Litter dynamics and fine root production in Schizolobium parahyba var. amazonicum plantations and regrowth forest in Eastern Amazon

Forest plantations and agroforestry systems with Schizolobium parahyba var. amazonicum have greatly expanded in the Brazilian Amazon, generally as an alternative for reforesting degraded areas. To our knowledge there are no reports of above- and below-ground production in these forest systems. We quantified litter and fine root production in 6-yr old Schizolobium-based plantation forests (monospecific: MON, mixture: MIX, and agroforestry system: AFS) and in ~25-yr old regrowth forest (REG) over 8–12 months. We used litter traps and ingrowth cores to quantify litter and fine root production, respectively. Annual litter production was significantly lower in Schizolobium-based plantations (mean ± standard error, MON?=?5.92?±?0.15, MIX?=?6.08?±?0.13, AFS?=?6.63?±?0.13 Mg ha^?1 year^?1) than in regrowth forest (8.64?±?0.08 Mg ha^?1 year^?1). Schizolobium-based plantations showed significantly higher litter stock (MON?=?7.7?±?1.0, MIX?=?7.4?±?0.1 Mg ha^?1) than REG (5.9?±?1.3 Mg ha^?1). Total fine root production over an 8-month period was significantly higher in Schizolobium-based plantations (MON?=?3.8?±?0.2, MIX?=?3.4?±?0.2, AFS?=?2.7?±?0.1 Mg ha^?1) than in REG (1.1?±?0.03 Mg ha^?1). Six-yr old Schizolobium-based plantations and ~25-yr old regrowth forests showed comparable rates of litter + fine root production, suggesting that young forest plantations may be an interesting alternative to restore degraded areas due to early reestablishment of organic matter cycling under the studied conditions.     

Litterfall production, decomposition and nutrient use efficiency varies with tropical forest types in Xishuangbanna, SW China: a 10-year study

Litterfall production, decomposition and nutrient use efficiency in three different tropical forest ecosystems in SW China were studied for 10 years. Annual mean litterfall production in tropical seasonal forest (TSF) (9.47?±?1.65 Mg ha^?1) was similar to that in man-made tropical forest (MTF) (9.23?±?1.29 Mg ha^?1) (P?>?0.05) but both were significantly lower than that in secondary tropical forest (STF) (12.96?±?1.71 Mg ha^?1) (P?<?0.05). The annual variation of litterfall was greater in TSF (17.4%, P?<?0.05) than in MTF (14.0%) or STF (13.2%). The annual mean decomposition rate of litterfall increased followed the order of MTF (2.72)?<?TSF (3.15)?<?STF (3.50) (P?<?0.05), which was not correlated with annual precipitation or annual mean temperature, but was rather related to litter quality. The nutrient use efficiency was found to be element-dependent and to vary significantly among the three forest types (P?<?0.05). These results indicate that litterfall production and decomposition rates in different tropical forest systems are related to plant species composition and are influenced strongly by coexisting species and their life stage (age) but less so by the species richness. Constructing multi-species and multistory man-made tropical forest is an effective way to enhance biological productivity and maintain soil nutrients on degraded tropical land.     

Continuous soil carbon storage of old permanent pastures in Amazonia

Amazonian forests continuously accumulate carbon (C) in biomass and in soil, representing a carbon sink of 0.42–0.65 GtC yr^?1. In recent decades, more than 15% of Amazonian forests have been converted into pastures, resulting in net C emissions (~200 tC ha^?1) due to biomass burning and litter mineralization in the first years after deforestation. However, little is known about the capacity of tropical pastures to restore a C sink. Our study shows in French Amazonia that the C storage observed in native forest can be partly restored in old (≥24 year) tropical pastures managed with a low stocking rate (±1 LSU ha^?1) and without the use of fire since their establishment. A unique combination of a large chronosequence study and eddy covariance measurements showed that pastures stored between ?1.27 ± 0.37 and ?5.31 ± 2.08 tC ha^?1 yr^?1 while the nearby native forest stored ?3.31 ± 0.44 tC ha^?1 yr^?1. This carbon is mainly sequestered in the humus of deep soil layers (20–100 cm), whereas no C storage was observed in the 0‐ to 20‐cm layer. C storage in C4 tropical pasture is associated with the installation and development of C3 species, which increase either the input of N to the ecosystem or the C:N ratio of soil organic matter. Efforts to curb deforestation remain an obvious priority to preserve forest C stocks and biodiversity. However, our results show that if sustainable management is applied in tropical pastures coming from deforestation (avoiding fires and overgrazing, using a grazing rotation plan and a mixture of C3 and C4 species), they can ensure a continuous C storage, thereby adding to the current C sink of Amazonian forests.     

