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1. Temporal controls on crown nonstructural carbohydrates in southwestern US tree species

   https://doi.org/10.1093/treephys/tpaa149  

   Peltier, Drew M; Guo, Jessica; Nguyen, Phiyen; Bangs, Michael; Gear, Linnea; Wilson, Michelle; Jefferys, Stacy; Samuels-Crow, Kimberly; Yocom, Larissa L; Liu, Yao; et al (November 2020, Tree Physiology)

   Meinzer, Frederick (Ed.)

   Abstract In trees, large uncertainties remain in how nonstructural carbohydrates (NSCs) respond to variation in water availability in natural, intact ecosystems. Variation in NSC pools reflects temporal fluctuations in supply and demand, as well as physiological coordination across tree organs in ways that differ across species and NSC fractions (e.g., soluble sugars vs starch). Using landscape-scale crown (leaves and twigs) NSC concentration measurements in three foundation tree species (Populus tremuloides, Pinus edulis, Juniperus osteosperma), we evaluated in situ, seasonal variation in NSC responses to moisture stress on three timescales: short-term (via predawn water potential), seasonal (via leaf δ13C) and annual (via current year’s ring width index). Crown NSC responses to moisture stress appeared to depend on hydraulic strategy, where J. osteosperma appears to regulate osmotic potentials (via higher sugar concentrations), P. edulis NSC responses suggest respiratory depletion and P. tremuloides responses were consistent with direct sink limitations. We also show that overly simplistic models can mask seasonal and tissue variation in NSC responses, as well as strong interactions among moisture stress at different timescales. In general, our results suggest large seasonal variation in crown NSC concentrations reflecting the multiple cofunctions of NSCs in plant tissues, including storage, growth and osmotic regulation of hydraulically vulnerable leaves. We emphasize that crown NSC pool size cannot be viewed as a simple physiological metric of stress; in situ NSC dynamics are complex, varying temporally, across species, among NSC fractions and among tissue types. 

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2. Intra-canopy leaf trait variation facilitates high leaf area index and compensatory growth in a clonal woody encroaching shrub

   https://doi.org/10.1093/treephys/tpac078  

   Tooley, E Greg; Nippert, Jesse B; Bachle, Seton; Keen, Rachel M (July 2022, Tree Physiology)

   Cavaleri, Molly (Ed.)

   Abstract Leaf trait variation enables plants to utilize large gradients of light availability that exist across canopies of high leaf area index (LAI), allowing for greater net carbon gain while reducing light availability for understory competitors. While these canopy dynamics are well understood in forest ecosystems, studies of canopy structure of woody shrubs in grasslands are lacking. To evaluate the investment strategy used by these shrubs, we investigated the vertical distribution of leaf traits and physiology across canopies of Cornus drummondii, the predominant woody encroaching shrub in the Kansas tallgrass prairie. We also examined the impact of disturbance by browsing and grazing on these factors. Our results reveal that leaf mass per area (LMA) and leaf nitrogen per area (Na) varied approximately threefold across canopies of C. drummondii, resulting in major differences in the physiological functioning of leaves. High LMA leaves had high photosynthetic capacity, while low LMA leaves had a novel strategy for maintaining light compensation points below ambient light levels. The vertical allocation of leaf traits in C. drummondii canopies was also modified in response to browsing, which increased light availability at deeper canopy depths. As a result, LMA and Na increased at lower canopy depths, leading to a greater photosynthetic capacity deeper in browsed canopies compared to control canopies. This response, along with increased light availability, facilitated greater photosynthesis and resource-use efficiency deeper in browsed canopies compared to control canopies. Our results illustrate how C. drummondii facilitates high LAI canopies and a compensatory growth response to browsing—both of which are key factors contributing to the success of C. drummondii and other species responsible for grassland woody encroachment. 

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3. Leaf Discoloration in Rhododendron Species Exposed to Phytophthora Cinnamomi Corresponds with Future Mortality

   https://doi.org/10.24266/0738-2898-42.3.109  

   Cryan, Anna; Liu, Yu; Medeiros, Juliana S; Burns, Jean H (September 2024, Journal of Environmental Horticulture)

