Seedling Functional Traits to Inform Plant Material Selection

Seedling Functional Traits to Inform Plant Material Selection

May 8, 2014

This study examines seedling growth of local and cultivated accessions of Sandberg bluegrass (Poa secunda) and cheatgrass (Bromus tectorum) in response to different temperatures.

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Native plant biotypes that germinate and emerge early in the season, and have fast coldtemperature growth rates, may have greater weed resistance and ability to establish in arid climates. This study examined seedling growth of local and cultivated accessions of Sandberg bluegrass (Poa secunda) and cheatgrass (Bromus tectorum) in response to different temperatures. We found that accessions differed in cold temperature germination timing and growth. Two commercial accessions had superior growth traits in cold temperatures compared to local biotypes. We identified relationships between accession origin and growth variables. Accessions sourced from areas with colder winter climates had earlier germination and greater seedling growth when incubated under cold conditions.

Seedling trait and ecology research can inform and improve restoration practices and outcomes (James et al. 2013). For example, James et al. (2011) identified seedling emergence and early establishment phases as the primary bottlenecks to restoration plant species survivability. Invasive species, climate variability, and edaphic factors such as soil crusting, all impede seedling emergence and early establishment (Call and Roundy 1991, Bakker et al. 2003, Madsen et al. 2012). Seedling growth traits influence seedling survivability but are understudied compared to adult plant traits (Jones et al. 2010).

Sandberg bluegrass (Poa secunda) is a cool season, native, perennial bunchgrass that establishes early in the spring. The phenological similarity of Sandberg bluegrass to cheatgrass (Bromus tectorum) makes it a good competitor. Previous studies demonstrate that adult populations of Sandberg bluegrass differ in their ability to tolerate and compete with cheatgrass (Georgen et al. 2011, Mummey et al., unpublished data), but adult competitive ability does not indicate ability to establish and compete at the seedling stage.

We evaluated six different accessions of Sandberg bluegrass for seedling growth traits: MT-1, Opportunity, High Plains, Mountain Home, and two populations from MPG Ranch.

We started the six Sandberg bluegrass accessions and cheatgrass from seed under warm (20°C day/ 15°C night) and cold (10°C day/ 5°C night) conditions. We grew seeds in seed germination pouches (CYG; Mega International, St. Paul, MN., USA). Seedling roots grew in nutrient solution between blotting paper and clear plastic. We grew seeds of each accession and cheatgrass in separate pouches.

We monitored pouches every other day for root initiation. After root initiation, we scanned germination pouch images every other day for the duration of the study (21 days) and used winRHIZO software to measure root lengths of scanned images.

Cheatgrass germinated earlier than all the Sandberg bluegrass accessions in both the cold and warm treatments. MT-1 germinated significantly earlier than the other Sandberg bluegrass accessions in the cold treatment. The High Plains accession germinated earlier than MPG populations in the cold treatment. Error bars are +1 S.D. Pairwise comparisons for all variables were performed using the Bonferroni adjustment of the significance level, here p<0.0005 (.05/91).

Cheatgrass had greater daily root growth than all Sandberg bluegrass accessions in both warm and cold treatments. High Plains had greater root growth in the cold temperature treatment than all other accessions. Pop. 10 had the least cold temperature root growth. In the warm treatment, we detected no significant differences in daily root growth between the accessions.

Accessions of Sandberg bluegrass respond differently to temperature in both germination timing and growth. High Plains and MT-1 germinated earlier in cold temperatures than other accessions and had greater root growth rates and longer final root lengths in cold temperatures than other biotypes. MPG populations had poor performance compared to other accessions in cold temperatures. Overall, cultivated varieties of Sandberg bluegrass tended to perform better than locally sourced accessions. High Plains and MT-1 seedlings had the greatest performance of seedlings tested in cold temperatures, but performance of both accessions was much lower than cheatgrass, which grew significantly better than all accessions at both temperatures.

These results support the results of our recent field study (Herget et al., in review). We planted High Plains, Mountain Home, Reliable and MPG populations 10 and 15 in the field, with and without cheatgrass competition. This experiment was conducted on a drought year that challenged biotypes even without competition from weeds. At the end of the season, High Plains had a significantly higher proportion of survivors compared to the other accessions with and without cheatgrass competition. Our results suggest that early seedling growth characteristics may be responsible for survivorship patterns observed in the field.

Some Sandberg bluegrass accessions performed better than others, but all are recommended for planting in our region. Each seed source evolved in a unique environment and their source climate may make some better adapted to harsh climates than others. We researched the historical climate (PRISM Climate Group, Oregon State University, http://prism.oregonstate.edu) of each seed source to examine these differences.

Regression analyses revealed relationships between seed origin minimum winter temperatures and seedling growth variables. Accessions sourced from areas with historically lower winter temperatures germinate earlier (Figure 11-A) and have longer root lengths when grown in colder temperatures (Figure 11-B).

Sandberg bluegrass begins to senesce and set seed in late spring and early summer as temperatures begin to rise. To survive the arid climate of our study region, accessions must be adapted to hot, dry conditions. The historical late spring and early summer temperatures of each source area are similar.

Our results suggest that High Plains and MT-1 have seedling growth traits beneficial for establishment, persistence, and invasion resistance on MPG Ranch. Our analyses suggest that seed source climate data can predict seedling growth characteristics adapted to resisting invasive species and climate change. Examination of seedling traits combined with seed provenance characteristics can be used to inform the selection of plant materials most suited to current and future environmental conditions.

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