Effects of desert plant communities on soil enzyme activities and soil organic carbon in the proluvial fan in the eastern foothills of the Helan Mountain in Ningxia,China

It is of great significance to study the effects of desert plants on soil enzyme activities and soil organic carbon(SOC)for maintaining the stability of the desert ecosystem.In this study,we studied the responses of soil enzyme activities and SOC fractions(particulate organic carbon(POC)and mineral-associated organic carbon(MAOC))to five typical desert plant communities(Convolvulus tragacanthoides,Ephedra rhytidosperma,Stipa breviflora,Stipa tianschanica var.gobica,and Salsola laricifolia communities)in the proluvial fan in the eastern foothills of the Helan Mountain in Ningxia Hui Autonomous Region,China.We recorded the plant community information mainly including the plant coverage and herb and shrub species,and obtained the aboveground biomass and plant species diversity through sample surveys in late July 2023.Soil samples were also collected at depths of 0–10 cm(topsoil)and 10–20 cm(subsoil)to determine the soil physicochemical properties and enzyme activities.The results showed that the plant coverage and aboveground biomass of S.laricifolia community were significantly higher than those of C.tragacanthoides,S.breviflora,and S.tianschanica var.gobica communities(P<0.05).Soil enzyme activities varied among different plant communities.In the topsoil,the enzyme activities of alkaline phosphatase(ALP)andβ-1,4-glucosidas(βG)were significantly higher in E.rhytidosperma and S.tianschanica var.gobica communities than in other plant communities(P<0.05).The topsoil had higher POC and MAOC contents than the subsoil.Specifically,the content of POC in the topsoil was 18.17%–42.73%higher than that in the subsoil.The structural equation model(SEM)indicated that plant species diversity,soil pH,and soil water content(SWC)were the main factors influencing POC and MAOC.The soil pH inhibited the formation of POC and promoted the formation of MAOC.Conversely,SWC stimulated POC production and hindered MAOC formation.Our study aimed to gain insight into the effects of desert plant communities on soil enzyme activities and SOC fractions,as well as the drivers of SOC fractions in the proluvial fan in the eastern foothills of the Helan Mountain and other desert ecosystems.

Microplastic Can Decrease Enzyme Activities and Microbes in Soil

An in vitro study was conducted to investigate the impacts of microplastics on enzyme activities and soil bacteria. The study included four different treatments of microplastics including a control. Different levels of microplastics were applied to the soil ranging from 0% to 5%, to assess the impacts of microplastics on soil enzymes and subsequent soil bacteria. After 30 days of incubation, the soil samples were collected and growth parameters of bacteria were assessed. Activities of β-glucosidase, urease and dehydrogenase enzymes were also determined. Our results showed that the presence of microplastics in the soil significantly reduced bacterial population together with bacterial strains. The activities of β-glucosidase, urease and dehydrogenase enzymes were reduced significantly to approximately 32%, 40% and 50% in microplastics treated soils respectively. Concentration of microplastic has a role to play towards this direction;the higher the concentration of microplastic the greater is the impact on enzymes and soil bacteria. The present study on the microbial soil health vis-à-vis microplastic application indicates that the material can have negative effect on the soil bacterial population of and thus ultimately may jeopardize soil health and crop production.

The Identification of Phenylalanine Ammonia-Lyase(PAL)Genes from Pinus yunnanensis and an Analysis of Enzyme Activity in vitro

Phenylalanine ammonia lyase(PAL)is the rate-limiting and pivotal enzyme of the general phenylpropanoid path-way,but few reports have been found on PAL genes in Pinus yunnanensis.In the present study,three PAL genes were cloned and identified from P.yunnanensis seedlings for thefirst time,namely,PyPAL-1,PyPAL-2,and PyPAL-3.Our results indicated that the open-reading frames of PyPAL genes were 2184,2157,and 2385 bp.Phylogenetic tree analysis revealed that PyPALs have high homology with other known PAL genes in other plants.In vitro enzymatic analysis showed that all three PyPAL recombinant proteins could catalyze the deamination of L-phenylalanine to form trans-cinnamic acid,but only PAL1 and PAL2 can catalyze the conversion of L-tyrosine toρ-coumaric acid.Three PyPAL genes were expressed in different tissues in 1-year-old P.yunnanensis,and such genes had different expression patterns.This study lays a foundation for further understanding of the biosynthesis of secondary metabolites in P.yunnanensis.

