Tree nutrition

Soil tillage with chisel ploughing is the conventional soil management system in chestnut stands for fruit production in Northern Portugal. A study was developed to assess the effects of three soil management systems on in situ soil N mineralization dynamics, tree nutrition status and fruit productivity, in a 50-yr old chestnut stand. The treatments were: conventional tillage with a chisel ploughing twice a year (CT), no-tillage with rainfed improved pasture with leguminous and grasses plants (NIP), and no-tillage with spontaneous herbaceous vegetation-natural pasture (NP). The CT treatment showed a strong increase of the soil N mineral concentration following soil disturbance by tillage, but the cumulative net N mineralized along the year was significantly lower (51.8 kg ha-1) than in the NIP (85.1 kg ha-1) treatment. The NP treatment (65.9 kg ha-1) did not cause a reduction in the soil N mineralization when compared to the CT treatment. The mineralization rate (g mineralized N kg-1 total N) in 2004 was about 26, 30 and 38 in the treatments CT, NP and NIP, respectively. Treatments showed different soil N dynamics, the proportion of mineralized NO 3-N being lower in the NP (10-48%) than in CT and NIP treatments (53-74%). Our study indicates that no-tillage systems improve the tree nutrition status and enhance productivity.

This study summarizes the main results obtained by the research group from the Instituto de Recursos Naturales y Agrobiología de Sevilla during ten years of study in the mine spill affected area of the Guadiamar river (SW Spain). This work is focussed on 1) trace element changes in soil (total and available concentrations) and plants (native and reforested), and 2) evaluation of the effectiveness of assisted natural remediation in the restoration of polluted soils.

Survey of soil contamination in river banks (Alegre 2014, Domínguez et al. 2015a) and barren spots (Cabrera et al. 2015). The remediation was very effective in the floodplain; however, there is persistent soil contamination of Cd, Zn, As and Pb in different sites of limited accessibility, 16 years after the mine-spill. Environmental monitoring and new remediation measures are recommended (Zingg 2014, Domínguez et al. 2015b)

