Grapevine energy production as seen through the lens of a Generalized Supply Chain model

A supply chain identifies the key steps in the process within which a set of raw materials is transformed into products that are acquired by an end customer.  The supply chain normally extends into the practices of suppliers and into the habits of the end customer.  A representative supply chain is illustrated below.

Generalized Supply Chain Model (Source: red-gray.co.uk)

I propose that the production of energy in the grapevine can be viewed through the lens of a supply-chain schema and that, within this model, viticultural science takes on the mantle of supply chain management.  In this model, the core product is energy, in both its refined and raw form, and the core manufacturing process is photosynthesis.  I will elaborate on this proposal in two posts with this initial post focusing on the alignment of the grapevine energy supply chain with a generalized supply chain model.

Logistics

Logistics is an integral part of the supply chain and is associated with the movement of raw materials, intermediate assemblies, and final products into and out of the manufacturing process. In some cases the demand is immediate and the product is moved directly to the customer where it is either consumed by the end user or used as a value-added input in a final assembly.  In other cases, production is shipped directly to a warehouse for allocation to the appropriate channel when the need arises.

Key logistics processes in the grapevine energy supply chain are transpiration and translocation.

Raw Materials

Inputs into the core production process of the supply chain are termed raw materials.  As indicated in my most recent post, the raw material inputs for photosynthesis are light, carbon dioxide, water, and nutrients.  The light energy is sourced from the sun and the carbon dioxide from the atmosphere.  Water is sourced from the soil (function of water accessibility, soil composition, soil drainage, and water retention) and is drawn up into the vine from the roots in a process called transpiration. Nutrients are brought into the roots by a combination of bulk flow, transpiration, and fungal action.

Manufacturing

Photosynthates are produced in photosynthesis, a complex, two-stage process which produces the energy to fuel its own metabolic needs while also producing the raw, unprocessed energy elements that will be utilized by the vine to fuel its growth, development, and reproductive processes.  A detailed technical description of photosynthesis is beyond the scope of this blog (and the capability of the author) but a few framing remarks are in order.

Photosynthesis is a two-part process wherein (i) the green parts of the vine uses light energy to create chemical energy and (ii) uses that energy to convert low-energy carbon into high-energy carbon compounds.  Photosynthesis is carried out in organelles (chloroplasts) which contain light-absorbing pigments called chlorophyll, the substance which gives the green color to leaves, stems, and inflorescences.  In the first step, chlorophyll absorbs photons and utilizes the captured energy to produce adenosine triphosphate (ATF), the chemical energy which is used by cells to power metabolic activity.

The second phase is light-independent and utilizes the energy and molecules from the first phase for carbon fixation and the production of photosynthates (sucrose, fructose, glucose, organic acids, proteins, fats, etc.).

Vine leaves, having the largest surface area, are the highest volume photosynthate producers.  The youngest (and most photosynthetically active) leaves can be found in the middle and upper parts of the shoot and on the laterals (Kuljancic et al.).

Distribution

The photosynthates are either utilized immediately or warehoused for later use depending on the state of vine development.  Photosynthates are allocated to “sources” and “sinks” based on time of season and needs of the vine and are moved between these poles in a process called translocation.  Most of the photosynthates produced post-harvest are translocated to the roots and trunk to be stored as carbohydrates for next season’s vine growth.  According to Lebon et al., starch is the most important part of the sugar reserves for all grapevine varieties and, during winter dormancy, can be as much as 1/3 of the root’s dry weight. 

Customers

The analog for customers in the grapevine energy supply chain are the totality of cells with metabolic needs.  Net consumers of photosynthates are shoot tips, root tips, and developing fruit during the growing season and the woody parts of the vine post-harvest.  When soil temperature reaches 10-12 degrees centigrade, metabolism is activated and carbohydrates from the woody parts of the vine are mobilized to support annual growth.

Regardless of whether it is sourced from stored carbohydrates, or from photosynthates fresh off the assembly line, the energy within these foods are released by a process called aerobic respiration.  The process is driven by cell-resident organelles called mitochondria which generate chemical energy (ATP) by “metabolizing sugars, fats, and other chemical fuels with the assistance of molecular oxygen sourced from the atmosphere and the soil.” 

Respiration is a continuous process in which critical vinous products such as proteins, enzymes, colors, aromas, and flavors are produced.

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In this post I mapped the grapevine energy supply chain to a generalized supply chain model.  In a follow-up post I will show how modern viticultural science can be viewed through supply chain management lens.

©Wine -- Mise en abyme

Grape vine nutrient requirements and acquisition

Adequate amounts of the appropriate nutrients are required to support proper growth of the grape vine, fruit development, and fruit maturity and those nutrients are obtained from the soil by the plant.  The table below shows the mineral requirements of the vine plant, the role of each mineral, acceptable ranges of each mineral in the soil, and the impact of mineral deficiency on the vine.

