Leaf trait network architecture shifts with species-richness and climate across forests at continental scale

Differences and driving factors of leaf functional traits between old tree and mature tree of Pinus tabulaeformis in the Loess Plateau

BACKGROUND

Study the leaf functional traits is highly important for understanding the survival strategies and climate adaptability of old trees. In this study, the old (over 100 years old) and mature trees (about 50 years old) of Pinus tabulaeformis in the Loess Plateau were studied, and the variation of 18 leaf functional traits (6 economic, 4 anatomical, 2 photosynthetic and 6 physiological traits) was analyzed to understand the differences of survival strategies between old and mature trees. Combined with transcriptome and simple sequence repeats (SSR) techniques, the effects of soil property factors and genetic factors on leaf functional traits and the potential molecular mechanisms of traits differences were studied.

RESULTS

Compared with mature trees, old trees presented greater economic traits (except leaf phosphorus content), anatomical traits (except the stomatal density), and physiological traits (except superoxide dismutase activity) and lower photosynthetic traits, and their survival strategies were more conservative. The difference was mainly driven by soil property and genetic factors (common explanation rate was 67.89%), and the independent effect of genetic factors (10.09%) was slightly higher than that of soil property factors (2.88%). In addition, by constructing weighted gene co-expression networks analysis WGCNA), this research identified 24 candidate hub genes that regulate leaf functional traits, most of which are related to plant growth and development and the stress response, and can be used for further regulatory mechanism analysis.

CONCLUSIONS

In conclusion, this study is helpful to understand the ecological adaptability of P. tabuliformis under the background of climate change in the Loess Plateau, and provides a theoretical basis related to leaf functional traits and molecular regulation for the protection of old trees.

Leaf trait networks of subtropical woody plants weaken along an elevation gradient

The leaf economic spectrum (LES) captures key leaf functional trait relationships, defining a conservative-acquisitive axis of plant resource utilization strategies. Examining the leaf trait network (LTN) is useful for understanding resource utilization strategies but also more broadly, the ecological strategies of plants. However, the relationship between the LES conservation-acquisition axis and LTN correlations across environmental gradients is unclear. To address this knowledge gap, we measured physiological, chemical, and structural traits in 52 broad-leaved tree species spanning an elevation gradient (1400 m, 1600 m, 1800 m) in Wuyi Mountain, China. A total of 12 leaf traits were selected, including: photosynthetic rate (A25), respiration rate (R25), optimum photosynthetic temperature (Topt), rate of photosynthesis at optimum temperature (Aopt), mean temperature at which 90% of Aopt is reached (T90), temperature sensitivity of respiration (Q10), N and P content, N/P, leaf mass per area (LMA), photosynthetic nitrogen use efficiency (PNUE) and photosynthetic phosphorus use efficiency (PPUE). We found that leaf physiological traits exhibited signs of thermal acclimation along the elevation gradient. We also observed significant changes in leaf N and P content, N/P, photosynthetic phosphorus utilization efficiency (PPUE) and LMA with elevation. The resource utilization strategies of plants changed from conservative to acquisitive as elevation increased. The LTN analysis showed that as elevation increased, the links among traits weakened and modularity (modularity is used to describe the degree of separation between networks) increased. Collectively, our results indicate that elevation changes can trigger moderate shifts in the resource utilization and ecological strategies of plants via leaf functional traits.

Balancing the nutrient needs: Optimising growth in Malus sieversii seedlings through tailored nitrogen and phosphorus effects

The impact of nitrogen (N) and phosphorus (P) on the physiological and biochemical processes crucial for tree seedling growth is substantial. Although the study of plant hydraulic traits in response to N and P is growing, comprehensive research on their combined effects remains limited. Malus sieversii, a key ancestral species of modern apples and a dominant species in Xinjiang's Tianshan wild fruit forest, is witnessing a decline due to climate change, pests and diseases, compounded by challenges in seedling regeneration. Addressing this, a 4-year study was conducted to determine the optimal fertilisation method for it. The experiment explored varying levels of N (N10, N20 and N40) and P (P2, P4 and P8), and their combined effects (N20Px: N20P2, N20P4, N20P8; NxP4: N10P4, N20P4 and N40P4), assessing their impact on gas exchange, hydraulic traits, and the interplay among functional traits in Tianshan Mountains' M. sieversii seedlings. Our study revealed that All N-inclusive fertilisers slightly promoted the net photosynthetic rate. N10 significantly increasing leaf hydraulic conductivity. All P-inclusive fertilisers adversely affected hydraulic conductivity. P8, N20P4 and N20P8 notably increased seedlings' vulnerability to embolism. Seedlings can adaptively adjust multiple functional traits in response to nutrient changes. The research suggests N10 and N20 as the most effective fertilisation treatments for M. sieversii seedlings in this region, while fertilisation involving phosphorus is less suitable. This study contributes valuable insights into the specific nutrient needs of it, vital for conservation and cultivation efforts in the Tianshan region.

