Responses of Caragana korshinskii to different aboveground shoot removal: combining defence and tolerance strategies.

BACKGROUND AND AIMS It is generally assumed that plants respond to natural enemies by either allocating resources to resistance traits or compensating for damage. This study evaluated how different methods of artificial shoot removal influence two alternative strategies (i.e. tolerance and defence) of Caragana korshinskii in the semi-arid area of China. METHODS Zero per cent (control), 30% (30%) and 60% (60%) of the main shoot length and 25% (25%), 50% (50%) and 100% (100%) of the numbers of main shoots were removed from shrubs. KEY RESULTS Moderate clipping treatments [30% removal of partial shoot length (RSL), 25% removal of shoot number (RSN) and 50% RSN] improved seed production, whereas the most intensive clipping treatments (60% RSL and 100% RSN) with most or total removal of potential flower buds reduced current reproduction fitness compared with controls. All treatments produced a similar leaf phenolic content, with the exception of 100% RSN which resulted in a low leaf phenolic content. In spite of a substantial investment in regrowth, clipped plants increased biomass allocation to physical defence. Control plants almost did not grow, had lower levels of physical defence and a lower photosynthetic rate, mobilized fewer carbohydrates from roots and produced more flowers. However, their current fitness was lower than that of plants undergoing clipping treatments (30% RSL, 25% RSN and 50% RSN) because of the high level of abortion of flowers and fruits. CONCLUSIONS Caragana korshinskii responded to aboveground shoot removal through combining defence and tolerance strategies.