Trace gas flux and the influence of short-term soil water and temperature dynamics in Australian sheep grazed pastures of differing productivity

Temperate pastures are often managed with P fertilizers and N₂-fixing legumes to maintain and increase pasture productivity which may lead to greater nitrous oxide (N₂O) emissions and reduced methane (CH₄) uptake. However, the diel and inter-daily variation in N₂O and CH₄ flux in pastures is poorly understood, especially in relation to key environmental drivers. We investigated the effect of pasture productivity, rainfall, and changing soil moisture and temperature upon short-term soil N₂O and CH₄ flux dynamics during spring in sheep grazed pasture systems in southeastern Australia. N₂O and CH₄ flux was measured continuously in a High P (23 kg P ha^?1 yr^?1) and No P pasture treatment and in a sheep camp area in a Low P (4 kg P ha^?1 yr^?1) pasture for a four week period in spring 2005 using an automated trace gas system. Although pasture productivity was three-fold greater in the High P than No P treatment, mean CH₄ uptake was similar (?6.3?±?SE 0.3 to ?8.6?±?0.4 μg C m^?2 hr^?1) as were mean N₂O emissions (6.5 to 7.9?±?0.8 μg N m^?2 hr^?1), although N₂O flux in the No P pasture did not respond to changing soil water conditions. N₂O emissions were greatest in the Low P sheep camp (12.4 μg?±?1.1 N m^?2 hr^?1) where there were also net CH₄ emissions of 5.2?±?0.5 μg C m^?2 hr^?1. There were significant, but weak, relationships between soil water and N₂O emissions, but not between soil water and CH₄ flux. The diel temperature cycle strongly influenced CH₄ and N₂O emissions, but this was often masked by the confounding covariate effects of changing soil water content. There were no consistently significant differences in soil mineral N or gross N transformation rates, however, measurements of substrate induced respiration (SIR) indicated that soil microbial processes in the highly productive pasture are more N limited than P limited after >20 years of P fertilizer addition. Increased productivity, through P fertilizer and legume management, did not significantly increase N₂O emissions, or reduce CH₄ uptake, during this 4 week measurement period, but the lack of an N₂O response to rainfall in the No P pasture suggests this may be evident over a longer measurement period. This study also suggests that small compacted and nutrient enriched areas of grazed pastures may contribute greatly to the overall N₂O and CH₄ trace gas balance.     

Significance of Over-Mature and Decaying Trees for Carbon Stocks in a Central European Natural Spruce Forest

Old-growth forests are important stores for carbon as they may accumulate C for centuries. The alteration of biomass and soil carbon pools across the development stages of a forest dynamics cycle has rarely been quantified. We studied the above- and belowground C stocks in the five forest development stages (regeneration to decay stage) of a montane spruce (Picea abies) forest of the northern German Harz Mountains, one of Central Europe’s few forests where the natural forest dynamics have not been disturbed by man for several centuries. The over-mature and decay stages had the largest total (up to 480 Mg C ha^?1) and aboveground biomass carbon pools (200 Mg C ha^?1) with biomass C stored in dead wood in the decay stage. The soil C pool (220–275 Mg C ha^?1, 0–60 cm) was two to three times larger than in temperate lowland spruce forests and remained invariant across the forest dynamics cycle. On the landscape level, taking into account the frequency of the five forest development stages, the total carbon pool was approximately 420 Mg C ha^?1. The results evidence the high significance of over-mature and decaying stages of temperate mountain forests not only for conserving specialized forest organisms but also for their large carbon storage potential.     

