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Modern cone scales and seeds of Pinus strobus and Sequoia sempervirens, and their fossil (Upper Miocene, c. 6 Mar) counterparts Pinus leitzii and Sequoia langsdorfi have been studied using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), electron-microprobe and scanning electron microscopy. Microscopic observations revealed only minor microbial activity and high-quality structural preservation of the fossil material. The pyrolysates of both modern genera showed the presence of ligno-cellulose characteristic of conifers. However, the abundance of (alkylated)phenols and 1,2-benzenediols in modern S. sempervirens suggests the presence of non-hydrolysable tannins or abundant polyphenolic moieties not previously...
Categories: Publication; Types: Citation; Tags: New Phytologist
• Theoretical and empirical research has supported the hypothesis that plant–plant interactions change from competition to facilitation with increasing abiotic stress. However, the consistency of such changes has been questioned in arid and semiarid ecosystems. • During a drought in the semiarid south-western USA, we used observations and a field experiment to examine the interactions between juveniles of a foundation tree (Pinyon pine, Pinus edulis ) and a common shrub (Apache plume, Fallugia paradoxa ) in replicated areas of high and low stress. • The presence of F. paradoxa reduced P. edulis performance at low-stress sites, but had the opposite effect at high-stress sites. However, the intensity of the...
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Tree mortality rates appear to be increasing in moist tropical forests (MTFs) with significant carbon cycle consequences. Here, we review the state of knowledge regarding MTF tree mortality, create a conceptual framework with testable hypotheses regarding the drivers, mechanisms and interactions that may underlie increasing MTF mortality rates, and identify the next steps for improved understanding and reduced prediction. Increasing mortality rates are associated with rising temperature and vapor pressure deficit, liana abundance, drought, wind events, fire and, possibly, CO2 fertilization‐induced increases in stand thinning or acceleration of trees reaching larger, more vulnerable heights. The majority of these...
Categories: Publication; Types: Citation; Tags: New Phytologist
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In semiarid western North American riparian ecosystems, increased drought and lower streamflows under climate change may reduce plant growth and recruitment, and favor drought-tolerant exotic species over mesic native species. We tested whether elevated atmospheric CO2 might ameliorate these effects by improving plant water-use efficiency. We examined the effects of CO2 and water availability on seedlings of two native (Populus deltoids spp. monilifera, Salix exigua) and three exotic (Elaeagnus angustifolia, Tamarix spp., Ulmus pumila) western North American riparian species in a CO2-controlled glasshouse, using 1-m-deep pots with different water-table decline rates. Low water availability reduced seedling biomass...
Categories: Publication; Types: Citation; Tags: New Phytologist
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? Rhizodeposition, or the addition of C from roots to soil C pools, is expected to increase if net primary production is stimulated and some excess C is allocated below-ground. We investigated the effects of 5 yrs of elevated CO2 on below-ground C dynamics in a native, C3?C4 grassland ecosystem in Colorado, USA. ? Cylinder harvests following each growing season and monolith excavation at the end of the experiment provided data on root biomass, root C : N ratios, and root and soil ?13C values. We applied an isotopic mixing model to quantify new soil C inputs on elevated and ambient CO2 treatments. ? Root biomass increased by 23% and root C : N ratios increased by 26% after 5 yrs of elevated CO2. Species-specific...
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* Vegetation change is expected with global climate change, potentially altering ecosystem function and climate feedbacks. However, causes of plant mortality, which are central to vegetation change, are understudied, and physiological mechanisms remain unclear, particularly the roles of carbon metabolism and xylem function. * We report analysis of foliar nonstructural carbohydrates (NSCs) and associated physiology from a previous experiment where earlier drought-induced mortality of Pinus edulis at elevated temperatures was associated with greater cumulative respiration. Here, we predicted faster NSC decline for warmed trees than for ambient-temperature trees. * Foliar NSC in droughted trees declined by 30% through...
Categories: Publication; Types: Citation; Tags: New Phytologist
The nitrogen-fixing lichen Pettigera aphthosa (L.) Willd. was treated under semi-natural conditions with simulated rain containing different combinations of ammonium, nitrate and sulphuric acid. Nitrogen in neutral solution had no negative effect on the nitrogen fixation rate. Sulphuric acid had a negative effect on nitrogen fixation rate, especially in combination with ammonium. The results could suggest an explanation for the sudden decline of P. aphthosa in southern Sweden. Published in New Phytologist, volume 120, issue 1, on pages 99 - 103, in 1992.