Root and shoot phenology, architecture, and organ properties: an integrated trait network among 44 herbaceous wetland species

Integrating traits across above- and belowground organs offers comprehensive insights into plant ecology, but their various functions also increase model complexity. This study aimed to illuminate the interspecific pattern of whole-plant trait correlations through a network lens, including a detailed analysis of the root system. Using a network algorithm that allows individual traits to belong to multiple modules, we characterize interrelations among 19 traits, spanning both shoot and root phenology, architecture, morphology, and tissue properties of 44 species, mostly herbaceous monocots from Northern Ontario wetlands, grown in a common garden. The resulting trait network shows three distinct yet partially overlapping modules. Two major trait modules indicate constraints of plant size and form, and resource economics, respectively. These modules highlight the interdependence between shoot size, root architecture and porosity, and a shoot-root coordination in phenology and dry-matter content. A third module depicts leaf biomechanical adaptations specific to wetland graminoids. All three modules overlap on shoot height, suggesting multifaceted constraints of plant stature. In the network, individual-level traits showed significantly higher centrality than tissue-level traits do, demonstrating a hierarchical trait integration. The presented whole-plant, integrated network suggests that trait covariation is essentially function-driven rather than organ-specific.

Innovations and prospectives of multidimensional trait integration

This article is a Commentary on Ye et al. (2024), 244: 436–450.

Temporal shifts in the phytoplankton network in a large eutrophic shallow freshwater lake subjected to major environmental changes due to human interventions

Phytoplankton communities are crucial components of aquatic ecosystems, and since they are highly interactive, they always form complex networks. Yet, our understanding of how interactive phytoplankton networks vary through time under changing environmental conditions is limited. Using a 29-year (339 months) long-term dataset on Lake Taihu, China, we constructed a temporal network comprising monthly sub-networks using "extended Local Similarity Analysis" and assessed how eutrophication, climate change, and restoration efforts influenced the temporal dynamics of network complexity and stability. The network architecture of phytoplankton showed strong dynamic changes with varying environments. Our results revealed cascading effects of eutrophication and climate change on phytoplankton network stability via changes in network complexity. The network stability of phytoplankton increased with average degree, modularity, and nestedness and decreased with connectance. Eutrophication (increasing nitrogen) stabilized the phytoplankton network, mainly by increasing its average degree, while climate change, i.e., warming and decreasing wind speed enhanced its stability by increasing the cohesion of phytoplankton communities directly and by decreasing the connectance of network indirectly. A remarkable shift and a major decrease in the temporal dynamics of phytoplankton network complexity (average degree, nestedness) and stability (robustness, persistence) were detected after 2007 when numerous eutrophication mitigation efforts (not all successful) were implemented, leading to simplified phytoplankton networks and reduced stability. Our findings provide new insights into the organization of phytoplankton networks under eutrophication (or re-oligotrophication) and climate change in subtropical shallow lakes.

Polyploidy and the evolution of phenotypic integration: Network analysis reveals relationships among anatomy, morphology, and physiology

Premise

Most traits are polygenic and most genes are pleiotropic, resulting in complex, integrated phenotypes. Polyploidy presents an excellent opportunity to explore the evolution of phenotypic integration as entire genomes are duplicated, allowing for new associations among traits and potentially leading to enhanced or reduced phenotypic integration. Despite the multivariate nature of phenotypic evolution, studies often rely on simplistic bivariate correlations that cannot accurately represent complex phenotypes or data reduction techniques that can obscure specific trait relationships.

Methods

We apply network modeling, a common gene co-expression analysis, to the study of phenotypic integration to identify multivariate patterns of phenotypic evolution, including anatomy and morphology (structural) and physiology (functional) traits in response to whole genome duplication in the genus Brassica.

Results

We identify four key structural traits that are overrepresented in the evolution of phenotypic integration. Seeding networks with key traits allowed us to identify structure-function relationships not apparent from bivariate analyses. In general, allopolyploids exhibited larger, more robust networks indicative of increased phenotypic integration compared to diploids.

