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Wheat yield and nitrogen use efficiency (NUE) have improved simultaneously with the genetic development of wheat varieties. However, wheat selection is carried out routinely in N‐rich field conditions, with breeding progress limited under low soil available nitrogen. Thus, we performed a 2‐year field investigation using eight milestone winter wheat varieties released between 1947 and 2017 in the Huang‐Huai‐Hai region of China with two N applications—normal (CK; 220 kg N ha−1) and reduced (RN; 110 kg N ha−1)—in Shaanxi, China, to examine changes in wheat yield, NUE, water use efficiency (WUE) and root biomass. Our findings revealed average annual yield increases of 49.615 kg ha−1 and 36.905 kg ha−1 under CK and RN, respectively. Notably, the NUE trend mirrored yield, increasing with the release year of wheat varieties, with average annual increases in NUE of 0.192 and 0.336 kg kg−1 under CK and RN, respectively. In the RN treatment, N uptake efficiency (UPE) increased with year of release, while N utilization efficiency (UTE) had no significant relationship. In the CK treatment, UTE increased with year of release, while UPE had no significant relationship. Across the 2‐year experiment, surface root biomass (0–20 cm layer) increased with year of release under CK but had no relationship under RN, while deep root biomass (20–200 cm layer) decreased with year of release under CK and increased under RN. The roots of modern wheat varieties responded better to soil nitrogen levels and produced higher yields, NUE and WUE than earlier varieties by adjusting root biomass distribution in soil. [ABSTRACT FROM AUTHOR]

The stump and coarse root biomass remaining after tree harvesting are often overlooked by researchers, which may lead to underestimation of their role in carbon cycling, so we constructed two sets of additive models for larch (Larix olgensis Henry) plantations in Northeast China. Due to the absence of tree diameter at breast height data after harvesting, only the sole predictor variable stump disc diameter could be used to predict stump and coarse root biomass, and the results showed that stump disc diameter predicted stump biomass with higher accuracy than coarse root biomass predictions. In addition, to investigate the effect of the site class of complex stands on the predictive capability of the model, the generic model in this study was employed with all site class data and a specific model was developed and employed with all the site class data. We found that the generic model had different degrees of error compared to the predicted results for each site class, overestimating the total biomass by 15% and underestimating it by 10%, especially for site class IV. In conclusion, to obtain a biomass prediction model with reliable results, the impact of more complex site class effects should be considered. [ABSTRACT FROM AUTHOR]

Most of the forest biomass models that have been developed so far focus on the study of the aboveground biomass of forest trees and the prediction of belowground biomass remains obviously insufficient. Moreover, most of the existing studies on the estimation of the belowground biomass of trees have considered roots as a whole, ignoring the differences in composition and function of roots within different diameter classes. In this study, we measured the root biomass of birch plantation forests in northeastern China using extensive destructive sampling, in which we divided the root system into three parts: coarse, medium, and fine roots. We selected the best model base form from three common allometric biomass equations and determined the most appropriate error structure for the two sets of models using likelihood comparisons. The additive and disaggregated models were fitted using maximum likelihood with open-source software. We also added the site factor as a dummy variable into the two models. Finally, the competency of the two models was tested using ten-fold cross-validation. The results showed that both models could provide relatively accurate estimates of birch root biomass but that the disaggregated model performed slightly better than the additive model. [ABSTRACT FROM AUTHOR]

