(Arboricultural-styled) 'Fact of the Day'

[Kveldssanger]

We were discussing mycorrhizal relationships today on the Lvl 4, so thought I'd make a post about how to improve mutual symbiosis between mycorrhizae and tree roots with regards to organic mulching / fertiliser application.

 

04/11/15. Fact #70.

 

In certain instances, such as with phosphorus-limited soils, the application of organic fertiliser (particularly the application of nitrogen) can increase species diversity, richness and funtionality of mycorrhizae, thereby providing benefits for the rooting systems of trees present on the site. However, application of nitrogen in phosphorus-rich soils has the opposite effect. Therefore, fertilisation can improve conditions for mycorrhizae, though not in all instances - application in poor soils is far more preferable, as an improved nutrient profile can foster more substantial mycorrhizal relationships.

 

Additional research highlights that organic fertilisation of soils increases the microbial respiration rate of mycorrhizae, in addition to their population density. Therefore, the relationship between roots and mycorrhiza is strengthened by fertilisation, given the benefits to the mycorrhizae. Furthermore, the application of phosphates can see marked increases in the assimilation of vital nutrients from the soil via the mycorrhiza, though care must of course be taken not to apply in excess.

 

To build on the concept of excess, increases in nitrogen availability through deposition or fertilisation may reduce root colonisation and fruit body production by mycorrhizal fungi. Therefore, before any organic materials are added to a soil, it must be proven that the soil would benefit, ecologically (wth regards to the symbionts of roots and mycorrhizae), from any additions (as is outlined in BS 3998:2010). In addition, many mycorrhizae appear to prefer poorer soils in terms of nutrient availablity, so fertilisation may render mycorrhizae of less importance to root systems as nutrients are no longer lacking and the symbiosis is not as necessary. In turn, mycorrhizae may potentially become parasitic upon the roots.

 

Additionally, fertilisation has the potential to make conditions more preferable for inferior mutualists, thereby having a negative impact upon the symbiosis of roots and mycorrhizae.

 

It also appears that soil type can impact upon the efficacy of fertilisation. Research highlights that fertilisation does not influence mycorrhizal colonisation or abundance of soil hyphae in sandy loam soil, but in clay soil metabolically-active hyphae were more abundant with manure application than with mineral fertilisation.

 

Sources:

 

Egerton-Warburton, L., Johnson, N., & Allen, E. (2007) Mycorrhizal community dynamics following nitrogen fertilization: a cross-site test in five grasslands. Ecological Monographs. 77 (4). p527-544.

 

Johnson, N. (1993) Can fertilization of soil select less mutualistic mycorrhizae?. Bulletin of the Ecological Society of America. 3 (4). p749-757.

 

Kabir, Z., O'halloran, I., Fyles, J., & Hamel, C. (1997) Seasonal changes of arbuscular mycorrhizal fungi as affected by tillage practices and fertilization: hyphal density and mycorrhizal root colonization. Plant and Soil. 192 (2). p285-293.

 

Shigo, A. (1991) Modern Arboriculture. USA: Shigo and Trees Associates.

 

Tiquina, S., Lloyd, J., Herms, D., Hoitink, H., & Michel, F. (2007) Effects of mulching on soil nutrients, microbial activity and rizosphere bacterial community structure determined by analysis of TRFLPs of PCR-amplified rRNA genes. Applied Soil Ecology. 21 (1). p31-48.

 

Treseder, K., & Allen, M. (2000) Mycorrhizal fungi have a potential role in soil carbon storage under elevated CO2 and nitrogen deposition. New Phytologist. 147 (1). p189-200.

 

Wiemken, V., Laczko, E., Ineichen, K., & Boller, T. (2001) Effects of elevated carbon dioxide and nitrogen fertilization on mycorrhizal fine roots and the soil microbial community in beech-spruce ecosystems on siliceous and calcareous soil. Microbial Ecology. 42 (2). p126-135.

Edited November 4, 2015 by Kveldssanger

[Kveldssanger]

I hope my own calculations are right for the below - brain is nackered after writing about branch attachment for over three hours!

 

05/11/15. Fact #71.

