Distinct responses of soil respiration to experimental litter manipulation in temperate woodland and tropical forest

Global change is affecting primary productivity in forests worldwide, and this, in turn, will alter long‐term carbon (C) sequestration in wooded ecosystems. On one hand, increased primary productivity, for example, in response to elevated atmospheric carbon dioxide (CO2), can result in greater inputs of organic matter to the soil, which could increase C sequestration belowground. On other hand, many of the interactions between plants and microorganisms that determine soil C dynamics are poorly characterized, and additional inputs of plant material, such as leaf litter, can result in the mineralization of soil organic matter, and the release of soil C as CO2 during so‐called “priming effects”. Until now, very few studies made direct comparison of changes in soil C dynamics in response to altered plant inputs in different wooded ecosystems. We addressed this with a cross‐continental study with litter removal and addition treatments in a temperate woodland (Wytham Woods) and lowland tropical forest (Gigante forest) to compare the consequences of increased litterfall on soil respiration in two distinct wooded ecosystems. Mean soil respiration was almost twice as high at Gigante (5.0 μmol CO2 m−2 s−1) than at Wytham (2.7 μmol CO2 m−2 s−1) but surprisingly, litter manipulation treatments had a greater and more immediate effect on soil respiration at Wytham. We measured a 30% increase in soil respiration in response to litter addition treatments at Wytham, compared to a 10% increase at Gigante. Importantly, despite higher soil respiration rates at Gigante, priming effects were stronger and more consistent at Wytham. Our results suggest that in situ priming effects in wooded ecosystems track seasonality in litterfall and soil respiration but the amount of soil C released by priming is not proportional to rates of soil respiration. Instead, priming effects may be promoted by larger inputs of organic matter combined with slower turnover rates

Winter soil respiration in a humid temperate forest: The roles of moisture, temperature, and snowpack

Winter soil respiration at midlatitudes can comprise a substantial portion of annual ecosystem carbon loss. However, winter soil carbon dynamics in these areas, which are often characterized by shallow snow cover, are poorly understood due to infrequent sampling at the soil surface. Our objectives were to continuously measure winter CO2 flux from soils and the overlying snowpack while also monitoring drivers of winter soil respiration in a humid temperate forest. We show that the relative roles of soil temperature and moisture in driving winter CO2 flux differed within a single soil-to-snow profile. Surface soil temperatures had a strong, positive influence on CO2 flux from the snowpack, while soil moisture exerted a negative control on soil CO2 flux within the soil profile. Rapid fluctuations in snow depth throughout the winter likely created the dynamic soil temperature and moisture conditions that drove divergent patterns in soil respiration at different depths. Such dynamic conditions differ from many previous studies of winter soil microclimate and respiration, where soil temperature and moisture are relatively stable until snowmelt. The differential response of soil respiration to temperature and moisture across depths was also a unique finding as previous work has not simultaneously quantified CO2 flux from soils and the snowpack. The complex interplay we observed among snow depth, soil temperature, soil moisture, and CO2 flux suggests that winter soil respiration in areas with shallow seasonal snow cover is more variable than previously understood and may fluctuate considerably in the future given winter climate change

Seasonal dynamics of soil respiration and nitrogen mineralization in chronically warmed and fertilized soils

Although numerous studies have examined the individual effects of increased temperatures and N deposition on soil biogeochemical cycling, few have considered how these disturbances interact to impact soil C and N dynamics. Likewise, many have not assessed season-specific responses to warming and N inputs despite seasonal variability in soil processes. We studied interactions among season, warming, and N additions on soil respiration and N mineralization at the Soil Warming × Nitrogen Addition Study at the Harvard Forest. Of particular interest were wintertime fluxes of C and N typically excluded from investigations of soils and global change. Soils were warmed to 5°C above ambient, and N was applied at a rate of 5 g m−2 y−1. Soil respiration and N mineralization were sampled over two years between 2007 and 2009 and showed strong seasonal patterns that mirrored changes in soil temperature. Winter fluxes of C and N contributed between 2 and 17% to the total annual flux. Net N mineralization increased in response to the experimental manipulations across all seasons, and was 8% higher in fertilized plots and 83% higher in warmed plots over the duration of the study. Soil respiration showed a more season-specific response. Nitrogen additions enhanced soil respiration by 14%, but this increase was significant only in summer and fall. Likewise, warming increased soil respiration by 44% over the whole study period, but the effect of warming was most pronounced in spring and fall. The only interaction between warming × N additions took place in autumn, when N availability likely diminished the positive effect of warming on soil respiration. Our results suggest that winter measurements of C and N are necessary to accurately describe winter biogeochemical processes. In addition, season-specific responses to the experimental treatments suggest that some components of the belowground community may be more susceptible to warming and N additions than others. Seasonal changes in the abiotic environment may have also interacted with the experimental manipulations to evoke biogeochemical responses at certain times of year

