Nutrient cycling by the subterranean termite Gnathamitermes tubiformans in a Chihuahuan desert ecosystem

Summary We estimated the density of subterranean termites Gnathamitermes tubiformans at 800,000 · ha^-1 for a standing crop biomass of 2 kg · ha^-1 Predation losses were estimated to be 5,73 kg · ha^-1 · yr^-1 representing the major release of nutrients from termites to surficial soil layers. Nutrient fluxes from termites to predators amounted to 410g N·ha^-1·yr^-1, 33 g S · ha^-1 · yr^-1 and 19 g P · ha^-1 · yr^-1. These fluxes account for 8% of the litter N, 1.5% of the litter P and 2.9% of the litter S. The termites fixed an estimated 66 g · ha^-1 · yr^-1 atmospheric N and returned an estimated 100 g · ha^-1 · yr^-1 in the surface gallery carton. Since losses of elements from subterannean termites were greater than standing crops, we estimated an annual turnover of N at 3.5 times per year, P of 2.5 times per year, and S of 2.5 per times per year.Since surface foraging, predation and alate flights are pulse regulated by rainfall, nutrient flows through subterranean termites are episodic and releases of nutrients accumulated in termite biomass preceeds or is coincident with productivity pulses of some shallow rooted plants. We propose that subterranean termites are important as regulators in desert nutrient cycles.     

Above- and belowground organic matter storage and production in a tropical pine plantation and a paired broadleaf secondary forest

The distribution of tree biomass and the allocation of organic matter production were measured in an 11-yr-old Pinus caribaea plantation and a paired broadleaf secondary forest growing under the same climatic conditions. The pine plantation had significantly more mass aboveground than the secondary forest (94.9 vs 35.6 t ha^-1 for biomass and 10.5 vs 5.0 t ha^{-1 for litter}), whereas the secondary forest had significantly more fine roots (⩽2 mm diameter) than the pine plantation (10.5 and 1.0 t ha^-1, respectively). Standing stock of dead fine roots was higher than aboveground litter in the secondary forest. In contrast, aboveground litter in pine was more than ten times higher than the dead root fraction. Both pine and secondary forests had similar total organic matter productions (19.2 and 19.4 t ha^-1 yr^-1, respectively) but structural allocation of that production was significantly different between the two forests; 44% of total production was allocated belowground in the secondary forest, whereas 94% was allocated aboveground in pine. The growth strategies represented by fast growth and large structural allocation aboveground, as for pine, and almost half the production allocated belowground, as for the secondary forest, illustrate equally successful, but contrasting growth strategies under the same climate, regardless of soil characteristics. The patterns of accumulation of organic matter in the soil profile indicated contrasting nutrient immobilization and mineralization sites and sources for soil organic matter formation.     

Mineral cycling in a tropical palm forest

Nutrient cycling and biomass characteristics of a tropical palm forest dominated byOrbignya cohune were found to be different from thsoe of hardwood dominated forests. The cohune palm forest had a high proportion of biomass in leaves (5%), a reduced sapling layer, a large amount of standing forest litter and an exceptionally low decomposition rate factor (0.1 year^–1). Mineral concentrations in palm leaves were generally lower than in hardwood species with the exception of Na, which was exceptionally high inOrbignya cohune. Biomass was estimated at 226 tons ha^–1 containing 1173 kg ha^–1 N; 126 kg ha^–1 P; 437 kg ha^–1 K; 1869 kg ha^–1 Mg; 125 kg ha^–1 Ca, and 2177 kg ha^–1 Na. Soils of cohune association did not differ significantly from those of neighbouring hardwood dominated associations with the exception of Na which occurred in higher concentration because of bioaccumulation in the dominant. The results suggest that the growth habits and physiology of a dominant can strongly influence some of the ecological parameters used to describe aforest association.     

