Concentrations In Leaf Litter Research Articles

Leaf litter nitrogen concentration as related to climatic factors in Eurasian forests

ABSTRACTAim The aim of this study is to determine the patterns of nitrogen (N) concentrations in leaf litter of forest trees as functions of climatic factors, annual average temperature (Temp, °C) and annual precipitation (Precip, dm) and of forest type (coniferous vs. broadleaf, deciduous vs. evergreen, Pinus, etc.).Location The review was conducted using data from studies across the Eurasian continent.Methods Leaf litter N concentration was compiled from 204 sets of published data (81 sets from coniferous and 123 from broadleaf forests in Eurasia). We explored the relationships between leaf litter N concentration and Temp and Precip by means of regression analysis. Leaf litter data from N2‐fixing species were excluded from the analysis.Results Over the Eurasian continent, leaf litter N concentration increased with increasing Temp and Precip within functional groups such as conifers, broadleaf, deciduous, evergreen and the genus Pinus. There were highly significant linear relationships between ln(N) and Temp and Precip (P < 0.001) for all available data combined, as well as for coniferous trees, broadleaf trees, deciduous trees, evergreen trees and Pinus separately. With both Temp and Precip as independent variables in multiple regression equations, the adjusted coefficient of determination () was evidently higher than in simple regressions with either Temp or Precip as independent variable. Standardized regression coefficients showed that Temp had a larger impact than Precip on litter N concentration for all groups except evergreens. The impact of temperature was particularly strong for Pinus.Conclusions The relationship between leaf litter N concentration and temperature and precipitation can be well described with simple or multiple linear regression equations for forests over Eurasia. In the context of global warming, these regression equations are useful for a better understanding and modelling of the effects of geographical and climatic factors on leaf litter N at a regional and continental scale.

Nutrient and Litter Patterns in Three Subalpine Coniferous Forests of Western Sichuan, China

ABSTRACT Investigations were conducted to quantify litterfall, and litter and nutrient accumulation in forest floor, and to acquire information on litter decomposition and nitrogen and phosphorus release patterns in three different subalpine coniferous forests, a plantation (PI), a secondary forest (SF), and a primitive forest (PF), in western Sichuan, China. The litter trap method was used to evaluate litterfall with the litterbag method being utilized for litter decomposition. Seasonal patterns of litterfall were similar in the three forests, with two peaks occurring in September-November and March-May. The plantation revealed an annual litterfall of 4.38 × 103 kg ha−1, which was similar to those of SF and PF, but PI had a lower mass loss rate and a higher C/N ratio. The C/N ratio may be a sound predictor for the decomposition differences. N concentrations of leaf litter in both the secondary forest and primitive forest increased first and then decreased, and the percentages of their final/initial values were 108.9% and 99.9%, respectively. P concentration in the three forests increased by the end of the study. The results of litterfall and decomposition indicated that in the plantation the potential to provide nutrients for soil organic matter was similar to those of SF and PF; however, its slower decomposition rate could result in a somewhat transient accumulation of litter in the forest floor.

Soil C and N dynamics induced by leaf-litter decomposition of shrubs and perennial grasses of the Patagonian Monte

We assessed soil N and C dynamics in a decomposition experiment at microcosm scale with leaf litter of evergreen shrubs and perennial grasses of the Patagonian Monte. We hypothesised that eventual changes in leaf-litter quality in arid Patagonian ecosystems disturbed by grazing would lead to changes in C and N dynamics in decaying leaf litter and the associated soil. We constructed microcosms with local soil and litterbags containing leaf litter of three perennial grass and three evergreen shrub species. Microcosms were incubated at field capacity during 12, 42 and 84 days. We assessed N, C, phenolics and lignin concentrations in leaf litter before incubation, and N and C concentrations after incubation. We estimated inorganic and total N and organic C in soil before and after incubation. We calculated C and N budgets and the associated rates of C and N losses from leaf litter, microbial respiration, N immobilisation in litter and soil, and N mineralisation at microcosms of each species by inverse modelling techniques. Initial leaf-litter N concentration was significantly higher and C:N ratio lower in evergreen shrubs than in perennial grasses. Leaf litter of perennial grasses was very similar in initial chemical composition among species. In contrast, evergreen shrubs displayed a large variability in the concentration of secondary compounds among species. Accordingly, microcosms of perennial grasses showed similar rates of C and N processes while those of evergreen shrubs showed diverse patterns and rates of processes among them. Process rates in microcosms of one of the evergreen shrub species were closely related to those of perennial grasses. In contrast, process rates in microcosms of the two other evergreen shrub species were quite different between them and from those of perennial grasses. We conclude that (i) the replacement of perennial grasses by evergreen shrubs or the shifting of species within evergreen shrubs in ecosystems disturbed by grazing could have different effects on ecosystem processes depending on the species involved, and (ii) species rather than life forms should be used to predict leaf-litter decomposability and associated soil C and N dynamics particularly in evergreen shrubs.

