Widespread Increase in Global Plant Water Stress Obscured by Greening

Facing a harsh climate: terrestrial plant functional strategies in a changing world

A machine learning approach and utilizing multi-source satellite remote-sensing and field-collected sPlotOpen measurements data, the first global community-level map of CSR functional strategy variations is generated, providing critical insights into global plant community dynamics under challenging abiotic conditions.

Beyond climatic drought indices : an hydraulic approach to quantifying forest water stress

The article introduces a new Forest Stress Index (ISF) based on a plant hydraulic modelling approach rather than classical climatic drought indices. Unlike other index like scPDSI or SPEI, ISF is grounded in xylem embolism dynamics simulated with the mechanistic SurEau model. The goal is to better link climatic anomalies to tree physiological functioning and mortality risk. ISF is defined using a locally adapted ideotype characterized by an optimal P50 value under a reference hydraulic functioning threshold. Simulations are performed across Europe and France using multiple climate datasets. The index is robust to model parameterization choices and assumptions about plant functional traits. Results show strong spatial and temporal consistency and significant correlations with SPEI and scPDSI. However, ISF more strongly highlights extreme drought years and exhibits a more skewed distribution. Future projections under SSP5-8.5 indicate a widespread increase in hydraulic stress with strong regional contrasts. Overall, ISF provides a mechanistic and complementary drought indicator more directly linked to forest mortality processes.

Flooding stress resilience and crop improvement

Monitoring phases of plant stress in juvenile commercial forest cuttings using contemporary nursery sensor technologies

Visual assessments of growing forest nursery plants are time-consuming and often result in a lack of information at a physiological level. There exists a need for health screening in nurseries, that is fast and efficient, to improve overall health monitoring and nursery productivity. Rapid handheld sensors such as rapid thermal devices, leaf porometers and moisture meters, can provide regular information at a physiological level, that can improve the understanding of the impact of stress on young plant cuttings and their decline in health over time. This paper evaluates the utility and reliability of contemporary sensor technologies, to operationally monitor stress phases in juvenile forest plant cuttings during progressive moisture (dry-down) conditions. Furthermore, to assess whether thermal sensors could be used as an indicator, in conjunction with other variables such as soil water content or stomatal conductance, is needed operationally for fast screening during limited planting windows. Near Infra-Red Analysis (NiRA) data was collected to understand detailed plant functions at a finer reflectance level. A relationship was found where the increase in thermal signals reflects a depletion of water content, resulting in an eventual decline in stomatal conductance and, ultimately, plant mortality. Several algorithms were used in a preliminary test, using RapidMiner software, to discriminate between the four phases of plant health decline using physiological variables and NiRA data. Both Gradient Boosting Trees (GBT) and Deep Learning (DL) showed the best performances, achieving favourable accuracies of 96.8% and 91.2% without NiRA data, 84.6% and 88.2% with NiRA data, with shorter training times. Using thermal technology weighted amongst the highest of the best performing variables using GBT, the utility and accuracy showed good discrimination between the stages of plant decline and is encouraged for future research in this field.

Detecting drought stress from the leaf to the landscape: is canopy structure or leaf desiccation more influential in tree canopy spectral responses to declining water?

Remotely sensed measurements of equivalent water thickness (EWT) derived from visible–shortwave infrared imaging spectroscopy data have the potential to revolutionize how we monitor drought in natural ecosystems. However, the mechanistic underpinnings of EWT measurements are still relatively unknown. We collected coincident measurements of leaf spectra, leaf water content, and leaf water potential over the course of a tabletop leaf drydown for 13 tree species. We then used a vegetation radiative transfer model to scale these measurements from the leaf to canopy scale, simulating how a leaf drying event would appear from an airborne or satellite instrument. We found that EWT responses to changes in leaf water content are strongly species‐specific at both the leaf and canopy level. Furthermore, changes in EWT associated with declining leaf water are relatively small compared to those associated with potential canopy structural changes, such as leaf shedding or shifting leaf angle distribution, and with retrieval errors of current instruments. Our results suggest that single point‐based EWT measurements are unlikely to reliably detect drought stress across species due to several confounding factors, but that time series data (newly available through operational and upcoming spaceborne imaging spectrometers) may enable approaches that circumvent many of these challenges.

Fine‐root responses to warming and elevated CO2 vary among plant functional types

The viability of peatlands as terrestrial carbon sinks is unknown as peatland carbon losses could be offset, or exacerbated, by increased plant growth. The response of fine‐roots to changing conditions in these ecosystems will be critical to understanding plant access to water, acquisition of nutrients, and ecosystem structure and function. We examined the plant functional type‐specific responses of fine‐root production to warming and elevated CO2 treatments, and to warming treatment‐induced deepening of water‐tables in a forested boreal bog. We hypothesized that shrubs would show the most dynamic responses of fine‐root production. We used minirhizotron cameras to estimate fine‐root production, depth and peak annual standing crop from images of individually tracked roots across 7 years (2015–2021) in the SPRUCE (Spruce and Peatland Responses Under Changing Environments) experiment. Fine‐root production increased with warming for shrubs 10.3, trees 2.2 and herbs 4.6%°C−1. When water‐tables dropped to their lows of 78 cm deep, shrubs deepened their fine‐root production from 7 to 29 cm deep, and trees from 9 to 17 cm, while herbs produced fine‐roots around 31 cm deep independent of shifts in water‐tables. Fine‐root standing crop increased with warming most strongly for shrubs, even more so under elevated CO2. Synthesis. We found that the fine‐roots of shrubs responded the most strongly to warming, elevated CO2 and lowered water‐tables. The greater responsiveness of shrub fine‐root production may partially explain increasing ‘shrubification’ at this site and in other peatlands with long‐term drainage.