Feedback Processes In A Subsurface Water Source Soil Plant Atmosphere Continuum

Many studies have elucidated the importance of water stress on plant growth, yield, quality and susceptibility to disease. Via the vascular network of xylem, a water conductive tissue, plant water stress responds dynamically to variations in evaporative demand defined by micrometeorological conditions over minutes to hours, and soil water availability over hours to months. Stem water potential is believed to be an integrator of water stress across the soil-plantatmosphere-continuum (SPAC), and is difficult to measure. Despite its destructive nature, 50 years after its invention, the manually operated Schölander pressure chamber (SPC) is still the most widely accepted tool for stem water potential measurements. Limitations in available techniques have hindered the study of dynamic water stress in plants. In this dissertation, we introduce a micro-tensiometer (μTM) as a new technique, for probing the dynamic water stress of plants in an accurate and continuous manner. We examine the reliability of μTM against SPC, on apple (2 months), grapevine (12 months), and almond (4 months), to represent woody species in wet, semi-arid, and arid environments respectively. We observe: 1) nighttime disequilibrium in stem water potential that is challenging to acquire with the labor-intensive SPC; 2) rapid response of stem water potential to evaporative demand in wet environment; and 3) slow dynamics and persistent disequilibrium of the water-stressed almond in dry environment. With the advantage of continuous measurements and inspired by van den Honert, we use circuit models to interpret the observed dynamics. In a wet environment, a simple circuit with a single hydraulic resistance and a single hydraulic capacitance, is sufficient for elucidating the rapid response of plants to the high frequent variations in environmental demand. In a dry environment,an additional soil compartment defined by the soil retention properties, is used to address the long transient of soil dehydration. We now have models as new tools to resolve the complex dynamics of water stress. We also measure the dynamic water stress in maize, the first examination on herbaceous crops with this tool. The measured stress is less coupled to the rapid variations in evaporative demand, but more to the soil water potential around the roots. In fact, we extract an empirical water retention curve for the soil that coincides with the theoretical prediction. The μTM, therefore, opens up an opportunity to monitor the root-zone soil stress, a challenging property to access. Finally, we explore the response of plants to fine control of irrigation events, and discover that the transient of root response to irrigation events is shorter when less stressed (nighttime) and longer when more stressed (daytime). This phenomenon suggests more effective irrigation events when plants are less stressed with reduced water loss. The micro-tensiometer and the developed circuit models, together, provide opportunities to unveil the full dynamics of plant water stress, address the transient factor in plant physiological responses to both short and long-term dehydration processes, and guide more efficient management of agricultural water use.

Soil Science - Emerging Technologies, Global Perspectives and Applications describes recent research that illustrates the universal importance of understanding soil and soil’s relationship to environmental stewardship and food security. Research supporting emerging technologies provides abilities to discern key soil attributes that influence soil behavior and development, understand soil biology to create sustainable land management, and sequester carbon to partially negate climate change. Soil science is an interdisciplinary field of inquiry that must consider resource allocation and social needs to foster a culture that protects and secures not only soil health but also water and air quality. Chapters in this book reflect the diversity of modern thinking within the discipline of soil science, but collectively illustrate that global sustainability of food, the environment, and biological diversity are critical to future generations.

An integrated textbook on the atmosphere-vegetation-soil continuum for students, researchers and professionals in meteorology, hydrology, soil science and environmental science.

Summary: "The parameters used to describe the flow of water, and energy to a lesser extent, through the soil-plant-atmosphere continuum are reviewed and the techniques used for estimating their values contrasted. The measurements which are necessary to satisfy various research objectives are discussed. The appropriate methods of measurement are suggested for given circumstances and the key references for each method presented." -- p. iv.

This book addresses the connections between the hydrologic cycle and plant ecosystems. It will appeal to advanced students and researchers from a large range of disciplines, including environmental science, hydrology, ecology, earth science, civil and environmental engineering, agriculture, and atmospheric science.

Ecohydrology emerges as a new field of research aiming at furthering our understanding of the earth system through the study of the interactions between the water cycle and vegetation. By combining the analysis of biotic and abiotic components of terrestrial ecosystems, this volume provides a synthesis of material on arid and semiarid landscapes, which is currently spread in a number of books and journal articles. The focus on water-limited ecosystems is motivated by their high sensitivity to daily, seasonal, and decadal perturbations in water availability, and by the ecologic, climatic, and economic significance of most of the drylands around the world. Conceived as a tool for scientists working in the area of the earth and environmental sciences, this book presents the basic principles of eco-hydrology as well as a broad spectrum of topics and advances in this research field. The chapters collected in this book have been contributed by authors with different expertise, who work in several arid areas around the World. They describe the various interactions among the biological and physical dynamics in dryland ecosystems, starting from basic processes in the soil-vegetation-climate system, to landscape-scale hydrologic and geomorphic processes, ecohydrologic controls on soil nutrient dynamics, and multiscale analyses of disturbances and patterns.

When considering biosphere–atmosphere exchange of trace gases and volatile aerosols, significant advances have been made both from an experimental and modelling point of view and on several scales. This was particularly stimulated by the availability of new datasets generated from improvements in analytical methods and flux measurement techniques. Recent research advances allow us, not only to identify major mechanisms and factors affecting the exchanges between the biosphere and the atmosphere, but also to recognize several gaps in the methodologies used in accounting for emissions and deposition in landscape and global scale models. This work aims at (i) reviewing exchange processes and modelling schemes, parameterisations and datasets, (ii) presenting a common conceptual framework to model soil-vegetation-atmosphere exchange of reactive trace gases and aerosols accounting for in-canopy transfer chemical interactions and (iii) discussing the key elements of the agreed framework.