Freezing can enhance plant drought tolerance because these stresses elicit similar physiological responses. However, the few studies that have explored this phenomenon of cross-acclimation at ecologically relevant time scales have tended to focus on single species. We examined how spring freezing influences the summer drought tolerance of 6 graminoid (Agrostis stolonifera, Arrhenatherum elatius, Bromus inermis, Festuca rubra, Lolium perenne, Poa compressa) and 2 forb species (Plantago lanceolata, Securigera varia), with the goal of examining the generality of cross-acclimation responses at the plant community level. We exposed individual plants to 5 °C or -5 °C for 3 days in the spring, then subjected the plants to a 3-week summer drought, and harvested the plants after a 3-week recovery period. In addition, we exposed intact plant-soil mesocosms collected from an old field to 5 °C or -5 °C for 3 days in the spring. These mesocosms were then exposed to a 3-week summer drought, and changes in the proportion of major functional groups were assessed at the end of the growing season.
Results/Conclusions
In terms of total dry biomass, we found that there was a significant interaction between freezing and drought stress for Agrostis stolonifera, Bromus inermis and Poa compressa and a marginally significant interaction for Plantago lanceolata. The decline in biomass for plants exposed to drought stress was lower for plants previously exposed to freezing when compared to non-frozen plants. In our mesocosm experiment, frozen mesocosms had the greatest decline in the proportion of non-leguminous forbs after exposure to drought stress. However, there was no significant interaction between freezing and drought stress for both total aboveground and belowground dry biomass, despite the significance of the main effects. Overall, our results indicate that while there is variation in cross-acclimation responses among species, the latter does not necessarily equate at the community level to substantial changes in the relative abundances of major plant functional groups.