scholarly journals Predation risk, stoichiometric plasticity and ecosystem elemental cycling

2012 ◽  
Vol 279 (1745) ◽  
pp. 4183-4191 ◽  
Author(s):  
Shawn J. Leroux ◽  
Dror Hawlena ◽  
Oswald J. Schmitz
Keyword(s):  
Predation Risk ◽  
Ecosystem Model ◽  
Soluble Carbohydrate ◽  
Dietary Nitrogen ◽  
Elemental Cycling ◽  
Stocks And Flows ◽  
C And N ◽  
And Shifts ◽  
Soluble C ◽  
Recalcitrant C

It is widely held that herbivore growth and production is limited by dietary nitrogen (N) that in turn constrains ecosystem elemental cycling. Yet, emerging evidence suggests that this conception of limitation may be incomplete, because chronic predation risk heightens herbivore metabolic rate and shifts demand from N-rich proteins to soluble carbohydrate–carbon (C). Because soluble C can be limiting, predation risk may cause ecosystem elemental cycling rates and stoichiometric balance to depend on herbivore physiological plasticity. We report on a stoichiometrically explicit ecosystem model that investigates this problem. The model tracks N, and soluble and recalcitrant C through ecosystem compartments. We evaluate how soluble plant C influences C and N stocks and flows in the presence and absence of predation risk. Without risk, herbivores are limited by N and respire excess C so that plant-soluble C has small effects only on elemental stocks and flows. With predation risk, herbivores are limited by soluble C and release excess N, so plant-soluble C critically influences ecosystem elemental stocks flows. Our results emphasize that expressing ecosystem stoichiometric balance using customary C : N ratios that do not distinguish between soluble and recalcitrant C may not adequately describe limitations on elemental cycling.

scholarly journals Closing the N-Budget: How Simulated Groundwater-Borne Nitrate Supply Affects Plant Growth and Greenhouse Gas Emissions on Temperate Grassland

Atmosphere ◽  
2018 ◽  
Vol 9 (10) ◽  
pp. 407 ◽  
Author(s):  
Ralf Liebermann ◽  
Lutz Breuer ◽  
Tobias Houska ◽  
Steffen Klatt ◽  
David Kraus ◽  
...  
Keyword(s):  
Plant Biomass ◽  
Ecosystem Model ◽  
Animal Manure ◽  
Temperate Grassland ◽  
N2o Emissions ◽  
Groundwater Transport ◽  
N Budget ◽  
Soil System ◽  
N Cycle ◽  
C And N

European groundwater reservoirs are frequently subject to reactive nitrogen pollution (Nr) owing to the intensive use of nitrogen (N) fertilizer and animal manure in agriculture. Besides its risk on human health, groundwater Nr loading also affects the carbon (C) and N cycle of associated ecosystems. For a temperate grassland in Germany, the long-term (12 years) annual average exports of Nr in form of harvest exceeded Nr inputs via fertilization and deposition by more than 50 kgN ha−1. We hypothesize that the resulting deficit in the N budget of the plant-soil system could be closed by Nr input via the groundwater. To test this hypothesis, the ecosystem model LandscapeDNDC was used to simulate the C and N cycle of the respective grassland under different model setups, i.e., with and without additional Nr inputs via groundwater transport. Simulated plant nitrate uptake compensated the measured N deficit for 2 of 3 plots and lead to substantial improvements regarding the match between simulated and observed plant biomass and CO2 emission. This suggests that the C and N cycle of the investigated grassland were influenced by Nr inputs via groundwater transport. We also found that inputs of nitrate-rich groundwater increased the modelled nitrous oxide (N2O) emissions, while soil water content was not affected.

scholarly journals Land-Use Change Depletes Quantity and Quality of Soil Organic Matter Fractions in Ethiopian Highlands

Forests ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 69
Author(s):  
Iftekhar U. Ahmed ◽  
Dessie Assefa ◽  
Douglas L. Godbold
Keyword(s):  
Land Use ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Natural Forest ◽  
Grazing Land ◽  
Eucalyptus Plantation ◽  
C And N ◽  
C And N Pools ◽  
Recalcitrant C

