Roots and Nutrients and Leaves

[gonewild]

There is some discussion about how roots take in nutrients on another thread, but a little off topic and distracting. So here is a place to discuss and argue about it.

How roots take in nutrients is not really well know about orchids.
Do non active roots take in nutrients?
Do roots only send nutrients to leaves or do leaves send nutrients to roots also?
Should you fertilize a plant with dead roots?

If interested discuss it here.

I have a few links to papers related to the subject I'll share. I've not read them totally but they may have some insight in how to fertilize orchids or how to better argue about it.

Roots Growth and Nutrient Uptake

Plants in Action

Nitrogen, Potassium and Magnesium Nutrition of Three Orchid Genera

:viking::fight:ity::noangel::crazy:

 

[naoki]

Lance, here is some info:

Experiments with radioactive phosphate and Cattleya Trimos.
Roots of all ages are capable of absorbing this element when it is applied as drench. In cattleya, both young and old roots are functional.

From p.204 (and Table 5-26) ofArditti, J. 1992. Fundamental of Orchid Biology. A bit expensive and a bit old, but it is a must-have if you are interested in the science of orchids.

This talks about only P, but if I find other refs with orchids, I'll add it here. I'm pretty sure I've read some more recent papers. Maybe Zot's 2013 velamen paper?

Nutrients can be reallocated in any directions (root to shoot or shoot to root). Most of the mineral nutrients are absorbed by roots primarily, so it is more likely to move toward the shoot system. But relocatable nutrients can be moved to roots if needed. Also there are some studies of foliar feeding, where radioactivity was used to trace the movement. The most important nutrient, carbon, (photosynthates) are mostly sourced from leaves, so roots get the supply from leaves (mostly in the form of sucrose). The movement of photosynthates (and many nutrients) follow source-to-sink pattern. Plants hormonally adjust the strengths of "sink". But maybe this isn't what you mean by "nutrients".

Absorption, short-distance transport, and long-distance transport is an important aspects of plant nutrition. For example, NH4 and NO3 has fairly different transport pattern (NO3 is more likely to be transported to shoot). Marschner's Mineral Nutrition of Higher Plants is pretty good for the basics. I wish it were a bit cheaper.

 

[gonewild]

The movement of photosynthates (and many nutrients) follow source-to-sink pattern. Plants hormonally adjust the strengths of "sink". But maybe this isn't what you mean by "nutrients".

Carbon certainly is a primary nutrient and one that we basically ignore. I've been setting up a CO2 generator to see if it makes a noticeable difference (it will).

I think we need to consider all elements that plants use to metabolize as being "nutrients". Amino acids and hormones that a plant absorbs from the environment are nutrients.

 

[gonewild]

Recently I read that plants move potassium and calcium to growing root tips from the upper plant. Something to the effect that the new root tip tissue could not take in certain elements. I can't remember which paper had that info but I'll look for it. I was not specific about orchids.

Since orchid roots tend to grow in very loose media or in the air I would guess the tips are not the major part that captures nutrients.

 

[Ray]

95% of a plant's mass is C, H, O, & N, yet we seem to focus on the remainder...

 

[gonewild]

95% of a plant's mass is C, H, O, & N, yet we seem to focus on the remainder...

Yeah and increasing carbon would be so easy. But it's to politically sensitive now.

 

[paphioboy]

Carbon certainly is a primary nutrient and one that we basically ignore. I've been setting up a CO2 generator to see if it makes a noticeable difference (it will).

Just curious, how do you partition the treated from control plants in this observational experiment? Or are you just treating them all?

 

[gonewild]

Just curious, how do you partition the treated from control plants in this observational experiment? Or are you just treating them all?

Well I'm not doing a science experiment. I'm looking for improved growth which I will use my experience to judge.
The area I plan to use CO2 is in an air conditioned sealed space we use induce spikes on Phals. I know the time it takes for spikes to emerge and how long from emergence until the spike reaches 10cm. If after adding CO2 the time is shorter I will assume the CO2 has speeded up the process (faster growth?).

