The danger of mycorrhizal traps?
Kuyper, T.W. ; Kiers, E.T. - \ 2014
New Phytologist 203 (2014)2. - ISSN 0028-646X - p. 352 - 354.
ectomycorrhizal fungi - nitrogen limitation - boreal forests - mutualism - plants - competition - symbiosis - patterns - partners - markets
Growth and temperature-related phenotypic plasticity in the cyanobacterium Cylindrospermopsis raciborskii
Soares, M.C.S. ; Lurling, M. ; Huszar, V.L.M. - \ 2013
Phycological Research 61 (2013)1. - ISSN 1322-0829 - p. 61 - 67.
nitrogen limitation - nostocales - cyanoprokaryote - photosynthesis - chlorophyceae - cyanophyceae - morphology - tolerance - cultures - waters
Cylindrospermopsis raciborskii is an invasive and potentially toxic cyanobacterium, which has recently spread worldwide, mainly because of its tolerance to a wide range of climatic conditions. C. raciborskii is able to change several traits in response to environmental changes and its morphology is also affected by these changes (especially in nutrients). We also expected temperature to affect the morphology of this cyanobacterium. We examined the growth and morphology of C. raciborskii at different temperatures and compared laboratory results to the morphology of this cyanobacterium in situ. As expected, growth rates increased with temperature. In addition, a high carrying capacity at 32°C suggests that this cyanobacterium is able to form more dense blooms at high temperatures. Fragile trichomes and low growth rates were observed at 12°C. An increase in the growth rate related to temperature resulted in a decrease in trichome length, with shorter trichomes at 32°C. The same pattern was observed in wild populations of C. raciborskii in a tropical reservoir, where shorter trichomes were observed in warmer months, when biomass was highest. This species’ high ability to adapt to different environmental conditions throughout the year (i.e., nutrients, temperature) may have provided it with an additional advantage to increase its perennial blooms, mainly in tropical regions.
Environmental change impacts on the C- and N-cycle of European forests: a model comparison study
Cameron, D.R. ; Oijen, M. Van; Werner, C. ; Butterbach-Bahl, K. ; Grote, R. ; Haas, E. ; Heuvelink, G.B.M. ; Kiese, R. ; Kros, J. ; Kuhnert, M. ; Leip, A. ; Reinds, G.J. ; Reuter, H.I. ; Schelhaas, M.J. ; Vries, W. de; Yeluripati, J. - \ 2013
Biogeosciences 10 (2013). - ISSN 1726-4170 - p. 1751 - 1773.
nitrogen limitation - temperate forests - carbon budget - soils - n2o - ecosystems - agriculture - emissions - growth - decomposition
Forests are important components of the greenhouse gas balance of Europe. There is considerable uncertainty about how predicted changes to climate and nitrogen deposition will perturb the carbon and nitrogen cycles of European forests and thereby alter forest growth, carbon sequestration and N2O emission. The present study aimed to quantify the carbon and nitrogen balance, including the exchange of greenhouse gases, of European forests over the period 2010–2030, with a particular emphasis on the spatial variability of change. The analysis was carried out for two tree species: European beech and Scots pine. For this purpose, four different dynamic models were used: BASFOR, DailyDayCent, INTEGRATOR and Landscape-DNDC. These models span a range from semi-empirical to complex mechanistic. Comparison of these models allowed assessment of the extent to which model predictions depended on differences in model inputs and structure. We found a European average carbon sink of 0.160 ± 0.020 kgC m-2 yr-1 (pine) and 0.138 ± 0.062 kgC m-2 yr-1 (beech) and N2O source of 0.285 ± 0.125 kgN ha-1 yr-1 (pine) and 0.575 ± 0.105 kgN ha-1 yr-1 (beech). The European average greenhouse gas potential of the carbon sink was 18 (pine) and 8 (beech) times that of the N2O source. Carbon sequestration was larger in the trees than in the soil. Carbon sequestration and forest growth were largest in central Europe and lowest in northern Sweden and Finland, N. Poland and S. Spain. No single driver was found to dominate change across Europe. Forests were found to be most sensitive to change in environmental drivers where the drivers were limiting growth, where changes were particularly large or where changes acted in concert. The models disagreed as to which environmental changes were most significant for the geographical variation in forest growth and as to which tree species showed the largest rate of carbon sequestration. Pine and beech forests were found to have differing sensitivities to environmental change, in particular the response to changes in nitrogen and precipitation, with beech forest more vulnerable to drought. There was considerable uncertainty about the geographical location of N2O emissions. Two of the models BASFOR and LandscapeDNDC had largest emissions in central Europe where nitrogen deposition and soil nitrogen were largest, whereas the two other models identified different regions with large N2O emission. N2O emissions were found to be larger from beech than pine forests and were found to be particularly sensitive to forest growth.
