Fall fertilization of Holm oak affects N and P dynamics,root growth potential,and post-planting phenology and growth

• Introduction   

For Holm oak (Quercus ilex L.), a flush growing species, nutrient loading during the growing season is difficult and can lead to a low nutrient status of the seedlings. To provide insights about Holm oak nutrient dynamics during fall in the nursery and subsequent planting performance, a factorial nursery experiment was conducted in a mild fall–winter area testing the effects of timing of fertilization (early and late fall) and rate (two doses of a NPK fertilizer that applied 28 and 56 mg N per seedling), followed by an experimental plantation.     

Why do large,nitrogen rich seedlings better resist stressful transplanting conditions? A physiological analysis in two functionally contrasting Mediterranean forest species

We analysed the physiological bases that explain why large and high nitrogen (N) concentration seedlings frequently have improved survival and growth relative to small seedlings in Mediterranean woodland plantations. Large seedlings of Aleppo pine (Pinus halepensis Mill.) and holm oak (Quercus ilex L.) with high N concentration (L+), and small seedlings with either high (S+) or low (S−) N concentration, were planted on two sites of different weed competition intensity that created contrasting stress conditions. Seedling survival, growth, gas exchange, N remobilization (N_R) and uptake (N_U), and water potential were assessed through the first growing season. Weeds reduced survival and growth, but seedling response to weed competition varied among phenotypes and between species. At the end of the first growing season, L+ Aleppo pine seedlings had higher survival than both small seedling types in presence of weeds but no differences were observed in absence of weeds. Mortality differences among phenotypes occurred in spring but not in summer. L+ Aleppo pines grew more than small Aleppo pines independently of weed competition. No holm oak seedling type survived in presence of weeds and no mortality differences among phenotypes where observed in absence of weeds, although L+ holm oak seedlings grew more than small seedlings. Mortality and growth differences in Aleppo pine were linked to marked physiological differences among phenotypes while physiological differences were small among holm oak phenotypes. L+ Aleppo pines had greater root growth, gas exchange, N_R, and N_U than small seedlings, irrespective of their N concentration. Seedling size in Aleppo pine had a greater role in the performance of transplanted seedlings than N concentration. The functional differences among oak phenotypes were small whereas they were large in pine seedlings, which led to smaller differences in transplanting performance in holm oak than in pine. This suggests that the nursery seedling quality improvement for planting in dry sites could depend on the species-specific phenotypic plasticity and functional strategy. Improved transplanting performance in large Aleppo pine seedlings relative to small seedlings was linked to greater gas exchange, root growth and N cycling.     

Predicting field performance of five irrigated tree species using seedling quality assessment in Burkina Faso,West Africa

Five exotic tree species (Acacia angustissima (Mil.) Kuntze, A. mangium Wild, Gliricidia sepium (Jacq.) Alp., Leucaena hybrid (L×L), and Leucaena leucocephala (Lam.) de Wit) were investigated to determine whether parameters of nursery seedling stock quality could be used to predict their field performance in a plantation irrigated with treated waste-water to produce fodder and wood. Plants were grown in the nursery in two contrasting rooting substrates (ordinary nursery soil and sand), predicted to have different effects on resource allocation. Three categories of morphological indicators were measured, i.e., plant dimensions (height, diameter, root length), plant weights (shoot, root and whole plant weights) and indices (sturdiness quotient ‘SQ’, shoot:root dry weight ratio ‘SRR’ and Dickson’s quality index ‘DQI’). In the nursery, all species performed better in the ordinary nursery soil for all growth parameters except root length. Thus ordinary nursery substrate appeared superior to sand in terms of plant quality. However, a follow up at plantation phase revealed that only some morphological attributes or ratios were suitable to predict field performance for the five tested species in irrigated plantation. In addition, the effect of the substrate observed at the nursery stage had disappeared 12 months after out planting due to the availability of water and nutrients provided by the treated waste water used for the irrigation. The results showed that root collar diameter and DQI appeared to be the most appropriate indicators to predict the outplanting performance of the five tested species in a short-rotation irrigated plantation in semi-arid Burkina Faso. The former measure is simpler and non-destructive.     

