A plethora of theories explain species invasion, yet when tested in isolation, support or falsification becomes contingent on study species, system and approach. Our objective was to examine community-level species invasion as a function of multiple competing hypotheses.

We used data from >3500 woodland plant species in 2750 plots in 49 national parks in eastern US deciduous forests to test multiple competing theories of species invasion: competition, empty niche, propagule pressure and latitude matching. We also tested interactions with residence time to account for non-native species naturalization and spread since arrival.

The non-native herbs generally thrived at latitudes similar to those from which they originated, but not necessarily where they were originally introduced to the eastern US. Overall, we found that each hypothesis explained at least some aspect of woodland plant species invasion, but examining them simultaneously allowed assessment of their relative strengths and interactions. Our results suggested that residence time is a strong predictor of non-native woodland plant success, particularly as it interacts with other mechanisms of invasion, such as competition (abundance of native woodland plants), climate matching (similar invaded latitude as home range), propagule pressure (distance to putative seed sources) and empty niche (relatedness to native plants). We found that initial barriers, such as distance from propagule source or suboptimal habitat, were overcome, as was resistance from native relatives. However, the biggest challenge for the non-native woodland plants appeared to be time, as they declined after ~1 to 2 centuries.

Understanding tree species richness at a global scale and the origin and maintenance of patterns of tree species richness across the world is crucial to preserving tree species diversity. The recently published global tree database (i.e. GlobalTreeSearch) is the only source with tree lists at both global and national scales. However, our review and assessment show that many species included in GlobalTreeSearch are not tree species. In addition, several thousands of tree species in the botanical literature have not been included in GlobalTreeSearch. The exact number of tree species in the world remains unknown. This study aims to correct errors with GlobalTreeSearch and to estimate the number of tree species in the world based on a large number of regional floras.

We standardized nomenclature and spellings of the species names according to The Plant List. We used 62 floristic sources, along with plant growth form and height, to assess the GlobalTreeSearch species checklist and to determine the degree to which GlobalTreeSearch incorrectly treated non-tree species as tree species.

Based on our review on 60.8% of the species in the GlobalTreeSearch database and the number of additional tree species that we have found from 62 continental, national, regional and local floristic sources, we found that about 8.7% of the species included in GlobalTreeSearch are not tree species (they are herbs, shrubs or vines). We estimate that there would be about 61 000 tree species (including approximately 5500 species that are primarily shrubs but occasionally trees) in the world.

Plants play an important role in ecosystem processes. Functional meaning of trait variation in wide environmental gradients is well known but is scarcely known across narrow gradients. We analyze the variation of morphological, physical and chemical traits of dominant plant species and the potential rates of dry mass loss and N release/immobilization during senesced leaf decomposition of these species across a narrow aridity gradient, and to identify indicative traits useful to set species functional groups sharing decomposition patterns.

We analyzed the variation of morphological, physical and chemical traits (specific leaf area, seed mass, N and soluble phenols in green and senesced leaves, plant height) in dominant plant species at 12 sites across an aridity gradient in northern Patagonia, Argentina. We collected senesced leaves of each plant species at each site and used them to estimate the potential rates of dry mass loss and N release/immobilization from decomposing senesced leaves in a microcosm experiment. We analyzed the variation of plant traits and decomposition rates across the aridity gradient. We grouped plants species according to growth forms (perennial grasses, deciduous shrubs, evergreen shrubs) and different combinations of morpho-physical and chemical traits of green and senesced leaves and compared the potential rates of dry mass loss and N release/immobilization during leaf decomposition among these groups delimited by each grouping criteria.

