Spring phenology is affected by fall non-structural carbohydrate concentration and winter sugar redistribution in three Mediterranean nut tree species

Abstract

Deciduous trees mostly rely on non-structural carbohydrates (NSC—soluble carbohydrates and starch) stored prior to dormancy to sustain both spring bloom and the initial phase of spring growth prior to the transition of leaves from sink to source. Winter management of NSC, their loss due to respiration, reallocation patterns and remobilization during spring, seems to be key to a timely and synchronous bloom. To assess tree dependence on NSC during dormancy, we tested whether the interruption of local branch NSC accumulation prior to dormancy by defoliation and the interruption of NSC translocation by phloem girdling influence spring phenology in three major deciduous Mediterranean nut crop species: Prunus dulcis (Mill.) D.A Webb, a hybrid between Pistacia integerrima (J. L. Stewart ex Brandis) and P. atlantica Desf. (referred to as P. integerrima), and Juglans regia L. Defoliation treatments had different effects on NSC concentration in different species depending on the time of application. However, despite the significant initial impact (increase or decrease of NSC concentration), with time this impact diminished resulting in overall similar concentrations between control and defoliated branches suggesting the presence of NSC reallocation during dormancy. Phloem girdling in P. dulcis and P. integerrima resulted in reduced export activity and greater NSC concentrations, while in J. regia girdling resulted in lower NSC concentrations, indicating that this species requires a net import of NSC during dormancy. Bud break was distinctly delayed by both defoliation and phloem girdling in all the three species, providing evidence of the significant roles that fall NSC accumulation and winter NSC management play in priming trees for spring growth resumption.

The impact of non-structural carbohydrates (NSC) concentration on yield in Prunus dulcis, Pistacia vera, and Juglans regia

“…Additionally, there is increasing evidence suggesting that conversions between NSC forms, soluble sugars and starches, may potentially serve as a ‘dormancy clock’ 6 . Hence, the timing and synchrony of bloom is strongly impacted by disturbances especially to the NSC accumulation and dispersion that flank dormancy 7 , 8 .…”

“…Surprisingly, despite the importance of NSC activity in providing protection against adverse weather conditions through dormancy and in influencing the timing and synchrony of bloom, little attention has been given to how trees physiologically prepare for this quintessential period of quiescence 6 , 7 , 9 . The amount of reserves needed to maintain dormancy and a healthy growth resumption (bloom/leafing) can be variable and not easily predicted.…”

A warmer growing season triggers earlier following spring phenology

“…Needle growth of Larix gmelinii in spring drew nearly 50% of the carbohydrates fixed in the previous year 81,82 . Phloem girdling showed that deficient carbon storage can significantly delay the timing of spring budbreak and reduce bud size 27 .…”

“…In fact, plants need to assimilate and store sufficient carbohydrates in the preceding growing season to resist to the frost temperatures in winter and support growth reactivation in spring [23][24][25][26] . In temperate regions, nonstructural carbohydrates (NSC; soluble sugar and starch) often reach the maximum levels in autumn before winter dormancy, but become depleted by early summer after spring growth [27][28][29] . Girdling experiments have demonstrated that a later budbreak is often associated with a lower NSC availability 30,31 .…”

Physiological characterization of the wild almond Prunus arabica stem photosynthetic capability

“…In most deciduous trees, like almonds, carbon is fixed by the leaves during the summer and is stored for the winter, mainly as starch in tree stems and roots. By the end of the winter, trees drop their leaves and rely on their residual carbohydrate resources to fuel bud-break, bloom, and the early stages of vegetative growth (Ito et al, 2012;Tixier et al, 2017Tixier et al, , 2020Fernandez et al, 2018;Amico Roxas et al, 2021). This fuel reservoir is the only energy source for the deciduous tree until new leaves emerge and become fully functional.…”