1,721,056 research outputs found
Nitrogen limitation in mycorrhizal Norway spruce (Picea abies) seedlings induced mycelial foraging for ammonium: implications for Ca and Mg uptake
No full textAlthough many studies support the importance of the external mycelium for nutrient acquisition of ectomycorrhizal plants, direct evidence for a significant contribution to host nitrogen nutrition is still scarce. We grew nonmycorrhizal seedlings and seedlings mycorrhizal with Paxillus involutus (Batsch) Fr. in a sand culture system with two compartments separated by a 45-mum Nylon mesh. Hyphae, but not roots, can penetrate this net. Nutrient solutions were designed to limit seedling growth by nitrogen. Hyphal density in the hyphal compartment, host N status and shoot growth of mycorrhizal seedlings significantly increased in response to NH4+ addition to the hyphal compartment. Labeling the compartment only accessible to hyphae with (NH4+)-N-15 showed that the increase in N uptake in the mycorrhizal seedlings was a result of hyphal N acquisition from the hyphal compartment. These results indicate that hyphae of P. involutus may actively forage into N-rich patches and improve host N status and growth. In the mycorrhizal seedlings, which received additional NH4+ via their external mycelium, the increase in NH4+ supply less negatively affected Ca and Mg uptake than in nonmycorrhizal seedlings, where the additional NH4+ was directly supplied to the roots. This was most likely due to the close link of NH4+ uptake and H+ extrusion, which, in the nonmycorrhizal seedlings, lead to a strong acidification in the root compartment, and subsequently reduced Ca and Mg uptake, whereas in the mycorrhizal seedlings the site of intensive NH4+ uptake and acidification was in the hyphal and not in the root compartment. Our data support the idea that the ectomycorrhizal mycelium connected to an N-deficient host may actively forage for N. The mycelium may also be important as a biological buffer system ameliorating negative influence of high NH4+ supply on cation uptake
Contrasting rooting patterns of some arid-zone fruit tree species from Botswana - II. Coarse root distribution
No full textSpatial coarse root distribution of the in situ grown species Strychnos cocculoides BAK., Strychnos spinosa LAM. (Loganiaceae), Vangueria infausta BURCH. (Rubiaceae) and Grewia. ava DC. (Tiliaceae) was investigated. The woody roots provide the scaffolding for fine roots, and thus underpin potential competition with. ne roots of other species. We developed a method for quantitative description of spatial patterns of coarse roots and correlated. ne root distribution with the spatial arrangement of the coarse root systems. In order to estimate different exploration and exploitation strategies, we used the spatial distribution of structural roots within the 'individual soil volumes' (ISV) of each root system, and compared the results with other published parameters. We defined a new parameter, "generalized efficiency of exploitation" GEE(φ), unifying different notions from the literature. Among all the investigated species and dependent on the considered parameter, either Vangueria infausta or Grewia. ava had the highest mean values of exploration, hence they could clearly be separated from both Strychnos species. For the exploitation indices, no significant differences were found. However, the generalized efficiency of exploitation GEE(φ) was again different between the species. For correlations between coarse and fine roots, the restriction to the ISV was useful to increase the strength of correlations
Contrasting rooting patterns of some arid-zone fruit tree species from Botswana - I. Fine root distribution
No full textTo assess the possible degree of root competition from fruit trees which could potentially be used in agroforestry systems,. ne root density of fruit trees Strychnos cocculoides BAK., Strychnos spinosa LAM. (Loganiaceae) and Vangueria infausta BURCH. (Rubiaceae), as well as from the shrubby species, Grewia flava DC. (Tiliaceae) was investigated. Vangueria infausta had the highest. ne root densities in both vertical and horizontal extensions. In Vangueria infausta. ne root density decreased with increasing soil depth. For the other species in the 80 cm soil pro. le investigated, no significant changes in. ne root density with soil depth were found. For Strychnos cocculoides almost no. ne roots were detected in the upper soil horizon (0-20 cm). Using fine root surface area densities, exploration and exploitation indices were calculated. Vangueria infausta had the highest value of the exploration index compared to the other species. For use in agroforestry systems Vangueria infausta was estimated to be the most competitive of the investigated species, whereas Strychnos cocculoides seems to be the less competitive. Strychnos cocculoides has additionally spatial arrangements of. ne roots favourable for agroforestry, slowly increasing with depth and additionally low concentrations in upper soil layers
Topology, scaling relations and Leonardo's rule in root systems from African tree species