Influence of water-stress acclimation and <Emphasis Type="Italic">Tuber melanosporum</Emphasis> mycorrhization on <Emphasis Type="Italic">Quercus ilex</Emphasis> seedlings

Mycorrhizal and non-mycorrhizal holm oak (Quercus ilex L.) seedlings inoculated with black truffle (Tuber melanosporum) were grown under nursery conditions and subjected to drought hardening for 4 months in autumn and winter followed by irrigation for 10 days. Leaf water potential and stomatal conductance were monitored during the 4 months of drought. When the test was completed (March), measurements were made for each treatment (inoculated or non-inoculated), and watering regime (watered and water-stressed). Pressure–volume curves, osmotic potential at full turgor, osmotic potential at zero turgor and the tissue modulus of elasticity near full turgor were calculated. Mycorrhizal colonization and growth, and the content of the main mineral nutrients N, P, K, Ca and Mg were measured. Water stress affected plant growth, caused an elastic adjustment of the plant tissues, and decreased the P and K content, and inoculation improved the nitrogen content. Drought acclimation apparently achieved the goal of improving the drought tolerance of holm oak seedlings, without depressing ectomycorrhizal root colonization by T. melanosporum. José Antonio Rodríguez Barreal—Deceased     

Performance and nutrient dynamics of holm oak (<Emphasis Type="Italic">Quercus ilex</Emphasis> L.) seedlings in relation to nursery nutrient loading and post-transplant fertility

Holm oak (Quercus ilex L.) seedlings were exponentially (E) nutrient loaded using incremental increases in fertilizer addition or conventionally (C) fertilized using a constant fertilizer rate during nursery culture. The fertility treatments (mg N plant⁻¹) were control (0), 25E, 100E, and 100C. Subsequently, 1-year-old plants were transplanted under simulated soil fertility gradients in a greenhouse to evaluate effects of nutrient loading and post-transplant fertility on seedling performance. Post-transplant fertility consisted of fertilizing plants at two rates (0 vs. 200 mg N plant⁻¹). A water-soluble fertilizer 20-20-20 was supplied in both nursery and post-transplant experiments. Nutrient loading increased plant N content by 73% in 100E and by 75% in 100C relative to controls, although no significant differences were detected between constant and exponential fertilization regimes at the 100 mg N plant⁻¹ rate. When transplanted, nutrient loading promoted post-transplant root growth relative to shoot, implicating potential to confer competitive advantage to loaded holm oak seedlings after trans-planting. In contrast, post-transplant fertility increased new shoot dry mass by 140% as well as N, P and K content relative to controls. Results suggest that holm oak seedlings can be successfully nutrient loaded in the nursery at higher fertility rates, improving its potential to extend new roots, but alternative fertilization regimes and schedules that better fit nutrient availability to the growth rhythm and conservative strategy of this species must be tested.     

Restoration of hard mast species for wildlife in Missouri using precocious flowering oak in the Missouri River floodplain, USA

Increased planting of hard mast oak species in the Lower Missouri River floodplain is critical as natural regeneration of oak along the Upper Mississippi and Lower Missouri Rivers has been limited following major flood events in 1993 and 1995. Traditional planting methods have limited success due to frequent flood events, competition from faster growing vegetation and white-tailed deer herbivory. Results of early growth response of swamp white oak (Quercus bicolor Willd.) seedlings in relation to initial acorn mass and size, and early rapid shoot growth for seedlings produced by containerized root production method (RPM™), are presented. Containerized RPM™ seedlings grown in the greenhouse under optimal conditions demonstrate that seed size had no discernable impact on first-year root or shoot size. Seedling survival for the first two years and acorn production for the first three years after outplanting are presented, comparing use of containerized RPM™ swamp white oak seedlings to nursery stock. Flood tolerant precocious RPM™ oak seedlings in the floodplain provide a source of food for acorn-consuming wildlife ten to fifteen years sooner than oaks originating from natural regeneration, direct seeding or traditional bare root planting. Compared to bare root nursery stock that produced no acorns, some RPM™ swamp white oak seedlings averaged 4.3, 5.2, and 6.3 acorns/seedling in the first three years after fall outplanting. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nitrogen budgeting and quality of exponentially fertilized <Emphasis Type="Italic">Quercus robur</Emphasis> seedlings in Ireland

