Priming effects in soils across Europe.

Land use is a key factor driving changes in soil carbon (C) cycle and contents worldwide. The priming effect (PE)-CO2 emissions from changed soil organic matter decomposition in response to fresh C inputs-is one of the most unpredictable phenomena associated with C cycling and related nutrient mobilization. Yet, we know very little about the influence of land use on soil PE across contrasting environments. Here, we conducted a continental-scale study to (i) determine the PE induced by 13 C-glucose additions to 126 cropland and seminatural (forests and grasslands) soils from 22 European countries; (ii) compare PE magnitude in soils under various crop types (i.e., cereals, nonpermanent industrial crops, and orchards); and (iii) model the environmental factors influencing PE. On average, PEs were negative in seminatural (with values ranging between -60 and 26 µg C g-1 soil after 35 days of incubation; median = -11) and cropland (from -55 to 27 µC g-1 soil; median = -4.3) soils, meaning that microbial communities preferentially switched from soil organic C decomposition to glucose mineralization. PE was significantly less negative in croplands compared with seminatural ecosystems and not influenced by the crop type. PE was driven by soil basal respiration (reflecting microbial activity), microbial biomass C, and soil organic C, which were all higher in seminatural ecosystems compared with croplands. This cross European experimental and modeling study elucidated that PE intensity is dependent on land use and allowed to clarify the factors regulating this important C cycling process.

Challenges of and opportunities for protecting European soil biodiversity.

Soil biodiversity and related ecosystem functions are neglected in most biodiversity assessments and nature conservation actions. We examined how society, and particularly policy makers, have addressed these factors worldwide with a focus on Europe and explored the role of soils in nature conservation in Germany as an example. We reviewed past and current global and European policies, compared soil ecosystem functioning in- and outside protected areas, and examined the role of soils in nature conservation management via text analyses. Protection and conservation of soil biodiversity and soil ecosystem functioning have been insufficient. Soil-related policies are unenforceable and lack soil biodiversity conservation goals, focusing instead on other environmental objectives. We found no evidence of positive effects of current nature conservation measures in multiple soil ecosystem functions in Europe. In German conservation management, soils are considered only from a limited perspective (e.g., as physicochemical part of the environment and as habitat for aboveground organisms). By exploring policy, evidence, and management as it relates to soil ecosystems, we suggest an integrative perspective to move nature conservation toward targeting soil ecosystems directly (e.g., by setting baselines, monitoring soil threats, and establishing a soil indicator system).

La biodiversidad del suelo y las funciones ambientales relacionadas se dejan de lado en la mayoría de las evaluaciones de la biodiversidad y de las acciones de conservación de la naturaleza. Analizamos cómo la sociedad, y particularmente los formuladores de políticas, han abordado estos factores a nivel mundial con un enfoque en Europa y exploramos como ejemplo el papel de los suelos en la conservación de la naturaleza en Alemania. Revisamos las políticas mundiales y europeas en el pasado y en la actualidad, comparamos el funcionamiento ambiental del suelo dentro y fuera de las áreas protegidas y examinamos el papel de los suelos en la gestión de la conservación por medio del análisis de textos. La protección y la conservación de la biodiversidad y el funcionamiento ambiental del suelo han sido insuficientes. Las políticas relacionadas con el suelo son inaplicables y carecen de objetivos de conservación para su biodiversidad, pues se enfocan más bien en otros objetivos ambientales. No descubrimos evidencias de los efectos positivos de las medidas actuales de conservación en múltiples funciones ambientales del suelo en Europa. En la gestión alemana de la conservación, los suelos sólo se consideran desde una perspectiva limitada (p. ej.: como una parte físico química del ambiente y como hábitat para los organismos que habitan por encima de él). Mediante la exploración de la política, evidencias y gestión conforme se relaciona con los ecosistemas del suelo, sugerimos una perspectiva integrada para dirigir a la conservación hacia el enfoque directo sobre los ecosistemas del suelo (p. ej.: al establecer líneas base, monitorear las amenazas para el suelo y establecer un sistema indicador del suelo).

