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1. Leaf trait coordination and variation of blue oak across topo-environmental scales

   https://doi.org/10.1093/treephys/tpad127  

   Wu, Angelica; Anderegg, Leander_D_L; Dawson, Todd_E; Trugman, Anna_T; Mencuccini, ed., Maurizio (October 2023, Tree Physiology)

   Abstract Trees are arguably the most diverse and complex macro-organisms on Earth. The equally diverse functions of trees directly impact fluxes of carbon, water and energy from the land surface. A number of recent studies have shed light on the substantial within-species variability across plant traits, including aspects of leaf morphology and plant allocation of photosynthates to leaf biomass. Yet, within-tree variability in leaf traits due to microclimatic variations, leaf hydraulic coordination across traits at different physiological scales and variations in leaf traits over a growing season remain poorly studied. This knowledge gap is stymieing the fundamental understanding of what drives trait variation and covariation from tissues to trees to landscapes. Here, we present an extensive dataset measuring within-tree heterogeneity in leaf traits in California’s blue oak (Quercus douglasii) across an edaphic gradient and over the course of a growing season at an oak–grass savanna in Southern CA, USA. We found a high level of within-tree crown leaf area:sapwood area variation that was not attributable to sample height or aspect. We also found a higher level of trait integration at the tree level, rather than branch level, suggesting that trees optimize water use at the organismal level. Despite the large variance in traits within a tree crown and across trees, we did not find strong evidence for adaptive plasticity or acclimation in leaf morphological traits (e.g., changes to phenotype which increased fitness) across temporal and spatial water availability gradients. Collectively, our results highlight strong variation in drought-related physiology, but limited evidence for adaptive trait plasticity over shorter time scales. 

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2. Global intraspecific trait–climate relationships for grasses are linked to a species' typical form and function

   https://doi.org/10.1111/ecog.06586  

   Griffin‐Nolan, Robert J.; Sandel, Brody (May 2023, Ecography)

   Plant traits are useful for predicting how species may respond to environmental change and/or influence ecosystem properties. Understanding the extent to which traits vary within species and across climatic gradients is particularly important for understanding how species may respond to climate change. We explored whether climate drives spatial patterns of intraspecific trait variation for three traits (specific leaf area (SLA), plant height, and leaf nitrogen content (Nmass)) across 122 grass species (family: Poaceae) with a combined distribution across six continents. We tested the hypothesis that the sensitivity (i.e. slope) of intraspecific trait responses to climate across space would be related to the species' typical form and function (e.g. leaf economics, stature and lifespan). We observed both positive and negative intraspecific trait responses to climate with the distribution of slope coefficients across species straddling zero for precipitation, temperature and climate seasonality. As hypothesized, variation in slope coefficients across species was partially explained by leaf economics and lifespan. For example, acquisitive species with nitrogen-rich leaves grew taller and produced leaves with higher SLA in warmer regions compared to species with low Nmass. Compared to perennials, annual grasses invested in leaves with higher SLA yet decreased height and Nmass in regions with high precipitation seasonality (PS). Thus, while the influence of climate on trait expression may at first appear idiosyncratic, variation in trait–climate slope coefficients is at least partially explained by the species' typical form and function. Overall, our results suggest that a species' mean location along one axis of trait variation (e.g. leaf economics) could influence how traits along a separate axis of variation (e.g. plant size) respond to spatial variation in climate. 

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3. Grass leaf structural and stomatal trait responses to climate gradients assessed over the 20th century and across the Great Plains, USA

   https://doi.org/10.1093/aobpla/plae055  

   Donnelly, Ryan C; Nippert, Jesse B; Wedel, Emily R; Ferguson, Carolyn J (October 2024, AoB PLANTS)

   Heskel, Mary (Ed.)

   Abstract Abstract. Using herbarium specimens spanning 133 years and field-collected measurements, we assessed intraspecific trait (leaf structural and stomatal) variability from grass species in the Great Plains of North America. We focused on two widespread, closely related grasses from the tribe Paniceae: Dichanthelium oligosanthes subsp. scribnerianum (C3) and Panicum virgatum (C4). Thirty-one specimens per taxon were sampled from local herbaria from the years 1887 to 2013 to assess trait responses across time to changes in atmospheric [CO2] and growing season precipitation and temperature. In 2021 and 2022, the species were measured from eight grasslands sites to explore how traits vary spatially across natural continental precipitation and temperature gradients. Δ13C increased with atmospheric [CO2] for D. oligosanthes but decreased for P. virgatum, likely linked to increases in precipitation in the study region over the past century. Notably, this is the first record of decreasing Δ13C over time for a C4 species illustrating 13C linkages to climate. As atmospheric [CO2] increased, C:N increased and δ15N decreased for both species and %N decreased for D. oligosanthes. Across a large precipitation gradient, D. oligosanthes leaf traits were more responsive to changes in precipitation than those of P. virgatum. In contrast, only two traits of P. virgatum responded to increases in temperature across a gradient: specific leaf area (increase) and leaf dry matter content (decrease). The only shared significant trend between species was increased C:N with precipitation. Our work demonstrates that these closely related grass species with different photosynthetic pathways exhibited various trait responses across temporal and spatial scales, illustrating the key role of scale of inquiry for forecasting leaf trait responses to future environmental change. 

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4. Aridity drives coordinated trait shifts but not decreased trait variance across the geographic range of eight Australian trees

   https://doi.org/10.1111/nph.16795  

   Anderegg, Leander D. L.; Loy, Xingwen; Markham, Ian P.; Elmer, Christina M.; Hovenden, Mark J.; HilleRisLambers, Janneke; Mayfield, Margaret M. (August 2020, New Phytologist)

   Summary Large intraspecific functional trait variation strongly impacts many aspects of communities and ecosystems, and is the medium upon which evolution works. Yet intraspecific trait variation is inconsistent and hard to predict across traits, species and locations.We measured within‐species variation in leaf mass per area (LMA), leaf dry matter content (LDMC), branch wood density (WD), and allocation to stem area vs leaf area in branches (branch Huber value (HV)) across the aridity range of seven Australian eucalypts and a co‐occurringAcaciaspecies to explore how traits and their variances change with aridity.Within species, we found consistent increases in LMA, LDMC and WD and HV with increasing aridity, resulting in consistent trait coordination across leaves and branches. However, this coordination only emerged across sites with large climate differences. Unlike trait means, patterns of trait variance with aridity were mixed across populations and species. Only LDMC showed constrained trait variation in more xeric species and drier populations that could indicate limits to plasticity or heritable trait variation.Our results highlight that climate can drive consistent within‐species trait patterns, but that patterns might often be obscured by the complex nature of morphological traits, sampling incomplete species ranges or sampling confounded stress gradients. 

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5. Contrasting intra‐annual population dynamics of two codominant species are consistent across spatial and temporal scales

   https://doi.org/10.1111/1365-2745.14055  

   Gray, Jesse E.; Smith, Melinda D. (March 2023, Journal of Ecology)

   Abstract Despite asymmetric competition and a wide array of functional similarities, two ecologically important C₄perennial grasses,Andropogon gerardiiandSorghastrum 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.WhileA. gerardiivegetative tiller densities peak in the early growing season and decline thereafter (determinate recruitment), those ofS. nutansmay 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. gerardiidecline 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. nutanstiller 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. 

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