No full textAspects of root architecture, including topology, link length, diameter and scaling relations, were analyzed in excavated coarse root systems of three field-grown fruit tree species (Strychnos cocculoides Bak., Strychnos spinosa Lam. and Vangueria infausta Burch) and the fruit-bearing shrub Grewia flava DC. We investigated the root systems using semi-automatic digitizing and computer-based 3-D reconstruction techniques. Topological analysis was carried out to investigate branching patterns as basic determinants of root architecture. New topological indices were developed and revealed significant differences among the species. The different architectural strategies can be explained in terms of cost-benefit relations and efficiency in soil resource exploration and exploitation. In addition, some well-known hypotheses about geometry and scaling, most of them previously unverified by empirical observations on root systems, were tested. For practical applications, the main emphasis is on the relationship between proximal root diameter, an easily determined parameter, and several parameters describing the size of the whole root system. We also tested the "pipe stem" theory, essentially dating back to Leonardo da Vinci, which underlies many models and which we found conformed to our measurement data with reasonable accuracy. A physiological consequence of the "constant cross-sectional area rule" may be a certain homogeneity of hydraulic architecture throughout root systems
Topology, scaling relations and Leonardo's rule in root systems from African tree species
No full textAspects of root architecture, including topology, link length, diameter and scaling relations, were analyzed in excavated coarse root systems of three field-grown fruit tree species (Strychnos cocculoides Bak., Strychnos spinosa Lam. and Vangueria infausta Burch) and the fruit-bearing shrub Grewia flava DC. We investigated the root systems using semi-automatic digitizing and computer-based 3-D reconstruction techniques. Topological analysis was carried out to investigate branching patterns as basic determinants of root architecture. New topological indices were developed and revealed significant differences among the species. The different architectural strategies can be explained in terms of cost-benefit relations and efficiency in soil resource exploration and exploitation. In addition, some well-known hypotheses about geometry and scaling, most of them previously unverified by empirical observations on root systems, were tested. For practical applications, the main emphasis is on the relationship between proximal root diameter, an easily determined parameter, and several parameters describing the size of the whole root system. We also tested the "pipe stem" theory, essentially dating back to Leonardo da Vinci, which underlies many models and which we found conformed to our measurement data with reasonable accuracy. A physiological consequence of the "constant cross-sectional area rule" may be a certain homogeneity of hydraulic architecture throughout root systems
Response of soil microbial community to afforestation with pure and mixed specie
Full text linkObjectivesAfforestation changes soil chemical properties over several decades. In contrast, microbial community structure can be shifted within the first decade and so, the direct effects of tree species can be revealed. The aim of this study was to determine the alteration of soil microbial community composition 10 years after afforestation by trees with contrasting functional traits.MethodsThe study was conducted at the BangorDIVERSE temperate forest experiment. Soil samples were collected under single, two and three species mixtures of alder and birch, beech and oak - early and secondary successional species, respectively, and contiguous agricultural field. Soil was analysed for total carbon (C) and nitrogen (N) contents, and microbial community structure (phospholipid fatty acids (PLFAs) analysis).Results and conclusionsThe total PLFAs content (370–640 nmol g−1 soil) in forest plots increased for 30 to 110 % compared to the agricultural soil (290 nmol g−1 soil). In contrast, soil C, N and C/N ratios were altered over 10 years much less - increased only up to 20 % or even decreased (for beech forest).Afforestation increased bacterial PLFAs by 20–120 %, whereas it had stronger impact on the development of fungal communities (increased by 50–200 %). These effects were proved for all forests, but were more pronounced under the monocultures compared to mixtures. This indicates that species identity has a stronger effect than species diversity. Principal component analysis of PLFAs revealed that under mono and three species mixtures similar microbial communities were formed. In contrast, gram-positive PLFAs and actinomycete PLFAs contributed mainly to differentiation of two species mixtures from other forests. Thus, at the early afforestation stage: i) soil biological properties are altered more than chemical, and ii) tree species identity affects more than species amount on both processes
The mycorrhizal fungus Paxillus involutus transports magnesium to Norway spruce seedlings. Evidence from stable isotope labeling
No full textAlthough it is well established that ectomycorrhizas improve the mineral nutrition of forest trees, there has been little evidence that they mediate uptake of divalent cations such as Mg. We grew nonmycorrhizal seedlings and seedlings mycorrhizal with Paxillus involutus Batsch in a sand culture system with two compartments separated by a 45-mu m Nylon mesh. Hyphae, but not roots, can penetrate this net. Labeling the compartment only accessible to hyphae with Mg-25 showed that hyphae of the ectomycorrhizal fungus Paxillus involutus transported Mg to their host plant. No label was found in nonmycorrhizal control plants. Our data support the idea that ectomycorrhizas are important for the Mg nutrition of forest trees
Cadmium-induced changes in antioxidative systems, hydrogen peroxide content, and differentiation in Scots pine roots.
