Rates of Water Loss and Uptake in Recalcitrant Fruits of Quercus Species Are Determined by Pericarp Anatomy

Abstract

Desiccation-sensitive recalcitrant seeds and fruits are killed by the loss of even moderate quantities of water. Consequently, minimizing the rate of water loss may be an important ecological factor and evolutionary driver by reducing the risk of mortality during post-dispersal dry-spells. For recalcitrant fruits of a range of Quercus species, prolonged drying times have been observed previously. However, the underlying mechanism(s) for this variation is unknown. Using nine Quercus species we investigated the major route(s) of water flow into and out of the fruits and analysed the relative importance of the different pericarp components and their anatomy on water uptake/loss. During imbibition (rehydration), the surface area of the cupule scar and the frequency and area of the vascular bundles contained therein were significantly correlated with the rates of water uptake across the scar. The vascular bundles serving the apex of the fruit were a minor contributor to overall water. Further, the rate of water uptake across the remainder of the pericarp surface was significantly correlated with the thickness of the vascularised inner layer in the pericarp. Fruits of Q. franchetii and Q. schottkyana dried most slowly and had a comparatively small scar surface area with few vascular bundles per unit area. These species inhabit drier regions than the other species studied, suggesting these anatomical features may have ecological value by reducing the risk of desiccation stress. However, this remains to be tested in the field.

Seed storage behaviour of 101 woody species from the tropical rainforest of southern China: a test of the seed-coat ratio–seed mass (SCR–SM) model for determination of desiccation sensitivity

“…However, different ecological factors and evolutionary drivers may result in exceptions. For example, the covering structure (pericarp) of desiccation-sensitive seeds of Quercus schottkyana and Q. franchetii minimises the rate of water loss, which reduces the risk of mortality during postdispersal dry spells (Xia et al 2012a(Xia et al , 2012b. The thick seed coat of the five desiccation-sensitive species in our study may reduce the rate of seed water loss; however, this has not been investigated.…”

Tree seed traits’ response to monsoon climate and altitude in Indian subcontinent with particular reference to the Himalayas

“…The desiccation‐sensitive seeds of PMS species might restrict the loss of seed moisture by having protective pericarp components and anatomical arrangements. In a study on desiccation‐sensitive seeds of some oaks, the role of anatomical adaptations of the pericarp was shown in resisting water loss (Xia, Daws, Stuppy, Zhou, & Pritchard, ; Xia, Hill, Li, & Walters, ).…”

“…In a way, species of this group employ desiccation tolerance and dormancy of seeds to achieve a monsoon‐desynchronized strategy. While desiccation‐sensitive seed‐bearing species in this category might have some protective pericarp components to restrict the loss of seed moisture like in seeds of some oaks (Xia et al., , ) in addition to dormancy.…”

Orthodoxy, recalcitrance and in-between: describing variation in seed storage characteristics using threshold responses to water loss

“…This practice confounds assessments of responses to level and duration of stress. Moreover, many recalcitrant seeds possess large, fleshy organs and thick covering layers surrounding the embryo as mechanisms to resist water loss (Daws et al 2006b;Xia et al 2012). In the classical sense, these features contribute to desiccation avoidance rather than tolerance per se (Levitt 1980).…”