[Inhibition of decomposing leaf litter of Cinnamomum camphora on growth of Capsicum annu- um and the alleviation effect of nitrogen application].

Effects of decomposing leaf litter of Cinnamomum camphora on growth, physiological and phenological traits of Capsicum annuum, and modification of these effects by nitrogen application were investigated using a pot experiment. C. camphora leaf litter was applied at rate of 0, 25, 50 100 g per pot, resulting into four treatments, i.e., CK (the control), L25, L50, and L100. Nitrogen application was firstly performed on the 39th d of decomposition (3.0 g urea was added to each pot six times). Leaf area, plant height, basal diameter and biomass production of C. annuum were all inhibited sharply by exposure to the leaf litter, and the inhibition effect increased with the increasing leaf litter in terms of both the intensity and the stability. Treated with L25, budding number reduced by 88.7% averagely during 55th-75th d, and the rate of fructification plant decreased by 40% on the 96th d of decomposition, while neither buds nor fruits were observed when exposed to L50 and L100 at that time. Pigment contents and net photosynthetic rate (Pn) were impacted due to leaf litter addition, and malonaldehyde (MDA) was only markedly promoted by L100. Inhibition on growth and development of C. annuum caused by leaf litter decomposition could be alleviated by nitrogen application. Leaf area treated with leaf litter recovered to the control level on the 52nd d after nitrogen application, and similar results appeared on the 83rd d after nitrogen application for other growth traits. Budding and fructification status were also visibly improved.

[Response of fine root decomposition to simulated nitrogen deposition in Pleioblastus amarus plantation, rainy area of West China].

As an important contributor to carbon (C) flux in the global C cycle, fine root litter decomposition in forests has the potential to be affected by the elevated nitrogen (N) deposition observed globally. From November 2007 to January 2013, a field experiment involving monthly simulated deposition of N in a Pleioblastus amarus plantation was conducted in the Rainy Area of West China. Four levels of nitrogen deposition were included as control (0 g N x m(-2) x a(-1)), low nitrogen (5 g N x m(-2) x a(-1)), medium nitrogen (15 g N x m(-2) x a(-1)) and high nitrogen (30 g N x m(-2) x a(-1)). After 3 years of simulated N deposition experiment (January 2011) , a two-year fine root decomposition experiment was conducted in the simulated N deposition plots using litterbag method, under monthly experimental N deposition. The decomposition rates of fine roots were fast first and then slow. Mass loss of fine roots in the first year of decomposition was up to 60%, and the change of the remaining mass was very slow in the second year. The time of 50% and 95% mass loss of fine roots was 1.20 and 5.17 years, respectively, under the conditions of no addition N input. In general, decomposition rates were underestimated using negative exponential model. Simulated N deposition significantly inhibited the decomposition of fine roots. The remaining mass in the high nitrogen treatment was 51.0% higher than that in the control, after two years of decomposition. Simulated N deposition increased C, P and K contents in the remaining mass of litter. Compared with the control, soil pH decreased significantly in the medium and high nitrogen treatments, soil organic C, total N, ammonium and nitrate contents and fine root biomass of P. amarus increased significantly in the high nitrogen treatment after simulated N deposition for 4. 5 years. Key words: nitrogen deposition; fine root decomposition; Pleioblastus amarus.

Soil biochemical responses to nitrogen addition in a bamboo forest.

