Changes in timing of seasonal peak photosynthetic activity in northern ecosystems

Abstract

Seasonality in photosynthetic activity is a critical component of seasonal carbon, water, and energy cycles in the Earth system. This characteristic is a consequence of plant's adaptive evolutionary processes to a given set of environmental conditions. Changing climate in northern lands (>30°N) alters the state of climatic constraints on plant growth, and therefore, changes in the seasonality and carbon accumulation are anticipated. However, how photosynthetic seasonality evolved to its current state, and what role climatic constraints and their variability played in this process and ultimately in carbon cycle is still poorly understood due to its complexity. Here, we take the “laws of minimum” as a basis and introduce a new framework where the timing (day of year) of peak photosynthetic activity (DOYPmax) acts as a proxy for plant's adaptive state to climatic constraints on its growth. Our analyses confirm that spatial variations in DOYPmax reflect spatial gradients in climatic constraints as well as seasonal maximum and total productivity. We find a widespread warming‐induced advance in DOYPmax (−1.66 ± 0.30 days/decade, p < 0.001) across northern lands, indicating a spatiotemporal dynamism of climatic constraints to plant growth. We show that the observed changes in DOYPmax are associated with an increase in total gross primary productivity through enhanced carbon assimilation early in the growing season, which leads to an earlier phase shift in land‐atmosphere carbon fluxes and an increase in their amplitude. Such changes are expected to continue in the future based on our analysis of earth system model projections. Our study provides a simplified, yet realistic framework based on first principles for the complex mechanisms by which various climatic factors constrain plant growth in northern ecosystems.

Characteristics, drivers and feedbacks of global greening

“…In addition to longer growing seasons, satellite greenness data also reveal important shifts in the timing and magnitude of the seasonal peak greenness 47,61 . For example, the timing of peak greenness has advanced by 1.2 days decade −1 during 1982-2015 (reF.…”

“…62 ) and 1.7 days decade −1 during 2000-2016 (reF. 61 ) over the extratropical Northern Hemisphere (Fig. 3a), with the boreal region peak greenness advancing twice as fast as the Arctic tundra and temperate ecosystem peaks 61 .…”

“…61 ) over the extratropical Northern Hemisphere (Fig. 3a), with the boreal region peak greenness advancing twice as fast as the Arctic tundra and temperate ecosystem peaks 61 . Since the 1980s, the magnitude of the peak greenness has also increased over the extratropical Northern Hemisphere by ~0.1 standardized NDVI anomaly per year 62 , with a stronger signal in the pan-Arctic region 63,64 .…”

Climatic Drivers of Greening Trends in the Alps

“…Accurate descriptions of greening dynamics and controls are crucial because increased greening is associated with increased carbon uptake by vegetation [3], with important implications on the carbon dioxide balance [4]. A large body of literature shows that Arctic and sub-Arctic environments are greening faster than temperate areas in response to accelerated warming in these regions [5][6][7][8]. However, substantially less work has been devoted to quantifying and understanding patterns of greening in temperate mountain regions, such as the European Alps.…”

Behavioral responses to spring snow conditions contribute to long-term shift in migration phenology in American robins

“…Post and Forchhammer 2008, Clausen and Clausen 2013, Gauthier et al 2013, phenological responses are proving especially strong in Arctic and boreal ecosystems. Plant growing seasons have advanced by nearly two days per decade at the pan-Arctic scale (Park et al 2019), and some animal species have shifted their migratory (e.g. Le Corre et al 2016) or reproductive phenologies (e.g.…”