Microclimatic conditions and water content fluctuations experienced by epiphytic bryophytes in an Amazonian rain forest

In the Amazonian rain forest, major parts of trees and shrubs are covered by epiphytic cryptogams of great taxonomic variety, but their relevance in biosphere–atmosphere exchange, climate processes, and nutrient cycling is largely unknown. As cryptogams are poikilohydric organisms, they are physiologically active only under moist conditions. Thus, information on their water content (WC) as well as temperature and light conditions experienced by them are essential to analyze their impact on local, regional, and even global biogeochemical processes. In this study, we present data on the microclimatic conditions, including water content, temperature, and light conditions experienced by epiphytic bryophytes along a vertical gradient, and combine these with above-canopy climate data collected at the Amazon Tall Tower Observatory (ATTO) in the Amazonian rain forest between October 2014 and December 2016. While the monthly average of above-canopy light intensities revealed only minor fluctuations over the course of the year, the light intensities experienced by the bryophytes varied depending on the location within the canopy, probably caused by individual shading by vegetation. In the understory (1.5 m), monthly average light intensities were similar throughout the year, and individual values were extremely low, remaining below 3 µmol m−2 s−1 photosynthetic photon flux density more than 84 % of the time. Temperatures showed only minor variations throughout the year, with higher values and larger height-dependent differences during the dry season. The indirectly assessed water content of bryophytes varied depending on precipitation, air humidity, dew condensation, and bryophyte type. Whereas bryophytes in the canopy were affected by diel fluctuations of the relative humidity and condensation, those close to the forest floor mainly responded to rainfall patterns. In general, bryophytes growing close to the forest floor were limited by light availability, while those growing in the canopy had to withstand larger variations in microclimatic conditions, especially during the dry season. For further research in this field, these data may be combined with CO2 gas exchange measurements to investigate the role of bryophytes in various biosphere–atmosphere exchange processes, and could be a tool to understand the functioning of the epiphytic community in greater detail.

Tropical forest CH4: from flux chambers to micrometeorological tower measurements

<p>Methane (CH<sub>4</sub>) is the second most important long-lived anthropogenic atmospheric greenhouse gas. Despite its importance, natural sources of methane, such as tropical wetlands, are still not well understood and a large source of uncertainty to the global CH<sub>4</sub> budget. The Amazonian rain forest is estimated to hold 90-120 Pg of carbon, which is approximately 14-27% of the carbon stored in vegetation worldwide. The region is characterized by high precipitation rates and large wetlands, and it has been estimated that the Amazon basin emits 7% of the annual total CH<sub>4</sub> emissions. Due to its remote location, micro-meteorological measurements are rare and absent for other gases than CO<sub>2</sub>.</p><p>The 50 m high K34 tower (field site ZF2) is located in a pristine tropical forest region 60 km northwest of Manaus (Brazil), and is located next to a waterlogged valley, a possible location for anaerobic CH<sub>4</sub> production. In October 2018, in addition to the existing EC CO<sub>2</sub> system, a Relaxed Eddy Accumulation (REA) system was set up at this tower, connected to an in-situ FTIR-analyzer. This set up continually measures fluxes and concentration profiles of CO<sub>2</sub>, CO, CH<sub>4</sub>, N<sub>2</sub>O and δ<sup>13</sup>CO<sub>2</sub>. In addition, CH<sub>4</sub>, CO<sub>2</sub>, and N<sub>2</sub>O uptake and emission processes were studied by flux chamber measurements in the footprint of the REA tower, focusing on different possible sources (soil, stream, trees and termites). In this presentation, an overview of the measured CH<sub>4</sub> and N<sub>2</sub>O forest concentrations and fluxes will be shown.</p>

Habitat filtering of six coexisting Heliconia species in a lowland tropical rain forest in Amazonian Ecuador

