Oak decline alters leaves and fruit of Persian oak (Quercus brantii Lindl.)

Abstract

Abstract Biotic and abiotic stressors are known to modify the morphology of forest trees. Nevertheless, there is little information on the effects of tree decline on leaf and fruit morphology of oaks. To understand morphological adaptations of Persian oak (Quercus brantii Lindl.) to oak decline, we compared leaves and fruit from healthy and declining Persian oaks from six populations in the Zagros Forest of Iran. Fruits and leaves were sampled from five healthy and five declining trees from each population (30 declining and 30 healthy trees total). Fifteen leaves and fruits were sampled from each tree, for a total of 900 leaves and 900 fruit. We measured fruit length and diameter, scar diameter, cupule length, cupule span diameter, and fruit cover length as well as leaf length, petiole length, maximum lamina width, width of the lamina base, and width of the lamina apex. The leaf area was estimated from the product of length, maximum width, and a shape coefficient. Leaf trichomes were examined with SEM and classified as either mostly stellate or non-stellate. Healthy Persian oaks from five of the six populations had larger leaves, with greater lamina area, when compared with declining individuals. Moreover, the trend was the same across all six populations. Leaves of declining oaks also had distorted trichomes. Moreover, declining Persian oaks had smaller (shorter) fruit. The impact of oak-decline on Persian oak morphology, however, varied greatly among the six populations, limiting leaf and fruit size as indices of oak-decline. Leaves and fruit are smaller in declining Persian oaks, and trichomes are degraded. Nevertheless, care must be taken in using these traits as reliable proxies for tree decline, simply because the effect varies among populations.