Land-use change in a tropical mountain rainforest region of southern Ecuador affects soil microorganisms and nutrient cycling

Over the past decades, the tropical mountain rainforest of southern Ecuador has been threatened by conversion to cattle pastures. Frequently, these pastures are invaded by bracken fern and abandoned when bracken becomes dominant. Changes in land-use (forest–pasture–abandoned pasture) can affect soil microorganisms and their physiological responses with respect to soil carbon and nutrient cycling. In situ investigations on litter decomposition and soil respiration as well as biogeochemical characterization of the soil were carried out to identify the driving factors behind. The conversion of forest to pasture induced a pronounced increase in CO₂–C effluxes to 12.2 Mg ha^?1 a^?1 which did not decrease after abandonment. Soil microbial activity and biomass showed a different pattern with lowest values at forest and abandoned pasture sites. With 3445 mg kg^?1 (0–5 cm) microbial biomass carbon (MBC by CFE-method), the active pasture had a more than three times higher value than forest and abandoned pasture, which was among the highest in tropical pasture soils. A shift in the microbial community structure (phospholipid fatty acid, PLFA) was also induced by the establishment of pasture land; the relative abundance of fungi and Gram-negative bacteria increased. PLFA fingerprints of the forest organic layer were more similar to pasture than to forest mineral soil. Chemical properties (pH value, exchangeable cations) were the main factors influencing the respective microbial structure. Bracken-invasion resulted in a decrease in the quantity and quality of above- and belowground biomass. The lower organic substance and nutrient availability induced a significant decline in microbial biomass and activity. After pasture abandonment, these differences in soil microbial function were not accompanied by pronounced shifts in the community structure and in soil pH as was shown for the conversion to pasture. A disconnection between microbial structure and function was identified. Similar soil CO₂–C effluxes between active and abandoned pasture sites might be explained by an underestimation of the effluxes from the active pasture site. All measurements were carried out between grass tussocks where fine-root density was about 2.6 times lower than below tussocks. Thus, lower proportions of root respiration were expected than below tussocks. Overall, soil microorganisms responded differently to changes in land-use from forest to pasture and from pasture to abandoned pasture resulting in pronounced changes of carbon and nutrient cycling and hence of ecosystem functioning.     

The role of soil in storing carbon in tropical rainforests: the case of Ankasa Park, Ghana

Tropical primary rainforests of Africa are an enormous reservoir of carbon (C), most of which, in the common perception, is stored in the biomass. We studied one of these forests, Ankasa, in the south-western part of Ghana, in terms of quantity and ¹⁴C activity of soil organic carbon (SOC) to elucidate the little known important role of soil in storing carbon in such biomass-rich environments. The stock of carbon in the mineral soil to a depth of 1 m was measured to be 151?±?20 Mg C ha^?1, a similar value in magnitude to the one of the aboveground biomass being 138–170 Mg C ha^?1, including live and dead wood. Surface litter C is roughly 10% (15?±?9 Mg C ha^?1) of the C in the biomass and soil. The radiocarbon measurements indicate that SOC was significantly affected by “bomb C” enrichment, so that “Modern C”, namely with a mean radiocarbon age lower than 200 years, is present also deeper than 45 cm in the Bo2 horizon. The mean residence time (MRT) estimated from radiocarbon content are of the order of a few decades in the topsoil and a few centuries in the deeper horizons. Altogether, the MRT values indicate a fast recycle of C compared to temperate or boreal forests, but not as fast as usually believed for tropical forest soils. Making a pondered mean, in the Ankasa forest the time an atom of C resides in soil is not much different from one atom of C in the woody aboveground biomass. Hence, the contribution of soil in storing C is substantial, implying that in primary rainforests it is mandatory to determine the SOC stock and its dynamics, too often neglected or underestimated.     

Are Mosses Required to Accurately Predict Upland Black Spruce Forest Soil Carbon in National-Scale Forest C Accounting Models?

