Responses Of Soil Enzyme Activities Research Articles

Dynamic Response of Soil Enzyme Activities in Riparian Zones: Insights From Vegetation Cover

Dynamic Response of Soil Enzyme Activities in Riparian Zones: Insights From Vegetation Cover

Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations.

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including β-1,4-glucosidase, β-D-cellobiosidase, β-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.

Temperature Matters More than Fertilization for Straw Decomposition in the Soil of Greenhouse Vegetable Field

As the largest organic carbon input to agroecosystems, crop straw can solve the problem of soil quality degradation in greenhouse vegetable fields, harmonize the balance between soil nutrients and energy, and improve soil quality to maintain the sustainable production of greenhouse vegetables. However, the microbial mechanism of the straw decomposition process under different temperatures and fertilization treatments in greenhouse vegetable soils has not been clarified. Soil samples were used to investigate the biology of straw decomposition in the soil at three incubation temperatures (15, 25, and 35 °C) through a soil incubation experiment (60 d) under different fertilization treatments. Fertilization treatments for this long-term field experiment included chemical fertilizer (CF), substitution of half of the chemical N fertilizer with manure (CM), straw (CS), or combined manure and straw (CMS). The results showed that soil hydrolase activities tended to decrease with increasing temperature during straw decomposition. Compared with the CF, organic substitutions (CM, CMS, and CS) increased soil β-glucosidase, β-cellobiosidase, N-acetyl-glucosaminidase, and β-xylosidase activities during straw decomposition. Soil CO2 emission rates were the highest at each incubation temperature on the first day, rapidly declining at 25 °C and 35 °C and slowly declining at 15 °C. The soil CO2 cumulative emissions tended to increase with increasing temperature under different fertilization treatments. PCA showed that the responses of soil enzyme activities to temperature at 7, 15, and 30 d of straw decomposition were stronger than those of fertilization. In summary, both fertilization treatment and incubation temperature could influence soil CO2 emissions by affecting soil physicochemical properties and enzyme activities during straw decomposition, whereas incubation temperature had a stronger effect on straw decomposition than fertilization, as indicated by PLS-PM and three-way ANOVA. Considering the influence for fertilization on the straw decomposition process at different incubation temperatures, the straw applications (CMS and CS) were more suitable to temperature changes.

Effects of experimental warming on soil enzyme activities in an alpine swamp meadow on the Qinghai-Tibetan Plateau

Information about the response of soil enzymes to field warming in permafrost regions is scarce, and the potential mechanisms by which warming combined with biotic and abiotic factors affect soil enzyme activities in alpine grasslands remain unclear. A 3-year in situ experiment with two warming levels (2.7 °C and 5.3 °C) was conducted in an alpine swamp meadow to investigate the effects of experimental warming on 5 soil enzyme activities involved in soil carbon and nitrogen cycling, and the relationships between soil enzyme activities and soil variables related to physicochemical properties and nutrient levels were examined. Results showed that warming had obvious positive effects on soil moisture (SM), soil organic carbon, total nitrogen, and NH4+-N contents, especially in the surface soil layer. Soil NO3--N tended to decrease under moderate warming, while it significantly increased under high warming. Meanwhile, during the entire growing season, warming strongly enhanced invertase and amylase activities by 39.2–49.0% and 109.9–191.0%, respectively. In contrast, urease activities were significantly decreased by 36.8–55.7% in warming plots and there were no significant differences in catalase or cellulase activities among treatments during the whole growing season, while catalase activities in warming plots were significantly decreased by 2.6–4.0% in June. These inconsistent responses of soil enzyme activities to experimental warming could be partially explained by warming-induced changes in soil variables. Redundancy analysis showed that soil NO3--N and SM were the most important factors, which explained 29.8% and 19.7% of the variations in soil enzyme activities, respectively, suggesting that the warming-induced increase in SM could weaken the soil aeration status and enhance enzyme and substrate diffusion, strongly affecting soil nitrification and microbial enzyme production.

Response and driving factors of soil enzyme activity related to acid rain: a meta-analysis.

