Leaf Litter Nitrogen Research Articles

Patterns and controls of leaf litter nitrogen and phosphorus of broad-leaved tree species across and within the tropics and the extra-tropics

Leaf litter nitrogen (N) and phosphorus (P), as the final products reflecting the foliar nutrient status after resorption, strongly influence forest production and nutrient cycling. However, our nuanced understanding of their general patterns and controls is still lacking, and whether differential regulatory mechanisms exist between climatic zones remains largely incomplete, which introduces substantial uncertainty in the comprehension of net ecosystem productivity and nutrient cycling. Here, we aimed to evaluate patterns of leaf litter N and P concentrations of broad-leaved tree species, and further quantify their controls from climatic, soil physical, soil chemical, and green foliar nutrient factors across and within the tropics and extra-tropics by updating a global dataset comprising 1171 records from 159 studies. We found that tropical tree species exhibited higher leaf litter N concentrations but lower leaf litter P concentrations than extra-tropical tree species. In contrast to previous findings, the effects of climatic and edaphic variables on leaf litter N and P concentrations are more pronounced in the tropics than in the extra-tropics. Different from past bivariate analyses of climate-nutrient relationships for leaf litter, climate exerted more indirect effects on leaf litter N and P concentrations through soil texture, hydrology, nutrient availability, and green foliar nutrients. We also observed direct effects of green foliar N and P concentrations on leaf litter N and P concentrations enhanced from tropical to extra-tropical zones. Overall, this study refines our understanding of differential controls over leaf litter N and P concentrations across climatic zones and highlights the crucial yet often overlooked role of soil physical and chemical properties. These insights further underscore the urgent need to integrate multiple climatic, edaphic, and green foliar nutrient variables into geographically explicit biogeochemical models to improve our understanding of leaf litter-driven forest nutrient cycling in response to future environmental changes for different climatic zones.

Carbon and nutrient cycling in cocoa agroforests under organic and conventional management

In cocoa agroforestry systems, cycling of leaves, pods, and branches are key for organic matter sustenance. We investigated annual total litterfall, annual nutrient stocks in total litterfall, cocoa pods and beans, as well as cocoa leaf decomposition rates in cocoa agroforestry systems under conventional and organic management in Suhum Municipality, Eastern Region of Ghana. The study was conducted using six cocoa agroforests for each management selected from a total of four villages. Litterfall was collected monthly using litterboxes and a litterbag technique was employed to study the rates of leaf decomposition and nutrient release for 12 months. In June and July, total litterfall in organic farms were 94% and 65%, respectively, higher than in conventional farms, but management had no effect on average annual total litterfall of 8.8 t ha−1 yr−1 litterfall. Due to the trees’ reduced transpiration, 61% of the annual total litterfall occurred during the dry season. Whereas average leaf litter nitrogen (N) concentration was 17% higher in the rainy season than dry season, potassium (K) concentration was 38% higher during the dry season than rainy season. This likely reflected the contribution of N rich green leaves to litterfall in the rainy season and plant coping strategy to drought leading to K accumulation. Cocoa leaf decomposition was not affected by management. Annual potassium (K) and calcium (Ca) stocks in cocoa pod husk were four and nine-fold, respectively, higher than in cocoa beans. We conclude that organic versus conventional management had no effect on litterfall and cocoa leaf decomposition rather season influenced litterfall quantity and chemistry. Irrespective of management the spreading of cocoa pod husk after harvest will improve internal nutrient cycling in cocoa agroforestry systems.

Functional composition outweighs taxonomic and functional diversity in maintaining ecosystem properties and processes of mangrove forests