Plant traits did not vary across the aridity gradient. The potential rate of dry mass loss was positively related to aridity, while the potential rate of N release/immobilization did not vary across the gradient. Grouping species by separately morpho-physical and chemical traits resulted in a large overlapping in mean values of decomposition rates among groups. In contrast, plant groupings based on growth forms and those including all morpho-physical and chemical traits of green or senesced leaves yielded groups with differentiated rates of decomposition processes. The two latter groupings clustered species from more than one growth form indicating some overlapping in the rates of decomposition processes among species of different growth forms. Among traits, N concentration in senesced leaves and plant height explained the highest variation in decomposition rates being positively related to potential rates of dry mass loss and N release/immobilization. We concluded that plant groupings based on morpho-physical and chemical traits of either green or senesced leaves may be more powerful to differentiate functional species groups sharing decomposition patterns than the growth form grouping. Moreover, plant height and N concentration in senesced leaves may be considered relevant synthetic functional traits in relation to decomposition processes in narrow aridity gradients.

South American Pampa grasslands are habitats of great conservation interest, with a distinct and rich flora, but have been intensely converted to other land uses, including tree plantations. While necessity for restoration grows, no information on restoration potential of grasslands after afforestation exists. Here, we aim at analyzing composition and structure of grassland vegetation with a history of eucalyptus plantations in order to assess recovery potential of these areas. We hypothesized that areas with history of eucalyptus would differ from reference grasslands with no history of land-use change in terms of floristic and functional composition and would present lower species richness.

Our study region comprised four sites in the southeastern part of the Pampa biome, in the coastal plain in the extreme south of Brazil, always with sites with long (50 years) history of eucalyptus plantation and reference grassland. We sampled vegetation at post-eucalyptus sites (with and without resprouting) 10 years after clearclutting and in natural grasslands. We analyzed data by analysis of variance and ordination techniques, considering compositional parameters and life forms, and indicator species analysis.

Species richness and vegetation cover were higher in reference grassland than in resprout areas but did not differ from post-eucalyptus areas. Exotic species cover was significantly higher in areas with afforestation history. In terms of total composition, natural grasslands differed significantly from areas with past plantation use. Indicator species analyses revealed considerable differences between grassland types. In conclusion, vegetation development led to grassland communities that are still quite distinct from reference sites. Likely, the specificity of grassland management has a high importance in defining vegetation trajectories in time and importance for grassland recovery, and restoration needs to be addressed in more studies.

Nitrogen (N) in natural environments is typically supplied by a mixture of ammonia (NH₄⁺) and nitrate (NO₃^-). However, factors that underlie either NH₄⁺ or NO₃^- preference, and how such preference will change across generations remain unclear. We conducted a series of experiments to answer whether: (i) NH₄⁺:NO₃^- ratio is the driving factor for plant N preference, and (ii) this preference is consistent across generations.

We conducted both: (i) field observations (as a proxy for parent or P generation) and (ii) greenhouse experiments (the first generation or F1 and the second generation or F2) using corn and soybean grown under different NH₄⁺:NO₃^- ratios.

Both corn and soybean had the physiological plasticity to prefer either NH₄⁺ or NO₃^- depending on NH₄⁺:NO₃^- ratios, and this plasticity was consistent across generations. Corn, however, showed a stronger preference towards NO₃^- while soybean showed a stronger preference towards NH₄⁺. While both plants would try to make use of the most available form of N in their growing medium, plant species, physiological characteristics (e.g. maturity) and plant nutrient status also determined the extent of N uptake. From the evolutionary and productivity perspective, this plasticity is beneficial, allowing plants to effectively acquire available N particularly in a changing climate.

Alpine plants have to cope with intense ultraviolet (UV) radiation and its altitudinal changes. It has been argued that leaf UV reflectance and absorbance should play a central role in acclimation and adaptation to changes in UV radiation, but evidence is limited from high altitudinal ecosystems. In this study, we assessed whether leaf UV reflectance and leaf pigments jointly vary with altitude in alpine broadleaved herbaceous species. The primary hypothesis is that leaves with higher UV reflectance should have lower UV absorbance and/or lower contents of photosynthetic pigments.

Leaf UV reflectance, leaf UV absorbance and photosynthetic pigments (chlorophyll a and b, carotenoids) were examined in four broadleaved herbaceous species in relation to their habitat altitudes. The leaf surface reflectance and leaf extract absorbance at wavelengths of 305 and 360 nm were measured to examine the leaf optical and photochemical characteristics in the UV-B and UV-A bands, respectively. The species included Saussurea katochaete Maxim., Saussurea pulchra Lipsch., Anaphalis lactea Maxim. and Rheum pumilum Maxim., which are distributed along the same slope from 3200 to 4200 m in the Qilian Mountains, Qinghai–Tibetan Plateau.

