Long-term changes in tree-ring–climate relationships at Mt. Patscherkofel (Tyrol,Austria) since the mid-1980s

Although growth limitation of trees at Alpine and high-latitude timberlines by prevailing summer temperature is well established, the loss of thermal response of radial tree growth during last decades has repeatedly been addressed. We examined long-term variability of climate–growth relationships in ring width chronologies of Stone pine (Pinus cembra L.) by means of moving response functions (MRF). The study area is situated in the timberline ecotone (ca. 2,000–2,200 m a.s.l.) on Mt. Patscherkofel (Tyrol, Austria). Five site chronologies were developed within the ecotone with constant sample depth (≥19 trees) throughout most of the time period analysed. MRF calculated for the period 1866–1999 and 1901–1999 for ca. 200- and ca. 100-year-old stands, respectively, revealed that mean July temperature is the major and long-term stable driving force of Pinus cembra radial growth within the timberline ecotone. However, since the mid-1980s, radial growth in timberline and tree line chronologies strikingly diverges from the July temperature trend. This is probably a result of extreme climate events (e.g. low winter precipitation, late frost) and/or increasing drought stress on cambial activity. The latter assumption is supported by a <10% increase in annual increments of ca. 50-year-old trees at the timberline and at the tree line in 2003 compared with 2002, when extraordinary hot and dry conditions prevailed during summer. Furthermore, especially during the second half of the twentieth century, influence of climate variables on radial growth show abrupt fluctuations, which might also be a consequence of climate warming on tree physiology.     

RFLP inheritance and linkage in walnut

Thirty-two low-copy-number genomic DNA clones from a walnut (Juglans sp.) Pst I genomic library were used to establish a molecular-marker linkage map for walnut. The clones were hybridized to restriction-endonuclease-digested DNA from parent walnut trees involved in an interspecific backcross of (J. hindsii x J. regia) x J. regia in order to identify parental polymorphism. Sixty-three backcross progeny were analyzed to determine the inheritance and linkage of 48 RFLP loci. Sixty-six percent of the walnut cloned sequences detected duplicated, but unlinked, loci. Twelve linkage groups were identified by 42 of the RFLP loci. A Poisson probability method for estimating genome size was utilized to calculate the approximate walnut genome length as 1660 cM and to estimate that 138 markers would be needed to cover 95% of the walnut genome within 20 cM of each marker.     

Long-term human impacts on genetic structure of Italian walnut inferred by SSR markers

Life history traits, historic factors, and human activities can all shape the genetic diversity of a species. In Italy, walnut (Juglans regia L.) has a long history of cultivation both for wood and edible nuts. To better understand the genetic variability of current Italian walnut resources, we analyzed the relationships among the genetic structure of local walnut populations (inferred by SSR markers) and human migrations along ancient routes, using the territory of Royal Tratturo Candela-Pescasseroli (RT) as a case study. Sixteen J. regia provenances were collected along RT and compared with 13 Italian provenances and the landrace Sorrento. Although the level of SSR polymorphism we observed was moderately high, AMOVA revealed that most of the diversity was located within individuals (92.58%), and geographical differentiation was low (D _est = 0.076). Evidence for human-mediated domestication bottleneck events was detected in about 95% of walnut provenances. A Bayesian approach divided 456 walnut samples into three clusters: (1) Sorrento genotypes, (2) trees from the island of Sicily, and (3) the remaining germplasm. The UPGMA tree based on Nei's distances distinguished northeastern provenances and weakly grouped 12 of 16 provenances of RT. The observed genetic differences derived mainly from gradations in allele frequencies. Separation of the Sicilian provenance from the mainland may be explained in terms of founder effects and prolonged geographic isolation. Two contrasting forces, selection, and frequent inter-regional transfer of propagules, appear to drive the patterns of genetic variability for J. regia.     

