Litter Production Rate Research Articles

Factors influencing litter delivery to streams

Leaves and needles are an important energy source for streams. However, relatively little is known about factors that determine width of the area contributing litter to streams. We assessed the relative effect of wind speed, wind direction, litter type, tree height and riparian topography on litter delivery to streams. Wind speed effect on litter travel distance was determined by releasing needles (Douglas-fir) and leaves (red alder) from mature and young tree canopies over a range of wind velocities. Short-term litter collections were conducted to determine the effect of wind speed on litter fall. Litter travel distance increased with increasing wind speed and increasing tree height. At low wind speeds leaves traveled further than needles. Litter fall increased with wind speed. These relationships were combined with literature values for seasonal rates of litter production and an annual wind speed and direction record from a riparian area in western Washington to evaluate the relative effect of various factors on litter delivery area width. We found that width of the contributing area for needles was about 35% greater in riparian stands supporting mature conifer trees than at sites with young trees. Increasing riparian area slope from 0° to 45° increased width of contributing area by 71–95%, depending on litter type and stand age. Doubling measured wind speed increased contribution zone width 67–82%. Estimated buffer width required to capture 95% of annual litter input ranged from about 14m to over 25m under the conditions which we evaluated. The variety of factors influencing litter delivery area width and the spatial and temporal variation in these factors indicates that the common practice of employing fixed-width buffers to protect stream–riparian interactions cannot be consistently effective.

VELOCIDAD DE DESCOMPOSICIÓN DE LA HOJARASCA EN DIFERENTES SUSTRATOS DE MANGLAR DURANTE LA ÉPOCA DE LLUVIAS EN SAN ANDRÉS ISLA, CARIBE COLOMBIANO

Litter degradation was studied in various substrates of three mangrove wetlands in San Andrés Island, Colombian Caribbean, during the rainy season. Decomposition rates of Rhizophora mangle L. (red mangrove), Laguncularia racemosa (L.) C.F. Gaertn. (white mangrove) and Avicennia germinans (L.) L. (black mangrove) were measured in mesh bags. Some bags were placed below ground, other submerged in water, and other on the ground. Two sites in the study were fringe wetlands and the other one was an inland wetland. Some physical-chemical factors inuencing the decomposition of vegetal organic matter were evaluated. The best regression model tted to the degradation trends was the single square root. The interactions of time with biotic and abiotic factors determined the loss of weight from leaves. The faster degradation rates were obtained in fringe wetlands; aquatic and moisten edaphic environments; on A. germinans; and at the sites with associated consumer macrofauna. The fastest velocities were presented In the early stages of decomposition. In general, the smaller average percentage of remaining biomass after 15 weeks of incubation was presented by A. germinans (10 %), respect to R. mangle (29 %) and L. racemosa (28 %). By means of the results obtained and those one related with the rates of litter production in the same wetlands in study, a basic conceptualquantitative model of litter production-decomposition dynamic in San Andrés Island is proposed.

Litter production rates and soil moisture influences interannual variability in litter respiration in the semi-arid Loess Plateau, China

A better understanding of the factors affecting interannual variability in litter respiration is critical to precisely understand local carbon cycling, especially under the changing climate. In this study, litter respiration was obtained by subtracting in situ soil respiration in a control (LCK) treatment by that in a litter removal (LR) treatment for the period 2009–2013 in a 30-year-old black locust plantation (Robinia pseudoacacia L.) on a ridge slope in a small watershed of Loess Plateau, China. Annual cumulative litter respiration ranged from 48 ± 15 to 165 ± 36 g C m−2 y−1, with mean value of 113 ± 45 g C m−2 y−1 and coefficient of variation (CV) of 40%; annual contribution rate of litter respiration to total soil respiration (hereafter refer to as litter contribution rate) also exhibited a similar interannual variability (ranged from 8 ± 3% to 20 ± 7%; mean = 15 ± 5%; CV = 31%). Additionally, annual mean soil moisture was highest in 2010 (53.2 ± 8.4% WFPS) and lowest in 2013 (31.4 ± 9.5% WFPS), with mean value of 41.6 ± 7.9% WFPS and CV of 19%; annual litter production rates also exhibited a similar interannual variability (ranged from 379 ± 34 to 565 ± 69 g m−2 y−1; mean = 477 ± 71 g m−2 y−1; CV = 15%). Annual mean soil moisture was mainly affected by the frequency and distribution of precipitation, and annual litter production rates varied with summer precipitation. Annual cumulative litter respiration and litter contribution rate increased linearly with both annual litter production rates and mean soil moisture content. The contribution of soil water to litter respiration was larger than that of litter production rates. Therefore, litter production rates and soil moisture resulted from precipitation needs to be taken into account for precisely predicting litter respiration in the dryland ecosystems, especially under the changing climate.