Nutrient use efficiency at ecosystem and species level in savanna areas of Central Brazil and impacts of fire

Nutrient resorption efficiency of woody plants, litterfall and nutrient fluxes were investigated in a burned and an unburned cerrado plot between October 1997 and September 1999. A large experiment (Fire Project, Brasília, Brazil) on the effects of prescribed burnings was initiated in 1992. Cerrado plots were delimited and subjected to different fire regimes. Seasonal trend of litterfall was similar in both plots but the production in the burned plot was 42.2 g m−2 y−1 before the fourth prescribed fire (September 1998) and decreased by 22% 1 y after burning while in the unburned plot it was around 230 gm−2 y−1. Although nutrient concentrations in leaf litter were higher in the burned plot, the nutrient fluxes were 60–80% lower than in the unburned plot. Nutrient use efficiency (ecosystem level) was 4373 for P and 137 for N. Measured resorption efficiency for 10 cerrado species ranged from 14.5 to 37.2% for N and from 40 to 70.4% for P and in general, there were no differences between plots. N is in short supply, partly because of fire history, but the results, both at ecosystem and species levels (mean N/P in fresh leaves was 18), indicated a stronger limitation by P than by N.

SOIL FAUNA AND LEAF LITTER DECOMPOSITION IN TROPICAL RAIN FOREST IN XISHUANGBANNA, SW CHINA: EFFECTS OF MESH SIZE OF LITTERBAGS

Background and Aims The influence of soil fauna on litter decomposition is rarely explored in tropical rain forest. This study examined the effect of soil fauna on the decomposition of mixed substrate by litter bag technical at two tropical seasonal rain forest plots in Xishuangbanna,SW China in year of 2000. The following questions were considered in the present study: 1) What roles do soil fauna play in regulating litter mass loss and decomposition rate? 2) How do soil fauna influence litter nutrient release? Methods In order to examine the role of soil macro-mesofauna in mass loss and nutrient release of litter,litter bags with both fine mesh size (0.15 mm) that excludes the soil macro-mesofauna population from litter and coarse mesh size (2 mm) that allows soil fauna access to litter were used in this experiment. Mass loss and C,N,P,S,K,Ca,and Mg concentrations of leaf litter were determined from the litter in two different mesh size litterbags at monthly intervals. The soil fauna were extracted by hand and by heating the samples. Key Results Higher relative density and taxonomic diversity of total soil fauna were found in the bags with 2 mm mesh size (22.3-21.77 individuals and 2.67-2.83 orders per g of dry litter) compared to the bags with 0.15 mm mesh size (2.88-2.77 individuals and 0.27-0.28 orders per g of dry litter). Collembola and Acari were the most abundant group,and Hymenoptera(ant),Coleoptera,Hemiptera,Diptera,Diplopoda,Isopoda,Araneae,Pseudoscorpiones were common groups of soil fauna in litter bags with 2 mm mesh size. There were very few individuals of Collembola and Acari in the 0.15 mm litter bags. Our results suggested that soil macro-mesofauna contributed more to the decomposition of leaf litter in 2 mm litter bags than that in 0.15 mm litter bags. The higher mass loss rate (around 71%),decomposition rate (k=1.88-2.44),and nutrient release in litter bags with 2 mm mesh size than in litter bags with 0.15 mm mesh size (34%-35%,k= 0.48- 0.58) indicated a significant influence of soil macro-mesofauna on mass loss and nutrient release in tropical seasonal rain forest. The release rates of N,S and Ca that could be attributable to the soil macro-mesofauna were higher than other elements whereas K release rate that could be attributable to the soil macro-mesofauna was the lowest. Soil macro-mesofauna caused greater decreases in C/N and C/P ratios in litter bags with 2 mm mesh size than litter bags with 0.15 mm mesh size. There were negative relationships of the percentage of litter mass remaining with order richness and individuals abundance of soil fauna. However,a positive relationship between Shannon-Wiener index of soil fauna and the decomposition rate was found. Conclusions This study suggests that the presence of soil fauna accelerated plant litter decomposition in the tropical seasonal rain forest. The litter mass loss attributable to the soil macro-mesofauna was about 46%. The effects of soil macro-mesofauna on the nutrient release rates were different among elements. The diversity of soil fauna may have important ecosystem consequences,particularly in tropical rain forest.

