The vulnerability of native and invasive conifer seedlings to simulated warming in north-western Patagonia

Abstract

On the context that climate change could increase opportunities of colonisation and spreading for invasive species, we examined whether or not exotic species will respond better than native species to warming effect. We analysed its effect on the water potential (Ψ) of Austrocedrus chilensis and Pseudotsuga menziesii seedlings, native and exotic conifers, respectively. We hypothesise that the native species will show more negative Ψ values than the exotic seedlings in warming conditions. A field experiment was set up in two sites in A. chilensis forests in north-western Patagonia. In each site, 14 blocks were installed, each consisting of an Open Top Chamber (OTC), which increases temperature by 2°C, and a control plot at current environmental temperature. In 7 blocks, 23 seedlings of P. menziesii were planted in each OTC and 23 in each control plot. In the remaining 7 blocks, A. chilensis seedlings were planted in the same way. Micro-environmental variables and Ψpd and Ψmd were measured over two growing seasons (2014–2015 and 2015–2016); the turgor threshold of each species was also estimated. The data were analysed by MLGM with repeated measures. Our study showed that warming caused a decrease in air and soil humidity, resulting in a reduction in the water potential of both species at predawn and midday. The most negative water potential values were always recorded in the OTC conditions, and the significant differences between sites could be explained by different tree densities and water consumption. In all plots, A. chilensis Ψ values were found to be more negative than those of P. menziesii, but in the warming scenario, this difference was stronger. Moreover, although neither of the species was favoured by the OTC conditions, A. chilensis could be at higher risk than P. menziesii in the mesic site (MA) in a climate warming scenario.