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Recently, widespread piñon pine die-off occurred in the southwestern United States. Here we synthesize observational studies of this event and compare findings to expected relationships with biotic and abiotic factors. Agreement exists on the occurrence of drought, presence of bark beetles and increased mortality of larger trees. However, studies disagree about the influences of stem density, elevation and other factors, perhaps related to study design, location and impact of extreme drought. Detailed information about bark beetles is seldom reported and their role is poorly understood. Our analysis reveals substantial limits to our knowledge regarding the processes that produce mortality patterns across space and...
Categories: Publication; Types: Citation; Tags: New Phytologist
Temperate and boreal forest ecosystems contain a large part of the carbon stored on land, in the form of both biomass and soil organic matter. Increasing atmospheric [CO2], increasing temperature, elevated nitrogen deposition and intensified management will change this C store. Well documented single-factor responses of net primary production are: higher photosynthetic rate (the main [CO2] response); increasing length of growing season (the main temperature response); and higher leaf-area index (the main N deposition and partly [CO2] response). Soil organic matter will increase with increasing litter input, although priming may decrease the soil C stock initially, but litter quality effects should be minimal (response...
Modern pollen assemblages from 18 small ponds and wetlands on the spatially isolated and forested Kaibab Plateau were studied to determine how the pollen assemblages recorded vegetation patterns. Vegetation of the Plateau consists of an inner core of subalpine Picea/Abies forests, surrounded by mixed Abies/Picea/Pseudotsuga/Pinus ponderosa forests, which are in turn surrounded by extensive Pinus ponderosa forests. The flanks of the Plateau are vegetated by Pinus edulis/Juniperus woodlands, with scattered Quercus populations. Arboreal pollen assemblages were dominated by Pinus (70-98%), which was most abundant in the P. ponderosa forests. Picea, Abies, Pseudotsuga and Populus pollen were abundant only at sites in...
* • Relative abundances of carbon and nitrogen isotopes in fungal sporocarps are useful in assessing mycorrhizal or saprotrophic status, and might provide insights into the evolutionary history of these traits. * • Sporocarps of known mycorrhizal or saprotrophic genera were collected at Woods Creek, OR, USA, and isotopically compared with foliage, litter, soils and wood collected from the same site. Possible trophic strategies were then isotopically assessed in archived specimens of the Pezizales of known molecular phylogeny from the western United States. * • At Woods Creek, mycorrhizal fungi were 3.5‰ ± 0.6‰ depleted in δ13C and 5.7‰ ± 0.4‰ enriched in δ15N compared with saprotrophic fungi. By...
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Understanding and predicting plant response to disturbance is of paramount importance in our changing world. Resprouting ability is often considered a simple qualitative trait and used in many ecological studies. Our aim is to show some of the complexities of resprouting while highlighting cautions that need be taken in using resprouting ability to predict vegetation responses across disturbance types and biomes. There are marked differences in resprouting depending on the disturbance type, and fire is often the most severe disturbance because it includes both defoliation and lethal temperatures. In the Mediterranean biome, there are differences in functional strategies to cope with water deficit between resprouters...
Categories: Publication; Types: Citation; Tags: New Phytologist
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Accumulating evidence highlights increased mortality risks for trees during severe drought, particularly under warmer temperatures and increasing vapour pressure deficit (VPD). Resulting forest die‐off events have severe consequences for ecosystem services, biophysical and biogeochemical land–atmosphere processes. Despite advances in monitoring, modelling and experimental studies of the causes and consequences of tree death from individual tree to ecosystem and global scale, a general mechanistic understanding and realistic predictions of drought mortality under future climate conditions are still lacking. We update a global tree mortality map and present a roadmap to a more holistic understanding of forest mortality...
Categories: Publication; Types: Citation; Tags: New Phytologist
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Mosses in northern ecosystems are ubiquitous components of plant communities, and strongly influence nutrient, carbon and water cycling. We use literature review, synthesis and model simulations to explore the role of mosses in ecological stability and resilience. Moss community responses to disturbance showed all possible responses (increases, decreases, no change) within most disturbance categories. Simulations from two process-based models suggest that northern ecosystems would need to experience extreme perturbation before mosses were eliminated. But simulations with two other models suggest that loss of moss will reduce soil carbon accumulation primarily by influencing decomposition rates and soil nitrogen...
