Night and day: Shrinking and swelling of stems of diverse mangrove species growing along environmental gradients

Abstract

Tree stems swell and shrink daily, which is thought to reflect changes in the volume of water within stem tissues. We observed these daily patterns using automatic dendrometer bands in a diverse group of mangrove species over five mangrove forests across Australia and New Caledonia. We found that mangrove stems swelled during the day and shrank at night. Maximum swelling was highly correlated with daily maxima in air temperature. Variation in soil salinity and levels of tidal inundation did not influence the timing of stem swelling over all species. Medium-term increases in stem circumference were highly sensitive to rainfall. We defoliated trees to assess the role of foliar transpiration in stem swelling and shrinking. Defoliated trees showed maintenance of the pattern of daytime swelling, indicating that processes other than canopy transpiration influence the temporary stem diameter increments, which could include thermal swelling of stems. More research is required to understand the processes contributing to stem shrinking and swelling. Automatic Dendrometer Bands could provide a useful tool for monitoring the response of mangroves to extreme climatic events as they provide high-frequency, long-term, and large-scale information on tree water status.

Fig 1. Typical stem circumference variation (Δc, mm) for A. marina using automatic dendrometer bands in a period of time with no rainfall.

(A) Circumference variation (Δc, mm) measured at Terranora Upper, and (B) air temperature (°C) data from a meteorological station ~7 km northeast of Terranora study sites, and tidal height data from a station ~3 km north of Terranora study sites (m). (C) Vapour pressure deficit (VPD, kPA). The shaded areas in (a) and (b) indicate night-time.

Fig 2. Mean daily patterns in residual variation in stem circumference (Δc_r, mm) of mangrove trees over five forests (black circles).

Forests are Giralia Bay (Western Australia), Daintree River (Queensland), Ouvéa Atoll (New Caledonia), Noosa (Queensland), and Terranora (Queensland). Different species included A. marina (blue), B. gymnorrhiza (green), R. apiculata (pink), R. stylosa (grey), and X. granatum (black). At some locations, stems were measured at multiple sites. At Giralia Bay and Terranora, A. marina trees growing in the more saline site are represented with blue dashed lines while trees in the less saline site are represented by blue solid lines. At Noosa, A. marina trees growing in the more saline site (outer estuarine) are represented by blue dashed lines, and trees from the less saline site (inner estuarine) by blue solid lines. The light grey shaded areas indicate the longest night, and the dark grey shaded areas indicate the shortest night, during the period of analyses.

Fig 3

Mean and standard deviation of the time (h) at which the daily maximum residual variation (Δc_r) occurred among: (A) A. marina stems over a range of sites, (B) Different species at the Daintree River, and (C) different species at Ouvéa Atoll. The dashed lines show 06:00, 12:00 and 18:00 h to facilitate the interpretation of the data. The asterisk in (C) indicates significant differences between the timing of maximum stem swelling between species at Ouvéa Atoll (BG-OU and RS-OU, (p < 0.05).

Fig 4

(A) Typical circumference variation (Δc, mm) pattern before and after defoliation of stems of Xylocarpus granatum from the Daintree River and (B) A. marina from Giralia Bay. (C) Mean and standard deviation of the time at which the daily maximum residual variation (Δc_r) in stem circumference occurred before and after defoliation, and (D) mean and standard deviation of the maximum Δc_r before and after defoliation for X. granatum from the Daintree River. (E) Mean and standard deviation of the time of maximum Δc_r before and after defoliation, and (F) mean and standard deviation of the maximum Δc_r before and after defoliation for A. marina from Giralia Bay. The analyses with and without thermal correction of the band are shown in black and green, respectively. The shaded areas in (A) and (B) indicate nighttime. The vertical dashed lines in (A) and (B) indicate the defoliation date. The horizontal dashed lines in (C) and (E) represent the time of sunrise, midday and sunset. The two asterisks in (C) indicate that there was a significant difference between before and after defoliation regardless whether the thermal correction was applied or not (p < 0.05).

Fig 5

Typical time course of the increment in stem circumference (Δc, mm) for A. marina trees at (A-C) Noosa Outer and (D-F) Terranora Lower. Plots (A) and (D) show stem circumference change (Δc, mm, blue line) and growth line (mm, dashed line). Plot (B) and (E) show variation in rainfall (mm) and air temperature (°C), and plot (C) and (F) show the stem water deficit (ΔW, mm) which was calculated as the difference between the growth line and the daily band measurements (see Materials and Methods).

Fig 6

Typical moving correlation analysis (MCA, moving window = 30 days) between stem water deficit (ΔW) and environmental variables of A. marina trees from (A-D) Noosa Outer and (E-H) Terranora Lower sites. Plots show the results of moving correlation analysis between ΔW and (A and E) rainfall (rain, circle), (B and F) relative humidity (RH, triangle), (C and G) mean air temperature (Temp, square), and (D and H) vapour pressure deficit (VPD, diamond). A one-day lag was considered in calculating the correlation between rainfall and ΔW. Lines with no markers indicate non-significant correlations. The dotted line indicates no correlation (Corr coef = 0).