Quantifying ecological memory in plant and ecosystem processes

Abstract

The role of time in ecology has a long history of investigation, but ecologists have largely restricted their attention to the influence of concurrent abiotic conditions on rates and magnitudes of important ecological processes. Recently, however, ecologists have improved their understanding of ecological processes by explicitly considering the effects of antecedent conditions. To broadly help in studying the role of time, we evaluate the length, temporal pattern, and strength of memory with respect to the influence of antecedent conditions on current ecological dynamics. We developed the stochastic antecedent modelling (SAM) framework as a flexible analytic approach for evaluating exogenous and endogenous process components of memory in a system of interest. We designed SAM to be useful in revealing novel insights promoting further study, illustrated in four examples with different degrees of complexity and varying time scales: stomatal conductance, soil respiration, ecosystem productivity, and tree growth. Models with antecedent effects explained an additional 18-28% of response variation compared to models without antecedent effects. Moreover, SAM also enabled identification of potential mechanisms that underlie components of memory, thus revealing temporal properties that are not apparent from traditional treatments of ecological time-series data and facilitating new hypothesis generation and additional research.

Water relations and photosynthesis along an elevation gradient for Artemisia tridentata during an historic drought

“…These results are in contrast with previous studies that describe decreases in V cmax in relation to drought for grassland species in central Europe, and also as part of a larger metaanalysis of 22 tree and shrub species (Signarbieux and Feller 2011;Zhou et al 2013). Antecedent water content helps determine photosynthetic responses to more recent precipitation events for many desert shrubs species of the western USA, including A. tridentata (Ogle et al 2015). The hypothesis that certain photosynthetic limitations are determined by antecedent water awaits further testing, such as whether there is a hierarchy of processes that downregulate as antecedent soil water dries over time.…”

“…Elsewhere, warming affects soil moisture and the ability of A. tridentata to conduct photosynthesis at 2070 m in Colorado, USA (Shaw et al 2000). Photosynthesis by A. tridentata is also dependent on antecedent soil water conditions (Ogle et al 2015). Moreover, at times when soil surface layers have dried, A. tridentata can spatially shift the depth of water access to deeper roots to maintain photosynthetic capacity (Leffler and Caldwell 2005).…”

Latitudinal gradients in tree ring stable carbon and oxygen isotopes reveal differential climate influences of the North American Monsoon System

“…This could bias LW isotope values toward those of the colder, drier spring period in years with limited summer moisture. More research will be needed to quantify the relative importance of stored versus recently acquired photoassimilates (i.e., the importance of "the memory effect" [Ogle et al, 2015]). …”

Host plant physiology and mycorrhizal functioning shift across a glacial through future CO2 gradient

“…Previous mycorrhizal-CO 2 studies have focused mainly on the effects of modern versus future conditions (Alberton et al, 2005;Mohan et al, 2014), and little is known about mycorrhizal responses to low [CO 2 ] of the past (Treseder et al, 2003;Procter et al, 2014). Assessing mycorrhizal responses to a broad, temporal [CO 2 ] gradient is critical to establish a baseline for how these symbioses functioned prior to anthropogenic forcing, which will provide insight into potential constraints on mycorrhizal responses to future conditions (Ogle et al, 2015). In addition, rising [CO 2 ] is known to cause nonlinear shifts in plant physiology and growth (Gerhart and Ward, 2010); therefore, nonlinear shifts in mycorrhizal functioning also are likely to occur.…”