[Soil respiration rate and its influencing factors in artificial land-bridge islands system]. / äººå·¥é™†æ¡¥å²›å±¿ç³»ç»ŸåœŸå£¤å‘¼å¸é€ŸçŽ‡åŠå ¶å½±å“å› å­.

It is of great significance to understand the pattern of soil respiration rate in fragmented forests for further revealing terrestrial ecosystem carbon cycling. With different habitats (island vs. mainland, island edge vs. island interior) of the artificial land-bridge island system in Thousand Island Lake (TIL) region as the objects, we analyzed the seasonal dynamics of soil respiration rate and its relationships with soil physicochemical factors. The results showed that: 1) Soil respiration rates varied significantly across different seasons, with an order of summer (3.74 µmol·m-2·s-1) > autumn (2.30 µmol·m-2·s-1) > spring (1.82 µmol·m-2·s-1) > winter (1.40 µmol·m-2·s-1). 2) Forest fragmentation had significant effects on soil respiration rate, with soil respiration rate of island (2.37 µmol·m-2·s-1) being significantly higher than that of mainland (2.08 µmol·m-2·s-1) and the soil respiration rate of island edge (2.46 µmol·m-2·s-1) being significantly higher than that of island interior (2.03 µmol·m-2·s-1). 3) Soil temperature significantly promoted soil respiration rate, explaining 56.1% of the total variation. 4) There was a significant positive correlation between soil respiration rate and soil total carbon, ammo-nium nitrogen content, and vegetation coverage. The soil total carbon and ammonium nitrogen content of island edge were significantly higher than those of island interior. In all, forest fragmentation promoted soil respiration rate, with soil physicochemical factors as the drivers for its variation.

[Effect of litterfall input on soil respiration and its temperature sensitivity in moso bamboo forest under simulated drought.] / æ¨¡æ‹Ÿå¹²æ—±ä¸‹å‡‹è½ç‰©è¾“å ¥å¯¹æ¯›ç«¹æž—åœŸå£¤å‘¼å¸åŠæ¸©åº¦æ•æ„Ÿæ€§çš„å½±å“.

Increases in drought frequency and intensity under climate change will have great impacts on the carbon cycle of forest ecosystems. Understanding the responses of soil respiration and its temperature sensitivity to drought is necessary, when we assess whether soil is a carbon sink or source. The effects of litterfall input on soil respiration, temperature sensitivity and its lagging effect were studied in moso bamboo forests under simulated drought by ceiling method in the field with three litterfall treatments, i.e., ambient litterfall (unchanged, LU), litter addition (LA) and litter removal (LR). The results showed that LU decreased annual soil respiration rate in drought treatment (2.34 Μmol·m-2·s-1), compared with that in the control (3.15 Μmol·m-2·s-1) with ambient natural rainfall. LR showed stronger effect on soil respiration than LA. Compared with LU, LR decreased soil respiration rate by 21.0% in ambient condition and by 20.9% in drought treatment, while LA led to 5.3% increase only in drought treatment. Such a result indicated that the effects of LA and LR on soil respiration rate were stronger than LU in the drought condition. Drought decreased the temperature sensitivity of soil respiration by 8.4%, while LA and LR reduced that by 15.4% and 7.6%, respectively. The cumulative CO2 emissions during the whole 18 months were 7.35 and 5.40 kg CO2·m-2 in the control and drought treatment. Compared with LU, LA increased the cumulative CO2 emissions by 1.8% and 10.7%, and LR decreased that by 19.9% and 18.0% in the control and drought treatments. Our results indicated that the relationship between the litterfall amount (addition or removal) and soil respiration rate was nonlinear. The significant lagging effect may be caused by the decrease in root growth and microbial activity due to decreased soil water availability in drought treatment. Litterfall played a more important role in soil CO2 emission under drought, and thus litterfall was a crucial factor in soil carbon emission in the context of climate change.