Enclosure is an effective strategy for enhancing soil carbon sequestration in the desert steppe. Soil organic carbon (SOC) and its stock during changes in the plant community influence soil fertility and the global carbon cycle. We studied changes in SOC and its stock along with six plant community types in the desert steppe of Inner Mongolia, northern China. The goal of this study was to explore differences in SOC and its stock among plant communities while accounting for the effects of environmental factors. We collected 336 soil samples at four soil depths (0–5 cm, 5–10 cm, 10–20 cm, and 20–30 cm) and vegetation attributes from 84 plots in the enclosure. The results revealed that plant community type and soil depth were the most influential factors for root biomass, SOC, and SOC stock. Total root biomass varied from 229.21 to 731.71 g·m−2 and was ranked as follows: Koeleria cristata > Leymus chinensis > Stipa krylovii >Allium mongolicum >Stipa breviflora > Convolvulus ammannii. Mean SOC and its stock of soils associated with K. cristata were 1.94 and 1.62 times higher than that measured for C. ammannii soils, respectively. Root biomass, SOC, and its stock gradually decreased with soil depth. Stratification ratios (SRs) of SOC increased with soil depth for different plant communities and showed better soil quality (except C. ammannii and A. mongolicum). Results from redundancy analysis (RDA) showed that root biomass, clay, coverage, and litter biomass had significant impacts on SOC and SOC stock. We conclude that the plant community had the greatest effect on improving SOC stock after enclosure, and plant root biomass contributed the most to SOC stock. [ABSTRACT FROM AUTHOR]

Grazing exclusion is a common management strategy for improving grasslands degraded due to overgrazing. Although previous meta‐analyses proved that grazing exclusion improved soil carbon (C) storage of grasslands in China, we know little about its effect on grassland ecosystems elsewhere and whether litter accumulation induced by grazing exclusion regulates soil C storage. Using meta‐analysis, we integrated 91 publications to examine the effects of grazing exclusion on community litter and soil C storage, accompanied by analysis of the regulating roles of body size of herbivore, climatic conditions, and grazing exclusion duration. We found that grazing exclusion enhanced litter biomass and decomposition rate but did not change litter chemical quality. Generally, grazing exclusion enhanced plant production and soil C storage across grassland worldwide. Exclusion of medium and small herbivores had stronger effects on aboveground litter production and soil C storage than exclusion of large herbivores, and grazing exclusion's enhancement on litter production and soil C storage tended to increase as grazing exclusion proceeded. Notably, grazing exclusion‐induced increase in aboveground litter biomass was attributed to the increase in biomass of graminoids, while root biomass, not aboveground litter biomass, primarily regulated the increase in soil C storage. The stimulating effect of grazing exclusion on soil C storage was enhanced possibly due to enhanced root biomass response along a precipitation gradient. Generally, our study provided new insights that management practice under grazing exclusion should take plant community dynamics, grazing exclusion duration, preceding grazer type, and climate conditions into account simultaneously. [ABSTRACT FROM AUTHOR]