Do ectomycorrhizas alter leaf‐litter decomposition in monodominant tropical forests of Guyana?

This work tested the hypothesis that ectomycorrhizas (EM) of Dicymbe corymbosa alter leaf-litter decomposition and residual litter quality in tropical forests of Guyana. Mass loss of leaf litter in litter bags was determined on three occasions, in two experiments, during a 12-month period. Paired root-exclusion plots were located randomly within a D. corymbosa forest. Both D. corymbosa and mixed-species leaf litters were reciprocally transplanted into their respective forest types. Elemental analysis was performed on the residual D. corymbosa leaf litter after 1 yr. Leaf litter mass loss in the D. corymbosa forest was not influenced by EM, despite high EM colonization. Elemental analysis of D. corymbosa leaf litter residues demonstrated reduced calcium levels in the presence of EM, which were negatively correlated with EM rootlet-colonizing mass. The lack of EM effect on the litter decomposition rate, coupled with high EM colonization, suggests an important but indirect role in mineral nutrient acquisition. Lowered Ca concentration in leaf litter exposed to EM may suggest a high Ca demand by the ectotroph system.

Effects of environmental factors and leaf chemistry on leaf litter colonization by fungi in a Mediterranean shrubland

Estimation of litter colonization by fungi, using ergosterol, an indicator of fungal biomass, is a reliable way to describe the process of leaf litter decomposition. This litter colonization by fungi is regulated both by exogenous or environmental factors, and endogenous factors, i.e. litter chemistry. In this work, we have examined the effects of some of these factors on litter fungal colonization in a Mediterranean ecosystem, by determining ergosterol content of Quercus coccifera leaf litter. Environmental factors have been studied through the fertility of the soil, by comparing plots amended with two rates of compost and plots without amendment. Results indicated that (i) compost had a significant effect on soil fertility but did not increase ergosterol content of leaf litter and (ii) soil humidity improved leaf litter colonization by fungi. Endogenous factors have been studied through measurements of total phenolic and ergosterol concentrations of seven shrub species leaf litter. We have shown (i) a negative significant correlation between total phenolic compounds and ergosterol concentrations of leaf litter and (ii) a positive significant correlation between total phenolic compound concentrations in green leaves and in leaf litter. We conclude that, in this Mediterranean shrub ecosystem, leaf litter colonization by fungi is controlled by soil moisture and plant leaf litter quality.

Effects of forest type and stand age on litterfall quality and soil N dynamics in Shikoku district, southern Japan

