European and Mediterranean hydroclimate responses to tropical volcanic forcing over the last millennium.

Volcanic eruptions have global climate impacts, but their effect on the hydrologic cycle is poorly understood. We use a modified version of superposed epoch analysis, an eruption year list collated from multiple datasets, and seasonal paleoclimate reconstructions (soil moisture, precipitation, geopotential heights, and temperature) to investigate volcanic forcing of spring and summer hydroclimate over Europe and the Mediterranean over the last millennium. In the western Mediterranean, wet conditions occur in the eruption year and the following 3 years. Conversely, northwestern Europe and the British Isles experience dry conditions in response to volcanic eruptions, with the largest moisture deficits in post-eruption years 2 and 3. The precipitation response occurs primarily in late spring and early summer (April-July), a pattern that strongly resembles the negative phase of the East Atlantic Pattern. Modulated by this mode of climate variability, eruptions force significant, widespread, and heterogeneous hydroclimate responses across Europe and the Mediterranean.

Changes in composition, structure and aboveground biomass over seventy-six years (1930-2006) in the Black Rock Forest, Hudson Highlands, southeastern New York State.

We sought to quantify changes in tree species composition, forest structure and aboveground forest biomass (AGB) over 76 years (1930-2006) in the deciduous Black Rock Forest in southeastern New York, USA. We used data from periodic forest inventories, published floras and a set of eight long-term plots, along with species-specific allometric equations to estimate AGB and carbon content. Between the early 1930s and 2000, three species were extirpated from the forest (American elm (Ulmus americana L.), paper birch (Betula papyrifera Marsh.) and black spruce (Picea mariana (nigra) (Mill.) BSP)) and seven species invaded the forest (non-natives tree-of-heaven (Ailanthus altissima (Mill.) Swingle) and white poplar (Populus alba L.) and native, generally southerly distributed, southern catalpa (Catalpa bignonioides Walt.), cockspur hawthorn (Crataegus crus-galli L.), red mulberry (Morus rubra L.), eastern cottonwood (Populus deltoides Bartr.) and slippery elm (Ulmus rubra Muhl.)). Forest canopy was dominated by red oak and chestnut oak, but the understory tree community changed substantially from mixed oak-maple to red maple-black birch. Density decreased from an average of 1500 to 735 trees ha(-1), whereas basal area doubled from less than 15 m(2) ha(-1) to almost 30 m(2) ha(-1) by 2000. Forest-wide mean AGB from inventory data increased from about 71 Mg ha(-1) in 1930 to about 145 Mg ha(-1) in 1985, and mean AGB on the long-term plots increased from 75 Mg ha(-1) in 1936 to 218 Mg ha(-1) in 1998. Over 76 years, red oak (Quercus rubra L.) canopy trees stored carbon at about twice the rate of similar-sized canopy trees of other species. However, there has been a significant loss of live tree biomass as a result of canopy tree mortality since 1999. Important constraints on long-term biomass increment have included insect outbreaks and droughts.

Endothelium-mediated relaxation of porcine collateral-dependent arterioles is improved by exercise training.

BACKGROUND: Endothelium-dependent modulation of coronary tone is impaired in the collateral-dependent coronary microcirculation. We used a porcine model of chronic coronary occlusion and collateral development to evaluate the hypothesis that exercise training enhances endothelium-mediated relaxation and increases endothelial nitric oxide synthase (ecNOS) mRNA levels of collateral-dependent microvasculature. METHODS AND RESULTS: Adult female miniature swine were subjected to chronic, progressive ameroid occlusion of the proximal left circumflex coronary artery (LCx); after 2 months, animals were randomly exposed to 16-week exercise-training (EX group; treadmill running) or sedentary (SED group; cage confinement) protocols. After completion of EX or SED programs, coronary arterioles ( approximately 100 microm in diameter) were isolated from collateral-dependent LCx (distal to occlusion) and nonoccluded left anterior descending coronary artery (LAD) regions of each heart. Arterioles were studied by in vitro videomicroscopy or frozen for ecNOS mRNA analysis (RT-PCR techniques). Relaxation to the endothelium-dependent vasodilator bradykinin was decreased (P<0.05) in arterioles isolated from collateral-dependent LCx versus nonoccluded LAD regions of SED animals. Bradykinin-mediated relaxation, however, was not different in LCx versus LAD arterioles isolated from EX animals. Nitroprusside-induced relaxation was unaffected by either chronic occlusion or exercise. Importantly, ecNOS mRNA expression was significantly decreased in arterioles isolated from LCx versus LAD regions of SED animals. After training, ecNOS mRNA expression was not different between LAD and LCx arterioles. CONCLUSIONS: These data indicate that exercise training enhances bradykinin-mediated relaxation of collateral-dependent LCx arterioles isolated after chronic coronary occlusion, most likely because of effects on ecNOS mRNA expression and increased production of NO.

