ABSTRACT
Vegetation productivity is defined as the process by which plants use sunlight to produce organic matter from carbon dioxide through photosynthesis. Gross primary productivity (GPP), or photosynthesis, is the rate of carbon fixation or total plant organic matter produced per unit of time and over a defined area, whereas the amount of carbon fixed by plants and accumulated as biomass is known as terrestrial net primary production (Cramer et al. 1999; Zhao and Running 2010). Productivity forms the basis of terrestrial biosphere functioning and carbon, energy, and water budgets. Accurate estimates of plant productivity across space and time are thus necessary for quantifying carbon balances at regional to global scales (Lieth 1975; Schimel 1998). Vegetation productivity is generally limited by the availability of spatially and temporally varying plant resources (e.g., nutrients, light, water, and temperature) (Field et al. 1995; Churkina and Running 1998; Nemani et al. 2003) (Figure 1.1). Improved knowledge of the main drivers and resource constraints of plant productivity is thus needed for predictable assessments of climate change.