Cadmium is a non-esscntial trace clemcnt wilh great potential to escape the soil-plant barrier, resulting in rcadily transmission through the food chain and high-risk for potential consumcrs. Although Cd was not a major component 01' the Aznalcóllar mine toxic spiU (SW Spain, 1998) sholt-and mid-term studies have shown that residual Cd conlamination in soil is a major problem for a safe and sustainable reutilízation of tbe afTected arca (about 4500 ha). We sUlllmarÍze a decade of experience dcaling witb soils contaminated with Cd in a dynalllic and changing landscape "the Guadiumar Valley", a fOflllerly agricultura! area redesigned as a nature reserve "Green Corridor" after the accident. The accl1Inulation, availability and remediation of Cd in soj] and its implications fol' the soil-plant-animal system are discussed within the context of the impact and mitigation of environmenta! disaslers. CADMIUM IN SOILS: SOURCES, USE AND TOXICITY Thc chemÍcal composition ofthe parent rock is the main factor controlling (he Cd content of the soH anel thus the weathel'Íng of minerals from the parent rock is the major natural so urce of Cd in soils. Otber natural phenomena which may contribute to the local accumulatioll of Cd in soils may inelude volcanic emissions, natural fires and dust stonns (Ross, 1994; Naidu et al. 2001). The earth's crust mean value ofCd is 0.1 mg kg'1 (Al1oway, 1990), whilst ranges of 0.01-2.0 mg kg• 1 (Bowen, 1979) and 0.06 and 1.1 mg kg'1 (Kabata-Pendias and Pendias, 1992) have been proposed as normal for non-contaminated soi[s. [n addition to natural phenomena there are various anthropogenic activities that can act as punctual and/or diffuse sources of Cd accumulation in soils and in other environmental compartments (water and air). These include: a) mining-related activíties derived from the transpor! and processíng of ores, the disposa! of generated mine wastes, and the abandonment offulJy-exploited mines (Gustafsson el al., 1999; Grimalt et al., 1999); b) industrial activities related to the manufactllring of iron and steel, batteries, textiles, plastics and refinerics (AguiJar et al., 1999); e) atmospheric deposition of contaminated particJes generated during the COmbllstion of fossil fuels (power plants, automobiles, etc.) (Ross 1994); d) phosphate fertilizers and sewage sludge used in agriclllture (Adriano, 2001) and e) landfills containing municipal wastes (Ross, 1994). Cadmium is produced commercialJy as a by-product of the Zn industry, in fact, no ores are mined exclusive1y to provide Cd. Cadmillm is mostly used in batteries (Ni-Cd and Ag-Cd) (35%), as protective agent for iron and steel against corrosion (25-30%), in electroplating (alltoindustry), in pigments (cadmium sulfide and cadmium selenide), and as a stabilizer for polyvinyl plastics and as alloys (5%) (Litz et al., 2004). Other uses of Cd include photography, Iithography, process engraving, rubber curing, and as a fungicide primarily for golf course greens (Adriano, 2001). As an impurity in Zn, significant amounts of Cd are present in galvanized metals. Consequently, Cd can be found in a wide variety of consumer goods, and virtually al! households and industries have products that contain some Cd. Until relatively recent, Cd was considered a non-essential trace el ement with unknown biological role. Lane et al. (2000, 2005) found tor !he first time a Cd-dependant anhydrase in marine diatoms. Cadmium has the same fUilction as Zn in other anhydrases, but the diatoms Uve in environments with very low Zn concentrations. Hence they have evolved to use Cd instead of Zn under these particular conditions. Apart irom this example, Cd has no other knownbiological role. Nonetl1eless, Cd can be ubiquitously found in biological tissues. In the case of plants Cd is mainly passively absorbed vía the roots or the leaves. As a result, high uptake ofCd may occur in contaminated soils. Consumption of contaminated tood (e.g. vegetables) and water is a potentia! source of Cd intake by animals and/or humans. In the decades followíng World War TI, Japanese mining operations contaminated lhe Jinzll River with Cd and traces of olher toxíc metals. As a consequence, Cd accul11ulated in tlle rice crops growing along the riverbanks downstream of tlle mines. The local agricultural coml11unities consllming the contaminated rice developed ltai-itai disease and renal abnormalities, including proteinuria and glucosuriaute (Nogawa el al., 2004). Olher routes of Cd exposure lor humans include tobacco smoking and inhalation of Cd-containing fumes in industrial settings. A major problem associated with Cd accumulation in soils is its relatively high mobility in relation to other metal s, resulting in readily absorption by plants and subsequent trallSlocation from roots to 5hoots. Here Cd may accumulate at levels that are not phytotoxic, bu! possib1y hazardous for potential consumers (animals and humans) in the mid-and longtenu through bioaccumulation and biomagnification (Litz el al., 2004). Nonetheless, bíomagnitication of Cd and other metal s is still a matter of debate, smce mercury is the only metal tllat has been so far unequivocally demonstrated lo undergo biomagni:fication (Wright and Welbourn, 2002). As a rule, transmission of trace elements throllgh the food chain is affected by the soil-plant barrier described by Chaney and Giordano (1977). There are (wo

The mineralization of nitrogen in apple orchard soil will increase the soil supply. An incubation study to test the soil potential and the validity of analytical methods was conducted at 3, 8, 15, and 20 °C for up to 128 days on soils from western and south-eastern Norway. Soils with the highest pH showed the highest mineralization. The mineralization increased with increasing temperature and time, but start-up N reduced mineralization. The mineralization cannot be estimated from standard soil chemical parameters because the different C/N ratio indicates organic material of different origin and quality. The increase in NO3-N started very quickly and ranged from 17 to 182% and 12 to 64% after 8 days at 3 °C and 20 °C, respectively. There was no correlation between total N in the soil and the amount of mineralized N. On average, the mineralization increased by 5–7% for a change of 1 °C in the interval from 8 to 15 °C in the soil. The chemical extraction method using heated KCl correla...

