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

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.

The three major axes of terrestrial ecosystem function

“…The undisturbed forest, which is likely to be taller, with higher LAI and carbon stocks, would probably have higher maximum photosynthetic rates and net ecosystem production, which are the most important variables loading on the first axis. Although, in time, the variability of climate controls the variability of gross and net CO 2 uptake and productivity 14 , 15 , which are variables related to the maximum productivity axis (PC1), in space (that is, across sites) we find only a marginal control in very cold and radiation-limited sites (Extended Data Fig. 5a for a PC1 map), or for very warm and high atmospheric aridity (high VPD) conditions (Extended Data Fig.…”

Disentangling the Role of Forest Structure and Functional Traits for the Thermal Balance in the Mediterranean-Temperate Ecotone

“…3b), the relatively lower ∆𝑇 could have been caused by a higher evaporative cooling enhanced by water availability (Yi et al, 2020). This points out that the thermal balance of forests is more constrained by the background climatic conditions than by the functional group dominating the ecosystem; the higher dependency of biosphere-atmosphere interactions on background climate over functional groups was recently found across multiple ecosystems (Krich et al, 2021).…”