Many vital ecosystem processes take place in the soils and are greatly affected by the increasing active nitrogen (N) deposition observed globally. Nitrogen deposition generally affects ecosystem processes through the changes in soil biochemical properties such as soil nutrient availability, microbial properties and enzyme activities. In order to evaluate the soil biochemical responses to elevated atmospheric N deposition in bamboo forest ecosystems, a two-year field N addition experiment in a hybrid bamboo (Bambusa pervariabilis × Dendrocalamopsis daii) plantation was conducted. Four levels of N treatment were applied: (1) control (CK, without N added), (2) low-nitrogen (LN, 50 kg N ha(-1) year(-1)), (3) medium-nitrogen (MN, 150 kg N ha(-1) year(-1)), and (4) high-nitrogen (HN, 300 kg N ha(-1) year(-1)). Results indicated that N addition significantly increased the concentrations of NH4(+), NO3(-), microbial biomass carbon, microbial biomass N, the rates of nitrification and denitrification; significantly decreased soil pH and the concentration of available phosphorus, and had no effect on the total organic carbon and total N concentration in the 0-20 cm soil depth. Nitrogen addition significantly stimulated activities of hydrolytic enzyme that acquiring N (urease) and phosphorus (acid phosphatase) and depressed the oxidative enzymes (phenol oxidase, peroxidase and catalase) activities. Results suggest that (1) this bamboo forest ecosystem is moving towards being limited by P or co-limited by P under elevated N deposition, (2) the expected progressive increases in N deposition may have a potential important effect on forest litter decomposition due to the interaction of inorganic N and oxidative enzyme activities, in such bamboo forests under high levels of ambient N deposition.

Nitrogen addition significantly affects forest litter decomposition under high levels of ambient nitrogen deposition.

BACKGROUND: Forest litter decomposition is a major component of the global carbon (C) budget, and is greatly affected by the atmospheric nitrogen (N) deposition observed globally. However, the effects of N addition on forest litter decomposition, in ecosystems receiving increasingly higher levels of ambient N deposition, are poorly understood. METHODOLOGY/PRINCIPAL FINDINGS: We conducted a two-year field experiment in five forests along the western edge of the Sichuan Basin in China, where atmospheric N deposition was up to 82-114 kg N ha(-1) in the study sites. Four levels of N treatments were applied: (1) control (no N added), (2) low-N (50 kg N ha(-1) year(-1)), (3) medium-N (150 kg N ha(-1) year(-1)), and (4) high-N (300 kg N ha(-1) year(-1)), N additions ranging from 40% to 370% of ambient N deposition. The decomposition processes of ten types of forest litters were then studied. Nitrogen additions significantly decreased the decomposition rates of six types of forest litters. N additions decreased forest litter decomposition, and the mass of residual litter was closely correlated to residual lignin during the decomposition process over the study period. The inhibitory effect of N addition on litter decomposition can be primarily explained by the inhibition of lignin decomposition by exogenous inorganic N. The overall decomposition rate of ten investigated substrates exhibited a significant negative linear relationship with initial tissue C/N and lignin/N, and significant positive relationships with initial tissue K and N concentrations; these relationships exhibited linear and logarithmic curves, respectively. CONCLUSIONS/SIGNIFICANCE: This study suggests that the expected progressive increases in N deposition may have a potential important impact on forest litter decomposition in the study area in the presence of high levels of ambient N deposition.

[Effects of Eucalyptus grandis leaf litter at its early stage of decomposition on the growth and photosynthetic characteristics of Cichorium intybus].

From March to May, 2010, a pot experiment was conducted to investigate the effects of Eucalyptus grandis leaf litter at its early stage of decomposition on the growth and photosynthetic characteristics of Cichorium intybus. Four treatments with different application rate of the leaf litter, i.e., 0 g x pot(-1) (CK), 30 g x pot(-1) (A1), 60 g x pot(-1) (A2), and 90 g x pot(-1) (A3), were installed. Each pot contained 12 kg soil mixed with the leaf litter, and then, C. intybus was sown. The growth indicators of the C. intybus were measured at the 30, 45, 60, and 75 d after sowing, and the photosynthetic characteristics of the C. intybus in treatment A3 were studied after the seedlings third leaf fully expanded. At each measured time, the biomass accumulation and leaf area growth of C. intybus in treatments A1, A2, and A3 were inhibited significantly. At the early stage of the leaf litter decomposition, the synthesis of photosynthetic pigments of the C. intybus seedlings was inhibited significantly, and the inhibition effect was getting stronger with the increasing amount of the leaf litter addition. The diurnal change of the seedlings photosynthetic rate in all treatments showed a bimodal curve with midday depression, the stomatal conductance and water use efficiency had the same variation trend with the net photosynthetic rate, and the total diurnal photosynthesis decreased in the order of CK > A1 > A2 > A3. The GC-MS analysis showed there were 33 kinds of small molecule compounds released gradually with the decomposition of the leaf litter, among which, allelopathic substance terpenoid dominated.

