A spatially hierarchical integration of close-range remote sensing, leaf structure and physiology assists in diagnosing spatiotemporal dimensions of field-scale ecosystem photosynthetic productivity

- A spatially hierarchical integration (PIXCAN) links UAV remote sensing and at-surface measurements.
- Spatiotemporal variations of per-field photosynthetic productivity were captured and interpreted.
- Occurrence of prolonged non-rainfall period led to severe constraints of GPPmax and significantly strengthened SV.
- Drought-stressed ecosystem GPPmax primarily due to constrained light-harvesting efficiency and less to stomatal conductance.
- Ecological implications of the integration in spatially hierarchical observation of ecosystem GPP.

There are great variations of inter-annual ecosystem photosynthetic productivity (GPP) in rice agricultural mosaic landscapes in Asian monsoon regions, consisting of relatively small land holdings. It is therefore of great importance to capture and interpret spatiotemporal aspects of per-field GPP. This goal, however, remains challenging partially due to absence of adequate methodology that applies ecophysiological data to broader spatial and temporal dimensions to explicitly quantify influences of environment change on per-field GPP. To accomplish the goal, field experiments were carried out at spatially adjacent flooding paddy (PD) and rainfed (RF) lowland rice (Oryza sativa) fields, taking year-round measurements in micrometeorological factors, leaf and canopy photosynthesis, and field reflectance with help from an unmanned aviation vehicle (UAV) system. A spatially hierarchical integration (PIXel based CANopy photosynthesis model, PIXCAN) that fuses measurements from leaf to canopy and field scales was then developed. Our results showed that the PIXCAN fusion could well capture and characterize spatial properties of per-field ecosystem GPP. Spatial variations (SV) of ecosystem carbon uptake capacity (GPPmax) at the PD and RF fields decreased over the growing season. However, occurrence of prolonged non-precipitation period due to climate anormaly in mid-August led to severe constraints of GPPmax and counter-seasonally strengthened SV that would decrease in the RF rice field, primarily due to drought impacts on light-harvesting efficiency and less to stomatal conductance. Collectively, we highlighted ecological implications of the integration applied at field niche in spatially hierarchical observation of ecosystem regulating/production provisions from leaf to landscape dimensions.