Widely accepted universal models and hypotheses such as ‘high vein density-faster growth and higher productivity' hold that high leaf vein density may promote higher coupling efficiency of carbon and water, indicating that rapid individual growth and high stand productivity, have attracted huge interest. However, these models and hypotheses do not include enough gymnosperm samples, especially conifers cultivated in subtropics. We here examined the values and scaling relationships between leaf vein density and leaf functional traits sampled from center region of the distribution range of Cunninghamia lanceolate, which has been well known for rapid growth. We also retrieved an empirical dataset that included photosynthetic, biochemical, anatomical and hydraulic traits of Cunninghamia lanceolata. The leaf vein density (ranging from 0.34 to 1.09 mm mm-2) is extremely low compared to the reported global range (1 to 25 mm mm-2), whereas C. lanceolata is famous for both fast-growing and high-yielding in China for a long time. We further verified that higher vein densities were associated with smaller leaves (r = -0.71, P < 0.001), which is consistent with that found in angiosperms. However, we found that vein density-thickness correlations and leaf lifespan plasticity showed opposite trends for C. lanceolate (negative) when compared with global species (positive), and such relationships may indicate the tradeoffs between functional efficiency and productivities. Our results provide an effective complementary assessment of general growth rules, including evaluation of the influence of regional plant trait characterization, configuration of plant species, and traits efficiency for hydraulic potential.

Hyphae of arbuscular mycorrhizal fungi (AMF) in soil often form complex mycorrhizal networks among roots of same or different plant species for transfer of nutrients from one plant to another. However, the effect of soil nitrogen (N) availability on nutrient transfer between different plant species via common mycorrhizal networks (CMNs) has not been experimentally examined. In order to quantify CMN-mediated nutrient transfer between Leymus chinensis (LC) and Cleistogene squarrosa (CS), two systems, i.e. the CS-LC system (CS and LC were donor and recipient, respectively) and the LC-CS system (LC and CS were donor and recipient, respectively) were established. Stable isotopic ¹⁵N was applied to track N transfer between heterospecific seedlings connected by CMNs under three levels of soil N additions: no N addition control (N0), N addition with 7 mg/kg (N1) and N addition with 14 mg/kg (N2). In the CS-LC system, the highest rate of AMF colonization and hyphal length density (HLD) were found at N1. In contrast, maximum AMF colonization rate and HLD were recorded at N2 in LC-CS system. Consequently, plant biomass was significantly higher under N1 and N2 levels in CS-LC and LC-CS systems, respectively. Moreover, in CS-LC system, ¹⁵N transfer rate ranged from 16% to 61%, with maximum transfer rate at N1. For LC-CS system, ¹⁵N transfer rate was much lower, with the maximum occurring at N0. These findings suggest that CMNs could potentially regulate N transfer from a donor to recipient plant depending upon the strength of individual plant carbon sink.

The stress gradient hypothesis (SGH) proposes that the frequency of positive interactions among plants is increased with stress. However, in alpine meadow ecosystems, the joint effects of herbivore grazing and resource stress on plant-plant interactions remain poorly understood. By investigating the spatial associations of two dominant, widely distributed species—Carex praeclara (unpalatable) and Carum carvi (palatable)—we explored changes in plant-plant interactions at three desertification levels (light, moderate and severe) under grazed and ungrazed conditions to test the generality of the SGH in the desertified alpine meadows on the eastern Qinghai-Tibetan Plateau. Without grazing disturbance, intraspecific interactions of C. praeclara and C. carvi changed from positive to negative, while their interspecific interactions shifted from negative to positive along the desertification gradient from light to severe level. However, intraspecific interactions of C. carvi under grazing remained neutral at all desertification levels, while the net interspecific interactions between these species changed from competitive to facilitative under moderate stress. But, the positive interactions collapsed under severe stress, which is inconsistent with the SGH prediction. Our results reinforced the evidence that livestock grazing strongly influences the balance of intra- and interspecific interactions along the stress gradients in the alpine ecosystems.

