In dry tropical forests, herbaceous species may have dormancy mechanisms and form persistent and transient seed banks in the soil. Evolutionarily acquired, these mechanisms are efficient for the establishment and survival of these herbs, especially in forests with unpredictable climates, such as the Caatinga. Thus, our objective was to verify whether the studied herbaceous species adopt the physical dormancy mechanism and how these natural barriers are overcome, to understand the temporal dynamics existing in the soil seed bank from a Brazilian dry tropical forest.

Seeds of five native herbaceous species from the Caatinga forests were selected and submitted to pre-germinative treatments for verifying the presence of physical dormancy. We collected soil samples in the rainy and dry seasons for four consecutive years and monitored the emergence of the selected herbaceous in the greenhouse. We verified the differences in germination and seed bank emergence in the soil by generalized linear models.

The presence and absence of physical dormancy were observed in seeds from Caatinga herbaceous species. We found intraspecific and interspecific differences in the herbaceous emergence from soil seed banks between years and climatic seasons. In perennial herbs, consecutive lack of emergence between seasons and years was frequent, which suggests a direct relationship with the mechanism of physical dormancy and the environmental conditions necessary to overcome integument barriers. In these species, seed dimorphism and dormancy may confer additional advantages to their survival. Moreover, presenting intermediate levels of physical dormancy in an annual species may be an evolutionary adjustment to rainfall unpredictability. In contrast, we found that the annual herb without dormancy is more sensitive to seasonal and interannual climate changes, as evidenced by the increase and significant reduction of its emergence in the soil seed bank. These differences acquired evolutionarily are advantageous for the establishment of herbaceous populations, mainly in semiarid regions with an unpredictable climate.

Litterfall is a key parameter in forest biogeochemical cycle and fire risk prediction. However, considerable uncertainty remains regarding the litterfall variations with forest ages. Quantifying the interannual variation of forest litterfall is crucial for reducing uncertainties in large-scale litterfall prediction.

Based on the available dataset (N = 318) with continuous multi-year (≥2 years) measurements of litterfall in Chinese planted and secondary forests, coefficient of variation (CV), variation percent (V_P), and the ratio of next-year litterfall to current-year litterfall were used as the indexes to quantify the interannual variability in litterfall.

The interannual variations of litterfall showed a declining trend with increasing age from 1 to 90 years. The litterfall variations were the largest in 1–10 years (mean CV = 23.51% and mean V_P = −28.59% to 20.89%), which were mainly from tree growth (mean ratio of next-year to current-year = 1.20). In 11–40 years, the interannual variations of litterfall gradually decreased but still varied widely, mean CV was ~18% and mean V_P ranged from −17.69% to 21.19%. In 41–90 years, the interannual variations minimized to 8.98% in mean CV and ~8% in mean V_P. As a result, forest litterfall remained relatively low and constant when stand age was larger than 40 years. This result was different from the previous assumptions that forest litterfall reached relatively stable when stand age was larger than 30, 20 or even 15 years. Our findings can improve the knowledge about forest litter ecology and provide the groundwork for carbon budget and biogeochemical cycle models at a large scale.

Harsh environmental conditions in alpine ecosystems shape vegetation structure into patches, where many different plant species cluster and grow together. Yet, which factors are important for the structure and dynamics of such plant–patch networks remains poorly understood. We aim to assess which and how environmental and biotic factors predict the assembly of plant–patch networks along a mountain range.

We examined the distribution of plant species in more than 5500 vegetation patches in 37 Mediterranean alpine grasslands distributed along a 500 m altitudinal gradient (National Park of Sierra Guadarrama, Spain). We established a plant–patch network for each grassland community and analyzed how nestedness and modularity vary with environmental (altitude, insolation and soil conditions) and biotic factors (number of species per plot, mean patch area and total pasture area).

Plant–patch networks showed consistent, non-random patterns characterized by a nested, but not modular, structure, which suggests that positive associations among co-occurring specialists promote their growth within patches as subsets of a pool with more generalist species. Both nestedness and modularity of plant–patch networks varied among grasslands. Specifically, nestedness decreased with increasing species per plot and increased with mean patch area, while it was independent of environmental variables; modularity increased with increasing pasture area and species per plot. The negative relationship between species per plot and nested patterns may be linked to the restricted number of species that can coexist within the same patch at a given size. Moreover, the positive relationship between patch size and nestedness indicates that the growth of rare plant species within vegetation patches occupied by more abundant species is facilitated in bigger rather than smaller patches. Furthermore, these results indicate that the nested assembly of vegetation patches may be independent of abiotic conditions. These findings suggest that large and unfragmented vegetation patches are fundamental for the maintenance of plant diversity in alpine grasslands. Looking at species distribution at fine spatial scales may shed new light on the biotic processes underlying plant network assembly and provide novel ways for conserving biodiversity.

