Fruit development, not GPP, drives seasonal variation in NPP in a tropical palm plantation

Abstract

We monitored seasonal variations in net primary production (NPP), estimated by allometric equations from organ dimensions, gross primary production (GPP), estimated by the eddy covariance method, autotrophic respiration (R(a)), estimated by a model, and fruit production in a coconut (Cocos nucifera L.) plantation located in the sub-tropical South Pacific archipelago of Vanuatu. Net primary production of the vegetative compartments of the trees accumulated steadily throughout the year. Fruits accounted for 46% of tree NPP and showed large seasonal variations. On an annual basis, the sum of estimated NPP (16.1 Mg C ha(-1) year(-1)) and R(a) (24.0 Mg C ha(-1) year(-1)) for the ecosystem (coconut trees and herbaceous understory) closely matched GPP (39.0 Mg C ha(-1) year(-1)), suggesting adequate cross-validation of annual C budget methods. However, seasonal variations in NPP + R(a) were smaller than the seasonal variations in GPP, and maximum tree NPP occurred 6 months after the midsummer peak in GPP and solar radiation. We propose that this discrepancy reflects seasonal variation in the allocation of dry mass to carbon reserves and new plant tissue, thus affecting the allometric relationships used for estimating NPP.

Net primary productivity, allocation pattern and carbon use efficiency in an apple orchard assessed by integrating eddy covariance, biometric and continuous soil chamber measurements

“…Our findings are consistent with other studies on apple trees of different growing conditions and varieties (Palmer, 1988;Minchin et al, 1997;Faqi et al, 2008), while a similar incidence of fruit production on total NPP was also found in other agro-ecosystems, such as a coconut palm plantation (Navarro et al, 2008), peach (Chalmers and van den Ende, 1975), orange (Liguori et al, 2009) and kiwifruit orchards (Rossi et al, 2007). For comparison with other croplands see Ciais et al (2010).…”

Major determinants of fruit set and yield fluctuation in coconut (Cocos nucifera L.)

“…A significant relationship between the number of days of exposure to high temperature and the percentage of fruit set has been reported in many greenhouse and field-grown crops (Vara Prasad et al, 2000; Wubs et al, 2009b). Abortion of female flowers or young fruits is common in coconut even when they are grown under favourable climatic conditions (Navarro et al, 2008). Within plant competition between organs is based on the source-sink relationships, representing the supply and demand of assimilates.…”

“…Within plant competition between organs is based on the source-sink relationships, representing the supply and demand of assimilates. The cause of seasonal variation in net primary productivity of coconut was due to the differences in fruit development and not due to the gross assimilate production under tropical climatic conditions (Navarro et al, 2008). Therefore, it could be assumed that the variation in sink strength of a palm is more critical than the variation in source strength in determining the variation in fruit set.…”

“…Step 2: Dry matter requirement for respiration of individual fruits of different developmental stages (from experiment 2): The dry matter requirement for respiration of fruits of each developmental stage was estimated according to Navarro et al (2008) and Ranasinghe and Thimothias (2012). The total dry matter requirement of a fruit was calculated as the sum of dry matter requirement for potential growth (PGR) and respiration (R) for each stage.…”

“…Sink strength and source: sink ratios have been used to explain the cyclical fluctuations observed in fruit set and also the differences between varieties (Wubs et al, 2009a). Navarro et al (2008) showed that fruit development is the driving force of yield variation in coconut, and the fruit production (number palm -1 month -1…”