Story about a tree that releases spores that destroy a species' appetite

As I remarked in the comments, I think his is almost certainly "The Harmonizer" by A.E. van Vogt, first published in Astounding in 1944. I left a fuller description at the linked question, so I'll just summarize the main points here.

Millions of years ago, a ship crashed on earth.

"That was eighty million years before. The ship, with the ibis plants aboard, was passing through the solar system when the catastrophe happened. It came down onto an earth of marsh, fog and fantastic reptilian monsters. It came hard and out of control..."

The tree survives and grows. It has silvery leaves and branches.

"It lived. And, having survived, having taken possession of a suitable area in which to develop without interference, it lost its feverishness, and expanded into a gracious silver-hued tree."

Exactly as you remember, a T. Rex passes by and kills and devours a brontosaurus. The ibis trees create pheromones which act to eliminate ferocity, and the carnivourous dinosaurs lose the will to hunt and subsequently die of starvation.

Fast forward some millennia: In one of the Soviet bloc countries, a disgruntled comrade comes home and finds an odd tree growing in his yard. He becomes furious, thinking perhaps it's a plot of some kind. The tree responds to his anger by shedding its pollen...

Well, 80 million years later, after having been buried in a cataclysm, the ibis tree returns to the surface. A soldier named "Wagner", presumably German, and given the time-frame probably fighting for the Nazis, returns home and

"...at first, as he kissed his wife, he didn’t notice that there had been bomb damage to his house. He finally saw the silver tree. He stared. He was about to exclaim, when he noticed that one whole wing of the house was an empty shell, a single wall standing vacuously in a precarious balance. "Die !-! ? !-! ? !? Americannerin!" he bellowed murderously. "!-! ?-! !?!-?-!" It was less than an hour later that the sensitive ibis tree began to give off a delicious perfume. First Germany, then the rest of the world breathed the spreading "peace." It all worked out as beautifully as that."

With reference to the OP's mention of "one of the Soviet bloc countries", it's interesting to see that the version published in "Away and Beyond" in 1963 has some slight differences to the Astounding version I quote above. The soldier is now called Wagnowski instead of Wagner, and when he returns to his home he shouts: "The !-!-?-! American fascists". The last two lines are then "First Russia, and then the rest of the world breathed the spreading 'peace'. World War III ended." It seems van Vogt updated it to make it more relevant to the Cold War.