The leaf UV absorbance was approximately twice as high at 305 nm (UV-B) than at 360 nm (UV-A) for all species except R. pumilum. Among the four species, the leaf UV absorbance was the highest and almost all values were within 2–6 Abs cm^?2 (absorbance cm^?2) in S. pulchra, but the lowest (frequently <1 Abs cm^?2) were observed in R. pumilum. Only R. pumilum showed significantly higher values at higher elevations. Leaf UV reflectance was generally higher at higher elevations for all species except for A. lactea, and exhibited much larger altitudinal variations compared to leaf UV absorbance. Anaphalis lactea showed a very high UV reflectance even at low altitudes. Among the four species, photosynthetic pigments tended to decrease with an increase in leaf UV reflectance but increased with leaf UV absorbance. The study suggests that leaf UV reflectance, rather than leaf UV absorbance, plays a more active role in acclimation to altitudinal changes in UV radiation, and a high investment in leaf UV reflectance may limit the accumulation of photosynthetic pigments in alpine plants.

Spatial patterns of fungal populations are affected by plant distribution, abiotic factors, fungal dispersal ability and inter-species interactions. While several studies have addressed spatial patterns of some mycorrhizal, saprotrophic and pathogenic fungi, the method based on fruit-body surveys is not efficient and unreliable to study the spatial pattern of root-associated fungal species because most fungi in plant roots do not have sporocarps and cannot be identified based only on morphological traits. Our aims are (i) to determine the spatial pattern of common root-associated fungi; (ii) to evaluate whether the abundance and spatial pattern of root-associated fungi and categories of fungi, reflect their biotic and abiotic niche constraints.

About 828 soil cores were collected from a 24-ha plot in a subtropical forest and Illumina Miseq was carried out to determine fungal composition in root samples and spatial patterns of 1009 common fungal Operational Taxonomic Units (OTUs) were studied using point pattern analyses. Biotic (plant community composition) and abiotic niche constraints on the presence/abundance of a fungal OTU was assessed as the n-dimensional niche hypervolumes of biotic and abiotic characteristics.

Our results showed that (i) most fungal OTUs were highly spatially aggregated at small scales (less than 30 m), but that the aggregated pattern decreased, while regular and random patterns increased, with the increasing distance; (ii) A significant positive correlation was found between fungal abundance and aggregation intensity of fungal OTUs, indicating that the dominant fungi tended to be more aggregated in natural forests; (iii) Mean abundance and spatial aggregation intensity of ectomycorrhizal and pathogenic fungi were relatively higher than those of saprotrophic fungi, indicating that host plants may play an important role in determining spatial pattern of root-associated fungi; (iv) Spatial patterns of root-associated fungi depended on fungal abundance, fungal functional group, fungal taxa, biotic and abiotic niche hypervolumes of fungal OTUs.

Desertification is a major concern in arid and semi-arid regions globally. Understanding interactions between vulnerable plant species and associated microbial symbionts may have important applications for conservation and restoration strategies in affected areas.

In this study, we evaluated the root-associated fungal endophyte community in Prosopis chilensis, a vulnerable and threatened arid-adapted tree of northern Chile. Host benefits in terms of physiological performance and plant growth were also assessed. Endophytic fungi were isolated from asymptomatic roots by the culture method for molecular identification of the 18S rRNA gene. The dominant fungal endophyte (Penicillium sp.) in the community was later used in inoculation experiments to assess its effect on maximum quantum efficiency of photosystem II (PSII), (Fv/Fm) actual PSII efficiency (Φ_PSII), and non-photochemical quenching (NPQ). Total sugars, starch content, malonaldehyde (MDA), nitrogen content (%) and growth traits were also measured.