The walnut (Juglans regia) genome sequence reveals diversity in genes coding for the biosynthesis of non‐structural polyphenols

The Persian walnut (Juglans regia L.), a diploid species native to the mountainous regions of Central Asia, is the major walnut species cultivated for nut production and is one of the most widespread tree nut species in the world. The high nutritional value of J. regia nuts is associated with a rich array of polyphenolic compounds, whose complete biosynthetic pathways are still unknown. A J. regia genome sequence was obtained from the cultivar ‘Chandler’ to discover target genes and additional unknown genes. The 667‐Mbp genome was assembled using two different methods (SOAPdenovo2 and MaSuRCA), with an N50 scaffold size of 464 955 bp (based on a genome size of 606 Mbp), 221 640 contigs and a GC content of 37%. Annotation with MAKER‐P and other genomic resources yielded 32 498 gene models. Previous studies in walnut relying on tissue‐specific methods have only identified a single polyphenol oxidase (PPO) gene (JrPPO1). Enabled by the J. regia genome sequence, a second homolog of PPO (JrPPO2) was discovered. In addition, about 130 genes in the large gallate 1‐β‐glucosyltransferase (GGT) superfamily were detected. Specifically, two genes, JrGGT1 and JrGGT2, were significantly homologous to the GGT from Quercus robur (QrGGT), which is involved in the synthesis of 1‐O‐galloyl‐β‐d ‐glucose, a precursor for the synthesis of hydrolysable tannins. The reference genome for J. regia provides meaningful insight into the complex pathways required for the synthesis of polyphenols. The walnut genome sequence provides important tools and methods to accelerate breeding and to facilitate the genetic dissection of complex traits.     

A new genomic tool for walnut (Juglans regia L.): development and validation of the high‐density Axiom™ J. regia 700K SNP genotyping array

Over the last 20 years, global production of Persian walnut (Juglans regia L.) has grown enormously, likely reflecting increased consumption due to its numerous benefits to human health. However, advances in genome‐wide association (GWA) studies and genomic selection (GS) for agronomically important traits in walnut remain limited due to the lack of powerful genomic tools. Here, we present the development and validation of a high‐density 700K single nucleotide polymorphism (SNP) array in Persian walnut. Over 609K high‐quality SNPs have been thoroughly selected from a set of 9.6 m genome‐wide variants, previously identified from the high‐depth re‐sequencing of 27 founders of the Walnut Improvement Program (WIP) of University of California, Davis. To validate the effectiveness of the array, we genotyped a collection of 1284 walnut trees, including 1167 progeny of 48 WIP families and 26 walnut cultivars. More than half of the SNPs (55.7%) fell in the highest quality class of ‘Poly High Resolution’ (PHR) polymorphisms, which were used to assess the WIP pedigree integrity. We identified 151 new parent‐offspring relationships, all confirmed with the Mendelian inheritance test. In addition, we explored the genetic variability among cultivars of different origin, revealing how the varieties from Europe and California were differentiated from Asian accessions. Both the reconstruction of the WIP pedigree and population structure analysis confirmed the effectiveness of the Applied Biosystems? Axiom? J. regia 700K SNP array, which initiates a novel genomic and advanced phase in walnut genetics and breeding.     

Population genetic structure and adaptive differentiation of iron walnut Juglans regia subsp. sigillata in southwestern China

Southwestern (SW) China is an area of active tectonism and erosion, yielding a dynamic, deeply eroded landscape that influences the genetic structure of the resident populations of plants and animals. Iron walnut (Juglans regia subsp. sigillata) is a deciduous tree species endemic to this region of China and cultivated there for its edible nuts. We sampled 36 iron walnut populations from locations throughout the species' range in SW China and genotyped a total of 765 individuals at five chloroplast DNA regions and 22 nuclear microsatellite loci. Species distribution models were produced to predict the evolution and historical biogeography of iron walnut and to estimate the impacts of climate oscillations and orographic environments on the species' demography. Our results indicated that J. regia subsp. sigillata had relatively low genetic diversity, high interpopulation genetic differentiation, and asymmetric interpopulation gene flow. Based on DIYABC analysis, we identified two lineages of J. sigillata in southwestern China. The lineages (subpopulations) diverge during the last glacial period (~1.34 Ma). Southwestern China was a glacial refuge during the last glacial period, but increasingly colder and arid climates might have fostered the fragmentation of J. regia subsp. sigillata within this refugium. Finally, we found that recent habitat fragmentation has led to a reduction in population connectivity and increased genetic differentiation by genetic drift in isolated populations. Our results support a conclusion that geological and climatic factors since the Miocene triggered the differentiation, evolutionary origin, and range shifts of J. sigillata in the studied region.     

