Tag: nitrogen fixation
Additions to the knowledge of Ganoderma in Thailand: Ganoderma casuarinicola, a new record; and Ganoderma thailandicum sp. nov.
Ganoderma is a cosmopolitan genus of mushrooms, which can cause root and butt rot diseases on many tree species. Members of this genus are particularly diverse in tropical regions. Some Ganoderma spp. are medicinally active and therefore are used to treat human diseases or as a dietary supplement. In this study, three Ganoderma strains were collected in tropical southern Thailand. Phylogenetic analyses of combined ITS, LSU, TEF1α and RPB2 sequence data indicated that the three strains grouped in a distinct lineage within laccate Ganoderma. One strain was collected from Surat Thani Province clustered in the G. casuarinicola clade with high statistical support (MLBS = 100% / MPBS = 98% / PP = 0.96), while the other two strains of Ganoderma, collected from Nakhon Si Thammarat Province, formed a distinct well-supported clade (MLBS = 100% / MPBS = 100% / PP = 1.00) and are described here as a new species. Ganoderma casuarinicola is reported here as a new record to Thailand. Morphological differences of the two taxa and their closely related taxa are discussed. Colour photographs of macro and micro morphological characteristics and a phylogenetic tree to show the placement of the new record and new species are provided.
Positive nitrogen balance of Acacia mangium woodlots as fallows in the Philippines based on 15N natural abundance data of N2 fixation
Nitrogen inputs from biological nitrogen fixation contribute to productivity and sustainability of agroforestry systems but they need to be able to offset export of N when trees are harvested. This study assessed magnitudes of biological nitrogen fixation (natural 15N abundance) and N balance of Acacia mangium woodlots grown in farmer’s fields, and determined if N2 fixation capacity was affected by tree age. Tree biomass, standing litter, understory vegetation and soil samplings were conducted in 15 farmer’s fields growing A. mangium as a form of sequential agroforestry in Claveria, Misamis Oriental, Philippines. The trees corresponded to ages of 4, 6, 8, 10 and 12 years, and were replicated three times. Samples from different plant parts and soils (0– 100 cm) were collected and analyzed for d15N and nutrients. The B-value, needed as a reference of isotopic discrimination when fully reliant on atmospheric N, was generated by growing A. mangium in an N2-free sand culture in the glasshouse. Isotopic discrimination occurring during N2 fixation and metabolic processes indicated variation of d15N values in the order of nodules[old leaves[young leaves[stems[litterfall and roots of the trees grown in the field, with values ranging from -0.8 to 3.5% except nodules which were enriched and significantly different from other plant parts (P.0001). Isotopic discrimination was not affected by tree age (P[0.05). Plants grown in N free sand culture exhibited the same pattern of isotopic discrimination as plants grown in the field. The estimated B-value for the whole plant of A. mangium was -0.86%. Mature tree stands of 12 years accumulated up to 1994 kg N ha-1 in aboveground biomass. Average proportion of N derived from N2 fixation of A. mangium was 54% (±22) and was not affected by age (P[0.05). Average yearly quantities of N2 fixed were 128 kg N ha-1 in above-ground biomass amounting to 1208 kg N fixed ha-1 over 12 years. Harvest of 12-year old trees removed approximately 91% of standing aboveground biomass from the site as timber and fuel wood. The resulting net N balance was 151 kg N ha-1 derived from remaining leaves, twigs, standing litter, and 562 kg N ha-1 when tree roots were included in the calculation. The fast growing A. mangium appears to be a viable fallow option for managing N in these systems. However, other nutrients have to be replaced by using part of the timber and fuel wood sales to compensate for large amounts of nutrient removed in order for the system to be sustainable.
