Pseudoacacia Plantations Research Articles

Changes in Soil Microbial Carbon-Degrading Enzymes and Their Relationships with Carbon Pool Components During the Restoration Process of Robinia pseudoacacia

To reveal the change in the characteristics of soil microbial C-degrading enzyme activities and the response to the components of C during the restoration process of Robinia pseudoacacia forests in the Loess Plateau, the components of the soil C pool, C-degrading enzyme activities, and microbial metabolic entropy of R. pseudoacacia in different restoration stages were studied, and the response relationship between C-degrading enzymes and soil C components was explored. The results showed that the microbial respiration (MR) first increased and then decreased with the restored years. We found that the microbial metabolic entropy (qCO2) decreased significantly with the restored years, but the microbial entropy (qMB) increased. Soil C-degrading enzymes increased significantly in the early-stage restoration of R. pseudoacacia; however, oxidizing enzymes (PO and PER) and cellobiohydrolase (CBH) decreased in the late stage of restoration. The soil organic C and recalcitrant organic C increased significantly with the restored years; however, there was no significant difference for the labile organic C. Correlation analysis and the partial least squares-path model (PLS-PM) showed that soil C-degrading enzymes and C components were significantly correlated with microbial respiration and entropy (qCO2 and qMB), respectively. The hydrolytic enzyme (BG+CBH) was significantly positively correlated with SOC, microbial biomass C, qMB, and recalcitrant and labile organic C. The oxidizing enzyme (PO+PER) was significantly positively correlated with the soil clay and qCO2. In addition, the recalcitrant organic C was the key driver of soil microbial metabolism affected by vegetation restoration. Overall, the ecosystem of R. pseudoacacia plantations would gradually stabilize with the increase in restored years and significantly increase the sequestration effect of soil C. These results will be helpful to understand the transformation rule and regulation mechanism of the soil C pool in vulnerable habitats and provide scientific basis for the restoration and management of vegetation in the Loess Plateau.

Soil ecoenzymatic stoichiometry reveals microbial phosphorus limitation after vegetation restoration on the Loess Plateau, China

Exploring the limitations of soil microbial nutrient metabolism would help to understand the adaptability and response mechanisms of soil microbes in semi-arid ecosystems. Soil ecoenzymatic stoichiometry is conducive to quantifying the nutrient limitations of microorganisms. To quantify microbial nutrient limitation during plant restoration, we measured soil physicochemical properties, microbial biomass, and the activities of four enzymes (ꞵ-1,4-glucosidase, leucine aminopeptidase, ꞵ-1,4-N-acetylglucosaminidase, and alkaline phosphatase) in the soils of the northern Loess Plateau. Vegetation restoration patterns significantly affected soil properties, microbial biomass, enzymatic activity, and associated stoichiometry. Soil enzymatic activity increased significantly after vegetation restoration, especially in Robinia pseudoacacia plantations (RP). Correlation analysis showed that soil nutrients (C and N), moisture and pH were significantly correlated with ecoenzymatic activities and their stoichiometries. Vector-threshold element ratio (VT) model analysis revealed that microbial nutrient metabolism was limited by P, and soil microbial C limitation was significantly weakened after vegetation restoration, particularly in RP. Correlation analysis indicated that microbial nutrient limitations represented by the VT model were significantly correlated with soil moisture, nutrients, and associated stoichiometry. Therefore, the soil microbial community was mainly limited by P rather than N in vegetation restoration on the Loess Plateau via the VT model, and this limitation was primarily associated with the variation in soil properties. In addition, the soil microbial C limitation was significantly negatively correlated with microbial nutrient (P or N) limitation, which illustrated that soil microbial nutrient metabolism has strong stoichiometric homeostasis.

