Browsing by Subject "NITROGEN"

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  • McCrackin, Michelle L.; Muller-Karulis, Baerbel; Gustafsson, Bo G.; Howarth, Robert W.; Humborg, Christoph; Svanbäck, Annika; Swaney, Dennis P. (2018)
    There is growing evidence that the release of phosphorus (P) from legacy stores can frustrate efforts to reduce P loading to surface water from sources such as agriculture and human sewage. Less is known, however, about the magnitude and residence times of these legacy pools. Here we constructed a budget of net anthropogenic P inputs to the Baltic Sea drainage basin and developed a three-parameter, two-box model to describe the movement of anthropogenic P though temporary (mobile) and long-term (stable) storage pools. Phosphorus entered the sea as direct coastal effluent discharge and via rapid transport and slow, legacy pathways. The model reproduced past waterborne P loads and suggested an similar to 30-year residence time in the mobile pool. Between 1900 and 2013, 17 and 27 Mt P has accumulated in the mobile and stable pools, respectively. Phosphorus inputs to the sea have halved since the 1980s due to improvements in coastal sewage treatment and reductions associated with the rapid transport pathway. After decades of accumulation, the system appears to have shifted to a depletion phase; absent further reductions in net anthropogenic P input, future waterborne loads could decrease. Presently, losses from the mobile pool contribute nearly half of P loads, suggesting that it will be difficult to achieve substantial near-term reductions. However, there is still potential to make progress toward eutrophication management goals by addressing rapid transport pathways, such as overland flow, as well as mobile stores, such as cropland with large soil-P reserves.
  • Chawade, Aakash; Armoniene, Rita; Berg, Gunilla; Brazauskas, Gintaras; Frostgard, Gunilla; Geleta, Mulatu; Gorash, Andrii; Henriksson, Tina; Himanen, Kristiina; Ingver, Anne; Johansson, Eva; Jorgensen, Lise Nistrup; Koppel, Mati; Koppel, Reine; Makela, Pirjo; Ortiz, Rodomiro; Podyma, Wieslaw; Roitsch, Thomas; Ronis, Antanas; Svensson, Jan T.; Vallenback, Pernilla; Weih, Martin (2018)
    The Baltic Sea is one of the largest brackish water bodies in the world. Eutrophication is a major concern in the Baltic Sea due to the leakage of nutrients to the sea with agriculture being the primary source. Wheat (Triticum aestivum L.) is the most widely grown crop in the countries surrounding the Baltic Sea and thus promoting sustainable agriculture practices for wheat cultivation will have a major impact on reducing pollution in the Baltic Sea. This approach requires identifying and addressing key challenges for sustainable wheat production in the region. Implementing new technologies for climate-friendly breeding and digital farming across all surrounding countries should promote sustainable intensification of agriculture in the region. In this review, we highlight major challenges for wheat cultivation in the Baltic Sea region and discuss various solutions integrating transnational collaboration for pre-breeding and technology sharing to accelerate development of low input wheat cultivars with improved host plant resistance to pathogen and enhanced adaptability to the changing climate.
  • Bieron, Jacek; Filippin, Livio; Gaigalas, Gediminas; Godefroid, Michel; Jönsson, Per; Pyykkö, Pekka (2018)
    The relativistic multiconfiguration Dirac-Hartree-Fock and the nonrelativistic multiconfiguration Hartree-Fock methods have been employed to calculate the magnetic dipole and electric quadrupole hyperfine structure constants of zinc. The calculated electric field gradients for the 4s4p P-3(1)degrees and 4s4p P-3(2)degrees states, together with experimental values of the electric quadrupole hyperfine structure constants, made it possible to extract a nuclear electric quadrupole moment Q((67) Zn) = 0.122(10) b. The error bar was evaluated in a quasistatistical approach-the calculations were carried out with 11 different methods, and then the error bar was estimated from the differences between the results obtained with those methods.
