Peer review report 1 On “ Responses of soil respiration to N addition, burning and clipping in temperate semiarid grassland in Northern China ”

Increasing atmospheric nitrogen (N) deposition has profound effects on carbon (C) cycling in forest ecosystems. As an important part of belowground C dynamics, soil respiration is potentially affected by changing N availability. However, the responses of total soil respiration (RST) and its three components, soil respiration derived from plant roots (RSR), root-free soil (RSS) and the litter layer (RSL), to such N enrichment remains poorly understood. To assess the effects of N enrichment on soil respiration components, three levels of N addition, namely low (LN, 50 kg N ha−1 year−1), medium (MN, 100 kg N ha−1 year−1) and high (HN, 150 kg N ha−1 year−1), were conducted over five growing seasons from 2011 to 2015 in a temperate Chinese pine (Pinus tabulaeformis) forest in northern China. A control plot without N addition (CK) was also established. The five-year mean annual rate of RST was 2.18 ± 0.43 μmol m−2 s−1, and the contributions of RSR, RSS and RSL were 8.8 ± 3.1%, 82.2 ± 4.5% and 9.0 ± 5.5%, respectively. Compared with CK, RST was significantly increased by 16.5% in the HN plots, but not in the LN or MN treatments. RSS was significantly decreased by 18.1%, 26.6% and 18.4% in the LN, MN and HN plots, respectively, due to the reduction of both microbial biomass carbon (MBC) and enzyme activity. In contrast, RSR was increased by more than twice under the MN treatment, which promoted root growth and activity (higher fine root biomass and N concentration). A significant elevation in RSL was only detected in the HN plots, where the increased litter input enhanced litter decomposition and hence RSL. Our findings clearly demonstrated that N addition of different intensities had different effects on soil components. In particular, the above- and belowground components of heterotrophic respiration, RSL and RSR, showed contrasting responses to high level addition of N. Thus, we highlight that the response of soil respiration components to N addition should be examined individually. Our results may contribute to a better understanding of soil respiration dynamics under future N scenarios, and have important implications in forest management.

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Water- and plant-mediated responses of soil respiration to topography, fire, and nitrogen fertilization in a semiarid grassland in northern China

Soil Biology and Biochemistry ◽

10.1016/j.soilbio.2007.10.003 ◽

2008 ◽

Vol 40 (3) ◽

pp. 679-687 ◽

Cited By ~ 114

Author(s):

Wenhua Xu ◽

Shiqiang Wan

Keyword(s):

Soil Respiration ◽

Nitrogen Fertilization ◽

Northern China ◽

Semiarid Grassland

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Response of soil respiration to nitrogen addition along a degradation gradient in a temperate steppe of northern China

10.5194/bg-2016-119 ◽

2016 ◽

Cited By ~ 1

Author(s):

Jinbin Chen ◽

Xiaotian Xu ◽

Hongyan Liu ◽

Wei Wang

Keyword(s):

Soil Respiration ◽

Soil Carbon ◽

Soil Ph ◽

Carbon Emissions ◽

Root Biomass ◽

Northern China ◽

N Addition ◽

Grassland Ecosystems ◽

The Difference ◽

Degraded Grassland

Abstract. Although numerous studies have been conducted on the responses of soil respiration (Rs) to nitrogen (N) addition in grassland ecosystems, it remains unclear whether a nonlinear relationship between Rs and N addition exists and whether there is a uniform response across grasslands with different degradation status. We established a field experiment with six N treatments (0, 10, 20, 30, 40, and 50 g N m−2 y−1) on four grassland sites, each with a varied degradation states in the Inner Mongolia steppe of northern China during the growing seasons of 2012 and 2013. Rs and its major influential factors, including aboveground biomass, root biomass, plant tissues carbon (C) and N concentrations, soil organic carbon (SOC) and soil total nitrogen (STN), microbial biomass and soil pH, were measured. Results show that N fertilization did not change the seasonal patterns of Rs but it changed the magnitude of Rs in grasslands with a different degradation status and only degradation had signification effects on Rs. This shows that variations of Rs in degraded grasslands were due to the difference in SOC content. The response of Rs to N addition differed with the severity of degradation. Furthermore, the response of Rs to N addition slowed down over time. The dominant factor controlling Rs changed across different degradation grasslands. The leading factors for Rs were SOC and STN in non-degraded and moderately degraded grassland; soil pH in severely degraded grassland; and aboveground biomass and root biomass in extremely degraded grassland. Our results highlight the importance of considering the degradation level of grassland to identify soil carbon emissions in grassland ecosystems, and N addition may alter the difference of soil carbon emissions in different degraded grasslands and change its soil carbon emissions pattern.