Changes in litter traits induced by vegetation restoration accelerate litter decomposition in Robinia pseudoacacia plantations

AbstractThe chemical traits of litter are among the most critical factors that affect its decomposition. During vegetation restoration of planted forests, increasing age of the planted species and succession of the understory species may lead to significant changes in litter traits. However, it is unclear how these changes occur and how they affect litter decomposition. Therefore, we studied the decomposition of litter from four Robinia pseudoacacia plantations in the Loess Plateau in China with stand ages of 10–43 years using an indoor simulation test. We measured changes in litter substrate quality and chemical diversity, structural properties of the litter microbial community, activity of litter enzymes, and mixed decomposition effects during vegetation restoration. Their relationships to changes in litter decomposition rate were analyzed using structural equation modeling. Improvements in substrate quality of forest litter induced by vegetation restoration drove changes in fungal community composition during late decomposition (day 358), which in turn increased the activity of lignin‐decomposing enzymes and ultimately accelerated litter decomposition. At the same time, decreases in the chemical diversity of forest litter induced by vegetation restoration reduced the diversity of litter fungi during middle and late decomposition (days 182 and 358). This caused significant negative mixed decomposition effects, thereby inhibiting litter decomposition. However, improvements in litter substrate quality dominated the changes in litter decomposition rate, and the decomposition rate of R. pseudoacacia plantation litter thus increased over the course of vegetation restoration.

КАРАГАНА ДРЕВОВИДНАЯ (CARAGANA ARBORESCENS LAM.) КАК КУСТАРНИКОВАЯ ПОРОДА ПРИ БИОЛОГИЧЕСКОЙ РЕКУЛЬТИВАЦИИ ТЕХНОГЕННЫХ ЛАНДШАФТОВ

Minerals are considered one of the components of the economy of any country. The negative side of technogenesis is the emergence of technogenic landscapes with developed exogenous processes. To prevent and eliminate them, biological reclamation is carried out, the most promising direction of which is forest reclamation. In forest reclamation, preference is given to soil-improving tree and shrub species. The research was carried out in the stands of the Caragana arborescens (Caragana arborescens Lam.) on the dumps of the Kursk magnetic anomaly in the Belgorod region of the Central Federal District of Russia. The work on the test areas was carried out according to generally accepted methods. On the sandy-chalk dump of loose overburden, the karagany cultures completely died by the age of 38. On a two-component technozem, with surface application of a fertile layer on a sand-chalk mixture, karagana showed positive results. The maximum safety (84.2-82.0%) is typical for the first four years of karagana's life. It does not depend much on environmental conditions. The growth of shoots in karagana begins only in the second decade of May. Shoots grow most actively in the third decade of May - 43.8%. The average biomass of one karagana bush at the age of 6 years is 503 g. At the same time, the average mass of one specimen of Robinia pseudoacacia is 2264 g. The total supply of phytomass in the 9-year-old karagana plantation is 69.5 c/ha, which is 2.6 times less than in the robinia pseudoacacia plantation. The reclamation role of caragana leaves is insignificant. The tree-like karagana is rich in mineral elements, which is reflected in their accumulation in substrates. The reserves of nitrogen – 4.06% and calcium – 1.46% are especially large in Karagan. The dump is located in the mining production zone, so the iron content in the assimilating organs of karagany exceeds 4 times the content on zonal soils, and titanium - 1.8 times. A significant part of the chemical elements falls on the green parts of plants. Caragana leaves are supplied with: nitrogen - 26.64 kg /ha, potassium - 1.78 kg/ ha, calcium - 17.52 kg/ ha and magnesium - 4.56 kg/ha. More than half of the chemical elements of root systems accumulate in small roots. When they die off, they enter directly into the substrate. The tree-like karagana can be recommended for forest reclamation of technogenically disturbed lands when mixed with more valuable tree and shrub species

Response of Root-Associated Bacterial Communities to Different Degrees of Soft Rot Damage in Amorphophallus konjac Under a Robinia pseudoacacia Plantation.

