Long-term nitrogen addition modifies fine root growth and vertical distribution by affecting soil nutrient availability in a Mongolian pine plantation.

Fine roots are the primary organ of tree species in water and nutrient acquisition, and are the major contributor of forest soil organic carbon (C). However, it remains largely unknown how fine root growth dynamics and vertical distribution respond to long-term nitrogen (N) enrichment, which prevents us from accurately evaluating forest C sequestration potential under N deposition. Here, we investigated the effects of nine-year N addition (0 and 10 g N m-2 year-1) on fine root nutrients, biomass, production, turnover rate and vertical distribution in three soil layers (0-10, 10-20 and 20-40 cm) of a Mongolian pine (Pinus sylvestris var. mongolica) plantation in the Keerqin Sandy Lands, Northeast China. We found that soil inorganic N was increased and Olsen-P was decreased by N addition. N addition increased fine root N, C:P and N:P ratios, but reduced fine root P and C:N ratio across all soil layers. N addition reduced fine root biomass in 0-10 cm soil layer but increased it in 20-40 cm soil layer. N addition accelerated fine root turnover rate in 0-10 cm soil layer, and increased fine root necromass across all soil layers. Moreover, N addition significantly enhanced biomass of ectomycorrhizal extraradical hyphae in the 0-10 cm soil layer. Redundancy analysis showed that variations of fine root traits were well explained by soil NO3--N in 0-10 and 10-20 cm soil layers, and by soil NH4+-N and Olsen-P in 20-40 cm soil layer. Collectively, our results highlight the shift from N limitation to P limitation of Mongolian pine plantations under long-term N addition, and suggest that changes in fine root growth and vertical distribution induced by N addition could accelerate belowground C allocation in Mongolian pine plantations.

Clinical and pathological characteristics of acute kidney injury caused by diquat poisoning.

Introduction: Diquat poisoning leads to kidney injury, hepatotoxicity, rhabdomyolysis, gastrointestinal hemorrhage, and respiratory failure. Diquat has high mortality and no specific antidote. The pathology of acute kidney injury caused by diquat poisoning has been mainly investigated in animal studies and autopsies, and typically shows renal tubular necrosis. To our knowledge, antemortem renal biopsy has not been reported in humans.Case reports: Two males and one female presented following deliberate diquat self-poisoning. Their main clinical manifestations were abdominal pain, nausea, and emesis. All developed acute kidney injury. Kidney biopsy was performed in two cases which showed acute tubular necrosis with renal interstitial edema and multifocal inflammatory cell infiltration. Treatments given included gastric lavage, catharsis, early hemoperfusion combined with continuous kidney replacement therapy or hemodialysis, administration of glucocorticoids, and antioxidant therapy. All patients survived.Discussion: Despite potentially lethal ingestions three patients survived oral diquat poisoning with intensive supportive care. No clear relationship can be made between any of the therapies given and patient outcome.Conclusions: Kidney biopsy in these patients confirmed proximal renal tubular injury was the major pathological finding although interstitial injury was also present. The role of therapies that address renal pathology requires further study.

[Role of photosynthesis in regulating soil respiration under nitrogen application in a sandy grassland]. / æ–½æ°®å¤„ç†ä¸‹æ¤ç‰©å ‰åˆå¯¹æ²™è´¨è‰åœ°åœŸå£¤å‘¼å¸çš„è°ƒæŽ§ä½œç”¨.

