When facilitation meets clonal integration in forest canopies

Clonal integration benefits Calystegia soldanella in heterogeneous habitats

Land-use change and tourism development have seriously threatened the ecosystems of coastal protection forests and beaches. Light and nutrients are spatially heterogeneously distributed between the two ecosystems. Clonal plants, such as Calystegia soldanella, which play a crucial role in maintaining the ecological stability of coastal habitats, are likely to encounter diverse environments. In this study, we investigated clonal integration and the division of labour in C. soldanella under heterogeneous (high nutrient and low light [HNLL]; low nutrient and high light [LNHL]) and homogeneous habitats. We cultivated pairs of connected and severed ramets of C. soldanella in these environments. Our results showed the total biomass (TB) of connected ramets was higher than that of severed ramets in heterogeneous environments, suggesting clonal integration enhances growth in heterogeneous habitats. The root shoot ratio was significantly lower in HNLL than in LNHL conditions for connected ramets, demonstrating a division of labour in growth under heterogeneous conditions. However, parameters of clonal propagation of C. soldanella did not significantly differ between connected and severed ramets in heterogeneous environments, indicating no division of labour in clonal propagation. In homogeneous environments, the growth of C. soldanella did not benefit from clonal integration. Connected ramets in heterogeneous habitats exhibited higher TB than in homogeneous habitats. The TB of one ramet in HNLL was consistently higher than that in LNHL, irrespective of ramet's states, which suggests that high soil nutrients may enhance the growth. We conclude that C. soldanella has the capability of clonal integration to achieve high biomass in heterogeneous but not in homogeneous conditions, and the establishment of coastal protection forests (high nutrient and low light) may foster the growth of C. soldanella.

Effects of clonal fragmentation on Pyrrosia nuda depend on growth stages in a rubber plantation

Introduction

Clonal fragmentation helps to assess clonal plants' growth resilience to human and environmental disturbance. Although clonal integration in epiphytes in tropical rubber plantations is important to understand their role in enhancing biodiversity and ecosystem services, research on this subject is limited. These plantations are typically monospecific economic forests that face increased anthropogenic disturbances.

Methods

In this study, we selected the clonal fern Pyrrosia nuda to study its survival status, biomass, maximum quantum yield of photosystem II (Fv/Fm), and frond length in response to the level of clonal fragmentation in a tropical rubber plantation.

Results and discussion

The results showed that (1) clonal fragmentation significantly negatively affected the survival rate, biomass, and frond length of clonal plants, but with minimal effects on Fv/Fm at different growth stages; (2) the performance of a ramet (e.g., biomass or frond length) increased with ramet developmental ages and decreased with the number of ramets in a clonal fragment. The age-dependent impacts of clonal fragmentation provide insights into the biodiversity conservation of epiphytes and forest management in man-made plantations. Therefore, to better conserve the biodiversity in tropical forests, especially in environment-friendly rubber plantations, there is a need to reduce anthropogenic disturbances and alleviate the level of fragmentation.

Vertical variation in leaf functional traits of Parashorea chinensis with different canopy layers

Introduction

Canopy species need to shift their ecological adaptation to improve light and water resources utilization, and the study of intraspecific variations in plant leaf functional traits based at individual scale is of great significance for evaluating plant adaptability to climate change.

Methods

In this study, we evaluate how leaf functional traits of giant trees relate to spatial niche specialization along a vertical gradient. We sampled the tropical flagship species of Parashorea chinensis around 60 meters tall and divided their crowns into three vertical layers. Fourteen key leaf functional traits including leaf morphology, photosynthetic, hydraulic and chemical physiology were measured at each canopy layer to investigate the intraspecific variation of leaf traits and the interrelationships between different functional traits. Additionally, due to the potential impact of different measurement methods (in-situ and ex-situ branch) on photosynthetic physiological parameters, we also compared the effects of these two gas exchange measurements.

Results and discussion

In-situ measurements revealed that most leaf functional traits of individual-to-individual P. chinensis varied significantly at different canopy heights. Leaf hydraulic traits such as midday leaf water potential (MWP) and leaf osmotic potential (OP) were insignificantly correlated with leaf photosynthetic physiological traits such as maximal net assimilation rate per mass (A mass). In addition, great discrepancies were found between in-situ and ex-situ measurements of photosynthetic parameters. The ex-situ measurements caused a decrease by 53.63%, 27.86%, and 38.05% in A mass, and a decrease of 50.00%, 19.21%, and 27.90% in light saturation point compared to the in-situ measurements. These findings provided insights into our understanding of the response mechanisms of P. chinensis to micro-habitat in Xishuangbanna tropical seasonal rainforests and the fine scale adaption of different resultant of decoupled traits, which have implications for understanding ecological adaption strategies of P. chinensis under environmental changes.