Bacterial soft rot is a destructive disease that restricts the development of the konjac (Amorphophallus konjac K. Koch ex N.E.Br) industry. The objective of this study was to investigate how soft rot disease affects bacterial communities associated with the roots of konjac plants growing under a pure Robinia pseudoacacia plantation. Three sampling sites affected by different degrees of soft rot damage were selected based on the disease incidence [0%, non-diseased (ND); 4.2%, moderately diseased (MD); and 18.6%, highly diseased (HD)]. The variation in soil and root bacterial diversity and community composition among the sampling sites was determined by Illumina HiSeq sequencing of the V3–V4 hypervariable regions of the bacterial 16S rRNA gene. The results showed that the contents of soil organic matter and available nutrients (N, P, and K) increased with increasing damage degree, whereas higher damage degree resulted in lower soil pH and enzymatic activity (sucrase, urease, catalase, and polyphenol oxidase). The composition of root-associated bacterial communities differed among the three sampling sites. Proteobacteria was the most dominant bacterial phylum in all soil and root samples. Pseudomonas, Bacillus, Rhizobium, and Streptomyces were the most abundant in all samples from the ND sites, whereas Pectobacterium carotovorum and Serratia were predominant in the samples from the MD and HD sites. The abundance and alpha diversity of root-associated bacteria were significantly higher (p < 0.05) in the ND sites than in the diseased sites. The results suggested pronounced differences in the abundance, alpha diversity, and community composition of bacteria associated with the roots of konjac plants affected by different degrees of soft rot damage. Such differences in bacterial community structure were related to dynamic changes in soil variables, especially soil available potassium content, sucrase activity, and urease activity. Analysis of the dominant root-associated bacterial taxa offers an approach to predict the damage degree due to soft rot in konjac and provides evidence for the prevention of this soil-borne disease via microecological regulation.

Response of water use efficiency and plant-soil C:N:P stoichiometry to stand quality in Robinia pseudoacacia on the Loess Plateau of China

The evaluation of stand quality is of great significance for forest management and sustainable development. Water use efficiency (WUE) and the carbon (C), nitrogen (N), and phosphorus (P) stoichiometric characteristics of plants and soil are important indexes used to evaluate plant water and nutrients adaptation strategies. However, little is known about the effects of stand quality on WUE and plant‑soil C:N:P stoichiometry. In this study, the growth characteristics of Robinia pseudoacacia plantations and understory plants in an age series of 8-, 15-, 25-, and 35-year-old stands were investigated, and the leaf-level WUE and C:N:P stoichiometry in plants and soil were measured on the Loess Plateau. The results showed that the species richness, Shannon-Weiner diversity index, and evenness index reached their peaks in the 35-year-old stands with increasing afforestation age. WUE reached its highest value in the 35-year-old stands but was only significantly higher than that in the 8-year-old stands. Stand age had different effects on C, N, and P nutrients and stoichiometry in leaves, fine roots, and soil. The most obvious trend was that soil total P decreased significantly with increasing afforestation age, and the leaf N:P ratio was greater than 16 in the four stand ages, which indicated that P was the main limiting factor in R. pseudoacacia plantations. Leaf nutrients and stoichiometry are closely related to forest growth characteristics, while root nutrients and stoichiometry are more related to understory plant composition and diversity. Importantly, the WUE had no significant change with the increase in the stand quality index, and the response of soil stoichiometry to stand quality was stronger than that of plant stoichiometry. These results help us further understand coordinated plant-soil restoration after afforestation.

The response of soil microbial communities to soil erodibility depends on the plant and soil properties in semiarid regions

AbstractNatural succession and afforestation are the two main restoration methods of degraded soil in semiarid and arid regions. Up to now, the soil microbial communities and their roles in soil erodibility have been unclear. Our work aimed to evaluate the effects of ecological restoration on the diversity and composition of soil microbial communities at depths of 0–20 cm and their interaction with soil erodibility. Four main restoration types, natural succession land andPinus tabuliformis,Armeniaca sibirica, andRobinia pseudoacaciaplantations were chosen. Restoration with different vegetation communities decreased the soil erodibilityK‐factor (K) by 13.37–20.64%. Proteobacteria, Acidobacteria, and Actinobacteria were dominant bacterial phyla at all sites. The dominant fungal phyla were Basidiomycota, Ascomycota, and Zygomycota. However, there were obvious differences in bacterial and fungal communities among restoration types due to variations in plant and soil properties. Redundancy analysis showed that the soil microbial communities explained 67.30% of the total variance in soil erodibility. Bacterial communities mainly affect the microaggregate formation, whereas fungal communities have a greater effect on macroaggregate formation. Additionally, the structural equation modeling also suggests that vegetation characteristics, soil organic carbon, and fungal communities, and macroaggregates (&gt; 5 mm) have positive effects on mean weight diameter. Therefore, the combination of vegetation community, soil properties, and microbial communities improves the soil structure against erosion in this area.