Studying the start (SOS) and end (EOS) of the vegetation growing season can improve vegetation prediction under climate change. Climatic factors have temporal effects on vegetation growth, including the no time effect (no), time-lag effect (lag), time-accumulation effect (acc), and both time-lag and -accumulation effects (lagacc). The linear regression equations between SOS/EOS and climatic factors were constructed for the Loess Plateau (LP). Subsequently, we analyzed the effects of single and multiple climatic factors on vegetation phenology under four temporal effect scenarios and investigated the response of vegetation phenology to the time-lag and time-accumulation effects of climatic factors, under the lagacc scenario. Among the four temporal effects, lagacc explained the effects of climate on vegetation phenology to the greatest degree, and it is the optimal temporal effect for simulating the relationship between vegetation phenology and climate on the LP. Moreover, the explanation degrees of multiple climatic factors were higher than those of single climatic factors across different temporal effects and vegetation types. Simultaneously considering multiple climatic factors improved predictability of their impact on vegetation phenology. Under lagacc, responses of SOS to temperature (TMP) and precipitation (PRE) exhibited 1.44 ± 0.43/3.49 ± 0.85 and 1.38 ± 0.30/3.38 ± 0.71 months lag/accumulation, respectively, and responses of EOS to TMP and PRE exhibited 1.35 ± 0.17/2.37 ± 0.34 and 1.59 ± 0.19/4.16 ± 0.50 months lag/accumulation, respectively, across the entire LP. The results show that both lagacc and multiple climatic factors require consideration when establishing relationships between climatic factors and vegetation phenology.

There is a debate about unmatched results between manipulative warming using constant warming rates every year (CW) and long-term observations warming affect temperature sensitivity of flowering phenology. This may be because long-term observations represent the actual yearly increase in temperature (i.e. a yearly stepwise warming rate per year, SW) which would differ from CW and their effects would be regulated by precipitation alteration. We conducted a warming experiment with CW (temperature increase by +1 °C and sustained this elevated temperature for the duration of the study) and SW (temperature increase by + 0.25 °C progressively each year) with precipitation addition in an alpine grassland for four years. Our results showed that neither warming rate affected community flowering phenology. However, precipitation addition advanced onsets of flowering for early-spring flowering (ESF) and midsummer flowering (MSF) groups, and advanced the end date of flowering for ESF but delayed it for the MSF group. Therefore, flowering duration remained stable for the ESF group and prolonged for the MSF group, and further prolonging the flowering duration of the community. There were no interactions between warming rates and precipitation addition on the community’s flowering phenology. A severe drought in a year significantly decreased the maximal number of community flowers in the following year. Therefore, a change in precipitation has a greater effect than warming on the community flowering phenology in the semi-arid alpine grassland.

Seed dormancy ensures seedling establishment in the favorable season in a seasonally changing environment. Korean pine (Pinus koraiensis Sieb. et Zucc.) seeds have morphophysiological dormancy after dispersal in autumn. A small fraction of seeds germinates in the first spring, but most seeds germinate in the second spring following dispersal. It is not clear how dormancy status changes and thus drives germination characteristic. Fresh Korean pine seeds were buried between litterfall and soil in Fenglin National Nature Reserves, Heilongjiang Province, northeastern China, in middle October 2018 and regularly exhumed. Field germination percentage, embryo growth, seed viability and laboratory germination percentage of exhumed seeds were determined. The physiological dormancy part of morphophysiological dormancy was gradually released during the first winter, but reinduced in the first summer following dispersal. The reinduced physiological dormancy was broken again in the second autumn and winter. The morphological dormancy part of morphophysiological dormancy was slowly released over the first summer but rapidly broken during the second early and middle autumn. In the second spring, Korean pine seeds completely escaped from morphophysiological dormancy. The physiological dormancy part of morphophysiological dormancy was completely released, but the morphological dormancy part was still maintained, leading to very low germination in the first spring in the field. Relief of morphophysiological dormancy enables a high percentage of seeds to germinate at relatively low temperature (alternating day/night temperature above 10/5 °C) in the second spring. Korean pine provides an example of the change in dormancy status of seeds with morphophysiological dormancy.

