Local adaptation to precipitation in the perennial grass Elymus elymoides: Trade-offs between growth and drought resistance traits

Plant functional trait responses to cope with drought in seven cool-season grasses

In semi-arid and arid regions, the selection of suitable grass species with high-yield production, tolerance to drought stress, and potential for recovery from drought is of special importance. Despite extensive research in cool-season grasses, inter-species differences in post-drought recovery, persistence, survival, and summer dormancy and their relationship with drought tolerance need more investigation. In the present study, 28 diverse genotypes belonged to seven cool-season grass species, including Festuca arundinacea (tall fescue), Festuca pratensis (meadow fescue), Festuca ovina (sheep fescue), Festuca rubra (red fescue), Lolium perenne (perennial ryegrass), Lolium multiflorum (Italian ryegrass) and Lolium × hybridum were evaluated during 2016-2019 under three irrigation regimes (normal, mild, and intense drought stress). Then in the fourth year (on August 2019), irrigation was withheld at all previous irrigation regimes for two months during summer, and then species were re-irrigated to study the effect of prolonged drought conditions. A wide range of genetic diversity was detected in all the measured traits among and within species in response to different irrigation levels. Recurrent drought stress decreased forage productivity, post-drought recovery, and survival in all grass species. Among the studied species, tall fescue had higher forage production, drought tolerance, survival, recovery rate, and persistence. Sheep fescue had low forage production and recovery after drought. Drought tolerance (based on stress tolerance score, STS) was highly associated with forage yield and post-drought recovery and partially with summer dormancy under both mild and intense drought stress conditions. This indicated that selection based on higher STS would lead to choosing genotypes with better recovery after prolonged drought. Superior species and preferable genotypes for forage use from species Festuca arundinacea and for turf application from species Festuca arundinacea, Lolium perenne and Lolium × hybridum were identified across different water environments for future programs.

Local adaptation of seed and seedling traits along a natural aridity gradient may both predict and constrain adaptive responses to climate change

PREMISE

Variation in seed and seedling traits underlies how plants interact with their environment during establishment, a crucial life history stage. We quantified genetic-based variation in seed and seedling traits in populations of the annual plant Plantago patagonica across a natural aridity gradient, leveraging natural intraspecific variation to predict how populations might evolve in response to increasing aridity associated with climate change in the Southwestern U.S.

METHODS

We quantified seed size, seed size variation, germination timing, and specific leaf area in a greenhouse common garden, and related these traits to the climates of source populations. We then conducted a terminal drought experiment to determine which traits were most predictive of survival under early-season drought.

RESULTS

All traits showed evidence of clinal variation-seed size decreased, germination timing accelerated, and specific leaf area increased with increasing aridity. Populations with more variable historical precipitation regimes showed greater variation in seed size, suggestive of past selection shaping a diversified bet-hedging strategy mediated by seed size. Seedling height, achieved via larger seeds or earlier germination, was a significant predictor of survival under drought.

CONCLUSIONS

We documented substantial interspecific trait variation as well as clinal variation in several important seed and seedling traits, yet these slopes were often opposite to predictions for how individual traits might confer drought tolerance. This work shows that plant populations may adapt to increasing aridity via correlated trait responses associated with alternative life history strategies, but that trade-offs might constrain adaptive responses in individual traits.

Invasive and native grasses exert negative plant-soil feedbacks on the woody shrub Artemisia tridentata

Displacement of diverse native plant communities by low-diversity invasive communities is a global problem. In the western United States, the displacement of sagebrush-dominated communities by cheatgrass has increased since the 1920s. Restoration outcomes are poor, potentially due to soil alteration by cheatgrass. We explored the poorly understood role of plant-soil feedbacks in the dominance of cheatgrass in a greenhouse study where uninvaded sagebrush soils were conditioned with either cheatgrass, a native bunchgrass or sagebrush. Sagebrush seedlings were grown in the soils that remained following the removal of conditioning plants. We expected cheatgrass to strongly suppress sagebrush due to a change in belowground microbial communities, conspecifics to have neutral effects and the native bunchgrass to have intermediate effects as it coevolved with sagebrush but belongs to a different functional group. We assessed the effects of conditioning on sagebrush growth, tissue nutrients, and carbon allocation. We also characterized the abundance, diversity and community composition of root microbial associates. Cheatgrass strongly suppressed sagebrush growth at high and low conditioning densities, the native bunchgrass showed suppression at high conditioning densities only and conspecific effects were neutral. Tissue nutrients, amount of root colonization by soil fungi or root microbial community composition were not associated with these plant-soil feedbacks. Although we did not identify the precise mechanism, our results provide key evidence that rapid soil alteration by cheatgrass results in negative plant-soil feedbacks on sagebrush growth. These feedbacks likely contribute to cheatgrass dominance and the poor success of sagebrush restoration.

Photochemical performance of reproductive structures in Great Basin bunchgrasses in response to soil-water availability

Active restoration, especially seeding, is necessary in sagebrush steppe rangelands degraded by the spread and dominance of exotic invasive annual grasses, in part due to low, episodic seed production of native perennial bunchgrasses. In contrast, the widespread exotic bunchgrass, crested wheatgrass, readily produces viable seed cohorts. How soil-water availability affects the ecophysiology of the reproductive structures that may underlie these differences are unclear. To address this, we measured pre- and post-anthesis chlorophyll fluorescence parameters of optimal (F _v/F _m) and light-adapted PSII quantum yield (ϕ _PSII) and ϕ _PSII-derived electron transport rate (ETR) response to photosynthetic photon flux density (PPFD) in seed heads and flag leaves of watered and unwatered crested wheatgrass and squirreltail wild rye. Watering increased F _v/F _m in the sampled structures of both species, but ϕ _PSII was similar between watering treatments. Pre- to post-anthesis F _v/F _m levels were maintained in crested wheatgrass seed heads but declined in flag leaves, with the opposite pattern apparent in squirreltail. Watering did not affect the ETR-PPFD response, but crested wheatgrass seed heads maintained higher ETR across saturating PPFD than did squirreltail. These findings suggest (i) photochemical efficiency is expressed in structures most closely associated with reproductive effort, and (ii) documented differences in seed head photosynthetic characteristics likely include some degree of allocation to individual floret photosynthetic capacity in addition to structural characteristics. We concluded that these physiological and structural differences may contribute to the differential ability of these species to establish from seed, and may help in effective plant material selection needed to improve restoration and conservation success in sagebrush steppe rangelands.

Widespread variation in heat tolerance and symbiont load are associated with growth tradeoffs in the coral Acropora hyacinthus in Palau

Climate change is dramatically changing ecosystem composition and productivity, leading scientists to consider the best approaches to map natural resistance and foster ecosystem resilience in the face of these changes. Here, we present results from a large-scale experimental assessment of coral bleaching resistance, a critical trait for coral population persistence as oceans warm, in 221 colonies of the coral Acropora hyacinthus across 37 reefs in Palau. We find that bleaching-resistant individuals inhabit most reefs but are found more often in warmer microhabitats. Our survey also found wide variation in symbiont concentration among colonies, and that colonies with lower symbiont load tended to be more bleaching-resistant. By contrast, our data show that low symbiont load comes at the cost of lower growth rate, a tradeoff that may operate widely among corals across environments. Corals with high bleaching resistance have been suggested as a source for habitat restoration or selective breeding in order to increase coral reef resilience to climate change. Our maps show where these resistant corals can be found, but the existence of tradeoffs with heat resistance may suggest caution in unilateral use of this one trait in restoration.