Qualitative Assessment of Postharvest Stomata and Chloroplast Degradation in Contrasting Abscission Resistant Balsam Fir (Abies balsamea (L.) Mill.)

Balsam fir is an important Christmas tree species, especially in eastern Canada. The natural Christmas tree industry faces a challenge in postharvest needle abscission. Though there have been many studies describing the physiological triggers and consequences in postharvest balsam fir, there have been no studies describing morphological or ultrastructural changes. Therefore, the objective of this study was to examine changes in stomata and chloroplast of postharvest needles. Branches were collected from low and high needle abscission resistance balsam fir genotypes, placed in water, and displayed in typical household conditions for 11 weeks. Needle abscission, chlorophyll fluorescence, and water uptake were monitored throughout. Needles stomata and chloroplasts were examined under a scanning and transmission electron microscope, respectively, each week. All branches had increased abscission, decreased chlorophyll fluorescence, and decreased water uptake over time. Needle surfaces accumulated fungal hyphae, especially in stomata. Chloroplasts demonstrated some dysfunction within two weeks, with notable decreases in chloroplast starch and increases in plastoglobulins. Within several weeks thylakoid membranes had been dismantled as chloroplasts transformed into gerontoplasts. All biophysical and structural changes were more pronounced in low needle abscission resistant genotypes. This research identifies a potential role for needle fungi in postharvest needle abscission and confirms the postharvest senescence of chloroplasts. Though it was previously speculated that chloroplasts must senesce postharvest, this study identifies how quickly this process occurs and that it occurs at different rates in contrasting genotypes.

N and P resorption as functions of the needle age class in two conifer trees

Aims Given the importance of resorption in nutrient conservations,nu-trient resorption should change with leaf age if resorption depends on nutrient content,and if nutrient content changes with leaf age.However,no study has addressed this issue.Methods Here,we measured N and P concentrations of needles of different ages in two woody evergreen conifer species-white spruce(Picea glauca Voss.)and balsam fir(Abies balsamea Mill.)-to determine the effects of needle aging on nutrient resorption.Important Findings For both species,N and P concentrations were higher in newer needles than in older needles.Nutrient resorption efficiency,i.e.percentage of nutrients resorbed during senescence,also declined significantly with needle age from 73 to 22%in these two evergreen conifer species.The difference in nutrient resorp-tion between old and young needles may be attributed to the size of N and P sink tissues,which is likely to decrease with needle age.These results suggest that needle age affects the extent of N and P resorption in these two evergreen conifer species.