Whereas Φ_PSII increased significantly in endophyte-inoculated plants, NPQ was found to decrease. No effect of endophyte inoculation on sugars and MDA was detected, but starch content, leaf nitrogen content, number of leaves and shoot biomass were found to increase. Results revealed that inoculation of endophytic Penicillium fungal isolate can provide significant physiological benefits to the host plant P. chilensis. Its presence resulted in greater PSII efficiency and higher leaf nitrogen and carbohydrate content, enhancing host plant growth. These findings highlight the importance of considering the fungal endophyte community of this vulnerable species as an important tool to the design of further revegetation and conservation programs.

Changes in habitat characteristics and species composition in successional gradients could determine temporal variation in phenology of second-growth forests. We evaluated phenological patterns in tree species occurring in successional forests in southern Brazil, aiming to assess community changes along succession. We tested for general patterns and phenophase seasonality of trees of forests in successional stages and for differences in occurrence, concentration, frequency and duration of phenophases.

Vegetative (flushing and leaf-fall) and reproductive (flowering and fruiting) phenophases of 149 individuals of 29 tree species were monitored monthly, for 2 years, in a successional gradient: early- (~10 years), mid- (~30 years) and late-successional (>80 years) forests in southern Brazil.

Forests in the successional gradient exhibited shared frequency and duration of phenological phases, probably due to climatic or historical constraints in phenology. However, we found differences in the rate of occurrence and concentration of phenological phases, suggesting that habitat changes caused by succession and species turnover are additional factors affecting phenological patterns in tropical forests.

Plant–plant interactions, being positive or negative, are recognized to be key factors in structuring plant communities. However, it is thought that root competition may be less important than shoot competition due to greater size symmetry belowground. Because direct experimental tests on the importance of root competition are scarce, we aim at elucidating whether root competition may have direct or indirect effects on community structure. Indirect effects may occur by altering the overall size asymmetry of competition through root–shoot competitive interactions.

We used a phytometer approach to examine the effects of root, shoot and total competition intensity and importance on evenness of experimental plant communities. Thereby two different phytometer species, Festuca brevipila and Dianthus carthusianorum, were grown in small communities of six grassland species over three levels of light and water availability, interacting with neighbouring shoots, roots, both or not at all.

We found variation in community evenness to be best explained if root and shoot (but not total) competition were considered. However, the effects were species specific: in Dianthus communities increasing root competition increased plant community evenness, while in Festuca communities shoot competition was the driving force of this evenness response. Competition intensities were influenced by environmental conditions in Dianthus, but not in Festuca phytometer plants. While we found no evidence for root–shoot interactions for neither phytometer species root competition in Dianthus communities led to increased allocation to shoots, thereby increasing the potential ability to perform in size-asymmetric competition for light. Our experiment demonstrates the potential role of root competition in structuring plant communities.

Faunal assemblage alterations due to anthropogenic impacts have changed herbivore–vegetation relationships in various ecosystems, but the influences of small vertebrates on revegetation processes remain unclear. In a peri-urban agricultural landscape in eastern Japan that lacks large ungulates but supports small generalist herbivores, fewer native seedlings have become established in thickets dominated by native dwarf bamboo, Pleioblastus chino (Franch. et Sav.) Makino. The mechanisms limiting tree seedling establishment are unknown. Our aim here was to evaluate the influence of interactions among the dwarf bamboo, its litter cover and small vertebrate herbivores on the microsite conditions governing the establishment of native tree seedlings from different successional stages in an old field in temperate Japan.

First, seedling emergence and survival of seeded Pinus densiflora Siebold et Zucc., Celtis sinensis Pers., Aphananthe aspera (Thunb.) Planch., Quercus serrata Murray, Quercus myrsinifolia Blume and Castanopsis sieboldii (Makino) Hatus. ex T. Yamaz. et Mashiba were observed in a factorial design that accounted for the presence or absence of dwarf bamboo and its litter cover, as well as the exclusion or access of small vertebrate fauna, in 2009 and 2010. To identify small vertebrate herbivores that reduced the emergence or survival of tree seedlings in the first experiment, reseeding experiments using P. densiflora, C. sinensis, A. aspera and Q. myrsinifolia were conducted by video trapping in 2011 and video and still-camera trapping in 2012.

