We used a climate-driven regression model to develop spatially resolved estimates of soil-CO{sub 2} emissions from the terrestrial land surface for each month from January 1980 to December 1994, to evaluate the effects of interannual variations in climate on global soil-to-atmosphere CO{sub 2} fluxes. The mean annual global soil-CO{sub 2} flux over this 15-y period was estimated to be 80.4 (range 79.3-81.8) Pg C. Monthly variations in global soil-CO{sub 2} emissions followed closely the mean temperature cycle of the Northern Hemisphere. Globally, soil-CO{sub 2} emissions reached their minima in February and peaked in July and August. Tropical and subtropical evergreen broad-leaved forests contributed more soil-derived CO{sub 2} to the atmosphere than did any other vegetation type ({approx}30% of the total) and exhibited a biannual cycle in their emissions. Soil-CO{sub 2} emissions in other biomes exhibited a single annual cycle that paralleled the seasonal temperature cycle. Interannual variability in estimated global soil-CO{sub 2} production is substantially less than is variability in net carbon uptake by plants (i.e., net primary productivity). Thus, soils appear to buffer atmospheric CO{sub 2} concentrations against far more dramatic seasonal and interannual differences in plant growth. Within seasonally dry biomes (savannas, bushlands, and deserts), interannual variability inmore » soil-CO{sub 2} emissions correlated significantly with interannual differences in precipitation. At the global scale, however, annual soil-CO{sub 2} fluxes correlated with mean annual temperature, with a slope of 3.3 PgCY{sup -1} per degree Celsius. Although the distribution of precipitation influences seasonal and spatial patterns of soil-CO{sub 2} emissions, global warming is likely to stimulate CO{sub 2} emissions from soils.« less

/pdf/interannual-variability-in-global-soil-respiration-on-a-0-5-5dl9wnaf74.pdf

Interannual Variability in Global Soil Respiration on a 0.5 Degree Grid Cell Basis (1980-1994)

The change of litter input can affect soil respiration (Rs) by influencing the availability of soil organic carbon and nutrients, regulating soil microenvironments, thus resulting in a profound influence on soil carbon cycle of the forest ecosystem. We conducted an aboveground litterfall manipulation experiment in different-aged Betula platyphylla forests (25-, 40- and 61-year-old) of the permafrost region, located in the northeast of China, during May to October in 2018, with each stand treated with doubling litter (litter addition, DL), litter exclusion (no-litter, NL) and control litter (CK). Our results indicated that Rs decreased under NL treatment compared with CK treatment. The effect size lessened with the increase in the stand age; the greatest reduction was found for young Betula platyphylla forest (24.46% for 25-year-old stand) and tended to stabilize with the growth of forest with the reduction of 15.65% and 15.23% for 40-and 61- year-old stands, respectively. Meanwhile, under DL treatment, Rs increased by 27.38%, 23.83% and 23.58% on 25-, 40- and 61-year-old stands, respectively. Our results also showed that the increase caused by DL treatment was larger than the reduction caused by NL treatment, leading to a priming effect, especially on 40- and 61-year-old stands. The change in litter input was the principal factor affecting the change of Rs under litter manipulation. The soil temperature was also a main factor affecting the contribution rate of litter to Rs of different-aged stands, which had a significant positive exponential correlation with Rs. This suggests that there is a significant relationship between litter and Rs, which consequently influences the soil carbon cycle in Betula platyphylla forests of the permafrost region, Northeast China. Our finding indicated the increased litter enhanced the Rs in Betula platyphylla forest, which may consequently increase the carbon emission in a warming climate in the future. It is of great importance for future forest management in the permafrost region, Northeast China.

https://www.mdpi.com/1999-4907/12/1/89/pdf

Increased Litter Greatly Enhancing Soil Respiration in Betula platyphylla Forests of Permafrost Region, Northeast China

