CORE Metadata, citation and similar papers at core.ac.uk Provided by Elsevier - Publisher Connector Available online at www.sciencedirect.com South African Journal of Botany 81 (2012) 61–70 www.elsevier.com/locate/sajb Water use strategies of seedlings of three Malagasy Adansonia species under drought ⁎ T. Randriamanana a, , F. Wang a, T. Lehto b, P.J. Aphalo a a Department of Biosciences, P.O. Box 65 (Viikinkaari 1), 00014 University of Helsinki, Finland b School of Forest Sciences, University of Eastern Finland, P.O. Box 111, 80101, Finland Received 21 August 2011; received in revised form 17 May 2012; accepted 25 May 2012 Available online 21 June 2012 Abstract Adansonia species, known by the common name “baobab,” have a very low regeneration rate in Madagascar. In order to determine if Malagasy Adansonia seedlings' vulnerability to drought may account for this low rate of regeneration, we compared growth, photosynthetic behavior and water use strategy of three species of Malagasy Adansonia (A. grandidieri, A. madagascariensis, A. rubrostipa). Our results indicated that drought depressed the growth, net assimilation rate, stomatal conductance and transpiration rate of Adansonia seedlings but increased their water use efficiencies. Adansonia species are able to withstand drought by reducing water loss through stomatal closure and their ability to store water within roots. Interspecific differences were attributed to diversity in water-use strategies, relative water content and biomass allocation. A. rubrostipa and A. grandidieri appeared to be more adapted to arid environments than A. madagascariensis. Ecological implications of these results are discussed. © 2012 SAAB. Published by Elsevier B.V. All rights reserved. Keywords: Baobabs; Growth; Madagascar; Photosynthetic responses; Water stress; Water use 1. Introduction Malagasy western forests. Species of the genus Adansonia are classified as “keystone mutualists” due to their likely role in Tropical dry forests have received less conservation and stabilizing dry forest ecosystems (Baum, 1996). Apart from their scientific attention in comparison with tropical wet forests ecological role (Baum, 1995, 1996; Metcalfe and Trevelyan, (Fajardo et al., 2005; WWF, 2010). Over 97% of Madagascar's 2007), they are multipurpose trees and have numerous economic western dry deciduous forests have been lost and are consequently functions in some Malagasy rural communities (Baum, 1996; considered as “Critical or Endangered” ecoregion according to the Marie et al., 2009; Seddon et al., 2000; Wickens and Lowe, Global 200 representation of WWF (Olson and Dinerstein, 1998; 2008). In Madagascar, Adansonia fruit pulps which are rich in WWF, 2010). vitamin C and with high antioxidant activity (Assogbadjo et al., Adansonia (BOMBACACEAE sensu stricto, MALVACEAE 2008; Chadare et al., 2009) are consumed by local communities. sensu lato), commonly known as “Baobab”, is a xeric genus that Moreover, Malagasy Adansonia leaves possess higher nutritional symbolizes Madagascar's floral biodiversity, as six out of eight value in terms of leaf vitamin and crude protein contents when world-wide species are endemic to the island. It was chosen as a compared to African baobab A. digitata L. (Maranz et al., 2007), model species in our studies because of its predominance in and can be consequently used to improve local population diet. In Madagascar, dried leaves of Adansonia are used for food ⁎ seasoning (Marie et al., 2009). Besides, Adansonia leaves are Corresponding author at: Natural Product Research Laboratory, Department of used in Malagasy traditional pharmacopeia, its bark and fibers are Biology, University of Eastern Finland, PO Box 111, 80101 Joensuu, Finland. Tel.: +358 504423402. confectioned to make rope, mats, baskets and roofing materials, E-mail address: tendry.randriamanana@uef.fi (T. Randriamanana). their seeds produce edible oil, and medicines (Baum, 1996; Marie 0254-6299/$ -see front matter © 2012 SAAB. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sajb.2012.05.005 62 T. Randriamanana et al. / South African Journal of Botany 81 (2012) 61–70 et al., 2009; Seddon et al., 2000; Wickens and Lowe, 2008). Their water for 12 h. Seeds were then sown at 1 cm depth in pots (at a trunks are sometimes hollowed out as tanks for water storage in density of 30 seeds per pot of 50 cm×30 cm dimension) dry areas of Madagascar (Baum, 1996; Marie et al., 2009). In containing sterile sand moistened with distilled water. The pots addition, due to their impressive appearance, species of the genus were kept at 30±1 °C under a 12 h photoperiod, illuminated with − − Adansonia are associated with some Malagasy superstitions and 175 μmol m 2 s 1 photosynthetic photon flux from fluorescent folklore which consider certain trees as sacred (Baum, 1995; lamps at ambient CO2. After 2 to 3 days, radicules emerged from Marie et al., 2009). almost 95% of the seeds and the germinating seeds were Field observations have reported a noticeably low survival