Plant Growth Along the Altitudinal Gradient — Role of Plant Nutritional Status, Fine Root Activity, and Soil Properties

Abstract

In tropical montane forests, aboveground net primary productivity (ANPP ) usually decreases with increasing altitude. Besides low photosynthesis (Kitayama and Aiba 2002) and direct impact of low temperatures on plant growth (Hoch and Korner 2003), low ANPP at high altitudes has often been attributed to nutrient limitation (Bruijnzeel et al. 1993; Bruijnzeel and Veneklaas 1998; Tanner et al. 1998). Plant growth is often correlated with nutrient availability in tropical montane forests. For example, the exceptionally high tree stature in a montane forest stand in Papua New Guinea was attributed to its nutrient rich soil parent material (Edwards and Grubb 1977). In montane forests of Jamaica (Tanner et al. 1990), Hawaii (Vitousek and Farrington 1997; Vitousek et al. 1993), and Venezuela (Tanner et al. 1992), trunk diameter growth and leaf production of several native tree species were enhanced by addition of N or P. The nutritional status of plants is governed by the amounts of chemically available nutrients in soil and the ability of fine roots for nutrient acquisition. The ability for nutrient acquisition comprises the spatial exploitation of the soil by roots and nutrient uptake activity. Chemical nutrient availability in tropical montane forests may be affected by parental substrate, weathering intensity, cation exchange capacity, the rates of litter decomposition, or extracellular phosphatase activity (Treseder and Vitousek 2001; Kitayama and Aiba 2002; Wilcke et al. 2007). Spatial nutrient availability is dependent on the exploitation of soil by roots or mycorrhizal hyphae and the mobility of the respective nutrient in soil. High abundance of mycorrhizal fungi contributes to high spatial availability of nutrients in the organic surface layer (Treseder and Vitousek 2001; Haug et al. 2004; Kottke et al. 2004). Also fine root abundance in the organic layers is generally very high (Hertel et al. 2003). Unfavourable soil conditions such as shallow mineral soils (Ostertag 2001), oxygen deficiency (Santiago 2000), low nutrient concentrations (Cavalier 1992), and low pH (Godbold et al. 2003) may cause a superficial distribution of fine roots , and may impair the physiologically based ability of roots for nutrient uptake in deeper soil layers.