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Into Horticulture

Issue 11   January 2013
Plant & Garden News
From annual to immortal

By altering a gene, German researchers have been able to prevent flowering in tobacco and expand the lifespan of a plant from about 4 months to "forever". Their oldest plant is now 8 years old. Besides indefinite growth, leaf senescence is also prevented. Applied to other crops that aren't dependent on flowering (e.g. potatoes), the discovery could potentially boost production while eliminating genetic contamination of the agricultural/natural environment through pollen or seed. Source: Giant tobacco plants that stay young forever

Floral enticements boost mango pollination

The relative unattractiveness of mango flowers to pollinating insects is a limitation to fruit production. Studies in South Africa have shown that small patches of wildflowers in non-productive areas of large farms could be a low-cost way to improve this situation. Further work is required to optimise the size and species composition of such patches. Pesticide management is also likely to influence the effectiveness of such measures. Source: Small patches of native plants help boost pollination services in large farms

Bacteria build soil

Research suggests that a significant proportion of soil organic matter may not derive from plant material directly, but from the remains of the soil microflora that feed on it. Bacterial cell wall fragments, resistant to further decay, thus contribute to the long-term soil carbon store. Bacterial products also coat mineral soil particles with an organic film, on which such particles can be accumulated. Source: Fertile soil doesn't fall from the sky. The contribution of bacterial remnants to soil fertility has been underestimated until now

With research, Frankincense trees can keep giving

Frankincense is obtained by collecting resin from the wounded bark of Boswellia papyrifera trees. Demand for the fragrance means that over-tapping is threatening the trees in Ethiopia (the main exporting country) and the people who rely on them for a living. An anatomical study of the resin canals of this species has provided new information which may help develop methods for more efficient collection with with less damage. Read more at Frankincense is for life, not just for Christmas

Close call with Varroa

A swarm of Asian honey bees carrying more than 150 Varroa mites were detected in NSW on a bulk vessel that arrived from Singapore. It's believed that all the bees associated with this incursion were eradicated. Source: Rapid response stops spread of Asian honey bee pest

Secrets of the black dahlia

A study of the "black" dahlia has revealed that the large amounts of red anthocyanins are produced due to a lack of flavones (associated with white flowers) competing for biochemical building blocks. It is not caused by increased activity of the anthocyanin pathway. The findings are a step towards engineering flavone content of plants. Source: Le Rouge et le Noir: Where the black dahlia gets its color

Alyssum gets industrial

"Cleaning Land for Wealth" is a UK research project that aims to rehabilitate contaminated soils while producing useful metallic nanoparticles, with the help of common plants like Alyssum. Properly developed, it's possible that plant "biofactories" will be able to produce particles of the right size and shape to be used in applications like catalytic converters or cancer treatments, without further processing. Source: Flower power to purge poison and produce platinum

More than one scribbler

Although a distinctive feature of some Eucalypts, the cause of the "scribbles" on their trunks has until recently been little studied. The Australian Scribbly Gum Moth was thought to be the only species responsible, but thanks to a team of "retired" CSIRO scientists, we now know that at least twelve species of moths can create the phenomenon. Source: 'Retired' scientists unmask bush graffiti artist

How to encourage birds in the city?

Environmental researchers from The University of Queensland have released a study suggesting urban birdlife can be better supported with compact development, provided suitable habitats can be retained in the form of parks and vegetated areas. Such habitats are not generally provided by urban sprawl. Source:Building bird-friendly cities

Native street trees benefit birds

A "world-first" study conducted in Canberra reveals that native street trees can have a significant effect on the number and diversity of bird species in the area. Exotic tree species, while having certain landscaping advantages, are not as good as eucalypts (especially large ones) in supporting birdlife, whether by food, shelter or nesting sites. Even though some management may be required to keep large eucalypts safe in a suburban environment, the researchers urge that the benefits to biodiversity be considered in vegetation planning. This includes proactively planting young trees to replace the large trees, which will eventually succumb to age. Source: Native street trees can boost birds' survival

