Physiological status of conifer seedlings treated with radiation, drought and frost stress mitigation techniques: a laboratory assessment

Abstract

Post planting assistance techniques during early ontogeny may be a determining factor for tree survival in stressful habitats. In the eastern region of NW Patagonia, stands of the fast-growing exotic conifers Pinus ponderosa (Ponderosa pine) and Pseudotsuga menziesii (Douglas fir) are being established in places which are currently, or were in the past, occupied by native Austrocedrus chilensis (mountain cypress) forests. We hypothesize that mitigation techniques could (1) reduce photoinhibition and consequently increase the net photosynthesis rate of plants under high radiation conditions due to increases in the dissipation of radiation with Kaolin, (2) improve water availability in soils using hydrogel, and (3) reduce the effects of chills and frosts events in the species that are most susceptible to environmental stress, A. chilensis and P. menziesii, achieving similar values to those measured in the most resistant species, P. ponderosa using film-forming polymers such as Poly-1-p-Menthene. The short-term responses of seedlings to solar radiation, soil water availability and air temperature were evaluated through gas exchange capacities. Our results indicate that the effects of the different techniques depend on the susceptibility of the species to environmental stress. Kaolin treatment increased stomatal conductance, photosynthesis and transpiration rates in all species. For the hydrogel assay, higher pot volumetric water content was observed in treated plants than in control plants. Pinus ponderosa showed a lower response to the application of hydrogel, while a positive response was observed in A. chilensis and no effect in P. menziesii. The frost mitigation technique evaluated proved unsuitable for the three study species, but appears to work as an anti-desiccant for P. menziesii. In order to optimize the process of planting and establishment for a particular species, the package of techniques needs to be evaluated regarding the requirements and susceptibility to environmental stress of that species.