The abiotic conditions under the dwarf bamboo were lethal to early- to mid-successional P. densiflora, C. sinensis, A. aspera and Q. serrata but led to better survival—although spindly growth—of late-successional Q. myrsinifolia and C. sieboldii. The main consumers and the plants they found palatable differed between the bamboo thickets and the intervening gaps. Predation by mice appeared to have severely limited the emergence of all species, particularly in the bamboo thickets but occasionally in the gaps, whereas litter cover slightly mitigated this limitation. However, bamboo litter cover reduced the emergence of P. densiflora in the gaps. Chinese bamboo partridge (Bambusicola thoracicus Temminck), an introduced game bird, selectively and severely fed on the cotyledons—and probably seeds—of A. aspera and moderately preyed upon those of P. densiflora in the gaps. Apparent consumption of seedlings in the gaps by the Japanese hare (Lepus brachyurus Temminck) suppressed the growth of all species but apparently did not severely affect emergence and survival. Thus, the net balance of positive and negative interactions at the bamboo thicket scale (i.e. the presence of dominant dwarf bamboo cover or intervening gaps and the herbivore behaviours in these two environments) and at the microsite level (i.e. litter cover) shapes the early establishment patterns of native tree seedlings, and this balance differs among tree seedling species.

Epiphytes are an abundant and diverse component of many wet temperate forests and have significant roles in ecosystem processes. Little is known about the processes and rates of their death and decomposition when they fall from the canopy, which limits our understanding of their role in forest carbon sequestration and nutrient cycling. In the temperate rainforest of the Quinault River Valley, Washington State, our aim was to test hypotheses regarding four elements of disturbance that might contribute to their decline.

We established set of experiments in which we placed samples of canopy epiphytes and their branch segments: (i) in the canopy versus forest floor microenvironment (stratum); (ii) attached to live versus dead branch substrates; (iii) subjected to physical disruption and ‘jarring’; and (iv) in direct versus indirect contact with the forest floor. Over the 2-year study, we assigned a non-destructive ‘vitality index’ (based on color and apparent mortality and dryness) to each sample every 2–3 months to compare effects of the experimental treatments and analyzed with a statistical model and post hoc pairwise comparisons of treatments.

The canopy versus ground stratum and live/dead branch status significantly affected epiphyte vitality. Effects of physical disruption and ground contact were not significant. There were seasonal effects (low vitality during the sampling times in the summer, revitalization upon sampling times in the winter) for all treatments except samples in contact with the ground. One implication of these results relates to effects of climate change, which is predicted to shift to hotter, drier summers and wetter winters. Climate change may affect forest dynamics and nutrient cycling in unpredictable ways. Results also point to future experiments to understand biotic and abiotic effects on epiphyte disturbance and dynamics.

The evolutionary history and functional traits of species can illuminate ecological processes supporting coexistence in diverse forest communities. However, little has been done in decoupling the relative importance of these mechanisms on the turnover of phylogenetic and functional characteristics across life stages and spatial scales. Therefore, this study aims to estimate the contribution of environment and dispersal on the turnover of phylogenetic and functional diversity across life stages and spatial scales, in order to build a coherent picture of the processes responsible for species coexistence.

We conducted the study in Xishuangbanna Forest Dynamics Plot in Yunnan Province, southwest China. We used four different spatial point process models to estimate the relative importance of dispersal limitation and environmental filtering. The functional traits and phylogenetic relationships of all individual trees were incorporated in the analyses to generate measures of dissimilarity in terms of pairwise and nearest-neighbor phylogenetic and functional characteristics across life stages and spatial scales.

We found non-random patterns of phylogenetic and functional turnover across life stages and spatial scales. Environmental filtering structured pairwise phylogenetic and functional beta diversity across spatial scales, while dispersal limitation alone, and in combination with environment filtering, shaped nearest neighbor phylogenetic and functional beta diversity. The relative importance of dispersal limitation and environmental filtering appeared to change with life stage but not with spatial scale. Our findings suggest that phylogenetic and functional beta diversity help to reveal the ecological processes responsible for evolutionary and functional assembly and highlight the importance of using a range of different metrics to gain full insights into these processes.