Current policy in Ireland calls for increased quality and quantity of broadleaved seedling plantings. Simultaneously, concerns regarding environmental contamination necessitate development of nursery production methods that minimize impacts. Exponential (E) fertilization has potential for producing high-quality seedlings through nutrient loading, while simultaneously minimizing nitrogen (N) losses during culture. We investigated the effects of a wide range (0.10–1.0 g N seedling⁻¹ year⁻¹) of E fertilization rates on seedling morphology and nutrition of Quercus robur L., as well as soil N status and N budget during one growing season in a bareroot nursery in County Carlow, Ireland. The N budget showed significant N losses, especially in the highest fertilizer treatments, due to high precipitation. Seedlings receiving the 0.5 E rate were morphologically and nutritionally superior to all other treatments. Results indicate that it may be possible to produce 1-0 bareroot seedlings meeting target specifications in Ireland and other countries of similar climate and soils if further manipulations to seedling culture are implemented; however, potential environmental degradation via N leaching must be considered when N loading in wet years.     

Assessing the effect of late-season fertilization on Holm oak plant quality: insights from morpho–nutritional characterizations and water relations parameters

Forest restoration projects with Holm oak (Quercus ilex) have had limited success, mostly due to water stress after planting and poor plant quality. Recent studies indicated that large and nutrient rich plants perform better in Mediterranean areas, suggesting that late-season fertilization may improve plant quality and field performance. The purpose of this study was to assess the effect of late-season fertilization on the quality of Holm oak seedlings, as determined by morphological, nutritional, and water relations analyses. We grew Holm oak nursery seedlings under 5 different late-season fertilization regimes and then analyzed morphological characteristics, nutritional status, and water relations parameters of the fertilization groups at the end of the nursery period. We also analyzed the effect of fertilization on nutritional status by use of vector nomograms. Our results indicated that late-season NPK fertilization improved shoot and root growth, and the overall nutritional status of seedlings. The lack of late-season fertilization leads to nutrient deficiency in plants, whilst the application of imbalanced fertilization treatments may trigger nutrient luxury consumption and nutrient dilution, pointing out the importance of NPK proportions in the fertilizer. Moreover, late-season fertilization with nitrogen might improve the drought resistance of seedling by enhancing their osmotic adjustment.     

Root preparation technique and storage affect results of seedling quality evaluation in Norway spruce

Evaluation of tree seedling quality is necessary for improving technology for forest nursery production and seedling handling. Nutrient status can be measured to determine seedling quality, but it can be affected by seedling handling techniques. In this study effects of root preparation technique and storage regime on content of macro nutrients (N, P, K, S, Ca, Mg) in fine roots of Norway spruce (Picea abies (L.) Karst.) plants were investigated. The root preparation techniques were: (a) rinse in tap or (b) deionised water, and (c) dry preparation. These techniques were tested on seedlings subjected to four storage regimes: (1) no storage, (2) deep freezing below −20°C, and long-term (3) cold (+1 to +3°C) and (4) frozen (−3 to −4°C) storage. From the results it was concluded that the nutrient status in needles is not sufficient to describe the whole plant nutrient status in stored dormant plants, fine roots should also be included. The results also showed that deep freezing of fine roots before nutrient analyses should be avoided. Losses of K, P, S, and Mg were substantial with this method. Deionised water or dry preparation is preferred since tap water contains substantial amounts of ions that may affect the analyses.     

Why seedlings survive: influence of plant attributes

Seedling survival and successful forest restoration involves many silvicultural practices. One important aspect of a successful forest restoration program is planting quality seedlings with high survival capability. Thus the nursery needs to create seedlings with plant attributes that allow for the best chance of success once a seedling is field planted. Since the mid-twentieth century, research foresters have critically examined plant attributes that confer improved seedling survival to field site conditions. This review describes the value of commonly measured seedling quality material (i.e. shoot height, stem diameter, root mass, shoot to root ratio, drought resistance, mineral nutrient status) and performance (i.e. freezing tolerance and root growth) plant attributes defined as important in answering the question of why seedlings survive after planting. Desirable levels of these plant attributes can increase the speed with which seedlings overcome planting stress, become ‘coupled’ to the forest restoration site, thereby ensuring successful seedling establishment. Although planting seedlings with these desirable plant attributes does not guarantee high survival rates; planting seedlings with desirable plant attributes increases chances for survival after field planting.     