As a global pollution, acid rain can significantly alter soil physicochemical and biochemical processes, but our knowledge of how acid rain affects soil enzyme activity is still limited. To quantify the overall magnitude and direction of the response of soil enzyme activity to acidrain, we conducted a linear mixed model-based meta-analysis of 40 articles. Our analysis revealed that acid rain decreased enzyme activity by an average of 4.87%. Soil dehydrogenase and protease activities were particularly sensitive to acid rain, with significant inhibitions observed. The effect of acid rain was moderated by acid rain intensity (i.e., H+ addition rate, total H+ added, and acid rain pH) and soil fraction (i.e., rhizosphere and bulk soil). Structural equation modelling further revealed that acid rain suppressed soil microbial biomass by acidifying the soil and that the reduction in microbial biomass directly led to the inhibition of enzyme activity in bulk soil. However, the enzyme activity in the rhizosphere soil was not affected by acid rain due to the rhizosphere effect, whichwas also not impacted by thedecreased soil pHinduced by acid rainin rhizosphere. Our study gives an insight into how bulk soil enzyme activity is impacted by acid rain and highlights the need to incorporate rhizosphere processes into acid rain-terrestrial ecosystem models.

Responses of Soil Enzyme Activity to Long-Term Nitrogen Enrichment and Water Addition in a Typical Steppe

Enzyme activity plays an important role in soil biochemical processes and is a key factor driving nutrient cycling. Although a great number of studies examined the effects of nitrogen (N) enrichment and water (W) addition on soil enzyme activity, most of them focused on the effect of only one resource and are based on short-term investigations. The separate and interactive effects of long-term changes in nitrogen and water on soil enzyme activity remain largely unexplored. In this study, we demonstrated the responses of two types of soil enzyme, β-1,4-glucosidase (BG) and acid phosphatase (APA), to increased nitrogen and water based on a 16-year experiment conducted in a typical grassland in northern China. The results show that: (1) nitrogen addition inhibited BG and APA in 2019 and 2020; (2) water addition had no significant effect on BG activity, but significantly reduced APA activity in 2020; and (3) redundancy analysis (RDA) showed that nitrogen and water addition affected soil enzyme activity mainly by affecting soil microbial biomass carbon (MBC). The present research offers a comprehensive explanation of how atmospheric nitrogen deposition and precipitation patterns affect the characteristics of microorganisms and the cycling of nutrients in grassland ecosystems.

Importance of Considering Enzyme Degradation for Interpreting the Response of Soil Enzyme Activity to Nutrient Addition: Insights from a Field and Laboratory Study

Soil enzyme activity can be affected by both production and degradation processes, as enzymes can be degraded by proteases. However, the impact of nutrient addition on enzyme activity is often solely attributed to changes in enzyme production without fully considering degradation. In this study, we demonstrate that the activities of β-1,4-glucosidase (BG), β-D-cellobiohydrolase (CBH), β-1,4-xylosidase (BX), and β-1,4-N-acetyl-glucosaminidase (NAG) in two tropical plantations exhibited comparable levels between nitrogen (N)- and phosphorus (P)-fertilized soils and the unfertilized control under field conditions. However, it was observed that the reduction in enzymatic activity was significantly higher in the fertilized soils during short-term laboratory incubation in the acacia plantation. Additionally, the eucalyptus plantation exhibited a similar tendency, although statistical significance was not achieved due to the high variance of the data. The results show that the interruption of the natural, continuous supply of organic matter or non-soil microbial-derived enzymes, which typically occurs under field conditions, leads to a more significant reduction in soil enzyme activities in fertilized soils compared to unfertilized control. This may be attributed to the higher abundance of protease in fertilized soils, resulting in faster enzyme degradation. Interestingly, P fertilization alone did not have a similar effect, indicating that N fertilization is likely the main cause of the larger decreases in enzyme activity during incubation in fertilized soils compared to unfertilized control soils, despite our study site being poor in P and rich in N. These findings highlight the importance of considering enzyme degradation when investigating material dynamics in forest ecosystems, including the impact of nutrient addition on enzyme activity, as enzyme production alone may not fully explain changes in soil enzyme activity.

Responses of soil enzyme activity to freeze-thaw alternation in Greater Khingan Mountains, China.

