Bringing a Micro-Ecosystem Box to the Apocalypse

(Post-apocalyptic + Farming) Chen Zhou woke up to find himself in the post-apocalyptic world three hundred years in the future. The entire planet had been contaminated by unknown radiation. The soil was barren, resources scarce, and mutated species were on the rise. The major factions stood behind towering walls... He faced the same predicament as the other survivors in the shelter: how could he get enough to eat and stay alive? At that moment, a microscopic ecosystem appeared before Chen Zhou. The ecosystem could grow without limit as long as it was bound to a patch of soil. And so began a series of microscopic operations. He sprinkled water to bring rain, made fertilizer fall from the sky, turned the soil with his finger, and carved irrigation ditches with a swipe of his fingertip... As the ecosystem continued to upgrade, he cultivated high-quality soil, turned wasteland into organic fertilizer, simulated changes in the climate and pest outbreaks in the sandbox, and eventually combined mutated genes to produce seeds for man-eating flowers and thorny guards... Years later, he looked at the enormous World Tree he'd grown with his own hands, its branches reaching straight into the sky, then lowered his eyes to the myriad races prostrate on the ground. Chen Zhou muttered to himself, "At first, I just wanted to fill my stomach. Do you believe me?"