Abstract This study examines carbon (C) and water dynamics in two East African dryland ecosystems: a savanna rangeland grazed by livestock and wildlife, and a rainfed cropland under minimal tillage. Over 185 days, both systems were showed a similar magnitude of C emissions with differing temporal patterns. The rangeland showed fluctuating C exchange, with losses followed by increased C uptake after rainfall events. The cropland initially acted as a C sink, and when lateral C export from chickpea harvest were accounted for, the overall C balance shifted to a net source. Cropland demonstrated higher carbon use efficiency (CUE), driven by efficient C allocation for crop growth, supported by fertilizers, pesticides, and minimum tillage practices. During the peak growing period, cropland also had greater water use efficiency (WUE) likely reflecting optimized agricultural management under favorable moisture conditions. However, over the entire period, WUE was significantly higher in the rangeland than in the cropland ( p &gt; 0.05) possibly due to more consistent vegetation cover and adaptive traits that minimize water loss. The cropland showed a complex relationship between WUE and CUE, where increased productivity also simultaneously drove higher respiration rates. Our findings, particularly the shift in cropland carbon balance following harvest emphasize the importance of including lateral C fluxes and intra‐annual variations in C balance assessments for accurate budgeting. Both ecosystems were co‐limited by water and nitrogen, with plant adaptations to drought and dry spells, including efficient water use and sustained photosynthesis under moisture stress playing a critical role in maintaining ecosystem CUE. Sustainable land management strategies that account for the interactions between C and water dynamics, biodiversity, and ecosystem functioning are vital to enhancing C storage, mitigating climate change, and improving resilience in rangelands and croplands. 

Contrasting Carbon and Water Flux Dynamics in an East African Rangeland and Cropland

Understanding the effects of agricultural managements (e.g., straw incorporation) on soil respiration (Rs) and its temperature sensitivity (Q10) is crucial for accurate estimation of the soil carbon sequestration potential under an increasing-temperature scenario in the future. However, how the influence drivers regulate Rs and whether their relative roles are changed under different agricultural practices remain unexplored. Static chambers were used to monitor field CO2 flux in one growing season for a straw return experiment, which had been amended with different amounts of straw (CK, no straw return; S4, straw amendment at 4000 kg ha−1; and S8, straw amendment at 8000 kg ha−1) for five consecutive years. Our monitoring showed that Rs was elevated with intensified use of straw and confirmed soil temperature, soil moisture, and rainfall were important seasonal drivers of Rs. Moreover, the lower coefficient of variations (CV) for each series of treatments of Rs was detected at the vigorous growth stage of the crop, implying the biotic factor of crop roots might also exert a role simultaneously. Straw addition tended to reduce Q10, probably due to the fact that the microbial degradation of SOC in S4 and S8 was less sensitive to temperature change. Interestingly, the Q10 of S4 but not S8 was significantly smaller (P < 0.05) than that of CK as the reduced magnitude of Q10 for S4 was more profound. This result corresponded with more proportional growth of crop root of S8 than S4. By comprehensively analyzing the seasonal variability of our data set, we inferred that for S8, the negative impact of straw incorporation on Q10 would be more offset by upregulated root metabolism. Although additional works were needed to corroborate and specify this explanation, present research highlighted the abiotic and biotic factors should both be incorporated to analyze the underlying mechanisms responsible for the seasonal dynamics of soil C emissions under agricultural managements.

The relative importance of influence factors to field soil respiration is shifted by straw incorporations: comprehensive analysis of the seasonal variability

Global warming will stimulate primary production, which is likely to drive shifts in litter production and lead to an increase in carbon (C) inputs to soil. However, the effects of such changes on soil C cycling in subtropical forests remain largely unknown. In a typical subtropical evergreen broadleaved forest in Southwestern China we conducted a controlled experiment that included addition and removal of litter, and trenching. Annual soil respiration in control, trenching, litter addition, and litter removal treatments were 1083.47, 521.50, 1363.30, and 896.15 g C m–2 y–1, respectively. Soil respiration was significantly related to temperature in all treatments, but was independent of soil moisture, except in control plots. Q10 values in control, trenching, litter addition, and litter removal treatments were 3.46, 6.36, 2.72, and 4.85, respectively. Litter addition reduced Q10, but litter removal and trenching increased it. Average heterotrophic soil respiration produced C in the amount equivalent to 48% of the efflux from the soil. Soil respiration in the litter addition treatment was 25% higher than in the control treatment; this increase is about 8% larger than the 17% decrease in soil respiration caused by litter removal. This implies a priming effect on soil respiration. Our results suggest that increases in litter production in response to human disturbances and global warming could have rapid and important consequences on soil respiration in subtropical evergreen broadleaved forests.

Litter priming and trenching greatly affect soil respiration in a mature subtropical evergreen broadleaf forest in Southwestern China

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Litter priming and trenching greatly affect soil respiration in a mature subtropical evergreen broadleaf forest in Southwestern China