Duration of xylogenesis in black spruce lengthened between 1950 and 2010

Background and Aims

Reconstructions have identified the 20th century as being uniquely warm in the last 1000 years. Changes in the phenology of primary meristems converged toward increases in length of the growing season. Has the phenology of secondary meristem changed during the last century, and to what extent?

Methods

Timings of wood formation in black spruce, Picea mariana, were monitored for 9 years on a weekly timescale at four sites in the boreal forest of Quebec, Canada. Models for assessing xylem phenology were defined and applied to reconstruct onset, ending and duration of xylogenesis between 1950 and 2010 using thermal thresholds on chronologies of maximum and minimum temperatures.

Key Results

All sites exhibited increasing trends of both annual and May–September temperatures, with the greatest changes observed at the higher latitudes. Phenological events in spring were more affected than those occurring in autumn, with cambial resumptions occurring 0·5–0·8 d decade⁻¹ earlier. The duration of xylogenesis has lengthened significantly since 1950, although the models supplied wide ranges of variations, between 0·07 and 1·5 d decade⁻¹, respectively.

Conclusions

The estimated changes in past cambial phenology demonstrated the marked effects of the recent increase in temperature on the phenological traits of secondary meristems. In the long run, the advancement of cambial activity could modify the short time window for growth of boreal species and dramatically affect the dynamics and productivity of trees in these temperature-limited ecosystems.     

Compensatory mechanisms mitigate the effect of warming and drought on wood formation

Because of global warming, high‐latitude ecosystems are expected to experience increases in temperature and drought events. Wood formation will have to adjust to these new climatic constraints to maintain tree mechanical stability and long‐distance water transport. The aim of this study is to understand the dynamic processes involved in wood formation under warming and drought. Xylogenesis, gas exchange, water relations and wood anatomy of black spruce [Picea mariana (Mill.) B.S.P.] saplings were monitored during a greenhouse experiment where temperature was increased during daytime or night‐time (+6 °C) combined with a drought period. The kinetics of tracheid development expressed as rate and duration of the xylogenesis sub‐processes were quantified using generalized additive models. Drought and warming had a strong influence on cell production, but little effect on wood anatomy. The increase in cell production rate under warmer temperatures, and especially during the night‐time warming at the end of the growing season, resulted in wider tree‐rings. However, the strong compensation between rates and durations of cell differentiation processes mitigates warming and drought effects on tree‐ring structure. Our results allowed quantification of how wood formation kinetics is regulated when water and heat stress increase, allowing trees to adapt to future environmental conditions.     

Effect of ecosystem warming on boreal black spruce bud burst and shoot growth

The boreal forest is predicted to experience the greatest warming of any forest biome during the next 50–100 years, but the effects of warming on vegetation phenology are not well known. The objectives of this study were to (1) examine the effects of whole ecosystem warming on bud burst and annual shoot growth of black spruce trees in northern Manitoba, Canada and (2) correlate bud burst to cumulative degree-days (CDD). The experimental design was a complete randomized block design that consisted of four replicated blocks. Each replicate block contained four treatments: soil warming only (heated outside, HO), soil and air warming (heated inside, HI), control outside (no chamber, no heating, CO), and inside a chamber maintained at ambient conditions (no soil or air warming, control inside, CI). Bud burst was measured during the first and second years of the experiment, starting in 2004, and annual shoot growth was measured for the first 3 years (2004–2006) of the study. On average, shoot bud burst occurred 11 and 9 days earlier in 2004 and 2005, respectively, for HI than for other treatments. However, mean CDD required for bud burst for HI was within the standard deviation of CO for both years. In year 1 of the treatments, shoot bud burst occurred earlier for HI than other treatments (CI, CO, HO), but final shoot length of HI trees was less than in CO trees. In the second year of warming, final shoot length was not different for HI than CO. By the third year of warming final shoot length was significantly greater for HI than all other treatments. Empirical results from this study suggest that soil and air warming causes an earlier bud burst for all years of observation and greater shoot lengths by the third season of warming. A longer growing season and greater annual shoot growth should increase carbon uptake by boreal black spruce trees in a warmer climate.     