Unusual Fine Root Distributions of Two Deciduous Tree Species in Southern France: What Consequences for Modelling of Tree Root Dynamics?

The spatial distribution of fine roots of two deciduous tree species was investigated in contrasting growing conditions in southern France. Hybrid walnut trees (Juglans regia×nigra cv. NG23) and hybrid poplars (Populus euramericana cv. I214) were both cultivated with or without annual winter intercrops for 10 years on deep alluvial soils. Soil samples for measuring the fine root distribution of both trees and crops were obtained by soil coring down to 3-m depth at several distances and orientations from the tree trunk. The distribution of live fine roots from walnut and poplar trees was patchy and sometimes unexpected. In the tree-only stands, fine root profiles followed the expected pattern, as fine root density decreased with increasing depth and distance from the tree trunk. However, many fine root profiles under intercropped trees were uniform with depth, and some inverse profiles were observed. These distributions may result from a high degree of plasticity of tree root systems to sense and adapt to fluctuating and heterogeneous soil conditions. The distortion of the tree root system was more pronounced for the walnut trees that only partially explored the soil volume: in the tree-only stand, the walnut rooting pattern was very superficial, but in the intercropped stand walnut trees developed a deep and dense fine root network below the crop rooting zone. The larger poplars explored the whole available soil volume, but the intercrop significantly displaced the root density from the topsoil to layers below 1 m depth. Most tree root growth models assume a decreasing fine root density with depth and distance from the tree stem. These models would not predict correctly tree–tree and tree–understorey competition for water and nutrients in 3D heterogeneous soil conditions that prevail under low-density tree stands. To account for the integrated response of tree root systems to such transient gradients in soils, we need a dynamic model that would allow for both genotypic plasticity and transient environmental local soil conditions.     

Barriers to interspecific hybridization between Juglans nigra L. and J. regia L species

Juglans nigra and Juglans regia are phylogenetically divergent species. Despite the economic interest in Juglans?×?intermedia (J. nigra?×? J. regia), walnut hybridization is rare under natural conditions and still difficult using controlled pollination. Here, we evaluated some reproductive mechanisms that may prevent successful natural hybridization. The study of flowering phenology of 11 J. nigra and 50 J. regia trees growing in a plantation provided information regarding the opportunity for interspecific crosses. Variation in flower size, pollen quality of putative donors, and variation in seed yield and rate of hybrid production among putative maternal trees were examined. DNA fingerprinting and parentage analyses based on nine microsatellites permitted the identification of hybrids and hybridogenic parent. Our data indicated that overlap occurred between the staminate flowering of protogynous J. regia and the beginning of pistillate flowering of protogynous J. nigra. Differences in floral size were computed between walnut species. Only three hybrids among 422 offspring of eleven J. nigra progenies were identified. Interspecific hybridization involving pollination of one early-flowering-protogynous J. nigra by three protogynous J. regia trees was detected. The correct development of J. regia male gametophytes, high pollen viability (86.5 %), and germination (57.6 %) ruled out the possibility that low pollen quality contributed to depressed hybrid production. Our findings indicated that these two species tended to remain reproductively isolated. The substantial disjunction in flowering time and additional prezygotic barriers such as differences in floral size and conspecific pollen advance may affect interspecific gene flow between J. regia and J. nigra.     

