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1. Hyperspectral Reflectance for Measuring Canopy‐Level Nutrients and Photosynthesis in a Salt Marsh

   https://doi.org/10.1029/2022JG007088  

   Vázquez‐Lule, Alma ; Seyfferth, Angelia L. ; Limmer, Matt A. ; Mey, Paul ; Guevara, Mario ; Vargas, Rodrigo ( November 2022 , Journal of Geophysical Research: Biogeosciences)

   Salt marsh ecosystems are underrepresented in process‐based models due to their unique location across the terrestrial–aquatic interface. Particularly, the role of leaf nutrients on canopy photosynthesis (F_A) remains unclear, despite their relevance for regulating vegetation growth. We combined multiyear information of canopy‐level nutrients and eddy covariance measurements with canopy surface hyperspectral remote sensing (CSHRS) to quantify the spatial and temporal variability of F_Ain a temperate salt marsh. We found that F_Ashowed a positive relationship with canopy‐level N at the ecosystem scale and for areas dominated bySpartina cynosuroides, but not for areas dominated by shortS. alterniflora. F_Ashowed a positive relationship with canopy‐level P, K, and Na, but a negative relationship with Fe, for areas associated withS. cynosuroides,S. alterniflora, and at the ecosystem scale. We used partial least squares regression (PLSR) with CSHRS and found statistically significant data–model agreements to predict canopy‐level nutrients and F_A. The red‐edge electromagnetic region and ∼770 nm showed the highest contribution of variance in PLSR models for canopy‐level nutrients and F_A, but we propose that underlying sediment biogeochemistry can complicate interpretation of reflectance measurements. Our findings highlight the relevance of spatial variability in salt marshes vegetation and the promising application of CSHRS for linking information of canopy‐level nutrients with F_A. We call for further development of canopy surface hyperspectral methods and analyses across salt marshes to improve our understanding of how these ecosystems will respond to global environmental change.

    

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2. Dead litter of resident species first facilitates and then inhibits sequential life stages of range‐expanding species

   https://doi.org/10.1111/1365-2745.13586  

   Smith, Rachel S. ; Blaze, Julie A. ; Byers, James E. ; Friess, ed., Daniel ( January 2021 , Journal of Ecology)

   Resident species can facilitate invading species (biotic assistance) or inhibit their expansion (biotic resistance). Species interactions are often context‐dependent and the relative importance of biotic assistance versus resistance could vary with abiotic conditions or the life stage of the invading species, as invader stress tolerances and resource requirements change with ontogeny. In northeast Florida salt marshes, the abundant dead litter (wrack) of the native marsh cordgrass,Spartina alterniflora, could influence the expansion success of the black mangrove,Avicennia germinans, a tropical species that is expanding its range northward.

   We used two field experiments to examine howS. alterniflorawrack affectsA. germinanssuccess during (a) propagule establishment and (b) subsequent seedling survival. We also conducted laboratory feeding assays to identify propagule consumers and assess how wrack presence influences herbivory on mangrove propagules.

   Spartina alterniflorawrack facilitatedA. germinansestablishment by promoting propagule recruitment, retention and rooting; the tidal regime influenced the magnitude of these effects. However, over timeS. alterniflorawrack inhibitedA. germinansseedling success by smothering seedlings and attracting herbivore consumers. Feeding assays identified rodents—which seek refuge in wrack—as consumers ofA. germinanspropagules.

   Synthesis. Our results suggest that the deleterious effects ofS. alterniflorawrack onA. germinansseedling survival counterbalance the initial beneficial effects of wrack onA. germinansseed establishment. Such seed‐seedling conflicts can arise when species stress tolerances and resource requirements change throughout development and vary with abiotic conditions. In concert with the tidal conditions, the relative importance of positive and negative interactions with wrack at each life stage can influence the rate of local and regional mangrove expansion. Because interaction strengths can change in direction and magnitude with ontogeny, it is essential to examine resident–invader interactions at multiple life stages and across environmental gradients to uncover the mechanisms of biotic assistance and resistance during invasion.

    

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3. Vascular epiphytes show low physiological resistance and high recovery capacity to episodic, short‐term drought in Monteverde, Costa Rica

   https://doi.org/10.1111/1365-2435.13613  

   Williams, Cameron B. ; Murray, Jessica G. ; Glunk, Andrew ; Dawson, Todd E. ; Nadkarni, Nalini M. ; Gotsch, Sybil G. ; Oliveira, ed., Rafael ( July 2020 , Functional Ecology)

   Tropical montane cloud forests support abundant epiphytic vascular plant communities that serve important ecosystem functions, but their reliance on atmospheric inputs of water may make them susceptible to the drying effects of rising cloud bases and more frequent droughts.