Simultaneous growth and neutral lipid accumulation in microalgae
Klok, A.J. ; Martens, D.E. ; Wijffels, R.H. ; Lamers, P.P. - \ 2013
Bioresource Technology 134 (2013). - ISSN 0960-8524 - p. 233 - 243.
neochloris-oleoabundans - triacylglycerol accumulation - chlamydomonas-reinhardtii - nitrogen limitation - unicellular algae - light - photobioreactor - photosynthesis - metabolism - irradiance
In this paper the hypothesis was tested whether TAG accumulation serves as an energy sink when microalgae are exposed to an energy imbalance caused by nutrient limitation. In our continuous culture system, excess light absorption and growth-limiting nitrogen supply rates were combined, which resulted in accumulation of TAG (from 1.5 to 12.4% w/w) in visible lipid bodies in Neochloris oleoabundans, while cell replication was sustained. A fourfold increase in TAG productivity showed that TAG indeed served as an energy sink. However, the bulk of excess energy was dissipated leading to a significantly reduced biomass productivity and yield of biomass on light. This demonstrates that when aiming at industrial TAG production, sustaining efficient light energy use under nutrient stress is an important trait to look for in potential production organisms.
Interactions to the fifth thropic level: secondary and tertiary parasitoi wasps show extraordinary efficiency in utilizing host resources
Harvey, J.A. ; Wagenaar, R. ; Bezemer, T.M. - \ 2009
Journal of Animal Ecology 78 (2009)3. - ISSN 0021-8790 - p. 686 - 692.
hyperparasitoids lysibia-nana - gelis-agilis hymenoptera - nitrogen limitation - development strategies - ichneumonidae - stoichiometry - constraints - complexity - evolution - insects
Parasitoid wasps are highly efficient organisms at utilizing and assimilating limited resources from their hosts. This study explores interactions over three trophic levels, from the third (primary parasitoid) to the fourth (secondary parasitoid) and terminating in the fifth (tertiary parasitoid). Host utilization and adult body mass of the secondary and tertiary parasitoid Gelis agilis was determined when developing on pre-pupae of its primary parasitoid host, Cotesia glomerata, and from pre-pupae of another secondary parasitoid, Lysibia nana that had developed initially on pre-pupae of C. glomerata. In both C. glomerata and G. agilis, the body mass of emerging adult parasitoids was strongly positively correlated with initial cocoon mass. For a given cocoon mass at parasitism, emerging adult G. agilis wasps were almost 90% as large as C. glomerata adults developing in healthy cocoons of comparable mass. Furthermore, G. agilis adults were still 75% as large as C. glomerata adults even when developing on L. nana that in turn had developed on C. glomerata. Otherwise, in terms of adult body mass per unit of host resources, there was no apparent difference in the quality of C. glomerata or L. nana hosts for the development of G. agilis. Analyses of carbon and nitrogen in body tissues of the parasitoids over the third to the fifth trophic level revealed that percentage nitrogen was higher and carbon lower in G. agilis and L. nana than in C. glomerata. Furthermore, percentage carbon was lower in adult G. agilis wasps that had developed from L. nana than from C. glomerata. We argue that the remarkable efficiency which characterizes the development of secondary and tertiary parasitoids is based on the very high nutritional quality of resources that increase in quality up the food chain and rigid selection optimizing allocation of limited host resources. Consequently, food webs involving secondary and tertiary parasitoids can go to levels hitherto unexplored thus far in empirical studies. The use of molecular markers in future studies may reveal just how long food chains involving these insects may extend
A fungal growth model fitted to carbon-limited dynamics of Rhizoctonia solani
Jeger, M.J. ; Lamour, A. ; Gilligan, C.A. ; Otten, W. - \ 2008
New Phytologist 178 (2008)3. - ISSN 0028-646X - p. 625 - 633.
steady-state approximation - heterogeneous environments - nitrogen limitation - biological-control - soil - translocation - mycelia - variability - networks - patterns
Here, a quasi-steady-state approximation was used to simplify a mathematical model for fungal growth in carbon-limiting systems, and this was fitted to growth dynamics of the soil-borne plant pathogen and saprotroph Rhizoctonia solani. The model identified a criterion for invasion into carbon-limited environments with two characteristics driving fungal growth, namely the carbon decomposition rate and a measure of carbon use efficiency. The dynamics of fungal spread through a population of sites with either low (0.0074 mg) or high (0.016 mg) carbon content were well described by the simplified model with faster colonization for the carbon-rich environment. Rhizoctonia solani responded to a lower carbon availability by increasing the carbon use efficiency and the carbon decomposition rate following colonization. The results are discussed in relation to fungal invasion thresholds in terms of carbon nutrition.
