DOI: 10.5061/dryad.0rxwdbs3k
title: Is Poaceae pollen size a useful proxy in palaeoecological studies? New insights from a Poaceae pollen morphological study in the Amazon

description: Aim: Grasslands occupy around 40% of the Earth’s land surface and can be
 regarded as the most common vegetation type in the world, with Poaceae
 being the most widespread angiosperm family of all.  
 Poaceae pollen size has previously been suggested as a proxy to
 reconstruct the past vegetation and climates in the Amazon area, but it is
 still controversial if this variable indeed can be used in broader spatial
 and deep-time scales. Here we set out to perform a comprehensive
 assessment and test the robustness of this proxy. Location: Amazon
 drainage basin (ADB). Taxon: Poaceae. Methods: One hundred and
 twenty-seven specimens from 58 species (non-crops) across the Poaceae
 phylogeny from the Amazon drainage basin (ADB) were prepared for pollen
 grain size analyses, in order to explore their relationship with abiotic
 and biotic variables (vegetation type, soil composition, climate
 conditions, photosynthetic pathway, and genome size). Phylogenetic
 generalized least squares (P-GLS) model and linear mixed models (LMM) were
 applied to assess the proxy. Results: Our measurement data show that
 Poaceae pollen size presents a very wide range (18.77 - 71.62 μm), not
 only at the genus and species levels but also within species. There is no
 obvious relationship between pollen size and the explanatory variables
 considered here, however. Main conclusion: Poaceae (non-crop) pollen size
 does not respond to explanatory variables, and therefore cannot as a
 useful proxy to reconstruct past vegetation and climate.
description: <strong>1. Sample collection and
 processing</strong> We sampled pollen grains 127
 plant specimens from 58 species belonging to 9 different Poaceae
 subfamilies.    <strong>2.
 Selected variables and data collection</strong>
 Poaceae occur in a wide range of ecosystems in South America,
 ranging from mountain to lowlands, cold to temperate grasslands,
 floodplains, and coastline.  2.1. Vegetation
 type We assigned each sampling locality to one of the
 following five vegetation types: desert, montane grassland shrubland,
 savanna, tropical dry forest, and tropical moist forest. 
 2.2. Soil type We used the Soil and Terrain
 Database (SOTER) for Latin America and the Caribbean (SOTERLAC), version
 2.0, at a scale of 1:5000000 to define soil categories for each site,
 using the WRB (World Reference Base) Soil Groups to assign each sampling
 locality to one of 19 soil types. DOMSOIL_UN represents the soil type
 corresponding to each sampled plant specimen. 2.3.
 Modern climate data We used the WorldClim 2.1 database
 and Climate Research Unit (CRU) TS4.04 database (Harris et al., 2020) to
 extract the mean annual temperature. cru.MAT and cru.TAP represents the
 climate data corresponding to each sampled plant specimen.
 2.4. C3/C4 photosynthetic pathway
 Photosynthetic pathways assigned to each species came from Klink
 and Joly (1989), Giraldo-Canas (2010), Bremond et al. (2012), and
 references therein. 2.5. Genome size
 We took genome size information from Kew Garden's C-values
 Database.
description: All code can be opened with RStudio.