Fine Root Productivity and Turnover in Two Evergreen Central Himalayan Forests

Fine root production and mortality in central Himalayan evergreenforests consisting of Quercus leucotrichophora (banj oak) andPinus roxburghii (chir pine) were measured. Fine root productionand mortality decreased with increasing soil depth. Annual fineroot production was higher in the broadleafed forest than inthe coniferous forest, across months and seasons (1.3 and 1.5-timesmore living and dead root biomass, respectively in banj oakthan in chir pine). Live fine root production was 2508 kg ha^-1year^-1inchir pine forest and 3631 kg ha^-1year^-1in banj oak forest. Deadfine roots accumulated at a rate of 1197 and 1525 kg ha^-1year^-1inchir pine and in banj oak forest, respectively. In both forests,the greatest fine root production was recorded in the rainyseason followed by summer and winter seasons. Both soil androot nitrogen concentration decreased with increasing soil depth.Nitrogen uptake was higher in banj oak forest (12.1 kg ha^-1year^-1)than chir pine forest (7.2 kg ha^-1year^-1).Copyright 1999 Annalsof Botany Company Fine root production, fine roots, necromass, banj oak, chir pine, Quercus leucotrichophora , Pinus roxburghii .     

六种温带森林类型凋落物量长期动态及其环境驱动

阐明凋落物动态及其环境控制机制，可以为森林生态系统生产力及碳汇功能的维持提供重要的数据支持和理论依据。以长白山系余脉张广才岭西坡林龄相近但立地条件不同的4种天然次生林（即硬阔叶林、杨桦林、杂木林和蒙古栎林）和2种人工林（落叶松人工林和红松人工林）为研究对象，对其地上凋落物产量及其组分以及相关环境因子进行了14年（2008-2021年）的连续测定，旨在揭示森林凋落物量及其组分的时空变化（林型间和年际变异）及其环境驱动机制。结果表明：6种森林类型的凋落总量（TL）无显著差异，波动范围为500.5-556.1 g m^-2 a^-1；但其叶凋落量（LL）、繁殖组织凋落量（RT）和其他组织凋落量（OT）均存在显著差异，波动范围依次分别为333.9-391.8 g m^-2 a^-1、8.43-69.93 g m^-2 a^-1和93.4-185.9 g m^-2 a^-1。6种森林类型的TL均存在显著的年际变化；其中LL和OT年际变化的显著性因森林类型而不同，而RT的年际变化不显著。除落叶松人工林外，其余5种森林类型的LL与生长季平均气温、日最低气温均值、土壤10 cm深度处的平均温度、最低温度（Ts_min）和土壤5 cm含水量（Ms）均呈显著正相关。杂木林、硬阔叶林和红松人工林的RT与Ms呈显著负相关；杂木林、杨桦林和硬阔叶林的OT与Ts_min呈显著负相关。样地水平的LL与土壤10 cm处含水量存在显著的正相关关系，而RT和OT则与其呈现显著负相关关系。这些结果表明林龄相似的温带森林地上凋落物总量有趋同趋势，但其通过改变组分分配格局来适应立地条件的变化；土壤湿度和温度变化会引起凋落物量的年际变化，但不同森林类型的凋落物量对环境波动的敏感性不同。     