Estimation and testing of linkages between forest structure and rainfall interception characteristics of a Robinia pseudoacacia plantation on China\u2019s Loess Plateau

Understanding the interaction between canopy structure and the parameters of interception loss is essential in predicting the variations in partitioning rainfall and water resources as affected by changes in canopy structure and in implementing water-based management in semiarid forest plantations. In this study, seasonal variations in rainfall interception loss and canopy storage capacity as driven by canopy structure were predicted and the linkages were tested using seasonal filed measurements. The study was conducted in nine 50 m × 50 m Robinia pseudoacacia plots in the semiarid region of China’s Loess Plateau. Gross rainfall, throughfall and stemflow were measured in seasons with and without leaves in 2015 and 2016. Results show that measured average interception loss for the nine plots were 17.9% and 9.4% of gross rainfall during periods with leaves (the growing season) and without leaves, respectively. Average canopy storage capacity estimated using an indirect method was 1.3 mm in the growing season and 0.2 mm in the leafless season. Correlations of relative interception loss and canopy storage capacity to canopy variables were highest for leaf/wood area index (LAI/WAI) and canopy cover, followed by bark area, basal area, tree height and stand density. Combined canopy cover, leaf/wood area index and bark area multiple regression models of interception loss and canopy storage capacity were established for the growing season and in the leafless season in 2015. It explained 97% and 96% of the variations in relative interception loss during seasons with and without leaves, respectively. It also explained 98% and 99% of the variations in canopy storage capacity during seasons with and without leaves, respectively. The empirical regression models were validated using field data collected in 2016. The models satisfactorily predicted relative interception loss and canopy storage capacity during seasons with and without leaves. This study provides greater understanding about the effects of changes in tree canopy structure (e.g., dieback or mortality) on hydrological processes.

Estimation of ecosystem evapotranspiration in aRobinia pseudoacaciaL. plantation with the use of the eddy covariance technique and modeling approaches

AbstractΤhe eddy covariance technique provides reliable ecosystem-level evapotranspiration (ET) measurements. These measurements, when combined with models and satellite products, could offer high spatiotemporal coverage and valuable mechanistic interpretation of the underlying processes. This study address one-year eddy covariance measurements from a Robinia pseudoacacia site in Northern Greece and remote sensing products: we (a) provide a medium-term description of daily ET fluxes for a R. pseudoacacia plantation in a degraded land, (b) assess the contribution of environmental drivers (e.g. net radiation, temperature etc.) on ET and (c) evaluate a simple satellite and meteorological driven model for larger-scale applications, based on the Land Surface Water Index (LSWI) and the FAO approach. R. pseudoacacia was found to have quite high water consumption, especially during leaf expansion. Net radiation and soil water content had the greatest effect on ecosystem evapotranspiration. LSWI was found to be correlated with both soil water content and evapotranspiration. Its use as an index for water limitation in models leads to high accuracy when compared to ET measurements. Our results (a) provide a significant contribution to the assessment of R. pseudoacacia ecophysiology and (b) highlight the potential of accurate ecosystem ET estimation with simple modeling approaches.

Response of root nutrient resorption strategies to rhizosphere soil microbial nutrient utilization along Robinia pseudoacacia plantation chronosequence

Understanding root nutrient resorption strategies and their drivers is essential to explore plant nutrient acquisition strategies in restored ecosystems. However, the interaction between root nutrient resorption and the nutrient utilization of rhizosphere soil microorganisms in restored ecosystems has yet to be determined. In this study, we investigated plant fine roots and rhizosphere soils in Robinia pseudoacacia plantations at four stages of forest succession (14, 20, 30, and 45 years of age) on the Loess Plateau in China. We studied the characteristics of root nitrogen and phosphorus resorption efficiencies (NRE and PRE) at different recovery stages and analyzed the relationships among nutrient resorption and rhizosphere soil variables (nutrients and microbial communities). We detected a tendency of an initial reduction and subsequent increase in root NRE and PRE with stand age (the lowest value at 30-y sites), whereas the nutrient contents of rhizosphere soil increased with stand age, and soil available nutrients initially increased and then declined. The diversity of rhizosphere soil microorganisms also showed an initial increase and subsequent decline. Proteobacteria were considered to be at an advantage during the nutrient-rich stage of restoration (30-y sites), whereas Acidobacteria were found to be dominant during the low-nutrient restoration stage (14-y sites). Furthermore, the microbial nutrient utilization ratios of soil microbial biomass carbon: soil organic carbon, microbial biomass nitrogen: soil total nitrogen, and microbial biomass phosphorus: soil total phosphorus also showed an initial increase and then decreased (with peaks at the 30-y sites). Redundancy analysis indicated that the nutrient contents of rhizosphere soil were significantly related to microbial communities and correlation analysis revealed that microbial nutrient-use efficiencies were significantly related to rhizosphere soil nutrient contents and the dominant microbial communities. We also detected a significant negative correlation between root nutrient resorption and microbial nutrient utilization. Partial least squares path modeling revealed that forest restoration influences the contents of nutrients in rhizosphere soil and the composition of microbial communities, whereas microbial biomass and nutrient utilization efficiency were shown to have a negative effect on root resorption efficiency. Based on our findings, we propose that the highly conservative nutrient utilization strategies of the rhizosphere soil microbial community may negatively drive root nutrient resorption strategies during the succession of R. pseudoacacia.

