No abstract

72Zero-order drainage basins, and their constituent hillslopes, are the fundamental geomorphic unit 73 comprising much of Earth's uplands. The convergent topography of these landscapes generates 74 spatially variable substrate and moisture content, facilitating biological diversity and influencing 75 how the landscape filters precipitation and sequesters atmospheric carbon dioxide. In light of 76 these significant ecosystem services, refining our understanding of how these functions are 77 affected by landscape evolution, weather variability, and long-term climate change is imperative. 78 In this paper we introduce the Landscape Evolution Observatory (LEO): a large-scale 79 controllable infrastructure consisting of three replicated artificial landscapes (each 330 m 2 80 surface area) within the climate-controlled Biosphere 2 facility in Arizona, USA. At LEO, 81 experimental manipulation of rainfall, air temperature, relative humidity, and wind speed are 82 possible at unprecedented scale. The Landscape Evolution Observatory was designed as a 83 community resource to advance understanding of how topography, physical and chemical 84 properties of soil, and biological communities coevolve, and how this coevolution affects water, 85 carbon, and energy cycles at multiple spatial scales. With well-defined boundary conditions and 86 an extensive network of sensors and samplers, LEO enables an iterative scientific approach that 87 includes numerical model development and virtual experimentation, physical experimentation, 88 data analysis, and model refinement. We plan to engage the broader scientific community 89 through public dissemination of data from LEO, collaborative experimental design, and 90 community-based model development. 91 coevolution 93 94 95 1. Introduction 96Hillslopes and their adjacent hollows (i.e., zero-order drainage basins, or ZOBs) 97 constitute a large fraction of upland areas over Earth's surface and provide critical ecosystem 98 services. Within ZOBs there is exchange of water, carbon dioxide, and energy with the 99 atmosphere and transport of soil, water, and solutes into fluvial drainage networks-processes 100 that link ZOBs with the climate system and downstream water quantity and quality. The time-101 varying rates of these exchange and transport processes are integrated responses to many 102 physical and biological phenomena that occur from below the base of the soil profile to the 103 vertical extent of the atmospheric boundary layer (e.g., see discussion by Chorover et al., 2011). 104 Zero-order basins evolve as climate varies, soils form and erode, and biological 105 communities establish, compete, and change in response to environmental stimuli. Across 106 spatial and topographic gradients, these interacting processes may result in consistently 107 observable correlations between temperature and precipitation dynamics, soil depth and hillslope 108 length, and plant biomass accumulation (e.g., Rasmussen et al., 2011; Pelletier et al., 2013). 109 Coupled soil-production and ...

No abstract

Plant respiration is an important physiological process in the global carbon cycle serving as a major carbon flux from the biosphere to the atmosphere. Respiration is sensitive to temperature providing a link between environmental variability, climate change and the global carbon cycle. We measured leaf respiration in Populus deltoides after manipulating the air temperature surrounding part of a single leaf, and compared this to the temperature response of the same leaves after manipulating the temperature of the stand. The short‐term temperature response of respiration (Q10– change in the respiration rate with a 10 °C increase in leaf temperature) was 1.7 when the leaf temperature was manipulated, but 2.1 when the stand‐level temperature was changed. As a result, total night‐time carbon release during the five‐day experiment was 21% lower when using the Q10 estimates from the tradition leaf manipulation compared to the stand‐level manipulation. We conclude that the temperature response of leaf respiration is related to whole plant carbon and energy demands, and that appropriate experimental procedures are required in examining respiratory CO2 release under variable temperature conditions.