Among terrestrial ecosystems, coastal sandy dunes are particularly prone to alien plant invasion. Many studies related the invasion of dune habitats to anthropic causes, but less is known about the role of soil properties and plant traits in plant invasion. In this study, we tested the relationships between soil features and alien plant invasion in dune systems, focusing on the interplay between soil nutrients, soil salinity and plant functional traits.

Study sites were sandy barrier islands of the Marano and Grado lagoon (northern Adriatic Sea). One hundred plots (4 m × 4 m) were selected within 10 areas according to the main habitats occurring along the ecological gradient of dune system (foredune, backdune and saltmarsh). In each plot, we recorded all plant species occurrence and abundance and we collected a soil core. For each soil sample, soil texture, conductivity (as proxy of soil salinity), organic carbon and nitrogen content were analyzed and related to the species number and cover of native and alien plants. Variation of main reproductive and vegetative functional traits among habitats was also analyzed for both alien and native species.

Soil properties were strongly related to overall plant diversity, by differently affecting alien and native species pools. In backdune, the most invaded habitat, a high soil conductivity limited the number of alien species, whereas the content of soil organic carbon increased along with alien plant abundance, suggesting also the occurrence of potential feedback processes between plant invasion and soil. We found a significant convergence between native and alien plant functional trait spectra only in backdune habitat, where environmental conditions ameliorate and plant competition increases. Our findings suggest that in harsh conditions only native specialized plants can thrive while at intermediate conditions, soil properties gradient acts in synergy with plant traits to curb/facilitate alien plant richness.

Global change factors (e.g. warming and nitrogen deposition) may influence biological invasions, but how these factors may influence the performance of invasive species and further mediate the interactions with native competitors remain still unknown.

Here, we conducted a 5-month greenhouse experiment to examine the effects of warming (using open-top chambers, +0.62°C) and N addition (adding NH₄NO₃ at a rate of 4.2 g m−2) on the performance of the native and invasive populations of an invasive species Plantago virginica in competition with a native Plantago asiatica.

Under warming treatment and its interaction with nitrogen addition treatment (W × N), invasive and native populations of P. virginica had different biomass allocation strategies to compete with native competitor P. asiatica. Native population of P. virginica (PV-Na) increased more below-ground biomass, whereas those from the invasive population (PV-In) increased more above-ground biomass. We also found that invasive species P. virginica had stronger responses to warming and N addition than the native species P. asiatica. The competitive ability of the invasive plants was significantly reduced by warming which indicated that the invasive plant were much stronger sensitivity to elevated temperature than native plant. Similarly, N addition and W × N reduced the competitive response of PV-In in below-ground biomass, but increased the competitive response of PV-Na in above-ground and total biomass when they grew with the P. asiatica. The results show that P. virginica have occurred differential biomass allocation strategies during its invasions and invasive population exhibit flexible competition ability to adapt to environmental changes (especially warming). These findings may potentially help to predict plant invasions and make management strategies in a world with changing climate.

Drought stress and the degree of drought severity are predicted to rise under highly variable patterns of precipitation due to climate change, while the capacity of trees to cope with drought recovery through physiological and biochemical adjustment remains unclear. We aimed to examine the coupling of physiology and biochemistry in trees during drought and the following recovery.

Potted seedlings of Cinnamomum camphora were grown under well watered conditions prior to the experimental drought stress, which was initiated by withholding water. Seedlings were rewatered following attainment of two drought severities: mild drought (stomatal closure) and moderate drought (ψ_xylem = −1.5 MPa). We measured leaf-level water potential, gas exchange (photosynthesis and stomatal conductance), abscisic acid (ABA), proline and non-structural carbohydrates (NSCs) concentrations in seedlings of C. camphora during drought and a 4-day recovery.