AbstractBiodiversity loss can have significant consequences for human well‐being, as it can affect multiple ecosystem properties and processes (MEPP) that drive ecosystem services. However, a comprehensive understanding of the link between environmental factors, biodiversity, and MEPP remains elusive, especially in mangrove ecosystems that millions of people along tropical coastlines worldwide depend upon. Here, we collated a comprehensive dataset on forest inventory, plant traits, and environmental factors across 93 plots in the Sundarbans Reserved Forests, Bangladesh. The functional composition (FC) of leaf area showed a stronger positive association with MEPP, being determined by total biomass and productivity of the mangroves, sediment organic carbon, and ammonium, phosphorus, and potassium contents of the sediment, than species richness (SR) or functional diversity (FD). Further, FC mediated a strong negative association of sediment salinity, and a positive association of SR, with MEPP. The similar but opposite total associations of SR and sediment salinity with MEPP suggest that species‐rich mangroves could offset the negative impacts of rising salinity on MEPP. When focusing on a single aspect of MEPP, both FD and FC mattered, with the FD of leaf area showing a strong association with mangrove productivity and sediment potassium content, while the FC of leaf litter nitrogen showed the strongest associations with sediment ammonium and phosphorus contents. Therefore, to sustain mangrove ecosystems as a reliable nature‐based solution for climate change mitigation, conservation and (re‐)establishment projects should prioritize regionally dominant species with high leaf area and nitrogen content, plus functionally different species to support the ecosystem processes and services provided by mangroves.

Root nutrient capture and leaf resorption efficiency modulated by different influential factors jointly alleviated P limitation in Quercus acutissima across the North-South Transect of Eastern China.

Soil and climatic conditions are known to have close associations with plant morphological and stoichiometric traits at a regional scale along latitudinal gradients; however, how latitude drives biotic and abiotic factors affecting plant nutrient acquisition to accommodate environmental nutrient deficiency remains unclear. We quantified soil, root, leaf, and leaf litter nitrogen (N) and phosphorus (P) concentrations to determine the potentially limiting nutrient and the simultaneous responses of root capture and leaf resorption to nutrient deficiency in seven Quercus acutissima forests across the North-South Transect of Eastern China. The results showed that the mean leaf and root N:P ratios in Q. acutissima were 21.58 and 20.23, respectively, which markedly exceeded the P limitation threshold of 16 for terrestrial plants. The mean leaf litter N and P were 10.63 mg/g and 0.51 mg/g, respectively, indicating that P resorption proficiency was relatively higher than N resorption proficiency. N displayed higher stoichiometric homeostasis than P in the leaf. The leaf and root N:P ratios showed a quadratic variation that first decreased and then increased as latitude increased, whereas the phosphorus resorption efficiency and root-soil accumulation factor of P displayed the opposite trend. Partial least square path modeling ( PLS-PM) analysis demonstrated that root nutrient capture and leaf nutrient resorption were regulated by different influential factors. Overall, these findings provide new insights into plant strategies to adapt to environmental nutrient deficiency, as well as the scientific basis for predicting the spatial and temporal patterns of nutrient acquisition in the context of climate change.

Global-scale latitudinal patterns of twelve mineral elements in leaf litter

Litter mineral elements carry out the cycling and storage of multiple nutrients and heavy metals in soil, and thus shape many key soil processes. Driving factors of global geographic patterns of multiple litter elements along with the driving factors are largely limited to N and P. By compiling data on 12 major mineral elements (nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, aluminium, iron, manganese, sodium, zinc, and copper) in leaf litter from 1, 666 species and 69 countries and 1, 018 studies, we conducted a global meta-analysis of the effects of climate, soil chemistry, plant functional types, and resorption on latitudinal patterns of multiple mineral elements in litter. We showed that leaf litter phosphorus and manganese concentrations increased and zinc concentration kept unchanged with latitude, while the other elements declined, indicative of specific climatic effects on plant physiology. The climate-related gradients including soil nutrients and woody plant distribution play a key role in the latitudinal patterns of elements (except N), while soil pH was a poor explanatory factor. Because of lower nitrogen resorption at higher temperature, nitrogen in leaf litters responded to latitude in a contrary manner as that in green leaves. Overall, we suggest that fundamental constraints on plant physiology and nutrient usage strategies lead to predictable global-scale patterns in multiple litter elements.