The boreal forest plays a key role in the global carbon (C) cycle, and black spruce (Picea mariana (Mill.) BSP) forests are the dominant coniferous forest type in the Canadian boreal forest. National-scale forest C models currently do not account for the contribution of moss-derived organic matter that we hypothesize to be significant in the C budget of black spruce ecosystems. One such model, the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3), is designed to meet Canada’s forest-related greenhouse gas reporting requirements. In this study our goal was to determine if black spruce forest soil C stocks are significantly underestimated by the CBM-CFS3, and if so, to determine if estimates could be improved by adding moss-derived C. We conclude that in black spruce sites, organic layer C is significantly underestimated by CBM-CFS3 compared to sites with all other leading tree species analyzed. We compiled and used published moss net primary productivity rates for upland forest systems, with decomposition rates, in mass-balance calculations to estimate mean moss-derived C in black spruce forests for feather mosses at 64 Mg C ha^?1, and for sphagnum mosses at 103 Mg C ha^?1. These C pools are similar to the CBM-CFS3 mean underestimation of black spruce soil organic layers (63 Mg C ha^?1). We conclude that the contribution of mosses is sufficiently large that a moss C pool should be added to national-scale models including the CBM-CFS3, to reduce uncertainties in boreal forest C budget estimation. Feather and sphagnum mosses should be parameterized separately.     

Soil Solution Nitrogen Losses During Clearing of Lowland Amazon Forest for Pasture

Losses of nitrogen (N) often follow severe disturbance of forest ecosystems. In tropical forests, losses of N associated with the disturbance of clearing may be particularly important because rates of soil N cycling are high and forest clearing now occurs on a large scale. We measured soil solution inorganic N concentrations and fluxes for 1 year in an intact forest in the Brazilian Amazon state of Rondônia and in an adjacent 3-ha forest plot that was cleared for pasture by cutting, burning and planting pasture grass and in established cattle pastures on the same soils that were 5 and 22 years old. The cleared forest had higher soil solution NO ₃ ^? concentrations than the intact forest, but the difference between the cleared and control forests declined with time after the start of the first post-clearing rainy season. Established pastures had much lower solution NH ₄ ⁺ and NO ₃ ^? concentrations than forest or cleared forest. Estimated annual dissolved inorganic solution N fluxes to below 1 m during the first year after clearing were 2.5 kg ha^?1 in forest and 24.4 kg ha^?1 in newly cleared forest compared with only 0.5–1.2 kg ha^?1 in established pastures. The solution fluxes from cleared forest during the first year after clearing were approximately 7 times greater than gaseous N oxide (N₂O+NO) losses estimated for the same time. These results were consistent with the characterization of moist tropical forests on weathered soils as N-rich and likely to respond to disturbances that elevate soil N availability with increased loss to both soil solution and the atmosphere. These results also suggest that the relative increase in N oxide loss is substantially less than the increase solution inorganic N loss.     

Net nitrogen mineralization and net nitrification rates in soils following deforestation for pasture across the southwestern Brazilian Amazon Basin landscape

Previous studies of the effect of tropical forest conversion to cattle pasture on soil N dynamics showed that rates of net N mineralization and net nitrification were lower in pastures compared with the original forest. In this study, we sought to determine the generality of these patterns by examining soil inorganic N concentrations, net mineralization and nitrification rates in 6 forests and 11 pastures 3 years old or older on ultisols and oxisols that encompassed a wide variety of soil textures and spanned a 700-km geographical range in the southwestern Brazilian Amazon Basin state of Rondônia. We sampled each site during October-November and April-May. Forest soils had higher extractable NO₃ ^?-N and total inorganic N concentrations than pasture soils, but substantial NO₃ ^?-N occurred in both forest and pasture soils. Rates of net N mineralization and net nitrification were higher in forest soils. Greater concentrations of soil organic matter in finer textured soils were associated with greater rates of net N mineralization and net nitrification, but this relationship was true only under native forest vegetation; rates were uniformly low in pastures, regardless of soil type or texture. Net N mineralization and net nitrification rates per unit of total soil organic matter showed no pattern across the different forest sites, suggesting that controls of net N mineralization may be broadly similar across a wide range of soil types. Similar reductions in rates of net N transformations in pastures 3 years old or older across a range of textures on these soils suggest that changes to soil N cycling caused by deforestation for pasture may be Basin-wide in extent. Lower net N mineralization and net nitrification rates in established pastures suggest that annual N losses from largely deforested landscapes may be lower than losses from the original forest. Total ecosystem N losses since deforestation are likely to depend on the balance between lower N loss rates from established pastures and the magnitude and duration of N losses that occur in the years immediately following forest clearing.     