We found that drought severity largely determined physiological and biochemical responses and affected the rate of recovery. Stomatal closure occurred at the mild drought stress, accompanied with ABA accumulation in leaves and decline in water potential, while leaf proline accumulation and variable NSC were evident at the moderate drought stress. More severe drought stress led to delayed recovery of gas exchange, but it did not have significant effect on water potential recovery. The relationships of water potential and gas exchange differed during drought stress and post-drought recovery. There was tight coupling between water potential and gas exchange during drought, but not during rewatering due to high ABA accumulation in leaves, thereby delaying recovery of stomatal conductance. Our results demonstrate that ABA could be an important factor in delaying the recovery of stomatal conductance following rewatering and after water potential recovery of C. camphora. Furthermore, greater drought severity had significant impacts on the rate of recovery of tree physiology and biochemistry.

Populus deltoides and P. euramericana are widely used in China as major forestry species. At present, little is known about their responses to nitrogen (N) deficiency when grown in monocultures or mixed plantations. The aim of this investigation was to analyze the growth, and morphological and physiological responses of P. deltoides and P. euramericana to different N levels under competition conditions.

We employed two Populus species (P. deltoides and P. euramericana) to discover how N deficiency affects plant traits under different competition types (P. deltoides × P. deltoides, intraspecific competition; P. euramericana × P. euramericana, intraspecific competition; P. deltoides × P. euramericana, interspecific competition). Potted seedlings were exposed to two N levels (normal N, N deficiency), and nitrogen- and competition-driven differences in growth, morphology and physiology were examined.

Under normal N conditions, interspecific competition significantly decreased the total root weight, root mass fraction (RMF), root–shoot ratio (R/S) and carbon/nitrogen ratio (C/N), and increased the leaf dry weight, leaf mass fraction and total leaf area of P. euramericana compared with intraspecific competition. The same conditions significantly affected the growth and morphological variables of P. deltoides, except for the dry weight of fine roots, R/S, specific leaf area, RMF, total nitrogen content and C/N compared with intraspecific competition. In addition, chlorophyll a (Chla), total chlorophyll (Tchl), carotenoid contents (Caro) and the carbon isotope composition (δ 13C) of P. deltoides were significantly lower in interspecific competition than in intraspecific competition, but no difference was detected in P. euramericana. The effects of N deficiency on P. deltoides under intraspecific competition were stronger than under interspecific competition. In contrast, the effects of N deficiency on P. euramericana between intraspecific and interspecific competition were not significantly different. These results suggest that under normal N condition, P. deltoides is expected to gain an advantage in monocultures rather than in mixtures with P. euramericana. Under N deficiency, the growth performance of P. euramericana was more stable than that of P. deltoides under both cultivation modes.

Grasslands are globally threatened by climate changes and unsustainable land-use, which often cause transitions among alternative stable states, and even catastrophic transition to desertification. Spatial vegetation patch configurations have been shown to signify such transitions at large spatial scale. Here, we demonstrate how small-scale patch configurations can also indicate state transitions.

The whole spatial series of degradation successions were chosen in alpine grasslands characterized as seven typical communities. Patch numbers, and perimeter and cover of each patch were recorded using adjacent quadrats along transects in each type of the communities. Species abundance within each patch was measured.

Across seven grazing-induced degradation stages in the world’s largest expanse of grassland, from dense ungrazed turf to bare black-soil crust, patch numbers and perimeters first increased as patch cover decreased. Numbers and perimeters then decreased rapidly beyond an intersection point at 68% of initial continuous vegetation cover. Around this point, the vegetation fluctuated back and forth between the sedge-dominated grassland breaking-up phase and the forb-dominated phase, suggesting impending shift of grassland state. This study thus demonstrates how ground-based small-scale vegetation surveys can provide a quantitative, easy-to-use signals for vegetation degradation, with promise for detecting the catastrophic transition to desertification.

Climate warming and increasing nitrogen (N) deposition have influenced plant nutrient status and thus plant carbon (C) fixation and vegetation composition in boreal peatlands. Phenols, which are secondary metabolites in plants for defense and adaptation, also play important roles in regulating peatland C dynamics due to their anti-decomposition properties. However, how the phenolic levels of different functional types of plants vary depending on nutrient availability remain unclear in boreal peatlands.

Here, we investigated total phenols contents (TPC) and total tannins contents in leaves of 11 plant species in 18 peatlands of the Great Hing’an Mountains area in northeastern China, and examined their variations with leaf N and phosphorus (P) and underlying mechanisms.