Effects of nursery shading on seedling quality and post-planting performance in two Mediterranean species with contrasting shade tolerance

In Mediterranean climates, seedlings are frequently shaded in the nursery to avoid heat damage and save water. However, the impact of this shading on the seedling quality and transplanting performance of Mediterranean species is not well known. We studied the effect of nursery shading on pre-planting features and post-planting performance of two Mediterranean tree species: the shade-intolerant pioneer Pinus halepensis and the shade-tolerant late-successional Quercus ilex. We grew one-year-old seedlings of both species under 100, 40 and 5% full sunlight. Shade had a low impact on the morphology and physiology of Q. ilex seedlings. In pines, only the deep shade treatment produced low quality seedlings with poor root development. In both species, transference to high light at planting in autumn did not impose any additional stress than that caused by frosts, but initial root growth was impaired in the two shaded treatments in pine. Post-planting growth and survival of oak seedlings showed no difference between treatments. Pine seedlings grown in deep shade showed higher mortality and lower growth after planting than those grown in full sun and intermediate light treatments, while intermediate light only reduced growth. For the nursery culture of Q. ilex seedlings, we advise using low light levels during summer to save water without impairing field performance. In P. halepensis, seedlings should be cultured under full sunlight conditions to maximize post-planting growth, but they can be cultured under intermediate light without impairing survival.     

Northern red oak planting stock: 6-year results

A northern red oak plantation was established in 1988 in a recently clearcut mixed oak stand to evaluate outplanting performance relative to type of planting stock (1--0, 2--0, 1--1, 2--1, 2-year-old containerized, and direct-seeded) and other cultural factors (undercutting in the nursery, raising stock in an extended growing season in Alabama vs a local Pennsylvania nursery, top-clipping at planting time, and tree shelters). Six years after outplanting, seedlings grown from 2-year-old containerized stock were tallest (averaging 3.3 m) and had excellent survival. Among other treatments, 2--0 bareroot stock, especially if undercut in the nursery and top-clipped at planting, performed best and averaged 3.0 m height and 100% survival. Remaining treatments, especially 1--0, were smaller and had reduced survival. Seedlings from direct-seeding were as tall as most 1--0 treatments. Undercutting, top-clipping, nursery transplanting, raising stock in different nurseries, and tree shelters minimally affected the height or survival of seedlings. Seedlings above average in height 3 years after outplanting when fencing was removed and herbiciding ceased, were most likely to survive after 6 years.     

Relationships between site and stock quality in Pinus halepensis Mill. reforestation on semiarid landscapes in eastern Spain

The influence of site and stock quality factors in Aleppo pine (Pinus halepensis Mill.) plantation establishment has been studied. Five stocklots with a contrasting seedling quality were planted on six different sites showing different ecologic conditions in a same regional context. This reciprocal study indicated that site factors (climate, meteorology and soil) explained most of the variability found over stock quality factors (material and performance attributes) in the overall performance results (F values for final survival were 64.2 and 14.1 for site and stocklot, respectively). There were significant interactions between both factors in survival (F = 2.03 for final survival) and first growth, indicating that the seedling quality attributes associated with a better performance depended on site conditions, with physiological attributes being more dependent on the site than morphological attributes. The lower the site quality (poor performance), the higher the importance of stock quality, especially that related with seedling size and macronutrient content, which showed positive correlations (p < 0.05) with survival, yielding differences of over 30% between stocklots. In general, a milder climate and a shallow site meant a higher mortality. The meteorology during the two years after planting confirmed this trend as survival was preferably correlated with temperature variables instead of with precipitation. In the first year, climate factors affected seedling performance more than the soil texture, whereas, in the second, growth was correlated (p < 0.01) with clay and silt percentages, confirming a predominant effect of site over time. Soil depth is discussed as a basic variable possessing a determinant influence on the overall results.     