For temperate regions such as Northern Europe, predicted climate change patterns include an increase in winter precipitation causing increased risk of flooding, whereas periods of droughts will become more frequent in summer. The aim of this study is to explore variations in plant functional trait distributions along a hydrological gradient spanning from recurrent drought events to recurrent flooding—mimicking future precipitation patterns.

The experiment was conducted in a controlled grassland experiment over a period of 3 years. A novel and more extreme hydrological regime was achieved by manipulating the flow of a nearby stream thereby creating a continuous hydrological gradient from flooding during winter to drought during summer. Plant community responses were recorded along this hydrological gradient. Community-weighted trait distribution changes along the gradient were described using null models. Six functional traits were considered: seed mass, leaf dry matter content (LDMC), leaf area, leaf thickness, specific leaf area (SLA) and height.

Over time, responses in plant functional traits changed at the community level. Over the study period consistent changes occurred in the mean trait value of several traits. Communities in relatively dry plots became dominated by species with water-conserving life strategies, represented by high seed mass and thick leaves. In contrast, disturbance-resistant species (high leaf dry matter content) became dominant in flooded plots, indicating that persistence to flooding was the most important factor controlling the functional structure in those communities. Furthermore, a high abundance of small-seeded species in flooded plots likely indicates higher frequency of species with higher dispersal ability through hydrochory.

In conclusion, plant traits are useful for predicting responses to climate change, but abrupt and extreme climate event may cause unexpected responses because they have no analog to previously more stable conditions. We suggest that traits related to dispersal and resistance to disturbance are useful in describing responses to flooding and that these traits should be included in future investigations of plant community responses to extreme hydrological events.

Episodic wildfires are expected to occur more frequently under future climate change scenarios, with substantial effects on CO₂ exchange between terrestrial ecosystems and the atmosphere. This study examined the effects of wildfire on soil respiration (R_S) and its heterotrophic (R_H) and autotrophic (R_A) components, as well as their temperature responses (temperature sensitivity, Q₁₀).

We began this study in January 2014, 8 months after a wildfire, in a montane coniferous forest in southwestern China. A trenching method was used to exclude plant roots and quantify R_H. R_A was calculated by subtracting R_H from R_S.

From 2014 to 2015, the wildfire significantly reduced R_S, R_H and R_A by 61.3%, 42.5% and 84.0%, respectively, leading to increases in the ratio of R_H to R_S, from 0.63 in the unburned stand to 0.85 in the burned stand. Ignoring diurnal differences, the wildfire did not affect the Q₁₀ of R_Sor R_H, but substantially decreased the Q₁₀ of R_A, from 2.62 in the unburned stand to 2.08 in the burned stand. However, the daytime Q₁₀ of R_S and R_H was suppressed following the wildfire by 25.1% and 28.8%, respectively, primarily due to increased daytime soil temperature. In the montane coniferous forest, monthly precipitation but not soil temperature drove seasonal dynamics of soil CO₂ release. Our findings help to clarify the mechanisms underlying carbon cycling responses to natural disturbance, especially under a warmer future climate.

Carbon (C), nitrogen (N) and phosphorus (P) stoichiometry strongly affect functions and nutrient cycling within ecosystems. However, the related researches in shrubs were very limited. In this study, we aimed to investigate leaf stoichiometry and its driving factors in shrubs, and whether stoichiometry significantly differs among closely related species.

We analyzed leaf C, N and P concentrations and their ratios in 32 species of Ericaceae from 161 sites across southern China. We examined the relationships of leaf stoichiometry with environmental variables using linear regressions, and quantified the interactive and independent effects of climate, soil and species on foliar stoichiometry using general linear models (GLM).