Discussion

Phenotypic network analysis may provide important insights into the effects of selection on non-target traits, even when they lack direct correlations with the target traits. Network analysis may allow for more nuanced predictions of both natural and artificial selection.

Characteristics, Relationships, and Anatomical Basis of Leaf Hydraulic Traits and Economic Traits in Temperate Desert Shrub Species

Shrubs are a key component of desert ecosystems, playing a crucial role in controlling desertification and promoting revegetation, yet their growth is often impeded by drought. Leaf hydraulic traits and economic traits are both involved in the process of water exchange for carbon dioxide. Exploring the characteristics, relationships, and anatomical basis of these two suites of traits is crucial to understanding the mechanism of desert shrubs adapting to the desert arid environment. However, the relationship between these two sets of traits currently remains ambiguous. This study explored the leaf hydraulic, economic, and anatomical traits of 19 desert shrub species. The key findings include the following: Relatively larger LT values and smaller SLA values were observed in desert shrubs, aligning with the "slow strategy" in the leaf economics spectrum. The relatively high P50leaf, low HSMleaf, negative TLPleaf, and positive HSMtlp values indicated that severe embolism occurs in the leaves during the dry season, while most species were able to maintain normal leaf expansion. This implies a "tolerance" leaf hydraulic strategy in response to arid stress. No significant relationship was observed between P50leaf and Kmax, indicating the absence of a trade-off between hydraulic efficiency and embolism resistance. Certain coupling relationships were observed between leaf hydraulic traits and economic traits, both of which were closely tied to anatomical structures. Out of all of the leaf traits, LT was the central trait of the leaf traits network. The positive correlation between C content and WPleaf and HSMleaf, as well as the positive correlation between N content and HSMtlp, suggested that the cost of leaf construction was synergistic with hydraulic safety. The negative correlation between SLA, P content, GCL, and SAI suggested a functional synergistic relationship between water use efficiency and gas exchange rate. In summary, this research revealed that the coupling relationship between leaf hydraulic traits and economic traits was one of the important physiological and ecological mechanisms of desert shrubs for adapting to desert habitats.

Functional characteristics and habitat suitability of threatened birds in northeastern China

Northeast China, rich in natural resources and diverse biodiversity, boasts a unique habitat for threatened bird species due to its remote location and perennial cold climate. An analysis assessed the adaptability of these species using data on their geographic distribution and functional traits collected through database queries. The results revealed that threatened bird species share similar functional traits and a stronger phylogenetic signal (Blomberg mean K = 0.39) compared to common species. The Biomod2 model analyzed potentially suitable ranges and environmental drivers under current and future climate scenarios, showing a pattern of larger suitable areas in southern regions and smaller suitable areas in the north. The most critically threatened species faced greater geographical constraints (0.989), with mean annual temperature being a key influence. Altitude and water system distribution were also key factors impacting the distribution of other threatened bird species. Simulated projections under different climate scenarios (RCP 45 and 85) indicated varying degrees of expansion in the suitable range for these species. This research sheds light on the functional traits and distribution of threatened bird species in Northeast China, providing a scientific foundation for future conservation and management efforts.

Soil warming affects sap flow and stomatal gas exchange through altering functional traits in a subtropical forest

Climate warming influences the structure and function of ecosystems. However, the mechanisms of plant water use and gas exchange responses to climate warming have been less studied, especially from the perspective of different functional traits. We conducted a field experiment to investigate how soil warming (+2 °C) affects sap flow and stomatal gas exchange through plant functional traits and nutrient characteristics in a subtropical forest. We measured stomatal gas exchange of trees (Acacia auriculiformis and Schima superba) and shrubs (Castanea henryi and Psychotria asiatica), and monitored long-term sap flow of both tree species. Besides, plant leaf nutrient contents, functional traits, and soil nutrients were also studied. It is demonstrated that soil warming significantly increased maximum sap flow density (Js_max, 35.1 %) and whole-tree transpiration (EL, 46.0 %) of A. auriculiformis, but decreased those of S. superba (15.6 % and 14.9 %, respectively). Warming increased the photosynthetic rate of P. asiatica (18.0 %) and water use efficiency of S. superba (47.2 %). Leaf nutrients and stomatal anatomical characteristics of shrubs were less affected by soil warming. Soil warming increased (+42.7 %) leaf K content of A. auriculiformis in dry season. Decomposition of soil total carbon, total nitrogen, and available nitrogen was accelerated under soil warming, and soil exchangeable Ca2+ and Mg2+ were decreased. Trees changed stomatal and anatomic traits to adapt to soil warming, while shrubs altered leaf water content and specific leaf area under soil warming. Warming had a greater effect on sap flow of trees, as well as on their leaf gas exchange (total effect: -0.27) than on that of shrubs (total effect: 0.06). In summary, our results suggest that the combination of functional and nutrient traits can help to better understand plant water use and gas exchange responses under climate warming.

