What limits land primary production primarily?

Land primary production is predominantly limited by the availability of water. This is because water is essential for photosynthesis, the process by which plants convert sunlight into chemical energy. In terrestrial ecosystems, especially in arid and semi-arid regions, the lack of sufficient water can significantly restrict plant growth and, consequently, the primary production of biomass.

While factors such as soil nutrients, sunlight availability, and temperature do influence primary production, water availability often becomes the most critical limiting factor, particularly in regions where precipitation is low or unevenly distributed. Without adequate moisture, plants cannot maintain their physiological processes, leading to reduced productivity and limiting the overall capacity of the ecosystem to support life. Therefore, the availability of water plays a crucial role in determining the extent of primary production in land ecosystems.