| 1. |
- Purcell, C., et al.
(författare)
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Increasing stomatal conductance in response to rising atmospheric CO2
- 2018
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Ingår i: Annals of Botany. - : Oxford University Press (OUP). - 0305-7364 .- 1095-8290. ; 121:6, s. 1137-1149
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Tidskriftsartikel (refereegranskat)abstract
- Background and Aims Studies have indicated that plant stomatal conductance (g(s)) decreases in response to elevated atmospheric CO2, a phenomenon of significance for the global hydrological cycle. However, g(s) increases across certain CO2 ranges have been predicted by optimization models. The aim of this work was to demonstrate that under certain environmental conditions, g(s) can increase in response to elevated CO2. Methods Using (1) an extensive, up-to-date synthesis of g(s) responses in free air CO2 enrichment (FACE) experiments, (2) in situ measurements across four biomes showing dynamic g(s) responses to a CO2 rise of similar to 50 ppm (characterizing the change in this greenhouse gas over the past three decades) and (3) a photosynthesis-stomatal conductance model, it is demonstrated that g(s) can in some cases increase in response to increasing atmospheric CO2. Key Results Field observations are corroborated by an extensive synthesis of g(s) responses in FACE experiments showing that 11.8 % of g(s) responses under experimentally elevated CO2 are positive. They are further supported by a strong data-model fit (r(2) = 0.607) using a stomatal optimization model applied to the field g(s) dataset. A parameter space identified in the Farquhar-Ball-Berry photosynthesis-stomatal conductance model confirms field observations of increasing g(s) under elevated CO2 in hot dry conditions. Contrary to the general assumption, positive g(s) responses to elevated CO2, although relatively rare, are a feature of woody taxa adapted to warm, low-humidity conditions, and this response is also demonstrated in global simulations using the Community Land Model (CLM4). Conclusions The results contradict the over-simplistic notion that global vegetation always responds with decreasing g(s) to elevated CO2, a finding that has important implications for predicting future vegetation feedbacks on the hydrological cycle at the regional level.
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| 2. |
- Reber, A, et al.
(författare)
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The expression and impact of antifungal grooming in ants.
- 2011
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 24:5, s. 954-64
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Tidskriftsartikel (refereegranskat)abstract
- Parasites can cause extensive damage to animal societies in which many related individuals frequently interact. In response, social animals have evolved diverse individual and collective defences. Here, we measured the expression and efficiency of self-grooming and allo-grooming when workers of the ant Formica selysi were contaminated with spores of the fungal entomopathogen Metarhizium anisopliae. The amount of self-grooming increased in the presence of fungal spores, which shows that the ants are able to detect the risk of infection. In contrast, the amount of allo-grooming did not depend on fungal contamination. Workers groomed all nestmate workers that were re-introduced into their groups. The amount of allo-grooming towards noncontaminated individuals was higher when the group had been previously exposed to the pathogen. Allo-grooming decreased the number of fungal spores on the surface of contaminated workers, but did not prevent infection in the conditions tested (high dose of spores and late allo-grooming). The rate of disease transmission to groomers and other nestmates was extremely low. The systematic allo-grooming of all individuals returning to the colony, be they contaminated or not, is probably a simple but robust prophylactic defence preventing the spread of fungal diseases in insect societies.
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| 3. |
- Reeves, Jessica M., et al.
(författare)
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Palaeoenvironmental change in tropical Australasia over the last 30,000 years - a synthesis by the OZ-INTIMATE group
- 2013
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 74, s. 97-114
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Tidskriftsartikel (refereegranskat)abstract
- The tropics are the major source of heat and moisture for the Australasian region. Determining the tropics' response over time to changes in climate forcing mechanisms, such as summer insolation, and the effects of relative sea level on exposed continental shelves during the Last Glacial period, is an ongoing process of re-evaluation. We present a synthesis of climate proxy data from tropical Australasia spanning the last 30,000 years that incorporates deep sea core, coral, speleothem, pollen, charcoal and terrestrial sedimentary records. Today, seasonal variability is governed largely by the annual migration of the inter-tropical convergence zone (ITCZ), influencing this region most strongly during the austral summer. However, the position of the ITCZ has varied through time. Towards the end of Marine Isotope Stage (MIS) 3, conditions were far wetter throughout the region, becoming drier first in the south. Universally cooler land and sea-surface temperature (SST) were characteristic of the Last Glacial Maximum, with drier conditions than previously, although episodic wet periods are noted in the fluvial records of northern Australia. The deglacial period saw warming first in the Coral Sea and then the Indonesian seas, with a pause in this trend around the time of the Antarctic Cold Reversal (c. 14.5 ka), coincident with the flooding of the Sunda Shelf. Wetter conditions occurred first in Indonesia around 17 ka and northern Australia after 14 ka. The early Holocene saw a peak in marine SST to the northwest and northeast of Australia. Modern vegetation was first established on Indonesia, then progressively south and eastward to NE Australia. Flores and the Atherton Tablelands show a dry period around 11.6 ka, steadily becoming wetter through the early Holocene. The mid-late Holocene was punctuated by millennial-scale variability, associated with the El Nino-Southern Oscillation; this is evident in the marine, coral, speleothem and pollen records of the region.
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