Biochemical and genetic characterisation of Agrobacterium tumefaciens the causal agent of walnut crown gall disease in Iran

In 2009–2010, crown tumours were collected from walnut (Juglans regia L.) trees in northern Iran. Gram-negative, rod shaped and aerobic bacteria with circular, convex and white-coloured colonies on potato dextrose agar plus CaCO3 medium were isolated from galls. In pathogenicity tests, tomato seedlings were inoculated with all strains and tumours started to appear three weeks after inoculation. Strains yielded a 224?bp amplicon from the virD2 gene in PCR. When the 16S rRNA gene sequence of strains was compared by BLASTn with nucleotide sequences from GenBank, it showed 99.6% identity with the 16S rRNA sequence of Agrobacterium tumefaciens ATCC 33970. Based on phenotypic and genotypic properties, the bacterium that causes crown gall of walnut trees was identified as A. tumefaciens.     

Altitude affects the distribution and abundance of two non‐native insect pests of the common walnut

The leaf miner Coptodisca lucifluella and the carpophagous Rhagoletis completa, of American origin, are two non‐native walnut (Juglans spp.) pests in Italy. For the Friuli Venezia Giulia region (FVG) (N‐E Italy), C. lucifluella is not yet listed, while R. completa has been present for over 25 years. During 2015, samples of leaves and fruits were collected from 219 single old common walnut trees (Juglans regia) placed at different altitudes (0–1,073 m a.s.l.) in FVG to detect the distribution and abundance of both pests. Samples of leaf miner larvae and their parasitoids were subjected to mitochondrial DNA analysis for identification. C. lucifluella has been found in 55 out of 219 sites. The species has been identified by typical leaf symptoms and by its DNA barcode. This is the first report of the species for FVG. The leaf miner distribution was negatively correlated with altitude. The species has not been observed at sites over 600 m a.s.l. Larvae were parasitized by native parasitoids identified as belonging to the genus Chrysocharis by morphological features and by DNA barcode. R. completa has been found in 89 out of 165 sites on walnut trees with fruits. The infestation level was very high in lowland localities. At sites over 700 m a.s.l., no infestation was found. Both species are widespread in the region, and their occurrence is significantly affected by altitude. Data suggest that walnut trees could be cultivated in some mountain areas without the need to control R. completa with insecticides.     

Climate warming and precipitation redistribution modify tree–grass interactions and tree species establishment in a warm‐temperate savanna

Savanna tree–grass interactions may be particularly sensitive to climate change. Establishment of two tree canopy dominants, post oak (Quercus stellata) and eastern redcedar (Juniperus virginiana), grown with the dominant C₄ perennial grass (Schizachyrium scoparium) in southern oak savanna of the United States were evaluated under four climatic scenarios for 6 years. Tree–grass interactions were examined with and without warming (+1.5 °C) in combination with a long‐term mean rainfall treatment and a modified rainfall regime that redistributed 40% of summer rainfall to spring and fall, intensifying summer drought. The aim was to determine: (1) the relative growth response of these species, (2) potential shifts in the balance of tree–grass interactions, and (3) the trajectory of juniper encroachment into savannas, under these anticipated climatic conditions. Precipitation redistribution reduced relative growth rate (RGR) of trees grown with grass. Warming increased growth of J. virginiana and strongly reduced Q. stellata survival. Tiller numbers of S. scoparium plants were unaffected by warming, but the number of reproductive tillers was increasingly suppressed by intensified drought each year. Growth rates of J. virginiana and Q. stellata were suppressed by grass presence early, but in subsequent years were higher when grown with grass. Quercus stellata had overall reduced RGR, but enhanced survival when grown with grass, while survival of J. virginiana remained near 100% in all treatments. Once trees surpassed a threshold height of 1.1 m, both tiller number and survival of S. scoparium plants were drastically reduced by the presence of J. virginiana, but not Q. stellata. Juniperus virginiana was the only savanna dominant in which neither survival nor final aboveground mass were adversely affected by the climate scenario of warming and intensified summer drought. These responses indicate that climate warming and altered precipitation patterns will further accelerate juniper encroachment and woody thickening in a warm‐temperate oak savanna.     

