Climate Change Impairs Nitrogen Cycling in European Beech Forests

European beech forests growing on marginal calcareous soils have been proposed to be vulnerable to decreased soil water availability. This could result in a large-scale loss of ecological services and economical value in a changing climate. In order to evaluate the potential consequences of this drought-sensitivity, we investigated potential species range shifts for European beech forests on calcareous soil in the 21st century by statistical species range distribution modelling for present day and projected future climate conditions. We found a dramatic decline by 78% until 2080. Still the physiological or biogeochemical mechanisms underlying the drought sensitivity of European beech are largely unknown. Drought sensitivity of beech is commonly attributed to plant physiological constraints. Furthermore, it has also been proposed that reduced soil water availability could promote nitrogen (N) limitation of European beech due to impaired microbial N cycling in soil, but this hypothesis has not yet been tested. Hence we investigated the influence of simulated climate change (increased temperatures, reduced soil water availability) on soil gross microbial N turnover and plant N uptake in the beech-soil interface of a typical mountainous beech forest stocking on calcareous soil in SW Germany. For this purpose, triple 15N isotope labelling of intact beech seedling-soil-microbe systems was combined with a space-for-time climate change experiment. We found that nitrate was the dominant N source for beech natural regeneration. Reduced soil water content caused a persistent decline of ammonia oxidizing bacteria and therefore, a massive attenuation of gross nitrification rates and nitrate availability in the soil. Consequently, nitrate and total N uptake of beech seedlings were strongly reduced so that impaired growth of beech seedlings was observed already after one year of exposure to simulated climatic change. We conclude that the N cycle in this ecosystem and here specifically nitrification is vulnerable to reduced water availability, which can directly lead to nutritional limitations of beech seedlings. This tight link between reduced water availability, drought stress for nitrifiers, decreased gross nitrification rates and nitrate availability and finally nitrate uptake by beech seedlings could represent the Achilles’ heel for beech under climate change stresses

GENETIC VARIABILITY OF SILVER FIR (ABIES ALBA MILL.) FROM THE CENTRAL PARTS OF BOSNIA AND HERZEGOVINA BY ANALYSIS OF BIOCHEMICAL MARKERS

U ovom istra`ivanju analizirana je genetska varijabilnost u četiri prirodne populacije obične jele (Abies alba) iz središnjeg dijela Bosne i Hercegovine (lokaliteteti Igman, Jahorina, Vlašić, Prusačka rijeka). Varijabilnost je istraživana uporabom devet standardiziranih enzimskih sustava, sa 17 gen lokusa i ukupno 38 različitih alela. Analizom je dobivena statistički značajna razlika između istraživanih populacija, a dobivena varijabilnost za neke gen lokuse i alele je klinalnog karaktera u smjeru jugoistok – sjeverozapad. Najveći prosječni broj alela registriran je u populaciji Prusačke rijeke 2,11, dok je najmanji broj alela prona|en u populaciji Jahorine 1,94 koja je u neposrednoj blizini skijaškog centra i pod stalnim je utjecajem čovjeka. Na temelju vrijednosti heterozigotnosti, koje su relativno velike, što govori da ove populacije posjeduju dovoljno genetičke varijabilnosti i da su kao takve vjerojatno adaptabilnije u odnosu na one iz središnje Europe. Najveću srednju heterozigotnost gen lokusa pokazuje lokus Lap-B sa 0,55 u populaciji Jahorine koja je najjužnije, pa je u sebi vjerojatno očuvala veliki dio izvornih balkanskih gena. Genetska odstupanja su najveća između populacije Prusačke rijeke i ostalih populacija. Tako su genotipska odstupanja izme|u populacija Prusačke rijeke i Jahorine veličine 0,0862. Najmanja vrijednost genetičkog odstupanja iznosi 0,0694 i registrirana je između populacija Jahorine i Igmana. Ovakvi rezultati su logični jer su i zemljopisno, populacije Prusačke rijeke i Jahorine najudaljenije, a Igmana i Jahorine najbliže jedna drugoj. Dobiveni rezultati pokazuju da naše prirodne populacije posjeduju značajnu genetsku varijabilnost. Međutim, radi održavanja genskog resursa trebalo bi uspostaviti mrežu banaka gena in situ i ex situ, nužnih za održanje genetičke raznolikosti populacija.The genetic variability in four natural populations of Silver fir (Abies alba Mill.), from the central part of Bosnia and Herzegovina (localities Igman, Jahorina, Vla{i}, Prusa~ka rijeka) was analysed in this research. For the molecular analysis we used nine standardized enzyme systems with 17 gene loci and 38 different alleles. The molecular analysis shows differences between the populations, and the variability of several gene loci and alleles is clinal in direction southeast to northwest. The largest mean number of alleles was registered in the Prusa~ka rijeka population - 2.11, whereas the smallest number (1.94) were found in the Jahorina population. This population is located near the local ski-center and is under direct human influence. A relatively high value of heterozygosity, therefore high genetic variability, suggests that these populations are more adaptive than those in central Europe. The gene locus Lap – B with 0,55 in the most southern Jahorina population showed the highest average heterozigosity, therefore probably preserving a major part of the original Balkan genes. Genetic distances between the populations were the largest between the population of Prusa~ka rijeka, on one side, and all other populations on the other. The largest genotype distance was determined between Prusa~ka rijeka and Jahorina populations (0,0862). The smallest genetic distance is 0,0694,,between populations of Jahorina and Igman. These results are logical because Prusa~ka rijeka and Jahorina are geographically most distant from each other, and Igman and Jahorina are the closest. These results show that our populations did not loose much of their genetic variability and adaptation potential. Therefore, in order to preserve the genetic resources it would be necessary to establish a network of gene banks in situ and ex situ, required for the maintainance of genetic differences of our populations