Changes in the activities of key enzymes and the abundance of functional genes involved in nitrogen transformation in rice rhizosphere soil under different aerated conditions

Soil microorganisms play important roles in nitrogen transformation. The aim of this study was to characterize changes in the activity of nitrogen transformation enzymes and the abundance of nitrogen function genes in rhizosphere soil aerated using three different methods(continuous flooding(CF), continuous flooding and aeration(CFA), and alternate wetting and drying(AWD)). The abundances of amoA ammonia-oxidizing archaea(AOA) and ammonia-oxidizing bacteria(AOB), nirS, nirK, and nifH genes, and the activities of urease, protease, ammonia oxidase, nitrate reductase, and nitrite reductase were measured at the tillering(S1), heading(S2), and ripening(S3) stages. We analyzed the relationships of the aforementioned microbial activity indices, in addition to soil microbial biomass carbon(MBC) and soil microbial biomass nitrogen(MBN), with the concentration of soil nitrate and ammonium nitrogen. The abundance of nitrogen function genes and the activities of nitrogen invertase in rice rhizosphere soil were higher at S2 compared with S1 and S3 in all treatments. AWD and CFA increased the abundance of amoA and nifH genes, and the activities of urease, protease, and ammonia oxidase, and decreased the abundance of nirS and nirK genes and the activities of nitrate reductase and nitrite reductase, with the effect of AWD being particularly strong. During the entire growth period, the mean abundances of the AOA amoA, AOB amoA, and nifH genes were 2.9, 5.8, and 3.0 higher in the AWD treatment than in the CF treatment, respectively, and the activities of urease, protease, and ammonia oxidase were 1.1, 0.5, and 0.7 higher in the AWD treatment than in the CF treatment, respectively. The abundances of the nirS and nirK genes, and the activities of nitrate reductase and nitrite reductase were 73.6, 84.8, 10.3 and 36.5% lower in the AWD treatment than in the CF treatment, respectively. The abundances of the AOA amoA, AOB amoA, and nifH genes were significantly and positively correlated with the activities of urease, protease, and ammonia oxidase, and the abundances of the nirS and nirK genes were significantly positively correlated with the activities of nitrate reductase. All the above indicators were positively correlated with soil MBC and MBN. In sum, microbial activity related to nitrogen transformation in rice rhizosphere soil was highest at S2. Aeration can effectively increase the activity of most nitrogen-converting microorganisms and MBN, and thus promote soil nitrogen transformation.

Effects of Different Planting Years on Physicochemical Properties and Enzyme Activities in Soil of Rice-Cherry Tomato Rotation

Crop rotation periodicity has always been one of the research focuses currently. In this study, the physicochemical properties, nutrient contents and enzyme activities were investigated in soils from rice-cherry tomato rotation for one year (1a), three years (3a), five years (5a), seven years (7a) and ten years (10a), respectively. The major objective was to analyze the optimal rotation years of rice-cherry tomato from soil perspective, so as to provide theoretical basis for effectively avoiding continuous cropping obstacles of cherry tomato via studying the response characteristics of soil physicochemical properties, nutrient contents and enzyme activities to planting years of rice-cherry tomato rotation system. The results were as follows: 1) Soil pH value was increased year by year during 1a to 5a, reached the highest value 5.32 at 5a. However, soil acidity was sharply enhanced during 7a to 10a (P P •kg-1 at 5a. 3) The content of soil available phosphorus was increased year by year with increasing of crop rotation years, and increased by 110% to 173% during 3a to 10a (P P P < 0.05). In conclusion, long-term single rotation pattern of rice-cherry tomato would aggravate soil acidification, prompt soil nutrient imbalance and reduce soil enzyme activity. 5a to 7a would be the appropriate rotation period for rice-cherry tomato, or else it would reduce soil quality, resulting in a new continuous cropping obstacle of cherry tomato.

