Edge effects on epiphytic communities in a Mediterranean Quercus pyrenaica forest

Question: What are the edge effect responses of epiphytic lichen communities in Mediterranean Quercus pyrenaica forest? Location: Central Spain. Methods: We established ten transects perpendicular to a road dissecting a well conserved remnant of Q. pyrenaica forest into two sections. Transects extended from the forest/road edge to 100 m into the forest. Data were collected from seven plots in each transect at different distances from the edge. Variables were grouped into stand scale variables (distance to edge, number of trees per plot, mean diameter per plot, irradiance) and tree scale variables (diameter and height of sampled trees, aspect of the sampled square and relative height of the square). We used General Mixed Linear Models and constrained ordination techniques to test the hypothesis that the spatio‐temporal heterogeneity of light and water controls the occurrence of lichens and bryophytes along the edge‐interior gradient in the Q. pyrenaica forest. Results: Microclimatic parameters vary in a non‐linear way; edge and interior stands showed the most divergent and extreme values. Although the micro‐environment within Mediterranean forests is heterogeneous, interior conditions are apparently suitable for the performance of some specific forest epiphytes. Consequently, species richness does not show significant differences along the gradient. Total epiphytic cover increases towards the forest interior, but distance to the edge together with other predictors at the tree scale (aspect and height of the square) are the most relevant predictors for the composition and structure of these communities. Conclusions: Composition and structure of epiphytic communities in a Mediterranean semi‐deciduous forest are affected by the edge between the forest and the road constructed. Since some extremely rare lichens only occur at interior stands, the conservation of these threatened elements requires urgent conservation measures because well preserved and unmanaged forests in the Mediterranean region are very rare.     

日本中部10种树木叶片中氮和磷的季节变化及其转移

从叶完全展开到生长季结束,对常绿阔叶树种日本米储、具柄冬青、铁冬青、红楠和海桐及落叶阔叶树种袍栎、栓皮栎、日本朴、银杏和日本树五加的叶N和P含量进行了测定．结果表明,在整个生长季中,常绿阔叶树种中的日本米储和铁冬青的新叶和老叶的N和P含量呈现初期高、中期较低、后期上升的趋势;具柄冬青和海桐新叶的N和P含量的变化趋势与日本米储和铁冬青相似,而其老叶的N和P含量随季节推移而逐渐下降;红楠新叶和老叶的N含量呈现上升的趋势,其新叶和老叶的P含量则呈下降趋势;落叶阔叶树种的叶N和P含量随着时间的推移不断减少．各树种的N转移率为43％～75％,P为62％～84％．常绿阔叶树种的N平均转移率与落叶阔叶树种相似,而其P平均转移率大于落叶阔叶树种．所有树种的N平均转移率小于P平均转移率．     

Autumn colours and the nutrient retranslocation hypothesis: a theoretical assessment

The adaptive value of the bright colours of leaves in autumn is still debated. It is possible that autumn colours are an adaptation to protect the tree against photoinibition and photooxidation, which allows a more efficient recovery of nutrients. It has been proposed that the preference of aphids for trees that retranslocate nitrogen more efficiently can explain the high diversity of aphids on tree species with bright autumn colours. This scenario however does not take into account the impact of insects on the fitness of the trees and has not been analysed theoretically. Its assumptions and predictions, therefore, remain uncertain. I show with a model of insect-tree interaction that the system can actually evolve under particular conditions. I discuss the differences with the coevolution theory of autumn colours, available evidence and possible tests.     

安徽马尾松人工林营养元素分配格局的研究

本文系统地研究了马尾松人工林营养元素的分配格局。结果表明马尾松不同器官营养元素含量是叶>枝皮>干皮>枝木>干木;同化器官——针叶中营养元素含量规律为N>K>Ca>Mg>P,非同化器官为Ca>N>K>Mg>P;不同器官营养元素的贮量为干木>干皮>叶>枝木>枝皮,同化器官对不同营养元素的贮量呈N>K>Ca>Mg>P,非同化器官为Ca>N>K>Mg>P;不同立地条件下,马尾松林生产1t干物质所贮存的营养元素不同,立地条件愈好,营养元素效率愈高,贮存愈少;母岩、土层厚度和养分总量是影响马尾松林地上各器官,特别是针叶营养元素含量的重要因子,土壤N、P含量越高,马尾松人工林生物量越大。     

