Root Turnover Research Articles

Short-Term Effects of Incorporation Depth of Straw Combined with Manure During the Fallow Season on Maize Production, Water Efficiency, and Nutrient Utilization in Rainfed Regions

Diminishing soil fertility and crop productivity due to traditional intensive cultivation has prompted the use of straw and manure to improve soil health in Northeast China. However, few comparative studies have explored the influence of varying straw and manure incorporation depths on crop growth. A field experiment in the rainfed black soil regions of Gongzhuling and Keshan assessed the effects of deep (30 cm) and shallow (15 cm) incorporations of straw and manure on soil fertility, maize root growth, and maize productivity. Deep incorporations, via subsoiling tillage (DST) and deep-plow (DDT) tillage, enhanced soil water storage of 30–100 cm soil layer during periods of low rainfall, improved the availability of nutrients (nitrogen, phosphorus, and potassium) and soil organic matter content, especially in deeper soil, compared to shallow incorporation using rotary tillage (SRT). Both DST and DDT induced a larger rooting depth and a higher fine root (diameter class 0–0.5 mm) length density by 31.0% and 28.9%, respectively, accompanied by reduced root turnover. Furthermore, the sub-surface foraging strategies of roots under the DST and DDT treatments boosted the total nitrogen, phosphorus, and potassium uptake (6.5–17.9%) and achieved a higher dry mass accumulation during the later growth period, thus leading to notable improvements in the 100-kernel weight and yield (16.1–19.7%) and enhancing water- and nutrient-use efficiencies by 2.5–20.5%. Overall, compared to shallow incorporation, deep incorporation of straw and manure significantly enhances root growth and spatial distribution of soil water and nutrients, which has great potential for increasing maize yield in rainfed agricultural areas.

The long-term effect of biochar application to Vitis vinifera L. reduces fibrous and pioneer root production and increases their turnover rate in the upper soil layers.

Fibrous and pioneer roots are essential in the uptake and transport of water and nutrients from the soil. Their dynamic may be influenced by the changing of soil physicochemical properties due to the addition of biochar, which, in turn, has been shown to improve plant growth and productivity in the short term. However, the long-term effects of biochar application on root dynamics are still widely unknown. In this study, we aimed to investigate the long-term effects of biochar application on grapevine fibrous and pioneer root dynamics and morphological traits in relation to soil characteristics. To this aim, grapevine plants amended in 2009 and 2010 respectively with one and two doses of biochar, were analyzed in their fibrous and pioneer root production and turnover rate, standing biomass, length, and specific root length, over two growing seasons. Our findings demonstrate that in the long term, biochar application significantly increased soil pH, nutrient availability, and water-holding capacity causing a decrease in the production of fibrous and pioneer roots which is reflected in a reduction of the root web characterized though by a higher turnover rate. Furthermore, we observed that these root morpho-dynamical changes were of higher magnitude in the upper soil layers (0-20 cm) and, at least in the long term, with no significant difference between the two doses. These results suggest that in the long term, biochar can be a powerful tool for improving soil quality, which in turn lowers carbon-cost investment toward the root production and maintenance of a reduced root web that might be directed into grapevine growth and productivity. Such effects shed some light on the root plastic and functional adaptation to modified soil conditions facilitated by the long-term application of biochar, which can be used for implementing adaptive agricultural practices to face the current climate change in a frame of sustainable agricultural policies.

Getting to the root of the problem: Soil carbon and microbial responses to root inputs within a buried paleosol along an eroding hillslope in southwestern Nebraska, USA