Intracanopy variation in nitrogen cycling through leaves is influenced by irradiance and proximity to developing fruit in mature walnut trees

Intracanopy variation in net leaf nitrogen (N) resorption and N cycling through leaves in mature walnut (Juglans regia L. cv Hartley) trees were monitored in 3 different years. Differential irradiance among the spurs sampled was inferred from differences among leaves in dry weight per unit area (LW/LA) which varied from 4.0 mg · cm^–2 to 7.0 mg · cm^–2 in shaded (S) and exposed (E) canopy positions, respectively. Our results, using ¹⁵N-depleted (NH₄)₂SO₄ validated the concept that N influx and efflux through fully expanded leaves occurred concurrently during the period of embryo growth. Additionally, it also suggested that N influx into leaves was substantially greater in exposed as compared with shaded canopy positions. Because of its well documented phloem immobility, leaf Ca accumulation was used to better estimate the relative influx of N into exposed and shaded leaves. N cycling varied locally within the tree canopy, i. e. Ca (and presumably N) influx was 100% greater in exposed than shaded tree canopy positions, but influx was not influenced significantly by the proximity of developing fruit. In contrast, both the amount and percentage N efflux was significantly greater during embryo growth in fruit-bearing than defruited spurs. Net leaf N resorption averaged 2–4 times greater (25–30%) in fruit-bearing spurs than the 5–10% decrease in the leaf N content in defruited spurs. Since about 90% of leaf N content reportedly occurs as protein, fruit N demand apparently influenced protein turnover and catalysis in associated spur leaves. The amount of leaf N resorption was greater in exposed than shaded positions in the tree canopy in 2 of the 3 years of data collection. Our data show that like leaf N content, N influx, N efflux and net leaf N resorption vary throughout mature walnut tree canopies under the combined local influences of fruiting and irradiance.     

A PCR based SNPs marker for specific characterization of English walnut (<Emphasis Type="Italic">Juglans regia</Emphasis> L.) cultivars

English walnut (Juglans regia L.) is the most economically important species from all the 21 species belonging to the genus Juglans and is an important and healthy food as well as base material for timber industry. The aim of this study was to develop a simple technique for specific characterization of English walnut using DNA method. The first and second internal transcribed spacers (ITS1 and ITS2) as well as the intervening 5.8S coding region of the rRNA gene for 18 cultivars of J. regia L. isolated from different geographic origins were characterized. The size of the spacers sequences ranged from 257 to 263 bases for ITS1 and from 217 to 219 bases for ITS2. Variation of GC contents has also been observed and scored as 55–56.7 and 57.1–58.9% for ITS1 and ITS2, respectively. This data exhibited the presence of polymorphism among cultivars. Alignment of the ITS1-5.8S-ITS2 sequences from 18 walnut cultivars showed that there were 244 single nucleotide polymorphisms (SNPs) and 1 short insertion–deletion (indel) at 5′ end ITS1. Amplification refractory mutation system strategy was successfully applied to the SNP markers of the ITS1 and ITS2 sequences for the fingerprinting analysis of 17 on 18 walnut cultivars. The prediction of ITS1 and ITS2 RNA secondary structure from each cultivar was improved by detecting key functional elements shared by all sequences in the alignments. Phylogenetic analysis of the ITS1-5.8S-ITS2 region clearly separated the isolated sequences into two clusters. The results showed that ITS1 and ITS2 region could be used to discriminate these walnut cultivars.     