Nitrogen distribution and cycling through water flows in a subtropical bamboo forest under high level of atmospheric deposition.

BACKGROUND: The hydrological cycle is an important way of transportation and reallocation of reactive nitrogen (N) in forest ecosystems. However, under a high level of atmospheric N deposition, the N distribution and cycling through water flows in forest ecosystems especially in bamboo ecosystems are not well understood. METHODOLOGY/PRINCIPAL FINDINGS: In order to investigate N fluxes through water flows in a Pleioblastus amarus bamboo forest, event rainfall/snowfall (precipitation, PP), throughfall (TF), stemflow (SF), surface runoff (SR), forest floor leachate (FFL), soil water at the depth of 40 cm (SW1) and 100 cm (SW2) were collected and measured through the whole year of 2009. Nitrogen distribution in different pools in this ecosystem was also measured. Mean N pools in vegetation and soil (0-1 m) were 351.7 and 7752.8 kg ha(-1). Open field nitrogen deposition at the study site was 113.8 kg N ha(-1) yr(-1), which was one of the highest in the world. N-NH4(+), N-NO3(-) and dissolved organic N (DON) accounted for 54%, 22% and 24% of total wet N deposition. Net canopy accumulated of N occurred with N-NO3(-) and DON but not N-NH4(+). The flux of total dissolved N (TDN) to the forest floor was greater than that in open field precipitation by 17.7 kg N ha(-1) yr(-1), due to capture of dry and cloudwater deposition net of canopy uptake. There were significant negative exponential relationships between monthly water flow depths and monthly mean TDN concentrations in PP, TF, SR, FFL and SW1. CONCLUSIONS/SIGNIFICANCE: The open field nitrogen deposition through precipitation is very high over the world, which is the main way of reactive N input in this bamboo ecosystem. The water exchange and N consume mainly occurred in the litter floor layer and topsoil layer, where most of fine roots of bamboo distributed.

[Effects of simulated nitrogen deposition on soil enzyme activities in a Betula luminifera plantation in Rainy Area of West China].

From January 2008 to January 2009, a field experiment was conducted to investigate the effects of simulated nitrogen (N) deposition (0, 5, 15, and 30 g N x m(-2) x a(-1)) on the soil enzyme activities in a Betula luminifera plantation in Rainy Area of West China. As compared with the control (0 g N x m(-2) x a(-1)), simulated N deposition stimulated the activities of soil hydrolases (beta-fructofuranosidase, cellulase, acid phosphatase, and urease) significantly, but depressed the activities of soil oxidases (polyphenol oxidase and peroxidase). These results suggested that the increased exogenous inorganic N could stimulate soil microbial activity and increase the demands of both B. luminifera and soil microbes for C and P, whereas the depress of soil polyphenol oxidase and peroxidase activities under N addition could inhibit the degradation of litter and promote its accumulation in soil, leading to the increase of soil C storage in the B. luminifera plantation ecosystem.

[Effects of drought stress and nitrogen fertilization rate on the accumulation of osmolytes in Jatropha curcas seedlings].

