Which is a better predictor of plant traits: Temperature or precipitation?

Moles A.T., Perkins S.E., Laffan S.W., Flores-Moreno H., Awasthy M., Tindall M.L., Sack L., Pitman A., Kattge J., Aarssen L.W., Anand M., Bahn M., Blonder B., Cavender-Bares J., Cornelissen J.H.C., Cornwell W.K., Diaz S., Dickie J.B., Freschet G.T., Griffiths J.G., Gutierrez A.G., Hemmings F.A., Hickler T., Hitchcock T.D., Keighery M., Kleyer M., Kurokawa H., Leishman M.R., Liu K., Niinemets U., Onipchenko V., Onoda Y., Penuelas J., Pillar V.D., Reich P.B., Shiodera S., Siefert A., Sosinski E.E., Soudzilovskaia N.A., Swaine E.K., Swenson N.G., van Bodegom P.M., Warman L., Weiher E., Wright I.J., Zhang H., Zobel M., Bonser S.P. (2014) Which is a better predictor of plant traits: Temperature or precipitation?. Journal of Vegetation Science. : 0-0.
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Doi: 10.1111/jvs.12190

Resum:

Question: Are plant traits more closely correlated with mean annual temperature, or with mean annual precipitation? Location: Global. Methods: We quantified the strength of the relationships between temperature and precipitation and 21 plant traits from 447,961 species-site combinations worldwide. We used meta-analysis to provide an overall answer to our question. Results: Mean annual temperature was significantly more strongly correlated with plant traits than was mean annual precipitation. Conclusions: Our study provides support for some of the assumptions of classical vegetation theory, and points to many interesting directions for future research. The relatively low R2 values for precipitation might reflect the weak link between mean annual precipitation and the availability of water to plants. © 2014 International Association for Vegetation Science.

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Effects of past growth trends and current water use strategies on scots pine and pubescent oak drought sensitivity

Moran-Lopez T., Poyatos R., Llorens P., Sabate S. (2014) Effects of past growth trends and current water use strategies on scots pine and pubescent oak drought sensitivity. European Journal of Forest Research. 133: 369-382.
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Doi: 10.1007/s10342-013-0768-0

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Drought-induced decline is affecting Pinus sylvestris populations in southern Europe, with very little impact on the more drought-tolerant Quercus pubescens. Although multiple studies have investigated interspecific differences in water use and growth strategies, the link between these two processes and how they vary within drought-exposed populations remains poorly understood. Here, we analysed tree ring and sap flow data from P. sylvestris and Q. pubescens stands in the Pyrenees in order to (1) evaluate differences in climate-growth responses among species, (2) disentangle the role of past growth trends and water use strategies in individual trees drought sensitivity and (3) assess whether such intraspecific patterns vary between species. Both species have suffered recent climatic constraints related to increased aridity. However, the effects of past growth trends and current water use traits on drought sensitivity varied among them. Initially, fast-growing 'drought-sensitive' pines displayed a higher gas exchange potential but were more sensitive to evaporative demand and soil moisture. They also showed lower water use efficiency for growth (WUEBAI) and current growth decline. In contrast, initially, slow-growing 'drought-tolerant' pines showed the opposite water use traits and currently maintain the highest growth rates. In comparison, neither current WUEBAI nor recent growth trends varied across Q. pubescens climate-growth groups. Nonetheless, 'drought-sensitive' oaks showed the lowest gas exchange potential and the highest growth rates under milder conditions. Our results show a strong effect of past growth trends and current water use strategies on tree resilience to increased aridity, which is more evident in P. sylvestris. © Springer-Verlag Berlin Heidelberg 2013.

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The synergy of the 0.05° (∼5km) AVHRR long-term data record (LTDR) and landsat TM archive to map large fires in the North American boreal region from 1984 to 1998

Moreno-Ruiz J.A., Garcia-Lazaro J.R., Riano D., Kefauver S.C. (2014) The synergy of the 0.05° (∼5km) AVHRR long-term data record (LTDR) and landsat TM archive to map large fires in the North American boreal region from 1984 to 1998. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 7: 1157-1166.
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Doi: 10.1109/JSTARS.2013.2292853

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A Bayesian network classifier-based algorithm was applied to map the burned area (BA) in the North American boreal region using the 0.05\circ (\sim5\nbsp\hbox{km} ) Advanced Very High Resolution Radiometer (AVHRR) Long-Term Data Record (LTDR) data version 3 time series. The results showed an overall good agreement compared to reference maps (slope = 0.62;\ {R2} = 0.75 ). The study site was divided into six sub-regions, where south-western Canada performed the worst (slope = 0.25;\ {R2} = 0.47 ). The algorithm achieved good results as long as a year with high fire incidence was employed to train the Bayesian network, and the vegetation response to fire remained consistent across the region. Years with higher fire activity and larger fires, which were easier to detect at the LTDR spatial scale, matched the reference maps better. The LTDR postfire signal remained detectable for 6-9 years, extending opportunities to map the full fire extent with Landsat Thematic Mapper (TM). For fires larger than 1000\nbsp\hbox{km}2 , Landsat TM mapped 99%, whereas LTDR caught 69% of the reference BA reported. Landsat TM took four satellite overpasses (2 months) to map these large fires, and in some cases even until the following year, but LTDR detected them within days. Thus, results suggest that LTDR could be used to trigger the search for fires and then map their perimeter with Landsat TM. This study demonstrates an LTDR BA algorithm that could be extrapolated to other boreal regions using a similar methodology, although reference fire perimeters would be needed to train the Bayesian classifier and its thresholds. © 2008-2012 IEEE.