Large quantities of soil carbon (C) can persist within paleosols for millennia due to burial and subsequent isolation from plant-derived inputs, atmospheric conditions, and microbial activity at the modern surface. Erosion exposes buried soils to modern root-derived C influx via root exudation and root turnover, thus stimulating microbial activity leading to SOC decomposition and accumulation through organo-mineral stabilization of modern C. With this study we aim to quantify how modern root-derived C inputs impact paleosol C decomposition and stabilization across varying degrees of isolation from modern surface conditions in southwestern Nebraska, USA, where hillslope erosion is bringing a buried Late-Pleistocene-early Holocene paleosol (the “Brady Soil”) closer to the modern surface. We collected Brady Soil samples from 0.2 m, 0.4 m, and 1.2 m below the modern surface and conducted two lab-based incubations. Soils were amended with either (1) a lab-synthesized mixture of low molecular weight compounds (12 atom% 13C), or (2) 13C enriched root residues (92 atom% 13C), in 30-day and 240-day incubation experiments, respectively. We determined microbial responses to synthetic root exudates and residues by partitioning the 13C label from Brady Soil C, including measurements of total, root, and primed C respiration, microbial biomass C (MBC), microbial C use efficiency (CUE). To assess the capacity of isolated paleosols to accrue modern plant C, we used Nano-scale Secondary Ion Mass Spectrometry imaging. We found that: (1) adding root-derived C inputs primed Brady Soil C across all depths, and was mediated by depth and composition of root additions; (2) root-derived C inputs stimulated microbial biomass C (MBC) growth similarly across depths, but the magnitude of CUE and MBC varied by chemistry of root-derived additions; (3) new particulate organic matter was incorporated into mineral-associated pools over time; (4) material from the added root residues was found in association with bacterial cells and fungal hyphae as well as with soil aggregate and mineral surfaces. Our study shows that paleosols defy expectations of C content and reactivity with depth, and changes in land cover and climate will expose buried paleosols to modern surface conditions, increasing respired C. This work highlights the importance of evaluating the role resurfacing buried soils through landscape change plays in C cycle feedbacks to the climate system.

Effects of Warming and Increased Precipitation on Root Production and Turnover of Stipa breviflora Community in Desert Steppe

Effects of Warming and Increased Precipitation on Root Production and Turnover of Stipa breviflora Community in Desert Steppe

Fine root production and turnover rate responses to long-term warming and nitrogen addition in a semi-arid grassland

Soil carbon pool is closely linked to fine root production and turnover rate. Lack of knowledge about the effects of nitrogen addition and warming on fine root production and turnover rate limits our ability to accurately predict soil carbon stocks. We studied the responses of fine root production and turnover rate with an 8-year soil warming (ambient +1 °C) and nitrogen addition (ambient + 4.42 g N m−2 yr−1) experiment in a semi-arid grassland on the Loess Plateau of China. Warming significantly decreased fine root production but increased fine root turnover rate due to warming-induced reduction in soil water content. Conversely, nitrogen addition significantly increased fine root production due to decreased soil phosphorus availability. Combined warming and nitrogen addition had no significant effect on fine root production, but decreased fine root turnover rate due to low phosphorus availability caused by nitrogen addition and low soil moisture induced by warming. Our findings have important implications for more accurately predicting the belowground responses of dryland to global changes.

Nitrogen and potassium limit fine root growth in a humid Afrotropical forest

Nutrient limitations play a key regulatory role in plant growth, thereby affecting ecosystem productivity and carbon uptake. Experimental observations identifying the most limiting nutrients are lacking, particularly in Afrotropical forests. We conducted an ecosystem-scale, full factorial nitrogen (N)-phosphorus (P)-potassium (K) addition experiment consisting 32 40 × 40 m plots (eight treatments × four replicates) in Uganda to investigate which (if any) nutrient limits fine root growth. After two years of observations, added N rapidly decreased fine root biomass by up to 36% in the first and second years of the experiment. Added K decreased fine root biomass by 27% and fine root production by 30% in the second year. These rapid reductions in fine root growth highlight a scaled-back carbon investment in the costly maintenance of large fine root network as N and K limitations become alleviated. No fine root growth response to P addition was observed. Fine root turnover rate was not significantly affected by nutrient additions but tended to be higher in N added than non-N added treatments. These results suggest that N and K availability may restrict the ecosystem’s capacity for CO2 assimilation, with implications for ecosystem productivity and resilience to climate change.

