Patterns and dynamics of canopy–root coupling in tropical tree saplings vary with light intensity but not with root depth

Abstract

Carbon (C) dynamics in canopy and roots influence whole-tree carbon fluxes, but little is known about canopy regulation of tree-root activity. Here, the patterns and dynamics of canopy-root C coupling are assessed in tropical trees.Large aeroponics facility was used to study the root systems of Ceiba pentandra and Khaya anthotheca saplings directly at different light intensities.In Ceiba, root respiration (R r ) co-varied with photosynthesis (A n ) in large saplings (3-to-7m canopy-root axis) at high-light, but showed no consistent pattern at low-light. At mediumlight and in small saplings (c. 1-m axis), R r tended to decrease transiently towards midday. Proximal roots had higher R r and nonstructural carbohydrate concentrations than distal roots, but canopy-root coupling was unaffected by root location. In medium-sized Khaya, no R r pattern was observed, and in both species, R r was unrelated to temperature.The early-afternoon increase in R r suggests that canopy-root coupling is based on mass flow of newly fixed C in the phloem, whereas the early-morning rise in R r with A n indicates an additional coupling signal that travels faster than the phloem sap. In large saplings and potentially also in higher trees, light and possibly additional environmental factors control the diurnal patterns of canopy-root coupling, irrespective of root location.

Patterns of total root and shoot carbon dioxide fluxes and their impact on daily tree carbon budget in large tropical tree saplings

“…Measuring RCF and SCF under high-light conditions should have allowed reaching maximal potential coupling (Oren et al 2020). Surprisingly, and contrary to our second hypothesis, we found that the patterns of RCF were not related to SCF, neither immediately nor with a time-lag on all four measuring days, spanning almost two months.…”

“…This suggests that the daily C dynamics of the root system is coupled to some degree to that of the shoot. Recently we showed that respiration of fine-roots is coupled to leaf C dynamics in tropical tree saplings on a daily time scale, with a maximal coupling under high-light conditions (Oren et al 2020). Our findings were based on measurements of fine-roots only, as direct respiration measurements on excised coarse-roots would mean damaging large portions of the root system, which might affect the root system sink size and potential coupling dynamics.…”

“…(Figure S1 available as Supplementary Data at Tree Physiology Online). Growing conditions in the aeroponics facility were similar in 2015 and 2016, though maximum daily PPFD was slightly higher and maximal daily vapour pressure deficit (VPD) was slightly lower in summer 2015 than in summer 2016 (see Oren et al 2020). Mean daily temperatures of the root and shoot compartments were similar in both years (see Oren et al 2020).…”

Orchard Planting Density and Tree Development Stage Affects Physiological Processes of Apple (Malus domestica Borkh.) Tree

“…According to Li et al [56] almost all of the sorbitol and half of the sucrose is converted to fructose in fruits. In agreement with Oren et al [57] plants with stronger sunlight accumulate more-another reserve material-starch. Greater distances between trees resulted the significant increase of starch, besides significantly more starch was accumulated in July and August (Figure 7C).…”

Filling gaps in our understanding of belowground plant traits across the world: an introduction to a Virtual Issue

“…For example, in tropical saplings Oren et al . (2020) found that root respiration was coupled with canopy photosynthetic patterns in response to changing light conditions, while in turn, Zhou et al . (2021) found that syndromes of root anatomical traits could be used to group plant functional types that differed in leaf physiological responses to changing precipitation regimes.…”