This video, we're going to talk about primary production in terrestrial ecosystems. And so terrestrial net primary production actually has a tendency to increase with increasing amounts of these three factors, which are moisture, temperature, and nutrients. And so in a graph like this one down below on the left-hand side where we have the amount of precipitation, temperature, and nutrients on the x-axis and the net primary production or NPP on the y-axis, we might expect this graph to look something like this here since we know that both of these factors tend to increase with each other. Now when it comes to nutrients, usually it's going to be nitrogen and phosphorus once again that are going to serve as the limiting nutrients. And so usually, it's going to be the addition of these specific nutrients that will actually lead to an increase in the net primary productivity.
Now terrestrial plants have evolved several different adaptations to help them maximize their nutrient uptake. And down below, we're highlighting one very important evolutionary adaptation, which is this mutualistic relationship between the roots of some plants and these nitrogen-fixing bacteria. And so some plant roots have these structures called root nodules that we're highlighting here, and these root nodules house these nitrogen-fixing bacteria that you can see here, which are capable of taking an unusable form of nitrogen gas and converting it into a more usable form of nitrogen that the plants can actually assimilate and use. And this is going to be critical for the nitrogen cycle, which we'll get to talk more about later in our course in a different video. Now, the very last note that I'll leave you all off with, is this reminder that tropical rainforests are actually the most productive terrestrial ecosystem.
And that's no surprise since we know that they receive very high precipitation and temperature throughout the year. While let me get out of the way here so that you can see this better. Deserts and tundra are the least productive terrestrial ecosystems, and that's because they receive very little precipitation and can also have relatively cold temperatures as well. And so this here concludes our lesson and we'll be able to get some practice applying these concepts moving forward. So I'll see you on our next video.