Microclimatic conditions and plant morpho-physiological development within a tree shelter environment during establishment of Quercus ilex seedlings

Abstract

Tree shelters are used commonly under a wide range of agriculture and forestry applications, and the presence of the shelter is known to influence plant development through shelter–plant interactions that affect microclimatic conditions. However, effects of tree shelter microclimates on development of relatively slow-growing forest tree species characteristic of semi-arid Mediterranean climates have yet to be examined. Under a controlled environment using mesic and xeric watering regimes, we examined microclimatic conditions within light and dark tree shelters relative to non-sheltered conditions and corresponding influences on morpho-physiological development of holm oak ( Quercus ilex L.) seedlings during initial establishment. Despite relatively low photosynthetic rates (<1 μmol CO 2 m −2 s −1), CO 2 concentrations within shelters oscillated widely during the day, reflecting respiration from late afternoon through night and rapid assimilation during the first 2–3 h after sunrise that dropped sharply around noon. In dark shelters within the mesic watering regime, reduced vapor pressure deficit (VPD) was associated with high plant transpiration. Higher irradiance inside light shelters stimulated photosynthesis, although higher VPD under xeric conditions led to decreased mid-day xylem water potential within light shelters. Additionally, decreased light transmittance among shelter treatments (control > light > dark) did not affect plant N or starch concentrations nor total plant biomass, but resulted in increased height, as well as leaf area production and shoot:root ratio under mesic conditions, morphological adaptations likely to increase drought susceptibility under hot, dry conditions characteristic of late summer in this region. We conclude that microclimatic conditions within tree shelters and corresponding influences on plant morpho-physiological development are interrelated through complex phenomena dependent upon environmental conditions and phenotypic characteristics of a given plant species. Consequentially, shelter configurations must be adapted to match climatic conditions of the outplanting site with species plasticity; we recommend light shelters with high light transmittance for planting holm oak in Mediterranean areas.