We examined the effects of freeze-thaw cycles (0, 1, 3, 5, 7, 15 cycles) on the activities of urease, invertase, and proteinase in the different layers of the soil under the four typical stands in the cold temperate zone, i.e., Pinus pumila stand, Rhododendron-Betula platyphylla stand, Rhododendron-Larix gmelinii stand, Ledum-Larix gmelinii stand, with the indoor freeze-thaw simulation culture method being used. The relationship between soil enzyme activity and multiple physicochemical variables was analyzed during freeze-thaw alternation. The results showed that the activity of soil urease was firstly increased and then inhibited during freeze-thaw alternation. After freeze-thaw, urease activity did not differ from that without freeze-thaw. Invertase activity was firstly inhibited and then increased during freeze-thaw alternation, and was significantly increased by 8.5%-40.3% after freeze-thaw. Proteinase activity was firstly increased and then inhibited during freeze-thaw alternation, and was significantly decreased by 13.8%-68.9% after freeze-thaw. After freezing and thawing, there was significant positive correlation between urease activity and ammonium nitrogen and soil water content in Ledum-L. gmelinii stand and P. pumila stand, respectively, and proteinase activity had significant negative correlation with inorganic nitrogen concentration in P. pumila stand, Rhododendron-B. platyphylla stand, and Ledum-L. gmelinii stand. Invertase activity had significant positive correlation with organic matter in Rhododendron-L. gmelinii stand and Ledum-L. gmelinii stand.

Effects of elevated CO2 concentration, warming, and winter wheat planting on soil enzyme activities.

Understanding the responses of soil enzyme activities to elevated CO2 concentration and warming can provide a scientific basis for nutrient management of croplands under global climate change. We conducted a pot expe-riment with climate chamber to examine the effects of elevated CO2 concentration and warming and winter wheat growth on soil enzyme activities. There were four climate scenarios: control (CK, 400 μmol·mol-1 CO2 concentration+normal ambient temperature), and CO2 concentration elevation (ECO2, 800 μmol·mol-1 CO2 concentration+normal ambient temperature), elevated temperature (ET, 400 μmol·mol-1 + temperature increased 4 ℃), and elevated CO2 concentration and temperature (ECO2+T, 800 μmol·mol-1 CO2 concentration + temperature increased 4 ℃). We measured the activities of soil β-glucosidase (βG), β-N-acetyl glucosidase (NAG), alkaline phosphate (ALP) and polyphenol oxidase (PPO) at four growth stages (JS, jointing stage; AS, anthesis stage; FS, filling stage and MS, maturity stage), with and without winter wheat planting. Without winter wheat planting, there was no significant difference in four kinds of soil enzyme activities between ECO2 and CK, while ET and ECO2+T treatments had significant negative effect on soil enzyme activities. With winter wheat planting, compared with CK, ECO2 and ECO2+T treatments did not affect the activities of those four soil enzyme; but the ET treatment had great impact on soil ALP and PPO activities. The activities of four kinds of soil enzyme were significantly diffe-rent between the ET and ECO2+T treatments. Compared with ET treatment, ECO2+T treatment increased soil βG activity at the JS, decreased NAG activity at the JS, increased ALP activity at both AS and FS, decreased PPO activity in the JS and increased in the AS. The interaction of elevated CO2 concentration and warming had significant effect on soil NAG and ALP activities with and without winter wheat planting. The interaction of warming and expe-rimental stage had significant effect on four kinds of soil enzyme activities without winter wheat planting, but the interaction of warming and crop growth stage had significant effect on ALP and PPO activities with winter wheat planting. The interaction of elevated CO2 concentration, warming and experimental period had significant effect on soil βG, ALP and PPO activities without winter wheat growth, while with winter wheat growth, it had significant impact on NAG, ALP and PPO activities. The winter wheat growth had significantly inhibitory effect on βG, NAG and ALP activities in the two early growth periods (JS+AS), significant promoting effect in the later growth periods (FS+MS), and significantly inhibitory effect on PPO activity during whole growth period. Overall, elevated CO2 concentration did not affect soil enzyme activities, while the elevation of CO2 concentration and temperature on soil enzyme activities differed among the soil enzymes at different growth stages. In addition, the responses of four soil enzyme activities to the interaction of elevated CO2 concentration and warming varied with and without winter wheat planting.

