Abstract
Abstract. Nitrogen and water availability alter canopy structure and physiology, and thus crop growth, yielding large impacts on ecosystem-regulating/production provisions. However, to date, explicitly quantifying such impacts remains challenging partially due to lack of adequate methodology to capture spatial dimensions of ecosystem changes associated with nitrogen and water effects. A data fitting, where close-range remote-sensing measurements of vegetation indices derived from a handheld instrument and an unmanned aerial vehicle (UAV) system are linked to in situ leaf and canopy photosynthetic traits, was applied to capture and interpret inter- and intra-field variations in gross primary productivity (GPP) in lowland rice grown under flooded conditions (paddy rice, PD) subject to three nitrogen application rates and under rainfed conditions (RF) in an East Asian monsoon region of South Korea. Spatial variations (SVs) in both GPP and light use efficiency (LUEcabs) early in the growing season were enlarged by nitrogen addition. The nutritional effects narrowed over time. A shift in planting culture from flooded to rainfed conditions strengthened SVs in GPP and LUEcabs. Intervention of prolonged drought late in the growing season dramatically intensified SVs that were supposed to seasonally decrease. Nevertheless, nitrogen addition effects on SV of LUEcabs at the early growth stage made PD fields exert greater SVs than RF fields. SVs of GPP across PD and RF rice fields were likely related to leaf area index (LAI) development less than to LUEcabs, while numerical analysis suggested that considering strength in LUEcabs and its spatial variation for the same crop type tends to be vital for better evaluation in landscape/regional patterns of ecosystem photosynthetic productivity at critical phenology stages.
Highlights
Agricultural landscape in most Asia monsoon regions is featured by multicultural cropping systems comprising relatively small land holdings under 2 ha (Devendra, 2007)
The rainfed conditions (RF) rice remained green around DOY 240 with approximately 23 % higher leaf area index (LAI) when plants in the paddy rice (PD) field started senescence (Fig. 2b), which resulted in a relatively higher at-surface normalized difference vegetation index (NDVI) that was captured by field images of NDVI derived from the unmanned aerial vehicle (UAV) system
LAI in the RF rice ranged between the PD low-nutrient and fertilization groups, while it remained higher on DOY 240
Summary
Agricultural landscape in most Asia monsoon regions is featured by multicultural cropping systems comprising relatively small land holdings under 2 ha (Devendra, 2007). Changes in phenology of those crop ecosystems, where rice makes up a larger portion and exerts a rapid completion of the life cycle in a short period of time with marked changes in canopy dynamics, are of significant importance in regional controls of carbon balance and biogeochemical processes (Kwon et al, 2010; Lindner et al, 2015; Xue et al, 2017) and tend to be one of the drivers causing seasonal fluctuations of atmospheric CO2 concentration in the Northern Hemisphere (Forkel et al, 2016) To better understand their ecological implications under current climate and environmental changes, one of the main concerns lies in the spatiotemporal aspects of ecosystem photosynthetic productivity in the staple crop that is subject to different methods of field management and anthropogenic interventions, and underlying physiological mechanisms that are responsible for such spatiotemporal dimensions. Multi-pragmatic solutions are suggested to develop spatial/temporal data fusions that integrate spatially hierarchical remote-sensing networks and in situ ground surface observations (Lausch et al, 2016; Pause et al, 2016), aiming to better monitor canopy dynamics and environmental impacts on them
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