Cadmium is a non-esscntial trace clemcnt wilh great potential to escape the soil-plant barrier, resulting in rcadily transmission through the food chain and high-risk for potential consumcrs. Although Cd was not a major component 01' the Aznalcóllar mine toxic spiU (SW Spain, 1998) sholt-and mid-term studies have shown that residual Cd conlamination in soil is a major problem for a safe and sustainable reutilízation of tbe afTected arca (about 4500 ha). We sUlllmarÍze a decade of experience dcaling witb soils contaminated with Cd in a dynalllic and changing landscape "the Guadiumar Valley", a fOflllerly agricultura! area redesigned as a nature reserve "Green Corridor" after the accident. The accl1Inulation, availability and remediation of Cd in soj] and its implications fol' the soil-plant-animal system are discussed within the context of the impact and mitigation of environmenta! disaslers. CADMIUM IN SOILS: SOURCES, USE AND TOXICITY Thc chemÍcal composition ofthe parent rock is the main factor controlling (he Cd content of the soH anel thus the weathel'Íng of minerals from the parent rock is the major natural so urce of Cd in soils. Otber natural phenomena which may contribute to the local accumulatioll of Cd in soils may inelude volcanic emissions, natural fires and dust stonns (Ross, 1994; Naidu et al. 2001). The earth's crust mean value ofCd is 0.1 mg kg'1 (Al1oway, 1990), whilst ranges of 0.01-2.0 mg kg• 1 (Bowen, 1979) and 0.06 and 1.1 mg kg'1 (Kabata-Pendias and Pendias, 1992) have been proposed as normal for non-contaminated soi[s. [n addition to natural phenomena there are various anthropogenic activities that can act as punctual and/or diffuse sources of Cd accumulation in soils and in other environmental compartments (water and air). These include: a) mining-related activíties derived from the transpor! and processíng of ores, the disposa! of generated mine wastes, and the abandonment offulJy-exploited mines (Gustafsson el al., 1999; Grimalt et al., 1999); b) industrial activities related to the manufactllring of iron and steel, batteries, textiles, plastics and refinerics (AguiJar et al., 1999); e) atmospheric deposition of contaminated particJes generated during the COmbllstion of fossil fuels (power plants, automobiles, etc.) (Ross 1994); d) phosphate fertilizers and sewage sludge used in agriclllture (Adriano, 2001) and e) landfills containing municipal wastes (Ross, 1994). Cadmium is produced commercialJy as a by-product of the Zn industry, in fact, no ores are mined exclusive1y to provide Cd. Cadmillm is mostly used in batteries (Ni-Cd and Ag-Cd) (35%), as protective agent for iron and steel against corrosion (25-30%), in electroplating (alltoindustry), in pigments (cadmium sulfide and cadmium selenide), and as a stabilizer for polyvinyl plastics and as alloys (5%) (Litz et al., 2004). Other uses of Cd include photography, Iithography, process engraving, rubber curing, and as a fungicide primarily for golf course greens (Adriano, 2001). As an impurity in Zn, significant amounts of Cd are present in galvanized metals. Consequently, Cd can be found in a wide variety of consumer goods, and virtually al! households and industries have products that contain some Cd. Until relatively recent, Cd was considered a non-essential trace el ement with unknown biological role. Lane et al. (2000, 2005) found tor !he first time a Cd-dependant anhydrase in marine diatoms. Cadmium has the same fUilction as Zn in other anhydrases, but the diatoms Uve in environments with very low Zn concentrations. Hence they have evolved to use Cd instead of Zn under these particular conditions. Apart irom this example, Cd has no other knownbiological role. Nonetl1eless, Cd can be ubiquitously found in biological tissues. In the case of plants Cd is mainly passively absorbed vía the roots or the leaves. As a result, high uptake ofCd may occur in contaminated soils. Consumption of contaminated tood (e.g. vegetables) and water is a potentia! source of Cd intake by animals and/or humans. In the decades followíng World War TI, Japanese mining operations contaminated lhe Jinzll River with Cd and traces of olher toxíc metals. As a consequence, Cd accul11ulated in tlle rice crops growing along the riverbanks downstream of tlle mines. The local agricultural coml11unities consllming the contaminated rice developed ltai-itai disease and renal abnormalities, including proteinuria and glucosuriaute (Nogawa el al., 2004). Olher routes of Cd exposure lor humans include tobacco smoking and inhalation of Cd-containing fumes in industrial settings. A major problem associated with Cd accumulation in soils is its relatively high mobility in relation to other metal s, resulting in readily absorption by plants and subsequent trallSlocation from roots to 5hoots. Here Cd may accumulate at levels that are not phytotoxic, bu! possib1y hazardous for potential consumers (animals and humans) in the mid-and longtenu through bioaccumulation and biomagnification (Litz el al., 2004). Nonetheless, bíomagnitication of Cd and other metal s is still a matter of debate, smce mercury is the only metal tllat has been so far unequivocally demonstrated lo undergo biomagni:fication (Wright and Welbourn, 2002). As a rule, transmission of trace elements throllgh the food chain is affected by the soil-plant barrier described by Chaney and Giordano (1977). There are (wo