   Abstract Phytophthora cinnamomi, which causes the disease root rot, is an oomycete pathogen that is damaging to woody plants, including many horticulturally important groups, such as Rhododendron. Infecting the root of plants, Phytophthora cinnamomi inhibits water uptake, leading to root damage, wilting, and increased rates of plant mortality. Some observations suggest that P. cinnamomi infection corresponds to changes in leaf coloration, though whether this indicates a plant stress response or plant damage is generally unknown. We used leaf color analysis to test for differences in leaf discoloration between plants inoculated with the pathogen and control plants. We demonstrate a significant link between leaf discoloration in Rhododendron species and Phytophthora cinnamomi inoculation. This method was most useful when mortality was not exceptionally high, and analyzers must consider mortality as well as leaf damage in quantifying effects of the pathogen. Plants with leaf discoloration were 3.3 times more likely to die 2 weeks from our leaf census than plants with no leaf discoloration (P =0.005). This method is particularly inexpensive to implement, making it a valuable alternative to multi-spectral or hyperspectral imaging, especially in contexts such as horticulture and citizen science, where the high speed and low-cost nature of this technique might prove valuable. Species used in this study: root rot disease pathogen (Phytophthora cinnamomi Rands); Rhododendron atlanticum (Ashe) Rehder; Rhododendron brachycarpum D.Don ex G.Don; Rhododendron kiusianum Makino; Rhododendron maximum L.; Rhododendron minus Michx.; Rhododendron calendulaceum (Michx.) Torr.; Rhododendron kaempferi Planch.; Rhododendron keiskei Miq. Chemicals used in this study: Fosal Select Aliette/aluminum phosphite. 

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4. Productivity and Nutrient Quality of Lemna minor as Affected by Microbiome, CO2 Level, and Nutrient Supply

   https://doi.org/10.3390/stresses3010007  

   Zenir, Madeleine C.; López-Pozo, Marina; Polutchko, Stephanie K.; Stewart, Jared J.; Adams, William W.; Escobar, Adam; Demmig-Adams, Barbara (March 2023, Stresses)

   Rising atmospheric carbon dioxide (CO2) levels can impact plant photosynthesis and productivity and threaten food security, especially when combined with additional environmental stressors. This study addresses the effects of elevated CO2 in combination with low nutrient supply on Lemna minor (common duckweed). We quantified plant growth rate and nutritional quality (protein content) and evaluated whether any adverse effects of elevated CO2, low nutrients, or the combination of the two could be mitigated by plant-microbe interaction. Plants were grown under controlled conditions and were either uninoculated or inoculated with microorganisms from a local pond that supported L. minor populations. Under low nutrients in combination with high CO2, growth (plant area expansion rate) decreased and biomass accumulation increased, albeit with lower nutritional quality (lower percentage of protein per plant biomass). Inoculation with plant-associated microorganisms restored area expansion rate and further stimulated biomass accumulation while supporting a high protein-to-biomass ratio and, thus, a high nutritional quality. These findings indicate that plant-microbe interaction can support a higher nutritional quality of plant biomass under elevated atmospheric CO2 levels, an important finding for both human and non-human consumers during a time of rapid environmental change. 

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5. Effects of elevated CO2 on MeHg and IHg in rice

   https://doi.org/10.1016/j.envadv.2024.100515  

   Strickman, Rachel J; Larson, Sarah; Farhat, Yasmine A; Hoang, Van_Anh T; Rothenberg, Sarah E; Neumann, Rebecca B (July 2024, Environmental Advances)

   Methylmercury (MeHg) and, to a lesser extent, inorganic mercury (IHg) contamination of rice is a global public health concern, but little is known about how soil and grain Hg concentrations respond to elevated CO2 (ECO2), or how ECO2 alters movement of Hg through the soil-plant-grain system. To advance knowledge of how Hg contamination of rice will change in the future, this study explored the effect of elevated CO2 (ECO2, c. 800 ppm) on soil, iron plaque, root, stem/leaf, and grain concentrations of MeHg and IHg. We observed evidence that ECO2 increased accumulation of MeHg, but not IHg, in rice grain. For IHg, ECO2 did not alter its uptake from the soil, translocation through the plant, or concentration in rice grain. However, ECO2 did reduce uptake of IHg from the air into leaf tissues, likely as a result of the reduced stomatal conductivity and thus more limited direct uptake from the air. Methylmercury concentrations in the grain of plants grown at ECO2 were significantly higher than those of plants grown at ambient CO2. Moreover, MeHg concentrations were also elevated in stem/leaf (82 %) and root tissue (37 %) for ECO2 plants, although the root-tissue results were not statistically significant. In contrast, soil MeHg concentrations were virtually indistinguishable between treatments, indicating that higher rice grain MeHg concentrations were not likely due to higher microbial IHg methylation in soil. Plant uptake of MeHg into stem/leaves and grain from the soil was significantly greater in the ECO2 treatment; however, translocation patterns of MeHg within the plant itself did not differ between treatments. Notably, these patterns existed despite consistently lower transpiration in the ECO2 treatment, and thus less mass flow of solute towards and through the plant. Our results indicate that as CO2 concentrations rise, the human health risks related to MeHg in grain will likely increase. 

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