Abstract
Having been introduced to the northern edge of Asian tropics, the rubber tree (Hevea brasiliensis) has become deciduous in this climate with seasonal drought and cold stresses. To determine its internal nutrient strategy during leaf senescence and deciduous periods, we investigated mature leaf and senescent leaf nutrients, water-soluble soil nutrients and characteristics of soil microbiota in nine different ages of monoculture rubber plantations. Rubber trees demonstrate complicated retranslocation of N, P, and K during foliar turnover. Approximately 50.26% of leaf nutrients and 21.47% of soil nutrients were redistributed to the rubber tree body during the leaf senescence and withering stages. However, no significant changes in the structure- or function-related properties of soil microbes were detected. These nutrient retranslocation strategy may be important stress responses. In the nutrient retranslocation process, soil plays a dual role as nutrient supplier and nutrient “bank.” Soil received the nutrients from abscised leaves, and also supplied nutrients to trees in the non-growth stage. Nutrient absorption and accumulation began before the leaves started to wither and fall.
Highlights
Land-use changes increasingly threaten tropical forests, where biodiversity and human pressures are both high (Dirzo and Raven, 2003; Gibson et al, 2011; Li et al, 2013)
Patterns for rubber-tree leaf total nitrogen (TN), total phosphorus (TP), and TK contents differed from total carbon (TC)
Leaf TN, TP, and TK contents were significantly higher in live mature leaves than in senescent leaves (Figure 2)
Summary
Land-use changes increasingly threaten tropical forests, where biodiversity and human pressures are both high (Dirzo and Raven, 2003; Gibson et al, 2011; Li et al, 2013). Rapid conversion of tropical forests to agriculture, timber production or other uses has generated vast, humandominated landscapes with negative consequences for tropical forest ecosystems (Gardner et al, 2009; Gibson et al, 2011). Global rubber plantations reached 10.06 million ha in 2010 (FAO, 2010) with 81% in South and Southeastern Asia (FAO, 2010). Malaysia, Thailand, and other countries are traditional planting regions, with expansion on the northern edge of Southeastern Asian tropics, especially in southwestern China, Laos, Cambodia, Myanmar, northeastern Thailand, and northwestern Vietnam. Rubber plantations in these regions cover more than 1.5 million ha (Li and Fox, 2012)
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