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[1] To test whether plant species influence greenhouse gas production in diverse ecosystems, we measured wet season soil CO 2 and N 2 O fluxes close to ∼300 large (>35 cm in diameter at breast height (DBH)) trees of 15 species at three clay-rich forest sites in central Amazonia. We found that soil CO 2 fluxes were 38% higher near large trees than at control sites >10 m away from any tree (P < 0.0001). After adjusting for large tree presence, a multiple linear regression of soil temperature, bulk density, and liana DBH explained 19% of remaining CO 2 flux variability. Soil N 2 O fluxes adjacent to Caryocar villosum, Lecythis lurida, Schefflera morototoni, and Manilkara huberi were 84%−196% greater than Erisma uncinatum and Vochysia maxima, both Vochysiaceae. Tree species identity was the most important explanatory factor for N 2 O fluxes, accounting for more than twice the N 2 O flux variability as all other factors combined. Two observations suggest a mechanism for this finding: (1) sugar addition increased N 2 O fluxes near C. villosum twice as much (P < 0.05) as near Vochysiaceae and (2) species mean N 2 O fluxes were strongly negatively correlated with tree growth rate (P = 0.002). These observations imply that through enhanced belowground carbon allocation liana and tree species can stimulate soil CO 2 and N 2 O fluxes (by enhancing denitrification when carbon limits microbial metabolism). Alternatively, low N 2 O fluxes potentially result from strong competition of tree species with microbes for nutrients. Species-specific patterns in CO 2 and N 2 O fluxes demonstrate that plant species can influence soil biogeochemical processes in a diverse tropical forest.

El Niñ o-La Niñ a cycles strongly influence dry and wet seasons in the tropics and consequently nitrous oxide (N 2 O) emissions from tropical rainforest soils. We monitored whole-system and soil chamber N 2 O fluxes during 5-month-long droughts in the Biosphere 2 tropical forest to determine how rainfall changes N 2 O production. A consistent pattern of N 2 O flux changes during drought and subsequent wetting emerged from our experiments. Soil surface drying during the first days of drought, presumably increased gas transport out of the soil, which increased N 2 O fluxes. Subsequent drying caused an exponential decrease in whole-system (4.0 AE 0.1% day À1 ) and soil chamber N 2 O flux (8.9 AE 0.8% day À1 ; south chamber; and 13.7 AE 1.1% day À1 ; north chamber), which was highly correlated with soil moisture content. Soil air N 2 O concentration ([N 2 O]) and flux measurements revealed that surface N 2 O production persisted during drought. The first rainfall after drought triggered a N 2 O pulse, which amounted to 25% of drought-associated reduction in N 2 O flux and 1.3 AE 0.4% of annual N 2 O emissions. Physical displacement of soil air by water and soil chemistry changes during drought could not account for the observed N 2 O pulse. We contend that osmotic stress on the microbial biomass must have supplied the N source for pulse N 2 O, which was produced at the litter-soil interface. After the pulse, N 2 O fluxes were consistently 90% of predrought values. Nitrate change rate, nutrient, [N 2 O], and flux analyses suggested that nitrifiers dominated N 2 O production during the pulse and denitrifiers during wet conditions. N 2 O flux measurements in Biosphere 2, especially during the N 2 O pulse, demonstrate that large-scale integration methods, such as flux towers, are essential for improving ecosystem N 2 O flux estimates.

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Understanding the process interactions and feedbacks among water, porous geological media, microbes, and vascular plants is crucial for improving predictions of the response of Earth's critical zone to future climatic conditions. However, the integrated coevolution of landscapes under change is notoriously difficult to investigate. Laboratory studies are limited in spatial and temporal scale, while field studies lack observational density and control. To bridge the gap between controlled laboratory and uncontrollable field studies, the University of Arizona built a macrocosm experiment of unprecedented scale: the Landscape Evolution Observatory (LEO). LEO comprises three replicated, heavily instrumented, hillslope-scale model landscapes within the environmentally controlled Biosphere 2 facility. The model landscapes were designed to initially be simple and purely abiotic, enabling scientists to observe each step in the landscapes' evolution as they undergo physical, chemical, and biological changes over many years. This chapter describes the model systems and associated research facilities and illustrates how LEO allows for tracking of multiscale matter and energy fluxes at a level of detail impossible in field experiments. Initial sensor, sampler, and soil coring data are already providing insights into the tight linkages between water flow, weathering, and microbial community development. These interacting processes are anticipated to drive the model systems to increasingly complex states and will be impacted by the introduction of vascular plants and changes in climatic regimes over the years to come. By intensively monitoring the evolutionary trajectory, integrating data with mathematical models, and fostering community-wide collaborations, we envision that emergent landscape structures and functions can be linked, and significant progress can be made toward predicting the coupled hydro-biogeochemical and ecological responses to global change. Hydrology of Artificial and Controlled Experiments 26Controlled Experiments of Hillslope Coevolution at the Biosphere 2 Landscape Evolution… http://dx.doi.org/10.5772/intechopen.72325 27 communities that inhabit them, and their water, biogeochemical, and energy cycles, (ii) determining whether simple or complex biological communities, weathering patterns, and flow networks arise as a consequence of differing climate regimes, (iii) understanding how point-to plot-scale processes impact integrated fluxes of mass and energy at the whole-landscape level, (iv) assessing whether knowledge of how and why multiscale heterogeneity in landscape structure forms can enable improved prediction of landscape function under change, and whether existing or new predictive tools are required, and (v) determining whether our present knowledge and observational capacity allow closing the balances of mass and energy at the landscape scale.The controlled experimentation and dense observations at LEO are combined with mathematical modeling to effectively advance our understanding of landscape ...

&lt;p&gt;Tropical rain forests are greatly dependent on water supply and are highly efficient in water cycling. Soil infiltration rates as well as tree transpiration rates are high in these often seasonally dry ecosystems. Both deforestation and climate change have been shown to cause drought stress in tropical forests, the former through the increase of runoff and reduction in evapotranspiration, the latter mainly through the reduction in precipitation and transpiration.&lt;/p&gt;&lt;p&gt;Although great efforts have been made to determine the ecosystem and species responses to variable water supply, many processes determining how tree species in tropical ecosystems impact and are impacted by the water cycle (water uptake and redistribution, and stem storage) remain poorly understood. Water movement through trees, as measured by a D&lt;sub&gt;2&lt;/sub&gt;O pulse label in the rainwater, was found to be high variable and species dependent in a previous experiment in the Biosphere 2 tropical rainforest (Evaristo et al. 2019). We hypothesized that differential rooting depth and/or stem water storage could be the main causes for the difference in water label transport through the trees.&lt;/p&gt;&lt;p&gt;Our study is part of a large-scale experiment in the Biosphere 2 tropical forest that uses isotope labeling (&lt;sup&gt;13&lt;/sup&gt;C and D) to trace C- and water-cycle processes underpinning ecosystem responses to drought from a molecular to an ecosystem-scale level. Here, we focus on the water cycling of this ecosystem and how it is impacted by controlled drought and rewetting conditions. Detailed continuous measurements of both the water pools (soil and stem) and movement (stems, atmospheric fluxes) will be used to determine individual tree (including different species) and whole ecosystem responses to drought. These data will be presented in light of their implications for tropical forest water movement and drought vulnerability.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Reference&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Evaristo J, Kim M, van Haren J, Pangle LA, Harman CJ, Troch PA, McDonnell JJ, (2019) Characterizing the fluxes and age distribution of soil water, plant water and deep percolation in a model tropical ecosystem. Water Resources Research, 55(4), 3307-3327.&lt;/p&gt;