Nitrogen uptake capacity of European beech (Fagus sylvatica L.) only partially depends on tree age

Nitrogen (N) acquisition is a major factor determining the processes and mechanisms involved in tree productivity, development, and competitiveness. However, only few studies have investigated changes in N capturing with tree age. We conducted 15N incubation experiments to quantify inorganic (i.e. ammonium and nitrate) and organic (i.e. glutamine-N and arginine-N) net N acquisition capacity of beech trees of five age classes. Our results showed no general pattern, but that net N uptake capacity was rather N source-specific. Inorganic and glutamine-N uptake did not differ between age classes at all. Arginine-N uptake was highest in the youngest and oldest stands reflecting a high N demand by seedlings for root foraging and biomass production despite low internal N storage capacities and by older trees for storage and reproduction. Organic N was preferred over inorganic N regardless of tree age. Overall, our study shows the high significance of organic N sources for N acquisition in beech trees.publishe

Preparation of Gold Nanocomposites with Tunable Charge and Hydrophobicity via the Application of Polymer/Surfactant Complexation

During the synthesis of gold nanoparticle (NP) assemblies, the interfacial charge and hydrophobicity of the primary particles play a distinguished role. In the present article, we demonstrate that the association of poly­(ethyleneimine) (PEI) capped gold NPs with sodium alkyl sulfates provide a powerful route for the manipulation of these interfacial properties. Dynamic light-scattering, electrophoretic mobility, UV–vis–near-infrared spectroscopy, nanoparticle tracking analysis, and transmission electron microscopy measurements were used to characterize the PEI/surfactant/gold nanoassemblies. The results indicate the formation of gold NPs surrounded by a PEI/surfactant shell with composition-dependent charge and hydrophobicity. The mean size and the aggregation of the nanoassemblies can be fine tuned by the amount of surfactant bound to the primary gold NPs as well as by the application of controlled mixing methods. The specific features of the prepared nanocomposites may be further exploited in next-generation applications

Nitrogen nutrition of native and introduced forest tree species in N-limited ecosystems of the Qinling Mountains, China