Shrubs had higher TPC than graminoids, indicating less C allocation to defense and less uptake of organic N in faster-growing and nonmycorrhizal graminoids than in slower-growing and mycorrhizal shrubs. For shrubs, leaf TPC decreased with increasing N contents but was not influenced by changing leaf phosphorus (P) contents, which suggested that shrubs would reduce the C investment for defense with increasing N availability. Differently, leaf TPC of graminoids increased with leaf N contents and decreased with leaf P contents. As graminoids are more N-limited and less P-limited, we inferred that graminoids would increase the defensive C investment under increased nutrient availability. We concluded that shrubs would invest more C in growth than in defense with increasing N availability, but it was just opposite for graminoids, which might be an important mechanism to explain the resource competition and encroachment of shrubs in boreal peatlands in the context of climate warming and ever-increasing N deposition.

Management of silvo-pastoral systems in planted and natural forests in semi-arid Mediterranean regions often employs seasonal night corrals for animal protection. This management system changes the spatial distribution of animal excreta, resulting in a net transfer of soil mineral resources and their accumulation in the corrals. After abandonment, corrals are colonized by ruderal species, becoming focal sources for their spread in the forest. We aimed to implement a rational management of seasonal sheep corrals based on a better understanding of the vegetation processes occurring in abandoned corrals, in order to alleviate their negative impact in the forest.

Relationships between temporal changes in the vegetation, the soil seed-bank and levels of soil nutrients were studied in a chronosequence of abandoned sheep corrals and compared with nearby reference plots in planted Eucalyptus forests grazed by sheep in the semi-arid North-Western Negev, Israel. The region has a bi-seasonal Mediterranean climate, with high dominance of annual species in the grazing range.

Abandoned sheep corrals were colonized by seeds of ruderals originating in older abandoned corrals. Subsequent successional changes occur at a slow rate, driven by the depletion of soil resources in the abandoned corrals, and were still in progress 20 years after abandonment. Ruderals were gradually replaced, first by taller grasses and followed by short grasses, but most forbs and particularly geophytes did not recover during this period. Recovery of the original herbaceous vegetation in the corrals was through seed dispersal from the surrounding vegetation, not from the original soil seed-bank remaining in the corrals after abandonment. Ruderal species in the grazed, planted forests behave as patch-tracking metapopulations. Their persistency depends on constant creation of new corrals compensating for the gradually dwindling populations in older abandoned corrals, and on the availability of dispersal vectors.

In forest ecosystems, different types of regression models have been frequently used for the estimation of aboveground biomass, where Ordinary Least Squares regression models (OLS) are the most common prediction models. Yet, the relative performance of Bayesian and OLS models in predicting aboveground biomass of shrubs, especially multi-stem shrubs, has relatively been less studied in forests.

In this study, we developed the biomass prediction models for Caragana microphylla Lam. which is a widely distributed multi-stems shrub, and contributes to the decrease of wind erosion and the fixation of sand dunes in the Horqin Sand Land, one of the largest sand lands in China. We developed six types of formulations under the framework of the regression models, and then, selected the best model based on specific criteria. Consequently, we estimated the parameters of the best model with OLS and Bayesian methods with training and test data under different sample sizes with the bootstrap method. Lastly, we compared the performance of the OLS and Bayesian models in predicting the aboveground biomass of C. microphylla.

The performance of the allometric equation (power=1) was best among six types of equations, even though all of those models were significant. The results showed that mean squared error (MSE) of test data with non-informative prior Bayesian method (NPB) and the informative prior Bayesian method (IPB) was lower than with the OLS method. Among the tested predictors (i.e. plant height and basal diameter), we found that basal diameter was not a significant predictor either in OLS or Bayesian methods, indicating that suitable predictors and well-fitted models should be seriously considered. This study highlights that Bayesian methods, the bootstrap method and the type of allometric equation could help to improve the model accuracy in predicting shrub biomass in sandy lands.