The development of irrigated agriculture in northwest China is restricted by shortages of fresh water and groundwater salinization. Saline water irrigation may cause salt accumulation in the soil, which results in salt stress to roots. The effects of water salinity and irrigation amount on wheat root distribution and yield, as well as soil salt distribution, were evaluated in field experiments conducted in 2014 and 2015 at the Shiyanghe Experimental Station of the China Agricultural University (102°52'E, 37°52'N), located in the Liangzhou District, in the city of Wuwei in northwest China. A total of 12 treatments including 4 levels of irrigation water salinity as indicated by electrical conductivity (0.65, 3.2, 5.2, and 7.1 dSm-1) and 3 levels of irrigation amount (205, 280, and 355 mm), were established using a randomized block design. Freshwater with an electrical conductivity of 0.65 dSm-1 and an irrigation amount of 355 mm was used as the control for salinity and irrigation level. The results showed that the influence of irrigation amount and water salinity on root distribution was mainly in the top 40-cm. Irrigation amount had no statistically significant (p > 0.05) effects on the average root length density (RLD) in the 2-year experiment. A decrease in irrigation amount reduced root biomass (RB) at maturity when water salinity ranged from 0.65 to 5.2 dSm-1. Water salinity less than 3.2 dSm-1 stimulated root growth in the soil layers 10-40-cm at the heading stage without obvious yield reduction or salt accumulation. However, water salinities of 5.2 and 7.1 dSm-1 led to decreases in RLD in the 0-10-cm layer and RB at the maturity stage, and a significant decrease in yield (p < 0.05) in both years. The interaction effects of irrigation amount and water salinity had no statistically significant (p > 0.05) effects on root parameters and yield. In the absence of rainfall, a regime with irrigation amounts between 205 and 355 mm and water salinity between 0.65 and 5.2 dSm-1 can ensure a 70% yield. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition and grazing (G) are two disturbances of grassland ecosystems and these can greatly affect soil respiration. To date, few studies have investigated this topic in sandy grasslands. Here, we conducted a manipulative experiment in a sandy grassland in Inner Mongolia, China in the year 2013 and 2014, to investigate the effects of N addition and grazing on soil respiration. The results showed that N addition significantly accelerated soil respiration in both 2013 and 2014. The respiration enhancement under N addition varied during the growing season, being larger in early May 2014 (0.40 μmol·m−2·s−1) and early July 2014 (1.29 μmol·m−2·s−1) than in October 2014 (0.03 μmol·m−2·s−1). Grazing plots yielded a lower cumulative soil respiration rate than the control plots (−5,68% in 2013 and −1.07% in 2014), although the difference was not significant. In this study, soil temperature rather than soil moisture was the main factor affecting the temporal variation in soil respiration during the growing season. The inter-plot analysis showed that the soil ammonium nitrogen (NH4+–N) content, C:N ratio, and root biomass were significantly correlated with soil respiration, indicating that soil respiration under N-addition or grazing treatment could be affected by changing soil microhabitat conditions, thus affecting soil respiration. [ABSTRACT FROM AUTHOR]

Worldwide, majority of the studies on root distribution have been confined to different tree species and monopodial bamboos in China with limited information on sympodial bamboos mainly due to methodological complexities. The present study therefore aims at understanding root distribution pattern of six commercial bamboo species and its impact on soil properties. Six bamboo species viz., Bambusa balcooa, Bambusa bambos, Bambusa nutans, Dendrocalamus asper, Dendrocalamus hamiltonii, and Dendrocalamus strictus were evaluated for their rooting pattern and impact on soil properties. Coarse root (CR) intensity was maximum in B. bambos (209.2) while, fine root (FR) intensity was highest in D. strictus (594.2). The FR contribution ranged from 69.9% in B. bambos to 80.1% in D. strictus. Coarse root biomass (in 0–50 cm soil profile) was highest in D. hamiltonii (1.19 Mg ha−1) and lowest in D. strictus (0.44 Mg ha−1). Maximum FR biomass (6.27 Mg ha−1) was observed in B. nutans which was closely followed by D. hamiltonii (6.19 Mg ha−1). In all the species, the share of fine root intensity was higher (70–80%) as compared to coarse roots. The contribution of FR was higher in genus Dendrocalamus (D. strictus, D. hamiltonii and D. asper) as compared to other species in genus Bambusa. Depth wise distribution of CR intensity revealed that roots were more or less uniformly distributed in 0–30 cm soil depth while fine root intensity was higher in 0–10 cm where 47% roots were observed. Soil physical properties viz., hydraulic conductivity, water stable aggregates and mean weight diameter showed significant improvement under different species. As compared to control treatment, soil organic carbon, NPK showed significant improvement. D. hamiltonii and B. balcooa were found better species are better species for maintaining soil fertility status. From the study it could be concluded that D. hamiltonii due to higher fine root biomass, is suitably recommended for resisting soil erosion, enhancing ground water recharge and maintaining soil fertility. B. balcooa can be preferred for agroforestry due to less root competition and compact canopy. [ABSTRACT FROM AUTHOR]

