Evaluation of nutrient deprivation on functional traits of plants produced in nurseries for restoration programs in the Mediterranean region of central Chile

Background/Question/Methods . Fight against desertification in Mediterranean environments involves many strategies for tending to the ecological restoration of degraded lands. However, the probability to achieve successful recovery has many technical problems imposed by the dry-summer period. Under such unfavorable conditions, seedling mortality is generally high after the first summer following outplanting and several restoration campaigns fail few years after these began. In this context, an important challenge for forest restoration efforts is to increase the efficiency in the water use of seedlings produced in nurseries once these are outplanted.

Tree seedling establishment in Mediterranean areas is strongly limited by water. The performance of planted seedlings is affected by seedling morphological and physiological traits. These traits can be modified by cultural practices such as fertilization. Increases in nutrient availability change the morphology, and regulates plant growth and balance in the allocation to the aerial biomass versus-root biomass. Some studies show a positive relationship between plant size and performance in the field. However, in environments where water limitation is high, a reduction of nutrients may be beneficial because it results in small plants with small leaf area, high allocation of biomass to below ground structures, which overall reduces water consumption and increases water use efficiency. Therefore small modifications on growing conditions can improve seedling performance and increase the probability of restoration efforts. The objective of this study was to determine the influence of different nutrient-fertilization treatments on both above-and below-ground growth of one-year old seedlings of two species of the sclerophyllous forest of central Chile, Quillaja saponaria and Rhaphithamnus spinosus. We produced seedlings under contrasted fertilization regimes. Seedlings were cultivated under an open-air nursery and received weekly applications of complete nutrient solution, diluted fertirrigation, or nutrient solutions containing no nitrogen or no phosphorus. At the end of the growth period, seedlings´s shoot height, shoot diameter, shoot and root biomass, root surface area, root volume and total root length were assessed.

Results/Conclusions . Fertilization had a strong effect on nutrient status, above and belowground biomass accumulation, and biomass allocation patterns. Root:shoot ratio was higher in nitrogen- and phosphorus-deficient seedlings than in seedlings receiving complete nutrient solution. Our results show that nutrient deprivation induced morphological changes advantageous to enhanced tolerance to drought. This suggests that there are opportunities for modifying nursery fertilization to produce stock for use on particularly droughty sites; and consideration of the severity of drought at a particular site should be made prior to fertilization.