Nitrogen as a limiting factor in the development of beech forests in the Sierra de la Demanda (Spain)

The leaf nitrogen contents of beech growing in the Sierra de la Demanda are studied, relating the contents with other structural population characteristics. For this, different experiments were conducted: (a) To analyze of nitrogen levels in shed leaves, in leaf biomass and in leaves decomposing on a test plot in the Tres Aguas beech forest. (b) To study leaf nitrogen contents over a vegetative cycle in the above beech forest. (c) To study the leaf nitrogen contents of thirty beech stands in the Sierra de la Demanda located at different altitudes and corresponding to three beech budding isophenes. Annual nitrogen accumulation in leaf biomass was 79.4 kg ha^-1yr^-1, of which 22.9 kg ha^-1yr^-1 return to the soil substrate through shedding and 2.1 kg ha^-1yr^-1 are actually incorporated into the soil. Nitrogen cannot be a limiting factor for the development of the beech stands studied because all of them surpassed the leaf deficiency threshold. Only other factors such as those of the soil or silvicultural treatment have a decisive effect on the production of the stands studied. Study of the correlations for leaf nitrogen contents and the structural population characteristics explored reveals that leaf nitrogen was only slightly correlated with the mean height of the trees at the plot.     

Seasonal nutrient variation in trembling aspen

Summary Variation in concentrations of N, K, Mg, and Ca in vegetative-buds, leaves, twigs, and male catkins of trembling aspen (Populus tremuloides Michx.), determined throughout a growing season in central Minnesota, reflected the different physiological roles of the nutrients. Practical implications are discussed.     

Large-Scale Patterns of Quercus ilex, Quercus suber, and Quercus pyrenaica Regeneration in Central-Western Spain

In Central-Western Spain, forests and woodlands composed of Quercus sp. support outstanding levels of biodiversity, but there is increasing concern about their long-term persistence due to a lack of regeneration. We hypothesize that this regenerative lack is operating on a large geographic scale; that there are differences in the abundance of regeneration between three oak species; that oak regeneration is governed mainly by forest management and structure; and that shrubs act as important physical protectors of seedlings and saplings. We analyzed whether densities of oak seedlings and saplings in several size classes were related to stand-structure, understory, and physiographic variables potentially affecting regeneration. Data collected at a regional level (1 km × 1 km grid) by the Spanish Forest Inventory were evaluated from 2,816 plots. Results revealed that regeneration failure was common for all size categories, from small seedlings to large saplings, and for the three oak species studied, especially the evergreens. Of the Quercus ilex, Q. suber, and Q. pyrenaica plots studied, 49%, 62%, and 20% were lacking any small seedlings, and 82%, 96%, and 56% did not have any large saplings, respectively. Regeneration was positively correlated with tree cover and density, especially of small and medium-sized trees, and negatively correlated with the presence of large trees, indicating that regeneration failure is mostly associated with more open, uniform, and/or aged woodlands. Regeneration densities of Q. ilex and Q. suber were positively correlated with all understory variables, suggesting that the presence of pioneer shrubs represent a major safe site for early tree recruitment, independent from specific shrub species.     

Litterflow chemistry and nutrient uptake from the forest floor in northwest Amazonian forest ecosystems