Multi-stemming supports plants’ resilience to disturbances and then contributes to soil stabilization and forest function, especially in mountain habitats. Many questions remain about (1) the ontogenetic phase at which multiple stems can occur; (2) how habitat drivers affect multi-stemming and (3) whether ontogenetic phase and habitat drivers interact. We asked these questions for Quercus glauca (ring-cupped oak), the dominant species and sprouter across large warm-temperate areas of Asia; its multi-stemmed trees reflect individual survival, population regeneration, and forest ecosystem stability.

In a 5-ha permanent plot of subtropical evergreen broad-leaved forest in eastern China, we examined the temporal patterns and spatial distribution of multi–stemmed trees of Q. glauca within 99 quadrats of 20 m × 20 m.

There were three temporal modes for multi-stemming among the Q. glauca trees and most of them appeared to produce multiple stems from an early stage. Environmental disturbances related to slope convexity appear to be the main drivers of multi-stemming of Q. glauca. Moreover, the closer to the ridge, the earlier the multi-stemming occurs. Thus, also for other woody species in other forests and climate zones, ontogeny and environmental drivers promoting disturbance (not only geomorphology, but also extreme weather events, soil drought, fire), as well as soil fertility, need to be considered in combination to better understand multi-stemming and its consequences for community structure.

Anthropogenic climate change is predicted to increase mean temperatures and rainfall seasonality. How tropical rainforest species will respond to this climate change remains uncertain. Here we analyzed the effects of a 4-year experimental throughfall exclusion on an Australian endemic palm (Normambya normanbyi) in the Daintree rainforest of North Queensland, Australia. We aimed to understand the impact of a simulated reduction in rainfall on the species’ physiological processes and fruiting phenology.

We examined the fruiting phenology and ecophysiology of this locally abundant palm to determine the ecological responses of the species to drought. Soil water availability was reduced overall by ~30% under a throughfall exclusion experiment (TFE), established in May 2015. We monitored monthly fruiting activity for 8 years in total (2009 - 2018), including four years prior to the onset of the TFE. In the most recent year of the study, we measured physiological parameters including photosynthetic rate, stomatal conductance and carbon stable isotopes (δ 13C, an integrated measure of water use efficiency) from young and mature leaves in both the dry and wet seasons.

We determined that the monthly fruiting activity of all palms was primarily driven by photoperiod, mean solar radiation and mean temperature. However, individuals exposed to lower soil moisture in the TFE decreased significantly in fruiting activity, photosynthetic rate and stomatal conductance. We found that these measures of physiological performance were affected by the TFE, season and the interaction of the two. Recovery of fruiting activity in the TFE palms was observed in 2018, when there was an increase in shallow soil moisture compared to previous years in the treatment. Our findings suggest that palms, such as the N. normanbyi, will be sensitive to future climate change with long-term monitoring recommended to determine population-scale impacts.

The last years, Central European forests have suffered from drought as a direct consequence of climate change. All these forests have a long management history and it lies in the landowner’s responsibility to replant damaged forests. Hence, landowners and the government are searching currently for species suitable to replant in areas affected by tree die-offs. It is a matter of fact that good knowledge of drought resistance of species is a critical measure for the current replanting efforts. We determined a widely recognized trait for leaf drought tolerance (leaf water potential at turgor loss point at full hydration, π_tlp) in 41 woody species native or introduced in Central Europe. The osmometric rapid assessment method was used to measure the leaf osmotic potential at full hydration (π_osm) of sun-exposed leaves and converted to π_tlp. Mean π_tlp of the native species was −2.33 ± 0.33 MPa. The less negative π_tlp was found in the introduced species Aesculus hypocastania and was at −1.70 ± 0.11 MPa. The most negative π_tlp, and thus the potentially highest drought tolerance, were found in the introduced species Pseudotsuga menzesii and was at −3.02 ± 0.14 MPa. High or less negative π_tlp is associated with lower drought tolerance, whereas low or more negative π_tlp stands for higher resistance to drought stress. For example, the two native species Illex aquifolium and Alnus glustinosa are species naturally associated with moist habitats and are characterized by the least negative π_tlp of −1.75 ± 0.02 and −1.76 ± 0.03 MPa, respectively.

