scholarly journals Non-rainfall moisture: a key driver of carbon flux from standing litter in arid, semiarid, and mesic grasslands

2019 ◽  
Author(s):  
Sarah E. Evans ◽  
Katherine E. O. Todd-Brown ◽  
Kathryn Jacobson ◽  
Peter Jacobson
Keyword(s):  
Mass Loss ◽  
Litter Decomposition ◽  
Tallgrass Prairie ◽  
Field Measurements ◽  
List Type ◽  
High Humidity ◽  
Microbial Response ◽  
Improve Model ◽  
Physical Features ◽  
Standing Litter

AbstractModels assume that rainfall is the major source of moisture driving decomposition. Non-rainfall moisture (NRM: high humidity, dew, and fog) can also induce standing litter decomposition, but there have been few standard measurements of NRM-mediated decompositions across sites, and no efforts to extrapolate the contribution of NRM to larger scales to assess whether this mechanism can improve model predictions. Here we show that NRM is an important, year-round source of moisture in grassland sites with contrasting moisture regimes using field measurements and modeling. We first characterized NRM frequency and measured NRM-mediated decomposition in sites on the extreme dry and wet end of grassland systems: at two sites in the Namib Desert, Namibia (hyperarid desert) and at one site in Iowa, USA (tallgrass prairie). NRM was frequent at all sites (85-99% of hours that litter was likely to be wet were attributed to NRM) and tended to occur in cool, high-humidity periods for several hours or more at a time. NRM also caused respiration of standing litter at all sites when litter became sufficiently wet (>5% for fine litter and >13% for coarse), and contributed to mass loss, even in the Namib West site that had almost no rain. When we modeled annual mass loss induced by NRM and rain, and extrapolated our characterization of NRM decomposition to a final site with intermediate rainfall (Sevilleta, New Mexico, semiarid grassland), we found that models driven by rainfall alone underestimated mass loss, while including NRM produced estimates within the range of observed mass loss. Together these findings suggest that NRM is an important missing component in quantitative and conceptual models of litter decomposition, but there is nuance involved in modeling NRM at larger scales. Specifically, temperature and physical features of the substrate emerge as factors that affect the common microbial response to litter wetting under NRM across grasslands sites, and require further study. Hourly humidity can provide an adequate proxy of NRM frequency, but site-specific calibration with litter wetness is needed to accurately attribute decomposition to periods when NRM wets litter. Greater recognition of NRM-driven decomposition and its interaction with other processes (e.g. photodegradation) is needed, especially since fog, dew, and humidity are likely to shift under future climates.Manuscript highlightsNon-rainfall moisture (NRM; humidity, fog, dew) induces decomposition in grasslandsNRM decomposition depends on substrate type, and occurs at colder times than rainIncluding NRM (instead of rain alone) improved predictions of litter decomposition

scholarly journals Non-rainfall Moisture: A Key Driver of Microbial Respiration from Standing Litter in Arid, Semiarid, and Mesic Grasslands

Ecosystems ◽  
2019 ◽  
Vol 23 (6) ◽  
pp. 1154-1169 ◽  
Author(s):  
Sarah Evans ◽  
Katherine E. O. Todd-Brown ◽  
Kathryn Jacobson ◽  
Peter Jacobson
Keyword(s):  
Mass Loss ◽  
Litter Decomposition ◽  
Tallgrass Prairie ◽  
Field Measurements ◽  
High Humidity ◽  
Microbial Response ◽  
Improve Model ◽  
Arid Desert ◽  
Physical Features ◽  
Standing Litter

