What type of relationship exists between Aboveground NPP and evapotranspiration (ET) globally across diverse biomes?

The relationship between aboveground net primary productivity (NPP) and evapotranspiration (ET) globally across diverse biomes is characterized as positive. Aboveground NPP refers to the amount of organic matter produced by plants in photosynthesis that becomes available for consumption by other organisms, while ET is the sum of evaporation from the land and transpiration from plants.

In ecosystems where moisture is abundant and conditions favor plant growth, increases in ET are typically associated with increased plant productivity. This occurs because higher rates of evapotranspiration usually indicate more available water for plants, which supports greater photosynthetic activity. Consequently, as plants transpire more water, they can also uptake more nutrients from the soil, leading to enhanced growth and, therefore, increased aboveground NPP.

This positive relationship is particularly evident in tropical and temperate forests, where lush vegetation and high rates of ET coincide with substantial NPP. Conversely, in arid biomes, lower ET corresponds with reduced NPP, reflecting the role of water availability in driving plant growth. Thus, the positive correlation highlights the importance of water as a limiting resource for production across different ecosystems.