Effects of land use and precipitation on above- and below-ground litter decomposition in a semi-arid temperate steppe in Inner Mongolia, China

Land use greatly affects litter production, quality, and decomposition rates, and therefore alters the soil carbon stocks and influences ecosystem carbon cycling. In this study, our aims were to investigate the effects of land use (grazing, mowing, and grazing exclusion), litter types, and precipitation on litter production, decomposition processes, and soil carbon stocks. Litter inputs, quality, and decomposition rates were significantly influenced by land use and differed greatly between 2011 (a dry year) and 2012 (a moist year). Above-ground litter production in 2012 ranged from 165 to 180gm−2, versus from 50 to 73gm−2 in 2011; below-ground litter production in 2012 was 1.9 to 6.0 times that in 2011. Decomposition rates of above-ground litter (ka) were greater than those of below-ground litter (kb). The ka in 2012 was 1.9 to 2.8 times those in 2011 and kb in 2012 was 6.5 to 10.8 times those in 2011. The ka was strongly positively correlated with the N content (R2=0.713) and strongly negatively correlated with the C/N ratio (R2=0.585), whereas kb was explained best by the C/N ratio. Precipitation was a main factor that controlled ecosystem C cycling processes, and increased litter decomposition increased soil carbon stocks. Land use therefore played an important role in litter input and decomposition processes and in carbon sequestration, but these processes responded to the initial litter quality and precipitation.

Plant and soil δ13C and δ15N are linked to community biomass, litter production, and litter turnover rate in mature subtropical forests

The natural abundance of 13C and 15N can integrate information on the dynamics of C and N, respectively. This study tested whether and how δ13C and δ15N of the plant and soil samples (including leaf, forest floor litters, fine roots, and 0–15 cm mineral soil) can detect local variations in community biomass, litter production, and litter turnover rate were explored in eight mature subtropical forests in southern China. Community biomass, litter production, and litter turnover rate were significantly positively correlated with each other and revealed similar correlations with other plant and soil parameters. Leaf δ13C was significantly negatively correlated with litter production, suggesting the stomatal regulation of leaf gas exchange. Similar correlations were also observed for δ13C of the mineral soil and other plant materials. Leaf and forest floor litters δ15N were positively correlated with community biomass, litter production, and litter turnover rate. Such correlations were significantly positively mediated by soil availability of P rather than N, as demonstrated by the multiple regression analysis. In contrast, fine roots δ15N was not related significantly to community biomass, litter production, or litter turnover rate. Significant differences in δ13C and δ15N among forests were related to the species composition, topography conditions, and land use history. Our results suggest that δ13C and δ15N of most plant and soil samples can indicate local variations in community biomass, litter production, and litter turnover rate in mature subtropical forests. Better understanding of these linkages could significantly improve our knowledge of C and N dynamics in forest ecosystems.

Influence of Tree Characters and Climate on Litter Characteristics in <i>Daniellia oliveri</i> (Rolfe) Hutch. & Dalziel

Litter production and decomposition rates have great importance in maintaining the fertility of the soil. The study was carried out to determine the relationship tree characters (girth size, canopy radius, tree height, leaf area and number of primary branches), litter production and quality, and climatic variables among stands of Daniellia oliveri (Rolfe) Hutch. & Dalziel growing in University of Ilorin campus. Twelve trees of different girth sizes were selected and their physiognomic characters measured. Litter samples (leaves and twigs) were collected from the stands on monthly basis (January to May) using 1 m2 traps. The collected litters were air-dried, ground and analysed for carbon, nitrogen, phosphorus, potassium, calcium and magnesium using standard methods. Rainfall and temperature data were collected during the sampling months. Girth size range was 0.32 – 0.67 m. Tree height range was 13.90 – 31.81 m. Primary branches range was 3 - 16, crown radii was 2.5 - 5.2 m and leaflet area between 24.62 cm2 and 90.90 cm2. Higher leaf litter was recorded in January and February, but twigs were more in the other months. Leaf and twig litters positively correlated with girth size (r = 0.572 and 0.614 respectively), but the former also correlated with crown radii (r = 0.834). Carbon, calcium and magnesium contents in leaves and twigs were lower in May compared to January, but reverse trend were observed for nitrogen and phosphorus. The number of rain (rainy days) negatively correlated with total monthly litter (r = -0.291). The study concluded that climatic conditions influence tree characters, which in turn affect litterfall and nutrient returns to the soil. ©JASEM

