Functional convergence of biosphere–atmosphere interactions in response to meteorological conditions

Christopher Krich,Guido Kraemer,Tarek S El-Madany,Markus Reichstein,Miguel D Mahecha,Diego G Miralles,Mirco Migliavacca,Jakob Runge

doi:10.5194/bg-18-2379-2021

Abstract

Abstract. Understanding the dependencies of the terrestrial carbon and water cycle with meteorological conditions is a prerequisite to anticipate their behaviour under climate change conditions. However, terrestrial ecosystems and the atmosphere interact via a multitude of variables across temporal and spatial scales. Additionally these interactions might differ among vegetation types or climatic regions. Today, novel algorithms aim to disentangle the causal structure behind such interactions from empirical data. The estimated causal structures can be interpreted as networks, where nodes represent relevant meteorological variables or land-surface fluxes and the links represent the dependencies among them (possibly including time lags and link strength). Here we derived causal networks for different seasons at 119 eddy covariance flux tower observations in the FLUXNET network. We show that the networks of biosphere–atmosphere interactions are strongly shaped by meteorological conditions. For example, we find that temperate and high-latitude ecosystems during peak productivity exhibit biosphere–atmosphere interaction networks very similar to tropical forests. In times of anomalous conditions like droughts though, both ecosystems behave more like typical Mediterranean ecosystems during their dry season. Our results demonstrate that ecosystems from different climate zones or vegetation types have similar biosphere–atmosphere interactions if their meteorological conditions are similar. We anticipate our analysis to foster the use of network approaches, as they allow for a more comprehensive understanding of the state of ecosystem functioning. Long-term or even irreversible changes in network structure are rare and thus can be indicators of fundamental functional ecosystem shifts.

Highlights

Terrestrial ecosystems and the atmosphere constantly exchange energy, matter, and momentum (Bonan, 2015). These interactions result in biosphere–atmosphere fluxes that are shaped by a variety of climatic conditions and states of the terrestrial biosphere (McPherson, 2007)
One reason for our incomplete understanding is that the causal dependencies underlying biosphere–atmosphere interactions might vary among ecosystems depending on vegeta
We investigate multivariate time series from FLUXNET tower data to understand how networks of biosphere–atmosphere interactions vary across vegetation types and climate zones

Summary

Introduction

Terrestrial ecosystems and the atmosphere constantly exchange energy, matter, and momentum (Bonan, 2015). These interactions result in biosphere–atmosphere fluxes (in particular carbon, water, and energy fluxes) that are shaped by a variety of climatic conditions and states of the terrestrial biosphere (McPherson, 2007). Understanding how biosphere– atmosphere fluxes interact and how they causally depend on the short-term meteorological and long-term climate conditions is crucial for building predictive terrestrial-biosphere models (Detto et al, 2012; Green et al, 2017). The exact causal structure of dependencies between surface and atmosphere variables is still subject to unknowns (Baldocchi et al, 2016; Miralles et al, 2019). One reason for our incomplete understanding is that the causal dependencies underlying biosphere–atmosphere interactions might vary among ecosystems depending on vegeta-

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