  • Karges, Kathleen; Bellingrath-Kimura, Sonoko D.; Watson, Christine A.; Stoddard, Frederick L.; Halwani, Mosab; Reckling, Moritz (2022)
    Soybean is one of the five crops that dominate global agriculture, along with maize, wheat, cotton and rice. In Europe, soybean still plays a minor role and is cultivated mainly in the South and East. Very little is known about the potential for soybean in higher latitudes with relatively cool conditions. To investigate the agronomic potential and limitations of soybean for feed (high grain yield) and food (high protein content, e.g., for tofu production) in higher latitudes, an organic soybean cropping system experiment was carried out from 2015 to 2017 in northeastern Germany. The objectives were: (1) to identify food- and feed-grade soybean cultivars that are adapted to a central European climate in terms of protein, grain yield, and yield stability, (2) to explore the effect of irrigation on soybean protein and grain yield under relatively dry growing conditions, and (3) to determine the agro-economic potential of soybean cultivation for both feed and food markets. Three soybean cultivars were tested with and without irrigation. The soybean feed-grade cultivars 'Sultana' and 'Merlin' were better adapted to the growing cycle and temperature, providing higher and more stable yields (average 2700 kg ha(-1)) than the food-grade cultivar 'Protibus' (average 1300 kg ha(-1)). Irrigation increased soybean grain yields by 41% on average. In the year with sufficient precipitation, no additional irrigation was necessary. Gross margins of organic soybean ranged between 750 (sic) ha(-1) for the rainfed food-grade soybean and 2000 (sic) ha(-1) for the irrigated feed-grade soybean and were higher than other crops. We demonstrated a large agro-economic potential for soybean as a novel grain legume crop to diversify cropping systems and increase the production of protein crops in central Europe.
  • Vuorinne, Ilja; Heiskanen, Janne; Maghenda, Marianne; Mwangala, Lucas; Muukkonen, Petteri; Pellikka, Petri K.E. (2021)
    Biomass is a key variable for crop monitoring and for assessing carbon stocks and bioenergy potential. This study aimed to develop an allometric model for predicting the dry leaf biomass of sisal, an agave plant with crassulacean acid metabolism grown for fibre production in the tropics and subtropics and whose biomass can be utilised as a feedstock to produce biogas through anaerobic digestion. The allometric model was used to estimate leaf biomass and productivity across different stand ages in a sisal plantation in semi-arid region in south-east Kenya (annual rainfall 611 mm and temperature 24.9 °C). Based on a sample of 38 leaves, the best predictor for biomass was leaf maximum width and plant height used as a combined variable in a log-log regression model (cross-validated R2 = 0.96 and root-mean-square error = 7.69 g). The mean productivity in nine 26- to 36-month-old plots was 11.1 Mg ha−1 yr−1, which could potentially yield approximately 3000 m3 CH4 ha−1 yr−1. The leaf biomass in 55 field plots (400 m2 in area) ranged from 2.7 to 42.7 Mg ha−1, with mean at 13.5 Mg ha−1, which equals to 6.3 Mg C ha−1. The yielded allometric equations can be utilised for predicting the leaf biomass of sisal in similar agro-ecological zones. The estimates on plantation biomass can be used in assessing the role of sisal plantations as a regional carbon storage. In addition, the results provide reference on the productivity of agave and crassulacean acid metabolism in semi-arid regions of East Africa, where such reports are few.
  • Kerst, Thomas; Malmbeck, Rikard; Banik, Nidhu lal; Toivonen, Juha (2019)
    When exposed to air, alpha particles cause the production of light by exciting the molecules surrounding them. This light, the radioluminescence, is indicative of the presence of alpha radiation, thus allowing for the optical sensing of alpha radiation from distances larger than the few centimeters an alpha particle can travel in air. While the mechanics of radioluminescence in air and other gas compositions is relatively well understood, the same cannot be said about the radioluminescence properties of liquids. Better understanding of the radioluminescence properties of liquids is essential to design methods for the detection of radioactively contaminated liquids by optical means. In this article, we provide radioluminescence images of Am-241 dissolved in aqueous nitric acid solution and present the recorded radioluminescence spectrum with a maximum between, and a steep decrease at the short wavelength side of the maximum. The shape of the spectrum resembles a luminescence process rather than Cerenkov light, bremsstrahlung, or other mechanisms with broadband emission. We show that the amount of light produced is about 150 times smaller compared to that of the same amount of Am-241 in air. The light production in the liquid is evenly distributed throughout the sample volume with a slight increase on the surface of the liquid. The radioluminescence intensity is shown to scale linearly with the Am-241 concentration and not be affected by the HNO3 concentration.
