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    Stronger microbial decay of recalcitrant carbon in tropical forests than in subtropical and temperate forest ecosystems in China

    Zhou, ShaChen, LanWang, JieyingHe, Liyuan...
    7页
    查看更多>>摘要：Soil enzymes are the most potent bioactive components in forest ecosystems. Cellulases and ligninases are vital carbon (C)-degrading enzymes that target different C pools. The ratio of ligninase-to-cellulase activity is good indicator for microbial soil C preference, play an important role in soil C cycling. However, our understanding of enzyme ratios and their drivers across forest ecosystems remains unclear. In this study, we hypothesized that (i) the ligninase-to-cellulase ratio increased from temperate forests to tropical forest ecosystems, and (ii) the dominant factors would be microbial abundances. About 2-3 kg of topsoil (0-10 cm) from each of the ten forest ecosystems were collected across a 3425 km gradient in China between July and August 2019. We analyzed the biogeographic patterns of ligninase and cellulase activities and the ratio of ligninase-to-cellulase activities to determine how this ratio responded to climatic factors, soil properties and substrates, and microbial abundances across the forest ecosystems along the latitudinal gradient. Our findings showed that the average soil ligninase activity was 3.49 nmol h(-1) g(-1), whereas the average soil cellulase activity was 525.26 nmol h(-1) g(-1) across the forest ecosystems sampled. The average activity ratio of ligninase-to-cellulase in tropical forest ecosystems was 27.9% higher than that in subtropical forests and 64.2% higher than that in temperate forest ecosystems. The partial least squares path model demonstrated that the ligninase-to-cellulase activity ratio was significantly negatively correlated with soil substrates (r =-0.94, p < 0.001) and significantly positively correlated with microbial abundances (r = 0.38, p < 0.01). The variation partitioning analysis further revealed that soil sub-strates explained 19.4% variation regarding ligninase-to-cellulase ratio, whereas microbial abundance (fungal abundance) contributed 2.8%. This study provides crucial information about the distribution of enzyme ratios along the latitude gradient, highlights the microbial utilization of recalcitrant C pools in tropical forests, and provides an insight into the response of the global C cycle under a changing climate.
      原文链接:
    • NSTL
    • Elsevier

    Vertical patterns and controlling factors of soil nitrogen in deep profiles on the Loess Plateau of China

    Wang, YunqiangZhang, PingpingSun, HuiJia, Xiaoxu...
    12页
    查看更多>>摘要：Soil nitrogen is highly variable both in horizontal and vertical directions and plays an important role in environmental quality. To explore the vertical distributions of soil total nitrogen (STN), nitrate nitrogen (NO3--N) and ammonium nitrogen (NH4+-N) in deep vadose zone soil, and to verify the notion that soil N is highly affected by land use and soil type and that is depth-dependent, we collected soil and fresh root samples to a maximum depth of 21 m at 25 sites across China's Loess Plateau (CLP). STN and NO3--N concentrations were significantly higher under orchard (0.41 g kg(-1) and 40.98 mg kg(-1), respectively) than under farmland, forest and shrub-grassland (p < 0.001), while NH4+-N (7.32 mg kg(-1)) was significantly lower under orchard than forest (8.32 mg kg(-1), p < 0.05). In silt clay loam soil, STN and NO3--N concentrations were significantly higher (0.39 and 26.16 mg kg(-1)) than in silt loam soil (0.22 and 1.89 mg kg(-1)). Soil N differed greatly (especially in the upper four meters) but generally decreased with soil depth (SampD). Random forest model (RFM) and multiple linear regression analyses showed that the most important variables for STN were LogSOC, LogSampD, clay, pH, soil inorganic carbon, soil water content and LogAltitude; for LogNO(3)(-)-N were pH, LogSampD, land use, LogSOC, and soil water content; and for LogNH(4)(+)-N were pH, clay, LogAltitude, slope gradient and LogSOC. RFM had comparable good performance in predicting LogSTN and LogNO(3)(-)-N (r > 0.915, p < 0.001), followed by LogNH(4)(+)-N (r = 0.653, p < 0.001). The amount, distribution and variation of soil N were co-controlled by land use, soil type, topography, soil properties and considered soil depth. Understanding this information is essential in estimating soil N budget, developing N cycling models and improving sustainable N management on the CLP and similar regions around the world.
      原文链接:
    • NSTL
    • Elsevier

    Wildfire drives the transition from deterministic- to stochastic-dominated community assembly of abundant bacterial in forest soils

