| 1. |
- Key, Timothy J., et al.
(författare)
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Carotenoids, retinol, tocopherols, and prostate cancer risk : pooled analysis of 15 studies
- 2015
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Ingår i: American Journal of Clinical Nutrition. - : Elsevier BV. - 0002-9165 .- 1938-3207. ; 102:5, s. 1142-1157
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Tidskriftsartikel (refereegranskat)abstract
- Background: Individual studies have suggested that circulating carotenoids, retinol, or tocopherols may be associated with prostate cancer risk, but the studies have not been large enough to provide precise estimates of associations, particularly by stage and grade of disease. Objective: The objective of this study was to conduct a pooled analysis of the associations of the concentrations of 7 carotenoids, retinol, alpha-tocopherol, and gamma-tocopherol with risk of prostate cancer and to describe whether any associations differ by stage or grade of the disease or other factors. Design: Principal investigators of prospective studies provided individual participant data for prostate cancer cases and controls. Risk by study-specific fifths of each biomarker was estimated by using multivariable-adjusted conditional logistic regression in matched case-control sets. Results: Data were available for up to 11,239 cases (including 1654 advanced stage and 1741 aggressive) and 18,541 controls from 15 studies. Lycopene was not associated with overall risk of prostate cancer, but there was statistically significant heterogeneity by stage of disease, and the OR for aggressive disease for the highest compared with the lowest fifth of lycopene was 0.65 (95% CI: 0.46, 0.91; P-trend = 0.032). No other carotenoid was significantly associated with overall risk of prostate cancer or with risk of advanced-stage or aggressive disease. For retinol, the OR for the highest compared with the lowest fifth was 1.13 (95% CI: 1.04, 1.22; P-trend = 0.015). For alpha-tocopherol, the OR for the highest compared with the lowest fifth was 0.86 (95% CI: 0.78, 0.94; P-trend < 0.001), with significant heterogeneity by stage of disease; the OR for aggressive prostate cancer was 0.74 (95% CI: 0.59, 0.92; P-trend = 0.001). gamma-Tocopherol was not associated with risk. Conclusions: Overall prostate cancer risk was positively associated with retinol and inversely associated with alpha-tocopherol, and risk of aggressive prostate cancer was inversely associated with lycopene and alpha-tocopherol. Whether these associations reflect causal relations is unclear.
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| 2. |
- Manzi, Olivier Jean Leonce, 1993, et al.
(författare)
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Drought stress recovery of hydraulic and photochemical processes in Neotropical tree saplings
- 2022
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Ingår i: Tree physiology. - : Oxford University Press (OUP). - 1758-4469. ; 42:1, s. 114-129
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Tidskriftsartikel (refereegranskat)abstract
- Climate models predict an increase in the severity and the frequency of droughts. Tropical forests are among the ecosystems that could be highly impacted by these droughts. Here, we explore how hydraulic and photochemical processes respond to drought stress and re-watering. We conducted a pot experiment on saplings of five tree species. Before the onset of drought, we measured a set of hydraulic traits, including minimum leaf conductance, leaf embolism resistance, and turgor loss point. During drought stress, we monitored traits linked to leaf hydraulic functioning (leaf water potential (ψmd) and stomatal conductance (gs)) and traits linked to leaf photochemical functioning (maximum quantum yield of photosystem II (Fv/Fm) and maximum electron transport rate (ETRmax)) at different wilting stages. After re-watering the same traits were measured after 3, 7, and 14days. Hydraulic trait values decreased faster than photochemical trait values. After re-watering, the values of the four traits recovered at different rates. Fv/Fm recovered very fast close to their initial values only three days after re-watering. This was followed by ETRmax, Ψmd and gs. Finally, we show that species with large stomatal and leaf safety margin and low πtlp are not strongly impacted by drought whereas they have a low recovery on photochemical efficiency. These results demonstrate that πtlp, stomatal and leaf safety margin are a good indicators of plant responses to drought stress and also to recovery for photochemical efficiency.
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| 3. |
- Ntawuhiganayo, E. B., et al.
(författare)
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Traits controlling shade tolerance in tropical montane trees
- 2020
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 40:2, s. 183-197
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Tidskriftsartikel (refereegranskat)abstract
- Tropical canopies are complex, with multiple canopy layers and pronounced gap dynamics contributing to their high species diversity and productivity. An important reason for this complexity is the large variation in shade tolerance among different tree species. At present, we lack a clear understanding of which plant traits control this variation, e.g., regarding the relative contributions of whole-plant versus leaf traits or structural versus physiological traits. We investigated a broad range of traits in six tropical montane rainforest tree species with different degrees of shade tolerance, grown under three different radiation regimes (under the open sky or beneath sparse or dense canopies). The two distinct shade-tolerant species had higher fractional biomass in leaves and branches while shade-intolerant species invested more into stems, and these differences were greater under low radiation. Leaf respiration and photosynthetic light compensation point did not vary with species shade tolerance, regardless of radiation regime. Leaf temperatures in open plots were markedly higher in shade-tolerant species due to their low transpiration rates and large leaf sizes. Our results suggest that interspecific variation in shade tolerance of tropical montane trees is controlled by species differences in whole-plant biomass allocation strategy rather than by difference in physiological leaf traits determining leaf carbon balance at low radiation.
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| 4. |
- Ziegler, Camille, et al.
(författare)
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Contrasting Dependencies of Photosynthetic Capacity on Leaf Nitrogen in Early- and Late-Successional Tropical Montane Tree Species
- 2020
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Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Differences in photosynthetic capacity among tree species and tree functional types are currently assumed to be largely driven by variation in leaf nutrient content, particularly nitrogen (N). However, recent studies indicate that leaf N content is often a poor predictor of variation in photosynthetic capacity in tropical trees. In this study, we explored the relative importance of area-based total leaf N content (N-tot) and within-leaf N allocation to photosynthetic capacity versus light-harvesting in controlling the variation in photosynthetic capacity (i.e.V-cmax,J(max)) among mature trees of 12 species belonging to either early (ES) or late successional (LS) groups growing in a tropical montane rainforest in Rwanda, Central Africa. Photosynthetic capacity at a common leaf temperature of 25x2da;C (i.e. maximum rates of Rubisco carboxylation,V(cmax25)and of electron transport,J(max25)) was higher in ES than in LS species (+ 58% and 68% forV(cmax25)andJ(max25), respectively). While N(tot)did not significantly differ between successional groups, the photosynthetic dependency on N(tot)was markedly different. In ES species,V(cmax25)was strongly and positively related to N(tot)but this was not the case in LS species. However, there was no significant trade-off between relative leaf N investments in compounds maximizing photosynthetic capacity versus compounds maximizing light harvesting. Both leaf dark respiration at 25x2da;C (+ 33%) and, more surprisingly, apparent photosynthetic quantum yield (+ 35%) was higher in ES than in LS species. Moreover, R(d25)was positively related to N(tot)for both ES and LS species. Our results imply that efforts to quantify carbon fluxes of tropical montane rainforests would be improved if they considered contrasting within-leaf N allocation and photosynthetic N(tot)dependencies between species with different successional strategies.
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