Sewage sludge may be used to increase the organic matter concentration into the soil, and, subsequently increase the N and P availability for plants. The amendment for forestry represents a valorization way, in particular, for the pine production. Soils from New Caledonia are usually characterized by a poor nutrient content and large quantities of heavy metals like Ni, Cr and Co, resulting in a slow installation and development of vegetal species. Some Pinus caribaea plantations on soil from the south of New Caledonia have not presented a great production success. An experiment was conducted to introduce different level of biosolids into the topsoil of an old pine forest. The aim of this study consisted in verifying that these biosolids represent an interesting response to promote the vegetal establishment on a lateritic soil. Fields results indicate that the 8 t dw.ha-1 dose seems the most interesting for the pine installation.

Soil tillage with chisel ploughing is the conventional soil management system in chestnut stands for fruit production in Northern Portugal. A study was developed to assess the effects of three soil management systems on in situ soil N mineralization dynamics, tree nutrition status and fruit productivity, in a 50-yr old chestnut stand. The treatments were: conventional tillage with a chisel ploughing twice a year (CT), no-tillage with rainfed improved pasture with leguminous and grasses plants (NIP), and no-tillage with spontaneous herbaceous vegetation-natural pasture (NP). The CT treatment showed a strong increase of the soil N mineral concentration following soil disturbance by tillage, but the cumulative net N mineralized along the year was significantly lower (51.8 kg ha-1) than in the NIP (85.1 kg ha-1) treatment. The NP treatment (65.9 kg ha-1) did not cause a reduction in the soil N mineralization when compared to the CT treatment. The mineralization rate (g mineralized N kg-1 total N) in 2004 was about 26, 30 and 38 in the treatments CT, NP and NIP, respectively. Treatments showed different soil N dynamics, the proportion of mineralized NO 3-N being lower in the NP (10-48%) than in CT and NIP treatments (53-74%). Our study indicates that no-tillage systems improve the tree nutrition status and enhance productivity.

