A BACKGROUND ABOUT LEAF ECONOMIC SPECTRUM IN TROPICAL VEGETATION

Plant functional traits are an important indicator for the comprehensive evaluation of community stability and resilience. Therefore, exploring the variations and relationships among leaf functional traits at different maturity levels during forest restoration can deepen the understanding of plant adaptation strategies and community assembly. In this study, we measured the leaf area (LA), specific leaf area (SLA), photosynthetic pigments, non-structural carbohydrates (NSCs), leaf nitrogen content (LNC), and leaf phosphorus content (LPC) of dominant tree species in three communities with different maturity levels (defined by species composition, biodiversity and spatial structure) in a monsoon forest located in the northern margin of the tropics in China, and explored the variation and relationships among different leaf traits at individual, species, and community scales. The results showed that maturity levels significantly affected leaf functional traits. With the increase in maturity levels, SLA increased, and leaf SS and NSCs decreased, while other leaf functional traits did not show a consistent pattern. In different communities, NSCs, Chl (a:b), SS:St or Car had a trade-off or synergistic relationship with leaf economic spectrum. Additionally, the LPC, LNC, and starch were the key traits in response to selection pressure at maturity levels, inter-specific and intra-specific scales, respectively, and the trait–trait relationships were stronger or more extreme as the scale was narrowed. Therefore, when evaluating the development and succession of tropical monsoon forest communities, the selection of leaf functional characteristics and the determination of the research scale should be comprehensively and systematically considered.

AimsExtensive research on the leaf economics spectrum (LES) has improved insights into functional traits and their environmental interactions. Several studies explored trait correlations in angiosperms and ferns, expanding their ecological significance. However, knowledge gaps persist, especially concerning East‐Asian ferns and the differences between terrestrial and epiphytic ferns in LES.LocationEast Asia, Northern Taiwan.MethodsData were collected along an elevation gradient (870–2130 m a.s.l.) in northern Taiwan, where we measured nine leaf traits for 47 terrestrial and 34 epiphytic ferns across 59 vegetation plots within subtropical forests. We explored trait–trait and trait–environment relationships at the species and community levels for both terrestrial and epiphytic ferns while accounting for phylogenetic constraints.ResultsEpiphytes had lower specific leaf area (SLA) and leaf nitrogen, greater trait variance and trait space than terrestrial species, suggesting they are ecologically distinct. These differences observed at species and community levels appear to emerge because epiphytes undergo stronger water and nutritional stress along the elevation gradient. In addition, three groups were detected within epiphytes reflecting their strategies for water and nutrient stress adaptation. Trait correlations largely resembled angiosperm LES patterns but were less apparent in epiphytes. SLA and leaf dry matter content (LDMC) were consistently correlated to water stress traits, which might contribute to the restricted LES trait range of both life forms in our study. Traits exhibited a strong phylogenetic signal, with marked differences between SLA and LDMC correlations in phylogenetics‐corrected vs raw data. Trait–environment relationships were similar for several water stress‐related traits across both species groups, but stronger relationships were more evident in terrestrial ferns.ConclusionsTrait patterns are not entirely equivalent for epiphytic and terrestrial species or communities and should not be extrapolated across life forms. Distantly related species with various evolutionary backgrounds could dismantle LES patterns at the species level. Strong phylogenetic constraints may influence the trait–environment response of epiphytic species.

Aims Grassland desertification is being accelerated because of adverse climate change effects and unsustainable land uses, resulting in several major environmental problems. However, there are few studies on the economics spectrum of different plant functional types in desert steppe. The objectives of the current study are to examine the relationships among leaf functional traits of native plant species, to compare the functional traits among different plant functional types, and to determine whether an economic spectrum exists for the majority of species in the desert steppe of Damao Banner, Nei Mongol, China. Methods Photosynthetic and chlorophyll fluorescence parameters, specific leaf area(SLA), and leaf nitrogen contents across 24 species of different functional types were measured in situ in the desert steppe ecosystem. Non-parametric tests were used to analyze leaf trait differences in plant species of different functional types. Linear regression analysis was used to determine the relationships among leaf traits in different plant species. Finally, a comprehensive analysis on these leaf traits in different plant species was conducted using the principal component analysis. All data analyses were performed using SPSS 16.0(SPSS, Chicago, USA). Important findings Significant differences among plant functional types were found in most of the leaf traits. SLA and mass-based nitrogen concentration(Nmass) in grasses were 2.39 and 1.20 folds, respectively, of that in shrubs; area-based photosynthetic capacity(Aarea), SLA, and photosynthetic nitrogen use efficiency(PNUE) in annual species were 1.93, 2.13, and 4.24 folds, respectively, of that in perennial species; and Aarea, SLA, and PNUE in C4 species were 2.25, 1.73, and 3.61 folds, respectively, of that in C3 species. Almost all relationships signifi-cantly differed(p 0.01) among the leaf traits, with exception of the relationships between Aarea and area-based nitrogen concentration(Narea) and between quantum yield of PSII electron transport(ΦPSII) and SLA, implying that an economic spectrum may exist in the desert steppe ecosystem. The relationships of Narea, mass-based photosynthetic capacity(Amass), and PNUE with SLA were most significantly strong(R2 = 0.54, 0.62, 0.60, respectively; p 0.01). Results in this study suggest that the annuals, grasses, and C4 species might be located at the end of the leaf economic spectrum with high area-based photosynthetic rate, high nitrogen concentration on mass basis, short leaf lifespan, and high SLA; whereas the perennials, shrubs, and C3 species could be located at the another end of the economic spectrum with contrasting traits.

