Hysteresis response of daytime net ecosystem CO<sub>2</sub> exchange during a drought

Abstract

Abstract. Continuous measurements of net ecosystem CO2 exchange (NEE) using the eddy-covariance method were made over an agricultural ecosystem in the southeastern US. During optimum environmental conditions, photosynthetically active radiation (PAR) was the primary climatic factor controlling daytime NEE, accounting for 67 to 89% of variations in NEE. However, soil water content (SWC) was the dominant factor limiting the NEE-PAR response during the peak growth stage, as NEE was significantly depressed when PAR exceeding 1300 μmol photons m−2 s−1 coincided with a very low soil water content (SWC<0.04 m3 m−3). Hysteresis was observed between daytime NEE and PAR during periods of water-stress resulting from high vapor pressure deficit (VPD). This is significant since it limits the range of applicability of the Michaelis-Menten equation, and the likes, to determine daytime NEE as a function of PAR. The systematic presence of hysteresis in the response of NEE to PAR suggests that the gap-filling technique based on a non-linear regression approach should take into account the presence of water-limiting field conditions. Including this step is therefore likely to improve current evaluations of ecosystem response to climate change.

Vegetation response to rainfall seasonality and interannual variability in tropical dry forests

“…In particular, the changes in timing and intensity of the wet season may disrupt the conditions amenable to vegetation growth. In turn, this will have potential feedbacks to the hydrological cycle through changes in rates of interception, infiltration, and evapotranspiration, with propagating effects to local agroecosystems (Pingintha et al, 2009;Porporato et al, 2015) and biodiversity (Henneron et al, 2015;Visoiu and Whinam, 2015).…”