Use of Extenday reflective groundcover in production of ‘Gala’ apples (Malus domestica) in New Brunswick, Canada: 1. Impact on canopy microclimate and leaf gas exchange

Abstract

A field study was conducted in New Brunswick, Canada to assess the impact of a reflective groundcover (Extenday) on ‘Gala’ (Malus domestica) apple tree microclimate (diurnal and seasonal distributions of incident and reflected photosynthetically active radiation (PAR) within the canopy, seasonal canopy air temperature and relative humidity (RH), soil temperature and moisture) and leaf gas exchange (net photosynthesis (Pn), stomatal conductance (g_s), intercellular CO₂ (Ci), and transpiration (E)). When installed between tree rows from full‐bloom until 3 weeks post‐harvest, the 3‐m wide reflective groundcover did not influence incident PAR within the tree canopy, but enhanced the reflection and distribution of light into all canopy levels (upper, middle, lower), relative to uncovered sod. Within the lower canopy, overall relative PAR levels were increased from 29% full‐sun to 39% full‐sun (on sunny days) and levels of reflected PAR were 5–9‐fold greater (over the season), with use of the reflective groundcover. On a seasonal basis, canopy RH was reduced by 3.8 ± 1.2%, and soil moisture was increased by 5.5 ± 0.28% to 7.7 ± 0.52%, with use of the reflective groundcover; canopy air temperature was unaffected. Soil temperature beneath the reflective groundcover was as much as 2.1–2.5°C lower than that below uncovered sod, with the differential greatest earlier in the growing season and decreasing over time. Under light‐saturated conditions, the reflective groundcover did not alter leaf temperature or leaf gas exchange or lead to photoinhibition.

Keywords:

• canopy temperature and relative humidity
• diurnal and seasonal light fluxes
• incident and reflected photosynthetically active radiation
• PAR
• photosynthesis
• reflective mulch
• soil moisture and temperature