The importance of density-dependent mortality in maintaining tree species diversity is widely accepted. However, density-dependent effects may vary in magnitude and direction with different abiotic conditions in forests. Theoretical predictions surmise that density-dependent effects may vary with soil available nitrogen (AN), but this still needs to be tested.

We analyzed the density-dependent effects on survival of newly germinated seedlings for 18 common species based on a long-term seedling census across environmental gradients in a subtropical forest. We also conducted a root lesion detection experiment for five species to investigate the potential effects of pathogens on variation in density-dependent disease between rich and poor AN environments.

The seedling dynamics analysis revealed that the strength of density-dependent effects increased with AN, shifting from neutral or positive with low AN to negative with high AN. Three of the five tree species had stronger density-dependent effects on root lesions in rich AN environments than in poor AN environments, which is consistent with the results of a long-term seedling dynamics analysis. We also found higher species diversity in rich AN environments, which may be promoted by the stronger negative density-dependent effects. Both the seedling dynamic analysis and root lesion detection experiment revealed stronger negative density-dependent effects in higher AN environment, resulting from stronger disease pressure by soil pathogens. Our study emphasized the importance of considering context dependence when testing the density dependence hypotheses.

The response pattern of terrestrial soil respiration to warming during non-growing seasons is a poorly understood phenomenon, though many believe that these warming effects are potentially significant. This study was conducted in a semiarid temperate steppe to examine the effects of warming during the non-growing seasons on soil respiration and the underlying mechanisms associated therewith.

This experiment was conducted in a semiarid temperate grassland and included 10 paired control and experimental plots. Experimental warming was achieved with open top chambers (OTCs) in October 2014. Soil respiration, soil temperature and soil moisture were measured several times monthly from November 2014 to April 2015 and from November 2015 to April 2016. Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and available nitrogen content of soil were measured from 0 to 20 cm soil depth. Repeated measurement ANOVAs and paired-sample t tests were conducted to document the effect of warming, and the interactions between warming and time on the above variables. Simple regressions were employed to detect the underlying causality for the observed effects.

Soil respiration rate was 0.24 µmol m−2 s−1 in the control plots during the non-growing seasons, which was roughly 14.4% of total soil carbon flux observed during growing seasons. Across the two non-growing seasons, warming treatment significantly increased soil temperature and soil respiration by 1.48°C (P < 0.001) and 42.1% (P < 0.01), respectively, when compared with control plots. Warming slightly, but did not significantly decrease soil moisture by 0.66% in the non-growing seasons from 2015 to 2016. In the non-growing seasons 2015–16, experimental warming significantly elevated MBC and MBN by 19.72% and 20.99% (both P < 0.05), respectively. In addition, soil respiration responses to warming were regulated by changes in soil temperate, MBC and MBN. These findings indicate that changes in non-growing season soil respiration impact other components in the carbon cycle. Additionally, these findings facilitate projections regarding climate change–terrestrial carbon cycling.

Understanding how tree species regulate multiple types of secondary chemicals along elevational gradients is critical for elucidating the physiological and ecological strategies of plants in response to varying biotic and/or abiotic environments. This study aims to examine how Chinese tallow tree (Triadica sebifera) allocates resources to the production of different secondary chemicals in response to varying environments across elevational gradients.

We conducted field surveys of different herbivore feeding guilds and their damage rates on Chinese tallow trees along an elevational gradient in China and measured secondary chemicals (tannins and flavonoids) in damaged and undamaged leaves.

The odds of a leaf being damaged (chewing or scarring) decreased with elevation. Flavonoid concentrations increased with elevation in undamaged leaves but decreased with elevation in damaged leaves, with quercitrin contributing most strongly to this pattern, likely as results of plant responding to changing biotic or abiotic stresses along elevational gradients. Tannin concentrations did not vary with elevation, so undamaged leaves had relatively lower tannin to flavonoid ratios at high elevation than at low elevation. Our study reveals variation in herbivory and contrasting trends in plant secondary metabolism along an elevation gradient and highlights the importance of simultaneously considering multiple types of secondary chemicals in plant physiological and ecological strategies.

