Individual study: Effect of fertilizer and water-holding gel addition on growth of Mediterranean sclerophyllous shrubs at a quarry restoration in the Arrábida Natural Park, Setúbal, Portugal
Clemente A.S., Werner C., Máguas C., Cabral M.S., , & Correia O. (2004) Restoration of a Limestone Quarry: Effect of Soil Amendments on the Establishment of Native Mediterranean Sclerophyllous Shrubs. Restoration Ecology, 12, 20-28
Amelioration of environmental conditions during the first phases of revegetation, especially by minimizing water and nutrient limitations, can improve plant establishment and accelerate revegetation. A restoration project was conducted in a limestone quarry in southwest Portugal, the surround area, a natural park, dominated by mediterranean maquis shrubland. Revegetation was attemted using three native evergreen sclerophyllous shrubs (carob tree Ceratonia siliqua, olive Olea europaea and mastic Pistacia lentiscus), and three techniques were evaluated to improve plant water and nutrient status during the initial stages of establishment in order to enhace survival and growth.
Study site: The study was performed at the SECIL quarry in the Arrábida Natural Park, 50 km south of Lisbon, in Outão, Portugal. The climate is mediterranean, with average annual rainfall of 747 mm and a pronounced summer drought from June to August. A well-preserved mediterranean maquis, dominated by evergreen sclerophyllous and summer deciduous shrubs, covers the area surrounding the quarry.
Experimental design & planting: Three native evergreen sclerophyllous species were selected: carob tree Ceratonia siliqua, olive Olea europaea var. sylvestris, and mastic tree Pistacia lentiscus They are drought tolerant and common components of the surrounding natural vegetation.
In March 1998, 2-year-old nursery plants (grown in sandy soil organic matter 4.2%, pH 5.5), were planted in a randomized factorial experiment. Two factors were considered: water (gel and control) and nutrition (Mycorrhiza, Fertilizer and Control). Six treatments were applied: Control, Gel, Myc, Gel × Myc, Fert and Gel × Fert. Five plants per species were randomly assigned to each of the six treatments in each of three bare rock planting blocks (n = 90 plants per species).
A marl layer from the quarry, about 1 m depth, was added to the surface of the bare rock before planting. The saplings (50–120 cm in height) were planted in holes about 50 cm in depth filled with sandy soil from the nursery and covered with marl. The applied gel was a water-holding polymer. Dry gel (100 g) was added to the soil in each hole. The fertilizer was supplied as 120 g of a slow-release NPK fertilizer (1:1:1). Mycorrhiza inoculum was supplied as an 85 g mixture of endo- and ecto-mycorrhiza inoculum and gel (Terra-Sorb). Plants were abundantly watered during the first week after planting. In April 1998, dead plants were replaced.
Monitoring: Plant survival, growth increments, leaf characteristics and water status were recorded to evaluate plant performance during the 1.5 year study period. Measurements of main shoot height and base stem diameter were taken on 23 April and 16–17 September 1998 and on 4 and 12 February and 15 and 19 July 1999. Leaf mass per area (LMA mg/cm2) was measured, oven dried leaf nitrogen content (N), total chlorophyll content were determined. Midday water potentials were measured during the second summer after planting, on four sunny days (15 and 16 and 21 and 22 July 1999).
Survival & growth: Survival after the first summer drought was high for all species, 98% for carob (95%), mastic (97%), and olive (98%). All three showed typical shoot growth patterns, with high growth during spring and low increments during summer and winter. Highest shoot growth (40 cm) was recorded for carob. Olive and mastic both had growth of about 11 cm. Basal growth was highest in olive (average 11 mm), followed by carob (9 mm) then mastic (4 mm). The water (gel) treatment alone did not significantly affect the growth of any species. Nutrition had a significant effect on shoot and basal growth of carob. The Fert and Gel × Fert treatments produced 1.5–2 times larger shoot and diameter increments, compared with other treatments. The Gel × Myc treatment produced the poorest results for carob. For olive, Fert and Gel × Fert also produced the highest mean shoot growth and resulted in longer internodes, but the effects of fertilizer alone was not significant. Mastic did not show any effects of water or fertilizer treatments on stem height or diameter growth.
Leaf mass per area: In the second summer average LMAs were: mastic (33.7 mg/cm²); carob (22.9 mg/cm²); and olive (22.1 mg/cm²). Gel addition significantly affected the mastic LMA, (Gel, Gel × Myc, and Gel × Fert treatments showed a lower LMA than the other treatments). In olive, there was a significant interaction between water andfertilizer treatments. The Gel treatment had lowest LMA values, and the Gel × Myc treatment the highest. Carob LMA was not affected by water or fertilizer.
Leaf chlorophyll: Total leaf chlorophyll concentration was highest in olive (on average 1.48 mg/dm²) and lowest in mastic (1.05 mg/dm²). Fertilizer produced the highest leaf chlorophyll concentration in all species (although this effect was barely significant in olive and mastic), but in olive an interaction between gel and fertilizer treatments produced the best results. For mastic, Myc, and Gel × Myc treatments showed the lowest values.
Leaf nitrogen: Leaf nitrogen content was significantly affected by fertilizer and gel in olive and mastic, but these effects were not independent: the Fert and Gel×Fert treatments increased nitrogen content in mastic. In olive the opposite trend was observed. The largest differences between treatments were observed for mastic, with the Fert, Gel × Fert, and Gel × Myc treatments having almost twice the nitrogen content than the others. Carob was not affected by any treatment.
Water potential: Olive and carob had lower leaf water potential during the second summer after planting (−3.7 and −3.5 MPa, respectively), than mastic (−2.8 MPa,). For carob water potential was significantly affected by gel, whilst fertilizer produced no effects. Highest values were recorded for Gel, Gel×Myc, and Gel×Fert treatments. In olive and mastic, Gel and Gel×Myc treatments improved the water status of plants, while the Gel×Fert treatment showed the opposite effect.
Conclusions: Of the three species, the beneficial effects of fertilizer and gel were most evident for carob. Carob exhibited highest growth rates and was the only species with growth stimulated by fertilizer. However, the application of fertilizer induced positive changes in leaf characteristics of mastic and olive, increasing chlorophyll and nitrogen content. The addition of the water-holding polymer induced higher midday plant water potentials in all three species, but for olive and mastic the simultaneous addition of gel and fertilizer induced the lowest water potentials and was not considered beneficial for these two species. The mycorrhiza inoculum did not produce any apparent benefits for these plants and appeared to have deleterious effects on growth, water potential and chlorophyll content in carob.
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