Similar root and stubble biomass carbon in grass–clover leys irrespective of yield, species composition, sward age, and fertilization

AbstractBackgroundCrop‐ and site‐specific quantification of non‐harvestable aboveground residues and root biomass is essential for predicting management‐induced changes in soil C storage.AimsThe aim of this study was to quantify stubble and root biomass C from productive grass–clover leys used for cutting as affected by fertilization and sward age.MethodsBased on an organic long‐term dairy crop rotations experiment with 4 years of grass–clover in a six‐course rotation, we examined the effects of fertilization (unfertilized and 300 kg total‐N ha−1 in cattle slurry) and sward age (1–4‐year‐old) on herbage yield and composition, stubble biomass, and composition and root biomass of grass–clover ley.ResultsLey duration and fertilization altered plant community composition and aboveground productivity but did not affect stubble and root biomass C.ConclusionsThe results question the use of yield‐dependent allometric functions for grass–clover ley used in simulation models and life cycle assessments for C accounting in agricultural systems. For predictions of soil C changes, we recommend the use of a fixed stubble‐derived C input from grass–clover ley regardless of sward age and fertilization‐induced differences in species composition, and herbage yield. Likewise, a fixed root‐derived C input for 1‐year‐old grass–clover, irrespective of fertilization, may be implemented. However, the contribution of continuous rhizodeposition and fine root turnover to root‐derived C input need to be accounted for.

Variation of root traits and its influences on soil organic carbon stability in response to altered precipitation in an alpine meadow

Soil organic carbon (SOC) dynamics are strongly controlled by plant roots. Yet, how variation of root traits under precipitation change influences SOC stability remains unclear. As part of a 5-year field experiment manipulating precipitation including 90 % (0.1P), 50 % (0.5P), 30 % (0.7P) decrease, and 50 % increase (1.5P), this study was designed to assess the effects of changing precipitation on root traits and production dynamics by minirhizotron and examine how such influences regulate SOC stability in an alpine meadow on the Qinghai-Tibetan Plateau. We found that root length density (RLD), specific root length (SRL), root branching intensity (RBI), and root residue carbon input (RC input) exhibited no significant response, whereas root turnover (RT), root carbon (C), nitrogen (N) concentrations and C/N ratio were altered by precipitation change with nonlinear trends. Absorptive root RT positively correlated to manipulated precipitation within the interannual precipitation range in topsoil, but it showed no significant change under extreme drought treatment. Alpine meadows can maintain the SOC content and density under varied precipitation. However, it showed significant variation in aggregate stability and organic carbon (OC) distribution in aggregates in topsoil, which were mainly due to the strong direct effects of soil moisture and partly related to RLD and RC input of transport roots. Although subsurface soil aggregate stability and OC associated with aggregates were not modified, our results indicated a risk of SOC stability variation in subsurface soil if absorptive root RT and SRL changed. These findings provide vital information to predict responses of SOC dynamics of alpine meadow to future climate change.

Response of root production to different restoration measures in a degraded meadow

Abstract Belowground parameters, e.g. root production and dynamics, play a pivotal role in evaluating the restoration degree of degraded grasslands. However, it remains unclear how roots respond to the combined restoration measures. To investigate root responses to different restoration treatments, a field experiment was conducted in a degraded Songnen meadow from 2013 to 2014. The treatments included: free grazing (FG), no ploughing (NP), only ploughing (OP), ploughing and fertilizer (PF), ploughing and mulching (PM), ploughing with fertilizer and mulching (PFM). Our results showed the seasonal dynamics pattern of roots was a unimodal pattern, which mainly was influenced by precipitation rather than restoration measures. The impacts of different restoration measures on root production were dependent on precipitation. In 2013, compared with FG, only PFM significantly increased root production by 242.34% (0–10 cm) and 90.8% (10–20 cm), which was mainly attributed to the increase of aboveground net primary production, soil moisture and root numbers. However, restoration measures had minor effects on root production in 2014. Root turnover ranged from 0.47 to 0.78 yr−1 and was not significantly changed by different restored measures. This is because the dominant annual species, Chloris virgata, exhibited relatively small changes in root turnover across different plots. Moreover, PFM improved soil conditions, leading to increased root lifespan and survival rate. Our results suggest that the combined measures are an effective way to accelerate belowground restoration in the degraded Songnen meadow.