We examined the role of photosynthesis in regulating soil CO2 emission under nitrogen enrichment in Keerqin sandy grassland. Results showed that nitrogen (N) application could affect soil respiration rate by altering the allocation of photosynthetic products to the belowground. Gross ecosystem photosynthesis rate (GEP) was positively correlated with soil respiration rate (Rs). Nitrogen application reduced slope of the fitting function from 0.236 to 0.161, with the equation intercept difference (0.51 µmol·m-2·s-1) being similar to the nighttime soil respiration rate increment (0.52 µmol·m-2·s-1). From May to October, the difference of photosynthetic rate (differential ratio) caused by nitrogen application was significantly correlated with that of soil respiration (differential ratio). Results from partial correlation confirmed the essential role of photosynthetic rate difference (ΔGEP) in driving soil respiration rate difference (ΔRs) caused by nitrogen application. In the nighttime, soil respiration rate was affected by the aboveground vegetation activities in daytime. The daily mean GEP was an important factor affecting the nighttime soil respiration rate difference (ΔRs) (P<0.01). Photosynthesis, rather than soil temperature, was the main factor affecting soil respiration rate difference (ΔRs) under nitrogen application. Thus, the role of photosynthetic assimilation-regulating may provide a novel supplement for elucidating the responses of soil respiration to nitrogen enrichment.

Foraging responses of sheep to plant spatial micro-patterns can cause diverse associational effects of focal plant at individual and population levels.

Multiple-scale foraging decisions by large herbivores can cause associational effects of focal plant individuals neighboured with different species. Spatial micro-patterns between the focal plant and its neighbouring species within patches can affect herbivore foraging selectivity at within- and between-patch scales, which may consequently lead to associational plant effects occurring at both plant individual and population levels. However, these associational effects have not been explored together in the plant-herbivore interaction studies. We aim to evaluate how plant spatial micro-pattern within different quality patches mediate herbivore foraging selectivity, thereby affecting the associational effects of focal plant individuals and population. Using sheep as the model herbivore and a medium preferred species as the focal plant, we conducted a manipulative experiment by allowing sheep grazing freely among three different quality patches, each of which consisted of preferred, unpreferred and focal plant species with different abundances forming spatially aggregated or dispersed micro-patterns. Results showed that, compared with the aggregated plant micro-pattern, dispersed plant micro-patterns within different quality patches increased sheep within-patch selectivity, and caused diverse associational effects of focal plant individuals. Focal plant individuals experienced neighbour contrast defence (i.e. got protection in the high quality patch) and associational defence (i.e. got protection in the low quality patch), respectively, when plants distributed dispersedly in the low and high quality patch. Focal plant individuals simultaneously experienced associational susceptibility (i.e. got damage in the high quality patch) and neighbour contrast susceptibility (i.e. got damage in the low quality patch) when plants distributed dispersedly in the medium quality patch. Furthermore, dispersed plant micro-patterns reduced sheep foraging selectivity between patches, and led to a lower consumption of focal plant population compared with the aggregated plant micro-pattern. Herbivores adopt different within- and between-patch foraging decisions to maintain a high intake of the preferred species in response to various plant micro-patterns, and consequently cause diverse associational effects of both focal plant individuals and population. These associational effects have important implications for understanding the species coexistence and plant community assembly in the grazing ecosystems.

Altered leaf functional traits by nitrogen addition in a nutrient-poor pine plantation: A consequence of decreased phosphorus availability.

This study aimed to determine how specific leaf area (SLA) and leaf dry matter content (LDMC) respond to N addition and understory vegetation removal in a 13-year-old Mongolian pine (Pinus sylvestris var. mongolica) plantation. Traits (SLA, LDMC, individual needle dry weight, N and P concentrations) of different-aged needles and their crown-average values were measured, and their relationships with soil N and P availability were examined. N addition and understory removal reduced soil Olsen-P by 15-91%. At the crown level, N addition significantly reduced foliar P concentration (by 19%) and SLA (by 8%), and elevated N concentration (by 31%), LDMC (by 10%) and individual leaf dry weight (by 14%); understory removal did not have a significant effect on all leaf traits. At the needle age level, traits of the previous year's needles responded more strongly to N addition and understory removal than the traits of current-year needles, particularly SLA and N concentration. SLA and LDMC correlated more closely with soil Olsen-P than with soil inorganic N, and LDMC correlated more closely with soil Olsen-P than SLA did. These results indicate that aggravated P limitation resulting from N addition and understory removal could constrain Mongolian pine growth through their effects on the leaf traits.