Rapid litter production and accumulation in Bornean mangrove forests

Litter fall and accumulation were measured weekly for one year (January–December 2007) at five mangrove forests within the Apar‐Adang Nature Reserve, East Kalimantan, Indonesia. Three forests were located near the sea edge, each co‐dominated by combinations of Sonnertia alba, Rhizophora apiculata, and Bruguiera parviflora; two forests were co‐dominated by Ceriops decandra, Exocoecaria agallocha, and Bruguiera sexangula (site IV), and by B. parviflora and B. sexangula (site V) and located further inland but subjected to intermittant freshwater inputs. Mean rates of annual litter production at forests I to V were 20.3, 19.7, 27.2, 24.2 and 27.6 Mg DW ha−1 yr−1 (mean of all forests = 23.7 Mg DW ha−1 yr−1) and rates of litter accumulation were 44.4, 50.2, 45.9, 61.3 and 66.2 Mg DW ha−1 yr−1 (mean of all forests = 57.8 Mg DW ha−1 yr−1), respectively, exhibiting peaks in the wet and dry seasons. Litter accumulation was greater than litter fall due to tidal advection of litter from forests closer to the sea edge coupled with slow decay rates. These rates of aboveground litter production and accumulation are the highest recorded for mangroves and higher than rates measured in tropical humid evergreen forests, suggesting that large expanses of equatorial mangrove forest, such as those on Borneo, may constitute an immense sink for coastal carbon.

THE STUDY ON MANGROVE LITTERS AS A SOURCE OF NUTRIENTS FOR BLANAKAN MANGROVE POND, SUBANG, WEST JAVA

Mangrove litters as a source of nutrients for sylvofishery pond (TS), sedimented pond (TT), and conservation pond (TP) was studied at Blanakan mangrove pond during April until June 2008. The variables of study were litter production, litter decomposition, and dissolved nutrients (ammonium, nitrite, nitrate, and phosphate). The obtained data were analyzed using F test and continued using Least Significant Different (LSD). The results showed that litter production at TS, TT, and TP were 19.55±4.34 ton/ha/year, 15.90±1.98 ton/ha/year, and 21.67±1.89 ton/ha/year respectively. The decomposition rate at TS, TT, and TP was 0.051±0.038, 0.051±0.018, and 0.081±0.041, respectively. Mangrove litters were potentially as a source of dissolved nutrients at Blanakan mangrove pond. Increasing both litter production and decomposition rate could increase ammonium, nitrite, and phosphate. Therefore, mangrove litters were play role for determined the fertility at Blanakan mangrove pond.

Litter Production and Decomposition Rate in the Reclaimed Mined Land under Albizia and Sesbania Stands and Their Effects on some Soil Chemical Properties

Vegetation establishment is considered as a critical step of mined land rehabilitation. The growing plants do not only prevent soil erosion, but also play important roles in soil ecosystem development. Their litterfall is the main process of transferring organic matter and nutrients from aboveground tree biomass to soil. Thus, its quantification would aid in understanding biomass and nutrient dynamics of the ecosystem. This study was aimed to investigate the litter production and its decomposition rate in a reclaimed mined land using albizia and sesbania, and theireffects on some soil properties. The litter under each stand was biweekly collected for four months. At the same time litter samples were decomposed in mesh nylon bags in soils and the remaining litters were biweekly measured. Soil samples were taken from 0-15 cm depths from each stand for analyses of soil organic C, total N, and cation exchange capacity (CEC). The results demonstrated that total litter production under albizia (10.58 t ha-1 yr-1) was almost twice as much as that under sesbania stands (5.43 t ha-1 yr-1). Albizia litter was dominated by leaf litter (49.26%) and least as understory vegetation (23.31%), whereas sesbania litter was more evenly distributed among litter types. Decomposition rates of all litters were fastest in the initial stage and then gradually decreased. Sesbania leaf litters decomposed fastest, while albizia twigs slowest. Differences in the litter production and decomposition rates of the two species had not sufficiently caused significant effects on organic-C, total N, and CEC of the soilsafter one year of revegetation.Keywords: Albizia (Paraserianthes falcataria), decomposition rates, litter, mined land, Sesbania grandiflora