The influence of the invasive alien nitrogen-fixing Robinia pseudoacacia L. on soil nitrogen availability in a mixed Mediterranean riparian forest

Robinia pseudoacacia L. occupies large areas of Mediterranean riparian zones of the northeast of the Iberian Peninsula. This study investigates the influence of the invasive alien nitrogen-fixing R. pseudoacacia on leaf litter nitrogen (N) inputs and soil N availability in a mixed riparian forest in NE Spain. We measured annual leaf litter N inputs, decomposition rates, soil N processes, and soil N concentrations at three sections (near-stream, intermediate, and hillslope) across a riparian forested zone. Moreover, we explored changes in soil N availability associated with the presence of R. pseudoacacia by means of an empirical forest floor model. Leaf litter N content was higher for R. pseudoacacia than for the native non-fixing species. Although the contribution of R. pseudoacacia to annual leaf litter N inputs increased from the near-stream to the hillslope section, soil N mineralization, nitrification, and N availability were similar among sections. Simulations suggest that soil N availability was higher at the near-stream than at the hillslope section without the presence of R. pseudoacacia. However, this pattern smoothed down as R. pseudoacacia spread across the riparian forest. Overall, our results suggest that the spreading of R. pseudoacacia across the riparian zone contributed to homogenize soil N availability over time, and highlight that an integrated spatiotemporal view of the invasive process is needed to assess its impact on soil N biogeochemistry.

Mangrove Leaf Litter Decomposition in a Seasonal Tropical Environment

Loria-Naranjo, M.; Sibaja-Cordero, J.A., and Cortes, J., 2019. Mangrove leaf litter decomposition in a seasonal tropical environment. Journal of Coastal Research, 35(1), 122–129. Coconut Creek (Florida), ISSN 0749-0208.Seasonal changes in rainfall might have an impact on the decomposition of mangrove leaf litter. This study analyzed the influence of weather conditions (season) on the decay rate, nitrogen, and phosphorus content as a decomposition indicator of leaf litter of Rhizophora racemosa. These measurements were taken at two sites in the Terraba–Sierpe National Wetland (TSNW) South Pacific, Coasta Rica, in 2013. The dry and wet season decay constants were similar and fast (k = 0.012 day–1). Decay constants were positively associated with salinity and water temperature (p <0.10). Moreover, season had an effect on the leaf litter nitrogen (high in dry season) and phosphorus content (high in rainy season). The effect of decomposition time on nitrogen and phosphorus content varies between sites. Leaf litter from R. racemosa acts as a substrate that releases nutrients to the ecosystem, contributing to carbon, nitrogen, and phosphorus budgets. The similar and fast decay constants among seasons is possibly because of the small difference in seasonal rainfall in TSNW, while seasonal variation in nitrogen and phosphorus is possibly a result of changes in microbial activity. This study highlights the need for an integral approach to research on nutrient cycling in mangrove forests because of its complex decay patterns.

Nitrogen recycling in coupled green and brown food webs: Weak effects of herbivory and detritivory when nitrogen passes through soil

Abstract The study of coupled green and brown food webs has improved our ability to understand how nutrient cycling and plant communities respond to perturbations. Yet, it is still difficult to predict how rapidly and consistently changes in one food web propagate to the other. An area of particular uncertainty is the response of plants to the changes in leaf litter nitrogen release caused by herbivores and detritivores. We combined a field experiment and theoretical analysis to assess how herbivory, fertilization, and detritivory changed leaf litter nitrogen release and plant growth. We produced leaf litter in greenhouse cages with a factorial combination of grasshopper herbivory and additional nitrogen fertilizer. Our experiment used the resulting 15N‐labelled leaf litter to measure isopod litter consumption, litter nitrogen release, and plant nitrogen uptake in the field. We then used a dynamical systems model to distinguish whether plant growth relied (a) directly on litter nitrogen release or (b) on other nitrogen pathways so that changes in litter nitrogen release have little immediate impact. Our empirical results show that the effect of nitrogen fertilization on isopod processing of leaf litter was stronger than the effect of herbivory. Regardless, the available soil nitrogen and plant growth were independent of litter nitrogen release. Our dynamical model attributes the independence to other nitrogen sources and sinks, which buffer the plant‐available nitrogen pool. Isopods and litter with a history of herbivory reduced above‐ground plant growth when we accounted for initial field mesocosm conditions, especially the abundance of the competitively dominant goldenrods. Consequently, the impact of isopods and litter traits do propagate to influence plant growth, but do not have a large enough effect to overcome initial differences in plant biomass and community composition in one year. Synthesis. Our results indicate animals in green and brown food webs can alter plant litter nitrogen release without any significant nutrient recycling effect on plant growth. Considering the availability of external and soil‐based nitrogen sources, as well as the current plant community and microbial biomass, may be critical to determining when plant growth will respond to animal‐mediated changes in litter decomposition.

