Field and controlled environment measurements show strong seasonal acclimation in photosynthesis and respiration potential in boreal Scots pine

Abstract

Understanding the seasonality of photosynthesis in boreal evergreen trees and its control by the environment requires separation of the instantaneous and slow responses, as well as the dynamics of light reactions, carbon reactions, and respiration. We determined the seasonality of photosynthetic light response and respiration parameters of Scots pine (Pinus sylvestris L.) in the field in southern Finland and in controlled laboratory conditions. CO2 exchange and chlorophyll fluorescence were measured in the field using a continuously operated automated chamber setup and fluorescence monitoring systems. We also carried out monthly measurements of photosynthetic light, CO2 and temperature responses in standard conditions with a portable IRGA and fluorometer instrument. The field and response measurements indicated strong seasonal variability in the state of the photosynthetic machinery with a deep downregulation during winter. Despite the downregulation, the photosynthetic machinery retained a significant capacity during winter, which was not visible in the field measurements. Light-saturated photosynthesis (Psat) and the initial slope of the photosynthetic light response (α) obtained in standard conditions were up to 20% of their respective summertime values. Respiration also showed seasonal acclimation with peak values of respiration in standard temperature in spring and decline in autumn. Spring recovery of all photosynthetic parameters could be predicted with temperature history. On the other hand, the operating quantum yield of photosystem II and the initial slope of photosynthetic light response stayed almost at the summertime level until late autumn while at the same time Psat decreased following the prevailing temperature. Comparison of photosynthetic parameters with the environmental drivers suggests that light and minimum temperature are also decisive factors in the seasonal acclimation of photosynthesis in boreal evergreen trees.

Measurement of Diurnal Variation in Needle PRI and Shoot Photosynthesis in a Boreal Forest

“…The growing season in this area, determined as the period for which mean temperature is above 5 • C, lasts between late April and October [26]. The site is located on mineral soils and dominated by Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst), with forest understory consisting of common vascular plant species [27].…”

Spatial Variation of Leaf Optical Properties in a Boreal Forest Is Influenced by Species and Light Environment

“…We used a rectangular-hyperbolic function (Kolari et al, 2014) to model A as function of PAR, for the purpose of estimating photosynthetic light response curve parameters, which we designated as photosynthetic traits: $\begin{array}{c}leftA(PAR)=\frac{1}{2\theta }(\alpha PAR+A_{max}\\ -\sqrt{{(\alpha PAR+A_{max})}^2-4PAR\theta \alpha A_{max}}-R_d)\end{array}$ Parameters (traits) θ, A max , α, and R d are the curvature parameter, the maximum quantum yield of photosynthesis, the light saturated rate of photosynthesis and the dark respiration rate respectively. We estimated θ, A max , α, and R d by fitting Equation (1) to the measurements of A at the above PAR levels, using the optimize.leastsq method (an Levenberg-Marquardt algorithm; Marquardt, 1963) from the Scipy Python package.…”

Evaluating Biosphere Model Estimates of the Start of the Vegetation Active Season in Boreal Forests by Satellite Observations

“…The photosynthesis module in JSBACH has the same temperature response for parameters describing the potential electron transport rate and maximum carboxylation rate for the whole year, thus indicating that the simulated vegetation is ready to immediately photosynthesize in spring with increasing air temperatures without any recovery period required, providing there is foliage present as in the case of ENF. However, the boreal coniferous forests have a recovery period in spring after the winter dormancy before they reach their full summertime photosynthetic capacity [89,90]. This may explain the differences between observed GPP at Sodankylä and simulated GPP using local weather observations (Figures 4 and 5).…”