•Differences in forest seasonal productivity cannot be explained by access to water or sunlight.•Equatorial climates benefit species that support high levels of dry-season photosynthesis.•PAR levels ...predicted the degree to which canopy photosynthetic capacity drives GEP.•Converted sites at Central Amazon show the disruption of the productivity cycle.
We investigated the seasonal patterns of Amazonian forest photosynthetic activity, and the effects thereon of variations in climate and land-use, by integrating data from a network of ground-based eddy flux towers in Brazil established as part of the ‘Large-Scale Biosphere Atmosphere Experiment in Amazonia’ project. We found that degree of water limitation, as indicated by the seasonality of the ratio of sensible to latent heat flux (Bowen ratio) predicts seasonal patterns of photosynthesis. In equatorial Amazonian forests (5° N–5° S), water limitation is absent, and photosynthetic fluxes (or gross ecosystem productivity, GEP) exhibit high or increasing levels of photosynthetic activity as the dry season progresses, likely a consequence of allocation to growth of new leaves. In contrast, forests along the southern flank of the Amazon, pastures converted from forest, and mixed forest-grass savanna, exhibit dry-season declines in GEP, consistent with increasing degrees of water limitation. Although previous work showed tropical ecosystem evapotranspiration (ET) is driven by incoming radiation, GEP observations reported here surprisingly show no or negative relationships with photosynthetically active radiation (PAR). Instead, GEP fluxes largely followed the phenology of canopy photosynthetic capacity (Pc), with only deviations from this primary pattern driven by variations in PAR. Estimates of leaf flush at three non-water limited equatorial forest sites peak in the dry season, in correlation with high dry season light levels. The higher photosynthetic capacity that follows persists into the wet season, driving high GEP that is out of phase with sunlight, explaining the negative observed relationship with sunlight. Overall, these patterns suggest that at sites where water is not limiting, light interacts with adaptive mechanisms to determine photosynthetic capacity indirectly through leaf flush and litterfall seasonality. These mechanisms are poorly represented in ecosystem models, and represent an important challenge to efforts to predict tropical forest responses to climatic variations.
Sugarcane croplands account for ~70% of global sugar production and ~60% of global ethanol production. Monitoring and predicting gross primary production (GPP) and transpiration (T) in these fields ...is crucial to improve crop yield estimation and management. While moderate-spatial-resolution (MSR, hundreds of meters) satellite images have been employed in several models to estimate GPP and T, the potential of high-spatial-resolution (HSR, tens of meters) imagery has been considered in only a few publications, and it is underexplored in sugarcane fields. Our study evaluated the efficacy of MSR and HSR satellite images in predicting daily GPP and T for sugarcane plantations at two sites equipped with eddy flux towers: Louisiana, USA (subtropical climate) and Sao Paulo, Brazil (tropical climate). We employed the Vegetation Photosynthesis Model (VPM) and Vegetation Transpiration Model (VTM) with C4 photosynthesis pathway, integrating vegetation index data derived from satellite images and on-ground weather data, to calculate daily GPP and T. The seasonal dynamics of vegetation indices from both MSR images (MODIS sensor, 500 m) and HSR images (Landsat, 30 m; Sentinel-2, 10 m) tracked well with the GPP seasonality from the EC flux towers. The enhanced vegetation index (EVI) from the HSR images had a stronger correlation with the tower-based GPP. Our findings underscored the potential of HSR imagery for estimating GPP and T in smaller sugarcane plantations.
The eddy covariance method was used to measure energy and water balance of a plantation of
Eucalyptus (
grandis
×
urophylla) hybrids over a 2
year period. The average daily evaporation rates were 5.4 ...(±2.0) mm
day
−1 in summer, but fell to 1.2 (±0.3) mm
day
−1 in winter. In contrast, the sensible heat flux was relatively low in summer but dominated the energy balance in winter. Evaporation accounted for 80% and 26% of the available energy, in summer and winter respectively. The annual evaporation was 82% (1124
mm) and 96% (1235
mm) of the annual rainfall recorded during the first and second year, respectively. Daily average canopy and aerodynamic conductance to water vapour were in the summer 51.9 (±38.4) mm
s
−1 and 84.1 (±25.6) mm
s
−1, respectively; and in the winter 6.0 (±10.5) mm
s
−1 and 111.6 (±24.6) mm
s
−1, respectively.