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Impacts of urea N addition on soil microbial community in a semi-arid temperate steppe in northern China

Plant and Soil ◽

10.1007/s11104-008-9650-0 ◽

2008 ◽

Vol 311 (1-2) ◽

pp. 19-28 ◽

Cited By ~ 102

Author(s):

Naili Zhang ◽

Shiqiang Wan ◽

Linghao Li ◽

Jie Bi ◽

Mingming Zhao ◽

...

Keyword(s):

Microbial Community ◽

Soil Microbial Community ◽

Northern China ◽

N Addition ◽

Temperate Steppe ◽

Soil Microbial ◽

Semi Arid

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Responses of soil respiration to elevated carbon dioxide and nitrogen addition in young subtropical forest ecosystems in China

Biogeosciences ◽

10.5194/bg-7-315-2010 ◽

2010 ◽

Vol 7 (1) ◽

pp. 315-328 ◽

Cited By ~ 84

Author(s):

Q. Deng ◽

G. Zhou ◽

J. Liu ◽

S. Liu ◽

H. Duan ◽

...

Keyword(s):

Soil Respiration ◽

Elevated Co2 ◽

Forest Ecosystems ◽

N Deposition ◽

Subtropical Forest ◽

N Addition ◽

Above Ground Biomass ◽

Respiration Rates ◽

Ambient Co2 ◽

Ambient N Deposition

Abstract. Global climate change in the real world always exhibits simultaneous changes in multiple factors. Prediction of ecosystem responses to multi-factor global changes in a future world strongly relies on our understanding of their interactions. However, it is still unclear how nitrogen (N) deposition and elevated atmospheric carbon dioxide concentration [CO2] would interactively influence forest floor soil respiration in subtropical China. We assessed the main and interactive effects of elevated [CO2] and N addition on soil respiration by growing tree seedlings in ten large open-top chambers under CO2 (ambient CO2 and 700 μmol mol−1) and nitrogen (ambient and 100 kg N ha−1 yr−1) treatments. Soil respiration, soil temperature and soil moisture were measured for 30 months, as well as above-ground biomass, root biomass and soil organic matter (SOM). Results showed that soil respiration displayed strong seasonal patterns with higher values observed in the wet season (April–September) and lower values in the dry season (October–March) in all treatments. Significant exponential relationships between soil respiration rates and soil temperatures, as well as significant linear relationships between soil respiration rates and soil moistures (below 15%) were found. Both CO2 and N treatments significantly affected soil respiration, and there was significant interaction between elevated [CO2] and N addition (p<0.001, p=0.003, and p=0.006, respectively). We also observed that the stimulatory effect of individual elevated [CO2] (about 29% increased) was maintained throughout the experimental period. The positive effect of N addition was found only in 2006 (8.17% increased), and then had been weakened over time. Their combined effect on soil respiration (about 50% increased) was greater than the impact of either one alone. Mean value of annual soil respiration was 5.32 ± 0.08, 4.54 ± 0.10, 3.56 ± 0.03 and 3.53 ± 0.03 kg CO2 m−2 yr−1 in the chambers exposed to elevated [CO2] and high N deposition (CN), elevated [CO2] and ambient N deposition (CC), ambient [CO2] and high N deposition (NN), and ambient [CO2] and ambient N deposition (CK as a control), respectively. Greater above-ground biomass and root biomass was obtained in the CN, CC and NN treatments, and higher soil organic matter was observed only in the CN treatment. In conclusion, the combined effect of elevated [CO2] and N addition on soil respiration was apparent interaction. They should be evaluated in combination in subtropical forest ecosystems in China where the atmospheric CO2 and N deposition have been increasing simultaneously and remarkably.

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