Which Has a Greater Impact on Plant Functional Traits: Plant Source or Environment?

The deterioration of water quality caused by human activities has triggered significant impacts on aquatic ecosystems. Submerged macrophytes play an important role in freshwater ecosystem restoration. Understanding the relative contributions of the sources and environment to the adaptive strategies of submerged macrophytes is crucial for freshwater restoration and protection. In this study, the perennial submerged macrophyte Myriophyllum spicatum was chosen as the experimental material due to its high adaptability to a variable environment. Through conducting reciprocal transplant experiments in two different artificial environments (oligotrophic and eutrophic), combined with trait network and redundancy analysis, the characteristics of the plant functional traits were examined. Furthermore, the adaptive strategies of M. spicatum to the environment were analyzed. The results revealed that the plant source mainly influenced the operational pattern among the traits, and the phenotypic traits were significantly affected by environmental factors. The plants cultured in high-nutrient water exhibited a higher plant height, longer leaves, and more branches and leaves. However, their physiological functions were not significantly affected by the environment. Therefore, the adaptation strategy of M. spicatum to the environment mainly relies on its phenotypic plasticity to ensure the moderate acquisition of resources in the environment, thereby ensuring the stable and efficient operation of plant physiological traits. The results not only offered compelling evidence on the adaptation strategies of M. spicatum in variable environments but also provided theoretical support for the conservation of biodiversity and sustainable development.

Growth form, regeneration mode, and vegetation type explain leaf trait variability at the species and community levels in Mediterranean woody vegetation

Leaf traits are good indicators of ecosystem functioning and plant adaptations to environmental conditions. We examined whether leaf trait variability at species and community levels in Mediterranean woody vegetation is explained by growth form, regeneration mode, and vegetation type. We studied several plant communities across five vegetation types - semi-closed forest, open forest, closed shrubland, open shrubland, and scrubland - in southwestern Anatolia, Türkiye. Using linear mixed models, community-weighted trait means, and principal component analysis, we tested how much variability in three leaf traits (specific leaf area, leaf thickness, and leaf area) is accounted for species, growth form, regeneration mode, and vegetation type. Despite a large amount of leaf trait variability both within- and among-species existed, functional groups still accounted for a significant part of this variability. Resprouters had higher SLA and leaf area and lower leaf thickness than non-resprouters. However, further functional separation in regeneration mode, by considering the propagule-persistence trait and the seed bank locality, explained leaf trait variability better than only resprouting ability. Although no consistent pattern was observed in three leaf traits in the growth form, we found evidence for the difference in SLA and leaf thickness between shrubs and large shrubs, and subshrubs had smaller leaves than other growth forms. Vegetation type also accounted for a substantial amount of leaf trait variability. Specifically, plant communities in closed habitats had larger leaf area than open ones, and those in scrublands had higher SLA, lower leaf thickness, and lower leaf area than other vegetation types. Climate and phylogeny had limited contribution to the results obtained, with the exception of a significant phylogenetic effect in explaining the differences in SLA between resprouters and non-resprouters. Our results suggest that multiple drivers are responsible for shaping plant trait variability in Mediterranean plant communities, including growth form, regeneration mode, and vegetation type.

Effects of light regimes and benthic fish disturbance on the foraging behavior of Vallisneria natans in heterogeneous sediments

In shallow eutrophic lakes, submersed macrophytes are significantly influenced by two main factors: light availability and benthic fish disturbance. Plant foraging is one of the most crucial aspects of plant behavior. The present study was carried out to effects of light regimes and fish disturbance on the foraging behavior of Vallisneria natans in heterogeneous sediments. V. natans was cultivated in heterogeneous sediments with four treatments: high-light regime (H), high-light regime with benthic fish (HF), low-light regime (L), and low-light regime with benthic fish (LF). We use plant trait network analysis to evaluate the relationships between traits in heterogeneous sediments. We found the plant foraging intensity was positively correlated with trait network modularity. The biomass of stem, maternal plant biomass ratio, and ramet number were the hub traits of plant growing in heterogeneous habitats. Although the plant relative growth rate (RGR) was positively correlated with foraging intensity, the hub traits had closer links with plant RGR than foraging intensity. Light regime and benthic fish indirectly affected the plant foraging intensity by changing the chlorophyll a content and pH of overlying water. Overall, our analysis provides valuable insights into plant foraging behavior in response to environmental changes.