Seasonal Variations in Carbon, Nitrogen, and Phosphorus Stoichiometry of a Robinia pseudoacacia Plantation on the Loess Hilly Region, China

Seasonal variations in stoichiometry are a crucial regulatory mechanism for plant communities that respond to environmental changes. However, the seasonal characteristics of stoichiometry in plants, litter, and soil are poorly understood, especially in plantation ecosystems. Therefore, we explored the seasonal variations of C, N, and P contents and ratios between plants, litter, and soil of a Robinia pseudoacacia plantation on the Loess Plateau in China in 2017. The results indicate that the C, N, P contents and ratios in plants, litter and soil showed different seasonal patterns. The N and P contents of tree and shrub leaves substantially decreased over the growing season, while the C:N, C:P, and N:P ratios exhibited the opposite trend. The utilization efficiency of the N and P elements by trees and shrubs gradually increased with the change of the growing season. These results suggest that the C:N:P stoichiometry of plants was more sensitive to seasonal changes than the litter and soil; therefore, the potential impacts of time should be considered when using stoichiometry to explore the utilization of plant nutrients. Additionally, the P content between tree leaves and soil and the N content between herb leaves and soil were significantly positively correlated, indicating that the growth of the tree and herb layer in the R. pseudoacacia plantation in the area was restricted by P and N, respectively. Meanwhile, the N content in the leaves between trees and herbs showed a significant negative correlation, indicating that N competition existed between R. pseudoacacia and understory herbs, which was not conducive to the effective use of environmental resources by the R. pseudoacacia plantation ecosystem. This study contributes to vegetation restoration and plantation management on the Loess Plateau and provides basic information for global stoichiometric analyses.

Nutrients of green and senesced leaves of a Robinia pseudoacacia plantation along a latitudinal gradient on the Loess Plateau, China

Plantations have been widely established to improve ecosystem services and functioning. Black locust, Robinia pseudoacacia L. is a common, widely planted species to control soil erosion on the Loess Plateau. Previous studies have focused on economic values but the interactions between soil and plant carbon (C), nitrogen (N) and phosphorus (P) remain unknown. Investigating variations of soil, green and senesced leaf C, N and P levels in R. pseudoacacia along a latitudinal gradient is useful to understanding its ecological functions. The results show that soil C, N and senesced leaf N and P significantly decreased with an increase in latitude, but there were no significant changes in the senesced leaf C and soil P. The resorption efficiency of N was related with latitude and soil N levels, and the relation between green leaf N and soil N was significant. These relations suggest that soil N was the key in affecting green leaf N levels. At higher latitudes, senesced leaves had lower N levels associated with higher N resorption efficiency to maintain a stable N content in green leaves. With a decrease of soil N, R. pseudoacacia can enhance N resorption efficiency to meet the demand of growth. Thus, it is an important species for reforestation, especially in nutrient-poor environments.

