| 1. |
- Henn, Jonathan, et al.
(author)
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Plant age affects intraspecific variation in functional traits
- 2021
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In: Plant Ecology. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 222:6, s. 669-680
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Journal article (peer-reviewed)abstract
- Functional traits are often used to examine ecological patterns and processes. Ontogeny-changes that occur over time as the result of development-generates variation in traits within individual organisms. We aimed to quantify the role of ontogeny in structuring functional trait variation across a range of co-existing herbaceous perennial species and hypothesized that ontogenetic variation in traits would be greater in younger vs. older plants. We grew eight herbaceous perennial forb species common in tallgrass prairies from seed in a greenhouse in Madison, Wisconsin, USA to determine how and when time-related variation in functional traits is large relative to other sources of variation, such as differences between leaves and species. We destructively measured common functional traits on four individuals of each species every two weeks for 19 weeks, including leaf mass fraction, root mass fraction, stem mass fraction, specific leaf area, leaf dry matter content, and leaf area. We found that most functional traits indeed change through time, that the direction of many changes are consistent between species but the magnitude of change is species specific, and most time-related variation occurred earlier in development. These results emphasize the importance of considering sampling timing and differences between young and old plants when measuring functional traits. Our results suggest that ontogenetic intraspecific variation can be substantial, especially early in life. It may be problematic to use traits measured from mature plants to interpret the importance of processes that occur at earlier life stages or vice versa; using seedling traits to understand adult plant responses may also be inappropriate.
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| 2. |
- Milberg, Per, et al.
(author)
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Site factors are more important than management for indicator species in semi-natural grasslands in southern Sweden
- 2020
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In: Plant Ecology. - : SPRINGER. - 1385-0237 .- 1573-5052. ; 221:7, s. 577-594
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Journal article (peer-reviewed)abstract
- Management of semi-natural grasslands is essential to retain the characteristic diversity of flora and fauna found in these habitats. To maintain, restore or recreate favourable conditions for grassland species, knowledge regarding how they occur in relation to grazing intensity and soil nutrient availability is crucial. We focused on grassland plant species, i.e., species selected to indicate high natural values in semi-natural grasslands. Environmental monitoring data collected at 366 grassland sites in southern Sweden between 2006 and 2010 were used to relate the occurrence of indicator species to factors describing geographic location, local site conditions related to nutrients and moisture, and management. Site productivity, soil moisture and cover of trees and shrubs were the main structuring factors, while other factors related to management had a lesser effect (grass sward height, amount of litter, type of grazer). Not surprisingly, these patterns were also reflected in species-wise analyses of the 25 most commonly occurring indicator species, with almost all species negatively related to site productivity and most also to soil moisture. Furthermore, many species were negatively affected by increasing sward height and litter. In contrast, species-wise responses varied among species in relation to increasing cover of trees and shrubs. In comparison to cattle grazing, sheep grazing was detrimental to six species and beneficial to none, while horse grazing was detrimental to no species and beneficial to four species. When evaluating species traits, taller plant species were favoured when site productivity, grass sward height and the amount of grass litter were high. There were no strong patterns related to the flowering time, leaf arrangement, or nutrient and light requirements of species. These results highlight the importance of nutrient-poor and dry sites, e.g., when selecting sites for conservation, and the importance of the type of management executed.
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| 3. |
- Nilsson Hegethorn, Marie-Charlotte
(author)
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Sphagnum and feather moss-associated N-2 fixation along a 724-year chronosequence in eastern boreal Canada
- 2021
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In: Plant Ecology. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 222, s. 1007-1022
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Journal article (peer-reviewed)abstract
- Dinitrogen (N-2) fixation associated with moss-dwelling bacteria (diazotrophs) is a N source in boreal forests. In feather moss-dominated understories of Fennoscandia, N-2 fixation rates increase with forest age due to N limitation. Whether this is applicable across different boreal ecosystems and successional pathways is not fully understood. In eastern Canada, increasing Sphagnum dominance starting about 100 years post-fire (paludification), is prevalent. Our main objectives were to determine how potential moss-associated N-2 fixation and relative contributions of Sphagnum and other mosses vary with time since fire and to explore the mechanisms driving observed patterns. Sampling was conducted in eight black spruce forests (Picea mariana; 64-724 years post-fire) in northwestern Quebec, Canada, along an established post-fire successional gradient. Potential N-2 fixation was measured with the acetylene reduction method in seven common moss species (Pleurozium schreberi, Hylocomium splendens, Dicranum polysetum, Sphagnum capillifolium, Sphagnum angustifolium, Sphagnum russowii, and Sphagnum magellanicum). N-2 fixation rates by moss communities were low and seemed to increase with stand age, but large variability was found between sites and species. The mechanisms underlying N-2 fixation rates were related to a switch in moss communities from feather moss to a Sphagnum dominance, which had the highest individual acetylene reduction rates, and to an increasing frequency of N-2-fixing samples in old forests. This study provided one of the first records of moss-associated N-2 fixation in eastern Canada and offers insights into how regional and cross-continental differences in moss community composition determine N cycling in boreal forests.
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