Many studies focus on the relationships between plant functional traits and tree growth performances. However, little is known about the ontogenetic shifts of the relationships between functional traits and tree growth. This study examined associations between stem and leaf functional traits and growth rates and their ontogenetic shifts across 20 tropical tree species in a tropical seasonal rainforest in Xishuangbanna, south-west China. For each species, physiological active branches of individual trees belonged to three size classes (i.e. small, diameter at breast height (DBH) 5-10 cm; middle, DBH 10-20 cm; big, DBH >20 cm) were sampled respectively. We measured 18 morphological and structural traits, which characterised plant hydraulic properties or leaf economic spectrum. Associations between diameter growth rates and functional traits were analysed across three size classes. Our results revealed that diameter growth rates of big-sized trees were mainly related to traits related to plant hydraulic efficiency (i.e. theoretical hydraulic conductivity (Ktheo) and leaf vein density (Dvein)), which suggests that the growth of large trees is limited mainly by their xylem water transport capacity. For middle-sized trees, growth rates were significantly related to traits representing leaf economic spectrum (i.e. specific leaf area (SLA), individual leaf mass (ILM), palisade thickness (PT) and spongy thickness (SP)). Diameter growth rates of small-sized trees were not correlated with hydraulic or leaf economic traits. Thus, the associations between tree growth rates and functional traits are size dependent. Our results suggest ontogenetic shift of functional traits which could potential contribute to different growth response to climate change.

Non‐structural carbohydrates (NSC) are considered as indicators of the balance between tree carbon sources and sinks and reflect functional strategies throughout different biomes. However, little is known about the contribution of NSC to tree economics, and in particular, whether leaf, stem and coarse root traits co‐ordinate together into a whole‐tree economics spectrum. Twenty‐four functional traits (including NSC content) were measured in leaves, stem and coarse root xylem of up to 90 angiosperm tree species in temperate, Mediterranean and tropical climates. By performing principal component analysis and standardized major axis regression, we explored the relationships between NSC and other functional traits, as well as the effects of climate and phylogeny on these relationships. Our results revealed a covariation between leaf and coarse root NSC content and leaf economic traits, whereas stem NSC content was largely decoupled from the leaf economics spectrum that was mostly driven by leaf nitrogen content and leaf mass per area. Coarse root xylem traits were closely correlated with leaf traits, while most stem xylem traits were independent from the leaf economics spectrum but covaried with coarse root traits. Trade‐offs among traits in tropical species opposed those from other climates. Evolutionary history affected relationships among certain traits but did not change overall patterns. We conclude that due to leaf habit, an extended growing season and heightened defences, tropical species form distinct conservative resource acquisition strategies. Across all climates, as the stem must provide an efficient transport route between roots and leaves, while maintaining the display of branch and leaf organs, stem xylem design and NSC storage capacity lead to a stem economics spectrum that is largely independent from the leaf spectrum, but is coupled with that of coarse roots due to anatomical continuity. Read the free Plain Language Summary for this article on the Journal blog.

Understanding the relationships between species' demography and functional traits is crucial for gaining a mechanistic understanding of community dynamics. While leaf morphology represents a key functional dimension for plants worldwide (i.e., the leaf economics spectrum), its ability to explain variation in trees' life history strategies remains limited. Plant growth is influenced by both leaf morphology and allocation; hence, incorporating both dimensions is essential but rarely done. Additionally, trait–performance relationships have mainly been studied in tropical communities, leaving gaps in our understanding of temperate forests where different seasonality patterns may alter these relationships. We examined whether species' leaf area index (leaf area per crown size, LAI), a measure of leaf allocation, explains the variation of juvenile tree species' potential growth rates in a winter‐deciduous broadleaf forest. LAI has not been characterized as a species‐level trait, but its ability to predict plant productivity at the ecosystem scale highlights its potential for explaining plant growth. We evaluated species' maximum LAI both individually and in conjunction with wood density (WD) and leaf mass per area (LMA). We expected that models would improve when both leaf morphology (LMA) and leaf allocation (LAI) were included and that species with denser crowns would have higher potential growth rates. LAI and LMA were significant predictors of growth but only when both were incorporated, and together explained a high proportion of species' growth variations (R2adj = 0.59). We found evidence of a trade‐off between LAI and LMA, with a negative relationship between them and each having a positive influence on species' growth, suggesting that there are multiple allocation strategies to achieve fast growth. A surprisingly positive LMA–growth relationship contrasts with observations from tropical forests. We did not find significant relationships with WD in this forest. Our results highlight that incorporating leaf allocation improves models of trait–performance relationships. They also suggest, in agreement with the limited literature, that temperate forests may exhibit different trait–performance relationships from those of tropical forests, where LMA is negatively related to growth and WD is often important. Clarifying the details and contexts of trait–performance relationships is crucial for applying the functional trait framework to understanding community structure and dynamics of forests globally.