Experimental warming altered plant functional traits and their coordination in a permafrost ecosystem

Knowledge about changes in plant functional traits is valuable for the mechanistic understanding of warming effects on ecosystem functions. However, observations have tended to focus on aboveground plant traits, and there is little information about changes in belowground plant traits or the coordination of above- and belowground traits under climate warming, particularly in permafrost ecosystems. Based on a 7-yr field warming experiment, we measured 26 above- and belowground plant traits of four dominant species, and explored community functional composition and trait networks in response to experimental warming in a permafrost ecosystem on the Tibetan Plateau. Experimental warming shifted community-level functional traits toward more acquisitive values, with earlier green-up, greater plant height, larger leaves, higher photosynthetic resource-use efficiency, thinner roots, and greater specific root length and root nutrient concentrations. However, warming had a negligible effect in terms of functional diversity. In addition, warming shifted hub traits which have the highest centrality in the network from specific root area to leaf area. These results demonstrate that above- and belowground traits exhibit consistent adaptive strategies, with more acquisitive traits in warmer environments. Such changes could provide an adaptive advantage for plants in response to environmental change.

Within-individual leaf trait variation increases with phenotypic integration in a subtropical tree diversity experiment

Covariation of plant functional traits, that is, phenotypic integration, might constrain their variability. This was observed for inter- and intraspecific variation, but there is no evidence of a relationship between phenotypic integration and the functional variation within single plants (within-individual trait variation; WTV), which could be key to understand the extent of WTV in contexts like plant-plant interactions. We studied the relationship between WTV and phenotypic integration in c. 500 trees of 21 species in planted forest patches varying in species richness in subtropical China. Using visible and near-infrared spectroscopy (Vis-NIRS), we measured nine leaf morphological and chemical traits. For each tree, we assessed metrics of single and multitrait variation to assess WTV, and we used plant trait network properties based on trait correlations to quantify phenotypic integration. Against expectations, strong phenotypic integration within a tree led to greater variation across leaves. Not only this was true for single traits, but also the dispersion in a tree's multitrait hypervolume was positively associated with tree's phenotypic integration. Surprisingly, we only detected weak influence of the surrounding tree-species diversity on these relationships. Our study suggests that integrated phenotypes allow the variability of leaf phenotypes within the organism and supports that phenotypic integration prevents maladaptive variation.

Plant diversity increases above- and below-ground biomass by regulating multidimensional functional trait characteristics

BACKGROUND AND AIMS

Nitrogen enrichment affects biodiversity, plant functional traits and ecosystem functions. However, the direct and indirect effects of nitrogen addition and biodiversity on the links between plant traits and ecosystem functions have been largely overlooked, even though multidimensional characteristics of plant functional traits are probably critical predictors of ecosystem functions.

METHODS

To investigate the mechanism underlying the links between plant trait identity, diversity, network topology and above- and below-ground biomass along a plant species richness gradient under different nitrogen addition levels, a common garden experiment was conducted in which those driving factors were manipulated.

KEY RESULTS

The study found that nitrogen addition increased above-ground biomass but not below-ground biomass, while species richness was positively associated with above- and below-ground biomass. Nitrogen addition had minor effects on plant trait identity and diversity, and on the connectivity and complexity of the trait networks. However, species richness increased above-ground biomass mainly by increasing leaf trait diversity and network modularity, and enhanced below-ground biomass through an increase in root nitrogen concentration and network modularity.

CONCLUSIONS

The results demonstrate the mechanistic links between community biomass and plant trait identity, diversity and network topology, and show that the trait network architecture could be an indicator of the effects of global changes on ecosystem functions as importantly as trait identity and diversity.