Predicting drought consequences on forests and fruit crop plantings requires improved understanding of drought responses of both leaf and fine-root resource acquisitive traits (specific leaf area—SLA, specific root surface area—SRA and specific root length—SRL). We hypothesize their responses are coordinated towards integrated plant resource conservation under severe drought.

We tested the hypothesis with a greenhouse-based drought experiment on saplings of six Prunus hybrids with a priori known contrasting drought sensitivity. Saplings were subjected to either control (100% field capacity) or severe drought stress treatment (33% evapotranspiration of hybrid-specific control plants). Sample collections were carried out at 30 and at 60 days after the start of treatments, for both control and stressed saplings.

No hybrid showed concurrent significant decrease of SLA and SRA (or SRL) under severe drought. The fine-root traits of the six hybrids showed two major drought-response scenarios, in particular: (i) increased root tissue density (RTD) and decreased average root diameter without significant change of SRL and (ii) increased RTD and decreased SRL without significant change of average root diameter. Drought responses of leaf gas exchange, SRA, SRL and RTD were closely correlated along a gradient towards resource conservation from control to drought-stressed plants in all hybrids, which was orthogonal to another gradient characterized by a hybrid-dependent decrease of SLA. These findings highlight (i) the multi-dimensionality of root-trait drought responses, (ii) the decoupling between leaf economics and leaf hydraulics and (iii) the covariation of leaf and root hydraulics in terms of trait drought responses. The study contributes to identifying the origin of the multi-dimensionality of root-trait drought response at intraspecific scale, and highlights differential drought–response combinations of leaf and fine-root traits among hybrids to survive under severe soil drought stress.

The ability to form persistent seed banks is one of the best predictors of species’ potential to establish in new ranges. Wild sunflower is native to North America where the formation of persistent seed banks is promoted by disturbance and it plays a key role on the establishment and persistence of native populations. However, the role of the seed banks on the establishment and persistence of invasive populations has not been studied. Here, we evaluated the role of seed bank and disturbance on the establishment and fitness, and seed persistence in the soil in several sunflower biotypes collected in ruderal (wild Helianthus annuus) and agrestal (natural crop–wild hybrid) habitats of Argentina as well as volunteer populations (progeny of commercial cultivars).

In a seed-bank experiment, we evaluated emergence, survival to reproduction, survival of emerged seedlings, inflorescences per plant and per plot under disturbed and undisturbed conditions over 2 years; in a seed-burial experiment, we evaluated seed persistence in the soil over four springs (6, 18, 30 and 42 months).

Overall, seedling emergence was early in the growing season (during winter), and it was promoted by disturbance, especially in the first year. Despite this, the number of inflorescences per plot was similar under both conditions, especially in ruderals. In the second year, emergence from the seed bank was much lower, but the survival rate was higher. In the seed-burial experiment, genetic differences were observed but seeds of ruderals and agrestals persisted up to 42 months while seeds of the volunteer did not persist longer than 6 months. The agrestal biotype showed an intermediate behavior between ruderals and volunteers in both experiments. Our findings showed that wild and crop–wild sunflower can form persistent seed banks outside its native range and that disturbance may facilitate its establishment in new areas.

Plants can benefit from heterogeneous environments via disproportionately increasing resource harvesting in resource-rich patches. Their initial growing positions with respect to resource patches may thus have important influences on their performance and relative competitive ability. Such impacts may differ between species with contrasting spatial architectures. However, the potential influence of initial growing positions in heterogeneous environment on plant growth and competition has largely been ignored.

We grew the phalanx plant Carex neurocarpa and the guerrilla plant Bolboschoenus planiculmis alone or in competition in a heterogeneous environment consisting of high- and low-nutrient soil patches. In treatments without competition, one ramet of each species was grown in either a high- or a low-nutrient patch in the heterogeneous environment. In treatments with competition, a ramet of the target species was grown in either a high- or a low-nutrient patch, and a ramet of the competitor species was grown in the same patch as the target species or an adjacent patch with a different nutrient level.

Without competition C. neurocarpa produced more biomass and ramets when initially grown in a high-nutrient patch than when initially grown in a low-nutrient patch. With competition, these differences disappeared. Consequently, competitive intensity on C. neurocarpa was higher when it initially grew in a high-nutrient patch than when it initially grew in a low-nutrient patch. These impacts were independent of the initial position of its competitor. By contrast, the initial positions of B. planiculmis did not influence its growth or competitive response. Therefore, in heterogeneous environments, initial growing positions of clonal plants may influence their performance in competition-free environments and may also affect their relative competitive ability, and these effects may depend on spatial architecture of the plants.