Viterbo area is naturally polluted with arsenic (As) as a result of geochemical mobilization of this metalloid through hydrothermal processes that lead to the up-flow of thermal waters. The area is characterised by thermal springs with arsenic concentrations ranging from 180 to 370 μgL -1 and the soils are calcareous. Soil samples were taken in the area surrounding Bullicame hot springs and inside the nearby University Botanical Gardens with the aim to assess: i) the distribution and bioavailability of arsenic in the soil, ii) the effect of plant cover on its distribution and iii) microbial functional diversity. The sampling points were then the Control (near the thermal springs), Pinus halepensis, Quercus spp., Mediterranean maquis and anot-planted area all found within theBotanical gardens. The results reflected a considerable amount of arsenic associated to the CaCO 3 fraction which may become unstable under changing environmental conditions thus potentially hazardous. The presence of different plant covers affects the arsenic content in the soil differently as was evident in the drastic reduction of As content under conifer plants (Pinus halepensis) cover. The presence of plant products favours a higher functional diversity of microbial processes as opposed to the drastic reduction in microbial functional diversity observed in the control site where the CaCO 3 content is elevated and no vegetation is present. These preliminary results offer an interesting opportunity to study the complex interactions of this toxic metalloid in a soil-plant system in a naturally polluted environment.

Iron chlorosis caused by an elevated soil pH remains an important selection criteria in evaluating hybrid Populus trials in northwest New Mexico. Compared to expensive extraction methods or visual ranking scales, the soil plant analysis development (SPAD) chlorophyll meter is a handheld tool that objectively indicates leaf color. SPAD calibration curves pertaining to Fe status in Populus leaves were developed for two clones: NM-6 (Populus nigra 9 Populus maximowiczii) and OP-367 (Populus deltoides 9 Populus nigra). Hybrids were grown in the greenhouse in a sandy loam soil of pH [ 8 and the same soil amended with composted biosolids enriched with 420 mg kg-1 Fe. SPAD measurements related to foliar Fe as follows: r 2 = 0.72 for NM-6 and r 2 = 0.58 for OP-367. SPAD measurements correlated with total chlorophyll as follows: r 2 = 0.66 for NM-6 and r 2 = 0.85 for OP-367. Based on the total chlorophyll content (supported with foliar element data), Fe sufficiency threshold values from SPAD measurements were estimated in these two clones.

The influence of Cd and Cu on growth, chlorophyll content and mineral nutrition of Pinus pinea L., Pinus pinaster Ait. and Fraxinus angustifolia Vahl. was investigated. Two-week old seedlings were grown for 4 weeks in a complete culture solution and range of metals were added as CuSO 4 (0.012-5 p.M) and CdSO 4 (0.0-5 ~M). The biomass of the Pinus species was significantly lower than that of controls only at the supply of 5 pM Cu, whereas in F angustifolia both shoot and root biomass decreased in heavy metal treatments. Chlorophyll content decreased in all species with increasing Cd or Cu supply. Cd-treated leaves of F. angustifolia were chlorotic. The Mn and Zn content of roots decreased in all species at increasing Cu and Cd concentrations, whereas the Ca and Mg uptake and distribution differed among species.

Iron chlorosis caused by an elevated soil pH remains an important selection criteria in evaluating hybrid Populus trials in northwest New Mexico. Compared to expensive extraction methods or visual ranking scales, the soil plant analysis development (SPAD) chlorophyll meter is a handheld tool that objectively indicates leaf color. SPAD calibration curves pertaining to Fe status in Populus leaves were developed for two clones: NM-6 (Populus nigra 9 Populus maximowiczii) and OP-367 (Popu-lus deltoides 9 Populus nigra). Hybrids were grown in the greenhouse in a sandy loam soil of pH [ 8 and the same soil amended with composted biosolids enriched with 420 mg kg-1 Fe. SPAD measurements related to foliar Fe as follows: r 2 = 0.72 for NM-6 and r 2 = 0.58 for OP-367. SPAD measurements correlated with total chlorophyll as follows: r 2 = 0.66 for NM-6 and r 2 = 0.85 for OP-367. Based on the total chlorophyll content (supported with foliar element data), Fe sufficiency threshold values from SPAD measurements were estimated in these two clones.