I've read that increasing the CO2 can increase growth in the induction room as much as 50%. if that is true I will see the improvement.

I also have another closed growing area that I may add CO2 to as well. It is about 50m3 air space. In this space at night it was pretty well closed to outside air and after reading research on CO2 it seems that in a full greenhouse space plants can deplete the CO2 level very quickly at night. In the space I have it seemed depletion could occur in about 2 hours so that leaves 10 hours of time that the plants don't have carbon as a nutrient.
As a possible solution I added an intake fan to suck in outside air at night to augment the CO2. Quickly we noticed an improvement. But the fan does not increase CO2 it only brings it back to near but below the normal level.
I want to triple the CO2 content at night.

And then I read some big Phal growers recommendations that say Phals don't benefit from CO2 addition. But in pictures you see CO2 generators in their grow areas.

 

[gonewild]

With regards to not fertilizing orchids when they appear to not be in active growth....

The following abstract indicates that nutrients are taken in by the entire root system of orchids and not only at the active growing tip. This would also indicate that orchid roots should not be considered as inactive and unreceptive to nutrient uptake simply because they are damaged or not in active growth at the tip.


Aerial roots of epiphytic orchids: the velamen radicum and its role in water and nutrient uptake.
Zotz G1, Winkler U.
Author information
Abstract

The velamen radicum, a spongy, usually multiple epidermis of the roots, which at maturity consists of dead cells, is frequently described as an important adaptation of epiphytic orchids. Yet, quantitative evidence for the alleged functions, e.g., efficient water and nutrient uptake, nutrient retention, reduction of water loss, mechanical protection, or the avoidance of overheating, is rare or missing. We tested the notion originally put forward by Went in 1940 that the velamen allows plants to capture and immobilize the first solutions arriving in a rainfall, which are the most heavily charged with nutrients. In a series of experiments, we examined whether all necessary functional characteristics are given for this scenario to be realistic under ecological conditions. First, we show that the velamen of a large number of orchid species takes up solutions within seconds, while evaporation from the velamen takes several hours. Charged ions are retained in the velamen probably due to positive and negative charges in the cell walls, while uncharged compounds are lost to the external medium. Finally, we demonstrate that nutrient uptake follows biphasic kinetics with a highly efficient, active transport system at low external concentrations. Thus, our results lend strong support to Went's hypothesis: the velamen fulfills an important function in nutrient uptake in the epiphytic habitat. Most of the other functions outlined above still await similar experimental scrutiny.http://www.ncbi.nlm.nih.gov/pubmed/23292456

 

[Ray]

I want to triple the CO2 content at night.

The current global average is now about 400 ppm. I remember reading somewhere that the optimum for plant growth is 1500 ppm. Double that and it's toxic, instead.

 

[cnycharles]

From what I've seen here and there in general, it may be helpful for quick-turn crops. Often there is a jump in growth, but then the plant 'gets used to' the higher co2 and growth stabilizes where it was before. For a long term crop there may be a bump but then usually not continuing

 

[gonewild]

The current global average is now about 400 ppm. I remember reading somewhere that the optimum for plant growth is 1500 ppm. Double that and it's toxic, instead.

From what I understand 900ppm to 1500ppm is optimum for greenhouse.
It's not detrimental to plant growth until it gets to 3000 ppm.
OSHA has a safe work environment level of 5000ppm for humans.

Most people want to keep the safe levels low for PC reasons so no telling what is optimum. I wonder why CO2 would be harmful to plants?

Burning an alcohol lamp at night will produce enough CO2 to raise a small greenhouse to 900ppm. It only takes about 1 cubic foot of CO2 to raise an 8'x12'x7' greenhouse to 900ppm. I wonder how much CO2 a rabbit exhales at night?

 

[gonewild]

Often there is a jump in growth, but then the plant 'gets used to' the higher co2 and growth stabilizes where it was before. For a long term crop there may be a bump but then usually not continuing

It seems strange the plant would stop using the extra carbon and slide back. Maybe all the other nutrients need to be raised also?