers. Male flowers did not produce more pollen grains than hermaphroditic flowers, but female flowers produced more ovules than hermaphroditic flowers. Flies were the most frequent flower visitors and preferred large flowers, but their movements between flowers did not show any preference to large flowers. Simulated pollen flows suggested that effective pollen transfer was generally low for both hermaphroditic and male flowers, corresponding to the low seed set of naturally pollinated flowers. DNA contents of male and female plants were ca. four times than those of hermaphroditic plants. These results suggest male and female individuals have undergone polyploidy events and thus are not compatible with hermaphroditic individuals. Sexual dimorphism in floral traits in relation to pollination of dioecious plants might show an advantage in female and male functions, but this advantage is masked largely by low effectiveness of pollen transfer.

Remote sensing (RS) is a technical method for effectively capturing real-world data on a large scale. We aimed to (i) realize the time synchronization of species and environmental variables, and extract variables related to the actual growth of species based on RS in habitat suitability modeling, and (ii) provide a reference for species management.

Taking invasive species Ambrosia artemisiifolia in China as an example for habitat suitability modeling. Temperature and precipitation variables were calculated from the land surface temperature provided by the moderate-resolution imaging spectroradiometer (MODIS), and climate station data, respectively. Besides, other variables that directly affect the growth or reproduction of A. artemisiifolia were also included, such as the relative humidity of the previous year’s flowering period (RHPFP), and the effective UV irradiance reaching the Earth’s surface (UVI). The random forest method was selected to model the habitat suitability. The environmental variables and samples were divided into four-time periods (i.e. 1990–2000, 2001–2005, 2006–2010 and 2011–2016) based on sampling time. Variables from the long-time series of RS (1990–2016) and WorldClim (1960–1990) were also modeled.

It was feasible to extract environmental variables from RS for habitat suitability modeling, and was more accurate than that based on the variables from WorldClim. The potential distribution of A. artemisiifolia in 1990–2000 and 2006–2010 was smaller than that in 2001–2005 and 2011–2016. The precipitation of driest months (bio14), precipitation coefficient of variation (bio15), RHPFP and UVI were the important environmental variables that affect the growth and reproduction of A. artemisiifolia. The results indicated that the time synchronization of species and environmental variables improved the prediction accuracy of A. artemisiifolia, which should be considered in habitat suitability modeling (especially for annual species). This study can provide an important reference for the management and prevention of the spread of A. artemisiifolia.

Plant size, environmental conditions and functional traits are important for plant growth; however, it is less clear which combination of these factors is the most effective for predicting tree growth across ontogenetic stages.

We selected 65 individuals of an evergreen coniferous species, Pinus koraiensis, with diameters at breast height (DBH) from 0.3 to 100 cm in Northeast China. For each individual, we measured the stem radius growth rate (SRGR, µm/year) for the current year, environmental factors (light, soil nutrient and soil water) and functional traits (leaf, branch and root traits).

SRGR increased with DBH when the DBH was lower than 58 cm, whereas it decreased with DBH when the DBH was larger than 58 cm. Structural equation modeling analysis suggested that, when the DBH was 0–15 cm, plant size had a direct negative influence on SRGR and an indirect positive influence on SRGR due to the light intensity above the plant. Plant size had direct positive and negative effects when the DBH was 16–58 cm and 59–100 cm, respectively. When the DBH was larger than 15 cm, soil parameters were more important than light intensity for SRGR. The functional traits selected for use in the best model were changed from the specific leaf area and wood density to the root nitrogen concentration with increasing tree size. In summary, plant size, environmental factors and functional traits jointly shaped tree growth, and their relative influence varied with size, suggesting that the resources limiting tree growth may change from light to soil nutrient with increasing tree size.

Screening tree species in tropical rainforest according to their shade tolerance is important to efficiently manage the native trees of economic significance in secondary forest enrichment regimes. The objective of this study was to determine the whole-plant light compensation point (WPLCP) and compare the phenotypic plasticity in relation to growth and carbon allocation of Cariniana legalis and Gallesia integrifolia seedlings under low light availability.

Seedlings were cultivated for 77 days under conditions of five photosynthetically active radiation (PAR) (0.02, 1.1, 2.3, 4.5 and 5.9 mol photons m−2 day−1) in three replicates. Growth and carbon allocation variables were determined.

Growth rates of C. legalis were higher and lower than those of G. integrifolia under 1.1 and 5.9 mol photons m−2 day−1, respectively. The WPLCP differed significantly between the two species. In accordance with the criteria of the shade tolerance classification for these two tropical tree species, our results showed that C. legalis had lower WPLCP and phenotypic plasticity in terms of higher growth rates and greater shade tolerance than G. integrifolia. From a practical point of view, we demonstrated that the differential linkage between growth and changing PAR between the two species can become a useful tool for comparing and selecting tree species in forest enrichment projects.

The relationships between plant species and soil microorganisms remain indeterminable in different ecosystems worldwide. In karst ecosystems, soil microbial (SM) community structure and their environmental driving factors are poorly explored, and the relationships between plant species and soil microorganisms are unclear. This study aimed to characterize the general patterns of SM community composition and biomass, and to explore the specific tree species and soil physiochemical properties highly related to SM community diversity and biomass in a karst forest.