Aliskiren Augments the Activities of Anti-Oxidant Enzymes in Liver Homogenates of DOCA Salt-Induced Hypertensive Rats

Hypertension is a serious problem that is recently thought to be associated with damaging effects on target organs partially via oxidative stress. On the other hand, there is accumulating literature describing some sort of therapeutic interaction between antioxidant enzymes in vital organs and hypertension. Therefore, the aim of this study is to investigate the possible effect of a direct renin inhibitor, aliskiren, used in treatment of hypertension via renin-angiotensin-aldosterone system (RAAS), on selected anti-oxidant enzymes in hepatic homogenates in DOCA salt-induced hypertesnive albino rats. Thirty male wister albino rats were assigned randomly into 3 groups (n = 10/ group). Group 1 received no treatement and serves as control. Group 2 received 0.5% carboxymethylcellulose sodium ip as a solvent of aliskiren, as a direct renin inhibitor (DRI). Group 3 received aliskiren 100 mg/kg/day ip for 4 weeks through gastric tube. Systolic blood pressure (SBP) was measured every week and its mean was recorded at the end of the study. Superoxide dismutase (SOD) enzyme in RBCs lysates, activities of catalase (CAT) and glutathione peroxidase enzymes and thiobarbituric acid reactive substance (TBARS), as a marker of lipid peroxidation, in hepatic homogenates were measured at the end of the study. DRI produced a marked reduction in mean SBP of hypertensive rats. It also significantly (p < 0.05) increased the activities of measured anti-oxidant enzymes while it significantly (p < 0.05) reduced TBARS in liver homogenates. These results indicated that renin possesses an oxidative effect in the liver in hypertensive rats. Aliskiren, in addition to its powerful anti-hypertensive effect, it could induce a great anti-oxidant effect in liver homogenates of DOCA salt-hypertensive rats.

Deadwood affects the soil organic matter fractions and enzyme activity of soils in altitude gradient of temperate forests

The main objective of our study has been to determine the role of deadwood in the shaping of the amount of soil organic matter fractions in mountain forest soils.For this purpose,a climosequence approach comprising north(N)and south(S)exposure along the altitudinal gradient(600,800,1000 and 1200 m a.s.l.)was set up.By comparing the properties of decomposing deadwood and those of the soils located directly beneath the decaying wood we drew conclusions about the role of deadwood in the shaping of soil organic matter fractions and soil carbon storage in different climate conditions.The basic properties,enzymatic activity and fractions of soil organic matter(SOM)were determined in deadwood and affected directly by the components released from decaying wood.Heavily decomposed deadwood impacts soil organic matter stabilization more strongly than the less decayed deadwood and the light fraction of SOM is more sensitive to deadwood effects than the heavy fraction regardless of the location in the altitude gradient.Increase in SOM mineral-associated fraction C content is more pronounced in soils under the influence of deadwood located in lower locations of warmer exposure.Nutrients released from decaying wood stimulate the enzymatic activity of soils that are within the range of deadwood influence.

Effects of Carbon Nanomaterials on Soil Enzyme Activity of Turfgrass

[Objectives]This study was conducted to evaluate the effects of carbon nanomaterials on soil ecosystem and explore the ecological risks of environmental exposure of carbon nanomaterials. [Methods] The effects of carbon nanomaterials on soil enzyme activity was studied by adding graphene, graphene oxide and carbon nanotubes to turfgrass soil. [Results] Compared with the control(CK), the activity of soil protease, sucrase, alkaline phosphatase and catalase was not significantly affected by carbon nanomaterials. Under the treatment of carbon nanotubes, urease activity was significantly lower than that of graphene and graphene oxide, and dehydrogenase activity was significantly lower than that of the CK, graphene and graphene oxide. [Conclusions] This study provides a theoretical basis for the safe application of carbon nanomaterials.

