Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation ...events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between NPP and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta‐analytical techniques to search for generalities and asymmetries of aboveground NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by ANPP responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.
Future changes in precipitation will strongly impact ecosystem functioning and services through changes in plant growth. Here, we synthesize 83 precipitation experiments to look at responses of above and belowground plant growth (ANPP and BNPP) across climatic gradients and levels of precipitation change extremity. Overall, we found that (1) ANPP was more responsive to precipitation increases than decreases, and this was especially evident in dry ecosystems; (2) BNPP responses were similar under precipitation increases vs. decreases; (3) under extreme wet conditions, NPP responses leveled off, creating a saturating function of NPP response vs. the magnitude of precipitation change. Based on these findings, we suggest that future research focus on BNPP and plant responses to extreme precipitation change.
Extreme events such as drought and heatwaves are among the biggest challenges to agricultural production and food security. However, the effects of cropping systems on drought resistance of arable ...crops via their hydraulic behaviour remain unclear. We investigated how hydraulic traits of a field‐grown pea‐barley (Pisum sativum L. and Hordeum vulgare L.) mixture were affected by different cropping systems, that is, organic and conventional farming with intensive or conservation tillage. Xylem vulnerability to cavitation of both species was estimated by measuring the pressure inducing 50% loss of hydraulic conductivity (P50), while the water stress plants experienced in the field were assessed using native percentage loss of hydraulic conductivity (nPLC). Pea and barley showed contrasting hydraulic behaviours: pea was less vulnerable to xylem cavitation and less stressed than barley; cropping systems affected the xylem vulnerability of barley, but not of pea. Barley grown under conventional farming with no tillage was more vulnerable and stressed than under organic farming with intensive tillage. nPLC proved to be a valuable indicator for plant water stress. Our results highlight the impact of cropping systems on crop xylem vulnerability and drought resistance, thus plant hydraulic traits, for protecting food security under future climate.
Effects of cropping systems on drought resistance of arable crops were investigated for a field‐grown Pisum sativum/Hordeum vulgare mixture. Pea was less vulnerable to xylem cavitation and less stressed than barley. Cropping systems only affected xylem vulnerability of barley, but not of pea.
Temperate C₃-grasslands are of high agricultural and ecological importance in Central Europe. Plant growth and consequently grassland yields depend strongly on water supply during the growing season, ...which is projected to change in the future. We therefore investigated the effect of summer drought on the water uptake of an intensively managed lowland and an extensively managed sub-alpine grassland in Switzerland. Summer drought was simulated by using transparent shelters. Standing above- and belowground biomass was sampled during three growing seasons. Soil and plant xylem waters were analyzed for oxygen (and hydrogen) stable isotope ratios, and the depths of plant water uptake were estimated by two different approaches: (1) linear interpolation method and (2) Bayesian calibrated mixing model. Relative to the control, aboveground biomass was reduced under drought conditions. In contrast to our expectations, lowland grassland plants subjected to summer drought were more likely (43–68 %) to rely on water in the topsoil (0–10 cm), whereas control plants relied less on the topsoil (4–37 %) and shifted to deeper soil layers (20–35 cm) during the drought period (29–48 %). Sub-alpine grassland plants did not differ significantly in uptake depth between drought and control plots during the drought period. Both approaches yielded similar results and showed that the drought treatment in the two grasslands did not induce a shift to deeper uptake depths, but rather continued or shifted water uptake to even more shallower soil depths. These findings illustrate the importance of shallow soil depths for plant performance under drought conditions.