 

Chlorophyll fluoresence can be used as a means to determing plant health. As fluorescence gives information on the health of the photosystem II process of photosynthesis of a plant, overall plant health can be theorised by measuring fluorescence. This can be done by measuring fluroescence levels in the dark (min), when all electron carries for PSII are open, and fluorescence levels in high light exposure after taking the plant out from the dark and shining bright light onto the surface (max) - at this stage, all electron carriers are assumed to be occupied and therefore closed. From these measurements, the variable fluorescence level can be reached by 'maximum light - minimum light' (simply put).

 

Basically, the closer to 1 then better, and the closer to 0 the worse health of the plant is. For instance if plant A is as follows:

 

- f(minimum) is 3

- f(maximum) is 9

- f(variable) is therefore 6 (max - min)

 

To calculate PSII efficiency, one divides f(variable) by f(maximum). In this case, that is 6/9, or 0.667.

 

And plant B is as follows:

 

- f(minimum) is 3

- f(maximum) is 4

- f(variable) is therefore 1 (max - min)

 

To calculate PSII efficiency, one divides f(variable) by f(maximum). In this case, that is 1/4, or 0.25.

 

Plant A is more efficient at PSII than plant B, as the figure is closer to 1 than in plant B. Plant B may therefore be under stress for whatever reason (drought, salinity, fungal attack, etc).

 

Typically speaking, a good tree is able to use 75-85% of sunlight received (so the reading would be 0.75-0.85) for photosynthesis. When a tree is under stress, it is not able to utilise such high amounts of total light, thereby dissipating more light energy back (known as chlorophyll fluorescence). As any forms of stress have impacts upon fluorescence, calculating such fluorescence can aid with identifcation of stress and the current functionality of photosystem II.

 

Sources:

 

Badeck, F. & Rizza, F. (2015) A Combined Field/Laboratory Method for Assessment of Frost Tolerance with Freezing Tests and Chlorophyll Fluorescence. Agronomy. 5 (1). p71-88.

 

Samy, É., Benoit, D., & Khanizadeh, S. (2014) Chlorophyll Fluorescence: A Novel Method to Screen for Herbicide Resistance. International Journal of Horticultural Science and Technology. 1 (2). p93-99.

 

Tatagiba, S., DaMatta, F., & Rodrigues, F. (2015) Leaf gas exchange and chlorophyll a fluorescence imaging of rice leaves infected with Monographella albescens. Phytopathology. 105 (2). p180-188.

[Gary Prentice]

I wrote a bit on this, I'm still not sure if it actually helps anyones understanding cos it bombarded my head:biggrin:

 

 

Chlorophyll Fluorescence

Fluorescence; the emission of light or other radiation, from atoms or molecules that are bombarded by particles such as electrons, or by radiation from a separate source. The bombarding radiation produces excited atoms, molecules, or ions and these emit photons as they fall back to the ground state. http://www.the freedictionary.com

 

 

Light energy absorbed by chlorophyll molecules during photosynthesis is used to drive photochemical reactions, dissipated as heat (non-photochemical quenching) or emitted as fluorescence. These three individual processes compete, with an increase in the efficiency of one resulting in a decrease of the yields of the other two. Thus, by being able to measure the yield or output of chlorophyll fluorescence, information about changes in the efficiency of photochemistry and heat dissipation can be acquired.

 

A continuous excitation fluorometer measures the Kautsky Induction or Fast Fluorescence Induction, using focused, high intensity light (from red LED’s) to induce fast chlorophyll fluorescence response from a dark-adapted sample leaf. A leaf clip attached to the leaf, excludes light to provide the dark-adaption necessary to measure maximum photochemical efficiency (Fm). It also defines the measurement area on the leaf and prevents ambient light leakage into the photodiode of the instrument used for fluorescence detection.

 

The Kautsky effect, or fluorescence transient, fluorescence induction or decay, is the phenomenon of typical behaviour when dark-adapted photosynthesizing cells are illuminated, chlorophyll fluorescence displays characteristic changes in activity accompanying the induction of photosynthetic activity. When a sample is illuminated, the fluorescence intensity increases with a time constant (in the millisecond - or microsecond range) until after a few seconds the intensity decreases to a steady, level state. This rise is explained as a result of the reduction of electron acceptors in the photosynthetic pathway, downstream of Photosystem II –notably platoquinone, particularly QA. Once PSII absorbs light and QA accepts an electron it can not receive further electrons until it has passed it on to a subsequent electron carrier - QB. In this state or position the reception center (RC) is termed as ‘closed’. The presence of a proportion of closed RC’s leads to an overall reduction in the efficiency of photochemistry and a subsequent increase in the fluorescence yield.

