| 1. |
- Dusenge, Mirindi Eric, 1986, et al.
(författare)
-
Photosynthetic capacities of mature tropical forest trees in Rwanda are linked to successional group identity rather than to leaf nutrient content
- 2014
-
Ingår i: EGU General Assembly 2014, held 27 April - 2 May, 2014 in Vienna, Austria.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Tropical forests are crucial in the global carbon balance, yet information required to estimate how much carbon that enter these ecosystems through photosynthesis is very limited, in particular for Africa and for tropical montane forests. In order to increases the knowledge of natural variability of photosynthetic capacities in tropical tree species in tropical Africa, measurements of leaf traits and gas exchange were conducted on sun and shade leaves of ten tree species growing in two tropical forests in Rwanda in central Africa. Seven species were studied in Ruhande Arboretum, a forest plantation at mid altitude (ca 1700 m), and six species in Nyungwe National Park, a cooler and higher altitude (at ca 2500 m) montane rainforest. Three species were common to both sites. At Nyungwe, three species each belonged to the successional groups pioneer and climax species. Climax species had considerably lower maximum rates of photosynthetic carboxylation (Vcmax) and electron transport (Jmax) than pioneer species. This difference was not related to leaf nutrient content, but rather seemed to be caused by differences in within-leaf N allocation between the two successional groups. With respect to N, leaves of climax species invested less N into photosynthetic enzymes (as judged by lower Vcmax and Jmax values) and more N into chlorophyll (as judged by higher SPAD values). Photosynthetic capacities, (i.e., Jmax and Vcmax), Jmax:Vcmax ratio and P content were significantly higher in Nyungwe than in Arboretum. Sun leaves had higher photosynthetic capacities and nutrient content than shade leaves. Across the entire dataset, variation in photosynthetic capacities among species was not related to leaf nutrient content, although significant relationships were found within individual species. This study contributes critical tropical data for global carbon models and suggests that, for montane rainforest trees of different functional types, successional group identity is a better predictor of photosynthetic capacities than leaf nutrient content.
|
|
| 2. |
- Dusenge, Mirindi Eric, 1986, et al.
(författare)
-
Photosynthetic capacity of tropical montane tree species in relation to leaf nutrients, successional strategy and growth temperature
- 2015
-
Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 177:4, s. 1183-1194
-
Tidskriftsartikel (refereegranskat)abstract
- Photosynthetic capacity of tree leaves is typically positively related to nutrient content and little affected by changes in growth temperature. These relationships are, however, often poorly supported for tropical trees, for which interspecific differences may be more strongly controlled by within-leaf nutrient allocation than by absolute leaf nutrient content, and little is known regarding photosynthetic acclimation to temperature. To explore the influence of leaf nutrient status, successional strategy and growth temperature on the photosynthetic capacity of tropical trees, we collected data on photosynthetic, chemical and morphological leaf traits of ten tree species in Rwanda. Seven species were studied in a forest plantation at mid-altitude (~1,700 m), whereas six species were studied in a cooler montane rainforest at higher altitude (~2,500 m). Three species were common to both sites, and, in the montane rainforest, three pioneer species and three climax species were investigated. Across species, interspecific variation in photosynthetic capacity was not related to leaf nutrient content. Instead, this variation was related to differences in within-leaf nitrogen allocation, with a tradeoff between investments into compounds related to photosynthetic capacity (higher in pioneer species) versus light-harvesting compounds (higher in climax species). Photosynthetic capacity was significantly lower at the warmer site at 1,700 m altitude. We conclude that (1) within-leaf nutrient allocation is more important than leaf nutrient content per se in controlling interspecific variation in photosynthetic capacity among tree species in tropical Rwanda, and that (2) tropical montane rainforest species exhibit decreased photosynthetic capacity when grown in a warmer environment.
|
|
| 3. |
- Dusenge, Mirindi Eric, 1986, et al.
