There is a broad consensus that climate change is occurring, and that it is linked to a build up of greenhouse gases in the atmosphere enhancing the natural greenhouse effect. Carbon dioxide (CO2) is, by far, the largest contributor to greenhouse effect. In addition to increased CO2, with climate changes, the plants have to adapt their ways to a new environment – in most cases warmer and possibly with the periods of extreme rainfall and drought.
As plantation researchers, we are mostly concerned about the changes in coconut yields by increased temperatures, precipitation differences and also from carbon fertilisation for plants. Whilst high temperature and long dry periods adversely affects the coconut yield, elevated CO2 positively affects plant productivity as the latter is a substrate for photosynthesis. The climate scientists predict future climates using different scenarios. However, projecting climate impacts is one thing, but plantation crops add multiple more dimensions of complexity – what are the sensitive stages of fruit development to stress condition, intensity of heat or drought stress, heat and drought tolerant coconut varieties, irrigation, soil moisture conservation, soil fertility and much more. In addition, the coconuts grown in different agro-climatic zones and different land suitability classes (There are five groups from very suitable to marginally suitable soils.) will respond differently to the climate change; some areas may be more vulnerable than the others. Therefore, one should understand that climatic change impacts on coconut sector are not a phenomenon controlled by a single factor.
Reproductive development is more sensitive to high temperature and water stress than vegetative development and the principal harmful effect of stress is on fruit set and development. The fruit set can be adversely affected, mainly due to a reduction in pollen quality and / or germination. The nut development can be affected mainly resulting small number of nuts, empty nuts or elongated nuts. Coconuts grown in intermediate and dry zones are often exposed to brief or sometimes prolonged period of heat stress, i.e. day time temperature warmer than 30-32ºC and long durations of dry period (more than 2 months rain-free period). The studies are under way to determine the most sensitive stages of coconut reproductive phase to high temperature and water stress and their impacts on coconut yield in different AER and land suitability classes and for different varieties. The degree of sensitivity and the pattern of reaction to high temperature stress and water stress may differ among varieties /cultivars.
In a country like Sri Lanka we do not have facilities to conduct field experiments with coconut and elevated CO2, therefore, with the available facilities; some experiments were conducted with coconut seedlings. The elevation of atmospheric CO2 concentration increased the photosynthetic rate of coconut seedlings by about 25% however; the effect on yield cannot be estimated in these studies.
On the other hand, tree plantation crops are particularly important for reducing CO2 concentration in the atmosphere. They act as carbon reservoirs because trees hold much more carbon per unit area than other types of vegetation. Coconut plantations could be used in four ways to reduce CO2 emissions and sequestrate carbon; substitution of fossil fuel using bio-diesel or biomass from coconut oil, sequestration of C (carbon) through coconut plantation, enhancing C sequestration through coconut plantation management and conserving C sink in coconut ‘forest’.
Therefore, it is clear that climate change will have negative effects on coconut plantations by increased temperature and extreme droughts and positive effects on yield by CO2 fertilization. In addition coconut plantations can be used to mitigate climate change.
The Writer is the head of the Plant Physiological Department at the Coconut Research Institute of Sri Lanka.