Tropical Forest In Southern China Research Articles

Effects of experimental nitrogen additions on plant diversity in an old‐growth tropical forest

AbstractResponse of plant biodiversity to increased availability of nitrogen (N) has been investigated in temperate and boreal forests, which are typically N‐limited, but little is known in tropical forests. We examined the effects of artificial N additions on plant diversity (species richness, density and cover) of the understory layer in an N saturated old‐growth tropical forest in southern China to test the following hypothesis: N additions decrease plant diversity in N saturated tropical forests primarily from N‐mediated changes in soil properties. Experimental additions of N were administered at the following levels from July 2003 to July 2008: no addition (Control); 50 kg N ha−1 yr−1(Low‐N); 100 kg N ha−1 yr−1(Medium‐N), and 150 kg N ha−1 yr−1(High‐N). Results showed that no understory species exhibited positive growth response to any level of N addition during the study period. Although low‐to‐medium levels of N addition (≤100 kg N ha−1 yr−1) generally did not alter plant diversity through time, high levels of N addition significantly reduced species diversity. This decrease was most closely related to declines within tree seedling and fern functional groups, as well as to significant increases in soil acidity and Al mobility, and decreases in Ca availability and fine‐root biomass. This mechanism for loss of biodiversity provides sharp contrast to competition‐based mechanisms suggested in studies of understory communities in other forests. Our results suggest that high‐N additions can decrease plant diversity in tropical forests, but that this response may vary with rate of N addition.

Three new species of Piricaudiopsis from southern China

Piricaudiopsis punicae sp. nov., P. rosae sp. nov. and P. rhaphidophorae sp. nov., occurring respectively on dead branches of Punica granatum, Rosa chinensis and Rhaphidophora decursiva were collected from tropical forest in southern China. They differ from the three previously described Piricaudiopsis species in conidial morphology and proliferation of the conidiogenous cell. The presence or absence of percurrent proliferation of the conidiogenous cells and conidial appendages and the height of conidia are recognized as important characters in the delimitation of species of Piricaudiopsis. A key to Piricaudiopsis species is provided.

Cumulative effects of nitrogen additions on litter decomposition in three tropical forests in southern China

A field-scale experiment with nitrogen (N) addition treatments was performed in three forest types - a pine (Pinus massoniana Lamb.) forest, a pine- broadleaf mixed forest (mixed) and a mature monsoon evergreen broadleaf forest (mature) - in tropical China. Two kinds of leaf litter, Schima superba Chardn. & Champ. and Castanopsis chinensis Hance, were studied using the litterbag technique after more than 2 years of continuous N additions. The objective of this study was to understand the cumulative effect of N addition on litter decomposition in the tropical forests and to determine if the initial effects of N addition changes over time. Results indicated that leaf litter decomposi- tion was significantly faster in the mature forest than in the mixed or pine forests. The mean fraction of mass remaining after 12-months of decomposition was: mature (0.22)<mixed (0.50)<pine (0.51) for the two litters. Nitrogen addition significantly depressed litter decomposition in the pine forest and the mature forest, but had no significant effect in the mixed forest. These results suggest that N deposition has significant cumulative effect on litter decomposition.

Methane uptake responses to nitrogen deposition in three tropical forests in southern China

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.

Emissions of nitrous oxide from three tropical forests in Southern China in response to simulated nitrogen deposition

Emissions of nitrous oxide (N2O) from the soil following simulated nitrogen (N) deposition in a disturbed (pine), a rehabilitated (pine and broadleaf mixed) and a mature (monsoon evergreen broadleaf) tropical forest in southern China were studied. The following hypotheses were tested: (1) addition of N will increase soil N2O emission in tropical forests; and (2) any observed increase will be more pronounced in the mature forest than in the disturbed or rehabilitated forest due to the relatively high initial soil N concentration in the mature forest. The experiment was designed with four N treatment levels (three replicates; 0, 50, 100, 150 kg N ha−1 year−1 for C (Control), LN (Low-N), MN (Medium-N), and HN (High-N) treatment, respectively) in the mature forest, but only three levels in the disturbed and rehabilitated forests (C, LN and MN). Between October 2005 to September 2006, soil N2O flux was measured using static chamber and gas chromatography methodology. Nitrogen had been applied previously to the plots since July 2003 and continued during soil N2O flux measurement period. The annual mean rates of soil N2O emission in the C plots were 24.1 ± 1.5, 26.2 ± 1.4, and 29.3 ± 1.6 μg N2O–N m−2 h−1 in the disturbed, rehabilitated and mature forest, respectively. There was a significant increase in soil N2O emission following N additions in the mature forest (38%, 41%, and 58% when compared to the C plots for the LN, MN, and HN plots, respectively). In the disturbed forest a significant increase (35%) was observed in the MN plots, but not in the LN plots. The rehabilitated forest showed no significant response to N additions. Increases in soil N2O emission occurred primarily in the cool-dry season (November, December and January). Our results suggest that the response of soil N2O emission to N deposition in tropical forests in southern China may vary depending on the soil N status and land-use history of the forest.