Categories: Publication; Types: Citation; Tags: New Phytologist
Shifts from nitrogen (N)- to phosphorus (P)-limited growth due to high N deposition may alter the functioning of wetland vegetation. This experiment tested how N vs P deficiency affects the growth and nutrient use of wetland sedges. Five wetland Carex species were grown at nine N : P supply ratios (0.6-405) with two absolute levels of N and P. Biomass and nutrient concentrations were determined after one and two growing seasons. Shoot biomass was maximal at N : P supply ratios of 15-26 after one season but 5-15 after two seasons. Photosynthesis after the first season, second-year growth, leaf longevity, and the fraction of nutrient supply retained by plants over two seasons were all negatively related to N : P supply...
The pattern of incorporation of 14C into the thallus during incubation with H14CO3- in the light suggested that a substance in the 80% ethanol insoluble fraction, an unknown compound (probably a sugar phosphate) and glucose were intermediates in the transfer of carbon to the fungus. Results are presented which are consistent with the hypothesis that the alga releases a glucan which the fungus hydrolyses extra cellularly to form glucose. This glucose is then taken up by the fungus and converted to mannitol. Published in New Phytologist, volume 71, issue 1, on pages 31 - 39, in 1972.
When air-dry thalli of Hypogymnia physodes are immersed in water, four main features characterize the rewetting phase. (1) There is an immediate and substantial release of gas, the `wetting burst'. Although the released gas appears to be mostly CO2, it is non-metabolic in origin and probably the result of a previous adsorption of gas onto polysaccharide sheaths surrounding fungal hyphae. (2) There is a period of 1-2 h increased respiration, `resaturation respiration', which, unlike basal respiration, is cyanide-sensitive. The cause of resaturation respiration remains obscure, but could result from exposure of respiratory substrate to enzymes from which they are normally separated. (3) There is a brief period (1-2...
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??? This study examined the activity, species richness, and species composition of the arbuscular mycorrhizal fungal (AMF) community of Populus-Salix stands on the Verde River (Arizona, USA), quantified patterns of AMF richness and colonization along complex floodplain gradients, and identified environmental variables responsible for structuring the AMF community. ??? Samples from 61 Populus-Salix stands were analyzed for AMF and herbaceous composition, AMF colonization, gravimetric soil moisture, soil texture, per cent organic matter, pH, and concentrations of nitrate, bicarbonate phosphorus and exchangeable potassium. ??? AMF species richness declined with stand age and distance from and elevation above the channel...
Categories: Publication; Types: Citation; Tags: New Phytologist
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Understanding the degree to which nitrogen (N) availability limits land carbon (C) uptake under global environmental change represents an unresolved challenge. First-generation ‘C-only’vegetation models, lacking explicit representations of N cycling,projected a substantial and increasing land C sink under rising atmospheric CO2 concentrations. This prediction was questioned for not taking into account the potentially limiting effect of N availability, which is necessary for plant growth (Hungate et al.,2003). More recent global models include coupled C and N cycles in land ecosystems (C–N models) and are widely assumed to be more realistic. However, inclusion of more processes has not consistently improved their...
Categories: Publication; Types: Citation; Tags: New Phytologist
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Myriad field, laboratory, and modeling studies show that nutrient availability plays a fundamental role in regulating CO2 exchange between the Earth's biosphere and atmosphere, and in determining how carbon pools and fluxes respond to climatic change. Accordingly, global models that incorporate coupled climate–carbon cycle feedbacks made a significant advance with the introduction of a prognostic nitrogen cycle. Here we propose that incorporating phosphorus cycling represents an important next step in coupled climate–carbon cycling model development, particularly for lowland tropical forests where phosphorus availability is often presumed to limit primary production. We highlight challenges to including phosphorus...
Categories: Publication; Types: Citation; Tags: New Phytologist


map background search result map search result map Rhizodeposition stimulated by elevated CO2 in a semiarid grassland Rhizodeposition stimulated by elevated CO2 in a semiarid grassland