The effects of tree species on SM community composition and biomass were firstly investigated on the basis of 212 soil samples collected from five dominant tree species (Lithocarpus confinis Huang, Platycarya longipes Wu, Itea yunnanensis Franch., Machilus cavaleriei H. Lév. and Carpinus pubescens Burkill) through phospholipid fatty acid (PLFA) analysis of a karst evergreen and deciduous broad-leaved mixed forest in central Guizhou Province, southwestern China. The relationships between SM community structure and tree species and soil physiochemical properties were statistically analysed.

A total of 132 SM-PLFA biomarkers were detected. The average number of SM-PLFA biomarkers and microbial biomass in each soil sample were 65.97 and 11.22 µg g−1, respectively. Tree species influenced the number of SM-PLFA biomarkers but not the SM biomass. The number of SM-PLFA biomarkers of C. pubescens was significantly higher than that of other species (P < 0.05); the numbers of SM-PLFA biomarkers amongst other species showed no significant difference. Microbial biomass showed no relationships with the soil physiochemical properties of nutrient-rich surface soils but positively correlated (P < 0.05) with soil organic carbon, nitrogen and phosphorus concentrations in deeper soils. The karst forest in the plateau-surface terrain of central Guizhou Province presented a low fungal-to-bacterial ratio, low microbial biomass storage and high microbial community diversity. Specific tree species affect the SM community diversity in this kind of karst forest.

Black spruce (Picea mariana [Mill.] B.S.P.) and white spruce (Picea glauca [Moench] Voss.) are congeneric species. Both are moderately shade tolerant and widely distributed across North American boreal forests.

To understand light effects on their ecophysiological responses to elevated CO₂, 1-year-old seedlings were exposed to 360 µmol mol−1 and 720 µmol mol−1 CO₂ at three light conditions (100%, 50% and 30% of full light in the greenhouse). Foliar gas exchanges were measured in the mid- and late-growing season.

Elevated CO₂ increased net photosynthesis (P_n) and photosynthetic water use efficiency, but it reduced stomatal conductance and transpiration. The stimulation of photosynthesis by elevated CO₂ was greatest at 50% light and smallest at 100%. Photosynthesis, maximum carboxylation rate (V_cmax) and light-saturated rate of electron transport (J_max) all decreased with decreasing light. Elevated CO₂ significantly reduced V_cmax across all light treatments and both species in mid-growing season. However, the effect of elevated CO₂ became insignificant at 30% light later in the growing season, with the response being greater in black spruce than in white spruce. Elevated CO₂ also reduced J_max in white spruce in both measurements while the effect became insignificant at 30% light later in the growing season. However, the effect on black spruce varied with time. Elevated CO₂ reduced J_max in black spruce in mid-growing season in all light treatments and the effect became insignificant at 30% light later in the growing season, while it increased J_max later in the season at 100% and 50% light. These results suggest that both species benefited from elevated CO₂, and that the responses varied with light supply, such that the response was primarily physiological at 100% and 50% light, while it was primarily morphological at 30% light.

Carbon and nutrient physiology of trees at their upper limits have been extensively studied, but those of shrubs at their upper limits have received much less attention. The aim of this study is to examine the general patterns of nonstructural carbohydrates (NSCs), nitrogen (N) and phosphorous (P) in shrubs at the upper limits, and to assess whether such patterns are similar to those in trees at the upper limits.

Across Eurasia, we measured the concentrations of soluble sugars, starch, total NSCs, N and P in leaves, branches and fine roots (<0.5 cm in diameter) of five shrub species growing at both the upper limits and lower elevations in both summer (peak growing season) and winter (dormancy season).

Neither elevation nor season had significant effects on tissue N and P concentrations, except for lower P concentrations in fine roots in winter than in summer. Total NSCs and soluble sugars in branches were significantly higher in winter than in summer. There were significant interactive effects between elevation and season for total NSCs, starch, soluble sugars and the ratio of soluble sugar to starch in fine roots, showing lower soluble sugars and starch in fine roots at the upper limits than at the lower elevations in winter but not in summer. These results suggest that the carbon physiology of roots in winter may play an important role in determining the upward distribution of shrubs, like that in the alpine tree-line trees.

South Africa is mainly dominated by savanna and grasslands ecosystems which have been previously reported to be acidic and nutrient deficient, specifically with regard to phosphorus (P) and nitrogen (N). Mucuna pruriens (L.) DC, commonly known as velvet bean, is an indigenous legume in most African countries and has been reported to withstand these adverse soil conditions. The legume is used in many countries of the world for their medicinal value as well as for soil fertilization purposes. Although there are reports on M. pruriens growth and establishment in nutrient stressed ecosystems, no investigation has been conducted on M. pruriens symbiotic interactions, N source preference and associated growth carbon costs when subjected to P deficiency. In this study, we determined the impact of microbial symbionts on N nutrition and growth carbon costs of M. pruriens under P deficiency.

