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1.
Charlotte C. Reed Ashley P. Ballantyne Leila Annie Cooper Anna Sala 《Global Change Biology》2018,24(9):3922-3937
Forests sequester large amounts of carbon annually and are integral in buffering against effects of global change. Increasing atmospheric CO2 may enhance photosynthesis and/or decrease stomatal conductance (gs) thereby enhancing intrinsic water‐use efficiency (iWUE), having potential indirect and direct benefits to tree growth. While increasing iWUE has been observed in most trees globally, enhanced growth is not ubiquitous, possibly due to concurrent climatic constraints on growth. To investigate our incomplete understanding of interactions between climate and CO2 and their impacts on tree physiology and growth, we used an environmental gradient approach. We combined dendrochronology with carbon isotope analysis (δ13C) to assess the covariation of basal area increment (BAI) and iWUE over time in lodgepole pine. Trees were sampled at 18 sites spanning two climatically distinct elevation transects on the lee and windward sides of the Continental Divide, encompassing the majority of lodgepole pine's northern Rocky Mountain elevational range. We analyzed BAI and iWUE from 1950 to 2015, and explored correlations with monthly climate variables. As expected, iWUE increased at all sites. However, concurrent growth trends depended on site climatic water deficit (CWD). Significant growth increases occurred only at the driest sites, where increases in iWUE were strongest, while growth decreases were greatest at sites where CWD has been historically lowest. Late summer drought of the previous year negatively affected growth across sites. These results suggest that increasing iWUE, if strong enough, may indirectly benefit growth at drier sites by effectively extending the growing season via reductions in gs. Strong growth decreases at high elevation windward sites may reflect increasing water stress as a result of decreasing snowpack, which was not offset by greater iWUE. Our results imply that increasing iWUE driven by decreasing gs may benefit tree growth in limited scenarios, having implications for future carbon uptake potential of semiarid ecosystems. 相似文献
2.
The Arctic is particularly sensitive to climate change, but the independent effects of increasing atmospheric CO2 concentration (pCO2) and temperature on high‐latitude forests are poorly understood. Here, we present a new, annually resolved record of stable carbon isotope (δ13C) data determined from Larix cajanderi tree cores collected from far northeastern Siberia in order to investigate the physiological response of these trees to regional warming. The tree‐ring record, which extends from 1912 through 1961 (50 years), targets early twentieth‐century warming (ETCW), a natural warming event in the 1920s to 1940s that was limited to Northern hemisphere high latitudes. Our data show that net carbon isotope fractionation (Δ13C), decreased by 1.7‰ across the ETCW, which is consistent with increased water stress in response to climate warming and dryer soils. To investigate whether this signal is present across the northern boreal forest, we compiled published carbon isotope data from 14 high‐latitude sites within Europe, Asia, and North America. The resulting dataset covered the entire twentieth century and spanned both natural ETCW and anthropogenic Late Twentieth‐Century Warming (~0.7 °C per decade). After correcting for a ~1‰ increase in Δ13C in response to twentieth century pCO2 rise, a significant negative relationship (r = ?0.53, P < 0.0001) between the average, annual Δ13C values and regional annual temperature anomalies is observed, suggesting a strong control of temperature on the Δ13C value of trees growing at high latitudes. We calculate a 17% increase in intrinsic water‐use efficiency within these forests across the twentieth century, of which approximately half is attributed to a decrease in stomatal conductance in order to conserve water in response to drying conditions, with the other half being attributed to increasing pCO2. We conclude that annual tree‐ring records from northern high‐latitude forests record the effects of climate warming and pCO2 rise across the twentieth century. 相似文献
3.
A. Fajardo 《Plant biology (Stuttgart, Germany)》2018,20(3):456-464
- The wood economics spectrum provides a general framework for interspecific trait–trait coordination across wide environmental gradients. Whether global patterns are mirrored within species constitutes a poorly explored subject. In this study, I first determined whether wood density co‐varies together with elevation, tree growth and height at the within‐species level. Second, I determined the variation of wood density in different stem parts (trunk, branch and twigs).
