Carbohydrate reserves as a competing sink: evidence from tapping rubber trees

Abstract

Carbohydrate reserve storage in trees is usually considered a passive function, essentially buffering temporary discrepancies between carbon availability and demand in the annual cycle. Recently, however, the concept has emerged that storage might be a process that competes with other active sinks for assimilate. We tested the validity of this concept in Hevea brasiliensis Müll. Arg. (rubber) trees, a species in which carbon availability can be manipulated by tapping, which induces latex regeneration, a high carbon-cost activity. The annual dynamics of carbohydrate reserves were followed during three situations of decreasing carbon availability: control (no tapping), tapped and tapped with Ethephon stimulation. In untapped control trees, starch and sucrose were the main carbohydrate compounds. Total nonstructural carbohydrates (TNC), particularly starch, were depleted following bud break and re-foliation, resulting in an acropetal gradient of decreasing starch concentration in the stem wood. During the vegetative season, TNC concentration increased. At the end of the vegetative season, there were almost no differences in TNC concentration along the trunk. In tapped trees, the vertical gradient of starch concentration was locally disturbed by the presence of the tapping cut. However, the main effect of tapping was a dramatic increase in TNC concentration, particularly starch, throughout the trunk and in the root. The difference in TNC concentration between tapped and untapped trees was highest when latex production was highest (October); the difference was noticeable even in areas of the trees that are unlikely to be directly involved in latex regeneration, and it was enhanced by Ethephon stimulation, which is known to increase latex metabolism and flow duration. Thus, contrary to what could be expected if reserves serve as a passive buffer, a decrease in carbohydrate availability resulted in a net increase in carbohydrate reserves at the trunk scale. Such behavior supports the view that trees tend to adjust the amount of carbohydrate reserves stored to the level of metabolic demand, at the possible expense of growth.

Autumnal N storage determines the spring growth, N uptake and N internal cycling of young peach trees

“…The utilisation of all stored N in order to sustain spring growth, evidenced here in trees receiving a broad range of autumn N supplies, was specific to N, since TNC may be sequestrated for several years (Millard and Grelet 2010). Indeed, starch accumulates more as trees are stressed, even if this penalises growth (Silpi et al 2007).…”

Effect of ethephon on the liver in albino rats: A histomorphometric study

“…In India, it is being extensively used to accelerate post-harvest ripening of bananas. [5] Unlike the other four classes of plant hormones, ethylene is a gas at room temperature and diffuses easily through the air from one plant to another. The saying "One bad apple spoils the barrel" has its basis in the effects of ethylene gas.…”

Whole-tree dynamics of non-structural carbohydrate and nitrogen pools across different seasons and in response to girdling in two temperate trees

“…NSC and N concentrations in storage organs typically decrease in springtime after bud flush and increase late in the growing season (Piispanen and Saranpää 2001; Gaucher et al 2005;Spann et al 2008). Correspondingly, the storage organs shift from being a source in the early growing season to becoming a sink in the late growing season (Palacio et al 2007;Silpi et al 2007). In our study, the seasonal variations in NSC and N concentrations in the storage organs were generally consistent with the reported pattern, thus supporting our first hypothesis that all organs showed similar seasonal dynamics despite the large differences in pool size.…”