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A model of plant isoprene emission based on available reducing power captures responses to atmospheric CO2

Morfopoulos C., Sperlich D., Penuelas J., Filella I., Llusia J., Medlyn B.E., Niinemets U., Possell M., Sun Z., Prentice I.C. (2014) A model of plant isoprene emission based on available reducing power captures responses to atmospheric CO2. New Phytologist. 203: 125-139.
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Doi: 10.1111/nph.12770

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Summary: We present a unifying model for isoprene emission by photosynthesizing leaves based on the hypothesis that isoprene biosynthesis depends on a balance between the supply of photosynthetic reducing power and the demands of carbon fixation. We compared the predictions from our model, as well as from two other widely used models, with measurements of isoprene emission from leaves of Populus nigra and hybrid aspen (Populus tremula × P. tremuloides) in response to changes in leaf internal CO2 concentration (Ci) and photosynthetic photon flux density (PPFD) under diverse ambient CO2 concentrations (Ca). Our model reproduces the observed changes in isoprene emissions with Ci and PPFD, and also reproduces the tendency for the fraction of fixed carbon allocated to isoprene to increase with increasing PPFD. It also provides a simple mechanism for the previously unexplained decrease in the quantum efficiency of isoprene emission with increasing Ca. Experimental and modelled results support our hypothesis. Our model can reproduce the key features of the observations and has the potential to improve process-based modelling of isoprene emissions by land vegetation at the ecosystem and global scales. © 2014 New Phytologist Trust.

Llegeix més

Acorn - weevil interactions in a mixed-oak forest: Outcomes for larval growth and plant recruitment

Munoz A., Bonal R., Espelta J.M. (2014) Acorn - weevil interactions in a mixed-oak forest: Outcomes for larval growth and plant recruitment. Forest Ecology and Management. 322: 98-105.
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Doi: 10.1016/j.foreco.2014.02.039

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Weevils are the most important pre-dispersal acorn predators in the Mediterranean region, where oaks often form mixed forests and different weevil species can coexist. The performance of weevil larvae depends in great extent on their feeding activities inside the infested acorns that, in turn, are known to reduce the viability of acorns. In this paper, we have analysed the interactions among the weevil community and four oak species (Quercus pyrenaica, Quercus suber, Quercus faginea and Quercus ilex) coexisting in a Mediterranean mixed-oak forest. DNA sequencing of weevil larvae revealed four different weevil species (Curculio elephas, Curculio glandium, Curculio pellitus and Curculio venosus) infesting the acorns of the four oak species. Oak species differed in acorn size, and weevil species also differed in body size. Weevil species showed some degree of specificity among the four oak species, but specificity was not related to variations in acorn size. By contrast, larval development and seedling recruitment were mostly driven by inter-specific differences in larval and acorn size. Larger seeded species suffered less seed damages by weevils (i.e. embryo predation and cotyledon consumption), thus reducing the impacts of acorn infestation in seedling emergence and seedling size. Larval development for the largest weevil species C. elephas was constrained by cotyledon depletion in all acorn species. Yet, this pattern was not observed for other weevil species. Larval size of the same weevil species also varied among different oak species after controlling for the amount of cotyledon eaten by larvae, thus, variation of other acorn traits among acorn species (e.g. chemical composition) may also have consequences for the performance of weevil larvae. It is likely that other variables operating at population level, such as temporal and spatial changes in acorn production or phenological variations of weevils and oaks, are also implicated in the complex functioning of these outstanding mixed-oak forests where natural regeneration seems to be threatened. © 2014 Elsevier B.V.

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Adapting the optimal selective-logging of Scots pine (Pinus sylvestris L.) stands in NE Spain to increasing CO2 concentrations

Mur R.J., Goetz R.-U., Xabadia A., Cordoba F., Gracia C. (2014) Adapting the optimal selective-logging of Scots pine (Pinus sylvestris L.) stands in NE Spain to increasing CO2 concentrations. Journal of Forest Economics. 20: 286-304.
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Doi: 10.1016/j.jfe.2014.09.001

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Predicted increases in CO2 concentrations will affect forest ecosystems. In particular, they will impact tree growth, which in turn affects reproduction and mortality and consequently, forest planning. This study integrates different climate change scenarios of future biogeochemical processes and an economic model into a forest management model to determine the optimal selective-logging regime of Scots pine stands. It analyzes the economic implications of the management changes in comparison with the business as usual strategy. Adaption to new climatic conditions shows that it is optimal to increase the number of standing trees and to reduce the age of the logged trees. The results suggest that the failure to adapt the management regime has clear implications on the profitability of forests. Moreover, they show that higher mortality is likely to have a significant impact on the optimal forest management regime.