Short-term response of soil enzyme activities and bacterial communities in black soil to a herbicide mixture: Atrazine and Acetochlor

Combined application of atrazine (ATZ) and acetochlor (ACE) was used as an emerging herbicidal method in black soil zone of northeastern China recently. However, the interaction toxic effect of the two herbicides on the soil biological characteristics has not been investigated yet. In this study, the alterations of soil enzyme activities and bacterial communities in black soil were assayed during a short term (28 days) exposure period by spiking ATZ, ACE or ATZ + ACE (1:1, w: w) at 0×, 1×, 2×, 5× and 10× the recommended dose in a microcosm experiment conducted under greenhouse condition. The results showed that ATZ and ACE had synergistic inhibitory effects on soil enzymes activities. Higher inhibition rates of urease, acid phosphatase, sucrase and catalase were observed in ATZ + ACE, and the enzyme activities could not recover to the level without herbicide application after 28 days. The higher IBRv2 value of ATZ + ACE also indicated that the comprehensive toxicity was stronger than that of ATZ or ACE. The microbial community structure was affected differently by ATZ, ACE and ATZ + ACE as the PLFAs analysis displayed, and ATZ + ACE was more harmful to bacteria than ATZ or ACE. The decrease in relative abundance of Proteobacteria was more sensitive to ATZ, and the decrease of Acidobacteriota was more sensitive to ACE, and the relative abundance of these two phyla decreased more obviously in ATZ + ACE. In addition, the PICRUSt analysis showed that the functions of the replication and repair, energy metabolism, cell motility and cellular processes and signaling were inhibited by ATZ and ACE, especially in the ATZ + ACE treatment. This means that combined application of ATZ and ACE has a greater potential risk on soil microbes and consequently the nutrient cycling process.

Responses of soil enzyme activities and bacterial community structure to different hydrological regimes during peatland restoration in the Changbai Mountain, northeast China.

Appropriate hydrological management is critical for peatland restoration. An important prerequisite for peatland restoration is a recovery of soil biological processes. However, little is known about the effects of different hydrological management practices on soil biological processes during peatland restoration. In this study, the variations in soil properties, enzyme activities, and bacterial communities across different peatlands, namely natural peatland (NP), peatland restored under high water level (HR), peatland restored under alternating high-low water level (HLR), peatland restored under low water level (LR), and degraded peatland (DP), in the Changbai Mountains were investigated. Results showed that soil organic carbon, soil water content, and total nitrogen in NP were significantly higher than those in restored and degraded peatlands, and these soil properties in restored peatlands increased with the water level. The activities of soil hydrolases including β-1, 4-glucosidase, β-1, 4-n-acetylglucosidase, and acid phosphatase in NP were higher than in restored and degraded peatlands, while the activity of polyphenol oxidase in NP was the lowest. In restored peatlands, all measured enzyme activities decreased with the decline in water level. Both bacterial diversity and richness in NP were the lowest, while the highest diversity and richness were observed in HR. Redundancy analysis indicated that soil organic carbon, water level, soil water content, total nitrogen, and pH were the most important factors that affected the soil enzyme activities and bacterial community. Our findings give insight into the effects of different hydrological regimes on soil biological processes during peatland restoration. Maintaining a high water level early in the restoration process is more beneficial to restoring the ecological functions of peatlands than other hydrological regimes.

Response of Soil Enzyme Activities to Natural Vegetation Restorations and Plantation Schemes in a Landslide-Prone Region

Soil enzyme activities in different plantation types and land use patterns could indicate changes in soil quality. This research was aimed at exploring the dynamics of soil enzyme activities involved in carbon, nitrogen and phosphorus cycling, and their responses to changes in soil physicochemical properties resulting from natural vegetation restorations and plantation schemes. Knowing about the effects of soil physicochemical properties on soil enzyme patterns is crucial for understanding ecosystem functions and processes. The study selected four main land-use types (natural forestland, natural grassland, artificial forestland, and artificial grassland) and one control plot (bare land) in the West Qinling Mountains, China, which is a typical landslide region. We collected the soil samples from each land use type and tested their physicochemical properties and enzyme activities compared with control land. The results showed that both natural vegetation restoration and artificial plantation schemes have significant effects on enzyme activities. Soil physicochemical properties explained 92.2% of the variation in soil enzyme activities for natural vegetation restoration, while it only explained 77.8% of the variation in soil enzyme activities for plantation schemes. Furthermore, natural vegetation had a greater effect than the plantation schemes on soil enzyme activities.