We aimed to evaluate how climatic fluctuations influence the plasticity of anatomical vessel traits and the width of annual tree-rings of two relict-endemic Mexican Magnolia species. Notwithstanding, few studies have assessed the drought effect on vessel traits in tropical montane cloud trees of eastern Mexico.

Through digital images of growth rings, we assessed the tree radial growth rate, age of the trees and plasticity in vessel traits regarding climatic fluctuations of the Mexican Magnoliaspecies studied. We compared vessel density, hydraulic diameter and percentage of conductive area in drought years (DY) and non-drought years (NDY) in two Mexican Magnolia species.

For the first time, the plasticity that occurs in porous wood vessel traits to long-term climatic fluctuations was analysed for two endangered Magnolia species (Magnolia vovidesii and M. schiedeana) from two tropical montane cloud forests in Mexico. We found that temperature and precipitation were strongly associated with differences in tree-ring width when DY and NDY were compared. Our analyses revealed that a high plasticity in vessel anatomy of diffuse-porous wood was related to temperature and/or water availability for both Magnolia species studied. We concluded that anatomical adaptations to DY resulted in a substantial reduction in vessel traits when compared with NDY, and that the plastic adaptations played an essential role in water transport and safety for the survival of the studied species during stressful long periods.

Pluchea indica is a mangrove-associate species, known for its medicinal properties in its native range and being invasive in part of its introduced range. This study aimed to assess geographic distribution of genetic variation of this species across its distribution range, identify the factors influencing its genetic structure and use this information to suggest conservation and management strategies in its native and introduced ranges, respectively.

We assessed the genetic diversity and population structure of 348 individuals from 31 populations across its native (Asia) and introduced (USA) ranges for 15 nuclear microsatellite loci. The spatial pattern of genetic variation was investigated at both large and regional spatial scales with the hypothesis that geographic distance and natural geographic barriers would influence the population structure with varying levels of differentiation across spatial scales.

We found relatively high genetic diversity at the population level and pronounced genetic differentiation in P. indica, as compared with the genetic diversity parameters of mangroves and mangrove associates in this region. Most of the populations showed heterozygote deficiency, primarily due to inbreeding and impediment of gene flow. Analysis of population structures at large spatial scale revealed the presence of two major clusters across the species’ natural range separating populations in China from those in Indonesia, Malaysia, Singapore, Thailand, Cambodia and Philippines, and that the USA population might have been introduced from the population cluster in China. Genetic differentiation between populations was also observed at the regional scale. A large number of populations showed evidence of genetic bottleneck, thereby emphasizing the risk of local extinction. Based on these findings, our study recommends in situ conservation strategies, such as to prioritize populations for conservation actions and to maintain genetic diversity.

Bee-pollinated flowers are rarely red, presumably because bees (which lack red receptors) have difficulty detecting red targets. Although the response of bees to red colour has been investigated in lab experiments, most stimuli have been pure red, while the subtle diversity of red as perceived by humans (human-red) has received very limited attention. Here we test the hypothesis that ultraviolet (UV) reflected from human-red flowers enhances their attractiveness to bees, through increased chromatic contrast.

Using Onosma confertum (Boraginaceae), a plant with UV-reflecting red flowers that are pollinated by bumblebees, we investigated the effects of UV reflection on pollinator responses by conducting phenotypic manipulation experiments in the field. Colour preferences of flower-naïve bumblebees were also examined. Colour perception by bumblebees was estimated in terms of chromatic and achromatic contrast, based on two different colour perception models.

We found that both natural and flower-naïve bumblebees strongly preferred visiting UV-reflecting targets compared with UV-absorbing ones. Colour models show that the UV-reflecting flowers exhibit higher spectral purity and higher chromatic contrast against the foliage background, whereas they have similar achromatic contrast in terms of green receptor contrast. These results indicate that the component of UV reflection increases chromatic contrast in O. confertum, enhancing the visual attractiveness of these red flowers to bumblebees. We further infer that the secondary reflectance might be a necessary component in human-red flowers that are primarily pollinated by animals without red receptors, such as bees.