Nitrogen dynamics of alpine swamp meadows are less responsive to climate warming than that of alpine meadows

The freeze-thaw cycle mediates permafrost soil hydrothermal status, nitrogen (N) mineralization, and loss. Furthermore, it affects root development and competition among nitrophilic and other species, shaping the pattern of N distribution in alpine ecosystems. However, the specific N dynamics during the growing season and N loss during the non-growing season in response to climate warming under low- and high-moisture conditions are not well documented. Therefore, we added 15N tracers to trace the fate of N in warmed and ambient alpine meadows and alpine swamp meadows in the permafrost region of the Qinghai-Tibet Plateau. During the growing season, warming increased 15N recovery (15Nrec) in shoots of K. humilis, litters, 0–5 and 5–20 cm roots in the alpine meadow by 149.94 % ± 52.87 %, 114.58 % ± 24.43 %, 61.11 % ± 32.27 %, and 97.12 % ± 42.92 %, respectively, while increased 15Nrec of litters by 151.55 % ± 27.06 % in the alpine swamp meadow. During the non-growing season, warming reduced 15N stored in roots by 486.77 % ± 57.90 %, though increased the 15N recovery in 5–20 cm soil depth by 76.68 % ± 39.42 % in the alpine meadow, whereas it did not affect N loss during the non-growing season in the alpine swamp meadow. Overall, warming promoted N utilization by increasing the plant N pool during the growing season, and enhanced root N loss and downward migration during the non-growing season due to the freeze-thaw process, which may result in fine root turnover and cell destruction releasing N in the alpine meadow. Conversely, the N dynamics of alpine swamp meadows were less responsive to climate warming.

Responses of vascular plant fine roots and associated microbial communities to whole-ecosystem warming and elevated CO2 in northern peatlands.

Warming and elevated CO2 (eCO2) are expected to facilitate vascular plant encroachment in peatlands. The rhizosphere, where microbial activity is fueled by root turnover and exudates, plays a crucial role in biogeochemical cycling, and will likely at least partially dictate the response of the belowground carbon cycle to climate changes. We leveraged the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment, to explore the effects of a whole-ecosystem warming gradient (+0°C to 9°C) and eCO2 on vascular plant fine roots and their associated microbes. We combined trait-based approaches with the profiling of fungal and prokaryote communities in plant roots and rhizospheres, through amplicon sequencing. Warming promoted self-reliance for resource uptake in trees and shrubs, while saprophytic fungi and putative chemoorganoheterotrophic bacteria utilizing plant-derived carbon substrates were favored in the root zone. Conversely, eCO2 promoted associations between trees and ectomycorrhizal fungi. Trees mostly associated with short-distance exploration-type fungi that preferentially use labile soil N. Additionally, eCO2 decreased the relative abundance of saprotrophs in tree roots. Our results indicate that plant fine-root trait variation is a crucial mechanism through which vascular plants in peatlands respond to climate change via their influence on microbial communities that regulate biogeochemical cycles.

Above- and belowground plant mercury dynamics in a salt marsh estuary in Massachusetts, USA

Abstract. Estuaries are a conduit of mercury (Hg) from watersheds to the coastal ocean, and salt marshes play an important role in coastal Hg cycling. Hg cycling in upland terrestrial ecosystems has been well studied, but processes in densely vegetated salt marsh ecosystems are poorly characterized. We investigated Hg dynamics in vegetation and soils in the Plum Island Sound estuary in Massachusetts, USA, and specifically assessed the role of marsh vegetation for Hg deposition and turnover. Monthly quantitative harvesting of aboveground biomass showed strong linear seasonal increases in Hg associated with plants, with a 4-fold increase in Hg concentration and an 8-fold increase in standing Hg mass from June (3.9 ± 0.2 µg kg−1 and 0.7 ± 0.4 µg m−2, respectively) to November (16.2 ± 2.0 µg kg−1 and 5.7 ± 2.1 µg m−2, respectively). Hg did not increase further in aboveground biomass after plant senescence, indicating physiological controls of vegetation Hg uptake in salt marsh plants. Hg concentrations in live roots and live rhizomes were 11 and 2 times higher than concentrations in live aboveground biomass, respectively. Furthermore, live belowground biomass Hg pools (Hg in roots and rhizomes, 108.1 ± 83.4 µg m−2) were more than 10 times larger than peak standing aboveground Hg pools (9.0 ± 3.3 µg m−2). A ternary mixing model of measured stable Hg isotopes suggests that Hg sources in marsh aboveground tissues originate from about equal contributions of root uptake (∼ 35 %), precipitation uptake (∼ 33 %), and atmospheric gaseous elemental mercury (GEM) uptake (∼ 32 %). These results suggest a more important role of Hg transport from belowground (i.e., roots) to aboveground tissues in salt marsh vegetation than upland vegetation, where GEM uptake is generally the dominant Hg source. Roots and soils showed similar isotopic signatures, suggesting that belowground tissue Hg mostly derived from soil uptake. Annual root turnover results in large internal Hg recycling between soils and plants, estimated at 58.6 µg m−2 yr−1. An initial mass balance of Hg indicates that the salt marsh presently serves as a small net Hg sink for environmental Hg of 5.2 µg m−2 yr−1.