A pot experiment with controlled water supply was conducted to study the effects of different drought stress degree (80% FC, 60% FC, 40% FC, and 20% FC) and nitrogen fertilization rate (0 g x pot(-1), 1.2 g x pot(-1), 3.6 g x pot(-1), and 6.0 g x pot(-1)) on the accumulation of osmolytes in different organs of Jatropha curcas seedlings. Under drought stress, the soluble protei and free proline in seedling shoots and roots and the soluble sugar in seedling shoots had a great accumulation, and the free proline content in seedling leaves had a great increase with increasing drought stress degree. Also under drought stress, the Na+, Ca2+, and Mg2+ all highly accumulated in seedling various organs, while K only accumulated greatly in shoots but slightly in leaves and roots. The effects of nitrogen fertilization on the accumulation of osmolytes in seedlings depended on drought stress degree and nitrogen fertilization rate. At 80% FC and 60% FC, increasing nitrogen fertilization rate could markedly promote the accumulation of osmolytes in the organs of J. curcas seedlings; at 40% FC, applying 6.0 g x pot(-1) weakened the promotion effect on the osmolytes accumulation; whereas at 20%, applying 1.2 g x pot(-1) made the plants have a higher capability in osmoregulation, but applying 3.6 g x pot(-1) and 6.0 g x pot(-1) had less promotion effect, and even, inhibited osmolytes accumulation.

[Characteristics of soil respiration components and their temperature sensitivity in a Pleioblastus amarus plantation in rainy area of West China].

To understand the characteristics of soil respiration components and their temperature sensitivity in a Pleioblastus amarus plantation in the Rainy Area of West China, a one-year periodic monitoring was conducted in a fixed plot of the plantation from February 2010 to January 2011. In the plantation, the mean annual soil respiration rate was 1.13 micromol x m(-2) x s(-1), and the soil respiration presented a clear seasonal pattern, with the maximum rate in mid-summer and the minimum rate in late winter. The contribution rates of the respiration of litter layer, root-free soil, and root to the total soil respiration of the plantation accounted for 30.9%, 20.8% and 48.3%, respectively, and the respiration of the components had a similar seasonal pattern to the total soil respiration, being related to temperature and litterfall. The annual CO2 efflux from the total soil respiration, litter layer CO2 release, root-free soil CO2 release, and root respiration was 4.27, 1.32, 0.87 and 2.08 Mg C x hm(-2) x a(-1), respectively. The total soil respiration and its components had significant positive linear correlations with litterfall, and significant positive exponential correlations with air temperature and the soil temperature at depth 10 cm. The Q10 values of total soil respiration, litter layer CO2 release, root-free soil CO2 release, and root respiration calculated based on the soil temperature were 2.90, 2.28, 3.09 and 3.19, respectively, suggesting that the temperature sensitivity of litter layer CO2 release was significantly lower than that of the total soil respiration and of its other components.

[Effects of Eucalyptus grandis leaf litter decomposition on the growth and photosynthetic characteristics of Cichorium intybus].

A pot experiment was conducted to study the effects of Eucalyptus grandis leaf litter during its early stage decomposition on the growth and the photosynthesis of Cichorium intybus. Each pot contained 12 kg soil mixed with different amounts of E. grandis leaf litter (30 g x pot(-1), A1; 60 g x pot(-1), A2; 90 g x pot(-1), A3; and 0 g x pot(-1), CK), and sowed with C. intybus. The growth indicators and the photosynthetic characteristics of C. intybus were measured after the third leaf of C. intybus seedlings fully expanded in treatment A3. At the early stage of leaf litter decomposition, the C. intybus biomass accumulation, leaf area growth, and synthesis of photosynthetic pigments were inhibited significantly, and the inhibition effect was getting stronger with the increasing amount of the leaf litter addition. The intercellular CO2 concentration of C. intybus was increased by litter addition, while the net photosynthetic rate, stomatal conductance, and transpiration rate were significantly lower than those of the control. With the increase of leaf litter addition, all the parameters of C. intybus light response and CO2 response except CO2 compensation point showed an obvious downward trend, and there existed significant differences between the treatments of litter additions and the control. It was suggested that during the decomposition of E. grandis leaf litter, its allelopathic substances released gradually and acted on receptor plants, inhibited the synthesis of photosynthetic pigments and the photosynthesis of the receptors, decreased the receptors environmental adaptation ability, and accordingly, inhibited the growth of C. intybus.

