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Litter inputs are expected to have a strong impact on soil N2O efflux. This study aimed to assess the effects of the litter decomposition process and nutrient efflux from litter to soil on soil N2O efflux in a tropical rainforest. A paired study with a control (L) treatment and a litter-removed (NL) treatment was followed for 2 years, continuously monitoring the effects of these treatments on soil N2O efflux, fresh litter input, decomposed litter carbon (LCI) and nitrogen (LNI), soil nitrate (NO3−-N), ammonium (NH4+-N), dissolved organic carbon (DOC), and dissolved nitrogen (DN). Soil N2O flux was 0.48 and 0.32 kg N2O-N ha−1 year−1 for the L and NL treatments, respectively. Removing the litter caused a decrease in the annual soil N2O emission by 33%. The flux values from the litter layer were higher in the rainy season as compared to the dry season (2.10 ± 0.28 vs. 1.44 ± 0.35 μg N m−2 h−1). The N2O fluxes were significantly correlated with the soil NO3−-N contents (P < 0.05), indicating that the N2O emission was derived mainly from denitrification as well as other NO3− reduction processes. Suitable soil temperature and moisture sustained by rainfall were jointly attributed to the higher soil N2O fluxes of both treatments in the rainy season. The N2O fluxes from the L were mainly regulated by LCI, whereas those from the NL were dominated jointly by soil NO3− content and temperature. The effects of LCI and LNI on the soil N2O fluxes were the greatest in the 2 months after litter decomposition. Our results show that litter may affect not only the variability in the quantity of N2O emitted, but also the mechanisms that govern N2O production. However, further studies are still required to elucidate the impacting mechanisms of litter decomposition on N2O emission from tropical forests. [ABSTRACT FROM AUTHOR]

Background and aims: Drought is expected to be more frequent and more intense with global warming. Our aim was to investigate how soil respiration would respond to different levels of precipitation exclusion (‘drought strength’).Methods: We conducted a two-year drought experiment in a woody savanna ecosystem in south west of China, which consisted of four treatments: a control treatment (CK); 30% precipitation exclusion (PE3), 50% precipitation exclusion (PE5) and 70% precipitation exclusion (PE7).Results: The cumulative soil respiration rates were significantly decreased in both rainy and dry seasons as drought became more intense. The sensitivity of soil respiration to soil moisture decreased as drought severity increased. There were bursts of CO2 emission when dry soils were rewetted by rainfall after the dry season. Unlike most other exponential relationships between soil respiration and soil temperature, a parabolic function was observed in all treatments (P < 0.05), which was due to higher soil temperature (>28 °C) coinciding with insufficient soil water content (<11% Vol). Respiration rate is best represented by a model which combines soil moisture and temperature.Conclusion: Soil respiration rates were significantly decreased as drought enhanced. The response of soil respiration to drought in the dry season should not be ignored especially when evaluating the effect of drought on soil respiration in a whole year in savanna ecosystems. The quadratic relationship between soil respiration and soil temperature may be important for modeling the response of soil respiration to climate change (drought) in savanna ecosystems. [ABSTRACT FROM AUTHOR]