Stable carbon isotope analysis reveals widespread drought stress in boreal black spruce forests

Unprecedented rates of climate warming over the past century have resulted in increased forest stress and mortality worldwide. Decreased tree growth in association with increasing temperatures is generally accepted as a signal of temperature‐induced drought stress. However, variations in tree growth alone do not reveal the physiological mechanisms behind recent changes in tree growth. Examining stable carbon isotope composition of tree rings in addition to tree growth can provide a secondary line of evidence for physiological drought stress. In this study, we examined patterns of black spruce growth and carbon isotopic composition in tree rings in response to climate warming and drying in the boreal forest of interior Alaska. We examined trees at three nested scales: landscape, toposequence, and a subsample of trees within the toposequence. At each scale, we studied the potential effects of differences in microclimate and moisture availability by sampling on northern and southern aspects. We found that black spruce radial growth responded negatively to monthly metrics of temperature at all examined scales, and we examined ?¹³C responses on a subsample of trees as representative of the wider region. The negative ?¹³C responses to temperature reveal that black spruce trees are experiencing moisture stress on both northern and southern aspects. Contrary to our expectations, ?¹³C from trees on the northern aspect exhibited the strongest drought signal. Our results highlight the prominence of drought stress in the boreal forest of interior Alaska. We conclude that if temperatures continue to warm, we can expect drought‐induced productivity declines across large regions of the boreal forest, even for trees located in cool and moist landscape positions.     

Effects of prolonged drought on the anatomy of sun and shade needles in young Norway spruce trees

Predicted increases in the frequency and duration of drought are expected to negatively affect tree vitality, but we know little about how water shortage will influence needle anatomy and thereby the trees’ photosynthetic and hydraulic capacity. In this study, we evaluated anatomical changes in sun and shade needles of 20‐year‐old Norway spruce trees exposed to artificial drought stress. Canopy position was found to be important for needle structure, as sun needles had significantly higher values than shade needles for all anatomical traits (i.e., cross‐sectional needle area, number of tracheids in needle, needle hydraulic conductivity, and tracheid lumen area), except proportion of xylem area per cross‐sectional needle area. In sun needles, drought reduced all trait values by 10–40%, whereas in shade needles, only tracheid maximum diameter was reduced by drought. Due to the relatively weaker response of shade needles than sun needles in drought‐stressed trees, the difference between the two needle types was reduced by 25% in the drought‐stressed trees compared to the control trees. The observed changes in needle anatomy provide new understanding of how Norway spruce adapts to drought stress and may improve predictions of how forests will respond to global climate change.     

Effects of nutrition and soil warming on stemwood production in a boreal Norway spruce stand

The boreal forest is expected to experience the greatest warming of all forest biomes. The extent of the boreal forest, the large amount of carbon contained in the soil, and the expected climate warming, make the boreal forest a key biome to understand and represent correctly in global carbon models. It has been suggested that an increase in temperature could stimulate the release of CO₂ caused by an increased decomposition rate, more than biomass production, which could convert current carbon sinks into carbon sources. Most boreal forests are currently carbon sinks, but it is unclear for how long in the future the carbon sink capacity of the boreal forest is likely to be maintained. The impact of soil warming on stem volume growth was studied during 6 years, in irrigated (I) and irrigated‐fertilized (IL) stands of 40‐year‐old Norway spruce in Northern Sweden. From May to October heating cables were used to maintain the soil temperature on heated‐irrigated plots (Ih and ILh) 5 °C above that on unheated control plots (Ic and ILc). After six seasons' warming, stem volume production (m³ ha^?1 a^?1) was 115% higher on Ih than on unheated (Ic) plots, and on heated and irrigated‐fertilized plots (ILh) it was 57% higher than on unheated plots (ILc). The results indicate that in a future warmer climate, an increased availability of nitrogen, combined with a longer growing season, may increase biomass production substantially, on both low‐ and high‐fertility sites. It is, however, too early to decide whether the observed responses are transitory or long lasting. It is therefore crucial to gain a better understanding of the responses of boreal forest ecosystems to climate change, and to provide data to test and validate models used in predicting the impact of climate change.     

