Effects of drought on needle anatomy of Pinus canariensis

Abstract

SummaryThe needles of Pinus canariensis exhibit morphological drought adaptations, such as special stomata morphology or rigid sclerenchymatic hypodermis. In the present paper the hypothesis that drought exposure during needle elongation triggers formation of xeromorphic traits was tested. With onset of the elongation growth of the new flush, 5-year old P. canariensis seedlings were exposed to 53 days of reduced water supply under controlled climate chamber conditions. The treatment resulted in a decrease of needle water potentials from -1.5 MPa to -4 MPa in drought stressed plants, whereas no change was observed in water potentials of control needles. Needles of drought exposed trees remained shorter and thinner. Cross-sections of elongating needles taken at 1 cm distance from the needle base were taken repeatedly during the experiment. Cross-section areas of different needle tissues were measured in an image analysis system. In needles of drought stressed trees sclerenchymatic tissues in the hypodermis and adjacent to the vascular bundles increased due to large increases in the number -not the size -of sclerenchymatic cells. The ratio of assimilation parenchyma to the vascular bundle (supplied versus supplying tissue) decreased. We conclude that these changes, which adapt needles to drought conditions, are triggered by drought stress experienced while needles are growing.

Growth response to climate and drought in Pinus nigra Arn. trees of different crown classes

“…Therefore, our results add further evidence that conifers in xeric sites might be better adapted to water scarcity and stand drought episodes than those at mesic sites. Adaptations to drought may include: developing deeper roots or increasing the root to shoot ratio (e.g., Lloret et al 1999), modifying the diameter of tracheids (e.g., Linton et al 1998) or developing anatomic features in needles to reduce water loss (e.g., Grill et al 2004).…”

Decline ofPinus thunbergiiParlat. stands due to excess soil moisture caused by a buried andosol layer at a coastal sand site in Hokkaido, northern Japan

“…Excess soil moisture causes water stress in most tree species, and produces responses similar to drought conditions (Kozlowski and Pallardy 2002). A decline in needle length with increased soil moisture content was also found in Picea glehnii (Masaka et al 2004), whereas Grill et al (2004) reported that needles of drought-exposed Pinus canariensis remained short. Taken together with other symptoms observed at the study site (crown dieback and intense lateral growth), we can thus conclude that the reduction in P. thunbergii needle length at the heavily damaged site was caused by excess soil moisture due to the less permeable buried concreted andosol layer.…”

Contrasting effects of wildfire and climate on radial growth of Pinus canariensis on windward and leeward slopes on Tenerife, Canary Islands

“…Leeward populations of P. canariensis exhibit xeromorphic traits allowing a tight regulation of transpirational water loss (Grill et al 2004). Accordingly, annual canopy transpiration lies significantly below the common values for other Mediterranean trees, suggesting a strong adaptation to low soil water availability during periods of great evaporative demand (Luis et al 2005).…”

“…Pinus canariensis also shows adaptations to xeric conditions, such as very deep root system, tight regulation of transpirational water loss, drought-induced xeromorphic adaptations of the needles, and xeriscent cone opening (Climent et al 2004;Grill et al 2004). In spite of these adaptations, however, it is sensitive to prominent water stress, a limiting factor at the upper altitudinal timberline of the species in the Canary archipelago (Gieger and Leuschner 2004;Jonsson et al 2002).…”