Herbaceous plants are often under-studied in tropical forests, despite their high density and diversity, and little is known about the factors that influence their distribution at microscales. In a 25-ha plot in lowland Amazonian rain forest in Yasuní National Park, Ecuador, we censused six species of Heliconia (Heliconiaceae) in a stratified random manner across three topographic habitat types. We observed distribution patterns consistent with habitat filtering. Overall, more individuals occurred in the valley (N = 979) and slope (N = 847) compared with the ridge (N = 571) habitat. At the species level, Heliconia stricta (N = 1135), H. spathocircinata (N = 309) and H. ortotricha (N = 36) all had higher abundance in the valley and slope than ridge. Further, H. vellerigera (N = 20) was completely absent from the ridge. Conversely, H. velutina (N = 903) was most common in the drier ridge habitat. The two most common species (H. stricta and H. velutina) had a reciprocal or negative co-occurrence pattern and occurred preferentially in valley versus ridge habitats. These results suggest that taxa within this family have different adaptations to the wetter valley versus the drier ridge and that habitat partitioning contributes to coexistence.

Microclimatic and ecophysiological conditions experienced by epiphytic bryophytes in an Amazonian rain forest

In the Amazonian rain forest, major parts of trees and shrubs are covered by epiphytic cryptogams of great taxonomic variety, but their relevance in biosphere-atmosphere exchange, climate processes, and nutrient cycling are largely unknown. As cryptogams are poikilohydric organisms, they are physiologically active only under moist conditions. Thus, information on their water content, as well as temperature and light conditions experienced by them are essential to analyzing their impact on local, regional, and even global biogeochemical processes. In this study, we present data on the microclimatic and ecophysiological conditions of epiphytic bryo-phytes along a vertical gradient and combine these with mesoclimate data collected at the Amazon Tall Tower Observatory (ATTO) in the Amazonian rain forest between October 2014 and December 2016. While the monthly average mesoclimatic ambient light intensities above the canopy revealed only minor variations, the light intensities incident on the bryophytes showed different patterns at different heights, probably depending on individual shading by vegetation. At 1.5 m height, monthly average light intensities were similar throughout the year and individual values were extremely low, exceeding 5 µmol m−2 s−1 pho-tosynthetic photon flux density only during 8 % of the time. Temperatures showed only minor variations throughout the year with higher values and larger height-dependent differences during the dry season. Water contents of bryophytes varied depending on precipitation and air humidity. Whereas bryophytes at higher levels were affected by frequent wetting and drying events, those close to the forest floor remained wet over longer time spans during the wet seasons. Based on estimates of the potential duration of net pho-tosynthesis and dark respiration, our data suggest that water contents are decisive for overall physiological activity, and light intensities determine whether net photosynthesis or dark respiration occurs, whereas temperature variations are only of minor relevance in this environment. In general, bryophytes growing close to the forest floor are limited by light availability, while those growing in the canopy must withstand larger variations in microclimatic conditions, especially in the dry season. Measurements of CO2 gas ex-change are essential to elucidate their physiological activity patterns in greater detail.

Quantification of four different post-dispersal seed deposition patterns after dung beetle activity

Primary seed dispersal of many rain-forest seeds occurs through defecation by mammals. Dung beetles are attracted to the defecations and through their dung-processing behaviour these insects change the initial pattern of seed deposition. Final seed deposition patterns, i.e. where and how seeds are deposited after dung beetle activity has taken place, may strongly depend on seed size. In this study we addressed the following question: Do different sizes of seeds have different deposition patterns following dung beetle processing? We conducted a field experiment in lowland Amazonian rain forest in Brazil using 200-g dung-piles containing seed mimics of three sizes: 3.5, 8.6 and 15.5 mm long. Seed deposition condition after dung beetle activity was dependent on seed size. Small seeds were more often buried in beetle tunnels, while medium and large seeds more often remained on the soil surface, either clean or still covered by dung. A low proportion of seeds of all sizes remained on the soil surface covered by loose soil excavated by dung beetles. We speculate that the latter deposition pattern, though not very frequent, might be highly favourable for both seed survival and seedling establishment.