Observational flooding effects on Rhizophora mangle

Background/Question/Methods:

Our main objective is to investigate how rising ocean levels alter mangrove (Rhizophora mangle) growth rate. There is a lack of research regarding individual R. mangle plant response to prolonged and deeper flooding. Here, we hypothesize that the growth of R. mangle under deep, constant flooding conditions will be inhibited. This was a randomized controlled study that compared an experimental group that was completely flooded to a control group that was not flooded for eight weeks. There were three groups of each treatment containing 25 plants each in individual tubs with a total of 150 mature R. mangle. Weekly data were taken on stem diameter, plant height to the top of the primary axis and total number of leaves on each plant. Emergence of fruit and chlorosis level of the leaves were taken. The experiment was conducted for eight weeks. Harvesting consisted of final stem diameter and plant height measurements, final leaf area, lenticel number, and root hair presence.

Results/Conclusions:

To analyze the significance of the root to shoot ratio, a Single-factor Analysis of Variance (ANOVA) was performed using PSAW with Scheffe post hoc analyses. The p-value of 0.006 rejects the null hypothesis that the root to shoot ratios of both treatment groups would be the same. The root to shoot ratio is higher in the control group than in the experimental group. The height growth shows that the control group grew more on average. To analyze lenticel differences and the root to shoot ratio using PSAW, an Independent Samples T-Test was taken. The Levene’s Test for Equity of Variances shows there was a significant difference (P=0.003) in the lenticels count between the control and experimental groups. The control group had a higher ratio of root to shoot ratio with a significant difference (P=0.006) which, could illustrate an adaptation of shifting biomass from shoot to root when flooded. Our results confirm that complete flooding of R. mangle produces stress on the plant, which is shown through the significantly lower root to shoot biomass ratio, and lenticel amount. This can help to predict the impacts of rising sea levels on mangrove forest.