This study seeks a further understanding on climate trends in a subtropical mountain forest, SW China. Air ( Ta) and soil temperature ( Ts), both in open land (1983-2010) and under a forest canopy (1986-2010), were investigated. Short-term radiation components were also measured simultaneously both in open land and understory to explore the relationships of microclimatic variables. Correlations of Ta and Ts with sunshine hours ( St) and wind speed ( Ws) were also analysed as driving factors of the temperature trends. The results showed that (1) Understory radiation components were greatly reduced by the forest canopy, showing a strong effect of forest canopy on microclimatic variables. Ts_0 in open land was significantly correlated with solar radiation. Wind speed had significant influences on differences between Ta and Ts_0, between open land Ts_0 and understory Ts_0. The long-term data showed that Ts_0 under forest canopy were closely coupled with Ta in open land. (2) Ta had a larger increase than Ts_0 in open land, and temperature increases in winter were greater than in other seasons. Soil temperature at depths under forest canopy had nearly twice the increases of those on open land; we attributed this to the higher relative increase of Ws over St. (3) A slope change in 1998 was detected in the Ts_0 and Ta difference ( Ts_0 − Ta) series, suggesting different response of Ts_0 and Ta since that year. Deceleration of St and stability of Ws may have been factors. This study improves our understanding of warming in a nature reserve where anthropogenic influences are absent. Further studies are needed for the biological and biochemical implications on subtropical mountain forest. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Abstract: CH4 and N2O fluxes from soil under a tropical seasonal rain forest in Xishuangbanna, Southwest China were measured for one year using closed static chamber technique and gas chromatography method. Three treatments were set in the studied field: (A) litter-free, (B) with litter, and (C) with litter and seedling. The results showed that the soil in our study was a sink of atmospheric CH4 and source of atmospheric N2O. The observed mean CH4 fluxes from treatments A, B, and C were –50.0 ± 4.0, –35.9 ± 2.8, –31.6 ± 2.8 μgC/(m2·h), respectively, and calculated annual fluxes in 2003 were –4.1, –3.1, and –2.9 kgC/hm2, respectively. The observed mean N2O fluxes from treatments A, B, and C were 30.9 ± 3.1, 28.2 ± 3.5, 50.2±3.7 μgN/(m2·h), respectively, and calculated annual fluxes in 2003 were –4.1, –3.1, and –2.9 kgC/hm2, respectively. The observed mean N2O fluxes from treatments A, B, and C were 30.9 ± 3.1, 28.2 ± 3.5, 50.2±3.7 μgN/(m2·h), respectively, and calculated annual fluxes in 2003 were 2.8, 2.6, and 3.7 kgN/hm 2, respectively. Seasonal variations in CH4 and N2O fluxes were significant among all the three treatments. The presence of litter decreased CH4 uptake during wet season (P < 0.05), but not during dry season. There was a similar increase in seedlings-mediated N2O emissions during wet and dry seasons, indicating that seedlings increased N2O emission in both seasons. A strong positive relationship existed between CH4 fluxes and soil moisture for all the three treatments, and weak relationship between CH4 fluxes and soil temperature for treatment B and treatment C. The N2O fluxes correlated with soil temperature for all the three treatments. [Copyright &y& Elsevier]

Savanna ecosystems play a crucial role in global N 2 O emissions. However, our understanding of N 2 O emissions under limiting precipitation conditions is lacking. This study evaluates the effects of precipitation reduction on soil N 2 O fluxes from a woody savanna ecosystem in Yunnan Province, Southwest China. Precipitation exclusion shelters were installed above the tree canopy, and four total treatments were established as follows: a control (CK) and precipitation exclusions of 30% (PE3), 50% (PE5), and 70% (PE7). Two years (2015–2016) of N 2 O fluxes, soil temperature and soil water content data were collected. The N 2 O fluxes were generally low, ranging from 0.039 to 0.245 mg N m −2 day −1 , and they were strongly linked to precipitation events. Additionally, the N 2 O fluxes during the rainy season were significantly greater than those during the dry season. The maximum N 2 O flux was observed in August, and the minimum flux occurred in December. Precipitation exclusion had a significant negative influence on the N 2 O fluxes. The N 2 O emissions of CK, PE3, PE5, and PE7 were 0.20, 0.17, 0.13, and 0.12 kg N ha −1 yr −1 , respectively. With the exacerbation of precipitation exclusion, the decrease rate of precipitation exclusion on the N 2 O emissions increased over the entire year (eventually reaching 41.8% in PE7), but the decrease rate of precipitation exclusion on the soil N 2 O emission during the dry season was stronger than that during the rainy season. Additionally, the proportion of dry season N 2 O emissions to total annual emissions decreased (from 45% to 41%), and that of rainy season N 2 O emissions to total annual emissions increased (from 55% to 59%) over the year, whereas they exhibited a stable trend from PE5. The data show that the Yuanjiang savanna is a net source of N 2 O; precipitation reduction decreases the N 2 O emissions in the savanna regions, indicating that precipitation reduction can only slow the increase in the N 2 O concentration in the atmosphere and can therefore slow global warming. In addition, the N 2 O emissions during the dry season may play a significant role in total N 2 O emissions and be more sensitive to precipitation reduction than those during rainy season. These possibilities should be considered in future studies, especially in those ecosystems that experience substantial inter-annual climatic fluctuations. [ABSTRACT FROM AUTHOR]