• Deep rooted vegetation significantly leads to soil water deficit with the depth and precipitation. • Relative deep soil water deficit in artificial forest decreases with precipitation increase. • Precipitation self-regulation responses to deep soil water deficit in space. • Soil water deficit is more sensitive in the sub-shallow soil layers at a depth of 1800 cm. In semi-arid and semi-humid regions, deep soil water resources are crucial for vegetation restoration to mediate the ecosystem sustainability. Yet it is still limited on understanding soil water deficit (SWD) caused by vegetation restoration and its response to soil depth and precipitation. To obtain a more accurate measurement of regional SWD, we conducted a two-year soil water monitoring to a depth of 1800 cm under typical vegetation restoration with a precipitation gradient ranging from 300 mm/y to more than 600 mm/y across the Loess Plateau of China. With increasing precipitation gradient, soil water storages in 0–1800 cm depth under both arable cropland and artificial vegetation significantly increased (p < 0.05). Compared to arable cropland, artificial vegetations (forest and shrub) had a significantly greater SWD regardless of either precipitation gradient or soil depth. In particular, the deep-rooted vegetations (R. pseudoacacia and C. korshinskii) on the Loess Plateau demonstrated the greatest SWD in the 0–1800 cm layer due to their great water consumption. Indeed, a positive relationship between the accumulated SWD and the accumulated root biomass was detected, suggesting that the increased root biomass in soil depth may promote soil water consumption. In addition, the relative SWD in artificial vegetation at a depth of 1800 cm decreased significantly (p < 0.05). These findings reveal that there is a mechanism of precipitation self-regulation on the deep SWD, of which is more sensitive in the sub-shallow soil layers. We conclude that the SWD depends on vegetation restoration, soil depth, and precipitation self-regulation, offering a reference for how afforestation affects deep soil water in the Loess Plateau region. This finding also benefits to mediate water balance processes and develop sustainable land management in water-limited regions around the world. [ABSTRACT FROM AUTHOR]

The potential increases in carbon stocks in arid regions due to recent shrub encroachment have attracted extensive interest among both ecologists and carbon policy analysts. Quantifying the shrub root biomass amount in these ecosystems is essential to understanding the ecological changes occurring. In this paper, we proposed a simple nondestructive method for estimating the coarse lateral root biomass of shrubs based on the root counts obtained from ground-penetrating radar (GPR) radargrams. Root data were gathered via field experiments using GPR with antenna center frequencies of 900 MHz and 400 MHz. Five Caragana microphylla Lam. shrubs of different sizes were selected for measuring objects, and a total of 40 GPR survey lines were established for GPR data acquisition. The soil profile wall excavation method was used to obtain the total root biomass from each radargram. A model for estimating the root biomass was built by establishing the relationship between the root biomass in each profile and the root counts interpreted from the radargrams. According to the mathematical relationship between the root diameter and root biomass, the proxy root radius was derived, which could explain the rationality of the proposed model from the biological mechanism. The established model provided high confidence in estimating the root dry biomass using the GPR data obtained at the two antenna frequencies (R 2 = 0.73 for 900 MHz and R 2 = 0.71 for 400 MHz). The leave-one-out cross-validation results showed that the model exhibits satisfactory performance. This study expands the application of geophysical methods in root research and offers a new simplified method for estimating the root biomass from GPR data under field conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

High O3 exposure affects the forest growth and soil characteristics. Although there is substantial evidence that O3 does impose a stress on forest trees, the effects of O3 on roots and soil of evergreen broad-leaved tree species in South China remain unknown. The effects of ozone (O3) fumigation on the root biomass, root morphology, root nutrient, soil physical, and chemical properties were examined in Cinnamomum camphora seedlings grown under four O3 treatments (charcoal-filtered air (CF) or O3 at 1×, 2× and 4× ambient concentration). O3 significantly decreased root biomass and root carbon (C). Regardless of O3 level, elevated O3 significantly resulted in reduced root surface area, volume, number of forks, and specific root length (SRL). The percentages of fine to total root in terms of root surface area and root volume of seedlings under the CF and 1 × O3 treatments were significantly higher than those of seedlings under the 4 × O3 treatment, indicating that high O3 level impaired the growth performance of fine roots. O3 affected root growth and structures, which increased soil bulk density and reduced soil total porosity and void ratio. The soil pH under all O3 fumigation treatments significantly increased compared with CF treatment, whereas the organic matter significantly decreased. In conclusion, although the increased O3 level enhanced root N and P under 2 and 4 × O3 treatments compared with 1 × O3 treatment as compensation mechanisms to prevent O3-induced decrease in root C gain and root functions, O3 still decreased the root biomass and root tips, and changed the soil physical and chemical properties. [ABSTRACT FROM AUTHOR]

