Back to grass roots

The roots of grass plants are hidden and concealed - they are dull and brown - they are ordinary and mundane.

But what grass roots do, how they function and the way they interact with other living creatures in the soil is anything but ordinary.

A brief tour of some of the highlights of the rhizosphere – the zone of intense biological life in and closely around roots in the soil – reveals some of the extraordinary things that grass roots ordinarily do to maintain the domesticated and wild grass swards that sustain most terrestrial animal and human life on the planet.

Grass plants have a dense, multi-branched, multitudinous network of fibrous roots that infiltrate and extend their fine filamentous fingers into every moist and nutrient-rich nook and cranny in the topmost layers of the soil. The grass root network has no predetermined, fixed structure or plan but roots branch adventitiously, elongating and extending dynamically (also dying and shrinking back rapidly in times of scarcity and stress) to gain a purchase in the soil and seek out and absorb moisture and nutrients. Roots get thinner as they branch; ending in a fine root tip sheathed with fine root hairs and tipped with a sensory elongation zone and a root cap that sensitively perceives and reflexively responds to changes in the physical and chemical state of its immediate environment.

Form and structure of the root tip

  

The leaves of a grass plant enjoy the luxury of easily accessible and mostly uniformly available sunlight and the atmospheric gases they absorb, but roots have to delve deeply into and unceasingly explore a highly heterogeneous environment, in which vital resources are patchily and unpredictably distributed. Water, and especially vital mineral nutrients the plant needs to function, grow, flower and reproduce, are hard to come by, often tightly bound to soil particles or in intractable organic forms. Myriad other tiny and microbial forms of life swarm through the rhizosphere (take a quick peek) also seeking and competing for the very resources the roots need to acquire.

Water and nutrients selectively filtered and absorbed by the root hairs are transported upwards to the leaves where they are synthesised into a range of simple and complex molecular products using solar energy and carbon harvested by the green leafy canopy. Roots also produce plant-stimulating hormones. In turn, the leaves supply the roots with the protein and energetic compounds they need to fuel their crucial exploratory, interactive and absorptive activities.

Roots are not just passive absorbers but actively work, through their plenteous and varied secretions, to modify the zone of soil and life activities in their immediate vicinity. Water and soil particles are bound and held to the root by mucilaginous ooze while root exudates serve to communicate with friends and foe lurking in the soil. Among the diverse array of chemicals exuded by the root are compounds that recognise and poison roots of foreign plants, pathogenic microbes or fierce root-devouring denizens such as nematode worms. 

Root exudates and root hairs create a rhizosheath of soil around the roots

 Intriguingly and perhaps most importantly, plants give away up to almost a fifth of their hard-earned energy by actively exuding sugars and other soluble molecules into the rhizosphere to feed hordes of insatiable soil bacteria. Energised by these root exudates, soil microbes set upon and transform complex organic material in the soil and release, for the roots to absorb, simple minerals and nitrogen-rich substances vital for plant life. Grass plants give up even more sweet secretions when grazed but are rewarded by a larger bounty of compounds they need for regrowth.

Many grasses and other plant species in natural vegetation connect to and interact closely with other living networks in the soil. Filaments of particular fungi (mycorrhizae) inosculate intimately with the root system, penetrating into the outer root cells to obtain food directly from the plant. The benefits to the grass of this symbiotic association are many (disease and pest protection, for instance) but most importantly, these ‘fungal-roots’ serve to vastly extend the reach of the roots. They fetch and transport water and many essential macro- and micronutrients – some of which do not easily move through the soil – back to the root. Different grasses have their own distinct mycorrhizal communities and these need to be purposely reintroduced (along with ample organic matter) into degraded soil of barren lands to restore the vital interactions and connections between plants and a living soil.

fine

grass roots

nourish, nurture, hold

Earth’s green

skin

The dyanamic interactive rhizosphere ecosystem

Sexy feathers from grass

A guest blog post by Dr Mark Brown (University of KwaZulu-Natal-Pietermaritzburg)

So here I am, an avid ornithologist asked to write about grass... wow, really? Is grass actually useful? Just kidding Craig! Well as the title suggests, grass is quite useful for some birds apart from just being a source of food (seed). For some species, it's what they get out of grass that turns the ladies’ eye...

Male Red Bishop

The colors in the feathers of a bird are formed in two different ways, from either pigments or from light refraction caused by the structure of the feather. In some cases feather colors are the result of a combination of pigment and structural colors. The greens of some parrots are the result of yellow pigments overlaying the blue-reflecting characteristic of the feathers.

Pigments are colored substances that can be found in both plants and animals. The coloration created by pigments is independent of the structure of the feather. Pigment colorization in birds comes from three different groups: melanins, carotenoids, and porphyrines. This is where the grass comes in... Carotenoids are found in low quantities in grass seeds, which many granivorous birds eat.

In South Africa it is the genus Euplectes, the bishops and widowbirds, that are the main users of these pigments. The beneficial effects of high levels of carotenoids are well documented by scientists: as antioxidants they are thought to improve bird’s health, and the resulting bright feathers signal to female birds that males are healthy, have less parasites and a good diet.

Male Red Bishop pimping up his feathers

  

What? Grass makes birds sexy? Yup! Several good local studies have showed that there are two sexual selection systems in the Euplectes: long tails are important, and bright colors are important. In terms of long tails; yes ladies, sometimes size DOES count, as long as it is symmetrical! Female red-collared and long-tailed widowbirds prefer males with long, symmetrical tails.

Color is important two, but operates differently in different species. In red bishops, brighter (plumage not IQ) males attract more females to their harem and have higher reproductive success (more fun...). In red-collared and fan-tailed widowbirds, however, the colorful badges have an additional role... In these species, Sarah Pryke, Staffan Andersson and colleagues have shown that colorful badges also signal quality and dominance to other males... Basically, the pecking order is reflected by the badges... By manipulating the badge size and color, they showed that the pecking order changed to reflect the new badge order. End point is that the redder the badge, the higher up the pecking order you are with other males...

Color signals in birds are so called "honest signals". Producing the bright colors is costly, only those males in good condition with access to good food resources can collect enough carotenoids and put enough energy into plumage development to produce the brightest signals. In addition, it's not just the ladies that bright colors attract either! Predators would find it easy to pick off weak but colorful males, were they able to scrape such a plumage together... So in essence, male and female Euplects birds can easily assess the quality of other males and females very effectively - there is no cheating involved - unlike for us where we can steal a Ferrari, wear fake raybans, don a Magnum PI shirt, pump pirated music out the windows and have the ladies think we might be a good catch...

So next time you see a tired looking brightly colored male red bishop at your feeder or in the grassland, give him some respect - it's hard work looking so good!

Male Fan-tailed Widowbird (formely Red-shouldered Widow)

Just four letters....

It takes just four repeating molecular letters - adenine (A), thymine (T), guanine (G) and cytosine (C), and a fifth, uracil (U) in RNA - to give you this:

and this

 
or this  

 
and this 

 A-T, G-C, T-A, C-G, A-T, .... C-G, A-T, G-C, A-T, G-C ....

Knit together

Wondorously

As YOU

ooooooooooooooooooooooooo

One purl, one plain
(courtesy Psalm 139)

 
For you created my inmost being

one purl, one plain

you knit me together in my mother's womb

one purl, one plain

My frame was not hidden from you

one purl, one plain

when I was made in the secret place

one purl, one plain

When I was woven together in the depths of the earth

one purl, one plain

I praise you

one purl, one plain

because I am fearfully,

one purl, one plain

and wonderfully,

one purl, one plain

made
 

One pearl, unplain

ooooooooooooooooo