Contrasting effects of plant inter- and intraspecific variation on community trait responses to nitrogen addition and drought in typical and meadow steppes

A simple new method to determine leaf specific heat capacity

BACKGROUND

Quantifying plant transpiration via thermal imaging is desirable for applications in agriculture, plant breeding, and plant science. However, thermal imaging under natural non-steady state conditions is currently limited by the difficulty of quantifying thermal properties of leaves, especially specific heat capacity (Cp). Existing literature offers only rough estimates of Cp and lacks simple and accurate methods to determine it.

RESULTS

We developed a non-invasive method to quantify k (the product of leaf thickness (lt), leaf density(ρ), and Cp), by fitting a leaf energy balance model to a leaf temperature (Tleaf) transient during and after a ~ 10 s light pulse. Cp was then estimated by dividing k by lt*ρ. Using this method, we quantified Cp for 13 horticultural and tropical plant species, and explored the relationship between Cp and leaf water content, specific leaf area and Tleaf response rate during the light pulse. Values of Cp ranged between 3200-4000 J kg-1 K-1, and were positively correlated with leaf water content. In species with very thick leaves, such as Phalaenopsis amabilis, we found leaf thickness to be a major factor in the temperature response to a short light pulse.

CONCLUSIONS

Our method allows for easy determination of leaf Cp of different species, and may help pave the way to apply more accurate thermal imaging under natural non-steady state conditions.

Effects of drought and moisture stress on the growth and ecophysiological traits of Schima superba seedlings

Changes in rainfall patterns are important environmental factors affecting plant growth, especially when larger precipitation events and prolonged drought periods occur in subtropical regions. There are many studies on how drought reduces plant biomass through drought-sensitive functional traits, but how excess water affects plant growth and ecophysiology is still poorly understood. Therefore, a greenhouse experiment was conducted on Schima superba (Theaceae), a dominant tree species in subtropical forests and commonly used in forestry, in a closed chamber under control (25% soil water content (SWC) as in local forests), drought stress (D, 15% SWC) and moisture stress (W, 35% SWC). Plant growth and ecophysiological traits related to morphology, leaf gas exchange, water potential and structural traits were measured. Compared to control, S. suberba under dry conditions significantly decreased its aboveground biomass, photosynthetic rate (A), leaf water potential and nitrogen use efficiency, but increased intrinsic water use efficiency, root to shoot ratio and specific root length. S. superba under wet conditions also significantly decreased its total biomass, aboveground biomass and specific root length, while W had no effect on A and leaf water potential. Our results indicate that S. superba shows a decrease in carbon gain under drought stress, but less response under wet conditions. This emphasizes the need to consider the strength and frequency of rainfall pattern changes in future studies because rainfall may either alleviate or intensify the effects of drought stress depending on the moisture level, thus suitable water conditions is important for better management of this tree species in subtropical China.

Responses of Intraspecific and Interspecific Trait Variations to Nitrogen Addition in a Tibetan Alpine Meadow

A community functional structure may respond to environmental changes such as nitrogen (N) enrichment by altering intraspecific and interspecific trait variations. However, the relative contributions of both components in determining the community response to N enrichment are unclear. In this study, we measured the plant height (H), leaf area (LA), leaf dry matter content (LDMC), and specific leaf area (SLA) based on a nine-year N addition gradient experiment in an alpine meadow on the Tibetan Plateau. We examined the intraspecific and interspecific variations within and among the communities, the responses of traits in terms of community weighted mean (CWM) and non-weighted mean (CM) to N addition, and the effects of these trait variations on aboveground net primary productivity (ANPP). Our results show that N addition increased the interspecific variation in H while decreasing that of LA within the community, whereas it had no significant effects on the intraspecific variations in the four traits within the community. In contrast, N addition significantly increased the intraspecific variation in H and decreased that of LA among the communities. Moreover, the contribution of intraspecific variation was greater than that of the interspecific variation in terms of CWM for all traits, while the opposite contribution was observed in terms of CM, suggesting that the dominant species would have greater resilience while subdominant species would become less resistant to N addition. Further, intraspecific variations of LA and LDMC within the community played an important role in explaining community productivity. Our results highlight the importance of both intraspecific and interspecific variations in mediating functional trait responses to N enrichment, and intraspecific variation within the communities has important implications for community functioning that should be considered to better understand and predict the responses of the alpine grasslands to N enrichment.

