IU Indianapolis ScholarWorks :: Browsing by Author "Jiao, Wenzhe"

Browsing by Author "Jiao, Wenzhe"

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Assessing variability of optimum air temperature for photosynthesis across site-years, sites and biomes and their effects on photosynthesis estimation
(Elsevier, 2021) Chang, Qing; Xiao, Xiangming; Doughty, Russell; Wu, Xiaocui; Jiao, Wenzhe; Qin, Yuanwei; Earth and Environmental Sciences, School of Science
Gross primary productivity (GPP) of vegetation is affected by air temperature. Biogeochemical models use the optimum air temperature (Topt) parameter, which comes from biome-specific look-up tables (Topt−b−LT). Many studies have shown that plants have the capacity to adapt to changes in environmental conditions over time, which suggests that the static Topt−b−LT parameters in the biogeochemical models may poorly represent actual Topt and induce uncertainty in GPP estimates. Here, we estimated biome-specific, site-year-specific, and site-specific optimum air temperature using GPP data from eddy covariance (EC) flux tower sites (GPPEC) (Topt−b−EC, Topt−sy−EC, Topt−s−EC), the Enhanced Vegetation Index (EVI) from MODIS images (Topt−b−EVI, Topt−sy−EVI, Topt−s−EVI), and mean daytime air temperature (TDT). We evaluated the consistency among the four Topt parameters (Topt−b, Topt−sy, Topt−s and Topt−b−LT), and assessed how they affect satellite-based GPP estimates. We find that Topt parameters from MODIS EVI agree well with those from GPPEC, which indicates that EVI can be used as a variable to estimate Topt at individual pixels over large spatial domains. Topt−b, Topt−sy, and Topt−s differed significantly from Topt−b−LT. GPP estimates using Topt−b and Topt−sy were more consistent with GPPEC than when using Topt−b−LT for all the land cover types. Our use of Topt−sy substantially improved 8-day and annual GPP estimates across biomess (from 1% to 34%), especially for cropland, grassland, and open shrubland. Our simple calculation shows that global GPP estimates differ by up to 10 Pg C/yr when using our suggested Topt−sy−EVI instead of using the static Topt−b−LT. Our new approach on estimating Topt has the potential to improve estimates of GPP from satellite-based models, which could lead to better understanding of carbon-climate interactions.
Comprehensive quantification of the responses of ecosystem production and respiration to drought time scale, intensity and timing in humid environments: A FLUXNET synthesis
(Wiley, 2022-05) Jiao, Wenzhe; Wang, Lixin; Wang, Honglang; Lanning, Matthew; Chang, Qing; Novick, Kimberly A.; Earth Sciences, School of Science
Drought is one of the most important natural hazards impacting ecosystem carbon cycles. However, it is challenging to quantify the impacts of drought on ecosystem carbon balance and several factors hinder our explicit understanding of the complex drought impacts. First, drought impacts can have different time dimensions such as simultaneous, cumulative, and lagged impacts on ecosystem carbon balance. Second, drought is not only a multiscale (e.g., temporal and spatial) but also a multidimensional (e.g., intensity, time-scale, and timing) phenomenon, and ecosystem production and respiration may respond to each drought dimension differently. In this study, we conducted a comprehensive drought impact assessment on ecosystem productivity and respiration in humid regions by including different drought dimensions using global FLUXNET observations. Short-term drought (e.g., 1-month drought) generally did not induce a decrease in plant productivity even under high severity drought. However, ecosystem production and respiration significantly decreased as drought intensity increased for droughts longer than one month in duration. Drought timing was important, and ecosystem productivity was most vulnerable when drought occurred during or shortly after the peak vegetation growth. We found that lagged drought impacts more significantly affected ecosystem carbon uptake than simultaneous drought, and that ecosystem respiration was less sensitive to drought time scale than ecosystem production. Overall, our results indicated that temporally-standardized meteorological drought indices can be used to reflect plant productivity decline, but drought timing, antecedent, and cumulative drought conditions need to be considered together.
