Abstract
Abstract. Increasing atmospheric CO2 and temperature may increase forest productivity, including litterfall, but the consequences for soil organic matter remain poorly understood. To address this, we measured soil carbon and nutrient concentrations at nine depths to 2 m after 6 years of continuous litter removal and litter addition in a semi-evergreen rain forest in Panama. Soils in litter addition plots, compared to litter removal plots, had higher pH and contained greater concentrations of KCl-extractable nitrate (both to 30 cm); Mehlich-III extractable phosphorus and total carbon (both to 20 cm); total nitrogen (to 15 cm); Mehlich-III calcium (to 10 cm); and Mehlich-III magnesium and lower bulk density (both to 5 cm). In contrast, litter manipulation did not affect ammonium, manganese, potassium or zinc, and soils deeper than 30 cm did not differ for any nutrient. Comparison with previous analyses in the experiment indicates that the effect of litter manipulation on nutrient concentrations and the depth to which the effects are significant are increasing with time. To allow for changes in bulk density in calculation of changes in carbon stocks, we standardized total carbon and nitrogen on the basis of a constant mineral mass. For 200 kg m−2 of mineral soil (approximately the upper 20 cm of the profile) about 0.5 kg C m−2 was “missing” from the litter removal plots, with a similar amount accumulated in the litter addition plots. There was an additional 0.4 kg C m−2 extra in the litter standing crop of the litter addition plots compared to the control. This increase in carbon in surface soil and the litter standing crop can be interpreted as a potential partial mitigation of the effects of increasing CO2 concentrations in the atmosphere.
Highlights
Tropical forests and their soils are an important part of the global carbon (C) cycle because they contain 692 Pg C, equivalent to 66 % of the C in atmospheric CO2 (Jobbagy and Jackson, 2000)
There is the potential for the amount of C in tropical soils to change over only a few years, with potentially important consequences for atmospheric CO2 concentrations
The similarity of the losses from litter removal and gains in litter addition probably has different causes: we speculate that losses from the soil in the litter removal plots are due to respiration being greater than additions; we did not physically remove organic matter from the mineral soil
Summary
Tropical forests and their soils are an important part of the global carbon (C) cycle because they contain 692 Pg C, equivalent to 66 % of the C in atmospheric CO2 (Jobbagy and Jackson, 2000). Atmospheric CO2 concentrations have been steadily increasing for decades and one of the effects of this could be widespread increases in forest growth (Nemani et al, 2003) and, as a result, increased litterfall. Körner (2006) reported that elevated CO2 caused increased litterfall in one of three studies in steady-state tree stands in temperate forests, but there have been no such studies in the tropics. The potential exists for increased CO2 to increase forest growth and litterfall – though we do not know how widespread and how large any increase in litterfall might be, especially in the tropics
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