Linking nitrogen and phosphorus dynamics in litter production and decomposition during secondary forest succession in the eastern Amazon

Land-use change, including tropical deforestation for agriculture and subsequent agricultural abandonment, may change the stoichiometry of nutrient cycling in tropical secondary forests relative to mature forests. While phosphorus (P) is conservatively cycled in these mature forests, nitrogen (N) losses during an agricultural phase may provoke conservative N cycling processes in young secondary forests. Here we explore differences in nutrient cycling properties among secondary and mature forests of the eastern Amazon, including litter nutrient concentrations and rates of litter production and decomposition. In a chronosequence of successional forest age, N production in litterfall and N loss during litter decomposition were low in young forests but increased with increasing forest age, whereas P was conservatively cycled in all forest ages. Litter N concentration was positively correlated with the rate of mass loss in a litterbag study and with a mass balance estimate of litter decomposition based on annual litterfall and litter stock measurements. Therefore, while P is conservatively cycled and may limit or co-limit productivity in these forests, variation in N content of litter among forest successional stages may be related to differences in decomposition rates and mean residence times of litter, thus linking N availability with rates of litter decomposition and P cycling.

Vegetation composition and soil nutrients status from polyculture to monoculture

The study was conducted on status of nutrients in three major types of forests namely, broad-leaved, mixed pine and pine forests in Meghalaya, considering altitude and seasonality as variables. The findings revealed that the change in micro-environmental conditions as influenced by attitude and seasonality has marked effect on status and release of nutrients in the soil of representative forest stands at markedly difference. The ambient and soil temperature was sharply greater at high altitude (Upper Shillong) and values were decreased from broad-leaved to pine forests. The soil temperature was lower than air temperature in all cases. The soil temperature at low altitude (Umroi) during post-monsoon season was higher than pre-monsoon season; however, on the contrary, it was higher during pre-monsoon season in other cases. The light interception decreased from broad-leaved to pine forests, and greater values were recorded at high altitude. The light interception and temperature played a key role in determining relative humidity, and as a result more relative humidity was recorded at high altitude and the values were decreased from broad-leaved to pine forests. The litter thickness and litter accumulation on forest floor at high altitude was about two fold greater than representative forest at low altitude. The values were higher during post-monsoon season, except that more litter thickness was noticed during pre-monsoon season at high altitude; this could be linked with high litter production and low rate of litter decomposition. Soil moisture content was always higher in top-soil, and post-monsoon season showed greater values. Soil pH ranged from 4.6 to 5.8 in top-soil, and from 4.8 to 6.3 in sub-soil. High rate of litter decomposition leads to greater soil pH in top-soil during post-monsoon season. The organic carbon, total nitrogen and available phosphorus contents were more in top-soil, with exception that the phosphorus content was generally higher in sub-soil during post-monsoon season. The values for soil moisture, organic carbon, nitrogen, and phosphorus were markedly higher at high altitude with respect to forest types and seasonality. Normally, the nutrient poor soil has high C:N ratio, and on account of this fertility of soil decreased from polyculture to monoculture. The finding reveal that the C:N ratio was increased from broad-leaved to pine forests, and more values were observed in sub-soil. Key words: Altitude, monoculture, nutrient release, polyculture, seasonality, top-soil and sub-soil, vegetation

Effects of afforestation and deforestation on boreal soil carbon stocks—Comparison of measured C stocks with Yasso07 model results

Land use changes like afforestation and deforestation are known to affect stocks of carbon in soils. We measured changes in soil carbon stocks in afforested and deforested sites. Repeated measurements were made at six sites which had been afforested with three different tree species 17–18 years before this sampling. The deforestation sites consisted of six field soils that were taken to cultivation 1–200 years before the sampling and adjacent forest sites representing the same soil types as the fields. The performance of the Yasso07 model in predicting the soil carbon stock changes in afforestation and deforestation was evaluated by simulating the changes in the carbon stocks and comparing the measured and simulated results for these sites. The mean observed 20-year carbon stock change after the land use change was − 9% in the afforested sites and − 19% in the deforested sites. The decrease in the mean carbon stock after afforestation was most pronounced during the first 9–10 years and was probably due to low rates of litter production in the early growth phase of the forests. The stock change in deforestation was lowest in fields with grasses as the main crop and highest in cereal monoculture. The simulation results were well in accordance with the measured carbon stocks on most sites.