transplanted to 410 mL pots containing vermiculite and white of seedlings in all species of Malagasy Adansonia especially in Sphagnum peat 1:1 (v/v). All pots were filled with the same arid areas of Madagascar (Baum, 1995, 1996; Miège and Morat, quantity of dry mixture (40 g perpot)andwerewateredevery 1974; Razanameharizaka, 2009; Wickens and Lowe, 2008). other day, ensuring that excess water drained through the 75% of newly established seedlings (particularly A. rubrostipa bottom of the pots. The content of fertilizer already in the limed Jum. & H. Perr.) die before their first rainy season in their natural peat (White 420 W, Kekkilä, Vantaa, Finland) was 1 g L− 1 of environment, apparently due to combined water deficit and high N–P2O5–K2O (14:9:24) plus micronutrients (Kekkilä starter light intensity (Razanameharizaka, 2009). Studies undertaken by fertilizer 1) plus 6.2 g L− 1 of dolomite lime. At the beginning Venter and Witkowski (2010) on African A. digitata reported that of the experiment, each seedling was watered with 40 mL the predicted drop in rainfall attributed to climate change may liquid fertilizer (Taimi Superex®, Kekkilä, Vantaa, Finland) increase Adansonia trees rate of mortality in the future. containing 19% N, 4.4% P, 20.2% K, 1.2% Mg, 0.03% B, The goal of this study is to investigate the physiological 0.001% Co, 0.008% Cu, 0.17% Fe, 0.08% Mn, 0.005% Mo, responses of Malagasy Adansonia seedlings to water stress and and 0.012% Zn (w/w) at a concentration of 1 g L− 1. whether such responses may explain their low regeneration rate Versatile MLR-350 294L test chambers (Sanyo Electric and their pattern of distribution across the island. We tested the Biomedical Ltd., Japan) were used to grow the seedlings under hypothesis that species-specific differences influence the effects of controlled environmental conditions. Photosynthetic photon drought on seedling growth and photosynthetic activity in three irradiance inside the growth chambers was measured using a species of Adansonia endemic to Madagascar, and predicted that LI-190 quantum sensor plus a LI-250A meter (LI-COR®, seedlings of Adansonia madagascariensis Baill. from the northern Biosciences, Lincoln, NE, USA). Photosynthetically Active dry deciduous and subhumid forests of Madagascar would be Radiation (PAR) photon irradiance was set at 175 μmol m−2 s−1 less drought tolerant during water stress when compared to with a photoperiod of 12 h. Temperatures were held at 29±1 °C A. rubrostipa and A. grandidieri Baill. which are from the arid during the day and 24±1 °C during the night, while air humidity spiny thickets and succulent woodlands of the south. To test this ranged between 26% during the day and 31% at night. hypothesis, we assessed under controlled conditions the photo- Temperature and relative humidity were logged at 10–15 cm synthetic behavior and water use strategy of these three species of above plant height in all chambers (iButton, DS1922L and Adansonia. DS1923, Maxim Integrated Products, Sunnyvale, CA, USA). Pots were assigned to three different complete randomized 2. Materials and methods blocks based on seedling size so that all chambers would have equal numbers of same-height seedlings. After transplantation Seeds from three species of Adansonia (A. rubrostipa, in pots, seedlings were allowed to grow for 28 days before A. grandidieri,andA. madagascariensis) were collected from the watering treatment so that they acquire well developed leaves western part of Madagascar at Ifaty, Marofandilia and Mahajanga and roots. Three replicates of 10 seedlings per species and per (Table 1; Fig. 1)by“URP Forêts et Biodiversité” (Madagascar). watering regime were grown in five separate growth chambers; each chamber contained two species. 2.1. Plant material establishment and experimental design 2.2. Watering treatment The experiment was carried out at the Department of Biosciences, University of Helsinki (Finland). Seeds of A. Starting 28 days after germination, the seedlings were subjected rubrostipa and A. madagascariensis were scalded in boiling to two water regimes: watering to 100% (“control”) and to 50% water for 60 s while seeds of A. grandidieri were soaked in tap field capacity (“water stressed”). Field capacity was determined in Table 1 Seed origin, altitude, annual rainfall, mean annual maximum and minimum temperatures for the three species of Adansonia collected in the western part of Madagascar in 2004. Seed origin Altitude (m) Annual rainfallª (mm) Mean annual maximum Mean annual minimum temperature a (°C) temperature a (°C) A. madagascariensis Mahajanga (15°40′S, 47°03′E) 89 2236 31.93 18.2 A. grandidieri Ifaty (20°08′S, 44°33′E) 36 1156 31.72 20.85 A. rubrostipa Marofandilia (23°08′S, 43°36′) 16 302 30.65 20.19 a Source: National meteorology service, 2004. T. Randriamanana et al. / South African Journal of Botany 81 (2012) 61–70 63 Fig. 1. Map of Madagascar's primary vegetation with occurrence zones (black symbols) of Adansonia rubrostipa (represented as stars), A.