Soil C, N, P and K stoichiometry affected by vegetation restoration patterns in the alpine region of the Loess Plateau, Northwest China

Biochar Addition Reduces the Effect of High Nitrogen on Soil-Microbial Stoichiometric Imbalance in Abandoned Grassland on the Loess Plateau of China

Progressively higher atmospheric nitrogen (N) deposition increasingly affects soil ecosystems' elemental cycling and stability. Biochar (BC) amendment has emerged as a possible means of preserving soil system stability. Nevertheless, the pattern of soil-microbial nutrient cycling and system stability in response to BC after high N deposition in ecologically sensitive regions remains uncertain. Therefore, we investigated the effects of high N (9 g N·m-2·a-1), BC (0, 20, 40 t·ha-1), and combinations of the treatments on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), microbial entropy (q MB), and stoichiometric imbalance (Cimb:Nimb:Pimb). We found that high N addition decreased topsoil (0-20 cm) TP, C:N, q MBN, and Cimb:Nimb values and increased TN, C:P, N:P, q MBP, Cimb:Pimb, and Nimb:Pimb values. However, BC addition increased 0-40 cm soil q MBC and Nimb:Pimb values and decreased q MBN, Cimb:Nimb, and Cimb:Pimb values. Meanwhile, high BC additions attenuated BC's promotion of soil-microbial nutrients. We observed that a mixture of high N and BC increased the 0-40 cm SOC and TP content, promoted the accumulation of MBN and MBP in the subsoil (20-40 cm), and decreased the topsoil Cimb:Pimb and Nimb:Pimb values compared to high N additions. The impact of high N and BC additions on N and P elements varied significantly between the different soil depths. In addition, redundancy analysis identified C:N, MBC, MBN, and C:P as pivotal factors affecting alterations in soil q MB and stoichiometric imbalance. Overall, adding BC reduced the negative impacts of high N deposition on the stability of soil-microbial systems in the Loess Plateau, suggesting a new approach for managing ecologically fragile areas.

Effects of vegetation restoration on soil aggregate characteristics and soil erodibility at gully head in Loess hilly and gully region

Vegetation restoration can be effective in containing gully head advance. However, the effect of vegetation restoration type on soil aggregate stability and erosion resistance at the head of the gully is unclear. In this study, five types of vegetation restoration-Pinus tabulaeformis (PT), Prunus sibirica (PS), Caragana korshinskii (CKS), Hippophae rhamnoides (HR), and natural grassland (NG, the dominant species is Leymus chinensis)-in the gully head were studied. Soil aggregate composition and nutrient contents in the 0-20, 20-40, and 40-60 cm soil layers were also determined, and the soil stability parameters were used to evaluate the soil conditions. The soil erodibility (K) was then determined by measuring the granulometric composition and organic matter. The results showed that the particle size of soil aggregates under different vegetation restoration types was mainly < 0.25 mm, and the percentage of aggregate disruption (PAD) was 22.08-76.07%. This further indicated that in Loess hilly and gully regions, water-stable aggregates were more reflective of the stability of soil aggregates in a gully head under vegetation restoration. The > 0.25 mm aggregates (R> 0.25 mm), geometric mean diameter (GMD), and mean weight diameter (MWD) values of the three soil layers were the highest in PT and the lowest in NG, while the opposite was true for fractal dimension (D) and the percentage of aggregate disruption (PAD). The K ranged from 0.052 to 0.065 t·hm2·h·MJ- 1 mm- 1·hm- 2. GMD can be used to characterize the anti-erosion ability of soil, and increasing the soil organic carbon, total nitrogen, and clay content can effectively reduce soil erodibility. The comprehensive analysis indicated that the soil aggregates of arbors planted in the gully head had the highest stability and anti-erodibility, followed by shrubs and grasslands, and can be used to evaluate vegetation restoration measures in gully heads.

Aeration Alleviated the Adverse Effects of Nitrogen Topdressing Reduction on Tomato Root Vigor, Photosynthetic Performance, and Fruit Development

To explore the compensation effect of aeration on tomato vegetative and reproductive growth in arid and semi-arid areas, a two-year field experiment was conducted with four micro-nano aeration ratios (0%, 5%, 10%, and 15%) and three nitrogen topdressing levels (80, 60, and 40 kg·ha-1) during the tomato growth period in Ningxia, China. The results showed that increasing the aeration ratio in the range of 0-15% was conducive to the enhancement of tomato root vigor (the ability of triphenyltetrazolium chloride to be reduced, 3-104%) and the leaf net photosynthetic rate (14-63%), favorable to the facilitation of plant dry matter accumulation (3-59%) and plant nitrogen accumulation (2-70%), and beneficial to the improvement of tomato yield (12-44%) and fruit quality. Interestingly, since the aeration ratio exceeded 10%, the increase in the aeration ratio showed no significant effects on the single-fruit weight, tomato yield, and fruit quality. Moreover, with aerated underground drip irrigation, properly reducing the traditional nitrogen topdressing level (80 kg·ha-1) by 25% was favorable for enhancing tomato root vigor (5-31%), increasing tomato yield (0.5-9%), and improving fruit soluble solid accumulation (2-5%) and soluble sugar formation (4-9%). Importantly, increasing the aeration ratio by 5% could compensate for the adverse effects of reducing the nitrogen topdressing level by 25% by improving the leaf photosynthetic rate, promoting plant dry matter accumulation, increasing tomato yield, and enhancing the soluble solid and soluble sugar accumulation in tomato fruits. Synthetically considering the decrease in the nitrogen topdressing amount, leading to plant growth promotion, a tomato yield increase, and fruit quality improvement, a favorable nitrogen topdressing level of 60 kg·ha-1 and the corresponding proper aeration ratio of 10% were suggested for tomato underground drip irrigation in the Yinbei Irrigation District of Ningxia.