Fine root production, mortality, and turnover in response to simulated nitrogen deposition in the subtropical Abies georgei (Orr) forest

Increased nitrogen deposition has important effects on below-ground ecological processes. Fine roots are the most active part of the root system in terms of physiological activity and the main organs for nutrient and water uptake by plants. However, there is still a limited understanding of how nitrogen deposition affects the fine root dynamics in subtropical Abies georgei (Orr) forests. Consequently, a three-year field experiment was conducted to quantify the effects of three forms of nitrogen sources ((NH4)2SO4, NaNO3, and NH4NO3) at four levels (0, 5, 15, and 30 kg N·ha−1·yr−1) on the fine root dynamics in Abies georgei forests using a randomized block-group experimental design and minirhizotron technique. The first year of nitrogen addition did not affect the first-class fine roots (FR1, 0 < diameter < 0.5 mm) and second-class fine roots (FR2, 0.5 < diameter < 1.0 mm). The next two years of nitrogen addition significantly increased the production, mortality, and turnover of FR1 and FR2; the three year of nitrogen addition did not affect the dynamics of the third- class fine roots (FR3, 1.0 < diameter < 1.5 mm) and fourth- class fine roots (FR4,1.5 < diameter < 2.0 mm). Nitrogen addition positively affected the dynamics of FR1, FR2, FR3 and FR4 by positively affecting the carbon, nitrogen, and phosphorus contents of fine roots and indirectly affecting the soil pH. Increased carbon allocation to FR1 and FR2 may represent a phosphorus acquisition strategy when nitrogen is not the limiting factor. The nitrogen addition forms and levels affected the fine root dynamics in the following orde: NH4NO3 > (NH4)2SO4 > NaNO3 and high nitrogen > medium nitrogen > low nitrogen. The results suggest that the different-diameter fine root dynamics respond differently to different nitrogen addition forms and levels, and linking the different-diameter fine roots to nitrogen deposition is crucial.

Patterns and mechanisms of belowground carbon responses to changes in precipitation

Abstract It is well known that aboveground productivity usually increases with precipitation. However, how belowground carbon (C) processes respond to changes in precipitation remains elusive, although belowground net primary productivity (BNPP) represents more than one-half of NPP and soil stores the largest terrestrial C in the biosphere. This paper reviews the patterns of belowground C processes (BNPP and soil C) in response to changes in precipitation from transect studies, manipulative experiments, modeling and data integration and synthesis. The results suggest the possible existence of nonlinear patterns of BNPP and soil C in response to changes in precipitation, which is largely different from linear response for aboveground productivity. C allocation, root turnover time and species composition may be three key processes underlying mechanisms of the nonlinear responses to changes in precipitation for belowground C processes. In addition, microbial community structure and long-term ecosystem processes (e.g. mineral assemblage, soil texture, aggregate stability) may also affect patterns of belowground C processes in response to changes in precipitation. At last, we discuss implications and future perspectives for potential nonlinear responses of belowground C processes to changes in precipitation.

Long-term nitrogen addition modifies fine root growth and vertical distribution by affecting soil nutrient availability in a Mongolian pine plantation