Source: Compiled from LGRGP.org and others

Soil is comprised of air, water, mineral particles (a mix of clay, silt, and sand), organic matter (decomposing plant material), and organisms (bacteria, algae, fungi, earthworms, insects, etc.).  Most of the solid soil matter is comprised of mineral particles while fully half of the overall content is pore space (in general a 50-50 mix of air and water).  Organic matter is: (i) critical in holding soil particles together; (ii) a reservoir of nutrients and water; and (ii) a food source for soil organisms.

Soil-based nutrients are resident either in the soil solution (water and dissolved minerals in the soil pores) or in the soil matrix (mineral particles and organic matter).  Two problems present themselves, however: (i) the concentration of nutrients in the soil solution is low and (ii) the nutrients that are resident in the soil matrix is immobile.  Plant roots have developed adaptions to allow growth into the soil matrix and capture of the nutrients needed for metabolic activity (Dr. Paul Schreiner, USDA-ARS) and we will discuss these later.

Soil composition affects the availability of nutrients for soil uptake.  Soil pH is a measure of the acidity (3.5 - 6.5) or alkalinity (7.4 - 9.0) of soil which, through its influence on nutrient solubility and micro-organism activity, affects the number and types of nutrients in the soil. Soil pH between 6 and 7 is considered optimal for vine plant growth as most of the needed nutrients and micro-organisms are available in that range.  The optimal soil type also has a moderate content of low cation exchange capability (CEC) clay (Clay minerals act as harbors for nutrients because the positive ions of the nutrients are trapped by the negative charge of the clay minerals.  The abundance and types of minerals determine whether the clay is classed as low- or high-CEC.).

Roots have developed a number of physical and chemical adaptations to allow them access to an immobile nutrient set resident in the soil matrix (Dr. Schreiner).  The first adaptation is the root size and structure.  The vine plant deploys an always-growing, three-part root structure to meet its needs for anchoring, water- and nutrient-acquisition, nutrient storage during plant dormancy, and hormone production.  As it relates to nutrition, the plant deploys quick-growing, short-lived roots close to the surface to aid in moisture collection and primary roots for nutrient uptake (The woody roots (anchoring and transport) take up limited amounts of nutrients due to the presence of a waxy coating designed to keep ions in.).  According to UCDavis, about 60% of a vine plant's root structure is located within two feet of the surface but individual roots can grow as deep as 20 feet depending on soil permeability, water table levels, and rootstock variety.

Source: bccs.bristol.ac.uk

The second adaptation is the formation of symbiotic relationships with arbuscular mycorrhizal fungi (AMF), a non-specific fungi which extends its apparatus beyond the plant's zone of influence in order to retrieve minerals such as Phosphorous and Zinc and, in return, utilizes plant-derived carbon for its growth and reproduction.  Both the plant and fungi benefit from this relationship.

A third adaptation is the ability to secrete protons, organic acids, and enzymes and release these into the surrounding soil in order to increase the solubility -- and absorbability -- of certain ions.

In order to effect nutrient transfer, the roots of the plant has to be in direct contact with the soil matrix and the nutrients have to be delivered to the root surface.  Nutrients reach the root surface in a combination of three ways: interception, bulk flow, and diffusion.

Source: baileybio.com

Only a small fraction of the plant's nutrient needs are met by interception.  In this case, as the root grows into new areas, it displaces nutrients resident in the soil matrix.  Once on the root surface, the nutrients transit through the root's plasma membrane using available ion-selective channels.  The transfer is effected as the ions flow from areas of high concentration to areas of low concentration.

Bulk flow is the movement of nutrients towards the root as a result of transpiration water uptake.  Water enters a vineyard through precipitation or irrigation and that water either runs off, flows to levels beyond which it can be accessed by the vine plant, or remains in the rooting zone where it is available for the plant's use.  The plant uses water as an internal distribution vehicle (in addition to other functions) and facilitates this by expelling water through pores (stomata) in the leaves.  As water is transpired from the leaves, replacement water is drawn in at the roots.  This replacement water moves undiluted nutrients to the root surface but also carries dissolved nutrients into the roots as a part of its transit. Nitrogen is the nutrient most frequently acquired by the roots in this manner.

Source: talktalk.co.uk

Diffusion is the mechanism whereby nutrients move toward the roots as a result of agitation caused by the concentration gradient that develops near the root surface as a result of nutrient uptake.  Phosphorous and Calcium are the nutrients most susceptible to this type of capture.

In addition to the above mechanisms, as mentioned previously, the plant can utilize AMF to reach beyond its depletion zone in order to bring Phosphorous to the root interface.

While the above treats "naturally" occurring nutrients, the viticulturist will fertilize if he/she determines that a nutrient deficiency exists.  The nutrients added to the soil will make their way into the plant in exactly the same manner.


©Wine -- Mise en abyme