Rapid Adaptation of Chimonobambusa opienensis Leaves to Crown-Thinning in Giant Panda Ecological Corridor, Niba Mountain

Leaf traits reflect the ecological strategy in heterogeneous contexts and are widely used to explore the adaption of plant species to environmental change. However, the knowledge of short-term effect of canopy management on understorey plant leaf traits is still limited. Here, we studied the short-term effect of crown-thinning on the leaf morphological traits of bamboo (Chimonobambusa opienensis), an important understorey plant and staple food for the giant panda (Ailuropoda melanoleuca) of Niba Mountain. Our treatments were two crown-thinnings (spruce plantation, CS, and deciduous broad-leaved forest, CB) and two controls (broad-leaved forest canopy, FC, and the bamboo grove of clearcutting, BC). The results showed that: the CS enhanced the annual leaf length, width, area, and thickness, CB decreased almost all annual leaf traits, and perennial leaf traits in CS and CB were the opposite. The log-transformed allometric relationships of length vs. width, biomass vs. area were significantly positive while those of specific leaf area vs. thickness were significantly negative, which varied largely in treatments and age. The leaf traits and allometric relationships suggested that the CS created a more suitable habitat for bamboo growth. This study highlighted that the understorey bamboo leaf traits could adapt the improved light environment induced by crown-thinning rapidly.

Plant trait networks reveal adaptation strategies in the drylands of China

BACKGROUND

Plants accomplish multiple functions by the interrelationships between functional traits. Clarifying the complex relationships between plant traits would enable us to better understand how plants employ different strategies to adapt to the environment. Although increasing attention is being paid to plant traits, few studies focused on the adaptation to aridity through the relationship among multiple traits. We established plant trait networks (PTNs) to explore the interdependence of sixteen plant traits across drylands.

RESULTS

Our results revealed significant differences in PTNs among different plant life-forms and different levels of aridity. Trait relationships for woody plants were weaker, but were more modularized than for herbs. Woody plants were more connected in economic traits, whereas herbs were more connected in structural traits to reduce damage caused by drought. Furthermore, the correlations between traits were tighter with higher edge density in semi-arid than in arid regions, suggesting that resource sharing and trait coordination are more advantageous under low drought conditions. Importantly, our results demonstrated that stem phosphorus concentration (SPC) was a hub trait correlated with other traits across drylands.

CONCLUSIONS

The results demonstrate that plants exhibited adaptations to the arid environment by adjusting trait modules through alternative strategies. PTNs provide a new insight into understanding the adaptation strategies of plants to drought stress based on the interdependence among plant functional traits.

Effects of N and P additions on twig traits of wild apple (Malus sieversii) saplings

BACKGROUND

Wild apple (Malus sieversii) is under second-class national protection in China and one of the lineal ancestors of cultivated apples worldwide. In recent decades, the natural habitation area of wild apple trees has been seriously declining, resulting in a lack of saplings and difficulty in population regeneration. Artificial near-natural breeding is crucial for protecting and restoring wild apple populations, and adding nitrogen (N) and phosphorous (P) is one of the important measures to improve the growth performance of saplings. In this study, field experiments using N (CK, N1, N2, and N3: 0, 10, 20, and 40 g m^- 2 yr^- 1, respectively), P (CK, P1, P2, and P3: 0, 2, 4, and 8 g m^- 2 yr^- 1, respectively), N20Px (CK, N2P1, N2P2, and N2P3: N20P2, N20P4 and N20P8 g m^- 2 yr^- 1, respectively), and NxP4 (CK, N1P2, N2P2, and N3P2: N10P4, N20P4, and N40P4 g m^- 2 yr^- 1, respectively) treatments (totaling 12 levels, including one CK) were conducted in four consecutive years. The twig traits (including four current-year stem, 10 leaf, and three ratio traits) and comprehensive growth performance of wild apple saplings were analyzed under different nutrient treatments.

RESULTS

N addition had a significantly positive effect on stem length, basal diameter, leaf area, and leaf dry mass, whereas P addition had a significantly positive effect on stem length and basal diameter only. The combination of N and P (NxP4 and N20Px) treatments evidently promoted stem growth at moderate concentrations; however, the N20Px treatment showed a markedly negative effect at low concentrations and a positive effect at moderate and high concentrations. The ratio traits (leaf intensity, leaf area ratio, and leaf to stem mass ratio) decreased with the increase in nutrient concentration under each treatment. In the plant trait network, basal diameter, stem mass, and twig mass were tightly connected to other traits after nutrient treatments, indicating that stem traits play an important role in twig growth. The membership function revealed that the greatest comprehensive growth performance of saplings was achieved after N addition alone, followed by that under the NxP4 treatment (except for N40P4).

CONCLUSIONS

Consequently, artificial nutrient treatments for four years significantly but differentially altered the growth status of wild apple saplings, and the use of appropriate N fertilizer promoted sapling growth. These results can provide scientific basis for the conservation and management of wild apple populations.