Convergent vegetation fog and dew water use in the Namib Desert
(Wiley, 2019) Wang, Lixin; Kaseke, Kudzai Farai; Ravi, Sujith; Jiao, Wenzhe; Mushi, Roland; Shuuya, Titus; Maggs-Kölling, Gillian; Earth Sciences, School of Science
Nonrainfall water inputs (e.g., fog and dew) are the least studied hydrological components in ecohydrology. The importance of nonrainfall waters on vegetation water status in arid ecosystems is receiving increasing attention. However, a clear understanding on how common plant water status benefits from nonrainfall waters, the impacts of different types of fog and dew events on vegetation water status, and the vegetation uptake mechanisms of nonrainfall waters is still lacking. In this study, we used concurrent leaf and soil water potential measurements from 3 years to investigate the species‐specific capacity to utilize moisture from fog and dew within the Namib Desert. Eight common plant species in the Namib Desert were selected. Our results showed that both fog and dew significantly increased soil water potential. Seven of the eight plant species studied responded to fog and dew events, although the magnitude of the response differed. Plants generally showed stronger responses to fog than to dew. Fog timing seemed to be an important factor determining vegetation response; for example, night fog did not affect plant water potential. We also found that Euclea pseudebenus and Faidherbia albida likely exploit fog moisture through foliar uptake. This study provides a first comprehensive assessment of the effects of nonrainfall waters on plant water status within the Namib Desert. Furthermore, this study highlights the importance of concurrent leaf and soil water potential measurements to identify the pathways of nonrainfall water use by desert vegetation. Our results fill a knowledge gap in dryland ecohydrology and have important implications for other drylands.
Dryland productivity under a changing climate
(Springer, 2022-11) Wang, Lixin; Jiao, Wenzhe; MacBean, Natasha; Rulli, Maria Cristina; Manzoni, Stefano; Vico, Giulia; D'Odorico, Paolo; Earth and Environmental Sciences, School of Science
Understanding dryland dynamics is essential to predict future climate trajectories. However, there remains large uncertainty on the extent to which drylands are expanding or greening, the drivers of dryland vegetation shifts, the relative importance of different hydrological processes regulating ecosystem functioning, and the role of land-use changes and climate variability in shaping ecosystem productivity. We review recent advances in the study of dryland productivity and ecosystem function and examine major outstanding debates on dryland responses to environmental changes. We highlight often-neglected uncertainties in the observation and prediction of dryland productivity and elucidate the complexity of dryland dynamics. We suggest prioritizing holistic approaches to dryland management, accounting for the increasing climatic and anthropogenic pressures and the associated uncertainties.
Drylands contribute disproportionately to observed global productivity increases
(Elsevier, 2023-01-30) Wang, Shuai; Fu, Bojie; Wei, Fangli; Piao, Shilong; Maestre, Fernando T.; Wang, Lixin; Jiao, Wenzhe; Liu, Yanxu; Li, Yan; Li, Changjia; Zhao, Wenwu; Earth and Environmental Sciences, School of Science
Drylands cover about 40% of the terrestrial surface and are sensitive to climate change, but their relative contributions to global vegetation greening and productivity increase in recent decades are still poorly known. Here, by integrating satellite data and biosphere modeling, we showed that drylands contributed more to global gross primary productivity (GPP) increase (65% ± 16%) than to Earth greening (33% ± 15%) observed during 1982–2015. The enhanced productivity per unit leaf area, i.e., light-use efficiency (LUE), was the mechanism behind this pattern. We also found that LUE was more sensitive to soil moisture than to atmospheric vapor pressure deficit (VPD) in drylands, while the opposite was observed (i.e., LUE was more sensitive to VPD) in humid areas. Our findings suggest the importance of using different moisture stress metrics in projecting the vegetation productivity changes of dry versus humid regions and highlight the prominent role of drylands as key controllers of the global carbon cycle.