Photosynthetic light-response (PLR) curves for leaves are important components of models related to carbon fixation in forest ecosystems, linking the Mitscherlich equation and Michaelis-Menten equation to traits of the leaf economics spectrum (LES). However, models do not consider changes in leaf habits (i.e., evergreen and deciduous) and within-canopy shading variation in these PLR curves. Here, we measured the PLR curves in sun and shade leaves of 44 evergreen and 31 deciduous species to examine the relationships between variables of the Mitscherlich equation and Michaelis-Menten equation, leaf nitrogen (N) and phosphorus (P) content, and leaf mass per area (LMA). Small changes were caused by different leaf habits and shade variations in relationships linking variables of the two equations to leaf N and P content and LMA. Values of the scaling exponents for PLR curve parameters did not differ regardless of canopy position and leaf habit (P > 0.05). The PLR curves in species with different leaf habits (i.e., evergreen and deciduous) at different canopy positions could be predicted using the general allometric relations between leaf traits and PLR parameters in the two equations. For photosynthetic photon flux densities from 0 to 2000 μmol m-2 s-1 , approximately 71% (Mitscherlich equation) and 70% (Michaelis-Menten equation) of the net assimilation rates could be predicted. These findings indicate that leaf net assimilation rates can be predicted through the large available data for LES traits. Incorporation of values for these traits available in the LES databases into ecosystem models of forest productivity and carbon fixation warrants further investigation.

Relationship between Maximum Leaf Photosynthesis, Nitrogen Content and Specific Leaf Area in Balearic Endemic and Non‐endemic Mediterranean Species

Functional leaf traits and leaf economics in the Paleogene — A case study for Central Europe

The leaf economics spectrum (LES) is an ecophysiological concept describing the trade-offs of leaf structural and physiological traits, and has been widely investigated on multiple scales. However, the effects of the breeding process on the LES in crops, as well as the mechanisms of the trait trade-offs underlying the LES, have not been thoroughly elucidated to date. In this study, a dataset that included leaf anatomical, biochemical, and functional traits was constructed to evaluate the trait covariations and trade-offs in domesticated species, namely rice (Oryza species). The slopes and intercepts of the major bivariate correlations of the leaf traits in rice were significantly different from the global LES dataset (Glopnet), which is based on multiple non-crop species in natural ecosystems, although the general patterns were similar. The photosynthetic traits responded differently to leaf structural and biochemical changes, and mesophyll conductance was the most sensitive to leaf nitrogen (N) status. A further analysis revealed that the relative limitation of mesophyll conductance declined with leaf N content; however, the limitation of the biochemistry increased relative to leaf N content. These findings indicate that breeding selection and high-resource agricultural environments lead crops to deviate from the leaf trait covariation in wild species, and future breeding to increase the photosynthesis of rice should primarily focus on improvement of the efficiency of photosynthetic enzymes.

Mohammed Armani.

The ecological niche is one of the central concepts in plant ecology. Understanding which biological traits influence plant niches remains limited, preventing large-scale generalizations. Using a representative pool of 94 herb-layer species frequently occurring in the Slovenian forest vegetation types and an extensive suite of 28 plant functional traits, we tested whether traits serve as predictors for the optimum and width of plant species ecological niche. Niche optimum (mean) and niche width (standard deviation) of each species were derived from community-level ecological indicator values for six environmental gradients, i.e., light, temperature, continentality, moisture, soil reaction and nutrients. We investigated relationships between niche parameters and functional traits through a random forest analysis to account for relatively high trait correlations. Our results suggest that niche optimum and width of forest plant species are related to their functional traits. The two niche parameters were best explained by similar set of traits; however, the relative importance of traits differed substantially. Traits associated with disturbances (frequency and severity), plant dispersal (seed mass, dispersal syndrome), leaf economics spectrum (specific leaf area) and life strategy (CSR scores) showed the highest overall significance in predicting niche optimum and width. Functional traits were, on average, better predictors for niche optimum (average variance explained across all six environmental factors: 20.2%) than for niche width (average variance explained: 7.7%). Intraspecific trait variability, not considered in this study, likely plays an important role in case of niche width. The analyses suggest that, while not all traits impact niche parameters to the same degree, it is crucial to consider traits representing different ecological dimensions and revealing leading patterns of trait coordination. We recommend that the relative importance of traits for species niche parameters should be tested on a larger spatial scale using broader pool of forest understory plants across Europe.