[Effects of simulated nitrogen deposition on soil respiration in a Bambusa pervariabilis x Dendrocala mopsi plantation in rainy area of West China].

From January 2008 to February 2009, a field experiment was conducted in Rainy Area of West China to understand the effects of nitrogen (N) deposition on the soil respiration in a Bambusa pervariabilis x Dendrocala mopsi plantation. Four treatments were installed, i. e., no N added (control), 5 g N m(-2) a(-1) (low-N), 15 g N m(-2) a(-1) (medium-N), and 30 g N m(-2) a(-1) (high-N), and soil respiration rate was determined by infra-red CO2 analyzer. In the plantation, soil respiration rate had an obvious seasonal change, with the maximum in July and the minimum in January. In control plot, the annual cumulative soil respiration was (389 +/- 34) g m(-2) a(-1). Soil respiration rate had significant positive exponential relationships with soil temperature at 10 cm depth and air temperature, and significant positive linear relationships with soil microbial biomass carbon (MBC) and nitrogen (MBN). Simulated N deposition promoted soil respiration significantly, with significant differences between the low- and medium-N and the control but no significant difference between high-N and the control. In control plot, surface soil (0-20 cm) MBC and MBN were 0.460 and 0.020 mg g(-1), respectively. In N-added plots, both the MBC and the MBN had significant increase. The fine root density in surface soil was 388 g m(-2), which was less affected by simulated N deposition. The soil respiration Q10 value calculated from soil temperature at 10 cm depth and air temperature was 2.66 and 1.87, respectively, and short-term N deposition had lesser effects on the Q10 value. The variation of soil respiration in the plantation was mainly controlled by temperature and soil microbial biomass, and simulated N deposition could increase the CO2 emission via increasing soil microbial biomass.

[Effects of simulated nitrogen deposition on soil respiration in a Neosinocalamus affinis plantation in rainy area of west China].

From December 2007 to November 2008, an in situ experiment was conducted to study the effects of simulated nitrogen deposition on the soil respiration in a Neosinocalamus affinis plantation in Rainy Area of West China. Four treatments were installed, i.e., 0 (CK), 50, 150, and 300 kg N x hm(-2) x a(-1), and soil respiration rate was measured by infrared gas analyzer. In the test plantation, soil respiration rate had a distinct seasonal fluctuation, with the highest (3.36 +/- 0.20 micromol x m(-2) x s(-1)) by the end of July and the lowest by the end of February (0.33 +/- 0.07 micromol x m(-2) x s(-1)). There was a significant exponential relationship (P<0.001) between soil respiration rate and soil temperature, and the temperature at 10 cm soil depth explained 91.6% of the seasonal change of soil respiration. However, less relationship was observed between soil respiration rate and soil moisture content (R2 = 0.0758). From June to November 2008, the contribution of root respiration to total soil respiration ranged from 46% to 59%. The annual release amount of CO2 in treatments 50, 150, and 300 kg x hm(-2) x a(-1) was 23.6% , 46.7%, and 50.5% lower than that in CK (2.17 x 10(4) kg x hm(-2)), and the Q10 value of soil respiration rate in treatments 0, 50, 150, and 300 kg x hm(-2) x a(-1) was 3.72, 3.51, 2.95, and 2.71, respectively.

[Fractal features of soil aggregate structure in slope farmland with different de-farming patterns in South Sichuan Province of China].