Effects of Combined Application of Biochar-based Organic Fertilizer and Reduced Nitrogen Fertilizer on Soil Enzyme Activity and Yield of Purple Cabbage(Brassica oleracea var.capita rubra)in Yuanmou County

[Objectives]In response to the issue of soil improvement in Yuanmou County,the effects of combined application of biochar-based organic fertilizer and reduced nitrogen fertilizer on soil nutrients,soil enzyme activity,and yield of purple cabbage(Brassica oleracea var.capita rubra)were investigated in the field base of Institute of Thermal Zone Ecological Agriculture,Yunnan Academy of Agricultural Sciences in Yuanmou County.[Methods]A total of 13 treatments were set up by applying biochar-based organic fertilizer at three levels of 15,30 and 45 t/hm^(2)(T_(1),T_(2),T_(3)),combined with top application of nitrogen fertilizer(urea)at four levels:375(N_1),300(N_(2)),225(N_(3))and 0 kg/hm^(2),with non-fertilizing treatment as control check(CK),in order to explore the optimal ratio for the combined application of biochar-based organic fertilizer with nitrogen fertilizer.[Results]The application of biochar-based organic fertilizer could significantly improve soil nutrients,enzyme activity,and purple cabbage yield.The improvement effect of combined application with nitrogen fertilizer was higher than that of single application of biochar-based organic fertilizer,and the improvement effect was enhanced with the application amount of biochar-based organic fertilizer increasing.The contents of organic matter and total nitrogen were the highest in treatment T_(3)N_(3),of which the values increased by 81.39%and 56.09%compared with the CK,respectively.The contents of soil hydrolyzable nitrogen,available phosphorus,and available potassium were all the highest under treatment T_(3)N_(2),with increases of 92.76%,171.01%and 235.50%,respectively.There was a significant positive correlation between the activity of soil catalase,urease,and sucrase and organic matter,total nitrogen,and available nutrients.The overall soil enzyme activity was relatively higher in treatment T_(3)N_(2).The yield of purple cabbage treated with biochar-based organic fertilizer combined with nitrogen fertilizer could reach 85750 kg/hm^(2),which was 94.78%higher than that treated with biochar-based organic fertilizer alone.Based on comprehensive analysis,the optimal combination ratio was 45 t/hm^(2)of biochar-based organic fertilizer and 300 kg/hm^(2)of urea(T_(3)N_(2)).[Conclusions]This study provides data support for the promotion of biochar-based organic fertilizers and reduced fertilizer in agricultural soil in the Dam area of Yuanmou County.

Effects of Bamboo Charcoal-based Biochar on Soil Enzyme Activity and Microbial Community Structure

[Objectives]This study was conducted to reveal the effects of bamboo charcoal-based biochar(or bamboo charcoal for short)on soil enzyme activity and microbial community structure.[Methods]The field experiment was carried out at the Modern Agriculture Demonstration Base of Gaoping Village,Gaoping Town,Suichang County,Zhejiang Province.Bamboo charcoal was applied at four different levels:T_(0)(no bamboo charcoal),T_(1)(1125 kg/hm^(2)bamboo charcoal),T_(2)(2250 kg/hm^(2)bamboo charcoal)and T_(3)(3375 kg/hm^(2)bamboo charcoal).Soil physicochemical properties and enzyme activities in different treatments were measured.[Results]The soil fungal,bacterial and actinomycete populations increased significantly in the soils surrounding capsicum roots.The bacterial population,fungal population and fungus/bacterium ratio peaked in Treatment T_(2),up to 7.32×10^(6)cfu/g,2.65×10^(4)cfu/g and 0.36×10^(-2),respectively.The effect of bamboo charcoal in promotingβ-glucoside,catalase,acid phosphatase and sucrase activities was T_(2)>T_(3)>T_(1)>T_(0).With bamboo charcoal increasing,the bacterium population,fungus population,fungus/bacterium ratio,β-glucoside,catalase,acid phosphatase and sucrase activities all increased at first and then decreased.T_(2)treatment showed the best effects in improving soil physicochemical properties and microbial community structure.[Conclusions]Bamboo charcoal significantly improves soil enzyme activity and increases soil microbial population,and thus has important positive effects on the soil ecosystem.