The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia

Summary Measurements of litter fall and litter removal by crabs, in conjunction with estimates of litter decay by microbes and tidal export of litter from three high-intertidal mangrove forests were made during a year-long study in tropical northeastern Australia. In forests dominated by Ceriops tagal and Bruguiera exaristata, litter standing stocks remained low on the forest floor (mean 6 g·m^-2), although litter fall was high; 822 and 1022 g·m^-2·y^-1, respectively. Sesarmid crabs removed 580 (Ceriops) and 803 (Bruguiera) g·m^-2·y^-1, or 71 and 79%, of the total annual litter fall from the forest floor. Relative to the rate of litter removal by crabs, microbial turnover of whole, unshredded litter was insignificant, accounting for <1% of annual litter fall. Export of litter by tides was estimated to remove 194 (Ceriops) and 252 (Bruguiera) g·m^-2·y^-1 or 24 and 25% of annual litter fall. In a forest dominated by Avicenniamarina, in which an ocypodid crab was more abundant than sesarmids, litter standing stocks were higher (mean 84 g·m^-2) and crabs removed less litter; 173 g·m^-2·y^-1 or 33% of the annual litter fall of 519 g·m^-2·y^-1. Microbial turnover of intact litter was more important in the Avicennia forest (168 g·m^-2·y^-1 or 32% of annual litter fall), and tides exported 107 g·m^-2·y^-1 or 21% of litter production. In areas where sesarmid crabs were absent or rare in Ceriops forests, there were significantly higher standing stocks of litter and slower rates of leaf removal. Taking into account the probable assimilation efficiencies of sesarmid crabs feeding on mangrove leaves, we estimate that in Ceriops and Bruguiera forests leaf processing by crabs turns litter over at >75 times the rate of microbial decay alone, thus facilitating the high sediment bacterial productivity in these forests. The importance of litter processing by crabs increases with height in the intertidal in tropical Australia, in contrast to New World mangrove forests, where the reverse is true.Contribution No. 445 from the Australian Institute of Marine Science     

Impacts of the exotic,nitrogen-fixing black locust (Robinia pseudoacacia) on nitrogen-cycling in a pine–oak ecosystem

We investigated the influence of the exotic nitrogen-fixing black locust (Robinia pseudoacacia) on nitrogen cycling in a pitch pine (Pinus rigida) −scrub oak (Quercus ilicifolia, Q. prinoides) ecosystem. Within paired pine-oak and adjacent black locust stands that were the result of a 20-35 year-old invasion, we evaluated soil nutrient contents, soil nitrogen transformation rates, and annual litterfall biomass and nitrogen concentrations. In the A horizon, black locust soils had 1.3-3.2 times greater nitrogen concentration relative to soils within pine-oak stands. Black locust soils also had elevated levels of P and Ca, net nitrification rates and total net N-mineralization rates. Net nitrification rates were 25-120 times greater in black locust than in pine-oak stands. Elevated net N-mineralization rates in black locust stands were associated with an abundance of high nitrogen, low lignin leaf litter, with 86 kg N ha^–1 yr^–1 in leaf litter returned compared with 19 kg N ha^–1 yr^–1 in pine-oak stands. This difference resulted from a two-fold greater litterfall mass combined with increased litter nitrogen concentration in black locust stands (1.1% and 2.6% N for scrub oak and black locust litter, respectively). Thus, black locust supplements soil nitrogen pools, increases nitrogen return in litterfall, and enhances soil nitrogen mineralization rates when it invades nutrient poor, pine-oak ecosystems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Coarse woody debris in Australian forest ecosystems: A review

Abstract Coarse woody debris (CWD) is the standing and fallen dead wood in a forest and serves an important role in ecosystem functioning. There have been several studies that include estimates of CWD in Australian forests but little synthesis of these results. This paper presents findings from a literature review of CWD and fine litter quantities. Estimates of forest‐floor CWD, snags and litter from the literature are presented for woodland, rainforest, open forest and tall open forest, pine plantation and native hardwood plantation. Mean mass of forest floor CWD in Australian native forests ranged from 19 t ha^?1 in woodland to 134 t ha^?1 in tall open forest. These values were generally within the range of those observed for similar ecosystems in other parts of the world. Quantities in tall open forests were found to be considerably higher than those observed for hardwood forests in North America, and more similar to the amounts reported for coniferous forests with large sized trees on the west coast of the USA and Canada. Mean proportion of total above‐ground biomass as forest floor CWD was approximately 18% in open forests, 16% in tall open forests, 13% in rainforests, and 4% in eucalypt plantations. CWD can be high in exotic pine plantations when there are considerable quantities of residue from previous native forest stands. Mean snag biomass in Australian forests was generally lower than the US mean for snags in conifer forests and higher than hardwood forest. These results are of value for studies of carbon and nutrient stocks and dynamics, habitat values and fire hazards.     