 

When the sample is exposed to light, the red LED’s of the fluorimeter, the photosystem II reaction centers progressively close increasing the chlorophyll fluorescence yield during the first second or two of illumination. Over a few minutes the level typically starts to fall due to fluorescence quenching. This is an increase in the rate of electron transport away from PSII, mainly due to the light-induced activation of enzymes involve in carbon metabolism and the stomata opening. This quenching is the photochemical quenching side of the fluorescence quenching, the non-chemical quenching part being the process of the increase in the efficiency that energy is converted to heat. Typically, changes in these two processes are completed within about fifteen to twenty minutes in plants and an approximate steady state is attained.

 

Another parameter that needs to be identified is the minimal fluorescence value, F0. This value is initiated by switching on the measuring light and an estimate of the level of fluorescence is calculated using mathematical algorithm. Deducting the minimal fluorescence from the maximal fluorescence provides the variable fluorescence- Fv= Fm¬-F0. The fluorimeter uses fast data acquisition system technology, recording every ten microseconds, and LED’s that reach full intensity almost immediately. The dark adapted sample is exposed to a flash of saturating light that provides a reading and measurement – via a series of formulae, of the maximal fluorescence.

Use of chlorophyll fluorescence (CF) to measure plant vitality and future growth potential.

 

Fv/Fm, the CF value is used as the maximum efficiency of photosystem II, the quantum efficiency if all PSII centres were open. The calculations however are far more complex than this formula, using parameters that measure the efficiency of the system and includes parameters of electron transfer rates, photochemical quenching and other variables. As a measurement of plant vitality in the form of a sensitive indicator of photosynthetic performance, optimum values of around 0.83 are measured in most plants. Lower values are seen when the plant has been exposed to stress, indicating in particular the phenomenon of photoinhibition.

 

 

Photoinhibition.

Most researchers agree that PSII is the most light sensitive part of the photosynthetic system and the term is defined as light-induced damage to the PSII. The system suffers a damaging reaction constantly during operation of gaining and losing electrons in the pathway, which is continuously being chemically repaired by the synthesis of a protein in the reaction centre. Normally, due to rapid synthesis, most PSII RC’s are not photo-inhibited unless environmental stresses, drought, salinity or extreme temperatures limit the availability of carbon dioxide for use in carbon fixation which decreases the rate of repair of the PSII through the suppression of protein synthesis. (How do environmental stresses accelerate photoinhibition? S Takahashi & N Murata. Trends in Plant Science 13 (4): 178–182. 2008)

 

The next bit was a table and hasn't copied with formating

 

CF Value(Fv/Fm) Health Status Tree Response

 

0.85 – 0.75 Healthy plant ‘Normal’ growth – representative of the species

0.65 – 0.75 Plant under some form of stress Leaf necrosis – 10% reduction in growth

0.45 – 0.65 Plant under moderate to severe stress Leaf necrosis – 30-50% reduction in growth

0.25 -0.45 Plant under severe stress Severe leaf necrosis – 50 -70% reduction in growth

<0.25 Plant likely to die Leaf drop – cessation of growth

 

From; Chlorophyll fluorescence – A beginners guide. Glynn C Percival & Kelly Noviss – Bartlett Research Laboratory

[Steve Bullman]

I wrote a bit on this, I'm still not sure if it actually helps anyones understanding cos it bombarded my head:biggrin:

 

Nope

[Gary Prentice]

Nope

 

Don't worry Steve, I wrote it and I'm not convinced that I do either:blushing:

[Kveldssanger]

I know some of those words!

[Kveldssanger]

07/11/15. Fact #72.