Direct and Indirect Effects of Atmospheric Carbon Dioxide Enrichment on Leaf Respiration of Glycine max (L.) Merr.

Long-term and short-term effects of CO2 enrichment on dark respiration were investigated using soybean (Glycine max [L.] Merr.) plants grown at either 35.5 or 71.0 Pa CO2. Indirect effects, or effects of growth in elevated CO2, were examined using a functional model that partitioned respiration into growth and maintenance components. Direct effects, or immediate effects of a short-term change in CO2, were examined by measuring dark respiration, first, at the CO2 partial pressure at which plants were grown, and second, after equilibration in the reciprocal CO2 partial pressure. The functional component model indicated that the maintenance coefficient of respiration increased 34% with elevated CO2, whereas the growth coefficient was not significantly affected. Changes in maintenance respiration were correlated with a 33% increase in leaf total nonstructural carbohydrate concentration, but leaf nitrogen content of soybean leaves was not affected by CO2 enrichment. Thus, increased maintenance respiration may be a consequence of increased nonstructural carbohydrate accumulation. When whole soybean plants were switched from low CO2 to high CO2 for a brief period, leaf respiration was always reduced. However, this direct effect of CO2 partial pressure was approximately 50% less in plants grown in elevated CO2. We conclude from this study that there are potentially important effects of CO2 enrichment on plant respiration but that the effects are different for plants given a short-term increase in CO2 partial pressure versus plants grown in elevated CO2.

Plants, CO2 and photosynthesis in the 21st century.

Human activity in the last 200 years has led to a marked increase in the level of CO2 in the atmosphere. Plants sense increases in CO2 levels and initially respond with an increase in photosynthetic rate, which may then slow as the plant adapts. This increase in photosynthetic rate may account in part for the 'disappearance' of an estimated 1.8 gigatons of carbon per year.

Exercise training improves endothelium-mediated vasorelaxation after chronic coronary occlusion.

The present study evaluated combined effects of chronic coronary occlusion and exercise training on endothelial function. Gradual occlusion was produced by placement of an ameroid constrictor around the proximal left circumflex (LCX) coronary artery of female swine. Two months after placement of the ameroid, animals were restricted to their pens or exercise trained for 16 wk. Epicardial arteries (>500 microm ID) were isolated from the collateral-dependent LCX coronary artery distal to the occlusion and the nonoccluded left anterior descending (LAD) coronary artery. Bradykinin- and ADP-mediated relaxation of LCX and LAD coronary arteries was enhanced after exercise training. Inhibition of nitric oxide synthase with N(G)-nitro-L-arginine methyl ester decreased bradykinin- and ADP-mediated relaxation in LCX and LAD myocardial regions. Importantly, combined inhibition of effects of endothelium-derived hyperpolarizing factor with increased extracellular K(+) (20-30 mM) and nitric oxide synthase completely abolished coronary LAD and LCX relaxation to bradykinin. Our data indicate that exercise training improves endothelium-mediated relaxation of arteries isolated after chronic coronary artery occlusion, likely as a result of enhanced production of nitric oxide and endothelium-derived hyperpolarizing factor.

Effects of low and elevated CO2 on C3 and C4 annuals : II. Photosynthesis and leaf biochemistry.