(författare)
-
Photosynthetic capacity of tropical montane tree species in relation to leaf nutrients, successional strategy and growth temperature
- 2015
-
Ingår i: 2015 Canadian Society of Plant Biologist/Eastern Regional meeting; University of Toronto, St George Campus, November 21-22nd, 2015.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Photosynthetic capacity of tree leaves is typically positively related to nutrient content and little affected by changes in growth temperature. These relationships are, however, often poorly supported for tropical trees, for which interspecific differences may be more controlled by within-leaf nutrient allocation than by absolute leaf nutrient content, and little is known regarding photosynthetic acclimation to temperature. To explore the influence of leaf nutrient status, successional strategy and growth temperature on the photosynthetic capacity of tropical trees, we collected data on photosynthetic, chemical and morphological leaf traits of ten tree species in Rwanda. Seven species were studied in a forest plantation at mid-altitude, whereas six species were studied in a cooler montane rainforest at higher altitude. Three species were common to both sites, and, in the montane rainforest, three pioneer species and three climax species were investigated. Across species, interspecific variation in photosynthetic capacity was not related to leaf nutrient content. Instead, this variation was related to differences in within-leaf nitrogen allocation, with a tradeoff between investments into compounds related to photosynthetic capacity (higher in pioneer species) versus light-harvesting compounds (higher in climax species). Photosynthetic capacity was significantly lower at the warmer site. We conclude that (1) within-leaf nutrient allocation is more important than leaf nutrient content per se in controlling interspecific variation in photosynthetic capacity among tree species in tropical Rwanda, and that (2) tropical montane rainforest species exhibit decreased photosynthetic capacity when grown in a warmer environment.
|
|
| 4. |
- Nsabimana, Donat, 1968
(författare)
-
Carbon stock and fluxes in Nyungwe forest and Ruhande Arboretum in Rwanda
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Conservation and sequestration of carbon in forest ecosystems are potential strategies to reduce or stabilize the atmospheric greenhouse gas concentrations and mitigate climate change. Estimating the... mer degree to which forest ecosystems may achieve that function requires continuous measurements of forest carbon stocks and fluxes from all over the world. The aim of this thesis was to collect quantitative data on climate, carbon stocks, annual carbon increment, litter production, and soil CO2 effluxes in Ruhande Arboretum, a plantation of both non-native and native tree species, and Nyungwe forest, a national park of afromontane tropical forest vegetation, both situated in Rwanda. The annual mean air temperature at the Ruhande Arboretum (19 ºC) was higher than in the Nyungwe forest (14.4 ºC), but both sites showed small seasonal variation in air temperature and Nyungwe forest received a higher monthly precipitation than the Ruhande Arboretum. The carbon stocks were dominated by above-ground biomass in both forests which was 70% in the Ruhande Arboretum and 57% in the Nyungwe forest. The annual litter production was 3.4 Mg C ha−1 yr−1, and followed a seasonal pattern. The mean annual soil CO2 efflux was 13.5 Mg C ha−1 yr−1 in the Ruhande Arboretum and 10.2 Mg C ha−1 yr−1 in the Nyungwe forest. No significant effect by the species on soil CO2 efflux was observed. The seasonal variation in soil CO2 efflux was strongly influenced by precipitation patterns and soil water content. Diurnal variation of soil CO2 efflux was bimodal and described a hysteresis relationship with soil temperature. Although, the daytime soil CO2 efflux correlated with soil temperature, the most of diurnal pattern was most likely affected by the supply of photosynthetic products to the roots. Spatial variation of soil CO2 efflux was mainly correlated to soil C and N stocks. The observed spatial, seasonal and annual soil CO2 effluxes were comparable to those observed in other tropical forests. This study should be replicated in other forests and in other land cover types in Rwanda, which can help to calculate a carbon balance for Rwanda.
|
|
| 5. |
- Nsabimana, Donat, 1968, et al.
(författare)
-
Soil carbon and nutrient accumulation under forest plantations in southern Rwanda
- 2008
-
Ingår i: African Journal of Environmental Science and Technology. - 1996-0786. ; 2:6, s. 142-149
-
Tidskriftsartikel (refereegranskat)abstract
- Tree and soil interactions may result in changes in soil carbon and nutrient contents. Forest plantations made up of monodominant stands of 17 different species, some native and some exotic to Rwanda, as well as a stand with mixed native tree species were investigated. Biosequential sampling was used followed by basic soil chemical analyses. Results revealed that the plantation species composition influenced the soil chemical properties. Total soil C and N, C: N ratio, available P, pH, and cation exchange capacity (CEC) differed significantly between plantation stands of different species (P < 0.001, N = 54). Increases in the levels of soil C, total N, CEC and base saturation (BS) were observed mainly in mixed native species (MNS), Polyscia fulva, Casuarina equisetifolia and Eucalyptus saligna. The pH declined slightly in soil beneath some Eucalyptus species treatments and increased in others. The high nutrient uptake by fast-growing trees and the acidic parent material were involved in the acidification process. The findings suggest that the species used in afforestation maintain soil fertility and protect the environment. It is recommended that afforestation of abandoned and less productive lands in Rwanda should utilize fast growing Eucalyptus species in combination with agroforestry and native species in order to maintain or improve soil chemical properties.
|
|
| 6. |
- Nsabimana, Donat, 1968, et al.