Comparing fruiting phenology across two historical datasets: Thoreau's observations and herbarium specimens.

BACKGROUND AND AIMS: Fruiting remains under-represented in long-term phenology records, relative to leaf and flower phenology. Herbarium specimens and historical field notes can fill this gap, but selecting and synthesizing these records for modern-day comparison requires an understanding of whether different historical data sources contain similar information, and whether similar, but not equivalent, fruiting metrics are comparable with one another. METHODS: For 67 fleshy-fruited plant species, we compared observations of fruiting phenology made by Henry David Thoreau in Concord, Massachusetts (1850s), with phenology data gathered from herbarium specimens collected across New England (mid-1800s to 2000s). To identify whether fruiting times and the order of fruiting among species are similar between datasets, we compared dates of first, peak and last observed fruiting (recorded by Thoreau), and earliest, mean and latest specimen (collected from herbarium records), as well as fruiting durations. KEY RESULTS: On average, earliest herbarium specimen dates were earlier than first fruiting dates observed by Thoreau; mean specimen dates were similar to Thoreau's peak fruiting dates; latest specimen dates were later than Thoreau's last fruiting dates; and durations of fruiting captured by herbarium specimens were longer than durations of fruiting observed by Thoreau. All metrics of fruiting phenology except duration were significantly, positively correlated within (r: 0.69-0.88) and between (r: 0.59-0.85) datasets. CONCLUSIONS: Strong correlations in fruiting phenology between Thoreau's observations and data from herbaria suggest that field and herbarium methods capture similar broad-scale phenological information, including relative fruiting times among plant species in New England. Differences in the timing of first, last and duration of fruiting suggest that historical datasets collected with different methods, scales and metrics may not be comparable when exact timing is important. Researchers should strongly consider matching methodology when selecting historical records of fruiting phenology for present-day comparisons.

Leaf longevity in temperate evergreen species is related to phylogeny and leaf size.

Leaf longevity (LL), the amount of time a photosynthetically active leaf remains on a plant, is an important trait of evergreen species, affecting physiological ecology and ecosystem processes. A long LL gives leaves more time to fix carbon but carries higher construction costs, while a short LL allows plants to respond more rapidly to changing environmental conditions. For many evergreen taxa, LL data are not readily available, and it is not known if LL is phylogenetically conserved. To address this gap, we measured LL for 169 temperate and boreal evergreen woody species at the Arnold Arboretum, a botanical garden in Boston, Massachusetts, along with metrics of leaf size and number known to be related to LL. We hypothesized that LL is phylogenetically conserved, and that longer LL is associated with a greater numbers of leaves, smaller leaves, and a colder hardiness zone of the species' native range. We found that average LL ranged from 1.4 years in Rhododendron tomentosum to 10.5 years in Abies cilicia. LL was phylogenetically conserved, with some genera, such as Abies and Picea, exhibiting long LL (> 3 years) and others, such as Ilex and Rhododendron, exhibiting short LL (< 3 years). Leaf length was negatively correlated with LL in conifers, due to differences between Pinus and other genera; however, there was no correlation between LL and number of leaves. This study highlights the considerable variation and phylogenetic pattern in LL among temperate evergreen species, which has implications for carbon budgets and ecosystem models.

Lessons from the WBF2020: extrinsic and intrinsic value of soil organisms.

Following our participation in the first World Biodiversity Forum in Davos, Switzerland, we provide a summary of the main themes of the conference, as well as an overview of the session that was focused on soil biodiversity. One of the main themes of the conference was the valuation of biodiversity and what contributes to the value of biodiversity. In this article we explore whether we should move away from the notion that we can only 'sell' soil biodiversity based on the function and services it provides, and rather shift towards valuing soil biodiversity based on its intrinsic value and our relationship with it.