Abutilon theophrasti (C3) and Amaranthus retroflexus (C4), were grown from seed at four partial pressures of CO2: 15 Pa (below Pleistocene minimum), 27 Pa (pre-industrial), 35 Pa (current), and 70 Pa (future) in the Duke Phytotron under high light, high nutrient, and wellwatered conditions to evaluate their photosynthetic response to historic and future levels of CO2. Net photosynthesis at growth CO2 partial pressures increased with increasing CO2 for C3 plants, but not C4 plants. Net photosynthesis of Abutilon at 15 Pa CO2 was 70% less than that of plants grown at 35 Pa CO2, due to greater stomatal and biochemical limitations at 15 Pa CO2. Relative stomatal limitation (RSL) of Abutilon at 15 Pa CO2 was nearly 3 times greater than at 35 Pa CO2. A photosynthesis model was used to estimate ribulose-1,5-bisphosphate carboxylase (rubisco) activity (Vcmax), electron transport mediated RuBP regeneration capacity (J max), and phosphate regeneration capacity (PiRC) in Abutilon from net photosynthesis versus intercellular CO2 (A-C i) curves. All three component processes decreased by approximately 25% in Abutilon grown at 15 Pa compared with 35 Pa CO2. Abutilon grown at 15 Pa CO2 had significant reductions in total rubisco activity (25%), rubisco content (30%), activation state (29%), chlorophyll content (39%), N content (32%), and starch content (68%) compared with plants grown at 35 Pa CO2. Greater allocation to rubisco relative to light reaction components and concomitant decreases in J max and PiRC suggest co-regulation of biochemical processes occurred in Abutilon grown at 15 Pa CO2. There were no significant differences in photosynthesis or leaf properties in Abutilon grown at 27 Pa CO2 compared with 35 Pa CO2, suggesting that the rise in CO2 since the beginning of the industrial age has had little effect on the photosynthetic performance of Abutilon. For Amaranthus, limitations of photosynthesis were balanced between stomatal and biochemical factors such that net photosynthesis was similar in all CO2 treatments. Differences in photosynthetic response to growth over a wide range of CO2 partial pressures suggest changes in the relative performance of C3 and C4 annuals as atmospheric CO2 has fluctuated over geologic time.

Canopy position and needle age affect photosynthetic response in field-grown Pinus radiata after five years of exposure to elevated carbon dioxide partial pressure.

Photosynthesis of tree seedlings is generally enhanced during short-term exposure to elevated atmospheric CO2 partial pressure, but longer-term studies often indicate some degree of photosynthetic adjustment. We present physiological and biochemical evidence to explain observed long-term photosynthetic responses to elevated CO2 partial pressure as influenced by needle age and canopy position. We grew Pinus radiata D. Don. trees in open-top chambers for 5 years in sandy soil at ambient (36 Pa) and elevated (65 Pa) CO2 partial pressures. The trees were well watered and exposed to natural light and ambient temperature. In the fourth year of CO2 exposure (fall 1997), when foliage growth had ceased for the year, photosynthetic down-regulation was observed in 1-year-old needles, but not in current-year needles, suggesting a reduction in carbohydrate sink strength as a result of increasing needle age (Turnbull et al. 1998). In 5-year-old trees (spring 1997), when foliage expansion was occurring, photosynthetic down-regulation was not observed, reflecting significantly large sinks for carbohydrates throughout the tree. Net photosynthesis was stimulated by 79% in trees growing in elevated CO2 partial pressure, but there was no significant effect on photosynthetic capacity or Rubisco activity and concentration. Current-year needles were more responsive to elevated CO2 partial pressure than 1-year-old needles, exhibiting larger relative increases in net photosynthesis to elevated CO2 partial pressure (98 versus 64%). Lower canopy and upper canopy leaves exhibited similar relative responses to growth in elevated CO2 partial pressure. However, needles in the upper canopy exhibited higher net photosynthesis, photosynthetic capacity, and Rubisco activity and concentration than needles in the lower canopy. Given that the ratio of mature to juvenile foliage mass in the canopy will increase as trees mature, we suggest that trees may become less responsive to elevated CO2 partial pressure with increasing age. We conclude that tree response to elevated CO2 partial pressure is based primarily on sink strength and not on the duration of exposure.

Responses of leaf respiration to temperature and leaf characteristics in three deciduous tree species vary with site water availability.

We measured responses of leaf respiration to temperature and leaf characteristics in three deciduous tree species (Quercus rubra L., Quercus prinus L. and Acer rubrum L.) at two sites differing in water availability within a single catchment in the Black Rock Forest, New York. The response of respiration to temperature differed significantly among the species. Acer rubrum displayed the smallest increase in respiration with increasing temperature. Corresponding Q(10) values ranged from 1.5 in A. rubrum to 2.1 in Q. prinus. Dark respiration at ambient air temperatures, expressed on a leaf area basis (Rarea), did not differ significantly between species, but it was significantly lower (P < 0.01) in trees at the wetter (lower) site than at the drier (upper) site (Q. rubra: 0.8 versus 1.1 micromol m(-2) s(-1); Q. prinus: 0.95 versus 1.2 micromol m(-2) s(-1)). In contrast, when expressed on a leaf mass basis (R(mass)), respiration rates were significantly higher (P < 0.01) in A. rubrum (12.5-14.6 micromol CO(2) kg(-1) s(-1)) than in Q. rubra (8.6-9.9 micromol CO(2) kg(-1) s(-1)) and Q. prinus (9.2-10.6 micromol CO(2) kg(-1) s(-1)) at both the lower and upper sites. Respiration on a nitrogen basis (R(N)) displayed a similar response to R(mass). The consistency in R(mass) and R(N) between sites indicates a strong coupling between factors influencing respiration and those affecting leaf characteristics. Finally, the relationships between dark respiration and A(max) differed between sites. Trees at the upper site had higher rates of leaf respiration and lower A(max) than trees at the lower site. This shift in the balance of carbon gain and loss clearly limits carbon acquisition by trees at sites of low water availability, particularly in the case of A. rubrum.