Quantifying the effects of Robinia pseudoacacia afforestation on plant community structure from a functional perspective: New prospects for management practices on the hilly and gullied Loess Plateau, China

Robinia pseudoacacia is regarded as a valuable but problematic plant due to its positive and negative environmental effects. A comprehensive and mechanistic understanding of the effects of R. pseudoacacia afforestation on ecosystems and striking a balance between ecosystem safety and functioning and R. pseudoacacia naturalization are crucially important. To achieve these goals, studying the community functional structure of R. pseudoacacia plantations is an essential prerequisite that remains understudied. Through quantifying and comparing the functional structure of R. pseudoacacia plantations and naturally restored communities relating to soil erosion control and plant ecology strategies along a 10–40-year chronosequence on the hilly and gullied Loess Plateau, China, we assessed the effects of R. pseudoacacia afforestation on plant community structure from a functional perspective. We found significant differences among restoration strategies in all the functional composition indices but only functional divergence (FDiv) indices, suggesting that the afforestation practice had a great impact on functional composition but not on functional diversity. Specifically, the plantations had relatively high community-weighted means (CWMs) of specific leaf area (SLA), plant height (PH), seed production, seed mass, root mean diameter, clonality and resprouting capacity and high FDivs of the leaf-height-seed scheme and persistence traits, partially suggesting that the exotic tree could naturalize and coexist with native plants in the study area. Moreover, the relatively high CWMs of woodiness, PH and SLA and high FDiv of erosion-control-related traits found in the plantations indicate that the plantations might have superiority in soil erosion control. R. pseudoacacia also had a homogenization effect on understory functional composition and divergence. Furthermore, we proposed a trait-based effect-and-response framework to find the balance, thus achieving sustainable coexistence of the exotic species with ecosystems. This study may provide new prospects for management practices of R. pseudoacacia plantations and a robust scaffold to maintain safe, resilient and functioning ecosystems.

Leaf nutrient resorption characteristics of Robinia pseudoacacia at different ages and their response to soil nutrient availability

To reveal nutrient resorption characteristics of Robinia pseudoacacia and their driving factors in hilly and gully regions, we measured the concentration of total nitrogen and total phosphorus in leaves and the concentrations and stoichiometry of organic carbon, total nitrogen, total phospho-rus, ammonium, nitrate and available phosphorus in soils of R. pseudoacacia plantations with different stand ages. We analyzed the relationship between leaf nitrogen and phosphorus resorption efficiencies and soil nutrient characteristics. The nutrients in plants and soil changed significantly with stand ages. The total and available phosphorus concentrations were low in the soil. Nitrogen resorption efficiency first increased and then decreased with the increases of stand age, with a range of 48.2%-54.0% and a mean value of 48.5%. Phosphorus resorption efficiency increased significantly with stand age, with a range of 45.2%-49.4% and a mean value of 46.9%. Nitrogen resorption efficiency showed negative response to soil nitrogen and N:P. Phosphorus resorption efficiency was significantly positively correlated to soil N:P and negatively correlated to soil available phosphorus. Our results indicated that soil nutrient availability negatively drove nutrient resorption efficiency. The strategies of leaf nutrient resorption responded strongly to soil N:P due to the N2-fixing effect and P-limitation of R. pseudoacacia.

Organic carbon, nitrogen accumulation, and soil aggregate dynamics as affected by vegetation restoration patterns in the Loess Plateau of China

Afforestation and natural succession on former croplands are typical measures used for revegetation in ecologically fragile areas worldwide. However, there are few studies regarding the differences between natural grasslands and artificial plantations in terms of soil aggregate dynamics, organic carbon (OC), and total nitrogen (TN) accumulation. We sampled soils from farmland (FL) and from two vegetation restoration patterns [Robinia pseudoacacia plantations (RP) and natural grasslands (NG)] of two age classes (18 and 42 years) on the Loess Plateau of China. The size-distribution and stability of soil aggregates, as well as OC and TN stocks in bulk soil and aggregates were measured. Revegetation of FL resulted in considerable increases in bulk soil OC and TN stocks at depths of 0–40 cm: OC increased by 101.3% in NG and 75.5% in RP, and TN by 77.5% in NG and 106.1% in RP. Bulk soil OC stocks in 18- and 42-year-old NG at depths of 0–40 cm were 9.0% and 17.4% higher, respectively, than those in RP of the same age. Conversely, the 18- and 42-year-old RP had 18.6% and 16.4% higher TN stocks than those in NG of the same age. Microaggregates dominated aggregate-size distribution in all land uses and had the highest OC and TN stocks. NG soils had higher proportions of macroaggregates and mesoaggregates and greater aggregate stability than RP soils of the same restoration age. However, there was no significant difference in macroaggregate- and mesoaggregate-associated OC and TN stocks between NG soils and RP soils of the same age. Furthermore, bulk soil OC and TN stocks were strongly associated with aggregate stability. Bulk soil OC stocks were positively correlated with mesoaggregate-associated OC stocks, whereas TN stocks in bulk soil were closely related to macroaggregate-associated TN stocks. Overall, the results of this study suggest that restoration with RP favors soil N accumulation, whereas NG may be optimal for increasing C sequestration and stabilizing soil aggregates in the Loess Plateau.

