National Postgraduate Entrance Exam Tree Physiology: practice questions

1 · Water relations: transpiration, cohesion-tension, xylem embolism · medium

A branch has maximum conductivity 5.0 units; after drought its conductivity is 2.0 units. What is the percentage loss of conductivity (PLC)?

1. 60%
2. 40%
3. 250%
4. 30%

2 · Water relations: transpiration, cohesion-tension, xylem embolism · hard

Species A has P50 of −3.0 MPa and reaches a minimum xylem water potential of −2.6 MPa in dry summers; species B has P50 of −6.0 MPa and reaches −3.5 MPa. Which statement is correct?

1. A has the larger hydraulic safety margin: 2.6 MPa versus 3.5 MPa
2. Both have equal safety because both stay above their own P50
3. B has the larger hydraulic safety margin: 2.5 MPa versus 0.4 MPa
4. A is safer because its P50 is closer to zero than that of B

3 · Photosynthesis in trees: C3 pathway, light response, shade tolerance · medium

On a light response curve, the light compensation point is the irradiance at which:

1. Net photosynthesis is zero
2. Photosynthesis is light-saturated
3. Quantum yield is at its maximum
4. Stomata first open in the morning

4 · Photosynthesis in trees: C3 pathway, light response, shade tolerance · hard

Tree rings from a drought-prone site show δ¹³C becoming less negative over a period. The most likely physiological interpretation is:

1. Lower intrinsic water-use efficiency because stomata opened more widely
2. A switch from C3 to C4 photosynthesis by the trees at the site
3. Higher intrinsic WUE through tighter stomatal control
4. Greater photorespiration, which enriches wood in the lighter carbon isotope

5 · Mineral nutrition and mycorrhizae · hard

Why are ectomycorrhizal trees thought to dominate many cold, organic-rich boreal and temperate soils?

1. ECM fungi fix atmospheric nitrogen in root nodules
2. ECM fungi need no carbon from the host tree
3. ECM fungi increase soil temperature in spring
4. Their fungi mine organic N and P with enzymes

6 · Cambial activity, wood formation and growth rings · medium

In temperate trees, spring reactivation of the cambium proceeds basipetally from the buds mainly because of:

1. Cytokinin moving up from the roots as soil warms
2. Auxin flowing down from expanding buds
3. Abscisic acid moving down from senescing leaves
4. Ethylene released by bark cracks in late winter

7 · Cambial activity, wood formation and growth rings · hard

A ring shows a band of latewood-like cells in mid-ring followed by earlywood-like cells, then normal latewood. This is most likely:

1. A missing ring from a year without growth
2. A false ring after mid-season drought
3. Compression wood from a leaning stem
4. Juvenile wood formed near the pith

8 · Plant growth regulators and their role in propagation · medium

Which hormone is the main signal for stomatal closure under water stress?

1. Gibberellin
2. Cytokinin
3. Auxin
4. Abscisic acid

9 · Dormancy, phenology and cold hardiness · medium

Warmer winters with insufficient chilling may affect spring phenology of some temperate species by:

1. Delaying or spreading out bud burst
2. Causing bud burst in midwinter in every species
3. Preventing leaf fall the previous autumn
4. Removing the need for any forcing temperatures

10 · Reproductive physiology: flowering, pollination, seed development · medium

Masting is best defined as:

1. Annual production of equal seed crops by every tree in a stand
2. Continuous flowering throughout the year in humid tropical trees
3. Synchronous, intermittent heavy seed crops across a whole population
4. Production of seeds without fertilisation, giving clonal offspring