Biological outliers: essential elements to understand the causes and consequences of reductions in maximum photochemical efficiency of PSII in plants

MAIN CONCLUSION

By studying Cistus albidus shrubs in their natural habitat, we show that biological outliers can help us to understand the causes and consequences of maximum photochemical efficiency decreases in plants, thus reinforcing the importance of integrating these often-neglected data into scientific practice. Outliers are individuals with exceptional traits that are often excluded of data analysis. However, this may result in very important mistakes not accurately capturing the true trajectory of the population, thereby limiting our understanding of a given biological process. Here, we studied the role of biological outliers in understanding the causes and consequences of maximum photochemical efficiency decreases in plants, using the semi-deciduous shrub C. albidus growing in a Mediterranean-type ecosystem. We assessed interindividual variability in winter, spring and summer maximum PSII photochemical efficiency in a population of C. albidus growing under Mediterranean conditions. A strong correlation was observed between maximum PSII photochemical efficiency (Fv/Fm ratio) and leaf water desiccation. While decreases in maximum PSII photochemical efficiency did not result in any damage at the organ level during winter, reductions in the Fv/Fm ratio were associated to leaf mortality during summer. However, all plants could recover after rainfalls, thus maximum PSII photochemical efficiency decreases did not result in an increased mortality at the organism level, despite extreme water deficit and temperatures exceeding 40ºC during the summer. We conclude that, once methodological outliers are excluded, not only biological outliers must not be excluded from data analysis, but focusing on them is crucial to understand the causes and consequences of maximum PSII photochemical efficiency decreases in plants.

Intraspecific variation in fine-root traits is larger than in aboveground traits in European herbaceous species regardless of drought

Differences within species (Intraspecific trait variation - ITV) contribute substantially to overall trait variability and environmental harshness can reduce among-species variation. While aboveground traits have received considerable attention, knowledge about ITV in fine-root traits and how it differs from ITV in aboveground traits remains limited. This study examined the partitioning of trait variation aboveground and fine-root traits in 52 European herbaceous species and how such proportions change in response to drought, offering valuable insights for accurate functional species characterization and inter-species comparisons. We studied seven morphological aboveground and fine-root traits under drought and well-watered conditions in a greenhouse experiment. Linear mixed effect models and permutational multivariate analysis of variance (PERMANOVA) were employed to decompose trait variation, ensuring the robustness of our results. We also calculated variance partitioning for the combination of aboveground traits and the combination of fine-root traits, as well as pairs of analogous leaf and fine-root traits (i.e., traits that fulfill similar functions) for each treatment (control and drought). Among-species trait differences explained a greater proportion of overall variance than within-species variation, except for root dry matter content (RDMC). Height and leaf area stood out, with species' identity accounting for 87-90% of total trait variation. Drought had no significant effect on the proportions of variation in any of the traits. However, the combination of fine-root traits exhibited higher intraspecific variability (44-44%) than aboveground traits (19-21%) under both drought and control. Analogous root traits also showed higher ITV (51-50%) than analogous leaf traits (27-31%). Our findings highlight substantial within-species variation and the nuanced responses of fine-root traits, particularly RDMC, suggesting root traits' flexibility to soil heterogeneity that fosters less differentiation among species. Among-species trait differences, especially aboveground, may underscore distinct strategies and competitive abilities for resource acquisition and utilization. This study contributes to elucidate the mechanisms underlying the multifunctionality of the above- and belowground plants compartments.

Linking functional composition moments of the sub-Mediterranean ecotone with environmental drivers

Introduction

Functional trait-based approaches are extensively applied to the study of mechanisms governing community assembly along environmental gradients. These approaches have been classically based on studying differences in mean values among species, but there is increasing recognition that alternative metrics of trait distributions should be considered to decipher the mechanisms determining community assembly and species coexistence. Under this framework, the main aim of this study is to unravel the effects of environmental conditions as drivers of plant community assembly in sub-Mediterranean ecotones.