  • Resovsky, Alex; Ramonet, Michel; Rivier, Leonard; Tarniewicz, Jerome; Ciais, Philippe; Steinbacher, Martin; Mammarella, Ivan; Mölder, Meelis; Heliasz, Michal; Kubistin, Dagmar; Lindauer, Matthias; Müller-Williams, Jennifer; Conil, Sebastien; Engelen, Richard (2021)
    We present a statistical framework to identify regional signals in station-based CO2 time series with minimal local influence. A curve-fitting function is first applied to the detrended time series to derive a harmonic describing the annual CO2 cycle. We then combine a polynomial fit to the data with a short-term residual filter to estimate the smoothed cycle and define a seasonally adjusted noise component, equal to 2 standard deviations of the smoothed cycle about the annual cycle. Spikes in the smoothed daily data which surpass this +/- 2 sigma threshold are classified as anomalies. Examining patterns of anomalous behavior across multiple sites allows us to quantify the impacts of synoptic-scale atmospheric transport events and better understand the regional carbon cycling implications of extreme seasonal occurrences such as droughts.
  • Lindström, Stafva; Timonen, Sari; Sundström, Liselotte; Johansson, Helena (2019)
    Biotic and abiotic characteristics shape the microbial communities in the soil environment. Manipulation of soil, performed by ants when constructing their nests, radically changes the soil characteristics and creates a unique environment, which differs in its composition, frequency and abundance of microbial taxa, from those in the reference soils. We sampled nests of the mound-building ant Formica exsecta, and the surrounding reference soils over a three-month period, and generated NGS (Illumina MiSeq), and T-RFLP data of the bacterial and fungal communities. We used ordination techniques and network analysis to disclose the community structure, and we assessed the variation in diversity, evenness and enrichment of taxa between the two environments. We also used indicator analysis to identify the potential core microbiome of the nests. Our results show that the bacterial and fungal communities, in the rigorously curated nest environment, are significantly different from those in the reference soils, in terms of community structure and enrichment of characteristic indicator taxa. We demonstrate that the nests represent a niche, where microbial species can adapt and diverge from the communities in the surrounding soils. Our findings contribute to our understanding of the composition and function of microbiomes in fragmented habitats.
  • Liu, Miao; Liu, Xingxing; Kang, Jieyu; Korpelainen, Helena; Li, Chunyang (2020)
    This study clarifies the mechanisms of Cd uptake, translocation and detoxification in Populus cathayana Rehder females and males, and reveals a novel strategy for dioecious plants to cope with Cd contamination. Females exhibited a high degree of Cd uptake and root-to-shoot translocation, while males showed extensive Cd accumulation in roots, elevated antioxidative capacity, and effective cellular and bark Cd sequestration. Our study also found that Cd is largely located in epidermal and cortical tissues of male roots and leaves, while in females, more Cd was present in vascular tissues of roots and leaves, as well as in leaf mesophyll. In addition, the distributions of sulphur (S) and phosphorus (P) were very similar as that of Cd in males, but the associations were weak in females. Scanning electron microscopy and energy spectroscopy analyses suggested that the amounts of tissue Cd were positively correlated with P and S amounts in males, but not in females (a weak correlation between S and Cd). Transcriptional data suggested that Cd stress promoted the upregulation of genes related to Cd uptake and translocation in females, and that of genes related to cell wall biosynthesis, metal tolerance and secondary metabolism in males. Our results indicated that coordinated physiological, microstructural and transcriptional responses to Cd stress endowed superior Cd tolerance in males compared with females, and provided new insights into mechanisms underlying sexually differential responses to Cd stress.