Patterns of Richness and Abundance in a Tropical African Leaf‐litter Herpetofauna1

I compared species richness and habitat correlates of leaf‐litter herpetofaunal abundance in undisturbed and selectively logged forests, and an abandoned pine plantation in Kibale National Park, Uganda. I sampled 50 randomly located 25 m² litter plots in each area during the wet and dry seasons in 1997. Ten anuran, five lizard, and three snake species were captured in plots over the study. Assemblage composition was most similar at logged and unlogged sites. The logged forest herpetofauna had higher species richness and abundance than the unlogged forest, but diversity was greater in the unlogged forest due to greater evenness. In contrast, the pine plantation site had the highest richness, abundance, and evenness of the three study sites, but species composition was distinct from the other areas. Herpetofaunal densities were significantly lower in all three areas during the dry season than in the wet season. During the dry season, soil moisture, litter mass, topography, shrub cover, and number of fallen logs were significant positive predictors of herpetofaunal presence in litter plots, but only soil moisture was significant in the wet season. The interaction of moisture and topography appears to be important in determining seasonal patterns of litter herpetofaunal distribution. Comparison of litter herpetofaunal studies across the tropics have shown that mid‐elevation faunas generally support fewer species than lowland faunas. Compared with other tropical mid‐elevation litter faunas, Kibale supports an intermediate number of species, but at lower densities than observed at any other mid‐elevation site reported in the literature.     

Fine litter input to terrestrial humus forms in Colombian Amazonia

A comparative litter fall study was made in five rain forest stands along a gradient of humus form development and soils in the Amazon lowlands of eastern Colombia. The total fine litter fall was highest in a plot on a well drained soil of the flood plain of the Caquetá River (1.07 kg · m^-2 · y^-1), lower in three plots on well drained upland soils (0.86, 0.69, and 0.68 kg · m^-2 · y^-1), and lowest in a plot on a poorly drained, upland podzolised soil (0.62 kg · m^-2 · y^-1). In the four upland plots, leaf litter fall patterns were highly associated, which points at climatic regulation. Litter resource quality, as represented by nutrient concentrations and area/weight ratio of the leaf litter fall, was comparatively high in the flood plain plot. In the upland plots, concentrations and fluxes of Ca, Mg, K, and P were as low as in oligotrophic central Amazonian upland forests. This questions generalisations that the western peripheral region of the Amazon basin should be less oligotrophic than central Amazonia. The upland plot on the podzolised soil showed the lowest concentrations and fluxes of N. Mean residence times of organic matter and nutrients in the L horizons hardly differed between the five plots, suggesting that edaphic properties and litter resource quality are of little importance in the first step of decomposition. Mean residence time of organic matter in all ectorganic horizons combined (estimated on the basis of litter input and necromass on the forest floor, and uncorrected for dead fine root input) varied from 1.0 y in the flood plain forest, 1.1–3.3 y in the well drained upland forests, and 10.2 y in the forest on the podzolised soil.     

The influence of subterranean termites on the hydrological characteristics of a Chihuahuan desert ecosystem

