Biotropica 46(2) Editor’s Choice: Phyllosphere Bacteria Improve Plant Nutrition
I’m pleased to announce the March 2014 Editor’s Choice article: Ana Z. Gonçalves, Fernando L. Hoffmann, Helenice Mercier,Paulo Mazzafera, and Gustavo Q. Romero: Phyllosphere Bacteria Improve Animal Contribution to Plant Nutrition 46(2): 170-174.
It has been long been recognized bacteria can play a critical role in plant nutrient acquisition. This study elegantly and experimentally demonstrates one pathway by which they do so – by enhancing the uptake of nitrogen from animals whose fecal material is used by plants as fertilizer. There is still much to be learned about the micro biome of the phyllosphere, but this paper demonstrates that the impact can be considerable and that the clever use of antibiotics can provide new insights into tropical biology. Congratulations to Ana and colleagues! EB
Brazilian savannas have an acidic and poor-nutrient soil where many plants have evolved symbiotic relationships with animals and microorganisms to obtain nutrients. One of such example is the symbiotic relationship between the jumping spider Psecas chapoda and the terrestrial bromeliad Bromelia balansae. Whereas spiders inhabit and breed strictly in B. balansae leaving their debris inside rosettes, B. balansae obtain N from spider feces. Bromeliads have their leaves organized in rosettes that are a suitable microcosm where invertebrates, vertebrates, other plants and microorganisms can occur. These organisms concentrate debris inside rosettes from which minerals and amino acids can be absorbed by specialized epidermic cells named trichomes. Bromelia balansae is a terrestrial root-based bromeliad that accumulates few millimeters of water inside its rosettes. Trichomes of this species are capable to absorb minerals, but they are probably unable to absorb amino acids from spider debris. Additionally to these two symbiotic species, in his PhD Thesis Dr. Gustavo Romero found bacteria on B. balansae phyllosphere that might be responsible for N mineralization from organic molecules (spider debris) becoming nutrients available for uptake by the plant.
Although a huge amount of bacteria lives on plant phyllosphere, we still do not know the species that live in there, the essential aspects of their biology and how they influence their host plants and ecosystem functioning. In her graduate course, Msc. Ana Gonçalves used this plant-spider system to investigate whether phyllosphere bacteria facilitate N mineralization from spider debris and if this N is absorbed into the leaves improving bromeliad growth. The authors conducted a greenhouse experiment by manipulating bacteria abundance on the bromeliad phyllosphere using antibiotics. Using stable isotope methods, we demonstrated that debris from spiders contributed more for bromeliads with the entire bacterial assemblage; these bromeliads accumulated 57% more soluble protein and grew 13% more than bromeliads under reduced bacterial density. Additionally, we showed that just part of the bacterial assemblage grew in guanine (guanine is the main source of N present in P. chapoda feces). Mineralizing bacteria appear to make an important and previously unappreciated contribution to plant nutrition and performance in this system.
As far as we know, our results demonstrate for the first time that mineralization in the phyllosphere is a source of nutrients to plants in the savanna biome. Furthermore, with this research we open new questions about the role of phyllosphere bacteria in other bromeliad systems (such as epiphytic and tank-forming bromeliads), the role of other phyllosphere microorganisms (such as fungi) in mineralization, if other nutrients than N are mineralized and what is the role of phyllosphere microorganisms in other biomes than savanna. Especially because of our restricted knowledge about the diversity of bacteria associated with plant phyllosphere, we do not know many of their roles in ecological systems.