Characteristics of plant trait network and its influencing factors in impounded lakes and channel rivers of South-to-North Water Transfer Project, China

Trait-based approaches have been widely used to evaluate the effects of variable environments on submerged macrophytes communities. However, little research focused on the response of submerged macrophytes to variable environmental factors in impounded lakes and channel rivers of water transfer project, especially from a whole plant trait network (PTN) perspective. Here, we conducted a field survey designed to clarify the characteristic of PTN topology among impounded lakes and channel rivers of the East Route of South-to-North Water Transfer Project (ERSNWTP) and to unravel the effects of determining factors on the PTN topology structure. Overall, our results showed that leaf-related traits and organ mass allocation traits were the hub traits of PTNs in impounded lakes and channel rivers of the ERSNWTP, which traits with high variability were more likely to be the hub traits. Moreover, PTNs showed different structures among impounded lakes and channel rivers, and PTNs topologies were related to the mean functional variation coefficients of lakes and channel rivers. Specially, higher mean functional variation coefficients represented tight PTN, and lower mean functional variation coefficients indicated loose PTN. The PTN structure was significantly affected by water total phosphorus and dissolved oxygen. Edge density increased, while average path length decreased with increasing total phosphorus. Edge density and average clustering coefficient showed significant decreases with increasing dissolved oxygen, while average path length and modularity exhibited significant increases with increasing dissolved oxygen. This study explores the changing patterns and determinants of trait networks along environmental gradients to improve our understanding of ecological rules regulating trait correlations.

Using leaf traits to explain species co-existence and its consequences for primary productivity across a forest-steppe ecotone

Trait-based approaches have been widely applied to uncover the mechanisms determining community assembly and biodiversity-ecosystem functioning relationships. However, they have rarely been used in forest-steppe ecotones. These ecosystems are extremely sensitive to disturbances due to their relatively complex ecosystem structures, functionings and processes. In this study, we selected seven sites along a transect from closed canopy forests (CF) to forest-steppe ecotones (FSE) and meadow steppes (MS) in northeast China. Six leaf functional traits (i.e. leaf nitrogen and phosphorus contents, leaf length and thickness, single leaf area and leaf mass per unit area, LMA) as well as the community composition and aboveground biomass at each site were measured. Both functional trait diversity indices (richness, evenness and divergence) and community-weighted mean trait values (CWMs) were calculated to quantify community trait distributions. We found that dominant species in the FSE communities showed acquisitive strategies with highest leaf nitrogen (Mean ± SE: 19.6 ± 0.5 mg g^-1) and single leaf area (19.2 ± 1.3 cm²), but the lowest LMA (59.6 ± 1.3 g cm^-2) values compared to adjacent CF and MS communities. The ecotone communities also exhibited the largest functional trait richness (TOP), evenness (TED) and divergence (FDis) values (0.46, 0.92 and 0.67, respectively). Overall, niche differentiation emerges as the main mechanism influencing the coexistence of plant species in ecotone ecosystems. In addition, CWMs of leaf traits were the most important predictors for estimating variations in aboveground productivity across the transect, suggesting a major influence of dominant species. Our findings suggest that vegetation management practices in forest-steppe ecotones should increasingly focus on community functional trait diversity, and support the establishment and regeneration of plant species with rapid resource acquisition strategies.

Linking trait network to growth performance of submerged macrophytes in response to ammonium pulse

Extreme precipitation events caused by climate change leads to large variation of nitrogen input to aquatic ecosystems. Our previous study demonstrated the significant effect of different ammonium pulse patterns (differing in magnitude and frequency) on submersed macrophyte growth based on six plant morphological traits. However, how connectivity among plant traits responds to nitrogen pulse changes, which in turn affects plant performance, has not yet been fully elucidated. The response of three common submersed macrophytes (Myriophyllum spicatum, Vallisneria natans and Potamogeton maackianus) to three ammonium pulse patterns was tested using plant trait network (PTN) analysis based on 18 measured physiological and morphological traits. We found that ammonium pulses enhanced trait connectivity in PTN, which may enable plants to assimilate ammonium and/or mitigate ammonium toxicity. Large input pulses with low frequency had stronger effects on PTNs compared to low input pulses with high frequency. Due to the cumulative and time-lagged effect of the plant response to the ammonium pulse, there was a profound and prolonged effect on plant performance after the release of the pulse. The highly connected traits in PTN were those related to biomass allocation (e.g., plant biomass, stem ratio, leaf ratio and ramet number) rather than physiological traits, while phenotype-related traits (e.g., plant height, root length and AB ratio) and energy storage-related traits (e.g., stem starch) were least connected. V. natans showed clear functional divergence among traits, making it more flexible to cope with unfavorable habitats (i.e., high input pulses with low frequencies). M. spicatum with high RGR revealed strong correlations among traits and thus supported nitrogen accumulation from favourable environments (i.e., low input pulses with high frequencies). Our study highlights the responses of PTN for submerged macrophytes to ammonium pulses depends on their intrinsic metabolic rates, the magnitude, frequency and duration of the pulses, and our results contribute to the understanding of the impact of resource pulses on the population dynamics of submersed macrophytes within the context of global climate change.

