Linking diffuse radiation and ecosystem productivity of a desert steppe ecosystem

Abstract

Radiation components have distinct effects on photosynthesis. In the desert steppe ecosystem, the influence of diffuse radiation on carbon fixation has not been thoroughly explored. We examined this diffusion and its effect on ecosystem productivity was examined during the growing season from 2014 to 2015 on the basis of eddy covariance measurements of CO2 exchange in a desert steppe ecosystem in northwest China. Our results indicated that the gross ecosystem production (GEP) and diffuse photosynthetically active radiation (PARdif) peaked when the clearness index (CI) was around 0.5. The maximum canopy photosynthesis (Pmax) under cloudy skies (CI < 0.7) was 23.7% greater than under clear skies (CI ≥ 0.7). When the skies became cloudy in the desert steppe ecosystem, PARdif had a greater effect on GEP. Additionally, lower vapor pressure deficits (VPD ≤ 1 kPa), lower air temperatures (Ta ≤ 20 °C), and non-stressed water conditions (REW ≥ 0.4) were more conducive for enhanced ecosystem photosynthesis under cloudy skies than under clear skies. This may be due to the comprehensive effects of VPD and Ta on stomatal conductance. We concluded that cloudiness can influence diffuse radiation components and that diffuse radiation can increase the ecosystem production of desert steppe ecosystems in northwest China.

Effect of diffuse fraction on gross primary productivity and light use efficiency in a warm-temperate mixed plantation

“…On cloudy days, the enhancement of α and P 1800 in low T a and VPD were higher than in high T a and VPD ( Table 2 ). It is similar to those results that were found in a poplar plantation ( Xu et al., 2017 ) and a desert steppe ( Li et al., 2020 ). Under cloudy sky conditions, low T a and VPD were more conducive to enhancing canopy photosynthesis.…”

“…Other studies, however, indicated that T a and VPD had little effect on regulating the ecosystem photosynthesis response to I f ( Jing et al., 2010 ; Kanniah et al., 2011 ; Oliphant et al., 2011 ). Changes in environmental conditions may affect GPP response to I f of forest and grassland ecosystems ( Xu et al., 2017 ; Li et al., 2020 ). The coupling between DF and environmental factors will have complex effect on ecosystem photosynthesis ( Kanniah et al., 2013 ; Gui et al., 2021 ).…”

Impact of sky conditions on net ecosystem productivity of a “floating blanket” wetland in southwest China

“…The light response curves under different sky conditions showed similar trends, and the curves under overcast conditions increased more steeply with PARt. This result was consistent with previous research (Li et al, 2020;Oliphant et al, 2011;Williams et al, 2014). The response of photosynthesis to sky conditions varied across seasons (Table 1).…”

“…where PARd and PARb was the diffuse and the direct photosynthetically active radiation (μmol m -2 s -1 ), respectively. In most previous studies, sky conditions were only classified as clear or cloudy conditions (Alton, 2008;Li et al, 2020;Xu et al, 2017), and the difference in NEP between cloudy and overcast conditions had not been determined. In this study, we divided sky conditions using daily average CI into sunny (0.6 ≤ CI < 1), cloudy (0.2 ≤ CI < 0.6) and overcast (0 < CI < 0.2) conditions according to Reindl et al, (1990).…”

“…The effects of sky conditions on the canopy photosynthetic characteristics and productivity have been conducted in different ecosystems, including forests (Dengel and Grace, 2010;Gu et al, 1999;Xu et al, 2017), grasslands (Bai et al, 2012;Li et al, 2020;Wang et al, 2016b), crops (Pearman and Garratt, 2022;Wang et al, 2008), and peatlands (Goodrich et al, 2015;Letts and Lafleur, 2005). Although many studies have been conducted to investigate the canopy photosynthetic characteristics under different sky conditions, there is still no consensus regarding the effects of sky conditions on ecosystem productivity and carbon sequestration capacity.…”