Response of carbon and nitrogen release to simulated nitrogen deposition in natural evergreen broad-leaved forests in a rainy area in Western China

Over the last several decades, human activities have increased the nitrogen input in terrestrial ecosystem, and the alteration of the N cycle has profoundly affected the cycles of many other elements, especially carbon (C). Litter decomposition is an important ecosystem process that plays a key role in the balance of global carbon and nitrogen cycles. To investigate the effects of simulated nitrogen (N) deposition on litter decomposition, a one-year field experiment on litter decomposition following N addition treatments was conducted in a natural evergreen broad-leaved forest in a rainy area of Western China. Beginning November 2013, we conducted a field experiment using the litterbag method that included four treatments: 0, 50, 150, and 300kgNhm−2a−1 as the control (CK), low (L), medium (M), and high (H) nitrogen deposition, respectively. Every 15days, NH4NO3 was added to the N-treated plots. The results indicated that after one year of decomposition, the remaining rate in each treatment was between 54.71% and 63.52%, L, M, and H rates were 4.18%, 6.53%, and 8.81% higher, respectively than the CK. N deposition significantly increased the remaining rate and inhibited the decomposition of leaf litter in this ecosystem because of the addition of N. Greater increases in N strengthened the inhibition effect. N addition significantly increased the concentration of carbon and nitrogen in leaf litter. The decomposition coefficient of C and N were in the order k(CK)>k(L)>k(M)>k(H), although N was released faster. The time for 95% C decomposition of foliar litter increased by 0.92–2.20 a from 4.09 a (T95% of CK) because of N addition, and that for N decomposition increased by 0.64–1.22 a from 3.73 a. After decomposing for 1 a, the C remaining rates for L, M, and H were 6.00%, 9.89%, and 14.11%, respectively, higher than CK, whereas the N remaining rate was 4.13%, 6.75% and 10.08%, respectively. Thus, nitrogen addition significantly increased the C and N remaining rates and significantly inhibited the release of carbon and nitrogen. The L, M, and H treatments increased the C/N ratio of the leaf litter by 3.33%, 5.40% and 6.38%, respectively, suggesting that the M and H treatments significantly increased the C/N ratio. Nitrogen treatments weakened the correlation between the mass remaining and C and N remaining, but strengthened the correlation between mass remaining and the C/N ratio. The correlation coefficient of mass remaining and C and N remaining was reduced by N deposition, whereas the C/N ratio was increased. Under simulated N deposition, C remaining was still a good indicator of litter decomposition relative to the N remaining and C/N ratio.

Controls over leaf litter decomposition in a mixed evergreen and deciduous broad-leaved forest, Central China

Our understanding of the determinants of leaf litter decomposition is lacking for mixed evergreen and deciduous broad-leaved forests compared with tropical and temperate forests. This study aimed to assess the relative importance of litter properties, climate and soil on decomposition in a mixed above-mentioned forest in a transitional zone, central China. We utilized leaf litter from seven canopy tree species in conjunction with a transplant litterbag experiment along an elevational gradient over three years by measuring decomposition rate. Initial leaf litter nitrogen (N), phosphorus (P) and magnesium (Mg) as well as C:P were robust predictors of leaf litter decomposition. Mg was the single best predictor of leaf litter decomposition across all species. Soil moisture and air temperature could predict leaf litter decomposition very well across the elevational gradient. The explanatory power of elevation-related variables (27.75 %) was much lower than that of species-related variables (38.97 %). More nutrients such as Mg than N and P commonly used in proposed indices should be taken into account when evaluating the decomposability of leaf litter. Tree species identity is the most important determinant of leaf litter decomposition in this target transitional mixed forest. Therefore, shifts in tree species composition may influence leaf litter decomposition rates more than changes in site conditions under the context of future climate change.