Species diversity and chemical properties of litter influence non-additive effects of litter mixtures on soil carbon and nitrogen cycling.

Decomposition of litter mixtures generally cannot be predicted from the component species incubated in isolation. Therefore, such non-additive effects of litter mixing on soil C and N dynamics remain poorly understood in terrestrial ecosystems. In this study, litters of Mongolian pine and three dominant understory species and soil were collected from a Mongolian pine plantation in Northeast China. In order to examine the effects of mixed-species litter on soil microbial biomass N, soil net N mineralization and soil respiration, four single litter species and their mixtures consisting of all possible 2-, 3- and 4-species combinations were added to soils, respectively. In most instances, species mixing produced synergistic non-additive effects on soil microbial biomass N and soil respiration, but antagonistic non-additive effects on net N mineralization. Species composition rather than species richness explained the non-additive effects of species mixing on soil microbial biomass N and net N mineralization, due to the interspecific differences in litter chemical composition. Both litter species composition and richness explained non-additive soil respiration responses to mixed-species litter, while litter chemical diversity and chemical composition did not. Our study indicated that litter mixtures promoted soil microbial biomass N and soil respiration, and inhibited net N mineralization. Soil N related processes rather than soil respiration were partly explained by litter chemical composition and chemical diversity, highlighting the importance of functional diversity of litter on soil N cycling.

[Effects of drying-rewetting on leaf litter decomposition and nutrient releases in forest plantations in Horqin Sandy Land, China]. / å¹²æ¹¿äº¤æ›¿å¯¹ç§‘å°”æ²æ²™åœ°äººå·¥æž—å¶å‡‹è½ç‰©åˆ†è§£å’Œå »åˆ†é‡Šæ”¾çš„å½±å“.

Soil drying-rewetting is a common phenomenon in arid and semi-arid regions. Under the background of global climate change, it is predicted that the intensity of soil drying-rewetting cycle in Horqin Sandy Land will be further strengthened in the future. In this study, we conducted an in-situ soil column incubation experiment for 180 days to investigate the effects of soil drying-rewetting on leaf litter decomposition and nutrient releases of Populus simonii and Pinus sylvestris var. mongo-lica in Horqin Sandy Land. There were three treatments: Constantly moist treatment (CM, 60% water holding capacity during whole incubation period), mild drying-rewetting treatment (DW1, gra-dual drought for 10 days plus 60% WHC for 20 days) and heavy drying-rewetting treatment (DW2, gradual drought for 20 days plus 60% WHC for 10 days). To evaluate their delayed effects, leaf litter in all three treatments were incubated for 60 days under same and constant humid condition (60% WHC) after four cycles of soil drying-rewetting. The responses of litter decomposition to soil drying-rewetting cycles and nutrient releases of P. simonii and P. sylvestris var. mongolica were similar during the drying and rewetting period. Litter mass loss and the release of C, lignin and total phenol were decreased by 17.4%, 23.8%, 35.2% and 32.7% in DW2 treatment compared with CM treatment. There was no significant difference in release of leaf litter N or P among the drying-rewetting treatments. There were consistent changes of litter mass loss and nutrient releases among the treatments at the end of drying-rewetting and delayed incubation period. However, litter decomposition rate and litter C and lignin release rates were increased in DW2 treatment compared with CM treatment during the delayed incubation period, indicating a short-term delayed effect.

How does the foraging behavior of large herbivores cause different associational plant defenses?

The attractant-decoy hypothesis predicts that focal plants can defend against herbivory by neighboring with preferred plant species when herbivores make decisions at the plant species scale. The repellent-plant hypothesis assumes that focal plants will gain protection by associating with nonpreferred neighbors when herbivores are selective at the patch scale. However, herbivores usually make foraging decisions at these scales simultaneously. The net outcomes of the focal plant vulnerability could depend on the spatial scale at which the magnitude of selectivity by the herbivores is stronger. We quantified and compared the within- and between-patch overall selectivity index (OSI) of sheep to examine the relationships between associational plant effects and herbivore foraging selectivity. We found that the sheep OSI was stronger at the within- than the between-patch scale, but focal plant vulnerability followed both hypotheses. Focal plants defended herbivory with preferred neighbors when the OSI difference between the two scales was large. Focal plants gained protection with nonpreferred neighbors when the OSI difference was narrowed. Therefore, the difference in selectivity by the herbivores between the relevant scales results in different associational plant defenses. Our study suggests important implications for understanding plant-herbivore interactions and grassland management.

