Hydraulic strategy defines contrasting responses to an abrupt precipitation during a successive lethal drought.

Background: As precipitation patterns are predicted to become more erratic, it's vital to understand how abrupt climate events will affect woody seedlings that develop different hydraulic strategies. We cultivated anisohydric Robinia pseudoacacia L. and isohydric Quercus acutissima Carr. in a greenhouse, and subjected an abrupt precipitation event during a successive drought. Patterns of leaf and root gas exchange, leaf and stem hydraulics, seedlings growth, and non-structural carbohydrate (NSC) patterns were determined.

Results: We found that as an anisohydric species, R. pseudoacacia seedlings adopted a strategy of sacrificing leaves in response to stress, resulting in the lowered photosynthesis and ultimately leading to a decrease in NSC accumulation. In contrast, isohydric Q. acutissima maintained the integrity of leaves by reducing respiratory consumption in response to drought stress, thereby ensured the stability of NSC pool.

Conclusion: R. pseudoacacia exhibited an extravagant strategy with efficient water transport, photosynthetic assimilation, and growth capabilities, but its resistance to embolism was relatively weak, while Q. acutissima adopted a resource-saving strategy with higher hydraulic safety. We also found that Q. acutissima seedlings were prone to allocate carbohydrates to maintain growth, while R. pseudoacacia preferred to sacrifice growth and aboveground NSC limitation only happened when precipitation was subjected after total stomatal closure. We thus believe that hydraulic strategy could define seedlings responses to drought and recovery, and further may adversely affect their re-sprouting capacity after drought stress relief.