Environmental Filtering and Positive Plant Litter Feedback Simultaneously Explain Correlations Between Leaf Traits and Soil Fertility

Plant traits covary with soil fertility, but determining whether this is the outcome of environmental filtering or plant feedback is not straightforward, especially in long-lived plant communities such as rain forests. Without explicitly accounting for the potential of plant litter to influence soil properties, it is difficult to interpret with confidence that covariation between soil nutrients and plant traits is the outcome of environmental filtering. We estimated abundance-weighted mean leaf dry matter content (LDMC), senesced leaf litter nitrogen resorption proficiency (litter N %), wood tissue density, and multiple metrics of soil fertility (pH, C:N ratio, and organic P concentrations) on 241 temperate rain forest plots throughout New Zealand. A non-recursive structural equation model indicated that environmental filtering and plant litter feedback were equally important reciprocal processes that explain covariation between leaf traits and soil fertility. Plant communities with high resorption proficiency, high LDMC, and high stem tissue density were strongly associated with low-fertility soils. Both structural (LDMC) and chemical (litter N %) leaf traits influenced soil fertility, but stem tissue density did not exhibit feedback effects. Here, we show that it is not a matter of ‘either–or’ when determining the relative importance of environmental filtering and plant feedback, but rather that both processes are equally important and occur simultaneously in temperate forest ecosystems. Although both leaf and wood traits were filtered by soil fertility, only leaf traits exhibited significant feedback effects on soil fertility.

Effects of litter traits, soil biota, and soil chemistry on soil carbon stocks at a common garden with 14 tree species

Tree species interact with soil biota to impact soil organic carbon (C) pools, but it is unclear how this interaction is shaped by various ecological factors. We used multiple regression to describe how ~100 variables were related to soil organic C pools in a common garden experiment with 14 temperate tree species. Potential predictor variables included: (i) the abundance, chemical composition, and decomposition rates of leaf litter and fine roots, (ii) species richness and abundance of bacteria, fungi, and invertebrate animals in soil, and (iii) measures of soil acidity and texture. The amount of organic C in the organic horizon and upper 20 cm of mineral soil (i.e. the combined C pool) was strongly negatively correlated with earthworm abundance and strongly positively correlated with the abundance of aluminum, iron, and protons in mineral soils. After accounting for these factors, we identified additional correlations with soil biota and with litter traits. Rates of leaf litter decomposition, measured as litter mass loss, were negatively correlated with size of the combined soil organic C pool. Somewhat paradoxically, the combined soil organic C pool was also negatively related to the ratio of recalcitrant compounds to nitrogen in leaf litter. These apparent effects of litter traits probably arose because two independent components of litter “quality” were controlling different aspects of decomposition. Leaf litter mass loss rates were positively related with leaf litter calcium concentrations, reflecting greater utilization and depolymerization of calcium-rich leaf litter by earthworms and other soil biota, which presumably led to greater proportional losses of litter C as CO2 or dissolved organic C. The fraction of depolymerized and metabolized litter that is ultimately lost as CO2 is an inverse function of microbial C use efficiency, which increases with litter nutrient concentrations but decreases with concentrations of recalcitrant compounds (e.g. lignin); thus, high ratios of recalcitrant compounds to nitrogen in leaf litter likely caused a greater fraction of depolymerized litter to be lost as CO2. Existing conceptual models of soil C stabilization need to reconcile the effects of litter quality on these two potentially counteracting factors: rates of litter depolymerization and microbial C use efficiency.

Seasonal changes in soil organic matter after a decade of nutrient addition in a lowland tropical forest