Hierarchical saturation of soil carbon pools near a natural CO2 spring
Kool, D.M. ; Chung, H. ; Tate, K.R. ; Ross, D.J. ; Newton, P.C.D. ; Six, J. - \ 2007
Global Change Biology 13 (2007)6. - ISSN 1354-1013 - p. 1282 - 1293.
elevated atmospheric co2 - long-term exposure - organic-matter - nitrogen limitation - no-tillage - aggregate stability - agricultural soils - grassland - dioxide - sequestration
Soil has been identified as a possible carbon (C) sink to mitigate increasing atmospheric CO2 concentration. However, several recent studies have suggested that the potential of soil to sequester C is limited and that soil may become saturated with C under increasing CO2 levels. To test this concept of soil C saturation, we studied a gley and organic soil at a grassland site near a natural CO2 spring. Total and aggregate-associated soil organic C (SOC) concentration showed a significant increase with atmospheric CO2 concentration. An asymptotic function showed a better fit of SOC and aggregation with CO2 level than a linear model. There was a shift in allocation of total C from smaller size fractions to the largest aggregate fraction with increasing CO2 concentration. Litter inputs appeared to be positively related to CO2 concentration. Based on modeled function parameters and the observed shift in the allocation of the soil C from small to large aggregate-size classes, we postulate that there is a hierarchy in C saturation across different SOC pools. We conclude that the asymptotic response of SOC concentration at higher CO2 levels indicates saturation of soil C pools, likely because of a limit to physical protection of SOC.
Soil 13C–15N dynamics in an N2-fixing clover system under long-term exposure to elevated atmospheric CO2
Groenigen, C.J. van; Six, J. ; Harris, D. ; Blum, H. ; Kessel, C. van - \ 2003
Global Change Biology 9 (2003). - ISSN 1354-1013 - p. 1751 - 1762.
symbiotic n-2 fixation - organic-matter dynamics - trifolium-repens l - carbon-dioxide - nitrogen limitation - microbial activity - white clover - grassland - ecosystems - turnover
Reduced soil N availability under elevated CO2 may limit the plant's capacity to increase photosynthesis and thus the potential for increased soil C input. Plant productivity and soil C input should be less constrained by available soil N in an N2-fixing system. We studied the effects of Trifolium repens (an N2-fixing legume) and Lolium perenne on soil N and C sequestration in response to 9 years of elevated CO2 under FACE conditions. 15N-labeled fertilizer was applied at a rate of 140 and 560 kg N ha-1 yr-1 and the CO2 concentration was increased to 60 Pa pCO2 using 13C-depleted CO2. The total soil C content was unaffected by elevated CO2, species and rate of 15N fertilization. However, under elevated CO2, the total amount of newly sequestered soil C was significantly higher under T. repens than under L. perenne. The fraction of fertilizer-N (fN) of the total soil N pool was significantly lower under T. repens than under L. perenne. The rate of N fertilization, but not elevated CO2, had a significant effect on fN values of the total soil N pool. The fractions of newly sequestered C (fC) differed strongly among intra-aggregate soil organic matter fractions, but were unaffected by plant species and the rate of N fertilization. Under elevated CO2, the ratio of fertilizer-N per unit of new C decreased under T. repens compared with L. perenne. The L. perenne system sequestered more 15N fertilizer than T. repens: 179 vs. 101 kg N ha-1 for the low rate of N fertilization and 393 vs. 319 kg N ha-1 for the high N-fertilization rate. As the loss of fertilizer-15N contributed to the 15N-isotope dilution under T. repens, the input of fixed N into the soil could not be estimated. Although N2 fixation was an important source of N in the T. repens system, there was no significant increase in total soil C compared with a non-N2-fixing L. perenne system. This suggests that N2 fixation and the availability of N are not the main factors controlling soil C sequestration in a T. repens system.