Summary Rainfall simulation at an average intensity of 124 mm·h^-1 was used to compare infiltration and run off on arid areas where subterranean termites had been eliminated four years prior to the initiation of the study (termite free) with adjacent areas populated by subterranean termites (termites present). Infiltration rates on termite free plots with less than 5% perennial plant cover were significantly lower 51.3±6.8 mm·h^-1 than rates on comparable termites present plots 88.4±5.6 mm·h^-1. On plots centered on Larrea tridentata shrubs, there were no differences in infiltration rates with or without termites. Plots with shrub cover had the highest infiltration rates 101±6 mm·h^-1. Highest run-off volumes were recorded from termite free <5% grass cover plots and the lowest from plots with shrubs. There were no differences in suspended sediment concentrations from termites present and termite free plots. Average bed load concentration was more than three times greater from termite free, <5% cover plots than from termites present, <5% cover plots.The reduction in infiltration, high run-off volumes and high bedloads from termite free areas without shrub cover is related to increased soil bulk density resulting from the collapse of subterranean galleries of the termites that provide avenues of bulk flow into the soil. Subterranean termites affect the hydrology of Chihuahuan desert systems by enhancing water infiltration and retention of top soil. The presence of a shrub canopy and litter layer cancels any effect of subterranean termites on hydrological parameters. Since approximately 2/3 of the area is not under shrub canopies, subterranean termites are considered to be essential for the maintenance of the soil water characteristics that support the present vegetation.     

Carbon sequestration following afforestation of agricultural soils: comparing oak/beech forest to short-rotation poplar coppice combining a process and a carbon accounting model

To compare the benefits for carbon (C) sequestration of afforestation with a multifunctional oak–beech forest vs. a poplar short‐rotation coppice (SRC), model simulations were run through a serial linkage of a mechanistic model and an accounting model. The process model SECRETS (Stand to Ecosystem CaRbon and EvapoTranspiration Simulator) was used to predict growth, C allocation and soil C. The output from SECRETS was used as an input for the C accounting model GORCAM (Graz Oak Ridge Carbon Accounting Model) yielding data on C sequestration in wood products, substitution of wood fuel for fossil fuel and total CO₂ emission reduction. Such C accounting based on a process model enables a more realistic calculation of forest growth, litter decomposition and soil processes. Moreover, it allows simulating the influence of climate change on the C budget. Net primary production of an oak–beech forest is low, a stable 2.5 t C ha^?1 yr^?1 after 150 years, compared to 6.2 t C ha^?1 yr^?1 for a SRC plantation. But while the yield from the SRC poplar is used as fuel and thus returns quickly to the atmosphere, the yield from the oak‐beech forest is used in long‐lasting wood products. The total C pool in the mixed forest (living biomass, wood products and soil) after 150 years amounts to 324 t C ha^?1 compared to 162 in the poplar coppice. However, when account is taken of the energy substitution, coppice culture reduces emissions with 24.3–29.3 t CO₂ ha^?1 yr^?1 while the mixed forest reduces only 6.2–7.1 t CO₂ ha^?1 yr^?1. These results demonstrate the added value of combining detailed process models with C‐accounting models to improve the predictive capacity of model simulations.     

Structure and Function of an Age Series of Poplar Plantations in Central Himalaya: I Dry Matter Dynamics

The biomass and net primary productivity (NPP) of 5- to 8-year-oldpoplar (Populus deltoides Marsh, Clone D₁₂₁) plantations growingin the Tarai belt (low-lying plains with high water table adjacentto foothills of central Himalaya) were estimated. Allometricequations for all the above-ground and below-ground componentsof trees and shrubs were developed for each stand. Understorey,forest floor biomass, and litter fall were also estimated fromstands. The biomass of plantation, forest floor litter mass,tree litter fall and net primary productivity (NPP) of treesand shrubs increased with increase in plantation age, whereasherb biomass and NPP significantly (P < 0·01) decreasedwith increasing plantation age. The total plantation biomassincreased from 84·0 in the 5-year-old to 170·0t ha^-1 in the 8-year-old plantation and NPP from 16·8t ha^-1 year^-1 in the 5- and 6-year-old to 21·8 t ha^-1year^-1 in the 8-year-old plantation. The biomass accumulationratio (biomass: net production, BAR) for different tree componentsincreased with the age of plantation increase. The BAR ratioranged from 4·9 in the 5-year-old to 7·7 in the8-year-old plantation.Copyright 1995, 1999 Academic Press Populus deltoides plantations (Clone D₁₂₁), biomass, dry matter turnover, net primary productivity, Tarai belt of Central Himalaya     