In Switzerland, the traditional three-stage grassland farming system consists of grazed or cut grasslands along a gradient from lowland to alpine elevations. We measured carbon dioxide (CO₂) fluxes ...at three grassland sites (400, 1000, and 2000m elevation) and estimated carbon sequestration for two different but exceptionally warm years (2006 and 2007). Grasslands at higher elevations (>1000m), managed at lower intensities, exhibited a larger net CO₂ uptake compared to intensively managed grasslands at lower elevations (400m). Taking into account harvest outputs as well as manure inputs, we calculated the carbon stocks and their changes for grasslands at 400m and 1000m during two years. Similar to the cumulative net ecosystem CO₂ fluxes, the seasonal course of carbon stock changes were strongly driven by management intensity, in particular by timing and amount of manure applications. Despite differences in environmental and management conditions with elevation, both grassland sites were carbon sinks during 2006 and 2007 (between 25 and 150gCm⁻² yr⁻¹).
The World Food System Summer School is an innovative two-week course that seeks to develop the knowledge, skills and attitudes of the next generation of decision makers to build sustainable food ...systems. Meaningful learning, where the participant is able to relate new information to existing knowledge, is a critical part of education about complex systems and requires the integration of reflective approaches to teaching and learning. We adapted the rich picture method in three summer schools in Switzerland, South Africa and Côte d’Ivoire (74 participants with 29 nationalities) to support the reflection of participants on their knowledge gained on complex food systems. Coding and comparing 51 pairs of pre- and post-course pictures of food systems clearly demonstrated newly gained knowledge: The number of sub-categories drawn significantly increased from 11 to 19 in the post-course pictures, the largest increase occurred for environmental sustainability (57%). The rich picture method is a highly valuable and simple tool to gain insight into how participants’ knowledge changes and where there are gaps in meeting the learning objectives. This is particularly useful within a highly diverse participant cohort, as it allows participants to discuss and reflect on their own learning experience in a personalized way. Additionally, the rich picture method provides insights for faculty to improve their approaches to teaching on food systems.
Summary
Investigating plant responses to climate change is key to develop suitable adaptation strategies. However, whether changes in land management can alleviate increasing drought threats to crops ...in the future is still unclear.
We conducted a management × drought experiment with winter wheat (Triticum aestivum L.) to study plant water and vegetative traits in response to drought and management (conventional vs organic farming, with intensive vs conservation tillage). Water traits (root water uptake pattern, stem metaxylem area, leaf water potential, stomatal conductance) and vegetative traits (plant height, leaf area, leaf Chl content) were considered simultaneously to characterise the variability of multiple traits in a trait space, using principal component analysis.
Management could not alleviate the drought impacts on plant water traits as it mainly affected vegetative traits, with yields ultimately being affected by both management and drought. Trait spaces were clearly separated between organic and conventional management as well as between drought and control conditions. Moreover, changes in trait space triggered by management and drought were independent from each other.
Neither organic management nor conservation tillage eased drought impacts on winter wheat. Thus, our study raised concerns about the effectiveness of these management options as adaptation strategies to climate change.
Agricultural production is under threat of water scarcity
due to increasingly frequent and severe drought events under climate change.
Whether a change in cropping systems can be used as an effective ...adaptation
strategy against drought is still unclear. We investigated how plant water
uptake patterns of a field-grown pea–barley (Pisum sativum L. and Hordeum vulgare L.) mixture, an
important fodder intercrop, responded to experimental drought under four
cropping systems, i.e. organic intensive tillage, conventional intensive
tillage, conventional no tillage, and organic reduced tillage. Drought was
simulated after crop establishment using rain shelters. Proportional
contributions to plant water uptake from different soil layers were
estimated based on stable water isotopes using Bayesian mixing models. Pea
plants always took up proportionally more water from shallower depths than
barley plants. Water uptake patterns of neither species were affected by
cropping systems. Both species showed similar responses to the drought
simulation and increased their proportional water uptake from the shallow soil
layer (0–20 cm) in all cropping systems. Our results highlight the impact of
drought on plant water uptake patterns for two important crop species and
suggest that cropping systems might not be as successful as adaptation
strategies against drought as previously thought.