Carbon storage in relation to soil size-fractions under tropical tree-based land-use systems

The extent of carbon (C) sequestration in soils under agroforestry systems in relation to soil types (fraction sizes) and vegetation structure remains largely unexplored. This study examined soil C storage, an indicator of C sequestration potential, in homegardens (HGs), natural forest, and single-species stands of coconut (Cocos nucifera), rice (Oryza sativa)-paddy, and rubber (Hevea brasiliensis), in Thrissur district, Kerala, India. Soil samples collected from four depth zones up to 1 m were fractionated to three size classes (250 – 2000 µm, 53 – 250 µm, ?<?53 µm) and their total C content determined. Total C stock (Mg ha^?1) was highest in forests (176.6), followed by managed tree-based systems, and lowest in rice-paddy field (55.6). The results show storage of higher amounts of C in the ?<?53 µm fraction, the most stable form of C in soil, up to one- meter depth, in land-use systems with high stand density of trees such as forests and small-sized HG. Although the results do not allow comparison of changes in soil C stock in different land-use systems, they show higher C storage in soils under tree-based land-use systems compared with the treeless (rice-paddy) system, especially in lower soil depths, suggesting the higher soil C sequestration potential of tree-based systems, and thereby their role in reducing atmospheric concentration of carbon dioxide.     

Belowground carbon input and translocation potential of fodder radish cover-crop

We compared the soil C input potential of a common catch-crop (fodder radish) established in 6-year-old direct-drilled (DD) plots with adjacent conventionally tilled (CT) plots on a Danish sandy loam soil by use of ¹⁴C-isotope labelling techniques. Intact monoliths of soil with actively growing fodder radish seedlings were extracted in Autumn of 2008 from DD and CT field plots and labelled with ¹⁴CO₂ at different time intervals during fodder radish growth. Labelled monoliths were then sampled 6 and 100 days after termination of labelling by clipping above-ground biomass at soil level and separating below-ground components into macro-roots and macro-root-free soil at 0?C10, 10?C25 and 25?C45 cm soil depth. Using fodder radish ¹⁴C data and the preceding spring barley biomass yield data we estimated C input from the spring barley-fodder radish cycle in addition to evaluating the effect of the removal of spring barley harvestable straw on soil C input. Potential soil C input under straw removal scenarios with and without an established fodder radish crop was also evaluated. Relative to other depths, over 70% of labelled below-ground C was found in the 0?C10 cm soil depth in both DD and CT treatments for each of the two samplings. For both macro-root and macro-root-free soil and in both tillage treatments, labelled C decreased significantly with depth (P?<?0.05). A decline of labeled C in macro-root but an increase of labeled C in macro-root-free soil was observed from day 6 to day 100 for both tillage treatments. Over the autumn-winter growing period, total below-ground C input by fodder radish within the 0?C45 cm soil depth was approximately 1.0 and 1.2 Mg C ha^?1 for CT and DD, respectively. We used data from 100 days after labelling, which coincided with the incorporation of the field fodder radish biomass, to estimate that the total fodder radish contribution to below-ground C after biomass incorporation would range between 1.6 and 1.7 Mg C ha^?1 for DD and CT, respectively. The figures for spring barley straw removal with fodder radish establishment would be between 4.9 and 5.1 Mg C ha^?1, while with no fodder radish establishment, C input to the soil would range between 3.2 Mg C ha^?1 and 3.4 Mg C ha^?1, which is approximately 0.6 Mg C ha^?1 lower than the 4 Mg C ha^?1 biomass C input required to maintain long-term soil organic C. In comparison, under straw retention and fodder radish catch-crop establishment the total spring barley and fodder radish C input would be approximately 6.1 and 6.5 Mg C ha^?1 for DD and CT, respectively. We conclude that fodder radish catch-crops have a potential for mitigating against soil C depletion resulting from export of cereal straw to other uses.     