Field released transgenic papaya effect on soil microbial communities and enzyme activities

Soil properties, microbial communities and enzyme activities were studied in soil amended with replicase （RP）-transgenic or non-transgenic papaya under field conditions. Compared with non-transgenic papaya, significant differences （P〈0.05） were observed in total nitrogen in soils grown with transgenic papaya. There were also significant differences （P〈0.05） in the total number of colony forming units （CFUs） of bacteria, actinomycetes and fungi between soils amended with RP-transgenic plants and non-transgenic plants. Compared with non-transgenic papaya, the total CFUs of bacteria, actinomycetes and fungi in soil with transgenic papaya increased by 0.43-1.1, 0.21-0.80 and 0.46-0.73 times respectively. Significantly higher （P〈0.05） CFUs of bacteria, actinomycetes and fungi resistant to kanamycin （Km） were obtained in soils with RP-transgenic papaya than those with non-transgenic papaya in all concentrations of Km. Higher resistance quotients for Km＇ （kanamycin resistant） bacteria, actinomycetes and fungi were found in soil planted with RP-transgenic papaya, and the resistance quotients for Km＇ bacteria, actinomycetes and fungi in soils with transgenic papaya increased 1.6-4.46, 0.63-2.5 and 0.75-2.30 times. RP-transgenic papaya and non-transgenic papaya produced significantly different enzyme activities in arylsulfatase （5.4-5.9x）, polyphenol oxidase （0.7-1.4x）, invertase （0.5-0.79x）, cellulase （0.23-0.35x） and phosphodiesterase （0.16-0.2x）. The former three soil enzymes appeared to be more sensitive to the transgenic papaya than the others, and could be useful parameters in assessing the effects of transgenic papaya. Transgenic papaya could alter soil chemical properties, enzyme activities and microbial communities.

Effects of Long-Term Combined Application of Organic and Mineral Fertilizers on Microbial Biomass,Soil Enzyme Activities and Soil Fertility

Soil health is important for the sustainable development of terrestrial ecosystem. In this paper, we studied the relationship between soil quality and soil microbial properties such as soil microbial biomass and soil enzyme activities in order to illustrate the function of soil microbial properties as bio-indicators of soil health. In this study, microbial biomass C and N contents （Cmic ＆ Nmic）, soil enzyme activities, and soil fertility with different fertilizer regimes were carried out based on a 15-year long-term fertilizer experiment in Drab Fluvo-aquic soil in Changping County, Beijing, China. At this site, 7 different treatments were established in 1991. They were in a wheat-maize rotation receiving either no fertilizer （CK）, mineral fertilizers （NPK）, mineral fertilizers with wheat straw incorporated （NPKW）, mineral fertilizers with incremental wheat straw incorporated （NPKW＋）, mineral fertilizers plus swine manure （NPKM）, mineral fertilizers plus incremental swine manure （NPKM＋） or mineral fertilizers with maize straw incorporated （NPKS）. In different fertilization treatments Cmic changed from 96.49 to 500.12 mg kg^-1, and Nmic changed from 35.89 to 101.82 mg kg^-1. Compared with CK, the other treatments increased Cmic ＆ Nmic, Cmic/Corg （organic C） ratios, Cmic/Nmic, urease activity, soil organic matter （SOM）, soil total nitrogen （STN）, and soil total phosphorus （STP）. All these properties in treatment with fertilizers input NPKM＋ were the highest. Meantime, long-term combined application of mineral fertilizers with organic manure or crop straw could significantly decrease the soil pH in Fluvo-aquic soil （the pH around 8.00 in this experimental soil）. Some of soil microbial properties （Cmic/Nmic, urease activity） were positively correlated with soil nutrients. Cmic/Nmic was significantly correlated with SOM and STN contents. The correlation between catalase activity and soil nutrients was not significant. In addition, except of catalase activity, the soil pH in this experiment was negatively correlated with soil microbial properties. In conclusion, soil microbial properties reflect changes of soil quality and thus can be used as bio-indicators of soil health.

