Process‐based vegetation models attempt to represent the wide range of trait variation in biomes by grouping ecologically similar species into plant functional types (PFTs). This approach has been successful in representing many aspects of plant physiology and biophysics but struggles to capture biogeographic history and ecological dynamics that determine biome boundaries and plant distributions. Grass‐dominated ecosystems are broadly distributed across all vegetated continents and harbour large functional diversity, yet most Land Surface Models (LSMs) summarise grasses into two generic PFTs based primarily on differences between temperate C3grasses and (sub)tropical C4grasses. Incorporation of species‐level trait variation is an active area of research to enhance the ecological realism of PFTs, which form the basis for vegetation processes and dynamics in LSMs. Using reported measurements, we developed grass functional trait values (physiological, structural, biochemical, anatomical, phenological, and disturbance‐related) of dominant lineages to improve LSM representations. Our method is fundamentally different from previous efforts, as it uses phylogenetic relatedness to create lineage‐based functional types (LFTs), situated between species‐level trait data and PFT‐level abstractions, thus providing a realistic representation of functional diversity and opening the door to the development of new vegetation models.
This content will become publicly available on June 7, 2024
Evolutionary history plays a key role driving patterns of trait variation across plant species. For scaling and modeling purposes, grass species are typically organized into C3vs C4plant functional types (PFTs). Plant functional type groupings may obscure important functional differences among species. Rather, grouping grasses by evolutionary lineage may better represent grass functional diversity. We measured 11 structural and physiological traits Critically, we found evidence that grass traits varied among lineages, including independent origins of C4photosynthesis. Using a rigorous model selection approach, tribe was included in the top models for five of nine traits for perennial species. Tribes were separable in a multivariate and phylogenetically controlled analysis of traits, owing to coordination of important structural and ecophysiological characteristics. Our findings suggest grouping grass species by photosynthetic pathway overlooks variation in several functional traits, particularly for C4species. These results indicate that further assessment of lineage‐based differences at other sites and across other grass species distributions may improve representation of C4species in trait comparison analyses and modeling investigations.
- NSF-PAR ID:
- 10421036
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 239
- Issue:
- 3
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 875-887
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Summary -
more » « less
Abstract Understanding the mechanisms that promote the coexistence of hundreds of species over small areas in tropical forest remains a challenge. Many tropical tree species are presumed to be functionally equivalent shade tolerant species but exist on a continuum of performance trade‐offs between survival in shade and the ability to quickly grow in sunlight. These trade‐offs can promote coexistence by reducing fitness differences.
Variation in plant functional traits related to resource acquisition is thought to predict variation in performance among species, perhaps explaining community assembly across habitats with gradients in resource availability. Many studies have found low predictive power, however, when linking trait measurements to species demographic rates.
Seedlings face different challenges recruiting on the forest floor and may exhibit different traits and/or performance trade‐offs than older individuals face in the eventual adult niche. Seed mass is the typical proxy for seedling success, but species also differ in cotyledon strategy (reserve vs. photosynthetic) or other leaf, stem and root traits. These can cause species with the same average seed mass to have divergent performance in the same habitat.
We combined long‐term studies of seedling dynamics with functional trait data collected at a standard life‐history stage in three diverse neotropical forests to ask whether variation in coordinated suites of traits predicts variation among species in demographic performance.
Across hundreds of species in Ecuador, Panama and Puerto Rico, we found seedlings displayed correlated suites of leaf, stem, and root traits, which strongly correlated with seed mass and cotyledon strategy. Variation among species in seedling functional traits, seed mass, and cotyledon strategy were strong predictors of trade‐offs in seedling growth and survival. These results underscore the importance of matching the ontogenetic stage of the trait measurement to the stage of demographic dynamics.
Our findings highlight the importance of cotyledon strategy in addition to seed mass as a key component of seed and seedling biology in tropical forests because of the contribution of carbon reserves in storage cotyledons to reducing mortality rates and explaining the growth‐survival trade‐off among species.
Synthesis : With strikingly consistent patterns across three tropical forests, we find strong evidence for the promise of functional traits to provide mechanistic links between seedling form and demographic performance. -
more » « less
Societal Impact Statement Grasses are significant drivers of fires and are the primary food source for cattle in Madagascar's Central Highlands. However, their extent and importance to animals and people in the past remain poorly understood. Clarifying the history of Malagasy grasslands is necessary for building climate resilient food systems and supporting carbon stores that also conserve biodiversity. We generated chemical data for grasses that grow in open habitats in central Madagascar, which will help improve our understanding of the ecological and economic importance of modern grassy ecosystems, reconstruct the regional history of grasses, and anticipate how vegetation may respond to changing climate and rising atmospheric carbon dioxide levels.
