More Like this

1. Chlorophyll fluorescence tracks seasonal variations of photosynthesis from leaf to canopy in a temperate forest

   https://doi.org/10.1111/gcb.13590  

   Yang, Hualei ; Yang, Xi ; Zhang, Yongguang ; Heskel, Mary A. ; Lu, Xiaoliang ; Munger, J. William ; Sun, Shucun ; Tang, Jianwu ( January 2017 , Global Change Biology)

   Accurate estimation of terrestrial gross primary productivity (GPP) remains a challenge despite its importance in the global carbon cycle. Chlorophyll fluorescence (ChlF) has been recently adopted to understand photosynthesis and its response to the environment, particularly with remote sensing data. However, it remains unclear how ChlF and photosynthesis are linked at different spatial scales across the growing season. We examined seasonal relationships between ChlF and photosynthesis at the leaf, canopy, and ecosystem scales and explored how leaf‐level ChlF was linked with canopy‐scale solar‐induced chlorophyll fluorescence (SIF) in a temperate deciduous forest at Harvard Forest, Massachusetts,USA. Our results show that ChlF captured the seasonal variations of photosynthesis with significant linear relationships between ChlF and photosynthesis across the growing season over different spatial scales (R² = 0.73, 0.77, and 0.86 at leaf, canopy, and satellite scales, respectively;P < 0.0001). We developed a model to estimateGPPfrom the tower‐based measurement ofSIFand leaf‐level ChlF parameters. The estimation ofGPPfrom this model agreed well with flux tower observations ofGPP(R² = 0.68;P < 0.0001), demonstrating the potential ofSIFfor modelingGPP. At the leaf scale, we found that leafF_q’/F_m’, the fraction of absorbed photons that are used for photochemistry for a light‐adapted measurement from a pulse amplitude modulation fluorometer, was the best leaf fluorescence parameter to correlate with canopySIFyield (SIF/APAR,R² = 0.79;P < 0.0001). We also found that canopySIFandSIF‐derivedGPP(GPP_SIF) were strongly correlated to leaf‐level biochemistry and canopy structure, including chlorophyll content (R² = 0.65 for canopyGPP_SIFand chlorophyll content;P < 0.0001), leaf area index (LAI) (R² = 0.35 for canopyGPP_SIFandLAI;P < 0.0001), and normalized difference vegetation index (NDVI) (R² = 0.36 for canopyGPP_SIFandNDVI;P < 0.0001). Our results suggest that ChlF can be a powerful tool to track photosynthetic rates at leaf, canopy, and ecosystem scales.

    

   more » « less
2. Seasonal and drought‐related changes in leaf area profiles depend on height and light environment in an Amazon forest

   https://doi.org/10.1111/nph.15726  

   Smith, Marielle N. ; Stark, Scott C. ; Taylor, Tyeen C. ; Ferreira, Mauricio L. ; de Oliveira, Eronaldo ; Restrepo‐Coupe, Natalia ; Chen, Shuli ; Woodcock, Tara ; dos Santos, Darlisson Bentes ; Alves, Luciana F. ; et al ( March 2019 , New Phytologist)

   Seasonal dynamics in the vertical distribution of leaf area index (LAI) may impact the seasonality of forest productivity in Amazonian forests. However, until recently, fine‐scale observations critical to revealing ecological mechanisms underlying these changes have been lacking.

   To investigate fine‐scale variation in leaf area with seasonality and drought we conducted monthly ground‐based LiDAR surveys over 4 yr at an Amazon forest site. We analysed temporal changes in vertically structuredLAIalong axes of both canopy height and light environments.

   Upper canopyLAIincreased during the dry season, whereas lower canopyLAIdecreased. The low canopy decrease was driven by highly illuminated leaves of smaller trees in gaps. By contrast, understoryLAIincreased concurrently with the upper canopy. Hence, tree phenological strategies were stratified by height and light environments. Trends were amplified during a 2015–2016 severe El Niño drought.

   Leaf area low in the canopy exhibited behaviour consistent with water limitation. Leaf loss from short trees in high light during drought may be associated with strategies to tolerate limited access to deep soil water and stressful leaf environments. Vertically and environmentally structured phenological processes suggest a critical role of canopy structural heterogeneity in seasonal changes in Amazon ecosystem function.

    

   more » « less
3. Spring photosynthetic onset and net CO 2 uptake in Alaska triggered by landscape thawing

   https://doi.org/10.1111/gcb.14283  

   Parazoo, Nicholas C. ; Arneth, Almut ; Pugh, Thomas A. M. ; Smith, Ben ; Steiner, Nicholas ; Luus, Kristina ; Commane, Roisin ; Benmergui, Josh ; Stofferahn, Eric ; Liu, Junjie ; et al ( May 2018 , Global Change Biology)