Response of soil surface CO2 flux in a boreal forest to ecosystem warming

Soil surface carbon dioxide (CO₂) flux (R_S) was measured for 2 years at the Boreal Soil and Air Warming Experiment site near Thompson, MB, Canada. The experimental design was a complete random block design that consisted of four replicate blocks, with each block containing a 15 m × 15 m control and heated plot. Black spruce [Picea mariana (Mill.) BSP] was the overstory species and Epilobium angustifolium was the dominant understory. Soil temperature was maintained (～5 °C) above the control soil temperature using electric cables inside water filled polyethylene tubing for each heated plot. Air inside a 7.3‐m‐diameter chamber, centered in the soil warming plot, contained approximately nine black spruce trees was heated ～5 °C above control ambient air temperature allowing for the testing of soil‐only warming and soil+air warming. Soil surface CO₂ flux (R_S) was positively correlated (P < 0.0001) to soil temperature at 10 cm depth. Soil surface CO₂ flux (R_S) was 24% greater in the soil‐only warming than the control in 2004, but was only 11% greater in 2005, while R_S in the soil+air warming treatments was 31% less than the control in 2004 and 23% less in 2005. Live fine root mass (< 2 mm diameter) was less in the heated than control treatments in 2004 and statistically less (P < 0.01) in 2005. Similar root mass between the two heated treatments suggests that different heating methods (soil‐only vs. soil+air warming) can affect the rate of decomposition.     

Drought tolerance in faster- and slower-growing black spruce (Picea mariana) progenies: II. Osmotic adjustment and changes of soluble carbohydrates and amino acids under osmotic stress

The possibility was considered that osmotic adjustment, the ability to accumulate solutes in response to water stress, may contribute to growth rate differences among closely-related genotypes of trees. Progeny variation in osmotic adjustment and turgor regulation was investigated by comparing changes in osmotic and pressure potentials, soluble carbohydrates, and amino acids in osmotically stressed seedlings in 4 full-sib progenies of black spruce [ Picea mariana (Mill.) B. S. P.] that differed in growth rate under drought. Osmotic stress was induced by a stepwise increase in the concentration of polyethylene glycol (PEG)-3350 from 10 (w/v) to 18 and 25%, which provided osmotic potentials in solution culture of -0.4, -1.0 and -2.0 MPa each for 3 days. All 4 progenies maintained a positive cell turgor even at 25% PEG, due to a significant decline in osmotic potential. Although total amino acids, principally proline, increased, ca 60% of the decrease in osmotic potential was attributable to soluble carbohydrates and glucose was the major osmoregulating solute. There was little progeny variation in any of measured parameters in unstressed seedlings. Compared to two slower-growing progenies, the two progenies capable of more vigorous growth under drought in the field accumulated more soluble carbohydrates (mainly glucose and fructose), developed lower osmotic potential and maintained higher turgor pressure when osmotically-stressed in solution culture. The ability to adjust osmotically and maintain turgor under drought stress could thus be a useful criterion for the early selection of faster-growing, drought-tolerant genotypes.     

A long-term record of carbon exchange in a boreal black spruce forest: means, responses to interannual variability, and decadal trends

We present a decadal (1994–2004) record of carbon dioxide flux in a 160‐year‐old black spruce forest/veneer bog complex in central Manitoba, Canada. The ecosystem shifted from a source (+41 g C m⁻², 1995) to a sink (−21 g C m⁻², 2004) of CO₂ over the decade, with an average net carbon balance near zero. Annual mean temperatures increased 1–2° during the period, consistent with the decadal trend across the North American boreal biome. We found that ecosystem carbon exchange responded strongly to air temperature, moisture status, potential evapotranspiration, and summertime solar radiation. The seasonal cycle of ecosystem respiration significantly lagged that of photosynthesis, limited by the rate of soil thaw and the slow drainage of the soil column. Factors acting over long time scales, especially water table depth, strongly influenced the carbon budget on annual time scales. Net uptake was enhanced and respiration inhibited by multiple years of rainfall in excess of evaporative demand. Contrary to expectations, we observed no correlation between longer growing seasons and net uptake, possibly because of offsetting increases in ecosystem respiration. The results indicate that the interactions between soil thaw and water table depth provide critical controls on carbon exchange in boreal forests underlain by peat, on seasonal to decadal time scales, and these factors must be simulated in terrestrial biosphere models to predict response of these regions to future climate.     

