Cloudiness regulates gross primary productivity of a poplar plantation under different environmental conditions

Abstract

Cloud cover regulates the gross primary productivity (GPP) of forest ecosystems by changing the radiation component and other environmental factors. In this study, we used an open-path eddy covariance system and microclimate sensors installed over a poplar plantation in northern China to measure the carbon exchange and climate variables during the mid-growing seasons (June to August) in 2014 and 2015. The results indicated that the GPP of the plantation peaked when the clearness index (CI) was between 0.45 and 0.65, at which point diffuse photosynthetically active radiation (PARdif) had reached its maximum. Cloudy skies increased the maximum ecosystem photosynthetic capacity (Pmax) by 28% compared with clear skies. PARdif and soil moisture were the most and the least crucial drivers for photosynthetic productivity of the plantation under cloudy skies, respectively. The ecosystem photosynthetic potential was higher under lower vapor pressure deficit (VPD < 1.5 kPa), lower air temperature (Ta < 30 °C), and nonstressed conditions (REW > 0.4) for cloudy skies due to effects of Ta and VPD on stoma. Overall, our research highlighted the importance of cloud-induced radiation component change and environmental variation in quantifying the GPP of forest ecosystems.

Modeling net CO2 assimilation (AN) within the crown of young planted Larix olgensis trees

“…8), presumably because the leaves in the upper crown are exposed to environmental stresses more frequently and because the variations in VPD in the upper crown are more sensitive and larger (Han et al 2003). Xu et al (2017) LMA has been positively related to A max (Bond et al 1999, Kenzo et al 2006, Meinzer et al 2008, Sperlich et al 2015, which was also observed in the present study (Fig. 4c).…”

Canopy photosynthetic capacity drives contrasting age dynamics of resource use efficiencies between mature temperate evergreen and deciduous forests

“…The response of photosynthetic productivity to PAR is commonly modeled by the Michaelis–Menten or Mitscherlich equation (Aubinet et al., 2012). We used the rectangle hyperbola equation, known as the Michaelis–Menten photosynthetic response model, to simulate the process of canopy‐level photosynthesis and estimate P max due to its widespread use in ecosystem‐scale studies (Cabral et al., 2011; Xu, Zhang, Chen, Zhu, & Kang, 2017; Zhou et al., 2013) as follows:where α is the apparent quantum yield (μmol·CO 2 /μmol PAR) and P max is the ecosystem maximum photosynthetic capacity at the light‐saturated conditions (μmol m −2 s −1 ). Only daytime (i.e., PAR > 4 μmol m –2 s –1 ) half‐hourly data were used to fit the model, and the growing season P max during the study period was considered constant at each site (Kljun et al., 2007).…”

“…We used the rectangle hyperbola equation, known as the Michaelis-Menten photosynthetic response model, to simulate the process of canopy-level photosynthesis and estimate P max due to its widespread use in ecosystem-scale studies (Cabral et al, 2011;Xu, Zhang, Chen, Zhu, & Kang, 2017;Zhou et al, 2013) as follows:…”

Water Use, Efficiency, and Stomatal Sensitivity in Eastern Cottonwood and Hybrid Poplar Varietals on Contrasting Sites in the Southeastern United States

“…We also found that canopy G S peaked at lower PPFD levels at high soil moistures compared with lower soil moistures at the Coastal Plain site whereas the opposite was true at the LMAV site. We expected that, at lower soil moistures, canopy G S would peak at lower PPFD values, however, the opposite findings at the Coastal Plain site could suggest other interacting factors between environmental parameters are causing lower peak PPFD values at high soil moistures (Xu et al, 2017). Overall, these findings can aid in modeling of water use in these Populus varietals under the interacting environmental drivers of soil moisture, VPD and incoming radiation.…”