Precipitation intensity and frequency affect plant performance but have limited effects on C and N content of wetland plants
The structure and function of wetland plant communities is sensitive to patterns of precipitation. In some regions, climate change is expected to result in intense but more infrequent rainfall, which could lead to deeper water tables. Typically, the response of wetland plants to changing precipitation regimes is documented under average precipitation amount or drought rather than alterations in precipitation intensity and frequency. Thus, we lack a clear understanding of the response of wetland plants to forecasted precipitation regimes and the factors governing these responses. Here, we seek to understand how changes in the intensity and frequency of precipitation affect: i) soil moisture; ii) plant performance; and iii) plant C and N content. We established a greenhouse study using eight species (four eudicots, five monocots) to which we applied three precipitation treatments ( control (80 mm, 3 d), infrequent (80 mm,15 d), intense-infrequent (110 mm, 15 d)).
Our results show a decrease in soil moisture by approx. 60% for plants grown under the infrequent (80 mm, 15 d) and intense-infrequent (110 mm, 15 d) treatments rather than the control (80 mm, 3 d) treatment. This contributed to a decrease in biomass production in all eudicots by 10-49% and two of five monocots examined by 25-54%, when subjected to the infrequent treatment in comparison to the control. In contrast, changes in C and N content were limited to two forb species and these species showed changes under the infrequent treatment. Our results show that some wetland species will be impacted by changes in precipitation frequency, and infrequent precipitation needs to be accompanied by larger precipitation events if drought-susceptible species are to maintain their performance.