Field performance potential of a somatic interior spruce seedlot

This study defined the field performance potential for 34 genotypes that composed a somatic seedlot of interior spruce (Picea glauca (Moench) Voss × Picea engelmannii Parry ex. Engelm.) crosses, white spruce (P. glauca (Moench) Voss) crosses, or a mixture. Each genotype was measured for morphological attributes: height, diameter, shoot dry weight, root dry weight, shoot-to-root ratio, height-to-diameter ratio at time of lifting. Each genotype was also measured for physiological attributes of cuticular transpiration (TFD_cut), osmotic potential at turgor loss point (Ψ_tlp) and freezing tolerance (index of injury at −6°C and −4°C; II_@−6 & II_@−4) during inactive and active shoot growth phases. Shoot growth potential (SGP = length of new leader elongation) and root growth potential (RGP) were conducted under four environmental regimes: nutrient-rich/well-watered, nutrient-poor/well-watered, low root temperature, and planting stress conditions. The somatic seedlot met target height, diameter and RGP standards for a plantable seedling crop in British Columbia, Canada, though genotypes differed in morphology at time of lifting. These genotypes also differed in their measured physiological attributes (TFD_cut, Ψ_tlp, II_@−6 and II_@−4) at time of lifting and during active shoot growth. Genotypic differences were also found for SGP and RGP under different testing environments. A stock quality assessment program describing elite genotypes within a seedlot can aid foresters in applying benefits of clonal forestry. Raymund S. Folk is now self employed.     

Plant quality assessment: an industrial perspective

The regions of the world using operational seedling testing to any significant extent are Canada, Britain, Sweden, and the Pacific Northwest region of the United States. Testing has been used operationally for batch culling (to ensure quality), as well as for research into improved nursery cultural practices. Savings from testing for seedling survival are substantial. However, growth gains from operational testing are more tenuous. Reduced rotation lengths and lower weeding costs are more likely to be associated with planting larger stock, rather than planting stock with higher physiological quality.Large opportunities for savings exist for regions and organizations that produce poor quality stock, have high planting costs, or both. New tests have been developed and some are becoming operational. New tests might be more effective than existing tests. However, in the regions most involved in seedling testing, plantation survival has increased over the last ten years. Subsequently, additional investments in operational testing will likely achieve diminishing returns.     

Half-sib seed source and nursery sowing density affect black walnut (<Emphasis Type="Italic">Juglans nigra</Emphasis>) growth after 5 years

The effect of seed source (half-sib family) and nursery bed density on the nursery stock quality and subsequent growth of black walnut (Juglans nigra L.) was investigated. Nine black walnut female genitors were selected to represent a range of phenotypes. Seeds were collected, cleaned, cold-treated, and pre-sprouted to ensure that germination was uniform and complete. The pre-sprouted seeds were planted in a randomized complete block design into standard nursery beds in Indiana, USA at three sowing densities, (11.2 plants m⁻²; 24.2 plants m⁻²; 29.4 plants m⁻²). After lifting, the trees were measured for height, ground-line diameter and root volume and then planted into a plantation in a randomized complete block design and re-measured after 1 and 5 years of growth. One year after planting, the effects of family (half-sib seed source) and density were significant or very highly significant for seedling height, and ground-line diameter, although family effects were greater than those for density, especially at moderate and high nursery bed density. After 5 years of growth, the same effects contributed significantly to ground-line diameter and dbh, but only family significantly influenced height. Family was more important than nursery bed density in determining the size of the trees after 5 years. Although there were no significant family × density interactions after 5 years, family variance for all the traits was considerably higher among seedlings grown at moderate and high density in the nursery. Phenotypic correlations among traits within and among years were generally very high (0.65 < r < 0.90) and insensitive to planting density in the nursery.     

Influences of seedling size,container type and mammal browsing on the establishment of <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> in plantation forestry

Rapid early growth of tree seedlings is critical to the success of plantation establishment. We investigated the effects of seedling size (small and large) and container types (small [Lannen 121], medium [Lannen 81] and large [Forestry Tube]) in the nursery and the effects of mammal browsing after planting on growth of Eucalyptus globulus in Tasmania’s Southern Forests. After planting, seedlings were either exposed to browsing or protected from browsing by wire-mesh cages until age 6 months. Low browsing pressure resulted in around 20% and 5–10% of foliage being browsed in the large and small size categories, respectively, between 1 and 3 months after planting the uncaged treatment. 6 months after planting, height growth increment was lower, and 4 years after planting, mortality was higher in uncaged large than caged large seedling treatments. Six and twelve months after planting, seedlings raised in Forestry Tube containers had significantly greater height increment and root collar diameter relative to other treatments. By 4 years after planting, trees of the small seedling treatment had significantly greater diameter than those of the large seedling treatment, but there was no effect of container type treatment. Four years after planting there was no effect on diameter growth by browsing of <30% of foliage up to 3 months after planting, although there was greater incidence of double leaders in trees that had been browsed as seedlings. Small seedlings produced more growth 4 years after planting than large seedlings of E. globulus.     