Abstract Models assume that rainfall is the major moisture source driving decomposition. Non-rainfall moisture (NRM: high humidity, dew, and fog) can also induce standing litter decomposition, but there have been few measurements of NRM-mediated decomposition across sites and no efforts to extrapolate the contribution of NRM to larger scales to assess whether this mechanism can improve model predictions. Here, we show that NRM is an important, year-round source of moisture in grassland sites with contrasting moisture regimes using field measurements and modeling. We first characterized NRM frequency and measured NRM-mediated decomposition at two sites in the Namib Desert, Namibia (hyper-arid desert), and at one site in Iowa, USA (tallgrass prairie). NRM was frequent at all sites (85–99% of hours that litter was likely to be wet were attributed to NRM) and tended to occur in cool, high-humidity periods for several hours or more at a time. NRM also resulted in CO2 release from microbes in standing litter at all sites when litter became sufficiently wet (> 5% gravimetric moisture for fine litter and > 13% for coarse), and significantly contributed to mass loss, particularly in the western Namib site that received almost no rain. When we modeled annual mass loss induced by NRM and rain and extrapolated our characterization of NRM decomposition to a final semiarid site (Sevilleta, New Mexico), we found that models driven by rainfall alone underestimated mass loss, while including NRM resulted in estimates within the range of observed mass loss. Together these findings suggest that NRM is an important missing component in quantitative and conceptual models of litter decomposition, but there is nuance involved in modeling NRM at larger scales. Specifically, temperature and physical features of the substrate emerge as factors that affect the microbial response to litter wetting under NRM in our sites, and require further study. Hourly humidity can provide an adequate proxy of NRM frequency, but site-specific calibration with litter wetness is needed to accurately attribute decomposition to periods when NRM wets litter. Greater recognition of NRM-driven decomposition and its interaction with other processes like photodegradation is needed, especially since fog, dew, and humidity are likely to shift under future climates.

Effects of nitrogen deposition on litter decomposition and nutrient release mediated by litter types and seasonal change in a temperate forest

2020 ◽  
Vol 100 (1) ◽  
pp. 11-25 ◽  
Author(s):  
Guoyong Yan ◽  
Xiongde Dong ◽  
Binbin Huang ◽  
Honglin Wang ◽  
Ziming Hong ◽  
...  
Keyword(s):  
Mass Loss ◽  
Litter Decomposition ◽  
Nutrient Release ◽  
N Deposition ◽  
Pinus Koraiensis ◽  
N Addition ◽  
Entire Study ◽  
Mixed Litter ◽  
Negative Effect ◽  
Four Levels

We conducted a field experiment with four levels of simulated nitrogen (N) deposition (0, 2.5, 5, and 7.5 g N m−2 yr−1, respectively) to investigate the response of litter decomposition of Pinus koraiensis (PK), Tilia amurensis (TA), and their mixture to N deposition during winter and growing seasons. Results showed that N addition significantly increased the mass loss of PK litter and significantly decreased the mass loss of TA litter throughout the 2 yr decomposition processes, which indicated that the different responses in the decomposition of different litters to N addition can be species specific, potentially attributed to different litter chemistry. The faster decomposition of PK litter with N addition occurred mainly in the winter, whereas the slower decomposition of TA litter with N addition occurred during the growing season. Moreover, N addition had a positive effect on the release of phosphorus, magnesium, and manganese for PK litter and had a negative effect on the release of carbon, iron, and lignin for TA litter. Decomposition and nutrient release from mixed litter with N addition showed a non-additive effect. The mass loss from litter in the first winter and over the entire study correlated positively with the initial concentration of cellulose, lignin, and certain nutrients in the litter, demonstrating the potential influence of different tissue chemistries.

Ants accelerate litter decomposition in a Costa Rican lowland tropical rain forest

2012 ◽  
Vol 28 (5) ◽  
pp. 437-443 ◽  
Author(s):  
Terrence P. McGlynn ◽  
Evan K. Poirson
Keyword(s):  
Mass Loss ◽  
Leaf Litter ◽  
Litter Decomposition ◽  
Rain Forest ◽  
Costa Rican ◽  
Tropical Rain Forests ◽  
Rain Forests ◽  
Food Web Structure ◽  
Litter Bags ◽  
Lowland Rain Forest