    Qin, QianqianWang, YinQiu, CongZheng, Dacheng...
    11页
    查看更多>>摘要：Wildfires are ecological disturbances that shift soil microbes and the ecosystem functions they drive in forests. The temporal dynamics and assembly processes of the bacterial community following fire are essential but remain unknown. This study aimed to investigate how the assembly processes and their associated factors mediate the abundant and rare bacterial communities across temporal trajectories (21 months from 2019 to 2020) in severely burned and contiguous unburned forest soils. Results revealed that the temporal turnover rate of abundant sub-community in unburned soils was lower than that of rare sub-community, and abundant taxa exhibited a wider niche breadth than rare taxa; null model analyses indicated that variable selection made a paramount contribution to bacterial community assembly, with stronger phylogenetic clustering of the rare taxa; soil ammonium nitrogen and pH were the most decisive factor for community assembly of abundant and rare taxa, as evidenced by how divergences in them decreased the proportion of stochasticity. Compared with the unburned soils, the temporal turnover of the soil bacterial community was accelerated in burned soils; moreover, determinism had more important roles in rare taxa, whereas the abundant taxa were primarily dominated by dispersal limitation; soil dissolved organic carbon and bulk density regulated the balance between deterministic and stochastic assembly of the abundant and rare bacteria, respectively. Overall, these findings suggested distinct community assembly of abundant taxa in burned and unburned forest soils, which is of great significance to understand the establishment and maintenance mechanism of the soil bacterial community in forests following wildfire.
      原文链接:
    • NSTL
    • Elsevier

    Changes in the soil nematode community among climate zones do not keep pace with changes in plant communities

    Ma, JinhaoWei, XueLiu, ShirongWu, Pengfei...
    10页
    查看更多>>摘要：Revealing the distribution patterns of soil nematode communities among climate zones helps uncover the spatial distribution patterns of belowground biodiversity. The aims of this study were to reveal the spatial distribution patterns of the taxonomic composition, diversity and trophic structure of soil nematode communities among continuous climate zones. Investigations were conducted for five altitudinal vegetation types, i.e., subtropical evergreen broad-leaved forest (SEB), subtropical evergreen and deciduous broad-leaved mixed forest (SEDB), warm temperate deciduous broad-leaved forest (WTDB), mid-temperate coniferous and broad-leaved mixed forest (MTC) and cold temperate coniferous forest (CTC), on the eastern slope of Gongga Mountain from 2014 to 2017. The taxonomic compositions of the soil nematode communities in the SEDB, WTDB, MTC and CTC were similar but differed markedly from that in the SED, with patterns varying among sampling years. Abundances and diversity showed unimodal distribution patterns, with maximum values occurring in the WTDB. The abundances of the four trophic groups varied significantly among the vegetation types. Relative abundances stabilized for bacterivores and plant parasites but declined for fungivores and increased for omnivores-predators from the SEB to the CTC. The ratio of fungivores to bacterivores in the SEB was significantly higher than those in the other vegetation types, implying that the trophic structure and material cycling channels differed among forest types. The spatial distribution of the soil nematode communities was mainly influenced by pH, total K, total P and soil temperature. These findings suggested that the taxonomic composition, abundance, diversity and trophic structure of soil nematode communities vary among climate zones, but the changes in the soil nematode communities among climate zones did not keep pace with those in aboveground plant communities.
      原文链接:
    • NSTL
    • Elsevier

    Combined effects of the wheat straw length and incorporation rate on reducing runoff and sediment yields

    Ma, JianyeMa, BoWang, YangxiuWang, Chenguang...
    15页
    查看更多>>摘要：Straw incorporation is a critical conservation tillage measure that effectively reduces slope runoff and sediment. This study used laboratory experiments to examine the combined effects of the straw length and incorporation rate on reducing runoff and sediment, under straw incorporation. The experiments involved three wheat straw lengths (3-5, 8-10, and 13-15 cm) and four incorporation rates (1.5, 2.5, 3.5, and 4.5 t.hm(-2)). Bare slopes were selected as the control, and the experimental soil was silty loam. Three hundred-cm-long, 100-cm-wide, and 50cm-deep soil tanks with 15 degrees slopes were subjected to artificial rainfall with a duration of 1 h and an intensity of 90 mm.h(-1). Straw incorporation reduced the runoff and sediment yields by 3.11-18.18% and 30.71-57.71%, respectively. When the straw length was combined with the incorporation rate, as the straw length increased, the sensitivity of the runoff and sediment yields to the incorporation rate decreased first and then increased. Similarly, the sensitivity to the straw length also decreased first and then increased, as the incorporation rate increased. In the combination mode, the greatest runoff and sediment reduction effects were achieved at a straw length of 8-10 cm and an incorporation rate of 3.5 t.hm(-2), which were the optimal straw length and incorporation rate values. The reduction effect of the straw length on the runoff and sediment yields was weaker than that of the incorporation rate. The incorporation rate was always the main factor affecting the runoff yield during the erosion process, while the main factor affecting the sediment yield changed gradually from the straw length to the incorporation rate. Thus, the incorporation rate is also a crucial factor inhibiting rill development. The effect of the straw length on sediment reduction primarily involves reducing hydrodynamic factors, such as flow velocity, while the incorporation rate plays a stronger role in reducing soil erodibility. This study provides a scientific basis for selecting and applying conservation tillage measures involving straw incorporation.
      原文链接:
    • NSTL
    • Elsevier