Light saturated RuBP oxygenation by Rubisco is a robust predictor of light inhibition of respiration in Triticum aestivum L.

Plant respiratory metabolism is complicated by the fact that the rate of non-photorespiratory mitochondrial CO2 release in the light (R light) may be lower than the rate of leaf respiration in the dark (R dark). A body of work on this topic implies a linkage between light inhibition of respiration and photorespiration, although the direction of effect and underlying mechanisms remain uncertain. In this study we used a variety of short- and long-term environmental manipulations to explicitly manipulate the rate of photorespiration (νo) and quantify the effect on the inhibition of mitochondrial respiration in the light (R light:R dark). We address the following three questions: (i) will the R light:R dark ratio increase or decrease with high CO2 or low O2 and at low temperatures; (ii) does νo correlate with R light:R dark, and if so, in what way; (iii) will suppression of respiration by light (the 'Kok effect') be seen to the same extent in Zea mays, a C4 plant, and in Triticum aestivum, a C3 plant? We found that Rlight :Rdark decreased under conditions that suppressed νo in wheat, and this resulted in a positive relationship between R light:R dark and νo. Inhibition of respiration by light in C4 maize did not respond to environmental treatment, and the fixed R light:R dark (0.46-0.72) was consistent with the wheat response, assuming a νo approaching zero. The most likely mechanism to explain this finding is that R light increases (or the inhibition of respiration by light decreases) when there is an increase in photorespiration and thus an increase in the demand for TCA cycle substrates associated with the recovery of photorespiratory cycle intermediates in the peroxisome. This work is significant because it combines a comparison of C3 and C4 metabolism with a range of environmental treatments to independently suppress νo.

Construction cost and invasive potential: comparing Lythrum salicaria (Lythraceae) with co-occurring native species along pond banks.

Lythrum salicaria (purple loosestrife) is a nonindigenous invasive species characterized by prolific growth and abundance in marshy and riparian habitats across North America. Given its invasive success, we hypothesized this species may require less energy and/or use energy more efficiently for biomass construction than co-occurring noninvasive plant species. We measured leaf construction cost (CC), leaf mass per unit area (LMA), and leaf organic nitrogen and carbon content of L. salicaria and the five most abundant co-occurring species, Parthenocissus quinquefolia, Erigeron philadelphicus, Asclepias syriaca, Spiraea latifolia, and Solidago graminifolia, along dammed ponds in the Black Rock Forest, Cornwall, New York, USA. Lythrum salicaria, which was highly abundant (2.52 individuals/m(2)), exhibited significantly lower area-based leaf CC (44.47 ± 4.24 g glucose/m(2) leaf) than relatively less abundant species, suggesting energetics may influence its invasive success. Conversely, least abundant Solidago graminifolia (0.67 individuals/m(2)) exhibited the significantly highest leaf CC per unit leaf area (141.87 ± 39.21 g glucose/m(2) leaf). Overall, a negative correlation between species abundance and area-based leaf CC (r(2) = 0.73) indicated low energy requirements and/or high energy efficiency may influence relative abundance in the plant species studied. As it correlates with species abundance in this study, CC may be a useful tool for evaluating invasive potential.

Phosphorus supply affects the photosynthetic capacity of loblolly pine grown in elevated carbon dioxide.

Effects of phosphorus supply and mycorrhizal status on the response of photosynthetic capacity to elevated CO(2) were investigated in loblolly pine (Pinus taeda L.) seedlings. Seedlings were grown in greenhouses maintained at either 35.5 or 71.0 Pa CO(2) in a full factorial experiment with or without mycorrhizal inoculum (Pisolithus tinctorius (Pers.) Coker & Couch) and with an adequate or a limiting supply of phosphorus. Assimilation versus internal CO(2) partial pressure (C(i)) curves were used to estimate maximum Rubisco activity (V(c,max)), electron transport mediated ribulose 1,5-bisphosphate regeneration capacity (J(max)), phosphate regeneration capacity (PiRC) and daytime respiration rates (R(d)). Nonmycorrhizal seedlings grown with limiting phosphorus had significantly reduced V(c,max) and PiRC compared to seedlings in other treatments. Elevated CO(2) increased photosynthetic capacity in nonmycorrhizal seedlings in the low phosphorus treatment by increasing PiRC, whereas it induced phosphorus limitation in mycorrhizal seedlings in the low phosphorus treatment and did not affect the photosynthetic capacity of seedlings in the high phosphorus treatment. Despite the variety of effects on photosynthetic capacity, seedlings in the elevated CO(2) treatments had higher net assimilation rates than seedlings in the ambient CO(2) treatments. We conclude that phosphorus supply affects photosynthetic capacity during long-term exposure to elevated CO(2) through effects on Rubisco activity and ribulose 1,5-bisphosphate regeneration rates.