The Green Valley Mine in Indiana was abandoned in 1963 after 15 years of coal mining. Reclamation began in 1994 and ended in 1999 with the dense planting of twelve different tree species. By 2006, only green ash (Fraxinus pennsylvanica Marsh.) and black locust (Robinia pseudoacacia L.) had survived in any significant numbers. Given the acid mine drainage found at the site, we sought to determine whether element toxicity originating from mine waste was responsible for the extirpation of the trees. Leaf samples taken from 125 mine trees and 29 control trees were acquired and assayed for 41 element concentrations using inductively coupled plasma mass spectrometry (ICPMS). Except for sodium, there was no compelling evidence to indicate that toxic elemental levels were responsible for the widespread tree deaths. In addition to sodium toxicity, we suspect that micronutrient deficiency was a primary factor explaining the extirpation of trees at the mine.

The Green Valley Mine in Indiana was abandoned in 1963 after 15 years of coal mining. Reclamation began in 1994 and ended in 1999 with the dense planting of twelve different tree species. By 2006, only green ash (Fraxinus pennsylvanica Marsh.) and black locust (Robinia pseudoacacia L.) had survived in any significant numbers. Given the acid mine drainage found at the site, we sought to determine whether element toxicity originating from mine waste was responsible for the extirpation of the trees. Leaf samples taken from 125 mine trees and 29 control trees were acquired and assayed for 41 element concentrations using inductively coupled plasma mass spectrometry (ICPMS). Except for sodium, there was no compelling evidence to indicate that toxic elemental levels were responsible for the widespread tree deaths. In addition to sodium toxicity, we suspect that micronutrient deficiency was a primary factor explaining the extirpation of trees at the mine.

The uptake of arsenic and other metals (iron, manganese, copper, zinc, lead, nickel and tungsten) by Pinus pinaster Aiton (the maritime pine tree) growing in soils and tailings around an abandoned mine (northern Portugal) was investigated. Aerial parts of Pinus pinaster trees were sampled from three substrate areas: a background area, in mine contaminated soils and in tailings. Vegetation material was separated into needles and stems and subdivided into tissues of different maturities (1-, 2-, 3-and 4-years-old). The sampling of the substrate in each area was also undertaken. In general, vegetation concentrations were strongly related to substrate concentrations. The results show that the contents of several elements depend as much on the plant organ as on the age of the tissue. For the researched elements, this species shows a great variability in behavior depending on the age of the organ. The data indicate that the older needles constitute the best samples for use in a conjunct biogeochemical analysis of these elements.

Seedling growth Mortality Sewage sludge a b s t r a c t Biosolids have been widely used for land reclamation, but information on their use in restoration, i.e., on less degraded areas, is scarce. Biosolids may be used to restore forest ecosystems by fostering tree establishment in degraded shrublands. Detailed knowledge on the effects of biosolid application is needed to optimize such practice. We evaluated the effect of different rates (0, 7.5 and 14.5 kg dry weight per plant) and types of biosolid application on the performance of Pinus halepensis and Quercus ilex seedlings, and operational costs. Biosolids increased seedling mortality in both species, particularly when seedlings were planted in direct contact with them. Mortality mostly occurred during the first year, and was probably favored by soil shrinking and salinity. Foliar and needle nitrogen concentration increased with biosolid rate in the short term, but biosolids affected negatively (P. halepensis), or had no effect (Q. ilex) on phosphorus and potassium concentration. Biosolids had a positive effect on P. halepensis growth, and a negative effect on Q. ilex growth at the highest rate when seedlings were in contact with biosolids. Cost of this type of biosolid application approximately doubled plantation cost, but were similar or cheaper that landfill disposal of biosolids. The lowest application rate showed the best balance between seedling response and costs for P. halepensis, whereas biosolid use cannot be recommended for Q. ilex.