Advances in the positional cloning of nodulation genes in soybean

The effect of liming on the decomposition of Norway spruce needle litter was studied in 40–60-year-old Norway spruce stands. Finely-ground limestone had been spread about 30 years ago at a dose of 2 t ha^–1 and reliming was carried out about 20 yr later at a dose of 4 t ha^–1. Needle litter was collected from both control and limed plots, and it was placed in litter bags in the middle of the humus layer of the plot from which they originated, and similarly to the other plot in May. Litter bags were sampled after 4, 12 and 16 months. The site of origin of the needle litter, whether from control plot or from limed plot, affected mainly the early stages of decomposition. Initially the effect of liming was seen as decreased concentration of water soluble material and then, during decomposition, as decreased mass loss and decreased degradation of lignin, and increased C/N ratio. The incubation site, whether the control or the limed plot, did not affect decomposition significantly.Decomposition of Scots pine needles in a young Scots pine plantation was also studied. The treatments were: 2 t ha^–1 of finely-ground limestone and 2.5 t ha^–1 of bark ash spread 8 months before this study. The treatments did not affect decomposition much, but some stimulation of the treatments on decomposition was observed. Compared to spruce needles, the C/N ratio of pine seedles was lower, they contained less lignin and more water soluble material, and decomposed faster in the first summer.     

The change of soil carbon stocks and fine root dynamics after land use change from a native pasture to a pine plantation

A published meta-analysis of worldwide data showed soil carbon decreasing following land use change from pasture to conifer plantation. A paired site (a native pasture with Themeda triandra dominant, and an adjacent Pinus radiata plantation planted onto the pasture 16 years ago) was set up as a case study to assess the soil carbon reduction and the possible reason for the reduction under pine, including the change in fine root (diameter <2 mm) dynamics (production and mortality). Soil analysis confirmed that soil carbon and nitrogen stocks to 100 cm under the plantation were significantly less than under the pasture by 20 and 15%, respectively. A 36% greater mass of fine root was found in the soil under the pasture than under the plantation and the length of fine root was about nine times greater in the pasture. Much less fine root length was produced and roots died more slowly under the plantation than under the pasture based on observations of fine root dynamics in minirhizotrons. The annual inputs of fine root litter to the top 100 cm soil, estimated from soil coring and minirhizotron observations, were 6.3 Mg dry matter ha⁻¹ year⁻¹ (containing 2.7 Mg C and 38.9 kg N) under the plantation, and 9.7 Mg ha⁻¹ year⁻¹ (containing 3.6 Mg C and 81.4 kg N) under the pasture. The reduced amount of carbon, following afforestation of the pasture, in each depth-layer of the soil profile correlated with the lower length of dead fine roots in the layer under the plantation compared with the pasture. This correlation was consistent with the hypothesis that the soil carbon reduction after land use change from pasture to conifer plantation might be related to change of fine root dynamics, at least in part.     

