Exploring SMAP and OCO-2 observations to monitor soil moisture control on photosynthetic activity of global drylands and croplands

Gonsamo, Alemu; Chen, Jing M.; He, Li; Sun, Ying; Rogers, Cheryl; Liu, Jane

doi:10.1016/j.rse.2019.111314

Cited by 26 publications

(18 citation statements)

References 60 publications

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“…Satellite observations of SM in drylands capture both instantaneous and antecedent precipitation inputs because a large fraction of precipitation remains in the surface SM for many days (McColl et al, 2017). Since vegetation density and soil water contents are low in drylands, both satellite‐based SM and LAI estimates have high retrieval accuracy (Gonsamo et al, 2019).…”

Section: Methodsmentioning

confidence: 99%

“…Since vegetation density and soil water contents are low in drylands, both satellite-based SM and LAI estimates have high retrieval accuracy (Gonsamo et al, 2019).…”

Section: Satellite Sm Datamentioning

confidence: 99%

“…Satellite greenness records capture both structural (i.e., leaf area index, LAI) and biochemical (e.g., foliage chlorophyll content) attributes that can be used as indicators of plant cover and growth. Since vegetation density and soil water content are relatively low in drylands, satellite observations of both SM and vegetation activity have high retrieval accuracy (Gonsamo et al, 2019). The satellite observations show persistent greening of drylands since the 1980s (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

“…Since vegetation density and soil water content are relatively low in drylands, satellite observations of both SM and vegetation activity have high retrieval accuracy (Gonsamo et al, 2019). The satellite observations show persistent greening of drylands since the 1980s (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Greening drylands despite warming consistent with carbon dioxide fertilization effect

Gonsamo

Ciais

Miralles

et al. 2021

Global Change Biology

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The rising atmospheric CO2 concentration leads to a CO2 fertilization effect on plants—that is, increased photosynthetic uptake of CO2 by leaves and enhanced water‐use efficiency (WUE). Yet, the resulting net impact of CO2 fertilization on plant growth and soil moisture (SM) savings at large scale is poorly understood. Drylands provide a natural experimental setting to detect the CO2 fertilization effect on plant growth since foliage amount, plant water‐use and photosynthesis are all tightly coupled in water‐limited ecosystems. A long‐term change in the response of leaf area index (LAI, a measure of foliage amount) to changes in SM is likely to stem from changing water demand of primary productivity in water‐limited ecosystems and is a proxy for changes in WUE. Using 34‐year satellite observations of LAI and SM over tropical and subtropical drylands, we identify that a 1% increment in SM leads to 0.15% (±0.008, 95% confidence interval) and 0.51% (±0.01, 95% confidence interval) increments in LAI during 1982‒1998 and 1999‒2015, respectively. The increasing response of LAI to SM has contributed 7.2% (±3.0%, 95% confidence interval) to total dryland greening during 1999‒2015 compared to 1982‒1998. The increasing response of LAI to SM is consistent with the CO2 fertilization effect on WUE in water‐limited ecosystems, indicating that a given amount of SM has sustained greater amounts of photosynthetic foliage over time. The LAI responses to changes in SM from seven dynamic global vegetation models are not always consistent with observations, highlighting the need for improved process knowledge of terrestrial ecosystem responses to rising atmospheric CO2 concentration.

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Section: Methodsmentioning

confidence: 99%

“…Since vegetation density and soil water contents are low in drylands, both satellite-based SM and LAI estimates have high retrieval accuracy (Gonsamo et al, 2019).…”

Section: Satellite Sm Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Greening drylands despite warming consistent with carbon dioxide fertilization effect