Dinitrogen fixation by the legume cover crop Pueraria phaseoloides and transfer of fixed N to Hevea brasiliensis—Impact on tree growth and vulnerability to drought
Rubber tree plantations (Hevea brasiliensis) are expanding into marginal areas with low soil fertility and long dry seasons with a high risk of soil erosion and drought damage to trees. Introducing an N2-fixing legume cover crop in rubber plantations may reduce runoff and soil erosion as well as increasing the availability of nutrients but may also increase competition for water. This study quantified the effect of the legume cover crop Pueraria phaseoloides on N, P and K nutrition, water status and growth of young rubber trees (three years old in 2007) over a four year period (2007-2010). The plantation was located on a toposequence with a range of soil depths and water storage capacities in northeast Thailand.The legume aboveground biomass production and its nutrient content and decomposition rate were measured and the N2 fixation was estimated using the abundance of 15N (15N) in the legume. Measurements were taken of the tree stem girth and height and tree leaf predawn water potential, nutrient content and greenness. The transfer of N2 fixed by the cover crop to the trees was estimated using 15N in the tree leaves.The annual biomass production of the legume was 8Mgha-1 year-1 and the N accumulation by the legume was 250kg N ha-1 year-1. The natural abundance method applied to the aboveground components of the legume gave N2 fixation rates varying from 85 to 93% depending on the year. The leaf 15N was similar in the three non-legumes (H. brasiliensis, Vetiveria zizanioides and Praxelis clematidea) used as reference plants for estimating the N2 fixation. The higher level of N and the much lower leaf 15N values for the rubber trees intercropped with P. phaseoloides, compared to rubber trees growing without a legume cover crop, showed that there was a relatively high transfer of fixed N from the legume to the trees, varying from 39% to 46% of tree leaf N depending on the year. Neither N2 fixation nor N transfer varied significantly along the toposequence. At the bottom of the toposequence, both the nutrient (N, P and K) and water status of trees was significantly improved with the legume cover crop, doubling the tree girth at seven years of age (tree girth: 28cm, tree height: 700cm). However, at the top of the toposequence with low water storage capacity, the legume cover crop improved tree nutrition and growth but reduced the trees’ ability to survive intense drought.These results raise concern about the resilience to drought of the rubber tree/. P. phaseoloides system, since the positive effect of the legume on rubber tree nutrition and growth may increase the risk of water stress and tree mortality. With future changes in climate, an increasing number of areas will be concerned by the question of optimizing the tradeoff between N inputs and water availability. © 2015.
Benefiting from N2 -fixation and managing rhizobia
Nodulation and nitrogen fixation in the Leguminosae (Fabaceae) family, classification of rhizobia, and quantification of N2 fixed by different legumes are reviewed. Some promising management options intended to improve N2-fixation by direct selection of rhizobia in soil or by screening and breeding of legumes for increased N2-fixation, are discussed. The effects of pruning, soil phosphorus and pH, available nitrogen, and interactions of nematodes and rhizobia on nodulation and N2-fixation are analysed. The fate of fixed nitrogen can be determined by the recovery efficiency of N and leaching and gaseous N losses.
Quantifying biological nitrogen fixation of agroforestry shrub species using 15N dilution techniques under greenhouse conditions
Some land-use systems in Saskatchewan, Canada include the nitrogen-fixing trees buffaloberry (Shepherdia argentea Nutt.), caragana (Caragana arborescens Lam.) and sea buckthorn (Hippophae rhamnoides L.). These species provide various ecological functions such as ameliorating soil moisture, light and temperature but little work has been done quantifying biological nitrogen fixation by these species. Greenhouse experiments were conducted to quantify N2-fixation using the 15N natural abundance and the 15N dilution methods. Buffaloberry failed to form nodules in all but one of the four replicates in the natural abundance experiment. Using the 15N dilution method, the percentage of N derived from atmosphere (%Ndfa) in the shoot of buffaloberry averaged 64 %. For caragana, the mean %Ndfa was 59 and 65 % and seabuckthorn was 70 and 73 % measured using the natural abundance and dilution methods, respectively. Because of large variability in biomass production between plants grown in the natural abundance experiment and the dilution experiment, the amounts of N2 fixed also were very variable. Buffaloberry fixed an average of 0.89 g N m-2; the average for caragana ranged from 1.14 to 4.12 g N m-2 and seabuckthorn ranged from 0.85 to 3.77 g N m-2 in the natural abundance and dilution experiments, respectively. This corresponds to 16 kg N ha-1 year-1 for buffaloberry; an average of 15-73 kg N ha-1 year-1 in caragana and 11-67 kg N ha-1 year-1 in seabuckthorn. The substantial amounts of N2 fixed by these species indicate that they have the potential to contribute to the overall N balance in land-use systems in which they are included
