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1. Environmental factors have a greater influence on photosynthetic capacity in C₄ plants than biochemical subtypes or growth forms

   https://doi.org/10.1111/nph.70525  

   Fan, Yuzhen; Noble, Daniel_W A; Medlyn, Belinda E; Monson, Russell K; Sage, Rowan F; Smith, Nicholas G; Ainsworth, Elizabeth A; Busch, Florian A; Danila, Florence R; Ermakova, Maria; et al (November 2025, New Phytologist)

   Our understanding of how photosynthetic capacity varies among C₄species and across growth and measurement conditions remains limited.We collated 1696 CO₂response curves of net CO₂assimilation rate (A/C_icurves) from C₄species grown and measured at various environmental conditions and used these data to estimate the apparent maximum carboxylation activity of phosphoenolpyruvate carboxylase (V_pmaxA) and CO₂‐saturated net photosynthetic rate (A_max), two key parameters describing photosynthetic capacity. We examined howV_pmaxAandA_maxvary with species‐specific traits, growth and measurement conditions.We found little systematic variation ofV_pmaxAandA_maxacross the classical C₄biochemical subtypes or growth forms, but showed that growth temperature and measurement conditions are major factors determining C₄photosynthetic capacity. We found no evidence that common C₄model species (e.g. maize, sorghum andSetaria viridis) differ in photosynthetic capacity from other C₄species when grown in controlled environments. However, C₄model species showed up to twice the photosynthetic capacity of other C₄species when grown in the field.Our multivariate model accounts for 47–51% of the variation reported inV_pmaxAandA_max, and we argue that environmental conditions have a greater influence on C₄photosynthetic capacity than biochemical subtypes or growth forms. 

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2. Limits of thermal and hydrological tolerance in a foundation tree species (Populus fremontii ) in the desert southwestern United States

   https://doi.org/10.1111/nph.19247  

   Moran, Madeline E; Aparecido, Luiza_M T; Koepke, Dan F; Cooper, Hillary F; Doughty, Christopher E; Gehring, Catherine A; Throop, Heather L; Whitham, Thomas G; Allan, Gerard J; Hultine, Kevin R (December 2023, New Phytologist)

   Atkin, Owen (Ed.)

   Summary Populus fremontiiis among the most dominant, and ecologically important riparian tree species in the western United States and can thrive in hyper‐arid riparian corridors. Yet,P. fremontiiforests have rapidly declined over the last decade, particularly in places where temperatures sometimes exceed 50°C.We evaluated high temperature tolerance of leaf metabolism, leaf thermoregulation, and leaf hydraulic function in eightP. fremontiipopulations spanning a 5.3°C mean annual temperature gradient in a well‐watered common garden, and at source locations throughout the lower Colorado River Basin.Two major results emerged. First, despite having an exceptionally highT_crit(the temperature at which Photosystem II is disrupted) relative to other tree taxa, recent heat waves exceededT_crit, requiring evaporative leaf cooling to maintain leaf‐to‐air thermal safety margins. Second, in midsummer, genotypes from the warmest locations maintained lower midday leaf temperatures, a higher midday stomatal conductance, and maintained turgor pressure at lower water potentials than genotypes from more temperate locations.Taken together, results suggest that under well‐watered conditions,P. fremontiican regulate leaf temperature belowT_critalong the warm edge of its distribution. Nevertheless, reduced Colorado River flows threaten to lower water tables below levels needed for evaporative cooling during episodic heat waves. 

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3. Sensitive Hydraulic and Stomatal Decline in Extreme Drought Tolerant Species of California Ceanothus

   https://doi.org/10.1111/pce.15208  

   Zailaa, Joseph; Trueba, Santiago; Browne, Marvin; Fletcher, Leila R; Buckley, Thomas N; Brodersen, Craig R; Scoffoni, Christine; Sack, Lawren (February 2025, Plant, Cell & Environment)