   We conducted a common garden experiment to explore the combined effects of decreasing cloud influence—lower humidity, warmer temperature, brighter light—and meteorological drought (i.e. absence of rain) on the physiology and morphology of vascular epiphytes native to primary forests of Monteverde, Costa Rica. The epiphytes, which exhibited C₃photosynthesis, were sourced from a lower montane cloud forest (CF) or a rainforest (RF) below the current cloud base and transplanted into nearby shadehouses (CF or RF shadehouse respectively). Vapour pressure deficit (VPD) and light availability, measured as photosynthetically active radiation, were 2.5 and 3.1 times higher in the RF than the CF shadehouse. Half of the plants were subjected to a severe 4‐week drought followed by a recovery period, and the other half were watered controls.

   Plants subjected to low VPD/light conditions of the CF shadehouse were physiologically and morphologically resistant to the drought treatment. However, compared to control plants, both sources of plants subjected to high VPD/light conditions of the RF shadehouse experienced declines in maximum net photosynthesis (A_max), stomatal conductance (g_s) and the proportion of healthy leaves (those not exhibiting chlorosis, desiccation or necrosis). At peak drought, leaves from the RF were 19% thinner than controls. Within 7–14 days after rewatering,A_max,g_sand leaf health recovered to nearly the levels of controls. Growth rate, mortality and phenology were unaffected by the treatments.

   The divergent responses to drought in the CF versus RF shadehouses, combined with the recovery in the RF shadehouse, indicate that these epiphytes possess adaptive properties that confer low resistance, but high recovery capacity, to episodes of short‐term drought over a range of cloud influence. In addition, the reduction inA_maxsuggests stomatal regulation that favours water conservation over carbon acquisition, a strategy that may inform epiphyte responses to rising clouds and increasing drought frequency expected in the long term.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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4. Elevation Changes in Restored Marshes at Poplar Island, Chesapeake Bay, MD: II. Modeling the Importance of Marsh Development Time

   https://doi.org/10.1007/s12237-024-01342-x  

   Morris, James T. ; Staver, Lorie W. ( April 2024 , Estuaries and Coasts)

   Tidal marshes in the Chesapeake Bay are vulnerable to the accelerating rate of sea-level rise (SLR) and subsidence. Restored and created marshes face the same risks as natural marshes, and their resilience to SLR may depend upon appropriate design and implementation. Here, the Coastal Wetland Equilibrium Model (CWEM) was used to assess the resilience of tidal marshes at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (PI) in mid-Chesapeake Bay, MD, where dredged material from navigation channels is being used to create new tidal marshes planted withSpartina alterniflorain the low marsh andS. patensin the high marsh. The site is microtidal with low inorganic sediment inputs, where the rate of marsh elevation change is dominated by the production of organic matter and, therefore, is proportional to net ecosystem production (NEP). The model demonstrated the importance of marsh development for surface elevation gain. In created marshes, the buildout of belowground biomass adds volume and results in faster growth of marsh elevation, but the gains slow as the marsh matures. Elevation gain is the lessor of the recalcitrant fraction of NEP sequestered in sediment or the rate of increase in accommodation space. Marshes can keep up with and fill accommodation space with sequestered NEP up to a tipping point determined by the rate of SLR. The PI low marsh platform was forecasted to drown in about 43 years after construction at the current rate of SLR. Marsh loss can be mitigated by periodic thin layer placement (TLP) of sediment. CWEM was used to simulate PI marsh responses to different TLP strategies and showed that there is an optimal design that will maximize carbon sequestration and resilience depending on the trajectory of mean sea level.

    

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5. Light-induced psbA translation in plants is triggered by photosystem II damage via an assembly-linked autoregulatory circuit

   https://doi.org/10.1073/pnas.2007833117  

   Chotewutmontri, Prakitchai ; Barkan, Alice ( August 2020 , Proceedings of the National Academy of Sciences)

   The D1 reaction center protein of photosystem II (PSII) is subject to light-induced damage. Degradation of damaged D1 and its replacement by nascent D1 are at the heart of a PSII repair cycle, without which photosynthesis is inhibited. In mature plant chloroplasts, light stimulates the recruitment of ribosomes specifically topsbAmRNA to provide nascent D1 for PSII repair and also triggers a global increase in translation elongation rate. The light-induced signals that initiate these responses are unclear. We present action spectrum and genetic data indicating that the light-induced recruitment of ribosomes topsbAmRNA is triggered by D1 photodamage, whereas the global stimulation of translation elongation is triggered by photosynthetic electron transport. Furthermore, mutants lacking HCF136, which mediates an early step in D1 assembly, exhibit constitutively highpsbAribosome occupancy in the dark and differ in this way from mutants lacking PSII for other reasons. These results, together with the recent elucidation of a thylakoid membrane complex that functions in PSII assembly, PSII repair, andpsbAtranslation, suggest an autoregulatory mechanism in which the light-induced degradation of D1 relieves repressive interactions between D1 and translational activators in the complex. We suggest that the presence of D1 in this complex coordinates D1 synthesis with the need for nascent D1 during both PSII biogenesis and PSII repair in plant chloroplasts.

    

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