Drought effects on trait space of winter wheat are independent of land management.

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.

Cropping systems alter hydraulic traits of barley but not pea grown in mixture.

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.

Asymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments.

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.

No shift to a deeper water uptake depth in response to summer drought of two lowland and sub-alpine C3-grasslands in Switzerland.

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.

Reliability and quality of water isotope data collected with a low-budget rain collector.

RATIONALE: Low-budget rain collectors for water isotope analysis, such as the 'ball-in-funnel type collector' (BiFC), are widely used in studies on stable water isotopes of rain. To date, however, an experimental quality assessment of such devices in relation to climatic factors does not exist. METHODS: We used Cavity Ring-Down Spectrometry (CRDS) to quantify the effects of evaporation on the δ(18)O values of reference water under controlled conditions as a function of the elapsed time between rainfall and collection for isotope analysis, the sample volume and the relative humidity (RH: 31% and 67%; 25 °C). The climate chamber conditions were chosen to reflect the warm and dry end of field conditions that favor evaporative enrichment (EE). We also tested the performance of the BiFC in the field, and compared our δ(2)H/δ(18)O data obtained by isotope ratio mass spectrometry (IRMS) with those from the Swiss National Network for the Observation of Isotopes in the Water Cycle (ISOT). RESULTS: The EE increased with time, with a 1‰ increase in the δ(18)O values after 10 days (RH: 25%; 25 °C; 35 mL (corresponding to a 5 mm rain event); p <0.001). The sample volume strongly affected the EE (max. value +1.5‰ for 7 mL samples (i.e., 1 mm rain events) after 72 h at 31% and 67% RH; p <0.001), whereas the relative humidity had no significant effect. Using the BiFC in the field, we obtained very tight relationships of the δ(2)H/δ(18)O values (r(2) ≥ 0.95) for three sites along an elevational gradient, not significantly different from that of the next ISOT station. CONCLUSIONS: Since the chosen experimental conditions were extreme compared with the field conditions, it was concluded that the BiFC is a highly reliable and inexpensive collector of rainwater for isotope analysis.