(författare)
-
Soil CO2 flux in six monospecific forest plantations in Southern Rwanda
- 2009
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 41:2, s. 396-402
-
Tidskriftsartikel (refereegranskat)abstract
- Forest soils contain the largest carbon stock of all terrestrial biomes and are probably the most important source of carbon dioxide (CO2) to atmosphere. Soil CO2 fluxes from 54 to 72-year-old monospecific stands in Rwanda were quantified from March 2006 to December 2007. The influences of soil temperature, soil water content, soil carbon (C) and nitrogen (N) stocks, soil pH, and stand characteristics on soil CO2 flux were investigated. The mean annual soil CO2 flux was highest under Eucalyptus saligna (3.92 mu mol m(-2) s(-1)) and lowest under Entandrophragma excelsum (3.13 mu mol m(-2) s(-1)). The seasonal variation in soil CO2 flux from all stands followed the same trend and was highest in rainy seasons and lowest in dry seasons. Soil CO2 flux was mainly correlated to soil water content (R-2 = 0.36-0.77), stand age (R-2 = 0.45), soil C stock (R-2 = 0.33), basal area (R-2 = 0.21), and soil temperature (R-2 = 0.06-0.17). The results contribute to the understanding of factors that influence soil CO2 flux in monocultural plantations grown under the same microclimatic and soil conditions. The results can be used to construct models that predict soil CO2 emissions in the tropics. (c) 2008 Elsevier Ltd. All rights reserved.
|
|
| 7. |
- Ntirugulirwa, Bonaventure, et al.
(författare)
-
Thermophilisation of Afromontane forest stands demonstrated in an elevation gradient experiment
- 2023
-
Ingår i: Biogeosciences. - 1810-6277. ; 20:24, s. 5125-5149
-
Tidskriftsartikel (refereegranskat)abstract
- The response of tropical trees and tree communities to climate change is crucial for the carbon storage and biodiversity of the terrestrial biosphere. Trees in tropical montane rain forests (TMFs) are considered particularly vulnerable to climate change, but this hypothesis remains poorly evaluated due to data scarcity. To reduce the knowledge gap in the response of TMF trees to warming, we established a field experiment along a 1300–2400m elevation gradient as a proxy for warming in Rwanda. Seedling-size trees of 20 species native to montane forests in eastern and central Africa were planted in multi-species plots at three sites along the gradient. They have overlapping distributions but primarily occur in either transitional rain forests (∼1600–2000 m a. s. l.) or mid-elevation TMFs (∼2000–3000 m a. s. l.), with both early- (ES) and late-successional (LS) species represented in each elevation origin group. Tree growth (diameter and height) and survival were monitored regularly over 2 years. We found that ES species, especially from lower elevations, grew faster at warmer sites, while several of the LS species, especially from higher elevations, did not respond or grew slower. Moreover, a warmer climate increased tree mortality in LS species, but not much in ES species. ES species with transitional rain forest origin strongly increased proportional to stand basal area at warmer sites, while TMF species declined, suggesting that lower-elevation ES species will have an advantage over higher-elevation species in a warming climate. The risk of higher-elevation and LS species of becoming outcompeted by lower-elevation and ES species due to a thermophilisation response in a warmer climate has important implications for biodiversity and carbon storage of Afromontane forests.
|
|
| 8. |
- Nyirambangutse, Brigitte, 1982, et al.
(författare)
-
Carbon stocks and dynamics at different successional stages in an Afromontane tropical forest
- 2016
-
Ingår i: Biogeosciences Discussions. - : Copernicus GmbH. - 1810-6277. ; , s. 1-39
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- As a result of different types of disturbance, forests are a mixture of stands at different stages of ecological succession. Successional stage is likely to influence forest productivity and carbon storage, linking the degree of forest disturbance to the global carbon cycle and climate. Although tropical montane forests are an important part of tropical forest ecosystems (c. 8%, elevation > 1000 m a.s.l.), there are still significant knowledge gaps regarding the carbon dynamics and 15 stocks of these forests, and how these differ between early (ES) and late successional (LS) stages. This study examines the carbon (C) stock, relative growth rate (RGR), and net primary production (NPP) of ES and LS forest stands in an Afromontane tropical rainforest using data from inventories of quantitatively important ecosystem compartments in fifteen 0.5 ha plots in Nyungwe National Park in Rwanda. The total C stock was 35% larger in LS compared to ES plots due to significantly larger above ground biomass (AGB; 185 and 76 Mg C ha-1 20 in LS and ES plots, respectively), while the soil and root C stock (down to 45 cm depth in the mineral soil) did not significantly differ between the two successional stages (178 and 204 Mg C ha-1 in LS and ES plots, respectively). The main reasons for the difference in AGB were that ES trees had significantly lower stature and wood density compared to LS trees. However, ES and LS stands had similar total NPP (canopy, wood and roots of all plots ~ 9.4 Mg C ha-1) due to counterbalancing effects of differences in AGB (higher in LS stands) and RGR (higher in ES stands). The AGB in the LS 25 plots was considerably higher than the average value reported for old-growth tropical montane forest of Southeast Asia and central and South America at similar elevations and temperatures, and of the same magnitude as in tropical lowland forest of different regions. The results of this study highlight the importance of accounting for disturbance regimes and differences in wood density and allometry of tree species dominating at different successional stages in attempts to quantify the C stock and sink strength of 30 tropical montane forests and how it may differ among continents.