Abstract:The decomposition of leaf litter is governed, in part, by litter invertebrates. In tropical rain forests, ants are dominant predators in the leaf litter and may alter litter decomposition through the action of a top-down control of food web structure. The role of ants in litter decomposition was investigated in a Costa Rican lowland rain forest with two experiments. In a mesocosm experiment, we manipulated ant presence in 50 ambient leaf-litter mesocosms. In a litterbag gradient experiment, Cecropia obtusifolia litter was used to measure decomposition rate constants across gradients in nutrients, ant density and richness, with 27 separate litterbag treatments for total arthropod exclusion or partial arthropod exclusion. After 2 mo, mass loss in mesocosms containing ants was 30.9%, significantly greater than the 23.5% mass loss in mesocosms without ants. In the litter bags with all arthropods excluded, decomposition was best accounted by the carbon: phosphorus content of soil (r2 = 0.41). In litter bags permitting smaller arthropods but excluding ants, decomposition was best explained by the local biomass of ants in the vicinity of the litter bags (r2 = 0.50). Once the microarthropod prey of ants are permitted to enter litterbags, the biomass of ants near the litterbags overtakes soil chemistry as the regulator of decomposition. In concert, these results support a working hypothesis that litter-dwelling ants are responsible for accelerating litter decomposition in lowland tropical rain forests.

scholarly journals Balanced conditions or slight mass gain of glaciers in the Lahaul and Spiti region (northern India, Himalaya) during the nineties preceded recent mass loss

2013 ◽  
Vol 7 (2) ◽  
pp. 569-582 ◽  
Author(s):  
C. Vincent ◽  
Al. Ramanathan ◽  
P. Wagnon ◽  
D. P. Dobhal ◽  
A. Linda ◽  
...  
Keyword(s):  
Mass Loss ◽  
Field Measurements ◽  
Mass Gain ◽  
Negative Mass ◽  
Northern India ◽  
Chhota Shigri Glacier ◽  
Digital Elevation ◽  
Recent Compilation ◽  
Spiti Region ◽  
Dem Differencing

Abstract. The volume change of the Chhota Shigri Glacier (India, 32° 20 N, 77° 30' E) between 1988 and 2010 has been determined using in situ geodetic measurements. This glacier has experienced only a slight mass loss between 1988 and 2010 (−3.8 ± 2.0 m w.e. (water equivalent) corresponding to −0.17 ± 0.09 m w.e. yr−1). Using satellite digital elevation models (DEM) differencing and field measurements, we measure a negative mass balance (MB) between 1999 and 2010 (−4.8 ± 1.8 m w.e. corresponding to −0.44 ± 0.16 m w.e. yr−1). Thus, we deduce a slightly positive or near-zero MB between 1988 and 1999 (+1.0 ± 2.7 m w.e. corresponding to +0.09 ± 0.24 m w.e. yr−1). Furthermore, satellite DEM differencing reveals that the MB of the Chhota Shigri Glacier (−0.39 ± 0.15 m w.e. yr−1) has been only slightly less negative than the MB of a 2110 km2 glaciarized area in the Lahaul and Spiti region (−0.44 ± 0.09 m w.e. yr−1) during 1999−2011. Hence, we conclude that the ice wastage is probably moderate in this region over the last 22 yr, with near equilibrium conditions during the nineties, and an ice mass loss after. The turning point from balanced to negative mass budget is not known but lies probably in the late nineties and at the latest in 1999. This positive or near-zero MB for Chhota Shigri Glacier (and probably for the surrounding glaciers of the Lahaul and Spiti region) during at least part of the 1990s contrasts with a recent compilation of MB data in the Himalayan range that indicated ice wastage since 1975. However, in agreement with this compilation, we confirm more negative balances since the beginning of the 21st century.