Methods

We set 60 plots in six plant communities of a sub-Mediterranean forest in Central Spain, and measured key above- and belowground functional traits in 411 individuals belonging to 19 species, along with abiotic variables. We calculated community-weighted mean (CWM), skewness (CWS) and kurtosis (CWK) of three plant dimensions, and used maximum likelihood techniques to analyze how variation in these functional community traits was driven by abiotic factors. Additionally, we estimated the relative contribution of intraspecific trait variability and species turnover to variation in CWM.

Results and discussion

The first three axes of variation of the principal component analyses were related to three main plant ecological dimensions: Leaf Economics Spectrum, Root Economics Spectrum and plant hydraulic architecture, respectively. Type of community was the most important factor determining differences in the functional structure among communities, as compared to the role of abiotic variables. We found strong differences among communities in their CWMs in line with their biogeographic origin (Eurosiberian vs Mediterranean), while differences in CWS and CWK indicate different trends in the functional structure among communities and the coexistence of different functional strategies, respectively. Moreover, changes in functional composition were primarily due to intraspecific variability.

Conclusion

We observed a high number of strategies in the forest with the different communities spreading along the acquisitive-conservative axis of resource-use, partly matching their Eurosiberian-Mediterranean nature, respectively. Intraspecific trait variability, rather than species turnover, stood as the most relevant factor when analyzing functional changes and assembly patterns among communities. Altogether, our data support the notion that ecotones are ecosystems where relatively minor environmental shifts may result in changes in plant and functional composition.

Distribution and morphological variation of tree ferns (Cyatheaceae) along an elevation gradient

Knowing how species and communities respond to environmental change is fundamental in the context of climate change. The search for patterns of abundance and phenotypic variation along altitudinal gradients can provide evidence on adaptive limits. We evaluated the species abundance and the variation in morphometric and stomatal characters in five tree ferns species (Cyathea fulva, C. divergens, C. myosuroides, Alsophila firma and Gymnosphaera salvinii) distributed along an elevation gradient in a well-preserved Mexican cloud forest. Variation at the community and species level was assessed using exploratory and multivariate data analysis methods. We wanted to explore if the species abundance is environmentally determined, to determine the degree of variation along the elevation gradient, to test for differences between zones and associations with elevation, humidity and soil nutrients, and to assess contribution of the intra- and interspecific variation to the community response to elevation and soil nutrients. The studied fern community showed strong species turnover along the elevation gradient, with some influence of soil nutrient concentration, supporting environmental determinism. All measured characters displayed variation along the gradient. Stomatal characters (size and density) had significantly less variation than morphometric characters (trunk diameter, stipe length and blade length), but stomatal density also shows interesting intraspecific patterns. In general, patterns within the fern community suggest a strong influence of species identity, especially of species inhabiting the lower edge of the cloud forest, which showed the clearest morphometric and stomatal patterns, associated to contrasting environments rather than to changes in elevation. The coincidence between morphometric and stomatal patterns in this area suggest hydraulic adjustments in response to contrasting environments. Our results provide evidence that tree ferns species respond to environmental changes through adjustments of morphometric plasticity and stomatal density, which is relevant to predict possible responses to variation in environmental conditions resulting from climate change.

Multifunctionality and maintenance mechanism of wetland ecosystems in the littoral zone of the northern semi-arid region lake driven by environmental factors