Gonsamo

Ciais

Miralles

et al. 2021

Global Change Biology

Self Cite

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show abstract

“…While microwave measurements are sensitive to the water in the top 5-10 centimeters of the soil profile, it has been shown that SM estimates averaged over several days are both physically and statistically correlated to deeper root zone soil moisture (Short Gianotti et al, 2019b;Akbar et al, 2018b). Studies investigating global drivers of photosynthesis tend to focus on linear relationships between these variables, which potentially neglects nonlinear conditions where photosynthesis is not-limited (Gonsamo et al, 2019;Teubner 90 et al, 2018). For example, the light use efficiency (LUE) model is widely used in Earth system modeling to simulate GPP as a linear function of absorbed light (Monteith, 1972).…”

mentioning

confidence: 99%

Observed Water- and Light-Limitation Across Global Ecosystems

Jonard

Feldman

Gianotti

et al. 2022

Preprint

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Abstract. With a changing climate, it is becoming increasingly critical to understand vegetation responses to limiting environmental factors. Here, we investigate the spatial and temporal patterns of light and water limitation on photosynthesis using an observational framework. Our study is unique in characterizing the nonlinear relationships between photosynthesis and water and light, acknowledging approximately two regime behavior (no limitation and varying degree of limitation). It is also unique in using an observational framework instead of using model-derived photosynthesis properties. We combine data from three different satellite sensors, i.e., solar-induced chlorophyll fluorescence (SIF) from TROPOMI, surface soil moisture from SMAP, and above-ground canopy density from MODIS. We find both single-regime and two-regime models describe SIF sensitivity to soil moisture and photosynthetically active radiation (PAR) across the globe. The distribution and strength of soil moisture limitation on SIF are mapped in the water-limited environments while distribution and strength of PAR limitations are mapped in the energy-limited environments. Two-regime behavior is detected in 73 % of the cases for water limitation on photosynthesis, while two-regime detection is much lower at 36 % for light limitation on photosynthesis. SIF sensitivity to PAR strongly increases along moisture gradients, reflecting mesic vegetation’s adaptation to making rapid usage of incoming light availability on the weekly timescales. The transition point detected between the two regimes is connected to soil type and mean annual precipitation for the SIF-soil moisture relationship and for the SIF-PAR relationship. These thresholds have therefore an explicit relation to properties of the landscape, although they may also be related to finer details of the vegetation and soil interactions not resolved by the spatial scales here. The simple functions and thresholds are emergent behaviors capturing the interaction of many processes. The observational thresholds and strength of coupling can be used as benchmark information for land surface and Earth system models, especially those that characterize gross primary production mechanisms and vegetation dynamics.

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Threshold of vapour–pressure deficit constraint on light use efficiency varied with soil water content

Gao

Wang

et al. 2021

Ecohydrology

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Understanding the constraints on light-use efficiency (LUE) induced by high evaporative water demand (vapour-pressure deficit; VPD) and soil water stress (soil moisture content; SMC) is crucial for understanding and simulating vegetation productivity, particularly in the arid and semi-arid regions. However, the relative impacts of VPD and SMC on LUE are unclear, as we lack a mechanistic understanding of impacts and their interactions. In this study, we quantified the relative roles of VPD and SMC in limiting LUE and analysed the interactions among VPD, SMC and LUE using data from CO 2 and water flux stations and weather stations along a climatic gradient in the Heihe River Basin, China. We found a threshold of VPD constraint on LUE; above the threshold, LUE decreased at only 3.6% to 23.1% of the rate below the threshold. As SMC decreased, however, the VPD threshold increased, and the reduction of LUE caused by VPD decreased significantly, which is more than half of that in moister regions. Therefore, both VPD and SMC played essential roles in LUE limitation caused by water stress. A threshold also existed for heat flux and the correlation between SMC and LUE; the strength of the correlation first decreased and then increased with increasing VPD. Our results clarified the relative impacts of VPD and SMC on LUE, and can improve simulation and prediction of plant productivity.

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Exploring SMAP and OCO-2 observations to monitor soil moisture control on photosynthetic activity of global drylands and croplands

Cited by 26 publications

References 60 publications

Greening drylands despite warming consistent with carbon dioxide fertilization effect

Greening drylands despite warming consistent with carbon dioxide fertilization effect

Observed Water- and Light-Limitation Across Global Ecosystems

Threshold of vapour–pressure deficit constraint on light use efficiency varied with soil water content

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