The depletion of soil organic matter (SOM) reserve after deforestation and subsequent management practices are well documented, but the impacts of land-use change on the persistence and vulnerability of storage C and N remain uncertain. We investigated soil organic C (SOC) and N stocks in a landscape of chrono-sequence natural forest, grazing/crop lands and plantation forest in the highlands of North-West Ethiopia. We hypothesized that in addition to depleting total C and N pools, multiple conversions of natural forest significantly change the relative proportion of labile and recalcitrant C and N fractions in soils, and thus affect SOM quality. To examine this hypothesis, we estimated depletion of SOC and N stocks and labile (1 & 2) and recalcitrant (fraction 3) C and N pools in soil organic matter following the acid hydrolysis technique. Our studies showed the highest loss of C stock was in grazing land (58%) followed by cropland (50%) and eucalyptus plantation (47%), while on average ca. 57% N stock was depleted. Eucalyptus plantation exhibited potential for soil C recovery, although not for N, after 30 years. The fractionation of SOM revealed that depletions of labile 1 C stocks were similar in grazing and crop lands (36%), and loss of recalcitrant C was highest in grazing soil (56%). However, increases in relative concentrations of labile fraction 1 in grazing land and recalcitrant C and N in cropland suggest the quality of these pools might be influenced by management activities. Also, the C:N ratio of C fractions and recalcitrant indices (RIC and RIN) clearly demonstrated that land conversion from natural forest to managed systems changes the inherent quality of the fractions, which was obscured in whole soil analysis. These findings underscore the importance of considering the quality of SOM when evaluating disturbance impacts on SOC and N stocks.

scholarly journals Pasture resilience reflects differences in root and shoot responses to defoliation, and water and nitrogen deficits

2021 ◽  
Vol 17 ◽  
Author(s):  
Derrick Moot ◽  
Alistair Black ◽  
Eric Lyons ◽  
Lucy Egan ◽  
Rainer Hofmann
Keyword(s):  
Leaf Area ◽  
Perennial Ryegrass ◽  
Water Soluble ◽  
Grass Species ◽  
Soluble Carbohydrate ◽  
Plant Responses ◽  
Water Deficits ◽  
C And N ◽  
Response To Water ◽  
Water Soluble Carbohydrate

The yield of a pasture is directly proportional to the amount of light plants intercept and allocate to different organs. When plants are carbon (C) limited, due to defoliation, they allocate more C preferentially to shoots to restore leaf area. In contrast, water and nitrogen (N) limitations lead to a greater allocation of C to roots. Changes in the root:shoot ratio therefore reflect changes in C and N partitioning and indicate their relative priority. A major factor that influences plant responses to stress is their ability to store and remobilise reserves to restore leaf area. Species with tap roots, like lucerne, have a large potential C and N storage capacity that is utilised seasonally for storage and remobilisation. This has been used to develop seasonally based grazing management rules. Similarly, recommendations to graze perennial ryegrass at the 2- or 3-leaf stage are based on the balance between maximizing growth rates and the need to replenish water-soluble carbohydrate reserves. However, perennial ryegrass has lower levels of perennial reserves than other grass species. This reduces its resilience to concurrent water deficits or N deficiency. Under these conditions maintaining the recommended 3-leaf grazing intervals and/or leaving higher post-grazing pasture masses are recommended to assist canopy recovery. Other grass species, such as cocksfoot and tall fescue, provide more resilience, particularly in response to water deficits.

Increased intake responses from beef steers zero-grazed on Lolium perenne selected for high levels of water soluble carbohydrate

2001 ◽  
Vol 2001 ◽  
pp. 86-86
Author(s):  
M.R.F. Lee ◽  
R.T. Evans ◽  
J.M. Moorby ◽  
M.O. Humphreys ◽  
M. K. Theodorou ◽  
...  
Keyword(s):  
Lolium Perenne ◽  
Microbial Population ◽  
Water Soluble ◽  
Soluble Carbohydrate ◽  
Beef Steers ◽  
Protein Nitrogen ◽  
Dietary Nitrogen ◽  
Available Energy ◽  
Low Levels ◽  
Water Soluble Carbohydrate

Fresh forages may result in the loss of up to 40% of dietary nitrogen as rumen ammonia, as the microbial population is unable to utilise all the non-protein nitrogen released from rapidly degradable plant proteins. This may be due to the characteristically low levels of readily available energy released in the rumen, primarily as a result of the low levels of water soluble carbohydrate (WSC) in traditional forages. In a previous experiment Lee et al, (1999) found an increase in liveweight gain of pre-weaned lambs grazing Lolium perenne selected for high WSC concentrations. This study examined whether the enhanced performance on high WSC grass may be related to increased supply of nitrogen to the small intestine.