Rocky regolith layer can restrain plant root growth, which may affect soil water unitization of deep-rooted fruit trees in rocky mountain areas. However, how and to what magnitude the rocky regolith layer shapes root features and thus changes trees' water consumption, remains unclear. Here, we investigated the root features and water uptake strategies of apple trees in three apple orchards with the underlying weakly (WWP), strongly (SWP), and completely (CK) weathered regolith layer within soil profiles, in the hilly areas of Jiaodong Peninsula, China. The results showed that the fine root biomass density (FRBD) of apple trees decreased while the specific root length (SRL) increased with increasing soil depths in the three orchards. The FRBD within the rocky regolith layer only accounted for 3–5% of the total FRBD in the WWP and SWP orchards, which were significantly lower than that in the CK orchard (3.31–5.11% vs. 29.96%) (P < 0.05). The maximum SRL was 76.61 m·g-1 and 72.38 m·g-1 in the WWP and SWP orchards, respectively, being significantly higher than that in the CK orchard (55.26 m·g-1). Both the FRBD and SRL within the rocky regolith layer showed no significant difference between the WWP and SWP, which indicated that it was the presence but not the weathering intensity of the rocky regolith layer shaped apple trees' root features. The MixSIAR model estimated that the water uptake of roots in the rocky regolith layer accounted for an average of 33.14% of the total water uptake in the WWP and SWP orchards. During the fruit expansion period (July-August) with high water consumption, apple trees' water uptake in the rocky regolith layer contributed 41.40% of water consumption in the WWP orchardand 34.77% in the SWP, which can be comparable to that in the corresponding soil depth in the CK orchard (46.70%). This suggested that apple trees may prime root activity to absorb more soil water with decreased root biomass in the rocky regolith layer. Overall, apple trees could utilize 3–5% of root biomass to absorb 33–34% of water consumption in the rocky regolith layer. Our study highlights the specific water use strategies in rocky mountain areas and will benefit the sustainable water management in the orchards in these areas. • The presence of rock regolith reduces apple trees' FRBD but increases their SRL. • The regolith weathering degree does not impact apple trees' root distribution. • Apple trees utilize 5% of root biomass to absorb 34% of water from rock regolith. [ABSTRACT FROM AUTHOR]

This study develops a modeling framework for utilizing the large footprint LiDAR waveform data from the Geoscience Laser Altimeter System (GLAS) onboard NASA's Ice, Cloud, and Land Elevation Satellite (ICESat), Moderate Resolution Imaging Spectro-Radiometer (MODIS) imagery, meteorological data, and forest measurements for monitoring stocks of total biomass (including aboveground biomass and root biomass). The forest tree height models were separately used according to the artificial neural network (ANN) and the allometric scaling and resource limitation (ASRL) tree height models which can both combine the climate data and satellite data to predict forest tree heights. Based on the allometric approach, the forest aboveground biomass model was developed from the field measured aboveground biomass data and the tree heights derived from two tree height models. Then, the root biomass should scale with the aboveground biomass. To investigate whether this approach is efficient for estimating forest total biomass, we used Northeast China as the object of study. Our results generally proved that the method proposed in this study could be meaningful for forest total biomass estimation (R2 = 0.699, RMSE = 55.86). [ABSTRACT FROM AUTHOR]