Response of Soil and Crop to Mixed Irrigation Using Brackish and Reclaimed Water

HighlightsMixed irrigation with brackish water-reclaimed water was introduced.IBRv2 was used to evaluate the effects of mixed irrigation on the soil–crop system.Reclaimed water could be used as an alternative source of freshwater to mix with brackish water, and the suitable mixed proportion should be 1:1 based on IBRv2.Abstract. To explore the reasonable utilization of brackish water in areas where freshwater is scarce, we used pot experiments to study the physical, chemical, and biological properties of soil and crop yield characteristics under mixed irrigation using brackish–reclaimed water at different ratios. There were six treatments, including brackish water irrigation (T1); mixed irrigation using brackish–reclaimed water at 1:1 (T2), 1:2 (T3), and reclaimed water irrigation (T4); pots with plants irrigated with freshwater (CK2); and pots without plants irrigated with freshwater (CK1) as the control. The salinity of the brackish water was 3 g L-1 (6.1 dS m-1). The results indicated that compared to T1, with the increase in the proportion of reclaimed water in the mixture, the water and salt contents in the soil gradually decreased significantly; the K+, Ca2+, and SO42– contents demonstrated an increasing trend; the Na+, Cl–, HCO3–, and Mg2+ contents showed a descending to ascending trend; and the soil water drop penetration time decreased first and then increased slightly. At the same time, the soil organic matter displayed an opposite trend, and the chlorophyll content of leaves and crop biomass both changed with an “N”-style curve. Differences existed in the responses of soil enzyme activities to different mixed water mixtures. There was a slight decrease in the enzyme activity, except for sucrase under T2 and T3. The Integrated Biological Response Version 2 (IBRv2) scored 3.97 in T2. Therefore, considering the characteristics of the soil and crop and the limits of reclaimed water, reclaimed water could be used as an alternative source of freshwater to mix with brackish water, and the suitable mixed proportion should be 1:1 based on IBRv2. Keywords: Brackish water, IBRv2, Reclaimed water, Repellency.

Changes in soil enzymatic activity in a P-limited Mediterranean shrubland subject to experimental nitrogen deposition

N deposition is a key driver of global environmental change (GEC). The effects of N addition on soil enzymes which play a key role in biogeochemical cycles and functioning of terrestrial ecosystems remain unclear, especially in vulnerable ecosystems such as P- or/and water-limited Mediterranean ecosystems. Here, we studied seasonal effects of N deposition on the activities of five soil extracellular enzymes in a semi-arid, P-deficient Mediterranean shrubland, and the association with physical and nutritional soil variables. Over the study period N deposition caused direct effects on soil enzymatic activities due to N-accumulation that increased its availability and triggered ecosystem mobilization of less available nutrients, such as P, in accordance with optimum allocation theory. N deposition intensified P limitation, enhanced the activity of phosphatases and reduced the activity of N- and C-mobilizing enzymes; it is likely this could lead to a longer term increase in soil C storage, due to a reduction in soil organic matter decomposition. The prompt response of soil enzyme activity to experimental N deposition indicates the high vulnerability of soil biogeochemical processes in this Mediterranean shrubland if submitted to prolonged N deposition.

Response of soil enzyme activity and bacterial community to copper hydroxide nanofertilizer and its ionic analogue under single versus repeated applications