Does moder development along a pure beech (Fagus sylvatica L.) chronosequence result from changes in litter production or in decomposition rates?

The development of temperate deciduous and conifers forests stands usually results in accumulation of forest floor organic matter and a shift from mull to moder humus forms. It has been suggested that an increase in nutrient uptake by trees during their rapid growth phase leads to topsoil acidification, decrease in earthworm density and thereby a decrease in litter turnover. The focus of this paper was to examine if the mull-moder shift with forest ageing results from higher leaf litter production and/or lower litter decay rates. The objectives of this research were to determine (1) changes in macro-morphological properties of humus forms, leaf litter production, litter decay rates, soil nutrients content and pH along a 130-year pure beech (Fagus sylvatica L.) chronosequence in Normandy (Northwest France), (2) if humus form varied from mull to moder with increasing stand age, and (3) if a shift from mull to moder resulted from increased litter production, decreased litter decay rates, or both. Annual litter production did not change significantly along the chronosequence (mean 2.41tha−1). In contrast, litter decay rates decreased significantly during the rapid growth phase of trees. In consequence, the litter turnover time (1/k) was lower in the youngest stands (20 months) compared to the oldest ones (31 months). Even in the absence of a significant pattern of variation, litter production was positively correlated with the thickness of the OF (Oi) horizon. In contrast, litter decay was strongly negatively correlated with maximum thickness of the OH (Oa) horizon, suggesting that the appearance of the humification layer was mainly due to a decrease in litter decay rate. We did not find significant changes in the main properties of the organo-mineral horizon, suggesting that soil nutrient availability may not directly affect litter dynamics. We concluded that moder development along the chronosequence resulted in decreasing litter decay rates during the aggradation phase while litter production was stable. Further studies are required to identify the ecological factors responsible for moder development along forest ageing.

Litter Production and Decomposition Rate in the Reclaimed Mined Land under Albizia and Sesbania Stands and Their Effects on some Soil Chemical Properties

Indonesian acid soils were used to determine an optimum population size of indigenous P-solubilizing bacteria (PSB) for solubilizating fixed P. The experiment consisted of two sub-experiments. Sub-experiment I was to isolate the indigenous PSB from Ultisols, Fresh-water lowland Inceptisols, and tidal-swamp Inceptisols. Subexpriment II was to study the capacity of the isolated PSB to correct P availability in acid soils by inoculating the isolated PSB into the tested soils at 0, 105, 1010, and 1015 cells. The population of the indigenous PSB in the tested soils increased as a result of the inoculation. Both Al-P and Fe-P content in the three tested soils decreased as compared with the initial content. The increases of available P were significantly correlated with the decreases both in Al-P (r2 = 0.68 for the Ultisols; r2 = 0.51 for the fresh-water Inceptisols; and r2 = 0.35 for the tidal-swamp Inceptisols) and in Fe-P (r2 = 0.91 for the Ultisols; r2 = 0.45 for the fresh-water lowland Inceptisols; and r2 = 0.78 for the tidal-swamp Inceptisols). The increases of available P were significantly correlated with the increases of the population of the PSB (r2 = 0.60 for the Ultisols; r2 = 0.55 for the fresh-water lowland Inceptisols; and r2 = 0.69 for the tidal-swamp Inceptisols). The available P in the three tested soils sharply increased if the population size of the PSB was about 1 × 109 cfu g-1 of soil. Keywords: Al-P, Fe-P, fresh-water lowland, isolated, Pikovskaya medium, tidal swamp

Insect biological control accelerates leaf litter decomposition and alters short‐term nutrient dynamics in aTamarix‐invaded riparian ecosystem