 

UK woodlands under private ownership may be at most risk of the threats of a warming climate and the evolving relationship between trees and their pests and diseases. A recent survey of private woodland owners highlighted that they are "not generally convinced of a need to adapt", as they "feel the future is uncertain, more usually in relation to tree disease than to climate change itself". Therefore, perhaps the (alleged) impending and growing threat is not simply due to climatic changes, but the lack of willingness to respond pro-actively. This may ring true for all threats of change, as well, if we use this research study as a proxy indicator.

 

Source: Lawrence, A. & Marzano, M. (2014) Is the private forest sector adapting to climate change? A study of forest managers in north Wales. Annals of Forest Science. 71 (2). p291-300.

[daltontrees]

Fluorescence - hmm, I didn't quite take all this in as a 'fact'. Whereas it is undoubtedly a complicated business, I souught out my own practical undestanding of this. Thanks to an article by Maxwell and Jonhson (2000) I seem to be getting my head round it. I will paraphrase that article.

 

But first a brief definition of PSII. It is the first chemical stage in photosynthesis. The front-end of how trees convert light energy to sugars, using green stuff (chlorophyll).

 

Chlorophyll fluorescence gives information about the state of Photosystem II. It can tell you the extent to which it is using the energy absorbed by chlorophyll and the extent to which it is being damaged by excess light. It does this by indirectly measuring the flow of electrons through PSII.

 

This flow is indicative, under many conditions, of the overall rate of photosynthesis. Chlorophyll fluorescence gives us the potential to estimate photosynthetic performance, under conditions in which other methods would fail, in a manner that is almost instantaneous.

 

PSII is also accepted to be the most vulnerable part of the photosynthetic apparatus to light‐induced damage. Damage to PSII will often be the first manifestation of stress in a leaf. Chlorophyll fluorescence allows some degree of prediction or diagnosis of this at early stages.

 

A slightly dodgy analogy (mine, blame no-one else

To me it is akin to diagnosing problems with machinery like chainsaws. If you can get a saw running it is OK when it's warmed up even if it is continuing to do damage to itself. But often all the problems show early signs when cold-starting it. Weak compression, a puff of black smoke, a faltering start etc. Modern chlorophyll fluorescence is like being able to do a cold-start diagnosis while the saw is already hot and running. As such it seems to be a great improvement on lab techniques that were previously needed.

 

A childish explanation

Daughter just asked me at breakfast what chlorophyll fluorescence is. After a few seconds I said it's a way of telling if a plant is getting unwell even if it looks green and healthy. To be honest, that explanation will do me too for now.

 

Gary, I couldn't understand your equation "variable fluorescence- Fv= Fm¬-F0". Is there wrong symbol in there? Should it be "variable fluorescence- Fv= Fm-F0"?

[Kveldssanger]

I am cursed by the name title of this thread, it seems!

 

Of course, there's a large element of CF I don't talk about, though for a topic that can be so absurdly obfuscated by endless texts I tried to simple it down in a way that I can understand, and hope others can as well.

 

Your addition, as well as Gary's, is great. And welcomed. This is exactly what I hoped this thread would do.

Edited November 8, 2015 by Kveldssanger

[Kveldssanger]

08/11/15. Fact #73.

 

Cladoptosis. We should by now, know what it means. If not, see this old fact I did.

 

With regards to the hormones behind the process, ethylene is one of the principal plant hormones that features within the process. Ethylene encourages the re-allocation of resources away from shaded areas of the crown. When we understand that branches may likely be abscised due to poor photosynthetic capability (heavy shading it normally the cause), it begins to fall into place on the hormonal level.

 

In certain species, such as oak, the process may in fact be staggered. The tree may first create a protection zone out at a distance from the junction, which leads to failure at that point. A long stub is then left, which can then be shed further down the line, by the same processes.

 

Conifers behave slightly different to broadleaves. Whilst a conifer branch is alive, resin is impregnated into the core wood of the branch (that can at times propagate out into the branch itself). As the branch begins to die and the shedding process begins, the tree seals off the small area surrounding the branch base to resist progress of potential pathogens. Once the branch has died, it will break where the resin core ends.

 

Sources:

 

Karban, R. (2015) Plant Sensing & Communication. USA: University of Chicago Press.

 

Shigo, A. (1986) A New Tree Biology. USA: Shigo and Trees Associates.