  • Angove, Charlotte; Norkko, Alf; Gustafsson, Camilla (2018)
    Aquatic plant meadows are valuable components to the 'coastal filter' and it is important to understand the processes that drive their ability to cycle nutrients. However, at present, the field-based evidence for understanding the drivers of nutrient uptake by plants is lacking. This study aimed to investigate how well individual shoots of aquatic plants could meet their nitrogen demands using the sediment nutrient pool (porewater ammonium) and to explore which traits helped to facilitate such uptake. Several species were investigated in shallow, submerged (2-4 m) mixed-species communities in the northern Baltic Sea using incubation experiments with enriched ammonium. After a 3.5 h incubation time, individuals were collected and analysed for nitrogen (% DW) and N-15 (at-%) concentrations. Uptake by plants was calculated per unit nitrogen in response to the N-15 labelled source and to overall nitrogen availability. Background porewater ammonium availability was highly variable between individual plants. Species identity did not significantly affect uptake metrics and the effect of ambient porewater availability was weak. As biomass increased there were significant logarithmic declines in the 95th quantiles of nutrient uptake rates, ambient porewater nutrient availability and aboveground nitrogen tissue concentrations (% DW). Such findings suggested that uptake rates of plants were significantly demand driven and the nutrient conditions of the porewater were significantly driven by the demands of the plant. Findings parameterised the unfulfilled potential for some aquatic plants to cycle nutrients more efficiently and highlighted the potential importance of access to new nutrient sources as a way of enhancing nutrient cycling by aquatic plants. Plant traits and community properties such as the activity of infauna could facilitate such an access and are likely important for nutrient uptake.
  • Piispanen, Wilhelm W.; Lundell, Richard V.; Tuominen, Laura J.; Räisänen-Sokolowski, Anne K. (2021)
    Introduction: Cold water imposes many risks to the diver. These risks include decompression illness, physical and cognitive impairment, and hypothermia. Cognitive impairment can be estimated using a critical flicker fusion frequency (CFFF) test, but this method has only been used in a few studies conducted in an open water environment. We studied the effect of the cold and a helium-containing mixed breathing gas on the cognition of closed circuit rebreather (CCR) divers. Materials and Methods: Twenty-three divers performed an identical dive with controlled trimix gas with a CCR device in an ice-covered quarry. They assessed their thermal comfort at four time points during the dive. In addition, their skin temperature was measured at 5-min intervals throughout the dive. The divers performed the CFFF test before the dive, at target depth, and after the dive. Results: A statistically significant increase of 111.7% in CFFF values was recorded during the dive compared to the pre-dive values (p < 0.0001). The values returned to the baseline after surfacing. There was a significant drop in the divers' skin temperature of 0.48 degrees C every 10 min during the dive (p < 0.001). The divers' subjectively assessed thermal comfort also decreased during the dive (p = 0.01). Conclusion: Our findings showed that neither extreme cold water nor helium-containing mixed breathing gas had any influence on the general CFFF profile described in the previous studies from warmer water and where divers used other breathing gases. We hypothesize that cold-water diving and helium-containing breathing gases do not in these diving conditions cause clinically relevant cerebral impairment. Therefore, we conclude that CCR diving in these conditions is safe from the perspective of alertness and cognitive performance.
