Abstract
Abstract. Severe droughts are expected to become more frequent and persistent. However, their effect on autumn leaf senescence, a key process for deciduous trees and ecosystem functioning, is currently unclear. We hypothesized that (I) severe drought advances the onset of autumn leaf senescence in temperate deciduous trees and (II) tree species show different dynamics of autumn leaf senescence under drought. We tested these hypotheses using a manipulative experiment on beech saplings and 3 years of monitoring mature beech, birch and oak trees in Belgium. The autumn leaf senescence was derived from the seasonal pattern of the chlorophyll content index and the loss of canopy greenness using generalized additive models and piecewise linear regressions. Drought and associated heat stress and increased atmospheric aridity did not affect the onset of autumn leaf senescence in both saplings and mature trees, even if the saplings showed a high mortality and the mature trees an advanced loss of canopy greenness. We did not observe major differences among species. To synthesize, the timing of autumn leaf senescence appears conservative across years and species and even independent of drought, heat and increased atmospheric aridity. Therefore, to study autumn senescence and avoid confusion among studies, seasonal chlorophyll dynamics and loss of canopy greenness should be considered separately.
Highlights
Autumn leaf senescence is a developmental stage of the leaf cells
The autumn leaf senescence was derived from the seasonal pattern of the chlorophyll content index and the loss of canopy greenness using generalized additive models and piecewise linear regressions
Our results showed that the timing of the onset of autumn leaf senescence in both tree saplings and mature trees was not significantly altered by severe drought, heat stress and increased atmospheric aridity induced by a decline in the soil moisture and relative humidity and an increase in the air temperature and vapor pressure deficit
Summary
Autumn leaf senescence is a developmental stage of the leaf cells. The process of autumn leaf senescence is highly coordinated and characterized by tight control over its timing. Its most manifest feature, the detoxification of chlorophyll, allows the degradation of leaf macromolecules and subsequent nutrient remobilization – the essence of autumn leaf senescence (Hörtensteiner and Feller, 2002; Munné-Bosch and Alegre, 2004; Matile, 2000). Chlorophyll degradation allows for the typical leaf coloration during autumn. Autumn leaf senescence is an important process at the ecosystem scale because it affects multiple ecological processes, such as trophic dynamics, tree growth, or the exchange of matter and energy between the ecosystem and atmosphere (Richardson et al, 2013)
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