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1. Eastern US deciduous tree species respond dissimilarly to declining soil moisture but similarly to rising evaporative demand

   https://doi.org/10.1093/treephys/tpaa153  

   Denham, Sander O ; Oishi, A Christopher ; Miniat, Chelcy F ; Wood, Jeffrey D ; Yi, Koong ; Benson, Michael C ; Novick, Kimberly A ( November 2020 , Tree Physiology)

   Whitehead, David (Ed.)

   Abstract Hydraulic stress in plants occurs under conditions of low water availability (soil moisture; θ) and/or high atmospheric demand for water (vapor pressure deficit; D). Different species are adapted to respond to hydraulic stress by functioning along a continuum where, on one hand, they close stomata to maintain a constant leaf water potential (ΨL) (isohydric species), and on the other hand, they allow ΨL to decline (anisohydric species). Differences in water-use along this continuum are most notable during hydrologic stress, often characterized by low θ and high D; however, θ and D are often, but not necessarily, coupled at time scales of weeks or longer, and uncertainty remains about the sensitivity of different water-use strategies to these variables. We quantified the effects of both θ and D on canopy conductance (Gc) among widely distributed canopy-dominant species along the isohydric–anisohydric spectrum growing along a hydroclimatological gradient. Tree-level Gc was estimated using hourly sap flow observations from three sites in the eastern United States: a mesic forest in western North Carolina and two xeric forests in southern Indiana and Missouri. Each site experienced at least 1 year of substantial drought conditions. Our results suggest that sensitivity of Gc to θ varies acrossmore »sites and species, with Gc sensitivity being greater in dry than in wet sites, and greater for isohydric compared with anisohydric species. However, once θ limitations are accounted for, sensitivity of Gc to D remains relatively constant across sites and species. While D limitations to Gc were similar across sites and species, ranging from 16 to 34% reductions, θ limitations to Gc ranged from 0 to 40%. The similarity in species sensitivity to D is encouraging from a modeling perspective, though it implies that substantial reduction to Gc will be experienced by all species in a future characterized by higher D.« less
2. Sustainable irrigation based on co-regulation of soil water supply and atmospheric evaporative demand

   https://doi.org/10.1038/s41467-021-25254-7  

   Zhang, Jingwen ; Guan, Kaiyu ; Peng, Bin ; Pan, Ming ; Zhou, Wang ; Jiang, Chongya ; Kimm, Hyungsuk ; Franz, Trenton E. ; Grant, Robert F. ; Yang, Yi ; et al ( December 2021 , Nature Communications)

   Abstract Irrigation is an important adaptation to reduce crop yield loss due to water stress from both soil water deficit (low soil moisture) and atmospheric aridity (high vapor pressure deficit, VPD). Traditionally, irrigation has primarily focused on soil water deficit. Observational evidence demonstrates that stomatal conductance is co-regulated by soil moisture and VPD from water supply and demand aspects. Here we use a validated hydraulically-driven ecosystem model to reproduce the co-regulation pattern. Specifically, we propose a plant-centric irrigation scheme considering water supply-demand dynamics (SDD), and compare it with soil-moisture-based irrigation scheme (management allowable depletion, MAD) for continuous maize cropping systems in Nebraska, United States. We find that, under current climate conditions, the plant-centric SDD irrigation scheme combining soil moisture and VPD, could significantly reduce irrigation water use (−24.0%) while maintaining crop yields, and increase economic profits (+11.2%) and irrigation water productivity (+25.2%) compared with MAD, thus SDD could significantly improve water sustainability.
3. Rhizosphere plant-microbe interactions under water stress

   https://doi.org/https://doi.org/10.1016/bs.aambs.2021.03.001  

   Bhattacharyya, A ; Pablo, CHD ; Mavrodi, OV ; Weller, DM ; Thomashow, LS ; Mavrodi, DV. ( June 2021 , Advances in applied microbiology)

   Gadd, GM ; Sariaslani, S. (Ed.)

