The effect of defoliation intensity and history on photosynthesis, growth and carbon reserves of two conifers with contrasting leaf lifespans and growth habits

Abstract

The effects of partial defoliation on photosynthesis, whole-seedling carbon allocation, partitioning and growth were studied for two species with contrasting foliar traits. Field-grown seedlings of deciduous Japanese larch (Larix leptolepis) and evergreen red pine (Pinus resinosa) were defoliated by hand in early summer for 2 consecutive years. In the first year (1990), seedlings were defoliated by removing the distal 0, 25, 50 or 75% of each needle. In the second year (1991), seedlings were defoliated either 0 or 50%, regardless of previous defoliation treatments. Defoliation had little effect on photosynthesis and starch concentration in whole seedlings of either species in the first year. In the second year, photosynthesis increased in both species in response to the 1991 defoliation treatment, and in red pine also increased in response to the 1990 defoliation treatment. Further, in 1991 both larch and pine had decreased whole-seedling total non-structural carbohydrate concentrations in all seedlings that were defoliated at least once over the 2-yr period. This decrease was noted mostly in the starch component of the nonstructural carbohydrates, and was similar in both species. In 1991, biomass was similarly decreased in both species in response to 1991 defoliation. Both species showed overcompensation in total and component biomass in seedlings defoliated by 25% in 1990. Overall, the results do not support the widely held belief that evergreen trees are substantially more affected than deciduous trees by defoliation.

Do artificial and natural defoliation have similar effects on physiology of Eucalyptus globulus Labill. seedlings?

“…Up-regulation of photosynthetic rates in the remaining leaves following natural and artificial defoliation has been observed in many tree species (Chen et al, 2001;Reich et al, 1993;Vanderklein and Reich, 1999) including in eucalypt species (Pinkard, 2003;Turnbull et al, 2007). Up-regulation is likely to play an important role in minimising the impact of defoliation on growth (e.g.…”

“…Up-regulation is likely to play an important role in minimising the impact of defoliation on growth (e.g. Chen et al, 2001;Heichel and Turner, 1983;Ovaska et al, 1993;Reich et al, 1993;Vanderklein and Reich, 1999). For example, reported that removal of 50% of leaf area of E. nitens seedlings had no impact on height growth 8 weeks later, which they related to enhanced photosynthetic rates and changes in patterns of carbon allocation to favour leaf area development .…”

“…Artificial defoliation methods are often selected based on logistical considerations such as time taken to defoliate plants, and may bear no resemblance to the spatial and temporal patterns of insect damage (e.g. Heichel and Turner, 1983;Hoogesteger and Karlsson, 1992;Ovaska et al, 1993;Reich et al, 1993;Vanderklein and Reich, 1999). Artificial defoliation studies with Eucalyptus globulus Labill.…”

“…For instance, increase in photosynthetic rate along with changes in foliar nitrogen and carbohydrate contents commonly occur following defoliation events in a large range of tree species (e.g. Chen et al, 2001;Hoogesteger and Karlsson, 1992;Ovaska et al, 1993;Reich et al, 1993;Vanderklein and Reich, 1999).…”

Effects of living crown reduction on needle element status of Scots pine

“…Overcompensation after defoliation is a common phenomenon in many higher plants, especially in nutrient-rich, favourable growing conditions (e.g. Vanderklein and Reich 1999, Rautio et al 2005, Ruiz et al 2008. In the studies of this thesis, the increases in the concentrations of many of the nutrients may have had a temporarily beneficial growth effect in tree recovery.…”