Plastic-film mulch is a globally applied agricultural practice. However, its effects on soil aggregation and pH have been hardly studied. We assessed the effects of plastic-film mulch on soil aggregate water-stability and pH in fields used for maize ( Zea mays L.) production, at two sites in a cold semiarid environment, China. Four treatments were used: (i) no plastic-film mulch and no straw incorporation, (ii) plastic-film mulch only, (iii) straw incorporation only, and (iv) straw incorporation plus mulch. Seven years after continuous treatment application, the use of plastic-film mulch increased the proportion of water-stable macroaggregates (>0.25 mm) in the top 15-cm soil layer by 16–28%, across sampling times and sites. Straw incorporation similarly increased the proportion of water-stable macroaggregates. However, the effects of mulch, on increasing the mean weight diameter of aggregates were greater in non-straw-incorporated soils than in straw-incorporated soils, and vice versa. Soil bulk density in the top 15-cm soil layer marginally increased in the mulched treatments, relative to the non-mulched treatments, while it decreased in straw-incorporated treatments. In addition, there was a decrease in soil pH, by 0.19–0.54 units, in the mulched, relative to the non-mulched soils. Combining our previous results, we suggested that increases in maize root growth and microbial activity were linked to the increased soil aggregation while accumulation in soil nitrate resulting from the stimulated soil nitrogen mineralization was responsible for the marginally decreased soil pH in the plastic-film mulched relative to the non-mulched soils, due to increased soil hydrothermal conditions. [ABSTRACT FROM AUTHOR]

Plastic-film mulch is widely used to increase soil temperature and reduce water evaporation in vegetable production. In China, it is also extensively used for growing grain crops, especially in temperature and rainfall limited areas. However, it remains unclear whether the technology is sustainable in terms of maintenance of soil organic carbon (SOC) balance. We assessed the effects of plastic-film mulch on the SOC balance in maize ( Zea mays L.) production in a range of cold semiarid environments. We imposed four treatments: (i) no plastic-film mulch or straw incorporation, (ii) plastic-film mulch, (iii) straw incorporation in soil without mulch, and (v) straw incorporation plus mulch, in ridge–furrow prepared fields at five sites along a hydrothermal gradient for up to six years. Maize root biomass across sites increased by 23–38% in mulched plots associated with the increase in aboveground biomass, indicating an increased SOC input, compared to that in non-mulched plots. The plastic-film mulch increased SOC mineralization, indicated by the stimulated decomposition of buried maize straw, and a 4–5% reduction in the concentration of light-fraction SOC (<1.8 g cm −3 ), but the total SOC concentration and stock in the 0–0.15 m soil layer did not change relative to no mulch after six years of continuous cropping. Plastic-film mulch did not affect the total non-cellulosic sugar content; however, it significantly increased the contribution of microbial-synthesized sugars to the total non-cellulosic sugars, indicating an intensified microbial action on the SOC pool compared to no mulch. Straw incorporation increased the root biomass, light and total SOC concentrations and non-cellulosic sugars, and changed the non-cellulosic sugar composition. We conclude that the increase in soil temperature and moisture by use of plastic-film mulch enhances productivity, but importantly maintains the SOC level in temperature- and rainfall-limited semiarid regions by balancing the increased SOC mineralization with increased root-derived C input. [ABSTRACT FROM AUTHOR]