- In situ trunk sapwood, trunk heartwood, branch and twig densities, in addition to stem growth rates and tree height were determined in adult trees of Nothofagus pumilio at four elevations in five locations spanning 18° of latitude. Mixed effects models were fitted to test relationships among variables.
- The variation in wood density reported in this study was narrow (ca. 0.4–0.6 g cm?3) relative to global density variation (ca. 0.3–1.0 g cm?3). There was no significant relationship between stem growth rates and wood density. Furthermore, the elevation gradient did not alter the wood density of any stem part. Trunk sapwood density was negatively related to tree height. Twig density was higher than branch and trunk densities. Trunk heartwood density was always significantly higher than sapwood density.
- Negative across‐species trends found in the growth–wood density relationship may not emerge as the aggregate of parallel intraspecific patterns. Actually, trees with contrasting growth rates show similar wood density values. Tree height, which is tightly related to elevation, showed a negative relationship with sapwood density.
4.
In the 45 years after legislation of the Clean Air Act, there has been tremendous progress in reducing acidic air pollutants in the eastern United States, yet limited evidence exists that cleaner air has improved forest health. Here, we investigate the influence of recent environmental changes on the growth and physiology of red spruce (Picea rubens Sarg.) trees, a key indicator species of forest health, spanning three locations along a 100 km transect in the Central Appalachian Mountains. We incorporated a multiproxy approach using 75‐year tree ring chronologies of basal tree growth, carbon isotope discrimination (?13C, a proxy for leaf gas exchange), and δ15N (a proxy for ecosystem N status) to examine tree and ecosystem level responses to environmental change. Results reveal the two most important factors driving increased tree growth since ca. 1989 are reductions in acidic sulfur pollution and increases in atmospheric CO2, while reductions in pollutant emissions of NOx and warmer springs played smaller, but significant roles. Tree ring ?13C signatures increased significantly since 1989, concurrently with significant declines in tree ring δ15N signatures. These isotope chronologies provide strong evidence that simultaneous changes in C and N cycling, including greater photosynthesis and stomatal conductance of trees and increases in ecosystem N retention, were related to recent increases in red spruce tree growth and are consequential to ecosystem recovery from acidic pollution. Intrinsic water use efficiency (iWUE) of the red spruce trees increased by ~51% across the 75‐year chronology, and was driven by changes in atmospheric CO2 and acid pollution, but iWUE was not linked to recent increases in tree growth. This study documents the complex environmental interactions that have contributed to the recovery of red spruce forest ecosystems from pervasive acidic air pollution beginning in 1989, about 15 years after acidic pollutants started to decline in the United States. 相似文献
5.
Robert J. Twohey Lucas M. Roberts Anthony J. Studer 《The Plant journal : for cell and molecular biology》2019,97(3):475-484
The increasing demand for food production and predicted climate change scenarios highlight the need for improvements in crop sustainability. The efficient use of water will become increasingly important for rain‐fed agricultural crops even in fertile regions that have historically received ample precipitation. Improvements in water‐use efficiency in Zea mays have been limited, and warrant a renewed effort aided by molecular breeding approaches. Progress has been constrained by the difficulty of measuring water‐use in a field environment. The stable carbon isotope composition (δ13C) of the leaf has been proposed as an integrated signature of carbon fixation with a link to stomatal conductance. However, additional factors affecting leaf δ13C exist, and a limited number of studies have explored this trait in Z. mays. Here we present an extensive characterization of leaf δ13C in Z. mays. Significant variation in leaf δ13C exists across diverse lines of Z. mays, which we show to be heritable across several environments. Furthermore, we examine temporal and spatial variation in leaf δ13C to determine the optimum sampling time to maximize the use of leaf δ13C as a trait. Finally, our results demonstrate the relationship between transpiration and leaf δ13C in the field and the greenhouse. Decreasing transpiration and soil moisture are associated with decreasing leaf δ13C. Taken together these results outline a strategy for using leaf δ13C and reveal its usefulness as a measure of transpiration efficiency under well‐watered conditions rather than a predictor of performance under drought. 相似文献
6.
