Browsing by Subject "BETULA-PENDULA"

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  • Kaitaniemi, Pekka; Lintunen, Anna; Sievänen, Risto; Perttunen, Jari (2018)
    Foliar nitrogen is one of the key traits determining the photosynthetic capacity of trees. It is influenced by many environmental factors that are often confounded with the photosynthetic photon flux density (PPFD), which alone strongly modifies the nitrogen content and other foliar traits. We combined field measurements and computational estimates of light transmittance in 3D stands with different combinations of Scots pine (Pinus sylvestris) and silver birch (Betula pendula) to decouple the effect of PPFD from other potential effects exerted by the species of neighbouring trees on the leaf nitrogen content per unit leaf area (Narea) and leaf mass per area (LMA). Independent of the level of PPFD, silver birch had a significantly lower Narea and LMA when Scots pine was abundant in its neighbourhood compared with the presence of conspecific neighbours. In Scots pine, Narea and LMA were only dependent on PPFD and the branching order of shoots. In both species, the relationships between PPFD and Narea or LMA were nonlinear, especially at intermediate levels of PPFD. The levels of PPFD did not show any dependence on the species of the neighbouring trees. The responses of silver birch suggest that the species composition of the surrounding stand can influence foliar nitrogen, independent of the level of PPFD within the canopy.
  • Mikola, Juha; Silfver, Tarja; Paaso, Ulla; Possen, Boy J. M. H.; Rousi, Matti (2018)
    Plants enhance N use efficiency by resorbing N from senescing leaves. This can affect litter N mineralization rate due to the C:N-ratio requirements of microbial growth. We examined genotypic links between leaf N resorption and litter mineralization by collecting leaves and litter from 19 Betula pendula genotypes and following the N release of litter patches on forest ground. We found significant genotypic variation for N resorption efficiency, litter N concentration, cumulative three-year patch N-input and litter N release with high broad-sense heritabilities (H-2 = 0.28-0.65). The genotype means of N resorption efficiency varied from 46% to 65% and correlated negatively with the genotype means of litter N concentration, cumulative patch N-input and litter N release. NH4+ yield under patches had a positive genotypic correlation with the cumulative patch N-input. During the first year of litter decomposition, genotypes varied from N immobilization (max 2.71 mg/g dry litter) to N release (max 1.41 mg/g dry litter), creating a genotypic tradeoff between the N conserved by resorption and the N available for root uptake during the growing season. We speculate that this tradeoff is one likely reason for the remarkably wide genotypic range of N resorption efficiencies in our birch population.
  • Meyer, Nele; Xu, Yi; Karjalainen, Katri; Adamczyk, Sylwia; Biasi, Christina; van Delden, Lona; Martin, Angela; Mganga, Kevin Z; Myller, Kristiina; Sietiö, Outi-Maaria; Suominen, Otso; Karhu, Kristiina (2022)
    Mountain birch forests (Betula pubescens Ehrh. ssp. czerepanovii) at the subarctic treeline not only benefit from global warming, but are also increasingly affected by caterpillar outbreaks from foliage-feeding geometrid moths. Both of these factors have unknown consequences on soil organic carbon (SOC) stocks and biogeochemical cycles. We measured SOC stocks down to the bedrock under living trees and under two stages of dead trees (12 and 55 years since moth outbreak) and treeless tundra in northern Finland. We also measured in-situ soil respiration, potential SOC decomposability, biological (enzyme activities and microbial biomass), and chemical (N, mineral N, and pH) soil properties. SOC stocks were significantly higher under living trees (4.1 +/- 2.1 kg m(2)) than in the treeless tundra (2.4 +/- 0.6 kg m(2)), and remained at an elevated level even 12 (3.7 +/- 1.7 kg m(2)) and 55 years (4.9 +/- 3.0 kg m(2)) after tree death. Effects of tree status on SOC stocks decreased with increasing distance from the tree and with increasing depth, that is, a significant effect of tree status was found in the organic layer, but not in mineral soil. Soil under living trees was characterized by higher mineral N contents, microbial biomass, microbial activity, and soil respiration compared with the treeless tundra; soils under dead trees were intermediate between these two. The results suggest accelerated organic matter turnover under living trees but a positive net effect on SOC stocks. Slowed organic matter turnover and continuous supply of deadwood may explain why SOC stocks remained elevated under dead trees, despite the heavy decrease in aboveground C stocks. We conclude that the increased occurrence of moth damage with climate change would have minor effects on SOC stocks, but ultimately decrease ecosystem C stocks (49% within 55 years in this area), if the mountain birch forests will not be able to recover from the outbreaks.