Clonal integration promotes the growth of Phragmites australis populations in saline wetlands of the Yellow River Delta

Estuarine wetlands are highly heterogeneous due to strong interactions between freshwater input and seawater intrusion. However, little is known about how clonal plant populations adapt to heterogeneous salinity in soil environments. In the present study, the effects of clonal integration on Phragmites australis populations under salinity heterogeneity were studied using field experiments with 10 treatments in the Yellow River Delta. Clonal integration significantly increased plant height, aboveground biomass, underground biomass, root-shoot ratio, intercellular CO₂ concentration, net photosynthetic rate, stomatal conductance, transpiration rate, and stem Na⁺ content under homogeneous treatment. Under the heterogeneous salt treatment, clonal integration significantly affected total aboveground and underground biomass, photosynthetic traits, and stem Na⁺ content under different salt gradients. The increase in salt concentration inhibited the physiological activity and growth of P. australis to varying degrees. Compared with the heterogeneous saline environment, clonal integration was more beneficial to P. australis populations in the homogeneous saline habitat. The results of the present study suggest that P. australis prefers homogeneous saline habitats; however, plants can adapt to heterogeneous salinity conditions via clonal integration.

Effects of Clonal Integration on Foraging Behavior of Three Clonal Plants in Heterogeneous Soil Environments

Environments are ubiquitously heterogeneous in nature, and clonal plants commonly benefit from both clonal integration and foraging responses in heterogeneous environments. While many studies have examined clonal integration and foraging responses separately, few have tested the effect of clonal integration on the foraging response of clonal plants to environmental heterogeneity. We grew offspring ramets of each of three clonal plants (Hydrocotyle vulgaris, Duchesnea indica, and Glechoma longituba) in both homogeneous and heterogenous soil environments and severed their stem connection to a mother ramet (to prevent clonal integration from the mother ramet) or kept it intact (to allow clonal integration). Without clonal integration from the mother ramet, soil heterogeneity had no effect on biomass or number of ramets for any of the three species. With clonal integration, soil heterogeneity also had no effect on biomass or number of ramets of D. indica and G. longituba, but significantly decreased biomass and marginally significantly decreased number of ramets of H. vulgaris. Without clonal integration, offspring ramets did not demonstrate either shoot or root foraging responses in terms of total, shoot and root biomass and ramet number in the heterogeneous soil environment in any of the three species. With integration, offspring ramets of H. vulgaris also did not demonstrate either root or shoot foraging responses, but offspring ramets of G. longituba demonstrated both root and shoot foraging responses, and those of D. indica demonstrated a root foraging response when they grew in the heterogeneous soil environment. We conclude that clonal integration can alter the foraging response of clonal plants, but this effect is species-specific. Our results also suggest that foraging responses of clonal plants in heterogeneous soil environments may not necessarily benefit the growth of clonal plants.

Incorporating clonality into the plant ecology research agenda

A longstanding research divide exists in plant ecology: either focusing on plant clonality, with no ambition to address nonclonal plants, or focusing on all plants, ignoring that many ecological processes can be affected by the fact that some plants are clonal while others are not. This gap cascades into a lack of distinction and knowledge about the similarities and differences between clonal and nonclonal plants. Here we aim to bridge this gap by identifying areas that would benefit from the incorporation of clonal growth into one integrated research platform: namely, response to productivity and disturbance, biotic interactions, and population dynamics. We are convinced that this will provide a roadmap to gain valuable insights into the ecoevolutionary dynamics relevant to all plants.

Host tree traits in pasture areas affect forest and pasture specialist epiphyte species differently

PREMISE

Epiphytes have commensal relationships with their host trees. Besides the influence of tree traits, little has been discussed concerning the ecology of epiphytes in disturbed habitats (e.g., pasture). We herein tested whether the occurrences of pasture and forest specialist epiphytes in pastures are affected differently by tree traits. We hypothesized that (H1) the richness and abundance of generalist epiphytes would be positively associated with area availability; (H2) the richness and abundance of forest epiphyte species would be associated both with (H2.a) area availability and (H2.b) tree traits related to higher seed adherence, and/or (H2.c) less severe habitat (e.g., high humidity and more shade).

METHODS

We sampled 9567 epiphyte individuals from 16 species on 759 scattered remnant trees. The epiphyte species were divided into two ecological groups: forest specialists and pasture specialists. We evaluated four host tree traits: two related to tree size (crown area and trunk diameter) and two related to habitat type (crown leaf density and bark rugosity).

RESULTS

The richness and abundance of both pasture and forest specialists were positively related with tree size. However, the abundance of pasture specialists was negatively related with crown leaf density, whereas richness of forest epiphytes was positively related with bark rugosity.