Samples of the fraction of net rainfall passing through the forest floor collected at monthly intervals in four pristine forests in Colombian Amazonia, during the period between 1995–1997 were analysed for solute concentrations to estimate the element fluxes from the forest floor into the mineral soil and root nutrient uptake from these forest floors. Results were compared with inputs by throughfall, stemflow, litterfall and fine root decay. Element concentrations were tested for their relationship with litterflow amounts, rainfall intensity and length of the antecedent dry period and differences in element fluxes between ecosystems were assessed. Concentrations of elements in litterflow followed a similar pattern as those in throughfall, which indicates that element outputs from the forest floor are strongly related to those inputs in throughfall. In the forests studied, the average concentrations of elements as K, Mg, orthoP and the pH of the litterflow decreased relative to that in throughfall in most events, while the concentration of elements such as dissolved organic carbon, H, SO₄ and Si increased in litterflow from these forests. Element concentrations in litterflow showed a poor correlation with variables such as litterflow amounts, rainfall intensity and antecedent dry period, except for K which showed a significant correlation (p>0.95) with analysed variables in all forests. Outputs were significantly different between forests (p>0.95); these fluxes, which particularly concerned cations, being the largest in the flood plain, while for anions outputs increased from the flood plain to the sedimentary plain. After adding the nutrient contributed by litter decomposition and fine root decay, the net outputs of main elements from the forest floors were still smaller than inputs by net precipitation (throughfall+stemflow) indicating that the litter layers clearly acted as a sink for most nutrients. Accordingly, the element balances confirm that the forest floors acted as a sink for nutrients coming in by throughfall, stemflow, litterfall and fine root decomposition. P, Mg and N appeared to be the most limiting nutrients and the forests studied efficiently recycled these nutrients.     

Seasonal and spatial patterns of foliar nutrients in cork oak (Quercus suber L.) growing on siliceous soils in Provence (France)

Cork oak forests in Mediterranean, southeastern France represent animportant ecosystem in terms of both ecological and economical values, but aredeclining due to conservation problems. While management protocols are now inplace for the long-term conservation of this ecotype, we require a betterunderstanding of cork oak nutrition to assist with management. Here we usefoliar nutrient analyses for two objectives: firstly, to assess to what extentvariations in nutrient content are explained by seasonal and spatialvariability, and second, to document the nutrient dynamics of cork oak trees innatural conditions during one biological cycle (16 months) in the Maures massif(western part of the siliceous Provence). Main results showed that time was theprimary factor influencing cork oak nutrition and was mainly expressed by leafageing process. Spatial variability was a 'secondary determinant' of nutrient variations, but was more important at the very early stages of leafgrowth according to leafing and nutrient flushing, and reduced with leaf age.Nutritional responses of cork oak trees fitted general trends observed in theliterature, with some regional differences. The properties of siliceous soilalso influenced the uptake of some nutrients.     

长白松人工林生态系统营养元素的分配格局和积累规律

对长白松人工林生态系统营养元素的分配格局和积累规律研究表明,乔木层不同器官营养元素含量为叶＞枝＞根＞干皮＞干材;同化器官──针叶中养分含量为Ｎ＞Ｋ＞Ｃａ＞Ｐ＞Ｍｇ;吸收器官──根中养分含量为Ｃａ＞Ｎ＞Ｋ＞Ｐ＞Ｍｇ;人工林生态系统中的养分含量为土壤＞凋落层＞草本层＞灌木层＞乔木层,乔木层养分贮量和积累率分别为８８．７９％和７６．４３％;长白松林生态系统中植物对Ｎ、Ｐ的吸收较强烈．     

Chloroplast-ultrastructure and chlorophyll content in leaves from Quercus branches with and without epiphytic lichen thalli

Abstract The effect that the massive presence of lichen thalli growing on the branches of Quercus pyrenaica and Q. rotundifolia leaves has on their chloroplasts been studied. In both species there were significant decreases in the amount of chlorophylls in the leaves of twigs with a dense cover of lichens in comparison with the leaves from thallus-free twigs. The areas and perimeter of chloroplasts in leaves from twigs with epiphytes did not differ significantly from those in leaves without epiphytes. However, in leaves with epiphytes the percentage of chloroplast area occupied by starch was higher. In Q. pyrenaica the number of grana per chloroplast section and per μm², the percentage of chloroplast stroma occupied by grana, the average number of thylakoids forming grana and the grana width was significantly smaller in leaves near lichen populations. These results are discussed and related to the great chelating capacity of the lichen's substances.     