  • Ma, Yang; Qu, Zhao-Lei; Liu, Bing; Tan, Jia-Jin; Asiegbu, Fred O.; Sun, Hui (2020)
    Pine wilt disease (PWD) caused by the nematode Bursaphelenchus xylophilus is a devastating disease in conifer forests in Eurasia. However, information on the effect of PWD on the host microbial community is limited. In this study, the bacterial community structure and potential function in the needles, roots, and soil of diseased pine were studied under field conditions using Illumina MiSeq coupled with Phylogenetic Investigation of Communities by Reconstruction of Unobserved states (PICRUSt) software. The results showed that the community and functional structure of healthy and diseased trees differed only in the roots and needles, respectively (p <0.05). The needles, roots, and soil formed unique bacterial community and functional structures. The abundant phyla across all samples were Proteobacteria (41.9% of total sequence), Actinobacteria (29.0%), Acidobacteria (12.2%), Bacteroidetes (4.8%), and Planctomycetes (2.1%). The bacterial community in the healthy roots was dominated by Acidobacteria, Planctomycetes, and Rhizobiales, whereas in the diseased roots, Proteobacteria, Firmicutes, and Burkholderiales were dominant. Functionally, groups involved in the cell process and genetic information processing had a higher abundance in the diseased needles, which contributed to the difference in functional structure. The results indicate that PWD can only affect the host bacteria community structure and function in certain anatomical regions of the host tree.
  • Miettinen, Jenni; Ollikainen, Markku; Aroviita, Jukka; Haikarainen, Soili; Nieminen, Mika; Turunen, Jarno; Valsta, Lauri (2020)
    Ditch network maintenance promotes forest growth in drained peatland forests but increases nutrient and sediment loads, which are detrimental to water quality. Society needs to balance the harvest revenue from improved forest growth against deteriorating water quality. We examine socially optimal even-aged forest management in drained peatlands when harvesting and ditch network maintenance cause nutrient and sediment loading. The means to reduce loading include establishing overland flow fields and abstaining from ditch network maintenance. We characterize this choice analytically in a rotation framework and examine, in a numerical model, the key factors affecting the choice of forest management and water protection measures. We choose a drained peatland forest site located in northeastern Finland in the vicinity of ecologically vulnerable forest headwater streams. On the given drained forest site, we find a set of parameters under which implementing ditch network maintenance is privately but not socially optimal.
  • Jansson, Torbjörn; Andersen, Hans Estrup; Hasler, Berit; Höglind, Lisa; Gustafsson, Bo G. (2019)
    In this study, quantitative models of the agricultural sector and nutrient transport and cycling are used to analyse the impacts in the Baltic Sea of replacing the current Greening measures of the EU’s Common Agricultural Policy with a package of investments in manure handling. The investments aim at improving nutrient utilization and reducing nitrogen leaching, based on the assumption that lagging farms and regions can catch up with observed good practice. Our results indicate that such investments could reduce nitrogen surpluses in agriculture by 18% and nitrogen concentrations in the Baltic Sea by 1 to 9% depending on the basin. The Greening measures, in contrast, are found to actually increase nitrogen leaching.
  • Seleiman, Mahmoud F.; Selim, Shaimaa; Jaakkola, Seija; Makela, Pirjo S. A. (2017)
    Maize cultivation for silage could be a sustainable option in Boreal conditions, especially when combined with nutrient recycling. Effects of digestate (sludge from biogas of domestic origin) application in comparison with synthetic fertilizer and two maturity stages on chemical composition and in vitro digestibility of whole-crop maize were investigated. Starch, neutral detergent fiber, water soluble carbohydrate (WSC) and digestible organic matter (DOM) contents of maize did not differ in response to the two fertilizer treatments. However, starch, DOM and metabolizable energy of maize increased, while ash, crude protein and WSC contents decreased with increasing maize maturity. Heavy metals in maize fertilized with digestate remained low. The results indicate that whole-crop maize fertilized with digestate and harvested at 150 days after sowing is a promising feed and has good nutritive value, even in Boreal conditions.
