Abstract
The aim of this study was to assess the effects on root deformations in Mediterranean cork oaks Quercus suber L. of container size and radicle length at the time of sowing. Acorns at five sowing methods – intact acorns, acorns that had germinated during storage, acorns that had germinated after moist stratification and acorns with radicles (R) less than 5 mm in length, 7 mm to 12 mm in length and more than 15 mm length – were planted individually in WM type containers of 400 cm3, 800 cm3 and 1,200 cm3. At the end of the nursery growth period, the roots of the 1,080 sampled seedlings were examined for root deformities. The experiment results showed that root deformation affected almost half (49%) of the container-grown cork oak seedlings and that the germination status of acorns at the time of planting had a significant effect on root deformations, whereas container volume had no clear effect. The largest number of deformed roots (91%) was observed in seedlings grown from germinated acorns, as compared to 9% of seedlings grown from intact acorns. Planting germinated acorns with radicles 15 < R < 20 mm and 7 < R < 12 mm in length produced the highest percentages of detrimental deformations. Irrespective of size, the bottomless WM container type was shown to be highly effective against the root spiralling frequently observed in closed cylindrical polyethylene bags. The results of this study could help to improve cork oak seedling quality for more successful reforestation programs.
Highlights
Cork oak (Quercus suber L.) is one of the major and valuable components of the natural forests in the Mediterranean region
The results show that almost half (49%) of the 1,080 seedlings inspected at the end of the nursery period were affected by root deformations
In accordance with a previous research (Chouial and Benamirouche, 2016), the greatest number of deformed roots was observed on seedlings grown from sowing of germinated acorns than on seedlings grown from direct sowing of intact acorns with respective percentages of 91% and 9% of the inspected seedlings
Summary
Cork oak (Quercus suber L.) is one of the major and valuable components of the natural forests in the Mediterranean region. In Algeria, this evergreen woody species occupies 357,582 hectares (Abbas, 2013) mainly located in the North-East of the country Despite their ecological and socio-economical interests, cork oak forests are subjected to degradation under the combined action of Human impacts (urbanization, wildfires, overgrazing, clearing and seed collection) and water stress due to recurring droughts under climate change. The combination of these factors, along with a lack of management practices adapted to the species resulted in a deficiency of natural regeneration. The poor survival of Quercus plantations in the field has most often been attributed to the low quality of the planted seedlings, the limited resources to growth (Tsakaldimi et al, 2005; Valdecanthos et al, 2006), the poor planting technique and the poor post-planting maintenance
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