亞馬遜黑土營養豐富 成全球森林復育新契機

Millions of Amerindian people living centuries ago in today’s Amazonia transformed the originally poor soil. The result is Amazonian dark earth, ADE, or terra preta, fertile and rich in nutrients and stable organic matter derived from charcoal, which imparts its black color.

Over many human generations between 450 BCE and 950 CE, soils were enriched with charcoal from low-intensity fires for cooking and burning refuse, animal bones, broken pottery, compost, and manure.

Now, scientists from Brazil show that ADE could boost reforestation, not only in the Amazon, where 18 percent or 780,000 km2 of forest has been lost since the 1970s, but around the world. The results are published in the journal “Frontiers in Soil Science,” under the title, “Amazonian dark earths enhance the establishment of tree species in forest ecological restoration.”

Zagatto and colleagues sampled ADE from the Caldeirão Experimental Research Station in the Brazilian state of Amazonas, and as a control, agricultural soil from the Luiz de Queiróz Superior School of Agriculture in the state of São Paulo.

One-third of the pots received only control soil, another third a 4:1 mixture of control soil and ADE, and another third 100 percent ADE.

To imitate pasture, they planted seeds of palisade grass (Urochloa brizantha), common forage for livestock in Brazil, in each pot and allowed its seedlings to grow for 60 days. They then cut the grass and let only its roots remain in the soil – virgin territory for reforestation in miniature.

The researchers then planted each of the three soils with tree seeds: either with the colonizing species Ambay pumpwood (Cecropia pachystachya), with Peltophorum dubium typical of secondary forests, or with cedro blanco (Cedrela fissilis), typical of climax forest.

At the start, ADEs showed greater amounts of nutrients than control soil. For example, there was 30 times more phosphorus and three to five times more of each of the other measured nutrients, except manganese.

After the experiment, soils contained less nutrients than at the start, reflecting take-up by the plants, but 100 percent ADE soils remained richer in these than control soils, while nutrient levels were intermediate in 20 percent ADE soils.

Throughout the experiment, 20 percent or 100 percent ADE soils supported a greater biodiversity of bacteria and archae micro-organisms than control soils.

The results also showed that adding ADE to soil improved the growth and development of plants. The dry mass of palisade grass, for example, was increased 3.4 times in 20 percent ADE, and 8.1 times in 100 percent ADE, compared to in control soil.

Addition of ADE also boosted the growth of the three tree species: seedlings of cedro blanco and P. dubium were 2.1 and 5.2 times taller in 20 percent ADE, and 3.2 and 6.3 times taller in 100 percent ADE, compared to in control soils.

The researchers concluded that ADE can boost plant growth. “Our data point to a mixture of soil nutrients and adapted microorganisms [in ADE] to improve the establishment of plant trees in restoration,” they wrote.

Senior author Dr. Siu Mui Tsai, a professor at the Cell and Molecular Biology Lab, Center for Nuclear Energy in Agriculture, University of São Paulo, cautioned, “ADE has taken thousands of years to accumulate and would take an equal time to regenerate in nature if used. Our recommendations aren’t to utilize ADE itself, but rather to copy its characteristics, particularly its microorganisms, for use in future ecological restoration projects.”