[Effects of nitrogen addition on microbial respiration and root respiration in a sandy grassland.] / æ°®æ·»åŠ å¯¹æ²™è´¨è‰åœ°å¾®ç”Ÿç‰©å‘¼å¸ä¸Žæ ¹ç³»å‘¼å¸çš„å½±å“.

Soil respiration includes root respiration and microbial respiration. Effects of nitrogen addition on root respiration and microbial respiration may be quite different. We examined the effects of N-addition on the releasing of soil CO2 and the responses of root respiration and microbial respiration in a Keerqin sandy grassland, Northeast China. Results showed that both soil respiration and microbial respiration firstly rose then declined during the growing season (May to October). Microbial respiration was the main contributor of soil respiration, accounting for 82.6%. Contribution rate of root respiration altered with months, peaking in May (49.4%) and August (41.9%), with an average contribution rate of 17.4% during the growing season. Root respiration (with a decrease of 17.7%) was more sensitive to N-addition compared with microbial respiration (with a decrease of 3.9%) at 10 ℃. N-addition increased Q10 values of soil respiration and microbial respiration, and enhanced their sensitivity to soil water content variation.

Effects of Nitrogen Addition on Litter Decomposition and CO2 Release: Considering Changes in Litter Quantity.

This study aims to evaluate the impacts of changes in litter quantity under simulated N deposition on litter decomposition, CO2 release, and soil C loss potential in a larch plantation in Northeast China. We conducted a laboratory incubation experiment using soil and litter collected from control and N addition (100 kg ha-1 year-1 for 10 years) plots. Different quantities of litter (0, 1, 2 and 4 g) were placed on 150 g soils collected from the same plots and incubated in microcosms for 270 days. We found that increased litter input strongly stimulated litter decomposition rate and CO2 release in both control and N fertilization microcosms, though reduced soil microbial biomass C (MBC) and dissolved inorganic N (DIN) concentration. Carbon input (C loss from litter decomposition) and carbon output (the cumulative C loss due to respiration) elevated with increasing litter input in both control and N fertilization microcosms. However, soil C loss potentials (C output-C input) reduced by 62% in control microcosms and 111% in N fertilization microcosms when litter addition increased from 1 g to 4 g, respectively. Our results indicated that increased litter input had a potential to suppress soil organic C loss especially for N addition plots.

Responses of plant nutrient resorption to phosphorus addition in freshwater marsh of Northeast China.

Anthropogenic activities have increased phosphorus (P) inputs to most aquatic and terrestrial ecosystems. However, the relationship between plant nutrient resorption and P availability is still unclear, and much less is known about the underlying mechanisms. Here, we used a multi-level P addition experiment (0, 1.2, 4.8, and 9.6 g P m(-2) year(-1)) to assess the effect of P enrichment on nutrient resorption at plant organ, species, and community levels in a freshwater marsh of Northeast China. The response of nutrient resorption to P addition generally did not vary with addition rates. Moreover, nutrient resorption exhibited similar responses to P addition across the three hierarchical levels. Specifically, P addition decreased nitrogen (N) resorption proficiency, P resorption efficiency and proficiency, but did not impact N resorption efficiency. In addition, P resorption efficiency and proficiency were linearly related to the ratio of inorganic P to organic P and organic P fraction in mature plant organs, respectively. Our findings suggest that the allocation pattern of plant P between inorganic and organic P fractions is an underlying mechanism controlling P resorption processes, and that P enrichment could strongly influence plant-mediated biogeochemical cycles through altered nutrient resorption in the freshwater wetlands of Northeast China.

