Photosynthetic decline and pigment loss during autumn foliar senescence in western larch (Larix occidentalis)

Abstract

We measured needle pigment content and photosynthetic rates of 1-year-old western larch (Larix occidentalis Nutt.) during autumn foliar senescence. Chlorophyll (Chl) and carotenoid (xanthophyll + b-carotene) contents of needles declined 11 and 17%, respectively, before CO(2) assimilation rate began to decline. Chlorophyll a/b ratio, Chl/carotenoid ratio, photochemical efficiency (F(v)/F(m)), and photochemical quenching did not begin to decline until late in senescence. Internal CO(2)/ambient CO(2) did not change during needle yellowing. In seedlings in warmed soil (average 3 degrees C above natural conditions), the decline in needle chlorophyll content was delayed by 10 days and the decline in CO(2) assimilation rate was delayed by 5 days, compared with seedlings in soil at ambient temperature. In seedlings exposed to an extended 16-h photoperiod, the decline in needle chlorophyll content was delayed by 32 days, and the decline in CO(2) assimilation rate was delayed by 21 days, compared with seedlings exposed to natural day lengths. In addition to delaying the onset of needle senescence, the treatments affected the sequence of events during senescence. Differences among treatment groups provide evidence that the onset of pigment loss and photosynthetic decline and the sequence of events during needle senescence are affected by soil temperature and day length.

Evaluating the effects of stomata development and senescence on the seasonal variation in stomatal conductance

“…senescence (e.g., Thomas et al, 1991;Rosenthal and Camm, 1997), and our results agree with these investigations. However, while gs apt increased, chlorophyll concentration was almost constant from spring to summer.…”

European larch phenology in the Alps: can we grasp the role of ecological factors by combining field observations and inverse modelling?

“…In order to obtain the finest achievable definition of morphological shading effects, we used a DEM with 10-m spatial resolution which gives a better description of local heterogeneity. Daily incoming global solar radiation was modelled at a 3-min time step and photoperiod was finally computed as the sum of time steps when the global radiation values were greater than a fixed threshold of 20 Wm −2 , as proposed in other studies (e.g., Rosenthal and Camm 1997;Repo et al 2004;Reichstein et al 2005).…”

Deciduous forest responses to temperature, precipitation, and drought imply complex climate change impacts

“…However, over the past 60 y (25,30,31), researchers studying the physiology of leaf senescence and dormancy have enumerated a range of other environmental conditions that may influence autumn phenology, including frost, moisture conditions, and extreme weather events (e.g., drought-and heat-stress, and flooding). Although the effects of a subset of these factors on plant leaf coloration and leaf drop were reported by a handful of physiological experiments (32,33), few studies have quantified the response of fall phenology to a full suite of potential explanatory factors. Ongoing climate changes are likely to introduce higher frequency and intensity of climatic stress factors (34), so it is important to include these in developing more predictive, mechanistic models of fall phenology.…”