Methane (CH4) uptake responses to simulated nitrogen (N) deposition in a mature forest, a rehabilitated forest and a disturbed forest in tropical China were studied. The experiment was designed with four N treatment levels (three replicates) (0, 50, 100, 150 kg N ha−1 a−1 for Control, Low‐N, Medium‐N, and High‐N treatment, respectively) in the mature forest, but only three levels (Control, Low‐N, and Medium‐N) in the disturbed and rehabilitated forests. Between October 2005 to September 2006, soil CH4 flux was measured once a week from April to September and once every other week in the other time using static chamber and gas chromatography techniques. Monthly ammonium‐nitrate (NH4NO3) application had been applied previously to the plots since July 2003 and continued during the CH4 flux measurement period. The average CH4 uptake rates in control plots were −41.1 ± 1.8, −28.6 ± 2.2, and −17.8 ± 1.6 μg CH4‐C m−2 h−1 in the mature, rehabilitated, and disturbed forest, respectively. For the mature forest, average CH4 uptake rates decreased by 6, 14, and 32% when compared to the control plots for the Low‐N, Medium‐N, and High‐N plots, respectively. These decreases in soil CH4 uptake mainly occurred in the fall (October and November). Nitrogen additions had no significant effect on CH4 uptake in the rehabilitated and disturbed forests. Our results suggest that the response of soil CH4 uptake to N deposition in tropical forests may vary depending on the soil N status directly, and on land‐use history of the forest indirectly.

Abstract. It is well established that tropical forest ecosystems are often limited by phosphorus (P) availability, and elevated atmospheric nitrogen (N) deposition may further enhance such P limitation. However, it is uncertain whether P availability would affect soil fluxes of greenhouse gases, such as methane (CH4) uptake, and how P interacts with N deposition. We examine the effects of N and P additions on soil CH4 uptake in an N saturated old-growth tropical forest in southern China to test the following hypotheses: (1) P addition would increase CH4 uptake; (2) N addition would decrease CH4 uptake; and (3) P addition would mitigate the inhibitive effect of N addition on soil CH4 uptake. Four treatments were conducted at the following levels from February 2007 to October 2009: control, N-addition (150 kg N ha−1 yr−1), P-addition (150 kg P ha−1 yr−1), and NP-addition (150 kg N ha−1 yr−1 plus 150 kg P ha−1 yr−1). Static chamber and gas chromatography techniques were used to quantify soil CH4 uptake every month throughout the study period. Average CH4 uptake rate was 31.2 ± 1.1 μg CH4-C m−2 h−1 in the control plots. The mean CH4 uptake rate in the N-addition plots was 23.6 ± 0.9 μg CH4-C m−2 h−1, significantly lower than that in the controls. P-addition however, significantly increased CH4 uptake by 24% (38.8 ± 1.3 μg CH4-C m−2 h−1), whereas NP-addition (33.6 ± 1.0 μg CH4-C m−2 h−1) was not statistically different from the control. Our results suggest that increased P availability may enhance soil mathanotrophic activity and root growth, resulting in potentially mitigating the inhibitive effect of N deposition on CH4 uptake in tropical forests.

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At most sites the magnitude of soil-atmosphere exchange of nitrous dioxide (N 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) was estimated based on a few chambers located in a limited area. Topography has been demonstrated to influence the production and consumption of these gases in temperate ecosystems, but this aspect has often been ignored in tropical areas. In this study, we investigated spatial variability of the net fluxes of these gases along a 100 m long slope of a evergreen broadleaved forest in southern China over a whole year. We expected that the lower part of slope would release more N 2 O and CO 2 , but take up less atmospheric CH 4 than the upper part due to different availability of water and nutrients. Our results showed that the soil moisture (Water Filled Pore Space, WFPS) decreased along the slope from bottom to top as we expected, but among the three gases only N 2 O emissions followed this pattern. Annual means of WFPS ranged from 27.7% to 52.7% within the slope, and annual emissions of N 2 O ranged from 2.0 to 4.4 kg N ha −1 year −1 , respectively. These two variables were highly and positively correlated across the slope. Neither potential rates of net N mineralization and nitrification, nor N 2 O emissions in the laboratory incubated soils varied with slope positions. Soil CO 2 release and CH 4 uptake appeared to be independent on slope position in this study. Our results suggested that soil water content and associated N 2 O emissions are likely to be influenced by topography even in a short slope, which may need to be taken into account in field measurements and modelling.

The responses of litter decomposition to nitrogen (N) and phosphorus (P) additions were examined in an old-growth tropical forest in southern China to test the following hypotheses: (1) N addition would decrease litter decomposition; (2) P addition would increase litter decomposition, and (3) P addition would mitigate the inhibitive effect of N addition. Two kinds of leaf litter, Schima superba Chardn. & Champ. (S.S.) and Castanopsis chinensis Hance (C.C.), were studied using the litterbag technique. Four treatments were conducted at the following levels: control, N-addition (150 kg N ha−1 yr−1), P-addition (150 kg P ha−1 yr−1) and NP-addition (150 kg N ha−1 yr−1 plus 150 kg P ha−1 yr−1). While N addition significantly decreased the decomposition of both litters, P addition significantly inhibited decomposition of C.C., but did not affect the decomposition of S.S. The negative effect of N addition on litter decomposition might be related to the high N-saturation in this old-growth tropical forest; however, the negative effect of P addition might be due to the suppression of “microbial P mining”. Significant interaction between N and P addition was found on litter decomposition, which was reflected by the less negative effect in NP-addition plots than those in N-addition plots. Our results suggest that P addition may also have negative effect on litter decomposition and that P addition would mitigate the negative effect of N deposition on litter decomposition in tropical forests.

The effect of corona treating the surfaces of components on tensile properties of wood fiber linear low-density polyethylene composites has been investigated. Corona treatment results in a significant increase in strength properties of the composites. Yield stress increases after treatment of one or both of the composite components. Pronounced improvement in ductility has been observed for composites containing 15 to 30% of the corona modified fiber. Relevant mechanisms involved are discussed.

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