Hydrological functions of litters under five typical plantations in southern and northern mountains of Lanzhou City, Northwest China

Combined with field observation and indoor water immersion test, water holding characteristics of litters from five typical plantations (Platycladus orientalis, Robinia pseudoacacia, Populus alba var. pyramidalis, P. orientalis+R. pseudoacacia, P. alba var. pyramidalis+R. pseudoacacia) in southern and northern mountains of Lanzhou City were examined. Results showed that litter mass under the plantations ranged from 13.50 to 47.01 t·hm-2, with an order of P. alba var. pyramidalis+R. pseudoacacia＞P. orientalis+R. pseudoacacia＞P. orientalis＞R. pseudoacacia＞P. alba var. pyramidalis. The percentage of un-decomposed litters was greater than that of semi-decomposed litters in all plantations except for P. orientalis plantations. The maximum water-holding rate of litters ranged from 190.8% to 262.7%, with the greatest value in the P. alba var. pyramidalis+R. pseudoa-cacia and the lowest in P. orientalis plantations. The maximum water-holding capacity of litters was 35.29-123.59 t·hm-2, with an order of P. alba var. pyramidalis+R. pseudoacacia＞P. orientalis+R. pseudoacacia＞R. pseudoacacia＞P. orientalis＞P. alba var. pyramidalis. Litter water absorption rate declined linearly within the first hour, and then decreased slowly. Semi-decomposed litters had a higher water-absorption rate than un-decomposed litters. The maximum water retaining amount and effective retaining amount of the litters were P. alba var. pyramidalis+R. pseudoacacia＞P. orientalis+R. pseudoacacia＞P. orientalis＞R. pseudoacacia＞P. alba var. pyramidalis. P. alba var. pyramidalis+R. pseudoacacia had the highest effective retaining rate. P. alba var. pyramidalis+R. pseudoacacia plantation had highest capacity for soil and water conservation in southern and northern mountains of Lanzhou City.

Kinetic parameters and temperature sensitivity of soil nitrogen and phosphorus transforming enzymes in Robinia pseudoacacia plantations under different vegetation zones on the Loess Plateau, China

Soil enzymes are catalysts for organic matter decomposition, the kinetic characteristics of which are important indicators of the catalytic performance of enzymes, with important role in evalua-ting soil health quality. We examined the responses of soil enzyme kinetic parameters to temperature change and the variation characteristics of their temperature sensitivity (Q10) in Robinia pseu-doacacia plantation soil under three different vegetation zones on the Loess Plateau. The results showed that the potential maximum reaction rate (Vmax) and the half-saturation constant (Km) of alanine transaminase (ALT), leucine aminopeptidase (LAP) and alkaline phosphatase (ALP) all increased linearly with the increasing incubation temperature. The zonal regularity of forest zone &gt; forest-steppe zone &gt; steppe zone was presented in Vmax. The temperature sensitivity of Vmax(Q10(Vmax)) ranged from 1.14 to 1.62, and the temperature sensitivity of Km(Q10(Km)) ranged from 1.05 to 1.47, with both values being lower in forest-steppe zone than other vegetation zones. In low and high temperature regions, the variations of Q10 in different soil enzymes differed among vegetation zones. Results from redundancy analysis showed that Q10 had a significant correlation with environmental variables, especially soil nutrients, indicating that Q10 would be affected by other environmental factors besides temperature.