Contribution of micro-organisms to the carbon dynamics in black spruce (Picea mariana) forest soil in Canada

In order to clarify the role of micro-organisms in the carbon cycle of the boreal forest ecosystem, the vertical distribution of soil carbon, soil microbial biomass and respiratory activity was studied in a black spruce forest near Candle Lake in Saskatchewan, Canada. The total amount of carbon contained in moss and soil layers (to the depth of 50cm beneath the mineral soil surface) was 7.2kgm^–2, about 47% of which was in the L and FH horizons of the soil. Soil microbial biomass per dry weight of soil was largest in the L horizon, while the biomass per ground area was largest in the FH horizon. Soil respiration rate, measured using a portable infrared gas analyzer, was highest in the FH horizon, exceeding 50% of the total soil respiration. Low but significant CO₂ emission was detected even in deeper soil horizon (E horizon). We also examined the respiration rate of cut roots and the effect of root excision on respiration. The contribution of root respiration to total soil respiration, calculated from root biomass and respiration rate of cut roots, was about 54%. The amount of carbon evolved through microbial respiration during the snow-free season (June–October) was estimated as 221gCm^–2. Micro-organisms in the L horizon showed high respiratory activity as compared with those in deeper soil horizons.     

Effect of elevated [CO2] on stem wood properties of mature Norway spruce grown at different soil nutrient availability

The objective of the present study was to investigate the interactive effects of elevated [CO₂] and soil nutrient availability on secondary xylem structure and chemical composition of 41‐year‐old Norway spruce (Picea abies (L.) Karst.) trees. The nonfertilized and irrigated‐fertilized trees were, for 3 years, continuously exposed to elevated [CO₂] in whole‐tree chambers. Elevated [CO₂] decreased concentrations of soluble sugars, acid‐soluble lignin and nitrogen in stem wood, but the effects were not consistent between sampling height and/or fertilization. The effect of 2*ambient [CO₂] on wood structure depended on the exposure year and/or fertilization. Radial lumen diameter decreased and annual ring width increased in the second year of exposure (1999) in elevated [CO₂]. In the latter, the CO₂ effect was significant only in the nonfertilized trees. Stem wood chemistry and structure were significantly affected by fertilization. Fertilization increased the concentrations of nitrogen and gravimetric lignin, annual ring width, and radial lumen diameter. Fertilization decreased C/N ratio, mean ring density, earlywood density, latewood density, cell wall thickness, cell wall index, and latewood percentage. We conclude that elevated [CO₂] had only minor effects on wood properties while fertilization had more marked effects and thus may affect ecosystem processes and suitability of wood for different end‐use purposes.     

Interactive effects of soil warming and fertilization on root production, mortality, and longevity in a Norway spruce stand in Northern Sweden

The effects of soil warming and nitrogen availability on root production, longevity and mortality were studied using minirhizotrons in irrigation (C), fertilized (F), heated (H), and heated‐fertilized (HF) plots in a Norway spruce stand in northern Sweden from October 1996 to October 1997. Irrigation was included in all treatment plots. Heating cables were used to maintain the soil temperature in heated plots at 5°C above that in unheated plots during the growing season. A Kaplan–Meier approach was used to estimate the longevity of fine roots and Cox proportional hazards regression to analyze the effects of the H, F, and HF treatments on the risk of root mortality. The proportion of annual root length production contributed by winter–spring production amounted to 52% and 49% in heated plots and heated‐fertilized plots, respectively. The annual root length production in C plots was significantly higher than in other treatments, while the HF treatment gave significantly greater production compared with the F treatment. The risk of mortality (hazard ratio) relative to C plots was higher in H plots (358%) and F plots (191%). The interaction between heating and fertilizing was strongly significant. The increase in the risk of root mortality in combined fertilization and heating (103%) was lower than that in the H or F plots. The results show that nitrogen addition combined with warmer temperatures decreases the risk of root mortality, and fine root production is a function of the length of the growing season. In the future, fertilization combined with the warmer temperatures expected to follow predicted climatic change may increase root production in boreal forests at low fertility sites.     