By using fractal model, this paper studied the fractal dimension of soil aggregate structure (D) in the slope farmland (CK), its 5-year de-farmed Neosinocalamus affinis plantation (NAP), Bambusa pervariabilis x Dendrocalamopsis oldhami plantation (BDP), Alnus crenastogyne + Neosinocalamus affinis plantation (ANP), and abandoned farmland (AFL) in south Sichuan Province of China, and analyzed the relationships between the D and soil physical and chemical properties. In the de-farmed plantations and abandoned farmland, the contents of > 0.25 mm soil aggregates and water-stable aggregates were increased significantly, compared with those in the slope farmland. The D was 1.377-2.826, being in the order of NAP < BDP < ANP < AFL < CK, and decreased with the increasing contents of > 0.25 mm soil aggregates and water-stable aggregates. Comparing with CK, de-farming increased the soil natural water content, capillary porosity, and contents of soil organic matter, total N, alkali-hydrolysable N, total P, and total K, and decreased soil bulk density, non-capillary porosity, and aeration porosity. There were close relationships between the fractal dimension of soil aggregate structure and the soil physical and chemical properties. All the results suggested that the de-farming of slope farmland was beneficial to the increase of the contents of > 0.25 mm soil aggregates and water-stable aggregates, and the enhancement of soil structure stability. The D could be used as an ideal index to evaluate soil fertility, and planting Neosinocalamus affinis on the de-farming slope farmland was a good measure for the improvement of soil fertility in the research area.

[Effect of drought on photosynthetic characteristics and growth of Jatropha curcas seedlings under different nitrogen levels].

A pot experiment with controlled water supply was conducted to study the effects of drought stress (continuous drought for 0 d, 5 d, 10 d, ... 45 d) on the photosynthetic characteristics and growth of Jatropha curcas seedlings under different nitrogen fertilization levels (N0, 0 kg N x hm(-2); N(L), 96 kg N x hm(-2; N(M), 288 kg N x hm(-2); N(H), 480 kg N x hm(-2)). With the enhancement of drought stress, the leaf relative water content (RWC1), height growth (Z(h)), basal diameter growth (Z(d), leaf area (L(a)), net photosynthetic rate ( P(n)), transpiration rate (T(r)), and stomatal conductance (G(s)) decreased significantly (P < 0.01), irrespective of nitrogen fertilization level. The chlorophyll (Chl) content and water use efficiency (WUE) increased first and decreased then, while the intercellular CO2, concentration (C(i)) had an increase after an initial decrease. Under adequate water condition, nitrogen fertilization promoted the photosynthesis and growth of J. curcas seedlings to different degrees, and the effect was increased with increasing nitrogen fertilization level. Under drought stress, the effects of nitrogen nutrition on the photosynthesis and growth were dependent on drought intensity and nitrogen fertilization level. Specifically, increasing nitrogen fertilization level could promote the photosynthesis and growth of J. curcas seedlings under mild drought, the promotion effect of N(M) was higher than that of N(L) and N(H) under moderate drought, and N(L) had the best promotion effect while N(H) weakened the effect or made it negative under severe drought.

[Effects of fertilization level on diurnal variation of gas exchange of young Eucalyptus grandis leaf].

Different levels (0, 90, 180, and 270 g per tree) of compound fertilizer containing 15% N, 15% P2O5, and 15% K2O were applied to young Eucalyptus grandis to study the diurnal variations of its leaf stomatal conductance (Gs), intercellular CO2 concentration (Ci), net photosynthesis rate (Pn), transpiration rate (Tr), water use efficiency (WUE), and vapor pressure deficit on leaf surface (Vpdl) as well as the variation of leaf chlorophyll content, aimed to approach the relationships of E. grandis photosynthesis with fertilization and environmental factors. In all treatments, the diurnal variation of Pn presented a single-peak curve, with the peak at 14:00 and not showing midday depression. The Gs, Tr, and Vpdl showed the similar trend with Pn, while the Ci had a minimum value at 14:00. The WUE demonstrated a double-peak curve, with the first and second peak occurred at 10:00 and 14:00, respectively. Comparing with the control, the mean values of Gs, Pn, Tr, WUE, and chlorophyll a, chlorophyll b, and total chlorophyll contents under fertilization increased by 4.6%-15.9%, 7.8%-21.8%, 4.8%-11.6%, 3.2%-8.8%, 15.5%-62.0%, 14.5%-44.5% and 15.3%-57.1%, respectively, and the increment increased with fertilization level. By contrast, the mean values of Ci and VPdl decreased by 14.5%-44.5% and 15.3%-57.1%, respectively, and the decrement increased with fertilization level. The Gs, Pn, and Tr were significantly correlated with air temperature, relative humidity (RH), and photosynthetic active radiation (PAR), and also, the Gs was significantly correlated with Pn and Tr. It was suggested that fertilization could promote E. grandis growth and enhance its WUE and biological carbon sequestration, and air temperature, RH, PAR, and Gs were the main factors causing the diurnal variations of photosynthesis and transpiration of E. grandis.