CHARLES A. NOCK PATRICK J. BAKER WOLFGANG WANEK ALBRECHT LEIS MICHAEL GRABNER SARAYUDH BUNYAVEJCHEWIN PETER HIETZ 《Global Change Biology》2011,17(2):1049-1063
Rising atmospheric carbon dioxide [CO2] can accelerate tree growth by stimulating photosynthesis and increasing intrinsic water‐use efficiency (iWUE). Little evidence exists, however, for the long‐term growth and gas‐exchange responses of mature trees in tropical forests to the combined effects of rising [CO2] and other global changes such as warming. Using tree rings and stable isotopes of carbon and oxygen, we investigated long‐term trends in the iWUE and stem growth (basal area increment, BAI) of three canopy tree species in a tropical monsoon forest in western Thailand (Chukrasia tabularis, Melia azedarach, and Toona ciliata). To do this, we modelled the contribution of ontogenetic effects (tree diameter or age) and calendar year to variation in iWUE, oxygen isotopes, and BAI using mixed‐effects models. Although iWUE increased significantly with both tree diameter and calendar year in all species, BAI at a given tree diameter was lower in more recent years. For one species, C. tabularis, differences in crown dominance significantly influence stable isotopes and growth. Tree ring Δ18O increased with calendar year in all species, suggesting that increasing iWUE may have been driven by relatively greater reductions in stomatal conductance – leading to enrichment in Δ18O – than increases in photosynthetic capacity. Plausible explanations for the observed declines in growth include water stress resulting from rising temperatures and El Niño events, increased respiration, changes in allocation, or more likely, a combination of these factors. 相似文献
7.
A. Magnin C. D. Torres R. Villalba J. G. Puntieri 《Plant biology (Stuttgart, Germany)》2017,19(6):917-925
- The extent to which a vertical trunk is differentiated from its branches is a key trait for the architecture of trees and may affect interspecific relationships.
- In this study, we analysed the effect of soil water availability on biomass partitioning for Nothofagus pumilio by means of a nursery experiment. Juvenile trees were subject to three irrigation conditions: no irrigation, intermediate irrigation and high irrigation. Irrigation conditions emulated the mean precipitation of the most representative environments inhabited by N. pumilio.
- Changes in soil water availability modified the biomass partitioning patterns of trees. In comparison to the other two conditions, high irrigation caused: (i) a higher ratio of biomass partitioning to stems than roots; (ii) more trunk growth in relation to its branches; and (iii) more photosynthetic organs relative to the aboveground biomass. Trunk size relative to that of its most recent branches was not increased by water availability.
- Water availability may play a significant role in the capacity of N. pumilio for space occupation due to the effects on axis differentiation.
8.
The rise in atmospheric CO2 concentrations (Ca) has been related to tree growth enhancement and increasing intrinsic water‐use efficiency (iWUE). However, the extent that rising Ca has led to increased long‐term iWUE and whether climate could explain deviations from expected Ca‐induced growth enhancement are still poorly understood. The aim of this research was to use Ca and local climatic variability to explain changes during the 20th century in growth and tree ring and needle δ13C in declining and nondeclining Abies alba stands from the Spanish Pyrenees, near the southern distribution limit of this species. The temporal trends of iWUE were calculated under three theoretical scenarios for the regulation of plant‐gas exchange at increasing Ca. We tested different linear mixed‐effects models by multimodel selection criteria to predict basal area increment (BAI), a proxy of tree radial growth, using these scenarios and local temperature together with precipitation data as predictors. The theoretical scenario assuming the strongest response to Ca explained 66–81% of the iWUE variance and 28–56% of the observed BAI variance, whereas local climatic variables together explained less than 11–21% of the BAI variance. Our results are consistent with a drought‐induced limitation of the tree growth response to rising CO2 and a decreasing rate of iWUE improvement from the 1980s onward in declining A. alba stands subjected to lower water availability. 相似文献
9.