The four alien farmland weeds of genus Veronica (i.e. V. arvensis, V. didyma, V. hederifolia and V. persica) have successfully colonized in China, but caused different ecological consequences in the colonized habitats. However, the key biological traits conferring bioinvasion differences under different light conditions among the four alien species of Veronica remain unknown. A comprehensive contrastive analysis experiment was conducted to assess the contribution of the intensity of photosynthetic and sexual and asexual reproductive traits of the four alien Veronica weeds to their invasion level in both field trial and laboratory. The field survey showed that V. persica had the highest invasion level, followed by V. didyma, V. hederifolia and V. arvensis. Their invasiveness was mainly attributed to photosynthetic-related parameters (LMA) and asexual reproduction traits (the ratio of adventitious roots) out of all the 22 tested indexes. The photosynthetic-related and some asexual reproduction indexes from separate determinations under both sun and shade conditions showed that V. persica was able to adapt to strong illumination but was more tolerant of shade than the other species. This adaptive differentiation to illumination conferred different competitiveness over crops on the four alien Veronica weeds by allocating resources to the biomass of each organ in farmland. It may be concluded that the adaptability to illumination conditions and the asexual reproduction traits may endow their successful invasion and become different important farmland weeds.

Bayesian belief networks (BBNs) have been increasingly used as a potential decision supporting tool useful in conservation management. We assessed the application of the BBN model to support management in conservation planning of Pulsatilla patens (L.) Mill., the endangered plant species on a European scale, as an example. The Bayesian network approach was used to develop a model of the impact of biotic and abiotic variables on the morphological-developmental features and demographic features of the population in northeast Poland. Field data collected from the total number of 47 sites in the 4 largest forest complexes were used to develop a model using GeNIe 2.0. The diagnostic testing and sensitivity analysis indicated that the greatest impact on the population features was the number of competing species in the forest undergrowth. Validation has shown that the developed model is effective for evaluation of the impact of habitat conditions on the population features deciding about the reproduction of this taxon. The BBN model was also used to define optimal habitat conditions ensuring regular growth and development of P. patens. Finally, we demonstrated the protective treatment to help preserving the species considered. Therefore, the developed model is recommended as a potential tool to support decision-making aimed at the conservation planning of endangered plant species.

Only targeted and sustainable management will preserve extensively managed grasslands, one of Europe's most species-rich habitats. Traditionally, largely abandoned irrigation might prove a sustainable management strategy, but the understanding of the interactions among irrigation, soil properties and plant species are low for a generally humid ecoregion. We aimed at advancing our understanding of plant ecology by disentangling plant community responses to traditional lowland meadow irrigation from traditionally low fertilization rates. We studied plant composition and diversity jointly with the underlying links to soil properties (Corg, total N, water holding capacity and mesofaunal activity) and soil nutrients (Nmin, P, K, Mg and B). In a field study, we compared 13 long-term traditionally irrigated and 13 non-irrigated (17 fertilized and 9 non-fertilized) meadows. We surveyed plant diversity, composition and soil nutrients as well as soil properties for 1 year assuming low annual variation. Irrigation and fertilization led to differences in soil properties and soil nutrients without impact on sheer plant species diversity but on plant species composition. Finer grain sizes due to siltation increased water holding capacity and nutrient storage. Hence, resource-acquisitive graminoid species had advantages in irrigated meadows. Thus, irrigation is not only a mean to preserve biodiversity of extensively used meadows of Central Europe but may prove a tool to differentiate between plant functional traits.

To maintain recruitment in orchid populations in an ecosystem setting, we must understand how surrounding floral resources affect fruiting success. We studied fruiting success in two endemic Australian species, Diuris pardina and Glossodia major, in relation to surrounding floral resources. Diuris pardina has a visually deceptive pollination strategy via mimicry of pea flowers, attracting pollinators associated with co-flowering plants of Pultenaea. Glossodia major displays dummy anthers and has a more generalist pollination strategy. We expected fruiting success of both species to positively correlate to conspecific and heterospecific floral density because orchid pollination should be enhanced by the attraction of higher densities of native bees. We expected fruiting success of D. pardina to positively correlate with abundance of Pultenaea flowers. Surveying 18 plots in South Australia, we counted species, individuals and flowers of conspecifics and heterospecifics and returned to count flowers that set fruit. We conducted Pearson correlations between fruiting success and density of conspecific flowers, richness, abundance and Shannon index of surrounding floral resources and floral abundance of individual species. Fruiting success was correlated with conspecific floral density for D. pardina but not G. major. No relationship was found between fruiting success and heterospecific floral resources. Fruiting success of D. pardina was not correlated with abundance of Pultenaea; instead it was positively correlated with the invasive species Lavandula stoechas.