[Effects of simulated nitrogen deposition on the fine root characteristics and soil respiration in a Pleioblastus amarus plantation in rainy area of West China].

Fine root is critical in the belowground carbon (C) cycling in forest ecosystem. Aimed to understand the effects of nitrogen (N) deposition on the fine root characteristics and soil respiration in Pleioblastus amarus plantation, a two-year field experiment was conducted in the Rainy Area of West China. Four treatments with different levels of N deposition were installed, i. e., CK (0 g N x m(-2) x a(-1)), low N (5 g N x m(-2) x a(-1)), medium N (15 g N x m(-2) x a(-1)), and high N (30 g N x m(-2) x a(-1)). There were great differences in the biomass and element contents of <1 mm and 1-2 mm fine roots among the treatments. Comparing with < 1 mm fine roots, 1-2 mm fine roots had higher contents of lignin, P, and Mg, but lower contents of cellulose and Ca. Nitrogen deposition increased the biomass of < 2mm fine roots significantly, with the values being (533 +/- 89) g x m(-2) in CK, and (630 +/- 140), (632 +/- 168), and (820 +/- 161) g x m(-2) in treatments low N, medium N, and high N, respectively. The N, K, and Mg contents of <2 mm fine roots also had an obvious increase under N deposition. The annual soil respiration rate in treatments CK, low N, medium N, and high N was (5.85 +/- 0.43), (6.48 +/- 0.71), (6.84 +/- 0.57), and (7.62 +/- 0.55) t C x hm(-2) x a(-1), respectively, indicating that N deposition had obvious promotion effects on soil respiration. There were significant linear relationships between the annual soil respiration rate and the biomass and N content of <2 mm fine roots. N deposition increased the fine root biomass and promoted the root metabolism, and stimulated the rhizospheric soil respiration rate via promoting microbial activities.

[Effects of simulated warming on the growth, leaf phenology, and leaf traits of Salix eriostachya in sub-alpine timberline ecotone of western Sichuan, China].

By using open-top chamber (OTC), the effects of simulated warming on the growth, leaf phenology, and leaf traits of Salix eriostachya in sub-alpine timberline ecotone of Western Sichuan were studied. The results showed that comparing with the control, the mean air temperature at 1.2 m above the ground throughout S. eriostachya growth season in OTC increased by 2.9 degrees C, while the soil temperature at the depth of 5 cm only increased by 0.4 degrees C. The temperature increase in OTC made S. eriostachya budding advanced and defoliation postponed obviously, and the leaf life-span longer. The leaf and branch growth rates as well as the specific leaf area in OTC increased obviously, whereas the leaf nitrogen concentration decreased significantly. In OTC, the stomata conductance, net photosynthetic rate, photorespiration, and dark respiration rate of S. eriostachya all exhibited an increasing trend. It was suggested that S. eriostachya had stronger capability to adapt to warming, and, under the background of future global climate change, the elevation of S. eriostachya distribution in the timberline ecotone would be likely to ascend.