Improved fallows come of age in the tropics
Improved fallows are the deliberate planting of fast-growing species — usually legumes — for rapid replenishment of soil fertility. Improved fallows are rapidly spreading in several regions of the tropics as a sensible way for in situ accumulation of large quantities of N in vegetation and soil, as well as for providing sustainability enhancing services. Research on improved fallows increased after the mid 1980s with the development of what is known as the second soil fertility paradigm, which is based on sustainability considerations. Many lessons have emerged from short-term improved fallows (<5 years duration). These include the diversity of farm sizes where improved fallows are used, the advantage of sequential versus simultaneous systems, the utilization of dry seasons unfavorable for crop production, the comparative advantages of woody versus herbaceous leguminous fallows, the magnitude of N accumulation, the strategic use of N fertilizers, and the importance of P. Other key services provided by fallows include fuelwood production, recycling of nutrients besides N, provision of a C supply to soil microorganisms, weed suppression, Striga control, and improved soil water storage. Natural fallows of non-legume shrubs belonging to the Asteraceae family, collectively called ‘daisy fallows’, may provide lessons for the development of improved fallows. The maintenance of genetic diversity in fallows is paramount. The main limiting factor in Africa is clearly the supply of germplasm of improved fallow species. This must be overcome though large-scale seed orchards and nursery development before impact at the scale of millions of farmers can take place.
Annual litter fall of nitrogen-fixing tree species in rotational woodlots at Tumbi (Tabora), western Tanzania
A rotational woodlot is a method involving growing trees with crops up to 2-3 years until trees start competing with crops. Thereafter the woodlot is left as a source of fuel wood, building poles or fodder while restoring soil fertility until farmers start cutting down the trees and growing crops between the stumps 4 to 5 years later. The method was designed and developed by the South African Development Countries (SADC) and the World Agroforestry Centre(ICRAF) and their partners to alleviate rural farmers from the problems of fuelwood scarcity and poor soil fertility in the tobacco cereal land use system. The method is currently being practised at farmers’ fields in Tabora rural district in western Tanzania involving a large number of farmers. This study reports an assessment of litter production and seasonal pattern of Acacia crassicarpa , A. julifera , A. leptocarpa, Leucaena pallida and Senna siamea grown in rotational woodlots at five years of age.
Soil fertility management in semi arid areas of east and southern Africa
The Arid and Semiarid areas in Sub-Saharan Africa occur mainly around the latitude 10 -15 N IN west Africa and roughly 10 -30S in Southern Africa.In addition there is also a large arid and semi-arid region in The Horn of Africa and East Africa.Another largo dry region exist in South-Western and South-Estern Africa, consisting of semi-arid strip that runs roughly North and South inland in Namib Desert, eastwards in a broad belt through Botswana, and then south through the center of South Africa.Smaller semi-arid areas are also found in Zimbabwe,Mozambique and Madagascar.
Infection potential of farm soils as mycorrhizal inocula for Leucaena leucocephala
A greenhouse experiment was conducted to assess the arbuscular mycorrhizal (AM) fungi inoculum potential for Leucaena leucocephala in a range of nutrient-depleted farm soils in western Kenya. Leucaena was grown in 12 uninoculated farm soils with pH 5.0–6.7, with or without rock P and farmyard manure. Root infection, nodulation, and shoot and root weight were determined 25, 46, and 69 days after planting. Spore concentrations in the farm soils at the start of the experiment ranged from 44 to 126 live spores per 100 g dry soil with 6–10 species per soil, principally Scutellospora spp. and Acaulospora spp. Nodulation was absent or poor in all soils, indicating the need for rhizobial inoculation of species belonging to the leucaena crossinoculation group in this agrosystem. Rock-P alone increased final shoot dry weight by a factor of 1.4, manure alone by 1.8, and rock-P plus manure by 1.9, compared with no ameliorant. Root infection with AM fungi was detected in all soils 25 days after planting and increased linearly in the different farm soils to values of 33–65% 69 days after planting. Soil pH and root infection 25 days after planting accounted for much of the variation in final shoot weight among soils with no amelioront (87%). As early root infection increased from 20 to 40% at soil pH 5.0, the predicted final shoot dry weight was doubled, and the response to ameliorants was reduced by two-thirds. The growth responses to increased infection became smaller as pH increased from 5.0 to 6.5.