Combined effect of water potential and temperature on seed germination and seedling development of cacti from a mesic Argentine ecosystem

"Global climatic change will be associated with an increase of droughts and heat waves, which can affect seed germination and plant population dynamics. Cactus species from mesic ecosystems are likely to be more affected by these events than species from arid ecosystems. The aim of the study was to assess the combined effect of water potentials and temperatures on seed germination and seedling traits in six globose cactus species from Córdoba Mountains: Echinopsis candicans, Gymnocalycium bruchii, G. capillense, G. mostii, G. quehlianum and Parodia mammulosa. A factorial experiment was performed in which four water potential levels (0, ?0.2, ?0.4 and ?0.6 MPa) were combined with two temperature levels (25 and 32 °C). Germination (%) and mean germination time (T50) were recorded and seedling shape (width and length) was measured. In general, a decrease in water potential and an increase in temperature resulted in low germination, with different behaviors among species. At 32 °C and low water potentials, germination was low or null for almost all species. There was not a clear trend in the response of T50 to the treatments. Seedling development was highly and negatively affected by the combination of factors, particularly at low water potentials. The responses of the analyzed cactus species to low water potential were similar to those of cactus species from more arid ecosystems. Our results suggest that the studied species would be severely affected by changes in temperature and precipitation as predicted under a climate change scenario.