Nanosized agrochemicals like nanofertilizers are being applied to soils. Adverse impacts of nanofertilizers on soil microflora were reported in past studies, but only considering a single application. Repeated applications are however more likely to occur in agriculture. We investigated effects of single versus repeated applications of a copper hydroxide nanofertilizer formulation (NFF) on soil enzyme activity and bacterial community. One or three applications were performed within 21 days to achieve same final level of Cu in soil (48 mg(Cu)/kg: the recommended dose of NFF). Besides, the active ingredient (i.e., copper hydroxide nanotubes (NT)) and dispersing agent (DA) of NFF, and an ionic fertilizer (i.e., CuSO4) were examined. Fluorescein diacetate hydrolase (FDAse), N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and urease (URE) showed negligible changes in the activities between the control and DA treatment. Bacterial community abundance, composition and diversity exhibited similar phenomena. Exposures to copper hydroxide NFF and NT or CuSO4 enhanced the activities of FDAse and NAG, weakened the activity of URE, and showed negligible changes in the LAP activity irrespective of single and repeated applications. Concentrations of NO3−-N and NH4+-N in soil were also affected by the application mode of NFF. More importantly, responses of soil bacterial community to copper hydroxide NFF were highly dependent on its application mode, whereas similar responses were observed in the CuSO4 treatment regardless of single or repeated applications. This study provided new insights into environmental risk of copper hydroxide NFF that were ignored in previous studies using a single exposure.

Response of soil enzyme activity and soil bacterial community to PCB dissipation across different soils

Soils are a repository for polychlorinated biphenyls (PCBs). A pot incubation experiment was performed with four soils (black soil, paddy soil, oasis soil, and fluvo-aquic soil) treated with Aroclor 1242 to achieve PCB concentrations of 5 mg kg−1. The soil enzyme activities of protease, phosphatase, catalase, dehydrogenase, and laccase were determined by spectrophotometry. The soil bacterial communities were investigated using Illumina sequencing analysis. The results showed that the characteristics of the test soils varied among the soil types. The fluvo-aquic soil had the greatest PCB dissipation rate (86.41%), followed by the oasis (79.31%), paddy (56.09%), and black (50.65%) soils. The soil pH, cation exchange capacity, soil organic matter content, and particle diameter played significant roles in PCB dissipation from soils. The soil type had a greater influence than PCB contamination on the soil enzyme activities and bacterial communities (alpha diversity, community structure, and composition). Among the four soils, the bacterial communities of the fluvo-aquic soil were the most susceptible to PCB contamination. However, the bacterial communities of the black soil were not changed by PCB contamination.

Response of Enzyme Activity of Cultivated Saline Soil to Sand Covering

In order to clarify the response of soil enzyme activities of cultivated salinealkali soil to sand cover in the Loess Plateau-Mu Us Sandy ecotone. In this study, the soil enzyme activities of the saline-alkali soils before and after sand-covering (CK) and after sand-covering for three consecutive years were taken as the research objects. The results showed that the activities of four soil enzymes (urease, catalase, protease, and alkaline phosphatase) all increased to varying degrees after covering with sand. Among them, the effect of covering with sand on soil urease and alkaline phosphatase was significant. In general, the activities of the four soil enzymes are negatively correlated with soil physical properties (except porosity) and positively correlated with soil chemical properties. This study provides data support for revealing the long-term effects of sand-covering on soil enzyme activities of cultivated saline-alkali soils, and provides a reasonable idea and theoretical reference for the feasibility of using sand-covered soil organic restructuring technology in saline-alkali soil management.

Responses of soil phosphorus pools accompanied with carbon composition and microorganism changes to phosphorus-input reduction in paddy soils

In rice-wheat rotation systems, changes in soil phosphorus (P) pools and microorganisms in rice-growing seasons have been studied; however, further investigations are required to test whether these indexes exhibit different responses in wheat-growing seasons. Additionally, such studies need to include potential variations in soil carbon (C) structure and microbial community composition. In this study, a long-term rice-wheat rotation P-input reduction experiment was conducted to observe the variations in soil P pools and C composition in the 7th wheat season and to investigate the responses of soil enzyme activity and microbial communities. Four P fertilization treatments were included in the experiment, i.e., P application for rice season only (PR), for wheat season only (PW), and for both rice and wheat seasons (PR+W) and no P application in either season (P zero ). Compared with PR+W treatment, P zero treatment significantly decreased ( P < 0.05) labile and stable P pools. Different P fertilization regimes altered soil microbial community composition and enzyme activity, whereas C composition did not vary. However, PW treatment resulted in relatively more O-alkyl-C than PR treatment and the highest number of microorganisms. Besides, the higher ratios of fungi/bacteria and Gram-positive bactetia/Gram-negative bactetia were related to labile C pools, particularly O-alkyl-C, as opposed to recalcitrant C. Our results clarified the status of soil P pools, C chemistry, and the response of microorganisms under dry-farming conditions in the P input-reduced rice-wheat rotation system.

