Seed and seedling traits affecting critical life stage transitions and recruitment outcomes in dryland grasses

Abstract

Agriculture and Natural Resources, Browns Valley, CA 95918, USA Summary 1. Seeding native plants is a key management practice to counter land degradation across the globe, yet the majority of seeding efforts fail, limiting our ability to accelerate ecosystem recovery. 2. Recruitment requires transitions through several seed and seedling stages, some of which may have overriding influences on restoration outcomes. We lack, however, a general framework to understand and predict differences in these critical demographic processes across species. Functional traits influence fitness, and consequently, trait variation could provide the basis for a framework to explain and predict variation in life stage transition probabilities. 3. We used seed and seedling traits, and field probabilities of germination, emergence, seedling establishment, and survival for 47 varieties of drylands grasses under two watering treatments to identify critical life stage transitions and quantify the effect of traits on cumulative survival through the first growing season. 4. Variation in germination and emergence probabilities explained over 90% of the variation in cumulative survival regardless of seedling survival probabilities or watering treatment, with emergence probability being the strongest predictor of cumulative survival. 5. Coleoptile tissue density and seed mass had significant effects on emergence and germination, respectively, explaining 10-23% of the variation in transition probabilities. 6. Synthesis and applications. While the majority of functional trait work has centred on linking leaf and root traits to resource acquisition and utilization, our study demonstrates that traits associated with germination and emergence may have prevailing influences on restoration outcomes. A portion of these traits have been examined, but there is substantial opportunity to identify other key traits driving these demographic processes. These advancements will underpin our ability to develop trait-based frameworks for overcoming recruitment barriers and facilitating recovery of degraded systems across the globe.

Advances in restoration ecology: rising to the challenges of the coming decades

“…There are limits to setting specific trait targets as knowledge of which traits drive fitness and performance along environmental gradients is still developing (Webb et al 2010). Recent work has highlighted the need to move beyond considering adult leaf and root traits to also assessing seed and seedling traits when considering the role of functional traits in restoration performance (Larson et al 2015). Assessment of multiple traits is likely to improve the ability of restoration practitioners to develop restoration that is more resilient to future environmental changes.…”

The potential of novel native plant materials for the restoration of novel ecosystems

“…Ecologically appropriate plant materials can conceivably play a role in their repair by virtue of specific functional traits they possess ( Jones et al, 2010). Indeed, plant functional traits are increasingly being used to inform restoration (Funk et al, 2008;Roberts et al, 2010;Clark et al, 2012;Larson et al, 2014). If functional traits that confer ecological fitness, i.e., the ability to establish, grow, and reproduce, can be identified, artificial selection for these traits may potentially lead to plant materials that are able to restore a degree of ecosystem functioning ( Jones and Monaco, 2009;Jones et al, 2010).…”

“…The four key life transitions that make up seedling recruitment are germination, seedling emergence, seedling establishment to an autotrophic state, and seedling survival through the end of the first growing season (Fenner and Thompson, 2005). Of these, emergence has been shown to be the most important for rangeland species ( James et al, 2011;Larson et al, 2014). Thus, native plant materials with an improved ability to emerge, particularly in unfavorable soil environments, may increase the probability of successful seedling recruitment.…”

“…Thus, native plant materials with an improved ability to emerge, particularly in unfavorable soil environments, may increase the probability of successful seedling recruitment. Low coleoptile tissue density, i.e., dry-matter percentage, is a functional trait associated with high emergence (Larson et al, 2014).…”

Climate and soil factors influencing seedling recruitment of plant species used for dryland restoration

“…However, direct seeding is inefficient in terms of the proportion of seeds that produce an established seedling; in arid ecosystems it is common for only 2-7 % of seeds to establish (Chambers, 2000;James et al, 2011;Larson et al, 2015), although the use of biochar has shown to increase these percentages (Drake et al, 2016). The early developmental life-stages of plants are usually more sensitive to environmental or edaphic constraints than the adult stages (Standish et al, 2012) and the transition from germinated seed to emerged seedling has been identified as the life-stage transition most limiting the success of direct seeding .…”