To evaluate the effects of forest type and stand age on forest N dynamics, we investigated the leaf-litter quality and soil N mineralization in four pairs of young and middle-aged forests in Shikoku district, southern Japan. The soil N mineralization rate determined by 28-day laboratory incubation ranges from 7.1 to 206.5 mg N kg −1 and was differed among forest types, decreasing in the order of hardwood > Japanese cedar > Japanese red pine = Hinoki cypress. The soil N mineralization rate was strongly correlated with the lignin/N ratio in leaf-litter. Leaf-litter N concentration and lignin/N ratio were different among forest types. Middle-aged forests had lower lignin concentration in leaf-litter, and marginally higher soil N mineralization than young forests. These results suggest that during stand development, the decrease in leaf-litter lignin concentration is an important mechanism that explains larger N cycling in older forests. In contrast, N concentration in leaf-litter was considered to represent the wide variation of N cycling among forest types. During stand development N use efficiency at the leaf level increased (lower N concentration in leaf-litter), whereas water use efficiency decreased (lower δ 13C in leaf-litter). The result suggests that there is a trade-off between NUE and WUE during stand development. However, in all eight forests, NUE and WUE were positively correlated. Japanese cedar and Hinoki cypress utilize both water and N resources more efficiently than hardwood species. Therefore, the efficient use of water and N of coniferous plantations may be related with high aboveground biomass production.

Metal dynamics of plant litter of Spartina alterniflora and Phragmites australis in metal-contaminated salt marshes. Part 1: Patterns of decomposition and metal uptake.

To investigate the decay rate and metal uptake in litter from two species of wetland plants, leaves and stems of senescent Spartina alterniflora and Phragmites australis (P) were obtained from the Hackensack Meadowlands (NJ, USA) in October 1998, and their initial metal contents were determined. Two types of S. alterniflora were obtained, one set from a natural site (NS) and one from a restored site (RS). Leaves and stems were placed in separate litterbags, and samples of each type were reciprocally transplanted into each of the three collection sites (NS, RS, and P) as well as in the laboratory, where they were alternately dried and wetted. Litterbags were retrieved from the field at four six-month intervals and after one year from the laboratory. Annual decay coefficients were greater for leaves than for stems. Stems of P. australis initially decomposed more slowly (37-63% remaining) than those of S. alterniflora (23-53 % remaining), but after two years, decay was comparable (8-40% remaining for both species). Decomposition was slower at the RS site than at the other field sites, and it was slowest in the laboratory. Metal concentrations initially were lower in stems than in leaves, and Cr, Pb, and Zn were lower in P. australis than in S. alterniflora. In the field, large increases (10- to 100-fold) in metal concentrations rapidly obliterated any initial differences between plant species. Metal concentrations in leaves rose more quickly and remained greater than in stems. For example, Cu approached 300 microg/g in leaves but was less than 200 microg/g in stems. In contrast to the modest rise in metal concentrations in the leaf tissue at the more contaminated RS site (Zn rose to approximately 200 microg/g in sediments containing approximately 400 microg/g), Cu and Zn concentrations in leaf litter at the P and NS sites increased to levels exceeding those in the surrounding sediment (Zn rose to approximately 500 microg/g in sediments containing approximately 200 microg/g). Temporal changes in metal pools (grams of metal per litterbag) were not discernable because of the negative correlation of mass remaining and metal concentrations as well as because of the great variability of metal concentrations within each treatment. Decomposition and the accumulation of metals may be influenced more by differences between tissue types than by species or sediment metal concentrations.

Nitrogen and phosphorus resorption efficiency and proficiency in six sub‐arctic bog species after 4 years of nitrogen fertilization

Summary 1 Plant growth at high-latitude sites is usually strongly nutrient-limited. The increased nutrient availability predicted in response to global warming may affect internal plant nutrient cycling, including nutrient resorption from senescing leaves. 2 The effect of increased N supply (10 g N m−2 year−1) on nitrogen and phosphorus resorption efficiency and proficiency in six sub-arctic bog species, belonging to four different growth-forms, was studied in northern Sweden. 3 We hypothesized that while increased N supply would not affect N or P resorption efficiency, it would lead to lower N resorption proficiency (higher N concentrations in leaf litter) and higher P resorption proficiency (lower P concentrations in leaf litter). We also investigated whether the basis on which resorption was expressed (leaf mass, leaf area or unit leaf) influenced the patterns observed. 4 Contrasting with our hypothesis, a general trend of decreased N resorption efficiency occurred in response to increased N supply, but the expected decrease in N resorption proficiency was seen in all species except Betula nana. 5 P resorption efficiency did not change in four species (B. nana, Empetrum hermaphroditum, Eriophorum vaginatum and Rubus chamaemorus) but it decreased in Andromeda polifolia, and increased in Vaccinium uliginosum. P resorption proficiency showed the expected increase in only two species (B. nana and V. uliginosum). 6 Apart from P resorption efficiency, the different calculation methods generally produced similar responses of resorption efficiency and proficiency to N supply. 7 Increased N supply at high-latitude sites clearly leads to more N being returned to the soil through leaf litter production. However, decomposition of such litter will probably become P-limited. 8 Considerable interspecific differences in nutrient resorption proficiency were found, indicating that long-term changes in vegetation composition need to be considered when evaluating plant-mediated effects on ecosystem nutrient cycling in response to increased nutrient supply.

