The measure of an ecosystem's rate of photosynthesis, converting solar energy into chemical energy, is its productivity.

The statement you've provided refers to the concept of ecosystem productivity, which is a crucial ecological metric. Ecosystem productivity is primarily measured through two key components: Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).

1. Gross Primary Productivity (GPP): This represents the total amount of solar energy that is captured by photosynthetic organisms, like plants, during a given time period. It is a measure of the total photosynthetic activity in the ecosystem.

2. Net Primary Productivity (NPP): This is derived from GPP and accounts for the energy used by plants for respiration. Thus, the formula can be expressed as: $\text{NPP} = \text{GPP} - \text{Respiration}$ NPP represents the actual energy available to consumers in the ecosystem.

The measurement of these productivity rates is vital for understanding the energy flow in an ecosystem and how it supports different trophic levels. High productivity indicates a robust ecosystem that can support a diverse array of life forms, while low productivity may signal environmental stresses or habitat degradation.

In summary, ecosystem productivity encompasses the efficiency with which photosynthetic organisms convert solar energy into chemical energy and forms the foundation of energy flow within ecosystems.