Lecturers:
Dr Tin Hang (Henry) Hung æīŠåĪĐæ [email protected]
Prof John MacKay [email protected]
Demonstrators: Dr Erola Fenollosa
Sitka spruce (Picea sitchensis)
Lawson cypress (Chamaecyparis lawsoniana)
Excess forest mortality is consistently linked to drought worldwide. Adaptation to drought has a complex underlying mechanism and has trade-offs with other life history traits. In particular, water regulation is closely related to photosynthetic activity and has significant effects on growth.
Today we will be studying two commercial conifer species widely bred and grown in the UK: Sitka spruce and Lawson cypress. We will characterise and compare their drought responses.
For each species, 4 trees are well-watered controls and 4 are drought-stressed. Drought stress is incurred by withholding the trees from water for ~14 days.
There are three hypothesised mechanisms underlying tree mortality, based on the relationship between the temporal length of drought (duration) and the relative decreased in water availability (intensity) in the hydraulic framework.
Carbon starvation can occur when drought duration is long enough to curtail photosynthesis longer than the equivalent storage of carbon reserves for maintenance of metabolism.
Hydraulic failure is when drought intensity pushes a plant past its threshold for irreversible desiccation before carbon starvation occurs.
Biotic agents (herbivory and diseases) can amplify or be amplified by both carbon starvation and hydraulic failure.