The Brazilian Cerrado biome is known for its high biodiversity, and the role of groundwater recharge and climate regulation. Anthropogenic influence has harmed the biome, emphasizing the need for ...science to understand its response to climate and reconcile economic exploration with preservation. Our work aimed to evaluate the seasonal and interannual variability of the surface energy balance in a woodland savanna (Cerrado) ecosystem in southeastern Brazil over a period of 19 years, from 2001 to 2019. Using field micrometeorological measurements, we examined the variation in soil moisture and studied its impact on the temporal pattern of energy fluxes to distinguish the effects during rainy years compared to a severe drought spell. The soil moisture measures used two independent instruments, cosmic ray neutron sensor CRNS, and FDR at different depths. The measures were taken at the Pé de Gigante (PEG) site, in a region of well-defined seasonality with the dry season in winter and a hot/humid season in summer. We gap-filled the energy flux measurements with a calibrated biophysical model (SiB2). The long-term averages for air temperature and precipitation were 22.5 °C and 1309 mm/year, respectively. The net radiation (Rn) was 142 W/m2, the evapotranspiration (ET) and sensible heat flux (H) were 3.4 mm/d and 52 W/m2, respectively. Soil moisture was marked by a pronounced negative anomaly in the 2014 year, which caused an increase in the Bowen ratio and a decrease in Evaporative fraction, that lasted until the following year 2015 during the dry season, despite the severe meteorological drought of 2013/2014 already ending, which was corroborated by the two independent measurements. The results showed the remarkable influence of precipitation and soil moisture on the interannual variability of the energy balance in this Cerrado ecosystem, aiding in understanding how it responds to strong climate disturbances.
•Seasonal variability of CO2 fluxes in a sugarcane perennial bioenergy crop.•Net carbon balance was measured during two climatically contrasting years.•The dependence of CO2 exchange from light and ...saturation deficits.•Water use efficiency during the main growth phases of a sugarcane bioenergy system.
Fluxes of CO2 were measured above a sugarcane plantation using the eddy-covariance method covering two growth cycles, representing the second and third re-growth (ratoons) harvested with stubble burning. The total net ecosystem exchange (NEE) in the first cycle (second ratoon, 393 days long) was −1964±44gCm−2; the gross ecosystem productivity (GEP) was 3612±46gCm−2 and the ecosystem respiration (RE) was 1648±14gCm−2. The NEE and GEP totals in the second cycle (third ratoon, 374 days long) decreased 51% and 25%, respectively and RE increased 7%. Accounting for the carbon emitted during biomass burning and the removal of stalks at harvest, net ecosystem carbon balance (NECB) totals were 102±130gCm−2 and 403±84gCm−2 in each cycle respectively. Thus the sugarcane agrosystem was approximately carbon neutral in the second ratoon. Yield in stalks fresh weight (SFW) attained the regional average (8.3kgSFWm−2). Although it was a carbon source to the atmosphere, observed productivity (6.2kgSFWm−2) of the third ratoon was 19% lower than the regional average due to the lower water availability observed during the initial 120 days of re-growth. However, the overall water use efficiency (WUE) achieved in the first cycle (4.3gCkg−1H2O) decreased only 5% in the second cycle.
Eddy-covariance measurements of net ecosystem exchange of CO₂ (NEE) and estimates of gross ecosystem productivity (GEP) and ecosystem respiration (R E) were obtained in a 2-4 year old Eucalyptus ...plantation during two years with very different winter rainfall. In the first (drier) year the annual NEE, GEP and R E were lower than the sums in the second (normal) year, and conversely the total respiratory costs of assimilated carbon were higher in the dry year than in the normal year. Although the net primary production (NPP) in the first year was 23% lower than that of the second year, the decrease in the carbon use efficiency (CUE=NPP/GEP) was 11% and autotrophic respiration utilized more resources in the first, dry year than in the second, normal year. The time variations in NEE were followed by NPP, because in these young Eucalyptus plantations NEE is very largely dominated by NPP, and heterotrophic respiration plays only a relatively minor role. During the dry season a pronounced hysteresis was observed in the relationship between NEE and photosynthetically active radiation, and NEE fluxes were inversely proportional to humidity saturation deficit values greater than 0.8kPa. Nighttime fluxes of CO₂ during calm conditions when the friction velocity (u *) was below the threshold (0.25ms⁻¹) were estimated based on a Q ₁₀ temperature-dependence relationship adjusted separately for different classes of soil moisture content, which regulated the temperature sensitivity of ecosystem respiration.
Sugarcane (complex hybrids of Saccharum spp., C4 plant) croplands provide cane stalk feedstock for sugar and biofuel (ethanol) production. It is critical for us to analyze the phenology and gross ...primary production (GPP) of sugarcane croplands, which would help us to better understand and monitor the sugarcane growing condition and the carbon cycle. In this study, we combined the data from two sugarcane EC flux tower sites in Brazil and the USA, images from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, and data-driven models to study the phenology and GPP of sugarcane croplands. The seasonal dynamics of climate, vegetation indices from MODIS images, and GPP from two sugarcane flux tower sites (GPPEC) reveal the temporal consistency in sugarcane phenology (crop calendar: green-up dates and harvesting dates) as estimated by the vegetation indices and GPPEC data. The Land Surface Water Index (LSWI) is shown to be useful to delineate the phenology of sugarcane croplands. The relationship between the sugarcane GPPEC and the Enhanced Vegetation Index (EVI) is stronger than the relationship between the GPPEC and the Normalized Difference Vegetation Index (NDVI). We ran the Vegetation Photosynthesis Model (VPM), which uses the light use efficiency (LUE) concept and is driven by climate data and MODIS images, to estimate the daily GPP at the two sugarcane sites (GPPVPM). The seasonal dynamics of the GPPVPM and GPPEC at the two sites agreed reasonably well with each other, which indicates that VPM is a powerful tool for estimating the GPP of sugarcane croplands in Brazil and the USA. This study clearly highlights the potential of combining eddy covariance technology, satellite-based remote sensing technology, and data-driven models for better understanding and monitoring the phenology and GPP of sugarcane croplands under different climate and management practices.