• Heavy thinning reduced soil respiration (SR) and its components in the sixth to eighth year after thinning. • Thinning improved the temperature sensitivity for heterotrophic respiration (HR). • Thinning reduced the temperature sensitivity for autotrophic respiration (AR). • Decreases in SR, HR, and AR were related to microbial biomass and fine root biomass. Mounting evidence has indicated that forest thinning would increase soil respiration (SR) in the early stage (c. < 5 years) after thinning. However, the responses of SR and its components to different thinning intensities in the long-term have not been sufficiently studied. In April 2010, four levels of thinning intensities including control (CK, no thinning), light thinning (LT, 20% basal are removed), moderate thinning (MT, 40% basal area removed), and heavy thinning (HT, 60% basal area removed) were conducted in a Chinese pine (Pinus tabulaeformis) plantation in northern China. SR and its components were measured monthly in growing seasons (May to October) from 2016–2018. After 6–8 years of thinning, on average, HT significantly reduced SR by 24.56%, compared to the control. Declines in SR were ascribed to the decreased heterotrophic respiration (HR) and autotrophic respiration (AR) in HT plots, because heavy thinning inhibited soil nutrients, microbial biomass carbon (MBC), and fine root biomass (FRB). Thinning increased temperature sensitivity (Q 10) of HR (CK = 2.24, LT = 2.58, MT = 2.82, HT = 2.51), but decreased the Q 10 values of AR (CK = 2.76, LT = 1.14, MT = 1.82, HT = 2.23). Soil moisture had a positive relationship with HR but did not correlate with AR (expect for MT). In addition, two-factor models combining soil temperature and soil moisture explained 40–64% and 1–12% of variation in the HR and AR, respectively. The effects of thinning on soil respiration and its components varied substantially over time. Our study highlights that fine root and microbial biomass should be incorporated into biogeochemical models when accurately predicting long-term effects of thinning on soil respiration and its components. [ABSTRACT FROM AUTHOR]

• SOC labile and stable fractions were measured across 30-year grassland restoration. • There are two turning points of SOC in the 30-year revegetation process. • The increase of SOC mainly result from the enhance of soil stable organic C. • Root cellulose is the primary factor to the changes of SOC sequestration. Revegetation is an effective means to increase the soil organic carbon (SOC) stock and reverse SOC loss worldwide. Restoration through grasslands has great potential primarily due to the contribution of the root system. However, the impacts of grassland restoration remain uncertain, as current understandings of the direction and magnitude of changes in different SOC fractions and the influence of root properties on SOC are still unclear. To address this problem, we conducted a field study to investigate variations in SOC fractions and root properties under different grassland restoration times (1, 5, 10, 15, 25 and 30 years following restoration) in the Loess Plateau, China. Specifically, we measured fractions of soil labile organic carbon including microbial biomass carbon (MBC) and dissolved organic carbon (DOC) and fractions of soil stable organic C including humus carbon (HS), fulvic acid carbon (FA) and humic acid carbon (HA) in the 1 m soil profile. Furthermore, we evaluated root biomass, root C, root lignin and cellulose as potential drivers of SOC patterns. We found that SOC, soil labile organic C and soil stable organic C fractions generally increased with the revegetation time, except for brief decreases at the 5- and 15-year marks. Across the entire period (year 1 to 30), the proportions of HS and FA to SOC increased by 10.64% and 14.72% at 30 years, respectively, while the ratios of MBC and DOC to SOC were relatively stable. The average SOC accumulation rate was 0.72 Mg ha−1 yr−1 in the 1 m soil profile over the 30-year grassland revegetation period. The average rate of change of FA (0.67 Mg ha−1 yr−1) was higher than that of the HA, HS and soil labile organic C fractions, which indicated that SOC stability increased and SOC accumulation was mainly derived from the enhancement of FA. Decreases in root biomass and cellulose storage drove reductions in SOC fraction stores with soil depth. The root cellulose exerted significant influences on the SOC and SOC fractions, especially on FA (R2 = 0.82, p < 0.01). These findings show that grassland restoration plays an important role in improving and increasing SOC; in particular, the increase of FA results from the augmentations of root cellulose. [ABSTRACT FROM AUTHOR]