An integrated leaf trait analysis of two Paleogene leaf floras

Objectives

This study presents the Integrated Leaf Trait Analysis (ILTA), a workflow for the combined application of methodologies in leaf trait and insect herbivory analyses on fossil dicot leaf assemblages. The objectives were (1) to record the leaf morphological variability, (2) to describe the herbivory pattern on fossil leaves, (3) to explore relations between leaf morphological trait combination types (TCTs), quantitative leaf traits, and other plant characteristics (e.g., phenology), and (4) to explore relations of leaf traits and insect herbivory.

Material and Methods

The leaves of the early Oligocene floras Seifhennersdorf (Saxony, Germany) and Suletice-Berand (Ústí nad Labem Region, Czech Republic) were analyzed. The TCT approach was used to record the leaf morphological patterns. Metrics based on damage types on leaves were used to describe the kind and extent of insect herbivory. The leaf assemblages were characterized quantitatively (e.g., leaf area and leaf mass per area (LM_A)) based on subsamples of 400 leaves per site. Multivariate analyses were performed to explore trait variations.

Results

In Seifhennersdorf, toothed leaves of TCT F from deciduous fossil-species are most frequent. The flora of Suletice-Berand is dominated by evergreen fossil-species, which is reflected by the occurrence of toothed and untoothed leaves with closed secondary venation types (TCTs A or E). Significant differences are observed for mean leaf area and LM_A, with larger leaves tending to lower LM_A in Seifhennersdorf and smaller leaves tending to higher LM_A in Suletice-Berand. The frequency and richness of damage types are significantly higher in Suletice-Berand than in Seifhennersdorf. In Seifhennersdorf, the evidence of damage types is highest on deciduous fossil-species, whereas it is highest on evergreen fossil-species in Suletice-Berand. Overall, insect herbivory tends to be more frequently to occur on toothed leaves (TCTs E, F, and P) that are of low LM_A. The frequency, richness, and occurrence of damage types vary among fossil-species with similar phenology and TCT. In general, they are highest on leaves of abundant fossil-species.

Discussion

TCTs reflect the diversity and abundance of leaf architectural types of fossil floras. Differences in TCT proportions and quantitative leaf traits may be consistent with local variations in the proportion of broad-leaved deciduous and evergreen elements in the ecotonal vegetation of the early Oligocene. A correlation between leaf size, LM_A, and fossil-species indicates that trait variations are partly dependent on the taxonomic composition. Leaf morphology or TCTs itself cannot explain the difference in insect herbivory on leaves. It is a more complex relationship where leaf morphology, LM_A, phenology, and taxonomic affiliation are crucial.

Linking the network topology of plant traits with community structure, functioning, and adaptive strategies of submerged macrophytes

Plant trait network analysis can calculate the topology of trait correlations and clarify the complex relationships among traits, providing new insights into ecological topics, including trait dimensions and phenotypic integration. However, few studies have focused on the relationships between network topology and community structure, functioning, and adaptive strategies, especially in natural submerged macrophyte communities. In this study, we collected 15 macrophyte community-level traits from 12 shallow lakes in the Yangtze River Basin in the process of eutrophication and analyzed the changes in trait network structure (i.e., total phosphorus, TP) by using a moving window method. Our results showed that water TP significantly changed the topology of trait networks. Specifically, under low or high nutrient levels, the network structure was more dispersed, with lower connectance and higher modularity than that found at moderate nutrient levels. We also found that network connectance was positively correlated with community biomass and homeostasis, while network modularity was negatively correlated with community biomass and homeostasis. In addition, modules and hub traits also changed with the intensity of eutrophication, which can reflect the trait integration and adaptation strategies of plants in a stressful environment. At low or high nutrient levels, more modules were differentiated, and those modules with higher strength were related to community nutrition. Our results clarified the dynamics of community structure and functioning from a new perspective of plant trait networks, which is key to predicting the response of ecosystems to environmental changes.