Isolation of Eutypa lata from Juglans regia, and Pathogenicity Studies on Different Wood Plants

The fungus Eutypa lata was isolated from diseased walnut trees (Juglans regia) exhibiting small cankers. The morphological characteristics of the culture and the pathogenicity were compared with those of known isolates of the fungus from other hosts. Inoculation tests with walnut isolates on grape, walnut, almond and apricot yielded characteristic cankers. Furthermore, pathogenicity tests on walnut with isolates from other different hosts resulted in differences in virulence. Similar differences in virulence were observed between 13 single ascospore isolates of the fungus ex apricot inoculated on walnut.     

华北山区核桃液流变化特征及对不同时间尺度参考作物蒸散量的响应

核桃是华北山区重要的经济树种,但该地区水资源紧缺,因此研究核桃液流耗水变化及其对气象因子的响应对于加强核桃水分管理、确定水分承载力具有指导意义。2008—2010年连续3个生长季节观测分析了华北山区核桃单株液流变化特征,研究了不同时间尺度(日尺度、月尺度)核桃液流与气象因子、参考作物蒸散量(ET0)的关系,并利用2009—2010年数据建立了拟合方程,在此基础上用拟合方程的估算值与2008年液流实测值进行了对比验证。结果表明:核桃液流具有明显的时间变化特征,最大液流量出现在5、6月份,2008—2010年生长季节(4—9月份)核桃液流量分别为893.23 L、854.88 L和841.77 L,日平均液流量分别为4.96 L、4.75 L和4.68 L。液流年际差异主要是由年降雨量引起。核桃液流与不同时间尺度下气象因子、ET0均有较好的相关性,且随着时间尺度的增加,二者间的相关性变大。利用2009—2010年液流实测值与气象因子、ET0建立的拟合方程,对2008年液流值进行了拟合,并与实测值进行了对比验证,发现不同时间尺度下液流拟合值与实测值均具有较好的一致性。在不能实现对液流进行连续观测的情况下,可以结合当地的气象资料、ET0等因子,利用建立的拟合方程对树木液流进行估算,弥补缺失的数据,具有较高的精确性,可用于指导当地核桃水分管理。     

Genetic diversity and population structure of common walnut (<Emphasis Type="Italic">Juglans regia</Emphasis>) in China based on EST-SSRs and the nuclear gene phenylalanine ammonia-lyase (<Emphasis Type="Italic">PAL</Emphasis>)

Common walnut (Juglans regia L.) is an economically important temperate tree species valued for both its nut and wood. We investigated the genetic diversity and population structure of J. regia germplasm from 13 locations in China using 10 markers derived from expressed sequences (EST-SSR) and sequence polymorphisms within the phenylalanine ammonia-lyase (PAL) gene. Analysis of the population genetic structure based on EST-SSRs showed distinct populations in northern versus southern China that were not reflected in the spatial distribution of PAL haplotypes. High levels of population differentiation were probably the result of reproductive isolation and in southern China, hybridization with Juglans sigillata. The results indicate the possible presence of distinct evolutionary lineages of J. regia in the Qinling and Daba Mountains of China and in Yunnan province that may require ecological management if they are to be retained as in situ resources.     

核桃种质资源遗传多样性的SSR分析

应用16对SSR引物对国内不同地理生态型的44个核桃样品、8个铁核桃样品和7个美国核桃样品进行了分析。结果显示,在16个SSR位点上共获得87个等位基因,每个位点扩增等位基因4～9个,平均5.4个。各SSR位点的观察杂合度为0～0.931 0,平均为0.389 4。各位点PIC值在0.376 2～0.786 3之间,平均为0.663 2。59个核桃样品的杂合度在0.133～0.813之间,平均0.387。聚类分析表明,来自秦岭山地的核桃样品与华北核桃属于同一生态类型;巩留的野核桃属于与新疆生态型和华北生态型不同的一个独立的生态型;美国核桃和铁核桃属于核桃种下不同的生态类型。     

Soil nitrogen mineralization in plantations ofJuglans nigra interplanted with actinorhizalElaeagnus umbellata orAlnus glutinosa