10.
JORDI VOLTAS JESÚS JULIO CAMARERO DAVID CARULLA MÒNICA AGUILERA ARACELI ORTIZ JUAN PEDRO FERRIO 《Plant, cell & environment》2013,36(8):1435-1448
Winter‐drought induced forest diebacks in the low‐latitude margins of species' distribution ranges can provide new insights into the mechanisms (carbon starvation, hydraulic failure) underlying contrasting tree reactions. We analysed a winter‐drought induced dieback at the Scots pine's southern edge through a dual‐isotope approach (Δ13C and δ18O in tree‐ring cellulose). We hypothesized that a differential long‐term performance, mediated by the interaction between CO2 and climate, determined the fates of individuals during dieback. Declining trees showed a stronger coupling between climate, growth and intrinsic water‐use efficiency (WUEi) than non‐declining individuals that was noticeable for 25 years prior to dieback. The rising stomatal control of water losses with time in declining trees, indicated by negative Δ13C‐δ18O relationships, was likely associated with their native aptitude to grow more and take up more water (suggested by larger tracheid lumen widths) than non‐declining trees and, therefore, to exhibit a greater cavitation risk. Freeze‐thaw episodes occurring in winter 2001 unveiled such physiological differences by triggering dieback in those trees more vulnerable to hydraulic failure. Thus, WUEi tightly modulated growth responses to long‐term warming in declining trees, indicating that co‐occurring individuals were differentially predisposed to winter‐drought mortality. These different performances were unconnected to the depletion of stored carbohydrates. 相似文献
11.
Teresa E. Gimeno Tim R. McVicar Anthony P. O'Grady David T. Tissue David S. Ellsworth 《Global Change Biology》2018,24(7):3010-3024
Elevated atmospheric CO2 concentration (eCa) might reduce forest water‐use, due to decreased transpiration, following partial stomatal closure, thus enhancing water‐use efficiency and productivity at low water availability. If evapotranspiration (Et) is reduced, it may subsequently increase soil water storage (ΔS) or surface runoff (R) and drainage (Dg), although these could be offset or even reversed by changes in vegetation structure, mainly increased leaf area index (L). To understand the effect of eCa in a water‐limited ecosystem, we tested whether 2 years of eCa (~40% increase) affected the hydrological partitioning in a mature water‐limited Eucalyptus woodland exposed to Free‐Air CO2 Enrichment (FACE). This timeframe allowed us to evaluate whether physiological effects of eCa reduced stand water‐use irrespective of L, which was unaffected by eCa in this timeframe. We hypothesized that eCa would reduce tree‐canopy transpiration (Etree), but excess water from reduced Etree would be lost via increased soil evaporation and understory transpiration (Efloor) with no increase in ΔS, R or Dg. We computed Et, ΔS, R and Dg from measurements of sapflow velocity, L, soil water content (θ), understory micrometeorology, throughfall and stemflow. We found that eCa did not affect Etree, Efloor, ΔS or θ at any depth (to 4.5 m) over the experimental period. We closed the water balance for dry seasons with no differences in the partitioning to R and Dg between Ca levels. Soil temperature and θ were the main drivers of Efloor while vapour pressure deficit‐controlled Etree, though eCa did not significantly affect any of these relationships. Our results suggest that in the short‐term, eCa does not significantly affect ecosystem water‐use at this site. We conclude that water‐savings under eCa mediated by either direct effects on plant transpiration or by indirect effects via changes in L or soil moisture availability are unlikely in water‐limited mature eucalypt woodlands. 相似文献
12.