The increasing concentration of surface ozone (O 3 ) was observed during recent decades in the world, which affects tree roots and forest soils. Meanwhile, the impact of ozone on tree roots is greatly affected by soil condition. However, there is a lack of knowledge about the possible effects of ozone on tree roots and soil processes. In this study, The influences of surface ozone (O 3 ) stress on the root biomass, morphology, nutrients, soil properties, and soil enzyme activity of Elaeocarpus sylvestris and Michelia chapensis seedlings were examined at four O 3 concentrations (charcoal-filtered air, 1 × O 3 air, 2 × O 3 air, and 4 × O 3 air). Elevated O 3 concentrations were found to significantly increase the root C content, N content, C/P ratio, and N/P ratio, and significantly decrease the root biomass, number of root tips, and root C/N ratio of both species. The soil organic matter content, pH, total N content, and urease and catalase activities of both species tended to increase. The limitation in root growth and responses in the root structure of E. sylvestris induced by elevated O 3 concentrations led to increased bulk density and decreased soil porosity and void ratio. These profound effects of O 3 concentrations on the roots and soil characteristics of these two species underscore the importance of research in O 3 science.

The effect of warming on soil nitrogen (N) pools and turnover in agro-ecosystems has rarely been investigated, particularly in middle-high latitudes where the temperature is predicted to increase more than that in low latitudes. In this study, we determined the dynamics of soil inorganic N pools and the net N mineralization in an agro-ecosystem from 2013 to 2015 in a field warming experiment in Northeast China. The objectives were to examine the effects of warming on soil N turnover and determine how the effects differ in the growing versus the non-growing seasons. We hypothesized that experimental warming would increase N mineralization and the inorganic N pools, and the effects of warming would be greater in the non-growing season than those in the growing season. In contrast to these predictions, the soil N mineralization and inorganic N pools in the soil solution were not affected by experimental warming either within or across year and season. The nitrification rate was 0.14 mg kg -1  d -1 higher, but the ammonification rate was 0.17 mg kg -1  d -1 lower in the growing season than that in the non-growing season. When averaged across all sources of variation, the net mineralization rate of the soil N was 0.09 mg kg -1  d -1 in both the control and warming treatments, while the total inorganic N in the soil solution was 34 and 41 mg kg -1 , respectively. Both the nitrification and ammonification processes were regulated by soil moisture and/or root biomass, which was not affected by warming. These results suggest that soil N turnover and availability will be less sensitive to future global warming in this middle-high latitude agro-ecosystem., (Copyright © 2018. Published by Elsevier B.V.)

Background and Objectives: Sweet potato [Ipomoea batatas (L.) Lam] is an important locally grown cash crop in China; it was demonstrated to suppress the invasive plant Mikania micrantha (M. micrantha) H.B.K through strong competitiveness, but its allelopathic effects on this weed were unknown. The present study aimed to explore the allelopathic potential of sweet potato on M. micrantha., Materials and Methods: The allelopathic effects of water extracts and soil incorporation from leaves of three sweet potato cultivars (SP1, SP0 and SP9) on the sprout seedling growth of invasive plant M. micrantha in Yunnan Province, China, were studied under laboratory and greenhouse conditions., Results: Stem length, root biomass, aboveground biomass and total biomass of M. micrantha were significantly reduced with increasing concentration in both leaf water extracts and leaf soil incorporation of three sweet potato cultivars. Among these, SP1 had the strongest inhibition and the next highest impact was from SP0 with the lowest effect from SP9. The highest inhibition rates were seen for root biomass, followed by total biomass, whereas the lowest impact was on aboveground biomass. The strong correspondence between results for both leaf water extracts and leaf soil incorporation provided a good demonstration that compounds produced by sweet potato have allelopathic effects on M. micrantha. The general inhibition of M. micrantha by sweet potato followed the order among the three sweet potato cultivars tested as SP1, SP0 and SP9. Moreover, the synthetical allelopathic indices of leaf soil incorporation of three cultivars on M. micrantha were generally higher than these of leaf water extracts., Conclusion: Competition and allelopathy have primarily been seen as separate ecological weed management tools, but as these have demonstrated in the case of sweet potato where both mechanisms inhibit weed growth, there is potential for synergism between competition and allelopathy in the reduction of weed infestations.