|
|
| 9. |
- Nyirambangutse, Brigitte, 1982, et al.
(författare)
-
Variation in leaf litter production and resorption of nutrients in abundant tree species in Nyungwe Afromontane tropical rainforest in Rwanda
- 2014
-
Ingår i: EGU General Assembly 2014, held 27 April - 2 May, 2014 in Vienna, Austria, id.14278.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- African tropical rainforests play many roles from local to global scale as providers of resources and ecosystem services. Although covering 30% of the global rainforest, only few studies aiming to better understand the storage and fluxes of carbon and nutrients in these forests have been conducted. To answer questions related to these issues, we have established 15 permanent 0.5 ha plots where we compare carbon and nutrient fluxes of primary and secondary forest tree communities in a tropical montane forest in central Africa. The studies are conducted in Nyungwe montane tropical rain forest gazetted as a National Park to protect its extensive floral and faunal diversity covering an area of 970 km2. Nyungwe is located in Southwest Rwanda (2o17'-2o50'S, 29o07'-29o26A'E). The forest is ranging between 1600-2950 m.a.s.l. and is one of the most biologically important rainforest in Albertine Rift region in terms of Biodiversity. Nyungwe consists of a mixture of primary and secondary forest communities supporting a richness of plant and animal life. More than 260 species of trees and shrubs have been found in Nyungwe, including species endemic to the Albertine Rift. The forest has a climate with a mean annual temperature of 15.5oC and annual rainfall of ca 1850 mm yr-1, with July and August being the only months when rainfall drops. A part of this study is focusing on the dynamics of nutrients through leaf turnover. This turnover of leaves is regulated to maximize the carbon gain through canopy photosynthesis and resource-use efficiency of the plant. It is known that about half of leaf nitrogen is invested in photosynthetic apparatus and that there normally is a strong correlation between the photosynthetic capacity and leaf nitrogen per unit area. Hence leaf nitrogen is an important factor for canopy photosynthesis. However, leaves are produced, senesce and fall. Some nitrogen in the leaf is lost when leaves senesce but other is resorbed. The resorption of nitrogen, phosphorus and other nutrients is being studied to analyse the nutrient saving efficiency of different species within the primary and secondary forest communities. This is made by analyzing the nutrient content within fresh and fallen leaves of most abundant pioneer and climax species. Results from litterfall patterns as well as foliar, litter and soil carbon and nutrients are currently being compiled and will be reported.
|
|
| 10. |
- Tarvainen, Lasse, 1977, et al.
(författare)
-
Handling the heat - photosynthetic thermal stress in tropical trees.
- 2022
-
Ingår i: The New phytologist. - : Wiley. - 1469-8137 .- 0028-646X. ; 233:1, s. 236-50
-
Tidskriftsartikel (refereegranskat)abstract
- Warming climate increases the risk for harmful leaf temperatures in terrestrial plants, causing heat stress and loss of productivity. The heat sensitivity may be particularly high in equatorial tropical tree species adapted to a thermally stable climate. Thermal thresholds of the photosynthetic system of sun-exposed leaves were investigated in three tropical montane tree species native to Rwanda with different growth and water use strategies (Harungana montana, Syzygium guineense and Entandrophragma exselsum). Measurements of chlorophyll fluorescence, leaf gas exchange, morphology, chemistry and temperature were made at three common gardens along an elevation/temperature gradient. Heat tolerance acclimated to maximum leaf temperature (Tleaf ) across the species. At the warmest sites, the thermal threshold for normal function of photosystem II was exceeded in the species with the highest Tleaf despite their higher heat tolerance. This was not the case in the species with the highest transpiration rates and lowest Tleaf . The results point to two differently effective strategies for managing thermal stress: tolerance through physiological adjustment of leaf osmolality and thylakoid membrane lipid composition, or avoidance through morphological adaptation and transpiratory cooling. More severe photosynthetic heat stress in low-transpiring montane climax species may result in a competitive disadvantage compared to high-transpiring pioneer species with more efficient leaf cooling.
|
|