[Effects of litterfall and root input on soil physical and chemical properties in Pinus massoniana plantations in Three Gorges Reservoir Area, China].

An investigation was made on the soil physical and chemical properties in different-aged Pinus massoniana plantations in Three Gorges Reservoir Area under effects of litterfall and roots. The annual litter production in mature stand was 19.4% and 65.7% higher than that in nearly mature and middle-aged stands, respectively. The litter standing amount was in the sequence of mature stand > middle-aged stand > nearly mature stand, while the litter turnover coefficient was in the order of nearly mature stand (0.51) > mature stand (0.40) > middle-aged stand (0.36). The total root biomass, live root biomass, and dead root biomass were the highest in middle-aged stand, and the lowest in nearly mature stand. In middle-aged stand, soil total porosity was the highest, and soil bulk density was the lowest. Soil organic matter and total nitrogen contents were in the order of mature stand > middle-aged stand > nearly mature stand, soil nitrate nitrogen occupied a larger proportion of soil mineral N in nearly mature stand, while ammonium nitrogen accounted more in middle-aged and mature stands. In nearly mature stand, litter production was moderate but turnover coefficient was the highest, and soil nutrient contents were the lowest. In middle-aged stand, root biomass and soil total porosity were the highest, and soil bulk density were the lowest. In mature stand, root biomass was lower while soil nutrient contents were the highest. The increase of root biomass could improve soil physical properties.

[Relationships between soil nutrient contents and soil enzyme activities in Pinus massoniana stands with different ages in Three Gorges Reservoir Area].

Based on the measurements of soil nutrient contents and enzyme activities and the canonical correspondence analysis (CCA), this paper studied the relationships between soil nutrient contents and soil enzyme activities in different age Pinus massoniana stands in Three Gorges Reservoir Area. Among the test stands, mature stand had the highest contents of organic matter, total nitrogen, ammonium nitrogen, and available phosphorus in 0-20 cm soil layer, followed by middle-aged stand, and nearly-mature stand. With the increase of the stand age, soil invertase activity increased after an initial decrease, cellulase and polyphenoloxidase activities decreased gradually, while urease and peroxidase activities decreased after an initial increase. CCA analysis showed that the effects of the main soil parameters on the soil enzyme activities in the stands ranked in the sequence of total nitrogen > organic matter > pH > bulk density > ammonium nitrogen > available phosphorus. Soil invertase activity had significant positive correlations with soil organic matter, total nitrogen, and total phosphorus, while soil peroxidase activity significantly negatively correlated with soil organic matter, total nitrogen, total phosphorus, and bulk density. The soil was rich in main nutrients, invertase activity was relatively high, while peroxidase activity was relatively low. The activities of soil invertase, cellulase and peroxidase could be used as the good biological indicators in evaluating soil quality and fertility.

[Fine root production and turnover in Pinus massoniana plantation in Three Gorges Reservoir area of China].

By the methods of sequential soil cores and buried bags, an investigation was conducted to study the seasonal dynamics of fine roots in a 20-year-old Pinus massoniana plantation in Three Gorges Reservoir Area from March to December 2011, with the annual production and turnover rate of the fine roots calculated. In the plantation, the annual mean biomass of <2 mm fine roots was 146.98 g x m(-2) x a(-1), in which, the living root biomass (102.92 g x m(-2) x a(-1)) was far greater than that of the dead root biomass (44.06 g x m(-2) x a(-1)). Among the fine roots with different sizes, <1 mm fine roots had an obvious seasonal dynamics in their biomass, showing a unimodal curve in the sampling period. The annual production and turnover rate of <2 mm fine roots were 104. 12 g x m(-2) x 1(-1) and 1.05 a(-1), respectively, in which, the annual production of <1 mm and 1-2 mm fine roots was 58.35 and 45.77 g x m(-2) x a(-1), and the turnover rate was 1.41 and 0.69 a(-1), respectively.