Nutrient resorption in autumn is a key mechanism of perennial plants for nutrient conservation and efficient use in grassland. Grazing effects on plant nutrient resorption may alter root nutrient conservation and affect plant growth in the subsequent spring. There are many studies on nutrient resorption and conservation of plants in grazing grassland, but few studies have investigated the effect of grazing on plant growth in subsequent spring. Taking Stipa grandis, a dominant perennial grass in a semi-arid steppe as a model plant, we examined plant nitrogen (N) and phosphorous (P) resorption traits (resorption efficiency, proficiency and flux) and root nutrient conservation traits (root biomass and nutrient pool) in autumn, and plant growth traits (height, biomass and nutrient pool) in the subsequent spring, in an experimental grassland under four grazing season treatments (i.e. grazing in spring, summer or autumn or no grazing). We found that (i) 51%-66% of N and 58%-80% of P in S. grandis shoots were resorbed in autumn, and the resorption flux was the lowest under autumn grazing, and highest under spring grazing. (ii) Root nutrient conservation traits were significantly reduced by summer grazing, slightly decreased by spring grazing, but not affected by autumn grazing. (iii) Plant growth in next spring was the best under early spring grazing and the worst under autumn grazing, which was mainly affected by soil moisture rather than root nutrient storage. Our study provides insights into the process of plant nutrient cycling and a theoretical basis for establishing grazing system for grassland protection and rational utilization.

Pesticides are widely used to enhance food production on a global scale. However, little information is available on the effects of pesticide application on leaf physiology and phyllosphere bacterial communities of dioecious plants. Therefore, this study aimed to assess the impact of λ-cyhalothrin, a broad-spectrum pesticide, on leaf physiology and phyllosphere bacterial communities in the dioecious Populus cathayana. Physiological leaf traits such as photosynthetic apparatus (net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration (E)) of males were significantly higher than those of females, independent of pesticide use. In contrast, pesticide application significantly reduced the photosynthetic apparatus for both sexes, and the reduction was greater in males relative to females. Also, pesticide application significantly increased peroxidase (POD) activity and malondialdehyde (MDA) content and maintained superoxide dismutase (SOD) activity and total chlorophyll content in leaves of males. The phyllosphere bacteria showed some conserved characteristics, in which, Simpson and Shannon diversity indices were not affected by sex or pesticide application. Phyllosphere bacterial community composition differed between females and males, indicating that intrinsic sex significantly shapes the phyllosphere bacterial community. However, pesticide application significantly increased the relative abundance of Actinobacteria but reduced the relative abundance of Proteobacteria. Principal component analysis showed associations between leaf physiology and specific bacterial taxa. For instance, Proteobacteria negatively correlated with leaf SOD activity and MDA content, while Actinobacteria showed an opposite pattern. Our study highlights sex-specific phyllosphere bacterial community composition and leaf physiological traits in dioecious plants.

Grazing exclusion using fencing has been considered an effective means of vegetation restoration in degraded grasslands. Increased plant growth during recovery requires more nitrogen (N), which is a major limiting factor in northern China. It remains unclear whether soil N supply in this region can support long-term vegetation restoration. In this study, a field inventory was conducted in seven temperate grasslands in northern China. At each site, grassland outside of the fencing experienced continuous grazing, whereas that within the fencing was protected. Results showed that grazing exclusion significantly increased aboveground biomass, species richness and the Shannon-Wiener diversity index by 126.2%, 42.6% and 18.8%, respectively. Grazing exclusion reduced the concentrations of nitrate and total inorganic N by 51.9% and 21.0%, respectively, suggesting that there may be a mismatch between N supply and plant demand during the growing season. The aboveground biomass, species richness and Shannon-Wiener diversity index in the restored grasslands were positively correlated with legume dominance within the community. These results indicate that the vegetation restoration in temperate grasslands could be constrained by soil N availability, which may be supplemented through biological N fixation.