Jessica A. Kettenbach Nicole Miller‐Struttmann Zoë Moffett Candace Galen 《Ecology and evolution》2017,7(17):6963-6971
Under climate change, shrubs encroaching into high altitude plant communities disrupt ecosystem processes. Yet effects of encroachment on pollination mutualisms are poorly understood. Here, we probe potential fitness impacts of interference from encroaching Salix (willows) on pollination quality of the alpine skypilot, Polemonium viscosum. Overlap in flowering time of Salix and Polemonium is a precondition for interference and was surveyed in four extant and 25 historic contact zones. Pollinator sharing was ascertained from observations of willow pollen on bumble bees visiting Polemonium flowers and on Polemonium pistils. We probed fitness effects of pollinator sharing by measuring the correlation between Salix pollen contamination and seed set in naturally pollinated Polemonium. To ascertain whether Salix interference occurred during or after pollination, we compared seed set under natural pollination, conspecific pollen addition, and Salix pollen addition. In current and past contact zones Polemonium and Salix overlapped in flowering time. After accounting for variance in flowering date due to latitude, Salix and Polemonium showed similar advances in flowering under warmer summers. This trend supports the idea that sensitivity to temperature promotes reproductive synchrony in both species. Salix pollen is carried by bumble bees when visiting Polemonium flowers and accounts for up to 25% of the grains on Polemonium pistils. Salix contamination correlates with reduced seed set in nature and when applied experimentally. Postpollination processes likely mediate these deleterious effects as seed set in nature was not limited by pollen delivery. Synthesis: As willows move higher with climate change, we predict that they will drive postpollination interference, reducing the fitness benefits of pollinator visitation for Polemonium and selecting for traits that reduce pollinator sharing. 相似文献
13.
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. 相似文献
14.
Amaru Magnin Ricardo Villalba Cristian Daniel Torres Marina Stecconi Alfredo Passo Claudia Maricel Sosa Javier Guido Puntieri 《Austral ecology》2017,42(1):103-112
Extreme environmental events such as volcanic eruptions can trigger plant responses that largely exceed those recorded for moderate‐intensity disturbances. We assessed the effects of the June 2011 eruption of the Puyehue – Cordón Caulle volcano on the length and radial growths of juvenile Nothofagus pumilio trees at two sites located 20 (with >40 cm ash accretion) and 75 (without ash) km from the volcano. Variations in length and radial growth were evaluated for the periods 1999–2013 and 1993–2013 respectively; pre‐ and post‐eruption growth rates were computed. The length growth of the N. pumilio trees located close to the volcano increased significantly after the eruption: shoot extensions during the growing season after the eruption were, on average, two to three times longer than average according to ontogenetic growth trends. Variations in radial growth after the eruption were comparatively less noticeable than those in length growth. No significant effects of the eruption were observed in those trees located 75 km from the volcano. In order to explain the exceptionally positive response of N. pumilio's length growth to the volcanic eruption, three non‐exclusive explanations were proposed: (i) thick ash layers increase water retention in the soil; (ii) volcanic ash facilitates the access of plants to nutrients; and (iii) volcanic ashes decrease herbivory and competition. The comparatively lower sensitivity of radial growth to this extreme volcanic event is also noteworthy. These findings highlight the need to further examine how large‐scale volcanic events influence structure and/or functioning of ecosystem in the Patagonian forest. 相似文献
15.