Soil lead contamination has become increasingly serious and phytoremediation can provide an effective way to reclaim the contaminated soils. This study aims to examine the growth, lead resistance and lead accumulation of mulberry (Morus alba L.) seedlings at four levels of soil lead contamination with or without biochar addition under normal or alternative partial root-zone irrigation (APRI).

We conducted a three-factor greenhouse experiment with biochar (with vs. without biochar addition), irrigation method (APRI vs. normal irrigation) and four levels of soil lead (0, 50, 200 and 800 mg·kg−1). The performance of the seedlings under different treatments was evaluated by measuring growth traits, osmotic substances, antioxidant enzymes and lead accumulation and translocation.

The results reveal that mulberry had a strong ability to acclimate to soil lead contamination, and that biochar and APRI synergistically increased the biomass and surface area of absorption root across all levels of soil lead. The seedlings were able to resist the severe soil lead contamination (800 mg·kg−1 Pb) by adjusting glutathione metabolism, and enhancing the osmotic and oxidative regulating capacity via increasing proline content and the peroxidase activity. Lead ions in the seedlings were primarily concentrated in roots and exhibited a dose–effect associated with the lead concentration in the soil. Pb, biochar and ARPI interactively affected Pb concentrations in leaves and roots, translocation factor and bioconcentration. Our results suggest that planting mulberry trees in combination with biochar addition and APRI can be used to effectively remediate lead-contaminated soils.

Many wetlands are polluted with both nutrients and toxic metals and vegetated largely by clonal plants. We hypothesized that eutrophication and clonal integration can increase phytoremediation of toxic metal pollution by increasing plant growth, even under the stress imposed by toxicity.

To test this hypothesis, single ramets of the common, widespread, floating, stoloniferous plant Pistia stratiotes L., were grown for 42 days at two levels of nutrient availability with and without 0.6 mg L−1 cadmium. Ramets were either severed from their vegetative offspring to prevent clonal integration or left connected, and severed offspring were either removed to eliminate intraclonal competition or left in place.

Plants subjected to cadmium addition accumulated almost twice as much dry mass if given the higher nutrient level, due mainly to a doubling of the number of clonal offspring. Severance had little effect on the final mass of the parent plus offspring ramets. Removing offspring following severance had no effect on the final mass of the parental ramet in the presence of added cadmium, but it did increase the final mass of the parent in the absence of cadmium. These results support the hypothesis that eutrophication can increase remediation of toxic metal pollution by aquatic macrophytes but provided no evidence that clonal integration can affect remediation. Species such as P. stratiotes may help remediate co-pollution of wetlands with toxic metals and nutrients, and fragmentation of clones may not affect their remediation capacity.

In desert ecosystems, water is a restricting factor for plant growth and vegetation dynamics. The relatively stable water source from deep soil profile or groundwater is important for plant survival during drought. Understanding water use strategy of endangered species, in desert ecosystem is essential for their conservation and restoration such as Ammopiptanthus mongolicus on the Mongolian Plateau.

The stable isotope method of δD and δ 18O was used to examine the main water sources of A. mongolicus and two companion shrubs, e.g. Artemisia ordosica and Artemisia xerophytica. The contribution of different water sources to each species was calculated by IsoSource model. Leaf δ 13C was used to compare long-term water use efficiency of three shrubs. Soil moisture and root distribution of three shrubs was measured to explain plant water use strategy.

The results showed that A. mongolicus relied on groundwater and 150–200 cm deep soil water, with the former contributing to almost half of its total water source. Artemisia ordosica mainly used 150–200 cm deep soil water, but also used shallow soil water within 100 cm in summer and autumn. Artemisia xerophytica mainly used 150–200 cm deep soil water and groundwater, with the latter contributing to about 30%–60% of its total water source. The three shrubs had dimorphic or deep root systems, which are in accord with their water sources. The WUE in the evergreen shrub A. mongolicus was higher than in two deciduous Artemisia shrubs, which may be an adaptive advantage in desert ecosystem. Therefore, groundwater is an important water source for the endangered shrub A. mongolicus in a drought year on Mongolian Plateau. Ammopiptanthus mongolicus and two Artemisia shrubs competed for deep soil water and groundwater.