Soil contamination may contribute to forest decline, by altering nutrient cycling and acquisition by plants. This may hamper the establishment of a woody plant cover in contaminated areas, thus limiting the success of a restoration program. We studied the nutritional status of planted saplings of Holm oak (Quercus ilex subsp. ballota (Desf.) Samp.), white poplar (Populus alba L.), and wild olive tree (Olea europaea var. sylvestris Brot.) in the Guadiamar Green Corridor (SW Spain) and compared it with established adult trees. Soils in this area were affected by a mine-spill in 1998 and a subsequent restoration program. The spill resulted in soil acidification, due to pyrite oxidation, and deposited high concentrations of some trace elements. In some sites, we detected a phosphorus deficiency in the leaves of Q. ilex and O. europaea saplings, as indicated by a high N:P ratio (>16). For O. europaea, soil contamination explained 40% of the variability in leaf P and was negatively related to chlorophyll content. Soil pH was a significant factor predicting the variability of several nutrients, including Mg, P, and S. The uptake of Mg and S by P. alba was greater in acidic soils. The monitoring of soil pH is recommended since long-term effects of soil acidification may negatively affect the nutritional status of the trees.

Iron chlorosis caused by an elevated soil pH remains an important selection criteria in evaluating hybrid Populus trials in northwest New Mexico. Compared to expensive extraction methods or visual ranking scales, the soil plant analysis development (SPAD) chlorophyll meter is a handheld tool that objectively indicates leaf color. SPAD calibration curves pertaining to Fe status in Populus leaves were developed for two clones: NM-6 (Populus nigra 9 Populus maximowiczii) and OP-367 (Populus deltoides 9 Populus nigra). Hybrids were grown in the greenhouse in a sandy loam soil of pH [ 8 and the same soil amended with composted biosolids enriched with 420 mg kg -1 Fe. SPAD measurements related to foliar Fe as follows: r 2 = 0.72 for NM-6 and r 2 = 0.58 for OP-367. SPAD measurements correlated with total chlorophyll as follows: r 2 = 0.66 for NM-6 and r 2 = 0.85 for OP-367. Based on the total chlorophyll content (supported with foliar element data), Fe sufficiency threshold values from SPAD measurements were estimated in these two clones.

Iron chlorosis caused by an elevated soil pH remains an important selection criteria in evaluating hybrid Populus trials in northwest New Mexico. Compared to expensive extraction methods or visual ranking scales, the soil plant analysis development (SPAD) chlorophyll meter is a handheld tool that objectively indicates leaf color. SPAD calibration curves pertaining to Fe status in Populus leaves were developed for two clones: NM-6 (Populus nigra 9 Populus maximowiczii) and OP-367 (Populus deltoides 9 Populus nigra). Hybrids were grown in the greenhouse in a sandy loam soil of pH [ 8 and the same soil amended with composted biosolids enriched with 420 mg kg -1 Fe. SPAD measurements related to foliar Fe as follows: r 2 = 0.72 for NM-6 and r 2 = 0.58 for OP-367. SPAD measurements correlated with total chlorophyll as follows: r 2 = 0.66 for NM-6 and r 2 = 0.85 for OP-367. Based on the total chlorophyll content (supported with foliar element data), Fe sufficiency threshold values from SPAD measurements were estimated in these two clones.

Seedling growth Mortality Sewage sludge a b s t r a c t Biosolids have been widely used for land reclamation, but information on their use in restoration, i.e., on less degraded areas, is scarce. Biosolids may be used to restore forest ecosystems by fostering tree establishment in degraded shrublands. Detailed knowledge on the effects of biosolid application is needed to optimize such practice. We evaluated the effect of different rates (0, 7.5 and 14.5 kg dry weight per plant) and types of biosolid application on the performance of Pinus halepensis and Quercus ilex seedlings, and operational costs. Biosolids increased seedling mortality in both species, particularly when seedlings were planted in direct contact with them. Mortality mostly occurred during the first year, and was probably favored by soil shrinking and salinity. Foliar and needle nitrogen concentration increased with biosolid rate in the short term, but biosolids affected negatively (P. halepensis), or had no effect (Q. ilex) on phosphorus and potassium concentration. Biosolids had a positive effect on P. halepensis growth, and a negative effect on Q. ilex growth at the highest rate when seedlings were in contact with biosolids. Cost of this type of biosolid application approximately doubled plantation cost, but were similar or cheaper that landfill disposal of biosolids. The lowest application rate showed the best balance between seedling response and costs for P. halepensis, whereas biosolid use cannot be recommended for Q. ilex.