Cell structural changes in the needles of Norway spruce exposed to long-term ozone and drought

Effects of ozone and/or drought on Norway spruce needles werestudied using light microscopy and electron microscopy. Saplingswere exposed to ozone in open-top chambers during 1992–1995and also to drought in the late summers of 1993–1995.Samples from current and previous year needles were collectedfive times during 1995. Ozone increased the numbers of peroxisomesand mitochondria, which suggests that defence mechanisms againstoxidative stress were active. The results from peroxisomes suggestthat the oxidative stress was more pronounced in the upper sideof the needles, and those from mitochondria that defence wasmore active in the younger needle generation. Possibly due tothe good nitrogen status and the active defence, no ozone-specificchloroplast alterations were seen. At the end of the season,older needles from ozone treatments had smaller central vacuolescompared with other needles. Cytoplasmic vacuoles around thenucleus were increased by ozone in the beginning of the experiment,and did not increase towards the end of the season as in thecontrols. These results from vacuoles may indicate that ozoneaffected the osmotic properties of the cells. Decreased numberand underdevelopment of sclerenchyma cells and proliferationof tonoplast were related to nutrient imbalance, which was enhancedby drought. Larger vascular cylinders and more effective starchaccumulation before and after the drought periods compensatedfor the reduced water status. Numbers of peroxisomes and mitochondriawere increased in the drought-exposed needles before the onsetof drought treatments of the study year, i.e. these changeswere memory effects. Interactions between ozone and droughtwere few.     

Artificial asymmetric warming reduces nectar yield in a Tibetan alpine species of Asteraceae

Background and Aims Asymmetric warming is one of the distinguishing features of global climate change, in which winter and night-time temperatures are predicted to increase more than summer and diurnal temperatures. Winter warming weakens vernalization and hence decreases the potential to flower for some perennial herbs, and night warming can reduce carbohydrate concentrations in storage organs. This study therefore hypothesized that asymmetric warming should act to reduce flower number and nectar production per flower in a perennial herb, Saussurea nigrescens, a key nectar plant for pollinators in Tibetan alpine meadows.Methods A long-term (6 years) warming experiment was conducted using open-top chambers placed in a natural meadow and manipulated to achieve asymmetric increases in temperature, as follows: a mean annual increase of 0·7 and 2·7 °C during the growing and non-growing seasons, respectively, combined with an increase of 1·6 and 2·8 °C in the daytime and night-time, respectively, from June to August. Measurements were taken of nectar volume and concentration (sucrose content), and also of leaf non-structural carbohydrate content and plant morphology.Key Results Six years of experimental warming resulted in reductions in nectar volume per floret (64·7 % of control), floret number per capitulum (8·7 %) and capitulum number per plant (32·5 %), whereas nectar concentration remained unchanged. Depletion of leaf non-structural carbohydrates was significantly higher in the warmed than in the ambient condition. Overall plant density was also reduced by warming, which, when combined with reductions in flower development and nectar volumes, led to a reduction of ∼90 % in nectar production per unit area.Conclusions The negative effect of asymmetric warming on nectar yields in S. nigrescens may be explained by a concomitant depletion of leaf non-structural carbohydrates. The results thus highlight a novel aspect of how climate change might affect plant–pollinator interactions and plant reproduction via induction of allocation shifts for plants growing in communities subject to asymmetric warming.     

Thermal acclimation of leaf respiration of tropical trees and lianas: response to experimental canopy warming,and consequences for tropical forest carbon balance

Climate warming is expected to increase respiration rates of tropical forest trees and lianas, which may negatively affect the carbon balance of tropical forests. Thermal acclimation could mitigate the expected respiration increase, but the thermal acclimation potential of tropical forests remains largely unknown. In a tropical forest in Panama, we experimentally increased nighttime temperatures of upper canopy leaves of three tree and two liana species by on average 3  ° C for 1 week, and quantified temperature responses of leaf dark respiration. Respiration at 25  ° C (R₂₅) decreased with increasing leaf temperature, but acclimation did not result in perfect homeostasis of respiration across temperatures. In contrast, Q₁₀ of treatment and control leaves exhibited similarly high values (range 2.5–3.0) without evidence of acclimation. The decrease in R₂₅ was not caused by respiratory substrate depletion, as warming did not reduce leaf carbohydrate concentration. To evaluate the wider implications of our experimental results, we simulated the carbon cycle of tropical latitudes (24 ° S–24 ° N) from 2000 to 2100 using a dynamic global vegetation model (LM3VN) modified to account for acclimation. Acclimation reduced the degree to which respiration increases with climate warming in the model relative to a no‐acclimation scenario, leading to 21% greater increase in net primary productivity and 18% greater increase in biomass carbon storage over the 21st century. We conclude that leaf respiration of tropical forest plants can acclimate to nighttime warming, thereby reducing the magnitude of the positive feedback between climate change and the carbon cycle.     

