By Dr. Thomas T. Yamashita
Extreme shifts in temperature, either cooling or heating, represent environmental pressures that can plunge a plant into physiological shock. The consequences are oftentimes manifested in acute toxic reactions such as freeze burning or heat induced necrosis. Physiological shock, however, is oftentimes subtly expressed:
- Reduced overall metabolic rate
- Reduction to temporary stasis in photosynthetic harvest
- Reduced tolerance or resistance to environmental stress and pest-disease pressures
- Reduced crop yields and quality
- Aggravation of tendency towards alternate bearing
- Other deleterious effects
This article touches upon salient considerations and concomitant, preventative cultural practices that may help mitigate the potential ravages of cold and/or heat stress.
Key Principles for Managing Effects of Cold Weather Shifts
Freezing damage to plant tissues is an event closely linked to an inability of plant cell membranes to remain elastic. During a freeze event, liquid from within the cell diffuses outwards to the space between cells, the intercellular space, where ice formation begins. Plants acclimated to the freeze are able to reabsorb the moisture in the intercellular spaces and reestablish metabolic activity.
Developing an elasticity of membranes is a key factor in cold acclimation, as we have found that freeze damage to plant tissues coincides with the irreversible fracturing of inelastic membranes.
Elasticity of membranes is imparted by:
- Relatively higher levels of unsaturated over saturated fatty acids
- Shorter over longer chain fatty acids
- Higher sterol content
- Higher solute content of the cell
Timely and efficient formation of necessary fatty acids, sterols and organic solutes are imperative to ensuring a ready supply of carbon and energy during lean periods. And, plants endowed with an abundant supply of carbon and energy and an overall efficient, operative physiology are better equipped to weather sudden cold or freezing weather.
Plant mineral balances are especially germane, whereby N is de-emphasized while heightened, relative levels of P, K, Ca, B and carbon constituents are secured to develop tissues of high integrity and cold tolerance. Not only must mineral nutrition per se be addressed effectively, but also overall nutrition aimed at maximizing photosynthetic harvest and total physiological efficiency.
Aside from standard clean cultivation, firm soils, and moist soil irrigation techniques, we have also learned that selectively generated microbiological activity can raise soil temperatures between 4 and 12 degrees Fahrenheit. Additionally, this same microbial activity frees locked minerals, thereby raising the quality of mineral nutrition and contributing to optimizing efficient plant physiology.
Key Principles for Managing Effects of Hot Weather Shifts
More than 98% of agronomic plant species fall into the botanical classification of carbon-3 (C-3) physiology. Briefly, C-3 plants are hypersensitive to warming temperatures, which exceed a 12 to 15 degree Fahrenheit shift from one day’s high to the next. In severe cases, plants shut down photosynthetic harvest while accelerating respiratory processes or carbon-energy utilization. We have found that cultural practices, which effectively mitigate cold stress or freezing damages, work equally well for minimizing the various deleterious effects of heat stress.
The deficit in carbon and energy that develops spawns a wave of negative reactions, among others, including:
- Flower or fruit abortion
- Decrease in various crop quality parameters
- Increased susceptibility to pest, disease and environmental pressures
- Initiation of alternate bearing
- Reduced tree or vine longevity
Effective Proven Practices for Mitigating Cold or Heat Stress
Successful management of cold or heat stress is akin to perfecting practices for improving a long list of factors and goals in agriculture. However, for the sake of simplicity and brevity, proven practices are as follows:
- Keep soil firm, clean and moist
- Stress-free irrigation
- Maintain a carbon to nitrogen ratio near or greater than (>) 25:1 in leaves and 30:1 in stems
- Enhance and increase photosynthetic harvest efficiency
- Provide balanced nutrition, including ancillary exotic micronutrients
- Selective microbial activation of the soil
- Maintain appropriate mineral ratios à N:P (< 11:1), N:K (< 1:1), N:Ca (< 1.5:1) and Ca:B (~350-400:1)
While items (a) and (b) are standard cultural tools, goals (c) through (g) require specialized, precise technologies. Sunburst PDC and its research and development arm, Fusion 360, were established for troubleshooting various agronomic maladies and to design and provide highly viable solutions.
In field test after field test, Sunburst PDC, Inc. and Fusion 360 Technologies have reduced and/or prevented altogether various potential agricultural disasters, including cold/heat stress. In pronounced situations, for example, these technologies have not only saved crops from the disc or bulldozer and freeze or heat damages, but exceeded standard remedial expectations to additionally increase yields and quality.
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