More shade for Brisbane pathways

Brisbane City Council has declared that its footpaths and cycleways will be cooler and greener in the future as a result of its Neighbourhood Shadeways initiative. The aim is to increase the city's street tree population by 35000 by 2026, taking shading along residential footpaths and cycle ways to 50% from a current 35%. A range of native shade tree species will be used. Council is encouraging residents to let them know where they'd like more trees planted. More information: Lord Mayor's growing plan to shade Brisbane streets

Green is Good
Economic, Environmental, and Health/Well-Being Benefits Associated with Green Industry Products and Services: A Review Charles R. Hall and Madeline W. Dickson, 2011. Journal of Environmental Horticulture 29(2):96-103

Everyone involved in the nursery and landscape industry should take a look at this 2011 review, which "summarizes the peer-reviewed research regarding the economic benefits, environmental benefits (eco-systems services), and health/well-being benefits of green industry products and services that serve to enhance the quality of life for consumers."

While it has an American focus, most of the conclusions should be generally applicable to other developed countries.

Landscapers or nursery staff might like to print off a copy so they can show prospective clients the sections on property values, occupancy rates and the effect beautified commercial spaces have on shoppers. Meanwhile, those in health and community care will be interested in the broad range of benefits in that area.

The paper contains an extensive list of references to the studies cited, for anyone wanting to delve deeper into the research.
Goodbye Gutenberg

Looking back on the horticultural scene here over last 12 months (as is customary about now), the demise of two of Australia's printed garden publications is worthy of note. Given that our small and geographically/climatically disperse population could only ever support a few such publications, this is more significant than it may at first appear.

Australian Horticulture was the nation's premier trade journal for the nursery and landscape industry and ceased publication mid-2012 [1].

Later in the year, an announcement was made that Burke's Backyard magazine will close in 2013 [2]. Its termination marks a further reduction of the Don Burke presence in the mainstream media after the cancellation of his popular lifestyle TV show some years ago.

It could be argued that years of bad weather, natural disasters and tightening water restrictions had something to do with these developments, but anyone familiar with the state of print media worldwide would not be surprised at the death of any printed magazine or newspaper. Incidentally, Australian circulation figures for about a hundred magazines can be viewed online [3], in case you're curious. Note the year-on-year drops across a range of titles.

Clearly, the future for both the dissemination of information and advertising is electronic and online. "Online" may mean the World Wide Web to most people at the moment. However, the convergence of internet in its various forms with traditional print media, television, radio and telephony that we're starting to see now will undoubtedly continue, and accelerate as the National Broadband Network is rolled out.

It's an evolving scene, but one that can't be ignored if the green industry is to compete with shoe shopping and sports betting for consumer dollars in the future. Perhaps the closure of these two paper magazines will serve as a sign to the industry generally, as well as individual businesses, to start thinking more seriously about their future online.

[1] Newsletter - Message from the AIH President Australian Institute of Horticulture
Queensland Garden Events 2013
A reminder to Queensland residents who might be organising a public garden-related event this year: if you have dates confirmed, be sure to send them in for free inclusion at Additional details such as guest speakers and other attractions can be added later, when information becomes available.
The Science of Horticulture

Plants and Iron (Part Two)

In Part One (see, the requirement that plants have for iron and symptoms of deficiency were discussed. In this issue, we'll look at the interaction between iron, plants and soil.

Iron in the soil

Iron (chemical symbol: Fe) is generally abundant in soil, but the chemical forms that usually predominate are unusable by plants. Unfortunately, a high total iron content does not necessarily mean that good plant growth can be supported.

Most soil iron exists in the oxidised ferric form, Fe3+. Under certain conditions, it can be converted to the more useful ferrous form, Fe2+. However, the concentration of this plant-available iron in soil is typically far lower and can be growth-limiting.

The formation of insoluble complexes with other soil components such as phosphorus are other impediments to adequate iron availability in soil.

