Ecological stoichiometry of the epiphyte community in a subtropical forest canopy

Vascular epiphyte populations with higher leaf nutrient concentrations showed weaker resilience to an extreme drought in a montane cloud forest

Leaf stoichiometry can characterize plant ecological strategies and correlate with plant responses to climate change. The role of vascular epiphytes in the ecosystem processes of tropical and subtropical forest ecosystems cannot be ignored. Vascular epiphytes are very vulnerable to climate change, however, the relationship between the response of epiphytes to climate change and leaf stoichiometry is not well understood. We present data for 19 vascular epiphyte species that were collected during four consecutive censuses (in 2005, 2010, 2015, and 2020) over 15 years in a subtropical montane cloud forest. We assessed the relationships between the population dynamics and leaf stoichiometry of these vascular epiphytes. Experiencing an extreme drought, 14 of the 19 epiphyte species showed an obvious decrease in the number of individuals, and all species showed negative growth in the number of populations. Subsequently, the total number of individuals gradually recovered, increasing from 7,195 in 2010 to 10,121 in 2015, then to 13,667 in 2020. The increase in the number of vascular epiphyte individuals from 2010 to 2015 was significantly negatively correlated with leaf nitrogen and phosphorus concentration, and was significantly positively correlated with the leaf carbon-nitrogen ratio. Vascular epiphyte populations with higher leaf nutrient concentrations exhibited weaker resilience to the extreme drought, which demonstrated that a resource-conservative strategy was advantageous for the recovery of epiphyte populations. Our findings suggest that ecological stoichiometry can be a useful framework for forecasting the dynamics of vascular epiphyte populations in response to climate change.

From atoms to ecosystems: elementome diversity meets ecosystem functioning

The elemental composition of plants (the elementome) is a reliable indicator of their functional traits and the ecological strategies that they follow, and thus represents a good predictor of how ecosystems work. Biodiversity and, especially, functional diversity are also widely recognized as important drivers of ecosystem functioning, mainly because of niche partitioning amongst different species. Here, I review evidence indicating that plant elementomes relate to their ecological niches and how plant elemental concentrations may shift in response to abiotic and biotic drivers. I propose the use of ecosystem elementome diversity as a universal metric to compare ecosystems and investigate diversity-ecosystem functioning relationships. Future research using this promising novel approach will bring together elementomes, diversity, and ecosystem functioning.

Do Bryophyte Elemental Concentrations Explain Their Morphological Traits?

Differences in the elemental composition of plants, mainly C, N, and P, have been shown to be related to differences in their nutritional status, and their morphological and functional traits. The relationship between morphological traits and micronutrients and trace elements, however, has been much less studied. Additionally, in bryophytes, research devoted to investigating these relationships is still very scarce. Here, we analysed 80 samples from 29 aquatic and semi-aquatic (hygrophytic) moss species living in Mediterranean springs to investigate the relationship between moss nutrient concentrations and their micro- and macroscopic morphological traits and growth forms. We found that, across species, the elemental concentration of mosses was more tightly linked to macroscopic traits than to microscopic traits. Growth forms could also be successfully explained by the concentration of elements in mosses. Apart from macronutrients and their stoichiometric ratios (C:N, C:P, and N:P), micronutrients and trace elements were also important variables predicting moss morphological traits and growth forms. Additionally, our results showed that microscopic traits were well related to macroscopic traits. Overall, our results clearly indicate that the elemental composition of mosses can be used to infer their morphological traits, and that elements other than macronutrients should be taken into account to achieve a good representation of their morphological and, potentially, functional traits when comparing the elemental composition across species.

Bryophyte C:N:P stoichiometry, biogeochemical niches and elementome plasticity driven by environment and coexistence

Ecological stoichiometry and studies of biogeochemical niches have mainly focused on plankton and vascular plants, but the phenotypically closest modern relatives of early plants, bryophytes, have been largely neglected. We analysed C:N:P stoichiometries and elemental compositions (K, Na, Mg, Ca, S, Fe) of 35 widely distributed bryophyte species inhabiting springs. We estimated bryophyte C:N:P ratios and their biogeochemical niches, investigated how elementomes respond to the environment and determined whether they tend to diverge more for coexisting than non-coexisting individuals and species. The median C:N:P was 145:8:1, intermediate between Redfield's ratio for marine plankton and those for vascular plants. Biogeochemical niches were differentiated amongst species and were phylogenetically conserved. Differences in individual and species-specific elementomes increased with coexistence between species. Our results provide an evolutionary bridge between the ecological stoichiometries of algae and vascular plants and suggest that differences in elementomes could be used to understand community assemblages and functional diversity.

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.