   ABSTRACT Identifying the physiological mechanisms by which plants are adapted to drought is critical to predict species responses to climate change. We measured the responses of leaf hydraulic and stomatal conductances (K_leafandg_s, respectively) to dehydration, and their association with anatomy, in seven species of CaliforniaCeanothusgrown in a common garden, including some of the most drought‐tolerant species in the semi‐arid flora. We tested for matching of maximum hydraulic supply and demand and quantified the role of decline ofK_leafin driving stomatal closure. AcrossCeanothusspecies, maximumK_leafandg_swere negatively correlated, and bothK_leafandg_sshowed steep declines with decreasing leaf water potential (i.e., a high sensitivity to dehydration). The leaf water potential at 50% decline ing_swas linked with a low ratio of maximum hydraulic supply to demand (i.e., maximumK_leaf:g_s). This sensitivity ofg_s, combined with low minimum epidermal conductance and water storage, could contribute to prolonged leaf survival under drought. The specialized anatomy of subg.Cerastesincludes trichomous stomatal crypts and pronounced hypodermis, and was associated with higher water use efficiency and water storage. Combining our data with comparative literature of other California species, species of subg. Cerastesshow traits associated with greater drought tolerance and reliance on leaf water storage relative to other California species. In addition to drought resistance mechanisms such as mechanical protection and resistance to embolism, drought avoidance mechanisms such as sensitive stomatal closure could contribute importantly to drought tolerance in dry‐climate adapted species. 

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4. Plant diversity and functional identity drive grassland rhizobacterial community responses after 15 years of CO₂ and nitrogen enrichment

   https://doi.org/10.1111/1365-2745.14271  

   Revillini, Daniel; Reich, Peter B; Johnson, Nancy Collins (April 2024, Journal of Ecology)

   Abstract Improved understanding of bacterial community responses to multiple environmental filters over long time periods is a fundamental step to develop mechanistic explanations of plant–bacterial interactions as environmental change progresses.This is the first study to examine responses of grassland root‐associated bacterial communities to 15 years of experimental manipulations of plant species richness, functional group and factorial enrichment of atmospheric CO₂(eCO₂) and soil nitrogen (+N).Across the experiment, plant species richness was the strongest predictor of rhizobacterial community composition, followed by +N, with no observed effect of eCO₂. Monocultures of C₃and C₄grasses and legumes all exhibited dissimilar rhizobacterial communities within and among those groups. Functional responses were also dependent on plant functional group, where N₂‐fixation genes, NO₃₋‐reducing genes and P‐solubilizing predicted gene abundances increased under resource‐enriched conditions for grasses, but generally declined for legumes. In diverse plots with 16 plant species, the interaction of eCO₂+N altered rhizobacterial composition, while +N increased the predicted abundance of nitrogenase‐encoding genes, and eCO₂+N increased the predicted abundance of bacterial P‐solubilizing genes.Synthesis: Our findings suggest that rhizobacterial community structure and function will be affected by important global environmental change factors such as eCO₂, but these responses are primarily contingent on plant species richness and the selective influence of different plant functional groups. 

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5. Save or spend? Diverging water‐use strategies of grasses and encroaching clonal shrubs

   https://doi.org/10.1111/1365-2745.14276  

   Keen, R M; Helliker, B R; McCulloh, K A; Nippert, J B (April 2024, Journal of Ecology)

   Abstract Shrub encroachment is one of the primary threats to mesic grasslands around the world. This dramatic shift in plant cover has the potential to alter ecosystem‐scale water budgets and responses to novel rainfall regimes. Understanding divergent water‐use strategies among encroaching shrubs and the grasses they replace is critical for predicting shifts in ecosystem‐scale water dynamics as a result of shrub encroachment, particularly if drought events become more frequent and/or severe in the future.In this study, we assessed how water‐use traits of a rapidly encroaching clonal shrub (Cornus drummondii) and a dominant C₄grass (Andropogon gerardii) impact responses to changes in water availability in tallgrass prairie. We assessed intra‐annual change in depth of water uptake, turgor loss point and stomatal regulation in each species. Sampling took place at Konza Prairie Biological Station (northeastern KS, USA) during the 2021 and 2022 growing seasons.Cornus drummondiishifted from shallow to deep soil water sources across the 2021 and 2022 growing seasons. This plasticity in depth of water uptake facilitated a ‘wasteful’ water‐use strategy inC. drummondii, where stomatal conductance and transpiration rates continued to increase even when no further gain in photosynthetic rate occurred.A. gerardiiphotosynthetic rates and stomatal conductance were more variable through time and were more responsive to changes in leaf water potential thanC. drummondii. However, intra‐annual adjustment of turgor loss point was more pronounced inC. drummondii(Δπ_TLP = −0.48 MPa ± 0.15 SD) than inA. gerardii(Δπ_TLP = −0.29 MPa ± 0.19 SD).Synthesis. These results suggest thatC. drummondiiis highly resilient to changes in water availability in surface soils and will likely remain unaffected by future droughts unless they are severe enough to reduce the availability of deep soil water. Given that clonal shrubs are key invaders of grasslands world‐wide, increased leaf‐level water loss is expected to accelerate ecosystem‐level drying as clonal shrub encroachment proceeds in mesic grasslands. 

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