Recent empirical and theoretical approaches have called for an understanding of the processes underpinning ecosystem service provision. Environmental gradients have shown effects on key plant functional traits that subsequently explain ecosystem properties of several systems. However, little is known concerning how associations between plant functional traits, including both below- and aboveground plant components, predict ecosystem properties and independently measured final ecosystem services. Here, we modeled (1) the responses of the leaf and plant economics spectrum, Plant size axis, and root growth to environmental gradients and (2) how associations between plant functional traits explain trade-offs and synergies between multiple ecosystem properties and final services. Forty-four plots were studied in a coastal marsh landscape of the German North Sea Coast. We used a partial least square structural equation model approach to test the hypothesized model. We found (1) a negative covariation between plant traits pertaining to a size axis and traits explaining both plant growth (roots and stems) and the leaf economics spectrum; (2) this trade-off responded significantly to the land use gradient and nutrient availability, which were both strongly driven by the groundwater gradient; (3) this trade-off explained an initial major trade-off between carbon stocks, at one extreme of the axis, and both the habitat value to conserve endangered plants and forage production for meat and dairy products at the other extreme. However, a secondary trade-off between nature conservation value and forage production, explained by a trade-off between leaf economics spectrum and plant growth in response to the land use intensity gradient, was also found.

Plant functional traits typically show strong covariation, e.g. as in the worldwide leaf economics spectrum (LES). Covariation is thought to arise from selective forces and physical constraints. However, processes shaping covariation at interspecific scales may differ from those at intraspecific scales. Potential sources of intraspecific trait variation include variation in genetics, abiotic environment, and biotic environment; any of these factors may cause divergence from interspecific patterns. Quaking aspen, Populus tremuloides (Salicaceae), is a widespread tree species ideal for assessing these processes' role in the intraspecific LES, due to its clonal growth along environmental gradients, intraspecific variation in cytotype (ploidy level), and variation in biotic interactions (herbivory pressure). Here, we investigate genotype, cytotype, microclimate and herbivory as potential drivers in shaping LES trait–trait and trait–environment relationships at intra‐specific scales. We studied 15 quaking aspen genotypes that varied in cytotype (diploid or triploid) along an elevation gradient in southwestern Colorado. We show that LES tradeoffs substantially weaken at the intraspecific scale in this species. Among genotypes, trait–trait slopes ranged from positive, weak, strong, negative, or absent compared to the global LES. We also found that cytotypes varied in resource‐use tradeoffs, and that increasing insect herbivory pressure decreased the strength of several trait–trait relationships. Microenvironment was a weak predictor of intraspecific functional trait variation in quaking aspen. Synthesis. In quaking aspen, there are relaxed constraints on LES trait co‐variation. Variation in genotype, cytotype, and herbivory pressure each contribute to this pattern. Relaxation of the LES may enable more flexible responses to environmental stressors through both genetic and plastic mechanisms.

Leaf mass per area (LMA), which is an important functional trait in leaf economic spectrum and plant growth analysis, is measured from leaf discs or whole leaves. Differences between the measurement methods may lead to large differences in the estimates of LMA values. We examined to what extent estimates of LMA based on whole leaves match those based on discs using 334 woody species from a wide range of biomes (tropics, subtropics, savanna, and temperate), whether the relationship varied by leaf morphology (tissue density, leaf area, leaf thickness), punch size (0.6- and 1.0-cm diameter), and whether the extent of intraspecifc variation for each species matches. Disc-based estimates of species mean LMA matched the whole-leaf estimates well, and whole-leaf LMA tended to be 9.69% higher than leaf-disc LMA. The ratio of whole-leaf LMA to leaf-disc LMA was higher for species with higher leaf tissue density and larger leaves, and variance in the ratio was greater for species with lower leaf tissue density and thinner leaves. Estimates based on small leaf discs also inflated the ratio. The extent of the intraspecific variation only weakly matched between whole-leaf and disc-based estimates (R2 = 0.08). Our results suggest that simple conversion between whole-leaf and leaf-disc LMA is difficult for species obtained with a small leaf punch, but it should be possible for species obtained with a large+ leaf punch. Accurately representing leaf traits will likely require careful selection between leaf-disc and whole-leaf traits depending on the objectives. Quantifying intraspecific variation using leaf discs should be also considered with caution.