Allometric Trajectories and “Stress”: A Quantitative Approach

Abstract

The term “stress” is an important but vague term in plant biology. We show situations in which thinking in terms of “stress” is profitably replaced by quantifying distance from functionally optimal scaling relationships between plant parts. These relationships include, for example, the often-cited one between leaf area and sapwood area, which presumably reflects mutual dependence between sources and sink tissues and which scales positively within individuals and across species. These relationships seem to be so basic to plant functioning that they are favored by selection across nearly all plant lineages. Within a species or population, individuals that are far from the common scaling patterns are thus expected to perform negatively. For instance, “too little” leaf area (e.g., due to herbivory or disease) per unit of active stem mass would be expected to incur to low carbon income per respiratory cost and thus lead to lower growth. We present a framework that allows quantitative study of phenomena traditionally assigned to “stress,” without need for recourse to this term. Our approach contrasts with traditional approaches for studying “stress,” e.g., revealing that small “stressed” plants likely are in fact well suited to local conditions. We thus offer a quantitative perspective to the study of phenomena often referred to under such terms as “stress,” plasticity, adaptation, and acclimation.

Leaf economics and plant hydraulics drive leaf : wood area ratios

“…Inverse scaling of H v with H max may, therefore, also be obtained if K s scaled with H max more than proportionally. Negative scaling of H v with H max may also be obtained if tall trees grow relatively less sapwood than shorter plants (for a given leaf area) to minimise sapwood construction and/or maintenance costs, instead of hydraulic resistance (Anfodillo et al ., ; Fajardo et al ., ). An inverse relationship between H v and K s is expected because of functional balance between water supply and demand (Whitehead & Jarvis, ; see derivation in the Supplementary Information Methods S1) and it has been found empirically before for smaller datasets (Choat et al ., ; Gleason et al ., ).…”

Tree differences in primary and secondary growth drive convergent scaling in leaf area to sapwood area across Europe

“…Below, conduits progressively increase in diameter (Anfodillo et al ., ), thus confining most of the total hydraulic resistance within a short distance from the apices of stem and branches (Petit & Anfodillo, ; Petit et al ., ). In addition, longer xylem path lengths in taller trees and limitations to photosynthesis imply that maintenance costs and biomass production are more expensive on a leaf area basis (Buckley & Roberts, ; Anfodillo et al ., ). In this respect, it has been shown that larger leaf biomass can be sustained along branches under drier conditions when the annual investment in primary and secondary growth is reduced, and more rings contribute to the total sapwood conductance (Petit et al ., ; Sterck & Zweifel, ).…”

Quantifying and modeling water availability in temperate forests: a review of drought and aridity indices

“…In the case of forests, the adaptation of vegetation properties to water availability is well documented (Grier & Running 1977). Some authors (Anfodillo et al 2016) have argued against the use of the term "stress" to describe long-term conditions that lead to adaptations such as slow growth rates or small leaf area. Indeed, Anfodillo et al (2016) show that these adaptations allow plants to maximize their fitness in the given environment.…”

“…Some authors (Anfodillo et al 2016) have argued against the use of the term "stress" to describe long-term conditions that lead to adaptations such as slow growth rates or small leaf area. Indeed, Anfodillo et al (2016) show that these adaptations allow plants to maximize their fitness in the given environment. In this review, the term stress is used in the narrow sense of physiological drought.…”