Natural vegetation plays an important role in global carbon cycling and storage. Thus, the Cerrado (Brazilian savannah) is considered a carbon sink because of its intrinsic characteristics. Our aim was to evaluate how the aboveground biomass and biodiversity relationship change between three Cerrado remnants with different protection status: a ‘control area’ (Legal Reserve area), a protected area (PA) and a non-protected area (Non-PA).

All three studied fragments are situated in northern Minas Gerais state, Brazil. We estimated the aboveground carbon stocks based on the forest inventory. We also measured three dimensions of biodiversity metrics for each plot: functional trait dominance, taxonomic diversity and functional diversity. The following functional traits were evaluated for the species: wood density, maximum diameter and seed size. We carried out generalized linear models seeking to evaluate how carbon stocks, community-weighted mean (CWM) trait values, species richness and diversity, and functional diversity indices differ among the remnants.

The Cerrado areas without protection status had lower carbon stocks, species richness, species diversity, functional richness and functional dispersion, whereas both PA and Non-PA had lower CWM maximum diameter and seed size compared with the Legal Reserve control area. Generalized linear models showed that carbon stocks, species and functional richness metrics were correlated within and across sites, and thus, species richness could serve as a good proxy for functional richness and carbon stocks. The carbon stocks were positively driven by species richness and CWM maximum diameter, while they were negatively driven by functional dispersion. Functional richness, species diversity and CWM seed size appeared in the set of best models, but with no significant direct effect on carbon stocks. Thus, we concluded that absence of protection in the Cerrado areas decreases both species richness and carbon stocks.

Alpine forest gaps can control understory ecosystem processes by manipulating hydrothermal dynamics. Here, we aimed to test the role of alpine forest gap disturbance on total phenol loss (TPL) from the decomposing litter of two typical shrub species (willow, Salix paraplesia Schneid., and bamboo, Fargesia nitida(Mitford) Keng f.).

We conducted a field litterbag experiment within a representative fir (Abies faxoniana Rehd.) forest based on ‘gap openness treatments’ (plot positions in the gap included the gap center south, gap center north, canopy edge, expanded edge and closed canopy). The TPL rate and litter surface microbial abundance (fungi and bacteria) of the two shrub species were measured during the following periods over 2 years: snow formation (SF), snow cover (SC), snow melting (ST), the early growing season (EG) and the late growing season (LG).

At the end of the study, we found that snow cover depth, freeze–thaw cycle frequency and the fungal copies g−1 to bacterial copies g−1 ratio had significant effects on litter TPL. The abundances of fungi and bacteria decreased from the gap center to the closed canopy during the SF, SC, ST and LG periods and showed the opposite trend during the EG periods. The rate of TPL among plot positions closely followed the same trend as microbial abundance during the first year of incubation. In addition, both species had higher rates of TPL in the gap center than at other positions during the first winter, first year and entire 2-year period. These findings suggest that alpine forest gap formation accelerates litter TPL, although litter TPL exhibits dual responses to gap disturbance during specific critical periods. In conclusion, reduced snow cover depth and duration during winter warming under projected climate change scenarios or as gaps vanish may slow litter TPL in alpine biomes.

Individual growth constitutes a major component of individual fitness. However, measuring growth rates of herbaceous plants non-destructively at the individual level is notoriously difficult. This study, based on an accurate non-destructive method of aboveground biomass estimation, aims to assess individual relative growth rates (RGRs) of some species, identify its environmental drivers and test its consequences on community patterning. We specifically address three questions: (i) to what extent environmental conditions explain differences in individual plant growth between sites, (ii) what is the magnitude of intraspecific variability of plant individual growth within and between sites and (iii) do species-averaged (dis-)advantage of individual growth compared with the whole vegetation within a site correlate with species ranking at the community level?

We monitored the growth of individuals of four common perennial species in 18 permanent grasslands chosen along a large pedoclimatic gradient located in the Massif Central, France. We measured soil properties, levels of resources and meteorological parameters to characterize environmental conditions at the site level. This design enables us to assess the influence of environmental conditions on individual growth and the relative extent of inter-individual variability of growth explained within and between sites. We determined the ranking of each of the four species in each site with botanical surveys to assess the relationship between species-averaged growth (dis-)advantage relative to the whole community and species rank in the community.

We found that environmental conditions explain a significant proportion of individual growth variability, and that this proportion is strongly variable between species. Light availability was the main driver of plant growth, followed by rainfall amount and potential evapotranspiration, while soil properties had only a slight effect. We further highlighted a moderate to high within-site inter-individual variability of growth. We finally showed that there was no correlation between species ranking and species-averaged individual growth.