The relationship between biodiversity and ecosystem multifunctionality (BEMF) has become an ecological research hot spot in recent years. Changes in biodiversity are non-randomly distributed in space and time in natural ecosystems, and the BEMF relationship is affected by a combination of biotic and abiotic factors. These complex, uncertain relationships are affected by research scale and quantification and measurement indicators. This paper took the Daihai littoral zone wetlands in Inner Mongolia as the research object to reveal the dynamic succession of wetland vegetation and ecosystem function change characteristics and processes during the shrinkage of the lake. The main findings were as follows: the combined effect of aboveground (species and functions) and belowground (bacteria and fungi) diversity was greater than the effect of single components on ecosystem multifunctionality (EMF) (R² = 80.00 %). Soil salinity (EC) had a direct negative effect on EMF (λ = -0.22), and soil moisture (SM) had a direct positive effect on EMF (λ = 0.19). The results of the hierarchical partitioning analysis showed that plant species richness (Margalef index) was the ideal indicator to explain the EMF and C, N, and P cycling functions in littoral zone wetlands with explanations of 12.25 %, 7.31 %, 7.83 %, and 5.33 %, respectively. The EMF and C and P cycles were mainly affected by bacterial diversity, and the N cycle was mainly affected by fungal abundance in belowground biodiversity. Margalef index and sand content affected EMF through cascading effects of multiple nutrients (FDis, CWM_RV, CWM_LCC, and bacterial and fungal abundance and diversity) in littoral zone wetlands. This paper provides a reference for exploring the multifunctionality maintenance mechanisms of natural littoral zone wetland ecosystems in the context of global change, and it also provides important theoretical support and basic data for the implementation of ecological restoration in Daihai lake.

Effects of Simulated Nitrogen Deposition and Micro-Environment on the Functional Traits of Two Rare and Endangered Fern Species in a Subtropical Forest

Although the effects of N deposition on forest plants have been widely reported, few studies have focused on rare and endangered fern species (REFs). Information is also lacking on the effects of micro-environments on REFs. We investigated the effects of N addition (canopy and understory N addition, CAN, and UAN) and micro-environments (soil and canopy conditions) on the functional traits (growth, defense, and reproduction; 19 traits in total) of two REFs-Alsophila podophylla and Cibotium baromet-in a subtropical forest in South China. We found that, compared to controls, CAN or UAN decreased the growth traits (e.g., plant height, H) of C. baromet, increased its defense traits (e.g., leaf organic acid concentrations, OA), delayed its reproductive event (all-spore release date), and prolonged its reproductive duration. In contrast, A. podophylla showed increased growth traits (e.g., H), decreased defense traits (e.g., OA), and advanced reproductive events (e.g., the all-spore emergence date) under CAN or UAN. Meanwhile, the negative effects on the C. baromet growth traits and A. podophylla defense traits were stronger for CAN than for UAN. In addition, the soil chemical properties always explained more of the variations in the growth and reproductive traits of the two REFs than the N addition. Our study indicates that, under simulated N deposition, C. baromet increases its investment in defense, whereas A. podophylla increases its investment in growth and reproduction; this may cause an increasing A. podophylla population and decreasing C. baromet population in subtropical forests. Our study also highlights the importance of considering micro-environments and the N-addition approach when predicting N deposition impact on subtropical forest REFs.

Disentangling the Interspecific and Intraspecific Variation in Functional Traits of Desert Plant Communities under Different Moisture Gradients

Studying the inter- and intraspecific variation in plant functional traits elucidates their environmental adaptation strategies and the mechanisms of community construction. This study selected the desert plant community in the Lake Ebinur watershed as the research object and considered five different traits: plant height (H), diameter at breast height/base diameter (DBH/BD), leaf length (LL), leaf width (LW), and leaf thickness (LT). This study used redundancy and correlation analyses to investigate the inter- and intraspecies variation in community-level traits, its relationship with soil physicochemical factors under different soil moisture conditions, and their change laws. We also used variance decomposition to analyze the contribution of inter- and intraspecific variation to community weighting. The results showed the following: (1) the values of the plant community functional traits varied according to the water gradient, and the LL (p = 0.01) and DBH/BD (p = 0.038) varied significantly; (2) for intraspecific variation, the DBH/BD variation was high at a low moisture gradient, LL (p = 0.018) and LT (p = 0.030) variation were high at a high moisture gradient, and the differences were significant; (3) under a high moisture gradient, inter- and intraspecific variation contributed 85.8% and 35.7% to community weighting, respectively, whereas under low moisture gradients, inter- and intraspecific variation contributed 53.3% and 25.1%, respectively.