DEL MODELO DE ANÁLISIS
TIPOS DE ACTIVIDADES
2. Taller Municipal de la Memoria
As explained in the introduction to this chapter Nematoceras orchid seed are produced in great numbers, the hypothesis being that a large number of seed provides a greater chance of survival in species that require a specific environment, host or is subject to transitory dispersal vectors, (Burrows, 1975; Howe, 1982; Nathan, 2006; Rasmussen, 1993; Soons, 2005; Teryokhin, 1982; Trakhtenbrot, 2005; van der Pijl, 1982). Various strategies to facilitate seed dispersal are apparent in Nematoceras spp.
Considering the seed mass to volume ratio and the average proportion of seed per pod, it would initially appear that the normal seed with viable embryos, amount to only 31.74% of total seed of an N. iridescens pod (Table A1. 5).
However it is possible, that the low seed mass to volume ratio (micro) seed (65.48%) are able to disperse to a greater distance ensuring a more complete coverage of downwind deposit sites, (Jersáková, 2007). Deposit shadow rings,
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(Fig. A1.21), (Nathan, 2006), formed between micro seed, with viable embryos and normal seed volume mass, would ensure a far greater range of seed distribution and plant survival rate.
Figure A1.21 Seed deposit shadows; A = normal seed deposit shadow, B = micro seed deposit shadow
A major difficulty of long distance wind born seed dispersal encounted with terrestrial plants growing in forested areas is the resistance and air flow disturbance provided by the forest canopy to upward airflow, (Cain, 2000).
All of the Nematoceras spp. observed by the author were situated on banks or in forest gaps within open airflow zones Extensions of the peduncles bearing the terminal seed pods, placed the pods into airflows of sufficient wind strength to shake the pods and free the “balloon” seed into valley wind flows. Seed morphology is such that the Nematoceras seed surface simulates an aerofoil effect and having “Dust Seed” characteristics enables the seed to move over great distances, Burrows, (1975), provides formulae and methods for the calculation of primary trajectories for “Dust Seed”, spores and pollen in unstable winds.
Valley wind currents tend to be strongest around mid-day and early afternoon, at the same period that vertical convection air currents occur, (Sturman, 1996). Any oscillation, with a wind speed greater than 1.3 ms-1, would enable the seed to be liberated into passing wind currents and then into the main valley wind currents. Differences, between seed testa cell numbers, of N. iridescens, N. longipetalum and N. papa do not appear to be of taxonomic value. Testa shapes all conformed to a fusiform morphology with a large range of gross difference within and between each species. This difference was not thought to be of value and was not calculated. However, apoplast walls and their patternation presented visual interspecies differences.
Having minute seed, limits predation to a size relevance basis, (Harper, 1970). Very minute seed is predated by very small herbivores. The only case of seed predation the author observed was by a Cryptostigmata mite (Fig. A1.15).
Seeds within the pod, mature in the final weeks, become lignified, dry and loose moisture. A waxy cuticle covers the hardened seed testa and produces seed which are extremely difficult to wet. Contours in the testa of hardened orchid seed, along
with their minute size, produce extremely high water tension levels when the liberated seed is immersed in water, (Arditti, 2000; Rasmussen, 1993, 1995). This condition provides good flotation ability and a further dispersal advantage for orchid seed.
The results seen in the symbiotic germination section, although disappointing, reflect the results of many terrestrial orchid workers in this field, (Batty, 2001; Bonnardeaux, 2007; Henrich, 1981; Kauth, 2006; Quay, 1995; Rasmussen, 1998; Zettler, 1997). No formal research appears to have been conducted on NZ terrestrial orchid seed symbiotic germination.
Differences in orchid seed germination and seedling development could be attributed to a process of adaptation to changes in differing environments as, Kauth, (2008), has suggested.
The results, seen in the symbiotic series 1 trial used fungal cultures from the culture library, all of which had been derived from root tissue of Nematoceras spp. Culture 19 (N3a1) was successfully sequenced and was nearest to an uncultured
Sebacinaceae, Genebank accession number, AY634132. The Sebacinaceae are known endophyte mycorrhizal fungi of orchids, (Rasmussen, 1992; Zettler, 1997). A comparison, between the immunity of successful orchid seed germination, to pathogenic fungi and bacteria, to that of the non-immune seed would provide a field of worthwhile study, especially since the period of orchid seed dormancy, in pathogen favourable environments, can extend for a year or more, (Arditti, 1992, 2000; Rasmussen, 1992; Yamazaki, 2006).
Based on the results reported in the Series 2, (Table A1.6), light regimes, play an important aspect in development of the fungi. Both continuous light, 24 / 24 and partial light 12 / 24, inhibited germination, apparently by affecting the fungal inoculant, rather than the seed, since the controls (seed alone) remained viable and imbibed in all of the light situations. The 24/24 dark group, A7 and N3, retained form, displayed imbibition and embryo colour throughout the experiment. A mite found in the M551 #1 asymbiotic culture was provisionally identified as an
Orbiculata mite member of the Cryptostigmata family. Most members of this group are fungal predators and so conjecture arises as to whether this species of mite is predating fungi or the orchid seed, (Luxton, 1985). All of the seed of M551 #1 had died by the 24/09/09.
The time taken for the final result of the field trial germination (Table A1.8) was one year from the initial sowing dates. This would indicate that the time allowed for two of the germination experiments, both symbiotic and asymbiotic could have been restrictive in the time allowed. Long-term seed dormancy could have inhibited germination. .
Vernilization, epicotyl dormancy (Kauth, 2006), could affect seed germination delay when consideration is accorded to the seasonal climatic variation of the sites in which plantsof the Nematoceras species can be found
Of the three asymbiotic culture media, T842 supported 71% of embryos for the total term of the trial, BM1 supported 0% and M551 14.3%. A major difference between the three media was the activated charcoal and pineapple powder that T842 contained (see Appendix 3 Media). In hindsight (time taken for field trial germination to become apparent) a longer period of trial would have been valuable.