Abstract Detail

Ecophysiology

Lopez-Portillo, Jorge [1], Mendez-Alonzo, Rodrigo [2], Ewers, Frank [3].

Does the osmolality of mangrove xylem sap decrease as stomata close and water potential increases?

Sap salinity in mangroves may play several roles, such as reducing the symplastic turgor pressure of living cells adjacent to the transport pathway and regulating the whole-plant hydraulic conductivity through the ionic effect. Previously, we found that the osmolality of the first 0.01 mL samples of xylem sap extracted by the pressure chamber technique is high and correlated with the amount of inorganic ions, mainly Na, K and Cl, and ruled out the possibility that such values are due to contamination. Given such results, we hypothesized that xylem sap osmolality would increase when water in vascular tissues is depleted (due to higher solute concentration) by transpiration during the day and decrease when water is replenished during the night after stomata close. We test these assumptions by following the circadian rhythms of stomatal conductance and shoot xylem and osmotic pressure in 63 shoots of the black mangrove (Avicennia germinans) and 63 shoots of the white mangrove (Laguncularia racemose) randomly selected from 100 shoots per species previously tagged along a trapline. We used a pressure chamber to measure xylem pressure (XP) and to extract the xylem sap to measure osmotic pressure (OP) in each shoot (three shoots per species every 2 hours) along a 54-hour period. During the same period, we measured adaxial and abaxial stomatal conductivity (SC) in three shoots of six trees per species. XP and OP varied across species (Laguncularia: mean XP (SE) = -2.7 (0.08) MPa; min=-3.5; max=-2.2; mean OP = 143 (8.6) mmol kg^-1; min=89; max=237; Avicennia: mean XP =-3.38 (0.14) MPa; min=-4.2; max=-2.4; mean OP = 218 (9.6); min=152; max=324). The SC was highly variable during the daytime (8:00-18:00) and very low from dusk to dawn (from 18:00 to 8:00 h). As expected, XP was minimum following midday, but SC peaked to its maximum values between 09:00 and 12:00 h. However, no significant correlation was found between XP and OP (r = 0.18; P = 0.4) or between XP and stomatal conductivity. This implies that XP follows SC along the day and that living cells are regulating OP within a determined range to control turgor.

1 - Instituto de Ecologí­a, A.C. (INECOL), Ecologí­a Funcional, Carretera antigua a Coatepec 351, Xalapa, Veracruz, 91070, Mexico
2 - Centro de Investigación Cientí­fica y de Educació, Biologí­a de la Conservación, Carretera Ensenada-Tijuana 3918, Zona Playitas, Ensenada, Baja California, 22860, Mexico
3 - California State Polytechnic University, Biological Sciences, 3801 West Temple Avenue, Pomona, Callifornia, CA, 91768, USA

Keywords:
mangroves
Avicennia germinans
Laguncularia racemosa
xylem and parenchyma.

Presentation Type: Oral Paper
Session: 3, Ecophysiology
Location: 104/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 10:15 AM
Number: 3009
Abstract ID:911
Candidate for Awards:None