Nitrogen availability and uptake capacity are key factors influencing forest growth and development in N-limited terrestrial ecosystems. With the aim to determine how species and forest management affect tree N nutrition, we conducted root N uptake experiments as well as soil N analyses at three forest stands with different native and introduced tree species (i.e. Larix principis-rupprechtii Mayr., Quercus aliena var. acutiserrata Maxim. ex Wenz. and Picea wilsonii Mast.) and two management approaches (i.e. monoculture versus mixed stand) in the Qinling Mountains of China. Across the native and introduced species studied, in general, investigated trees take up both, organic and inorganic N compounds, but prefer organic N (Gln- and Arg-) over inorganic NH4+–N. The introduced conifer species (L. principis-ruprechtii) showed higher root N acquisition capacities compared to a native conifer species (P. wilsonii) under N-limited conditions. Moreover, the mixed forest stand with L. principis-ruprechtii and Q. alinea var. acutesserata accumulated more nitrogen in soil pools and showed improved C and N retention capability through the whole soil profile as compared to the monocultures of P. wilsonii or L. principis-ruprechtii. Similar acquisition strategies were observed for specific N sources (i.e. organic versus inorganic) across all investigated tree species. Still the introduced species Larix exhibited a superior root N acquisition capacity and, therefore, may be a good candidate for afforestation programs in the studied region. The present results underpin the significance of forest management practices that achieve a mixed species structure with broadleaved tree species such as Quercus for restoration of soil C and N pools in order to stabilize forest ecosystems and to achieve sustainable forest development

Comparison of nitrogen nutrition and soil carbon status of afforested stands established in degraded soil of the Loess Plateau, China

The Loess Plateau in China constitutes an area short of soil nitrogen and organic carbon due to local land degradation induced by various factors (i.e. long term changes of land use, climate conditions, and soil properties). The present study aimed to examine the effects of species and land management by afforestation on tree N acquisition capacity and soil N and C availability in degraded soils of the Loess Plateau area. We quantified root N uptake of inorganic and organic N sources as well as soil N and C availability, both at the tree species (i.e. Robinia pseudoacacia L., Juglans regia L. and Pinus tabulaeformis Carr.) and the land management (i.e. arable vs. monoculture vs. mixed afforested stands) levels. Our results indicated that afforestation improved soil N and organic C availabilities compared to abandoned arable land (p < 0.05). In particular, the presence of N2-fixing R. pseudoacacia enhanced root N concentrations (ca. 3.0 times) and soil NO3- (ca. 5.4 times), soil total N (ca. 1.9 times) and organic C (ca. 3.4 times) availabilities, but decreased soil NH4+ (ca. −33%), microbial biomass carbon (ca. −74%) and nitrogen (ca. −54%) in the mixed stand compared to J. regia monoculture. Under the experimental conditions applied, the afforested trees preferred organic over inorganic N compounds as well as NO3− over NH4+; J. regia in monoculture had a highest root amino acids N uptake capacities (i.e. 76.6 ± 7.7 nmol N (g fw)−1 h−1 for glutamine, 90.3 ± 8.9 nmol N (g fw)−1 h−1 for arginine) compared to other tree species whereas such high uptake capacities were largely repressed in the mixed stand with R. pseudoacacia. Thus, in the Loess Plateau area, the inter-planting system of J. regia with N2-fixing R. pseudoacacia could improve the total soil N and organic C pools as well as plant N cycling compared to traditional arable land use and J. regia monoculture system. This study shows that inter-planting R. pseudoacacia with economic fruit trees can be considered a successful strategy for soil regeneration by afforestation in future land management projects

A case study on nitrogen nutrition of native and introduced forest tree species in the Qinling Mountains, China

<p>The manuscript entitled "A case study on nitrogen nutrition of native and introduced forest tree species in the Qinling Mountains, China" was submitted to Frontiers in Plant Science. The attached raw data for root N, C uptake and soil parameters analyses are supplied and uploaded for matching the additional data available policy for future readers.</p

Modelled potential distribution of beech forests on calcareous soils in Europe (green colour) under current climatic conditions (left panel).

<p>I.e., For the SRES A2 scenario, we computed a potential distribution of 7.2 million ha in the year 2080 (right panel), i.e., a reduction to 22% of the current distribution. Made with Natural Earth under CC0 license.</p

Percentage of vital root tips colonized with mycorrhizal fungi.

<p>Percentage of vital root tips colonized with mycorrhizal fungi.</p

Soil temperature differences (5 cm depth) between beech-soil-mesocosms incubated at SW exposure (warm-dry microclimate, climate change treatment) and at NW exposure (cool-moist microclimate, control treatment).

<p>Data represent mean values of five temperature probes per treatment directly installed horizontally in soil of transferred beech-soil-mesocosms. Arrows indicate the three sampling campaigns. The period between the sampling in June and August equals the roof period of 39 days.</p