*Article* **WUE and CO2 Estimations by Eddy Covariance and Remote Sensing in Different Tropical Biomes**

**Gabriel B. Costa 1,2,3,\*, Cláudio M. Santos e Silva 2,4, Keila R. Mendes 4, José G. M. dos Santos 5, Theomar T. A. T. Neves 6, Alex S. Silva 6, Thiago R. Rodrigues 7, Jonh B. Silva 8, Higo J. Dalmagro 9, Pedro R. Mutti 2,4, Hildo G. G. C. Nunes 10, Lucas V. Peres 6, Raoni A. S. Santana 6, Losany B. Viana 6, Gabriele V. Almeida 6, Bergson G. Bezerra 2,4, Thiago V. Marques 11, Rosaria R. Ferreira 4, Cristiano P. Oliveira 2,4, Weber A. Gonçalves 2,4, Suany Campos 2 and Maria U. G. Andrade 2**

	- losany.viana@discente.ufopa.edu.br (L.B.V.); gabriele.almeida@discente.ufopa.edu.br (G.V.A.) Laboratório de Ciências Atmosféricas, Universidade Federal de Mato Grosso Do Sul, Grande
	- Campo 79070-900, Brazil; thiago.r.rodrigues@ufms.br Programa de Pós-Graduação em Física Ambiental, Instituto de Física, Universidade Federal de Mato Grosso, Cuiabá 78060-900, Brazil; jonh\_billy@fisica.ufmt.br

**Abstract:** The analysis of gross primary production (GPP) is crucial to better understand CO2 exchanges between terrestrial ecosystems and the atmosphere, while the quantification of water-use efficiency (WUE) allows for the estimation of the compensation between carbon gained and water lost by the ecosystem. Understanding these dynamics is essential to better comprehend the responses of environments to ongoing climatic changes. The objective of the present study was to analyze, through AMERIFLUX and LBA network measurements, the variability of GPP and WUE in four distinct tropical biomes in Brazil: Pantanal, Amazonia, Caatinga and Cerrado (savanna). Furthermore, data measured by eddy covariance systems were used to assess remotely sensed GPP products (MOD17). We found a distinct seasonality of meteorological variables and energy fluxes with different latent heat controls regarding available energy in each site. Remotely sensed GPP was satisfactorily related with observed data, despite weak correlations in interannual estimates and consistent overestimations and underestimations during certain months. WUE was strongly dependent on water availability, with values of 0.95 gC kg−<sup>1</sup> H2O (5.79 gC kg−<sup>1</sup> H2O) in the wetter (drier) sites. These values reveal new thresholds that had not been previously reported in the literature. Our findings have crucial implications for ecosystem managemen<sup>t</sup> and the design of climate policies regarding the conservation

**Citation:** Costa, G.B.; Santos e Silva, C.M.; Mendes, K.R.; dos Santos, J.G.M.; Neves, T.T.A.T.; Silva, A.S.; Rodrigues, T.R.; Silva, J.B.; Dalmagro, H.J.; Mutti, P.R.; et al. WUE and CO2 Estimations by Eddy Covariance and Remote Sensing in Different Tropical Biomes. *Remote Sens.* **2022**, *14*, 3241. https://doi.org/10.3390/rs14143241

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**\*** Academic Editors: Xiaolin Zhu, Xuanlong Ma, Jiaxin Jin, Yuke Zhou and Qiaoyun Xie

Received: 30 May 2022 Accepted: 23 June 2022 Published: 6 July 2022

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of tropical biomes, since WUE is expected to change in the ongoing climate change scenario that indicates an increase in frequency and severity of dry periods.

**Keywords:** gross primary production; evapotranspiration; water use efficiency
