Improving seed germination and seedling growth of Omphalea oleifera (Euphorbiaceae) for restoration projects in tropical rain forests. For Ecol Manage

Estación de Biología Tropical “Los Tuxtlas”, Instituto de Biología, Universidad Nacional Autónoma de México, Apartado Postal 94, San Andrés Tuxtla, 95701 Veracruz, Mexico
Forest Ecology and Management (Impact Factor: 2.67). 05/2007; 243(1)(1):144-155. DOI: 10.1016/j.foreco.2007.03.001

ABSTRACT To improve the restoration of tropical rain forests, we tested the germination of seeds of Omphalea oleifera collected from soil (S) and from trees (T) in the 2001 dry season (Spring), at the beginning of a dry season (2005a, winter) and in the rainy season (2005b, winter). All seeds had high water content (WC, 31–33%), and the lipid content varied from 14 to 46%. Seedlings from seeds collected in 2001 were subjected to moderate water stress as a preconditioning treatment for severe stress. T-seeds collected in the dry season had high WC, rapid and high germination percentage; S and T-seeds collected in winter (2005) had also high WC but were dormant. GA3 (250 ppm) broke this dormancy. S-seeds collected in the dry season or at the beginning of it had relatively low WC and low and delayed germination. Some 2001 S-seeds produced albino seedlings. The critical water content for maintaining ecological longevity in these seeds was ∼15%. Seeds collected in 2005b that were dehydrated for 20 days in a moist and fresh atmosphere lost their viability, showing recalcitrant behavior. T-seeds with the lowest lipid content (2005a) after dehydration maintained low germination (15 ± 18%). In all samples the seed size varied widely and was not predictive of seed WC. Embryos taken from dehydrated seeds had two to four times higher WC than the seeds, but germination did not take place. Laboratory and field germination of dormant seeds showed that viability may be maintained for at least 2–3 months on a moist substrate (soil or agar). Moderate water stress at the seedling stage reduced the efficiency of biomass production. Response to this water stress was expressed more in physiological traits than in morphological characters, consequently biomass allocation was maintained and plants retained most of their morphological characteristics (root:shoot ratio, leaf area ratio, specific leaf area, leaf weight ratio). Moderate water stress did not increase the tolerance of seedlings to severe stress, causing leaf shedding and plant death. For restoration purposes we recommend that T-seeds be germinated immediately avoiding dehydration. The use of S-seeds could result in unhealthy seedlings. Seed recalcitrance and the response to moderate water stress restrict germination and establishment to small gaps, where this species naturally grows. We suggest that before introducing O. oleifera in restoration programs, a plant cover should be built to reduce soil water deficit. It is necessary to improve methods to increase potential seed longevity in storage.

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    • "These species owing to the high capacity of water storage at stem and branch, and the good rooting in soil are able to well bear the drought status and to overcome the drought stress (Oliet et al., 2002; Tabari et al., 2011). Since the vast regions of world have dry climate, strategies for perfect use of the water resources and the drought-resistant species, which are able to highly benefit from the soil moisture, can be the main targets of plantation in such regions (Oliet et al., 2002; Sanchez-Coronado et al., 2007). Juniperus excelsa is distributed in vast areas of Irano-Touranian growing regions (Zare, 2001). "
    Water Quality, Soil and Managing Irrigation of Crops, 03/2012; , ISBN: 978-953-51-0426-1
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    • "The total amount of rainfall sets limits to distribution of forests in the tropics (Holdridge 1967; Walter 1979; White 1983; Woodward 1987; Portillo-Quintero and Sánchez- Azofeifa 2010). Research indicates that spatial and temporal variation in soil water availability determines intra-and inter-annual patterns of growth, productivity and survival within seasonal forests (Baker et al. 2003a; Baker et al. 2003b; Urbeita et al. 2008; Sánchez-Coronado et al. 2007; Namirembe et al. 2008). The annual girth increment of deciduous species correlates positively with rainfall during the middle of the wet season (Bullock 1997) and also with total rainfall during the previous 2 years (Whigham et al. 1990). "
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