Effects of elevated atmospheric CO2 concentration on leaf dark respiration of Xanthium strumarium in light and in darkness.

Leaf dark respiration (R) is an important component of plant carbon balance, but the effects of rising atmospheric CO(2) on leaf R during illumination are largely unknown. We studied the effects of elevated CO(2) on leaf R in light (R(L)) and in darkness (R(D)) in Xanthium strumarium at different developmental stages. Leaf R(L) was estimated by using the Kok method, whereas leaf R(D) was measured as the rate of CO(2) efflux at zero light. Leaf R(L) and R(D) were significantly higher at elevated than at ambient CO(2) throughout the growing period. Elevated CO(2) increased the ratio of leaf R(L) to net photosynthesis at saturated light (A(max)) when plants were young and also after flowering, but the ratio of leaf R(D) to A(max) was unaffected by CO(2) levels. Leaf R(N) was significantly higher at the beginning but significantly lower at the end of the growing period in elevated CO(2)-grown plants. The ratio of leaf R(L) to R(D) was used to estimate the effect of light on leaf R during the day. We found that light inhibited leaf R at both CO(2) concentrations but to a lesser degree for elevated (17-24%) than for ambient (29-35%) CO(2)-grown plants, presumably because elevated CO(2)-grown plants had a higher demand for energy and carbon skeletons than ambient CO(2)-grown plants in light. Our results suggest that using the CO(2) efflux rate, determined by shading leaves during the day, as a measure for leaf R is likely to underestimate carbon loss from elevated CO(2)-grown plants.

EcoCELLs: tools for mesocosm scale measurements of gas exchange.

We describe the use of a unique plant growth facility, which has as its centerpiece four 'EcoCELLs', or 5x7 m mesocosms designed as open-flow, mass-balance systems for the measurement of carbon, water and trace gas fluxes. This system is unique in that it was conceived specifically to bridge the gap between measurement scales during long-term experiments examining the function and development of model ecosystems. There are several advantages to using EcoCELLs, including (i) the same theory of operation as leaf level gas exchange systems, but with continuous operation at a much larger scale; (ii) the ability to independently evaluate canopy-level and ecosystem models; (iii) simultaneous manipulation of environmental factors and measurement of system-level responses, and (iv) maximum access to, and manipulation of, a large rooting volume. In addition to discussing the theory, construction and relative merits of EcoCELLs, we describe the calibration and use of the EcoCELLs during a 'proof of concept' experiment. This experiment involved growing soybeans under two ambient CO2 concentrations (approximately 360 and 710 micromoles mol-1). During this experiment, we asked 'How accurate is the simplest model that can be used to scale from leaf-level to canopy-level responses?' in order to illustrate the utility of the EcoCELLs in validating canopy-scale models.

Plant growth in elevated CO2 alters mitochondrial number and chloroplast fine structure.

With increasing interest in the effects of elevated atmospheric CO(2) on plant growth and the global carbon balance, there is a need for greater understanding of how plants respond to variations in atmospheric partial pressure of CO(2). Our research shows that elevated CO(2) produces significant fine structural changes in major cellular organelles that appear to be an important component of the metabolic responses of plants to this global change. Nine species (representing seven plant families) in several experimental facilities with different CO(2)-dosing technologies were examined. Growth in elevated CO(2) increased numbers of mitochondria per unit cell area by 1.3-2.4 times the number in control plants grown in lower CO(2) and produced a statistically significant increase in the amount of chloroplast stroma (nonappressed) thylakoid membranes compared with those in lower CO(2) treatments. There was no observable change in size of the mitochondria. However, in contrast to the CO(2) effect on mitochondrial number, elevated CO(2) promoted a decrease in the rate of mass-based dark respiration. These changes may reflect a major shift in plant metabolism and energy balance that may help to explain enhanced plant productivity in response to elevated atmospheric CO(2) concentrations.