Summary Stable carbon isotope (δ13C) data for Malagasy grasses are needed to establish expected values for C3and C4grasses from particular regions in Madagascar, and possible differences among different grass lineages, or species with different distributions or adaptations. These data, in turn, may help inform how widespread grasses were in the past, and the importance of grasses to endemic and domesticated animals as well as people over time.
We analysed both δ13C and weight %C:N from 63 Poaceae species that grow in open grassy biomes in Madagascar's Central Highlands and explored how these values relate to multiple variables, including encounter frequency, distribution, lineage, adaptations to grazing and fire and the typical floral assemblage in which each species occurs.
Of the species sampled, 56 are C4and seven are C3. There are no differences in δ13C or weight %C:N among either C3or C4species with different distributions or adaptations, from different assemblages, or that are frequently or infrequently encountered. However, there are differences in both δ13C and weight %C:N among C4lineages, and the single C3arundinoid (
Styppeiochloa hitchcockii ) has larger weight %C:N than C3Paniceae.Our results provide a foundation for evaluating reliance on C4resources by people, as well as domesticated and endemic animals both today and in the past. We encourage gathering additional comparative data for co‐occurring individual plants from the same open grassy biome localities, as well as other species, habitats and regions in Madagascar.
-
more » « less
Abstract Despite asymmetric competition and a wide array of functional similarities, two ecologically important C4perennial grasses,
Andropogon gerardii andSorghastrum nutans , frequently codominate areas of the mesic tallgrass prairie of the US Great Plains. A subtle difference in their vegetative reproduction strategies may play a role in preventing the exclusion ofS. nutans , the presumed weaker competitor in such regions.While
A. gerardii vegetative tiller densities peak in the early growing season and decline thereafter (determinate recruitment), those ofS. nutans may continue to increase throughout the growing season (indeterminate recruitment), providing a potential avenue for recovery from more intensive early season competition. However, until now these patterns have only been informally observed in the field.We examined the year‐to‐year consistency of growing season vegetative tiller dynamics (measured as seasonal change in tiller densities) of each grass species from an intact tallgrass prairie in Kansas – a site within the core of both species' distributions – over a period of 8 years. Then, to investigate environmental effects on these dynamics, we examined whether they differ across a Kansas landscape varying in topography, fire management regimes, and the abundances of the study species. Finally, we expanded the investigation of environmental effects on growing season tiller dynamics by observing them at the periphery of the species' distributions in central Colorado, where climatic conditions are dryer and the study species' abundances are reduced.
Synthesis . We found that the tiller densities ofA. gerardii decline within seasons with striking consistency regardless of spatio‐temporal scale or environmental factors (topography and fire regimes). In contrast, we found the seasonal dynamics ofS. nutans tiller densities were dependent on environmental factors, with seasonal tiller density increases occurring only within the Kansas populations but not consistent between years. These observations lay the groundwork for establishing differences in tiller recruitment determinacy as a potentially important yet underappreciated mechanism for promoting coexistence and codominance among perennial plant species. -
more » « less
Abstract The effect of species loss on ecosystem productivity is determined by both the functional contribution of the species lost, and the response of the remaining species in the community. According to the mass ratio hypothesis, the loss of a dominant plant species, which has a larger proportionate contribution to productivity, is expected to exert an overwhelming effect on this important ecosystem function. However, via competitive release, loss of a dominant species can provide the opportunity for other plant species to establish, thrive and become abundant in the community, potentially compensating for the function lost. Furthermore, if resource limitation is removed, then the compensatory response of function to the loss of a dominant species should be greater and more rapid than if resources are more limiting.
To evaluate how resources may limit compensation of above‐ground productivity to the loss of a dominant plant species, we experimentally removed the C4perennial tallgrass,
Andropogon gerardii , from intact plant communities. We added water for 4 years, as well as nitrogen in the fourth year, to test the effect of resource limitation on the compensatory response.Overall, above‐ground biomass production increased in the remaining community with both water and nitrogen addition. However, this increase in biomass production was not sufficient to fully compensate for the loss of
A. gerardii , indicating water and nitrogen were not limiting short‐term compensation in this community.Following the removal of the dominant species, there was reordering of species abundances in the community, rather than changes in species richness. The C4grass
Bouteloua curtipendula was the most responsive species, increasing by 57.9% in abundance with water addition and 91.0% with both water and nitrogen addition. Despite this dramatic increase in abundance, its short stature and lower per capita biomass production prevented this species from compensating for the loss ofA. gerardii .Synthesis . Short‐term compensation after the loss of a dominant plant species can be hastened by increased resource availability, but ultimately full compensation appears to be limited by the presence and abundance of species in the remaining community that possess traits that allow them compensate for the species lost.
