(Arboricultural-styled) 'Fact of the Day'

[Kveldssanger]

Old books certainly do smell...!

 

15/11/15. Fact #81.

 

In young trees in particular, one can observe a loss in weight on a local level during growth periods. This is because, for the young bud to grow (elongate), respiration on a local level will be required to supply the growing bud with much-needed nutrients (this requires sugars to be burned). As the bud cannot initially create and then immediately 'repay' the energy 'debt' it has accrued, there is a period of time where the weight of the stem drops as the stored sugars are 'allocated' to the new growth areas. The overall mass of the tree does not necessarily decline.

 

Simultaneously, nutrients will also be trans-located into the new growth, which further changes localised weight distribution. Resources will also be trans-located from roots during the growing season, which also indicates that root 'weight' will be greater during the late summer to late winter, and lesser during early spring to mid summer (phenologically, it will vary for species, of course).

 

To illustrate this, we can observe the following differences in weight distribution over (part of) a growing season (would have been 1911 or 1912, I think). Presentation of the data will be as follows:

 

Species: [Time period] - Loss is weight (%) in stem / root

 

Norway maple: [2/5-21/5] - 47.0 / 44.4

Black alder: [27/4-8/8] - 1.2 / 46.4

Ash: [4/5-21/5] - 29.6 / 36.1

Beech: [27/4-21/5] - 16.6 / 28.9

English elm: [2/5-18/5] - 27.0 / 36.2

Larch: [27/4-21/5] - 20.5 / 15.5

Spruce: [27/2-22/5] - 6.0 / 23.0

Silver fir: [25/5-14/5*] - 7.1 / 5.9

Scots pine: [11/3-22/5] - 19.9 / 19.9

 

*might be a typo.

 

From this, we can observe differences between species. This may be genetic, environmentally-induced, or otherwise. It is important we recognise that there is such difference, of course.

 

Source: Busgen, M., Munch, E., & Thomson, T. (1929) The Structure and Life of Forest Trees. UK: Chapman & Hall.

Edited November 15, 2015 by Kveldssanger

[daltontrees]

What? Norway maples lose almost half their weight in a few weeks? Get that on the shopping channels right away. The platanoides plan.

[Kveldssanger]

I think it means the stem 'weight' (mobile weight from stored starch and such) is re-allocated to the growth tips.

 

But yeah, get on that diet. Doctors hate this tree! Find out its secret in only three simple steps. Subscribe now!!

[Jon Heuch]

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.

 

......but for the most part some 35+ years out of date....!

 

Even the third edition of Physiology of Trees didn't seem to bring things up todate. As for the North American bias which implies that all trees behave as northern temperate trees you have to see the limits. However, the depth and scope of observations are remarkable and well worth reading.

[Jon Heuch]

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.

 

Think he's got that wrong - the ecotype is normally a genetic strain arising from environmental pressure/selection in a particular environment. Collect the seed from a particular ecotype and you would expect certain features to be expressed in all trees (e.g. lodgepole pine provenances). It forms the whole basis for provenance testing in forestry. The use of the term "genetic coding" implies that the environment is influencing the coding itself rather than the form of the tree. Whilst epigenetic issues are no longer dismissed as Lamarkian phenotypic variation reflects a whole range of factors, some of which have nothing to do with genetics - competition for water, nutrients, light and the physical presence of objects whether they be stones in the soil, nearby trees, walls, roads etc. and/or wind. On the other hand with care we can select uniform trees, sometimes from seedlings but more readily from clones resulting in much less phenotypic variation.

[Kveldssanger]

......but for the most part some 35+ years out of date....!

 

Even the third edition of Physiology of Trees didn't seem to bring things up todate. As for the North American bias which implies that all trees behave as northern temperate trees you have to see the limits. However, the depth and scope of observations are remarkable and well worth reading.

 

Of course, but one can hardly say the material is not relevant. Even where there are issues with how the text translates to nowadays, or where something may be entirely wrong, it gives a timeline and provides context.

 

If someone writes a lot of books, each in huge detail, and publishes them tomorrow, then awesome. But there isn't a huge amount of decent and new literature that goes to such depths on such an array of topics.

 

Kozlowski was an American (at least, if memory serves correctly), so it makes sense (assuming he is American) that he wrote with a tendency towards the temperate US regions. A bit like I'd expect an Australian to write about the Eucalypts.

[Kveldssanger]

Think he's got that wrong - the ecotype is normally a genetic strain arising from environmental pressure/selection in a particular environment. Collect the seed from a particular ecotype and you would expect certain features to be expressed in all trees (e.g. lodgepole pine provenances). It forms the whole basis for provenance testing in forestry. The use of the term "genetic coding" implies that the environment is influencing the coding itself rather than the form of the tree. Whilst epigenetic issues are no longer dismissed as Lamarkian phenotypic variation reflects a whole range of factors, some of which have nothing to do with genetics - competition for water, nutrients, light and the physical presence of objects whether they be stones in the soil, nearby trees, walls, roads etc. and/or wind. On the other hand with care we can select uniform trees, sometimes from seedlings but more readily from clones resulting in much less phenotypic variation.

 

Good post!

[Kveldssanger]

17/11/15. Fact #82.

 

There are many factors that impact upon leaf conductivity (related directly to stomatal activity). These include: solar radiation, humidity, leaf temperature, carbon dioxide concentrations (internally and externally), leaf water balance, and abscisic acid. Each will be explained, in brief, below.