Fungal richness does not buffer the effects of streams salinization on litter decomposition

2021 ◽  
Vol 57 ◽  
pp. 5
Author(s):  
Janine Pereira da Silva ◽  
Aingeru Martínez ◽  
Ana Lúcia Gonçalves ◽  
Felix Bärlocher ◽  
Cristina Canhoto
Keyword(s):  
Mass Loss ◽  
Litter Decomposition ◽  
Fungal Biomass ◽  
Fungal Species ◽  
Aquatic Hyphomycetes ◽  
Negative Effects ◽  
Stream Functioning ◽  
Induced Changes ◽  
Sporulation Rate ◽  
The Impact

Freshwater salinization is a world-wide phenomenon threatening stream communities and ecosystem functioning. In these systems, litter decomposition is a main ecosystem-level process where fungi (aquatic hyphomycetes) play a central role linking basal resource and higher levels of food-web. The current study evaluated the impact of aquatic hyphomycete richness on leaf litter decomposition when subjected to salinization. In a microcosm study, we analysed leaf mass loss, fungal biomass, respiration and sporulation rate by fungal assemblages at three levels of species richness (1, 4, 8 species) and three levels of salinity (0, 8, 16 g NaCl L‑1). Mass loss and sporulation rate were depressed at 8 and 16 g NaCl L‑1, while fungal biomass and respiration were only negatively affected at 16 g L‑1. A richness effect was only observed on sporulation rates, with the maximum values found in assemblages of 4 species. In all cases, the negative effects of high levels of salinization on the four tested variables superimposed the potential buffer capacity of fungal richness. The study suggests functional redundancy among the fungal species even at elevated salt stress conditions which may guarantee stream functioning at extreme levels of salinity. Nonetheless, it also points to the possible importance of salt induced changes on fungal diversity and identity in salinized streams able to induce bottom-up effects in the food webs.

scholarly journals Dynamics and variability of winds from single Wolf-Rayet stars

1999 ◽  
Vol 193 ◽  
pp. 157-167
Author(s):  
Stanley P. Owocki ◽  
Kenneth G. Gayley
Keyword(s):  
Mass Loss ◽  
Multiple Scattering ◽  
Optical Depth ◽  
Spectral Distribution ◽  
Radiation Flux ◽  
Emission Lines ◽  
List Type ◽  
Type Number ◽  
Ob Stars ◽  
Realistic Line

We review the dynamics of winds from single Wolf-Rayet stars, with emphasis on the following specific points: (a)The classical “momentum problem” (to explain the large inferred ratio of wind to radiative momentum, η Mv∞/(L/c) ≫ 1) is in principle readily solved through multiple scattering of radiation by an opacity that is sufficiently “gray” in its spectral distribution. In this case, one simply obtains η ≃ τ, where τ is the wind optical depth;(b)Lines with a Poisson spectral distribution yield an “effectively gray” cumulative opacity, with multi-line scattering occuring when the velocity separation between thick lines Δv is less than the wind terminal speed v∞. In this case, one obtains η ≃ v∞/Δv;(c)However, realistic line lists are not gray, and leakage through gaps in the line spectral distribution tends to limit the effective scattering to η ≲ 1;(d)In WR winds, ionization stratification helps spread line-bunches and so fill in gaps, allowing for more effective global trapping of radiation, and thus η > 1;(e)However, photon thermalization can reduce the local effectiveness of line-driving near the stellar core, making it difficult for radiation alone to initiate the wind;(f)The relative complexity of WR wind initiation may be associated with the extensive turbulent structure inferred from observed variabililty in WR wind emission lines;(g)Overall, the understanding of WR winds is perhaps best viewed as an “opacity problem”, i.e., identifying the enhanced opacity that can adequately block the radiation flux throughout the wind, and thus drive a WR mass loss that is much greater than from OB stars of comparable luminosity.

scholarly journals Observations of Mass Loss from OB and Wolf-Rayet Stars

1982 ◽  
Vol 99 ◽  
pp. 149-172 ◽  
Author(s):  
M. J. Barlow
Keyword(s):  
Mass Loss ◽  
List Type ◽  
Type Number ◽  
Loss Rates

In this review, three observationally accessible parameters of the winds of OB and Wolf-Rayet stars will be discussed: (1)Terminal velocities(2)Velocity laws(3)Mass loss rates

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