Carbon stocks of mangroves and losses arising from their conversion to cattle pastures in the Pantanos de Centla,Mexico

The conservation of mangroves and other coastal “blue carbon” ecosystems is receiving heightened attention because of recognition of their high ecosystem carbon stocks as well as vast areas undergoing land conversion. However, few studies have paired intact mangroves with degraded sites to determine carbon losses due to land conversion. To address this gap we quantified total ecosystem carbon stocks in mangroves and cattle pastures formed from mangroves in the large wetland complex of the Pantanos de Centla in SE Mexico. The mean total ecosystem carbon stocks of fringe and estuarine tall mangroves was 1358 Mg C/ha. In contrast the mean carbon stocks of cattle pastures was 458 Mg C/ha. Based upon a biomass equivalence of losses from the top 1 m of mangrove soils, the losses in carbon stocks from mangrove conversion are conservatively estimated at 1464 Mg CO₂e/ha. These losses were 7-fold that of emissions from tropical dry forest to pasture conversion and 3-fold greater than emissions from Amazon forest to pasture conversion. However, we found that limiting ecosystem carbon stocks differences to the surface 1 m or even 2 m soil depth will miss losses that occurred from deeper horizons. Mangrove conversion to other land uses comes at a great cost in terms of greenhouse gas emissions as well losses of other important ecosystem services.     

Temporal patterns of net soil N mineralization and nitrification through secondary succession in the subtropical forests of eastern China

Linking temporal trends of soil nitrogen (N) transformation with shifting patterns of plants and consequently changes of litter quality during succession is important for understanding developmental patterns of ecosystem function. However, the successional direction of soil N mineralization and nitrification in relation to species shifts in the subtropical regions remains little studied. In this study, successional patterns of net soil N mineralization and nitrification rates, litter-fall, forest floor litter, fine root and soil properties were quantified through a successional sequence in the subtropical forests of eastern China. Net N mineralization rate was ‘U-shaped’ through succession: highest in climax evergreen broad-leaved forest (CE: 1.6?±?0.2 mg-N kg^?1 yr^?1) and secondary shrubs (SS: 1.4?±?0.2 mg-N kg^?1 yr^?1), lowest in conifer and evergreen broad-leaved mixed forest (MF: 1.1?±?0.1 mg-N kg^?1 yr^?1) and intermediate in conifer forest (CF: 1.2?±?0.1 mg-N kg^?1 yr^?1) and sub-climax forest (SE: 1.2?±?0.2 mg-N kg^?1 yr^?1). Soil nitrification increased with time (0.02?±?0.1, 0.2?±?0.1, 0.5?±?0.1, 0.2?±?0.1, and 0.6?±?0.1 mg-N kg^?1 yr^?1 in SS, CF, MF, SE and CE, respectively). Annual production of litter?fall increased through succession. Fine root stocks and total N concentration, soil total N, total carbon (C) and microbial biomass C also followed ‘U?shaped’ temporal trends in succession. Soil bulk density was highest in MF, lowest in CE, and intermediate in SS, CF and SE. Soil pH was significantly lowest in CE. Temporal patterns of soil N mineralization and nitrification were significant related to the growth of conifers (i.e. Pinus massoniana) and associated successional changes of litter-fall, forest floor, fine roots and soil properties. We concluded that, due to lower litter quality, the position of Pinus massoniana along the succession pathway played an important role in controlling temporal trends of soil N transformation.     

Simulating seasonal and inter-annual variations in energy and carbon exchanges and forest dynamics using a process-based atmosphere�Cvegetation dynamics model

The present paper shows simulated results of seasonal and inter-annual variations in energy and carbon exchanges and forest dynamics in a sub-boreal deciduous forest using a fully coupled atmosphere?Cvegetation interaction model [multilayered integrated numerical model of surface physics-growing plants interaction (MINoSGI)]. With careful adjustment of site-specific eco-physiological parameters, MINoSGI reproduced successfully stand biomass?Ctree density relationship based on the forest inventory data for 7 years (1999?C2005) and seasonal and inter-annual variations in energy and CO₂ fluxes measured by means of eddy covariance technique for 3 years (2003?C2005) in the sub-boreal forest, northern Japan. In addition, MINoSGI estimated annual evapotranspiration (E _vt) at 328.6 ± 25.8 mm year^?1, net primary production (NPP) at 372.1 ± 31.5 gC m^?2 year^?1 and net ecosystem exchange (NEE) at ?224.2 ± 32.2 gC m^?2 year^?1. We found the estimate of annual NEE in our site lies among the estimates at other forest stands with the almost same climatic conditions in northern Japan, although the tree species and stand age of these forests are different from those of our site. Overall, MINoSGI was found useful to present simultaneous simulations of forest dynamics, surface energy, and carbon exchanges of a forest stand in the future from micro-meteorological and ecophysiological points of view.     