Soil organic matter is an important pool of carbon and nutrients in tropical forests. The majority of this pool is assumed to be relatively stable and to turn over slowly over decades to centuries, although changes in nutrient status can influence soil organic matter on shorter timescales. We measured carbon, nitrogen, and phosphorus concentrations in soil organic matter and leaf litter over an annual cycle in a long-term nutrient addition experiment in lowland tropical rain forest in the Republic of Panama. Total soil carbon was not affected by a decade of factorial combinations of nitrogen, phosphorus, or potassium. Nitrogen addition increased leaf litter nitrogen concentration by 7 % but did not affect total soil nitrogen. Phosphorus addition doubled the leaf litter phosphorus concentration and increased soil organic phosphorus by 50 %. Surprisingly, concentrations of carbon, nitrogen, and phosphorus in soil organic matter declined markedly during the four-month dry season, and then recovered rapidly during the following wet season. Between the end of the wet season and the late dry season, total soil carbon declined by 16 %, total nitrogen by 9 %, and organic phosphorus by between 19 % in control plots and 25 % in phosphorus addition plots. The decline in carbon and nitrogen was too great to be explained by changes in litter fall, bulk density, or the soil microbial biomass. However, a major proportion of the dry-season decline in soil organic phosphorus was explained by a corresponding decline in the soil microbial biomass. These results have important implications for our understanding of the stability and turnover of organic matter in tropical forest soils, because they demonstrate that a considerable fraction of the soil organic matter is seasonally transient, despite the overall pool being relatively insensitive to long-term changes in nutrient status.

Leaf litter decomposition rates increase with rising mean annual temperature in Hawaiian tropical montane wet forests.

Decomposing litter in forest ecosystems supplies nutrients to plants, carbon to heterotrophic soil microorganisms and is a large source of CO2 to the atmosphere. Despite its essential role in carbon and nutrient cycling, the temperature sensitivity of leaf litter decay in tropical forest ecosystems remains poorly resolved, especially in tropical montane wet forests where the warming trend may be amplified compared to tropical wet forests at lower elevations. We quantified leaf litter decomposition rates along a highly constrained 5.2 °C mean annual temperature (MAT) gradient in tropical montane wet forests on the Island of Hawaii. Dominant vegetation, substrate type and age, soil moisture, and disturbance history are all nearly constant across this gradient, allowing us to isolate the effect of rising MAT on leaf litter decomposition and nutrient release. Leaf litter decomposition rates were a positive linear function of MAT, causing the residence time of leaf litter on the forest floor to decline by ∼31 days for each 1 °C increase in MAT. Our estimate of the Q10 temperature coefficient for leaf litter decomposition was 2.17, within the commonly reported range for heterotrophic organic matter decomposition (1.5–2.5) across a broad range of ecosystems. The percentage of leaf litter nitrogen (N) remaining after six months declined linearly with increasing MAT from ∼88% of initial N at the coolest site to ∼74% at the warmest site. The lack of net N immobilization during all three litter collection periods at all MAT plots indicates that N was not limiting to leaf litter decomposition, regardless of temperature. These results suggest that leaf litter decay in tropical montane wet forests may be more sensitive to rising MAT than in tropical lowland wet forests, and that increased rates of N release from decomposing litter could delay or prevent progressive N limitation to net primary productivity with climate warming.

Impact of episodic herbivory by the tamarisk leaf beetle on leaf litter nitrogen and stem starch content: A short communication

Tamarisk (Tamarix spp.) has in recent decades come to dominate riparian corridors throughout much of the western U.S. The implementation of biological control, utilizing the tamarisk leaf beetle (Diorhabda spp., particularly Diorhabda carinulata), has focused attention and research on this method for Tamarix suppression. Researchers are just beginning to understand how herbivory by Diorhabda affects Tamarix physiology and nutritional dynamics. The purpose of this study was to investigate whether herbivory by D. carinulata altered leaf litter nitrogen and stem starch content, and if so, how such alteration varied across a gradient of herbivory chronosequence. Leaf litter and stem analysis showed significantly higher levels of both nitrogen and stem starch content in trees that had experienced herbivory by the leaf beetle. However, there were no significant differences in nitrogen or stem starch content based on years of beetle herbivory. Higher levels of nitrogen in leaf litter from beetle-affected trees may be a result of herbivory-induced desiccation and foliar mortality prior to the translocation of nitrogen back into plant reserves. Additionally, higher stem starch may be a result of either phloem damage reducing the translocation of photoassimilates, or an increase in the shunting of carbohydrates to the site of new leaf growth. Finally, the lack of correlation between years of herbivory and both leaf litter nitrogen and stem starch may indicate that as of yet there have not been sufficient defoliation events to yield anticipated host plant impact.