Effects of elevated carbon dioxide on green leaf tissue and leaf litter quality in an intact Mojave Desert ecosystem

AbstractThe effects of elevated carbon dioxide (CO2) on plant litter are critical determinants of ecosystem feedback to changing atmospheric CO2 concentrations. We measured concentrations of nitrogen (N) and carbon (C) and calculated C : N ratios of green leaves of two desert perennial shrubs, and the same quality parameters plus lignin and cellulose content of leaf litter from four shrub species exposed to elevated CO2 (FACE technology; Hendrey & Kimball, 1994) for 3 years in an intact Mojave Desert ecosystem. Shrubs tested were Larrea tridentata, Lycium pallidum, Lycium andersonii and Ambrosia dumosa. We calculated resorption efficiency from green tissue and leaf litter N data and measured lignin and cellulose content in litter in the last year study. Green leaves of L. tridentata grown under elevated CO2 had significantly lower N concentrations and higher C : N ratios than shrubs grown in ambient conditions in 1999 (P < 0.05). Lycium pallidum green leaves grown under elevated CO2 had significantly lower N concentrations and higher C : N ratios than shrubs grown under ambient conditions in 2000 (P < 0.05). There was no CO2 effect on C content of either species. We found no effect of CO2 on N or C content, C : N ratios, or lignin or cellulose concentrations in leaf litter of L. tridentata, L. pallidum, L. andersonii, or A. dumosa. There was no significant effect of CO2 on estimates of shrub resorption efficiency. There was a seasonal effect on green tissue and litter tissue quality for L. tridentata, with lower tissue N content in summer than in spring or winter months. These data suggest that any productivity increases with elevated CO2 in desert ecosystems may not be limited by lower leaf litter quality and that resorption efficiency calculations are best performed on an individual leaf basis.

Composition of Casuarina leaf litter and its influence on Frankia-Casuarina symbiosis in soil.

Plant needles of Casuarina equisetifolia were collected and analyzed in parallel with soil analysis. In three strains of Frankia--symbionts of Casuarina--their infectivity and plant performance was determined in vitro after soil amendment with different leaf litter concentrations. Only one strain was able to nodulate the plant at all litter concentrations (0.5, 3 and 5%) although the nodules were very small. However, all treated plants grew poorly; their growth was reduced by approximately 90% (for 5% litter concentration) compared to plants grown on untreated soil, on the basis of total dry mass. Inhibition of nodulation can be attributed to high concentrations of some elements and compounds that were either found in C. equisetifolia litter or originally found in soil (i.e. chloride, cyanide, copper, manganese and phenols). In general, plant growth decreased as more litter was added. Plant total nitrogen content was also reduced after increasing the litter concentration. The inhibitory effect of high litter concentrations was mainly on plant growth and to a lesser extent on plant nodulation by Frankia strains.

