Respuesta de Fragaria mexicana y comunidades microbianas rizosféricas al aumento de temperature / Response of Fragaria Mexicana and rhizophere microbial communitites to temperature increase

Resumen Para los próximos 100 años se pronostica un incremento en la temperatura del planeta de casi 4 °C, lo cual pondrá en riesgo las especies que no logren adaptarse. En esta investigación se determinaron las respuestas morfofisiológicas de F. mexicana y los cambios en la población de bacterias fijadoras de nitrógeno atmosférico (BFN) asociadas a sus raíces, debido a dos condiciones ambientales con diferencias medias de temperatura de 5.1 oC: invernadero (temperatura alta, TA) y campo abierto (temperatura baja, TB); y con cuatro tratamientos: sin inocular (T), inoculadas con la cepa ocho (CP8), cepa cuatro (CP4) y con ambas cepas (CP8 + 4). Las BFN fueron aisladas de la rizosfera de F. mexicana y transformadas genéticamente con reporteros, para cuantificar la población al final del experimento. Se midió el peso seco de la parte aérea y la raíz, la tasa de asimilación de CO2 (A), el inicio de la floración, el número de flores y frutos; y la persistencia de las bacterias fijadoras de N atmosférico (BFN). Además, se evaluó la concentración de NO3, NH4, P y materia orgánica (MO) en el sustrato, al inicio y final del experimento. Las plantas sometidas a alta temperatura presentaron mayor peso seco de la parte aérea y fotosíntesis; con una disminución en el peso seco de la raíz, y en el número de flores y frutos. La MO en el sustrato disminuyó, mientras que la disponibilidad de NO3, NH4 y P aumentó. El incremento de temperatura y la mayor presencia de N en el substrato provocaron reducción en la población de BFN. Estos resultados sugieren que temperaturas altas estimulan el crecimiento de F. mexicana y tienen un impacto negativo sobre su reproducción y en las BFN asociadas a sus raíces.(AU)

Abstract The earth could experience a warming of 4 °C in the next one hundred years. This would put at risk the plants that can´t adapt. Fragaria mexicana is an endemic plant of temperate forest of Mexico. The response of this wild strawberry to temperature increasing has not been studied and could play an important role for event of global warming. This study determinate the morphological and physiological responses of F. mexicana and changes in the N2-fixing bacteria (BFN) population on its roots, due to two environmental conditions with differences of temperature 5.1 °C: greenhouse (high temperature, TA) and open land (low temperature, TB); and with four free-living nitrogen-fixing bacteria (BFN) treatments: non-inoculated (T), inoculated with strain eight (CP8), strain four (CP4), and strains eight and four mixed (CP8 + 4). BFN were isolated from the rhizosphere of F. mexicana and were genetically transformed with reporters to quantify the population at the end of the experiment. NO3, NH4 and P and organic matter (MO) in the substrate were determined at beginning and finish of the experiment. Shoot and root dry weight, photosynthetic rate, flowering and fructification starting, flowers and fruits number, were measured. Shoot dry weight and photosynthetic rate were lower in TB than TA, decreasing 3.1 g and 0.94 µmol m-2 s-1, respectively. Root dry weight was 3.0 g less in TA compared with TB. Number flowers decrease in 40.89 % and number fruits in 38.11 % on TA than TB. F. mexicana plants start flowering 14 days previously in TB than TA. MO in the substrate decrease in TA, while the concentration of NO3, NH4 and P, increased. Population of BFN was lower in TA. Results obtained indicated that higher temperature promotes the growth of F. mexicana and reduce its reproduction and BNF population associated with its roots.(AU)

Formononetin associated with phosphorus influences soybean symbiosis with mycorrhizal fungi and Bradyrhizobium / Formononetina associada com fósforo influencia a simbiose de soja com fungos micorrízicos e Bradyrhizobium

Arbuscular mycorrhizal fungi play an important role on nutrient supply to plants, specially P. However, the availability of inoculants for large-scale usage in agriculture is still limited because these organisms are obligatory symbionts. The use of symbiosis stimulants such as flavonoids can be an alternative to improve the beneficial effects of mycorrhiza for plant nutrition. The aim of this study was to evaluate the effect of the isoflavonoid biostimulant formononetin (7-hydroxy, 4'-methoxy isoflavone) in combination with three levels of phosphorus fertilization on mycorrhizal colonization, nodulation, and productivity of soybean, under field conditions. A 3 x 4 factorial scheme (levels of P: 0, 60 and 120 kg ha-1 P2O5 and doses of formononetin: 0, 25, 50 and 100 g ha-1) was used with five replicates. The following parameters were quantified at full bloom: plant height, shoot dry weight, nodule number, nodule dry weight, mycorrhizal colonization, and shoot N and P concentrations. Productivity was also evaluated at the end of the crop cycle. Formononetin stimulated mycorrhizal colonization at lower levels of P (0 and 60 kg ha-1), with colonization increasing from 56 to 64%. When applied with 60 kg ha-1 P2O5, formononetin increased soybean productivity to values similar to those observed when 120 kg ha-1 de P2O5, was applied. At doses above 50 g ha-1, formononetin applied to the seeds can reduce the need of P fertilization by 50%.

Os Fungos micorrízicos arbusculares desempenham papel importante no fornecimento de nutrientes para as plantas, especialmente P. No entanto, a disponibilidade de inoculantes com esses fungos, para o uso em larga escala na agricultura é ainda limitada, porque estes organismos são simbiontes obrigatórios. O uso de estimulantes simbióticos, como os flavonóides, podem ser uma alternativa para melhorar os efeitos benéficos da micorrrização na nutrição das plantas. O objetivo neste estudo foi avaliar o efeito do isoflavonóide bioestimulante formononetina (7-hidroxi, 4'-metoxi isoflavona) em combinação com três níveis de adubação fosfatada sobre a colonização micorrízica, a nodulação e a produtividade da soja, em condições de campo. Um esquema fatorial 3 x 4 (níveis de P: 0, 60 e 120 kg ha-1 de P2O5 e doses de formononetina: 0, 25, 50 e 100 g ha-1) foi utilizado, com cinco repetições. Os seguintes parâmetros foram quantificados em plena floração: altura da planta, matéria seca da parte aérea, número e matéria seca de nódulos, colonização micorrízica, e concentrações de N e P na parte aérea das plantas. A produtividade também foi avaliada no final do ciclo da cultura. A Formononetina estimulou a colonização micorrízica em níveis mais baixos de P (0 e 60 kg ha- 1), com aumentos de 56-64%. Quando aplicado com 60 kg ha-1 de P2O5, a formononetina aumentou a produtividade da soja, alcançando valores semelhantes aos observados quando foi aplicado 120 kg ha-1 de P2O5. Em doses acima de 50 g ha- 1, a formononetina aplicada na semente pode reduzir a necessidade de fertilização fosfatada em 50%.

INFLUENCE OF EXUDATES OF AMMONIUM-RESISTANT N_2 -FIXING BACTERIA ON THE GROWTH OF RICE SEEDLING / 微生物学通报

By using cup culture, influence of different strains (ammonium-resistant N2-fixing type, wild type, none N2-fixing type) of Klebsiella oxytoca on the growth of rice seedling was compared. It was discovered that ammonium-resistant N2 -fixing bacteria could excrete some plant growth promoting substance, which could be adsorbed by cation resin. It' s activity wouldn't be affected at 80℃. At optimal concentration, the weight of rice root and seedling were increased by