   Climate change, with its extreme temperature, weather and precipitation patterns, is a major global concern of dryland farmers, who currently meet the challenges of climate change agronomically and with growth of drought-tolerant crops. Plants themselves compensate for water stress by modifying aerial surfaces to control transpiration and altering root hydraulic conductance to increase water uptake. These responses are complemented by metabolic changes involving phytohormone network-mediated activation of stress response pathways, resulting in decreased photosynthetic activity and the accumulation of metabolites to maintain osmotic and redox homeostasis. Phylogenetically diverse microbial communities sustained by plants contribute to host drought tolerance by modulating phytohormone levels in the rhizosphere and producing water-sequestering biofilms. Drylands of the Inland Pacific Northwest, USA, illustrate the interdependence of dryland crops and their associated microbiota. Indigenous Pseudomonas spp. selected there by long-term wheat monoculture suppress root diseases via the production of antibiotics, with soil moisture a critical determinant of the bacterial distribution, dynamics and activity. Those pseudomonads producing phenazine antibiotics on wheat had more abundant rhizosphere biofilms and provided improved tolerance to drought, suggesting a role of the antibiotic in alleviation of drought stress. The transcriptome and metabolome studies suggest the importance of wheat root exudate-derived osmoprotectants for themore »adaptation of these pseudomonads to the rhizosphere lifestyle and support the idea that the exchange of metabolites between plant roots and microorganisms profoundly affects and shapes the belowground plant microbiome under water stress.« less
4. Transport in a coordinated soil-root-xylem-phloem leaf system

   https://doi.org/org/10.1016/j.advwatres.2018.06.002.06.002  

   Cheng-Wei, Huang ; domec, Jean-Christophe ; Palmroth, Sari ; Pockman, William T. ; Litvak, Marcy E ; Katul, Gabriel G ( September 2018 , Advances in water resources)

   Links between the carbon and water economies of plants are coupled by combining the biochemical demand for atmospheric CO2 with gas transfer through stomates, liquid water transport in the soil-xylem hydraulic system and sucrose export in the phloem. We formulated a model to predict stomatal conductance (gs), consistent with the maximum energy circulation concept of Lotka and Odum, by maximizing the sucrose flux out of photosynthesizing leaves. The proposed modeling approach recovers all prior results derived from stomatal optimization theories and profit-maximization arguments for the xylem hydraulic system aimed at predicting gs. The novel features of this approach are its ability to 1) predict the price of losing water in carbon units using xylem and phloem properties (i.e., the marginal water use efficiency) and 2) explain why water molecules become more expensive to exchange for CO2 molecules when soil moisture becomes limiting or when plants acclimate to new elevated atmospheric CO2 concentration. On short time-scales (sub-daily), predicted gs under many environmental stimuli were consistent with measurements reported in the literature, including a general sensitivity of gs to vapor pressure deficit and leaf water potential. During progressive droughts, differences in the coordination among the leaf, xylem, and phloem functioning determine themore »isohydric-to-anisohydric behavior among plants.« less
5. Plant functional traits and climate influence drought intensification and land–atmosphere feedbacks

   https://doi.org/10.1073/pnas.1904747116  

   Anderegg, William R. ; Trugman, Anna T. ; Bowling, David R. ; Salvucci, Guido ; Tuttle, Samuel E. ( July 2019 , Proceedings of the National Academy of Sciences)

   The fluxes of energy, water, and carbon from terrestrial ecosystems influence the atmosphere. Land–atmosphere feedbacks can intensify extreme climate events like severe droughts and heatwaves because low soil moisture decreases both evaporation and plant transpiration and increases local temperature. Here, we combine data from a network of temperate and boreal eddy covariance towers, satellite data, plant trait datasets, and a mechanistic vegetation model to diagnose the controls of soil moisture feedbacks to drought. We find that climate and plant functional traits, particularly those related to maximum leaf gas exchange rate and water transport through the plant hydraulic continuum, jointly affect drought intensification. Our results reveal that plant physiological traits directly affect drought intensification and indicate that inclusion of plant hydraulic transport mechanisms in models may be critical for accurately simulating land–atmosphere feedbacks and climate extremes under climate change.