Effects of Water Stress on the Protective Enzyme Activities and Lipid Peroxidation in Roots and Leaves of Summer Maize

A systematic study was conducted to determine the effects of water stress on the activities of protective enzymes and lipid peroxidation in maize. The results showed that, under water stress, the activities of superoxide dismutase （SOD）, catalase （CAT）, and peroxidase （POD） in leaves and roots increased sharply at prophase and metaphase growth stages, such as, male tetrad stage, but then declined towards the physiological maturity. The protective enzyme activities in roots were lower than those in leaves. The content of malondialdehyde （MDA） increased according to the severity of water stress. The content of MDA in roots was lower than that in leaves. The activities of protective enzymes and lipid peroxidation in roots were positively related to that in leaves with most of the correlation coefficients being significant. The content of soluble proteins in roots and leaves decreased with increasing drought stress. The ear characteristics deteriorated and the economic yields of maize decreased significantly under water stress. The main factors that caused reduction of yields were the decrease in the number of ear kernels and 100-kernel weight.

Association of residual feed intake with abundance of ruminal bacteria and biopolymer hydrolyzing enzyme activities during the peripartal period and early lactation in Holstein dairy cows

Background: Residual feed intake(RFI) in dairy cattle typically calculated at peak lactation is a measure of feed efficiency independent of milk production level. The objective of this study was to evaluate differences in ruminal bacteria, biopolymer hydrolyzing enzyme activities, and overall performance between the most-and the leastefficient dairy cows during the peripartal period. Twenty multiparous Holstein dairy cows with daily ad libitum access to a total mixed ration from d-10 to d 60 relative to the calving date were used. Cows were classified into most-efficient(i.e. with low RFI, n = 10) and least-efficient(i.e. with high RFI, n = 10) based on a linear regression model involving dry matter intake(DMI), fat-corrected milk(FCM), changes in body weight(BW), and metabolic BW.Results: The most-efficient cows had ~ 2.6 kg/d lower DMI at wk 4, 6, 7, and 8 compared with the least-efficient cows. In addition, the most-efficient cows had greater relative abundance of total ruminal bacterial community during the peripartal period. Compared with the least-efficient cows, the most-efficient cows had 4-fold greater relative abundance of Succinivibrio dextrinosolvens at d-10 and d 10 around parturition and tended to have greater abundance of Fibrobacter succinogenes and Megaspheara elsdenii. In contrast, the relative abundance of Butyrivibrio proteoclasticus and Streptococcus bovis was lower and Succinimonas amylolytica and Prevotella bryantii tended to be lower in the most-efficient cows around calving. During the peripartal period, the most-efficient cows had lower enzymatic activities of cellulase, amylase, and protease compared with the least-efficient cows.Conclusions: The results suggest that shifts in ruminal bacteria and digestive enzyme activities during the peripartal period could, at least in part, be part of the mechanism associated with better feed efficiency in dairy cows.

Changes in Enzyme Activities Involved in Starch Synthesis and Hormone Concentrations in Superior and Inferior Spikelets and Their Association with Grain Filling of Super Rice

The changes in activities of key enzymes involved in sucrose-to-starch conversion and concentrations of hormones in superior and inferior spikelets of super rice were investigated and their association with grain filling was analyzed.Four super rice cultivars,Liangyoupeijiu,IIyou 084,Huaidao 9 and Wujing 15,and two high-yielding and elite check cultivars,Shanyou 63 and Yangfujing 8,were used.The activities of sucrose synthase （SuSase）,adenosine diphosphoglucose pyrophosphorylase （AGPase）,starch synthase （StSase） and starch branching enzyme （SBE）,and the concentrations of zeatin ＋ zeatin riboside （Z ＋ ZR）,indole-3-acetic acid （IAA） and abscisic acid （ABA） in superior and inferior spikelets were determined during the grain filling period and their relationships with grain filling rate were analyzed.Maximum grain filling rate,the time reaching the maximum grain-filling rate,mean grain filling rate and brown rice weight for superior spikelets showed a slight difference between the super and check rice cultivars,but were significantly lower in the super rice than in the check rice for inferior spikelets.Changes of enzyme activities and hormone concentrations in grains exhibited single peak curves during the grain filling period.The peak values and the mean activities of SuSase,AGPase,StSase and SBE were lower in inferior spikelets than in superior ones,as well as the peak values and the mean concentrations of Z ＋ ZR and IAA.However,the peak value and the mean concentration of ABA were significantly higher in inferior spikelets than in superior ones and greater in the super rice than in the check rice.The grain filling rate was positively and significantly correlated with the activities of SuSase,AGPase and StSase and the concentrations of Z ＋ ZR and IAA.The results suggested that the low activities of SuSase,AGPase and StSase and the low concentrations of Z ＋ ZR and IAA might be important physiological reasons for the slow grain filling rate and light grain weight of inferior spikelets in super rice.

