The impact of extreme precipitation on plant growth and water relations

Background/Question/Methods

The global hydrological cycle is predicted to become more intense, or extreme in future climates, with both larger precipitation events and longer times between events. The resulting wide fluctuations in soil water content (long droughts followed by flooding) may dramatically affect terrestrial ecosystems. Although effects of drought are well studied, tree responses to changed timing of precipitation are mostly unknown. Further, in future extreme precipitation is likely to occur in conjunction with elevated atmospheric CO₂ concentrations [CO₂]. We tested the impact of extreme precipitation and elevated [CO₂] on plant growth and water relations. 

Ten Acacia auriculiformis and Eucalyptus tetradonta saplings were grown in glasshouses, with ambient (380 p.p.m.) and elevated (600 p.p.m.) [CO₂] and subject to ambient (1L weekly) and extreme (2L fortnightly) watering conditions (four treatments). We tested whether: (1) plants would show differential water stress and growth under extreme precipitation compared with ambient water treatments; and (2) plants would show differential water stress and growth responses under elevated compared with ambient [CO₂] treatments.

 Results/Conclusions

We found that the extreme precipitation, compared to ambient precipitation, lead to more water stressed plants, with more negative leaf water potential and lower stomatal conductance in both species. Further, plants experiencing extreme precipitation had a higher proportion of root volume at depth within the Eucalyptus. In contrast, the root depth of Acacia was similar across all treatments. Leaf area was smaller in extreme precipitation compared with ambient for Acacias, whereas leaf area was comparable across watering treatments in Eucalypts.

 Elevated CO₂had no impact on leaf water potential, stomatal conductance during the day or proportion of root depth.

The Acacia, from tropical dry forest ecosystems, showed more signs of water stress (more negative leaf water potential and lower stomatal conductance) than the Eucalyptus, from savanna ecosystems. This suggests Eucalyptus saplings may tolerate water stress imposed by extreme precipitation better than Acacias, perhaps influencing community structure in tropical ecosystems.