In Australia, there are many soils so high in iron oxide they have a rusty red color. In some parts of coastal Australia, however, iron sulfide is laid down under waterlogged conditions. These are the notorious acid sulfate soils. Sulfuric acid is formed on exposure to air by agriculture or development, with subsequent problems for infrastructure and environment.

Organic residues in soil can also contain iron, and certain molecules such as humic acid can act as natural chelating agents (see below).

Conditions exacerbating iron deficiency

Deficiency in otherwise iron-sufficient soils can be induced by various environmental conditions including certain horticultural practices.

Iron deficiency is a common problem of calcareous soils, when it is sometimes called "lime-induced chlorosis" (referring to the resultant symptom). Bicarbonate (HCO3-) released into the soil solution interferes with iron uptake and transport by plants. Calcium ions can also interfere with uptake.

Excessive application of agricultural lime can likewise induce iron deficiency.

Soil alkalinity in general or irrigation with alkaline water can be a problem because iron becomes increasingly unavailable as pH rises.

Over-fertilisation with phosphate or other nutrients which interact negatively in the soil or within the plant can induce deficiency. Manganese, zinc, copper, molybdenum have been implicated in various cases. Over-use of copper fungicides is a potential danger in this regard.

Anything affecting the number and health of roots, such as temperature extremes, waterlogging, other causes of oxygen deprivation, pests and diseases or other mineral deficiencies/toxicities could contribute to iron deficiency in the plant by restricting uptake.

Waterlogging can also induce deficiency by causing more bicarbonate to become available in calcareous soils.

Plant uptake

Given the reactive nature of iron, it's not surprising that plants employ complex processes to ensure uptake and transport. Most iron uptake occurs near the growing root tips. An enzyme (reductase) in the root cell membrane coverts Fe3+ to Fe2+, which is carried into the cell by a transporter protein. It's an active metabolic process that requires energy.

When iron availability becomes limiting, additional mechanisms are activated. Responses fall into two categories:

"Strategy I" is employed by most plants except grasses (but including other monocots). Response includes excretion of hydrogen ions to acidify the soil around the roots, secretion of iron-capturing molecules and increased reductase production. There may also be proliferation of roots and development of specialised cells to enhance uptake.

"Strategy II" is used by the grasses. They exude phytosiderophores from their roots. These are natural chelating agents that can bind Fe3+ and allow it to be transported across the roots' cell membranes.


Chelation is very important in biology because it provides a way for organisms to move elements such as iron and control their reactivity.

A chelating agent is a molecule that is able to "grab" a metal ion. The resultant compound is called a chelate, derived from the Greek word for the claw of a lobster or crab. Among the most significant chelates in nature is chlorophyll, which contains magnesium. The leghemoglobin of plant nitrogen-fixing nodules (see part 1 of this article) is an iron chelate.

Grasses manufacture and secrete their own chelating agents - phytosiderophores - to capture iron from soil and allow it to be transported into the root.

Furthermore, some bacteria and fungi produce siderophores for their own iron uptake and certain components of soil organic matter such as humic acid have natural chelating properties. These can potentially be exploited by plants.

In horticulture, artificial chelates are a way of formulating iron fertilisers to avoid soil immobilisation and improve plant availability (compared to simple compounds like iron sulfate, for example).

EDTA is one commercially-produced synthetic chelator which may be familiar, although better chelates for use in agriculture have since been developed.


While less commonly encountered than deficiency, iron toxicity is also possible. It can be a problem in nursery production of ornamentals, especially with sensitive species.

Iron sulfate is a long-used treatment for moss infestation of turf. The greater sensitivity of the moss provides a certain selectively of action when applied at suitable concentrations, and has the additional benefit of supplementing the surviving grass with iron.

Coming in Part Three...

Prevention and treatment of iron deficiency will be discussed in the final part of this article. In the meantime, refer to the links on if you'd like to learn more about iron nutrition in plants.

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