Oak Hill Case Atmospheric Problems

Shading PAR (red & blue light) intensity are reduced by shading. Light transmitted through tree canopies comes through at longer wavelengths, including far red light.

Shade Effects QUANTITATIVE reduced photosynthetically active radiation (PAR) QUALITATIVE photomorphogenetic response due to phytochrome

Light Quantity

Alteration of Light Quality SOLAR RADIATION absorption transmission reflection rich in red light, low in far-red light lower in red light, richer in far-red light

Phytochrome (P r & P fr ) P r - blue pigment (inactive) absorbs red light P r is converted to P fr by red light. P r P fr red light far-red light P fr - olive-green pigment (active) absorbs far-red light P fr is converted to P r by far-red light (or by darkness).

Phytochrome Effect Active (P fr ) Inhibits stem and leaf elongation, resulting in smaller plants Promotes tillering, increasing shoot density Inactive (P r ) Promotes stem and leaf elongation, resulting in larger plants Inhibits tillering, reducing shoot density

Other Shade Effects Thinner leaves and cuticles Shallower rooting Reduced carbohydrate reserves A “shade” turf is thus more delicate and less tolerant of wear, disease, and environmental stresses.

Poor Air Circulation Closely planted trees and shrubs restrict air flow, resulting in a warmer, more humid microenvironment. As a consequence, disease pressure is greater.

Wind Effect Wind moves parcels of air from the turf and incorporates them into the larger volume of air above it. Thus, the accumulation of heat and humidity are dissipated.

Moisture Moisture accumulation within a turfgrass canopy comes primarily from an evaporative process, called transpiration.

Transpiration Water is absorbed by roots, translocates upward, and accumulates as films of moisture on internal leaf cells. Water films evaporate and exist the leaf through pores, called stomates.

Boundary Layer Water vapor exiting the stomates accumulates in a layer of humid air immediately around the leaf. With the development of boundary layers around all leaves, the environment of the turfgrass canopy can become quite humid.

Wind Effect With moderate air movement across the turf, however, the humidity of this environment can be substantially reduced. And the potential for disease is proportionately reduced.