Fine roots are the primary organ of tree species in water and nutrient acquisition, and are the major contributor of forest soil organic carbon (C). However, it remains largely unknown how fine root growth dynamics and vertical distribution respond to long-term nitrogen (N) enrichment, which prevents us from accurately evaluating forest C sequestration potential under N deposition. Here, we investigated the effects of nine-year N addition (0 and 10 g N m−2 year−1) on fine root nutrients, biomass, production, turnover rate and vertical distribution in three soil layers (0–10, 10–20 and 20–40 cm) of a Mongolian pine (Pinus sylvestris var. mongolica) plantation in the Keerqin Sandy Lands, Northeast China. We found that soil inorganic N was increased and Olsen-P was decreased by N addition. N addition increased fine root N, C:P and N:P ratios, but reduced fine root P and C:N ratio across all soil layers. N addition reduced fine root biomass in 0–10 cm soil layer but increased it in 20–40 cm soil layer. N addition accelerated fine root turnover rate in 0–10 cm soil layer, and increased fine root necromass across all soil layers. Moreover, N addition significantly enhanced biomass of ectomycorrhizal extraradical hyphae in the 0–10 cm soil layer. Redundancy analysis showed that variations of fine root traits were well explained by soil NO3−-N in 0–10 and 10–20 cm soil layers, and by soil NH4+-N and Olsen-P in 20–40 cm soil layer. Collectively, our results highlight the shift from N limitation to P limitation of Mongolian pine plantations under long-term N addition, and suggest that changes in fine root growth and vertical distribution induced by N addition could accelerate belowground C allocation in Mongolian pine plantations.

Diazotrophic nitrogen fixation through aerial roots occurs in Avicennia marina: implications for adaptation of mangrove plant growth to low-nitrogen tidal flats.

Nitrogen limitation of primary production is common in coastal ecosystems. Mangrove trees maintain high levels of nitrogen fixation around their roots. The interior aerial space of mangrove roots, in which atmospheric gas is supplied through lenticels, could be efficient sites for nitrogen fixation. We measured tidal variations of partial pressure of N2 in root aerenchyma and conducted field experiments using 15 N2 as a tracer to track N2 movement through aerial roots of Avicennia marina. We used the acetylene reduction assay to identify the root parts harboring diazotrophs. The nitrogenase activity and estimated nitrogen fixation through aerenchyma were higher in pneumatophores and absorbing roots than in cable roots. Positive correlations between root nitrogen contents and turnover rates of root nitrogen derived from N2 through aerenchyma suggested that the internal supply of N2 to diazotrophs could be the main source for nitrogen assimilation by A. marina roots. Our results confirmed that N2 is supplied to diazotrophs through aerial roots and that nitrogen fixation occurs in A. marina roots. The aerial root structures, which occur across families of mangrove plants, could be an adaptation to survival in not only low-oxygen environments but also tidal flats with little plant-available nitrogen.

Fine‐root turnover and leaf litterfall of Salsola passerina facilitate soil restoration in Alxa steppe desert of northwest China

Nutrient cycling in desert ecosystems is heavily reliant on the fine root turnover and litter decomposition processes of dominant plant species. Based on field investigations and laboratory experiments, we explored fine root production (FRP) and turnover of Salsola passerina in Alxa steppe desert, and assessed fine root and leaf litter input and its correlation with soil C and N stocks, and then compared the variability of soil physicochemical properties at the site below and the interspace of S. passerina canopy. Results showed that fine root biomass dynamics of S. passerina were consistent with soil water content. Annual FRP of S. passerina was 243.3 g m−2 yr−1 and the turnover rate was 2.0 per year. S. passerina contributed 172.2 g C m−2 and 6.8 g N m−2 to soil from its fine root senescence and leaf litter input annually. Compared to the canopy interspace, the soil texture and fertility beneath the shrubs significantly improved, while the soil salinity decreased. The results indicated that the activities of desert shrub growth provided the degraded soil with abundant nutrients through fine root turnover and litter decomposition processes, which promoted soil texture and nutrition heterogeneity at the stand scale, and played an important role in degraded dryland restoration.

A new method for estimating carbon dioxide emissions from drained peatland forest soils for the greenhouse gas inventory of Finland

