Which factor is crucial in determining the efficiency of gross primary productivity?

Sunlight intensity plays a critical role in determining the efficiency of gross primary productivity (GPP) because it is the primary source of energy for photosynthesis in plants. During photosynthesis, plants convert light energy into chemical energy, producing glucose and oxygen. The rate at which this process occurs directly influences the amount of biomass generated, which is indicative of GPP. Higher sunlight intensity generally leads to greater rates of photosynthesis, assuming that other conditions, such as carbon dioxide availability and temperature, are also favorable.

While soil nutrients, water availability, and temperature are important factors that can influence plant growth and productivity, they generally act in conjunction with the availability of sunlight. For example, if a plant lacks sufficient sunlight, it will not effectively carry out photosynthesis, regardless of the nutrient levels in the soil or the amount of water it receives. Thus, sunlight intensity is fundamental in driving the process of GPP, making it a key factor in evaluating the productivity of ecosystems.