Elevated CO2, litter chemistry, and decomposition: a synthesis

The results of published and unpublished experiments investigating the impacts of elevated [CO2] on the chemistry of leaf litter and decomposition of plant tissues are summarized. The data do not support the hypothesis that changes in leaf litter chemistry often associated with growing plants under elevated [CO2] have an impact on decomposition processes. A meta-analysis of data from naturally senesced leaves in field experiments showed that the nitrogen (N) concentration in leaf litter was 7.1% lower in elevated [CO2] compared to that in ambient [CO2]. This statistically significant difference was: (1) usually not significant in individual experiments, (2) much less than that often observed in green leaves, and (3) less in leaves with an N concentration indicative of complete N resorption. Under ideal conditions, the efficiency with which N is resorbed during leaf senescence was found not to be altered by CO2 enrichment, but other environmental influences on resorption inevitably increase the variability in litter N concentration. Nevertheless, the small but consistent decline in leaf litter N concentration in many experiments, coupled with a 6.5% increase in lignin concentration, would be predicted to result in a slower decomposition rate in CO2-enriched litter. However, across the assembled data base, neither mass loss nor respiration rates from litter produced in elevated [CO2] showed any consistent pattern or differences from litter grown in ambient [CO2]. The effects of [CO2] on litter chemistry or decomposition were usually smallest under experimental conditions similar to natural field conditions, including open-field exposure, plants free-rooted in the ground, and complete senescence. It is concluded that any changes in decomposition rates resulting from exposure of plants to elevated [CO2] are small when compared to other potential impacts of elevated [CO2] on carbon and N cycling. Reasons for experimental differences are considered, and recommendations for the design and execution of decomposition experiments using materials from CO2-enrichment experiments are outlined.

Nitrogen resorption in senescing tree leaves in a warmer, CO2-enriched atmosephere

The prediction that litter quality, and hence litter decomposition rates, would be reduced when plants are grown in a CO2-enriched atmosphere has been based on the observation that foliar N concentrations usually are lower in elevated [CO2]. The implicit assumption is that the N concentration in leaf litter reflects the N concentration in green leaves. Here we evaluate that assumption by exploring whether the process of seasonal nutrient resorption is different in CO2-enriched plants. Nitrogen resorption was studied in two species of maple trees (Acer rubrum L. and A. saccharum Marsh.), which were planted in unfertilized soil and grown in open-top chambers with ambient or elevated [CO2] in combination with ambient or elevated temperature. In the second growing season, prior to autumn senescence, individual leaves were collected and analyzed for N and dry matter content. Other leaves at the same and an adjacent node were collected for analysis as they senesced and abscised. This data set was augmented with litter samples from the first growing season and with green leaves and leaf litter collected from white oak (Quercus alba L.) saplings grown in ambient and elevated [CO2] in open-top chambers. In chambers maintained at ambient temperature, CO2 enrichment reduced green leaf N concentrations by 25% in A. rubrum and 19% in A. saccharum. CO2 enrichment did not significantly reduce resorption efficiency so the N concentration also was reduced in litter. There were, however, few effects of [CO2] on N dynamics in these leaves; differences in N concentration usually were the result of increased dry matter content of leaves. The effects of elevated [CO2] on litter N are inherently more difficult to detect than differences in green leaves because factors that affect senescence and resorption increase variability. This is especially so when other environmental factors cause a disruption in the normal progress of resorption, such as in the first year when warming delayed senescence until leaves were killed by an early frost. The results of this experiment support the approach used in ecosystem models in which resorption efficiency is constant in ambient and elevated [CO2], but the results also indicate that other factors can alter resorption efficiency.

Microbial biomass, growth, and respiration associated with submerged litter of Phragmites australis decomposing in a littoral reed stand of a large lake