How C:N:P stoichiometry in soils and plants responds to succession in Robinia pseudoacacia forests on the Loess Plateau, China

Ecological stoichiometry in plants and soils is an important indicator of element cycling and ecosystem stability that has been used to indicate nutrient limitation. However, the stoichiometric responses of plants and soils along a chronosequence on the Loess Plateau of China has not been studied. In this study, we chose four stand ages (5–10 years old, YF; 10–20 years old, NF; 30 years old, MF; 40–50 years old, OF) of Robinia pseudoacacia and abandoned land (AC) as research subjects to illustrate the C:N:P stoichiometry interactions among soils, plant tissues (green leaves, leaf litter, and roots), and soil microbes. The results demonstrated that the soil organic C, total N, soil microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP) contents increased significantly with afforestation age and reached a peak in the OF stand. The soil C:N ratio showed a significant increase from 9.2 to 13.1, while no significant differences were observed in the soil MBC:MBN ratios. Compared with the R. pseudoacacia forests, AC had the lowest soil C:N, N:P, and C:P ratios. Forest stand age had different influences on the C, N, and P contents in leaves, leaf litter, and fine roots. The most obvious trends were that the N contents in leaves and litter increased with stand age, indicating that old forests could accumulate more N in their leaves and litter. The leaf N:P ratio increased from 16 to 20 along the chronosequence, which demonstrated that P was the limiting element for the growth of R. pseudoacacia plantations on the Loess Plateau. The P demand increased with stand age. Therefore, our results indicated that R. pseudoacacia plantations enhance the C and N contents in soils and microbes in the first 30 years of growth and show an increasing demand for P over time. Therefore, attention should be paid to the application of phosphate fertilizer for the management of R. pseudoacacia plantations.

Legacies of past land use challenge grassland recovery – An example from dry grasslands on ancient burial mounds

Due to large-scale agricultural intensification, grasslands are often restricted to habitat islands in human-transformed landscapes. There are approximately half a million ancient burial mounds built by nomadic steppic tribes in the Eurasian steppe and forest steppe zones, which act as habitat islands for dry grassland vegetation. Land use intensification, such as arable farming and afforestation by non-native woody species are amongst the major threats for Eurasian dry grasslands, including grasslands on mounds. After the launch of the Good Agricultural and Environmental Condition framework of the European Union, in Hungary there is a tendency for ceasing crop production and cutting non-native woody plantations, in order to conserve these unique landmarks and restore the historical grassland vegetation on the mounds. In this study, restoration prospects of dry grassland habitats were studied on kurgans formerly covered by croplands andRobinia pseudoacaciaplantations. Soil and vegetation characteristics were studied in thespontaneously recovering grasslands. The following questions were addressed: 1; How does site history affect the spontaneous grassland recovery? 2; Do residual soil nutrients play a role in grassland recovery? In former croplands, excess phosphorus, while in formerRobiniaplantations, excess nitrogen was present in the soil even four years after the land use change and grassland vegetation was in an early or mid-successional stage both on the mounds. The results showed that, without proper management measures, recovery of grassland vegetation is slow on mounds formerly used as cropland or black locust plantation. However, restoration efforts, focused on the restoration of mounds formerly covered by croplands, can be more effective compared to the restoration of mounds formerly covered by forest plantations.

Water use characteristics of the common tree species in different plantation types in the Loess Plateau of China

Knowledge concerning the water use characteristics of revegetated species has profound implications for understanding soil–plant interaction mechanisms and guiding ecological restoration strategies in water-limited ecosystems. Although afforestation is an important way to improve ecosystem functions and services in degraded ecosystems, there is limited understanding about the water use characteristics of dominant species within and between different types of plantations. We investigated plant water use characteristics in three representative types of plantations on the Chinese Loess Plateau: mixed plantation consisting of three deciduous tree species Robinia pseudoacacia, Armeniaca sibirica and Ailanthus altissima (Mspa), pure R. pseudoacacia plantation (Pp) and pure A. sibirica plantation (Ps). We measured the leaf δ13C of the dominant species within each plantation type and the δ2H and δ18O of xylem and soil water within 400 cm of the soil surface. The results showed that three main species in the mixed plantation exhibited significant difference (p < 0.05) in proportional contributions of water sources, suggesting that the plants had water source segregation. A. sibirica in the mixed plantation utilized more proportional shallow soil water than that in the pure plantation and correspondingly lessened deep soil water depletion. However, no significant difference was found in the water uptake proportions of R. pseudoacacia between the different plantation types. The leaf δ13C values of the plant species in the mixed plantation were significantly higher than those in the pure plantations. The leaf δ13C values of R. pseudoacacia under different plantation were positively associated with SWCs, but this relationship was not observed in A. sibirica. These results indicate that plantation type affected plant water use characteristics with species-specific responses to plantation type and different water source competition effects between interspecific versus intraspecific competition.