Visualizing land‐use and management complexity within biogeochemical cycles of an agricultural landscape

Crop fields are cultivated across continuities of soil, topography, and local climate that drive biological processes and nutrient cycling at the landscape scale; yet land management and agricultural research are often performed at the field scale, potentially neglecting the context of the surrounding landscape. Adding to this complexity is the overlap of ecosystems and their biogeochemical legacies, as a patchwork of crops fields, natural grasslands, and forests develops across the landscape. Furthermore, as new technologies and policies are introduced, management practices change, including fertilization strategies, which further alter biological productivity and nutrient cycling. All of these environmental, biological, and historical legacies are potentially recorded in the isotopic signal of plant, soil, and sediment organic matter across the landscape. We mapped over 1500 plant, soil, and sediment isotopic values and generated an isotopic landscape (isoscape) over a 40-km² agricultural site in NE Germany. We observed distinct patterns in the isotopic composition of organic matter sampled from the landscape that clearly reflect the landscape complexity. C₃ crop intrinsic water-use efficiency reflected a precipitation gradient, while native forest and grassland plant species did not, suggesting that native plants are more adapted to predominant climatic conditions. δ¹³Csoil patterns reflected both the long-term input of plant organic matter, which was affected by the local climate conditions, and the repeated cultivation of corn. Soil organic matter ¹⁵N isotopic values also revealed spatial differences in fertilization regimes. Forest fragments, in which the nitrogen cycle was relatively open, were more water-use efficient. Sediments from small water bodies received substantial inputs from surrounding field vegetation but were also affected by seasonal drying. These isotopic maps can be used to visualize large spatial heterogeneity and complexity, and they are a powerful means to interpret past and current trends in agricultural landscapes

Genotypic variability enhances the reproducibility of an ecological study

Many scientific disciplines are currently experiencing a “reproducibility crisis” because numerous scientific findings cannot be repeated consistently. A novel but controversial hypothesis postulates that stringent levels of environmental and biotic standardization in experimental studies reduces reproducibility by amplifying impacts of lab-specific environmental factors not accounted for in study designs. A corollary to this hypothesis is that a deliberate introduction of controlled systematic variability (CSV) in experimental designs may lead to increased reproducibility. We tested this hypothesis using a multi-laboratory microcosm study in which the same ecological experiment was repeated in 14 laboratories across Europe. Each laboratory introduced environmental and genotypic CSV within and among replicated microcosms established in either growth chambers (with stringent control of environmental conditions) or glasshouses (with more variable environmental conditions). The introduction of genotypic CSV led to lower among-laboratory variability in growth chambers, indicating increased reproducibility, but had no significant effect in glasshouses where reproducibility was generally lower. Environmental CSV had little effect on reproducibility. Although there are multiple causes for the “reproducibility crisis”, deliberately including genetic variation may be a simple solution for increasing the reproducibility of ecological studies performed in controlled environments

GROUP SELECTION EDGE EFFECTS ON THE VASCULAR PLANT COMMUNITY OF A SIERRA NEVADA OLD-GROWTH FOREST

Volume: 52Start Page: 262End Page: 26

Visualizing land-use and management complexity within biogeochemical cycles of an agricultural landscape

Crop fields are cultivated across continuities of soil, topography, and local climate that drive biological processes and nutrient cycling at the landscape scale; yet land management and agricultural research are often performed at the field scale, potentially neglecting the context of the surrounding landscape. Adding to this complexity is the overlap of ecosystems and their biogeochemical legacies, as a patchwork of crops fields, natural grasslands, and forests develops across the landscape. Furthermore, as new technologies and policies are introduced, management practices change, including fertilization strategies, which further alter biological productivity and nutrient cycling. All of these environmental, biological, and historical legacies are potentially recorded in the isotopic signal of plant, soil, and sediment organic matter across the landscape. We mapped over 1500 plant, soil, and sediment isotopic values and generated an isotopic landscape (isoscape) over a 40-km2 agricultural site in NE Germany. We observed distinct patterns in the isotopic composition of organic matter sampled from the landscape that clearly reflect the landscape complexity. C3 crop intrinsic water-use efficiency reflected a precipitation gradient, while native forest and grassland plant species did not, suggesting that native plants are more adapted to predominant climatic conditions. δ13Csoil patterns reflected both the long-term input of plant organic matter, which was affected by the local climate conditions, and the repeated cultivation of corn. Soil organic matter 15N isotopic values also revealed spatial differences in fertilization regimes. Forest fragments, in which the nitrogen cycle was relatively open, were more water-use efficient. Sediments from small water bodies received substantial inputs from surrounding field vegetation but were also affected by seasonal drying. These isotopic maps can be used to visualize large spatial heterogeneity and complexity, and they are a powerful means to interpret past and current trends in agricultural landscapes

Divergent roles of iron and aluminum in sediment organic matter association at the terrestrial–aquatic interface

Organic matter (OM) can be protected from abiotic and biotic breakdown via its association with iron (Fe) and aluminum (Al) in both terrestrial and aquatic ecosystems. We hypothesized that the natural variation in sediment redox and pH regime govern how the two metals interact with OM in near-surface mineral sediments of 40 kettle holes of varying hydroperiod in NE Germany. Sediments were separated by density, and Fe and Al present in the high-density fractions (> 1.6 g cm−3, HF) were quantified by pyrophosphate (PP) and dithionite-citrate (DC) extractions. The OM in HF was analyzed for δ13C and δ15N values before and after the extractions to assess the possible origin and its degradation state. While only < 20% of OM in HF were dissolved by PP and DC extractions, OC in HF showed significant positive correlation with the extractable Fe and Al. DC-extractable Fe was predominantly present as low-crystallinity phase, and mostly overlapped with PP-extractable and, for the selected samples examined, with acid-oxalate and ascorbic acid extractable Fe pool. Across the HF samples, high levels of AlPP and AlDC contents corresponded to sediments having lower pH and OM with lower δ15N and higher C:N ratio. In contrast, the sediments with higher FeDC contents corresponded to shorter hydroperiod and showed OM with higher δ15N and lower C:N ratio. These results support the idea that reactive monomeric Al preferentially binds with organic ligands derived from less-decomposed OM under more acidic and anoxic conditions, whereas low-crystallinity Fe formed under more oxic conditions tend to bind with more microbially-processed OM

Drought response of mesophyll conductance in forest understory species - impacts on water-use efficiency and interactions with leaf water movement

Regulation of stomatal (gs) and mesophyll conductance (gm) is an efficient means for optimizing the relationship between water loss and carbon uptake in plants. We assessed water-use efficiency (WUE)-based drought adaptation strategies with respect to mesophyll conductance of different functional plant groups of the forest understory. Moreover we aimed at assessing the mechanisms of and interactions between water and CO2 conductance in the mesophyll. The facts that an increase in WUE was observed only in the two species that increased gm in response to moderate drought, and that over all five species examined, changes in mesophyll conductance were significantly correlated with the drought-induced change in WUE, proves the importance of gm in optimizing resource use under water restriction. There was no clear correlation of mesophyll CO2 conductance and the tortuosity of water movement in the leaf across the five species in the control and drought treatments. This points either to different main pathways for CO2 and water in the mesophyll either to different regulation of a common pathway