This study examined the microbial dynamics associated with decomposing litter of the widespread emergent macrophyte Phragmites australis in a littoral reed stand of a large lake. Stand- ing dead leaf and stem litter were collected, placed into fine and coarse mesh litter bags, and sub- merged in the reed stand. Litter bags were retrieved periodically and analyzed for fungal and bacte- rial biomass, fungal growth rates and production, rates of microbial respiration, litter mass loss, nutrient concentrations (N and P), and rates of dissolved organic carbon (DOC) release. Microbial biomass associated with both leaf and stem litter (12 to 85 mg C g -1 detrital C) was predominantly fungal (always ♢90% of the total biomass), even though bacterial biomass (0.13 to 5.6 mg C g -1 detri- tal C) increased and fungal biomass decreased or remained constant as litter decay proceeded. Although rates of fungal growth (0.02 to 0.08% h -1 ) and production (leaves only; 3 to 51 µg C g -1 detrital C h -1 ), and rates of microbial respiration (11 to 257 µg C g -1 detrital C h -1 ) decreased follow- ing litter submergence, fungi continued to be metabolically active in both leaf and stem litter. Signif- icant differences in fungal and bacterial biomass, fungal production rates, and rates of respiration were observed between leaf and stem material, with leaves often having 5 times higher values than corresponding stems. Rates of mass loss differed significantly between leaf litter in fine and coarse mesh bags, with less than 10% of the initial mass remaining in coarse mesh bags after 86 d, versus nearly 60% remaining in fine mesh bags. Nitrogen and P concentrations of leaf litter enclosed in fine mesh bags increased during litter decay, whereas N concentrations of leaf litter in coarse mesh bags remained unchanged and P concentrations decreased. Both N and P concentrations of stem litter were similar among litter bags and varied little throughout the study period. Results obtained in this study indicate that significant changes in microbial colonization and activity associated with P. aus- tralis litter can occur following the collapse of standing dead plant matter to the water. Furthermore, these findings suggest that fungi are active on submerged litter and thus play a vital role in the decomposition of P. australis litter in the aquatic environment.

EFFECT OF NATURAL FOREST ON THE CHEMICAL PROPERTIES OF SOILS

The effects of natural forest on the chemical properties of soil at different depths (0 to 30, 30 to 60 and 60 to 90 cm) were studied. There was a slight increase in pH in the sites under vegetation compared to open space, whereas no appreciable change in EC was observed. But substantial increase in cation exchange capacity, organic carbon content, total and available primary nutrients were recorded in the sites under vegetation compared to the contents in the open space. The effect of natural forest was more in surface soil (0 to 30cm) than in subsurface soil (30 to 60 and 60 to 90cm ). The underwood vegetation in the study area, leaf litter production over the period of establishment and nutrient concentration in leaf litter were also recorded.

Woody Debris Accumulations — Important Ecological Components in a Low Order Forest Stream (Weidlingbach, Lower Austria)

AbstractFrom May 1996 to February 1998, the density of debris dams was surveyed in monthly intervals along a 750‐m‐long, third order section of the Weidlingbach, a fourth order sandstone brook in the Wienerwald. The mean density over the whole study period was one woody debris accumulation per 35 m stream length. The longevity of these structures ranged from one month to over one year, depending on the hydrology of the stream. More than 50% of the accumulations outlasted moderate floods (0.3–0.4 m3 s−1); of these, 52% were tightly fixed to the bank vegetation. However, only 12% of the destroyed dams were anchored in any way. In addition, two dams were sampled for macroinvertebrate colonisation every other month from June 1996 to June 1997. Dry weights of the leaf and wood fraction were determined and macroinvertebrates identified. Within dams, organismic densities were lowest in temporarily dry levels at the top of debris accumulations (mean density =171 specimens dm−3) and highest in permanently submerged levels near the water surface as well as in patches with high leaf litter concentrations (mean density = 1240 specimens dm−3). Within the topmost 5 cm sediment layer mean macroinvertebrate density was 67.7 specimens dm−3. Within debris dams, taxa composition was not significantly different between the lowermost level 1 and the sediment surface and among levels within dams; however, significant differences existed between the topmost level 4 and all other dam levels. In level 4, we observed significantly more terrestrial Diptera taxa and Coleoptera and significantly fewer Plecoptera and Gammaridae.