Vegetation restoration improved aggregation stability and aggregated-associated carbon preservation in the karst areas of Guizhou Province, southwest China

Background

The change in the soil carbon bank is closely related to the carbon dioxide in the atmosphere, and the vegetation litter input can change the soil organic carbon content. However, due to various factors, such as soil type, climate, and plant species, the effects of vegetation restoration on the soil vary. Currently, research on aggregate-associated carbon has focused on single vegetation and soil surface layers, and the changes in soil aggregate stability and carbon sequestration under different vegetation restoration modes and in deeper soil layers remain unclear. Therefore, this study aimed to explore the differences and relationships between stability and the carbon preservation capacity (CPC) under different vegetation restoration modes and to clarify the main influencing factors of aggregate carbon preservation.

Methods

Grassland (GL), shrubland (SL), woodland (WL), and garden plots (GP) were sampled, and they were compared with farmland (FL) as the control. Soil samples of 0-40 cm were collected. The soil aggregate distribution, aggregate-associated organic carbon concentration, CPC, and stability indicators, including the mean weight diameter (MWD), fractal dimension (D), soil erodibility (K), and geometric mean diameter (GMD), were measured.

Results

The results showed that at 0-40 cm, vegetation restoration significantly increased the >2 mm aggregate proportions, aggregate stability, soil organic carbon (SOC) content, CPC, and soil erosion resistance. The >2 mm fractions of the GL and SL were at a significantly greater proportion at 0-40 cm than that of the other vegetation types but the CPC was only significantly different between 0 and 10 cm when compared with the other vegetation types (P < 0.05). The >2 mm aggregates showed a significant positive correlation with the CPC, MWD, and GMD (P < 0.01), and there was a significant negative correlation with the D and K (P < 0.05). The SOC and CPC of all the vegetation types were mainly distributed in the 0.25-2 mm and <0.25 mm aggregate fractions. The MWD, GMD, SOC, and CPC all gradually decreased with increasing soil depth. Overall, the effects of vegetation recovery on soil carbon sequestration and soil stability were related to vegetation type, aggregate particle size, and soil depth, and the GL and SL restoration patterns may be more suitable in this study area. Therefore, to improve the soil quality and the sequestration of organic carbon and reduce soil erosion, the protection of vegetation should be strengthened and the policy of returning farmland to forest should be prioritized.

Eco-Stoichiometric Characteristics of Rhizosphere and Bulk Soils of Smilax china L. along Vertical Zone Spectrum of Fanjing Mountain

To explore the correlations between nutrients and stoichiometric characteristics in the rhizosphere and bulk soils of understory Smilax china L. in forest ecosystems at different altitudes and to clarify the rhizosphere effect of understory vegetation in forest ecosystems and its response strategy to altitude, providing a theoretical basis for better forest ecological environment protection and high-quality development in Fanjing Mountain. Understory Smilax china L. at four different altitudes were selected, with the differences and influencing factors of carbon (C), nitrogen (N), phosphorus (P) and potassium (K) mass fractions and stoichiometric ratios in their rhizosphere and bulk soils analyzed. The average mass fractions of total C, total N and alkali-hydrolyzed N in the rhizosphere and bulk soils of Smilax china L. at different altitudes were 224.43 and 181.55 g·kg⁻¹; 9.56 and 6.81 g·kg⁻¹; and 648.19 and 600.70 g·kg⁻¹, respectively. The rhizosphere effect of Smilax china L. was significant at altitudes of 500 m and 1000 m but became not so prominent with the rise of altitude. The C:N ratio in the rhizosphere and bulk soils ranged from 19.51 to 39.75 and the C:P ratio ranged from 225.29 to 543.05. C accumulation is greater than N accumulation in the rhizosphere and bulk soils of Smilax china L., and both present P limitation. Based on the comprehensive analysis of the mass fractions and eco-stoichiometric ratios of soil nutrients, the P limitation in Fanjing Mountain forest ecosystem is commonly seen and should be addressed.

Characteristics of Soil Nutrients and Their Ecological Stoichiometry in Different Land Use Types in the Nianchu River Basin

Land use types can cause changes in soil chemical characteristics, such as altering soil C, N, and P contents and distribution. The aim of this study was to investigate the status of soil C, N, P and other nutrient contents and their stoichiometric ratios in the terrestrial ecosystem of Nianchu River Basin, Tibet. A total of 102 sample plots with 306 soil samples and 102 plant samples were investigated in August 2021 along the Nianchu River basin by selecting four land-use types: grassland, shrubland, forestland, and farmland. The soil’s basic physical and chemical properties (soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), alkaline nitrogen (AN), available phosphorus (AP), pH, and soil particle composition) were examined at each sampling point, and the stoichiometric characteristics of C, N, and P of the soils were analyzed using one-way analysis of variance (ANOVAs). The results revealed that the C and N contents of shrubland were significantly lower than those of grassland, forestland, and farmland, with farmland having the highest P content. For all land types, C:N increased with increasing soil depth, while C:P and N:P decreased with increasing soil depth. PCA and RDA analyses revealed that soil texture and pH had an impact on soil C, N, and P contents, as well as stoichiometric ratios.