Initiation and termination of liquid flow controlled drying collapse of interconnected parenchyma cells in palm wood

Abstract

The underlying mechanisms of drying collapse in liquid-filled oil palm wood (OPW) have been explored. By systematically varying the liquid surface tension inside the OPW, different degrees of drying collapse commonly observed throughout the whole trunk were shown to be initiated at identical threshold capillary pressure. Microstructural examination confirmed that despite having different sizes and wall thicknesses, the thin-wall parenchyma cells possess a roughly constant wall thickness-to-radius ratio to resist buckling. The equivalent behavior of drying collapse and mechanical collapse under compression of saturated OPW was demonstrated to prove that the drying collapse is controlled by the flow of liquid through the wood. Less collapse corresponds to the lower permeability of the liquid through the wood cells. Variation in the post-collapse behavior is a result of the initiation and termination of the liquid flow inside the interconnected parenchyma cell cavities through small pit openings of plasmodesmata of various distributions. This new understanding provides insight into the drying collapse mechanism of the liquid-filled partially closed-cell foam of a similar structure.