Seeing right through it: X-ray analyses of Uniola paniculata L. spikelets reveal seed production patterns across a wide spatial distribution

TL;DR

This study examines how the seed production of sea oats, a key coastal dune-building plant, varies across a wide geographic range and identifies factors influencing it.

Contribution

The study provides new insights into seed production patterns of Uniola paniculata across fragmented populations over a large spatial scale.

Findings

Panicle density and dune type are strong predictors of normal seed production and seeds per spikelet.

Latitude and drought intensity have small-to-medium effects on seed production.

A threshold panicle density may exist below which seed production declines significantly.

Abstract

Coastal dunes represent globally important ecosystems heavily impacted by human activities and requiring nature-based restoration solutions. Plants with dune building and stabilizing traits typically represent the dominant vegetation. Such species can have ranges extending >1000 km albeit in fragmented populations. Seeds of dominant species are in high demand for establishing dune restoration planting material, but supply may be limited given variable in planta seed production across their range. The broad geographic occurrence of such species presents opportunities to question the influence of various abiotic and biotic gradients on seed production while providing answers that can inform seed-based restoration efforts. We modelled seed production of Uniola paniculata over a 2-year period from 17 populations spread over 12° of latitude (ca. 1357 km). Panicle density and dune type were strong predictors of normal seed production and number of seeds per spikelet. Interactions between eco-spatial zonation or haplotype and collection year were evident regarding the number of seeds per spikelets, but the effects were mostly negligible. Likewise, latitude and drought intensity yielded small-to-medium effects on the number of seeds per spikelet. The proportion of abnormal seeds was not unusual for wild species, and panicle density was not a strong predictor of this response. We hypothesize that a threshold panicle density exists below which seed production decreases substantially. Practitioners should assess relative panicle density at donor sites when creating seed collection plans and may consider sites with low panicle density as priority augmentation targets.

Many geographical, environmental, and biological factors influence a plant's ability to produce seeds. We found that the relative amount of sea oats (Uniola paniculata ) flowering structures has the largest effects on seed production of this crucial coastal dune-building species. Such information can be beneficial for dune restoration programs. Future studies aim to more fully quantify the flowering structure to seed production relationship.

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