  • Portillo-Estrada, Miguel; Pihlatie, Mari; Korhonen, Janne F. J.; Levula, Janne; Frumau, Arnoud K. F.; Ibrom, Andreas; Lembrechts, Jonas J.; Morillas, Lourdes; Horvath, Laszlo; Jones, Stephanie K.; Niinemets, Uelo (2016)
    Carbon (C) and nitrogen (N) cycling under future climate change is associated with large uncertainties in litter decomposition and the turnover of soil C and N. In addition, future conditions (especially altered precipitation regimes and warming) are expected to result in changes in vegetation composition, and accordingly in litter species and chemical composition, but it is unclear how such changes could potentially alter litter decomposition. Litter transplantation experiments were carried out across six European sites (four forests and two grasslands) spanning a large geographical and climatic gradient (5.6-11.4 degrees C in annual temperature 511-878mm in precipitation) to gain insight into the climatic controls on litter decomposition as well as the effect of litter origin and species. The decomposition k rates were overall higher in warmer and wetter sites than in colder and drier sites, and positively correlated with the litter total specific leaf area. Also, litter N content increased as less litter mass remained and decay went further. Surprisingly, this study demonstrates that climatic controls on litter decomposition are quantitatively more important than species or site of origin. Cumulative climatic variables, precipitation, soil water content and air temperature (ignoring days with air temperatures below zero degrees Celsius), were appropriate to predict the litter remaining mass during decomposition (M-r). M-r and cumulative air temperature were found to be the best predictors for litter carbon and nitrogen remaining during the decomposition. Using mean annual air temperature, precipitation, soil water content and litter total specific leaf area as parameters we were able to predict the annual decomposition rate (k) accurately.
  • Parmentier, Dries; Paradis, Sarah; Metz, Sybrand J.; Wiedmer, Susanne K.; Kroon, Maaike C. (2016)
    This work describes for the first time a continuous process for selective metal extraction with an ionic liquid (IL) at room temperature. The hydrophobic fatty acid based IL tetraoctylphosphonium oleate ([P-8888][oleate]) was specifically chosen for its low viscosity and high selectivity towards transition metals. Applying [P-8888][oleate] for continuous metal ion extraction with 0.1 M sodium oxalate for regeneration resulted in a process with good and stable extraction efficiencies over time. The selectivity of the IL resulted in a process in which cobalt was selectively removed from two mixed salt solutions (Co/Na, Ca/Co/K) to obtain a pure cobalt stream after stripping the IL. The performed experiments showed that the contact time of the IL for extraction and stripping strongly influenced the achieved efficiencies. The stability of the IL was tested and it was shown that the fatty acid based IL was stable for the duration of the experiment. Liposome tests showed that the IL is very hydrophobic, which limits its leakage towards the water phase, but also results in a higher toxicity towards cell membranes. Economic analysis shows that the IL based process is not (yet) economical compared to ion-exchange resins, in case demineralised water is the only product. However, if the recovery of valuable metals is also taken into account and/or if brine disposal is an issue, then continuous IL metal extraction systems must be regarded as promising alternatives. (C) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
  • Walker, Anthony P.; De Kauwe, Martin G.; Medlyn, Belinda E.; Zaehle, Soeke; Iversen, Colleen M.; Asao, Shinichi; Guenet, Bertrand; Harper, Anna; Hickler, Thomas; Hungate, Bruce A.; Jain, Atul K.; Luo, Yiqi; Lu, Xingjie; Lu, Meng; Luus, Kristina; Megonigal, J. Patrick; Oren, Ram; Ryan, Edmund; Shu, Shijie; Talhelm, Alan; Wang, Ying-Ping; Warren, Jeffrey M.; Werner, Christian; Xia, Jianyang; Yang, Bai; Zak, Donald R.; Norby, Richard J. (2019)
    Increasing atmospheric CO2 stimulates photosynthesis which can increase net primary production (NPP), but at longer timescales may not necessarily increase plant biomass. Here we analyse the four decade-long CO2-enrichment experiments in woody ecosystems that measured total NPP and biomass. CO2 enrichment increased biomass increment by 1.05 +/- 0.26 kg C m(-2) over a full decade, a 29.1 +/- 11.7% stimulation of biomass gain in these early-secondary-succession temperate ecosystems. This response is predictable by combining the CO2 response of NPP (0.16 +/- 0.03 kg C m(-2) y(-1)) and the CO2-independent, linear slope between biomass increment and cumulative NPP (0.55 +/- 0.17). An ensemble of terrestrial ecosystem models fail to predict both terms correctly. Allocation to wood was a driver of across-site, and across-model, response variability and together with CO2-independence of biomass retention highlights the value of understanding drivers of wood allocation under ambient conditions to correctly interpret and predict CO2 responses.