The foliar C, N and P contents of Ericaceae were 484.66, 14.44 and 1.06 mg g?1, respectively. Leaf C, N and P concentrations and their ratios in Ericaceae were significantly related with latitude and altitude, except the N:P insignificantly correlated with latitude. Climate (mean annual temperature and precipitation) and soil properties (soil C, N and P and bulk density) were significantly influenced element stoichiometry. The GLM analysis showed that soil exerted a greater direct effect on leaf stoichiometry than climate did, and climate affected leaf traits mainly via indirect ways. Further, soil properties had stronger influences on leaf P than on leaf C and N. Among all independent factors examined, we found species accounted for the largest proportion of the variation in foliar stoichiometry. These results suggest that species can largely influence foliar stoichiometry, even at a lower taxonomic level.

We aim to investigate variations in the resorption efficiencies of 10 mineral nutrients [i.e. nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), zinc (Zn), aluminum (Al), iron (Fe) and copper (Cu)] in leaves of desert shrubs and to explore effects of aridity on resorption efficiency of these nutrients.

Plant samples were collected from 10 sites in northern Xinjiang Uygur Autonomous Region of China. Samples of green and senesced leaves were analysed to determine concentrations of N, P, K, Mg, Ca, Mn, Zn, Al, Fe and Cu and thus the nutrient resorption efficiency.

The mean nutrient concentrations in the desert shrubs varied, with the stoichiometric ratio Ca:N (19.3 mg g^?1):K (10.5 mg g^?1):Mg:P (1.01 mg g^?1):Al:Fe:Mn:Zn:Cu (4.78 mg kg^?1) = 4038:2950:2199:1816:211:37:32:11:2:1 in green leaves; and Ca:N (12.6 mg g^?1):Mg:K (7.6 mg g^?1):P (0.56 mg g^?1):Fe:Al:Mn:Zn:Cu (2.85 mg kg^?1) = 5583:3710:2943:2523:178:133:119:19:3.7:1 in senesced leaves. Resorption generally occurred for six elements (N, P, K, Cu, Mg and Mn, with average resorption efficiency 47.8%, 52.0%, 38.6%, 41.0%, 12.7% and 7.89%, respectively) during leaf senescence, while the other four nutrients tended to accumulate in senesced leaves, showing averagely negative resorption efficiencies [Ca (–3.87%), Al (?57.1%), Zn (?62.6%), Fe (?89.6%)]. Aridity showed strikingly different effects on the resorption process of the 10 nutrients. Of the four elements with totally (N/P/K) or mostly (Cu) positive observations of resorption efficiency, their resorption generally decreased with aridity, suggesting that drought stress had negative effects on the resorption efficiencies of these elements. In contrast, with at least one-third observations of resorption efficiency being negative, the other elements (Mg/Mn/Ca/Zn/Al/Fe) showed generally increasing resorptive tendency with aridity, except for Zn. This research provided a systematic analysis on the large variation and contrasting responses of the resorption of multi-elements to aridity in typical desert shrubs. Our findings foster the understanding of nutrient resorption patterns of desert plants and enable us to better predict the contrastive effects of drought stress on the cycling of diverse nutrients and the consequent stoichiometric decoupling in plants of desert ecosystems.

Human land use such as agriculture and logging can have cascading effects on the environment and severely influence forest ecosystems by altering structure, species composition and community processes. These activities may have long-term consequences, which impact forest recovery. We investigated the legacy of historical anthropogenic land use on the current reproductive effort (RE) and success of the understory, myco-heterotrophic orchid, Wullschlaegelia calcarata in Puerto Rico’s tropical rain forest after 80 years of forest recovery.

Our study site was the 16-ha Luquillo Forest Dynamics Plot in the Luquillo Experimental Forest. We used six 10 m × 500 m transect lines that spanned areas with differing levels of historic canopy coverage which are correlated with land use history. We recorded the abundance of W. calcarata plants and measured shoot height, number of flowers, fruit set for all plants and seed set from the most mature, undehisced fruit on a random subset of plants measured. We sought to determine whether or not there is a legacy of land use history on the RE and success of W. calcarata. Of the varying degrees of historic disturbance, we predicted that RE and success would be highest in minimally disturbed old-growth forest, and that soil type differences would be insufficient to affect RE or success.