REGIONAL ESTIMATION OF NITROGEN MINERALIZATION IN FOREST ECOSYSTEMS USING GEOGRAPHIC INFORMATION SYSTEMS

A knowledge-based geographic information system (GIS) model was developed and used to predict net nitrogen mineralization within forest ecosystems of the Midwestern Great Lakes region, USA (Illinois, Indiana, Michigan, Ohio, and Wisconsin). Climate, soil, and forest inventory data were used in conjunction with data relating initial N and lignin concentrations of leaf litter. Net N mineralization (Nnet) from leaf litter of forest ecosystems of the entire region was predicted as a function of litter quality (N:C ratio), annual actual evapotranspiration, soil texture, and litter production. Regional variation was evident in the model results: Nnet decreased from rates exceeding 120 kg·ha−1·yr−1 in the deciduous forest soils of southern Illinois, Indiana, and Ohio to 20 kg·ha−1·yr−1 in the coniferous forest soils of northern and eastern Michigan. Wisconsin’s forest soils had intermediate Nnet rates, predominantly 40–90 kg·ha−1·yr−1. The model was most sensitive to N concentration of litter, which indicated that litter quality of plant species is the most important factor controlling spatial distribution of N mineralization of ecosystems, even at the regional scale. The GIS model in this research provides a means for scaling between stand and regional scales. The model was a practical approach for estimating net N mineralization in forest ecosystems at the regional scale. Such models will become increasingly important in simulating the impacts of global environmental change on forest ecosystems.

Elevated Atmospheric Carbon Dioxide and Leaf Litter Chemistry: Influences on Microbial Respiration and Net Nitrogen Mineralization

AbstractElevated atmospheric CO2 has the potential to influence rates of C and N cycling in terrestrial ecosystems by altering plant litter chemistry and slowing rates of organic matter decomposition. We tested the hypothesis that the chemistry of leaf litter produced at elevated CO2 would slow C and N transformations in soil. Soils were amended with Populus leaf litter produced under two levels of atmo‐spheric CO2 (ambient and twice‐ambient) and soil N availability (low and high). Kinetic parameters for microbial respiration and net N mineralization were determined on soil with and without litter during a 32‐wk lab incubation. Product accumulation curves for CO2‐C and inorganic N were fit to a first order rate equation [y = A(1 − e−kt)] using nonlinear regression analyses. Although CO2 treatment affected soluble sugar concentration in leaf litter (ambient = 120 g kg−1, elevated = 130 g kg−1), it did not affect starch concentration or C/N ratio. Microbial respiration, microbial biomass, and leaf litter C/N ratio were affected by soil N availability but not by atmospheric CO2. Net N mineralization was a linear function of time and was not significantly different for leaves grown at ambient (50 mg N kg−1) and elevated CO2 (35 mg N kg−1). Consequently, we found no evidence for the hypothesis that leaf litter produced at elevated atmospheric CO2 will dampen the rates of C and N cycling in soil.

High Foliar Nitrogen in Desert Shrubs: An Important Ecosystem Trait or Defective Desert Doctrine?

Nitrogen concentrations in green and senesced leaves of perennial desert shrubs were compiled from a worldwide literature search to test the validity of the doctrine that desert shrubs produce foliage and leaf litter much richer in nitrogen than that in the foliage of plants from more mesic environments. Mean nitrogen concentration in the green leaves of 78 species of shrubs growing in 11 deserts on five continents (2.2%) was not different from that in 67 species of trees and shrubs growing in deciduous, and mixed deciduous forests (2.2%), and only slightly higher than that in overstory (2.0%) and understory (2.1%) plants growing in tropical wet forest. Mean nitrogen concentration in the green leaves of a ubiquitous shrub that dominates large areas of desert in the United States (Larrea tridentata, 2.1%), and in the green—stem tissues of leafless desert shrubs (2.1%) were also similar to that in plants from mesic environments. Mean green—leaf nitrogen was similar in shrubs growing in different deserts. Mean nitrogen concentration in leaf litter was 1.1% for 11 species of desert shrubs, and 1.0% for the 10 species of this group that were not capable of symbiotic nitrogen fixation. Both concentrations were lower than those routinely provided to describe nitrogen in the litter of desert shrubs (1.5—1.7%), and only slightly higher than the mean nitrogen concentration in 77 species of woody perennials growing in a wide variety of environments worldwide (0.9%). Nitrogen in the leaf litter of one desert shrub (0.4%, Brickellia laciniata) was nearly as low as the lowest leaf—litter nitrogen concentration known for any woody species (0.3%). Because nitrogen concentrations in the foliage of desert shrubs are not higher than those in plants growing in more mesic environments, the tenet that desert shrubs support extraordinarily nitrogen—rich foliage can no longer be supported.