Carbon density and distribution of six Chinese temperate forests

Quantifying forest carbon (C) storage and distribution is important for forest C cycling studies and terrestrial ecosystem mod-eling. Forest inventory and allometric approaches were used to measure C density and allocation in six representative temper-ate forests of similar stand age (42–59 years old) and growing under the same climate in northeastern China. The forests were an aspen-birch forest, a hardwood forest, a Korean pine plantation, a Dahurian larch plantation, a mixed deciduous forest, and a Mongolian oak forest. There were no significant differences in the C densities of ecosystem components (except for detritus) although the six forests had varying vegetation compositions and site conditions. However, the differences were significant when the C pools were normalized against stand basal area. The total ecosystem C density varied from 186.9 tC hm^-2 to 349.2 tC hm^-2 across the forests. The C densities of vegetation, detritus, and soil ranged from 86.3–122.7 tC hm^-2, 6.5–10.5 tC hm^-2, and 93.7–220.1 tC hm^-2, respectively, which accounted for 39.7%±7.1% (mean±SD), 3.3%±1.1%, and 57.0%±7.9% of the total C densities, respectively. The overstory C pool accounted for > 99% of the total vegetation C pool. The foliage bio-mass, small root (diameter < 5mm) biomass, root-shoot ratio, and small root to foliage biomass ratio varied from 2.08–4.72 tC hm^-2, 0.95–3.24 tC hm^-2, 22.0%–28.3%, and 34.5%–122.2%, respectively. The Korean pine plantation had the lowest foliage production efficiency (total biomass/foliage biomass: 22.6 g g^-1) among the six forests, while the Dahurian larch plantation had the highest small root production efficiency (total biomass/small root biomass: 124.7 g g^-1). The small root C density de-creased with soil depth for all forests except for the Mongolian oak forest, in which the small roots tended to be vertically dis-tributed downwards. The C density of coarse woody debris was significantly less in the two plantations than in the four natu-rally regenerated forests. The variability of C allocation patterns in a specific forest is jointly influenced by vegetation type, management history, and local water and nutrient availability. The study provides important data for developing and validating C cycling models for temperate forests.     

Accelerated soil CO<Subscript>2</Subscript> efflux after conversion from secondary oak forest to pine plantation in southeastern China

Soil respiration (R _s) is an important component of the carbon cycle in terrestrial ecosystems, and changes in soil respiration with land cover alteration can have important implications for regional carbon balances. In southeastern China (Xiashu Experimental Forest, Jiangsu Province), we used an automated LI-8100 soil CO₂ flux system to quantify diurnal variation of soil respiration in a secondary oak forest and a pine plantation. We found that soil respiration in the pine plantation was significantly higher than that in the secondary oak forest. There were similar patterns of soil respiration throughout the day in both the secondary oak forest and the pine plantation during our 7-month study (March–September 2005). The maximum of R _s occurred between 4:00 pm and 7:00 pm. The diurnal variations of R _s were usually out of phase with soil surface (0.5 cm) temperature (T _g). However, annual variation in R _s correlated with surface soil temperature. Soil respiration reached to a maximum in June, and decreased thereafter. The Q₁₀ of R _s in the secondary oak forest was significantly higher than that in the pine plantation. The higher Q₁₀ value in the secondary oak forest implied that it might release more CO₂ than the pine plantation under a global-warming scenario. Our results indicated that land-use change from secondary forest to plantation may cause a significant increase in CO₂ emission, and reduce the temperature sensitivity of soil respiration in southeastern China.     

Carbon cycling and sequestration in a Japanese red pine (Pinus densiflora) forest on lava flow of Mt. Fuji

Biometric-based carbon flux measurements were conducted in a pine forest on lava flow of Mt. Fuji, Japan, in order to estimate carbon cycling and sequestration. The forest consists mainly of Japanese red pine (Pinus densiflora) in a canopy layer and Japanese holly (Ilex pedunculosa) in a subtree layer. The lava remains exposed on the ground surface, and the soil on the lava flow is still immature with no mineral soil layer. The results showed that the net primary production (NPP) of the forest was 7.3 ± 0.7 t C ha^?1 year^?1, of which 1.4 ± 0.4 t C ha^?1 year^?1 was partitioned to biomass increment, 3.2 ± 0.5 t C ha^?1 year^?1 to above-ground fine litter production, 1.9 t C ha^?1 year^?1 to fine root production, and 0.8 ± 0.2 t C ha^?1 year^?1 to coarse woody debris. The total amount of annual soil surface CO₂ efflux was estimated as 6.1 ± 2.9 t C ha^?1 year^?1, using a closed chamber method. The estimated decomposition rate of soil organic matter, which subtracted annual root respiration from soil respiration, was 4.2 ± 3.1 t C ha^?1 year^?1. Biometric-based net ecosystem production (NEP) in the pine forest was estimated at 2.9 ± 3.2 t C ha^?1 year^?1, with high uncertainty due mainly to the model estimation error of annual soil respiration and root respiration. The sequestered carbon being allocated in roughly equal amounts to living biomass (1.4 t C ha^?1 year^?1) and the non-living C pool (1.5 t C ha^?1 year^?1). Our estimate of biometric-based NEP was 25 % lower than the eddy covariance-based NEP in this pine forest, due partly to the underestimation of NPP and difficulty of estimation of soil and root respiration in the pine forest on lava flows that have large heterogeneity of soil depth. However, our results indicate that the mature pine forest acted as a significant carbon sink even when established on lava flow with low nutrient content in immature soils, and that sequestration strength, both in biomass and in soil organic matter, is large.     