The digestion of chopped and ground roughages by sheep. II. Digestion of nitrogen and some carbohydrate fractions in the stomach and intestines

1967 ◽  
Vol 18 (5) ◽  
pp. 803 ◽  
Author(s):  
JP Hogan ◽  
RH Weston
Keyword(s):  
Cell Wall ◽  
Organic Matter ◽  
Crude Protein ◽  
Soluble Carbohydrate ◽  
Relative Importance ◽  
Feed Processing ◽  
Dietary Nitrogen ◽  
Relative Extent ◽  
Ad Libitum ◽  
Per Se

A study of the intake and digestion of lucerne and wheaten hays was made with Merino wethers offered chopped hay near ad libitum, ground hay at the same level as the chopped hay, and ground hay near ad libitum. These treatments were imposed to separate the effects of grinding per se from those associated with the increased intakes of roughages permitted by grinding. The following conclusions were reached: (1) Grinding permitted a substantial increase in food consumption on both diets. (2) Grinding per se of both hays produced little change in the relative importance of stomach and intestines as sites of digestion of any of the feed components studied. Grinding had no effect on the digestibility of lucerne hay but reduced that of wheaten hay, mainly by reducing the digestion of the cell wall constituents. (3) When both ground hays were offered near ad libitum, digestibility was reduced, mainly because of a fall in digestibility of the cell wall constituents. With lucerne hay, grinding increased the organic matter intake by 37% above chopped hay but the organic matter digested was increased by only 27%. By contrast, on wheaten hay an increase of 42% in organic matter intake on ground hay resulted in the digestion of only 18% more organic matter than on chopped hay. On both diets the relative extent of digestion occurring in stomach and intestines was similar to that observed with chopped hay. (4) On all three lucerne diets there was a net loss of 22–25% of dietary nitrogen from the stomach. By contrast, on the wheaten hay diets a substantial gain of nitrogen occurred during the passage of digesta through the stomach; the amount of nitrogen gained was independent of feed processing and feed intake. The crude protein apparently digested in the intestines was approximately 17% of the total organic matter digested on the lucerne diets and 10–12% of that digested on the wheaten hay diets. (5) Within diets the relative proportions of individual rumen VFA were the same on chopped and ground hay offered near ad libitum. (6) Grinding probably did not cause any change in the composition of the end products of digestion. (7) On the lucerne hay diets, 16–20% of the organic matter digested in the rumen was soluble carbohydrate, on wheaten hay approximately 40–50%.

scholarly journals The effects of biodiversity gradient on plant mass and metabolism of individual submerged macrophytes

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Liang-Yu Qi ◽  
Hong-Yuan Zeng ◽  
Zhong-Xi Bai ◽  
Yan-Hong Wang ◽  
Li Liu ◽  
...  
Keyword(s):  
Species Richness ◽  
Amino Acid ◽  
Free Amino ◽  
Plant Species Richness ◽  
Species Level ◽  
Individual Species ◽  
Soluble Carbohydrate ◽  
N Metabolism ◽  
C And N ◽  
Biodiversity Effects

Abstract Background The effects of biodiversity on community function and services are frequently studied in the history of ecology, while the response of individual species to biodiversity remains great elusive. In this study, we determined the biodiversity effects on community productivity as well as species level plant mass and carbon (C) and nitrogen (N) metabolism of eight submerged plants. These macrophytes in Lake Erhai were selected and planted in a water depth of one meter along a diversity gradient of 1, 2, 4 or 8 species. Then, the community productivity or species level plant mass, soluble protein, free amino acid and soluble carbohydrate were correlated to species richness to determine the biodiversity effects on community and single species. Results The results showed that the community level biomass was positively correlated to plant species richness although the species level plant mass of individual species responded differently to the overall plant species richness. Namely, only one plant mass positively correlated to species richness and the others decreased or showed no significant correlation with the increase of species richness. The soluble proteins of most macrophytes were positively correlated to species richness; however, both the free amino acid and soluble carbohydrate of the plants were negatively or not significantly correlated to species richness. Conclusions These results indicated that the selection effects might dominate in our aquatic communities and the negative impacts of biodiversity on C and N metabolism of the macrophytes increased with the increase of species richness, which might result from the strong competition among the studied species. The biodiversity effects on the plant mass, and C and N metabolism of individual submerged species were first reported in this study, while more such field and control experiments deserve further research.

Sign in / Sign up

Export Citation Format

Share Document