   The springtime transition to regional‐scale onset of photosynthesis and net ecosystem carbon uptake in boreal and tundra ecosystems are linked to the soil freeze–thaw state. We present evidence from diagnostic and inversion models constrained by satellite fluorescence and airborneCO₂from 2012 to 2014 indicating the timing and magnitude of spring carbon uptake in Alaska correlates with landscape thaw and ecoregion. Landscape thaw in boreal forests typically occurs in late April (DOY111 ± 7) with a 29 ± 6 day lag until photosynthetic onset. North Slope tundra thaws 3 weeks later (DOY133 ± 5) but experiences only a 20 ± 5 day lag until photosynthetic onset. These time lag differences reflect efficient cold season adaptation in tundra shrub and the longer dehardening period for boreal evergreens. Despite the short transition from thaw to photosynthetic onset in tundra, synchrony of tundra respiration with snow melt and landscape thaw delays the transition from net carbon loss (at photosynthetic onset) to net uptake by 13 ± 7 days, thus reducing the tundra net carbon uptake period. Two globalCO₂inversions using aCASA‐GFEDmodel prior estimate earlier northern high latitude net carbon uptake compared to our regional inversion, which we attribute to (i) early photosynthetic‐onset model prior bias, (ii) inverse method (scaling factor + optimization window), and (iii) sparsity of available AlaskanCO₂observations. Another global inversion with zero prior estimates the same timing for net carbon uptake as the regional model but smaller seasonal amplitude. The analysis of Alaskan eddy covariance observations confirms regional scale findings for tundra, but indicates that photosynthesis and net carbon uptake occur up to 1 month earlier in evergreens than captured by models orCO₂inversions, with better correlation to above‐freezing air temperature than date of primary thaw. Further collection and analysis of boreal evergreen species over multiple years and at additional subarctic flux towers are critically needed.

    

   more » « less
4. Jasmonate‐mediated stomatal closure under elevated CO 2 revealed by time‐resolved metabolomics

   https://doi.org/10.1111/tpj.13296  

   Geng, Sisi ; Misra, Biswapriya B. ; de Armas, Evaldo ; Huhman, David V. ; Alborn, Hans T. ; Sumner, Lloyd W. ; Chen, Sixue ( October 2016 , The Plant Journal)

   Foliar stomatal movements are critical for regulating plant water loss and gas exchange. Elevated carbon dioxide (CO₂) levels are known to induce stomatal closure. However, the current knowledge onCO₂signal transduction in stomatal guard cells is limited. Here we report metabolomic responses ofBrassica napusguard cells to elevatedCO₂using three hyphenated metabolomics platforms: gas chromatography‐mass spectrometry (MS); liquid chromatography (LC)‐multiple reaction monitoring‐MS; and ultra‐high‐performanceLC‐quadrupole time‐of‐flight‐MS. A total of 358 metabolites from guard cells were quantified in a time‐course response to elevatedCO₂level. Most metabolites increased under elevatedCO₂, showing the most significant differences at 10 min. In addition, reactive oxygen species production increased and stomatal aperture decreased with time. Major alterations in flavonoid, organic acid, sugar, fatty acid, phenylpropanoid and amino acid metabolic pathways indicated changes in both primary and specialized metabolic pathways in guard cells. Most interestingly, the jasmonic acid (JA) biosynthesis pathway was significantly altered in the course of elevatedCO₂treatment. Together with results obtained fromJAbiosynthesis and signaling mutants as well asCO₂signaling mutants, we discovered thatCO₂‐induced stomatal closure is mediated byJAsignaling.

    

   more » « less
5. Contrasting ecosystem CO 2 fluxes of inland and coastal wetlands: a meta‐analysis of eddy covariance data

   https://doi.org/10.1111/gcb.13424  

   Lu, Weizhi ; Xiao, Jingfeng ; Liu, Fang ; Zhang, Yue ; Liu, Chang'an ; Lin, Guanghui ( August 2016 , Global Change Biology)

   Wetlands play an important role in regulating the atmospheric carbon dioxide (CO₂) concentrations and thus affecting the climate. However, there is still lack of quantitative evaluation of such a role across different wetland types, especially at the global scale. Here, we conducted a meta‐analysis to compare ecosystemCO₂fluxes among various types of wetlands using a global database compiled from the literature. This database consists of 143 site‐years of eddy covariance data from 22 inland wetland and 21 coastal wetland sites across the globe. Coastal wetlands had higher annual gross primary productivity (GPP), ecosystem respiration (R_e), and net ecosystem productivity (NEP) than inland wetlands. On a per unit area basis, coastal wetlands provided largeCO₂sinks, while inland wetlands provided smallCO₂sinks or were nearlyCO₂neutral. The annualCO₂sink strength was 93.15 and 208.37 g C m⁻²for inland and coastal wetlands, respectively. AnnualCO₂fluxes were mainly regulated by mean annual temperature (MAT) and mean annual precipitation (MAP). For coastal and inland wetlands combined,MATandMAPexplained 71%, 54%, and 57% of the variations inGPP,R_e, andNEP, respectively. TheCO₂fluxes of wetlands were also related to leaf area index (LAI). TheCO₂fluxes also varied with water table depth (WTD), although the effects ofWTDwere not statistically significant.NEPwas jointly determined byGPPandR_efor both inland and coastal wetlands. However, theNEP/R_eandNEP/GPPratios exhibited little variability for inland wetlands and decreased for coastal wetlands with increasing latitude. The contrasting ofCO₂fluxes between inland and coastal wetlands globally can improve our understanding of the roles of wetlands in the global C cycle. Our results also have implications for informing wetland management and climate change policymaking, for example, the efforts being made by international organizations and enterprises to restore coastal wetlands for enhancing blue carbon sinks.

    

   more » « less