We found 1607 plants of W. calcarata, and only one was detected in the most historically disturbed area of the forest. The orchids were most abundant in the two least historically disturbed sites. However, the prevailing trend in all measures of RE is in the opposite direction with greater RE in the forest plots with intermediate levels of historical disturbance. Furthermore, the best model (as a function of AICc and weights) to predict RE is a combination of soil type and cover class. Nevertheless, our measures of reproductive success (fruit and seed set) were best in the least historically disturbed sites and were not associated with soil type. Thus, the best sites for growth are not always the same as those for abundance and reproduction, and after >80 years of recovery, components of the rainforest community have not fully recovered.

Anthropogenic activities have drastically increased nutrient availability, resulting in declines in species richness in many plant communities. However, most previous studies have explored only species-loss patterns and mechanisms over small sampling areas, so their results might overestimate species loss at larger spatial scales. The aim of this research was to explore species diversity change patterns and species-loss rates at multiple scales in alpine meadow communities following nutrient enrichment. Specifically, we asked two closely related questions: (i) do changes in species diversity and species-loss patterns differ among spatial scales? and (ii) how does community compositional dissimilarity and species turnover change among spatial scale?

This study was implemented in an alpine meadow community, which is regarded as one of the most sensitive and vulnerable terrestrial ecosystems to anthropogenic nutrient enrichment. We conducted a fertilization experiment that involved the addition of nitrogen (N), phosphorus (P) and a mixture of both to a series of quadrats ranging from 1 to 16 m2 over 5 years to study the variations in the patterns of species diversity in response to nutrient additions at different spatial scales.

Our results showed that the changes in species diversity and species loss were dependent on the type of fertilization and the spatial scale. After N and NP fertilization, species diversity significantly decreased at the small scale but not at the large scale, and the rate of species loss decreased as the spatial scale increased. In contrast, the differences between the P addition and control communities were negligible at both the small and large spatial scales. N fertilization caused species to be lost from the small sampling scale, but because different species were lost from different samples, there was an increase in compositional dissimilarity at larger spatial scales, which reduced the total number of species lost when measured at larger scales. These findings highlight spatial scale in evaluating the biodiversity loss after fertilization and suggest that the compositional dissimilarity might play an important role in mediating species loss after fertilization. Our study significantly improved our understanding of changes in species diversity and species loss at different spatial scales under nutrient-enrichment scenarios.

The role of tissue acid phosphatase (APase) activity of legumes and non-legumes in their P nutrition and adaptation to low-P soils is not well understood. To better understand this, a relationship between APase activity and P concentration in leaves, stems, roots and nodules of legumes, Cyclopia and Aspalathus and a non-legume, Leucadendron strictum, all native to the P-poor soils of the Cape fynbos biome, was assessed.

Plants were collected and each separated into leaves, stems and roots. Phosphatase enzyme activity was assayed in soil using the p-nitrophenol method, while soil P and shoot P were measured using ICP-MS. To measure tissue APase activity, an acetate buffer was added into ground plant material and contents filtered. An acetate buffer and a p-nitrophenyl solution were added to the supernatant and contents incubated. After incubation, NaOH (0.5 M) was added and absorbance read at 405 nm.

At Koksrivier, Cyclopia genistoides exhibited the highest leaf enzyme activity whilst Aspalathus aspalathoides showed the highest enzyme activity in the stems. At both Kleinberg and Kanetberg, Cyclopia subternata and Cyclopia longifolia showed the highest APase activity in leaves, followed by stems and lowest in roots. P concentration closely mirrored enzyme activity in organs of all test species from each site. APase activity positively correlated with P concentration in organs of all the test Cyclopia and Leucadendron species, indicating that intracellular APase activity is directly linked to P mobilization and translocation in these species. Percentage of N derived from fixation was positively correlated with tissue APase activity in C. genistoides (r = 0.911*), A. aspalathoides (r = 0.868*) and Aspalathus caledonensis (r = 0.957*), suggesting that APase activity could be directly or indirectly linked to symbiotic functioning in these fynbos legumes, possibly via increased P supply to sites of N₂ fixation.