Abstract. In peatlands drained for forestry, the soil carbon (C) or carbon dioxide (CO2) balance is affected by both (i) higher heterotrophic CO2-C release from faster decomposing soil organic matter (SOM) and (ii) higher plant litter C input from more vigorously growing forests. This balance and other greenhouse gas (GHG) sinks and sources in managed lands are annually reported by national GHG inventories to the United Nations Climate Change Convention. In this paper, we present a revised, fully dynamic method for reporting the CO2 balance of drained peatland forest soils in Finland. Our method can follow temporal changes in tree biomass growth, tree harvesting and climatic parameters, and it is built on empirical regression models of SOM decomposition and litter input in drained peatland forests. All major components of aboveground and belowground litter input from ground vegetation as well as live trees and trees that died naturally are included, supplemented by newly acquired turnover rates of woody plant fine roots. Annual litter input from harvesting residues is calculated using national statistics of logging and energy use of trees. Leaching, which also exports dissolved C from drained peatlands, is not included. The results are reported as time series from 1990–2021 following the practice in the GHG inventory. Our revised method produces an increasing trend of annual emissions from 0.2 to 2.1 t CO2 ha−1 yr−1 for the period 1990–2021 in Finland (equal to a trend from 1.4 to 7.9 Mt CO2 yr−1 for the entire 4.3 Mha of drained peatland forests), with a statistically significant difference between the years 1990 and 2021. Across the period 1990–2021, annual emissions are on average 1.5 t CO2 ha−1 yr−1 (3.4 Mt CO2 yr−1 for 2.2 Mha area) in warmer southern Finland and −0.14 t CO2 ha−1 yr−1 (−0.3 Mt CO2 yr−1 for 2.1 Mha area) in cooler northern Finland. When combined with data on the CO2 sink created by the growing tree stock, in 2021 the drained peatland forest ecosystems were a source of 1.0 t CO2 ha−1 yr−1 (2.3 Mt CO2 yr−1) in southern Finland and a sink of 1.2 t CO2 ha−1 yr−1 (2.5 Mt CO2 yr−1) in northern Finland. We compare these results to those produced by the semi-dynamic method used earlier in the Finnish GHG inventory and discuss the strengths and vulnerabilities of the new revised method in comparison to more static emission factors.

Elevated CO2, O3 and their interaction have differential impact on soil microbial diversity and functions in wheat agroecosystems

Elevated carbon dioxide (EC) and elevated ozone (EO) due to changing climate have a significant impact on the plant growth rate, primary productivity, and root turnover. EC and EO could have a differential impact on the structure and functioning of soil microbial communities in terrestrial ecosystems via modifications in the microbial population, soil enzyme activity, decomposition of organic compounds and cycling of nutrients. For the development of sustainable agroecosystems, soil microbial communities are essential due to their major roles in nutrient cycling, crop-microbe interplay and resistance towards biotic/abiotic factors. However, it remains difficult to project how multiple climate change factors would affect below-ground functions. Free-Air CO2 and O3 enrichment facility (FAOCE) was used to explore the effects of EC (550 ± 50 ppm) and EO (65 ± 10 ppb) along with their combined interactive treatment ECO on the structure and abundance of soil microbial community, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbes involved in N cycling in wheat crop (Triticum aestivum) under field conditions. The MBC increased by 20% in EC and declined by 5% in EO to ambient control. Treatments EC and ECO stimulated the growth of ammonia and nitrite-oxidizing bacteria. Heterotrophic microbial populations were favoured under EC and inhibited under EO. Treatments indirectly affected the soil microbial community structure by altering N-cycling microbes and modifying MBC and MBN which eventually changed soil fertility and biogeochemistry.

Soil Carbon Stock and Carbon Pool Indices under Major Land Use Systems of Mayiladuthurai District, Cauvery Delta Zone, India

Background- Soil organic carbon serves as potential indicator of the soil quality which is influenced by the changes in management practices. The conversion of natural ecosystem by anthropogenic activities resulted in decline of SOC. So, this study was conducted to assess the carbon indices and understand the dynamics to develop the management strategies for enhancing the C pool in the soil. Methods- The present study was conducted in major land use systems of Mayiladuthurai district of Cauvery delta zone in Tamil Nadu. Soil samples were collected by stratified random sampling at two different depths and estimated for soil carbon indices. Result- The SOC, C stock, bulk density, microbial biomass carbon, dehydrogenase, carbon management index of the study area varied with the mean value of 12.51 Mg ha-1, 10.57 t ha-1, 1.26 Mgm-3, 302.52 µg kg-1, 38.21 µg TPF g-1 day-1and 126.91 % respectively. C stock were in the order of forestry greater than rice-pulses greater than rice-cotton greater than sugarcane greater than uncultivated among the different land uses of the study area. The difference in vegetation, litterfall, soil chemistry, microbial activity, substrate, root exudate, root biomass and root turnover influenced the variation in carbon pool under different land uses of the study area.