Negative photoblastism in the invasive specie Eschscholzia californica Cham. (Papaveraceae): Patterns of altitudinal variation in native and invasive range

Abstract

Negative photoblastism is defined as the inhibitory effect of light on seed germination. This effect can be modulated by abiotic variables, such as temperature, light condition and water potential. This conditions change notoriously at higher altitudes, could promote differentiations in the photoblastic response among populations. Also, this physiological attribute poses an interesting conflict for plant regeneration, because prevents seed germination on the soil surface, however, it can also to reduce the mortality of seeds germinants in unsuitable conditions and consequently, seedling mortality. Eschscholzia californica is one of the few species with negative photoblastism and it is invasive in Chile, growing primarily in open and disturbed places. Some invasive species have the potential to adapt their morphological and ecophysiological characteristics faced to new environmental conditions. In this study, we examined variation in negative photoblastism between populations from central Chile (invasive) and California (native) located at the extremes of their altitudinal distribution. We used common garden experiments where seeds from different origins were germinated under controlled lab condition in Chile. If negative photoblastism is conserved, we would see similar responses among seeds original from this climatic analogues regions. Also, we evaluated whether seed burial increases seed germination of this species as a mechanism for escaping the intense luminosity at the soil surface, by planting seeds at different soil depths. For this experiment, we expected an increase of germination at higher soil depth. The results indicate no differences in negative photoblastism between Chilean and Californian populations. A significant variation across altitudinal range in California suggests the existence of genetic differentiation in the native region, however, the absence of differences across the altitudinal range in Chile suggests trait conservatism at local scale. Seed germination was zero at the soil surface and increased when seeds were experimentally buried, suggesting that negative photoblastism is inhibited. Three possible explanations are given to explain the pattern of establishment of E. californica despite having negative photoblastism. This is a fairly specialist trait, related with Mediterranean climates and does not explain by itself the invasiveness described for this specie. In any case, is clear that more studies are necessary to disentangle the adaptive value of this physiological trait.