Fertilization and allelopathy modify

Pinus halepensis Mill. is a Mediterranean pioneer forest species with shade intolerance features. The 15 purpose of this study is to better understand how stand fertility and allelopathic properties of adult trees influence 16 shade acclimation of saplings. Crown growth and morphological plasticity were studied under different light, 17 fertilization, and allelopathic conditions in a nursery experiment. We tested whether shade-acclimation capacity 18 increases with fertilization, and is affected by autotoxicity due to pine leachates. We examined stem diameter, 19 and crown characteristics (length, width, shape and density) in a factorial experiment with two levels for each 20 tested factor: light (full and 20 % reduced light), fertilization (low and high rate of NPK fertilizer) and 21 allelopathy (control and allelopathic leachates uptake). In our study, shading induced a significantly higher 22 crown length, width and surface. Fertilization strongly increased crown length and vertical expended crown 23 shape (the ratio crown length/crown width). Leachates uptake reduced crown length and density, highlighting an 24 autotoxicity phenomenon. We concluded that P. halepensis saplings presented a shade avoiding syndrome and 25 that the crown shade-acclimation response increased with fertilization but was severely compromised by 26 autotoxicity. We finally discuss the role of fertilization and allelopathy in early P. halepensis acclimation ability. 27