    Stability of soil organic carbon pools affected by land use and land cover changes in forests of eastern Himalayan region, India

    Ahirwal, JitendraGogoi, AnudipSahoo, Uttam Kumar
    8页
    查看更多>>摘要：Forests are among the largest terrestrial carbon pools that are most vulnerable to land use and land cover change (LULC). Therefore, it is essential to manage forest ecosystems to enhance soil organic carbon (SOC) pools and soil functionality. The present study was carried out to analyze C stability and change in SOC stock under different forest types in the eastern Himalayan region of India. Topsoil (0-15 and 15-30 cm) samples from six dominant forests i. e. tropical wet evergreen, montane subtropical, temperate, Quercus, bamboo, and shifting cultivation (Jhum) lands were collected and analyzed for selected soil properties and SOC stock. Active (very labile + labile), slow (less labile), and passive (non-labile) C fractions were also analyzed to determine the stability of the SOC pool under the LULC scenario. Results show that the percentage contribution of active C to total organic carbon in topsoil was highest in a temperate forest (74.1%) while lowest in a bamboo forest (48.1%). Unlike, slow C (18.4%) and passive C (26.6%) were highest in Quercus forest. Pearson correlation analysis shows significant positive relation of active and slow C pool with SOC and total nitrogen concentration. The estimates of SOC stock (0-30 cm) were significantly higher in temperate forests (132.7 Mg C ha(-1)). However, the conversion of natural forests to bamboo forest and jhum land reduced SOC stock by 29% and 68%, respectively. C lability index shows higher labile C in jhum land while recalcitrancy index was highest in a bamboo forest. Our study concluded that LULC change significantly altered the stability and stock of SOC in natural forests. Owing to a higher percentage of slow and passive C pools, Quercus forests play a major role in C sink management.
      原文链接:
    • NSTL
    • Elsevier

    Influence of climate and land-use changes on the sensitivity of SWAT model parameters and water availability in a semi-arid river basin

    Sharma, AlkaPatel, P. L.Sharma, Priyank J.
    20页
    查看更多>>摘要：The present study assesses the impact of climate change (CC) and land use land cover change (LULCC) on model parameter variability and alterations in streamflow and water balance components of a semi-arid river basin in western India. The Dharoi catchment in the Sabarmati River basin is a water-scarce region with India's lowest per-capita water availability. The water scarcity conditions are likely to aggravate due to changing climate and landscape modifications through human interventions. A hydrological modelling framework using a semi distributed Soil and Water Assessment Tool (SWAT) is adopted in this study, considering two approaches: a variable-period calibration and a fixing-changing approach. Several model scenarios considered in these approaches are simulated through both single-site (SSC) and simultaneous multi-site calibration (SMSC) techniques. The variable-period calibration is adopted to assess the individual and combined influences of CC and LULCC on SWAT model parameter variability and change in water balance ratios. The fixing-changing approach evaluates the relative contribution of CC and LULCC to streamflow changes. The temporal changes in the hydroclimatic variables are analysed using non-parametric Pettitt, Mann-Whitney, Modified Mann-Kendall, and Spearman's rho tests. The results indicated an abrupt increase in the streamflow in 2004, attributed to a significant increase in total and extreme rainfall magnitude and frequency in the catchment. The SSC and SMSC techniques yielded satisfactory and comparable performance for all model scenarios. The results showed that CC has a more significant impact on SWAT model parameter variability than LULCC. Thus, CC is the primary driver of streamflow changes in the Dharoi catchment, wherein a four-fold increase in the streamflow is noticed in the period 2005-2014 vis-`a-vis 1995-2004. Thus, a transition from drier to wetter hydroclimatic conditions is evident in the Dharoi catchment, which would enhance water sufficiency in the region if appropriately managed.
      原文链接:
    • NSTL
    • Elsevier

    Latitudinal patterns of light and heavy organic matter fractions in arid and semi-arid soils