Effects of different remediation treatments on crude oil contaminated saline soil.

Remediation of the petroleum contaminated soil is essential to maintain the sustainable development of soil ecosystem. Bioremediation using microorganisms and plants is a promising method for the degradation of crude oil contaminants. The effects of different remediation treatments, including nitrogen addition, Suaeda salsa planting, and arbuscular mycorrhiza (AM) fungi inoculation individually or combined, on crude oil contaminated saline soil were assessed using a microcosm experiment. The results showed that different remediation treatments significantly affected the physicochemical properties, oil contaminant degradation and bacterial community structure of the oil contaminated saline soil. Nitrogen addition stimulated the degradation of total petroleum hydrocarbon significantly at the initial 30d of remediation. Coupling of different remediation techniques was more effective in degrading crude oil contaminants. Applications of nitrogen, AM fungi and their combination enhanced the phytoremediation efficiency of S. salsa significantly. The main bacterial community composition in the crude oil contaminated saline soil shifted with the remediation processes. γ-Proteobacteria, ß-Proteobacteria, and Actinobacteria were the pioneer oil-degraders at the initial stage, and Firmicutes were considered to be able to degrade the recalcitrant components at the later stage.

[Biomechanical study on a net-fixation of Kirschner wire in treating depressed tibial plateau fractures].

OBJECTIVE: To evaluate the biomechanical properties of tibial plateau depressed fracture fixed with a net-fixation of Kirschner wires. METHODS: Twenty homemade fracture models were fixed with eight 1.5 mm Kirschner wires in a net-fixation; 20 homemade fracture models were fixed with two 3.5 mm cortical screws. Plane-compressed and dot-compressed test were made on each 10 models of the two groups. The maximal force of anti-ompress and stiffness were measured and evaluated. RESULTS: In plane-compressed test,mean maximal force of anti-compress and stiffness for screw fixation was (1,925.31 +/- 444.26) N and (2.28 +/- 0.53) N/mm2, respectively, for net-fixation was (1,609.62 +/- 277.72) N and (1.90 +/- 0.33) N/mm2, respectively. There was no statistical difference between the two fixation methods (P > 0.05). In dot-compressed test,mean maximal force of anti-compress and stiffness for screw fixation was (411.13 +/- 233.88) N and (2.66 +/- 1.52) N/mm2,respectively,for net-fixation was (1,105.58 +/- 290.66) N and (7.18 +/- 1.89) N/mm2,respectively,the net-fixation was better than that of the screw fixation (P< 0.01). CONCLUSION: Treatment of tibial plateau depressed fracture with a net-fixation of Kirschner wires is a biological fixation and is a reliably method.

Dynamics and sources of soil organic C following afforestation of croplands with poplar in a semi-arid region in northeast China.

Afforestation of former croplands has been proposed as a promising way to mitigate rising atmospheric CO2 concentration in view of the commitment to the Kyoto Protocol. Central to this C sequestration is the dynamics of soil organic C (SOC) storage and stability with the development of afforested plantations. Our previous study showed that SOC storage was not changed after afforestation except for the 0-10 cm layer in a semi-arid region of Keerqin Sandy Lands, northeast China. In this study, soil organic C was further separated into light and heavy fractions using the density fractionation method, and their organic C concentration and (13)C signature were analyzed to investigate the turnover of old vs. new SOC in the afforested soils. Surface layer (0-10 cm) soil samples were collected from 14 paired plots of poplar (Populus × xiaozhuanica W. Y. Hsu & Liang) plantations with different stand basal areas (the sum of the cross-sectional area of all live trees in a stand), ranging from 0.2 to 32.6 m(2) ha(-1), and reference maize (Zea mays L.) croplands at the same sites as our previous study. Soil ΔC stocks (ΔC refers to the difference in SOC content between a poplar plantation and the paired cropland) in bulk soil and light fraction were positively correlated with stand basal area (R (2) = 0.48, p<0.01 and R (2) = 0.40, p = 0.02, respectively), but not for the heavy fraction. SOCcrop (SOC derived from crops) contents in the light and heavy fractions in poplar plantations were significantly lower as compared with SOC contents in croplands, but tree-derived C in bulk soil, light and heavy fraction pools increased gradually with increasing stand basal area after afforestation. Our study indicated that cropland afforestation could sequester new C derived from trees into surface mineral soil, but did not enhance the stability of SOC due to a fast turnover of SOC in this semi-arid region.