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Stem injection of 15N-NH4NO3 into mature Sitka spruce (Picea sitchensis)

Nair R., Weatherall A., Perks M., Mencuccini M. (2014) Stem injection of 15N-NH4NO3 into mature Sitka spruce (Picea sitchensis). Tree Physiology. 34: 1130-1140.
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Doi: 10.1093/treephys/tpu084

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Stem injection techniques can be used to introduce 15N into trees to overcome a low variation in natural abundance and label biomass with a distinct 15N signature, but have tended to target small and young trees, of a variety of species, with little replication. We injected 98 atom% 15N ammonium nitrate (NH4NO3) solution into 13 mature, 9- to 13-m tall edge-profile Sitka spruce trees in order to produce a large quantity of labelled litter, examining the distribution of the isotope throughout the canopy after felling in terms of both total abundance of 15N and relative distribution of the isotope throughout individual trees. Using a simple mass balance of the canopy alone, based on observed total needle biomass and modelled branch biomass, all of the isotope injected was accounted for, evenly split between needles and branches, but with a high degree of variability both within individual trees, and among trees. Both 15N abundance and relative within-canopy distribution were biased towards the upper and middle crown in foliage. Recovery of the label in branches was much more variable than in needles, possibly due to differences in nitrogen allocation for both growth and storage, which differ seasonally between foliage and woody biomass. © The Author 2014. Published by Oxford University Press.

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Physiological and antioxidant responses of Quercus ilex to drought in two different seasons

Nogues I., Llusia J., Ogaya R., Munne-Bosch S., Sardans J., Penuelas J., Loreto F. (2014) Physiological and antioxidant responses of Quercus ilex to drought in two different seasons. Plant Biosystems. 148: 268-278.
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Doi: 10.1080/11263504.2013.768557

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Climate change projections forecast a warming and an associated change in the distribution and intensity of rainfalls. In the case of the Mediterranean area, this will be reflected in more frequent and severe drought periods in the future. Within a long-term (9 years) manipulation experiment, we aimed to study the effect of the soil drought projected for the coming decades (an average of 10% soil moisture reduction) onto photosynthetic rates and water relations, and onto the antioxidant and anti-stress defense capacity of Quercus ilex, a dominant species in Mediterranean forests, in two different seasons, spring and summer. Results showed that photosynthesis was limited by stomatal closure in summer. However, a decrease in photosynthesis as a consequence of drought was observed only during spring, possibly due to a low pigment concentration and to an insufficient antioxidant protection. In summer, the increased resistance to CO2 entry reduced photosynthesis in control and drought-treated leaves, though the higher pigment content and antioxidant levels in summer leaves prevented a further decrease in photosynthesis as a consequence of drought. Also total monoterpene emission rates were higher in summer than in spring, though they did not change with drought, as happened with photosynthetic pigments. On the other hand, the antioxidant defense system was induced by drought in both studied seasons, indicating an efficient activation of defense responses aiming at scavenging reactive oxygen species produced in Q. ilex leaves under drought. © 2013 © 2013 Società Botanica Italiana.

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Foliar CO2 in a holm oak forest subjected to 15 years of climate change simulation

Ogaya R., Llusia J., Barbeta A., Asensio D., Liu D., Alessio G.A., Penuelas J. (2014) Foliar CO2 in a holm oak forest subjected to 15 years of climate change simulation. Plant Science. 226: 101-107.
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Doi: 10.1016/j.plantsci.2014.06.010

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A long-term experimental drought to simulate future expected climatic conditions for Mediterranean forests, a 15% decrease in soil moisture for the following decades, was conducted in a holm oak forest since 1999. Net photosynthetic rate, stomatal conductance and leaf water potential were measured from 1999 to 2013 in Quercus ilex and Phillyrea latifolia, two co-dominant species of this forest. These measurements were performed in four plots, two of them received the drought treatment and the two other plots were control plots. The three studied variables decreased with increases in VPD and decreases in soil moisture in both species, but the decrease of leaf water potential during summer drought was larger in P. latifolia, whereas Q. ilex reached higher net photosynthetic rates and stomatal conductance values during rainy periods than P. latifolia. The drought treatment decreased ca. 8% the net photosynthetic rates during the overall studied period in both Q. ilex and P. latifolia, whereas there were just non-significant trends toward a decrease in leaf water potential and stomatal conductance induced by drought treatment. Future drier climate may lead to a decrease in the carbon balance of Mediterranean species, and some shrub species well resistant to drought could gain competitive advantage relative to Q. ilex, currently the dominant species of this forest. © 2014 Elsevier Ireland Ltd.

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The effect of fungal pathogens on the water and carbon economy of trees: Implications for drought-induced mortality

Oliva J., Stenlid J., Martinez-Vilalta J. (2014) The effect of fungal pathogens on the water and carbon economy of trees: Implications for drought-induced mortality. New Phytologist. 203: 1028-1035.
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Doi: 10.1111/nph.12857

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[No abstract available]

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