Rubber tree (Hevea brasiliensis) was introduced to tropical Asia at the end of 19th century and Xishuangbanna has become a top rubber-producing regions in China. Previous studies on rubber plantations focused on impacts of land-use conversion on tropical biodiversity, soil and water conservation, and local climate change. However, little research has been conducted on nutrient strategies of rubber trees and soil roles in these processes under drought and cold stresses; nor impacts on soil nutrients and microbiota.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) investigated mature leaf and senescent leaf (leaf litter) nutrients, water-soluble soil nutrients and some aspects of soil microbes in monoculture rubber plantations of nine different ages (1 to 48 years) in Xishuangbanna.
The researchers chose four nutrient variables: total carbon (TC), total nitrogen (TN), total phosphorus (TP) and total potassium (TK) for the analysis of the leaf and litter-fall samples. They used changes in water-soluble soil-nutrient pools to examine nutrient retranslocation effects on soil nutrient properties.
They found that rubber trees demonstrateda clear retranslocation process. Facing annual drought and cold stresses, rubber tree mature leaves clearly retranslocate nutrients from leaf senescence period to deciduous period in adaptation to environmental pressures in Xishuangbanna. Approximately 50.26% of leaf nutrients and 21.47% of the soil nutrients were redistributed to rubber tree body.
In nutrient retranslocation process, soil not only received nutrients (N and P) from leaves, but also supplied nutrient (K)to trees in the non-growth stage. Soil played a dual role, as nutrients supplier and free-withdrawing nutrient “bank” in those stages. Moreover, rubber trees started to absorb and accumulate nutrients before leaves began to wither and fall, rather than starting after defoliation and before sprouting.