Aníbal Pauchard Adrián Escudero Rafael A. García Marcelino de la Cruz Bárbara Langdon Lohengrin A. Cavieres Jocelyn Esquivel 《Ecology and evolution》2016,6(2):447-459
Understanding biological invasions patterns and mechanisms is highly needed for forecasting and managing these processes and their negative impacts. At small scales, ecological processes driving plant invasions are expected to produce a spatially explicit pattern driven by propagule pressure and local ground heterogeneity. Our aim was to determine the interplay between the intensity of seed rain, using distance to a mature plantation as a proxy, and microsite heterogeneity in the spreading of Pinus contorta in the treeless Patagonian steppe. Three one‐hectare plots were located under different degrees of P. contorta invasion (Coyhaique Alto, 45° 30′S and 71° 42′W). We fitted three types of inhomogeneous Poisson models to each pine plot in an attempt for describing the observed pattern as accurately as possible: the “dispersal” models, “local ground heterogeneity” models, and “combined” models, using both types of covariates. To include the temporal axis in the invasion process, we analyzed both the pattern of young and old recruits and also of all recruits together. As hypothesized, the spatial patterns of recruited pines showed coarse scale heterogeneity. Early pine invasion spatial patterns in our Patagonian steppe site is not different from expectations of inhomogeneous Poisson processes taking into consideration a linear and negative dependency of pine recruit intensity on the distance to afforestations. Models including ground‐cover predictors were able to describe the point pattern process only in a couple of cases but never better than dispersal models. This finding concurs with the idea that early invasions depend more on seed pressure than on the biotic and abiotic relationships seed and seedlings establish at the microsite scale. Our results show that without a timely and active management, P. contorta will invade the Patagonian steppe independently of the local ground‐cover conditions. 相似文献
16.
Lupe León‐Sánchez Emilio Nicolás Pedro A. Nortes Fernando T. Maestre José I. Querejeta 《Ecology and evolution》2016,6(9):2725-2738
Whereas warming enhances plant nutrient status and photosynthesis in most terrestrial ecosystems, dryland vegetation is vulnerable to the likely increases in evapotranspiration and reductions in soil moisture caused by elevated temperatures. Any warming‐induced declines in plant primary production and cover in drylands would increase erosion, land degradation, and desertification. We conducted a four‐year manipulative experiment in a semi‐arid Mediterranean ecosystem to evaluate the impacts of a ~2°C warming on the photosynthesis, transpiration, leaf nutrient status, chlorophyll content, isotopic composition, biomass growth, and postsummer survival of the native shrub Helianthemum squamatum. We predicted that warmed plants would show reduced photosynthetic activity and growth, primarily due to the greater stomatal limitation imposed by faster and more severe soil drying under warming. On average, warming reduced net photosynthetic rates by 36% across the study period. Despite this strong response, warming did not affect stomatal conductance and transpiration. The reduction of peak photosynthetic rates with warming was more pronounced in a drought year than in years with near‐average rainfall (75% and 25–40% reductions relative to controls, respectively), with no indications of photosynthetic acclimation to warming through time. Warmed plants had lower leaf N and P contents, δ13C, and sparser and smaller leaves than control plants. Warming reduced shoot dry mass production by 31%. However, warmed plants were able to cope with large reductions in net photosynthesis, leaf area, and shoot biomass production without changes in postsummer survival rates. Our findings highlight the key role of nonstomatal factors (biochemical and/or nutritional) in reducing net carbon assimilation rates and growth under warming, which has important implications for projections of plant carbon balance under the warmer and drier climatic scenario predicted for drylands worldwide. Projected climate warming over the coming decades could reduce net primary production by about one‐third in semi‐arid gypsum shrublands dominated by H. squamatum. 相似文献
17.
Marko J. Spasojevic Susan Harrison Howard W. Day Randal J. Southard 《Ecology letters》2014,17(6):700-709
One important but largely unanswered question about floristic responses to climate change is how interactions such as competition, facilitation and plant–soil feedbacks will influence the ability of species to track shifting climates. In a rugged and moisture‐limited region that has recently warmed by 2° (Siskiyou Mountains, OR, USA), we planted three species into cooler aspects and elevations than those they currently inhabit, with and without removal of neighbouring plants, and tracked them over 2 years. Two species had higher success in cooler topographic locations, and this success was enhanced by neighbouring plants, which appeared to modulate minimum growing season temperatures. One species' success was also facilitated by the higher soil organic matter found in cooler sites. These results are a novel experimental demonstration of two important factors that may buffer climate change impacts on plants: rugged topography and plant–plant facilitation. 相似文献
18.