  • Kalliokoski, Tuomo; Makela, Annikki; Fronzek, Stefan; Minunno, Francesco; Peltoniemi, Mikko (2018)
    We are bound to large uncertainties when considering impacts of climate change on forest productivity. Studies formally acknowledging and determining the relative importance of different sources of this uncertainty are still scarce, although the choice of the climate scenario, and e.g. the assumption of the CO2 effects on tree water use can easily result in contradicting conclusions of future forest productivity. In a large scale, forest productivity is primarily driven by two large fluxes, gross primary production (GPP), which is the source for all carbon in forest ecosystems, and heterotrophic respiration. Here we show how uncertainty of GPP projections of Finnish boreal forests divides between input, mechanistic and parametric uncertainty. We used the simple semi-empirical stand GPP and water balance model PRELES with an ensemble of downscaled global circulation model (GCM) projections for the 21st century under different emissions and forcing scenarios (both RCP and SRES). We also evaluated the sensitivity of assumptions of the relationships between atmospheric CO2 concentration (C-a), photosynthesis and water use of trees. Even mean changes in climate projections of different meteorological variables for Finland were so high that it is likely that the primary productivity of forests will increase by the end of the century. The scale of productivity change largely depends on the long-term C-a fertilization effect on GPP and transpiration. However, GCM variability was the major source of uncertainty until 2060, after which emission scenario/pathway became the dominant factor. Large uncertainties with a wide range of projections can make it more difficult to draw ecologically meaningful conclusions especially on the local to regional scales, yet a thorough assessment of uncertainties is important for drawing robust conclusions.
  • Guo, Qingxue; Song, Haifeng; Kang, Jieyu; Korpelainen, Helena; Li, Chunyang (2018)
    Knowledge of how competition and facilitation affect photosynthetic traits and nitrogen metabolism contributes to understanding of plant-plant interaction mechanisms. We transplanted two larch species, Larix kaempferi and L. olgensis, to establish intra- and interspecific interaction experiments under different types of soil. Experiment 1: Two different soil types were selected, one from a c. twenty years old L. kaempferi plantation (named larch soil) and another from a secondary natural forest (named mixed forest soil). The experiment included three types of plant interactions (L kaempferi + L. kaempferi, L. olgensis + L. olgensis, and L. kaempferi + L. olgensis) and two soil types. Experiment 2: N fertilization was applied to larch soil. The experiment included the same three types of plant interactions as in Experiment 1 and two N treatments. The growth of L kaempferi was negatively affected by larch soil and accelerated by N fertilization, particularly under interspecific interaction. The effects of soil type combined with plant-plant interactions or N fertilization influenced the chlorophyll pigment content, net photosynthetic rate (Pn), photosynthetic N use efficiency (PNUE) and total non-structural carbohydrates of leaves (TNC). CM a/Chl b (ratio of chlorophyll a to chlorophyll b) was higher when the growth of L. kaempferi was facilitated by the presence of L olgensis in mixed forest soil. However, the ratio significantly declined when L. kaempferi confronted strong competition from L. olgensis in larch soil without N fertilization. Under N fertilization in larch soil, Chl a/Chl b of L. olgensis significantly increased by the presence of L. kaempferi. Plant-plant interactions and soil types affected the number of chloroplasts, especially in L. kaempferi, which had a greater number of chloroplasts under interspecific interactions than in monoculture when growing in mixed forest soil. L. olgensis enhanced its ability to absorb N-NO3- under interspecific interactions in larch N- soil, while L. kaempferi enhanced its ability to absorb N-NH4+ under interspecific competition in mixed forest soil. Competition or facilitation modified the photosynthetic traits and nitrogen metabolism depending on the type of soil. Differences in these physiological processes contribute to divergent performance among individuals growing under interspecific or intraspecific competition, or in isolation.