    Li, XiaojuanYang, TinghuiHicks, Lettice C.Hu, Bin...
    12页
    查看更多>>摘要：Semi-arid and arid ecosystems are important for the global C cycle. Despite this, it remains unclear how organic matter fractions vary across latitudinal gradients, and what drives this variation, in dry ecosystems. In this study, we sampled soils from 100 sites across a latitudinal gradient in the dry valleys of southwestern China to explore the latitudinal patterns of light fraction organic matter (LFOM) and heavy fraction organic matter (HFOM) at two soil depths (0-10 cm and 10-20 cm). Across the studied gradient, HFOM accounted for a larger fraction of soil organic matter than LFOM. LFOM increased exponentially with increasing latitude at both 0-10 cm and 10-20 cm depths. Heavy fraction organic C increased linearly with increasing latitude at both depths, while heavy fraction organic N only increased with latitude in soils from 10 to 20 cm depth. Latitudinal patterns of LFOM were mainly explained by climate, with the most important driver being mean annual temperature, followed by mean annual precipitation. Soil physicochemical factors - in particular cation exchange capacity and silt content - explained the most variation in HFOM. Total microbial biomass was also important in explaining variation in HFOM, especially in the 10-20 cm soil layer. Overall, our results shed light on the spatial distribution of organic matter fractions in arid and semi-arid regions. We also identify candidate drivers of the variation in LFOM and HFOM in arid and semi-arid regions, finding that climate primarily explains variation in LFOM while soil physiochemistry primarily explains variation in HFOM.
      原文链接:
    • NSTL
    • Elsevier

    Pedogenic processes in a chronosequence of very deeply weathered soils in southeastern Brazil

    Franzmeier, Donald P.de Rezende, Servulo BatistaResende, MauroMancini, Marcelo...
    15页
    查看更多>>摘要：Brazil has some of the oldest soils of the world. Landscapes in southeastern Brazil are very old and stable. Some of the soils formed therein have suffered many pedogenetic cycles and hence are difficult to study thoroughly due to their depth and age. In the southeastern State of Minas Gerais, Brazil, we studied four soils developed from gneiss formed on these old surfaces (one sampled to a depth of 26 m) that comprised a chronosequence. For most soils of the world, the major change in properties is at the C/B horizon interface, but in these soils the major change is at the R/C interface. In each soil, a certain suite of clay minerals (kaolinite, gibbsite, goethite, and hematite) had weathered from the primary minerals of gneiss. The composition of the suite differed among the four soils, but in an individual soil it was relatively constant with depth, including through the C/B boundary. In the C horizon, many of the minerals were in the form of aggregates in the silt fraction. Across the C/B boundary there was little change in chemistry and mineralogy, but there the aggregates broke down to clay particles that were incorporated into soil structure. Overall, the chronosequence showed that soil properties changed greatly from the youngest, lowest part of the landscape, while between the older soils, higher in the landscape, the change was small. Soil properties appeared influenced by the different zones of the weathered mantle, hypothesized to be gibbsitic on the very top, kaolinitic in the most part, and bissialitic (2:1 clay minerals) closer to the fresh rock.
      原文链接:
    • NSTL
    • Elsevier

    Response of soil aggregate stability and rill erodibility to soil electric field

    Liu, JunyangYang, YananZheng, QunweiSu, Xuemeng...
    9页
    查看更多>>摘要：Soil electric field (E0) might have strong effects on rill erosion, and it is in turn largely affected by root growth. This study aimed to quantify the ability of roots to predict E0 and elucidate the effects of E0 on the mean weighted diameter of soil aggregates (MWD) and rill erodibility (Kr). Samples were collected from three typical areas in the Loess Plateau of China, and each area had two typical grasslands. Soil detachment rates were measured using a hydraulic flume under five discharges (0.1, 0.2, 0.3, 0.4, and 0.6 L s-1) on a slope of 15 degrees. The results indicated that plant roots negatively contributed to E0. The mean E0 of grasslands (rooted soil) was lower by 3.27 times compared with that of fallow lands (root-free soil). With significant correlation (P < 0.05), root length density (RLD) and root surface area density (RSAD) were found to be suitable parameters for predicting E0, which decreased exponentially with RLD (R2 = 0.306) and RSAD (R2 = 0.381). In addition, E0 strongly affected MWD and Kr by influencing soil repulsive forces. E0 was negatively correlated to MWD (logarithmic function, R2 = 0.96), but positively correlated to Kr (linear function, R2 = 0.88). Our results provide new insight into the mechanism of rill erosion considering plant roots.
      原文链接:
    • NSTL
    • Elsevier