Effects of phytoremediation on soil enzyme activity and thermodynamic characteristics of enzymatic reaction in severe saline-alkali land.

With the environmental changes and the increases of anthropogenic disturbance, the area and degree of salinization in saline-alkaline lands of Songnen Plain have been increasing with an unprecedented rate. In this study, the effects of restoration of natural vegetation, Leymus chinensis, Avena sativa and Medicago sativa, on the enzymatic activities and thermomechanical characteristics of enzyme catalyzed reaction of two oxidoreductases (catalase, polyphenol oxidase) and three hydrolases (alkaline phosphatase, sucrase, urease) were investigated in heavily saline-alkaline soils from western Songnen Plain. The results showed that the activities of those five soil enzyme as well as the activation free energy (ΔG) increased with increasing temperature, reaching respective maximum at 40 and 45 ℃. The activation enthalpy (ΔH) and entropy (ΔS) of soil enzyme did not change with increasing temperature. The temperature coefficient (Q10) slightly changed and ranged from 1.05 to 1.36 by every 10 ℃ enhancement of temperature. Compared with the bare land, catalase activity increased in natural vegetation and L. chinensis rehabilitated land, but decreased in A. sativa and M. sativa remediation land. The change of ΔG of catalase showed a contrary trend with that of enzyme activities, while ΔH and ΔS increased in the restoration areas of L. chinensis and A. sativa, and decreased in the restoration of natural vegetation and M. Sativa. The activity of polyphenol oxidase decreased or remained unchanged in all restoration sites, and ΔH and ΔS decreased in natural vegetation and L. chinensis restoration sites, while remained unchanged in A. sativa and M. sativa restoration sites. ΔG of polyphenol oxidase reached the maximum at 40 ℃ in each restoration site and decreased or remained unchanged at other temperatures. The activities of three hydrolytic enzymes increased in each restoration site compared with the bare land, and the ΔG of the enzymes decreased or remained unchanged in each repaired area, while ΔH and ΔS varied greatly among the restoration sites. Taken together, significant responses of soil enzyme activity and their thermodynamic characteristics to temperature change and vegetation restoration were detected, which would provide better understanding for the restoration of heavily salinized soil.

Responses of soil enzyme activity and soil organic carbon stability over time after cropland abandonment in different vegetation zones of the Loess Plateau of China

The effects of cropland abandonment on soil enzyme activity and soil organic carbon (SOC) stability, along with the driving factors, are poorly understood. Here, we aimed to systematically and comprehensively evaluate soil enzyme activity, SOC stability, and the associated driving factors in different vegetation zones after cropland abandonment on the Loess Plateau, China. We selected grasslands with different recovery times along a rainfall gradient encompassing the steppe zone (SZ), forest-steppe zone (FSZ), and forest zone (FZ). We measured and compared the changes in soil enzyme activity (saccharase, polyphenol oxidase, urease, phosphatase, and catalase) and SOC stability as a function of recovery time; we also evaluated the relationships between these two parameters. In SZ and FSZ, soil enzyme activity, fractions of oxidizable carbon (including very labile [C1], labile [C2], and less labile [C3]), and the carbon management index (CMI) increased with recovery time, whereas the SOC stability index (SI) decreased. Conversely, in FZ, polyphenol oxidase activity increased linearly, urease and catalase activities decreased linearly, and the change in saccharase activity was represented by a cubic equation regression. SI showed no obvious changes with recovery time, whereas C1, C2, and C3 initially decreased and then increased. Redundancy analysis showed that, in FSZ and FZ, soil enzyme activity, C1, C2, C3, and SI were influenced by vegetation diversity, coverage, and soil nutrient levels. In comparison, in SZ, these parameters were mainly influenced by soil nutrient levels. Soil enzyme activity was strongly correlated with C1 and C3 in SZ and FSZ, but not in FZ. Overall, in SZ and FSZ, soil enzyme activity increased with recovery time, whereas SOC stability decreased. In contrast, both parameters were relatively stable in FZ, which had higher mean annual precipitation and mean annual temperature.