Soil respiration, the second largest CO 2 flux in terrestrial ecosystems, involves the microbial respiration of litter from aboveground sources, belowground litter and root respiration, from rhizodeposition. In the subtropical forests of the Ailao Mountain, a chamber with automated CO 2 efflux was set up with two treatments: a control treatment with litterfall to measure the total soil respiration (R T) and a litter removal treatment to measure aboveground litterfall respiration (R L). This study aimed to examine the responses of R L to unexpected heavy snowfall events and soil temperature (ST), soil moisture (SM), rainfall (RF), total litterfall (TL), litter water content (LWC), nitrate nitrogen (NO 3 −-N), and ammonium nitrogen (NH 4 +-N). The period of the study was divided into two: before the heavy snowfall event (BS) and during and after the heavy snowfall event (AS). The rate of R L was slightly decreased in AS (1.18 ± 0.03 μmol CO 2 m−2 s−1) compared with that in BS (1.19 ± 0.02 μmol CO 2 m−2 s−1). The relationships between R L and ST, SM, RF, and LWC, respectively, were all statistically significant (p < 0.05) in both periods. However, the relationships between R L and TL and NH 4 +-N, respectively, were not statistically significant for either period. The relationship between R L and NO 3 −-N was statistically significant for AS but not for BS. The relationship between R L and RF was statistically significant from 2011 to 2018. The temperature dependence of soil respiration was higher in BS than in AS, and the effect of litter removal was 2.55 % and 2.32 % for AS and BS respectively. The results indicate that current global terrestrial models underestimate R L trends for the feedback of global climate change in subtropical forests. Aboveground litterfall respiration (R L) had strong connection with soil temperature, soil moisture, rainfall and litter water content for two periods but not for ammonium nitrogen (NH 4 +-N). Unexpected snowfall events took effects the connection between R L and total litterfall. Heavy snowfall events declined the relationship between R L and nitrate nitrogen (NO 3 −-N). [Display omitted] [ABSTRACT FROM AUTHOR]

Climate models predict that droughts will increase in Southeast Asia, yet little is known about how soil respiration (Rs) and its components heterotrophic respiration (Rh) and autotrophic respiration (Ra) will change following drought years. To clarify this issue and to detect underlying mechanisms, we conducted a 2-year field experiment in the seventh and eighth year of long-term artificially droughted plots within a tropical rainforest in Xishuangbanna, southwest China. We separated Rh and Ra by trenching and we measured dissolved organic carbon in the soil and microbial biomass. In average, the drought stress, reduced through-fall by 50%, reduced fine root biomass by 36%. Although Ra declined by 35%, active inorganic N and Rh increased by 31% and 29%. Further, the coefficient of determination (R2) between soil microbial community composition, mainly, group-specific phospholipid fatty acid and the variation of Rh was among 17%–59% during the dry and rainy season of 2018. However, changes in dissolved organic carbon, microbial biomass carbon and nitrogen, ammonium nitrogen, were inconsistent with the increase in Rh. There was an inconsistent significant positive correlation between seasonal change of CO 2 flux and these processes dynamic across 2017 and 2018. Soil temperature, soil moisture, and litterfall jointly determined annual variation in Rs and Rh across two years. These findings have improved understanding of how long-term drought stress influences soil CO2 effluxes via change of soil-based biochemical indicators (like fine root, active inorganic nitrogen, and soil microorganisms). • Through-fall reduction decreased fine root and autotrophic respiration. • Nitrate-N and heterotrophic respiration increased under through-fall reduction. • Effect of through-fall reduction on soil respiration decreased after 6-year. • PLFAs correlated with heterotrophic respiration. [ABSTRACT FROM AUTHOR]