Effects of Zn Stress on Zn Accumulation and Anti-Oxidant Enzymes Activity in Four Varieties of Ryegrass

We investigated the influence of different content of Zn^2＋（0, 2, 4, 8, 16 mmol·kg^-1） on plant growth, activities of peroxidase （POD） and superoxide dismutase （SOD）, free proline content and Zn accumulation in four varieties of ryegrass （Loliurn perenne L.） hy pot cuhure experiment. The results showed that plant hiomass increased at the ranges of 0-2 （Tuoya）, 0-4 （Yey- ing）, 0-8 mmol·kg^-1（Airuisi and Taide）, respectively, and then decreased under excess Zn. The activities of POD ,SOD and proline content in shoots decreased firstly, and then increased with the in crease of Zn content. The plaut biomass, activities of POD and SOD in Taide were evidently higher than in the other three varie ties. Root tolerance index （RTI） and Zn transport ratio from root to shoot （S/R） in Taide were exceed 1. 0. The maximum of Zn content was 583.9 mg/kg （ at 16 mmol·kg^-1） in Taide＇s shoot.

Influence of water potential and soil type on conventional japonica super rice yield and soil enzyme activities

We carried out a pool culture experiment to determine the optimal water treatment depth in loam and clay soils during the late growth stage of super rice. Three controlled water depth treatments of 0-5, 0-10 and 0-15 cm below the soil surface were established using alternate wetting and drying irrigation, and the soil water potential （0 to -25 kPa） was measured at 5, 10 and 15 cm. A 2-cm water layer was used as the control. We measured soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and rice yield. The results showed that the 0-5-cm water depth treatment significantly increased root antioxidant enzyme activities in loam soil compared with the control, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield did not differ from those of the control. The 0-10- and 0-15-cm water depth treatments also increased root antioxidant enzyme activities, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield decreased. In clay soil, the soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and yield did not change with the 0-5-cm water treatment, whereas the 0-10- and 0-15-cm water treatments improved these parameters. Therefore,the appropriate depths for soil water during the late growth period of rice with a 0 to -25 kPa water potential were 5 cm in loam and 15 cm in clay soil.

Saline soil enzyme activities of four plant communities in Sangong River basin of Xinjiang,China

Soil enzyme activity plays an important role in the conversion of soil organic carbon into inorganic carbon, which is significant for the global carbon cycle. In this study, we investigated the soil enzyme activities of two ligninolytic enzymes （peroxidase and polyphenol oxidase） and five non-ligninolytic enzymes （a-l,4-glucosidase （AG）; 13-1,4-gluco- sidase （BG）; N-acetyl-[3-glucosaminidase （NAG）; ~3-D-cellobiosidase （CBH）; and ^-xylosidase （BXYL）） in four plant communities of the Sangong River basin in Fukang, North Xinjiang, China. The four typical plant communities were dominated by Haloxylon ammodendron, Reaumuria soongonica, Salsola passerina, and Tamarix rarmosissima, respec- tively, with saline soils of varied alkalinity. The results showed that the soil peroxidase activity decreased seasonally. The activities of the five non-ligninolytic enzymes decreased with increasing soil depths, while those of the two ligninolytic enzymes did not show such a trend. In the four plant communities, BG had the highest activity among the five non-ligninolytic enzymes, and the activities of the two ligninolytic enzymes were higher than those of the four non-ligninolytic ones （AG, NAG, CBH, and BXYL）. The community of H. ammodendron displayed the highest activity with respect to the two ligninolytic enzymes in most cases, but no significant differences were found among the four plant communities. The geometric mean of soil enzyme activities of the four plant communities was validated through an inde- pendently performed principal component analysis （PCA）, which indicated that different plant communities had different soil enzyme activities. The correlation analysis showed that soil polyphenol oxidase activity was significantly positively correlated with the activities of the five non-ligninolytic enzymes. The soil pH value was positively correlated with the ac- tivities of all soil enzymes except peroxidase. Soil microbial carbon content also showed a significant positive correlation （P〈0.01） with the activities of all soil enzymes except polyphenol oxidase. The results suggested that the H. ammoden- dron community has the highest ability to utilize soil organic carbon, and glucoside could be the most extensively utilized non-ligninolytic carbon source in the saline soil of arid areas in Xinjiang.