Prediction of planted seedling survival of five Mediterranean species based on initial seedling morphology

Field performance can be predicted by evaluating nursery stock quality, but optimal morphological variables for use in these assessments may vary by species especially under dry Mediterranean conditions. Our objective was to identify initial seedling morphological characteristics that successfully predict field performance of five Mediterranean species (Pinus halepensis, Quercus ilex, Quercus coccifera, Ceratonia silqua and Pistacia lentiscus). Container seedling morphology was evaluated following the nursery phase, and then seedlings were outplanted in the field where field survival was monitored for two successive years. Results indicate that survival can successfully be predicted from seedling initial morphological characteristics for all these species, yet not all the initial characteristics were good predictors. Survival of P. halepensis and Pist. lentiscus seedlings was positively correlated to initial seedling root-collar diameter, total dry weight and Dickson’s quality index, and can be reliably predicted by these variables. In contrast, seedling field survival of the two Mediterranean evergreen oak species was correlated with few initial morphological attributes; initial diameter provided an accurate index to predict second-year outplanting survival for both species while height/diameter was a good survival predictor for Q. coccifera seedlings. For C. siliqua seedlings, seedlings with larger initial diameter and total biomass survive better in the field. Thus, diameter was the common variable that accurately predicted survival for all species, which should be >5 mm for P. halepensis seedlings and >7 mm for the remaining species.     

Field performance of <Emphasis Type="Italic">Pinus halepensis</Emphasis> planted in Mediterranean arid conditions: relative influence of seedling morphology and mineral nutrition

In Mediterranean arid regions, relatively small planting stock has traditionally been used in an attempt to reduce drought susceptibility, though few studies have examined influences of initial seedling morphology and nutrition on long-term plantation establishment. We fertilized Pinus halepensis Mill. seedlings in the nursery with controlled release fertilizer (CRF) varying in formulations and rates; 9-13-18 and 17-10-10 (N-P-K) formulations at 3, 5 and 7 g l⁻¹ substrate plus an unfertilized control and we evaluated growth and survival 7 years after planting in arid conditions in Almería province, southeast Spain. Interactions between initial height and fertilizer treatments occurred during the first 3 years; initial size advantages of specific fertilizer treatments (7 g l⁻¹ of 9-13-18 and 17-10-10 at 3 g l⁻¹) persisted after 7 years. The largest and most nutrient-rich seedlings from 9-13-18 at 7 g l⁻¹ (41.0 cm tall, 4.4 mg of P per g of root tissue at time of planting) exhibited the highest survival after 7 years (79%), while survival declined to 42% for non-fertilized plants (12.9 cm tall and 0.6 mg of P per g of root tissue). Initial seedling morphological parameters were most consistently correlated with field performance. Root P concentration was the nutrient variable most closely related to survival. Our data emphasizes importance of longer-term experiments to accurately assess influences of nursery treatments on field responses, particularly in arid areas. We suggest that larger seedlings with greater nutrient reserves than are currently being used should be incorporated into Mediterranean plantations.     

Narrow genetic base in forest restoration with holm oak (Quercus ilex L.) in Sicily

In order to empirically assess the effect of actual seed sampling strategy on genetic diversity of holm oak (Quercus ilex) forestations in Sicily, we have analysed the genetic composition of two seedling lots (nursery stock and plantation) and their known natural seed origin stand by means of six nuclear microsatellite loci. Significant reduction in genetic diversity and significant difference in genetic composition of the seedling lots compared to the seed origin stand were detected. The female and the total effective number of parents were quantified by means of maternity assignment of seedlings and temporal changes in allele frequencies. Extremely low effective maternity numbers were estimated (Nf _e ≈ 2–4) and estimates accounting for both seed and pollen donors gave also low values (N _e ≈ 35–50). These values can be explained by an inappropriate forestry seed harvest strategy limited to a small number of spatially close trees.