Genotypic variation in yellow autumn leaf colours explains aphid load in silver birch

• It has been suggested that autumn-migrating insects drive the evolution of autumn leaf colours. However, evidence of genetic variation in autumn leaf colours in natural tree populations and the link between the genetic variation and herbivore abundances has been lacking. • Here, we measured the size of the whole aphid community and the development of green-yellow leaf colours in six replicate trees of 19 silver birch (Betula pendula) genotypes at the beginning, in the middle and at the end of autumn colouration. We also calculated the difference between green leaf and leaf litter nitrogen (N) and estimated the changes in phloem sap N loading. • Autumn leaf colouration had significant genetic variation. During the last survey, genotypes that expressed the strongest leaf reflectance 2-4 wk earlier had an abundance of egg-laying Euceraphis betulae females. Surprisingly, the aphid community size during the first surveys explained N loss by the litter of different birch genotypes. • Our results are the first evidence at the tree intrapopulation genotypic level that autumn-migrating pests have the potential to drive the evolution of autumn leaf colours. They also stress the importance of recognizing the role of late-season tree-insect interactions in the evolution of herbivory resistance.

Global pattern of leaf litter nitrogen and phosphorus in woody plants

• Forest ecosystems exert an important influence on global biogeochemical cycles. A global dataset of nitrogen (N) and phosphorus (P) concentrations in leaf-litter of woody plants was compiled from the literature. Among the 677 data sets, 482 included P concentrations and the N:P ratio. • At a global scale, the mean leaf-litter N and P and N:P ratio were 10.9 mg g -1 , 0.85 mg g -1 and 18.3, respectively. Leaf-litter N and P were significantly correlated. When the data was grouped by continents, the highest mean N was found in Africa (19.5 mg g -1 ), and the lowest in North America (8.18 mg g -1 ). P was significantly smaller in the Asian Islands (Japan and Malaysia, 0.44 mg g -1 ) than on the Asian mainland. For the global dataset, leaf-litter N increased linearly with mean annual temperature and annual precipitation and decreased with latitude. Although leaf-litter P showed no significant relationship with temperature, it declined linearly with precipitation and there was a convex quadratic relationship with latitude. For the global dataset and also for different functional groups (e.g. shrubs, evergreen broadleaf, deciduous broadleaf, and conifers) the leaf-litter N:P ratio generally followed a positive linear relationship with temperature and precipitation, and showed a concave quadratic response with latitude. • The differences in leaf-litter N:P ratio among functional groups and among continents should be taken into account when modeling biogeochemical cycles in different regions as well as on a global scale.

Mixed litter decomposition in a managed Missouri Ozark forest ecosystem

We monitored the decomposition of mixed leaf litter ( Quercus spp., Carya spp., and Pinus echinata) in a Missouri Ozark forest eight years after experimental harvest. Leaf litter mass losses and changes in carbon chemistry (extractive, acid soluble, and acid insoluble fractions) were measured over 32 months in field incubations to determine the effects of litter composition and stand manipulation on decomposition and nitrogen (N) concentration in the remaining litter. The decay ( k) rate over this period ranged between 0.39 (±0.010) and 0.51 (±0.002) year −1 for oak, oak–hickory, and oak–pine litter. There were significant main effects of stand manipulation ( p = 0.03) and litter type ( p < 0.01) on decay. Mass losses of oak and oak–hickory litter were 7% ( p = 0.02) and 4% ( p = 0.04) higher on harvested stands than controls, respectively. Mass loss of oak–hickory litter was 3% faster than oak–pine ( p = 0.03) and 6% faster than oak ( p = 0.02) litter on control stands, whereas the oak–hickory litter mass loss was 5% higher than oak litter on harvested stands ( p = 0.01). The decay ( k) rate had a linear relationship with initial leaf litter nitrogen content and lignin-to-N ratio. The nitrogen concentration in remaining litter had a nonlinear relationship to cumulative mass loss suggesting an exogenous source of N. In summary, this study demonstrated significant effects of timber harvest and litter mixtures on decomposition and N dynamics in a managed Missouri Ozark forest.

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

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

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 &lt; 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.