Alireza Houshmandfar Noboru Ota Garry J. O'Leary Bangyou Zheng Yang Chen Sabine Tausz‐Posch Glenn J. Fitzgerald Richard Richards Greg J. Rebetzke Michael Tausz 《Global Change Biology》2020,26(7):4056-4067
Reducing the number of tillers per plant using a t iller in hibition (tin) gene has been considered as an important trait for wheat production in dryland environments. We used a spatial analysis approach with a daily time‐step coupled radiation and transpiration efficiency model to simulate the impact of the reduced‐tillering trait on wheat yield under different climate change scenarios across Australia's arable land. Our results show a small but consistent yield advantage of the reduced‐tillering trait in the most water‐limited environments both under current and likely future conditions. Our climate scenarios show that whilst elevated [CO2] (e[CO2]) alone might limit the area where the reduced‐tillering trait is advantageous, the most likely climate scenario of e[CO2] combined with increased temperature and reduced rainfall consistently increased the area where restricted tillering has an advantage. Whilst long‐term average yield advantages were small (ranged from 31 to 51 kg ha?1 year?1), across large dryland areas the value is large (potential cost‐benefits ranged from Australian dollar 23 to 60 MIL/year). It seems therefore worthwhile to further explore this reduced‐tillering trait in relation to a range of different environments and climates, because its benefits are likely to grow in future dry environments where wheat is grown around the world. 相似文献
19.
In the wet forests of Panama, El Niño typically brings a more prolonged and severe dry season. Interestingly, many trees and lianas that comprise the wet forests increase their productivity as a response to El Niño. Here, we quantify the abundance of migrating Marpesia chiron butterflies over 17 yr and the production of new leaves of their hostplants over 9 yr to test the generality of the El Niño migration syndrome, i.e., whether increased abundance of migrating insects and productivity of their food plants are associated with El Niño and La Niña events. We find that the quantity of M. chiron migrating across the Panama Canal was directly proportional to the sea surface temperature (SST) anomaly of the Pacific Ocean, which characterizes El Niño and La Niña events. We also find that production of new leaves by its larval host trees, namely Brosimum alicastrum, Artocarpus altilis, and Ficus citrifolia, was directly proportional to the SST anomaly, with greater leaf flushing occurring during the period of the annual butterfly migration that followed an El Niño event. Combining these and our previously published results for the migratory butterfly Aphrissa statira and its host lianas, we conclude that dry season rainfall and photosynthetically active radiation can serve as primary drivers of larval food production and insect population outbreaks in Neotropical wet forests, with drier years resulting in enhanced plant productivity and herbivore abundance. Insect populations should closely track changes in both frequency and amplitude of the El Niño Southern Oscillation with climate change. 相似文献
20.
Most research examining how herbivores and pathogens affect performance of invasive plants focuses on aboveground interactions. Although important, the role of belowground communities remains poorly understood, and the relative impact of aboveground and belowground interactions is still debated. As well, most studies of belowground interactions have been carried out in controlled environments, so little is known about the role of these interactions under natural conditions or how these relationships may change across a plant's range. Using the invasive plant Cirsium arvense, we performed a reciprocal transplant experiment to test the relative impacts of above‐ and belowground interactions at three sites across a 509‐km latitudinal gradient in its invaded range in Ontario, Canada. At each site, C. arvense seedlings were protected with above‐ and/or belowground exclosures in a factorial design. Plant performance (biomass, height, stem thickness, number of leaves, length of longest leaf, maximum rhizome length) was greatest when both above‐ and belowground exclosures were applied and lowest when no exclosures were applied. When only one type of exclosure was applied, biomass generally improved more with belowground exclosures than with aboveground exclosures. Despite site‐to‐site differences in foliar damage, root damage, and mesofaunal populations, belowground interactions generally had a greater negative impact on performance than aboveground herbivory alone. These results stress the importance of including both aboveground enemy interactions and plant–soil interactions in studies of plant community dynamics and invader performance. 相似文献