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Differential adaptation capacity of dryland grasses to directional changes in water availability (DIAGRASS).

Periodic Reporting for period 1 - DIAGRASS (Differential adaptation capacity of dryland grasses to directional changes in water availability (DIAGRASS).)

Reporting period: 2018-04-01 to 2020-03-31

Understanding how the intensification of the water cycle, as projected by several climate models, will impact grassland ecosystems will be critical for evaluating their future capacity to provide services and for developing sustainable management policies. This will be especially important in dryland regions, where water availability is the main driver of many ecological processes. To date, several studies have detected responses of vegetation to extreme events from molecular to regional scales, although the duration and heritability of these effects are still unclear. DIAGRASS aims to evaluate the adaptation capacity of dryland grass species to changes in water availability. The target species in this first phase of the project was Bouteloua eriopoda, considered a key forage species for both domesticated and wild animals in the Southwest States of USA. B. Eriopoda is distributed in ten Southwest States of USA, and in rangelands where it is dominant, a net annual financial return of around $2/ha has been estimated. Also, its spread by runners makes it one of the best erosion control plants in its distribution area. It is known that this species has a very negative response to the interaction between drought and grazing. Thus, testing the probability that in this species could take place microevolution processes that enable its adaptation to increasingly more extreme hydrological events is crucial for the assessment of the future economic viability of most ranches located in its natural range. In the second phase of the project, Brachypodium distachyon complex will be the target species. This complex offers a main direct economic and environmental benefit when it is used as a protective plant cover against erosion in human-managed lands in the Mediterranean Basin. Furthermore, B. distachyon is emerging as the new model system for the study of temperate crop grasses, such as wheat, barley and forage grasses, as well as for herbaceous energy crops, through the development of genetic resources to explore the diversity of forms and functions that underlies economically important traits. It is also an interesting complex of species for ecological studies of typical Mediterranean plants and the investigation of plant polyploid speciation.
Rainfall manipulation experiments (RMEs) were used and three different approaches (population, phenotypic and genomic level) were established to monitor grasses responses to different rainfall legacies and extreme rainfall events. This reporting period covers the two-year outgoing phase at Arizona State University (ASU), where the experienced researcher (ER) has implemented the RMEs at The Jornada Long Term Ecological Research site (JRN LTER, New Mexico), located in the Chihuahuan Desert, and has monitored changes in population structure, coverage, phenology and traits in a grass species. Besides, she has performed a litter matter decomposition trial to determine in which degree rainfall characteristics affect soil microorganisms and the carbon and nutrient cycles. In parallel with the implementation to these experiments in the USA, the ER has coordinated the preparation of the second phase of the project in Spain, which consisted in: the seed collection of the target species (Brachypodium distachyon) proposed in the Annex I-Description of the Action (DoA) near the selected experimental area (Garraf experimental station, south of Barcelona, Spain); the plantation of these seeds in plots to obtain, in the second generation of plants, the required quantity of seeds for the experiment; the selection of the experimental plots at Garraf and the preparation of the terrain for the seed sowing; the accurate identification of the collected species within the B. distachyon complex; and the sending of seed samples to the Joint Genome Institute (JGI) for their genome sequencing.

In this first phase of the project, the ER has proven that 1) the duration and magnitude of extreme rainfall events shaped the distribution of patch-sizes in B. eriopoda and had a very significant effect in its coverage; 2) rainfall legacies modulated in different ways the response of the traits and phenology to extreme rainfall events in this species; 3) but these legacies did not affect litter decomposition. In addition, we identified our target species in Garraf as Brachypodium hybridum, a tetraploid annual grass with subgenomes of B. distachyon and B. stacei.
This project is helping to understand how a key grass species responds to extreme rainfall events at population and phenotypic level and how rainfall legacies modulate these responses. In the next phase of the project, it is expected to achieve this better understanding at molecular level. We hypothesise that natural selection and plastic adaptation are the main drivers of grass population dynamics in a more extreme hydrological cycle scenario. It is estimated that 2 billion people live in drylands, about 90% of them in developing countries. Most of this population depends on grasslands for their livelihoods and to meet their basic needs. Therefore, a comprehension of the principles that will govern the dynamics of these ecosystems under climate change is key for the socio-economic sustainability of the regions located in drylands.
Photo of the rainfall manipulation experiment
Photo of the study area with the typical summer storms in the background