The role of CAM photosynthesis in the soil-plant-atmosphere continuum

Abstract

Vegetation is a key regulator of the coupled global carbon and water cycles, and must sensitively balance carbon uptake and water loss contingent upon local environmental conditions. This balance is strongly influenced by hydroclimatic variability at various temporal scales, ranging from daily fluctuations in vapor pressure deficit, to weekly changes in soil moisture, to seasonal and longer term climate variations. In turn, vegetation response to environmental forcing is mediated by several factors, including photosynthetic pathway, hydraulic properties, and prior history.

To understand and predict coupled soil-plant-atmosphere interactions it is crucial to account for such factors in modeling approaches. This dissertation explores key aspects of plant adaptations to water stress including photosynthetic and hydraulic traits. In the first part of the thesis, particular emphasis is placed on dryland ecosystems, which are often primarily controlled by moisture availability. In such environments, Crassulacean Acid Metabolism (CAM) and plant water storage are common adaptations which help vegetation to cope with water scarcity and hydroclimatic variability. We evaluate how simplified modeling of these properties may enable predictions of the productivity and water use of dryland agroecosystems. In the second part of the thesis, we introduce a unified modeling framework for the three photosynthetic pathways with full coupling to the soil-plant-atmosphere system based on an understanding of these properties, and introduce an analogy for thinking about these adaptations through a comparison of natural and man-made systems.