This paper reports a simple and effective approach to control statistical pore size distributions within electrospun nanofibrous membranes (ENMs), by choosing appropriate spinning times of electrospinning deposition. Mean pore diameter of ENMs decreases exponentially with increasing spinning time. This pore-size control method is demonstrated to regulate amount of heat energy reaching microfluidic seed growth chips (SGC) and thus growth temperature of seeds on the chips, without using sophisticated semiconductor manufacturing techniques or additional on-chip electronic circuits. Decreasing mean pore diameter of ENMs causes to decrease the on-chip temperature, following a second-order polynomial trend. Phenotypic study based on real-time observation of root architecture is conducted on multiple SGCs under various temperature conditions obtained by using ENMs with different pore size distributions.