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Litter Addition (litter + addition)
Selected AbstractsSources of plant-derived carbon and stability of organic matter in soil: implications for global changeGLOBAL CHANGE BIOLOGY, Issue 8 2009SUSAN E. CROW Abstract Alterations in forest productivity and changes in the relative proportion of above- and belowground biomass may have nonlinear effects on soil organic matter (SOM) storage. To study the influence of plant litter inputs on SOM accumulation, the Detritus Input Removal and Transfer (DIRT) Experiment continuously alters above- and belowground plant inputs to soil by a combination of trenching, screening, and litter addition. Here, we used biogeochemical indicators [i.e., cupric oxide extractable lignin-derived phenols and suberin/cutin-derived substituted fatty acids (SFA)] to identify the dominant sources of plant biopolymers in SOM and various measures [i.e., soil density fractionation, laboratory incubation, and radiocarbon-based mean residence time (MRT)] to assess the stability of SOM in two contrasting forests within the DIRT Experiment: an aggrading deciduous forest and an old-growth coniferous forest. In the deciduous forest, removal of both above- and belowground inputs increased the total amount of SFA over threefold compared with the control, and shifted the SFA signature towards a root-dominated source. Concurrently, light fraction MRT increased by 101 years and C mineralization during incubation decreased compared with the control. Together, these data suggest that root-derived aliphatic compounds are a source of SOM with greater relative stability than leaf inputs at this site. In the coniferous forest, roots were an important source of soil lignin-derived phenols but needle-derived, rather than root-derived, aliphatic compounds were preferentially preserved in soil. Fresh wood additions elevated the amount of soil C recovered as light fraction material but also elevated mineralization during incubation compared with other DIRT treatments, suggesting that not all of the added soil C is directly stabilized. Aboveground needle litter additions, which are more N-rich than wood debris, resulted in accelerated mineralization of previously stored soil carbon. In summary, our work demonstrates that the dominant plant sources of SOM differed substantially between forest types. Furthermore, inputs to and losses from soil C pools likely will not be altered uniformly by changes in litter input rates. [source] Effects of throughfall and litterfall manipulation on concentrations of methylmercury and mercury in forest-floor percolatesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2007Maria Hojdová Abstract The forest floor was shown to be an effective sink of atmospherically deposited methylmercury (MeHg) but less for total mercury (Hgtotal). We studied factors controlling the difference in dynamics of MeHg and Hgtotal in the forest floor by doubling the throughfall input and manipulating aboveground litter inputs (litter removal and doubling litter addition) in the snow-free period in a Norway spruce forest in NE Bavaria, Germany, for 14 weeks. The MeHg concentrations in the forest-floor percolates were not affected by any of the manipulation and ranged between 0.03 (Oa horizon) and 0.11 (Oi horizon) ng Hg L,1. The Hgtotal concentrations were largest in the Oa horizon (24 ng Hg L,1) and increased under double litterfall (statistically significant in the Oi horizon). Similarly, concentrations of dissolved organic C (DOC) increased after doubling of litterfall. The concentrations of Hgtotal and DOC correlated significantly in forest-floor percolates from all plots. However, we did not find any effect of DOC on MeHg concentrations. The difference in the coupling of Hgtotal and MeHg to DOC might be one reason for the differences in the mobility of Hg species in forest floors with a lower mobility of MeHg not controlled by DOC. [source] DOC leaching from a coniferous forest floor: modeling a manipulation experiment,JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2005Edward Tipping Abstract The DyDOC model simulates the C dynamics of forest soils, including the production and transport of dissolved organic matter (DOM), on the basis of soil hydrology, metabolic processes, and sorption reactions. The model recognizes three main pools of soil C: litter, substrate (an intermediate transformation product), and humic substances. The model was used to simulate the behavior of C in the O horizon of soil under a Norway spruce stand at Asa, Sweden, that had been subjected to experimental manipulations (addition and removal) of above-ground litter inputs and to removal of the Oi and Oe layers. Initially, the model was calibrated using results for the control plots and was able to reproduce the observed total soil C pool and 14C content, DOC flux and DO14C content, and the pool of litter C, together with the assumed content of C in humic substances (20% of the total soil C), and the assumed distribution of DOC between hydrophilic and hydrophobic fractions. The constant describing DOC exchange between micro- and macropores was estimated from short-term variations in DOC concentration. When the calibrated model was used to predict the effects of litter and soil manipulations, it underestimated the additional DOC export (up to 33%) caused by litter addition, and underestimated the 22% reduction in DOC export caused by litter withdrawal. Therefore, an additional metabolic process, the direct conversion of litter to DOC, was added to the model. The addition of this process permitted reasonably accurate simulation of the results of the manipulation experiments, without affecting the goodness-of-fit in the model calibration. The results suggest that, under normal conditions, DOC exported from the Asa forest floor is a mixture of compounds derived from soil C pools with a range