Examining Ecosystem Drought Responses Using Remote Sensing and Flux Tower Observations
(2022-09) Jiao, Wenzhe; Wang, Lixin; Novick, Kimberly A.; Filippelli, Gabriel; Wang, Honglang; Li, Lin
Water is fundamental for plant growth, and vegetation response to water availability influences water, carbon, and energy exchanges between land and atmosphere. Vegetation plays the most active role in water and carbon cycle of various ecosystems. Therefore, comprehensive evaluation of drought impact on vegetation productivity will play a critical role for better understanding the global water cycle under future climate conditions. In-situ meteorological measurements and the eddy covariance flux tower network, which provide meteorological data, and estimates of ecosystem productivity and respiration are remarkable tools to assess the impacts of drought on ecosystem carbon and water cycles. In regions with limited in-situ observations, remote sensing can be a very useful tool to monitor ecosystem drought status since it provides continuous observations of relevant variables linked to ecosystem function and the hydrologic cycle. However, the detailed understanding of ecosystem responses to drought is still lacking and it is challenging to quantify the impacts of drought on ecosystem carbon balance and several factors hinder our explicit understanding of the complex drought impacts. This dissertation addressed drought monitoring, ecosystem drought responses, trends of vegetation water constraint based on in-situ metrological observations, flux tower and multi-sensor remote sensing observations. This dissertation first developed a new integrated drought index applicable across diverse climate regions based on in-situ meteorological observations and multi-sensor remote sensing data, and another integrated drought index applicable across diverse climate regions only based on multi-sensor remote sensing data. The dissertation also evaluated the applicability of new satellite dataset (e.g., solar induced fluorescence, SIF) for responding to meteorological drought. Results show that satellite SIF data could have the potential to reflect meteorological drought, but the application should be limited to dry regions. The work in this dissertation also accessed changes in water constraint on global vegetation productivity, and quantified different drought dimensions on ecosystem productivity and respiration. Results indicate that a significant increase in vegetation water constraint over the last 30 years. The results highlighted the need for a more explicit consideration of the influence of water constraints on regional and global vegetation under a warming climate.
Increased Global Vegetation Productivity Despite Rising Atmospheric Dryness Over the Last Two Decades
(AGU, 2022-07) Song, Yang; Jiao, Wenzhe; Wang, Jing; Wang, Lixin; Earth and Environmental Sciences, School of Science
Rising atmospheric dryness [vapor pressure deficit (VPD)] can limit photosynthesis and thus reduce vegetation productivity. Meanwhile, plants can benefit from global warming and the fertilization effect of carbon dioxide (CO2). There are growing interests to study climate change impacts on terrestrial vegetation. However, global vegetation productivity responses to recent climate and CO2 trends remain to be fully understood. Here, we provide a comprehensive evaluation of the relative impacts of VPD, temperature, and atmospheric CO2 concentration on global vegetation productivity over the last two decades using a robust ensemble of solar-induced chlorophyll fluorescence (SIF) and gross primary productivity (GPP) data. We document a significant increase in global vegetation productivity with rising VPD, temperature, and atmospheric CO2 concentration over this period. For global SIF (or GPP), the decrease due to rising VPD was comparable to the increase due to warming but far less than the increase due to elevated CO2 concentration. We found that rising VPD counteracted only a small proportion (approximately 8.1%–15.0%) of the warming and CO2-induced increase in global SIF (or GPP). Despite the sharp rise in atmospheric dryness imposing a negative impact on plants, the warming and CO2 fertilization effects contributed to a persistent and widespread increase in vegetation productivity over the majority (approximately 66.5%–72.2%) of the globally vegetated areas. Overall, our findings provide a quantitative and comprehensive attribution of rising atmospheric dryness on global vegetation productivity under concurrent climate warming and CO2 increasing.
Investigating the role of evaporation in dew formation under different climates using 17O-excess
(Elsevier, 2021-01) Tian, Chao; Jiao, Wenzhe; Beysens, Daniel; Kaseke, Kudzai Farai; Medici, Marie-Gabrielle; Li, Fadong; Wang, Lixin; Earth Sciences, School of Science
With increasing aridity in many regions, dew is likely to play an increasingly important role in the ecohydrological processes in many ecosystems, especially in arid and semiarid regions. Few studies investigated the role of evaporation during dew formation and how it varies under different climate settings. 17O-excess, as a new tracer, could be used to extract information of evaporation dynamics from natural water samples (e.g., precipitation, river, and lake). Therefore, to fill the knowledge gap in evaporation mechanisms during dew formation, we report the isotopic variation (δ2H, δ18O, δ17O, and 17O-excess) of dew and precipitation from three distinct climatic regions (i.e., Gobabeb in the central Namib Desert, Nice in France with Mediterranean climate, and Indianapolis in the central United States with humid continental climate). We examined whether dew formed in different climate settings was affected by different degree of evaporation using observed isotopic values and evaporation models during the formation processes, and modeled the effects of key meteorological variables (i.e., temperature and relative humidity) on 17O-excess variations. The results showed that dew in Gobabeb experienced kinetic fractionation associated with evaporation under non-steady state conditions during dew formation with enriched δ18O and low 17O-excess values. Dew formations with temperatures over 14.7 °C in Indianapolis were also influenced by evaporation under non-steady state conditions. However, dew formation in Nice did not experience significant evaporation. Evaporation processes (equilibrium or kinetic fractionation) occurring during nights with heavy dew under three climate settings were mainly related to the variation of atmosphere relative humidity. The 17O-excess tracer provides a new method to distinguish the different evaporation processes (equilibrium or kinetic fractionation) during dew formation and our result provides an improved understanding of dew formation.