Gibberellin is required for the formation of tension wood and stem gravitropism in Acacia mangium seedlings

Background and Aims Angiosperm trees generally form tension wood on the upper sides of leaning stems. The formation of tension wood is an important response to gravitational stimulus. Gibberellin appears to be involved in the differentiation of secondary xylem, but it remains unclear whether gibberellin plays a key role in the formation of tension wood and plant gravitropism. Therefore, a study was designed to investigate the effects of gibberellin and of inhibitors of the synthesis of gibberellin, namely paclobutrazole and uniconazole-P, on the formation of tension wood and negative stem gravitropism in Acacia mangium seedlings. Methods Gibberellic acid (GA(3)), paclobutrazole and uniconazole-P were applied to seedlings via the soil in which they were growing. Distilled water was applied similarly as a control. Three days after such treatment, seedlings were tilted at an angle of 45° from the vertical, and samples of stems were collected for analysis 2 weeks, 2 months and 6 months after tilting. The effects of treatments on the stem recovery degree (Ro) were analysed as an index of the negative gravitropism of seedlings, together the width of the region of tension wood in the upper part of inclined stems. Key Results It was found that GA(3) stimulated the negative gravitropism of tilted seedling stems of A. mangium, while paclobutrazole and uniconazole-P inhibited recovery to vertical growth. Moreover, GA(3) stimulated the formation of tension wood in tilted A. mangium seedlings, while paclobutrazole and uniconazole-P strongly suppressed the formation of tension wood, as assessed 2 weeks after tilting. Conclusions The results suggest that gibberellin plays an important role at the initial stages of formation of tension wood and in stem gravitropism in A. mangium seedlings in response to a gravitational stimulus.     

Contrasting growth changes in two dominant species of a Mediterranean shrubland submitted to experimental drought and warming

BACKGROUND AND AIMS: Climate projections predict drier and warmer conditions in the Mediterranean basin in the next decades. The possibility of such climatic changes modifying the growth of two Mediterranean species, Erica multiflora and Globularia alypum, which are common components of Mediterranean shrublands, was assessed. METHODS: A field experiment was performed from March 1999 to March 2002 to prolong the drought period and to increase the night-time temperature in a Mediterranean shrubland, where E. multiflora and G. alypum are the dominant species. Annual growth in stem diameter and length of both species was measured and annual stem biomass production was estimated for 1999, 2000 and 2001. Plant seasonal growth was also assessed. KEY RESULTS: On average, drought treatment reduced soil moisture 22 %, and warming increased temperature by 0.7-1.6 degrees C. Erica multiflora plants in the drought treatment showed a 46 % lower annual stem elongation than controls. The decrease in water availability also reduced by 31 % the annual stem diameter increment and by 43 % the annual stem elongation of G. alypum plants. New shoot growth of G. alypum was also strongly reduced. Allometrically estimated biomass production was decreased by drought in both species. Warming treatment produced contrasting effects on the growth patterns of these species. Warmer conditions increased, on average, the stem basal diameter growth of E. multiflora plants by 35 %, raising also their estimated stem biomass production. On the contrary, plants of G. alypum in the warming treatment showed a 14 % lower annual stem growth in basal diameter and shorter new shoots in spring compared with controls. CONCLUSIONS: The results indicate changes in the annual productivity of these Mediterranean shrubs under near future drier and warmer conditions. They also point to alterations in their competitive abilities, which could lead to changes in the species composition of these ecosystems in the long term.     

