(Arboricultural-styled) 'Fact of the Day'

[Gary Prentice]

Yet there's many examples of these in open wounds, where light levels are only subdued. Could there be variance amongst species, maybe?

[Kveldssanger]

Of course - inter- and intra-specific variation will play a role. Unfortunately, Bob Watson provides only a few references, so I do not know where he got the information from. I suppose it would be more correct to suggest that low light and high humidity conditions provide an increased propensity for undifferentiated cells to form aerial roots. Ultimately, as long as the environmental and hormonal triggers are there, aerial roots can occur. And we don't know all of how a tree functions anyway, so we could be missing something from the equation.

 

Karban's Plant Sensing and Communication publication from this year really opened my eyes to the fact that we are only just starting to comprehend the intricate inner-workings of plants, particularly on the chemical level.

[Kveldssanger]

I got these books earlier this week:

 

The Structure and Life of Forest Trees

Response of Plants to Multiple Stresses

Growth and Development of Trees Volume I: Seed Germination, Ontogeny, and Shoot Growth.

Growth and Development of Trees Volume II: Cambial Growth, Root Growth, and Reproductive Growth.

 

Take your pick.

[Gary Prentice]

Can you write a Readers Digest precis version of these in the following order?

 

Response of Plants to Multiple Stresses

 

Growth and Development of Trees Volume II: Cambial Growth, Root Growth, and Reproductive Growth.

 

Growth and Development of Trees Volume I: Seed Germination, Ontogeny, and Shoot Growth.

 

The Structure and Life of Forest Trees.

 

No particular rush like, relax over the weekend and start posting on monday.

[Kveldssanger]

Yeah, sure.

 

WIll do one later, anyway. Not reading this book all day! Hahah.

[Kveldssanger]

For anyone looking to buy any books, look at T. T. Kozlowski's publications. His writing style is incredible. Also look to invest in the Physiological Ecology series by Academic Press. Again, wonderful writing format. Unlike anything else I own. So straightforward.

[Kveldssanger]

14/11/15. Fact #78.

 

Where population density of plants is at a point where there will be competition between individuals for resources, one can begin by stating that each individual acts as a direct stressor to its neighbours. Where a pathogen (or multiple) is then introduced into the equation and it infects particular hosts, this will then exacerbate existing stress levels (by lessening individual plant fitness) brought about by competiton between individuals - both on an inter- and intra-specific level. Of course, when one understands that multiple pathogens will impact upon multiple individuals (or the same and / or different species) in a given spatial environment, pathogens really do, at least in part, take competition between individuals to that next level.

 

For instance, when a leaf rust was introduced to a mixed culture of lettuce and groundsel, it was observed that infected lettuce suffered less significantly than infected groundsel. Observations suggest that rust, in this case, impacted upon inter-specific competition, though also facilitated increased growth rates in uninfected individuals (given their higher fitness in comparison to infected individuals - a divide that may widen with time, in fact, given the adverse cumulative impacts of poor competitive ability).

 

The aforementioned observation also looked into groundsel at an intra-specific level, by studying infected individuals in monocultures and in mixed culture with lettuce. In the monoculture, rust-infected individuals had reduced growth rates, as did those in the mixed culture - this was, obviously, expected.

 

What we can draw from this, with regards to plants, is that infection by pathogens will increase diversity in plant fitness of individuals within a wider community. By default, there exists sometimes marked variation between individuals of the same, and different, species, though pathogens serve to magnify this disparity. This may even lead to many plants remaining rather small, and allow only a few successful, fitter individuals, to achieve significant heights.

 

Interestingly however, the study did remark that, where groundsel were grown in monocultures, plant density within rust-infected individuals was lower than density for uninfected monocultures. As winter kills off rust diseases however, the growth-stunted and stressed individuals in the infected monoculture were actually able to take advantage of the lower population density and improve growth rates dring periods where rust was not present, to the point that productive ability raised to 55% (in winter) from 40% over the summer, when compared to healthy groundsel populations (that would be assumed to operate at 100%).

 

A proxy indicator for trees, no doubt.

 

Source: Ayres, P. (1991) Growth responses induced by pathogens and other stresses. In Mooney, H., Winner, W., & Pell, E. (eds.) Response of Plants to Multiple Stresses. USA: Academic Press.

Edited November 14, 2015 by Kveldssanger

[Kveldssanger]

15/11/15. Fact #79.

 

Natural root grafting can be considered rather common, when trees, particularly of the same species, exist in close proximity to one another (intra-specific grafting). However, self-grafts are even more frequent, and this involves two roots of an individual grafting together. Inter-specific (between different species) grafts occur very infrequently.

 

A 'true' graft requires an entire vascular connection to be present (union of cambium, xylem, and phloem), and is far more likely to be observed where two different roots grow in roughly the same direction (anatomically and physiological similarity) and then, upon contact, fuse together. Where roots do not share aforementioned similarities, they will either not fuse or fuse with discernible abnormalities. This is particularly the case with roots of different species appearing to fuse together - in fact, they rarely will. This is described as a 'false' graft. Vascular connectivity between the two fused roots is not evident.

 

Age also plays a role in the abundance of visible root grafts. Older trees will, of course, have more grafts on average than younger trees, by sheer virtue of the fact the tree has had a greater time in which to develop grafts of any nature.

 

Additionally, it seems that where roots grow against an object such as a stone or rock, grafting between two roots is more likely - this is considered to be due to the localised increase in pressure one root will exert upon another, assuming two roots are growing onto the same stone. However, this does not mean that where there are no stones no grafts will be evident, as grafts still occur in stone-free soils.

 

Plantations, on the other hand, will very rarely show grafted roots until trees have begun to significantly establish. This is because the distance between individuals is usually greater than in a naturally-occurring woodland stand.

 

Source: Kozlowski, T. (1971) Growth and Development of Trees Volume II: Cambial Growth, Root Growth, and Reproductive Growth. USA: Academic Press.

[Kveldssanger]

Ordered Kozlowski's series 'Water Deficits and Plant Growth'. Managed to buy all seven volumes for a total of £50 including postage - that's easily 1,500 pages of information! Once they're through I'll pick out some good stuff.

[Kveldssanger]

15/11/15. Fact #80.

 

Every individual tree we see is classed as a phenotype. A phenotype is the summation of genetic coding (genotype) and environmental factors (ecotype) that influence how that genetic coding actualises. The resulting influence of the environment on genetic coding (from the seed) means every individual tree is unique in its outward appearance. We can therefore conclude that there is significant phenotypic variation amongst tree populations - or distinct heterogeneity.

 

Source: Watson, B. (2006) Trees: their use, management, cultivation, and biology. India: The Crowood Press.