No full textTo investigate whether Cd induces common plant defense pathways or unspecific necrosis, the temporal sequence of physiological reactions, including hydrogen peroxide (H(2)O(2)) production, changes in ascorbate-glutathione-related antioxidant systems, secondary metabolism (peroxidases, phenolics, and lignification), and developmental changes, was characterized in roots of hydroponically grown Scots pine (Pinus sylvestris) seedlings. Cd (50 microM, 6 h) initially increased superoxide dismutase, inhibited the systems involved in H(2)O(2) removal (glutathione/glutathione reductase, catalase [CAT], and ascorbate peroxidase [APX]), and caused H(2)O(2) accumulation. Elongation of the roots was completely inhibited within 12 h. After 24 h, glutathione reductase activities recovered to control levels; APX and CAT were stimulated by factors of 5.5 and 1.5. Cell death was increased. After 48 h, nonspecific peroxidases and lignification were increased, and APX and CAT activities were decreased. Histochemical analysis showed that soluble phenolics accumulated in the cytosol of Cd-treated roots but lignification was confined to newly formed protoxylem elements, which were found in the region of the root tip that normally constitutes the elongation zone. Roots exposed to 5 microM Cd showed less pronounced responses and only a small decrease in the elongation rate. These results suggest that in cells challenged by Cd at concentrations exceeding the detoxification capacity, H(2)O(2) accumulated because of an imbalance of redox systems. This, in turn, may have triggered the developmental program leading to xylogenesis. In conclusion, Cd did not cause necrotic injury in root tips but appeared to expedite differentiation, thus leading to accelerated aging
Root turnover and root necromass accumulation of Norway spruce (Picea abies) are affected by soil acidity
No full textFine root distribution and turnover were investigated in ca. 40-year-old pure Norway spruce (Picea abies Karst.) stands in Germany, growing on four sites that differed in soil acidity (Ebergotzen < Barbis < Fichtelgebirge = Harz). The density of fine root biomass and necromass in different soil horizons differed among the sites. At one of the most acidic sites (Harz), fine root density in the humus layer was more than twice that at the least acidic site (Ebergotzen). At the two most acidic sites, Fichtelgebirge and Harz, the ratio of biomass to necromass was significantly lower than at Ebergotzen and Barbis, particularly in the subsoil layer. In each stand, clear vertical gradients in fine root length density and root tip density were observed. Most of the roots and the root tips were in the humus layer and in the first mineral soil horizon (0-10 cm). There was a significantly different decrease in specific root length (cm g(DM)(-1)) and specific root tip density (root tips g(DM)(-1)) in the more acidified stands Fichtelgebirge and Harz compared with Ebergotzen and Barbis. Fine root production estimated by ingrowth cores and a net method was approximately twice as high in the more acidic stands Fichtelgebirge and Harz compared with Ebergotzen and Barbis. Rates of living fine root biomass turnover were higher at the Fichtelgebirge and Harz sites than at the Ebergotzen site. Rates of necromass turnover were similar at all sites. The results suggest that the accumulation of necromass was not due to a slower disappearance at the more acid sites, but to earlier root death. Roots contributed 46% to root + needle litter and 32% to root + total aboveground litter at the Harz site in 1997
Root turnover and root necromass accumulation of Norway spruce (Picea abies) are affected by soil acidity
No full textFine root distribution and turnover were investigated in ca. 40-year-old pure Norway spruce (Picea abies Karst.) stands in Germany, growing on four sites that differed in soil acidity (Ebergotzen < Barbis < Fichtelgebirge = Harz). The density of fine root biomass and necromass in different soil horizons differed among the sites. At one of the most acidic sites (Harz), fine root density in the humus layer was more than twice that at the least acidic site (Ebergotzen). At the two most acidic sites, Fichtelgebirge and Harz, the ratio of biomass to necromass was significantly lower than at Ebergotzen and Barbis, particularly in the subsoil layer. In each stand, clear vertical gradients in fine root length density and root tip density were observed. Most of the roots and the root tips were in the humus layer and in the first mineral soil horizon (0-10 cm). There was a significantly different decrease in specific root length (cm g(DM)(-1)) and specific root tip density (root tips g(DM)(-1)) in the more acidified stands Fichtelgebirge and Harz compared with Ebergotzen and Barbis. Fine root production estimated by ingrowth cores and a net method was approximately twice as high in the more acidic stands Fichtelgebirge and Harz compared with Ebergotzen and Barbis. Rates of living fine root biomass turnover were higher at the Fichtelgebirge and Harz sites than at the Ebergotzen site. Rates of necromass turnover were similar at all sites. The results suggest that the accumulation of necromass was not due to a slower disappearance at the more acid sites, but to earlier root death. Roots contributed 46% to root + needle litter and 32% to root + total aboveground litter at the Harz site in 1997
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