Abstract: Plant-arbuscular mycorrhizal fungal (AMF) associations can mediate soil resources among competing plants to influence plant resource capture and fitness, making AMF a potential agent of plant coexistence. We assessed plant coexistence, via niche and fitness differences, using six plant species varying in their mycorrhizal status. We grew the species in 15 competitive pairs with or without AMF. Effects of AMF on coexistence were determined by parametrizing pair-wise Lotka-Volterra plant competition models. Responses of the six plant species to AMF were determined by comparing the shoot biomass of single plants grown in the absence of any competition with AMF to the shoot biomass without AMF. The inoculation with AMF reduced the fitness differences between competitors, but the degree of AMF-mediated coexistence depended on the identity of the competing plant species. A greater AMF response difference between competing plant species reduced niche overlap and increased coexistence. These results show that while AMF generally reduce fitness differences, the equalizing effect of AMF is not always strong enough to overcome a competitive imbalance due to niche overlap and thus does not always lead to coexistence. Instead, it is the intrinsic growth response of different plant species to AMF, which can predict reduced niche overlap that in turn leads to coexistence. This implies that mycorrhizal dependence is a plant strategy to reduce niche overlap with competitors, thus allowing for greater coexistence.

Multiple elements are critical for plant growth and survival, community structure and vegetation function. Chemical diversity, defined as the ranges in element concentrations of plant species within communities, could provide essential insights into plant nutrient strategies and community assembly rules. However, little is known about the chemical diversity of multi-elements besides N and P, and current understanding of chemical diversity is largely based on aboveground plant traits. We investigated understory plant communities in forest swamps along a local soil chemical gradient and determined 11 major and trace elements in leaves and roots of dominant and subordinate plants. Using n-dimensional hypervolume, we examined the changes in leaf and root chemical diversity and their linkages with soil properties. Plant chemical diversity decreased significantly with soil Al, Mn, Mg and Zn concentrations, but showed no relationships with soil N, P, K, Na, and Fe concentrations, soil pH and C:N. These patterns also held after controlling for species richness and soil moisture. Furthermore, leaf and root chemical diversity was positively correlated and showed similar relationships with soil factors. Root chemical diversity was not significantly higher than leaf chemical diversity. Our results emphasized the important role of soil trace elements for plant chemical diversity along the local soil chemical gradient. Similar patterns and extent of leaf and root chemical diversity may indicate similar local-scale environmental constraint on aboveand belowground plant chemical diversity. These findings have important implications for plant community assembly and ecosystem functioning influenced by soil nutrient changes.

The rapid uplift of the Qinghai-Tibet Plateau and its aridification has significantly affected the distribution and community structure of the plants in these regions. However, most of the studies have focussed on vascular plants, and it has been unclear whether bryophytes, which are haploid plants, had similar historical population dynamics to other vascular plants during the dramatic geological and climatic environment changes of the Quaternary. This study used Syntrichia caninervis Mitt as the research object and investigated its genetic variation, differentiation and population dynamic history in China. We genotyped 27 populations throughout the distributional range of S. caninervis using two chloroplast DNA regions and 19 nuclear microsatellite loci and supplemented these data with ecological niche modelling of the potential distribution areas from the last interglacial period. The results showed that genetic data consistently identified three clades: the Qinghai-Tibet Plateau, Pamir Plateau-TienShan and Central Asia. The genetic variation of Syntrichia caninervis mainly occurred within populations and in the populations within a specific region. However, there was a significant gene exchange between the different regions. S. caninervis may have expanded during the glacial period and shrank during the interglacial period. This study provides new evidence for the dynamic population history of drought-tolerant bryophytes in response to severe environmental changes during the Quaternary glacial and interglacial cycles.