CONCLUSIONS

Large scattered trees tend to present higher richness and abundance of both pasture and forest specialist epiphytes compared to the smaller trees. However, high crown leaf density limits abundance of pasture specialist epiphytes, whereas rugose bark increases the richness of forest epiphytes.

Divergent Adaptation Strategies of Vascular Facultative Epiphytes to Bark and Soil Habitats: Insights from Stoichiometry

Understanding the stoichiometric traits of plants is critical for studying their ecological adaptation strategies. Facultative epiphytes (which can also live on the ground) are an important component of epiphytic flora of montane forest ecosystems. However, a key gap persists in our understanding how facultative epiphytes can adapt different nutritional conditions of ground and canopy habitats? To study adaptive strategies of facultative epiphytes and the characteristics of the content and stoichiometric homeostasis of C, N, and P elements, we conducted a field experiment and a greenhouse N and P additions cultivation experiment. We found that epiphytic individuals of facultative epiphytes showed lower C:N and C:P ratios, higher variation in elemental composition, and more pronounced N limitation than terrestrial individuals. Moreover, facultative epiphytes showed strong control over the elemental composition of leaves, and their stoichiometric homeostasis of leaves and stems were stronger than roots. Furthermore, the homeostasis of facultative epiphytes decreased in the order N > P. Our results indicated that epiphytic and terrestrial individuals of facultative epiphytes have difference in nutrient limitation, and they use plastic strategies in different habitats. Epiphytic individuals survive in the intermittent habitat through luxury consumption of nutrient while terrestrial individuals were relatively conservative nutrient users. Furthermore, our results implied that facultative epiphytes maintain stable metabolic leaf activity via variable element concentrations of roots to adapt to highly heterogeneous forest habitats.

Clonal integration in Phragmites australis alters soil microbial communities in an oil-contaminated wetland

Clonal plants can share information and resources among connected ramets (asexual individuals). Such clonal integration can promote ramet growth, which may further influence soil microbial communities in the rooting zone. Crude oil contamination can negatively affect plant growth and alter soil microbial community composition. However, we still know little about how clonal integration affects soil microbial communities, especially under crude oil contamination. In a coastal wetland, ramets of the rhizomatous plant Phragmites australis in circular plots (60 cm in diameter) were subjected to 0, 5 and 10 mm depth of crude oil, and the rhizomes at the edge of the plots were either severed (preventing clonal integration) or left intact (allowing clonal integration). After three years of treatment, we analysed in each plot soil physiochemical properties and soil microbial community composition. The alpha-diversity of the soil microbial communities did not differ between intact and severed plots, but was overall lower in 10-mm than in 0-mm and 5-mm oil plots. Considering all three oil treatments together, soil microbial community dissimilarity (beta-diversity) was positively correlated with soil property distance in both severed and intact plots. Considering the three oil treatments separately, this pattern was also observed in 10-mm oil plots, but not in 0-mm or 5-mm oil plots. The soil microbial community composition was more sensitive to the oil addition than to the clonal integration. Moreover, the relative abundance of the nitrogen-cycling bacterial taxa was lower in intact than in severed plots, and that of the oil-degrading bacterial taxa increased with increasing oil-addition levels. Our results indicate that clonal integration and oil contamination can influence soil microbial communities independently through changing the relative abundance of the component bacteria taxa, which has important implications for ecosystem functions of the soil food web mediated by clonal plants.

Growth and Morphological Responses of Duckweed to Clonal Fragmentation, Nutrient Availability, and Population Density

Connected ramets of aquatic clonal plants are susceptible to fragmentation by disturbance. Such clonal fragmentation may interact with nutrient availability and individual density to affect growth and morphology of aquatic clonal plants. We grew the widespread floating clonal plant Spirodela polyrhiza (duckweed) under three levels of population density (low, medium, or high), two levels of nutrient availability (low or high), and two levels of clonal fragmentation (with or without). Clonal fragmentation and high nutrients increased biomass and ramet number, but decreased frond width, frond length, and specific frond area of S. polyrhiza. Increasing population density decreased growth (biomass and ramet number) and frond and root size, and increased frond thickness of individual ramets of S. polyrhiza. The negative effect of population density on growth of S. polyrhiza was greater under high than under low nutrient availability. Furthermore, the negative effect of population density on total mass and frond mass of S. polyrhiza was greater with fragmentation than without. These results suggest that clonal fragmentation, nutrient availability and population density can interact to affect growth and morphology of clonal floating plants. Competition for nutrients and space, rather than light, may be the mechanisms underlying reduced growth of clonal floating plants. As clonal fragmentation can increase biomass and ramet production of S. polyrhiza, disturbance that potentially causes clonal fragmentation cannot be recommended as a measure to limit the spread of clonal floating plants.