Whole-tree distribution and temporal variation of non-structural carbohydrates in broadleaf evergreen trees

Abstract

Non-structural carbohydrates (NSCs) form a fundamental yet poorly quantified carbon pool in trees. Studies of NSC seasonality in forest trees have seldom measured whole-tree NSC stocks and allocation among organs, and are not representative of all tree functional types. Non-structural carbohydrate research has primarily focussed on broadleaf deciduous and coniferous evergreen trees with distinct growing seasons, while broadleaf evergreen trees remain under-studied despite their different growth phenology. We measured whole-tree NSC allocation and temporal variation in Eucalyptus obliqua L'Hér., a broadleaf evergreen tree species typically occurring in mixed-age temperate forests, which has year-round growth and the capacity to resprout after fire. Our overarching objective was to improve the empirical basis for understanding the functional importance of NSC allocation and stock changes at the tree- and organ-level in this tree functional type. Starch was the principal storage carbohydrate and was primarily stored in the stem and roots of young (14-year-old) trees rather than the lignotuber, which did not appear to be a specialized starch storage organ. Whole-tree NSC stocks were depleted during spring and summer due to significant decreases in starch mass in the roots and stem, seemingly to support root and crown growth but potentially exacerbated by water stress in summer. Seasonality of stem NSCs differed between young and mature trees, and was not synchronized with stem basal area increments in mature trees. Our results suggest that the relative magnitude of seasonal NSC stock changes could vary with tree growth stage, and that the main drivers of NSC fluctuations in broadleaf evergreen trees in temperate biomes could be periodic disturbances such as summer drought and fire, rather than growth phenology. These results have implications for understanding post-fire tree recovery via resprouting, and for incorporating NSC pools into carbon models of mixed-age forests.

Unearthing belowground bud banks in fire‐prone ecosystems

“…Overall, these data indicate that lignotubers should only be selected for when they are the key to postdisturbance survival, as in fire-prone ecosystems. Lignotubers store starch, in addition to buds (Table S2); however, most of the starch sustaining resprouting is stored in the root system (Smith et al, 2018).…”

Leaf Physiological Responses to Drought Stress and Community Assembly in an Asian Savanna

“…During more intense and prolonged drought, when the below-ground organs may encounter hydraulic dysfunction [54], seedlings may not be able to resprout, leading to whole-plant mortality. This may be more serious for 1-2-year-old seedlings because their carbohydrate reserves are lower due to lower biomass compared to larger saplings and trees that often also do not show large seasonal variations in carbohydrate reserves [55,56].…”

Whole‐tree nonstructural carbohydrate storage and seasonal dynamics in five temperate species

“…While previous studies have estimated total NSC storage at the whole‐tree level (Gholz & Cropper, ; Barbaroux et al ., ; Hoch et al ., ; Würth et al ., ; Gough et al ., ; Richardson et al ., ; Smith et al ., ), whole‐tree total NSC storage has not been assessed throughout the year with high temporal resolution. Generating estimates of whole‐tree total NSC storage requires a detailed assessment in which NSC concentrations are frequently measured across organs, scaled up to the whole‐organ level, and then summed together.…”

“…Furthermore, our understanding of the seasonal dynamics of whole‐tree total NSC storage is limited (Würth et al ., ; Smith et al ., ). While total NSC concentrations at the organ level have been found to be only weakly seasonal (Hoch et al ., ; Richardson et al ., ; Hoch, ), a detailed within‐year study is needed to assess seasonality at the whole‐tree level.…”