Rhizosphere microbial diversity as influenced by humic substance amendments and chemical composition of rhizodeposits

Chem. Biol. Technol. Agric.

Oliveira

et al. 2014

Background: Co-inoculation of maize with Herbaspirillum seropedicae and humic substances increases the sizes of plant-associated bacterial populations and enhances grain yields under laboratory and field conditions. Root exudation is a key mechanism in the regulation of plant-bacterial interactions in the rhizosphere; humic matter supplementation is known to change the exudation of H + ions and organic acids from maize roots. Our starting premise was that H. seropedicae and humic acids would modify maize seedling exudation profiles. We postulated that a better understanding of these shifts in exudate profiles might be useful in improving the chemical environment to promote better performance of plant growth-promoting bacteria delivered as bioinoculants. Thus, root exudates of maize were collected and analyzed by gas chromatography-mass spectrometry (GC-MS) and proton nuclear magnetic resonance (

Section: Discussionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Root exudate profiling of maize seedlings inoculated with Herbaspirillum seropedicaeand humic acids

Lima

Chem. Biol. Technol. Agric.

Oliveira

et al. 2014

“…The growth of blueberry and N and K uptake increased and the authors find a very interesting and significant change on the bacterial structure community at rhizosphere when HA was used. Previously, this kind of change on bacteria diversity at maize rhizosphere induced by HA presence [51] opening a wide avenue to study changes in the microbiota and the interaction of these microbiota changes with crop productivity. Two papers found no significant differences on yield by PGPB and HS treatments [55,56].…”

Section: Pgpb + Hs: Why Is It So Little Explored?mentioning

confidence: 99%

“…Despite humus is a direct product of microbiological activity, the soil chemistry and soil microbiology have established faint scientific connections around the world. Increase in the sustainable intensification of agriculture is important developments towards new ways of training future scientist [50,51]. Inter-disciplinarily and boundary-crossing in terminology and concepts are needed.…”

Section: Pgpb + Hs: Why Is It So Little Explored?mentioning

confidence: 99%

Plant growth promoting bacteria and humic substances: crop promotion and mechanisms of action

Chem. Biol. Technol. Agric.

Busato

Paula

et al. 2017

127

102

High-external input agriculture is one of the most disruptive human activities, which have been justified by the current economic paradigm due to high productivity and the need to feed a growing population. However, we are dangerously close to the edge of the planet resources and both hunger and food insecurity has increased. Limiting the use of non-renewable chemical fertilizers and pesticides, changing water management, enhancing diversity and considering the often-neglected social dimension of agriculture are the bases to other chemical and biological technologies to agriculture. Biological inputs can stimulate the substitution of chemical inputs without questioning the current fundaments or can be adopted as a turning point to intensify the harsh processes of transition to more environmental friendly agriculture. The debate is open and our contribution is to develop the scientific basis for biological inputs that, unlike soluble fertilizers and pesticides, depend on a number of factors for its success in promoting crop yield. In this review, we showed the results obtained with the combined use of diazotrophic endophytic bacteria and humic substances in diverse crops (sugarcane, maize, tomato, common beans and pineapple), presenting the main morphological and physiological changes induced by biological technology. A snapshot of the state of the art of the use of plant growth promoting bacteria together with humic substances was provided, showing their potential especially when plants are subjected to moderate to severe abiotic stress. The number of studies reporting the combined use of plant growth promoting bacteria and humic substances is surprisingly low. There is an open avenue for research and encouraging debate is the goal. To overcome the conventional agriculture, maintaining productivity levels is more than scientific challenge, is a humanitarian duty. The biological inputs can help in this purpose.

“…Puglisi et al [37]; [54]) showed that the addition of HS had a significant effect on the amount of bioavailable C deposited by maize plant roots, thus resulting in a significant change in the structure of soil microbial communities. More recently, Puglisi et al [55] used DGGE analysis and showed that the influence of HS on microorganism diversity reaches the bulk soil beyond the rhizosphere zone. Plants thus select their microbial community in order to improve their physiological processes involved in defence against pathogens, and mineralization and solubilization of nutrients.…”

Section: Hs and Plant Growth-promoting Bacteriamentioning

confidence: 99%

Physiological responses to humic substances as plant growth promoter

Canellas

2014

Chem Biol Techn Agric

387

243

Humic substances (HS) have been widely recognized as a plant growth promoter mainly by changes on root architecture and growth dynamics, which result in increased root size, branching and/or greater density of root hair with larger surface area. Stimulation of the H + -ATPase activity in cell membrane suggests that modifications brought about by HS are not only restricted to root structure, but are also extended to the major biochemical pathways since the driving force for most nutrient uptake is the electrochemical gradient across the plasma membrane. Changes on root exudation profile, as well as primary and secondary metabolism were also observed, though strongly dependent on environment conditions, type of plant and its ontogeny. Proteomics and genomic approaches with diverse plant species subjected to HS treatment had often shown controversial patterns of protein and gene expression. This is a clear indication that HS effects of plants are complex and involve non-linear, cross-interrelated and dynamic processes that need be treated with an interdisciplinary view. Being the humic associations recalcitrant to microbiological attack, their use as vehicle to introduce beneficial selected microorganisms to crops has been proposed. This represents a perspective for a sort of new biofertilizer designed for a sustainable agriculture, whereby plants treated with HS become more susceptible to interact with bioinoculants, while HS may concomitantly modify the structure/activity of the microbial community in the rhizosphere compartment. An enhanced knowledge of the effects on plants physiology and biochemistry and interaction with rhizosphere and endophytic microbes should lead to achieve increased crop productivity through a better use of HS inputs in Agriculture.