Insect herbivory can strongly influence ecosystem nutrient dynamics, yet the indirect effects of herbivore‐altered litter quality on subsequent decomposition remain poorly understood. The northern tamarisk beetleDiorhabda carinulatawas released across several western states as a biological control agent to reduce the extent of the invasive treeTamarixspp. in highly‐valued riparian ecosystems; however, very little is currently known about the effects of this biocontrol effort on ecosystem nutrient cycling. In this study, we examined alterations to nutrient dynamics resulting from beetle herbivory in aTamarix‐invaded riparian ecosystem in the Great Basin Desert in northern Nevada, USA, by measuring changes in litter quality and decomposition, as well as changes in litter quantity. Generally, herbivory resulted in improved leaf litter chemical quality, including significantly increased nitrogen (N) and phosphorus (P) concentrations and decreased carbon (C) to nitrogen (C:N), C:P, N:P, and lignin:N ratios. Beetle‐affected litter decomposed 23% faster than control litter, and released 16% more N and 60% more P during six months of decomposition, as compared to control litter. Both litter types showed a net release of N and P during decomposition. In addition, herbivory resulted in significant increases in annual rates of total aboveground litter and leaf litter production of 82% and 71%, respectively, under theTamarixcanopy. Our finding that increased rates of N and P release linked with an increased rate of mass loss during decomposition resulting from herbivore‐induced increases in litter quality provides new support to the nutrient acceleration hypothesis. Moreover, results of this study demonstrate that the introduction of the northern tamarisk beetle as biological control to aTamarix‐invaded riparian ecosystem has lead to short‐term stimulation of nutrient cycling. Alterations to nutrient dynamics could have implications for future plant community composition, and thus the potential for restoration ofTamarix‐invaded ecosystems.

Numerical modeling of the effects of water flow, sediment transport and vegetation growth on the spatiotemporal patterning of the ridge and slough landscape of the Everglades wetland

A numerical model has been developed to simulate the spatiotemporal patterning of the ridge and slough landscape in wetlands, characterized by crests (ridges) and valleys (sloughs) that are elongated parallel to the direction of water flow. The model formulation consists of governing equations for integrated surface water and groundwater flow, sediment transport, and soil accretion, as well as litter production by vegetation growth. The model simulations show how the spatial pattern self-organizes over time with the generation of ridges and sloughs through sediment deposition and erosion driven by the water flow field. The spatial and temporal distributions of the water depth, flow rates and sediment transport processes are caused by differential flow due to vegetation and topography heterogeneities. The model was parameterized with values that are representative of the Everglades wetland in the southern portion of the Florida peninsula in the USA. Model simulation sensitivity was tested with respect to numerical grid size, lateral vegetation growth and the rate of litter production. The characteristic wavelengths of the pattern in the directions along and perpendicular to flow that are simulated with this model develop over time into ridge and slough shapes that resemble field observations. Also, the simulated elevation differences between the ridges and sloughs are of the same order of those typically found in the field. The width of ridges and sloughs was found to be controlled by a lateral vegetation growth distance parameter in a simplified formulation of vegetation growth, which complements earlier modeling results in which a differential peat accretion mechanism alone did not reproduce observations of ridge and slough lateral wavelengths. The results of this work suggest that ridge and slough patterning occurs as a result of vegetation's ability to grow laterally, enhancing sediment deposition in ridge areas, balanced by increased sediment erosion in slough areas to satisfy flow continuity. The interplay between sediment transport, water flow and vegetation and soil dynamic processes needs to be explored further through detailed field experiments, using a model formulation such as the one developed in this work to guide data collection and interpretation. This should be one of the focus areas of future investigations of pattern formation and stability in ridge and slough areas.

Juvenile compensatory growth has negative consequences for reproduction in Trinidadian guppies (Poecilia reticulata)

Compensatory or 'catch-up' growth may be an adaptive mechanism that buffers the growth trajectory of young organisms from deviations caused by reduced food availability. Theory generally assumes that rapid juvenile compensatory growth impacts reproduction only through its positive effects on age and size at maturation, but potential reproductive costs to juvenile compensatory growth remain virtually unexplored. We used a food manipulation experiment to examine the reproductive consequences of compensatory growth in Trinidadian guppies (Poecilia reticulata). Compensatory growth did not affect adult growth rates, litter production rates or investment in offspring size. However, compensatory growth had negative effects on litter size, independent of the effects of female body length, resulting in a 20% decline in offspring production. We discuss potential mechanisms behind this observed cost to reproduction.