In degraded Mediterranean woodlands, nutrients, in addition to water, may be the major factors controlling reforestation success. But information on nutritional status of planted seedlings is scarce. We aimed to evaluate the nutritional status and field performance of Pinus halepensis and Quercus ilex seedlings planted on two characteristic Mediterranean forest soils developed from marl and limestone. We used root growth response to localized N and P enrichment, and foliar analysis as indicators of nutrient limitation. Vermiculite cores enriched with P showed higher root density than N-enriched and control cores, particularly on soils derived from marl three years after planting. Seedlings showed low foliar P and K as compared to other species and adult trees. Principal Component Analysis conducted on foliar macronutrient concentration clearly separated species and soil type. Foliar K and Mg depended on soil type (higher on limestone and marl, respectively), whereas N, P and Ca concentration in leaves and needles differed between species (higher N and P in pine, higher Ca in oak). Survival and growth depended on species and site, but we found no effect of soil type on these variables, suggesting that seedling performance may not be strongly affected by nutrient status within the range of soils evaluated.

Soil contamination may contribute to forest decline, by altering nutrient cycling and acquisition by plants. This may hamper the establishment of a woody plant cover in contaminated areas, thus limiting the success of a restoration program. We studied the nutritional status of planted saplings of Holm oak (Quercus ilex subsp. ballota (Desf.) Samp.), white poplar (Populus alba L.), and wild olive tree (Olea europaea var. sylvestris Brot.) in the Guadiamar Green Corridor (SW Spain) and compared it with established adult trees. Soils in this area were affected by a mine-spill in 1998 and a subsequent restoration program. The spill resulted in soil acidification, due to pyrite oxidation, and deposited high concentrations of some trace elements. In some sites, we detected a phosphorus deficiency in the leaves of Q. ilex and O. europaea saplings, as indicated by a high N:P ratio (>16). For O. europaea, soil contamination explained 40% of the variability in leaf P and was negatively related to chlorophyll content. Soil pH was a significant factor predicting the variability of several nutrients, including Mg, P, and S. The uptake of Mg and S by P. alba was greater in acidic soils. The monitoring of soil pH is recommended since long-term effects of soil acidification may negatively affect the nutritional status of the trees.

The impairment of root growth and photosynthetical functioning are the main impacts of trace elements on woody plant seedlings. In this work, we assessed the response of Holm oak (Quercus ilex subsp. ballota) and mastic shrub (Pistacia lentiscus) seedlings to high concentrations of Cd and Tl in the rhizosphere. These are non-essential trace elements, with a potential high mobility in the soil-plant system. Seedlings of these species are frequently used in the afforestation of degraded soils in mining areas. Plants were exposed to different levels of Cd (20, 80 and 200 mg L(-1)) and Tl (2, 10 and 20 mg L(-1)) in a sand culture. Biomass allocation, growth rates, chlorophyll fluorescence and gas exchange were studied. Both metals affected root biomass. Cadmium produced an increase in the root mass ratio and a decrease in the specific leaf area of the plants in oak seedlings, while Tl did not provoke such response. Mastic plants were more sensitive to Tl and Cd than oak plants. Between elements, Tl provoked more severe toxic effects in the plants, affecting the antennae complexes and reaction centers of the photosystem II. Both elements decreased net assimilation rates (down to a 20% of the control plants) and stomatal conductance (5-10% of the values for the control plants). Cadmium was highly retained in the roots of both species, while Tl was highly translocated into the leaves. In general, Holm oak showed a higher tolerance for Cd than for Tl, and a higher resistance to both metals than mastic shrub, due to a high capacity for Cd retention at the root level. However, such accumulation in roots may induce water stress in the seedling exposed to Cd.