  • Robson, T. Matthew; Klem, Karel; Urban, Otmar; Jansen, Marcel A. K. (2015)
    There is a need to reappraise the effects of UV-B radiation on plant morphology in light of improved mechanistic understanding of UV-B effects, particularly elucidation of the UV RESISTANCE LOCUS 8 (UVR8) photoreceptor. We review responses at cell and organismal levels, and explore their underlying regulatory mechanisms, function in UV protection and consequences for plant fitness. UV-induced morphological changes include thicker leaves, shorter petioles, shorter stems, increased axillary branching and altered root:shoot ratios. At the cellular level, UV-B morphogenesis comprises changes in cell division, elongation and/or differentiation. However, notwithstanding substantial new knowledge of molecular, cellular and organismal UV-B responses, there remains a clear gap in our understanding of the interactions between these organizational levels, and how they control plant architecture. Furthermore, despite a broad consensus that UV-B induces relatively compact architecture, we note substantial diversity in reported phenotypes. This may relate to UV-induced morphological changes being underpinned by different mechanisms at high and low UV-B doses. It remains unproven whether UV-induced morphological changes have a protective function involving shading and decreased leaf penetration of UV-B, counterbalancing trade-offs such as decreased photosynthetic light capture and plant-competitive abilities. Future research will need to disentangle seemingly contradictory interactions occurring at the threshold UV dose where regulation and stress-induced morphogenesis overlap. We review the effects of UV-B on plant morphology, using the improved mechanistic understanding of UV perception and signalling following elucidation of the UVR8 photoreceptor to reappraise published results. Despite a substantially improved understanding of molecular, cellular and organismal UV-B responses, there remains a clear gap in our knowledge of the interactions between these organisational levels, their function in UV-protection, and consequences for plant fitness and plant-plant interactions. Future research will need to disentangle the seemingly contradictory interactions and substantial diversity in reported phenotypes that occur at the threshold UV dose where regulation and stress-induced morphogenesis overlap.
  • Hellen, Heidi; Praplan, Arnaud P.; Tykka, Toni; Helin, Aku; Schallhart, Simon; Schiestl-Aalto, Piia P.; Back, Jaana; Hakola, Hannele (2021)
    Biogenic volatile organic compounds (BVOCs) emitted by the forests are known to have strong impacts in the atmosphere. However, lots of missing reactivity is found, especially in the forest air. Therefore better characterization of sources and identification/quantification of unknown reactive compounds is needed. While isoprene and monoterpene (MT) emissions of boreal needle trees have been studied quite intensively, there is much less knowledge on the emissions of boreal deciduous trees and emissions of larger terpenes and oxygenated volatile organic compounds (OVOCs). Here we quantified the downy birch (Betula pubescens) leaf emissions of terpenes, oxygenated terpenes and green leaf volatiles (GLVs) at the SMEAR II boreal forest site using in situ gas chromatographs with mass spectrometers. Sesquiterpenes (SQTs) and oxygenated sesquiterpenes (OSQTs) were the main emitted compounds. Mean emission rates of SQTs and OSQTs were significantly higher in the early growing season (510 and 650 ng g(dw)(-1) h(-1), respectively) compared to in the main (40 and 130 ng g(dw)(-1) h(-1), respectively) and late (14 and 46 ng g(dw)(-1) h(-1), respectively) periods, indicating that early leaf growth is a strong source of these compounds. The emissions had a very clear diurnal variation with afternoon maxima being on average 4 to 8 times higher than seasonal means for SQTs and OSQTs, respectively. fi Caryophyllene and fi-farnesene were the main SQTs emitted. The main emitted OSQTs were tentatively identified as 14-hydroxy-beta-caryophyllene acetate (M = 262 g mol(-1)) and 6-hydroxy-beta-caryophyllene (M D 220 g mol(-1)). Over the whole growing season, the total MT emissions were only 24% and 17% of the total SQT and OSQT emissions, respectively. A stressed tree growing in a pot was also studied, and high emissions of ff -farnesene and an unidentified SQT were detected together with high emissions of GLVs. Due to the relatively low volatility and the high reactivity of SQTs and OSQTs, downy birch emissions are expected to have strong impacts on atmospheric chemistry, especially on secondary organic aerosol (SOA) production.
  • Rousi, Matti; Possen, Boy J. M. H.; Pulkkinen, Pertti; Mikola, Juha (2019)
    Silver (Betula pendula) and pubescent birch (B. pubescens) are the two main broad-leaved tree species in boreal forests and Subarctic areas, with great significance for both northern societies and ecosystems. Silver birch has more economical importance as it grows taller, but pubescent birch reaches much further North. The adaptability and genetic diversity of Subarctic birch populations are assumed to derive from inter- and intraspecific hybridization. Southern pollen clouds could in turn increase the adaptability of northern populations to warming climate. In the boreal forest zone of warmer climate, incompatibility reactions may prevent interspecific hybridization and much depends on the synchrony of flowering. Direct in situ observations are, however, mostly lacking and earlier results concerning the spatial and temporal match of flowering phenology between the species are contradictory. Conclusions based on pollen catches may also be biased as the pollen of silver and pubescent birch are notoriously difficult to sort out and the geographical origin of pollen is virtually impossible to determine. Here we employ direct flowering observations and reanalyze old pollen and seed production data, collected along a South-North gradient in Finland, to shed more light on these issues. Our results suggest that interspecific hybridization is an unlikely mechanism of adaptation in silver and pubescent birch as there is no significant overlap in flowering either near Subarctic or in more southern boreal areas (covering latitudes 60-68 degrees N). Long-distance southern gene flow also unlikely has importance in the adaptation of northern populations to a warming climate as heat sum requirements for flowering in northern and southern populations are equal and northern birches are therefore not receptive at the time of southern flowering. Long-term data of pollen and seed production in turn suggest that pubescent birch is more effective in seed production through the whole South North gradient, but increasingly so towards the North. However, it appears that this difference is not due to silver birch flowering and regeneration being more sensitive to interannual variation as earlier suggested. Although there are more factors than reproduction alone that can affect species distributions, these two findings indicate that climate warming may not significantly alter the relative abundances of silver and pubescent birch in Subarctic Fennoscandia.