Mixing effects of understory plant litter on decomposition and nutrient release of tree litter in two plantations in Northeast China.

Understory vegetation plays a crucial role in carbon and nutrient cycling in forest ecosystems; however, it is not clear how understory species affect tree litter decomposition and nutrient dynamics. In this study, we examined the impacts of understory litter on the decomposition and nutrient release of tree litter both in a pine (Pinus sylvestris var. mongolica) and a poplar (Populus × xiaozhuanica) plantation in Northeast China. Leaf litter of tree species, and senesced aboveground materials from two dominant understory species, Artemisia scoparia and Setaria viridis in the pine stand and Elymus villifer and A. sieversiana in the poplar stand, were collected. Mass loss and N and P fluxes of single-species litter and three-species mixtures in each of the two forests were quantified. Data from single-species litterbags were used to generate predicted mass loss and N and P fluxes for the mixed-species litterbags. In the mixture from the pine stand, the observed mass loss and N release did not differ from the predicted value, whereas the observed P release was greater than the predicted value. However, the presence of understory litter decelerated the mass loss and did not affect N and P releases from the pine litter. In the poplar stand, litter mixture presented a positive non-additive effect on litter mass loss and P release, but an addition effect on N release. The presence of understory species accelerated only N release of poplar litter. Moreover, the responses of mass loss and N and P releases of understory litter in the mixtures varied with species in both pine and poplar plantations. Our results suggest that the effects of understory species on tree litter decomposition vary with tree species, and also highlight the importance of understory species in litter decomposition and nutrient cycles in forest ecosystems.

[Effects of understory removal and nitrogen addition on the soil chemical and biological properties of Pinus sylvestris var. mongolica plantation in Keerqin Sandy Land].

A full factorial experiment was conducted to study the effects of understory removal and nitrogen addition (8 g x m(-2)) on the soil NO(3-)-N and NH(4+)-N concentrations, potential net nitrogen mineralization rate (PNM) and nitrification rate (PNN), microbial biomass C (MBC) and N (MBN), MBC/MBN, urease and acid phosphomonoesterase activities, and Olsen-P concentration in a Pinus sylvestris var. mongolica plantation in Keerqin Sandy Land during a growth season. Understory removal decreased the soil NH(4+)-N concentration, PNM, MBC, and MBN/MBN significantly, increased the soil Olsen-P concentration, but had little effects on the soil NO(3-)-N concentration, PNN, and urease and acid phosphomonoesterase activities. Nitrogen addition increased the soil NO(3-)-N concentration, PNM and PNN significantly, but had little effects on the other test properties. The interaction between understory removal and nitrogen addition had significant effects on the soil NH(4+)-N concentration, but little effects on the soil NO(3-)-N concentration. However, the soil NO(3-)-N concentration in the plots of understory removal with nitrogen addition was increased by 27%, compared with the plots of nitrogen addition alone, which might lead to the leaching of NO3-. It was suggested that understory vegetation could play an important role in affecting the soil chemical and biological properties in Mongolian pine plantations, and hence, the importance of understory vegetation should not be neglected when the forest management and restoration were implemented.

Changes in labile soil organic matter fractions following land use change from monocropping to poplar-based agroforestry systems in a semiarid region of Northeast China.