Water use in a sugarcane plantation Cabral, Osvaldo M. R.; Rocha, Humberto R.; Gash, John H. ...
Global change biology. Bioenergy,
September 2012, Letnik:
4, Številka:
5
Journal Article
Odprti dostop
The evapotranspiration (E) from a sugarcane plantation in the southeast Brazil was measured by the eddy‐covariance method during two consecutive cycles. These represented the second (393 days) and ...third year (374 days) re‐growth (ratoon). The total E in the first cycle was 829 mm, accounting for 69% of rainfall, whereas in the second cycle, it was 690 mm, despite the total rainfall (1353 mm) being 13% greater. The ratio of E to available energy, the evaporative fraction, exhibited a smaller variation between the first and second cycles: 0.58 and 0.51, respectively. The estimated interception losses were 88 and 90 mm, respectively, accounting for approximately 7% of the total rainfall. The sugarcane yield in the second cycle (61.5 ± 4.0 t ha−1) was 26% lower than the first cycle, as well as lower than the regional average for the third ratoon (76 t ha−1). The below average yield was associated with less available soil water at the beginning of the cycle, with the amount of rainfall recorded during the first 120 days of re‐growth in the second cycle being 16% of that recorded in the first (203 mm).
•This sugarcane agro-system was a carbon sink.•The NEE of CO2 fluxes (assimilation versus respiration) dominated the balances.•The N2O and CH4 emitted totals were offset by the C gain.
The ...sustainability of sugarcane farming for biofuel has recently become a subject of debate, because its expansion may contribute significantly to global climate change mitigation. Here we report greenhouse gases (GHG) fluxes, measured by the eddy covariance method, from a commercial scale rain-fed sugarcane plantation representative of the leading bioethanol production area in southeast Brazil. The measurements covered two harvests, during which the field received nitrogen fertilization and trash was not removed.
The cumulative fluxes for nitrous oxide (N2O) (62.4 ± 1.3 and 52.3 ± 1.8 g N2OCO2 eq. m−2 for the first and second years, respectively) and methane (CH4) (12.1 ± 1.7 and 10.4 ± 2.3 g CH4CO2 eq. m−2 for the first and second years, respectively) were minor sources to the atmosphere in comparison with the net ecosystem exchange (NEE) of carbon dioxide (CO2), whose sink dominated the balances (−7643. ± 129. and -4615. ± 124. g CO2 m−2 for the first and second years, respectively). Compared to the first year, the observed NEE in the second year decreased by 40%, as it covered the first re-growth from the stubble (ratoon) and exhibited a shorter growth cycle than the first year (304 versus 390 days). The second year also included the partial decomposition of the trash remaining on the soil after the first harvest (1581 ± 301 g CO2 m−2).
The net ecosystem carbon balances (NECB), obtained as the cumulative fluxes of GHGs and the stalk dry biomass removed in the harvests (4923 ± 459 and 3929 ± 352 g CO2 m−2 for the first and second years, respectively) were -2646 ± 459 and -623 ± 352 g CO2 m−2 for the first and second years, respectively. Although the yields in stalk fresh weight (SFW) were representative of the region (9.9 and 8.2 kg SFW m−2, in the first and second year respectively) other factors caused a decrease of 76% in NECB, stressing the importance of the CO2 balance (assimilation versus respiration). Nevertheless, this sugarcane agro-system was an overall carbon sink with the N2O and CH4 emitted totals being offset by the net carbon gain.
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•Seasonal variability of evapotranspiration in a woodland savanna.•The dependence of bulk canopy conductance on saturation deficits.•Annual evapotranspiration was constant during three climatically ...contrasting years.•Soil profile and groundwater recharge was significantly increased in the wetter year.
The area of woodland savanna (cerrado) is located in southeast Brazil (21°36′ to 44′S, 47°34′ to 41′W).
The cerrado sensu-stricto savanna evapotranspiration was observed using the eddy-covariance method over three years.
The first year total rainfall (R=1664mm) was 11% above the long-term rainfall (1498mm) and the total evapotranspiration (ET=1242mm) and water equivalent of available energy (Av=1835mm) were approximately 4% and 2% greater, respectively, than in the second year when the rainfall total was 5% lower than the long-term average. In the third year despite the total rainfall (1259mm) being 24% lower than the first year and 16% lower than the average, the totals of ET (1242mm) and Av (1815mm) were approximately the same.
The small variation in the observed annual ET totals shows that in this cerrado vegetation the deep soil moisture content supports the ET in a dry year and the water available for recharging the soil profile and groundwater (∼R−ET) was dominated by the rainfall amount being significantly greater in the wet year (422mm) than in the dry year (13mm).
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