Short Note: Root Restriction Hindered Early Allometric Differentiation Between Seedlings of Two Provenances of Canary Island Pine

Based on the optimal partitioning theory, the comparative assessment of seedling allometry is a common task in retrospective genetic tests and early testing of forest reproductive material. Our hypothesis was that root restriction imposed by the container might hinder or rule out genetic differences in biomass allocation. We grew seedlings of two contrasted provenances of Canary Islands pine in mini-rhizotrons, 60 and 90 cm deep, and alternatively in standard bottom-open 200 cc forest containers. In the mini-rhizotrons, plants from the drier provenance allocated more biomass to roots, especially to the tap root and invested less in needles, both in a biomass and leaf area basis, and this morphological divergence increased between two harvests, undertaken at 57 and 115 days after planting. By contrast, confirming our hypothesis, at the 115 days harvest, the plants grown in standard containers did not exhibited significant differences between provenances for Leaf Mass Fraction, Root Mass Fraction and Leaf Area Ratio. We conclude that the physical constraint for root development imposed by small containers increases the probability of dismissing the genetic effect in biomass allocation when assessing forest reproductive materials at the short term, even when the whole plant growth (total dry weight) might be unaffected.

Relationship between heartwood radius and early radial growth, tree age, and climate in Pinus canariensis

Heartwood radius at breast height was studied in 31 sampling sites from natural stands of Canary Islands pine (Pinus canariensis Chr. Sm. ex DC) covering the natural range of the species. After withdrawal of defective and nonheartwood samples, 1640 sound radial cores ranging in age from 30 to 265 years were analysed. Linearized models for the prediction of heartwood radius at breast height were obtained using stepwise regression methods. The best fit was attained including age and early radial growth variables (radius of the 25 or to the 50 inner rings), while stem radius inside bark and whole radial growth rate did not improve the prediction. Sampling sites were classified into five climate types, established according to the main plant communities associated with Pinus canariensis. The use of separate models for each climate type led to a significant reduction of the residual variance compared with multiple climate models. This confirmed that climate is an essential factor in heartwood development in Pinus canariensis even when 51–73% of heartwood radius variation is explained by age and early growth. For fixed values of age and early growth, models predicted wider heartwood in drier climate types than in wet and high-altitude (supra-nubius) climate types.