Labile fractions of soil organic matter (SOM) respond rapidly to land management practices and can be used as a sensitive indicator of changes in SOM. However, there is little information about the effect of agroforestry practices on labile SOM fractions in semiarid regions of China. In order to test the effects of land use change from monocropping to agroforestry systems on labile SOM fractions, we investigated soil microbial biomass C (MBC) and N, particulate organic matter C (POMC) and N (POMN), as well as total organic C (TOC) and total N (TN) in the 0- to 15-cm and the 15- to 30-cm layers in 4-year-old poplar-based agroforestry systems and adjoining monocropping systems with two different soil textures (sandy loam and sandy clay loam) in a semiarid region of Northeast China. Our results showed that poplar-based agroforestry practices affected soil MBC, POMC, and POMN, albeit there was no significant difference in TOC and TN. Agroforestry practices increased MBC, POMC, and POMN in sandy clay loam soils. However, in sandy loam soils, agroforestry practices only increased MBC and even decreased POMC and POMN at the 0- to 15-cm layer. Our results suggest that labile SOM fractions respond sensitively to poplar-based agroforestry practices and can provide early information about the changes in SOM in semiarid regions of Northeast China and highlight that the effects of agroforestry practices on labile SOM fractions vary with soil texture.

Changes in soil particulate organic matter, microbial biomass, and activity following afforestation of marginal agricultural lands in a semi-arid area of northeast China.

Afforestation of agricultural lands has been one of the major land use changes in China in recent decades. To better understand the effect of such land use change on soil quality, we investigated selected soil physical, chemical and microbial properties (0-15 cm depth) in marginal agricultural land and a chronosequence of poplar (Populus euramericana cv. 'N3016') plantations (5-, 10-, 15- and 20-years old) in a semi-arid area of Northeast China. Soil bulk density significantly declined after conversion of agricultural lands to poplar plantations. Soil total organic carbon (TOC) and nitrogen (TN) concentrations, microbial biomass C (MBC) and potential N mineralization rate (PNM) decreased initially following afforestation of agricultural lands, and then increased with stand development. However, soil metabolic quotient (qCO(2)) exhibited a reverse trend. In addition, soil particulate organic matter C (POM-C) and N (POM-N) concentrations showed no significant changes in the first 10 years following afforestation, and then increased with stand age. These findings demonstrated that soil quality declined initially following afforestation of agricultural lands in semi-arid regions, and then recovered with stand development. Following 15 years of afforestation, many soil quality parameters recovered to the values found in agricultural land. We propose that change in soil quality with stand age should be considered in determining optimum rotation length of plantations and best management practices for afforestation programs.

[Effects of nitrogen addition on grassland species diversity and productivity in Keerqin Sandy Land].

Species diversity and productivity are the important indices of the structure and functioning of ecosystems. With Keerqin sandy grassland as test object, this paper studied its species composition, species diversity, and productivity under effects of different level nitrogen (N) addition. Nitrogen addition altered the species composition and the dominant species in the community, increased the vegetation height and coverage, and decreased vegetation light penetration. With the increase of N addition, both the species richness and the diversity decreased. Nitrogen addition increased the aboveground biomass significantly (P<0.01). There was a significant positive relationship between species richness and vegetation light penetration (P<0.01), and a significant negative relationship between species richness and vegetation coverage (P<0.01). It was suggested that nitrogen deposition and artificial nitrogen addition would affect the species composition, species diversity, and productivity of sandy grassland ecosystem.

[Soil microbial biomass and activity in relation to stand age of poplar shelterbelts].

Taking 5-, 10-, 15-, and 20 years old poplar (Populus euramericana cv. "N 3016") shelterbelts in Jianping County, Liaoning Province as test objects, the effects of establishing shelterbelts on the farmland soil microbial biomass carbon and nitrogen, and microbial activity were evaluated. After the establishment of shelterbelts, the concentrations of organic carbon and total nitrogen, the microbial biomass carbon and nitrogen, and the basal respiration in 0-15 cm soil layer increased after an initial decrease, being reached or exceeded the levels of the control after 20 years afforestation. The metabolic quotient increased significantly after 5 years afforestation, but decreased with increasing stand age. All the results suggested that under the effects of shelterbelt establishment, farmland soil microbial biomass and activity had obvious change.