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Global warming causes night temperature (NT) to increase faster than day temperature in the tropics. According to crop growth models, respiration incurs a loss of 40-60% of photosynthate. The thermal sensitivity of night respiration (Rn) will thus reduce biomass. Instantaneous and acclimated effects of NT on Rn of leaves and seedlings of two rice cultivars having a variable level of carbohydrates, induced by exposure to different light intensity on the previous day, were investigated. Experiments were conducted in a greenhouse and growth chambers, with Rn measured on the youngest fully expanded leaves or whole seedlings. Dry weight-based Rn was 2.6-fold greater for seedlings than for leaves. Leaf Rn was linearly related to starch (positive intercept) and soluble sugar concentration (zero intercept). Increased NT caused higher Rn at a given carbohydrate concentration. The change of Rn at NT increasing from 21 °C to 31 °C was 2.4-fold for the instantaneous response but 1.2- to 1.7-fold after acclimation. The maintenance component of Rn (Rm'), estimated by assimilate starvation, averaged 28% in seedlings and 34% in leaves, with no significant thermal effect on this ratio. The acclimated effect of increased NT on Rm' across experiments was 1.5-fold for a 10 °C increase in NT. No cultivar differences were observed in Rn or Rm' responses. The results suggest that the commonly used Q10=2 rule overestimates thermal response of respiration, and Rn largely depends on assimilate resources. [ABSTRACT FROM AUTHOR]

Background and Aims: Despite its simple architecture and small phenotypic plasticity, oil palm has complex phenology and source–sink interactions. Phytomers appear in regular succession but their development takes years, involving long lag periods between environmental influences and their effects on sinks. Plant adjustments to resulting source–sink imbalances are poorly understood. This study investigated oil palm adjustments to imbalances caused by severe fruit pruning. [ABSTRACT FROM PUBLISHER]

Oil palm (Elaeis guineensis Jacq.) is a perennial, tropical, monocotyledonous plant characterized by simple architecture and low phenotypic plasticity, but marked by long development cycles of individual phytomers (a pair of one leaf and one inflorescence at its axil). Environmental effects on vegetative or reproductive sinks occur with various time lags depending on the process affected, causing source–sink imbalances. This study investigated how the two instantaneous sources of carbon assimilates, CO2 assimilation and mobilization of transitory non-structural carbohydrate (NSC) reserves, may buffer such imbalances. An experiment was conducted in Indonesia during a 22-month period (from July 2006 to May 2008) at two contrasting locations (Kandista and Batu Mulia) using two treatments (control and complete fruit pruning treatment) in Kandista. Measurements included leaf gas exchange, dynamics of NSC reserves and dynamics of structural aboveground vegetative growth (SVG) and reproductive growth. Drought was estimated from a simulated fraction of transpirable soil water. The main sources of variation in source–sink relationships were (i) short-term reductions in light-saturated leaf CO2 assimilation rate (Amax) during seasonal drought periods, particularly in Batu Mulia; (ii) rapid responses of SVG rate to drought; and (iii) marked lag periods between 16 and 29 months of environmental effects on the development of reproductive sinks. The resulting source–sink imbalances were buffered by fluctuations in NSC reserves in the stem, which mainly consisted of glucose and starch. Starch was the main buffer for sink variations, whereas glucose dynamics remained unexplained. Even under strong sink limitation, no negative feedback on Amax was observed. In conclusion, the different lag periods for environmental effects on assimilate sources and sinks in oil palm are mainly buffered by NSC accumulation in the stem, which can attain 50% (dw:dw) in stem tops. The resulting dynamics of growth and production are complex because several dozen phytomers of different phenological ages develop at any given time and interact with a common pool of reserves. [ABSTRACT FROM PUBLISHER]

Coconut (Cocos nucifera L.) is a perennial tropical monocotyledon that produces fruit continuously. The physiological function of the large amounts of sucrose stored in coconut stems is unknown. To test the hypothesis that reserve storage and mobilization enable the crop to adjust to variable sink–source relationships at the scale of the whole plant, we investigated the dynamics of dry matter production, yield and yield components, and concentrations of nonstructural carbohydrate reserves in a coconut plantation on Vanuatu Island in the South Pacific. Two treatments were implemented continuously over 29 months (April 2002 to August 2004): 50% leaf pruning (to reduce the source) and 100% fruit and inflorescence pruning (to reduce the sink). The pruning treatments had little effect on carbohydrate reserves because they affected only petioles, not the main reserve pool in the stem. Both pruning treatments greatly reduced dry matter production of the reproductive compartment, but vegetative growth and development were negligibly affected by treatment and season. Leaf pruning increased radiation-use efficiency (RUE) initially, and fruit pruning greatly reduced RUE throughout the experiment. Changes in RUE were negatively correlated with leaflet soluble sugar concentration, indicating feedback inhibition of photosynthesis. We conclude that vegetative development and growth of coconut show little phenotypic plasticity, assimilate demand for growth being largely independent of a fluctuating assimilate supply. The resulting sink–source imbalances were partly compensated for by transitory reserves and, more importantly, by variable RUE in the short term, and by adjustment of fruit load in the long term. Possible physiological mechanisms are discussed, as well as modeling concepts that may be applied to coconut and similar tree crops. [ABSTRACT FROM AUTHOR]