Effects of elevated CO2 on nutrient cycling in a sweetgum plantation

The effects of elevated CO₂ on nutrient cycling and selected belowground processes in the closed-canopy sweetgum plantation were assessed as part of a free-air CO₂ enrichment (FACE) experiment at Oak Ridge, Tennessee. We hypothesized that nitrogen (N) constraints to growth response to elevated CO₂ would be mitigated primarily by reduced tissue concentrations (resulting in increased biomass production per unit uptake) rather than increased uptake. Conversely, we hypothesized that the constraints of other nutrients to growth response to elevated CO₂ would be mitigated primarily by increased uptake because of adequate soil supplies. The first hypothesis was not supported: although elevated CO₂ caused reduced foliar N concentrations, it also resulted in increased uptake and requirement of N, primarily because of greater root turnover. The additional N uptake with elevated CO₂ constituted between 10 and 40% of the estimated soil mineralizeable N pool. The second hypothesis was largely supported: elevated CO₂ had no significant effects on tissue concentrations of P, K, Ca, or Mg and caused significantly increased uptake and requirement of K, Ca, and Mg. Soil exchangeable pools of these nutrients are large and should pose no constraint to continued growth responses. Elevated CO₂ also caused increased microbial biomass, reduced N leaching and increased P leaching from O horizons (measured by resin lysimeters), reduced soil solution NH ₄ ⁺ , SO ₄ ^2– , and Ca²⁺ concentrations, and increased soil solution pH. There were no statistically significant treatment effects on soil nutrient availability as measured by resin capsules, resin stakes, or in situ incubations. Despite significantly lower litterfall N concentrations in the elevated CO₂ treatment, there were no significant treatment effects on translocation or forest floor biomass or nutrient contents. There were also no significant treatment effects on the rate of decomposition of fine roots. In general, the effects of elevated CO₂ on nutrient cycling in this study were not large; future constraints on growth responses imposed by N limitations will depend on changes in N demand, atmospheric N deposition, and soil mineralization rates.     

Seasonal patterns of nutrient deposition in a Quercus douglasii woodland in central California

The monthly deposition of total nitrogen, phosphorus, potassium, calcium and magnesium via canopy throughfall, and various components of the litterfall was measured for 31 months under mature Quercus douglasii and in the bulk precipitation in the surrounding open grassland. Seasonal patterns of nutrient concentration in leaf litter, throughfall, and precipitation were also measured. Total annual subcanopy deposition exceeded open precipitation deposition by approximately 45–60x for nitrogen, 5–15x for phosphorus, 30–35x for potassium, 25–35x for calcium, and 5–10x for magnesium. Total annual subcanopy deposition was low in comparison to other oak woodland sites reported in the literature. Throughfall and leaf litter were the primary sources of nutrients and thus determined the seasonal peaks of nutrient deposition. The first autumn rains and leaf fall were associated with one peak in nutrient deposition, and throughfall during early spring leaf emergence was associated with a second peak in potassium, magnesium and phosphorus. Non-leaf plant litter (excluding acorns) provided approximately 15–35% of most nutrients, with twigs and bark depositing over 12% of the annual calcium flux in 1987–1988, and flower litter depositing over 8% of the annual nitrogen flux in 1986–1987. Acorns had high concentrations of phosphorus and nitrogen and during the mast season of 1987–1988 they contained a large proportion of the total subcanopy annual flux of these elements. With acorns excluded, total annual nutrient deposition was similar between years, but timing of nutrient deposition differed. Late summer leaf fall associated with drought, variation in precipitation, and variation in deposition of non-leaf parts were associated with seasonal differences in nutrient deposition between years.     

Seasonal variation of vesicular-arbuscular mycorrhizae in eroded soils from southern Spain

A survey was carried out of the seasonal variations in the number of spores in the soil and of the percentage of root infection. The stage of development of the host plants, environmental variations and physicochemical characteristics of the soil were taken into account. Fifteen plants valid as forage and adaptable to semi-arid conditions and poor soils were selected. In general, the maximum spore density was reached in the fruit-bearing period of the plants. It remained high during autumn, fell to a minimum in winter and tended to increase in spring. Root infection was at a maximum when the plants flowered, after which it decreased to a minimum in summer.     

The occurrence of lichen phenolics in the xylem sap of Quercus pyrenaica,their translocation to leaves and biological significance

Oak branches supporting the epiphytic lichens Evernia prunastri and Ramalina calicaris do contain both evernic and everninic acids which are acropetally translocated, via xylem, to reach the leaves. However, lichen phenolics have not been found in the mesophyllic cells and thus the photosynthetic ability of is not affected.     

