Effect of shade stress on growth, morphology, and carbon dynamics of loblolly pine branches

Abstract

Summary. Shade treatments were applied to the terminal portions of branches in loblolly pine trees to test whether portions of branches were autonomous with respect to carbohydrates. The shade treatments reduced light by 50% and 72% compared with full sun conditions resulting in significant reductions in net photosynthesis. Branch growth (branch diameter and length, branch and needle biomass) decreased significantly within the shaded portion of the branch. Branch and needle morphology were also affected by shading. Lateral branches subtending terminal shoots were labelled with 14C 2 times during the growing season. No movement of 14C into the terminal portions of the branch was evident during the first growth flush. However, during the second flush of growth small but statistically significant amounts of 14C were imported into the terminal portion of the shaded branches from subtending laterals. It was concluded that loblolly pine shoots were usually autonomous with respect to carbohydrate supply, but that carbohydrate movement into the terminal shoot from subtending foliage could occur under conditions of very high stress.

Second-Log Branching in Multiaged Redwood and Douglas-Fir: Influence of Stand, Site, and Silviculture

“…conifer's own upper branches grew and shaded their own second-log branches. The reduction of BGR with increased shade is consistent with the hierarchal order of branch development for loblolly pine, where branch diameter growth was least important [36]. Douglas-fir responded to the harvest and herbicide treatments more than redwood throughout the range we sampled.…”

“…The release should have carried into the beginning of the second five-year period, but the effect may have been limited as each conifer's own upper branches grew and shaded their own second-log branches. The reduction of BGR with increased shade is consistent with the hierarchal order of branch development for loblolly pine, where branch diameter growth was least important [36]. conifer's own upper branches grew and shaded their own second-log branches.…”

Field performance of various Pinus radiata breeding families established on a drought-prone site in central Chile

“…Differences in physiology have been reported in species such as Pinus taeda L. (Yang et al 2002), but no studies have been reported hitherto for P. radiata. Gas exchange (CO 2 assimilation) values of firstgeneration half-sib families of P. taeda (McGarvey et al 2004) were similar to those reported for unimproved material (Cregg et al 1993). These results could preliminarily indicate that changes in growth associated with breeding are not necessarily associated with changes in easily measured ecophysiological traits.…”

“…This effect was attributed by both sets of authors to the competition by weeds for water. No clear differences in physiology could be found by comparing net photosynthetic rates from studies involving unimproved P. taeda seedlings (Cregg et al 1993) and improved family varieties (McGarvey et al 2004). Similarly, it seems that three generations of breeding of P. radiata with truncation selection applied to the species have not substantially changed phenotypic variability for the ecophysiological traits, which could be advantageous under changing environmental conditions, since resource capture and stand productivity could be greater (Bettinger et al 2009).…”

Needle longevity, shoot growth and branching frequency in relation to site fertility and within-canopy light conditions in Pinus sylvestris

“…Conifers may decrease needle to shoot axis mass ratio with increasing irradiance [14,33,39,44], thereby allowing more extensive needle area development at a common biomass investment in branches in low light. However, in our study, there was an increase in the fractional investment in needles with increasing Q int in the fertile site, and no effect of Q int in the other site ( figure 4D).…”