A modified isotope-based method for potential high-frequency evapotranspiration partitioning
(Elsevier, 2022-02) Yuan, Yusen; Wang, Lixin; Wang, Honglang; Lin, Wenqing; Jiao, Wenzhe; Du, Taisheng; Earth Sciences, School of Science
To better understand water and energy cycles, numerous efforts to partition evapotranspiration (ET) into evaporation (E) and transpiration (T) have been made over the recent half century. One of the analytical methods is the isotopic approach. The isotopic composition of ET (δET) is a crucial parameter in the traditional isotope-based ET partitioning model, which however, has considerable uncertainty and high sensitivity. Here we proposed a modified T fraction in total ET (FT) calculation using Keeling plot slope (k), the atmospheric vapor concentration (Cv), and the isotopic composition of atmospheric vapor (δv), to avoid the direct use of δET. Following the traditional method, we used the Craig-Gordon model for the isotopic composition of evaporation (δE) and chamber method for the isotopic composition of transpiration (δT) in our modified method. The modified FT calculation method (FT (m)) can be applied at a 15-min time scale using the average values (FTi (mp)) and at a 1 Hz time scale for high-frequency method (FTi). The modified method was verified by both theoretical derivations and field observations. FTi (mp) was equivalent to those using the traditional isotopic method at a 15-min time scale. However, FTi eliminated the highly sensitive parameter δET, and redistributed the sensitivity of δET into three less sensitive parameters. Additionally, FTi has two main advantages. First, the high-frequency method avoids the extrapolation of the Keeling plot regression line intercept. Second, the high-frequency method can produce a 95% confidence interval of FT in a measurement cycle (e.g., 15 min). The calculated confidence interval was different from that of traditional uncertainty analysis. The high-frequency method might be useful when investigating evapotranspiration partitioning under short-term extreme weather events and flush agricultural irrigation.
Multi-sensor remote sensing for drought characterization: current status, opportunities and a roadmap for the future
(Elsevier, 2021-04) Jiao, Wenzhe; Wang, Lixin; McCabe, Matthew F.; Earth Sciences, School of Science
Satellite based remote sensing offers one of the few approaches able to monitor the spatial and temporal development of regional to continental scale droughts. A unique element of remote sensing platforms is their multi-sensor capability, which enhances the capacity for characterizing drought from a variety of perspectives. Such aspects include monitoring drought influences on vegetation and hydrological responses, as well as assessing sectoral impacts (e.g., agriculture). With advances in remote sensing systems along with an increasing range of platforms available for analysis, this contribution provides a timely and systematic review of multi-sensor remote sensing drought studies, with a particular focus on drought related datasets, drought related phenomena and mechanisms, and drought modeling. To explore this topic, we first present a comprehensive summary of large-scale remote sensing datasets that can be used for multi-sensor drought studies. We then review the role of multi-sensor remote sensing for exploring key drought related phenomena and mechanisms, including vegetation responses to drought, land-atmospheric feedbacks during drought, drought-induced tree mortality, drought-related ecosystem fires, post-drought recovery and legacy effects, flash drought, as well as drought trends under climate change. A summary of recent modeling advances towards developing integrated multi-sensor remote sensing drought indices is also provided. We conclude that leveraging multi-sensor remote sensing provides unique benefits for regional to global drought studies, particularly in: 1) revealing the complex drought impact mechanisms on ecosystem components; 2) providing continuous long-term drought related information at large scales; 3) presenting real-time drought information with high spatiotemporal resolution; 4) providing multiple lines of evidence of drought monitoring to improve modeling and prediction robustness; and 5) improving the accuracy of drought monitoring and assessment efforts. We specifically highlight that more mechanism-oriented drought studies that leverage a combination of sensors and techniques (e.g., optical, microwave, hyperspectral, LiDAR, and constellations) across a range of spatiotemporal scales are needed in order to progress and advance our understanding, characterization and description of drought in the future.

Browsing by Author "Jiao, Wenzhe"

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