ENVIRONMENTAL EFFECTS ON APPLE TREE PHYSIOLOGY

The aim of this three-year project was to assess the photosynthetic potential of deciduous apple trees in autumn and factors which restrict translocation processes between harvest and leaf fall and appear responsible for the discrepancy between two-fold larger yields in New Zealand compared to the Northern Hemisphere.
The findings were:

1. After harvest, apple leaf stomata appeared active and functioning.
   
2. Apple leaf photosynthesis in the autumn was saturated above 800 µmol PAR m^-2 s^-1.
   
3. The photosynthetic potential of apple leaves remained high at 10-12 µmol CO2 m^-2 s^-1 until the first frost.
   
4. Maximum photochemical efficiency (Fv/Fm) of apple leaves declined slowly from 0.81 to 0.71 after harvest with a more rapid decrease to 0.40 after the first frost.
   
5. Apple leaf chlorophyll and nitrogen content appeared sufficient for photosynthesis after harvest until the end of October, but limiting in November, irrespective of frost incidence, and was used to assess for the degree of senescence.
   
6. Carbohydrate and nutrient content did not appear limiting for apple leaf photosynthesis.
   

In conclusion, harvest induced the onset of carbon translocation and accelerated the translocation of nitrogen, potassium and phosphorus.
Apple photosynthesis in the autumn was not restricted by stomatal function, chlorophyll, carbohydrate or nutrient, except later on for nitrogen content.
However, photosynthesis was primarily limited by the environment such as frost, decreasing light and temperature, shorter days and number of days with favourable weather conditions between harvest and first frost or leaf fall.

VII International Symposium on Orchard and Plantation Systems

I. Tartachnyk, M.M. Blanke

Malus domestica Borkh., carbohydrates, chlorophyll, chlorophyll fluorescence, ecophysiology, nutrients, senescence, source-sink relationship, stomata, stress physiology, translocation

https://doi.org/10.17660/ActaHortic.2001.557.62