Changes in agricultural practices of semi-natural mountain grasslands are expected to modify plant community structure and shift dominance patterns. Using vegetation surveys of 11 sites in ...semi-natural grasslands of the Swiss Jura and Swiss and French Alps, we determined the relative contribution of dominant, subordinate and transient plant species in grazed and abandoned communities and observed their changes along a gradient of productivity and in response to abandonment of pasturing.
The results confirm the humpbacked diversity–productivity relationship in semi-natural grassland, which is due to the increase of subordinate species number at intermediate productivity levels. Grazed communities, at the lower or higher end of the species diversity gradient, suffered higher species loss after grazing abandonment. Species loss after abandonment of pasturing was mainly due to a higher reduction in the number of subordinate species, as a consequence of the increasing proportion of dominant species.
When plant biodiversity maintenance is the aim, our results have direct implications for the way grasslands should be managed. Indeed, while intensification and abandonment have been accelerated since few decades, our findings in this multi-site analysis confirm the importance of maintaining intermediate levels of pasturing to preserve biodiversity.
Änderungen in der Bewirtschaftung naturnaher Bergwiesen können die Struktur von Pflanzengesellschaften und deren Dominanzmuster verändern. Anhand von Vegetationsaufnahmen 11 naturnaher Wiesen des Schweizer Juras und der Schweizer und Französischen Alpen erfassten wir den Anteil der dominanten, untergeordneten und transienten Pflanzenarten in beweideten und aufgelassenen Pflanzengemeinschaften, beobachteten ihre Veränderungen entlang eines Produktivitätsgradienten und ihre Antwort auf die Aufgabe der Beweidung.
Die Ergebnisse bestätigen den glockenförmigen Zusammenhang zwischen Artenreichtum und Produktivität in naturnahem Grünland, insbesondere aufgrund der Zunahme von untergeordneten Arten bei mittlerer Produktivität. Beweidete Pflanzengesellschaften am unteren oder oberen Ende des Pflanzenvielfalts-Gradienten verloren nach Aufgabe der Beweidung mehr Arten. Der Artenverlust nach der Beweidungsaufgabe war vor allem ein Resultat der höheren Reduktion von untergeordneten Arten als Folge des steigenden Anteils hochwachsender Arten.
Unsere Ergebnisse haben direkte Auswirkungen auf die Art und Weise, wie Grünland bewirtschaftet werden sollte. Während die Intensivierung und die Aufgabe beweideter Flächen seit Jahrzehnten schneller vorangehen, bestätigen die Ergebnisse dieser Multi-Site-Analyse die Bedeutung einer mittleren Beweidungsintensität für den Erhalt der Artenvielfalt.
Climate models predict decreasing amounts of precipitation for future summers in Switzerland. Since grasslands cover about one quarter of the area, severe consequences might be expected for Swiss ...agriculture, ranging from loss of grassland productivity to changes in vegetation composition. Since stressed ecosystems are also more susceptible to invasion, future drier conditions might favour the emergence of weeds. However, the response of temperate grasslands to drought has not been investigated in great detail so far. Using transparent rain shelters, we simulated extreme summer drought conditions in intensively managed temperate grassland in the Swiss lowlands at 400
m (Chamau, located near the city of Lucerne) and studied the drought response of
Rumex obtusifolius, one of the most troublesome weeds for forage production. We quantified above-ground biomass and assessed the resource use in terms of carbon, nitrogen and water.
R. obtusifolius increased its above-ground biomass production in response to drought, comprising up to 80% of the total community biomass in 2006. Within the drought plots, highest pre-dawn leaf water potentials, high values for midday leaf water potentials, stomatal conductance and assimilation clearly indicated that
R. obtusifolius was much less affected by drought than other plant species. In general, no significant differences were found for these variables between drought and control
R. obtusifolius plants, in contrast to the other plant species. Higher water use efficiency together with a change in N acquisition patterns resulted in a competitive advantage of
R. obtusifolius over other species, favouring the spread of this weed. Thus, our results suggest a potential increase of weed pressure by
R. obtusifolius under future climatic conditions, demanding additional management measures to limit its success.
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