of residence times. Approximately equal amounts come from the litter pool (turnover time 4.6 yr), the substrate pool (26 yr), and the humic-substances pool (36 yr). [source] Direct and indirect effects of exotic annual grasses on species composition of a South Australian grasslandAUSTRAL ECOLOGY, Issue 1 2003TANJA I. LENZ Abstract Invasion by Mediterranean annual grasses, such as Avena L. spp. and Bronms L. spp, is one of the major threats to temperate perennial grassland. This study investigated the effects of annual grasses and their litter on the species composition of a grassland near Burra, South Australia. The placement of annual grass litter on soil samples in the glasshouse decreased the establishment or growth of several exotic annual dicots. In the field the addition of annual grass litter slightly decreased the frequency of Danthonia Lam. & DC. tussocks. Furthermore, litter strongly reduced the species richness from 13 species in plots with no litter to nine species in plots with the highest litter level, mainly by decreasing the frequency of common exotic dicots. Native dicot frequency similarly appeared to be decreased by litter addition. In addition to the negative effects of their litter, annual grasses also directly competed with perennial grasses. The magnitude of the competitive effect varied systematically along a slope, suggesting that other factors such as soil properties may control competitive inter actions. The biomass of annual grasses also tended to increase with the addition of their own litter. This combination of positive and negative feedback mechanisms suggests that brief periods favourable for annual grasses, either through management changes or environmental conditions, can lead to persistent changes in the species composition of the system. [source] Sources of plant-derived carbon and stability of organic matter in soil: implications for global changeGLOBAL CHANGE BIOLOGY, Issue 8 2009SUSAN E. CROW Abstract Alterations in forest productivity and changes in the relative proportion of above- and belowground biomass may have nonlinear effects on soil organic matter (SOM) storage. To study the influence of plant litter inputs on SOM accumulation, the Detritus Input Removal and Transfer (DIRT) Experiment continuously alters above- and belowground plant inputs to soil by a combination of trenching, screening, and litter addition. Here, we used biogeochemical indicators [i.e., cupric oxide extractable lignin-derived phenols and suberin/cutin-derived substituted fatty acids (SFA)] to identify the dominant sources of plant biopolymers in SOM and various measures [i.e., soil density fractionation, laboratory incubation, and radiocarbon-based mean residence time (MRT)] to assess the stability of SOM in two contrasting forests within the DIRT Experiment: an aggrading deciduous forest and an old-growth coniferous forest. In the deciduous forest, removal of both above- and belowground inputs increased the total amount of SFA over threefold compared with the control, and shifted the SFA signature towards a root-dominated source. Concurrently, light fraction MRT increased by 101 years and C mineralization during incubation decreased compared with the control. Together, these data suggest that root-derived aliphatic compounds are a source of SOM with greater relative stability than leaf inputs at this site. In the coniferous forest, roots were an important source of soil lignin-derived phenols but needle-derived, rather than root-derived, aliphatic compounds were preferentially preserved in soil. Fresh wood additions elevated the amount of soil C recovered as light fraction material but also elevated mineralization during incubation compared with other DIRT treatments, suggesting that not all of the added soil C is directly stabilized. Aboveground needle litter additions, which are more N-rich than wood debris, resulted in accelerated mineralization of previously stored soil carbon. In summary, our work demonstrates that the dominant plant sources of SOM differed substantially between forest types. Furthermore, inputs to and losses from soil C pools likely will not be altered uniformly by changes in litter input rates. [source] Changes in forest understory associated with Juniperus encroachment in Oklahoma, USAAPPLIED VEGETATION SCIENCE, Issue 3 2010Paul Van Els Abstract Question: Does understory vegetation cover and richness decline along a gradient of increasing Juniperus virginiana midstory canopy cover and is that decline best correlated with litter accumulation? Location: Cross Timbers Forest in Payne County, OK, USA. Methods: We measured vegetation in forest gaps as well as forest areas without J. virginiana, at the inner and outer edge of J. virginiana canopies and near J. virginiana trunks (200 plots) and compared vegetation differences among location to light, litter, soil and microclimate variables. Results: Species richness (11 spp m,2 to 6 spp m,2) and summer vegetation cover (53.3% to 12.7%) declined with proximity to trunks. Regression indicated that richness declines (R2=0.08) and cover (R2=0.18) were best correlated with J. virginiana litter accumulation. Partial canonical correspondence analysis (pCCA) revealed two strong canonical axes, one related to litter/light and another to cover of Quercus spp. versus J. virginiana. Tree seedlings and woody vines dominated near J. virginiana. Forbs, graminoids and Quercus spp. seedlings were more common in areas without J. virginiana. Conclusions: Increasing J. virginiana and consequent litter additions alter understory biomass and composition and, through inhibiting Quercus spp. recruitment, may lead to changes in overstory composition. Decreases in herbaceous litter, which historically contributed to fuel accumulation, may have positive feedback effects on midstory encroachment by reducing the potential for prescribed burning. [source] | |||||||||||||