Nitrogen addition reduces soil respiration in a mature tropical forest in southern China

AbstractResponse of soil respiration (CO2 emission) to simulated nitrogen (N) deposition in a mature tropical forest in southern China was studied from October 2005 to September 2006. The objective was to test the hypothesis that N addition would reduce soil respiration in N saturated tropical forests. Static chamber and gas chromatography techniques were used to quantify the soil respiration, following four‐levels of N treatments (Control, no N addition; Low‐N, 5 g N m−2 yr−1; Medium‐N, 10 g N m−2 yr−1; and High‐N, 15 g N m−2 yr−1 experimental inputs), which had been applied for 26 months before and continued throughout the respiration measurement period. Results showed that soil respiration exhibited a strong seasonal pattern, with the highest rates found in the warm and wet growing season (April–September) and the lowest rates in the dry dormant season (December–February). Soil respiration rates showed a significant positive exponential relationship with soil temperature, whereas soil moisture only affect soil respiration at dry conditions in the dormant season. Annual accumulative soil respiration was 601±30 g CO2‐C m−2 yr−1 in the Controls. Annual mean soil respiration rate in the Control, Low‐N and Medium‐N treatments (69±3, 72±3 and 63±1 mg CO2‐C m−2 h−1, respectively) did not differ significantly, whereas it was 14% lower in the High‐N treatment (58±3 mg CO2‐C m−2 h−1) compared with the Control treatment, also the temperature sensitivity of respiration, Q10 was reduced from 2.6 in the Control with 2.2 in the High‐N treatment. The decrease in soil respiration occurred in the warm and wet growing season and were correlated with a decrease in soil microbial activities and in fine root biomass in the N‐treated plots. Our results suggest that response of soil respiration to atmospheric N deposition in tropical forests is a decline, but it may vary depending on the rate of N deposition.

Cumulative effects of nitrogen additions on litter decomposition in three tropical forests in southern China

Cumulative effects of nitrogen additions on litter decomposition in three tropical forests in southern China

Response of soil respiration to simulated N deposition in a disturbed and a rehabilitated tropical forest in southern China

Responses of soil respiration (CO2 emission) to simulated N deposition were studied in a disturbed (reforested forest with previous understory and litter harvesting) and a rehabilitated (reforested forest with no understory and litter harvesting) tropical forest in southern China from October 2005 to September 2006. The objectives of the study were to test the following hypotheses: (1) soil respiration is higher in rehabilitated forest than in disturbed forest; (2) soil respiration in both rehabilitated and disturbed tropical forests is stimulated by N additions; and (3) soil respiration is more sensitive to N addition in disturbed forest than in rehabilitated forest due to relatively low soil nutrient status in the former, resulting from different previous human disturbance. Static chamber and gas chromatography techniques were employed to quantify the soil respiration, following different N treatments (Control, no N addition; Low-N, 5 g N m−2 year−1; Medium-N, 10 g N m−2 year−1), which had been applied continuously for 26 months before the respiration measurement. Results showed that soil respiration exhibited a strong seasonal pattern, with the highest rates observed in the hot and wet growing season (April–September) and the lowest rates in winter (December–February) in both rehabilitated and disturbed forests. Soil respiration rates exhibited significant positive exponential relationship with soil temperature and significant positive linear relationship with soil moisture. Soil respiration was also significantly higher in the rehabilitated forest than in the disturbed forest. Annual mean soil respiration rate in the rehabilitated forest was 20% lower in low-N plots (71 ± 4 mg CO2-C m−2 h−1) and 10% lower in medium-N plots (80 ± 4 mg CO2-C m−2 h−1) than in the control plots (89 ± 5 mg CO2-C m−2 h−1), and the differences between the control and low-N or medium-N treatments were statistically significant. In disturbed forest, annual mean soil respiration rate was 5% lower in low-N plots (63 ± 3 mg CO2-C m−2 h−1) and 8% lower in medium-N plots (61 ± 3 mg CO2-C m−2 h−1) than in the control plots (66 ± 4 mg CO2-C m−2 h−1), but the differences among treatments were not significant. The depressed effects of experimental N deposition occurred mostly in the hot and wet growing season. Our results suggest that response of soil respiration to elevated N deposition in the reforested tropical forests may vary depending on the status of human disturbance.