 

Solar radiation

 

Stomata appear to, on average, open fully at light levels of 5-20% of full sunlight (100-400 umoles m(-2) sec (-1)). Where lights levels are below the saturation threshold, shade-tolerant species' (e.g. 3 mins for Fagus grandiflora) stomata open both faster and at lower light levels than non-shade-tolerant species' (e.g. 20 mins for Liriodendron tulipifera), though there was, at the time of this publication, no significant difference between shade-tolerant and non-shade-tolerant species in this regard.

 

Humidity

 

As the reative humidity between the leaf and the air widens, stomata will close. However, stomatal closure can also - but not always - be regulated by pre-dawn water potentials of the leaf as a whole. Prunus, Citrius, and Picea species are particularly sensitive to humidity changes, and this is primarily down to the lack of a cuticle in the lower part of the guard cell and the water supply to the epidermis being relatively slow.

 

Leaf temperature

 

Optimal temperatures for leaf conductivity are between 22-34 degrees Celsius for deciduous hardwoods, and slightly lower for conifers. Temperatures either side of this range will usually mean stomatal response to other factors is delayed, which inhibits the photosynthetic process.

 

Carbon dioxide concentrations

 

External carbon dioxide concentrations were, at the time of this publication, largely considered to be of relative unimportance to leaf conductivity, in the sense that other factors are far more influential, and because ambient carbon dioxide concentrations can vary significantly. Conversely, internal concentrations do impact upon leaf conductivity - internal concentrations are driven both by ambient concentrations and also the rate of photosynthesis within the leaf. High concentrations of carbon dioxide cause closure, and low concentrations cause stomata to open.

 

Leaf water balance

 

As pre-dawn water potentials of the leaf fall, and leaf water balances drop on the whole, stomata will close due to the loss of water from their structure (this is governed, in part, by potassium (K+) concentrations in the guard cell decreasing alongside, though also by abscisic acid). Stomata can respond by abruptly closing or gradually closing at either critical leaf water balance or pre-dawn water balance. Abrupt closure will occur when turgor pressure reaches a critical point, as will, albeit slightly differently, gradual closure once a critical leaf water balance is reached. With regards to gradual closure as a result of pre-dawn water balance, is considered to be governed primarily by abscisic acid.

 

Abscisic acid

 

As abscisic acid levels increase, stomata will close. In Malus domestica, abscisic acid levels were observed to increase linearly in response to falling turgor pressure - it is not known which drives which, in this relationship. When moisture int he photosynthetic tissue falls, abscisic acid is secreted where it moves to the guard cells and triggers stomatal closure via the induction of K+ movement out of the guard cells. Only when moisture levels recover do the photosynthetic tissues stop releasing abscisic acid.

 

Abscisic acid, in deciduous hardwoods, is also observed to possess anti-transpirant qualities, though the efficacy of abscisic acid in this regard relates to how quickly the abscisic acid penetrates the leaf, how quickly it leaves when moisture levels recover, and the water-use efficiency of the species.

 

Other factors

 

High wind speeds incude stomatal closure through the drying effect (increased evapotranspiration) the winds have upon the leaves, though wind also has an abrasive effect when it causes particulates to rub against the leaf cuticles at high velocity and erode the protective waxes.

 

Mineral deficiencies, particularly potassium and calcium, can also influence upon leaf conductivity. Conversely, ozone and sulphur dioxide appear to induce stomatal opening, though high dosages of sulphur dioxide will cause stomatal closure. Hydrogen fluoride also induces closure.

 

Source: Hinckley, T., Teskey, R., Duhme, F., & Richter, H. (1981) Temperate hardwood forests. In Kozlowski, T. (ed.) Water Deficits and Plant Growth Vol. VI: Woody Plant Communities. USA: Academic Press.

Edited November 17, 2015 by Kveldssanger

[Kveldssanger]

Think I have the flu, or at least something drastically similar, so I shan't be posting facts until I recover enough to actually concentrate on something for more than 30 seconds before wanting to go to sleep! Cheers.

[Kveldssanger]

21/11/15. Fact #83.

 

Broadly-speaking, the larger the size of the vessel within the vascular system of a tree, the greater the risk of cavitation, under freeze-thaw conditions. This is because large vessels carry more water both in total and in a cross-section, which means air bubbles borne by freezing water are potentially both more frequently-occurring and larger when they do occur. These air bubbles have less likelihood of 'dissolving' into the sap again when it thaws, and therefore are more prone to causing vascular damage.

 

Of course, larger vessels means greater efficiency at conducting, though with the trade-off of greater risk of vascular damage. We do still see large vessels, however - particularly in ring-porous trees such as elm and oak. Though, in general, vessel size decreases as we go from ring-porous to diffuse-porous deciduous hardwoods, and from there decreases further as we enter the realm of coniferous softwoods.

 

It seems that species physiology, with regards to vascular properties, may likely dictate climatic ranges - at least, in part. For example, conifers with large vessels would be hugely imparied in areas where freezing (and subsequent thawing) conditions are frequent, so it is likely that they will not frequent such areas and may instead lurk up to and at their preferable 'maximum(s)'. However, where freezing conditions are common but prolonged (thawing is not so common), or just generally infrequent, vascular anatomy may not be so important (such as at high and low latitudes) - therefore, near to the equator, or right up in the arctic where freezing is common but thawing is not, vascular properties may potentially be more varied.

 

Source: Sperry, J. (1995) Limitations on Stem Water Transport and Their Consequences. In Gartner, B. (ed.) Plant Stems: Physiology and Functional Morphology. USA: Academic Press.