Starch Accumulation and Enzyme Activities Associated with Starch Synthesis in Maize Kernels

The filling rate and the starch accumulation in developing maize kernel were analyzed. The changes of enzyme activities associated with sucrose metabolism and starch biosynthesis were investigated. The purpose is to discuss the enzymatic mechanisms responsible for starch synthesis. Two types of maize cultivars （Zea mays）, high starch maize （Feiyu 3） and normal maize （Yuyu 22）, were grown in a corn field. The factors involved in starch synthesis were performed during the growth period. The kernel filling rate, the sucrose content, the starch accumulating rates and the activities of SS （sucrose synthase）, GBSS （granule-bound starch synthase）, SBE （starch branching enzyme） of Feiyu 3, which has high starch content, were significantly higher than those of Yuyu 22, which has low starch content, after 10 DAP （days after pollination）. Correlation analysis indicated that ADPGPPase （ADP-glucose pyrophosphorylase） and DBE （starch debranching enzyme） were not correlated with the starch accumulating rates and the kernel filling rate, but the SS activity at the middle and late period were highly significantly correlated with the starch accumulating rates and the kernel filling rate. The GBSS activity was highly significantly correlated with the amylose accumulating rate, but not correlated with the kernel filling rate. The SBE activity was highly significantly correlated with the amylopectin accumulating rate and the kernel filling rate. It was not ADPGPPase and DBE, but SS was the rate-limiting factor of starch biosynthesis in developing maize kernels. GBSS had an important effect on amylose accumulation, and SBE had a significant effect on amylopectin accumulation.

Rhizosphere and bulk soil enzyme activities in a Nothotsuga longibracteata forest in the Tianbaoyan National Nature Reserve,Fujian Province,China

The rhizosphere, distinct from bulk soil, is defined as the volume of soil around living roots and influenced by root activities. We investigated protease, invertase, cellulase, urease, and acid phosphatase activities in rhizosphere and bulk soils of six Nothotsuga longibracteata forest communities within Tianbaoyan National Nature Reserve, including N. longibracteata ＋ either Phyllostachys pubescens, Schima superba, Rhododendron simiarum, Cunninghamia lanceolata, or Cyclobalanopsis glauca, and N. longibracteata pure forest. Rhizosphere soils possessed higher protease, invertase, cellulase, urease, and acid phosphatase activities than bulk soils. The highest invertase, urease, and acid phosphatase activities were observed in rhizosphere samples of N. longibracteata ＋ S. superba. Protease was highest in the N. longibracteata ＋ R. simiarum rhizosphere, while cellulase was highest in the pure N. longibracteata forest rhizosphere. All samples exhibited obvious rhizosphere effects on enzyme activities with a significant linear correlation between acid phosphatase and cellulase activities （p 〈 0.05） in rhizosphere soils and between protease and acid phosphatase activities （p 〈 0.05） in bulk soils. A principal component analysis, correlating 13 soil chemical properties indices relevant to enzyme activities, showed that protease, invertase, acid phosphatase, total N, and cellulase were the most important variables impacting rhizosphere soil quality.