Reconstructing the reproductive history of female polar bears using cementum patterns of premolar teeth

Premolar teeth collected from 220 adult female polar bears (Ursus maritimus) from western Hudson Bay, Canada, were examined to determine whether past reproductive events are recorded in cementum. The widths of annular cementum growth layer groups (GLGs) were measured and compared as proportional width index (PWI) values to correct for age and body size bias. Known reproductive states (pregnant, with cubs, or with yearlings) were used to confirm and calibrate cementum annuli. Significant differences in PWI were observed between GLGs formed the year females were pregnant versus when accompanied by cubs or yearlings. The probability of a female having produced a cub in adulthood was determined by fitting a logistic regression model between the ΔPWI of females when pregnant and with their cubs. Logistic regression of ΔPWI (β0 = −0.229, β1 = −13.465, G 2 = 46.55, df = 1, P < 0.001) correctly classified the presence or absence of cubs in 72% of GLGs. Cementum width did not vary between different litter sizes. Observations of females with early litter loss suggests that longer periods of lactation contributes to decreased cementum width and therefore cementum may record a minimum age of litter survival. Predictions of litter production rate (0.43 litters/female/year) derived from cementum were similar to field observations; however, age at first parturition was underestimated by 1 year. We conclude that patterns of cementum deposition may be useful to determine individual reproductive histories and establish course estimates of reproductive parameters when regular field observations are not feasible. We also conclude that reproductive parameters derived from cementum are not adequate on their own for monitoring populations which are in decline or under stress and field observation should not be replaced under these conditions.

Does thinning affect litterfall, litter decomposition, and associated nutrient release inAcacia mangiumstands of Kerala in peninsular India?

Litter plays a vital role in the nutrient cycling of plantations and agroforests. Silvicultural interventions can alter litter production and decay rates, thereby varying nutrient fluxes. We evaluated the effect of various thinning densities on litter dynamics of 9-year-old Acacia mangium Willd. stands. To quantify litterfall, we placed traps at four random grid points in 24 plots in which none, one-third, one-half, or two-thirds of stems had been removed. In each plot, 48 litterbags were also placed to evaluate litter decay. Annual litterfall ranged from 5.73 (two-thirds thinning) to 11.18 Mg·ha−1(unthinned) and showed a significant linear relationship to basal area (p &lt; 0.0001). Nitrogen (N), phosphorus (P), and potassium (K) concentrations were highest during the wet season, when litterfall production was low, implying an inverse relationship between litterfall quality and quantity. The highest annual N, P, and K additions (82.9, 3.3, and 71.9 kg·ha−1, respectively) occurred in the unthinned stands. High thinning intensities resulted in accelerated decay rates, which we attribute to changes in microenvironment. Soil N concentrations were highest in the one-half thinning treatment, followed by the two-thirds treatment, signifying a trade-off between litterfall production and decay. The highest soil organic C concentrations were in the unthinned stands, reflecting the potential of high stand densities for promoting C sequestration.

Enhanced litter input rather than changes in litter chemistry drive soil carbon and nitrogen cycles under elevated CO2: a microcosm study

AbstractElevated CO2 has been shown to stimulate plant productivity and change litter chemistry. These changes in substrate availability may then alter soil microbial processes and possibly lead to feedback effects on N availability. However, the strength of this feedback, and even its direction, remains unknown. Further, uncertainty remains whether sustained increases in net primary productivity will lead to increased long‐term C storage in soil. To examine how changes in litter chemistry and productivity under elevated CO2 influence microbial activity and soil C formation, we conducted a 230‐day microcosm incubation with five levels of litter addition rate that represented 0, 0.5, 1.0, 1.4 and 1.8 × litterfall rates observed in the field for aspen stand growing under control treatments at the Aspen FACE experiment in Rhinelander, WI, USA. Litter and soil samples were collected from the corresponding field control and elevated CO2 treatment after trees were exposed to elevated CO2 (560 ppm) for 7 years. We found that small decreases in litter [N] under elevated CO2 had minor effects on microbial biomass carbon, microbial biomass nitrogen and dissolved inorganic nitrogen. Increasing litter addition rates resulted in linear increase in total C and new C (C from added litter) that accumulated in whole soil as well as in the high density soil fraction (HDF), despite higher cumulative C loss by respiration. Total N retained in whole soil and in HDF also increased with litter addition rate as did accumulation of new C per unit of accumulated N. Based on our microcosm comparisons and regression models, we expected that enhanced C inputs rather than changes in litter chemistry would be the dominant factor controlling soil C levels and turnover at the current level of litter production rate (230 g C m−2 yr−1 under ambient CO2). However, our analysis also suggests that the effects of changes in biochemistry caused by elevated CO2 could become significant at a higher level of litter production rate, with a trend of decreasing total C in HDF, new C in whole soil, as well as total N in whole soil and HDF.