Short-term simulated nitrogen deposition increases carbon sequestration in a Pleioblastus amarus plantation

In order to understand the influence of nitrogen (N) deposition on the key processes relevant to the carbon (C) balance in a bamboo plantation, a two-year field experiment involving the simulated deposition of N in a Pleioblastus amarus plantation was conducted in the rainy region of SW China. Four levels of N treatments: control (no N added), low-N (50 kg N ha^?1 year^?1), medium-N (150 kg N ha^?1 year^?1), and high-N (300 kg N ha^?1 year^?1) were set in the present study. The results showed that soil respiration followed a clear seasonal pattern, with the maximum rates in mid-summer and the minimum in late winter. The annual cumulative soil respiration was 585?±?43 g CO₂-C m^?2 year^?1 in the control plots. Simulated N deposition significantly increased the mean annual soil respiration rate, fine root biomass, soil microbial biomass C (MBC), and N concentration in fine roots and fresh leaf litter. Soil respirations exhibited a positive exponential relationship with soil temperature, and a linear relationship with MBC. The net primary production (NPP) ranged from 10.95 to 15.01 Mg C ha^?1 year^?1 and was higher than the annual soil respiration (5.85 to 7.62 Mg C ha^?1 year^?1) in all treatments. Simulated N deposition increased the net ecosystem production (NEP), and there was a significant difference between the control and high N treatment NEP, whereas, the difference of NEP among control, low-N, and medium-N was not significant. Results suggest that N controlled the primary production in this bamboo plantation ecosystem. Simulated N deposition increased the C sequestration of the P. amarus plantation ecosystem through increasing the plant C pool, though CO₂ emission through soil respiration was also enhanced.     

Selenium fertilization strategies for bio-fortification of food: an agro-ecosystem approach

Background and aims

Although numerous studies have quantified the effects of land-use changes on soil organic carbon (SOC) stocks, few have examined simultaneously the weight of carbon (C) inputs vs. outputs in shaping these changes. We quantified the relative importance of soil C inputs and outputs in determining SOC changes following the conversion of natural ecosystems to pastures or tree plantations, and evaluated them in light of variations in biomass production, its quality (C:N) and above/belowground allocation patterns.

Methods

We sampled soils up to one-meter depth under native grasslands or forests and compared them to adjacent sites with pastures or plantations to estimate the proportion of new SOC (SOC_new) retained in the soil and the decomposition rates of old SOC (k _SOC-old ) based on δ ¹³C shifts. We also analyzed these changes in the particulate organic matter fraction (POM) and estimated above and belowground net primary production (ANPP and BNPP) from satellite images, as well as changes in vegetation and soil’s C:N ratios.

Results

The conversion of grasslands to tree plantations decreased total SOC contents while the conversion of forests to pastures increased SOC contents in the topsoil but decreased them in deep layers, maintaining similar soil stocks up to 1 m. Changes in POM were less important and occurred only in the topsoil after cultivating pastures, following SOC changes. Surprisingly, both land-use trajectories showed similar decomposition rates in the topsoil and therefore overall SOC changes were not correlated with C outputs (k _SOC-old ) but were significantly correlated with C inputs and their stabilization as SOC_new (similar results were obtained for the POM fraction). Pastures although decreased ANPP (as compared to forest) they increased belowground allocation and C:N ratios of their inputs to the soil, probably favoring the retention and stabilization of their new C inputs. In contrast, tree plantations increased ANPP but decreased BNPP (as compared to grasslands) and scarcely accumulated SOC_new probably as a result of the high C retention in standing biomass.

Conclusions

Our results suggest that SOC changes are mainly controlled by the quantity and quality of C inputs and their retention in the soil, rather than by C outputs in these perennial subtropical ecosystems.

