Inter- and intraspecific variation in the germination response to light quality and scarification in grasses growing in two-phase mosaics of the Chihuahuan Desert

BACKGROUND AND AIMS: In many locations, plants are faced with adjacent, contrasting environments, and the between-species differential evolution of life history traits can be interpreted as an evolutionary response to this environmental heterogeneity. However, there has been little research on the intraspecific variability in these attributes as a possible evolutionary response of plants. METHODS: In the two-phase mosaic of the Chihuahuan Desert (adjacent patches with contrasting resource availability), analyses were carried out of the germination response to the scarification and light quality to which grass seeds growing on these patches are exposed (open and closed habitats). KEY RESULTS: Species that grow in open habitats exhibited a higher germination success than those from closed habitats after scarification. At both the inter- and intraspecific level, there were differences in the germination percentage and in the germination speed in response to light quality. Intraspecific variation in the species from the closed habitat (Pleuraphis mutica and Trichloris crinita) and in Chloris virgata (which grows in both habitats) was due to genetic variation (the family factor was significant), but there was no genetic variation in phenotypic plasticity (non-significant interaction between family and light quality). In contrast, for the species that grows only in the open habitat (Dasyochloa pulchella), the family did not have a significant effect, but there was genetic variation in the phenotypic plasticity (significant interaction between family and light quality). CONCLUSIONS: In C. virgata, P. mutica and T. crinita, natural selection could be favouring those genotypes that responded better in each light environment, but it is not possible that the natural selection resulted in different optimal phenotypes in each habitat. On the contrary, in D. pulchella, selection could have reduced the genetic variation, but there is the possibility of the evolution of reaction norms, resulting in the selection of alternative phenotypes for each habitat.     

Effects of drought in biomass production and allocation in three varieties of Trichloris crinita P. (Poaceae) a forage grass from the arid Monte region of Argentina

Trichloris crinita, a perennial forage grass nativeto the west arid Monte region of Argentina, has shown great variability inforage production among populations originated in different environments. In aprevious study under irrigated conditions we concluded that higher productivityof some varieties was associated with larger total plant biomass and higher drymatter partitioning to aboveground organs. The goal of the present study was toinvestigate the ecophysiological basis of differential productivity in threevarieties of T. crinita under water stress conditions.Varieties PICHI, ARROYITO and ENCON of high, medium and low productivity wereevaluated under high and low water availability. Two cycles of water stress,maintained until leaves folded, were applied to each variety. Leaf foldingoccurred at different leaf water potential (_L) for eachvariety.At the end of the first stress cycle _L were: PICHI –4.27MPa, ARROYITO –3.26 MPa and ENCON –1.82MPa. Each variety finished the stress cycle at a different time.Shoot/root ratio and DM partitioning to different organs were not modified bythe water stress treatment for the three varieties thus, the relativedifferences among them were maintained. Shoot/root ratio of PICHI (3.2) wasmorethan double of the least productive variety (ENCON). The higher productivity ofPICHI is associated to a larger shoot/root ratio, faster production of leafareaand higher leaf, sheath, culm and panicle DM production. Root DM was notdifferent among varieties. ENCON, coming from an area with lower rainfall andhigher temperature, was the last to fold their leaves and had a higher leafwater potential at the end of the drought cycle, probably linked to its smallerleaf area and relatively larger root system.     

Genetic and environmental variation of seed weight in Trichloris species (Chloridoideae,Poaceae) and its association with seedling stress tolerance

Background: Seed weight is a key fitness-related trait associated with plant adaptation and is commonly targeted in plant breeding.

Aims: We evaluated seed weight variation within and between Trichloris crinita and Trichloris pluriflora across their geographical ranges in Argentina.

Methods: Genetic variation in seed weight was evaluated through a common garden experiment. To examine the possible role of such variation in local adaptation, we compared the seed weight of plants of populations raised in the common garden with seed weight variation and ecogeographical variables across their original habitats. We also evaluated experimentally the effects of seed weight variation upon osmotic stress tolerance at germination.

Results: Variation in seed weight existed in both species. Such variation had a genetic basis in T. crinita related to several ecogeographical variables. Larger seeds of T. crinita were associated with more stressful environments and produced larger seedlings under both osmotic stress and non-stress conditions.

Conclusions: Our results suggest that seed weight variation in T. crinita is likely adaptive, with large seed having an advantage during early developmental stages, particularly under stressful conditions. Such knowledge should prove helpful in selecting the most suitable populations for restoration and plant breeding.