Significance of temperature and soil water content on soil respiration in three desert ecosystems in Northwest China

It is crucial to understand how abiotic factors influence soil respiration and to determine, in a quantitative manner, the site variation of abiotic regulators in desert ecosystems. In this study, soil respiration was measured using an automated CO2 efflux system (LI-COR 8100) in 2005 and 2006. Additionally, the effects of soil temperature, moisture and a short-term precipitation manipulation on the rate of soil respiration were examined in Haloxylon ammodendron, Anabasis aphylla and Halostachys caspica in three distinct desert ecosystems. The difference in soil respiration among sites was significant. Air temperature explained 35-65% of the seasonal changes in soil respiration when an exponential equation was used. The effect of temperature on soil respiration and temperature sensitivity was stronger at sites with higher soil moisture. Soil respiration was significantly positively correlated with soil moisture. Amounts of variation in soil respiration explained by temperature and gravimetric water content were 41-44% in H. ammodendron, 62-65% in A. aphylla and 67-84% in H. caspica sites. Artificial rainfall treatments of 5 mm, 2.5 mm and 0 mm (control) were conducted. Soil respiration increased in a small pulse following rainfall. Temperature dominantly influenced soil respiration and soil water content enhanced the response of respiration to temperature. (C) 2010 Elsevier Ltd. All rights reserved

Plant species richness regulates soil respiration through changes in productivity

Soil respiration is an important pathway of the C cycle. However, it is still poorly understood how changes in plant community diversity can affect this ecosystem process. Here we used a long-term experiment consisting of a gradient of grassland plant species richness to test for effects of diversity on soil respiration. We hypothesized that plant diversity could affect soil respiration in two ways. On the one hand, more diverse plant communities have been shown to promote plant productivity, which could increase soil respiration. On the other hand, the nutrient concentration in the biomass produced has been shown to decrease with diversity, which could counteract the production-induced increase in soil respiration. Our results clearly show that soil respiration increased with species richness. Detailed analysis revealed that this effect was not due to differences in species composition. In general, soil respiration in mixtures was higher than would be expected from the monocultures. Path analysis revealed that species richness predominantly regulates soil respiration through changes in productivity. No evidence supporting the hypothesized negative effect of lower N concentration on soil respiration was found. We conclude that shifts in productivity are the main mechanism by which changes in plant diversity may affect soil respiration

Effects of drying-wetting cycle caused by rainfall on soil respiration: Progress and prospect

Soil respiration is an important part of the carbon cycle in terrestrial ecosystems. The changes of soil respiration caused by rainfall directly affect global carbon balance. Therefore, it is important to explore the mechanism underlying the effects of rainfall on soil respiration, which is necessary for understanding the carbon cycle and carbon budget of terrestrial ecosystems. Here, we summarized the research progress on the mechanism of drying-wetting cycle caused by rainfall on soil respiration. Soil respiration can be promoted at intermediate moisture conditions, but suppressed in both wetter and drier conditions. Dryingwetting cycles caused by rainfall affect soil respiration by changing soil moisture. On one hand, under the condition of drought, dryingwetting cycle caused by rainfall improve soil respiration rate by shortterm replacement of CO2 in soil, increases of soil microbial respiratory substrate, increases of microbial activity, and enhancement of litter decomposition. On the other hand, soils with high moisture could reach saturation more quickly or even be waterlogged after a short period of rainfall. Dryingwetting cycle caused by rainfall can significantly suppress soil respiration through restricting the entrance of O2 to the soil, forming an anaerobic environment, and inhibiting microbial and root respiration. In addition, dryingwetting cycle caused by rainfall could significantly inhibit root respiration by flooding part of the plant, reducing plant leaf area and photosynthetic products. In order to accurately estimate the interference of soil respiration on carbon budget of terrestrial ecosystems, future studies on the effects of rainfall on soil respiration should focus on three aspects: (1) microbiological response mechanisms underlying the effects of rainfall on soil respiration; (2) differentiating response mechanisms of soil autotrophic respiration and heterotrophic respiration to rainfall; and (3) modeling the effect of rainfall on soil respiration