     

Biomass Stock and Productivity of Primeval and Production Beech Forests: Greater Canopy Structural Diversity Promotes Productivity

Our knowledge of temperate broadleaf forest ecology is based mostly on the study of production forests, which lack the terminal stage of forest development and have a simpler stand structure than old-growth and primeval forests. How primeval and production forests differ in net primary production (NPP) is not well known. In three primeval and three nearby production forests of European beech (Fagus sylvatica) in the Slovakian Carpathians, we measured aboveground biomass stocks (live and dead), aboveground NPP (ANPP) and parameters characterizing canopy structural diversity (leaf area index and its spatial variation). Our study aims were (1) to explore the role of canopy structural diversity for ANPP and (2) to assess evidence of a productivity decline in the terminal stage. While aboveground live biomass stocks were on average 20% greater in the primeval forests (386 vs. 320 Mg ha^?1; insignificant difference at two sites), deadwood mass stocks were on average four times larger than in the production forests (86 vs. 19 Mg ha^?1). ANPP was similarly high in the primeval and production forests (10.0 vs. 9.9 Mg ha^?1 y^?1) and did not decrease towards the terminal stage. Production models indicate that, in the primeval forests, about 10% of ANPP (ca. 1 Mg ha^?1 y^?1) was generated by effects related to leaf area heterogeneity, evidencing a positive effect of structural diversity on forest productivity, even though species diversity was low. This study helps to better understand the impact of forest management on the productivity and carbon storage in temperate woodlands.     

Carbon, nitrogen and Greenhouse gases budgets over a four years crop rotation in northern France

Croplands mainly act as net sources of the greenhouse gases carbon dioxide (CO₂) and nitrous oxide (N₂O), as well as nitrogen oxide (NO), a precursor of troposheric ozone. We determined the carbon (C) and nitrogen (N) balance of a four-year crop rotation, including maize, wheat, barley and mustard, to provide a base for exploring mitigation options of net emissions. The crop rotation had a positive net ecosystem production (NEP) of 4.4?±?0.7 Mg C ha^-1 y^-1 but represented a net source of carbon with a net biome production (NBP) of -1.3?±?1.1 Mg C?ha^-1 y^-1. The nitrogen balance of the rotation was correlated with the carbon balance and resulted in net loss (?24?±?28 kg N ha^-1 y^-1). The main nitrogen losses were nitrate leaching (?11.7?±1.0 kg N ha^-1 y^-1) and ammonia volatilization (?9 kg N ha^-1 y^-1). Dry and wet depositions were 6.7?±?3.0 and 5.9?±0.1 kg N ha^-1 y^-1, respectively. Fluxes of nitrous (N₂O) and nitric (NO) oxides did not contribute significantly to the N budget (N₂O: -1.8?±?0.04; NO: -0.7?±?0.04 kg N ha^-1 y^-1) but N₂O fluxes equaled 16% of the total greenhouse gas balance. The link between the carbon and nitrogen balances are discussed. Longer term experiments would be necessary to capture the trends in the carbon and nitrogen budgets within the variability of agricultural ecosystems.     

Gross Primary Productivity of a High Elevation Tropical Montane Cloud Forest

For decades, the productivity of tropical montane cloud forests (TMCF) has been assumed to be lower than in tropical lowland forests due to nutrient limitation, lower temperatures, and frequent cloud immersion, although actual estimates of gross primary productivity (GPP) are very scarce. Here, we present the results of a process-based modeling estimate of GPP, using a soil–plant–atmosphere model, of a high elevation Peruvian TMCF. The model was parameterized with field-measured physiological and structural vegetation variables, and driven with meteorological data from the site. Modeled transpiration corroborated well with measured sap flow, and simulated GPP added up to 16.2 ± SE 1.6 Mg C ha^?1 y^?1. Dry season GPP was significantly lower than wet season GPP, although this difference was 17% and not caused by drought stress. The strongest environmental controls on simulated GPP were variation of photosynthetic active radiation and air temperature (T _air). Their relative importance likely varies with elevation and the local prevalence of cloud cover. Photosynthetic parameters (V _cmax and J _max) and leaf area index were the most important non-environmental controls on GPP. We additionally compared the modeled results with a recent estimate of GPP of the same Peruvian TMCF derived by the summing of ecosystem respiration and net productivity terms, which added up to 26 Mg C ha^?1 y^?1. Despite the uncertainties in modeling GPP we conclude that at this altitude GPP is, conservatively estimated, 30–40% lower than in lowland rainforest and this difference is driven mostly by cooler temperatures than changes in other parameters.