Differential and interactive effects of temperature and photoperiod on budburst and carbon reserves in two co-occurring Mediterranean oaks

Effects of temperature and photoperiod and their interactions on budburst and on the use of carbon reserves were examined in two Mediterranean oaks differing in wood anatomy and leaf habit. Seedlings of Quercus ilex subsp. ballota (evergreen and diffuse-porous wood) and Q. faginea (semi-deciduous and ring-porous wood) were grown under two temperatures (12 and 19 °C) and two photoperiods (10 and 16 h) in a factorial experiment. In the 16 h photoperiod at 19 °C, photosynthesis was suppressed in half of the seedlings by covering leaves with aluminium foil. The concentration of soluble sugars, starch and lipids in leaves, stems and roots was assessed before and after budburst. Under the 12 °C treatment (mean current temperature in early spring in the Iberian Peninsula), budburst in Q. faginea occurred earlier than in Q. ilex . Higher temperature promoted earlier budburst in both species, mostly under the 16 h photoperiod. This response was less pronounced in Q. faginea because its budburst was also controlled by photoperiod, and because this species needs to construct a new ring of xylem before budburst to supply its growth demands. Therefore, dates of budburst of the two species became closer to each other in the warmer treatment, which might alter competitive relations between the species with changing climate. While Q. ilex relied on carbon reserves for budburst, Q. faginea relied on both carbon reserves and current photoassimilates. The different responses of the two Quercus species to temperature and photoperiod related more to xylem structure than to the source of carbon used for budburst.     

Differences in growth characteristics and dynamics of elements absorbed in seedlings of three spruce species raised on serpentine soil in northern Japan

BACKGROUND AND AIMS: Serpentine soils are characterized by the presence of heavy metals (Ni and Cr) and excess Mg; these elements often suppress plant growth. Picea glehnii is nevertheless distributed widely on serpentine soils in northern Japan. Growth characteristics were compared among P. glehnii, Picea jezoensis (distributed in the same region) and Picea abies (planted for timber production), and concentrations of elements in various tissues over time and the amount of ectomycorrhizal infection in short roots were evaluated. METHODS: Seedlings of three spruce species were planted in two types of experimental plots, comprising serpentine soil and brown forest (non-serpentine) soil, and these seedlings were grown for 3 years. Growth, ectomycorrhizal infection of short roots, and elemental composition of tissues were examined. KEY RESULTS: The total dry mass of P. glehnii planted on serpentine soil was almost the same as on brown forest soil, and a large number of needles survived to reach later age classes. By contrast, growth of P. jezoensis and P. abies in serpentine soil was significantly less than in brown forest soil, and needle shedding was accelerated. Moreover, roots of seedlings of P. glehnii on serpentine soil were highly infected with ectomycorrhiza, and the concentration of Ni in needles and roots of P. glehnii was the lowest of the three species. CONCLUSIONS: Picea glehnii has a high ability to maintain a low concentration of Ni, and the ectomycorrhizal infection may have the positive effect of excluding Ni. As a result, P. glehnii is more tolerant than the other spruce species to serpentine soil conditions.     

Changes in chromosomal polymorphism and global warming: The case of Drosophila subobscura from Apatin (Serbia)

In this study, chromosomal inversion polymorphism data for a natural population of Drosophila subobscura from a swampy region near the town of Apatin (Serbia) were compared with data for the same population collected approximately 15 years earlier. The pattern of chromosomal inversion polymorphism changed over time. There were significant increases in the frequency of characteristic southern latitude ("warm" adapted) chromosomal arrangements and significant decreases in the frequency of characteristic northern latitude ("cold" adapted) chromosomal arrangements in the O and U chromosomes. The chromosomal arrangements O(3+4) and O(3+4) (+) (22) (derived from the O(3+4) arrangement) showed significant increases in 2008 and 2009 with regard to the 1994 sample. There was also a significant increase (～50%) in the U(1) (+) (2) arrangement, while U(1+8) (+) (2) (a typical southern arrangement) was detected for the first time. Since the Apatin swampy population of D. subobscura has existed for a long time in a stable habitat with high humidity that has not been changed by man our results indicate that natural selection has produced chromosomal changes in response to the increase in temperature that has occurred in the Balkan Peninsula of central southeastern European.