Seasonal variation of airborne fungal spore concentrations in a vineyard of North-West Spain

Conidial types collected daily in the air above a vineyard in northwest Spain were identified and counted. A total of 26 fungal spore types were recognised; ten of which (Cladosporium, Botrytis, Fusarium-Leptosphaeria type,Torula, Puccinia, Alternaria, Uncinula, Helminthosporium type,Agrocybe andStemphylium) gave a seasonal total concentration exceeding 1000 spores. Seasonal patterns are shown for 12 of the identified taxa.     

Genetic variation in nutrient response functions

Summary Genetic differences in the non-linear growth response function of Pinus sylvestris seedlings to five nutrient levels are analyzed to estimate the causes of variation. Analyses of genotypic differences as quadratic response functions, as stability coefficients, and as separable functions indicate that the estimation of genetic effects can vary widely depending on the analytical model assumed. The existence of different reaction norms is demonstrated.     

Biogeographic patterns of nutrient resorption from Quercus variabilis Blume leaves across China

The variation in nutrient resorption has been studied at different taxonomic levels and geographic ranges. However, the variable traits of nutrient resorption at the individual species level across its distribution are poorly understood. We examined the variability and environmental controls of leaf nutrient resorption of Quercus variabilis, a widely distributed species of important ecological and economic value in China. The mean resorption efficiency was highest for phosphorus (P), followed by potassium (K), nitrogen (N), sulphur (S), magnesium (Mg) and carbon (C). Resorption efficiencies and proficiencies were strongly affected by climate and respective nutrients concentrations in soils and green leaves, but had little association with leaf mass per area. Climate factors, especially growing season length, were dominant drivers of nutrient resorption efficiencies, except for C, which was strongly related to green leaf C status. In contrast, green leaf nutritional status was the primary controlling factor of leaf nutrient proficiencies, except for C. Resorption efficiencies of N, P, K and S increased significantly with latitude, and were negatively related to growing season length and mean annual temperature. In turn, N, P, K and S in senesced leaves decreased with latitude, likely due to their efficient resorption response to variation in climate, but increased for Mg and did not change for C. Our results indicate that the nutrient resorption efficiency and proficiency of Q. variabilis differed strongly among nutrients, as well as growing environments. Our findings provide important insights into understanding the nutrient conservation strategy at the individual species level and its possible influence on nutrient cycling.     

Dominance of legume trees alters nutrient relations in mixed species forest restoration plantings within seven years

Failures in reforestation are often attributed to nutrient limitation for tree growth. We compared tree performance and nitrogen and phosphorus relations in adjacent mixed-species plantings of contrasting composition, established for forest restoration on Ultisol soil, originally covered by tropical semi-deciduous Atlantic Forest in Southeast Brazil. Nutrient relations of four tree species occurring in both planting mixtures were compared between a legume-dominated, species-poor direct seeding mixture of early-successional species (“legume mixture”), and a species-diverse, legume-poor mixture of all successional groups (“diverse mixture”). After 7 years, the legume mixture had 6-fold higher abundance of N₂-fixing trees, 177% higher total tree basal area, 22% lower litter C/N, six-fold higher in situ soil resin-nitrate, and 40% lower in situ soil resin-P, compared to the diverse mixture. In the legume mixture, non-N₂-fixing legume Schizolobium parahyba (Fabaceae-Caesalpinioideae) had significantly lower proportional N resorption, and both naturally regenerating non-legume trees had significantly higher leaf N concentrations, and higher proportional P resorption, than in the diverse mixture. This demonstrate forms of plastic adjustment in all three non-N₂-fixing species to diverged nutrient relations between mixtures. By contrast, leaf nutrient relations in N₂-fixing Enterolobium contortisiliquum (Fabaceae-Mimosoideae) did not respond to planting mixtures. Rapid N accumulation in the legume mixture caused excess soil nitrification over nitrate immobilization and tighter P recycling compared with the diverse mixture. The legume mixture succeeded in accelerating tree growth and canopy closure, but may imply periods of N losses and possibly P limitation. Incorporation of species with efficient nitrate uptake and P mobilization from resistant soil pools offers potential to optimize these tradeoffs.