Microbe inoculation soils were collected from four geographical distinct KwaZulu-Natal locations. Thereafter, seeds were germinated in these natural soils and in early stages of nodule development, then seedlings were transferred in sterile quartz sand and supplied with Long Ashton nutrient media with varying P concentrations.

The 16S RNA sequence results revealed that M. pruriens was nodulated by Burkholderia sp., Paenibacillus sp. and Bacillus irrespective of P concentrations. Even though P deficiency resulted in decreased overall biomass/growth, the root biomass, nodule number and carbon costs increased. In addition, low P supplied saplings showed the highest arbuscular mycorrhiza fungi percentage root colonization. In M. pruriens, nitrogen derived from atmosphere had a positive correlation with P level and the saplings had a dual reliance on atmospheric derived N and soil derived N with increased reliance on soil N in low P supplied plants. Therefore, M. pruriens exhibited different morphological and microbial symbiosis when subjected to P deficiency.

The effects of fertilization on fungal plant pathogens in agricultural soils have been studied extensively. However, we know little about how fertilization affects the relative abundance and richness of soil fungal plant pathogens in natural ecosystems, either through altering the soil properties or plant community composition.

Here, we used data from a 7-year nitrogen (N) addition experiment in an alpine meadow on the Qinghai-Tibetan Plateau to test how N addition affects the relative abundance and richness of soil fungal plant pathogens, as determined using Miseq sequencing of ITS1 gene biomarkers. We also evaluated the relative importance of changes in soil properties versus plant species diversity under N addition.

Using general linear model selection and a piecewise structural equation model, we found that N addition increased the relative abundance of soil fungal plant pathogens by significantly altering soil properties. However, higher host plant species richness led to higher soil fungal plant pathogen richness, even after excluding the effects of N addition. We conclude that the relative abundance and richness of soil fungal plant pathogens are regulated by different mechanisms in the alpine meadow. Continuous worldwide N inputs (through both fertilizer use and nitrogen deposition) not only cause species losses via altered plant species interactions, but also produce changes in soil properties that result in more abundant soil fungal plant pathogens. This increase in pathogen relative abundance may seriously threaten ecosystem health, thus interrupting important ecosystem functions and services.

Climate warming and agricultural non-point source pollution both resulting from anthropogenic activities have been projected to affect plant reproduction and growth in wetlands worldwide. In order to predict and mitigate impacts of these anthropogenic activities, it is important to investigate how marsh plants respond to such environmental changes.

In this study, Bolboschoenus planiculmis, a tuberous sedge with a wide distribution range in Eurasia, was selected to examine the effect of air temperature changes (15, 20 and 25 °C over 24 h; 20/10 and 30/15 °C, day/night) and K supply (0, 1, 3, 9 and 18 mmol/L) on its reproductive and growth traits in climate chambers.

We found that high constant temperatures (20 and 25 °C) were more beneficial for tuberization of B. planiculmis than high alternating temperatures (30/15 °C), whereas aboveground biomass and shoot height were generally largest at high temperatures (30/15 and 25 °C). Both reproductive and growth traits of B. planiculmis showed hump-shaped relationships with K supply, with an optimum K concentration of around 1–3 mmol/L. The combination of high constant temperatures and optimal K concentrations promoted reproductive traits the most, whereas the combination of higher temperatures (30/15 and 25 °C) and K concentrations up to 9 mmol/L increased growth traits only. We therefore conclude that population abundance of B. planiculmis might benefit from global warming and the additional K supply.

Germination is the earliest life-history transition of a plant species. It determines the ecological breadth and geographic ranges of a species and has major effects on its invasion potential. The largest spread of the invasive salt-marsh cordgrass Spartina alterniflora in China, where it extends to latitudes lower than its native range in North America, provides an opportunity to examine germination trait variation across latitudes within and among its invasive and native ranges.

We studied seed germination traits of S. alterniflora using seeds collected from 10 locations across latitudes in its invasive range (China, 20°–40° N) and 16 locations across latitudes in its native range (USA, 27°–43° N) in growth chambers with 0 PSU sterilized distilled water. We further evaluated how climate and tide range in the original locations influenced germination traits.

Native populations showed higher (~10%) germination percentage and significantly higher (~20%) germination index than invasive populations did, but invasive populations germinated significantly earlier (~3 days) than native populations. Germination percentage and germination index increased with latitude in the invasive range but decreased with latitude in the native range. The mean germination time decreased with latitude in the invasive range and paralleled that in the native range. Germination percentage and germination index were negatively correlated with mean daily temperature (Tmean), mean daily maximum temperature (Tmax) and mean daily minimum temperature (Tmin), and inversely correlated with Tmean, Tmax and Tmin in the native range. However, the mean germination time was positively correlated with Tmean, Tmax and Tmean in both ranges. Our results demonstrate that invasive and native populations have evolved different latitudinal clines in germination percentage and index, but the mean germination time of the invasive population mirrored the latitudinal cline observed in the native range, suggesting that germination strategy across latitudes may change during invasion process.