Nitrogen mineralization rates were estimated in 19-year-old interplantings of black walnut (Juglans nigra L.) with dinitrogen fixing autumn-olive (Elaeagnus umbellata Thunb.) or black alder (Alnus glutinosa L. Gaertn.) and in pure walnut plantings at two locations in Illinois USA. N mineralization rates were measured repeatedly over a one year period usingin situ incubations of soil cores in oxygen-permeable polyethylene bags at 0–10 and 10–20 cm soil depths, and also by burying mixed-bed ion-exchange resin in soil. Mineralization rates were highest in summer and in plots containing actinorhizal Elaeagnus and Alnus in contrast with pure walnut plots. Elaeagnus plots at one location yielded 236 kg of mineral N ha^–1 yr^–1 in the upper 20 cm of soil, a value higher than previously reported for temperate decidous forest soils in North America. The highest mean plot values for N mineralization in soil at a location were 185 kg ha^–1 yr^–1 for Alnus interplantings and 90 kg ha^–1 yr^–1 for pure walnut plots. Plots which had high N mineralization rates also had the largest walnut trees. Despite low pH (4.1 and 6.5) and low extractable P concentrations (1.4 and 0.7 mg kg^–1 dry mass) at the two locations, nitrification occurred in all plots throughout the growing season. NO ₃ ^– –N was the major form of mineralized N in soil in the actinorhizal interplantings, with NH ₄ ⁺ –N being the major form of mineral N in control plots. Walnut size was highly correlated with soil nitrogen mineralization, particularly soil NO ₃ ^– –N production in a plot.     

Regulation of nitrogen partitioning in field-grown almond trees: Effects of fruit load and foliar nitrogen applications

Two treatments were employed to influence the amount of amino nitrogen (N) transport in phloem. In walnut trees (Juglans regia L.), developing fruit significantly reduced the efflux of foliar-applied ¹⁵N-enriched urea from treated spurs over a 33-day period in comparison with similarly-treated defruited spurs. Those data suggest that local aboveground demand for N influences vascular transport of amino N. In another experiment, a 1% urea solution was applied foliarly to 5-year old `Mission' almond trees [Prunus dulcis (Mill.) D. A. Webb] to increase the concentration of amino N in the phloem. The effect of foliar N treatments on a) the transport and distribution of labelled urea N within the trees over the experimental period and b) the uptake of soil-applied labelled N were determined by replicated whole tree excavation, fractionation into various tree components and mass spectrometric analyses of the ¹⁴N/¹⁵N ratios. Concentrations and composition of amino acids in the phloem and xylem saps of control trees and trees receiving foliar-applied urea were also determined. In foliar urea-treated trees, the amino acid concentrations increased significantly in leaf and bark phloem exudate, within 24 and 96 h, respectively. Foliar-applied urea N was translocated to the roots of almond trees over the experimental period and decreased soil N uptake. The results of these experiments are consistent with the hypothesis that aboveground N demand affects the amount of amino N cycling between shoots and roots, and may be involved in the regulation of soil N uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

A life cycle assessment case study for walnut tree (<Emphasis Type="Italic">Juglans regia</Emphasis> L.) seedlings production

Purpose  

High-quality wood production is based on both natural forestry populations and dedicated tree plantations, also mentioned as industrial plantations. The establishment of dedicated plantations needs high-quality seedlings, often grown in a nursery, having specific genetic and morphological features. From seed gathering to final selling, the growth of the seedlings needs human interventions and specific inputs such as fertilizers, pesticides, substrates, and capital goods (e.g., pots and greenhouses). All these inputs of course can cause not negligible environmental impacts, due to their production, maintenance, and final disposal. For these reasons, the environmental impact due to seedlings production in a nursery deserves deep analysis to assess the overall impact linked to wood supply chain: it is important that wood products are able to meet high environmental standards. This study is focused on 1- and 2-year-old walnut tree (Juglans regia L.) seedlings, aimed to high-quality timber production.