[Effects of simulated nitrogen deposition on litter decomposition in Neosinocalamus affinis stands in rainy area of West China].

An in situ experiment was conducted to study the effects of simulated nitrogen deposition on the litter decomposition in Neosinocalamus affinis stands in rainy area of West China. Four treatments were installed, i.e., null N (CK, 0 kg x hm(-2) x a(-1)), low N (LN, 50 kg x hm(-2) x a(-1)), medium N (MN, 150 kg x hm(-2) x a(-1)), and high N (HN, 300 kg x hm(-2) x a(-1)). Among the litters, leaf had the highest decomposition rate, followed by sheath, and twig, with a remaining rate after decomposing for 15 months being 26.38%, 46.18%, and 54.54%, respectively (P < 0.01). Leaf litter decomposed faster during the first 2 months and the 7th-10th month, while the decomposition of sheath and twig was faster from the 5th to the 8th month. It took 2.573 years to decompose 95% of leaf litter mass, 1.686 years and 3.319 years shorter than that of sheath and twig, respectively. After 15 months decomposition of leaf litter, no significant differences were observed among different treatments. To decompose 95% of sheath litter needed 2.679-4.259 years, being the longest in CK and the shortest in treatment MN. After decomposing for 15 months, the decomposition rate of twig litter was in the order MN > HN > LN > CK, and significant difference existed between treatments MN and LN. Nitrogen deposition had obvious promotion effect on the litter decomposition in the N. affinis stands, but this effect decreased with increasing deposited N concentration and time extension.

[Soil enzyme activities in a Pleioblastus amurus plantation in Rainy Area of West China under simulated nitrogen deposition].

From November 2007 to May 2009, a simulation test was conducted in a Pleioblastus amarus plantation in Rainy Area of West China to study the effects of nitrogen deposition on the activities of soil enzymes. Four treatments were installed, i.e., control (0 g N x m(-2) x a(-1)), low nitrogen (5 g N x m(-2) x a(-1)), medium nitrogen (15 g N x m(-2) x a(-1)), and high nitrogen (30 g N x m(-2) x a(-1)). Half year after N deposition, 0-20 cm soil samples were collected monthly, and the activities of peroxidase, polyphenol oxidase, cellulase, sucrase, urease, and acid phosphatase were determined. All test enzyme activities had apparent, seasonal variation, with the peak of cellulase, suerase, and acid phosphatase activities in spring, of urease activity in autumn, and of peroxidase and polyphenol oxidase activities in winter. Nitrogen deposition stimulated the activities of polyphenol oxidase, sucrase, urease, and acid phosphatase, inhibited cellulase activity, but had no significant effects on peroxidase activity. The test P. amurus plantation ecosystem was N-limited, and nitrogen deposition stimulated the decomposition of soil organic matter by microbe-enzyme system.

[Physiological bases of herbages shade-tolerance in Eucalyptus grandis and herbage inter-cultivated system].

The study on the physiological bases of the shade-tolerance of Dactylis glomerata, Lolium perenne, and Hemarthria compressa inter-cultivated in Eucalyptus grandis forests with different canopy densities showed that with increasing canopy density, the light saturation point (LSP), light compensation point (LCP), chlorophyll a/b (Chla/Chlb), and the contents of proline (Pro), soluble sugar (SS) and soluble protein (SP) of the three herbages decreased gradually, but the apparent quantum yield (AQY), chlorophyll content (Chl), malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity were in adverse. The daily average net photosynthesis rates (P(n)) of H. compressa decreased gradually, while that of D. glomerata and L. perenne increased first and decreased then. When the canopy density was below 0.54 for D. glomerata and below 0.27 for L. perenne, the P(n) of the two herbages was higher than CK. There existed significant correlations (P < 0.05) between 11 physiological indices of the three herbages and canopy density, and the shade-tolerance of the three herbages was in the order of D. glomerata > L. perenne > H. compressa, based on the ordination with average subjection function method.