How to control brightness of high power LED with PWM microcontroller (ATMEGA16)
To start, check out 


this question, with answers explaining using a MOSFET as a switch.
This question, with answers about using a MOSFET to drive LEDs.
And this question, with answers discussing PWM for servos (basically the same concept).


For a better answer, you need to specify:


What MCU pin or driver board output you are trying to use.
What you are doing in code to configure the hardware &amp; drive the LED
What level electrical knowledge you actually possess. From the comments above, it doesn't seem like you have any idea what you are doing.


Hardware

In your schematic, you are driving a 72V, 2A LED from a 72V power source. When the FET is ON, the current is going through the LED, through the FET, and through R2 to ground. So, how much voltage is dropping across R2 during this time? I honestly don't know, since I don't have the data sheet for these LEDs, but I imagine it's not very much since the LED wants such a high voltage to turn on. If it were 1V, that's only 0.0001 A going through the LED.

Also, since FETs are voltage controlled, not current controlled like BJTs, you don't need a current limiting resistor going to the gate (R1). You can put one there for basic isolation, but it should be much higher (1k ~ 10k). You DO need a pull-down resistor pulled to ground at the gate to keep the FET OFF when the signal at the gate is low. This should also be (1k ~ 10k). If you do use a resistor between your driver and the gate, this pull-down should be on the driver side so you don't create a voltage divider at the gate.

I sincerely hope you are NOT doing this on the output of the motor driver. Those are pins designed to drive current to a motor, not what you are trying to do. If this is the case, you've likely destroyed the MOSTFET gate with the excessively high current output. All you need is a basic MCU output pin and a "logic-level" MOSFET, of which the FET linked in one of the comments is (meaning it can "turn on" at a lower logic level - look for the "gate-source threshold voltage" or Vgs parameter in the datasheet).