Effect of different land use on soil respiration in winter

The effect of different land uses on soil respiration was investigated in winter 2009 in black locust, grassland, apple orchard (apple trees and grass) and walnut areas in Seyitler Village, Artvin, Turkey. Soil respiration was measured in December by the soda-lime (NaOH, KOH) technique. Mean daily soil respiration ranged from 0.29 to 1.26 g C m-2 d-1 . Mean daily soil respiration in black locust was greater than the other areas. Soil respiration was different in the investigated four vegetation types. Established difference was non significant and correlations were negative among soil respiration, soil moisture and soil temperature. These results show that black locust has higher soil biological activity compared to the other areas in this season

Factors controlling spatio-temporal variation in carbon dioxide efflux from surface litter, roots, and soil organic matter at four rain forest sites in the eastern Amazon

[1] This study explored biotic and abiotic causes for spatio-temporal variation in soil respiration from surface litter, roots, and soil organic matter over one year at four rain forest sites with different vegetation structures and soil types in the eastern Amazon, Brazil. Estimated mean annual soil respiration varied between 13-17 t C ha(-1) yr(-1), which was partitioned into 0-2 t C ha(-1) yr(-1) from litter, 6-9 t C ha(-1) yr(-1) from roots, and 5-6 t C ha(-1) yr(-1) from soil organic matter. Litter contribution showed no clear seasonal change, though experimental precipitation exclusion over a one-hectare area was associated with a ten-fold reduction in litter respiration relative to unmodified sites. The estimated mean contribution of soil organic matter respiration fell from 49% during the wet season to 32% in the dry season, while root respiration contribution increased from 42% in the wet season to 61% during the dry season. Spatial variation in respiration from soil, litter, roots, and soil organic matter was not explained by volumetric soil moisture or temperature. Instead, spatial heterogeneity in litter and root mass accounted for 44% of observed spatial variation in soil respiration (p < 0.001). In particular, variation in litter respiration per unit mass and root mass accounted for much of the observed variation in respiration from litter and roots, respectively, and hence total soil respiration. This information about patterns of, and underlying controls on, respiration from different soil components should assist attempts to accurately model soil carbon dioxide fluxes over space and time

Carbon dioxide fluxes across the Sierra de Guadarrama, Spain

Understanding the spatial and temporal variation in soil respiration within small geographic areas is essential to accurately assess the carbon budget on a global scale. In this study, we investigated the factors controlling soil respiration in an altitudinal gradient in a southern Mediterranean mixed pine&#8211;oak forest ecosystem in the north face of the Sierra de Guadarrama in Spain. Soil respiration was measured in five Pinus sylvestris L. plots over a period of 1 year by means of a closed dynamic system (LI-COR 6400). Soil temperature and water content were measured at the same time as soil respiration. Other soil physico-chemical and microbiological properties were measured during the study. Measured soil respiration ranged from 6.8 to 1.4 lmol m-2 s-1, showing the highest values at plots situated at higher elevation. Q10 values ranged between 1.30 and 2.04, while R10 values ranged between 2.0 and 3.6. The results indicate that the seasonal variation of soil respiration was mainly controlled by soil temperature and moisture. Among sites, soil carbon and nitrogen stocks regulate soil respiration in addition to soil temperature and moisture. Our results suggest that application of standard models to estimate soil respiration for small geographic areas may not be adequate unless other factors are considered in addition to soil temperature