Nitrogen supply rate in Scots pine (Pinus sylvestris L.) forests of contrasting slope aspect

We studied Nitrogen (N) transformations in Pinus sylvestris forest stands in the foothills of the SE Pre-Pyrenees (NE Spain). Plots were selected in two contrasting aspects (two plots per aspect) and N supply rate was measured by the resin-core incubation technique once every three months. N leaching through litter layers (L and F horizons) was evaluated by 5 zero-tension lysimeters in each plot. NH₄ ⁺-N, NO₃ ^--N and soluble organic-N were determined in all solutions. N supply rate showed a clear seasonal pattern. Ammonification and nitrification were segregated in space and in time. While ammonification showed a peak in spring, nitrification was higher in summer. There was evidence suggesting that nitrification occurs mostly in A1 horizon. Nitrification rates differed significantly among plots. N supply rate was 12.7–23.5 kg N·ha^-1·yr^-1 but it did not differ between aspects or plots. Inorganic-N leached through litter layers was 14–17 kg N·ha^-1·yr^-1, and represented a high proportion of N supply rate. Organic-N leached through litter layers (27.8–37.0 kg N·ha^-1·yr^-1) was higher than leached inorganic-N. However, in most cases organic-N did not represent a high proportion of changes in soluble organic-N pools in H and A1 horizons (about 240 kg N·ha^-1·yr^-1). This large decrease in soluble organic-N was much greater than the increase in inorganic-N. The possible fate of these large amounts of organic-N is discussed.     

Does nitrogen availability control rates of litter decomposition in forests?

The effects of increased exogenous N availability on rates of litter decomposition were assessed in several field fertilization trials. In a jack pine (Pinus banksiana Lamb.) forest, needle litter decomposed at the same rate in control plots and in plots fertilized with urea and ammonium nitrate (1350 kg N ha^-1) with or without P and K. Mixed needle litter of western hemlock (Tsuga heterophylla (Raf.) Sarg.), western red cedar (Thuja plicata Donn) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) incubated in plots recently amended with sewage sludge (500 kg N ha^-1) lost less weight during 3 years than did litter in control plots. Forest floor material also decomposed more slowly in plots amended with sewage sludge. Paper birch (Betula papyrifera Marsh.) leaf litter placed on sewage sludge (1000 kg N ha^-1), pulp sludge, or sewage-pulp sludge mixtures decomposed at the same rate as leaf litter in control plots. These experiments demonstrate little effect of exogenous N availability on rates of litter decomposition.The influence of endogenous N availability on rates of litter decomposition was examined in a microcosm experiment. Lodgepole pine (Pinus contorta var. latifolia Engelm.) needle litter collected from N-fertilized trees (525 kg N ha^-1 in ammonium nitrate) were 5 times richer in N than needles from control trees (1.56% N versus 0.33% N in control trees), but decomposed at the same rate. Green needles from fertilized trees contained twice as much N as needles from control trees (1.91% N versus 0.88% N), but decomposed at the same rate. These experiments suggest that N availability alone, either exogenous or endogenous, does not control rates of litter decomposition. Increased N availability, through fertilization or deposition, in the absence of changes in vegetation composition, will not alter rates of litter decomposition in forests.