H2 S works synergistically with rhizobia to modify photosynthetic carbon assimilation and metabolism in nitrogen-deficient soybeans.

Hydrogen sulfide (H2 S) performs a crucial role in plant development and abiotic stress responses by interacting with other signalling molecules. However, the synergistic involvement of H2 S and rhizobia in photosynthetic carbon (C) metabolism in soybean (Glycine max) under nitrogen (N) deficiency has been largely overlooked. Therefore, we scrutinised how H2 S drives photosynthetic C fixation, utilisation, and accumulation in soybean-rhizobia symbiotic systems. When soybeans encountered N deficiency, organ growth, grain output, and nodule N-fixation performance were considerably improved owing to H2 S and rhizobia. Furthermore, H2 S collaborated with rhizobia to actively govern assimilation product generation and transport, modulating C allocation, utilisation, and accumulation. Additionally, H2 S and rhizobia profoundly affected critical enzyme activities and coding gene expressions implicated in C fixation, transport, and metabolism. Furthermore, we observed substantial effects of H2 S and rhizobia on primary metabolism and C-N coupled metabolic networks in essential organs via C metabolic regulation. Consequently, H2 S synergy with rhizobia inspired complex primary metabolism and C-N coupled metabolic pathways by directing the expression of key enzymes and related coding genes involved in C metabolism, stimulating effective C fixation, transport, and distribution, and ultimately improving N fixation, growth, and grain yield in soybeans.

Hydrogen sulfide and rhizobia synergistically regulate nitrogen (N) assimilation and remobilization during N deficiency-induced senescence in soybean.

Hydrogen sulfide (H2 S) is emerging as an important signalling molecule that regulates plant growth and abiotic stress responses. However, the roles of H2 S in symbiotic nitrogen (N) assimilation and remobilization have not been characterized. Therefore, we examined how H2 S influences the soybean (Glycine max)/rhizobia interaction in terms of symbiotic N fixation and mobilization during N deficiency-induced senescence. H2 S enhanced biomass accumulation and delayed leaf senescence through effects on nodule numbers, leaf chlorophyll contents, leaf N resorption efficiency, and the N contents in different tissues. Moreover, grain numbers and yield were regulated by H2 S and rhizobia, together with N accumulation in the organs, and N use efficiency. The synergistic effects of H2 S and rhizobia were also demonstrated by effects on the enzyme activities, protein abundances, and gene expressions associated with N metabolism, and senescence-associated genes (SAGs) expression in soybeans grown under conditions of N deficiency. Taken together, these results show that H2 S and rhizobia accelerate N assimilation and remobilization by regulation of the expression of SAGs during N deficiency-induced senescence. Thus, H2 S enhances the vegetative and reproductive growth of soybean, presumably through interactions with rhizobia under conditions of N deficiency.

Hydrogen sulphide improves adaptation of Zea mays seedlings to iron deficiency.

Hydrogen sulphide (H2S) is emerging as a potential molecule involved in physiological regulation in plants. However, whether H2S regulates iron-shortage responses in plants is largely unknown. Here, the role of H2S in modulating iron availability in maize (Zea mays L. cv Canner) seedlings grown in iron-deficient culture solution is reported. The main results are as follows: Firstly, NaHS, a donor of H2S, completely prevented leaf interveinal chlorosis in maize seedlings grown in iron-deficient culture solution. Secondly, electron micrographs of mesophyll cells from iron-deficient maize seedlings revealed plastids with few photosynthetic lamellae and rudimentary grana. On the contrary, mesophyll chloroplasts appeared completely developed in H2S-treated maize seedlings. Thirdly, H2S treatment increased iron accumulation in maize seedlings by changing the expression levels of iron homeostasis- and sulphur metabolism-related genes. Fourthly, phytosiderophore (PS) accumulation and secretion were enhanced by H2S treatment in seedlings grown in iron-deficient solution. Indeed, the gene expression of ferric-phytosiderophore transporter (ZmYS1) was specifically induced by iron deficiency in maize leaves and roots, whereas their abundance was decreased by NaHS treatment. Lastly, H2S significantly enhanced photosynthesis through promoting the protein expression of ribulose-1,5-bisphosphate carboxylase large subunit (RuBISCO LSU) and phosphoenolpyruvate carboxylase (PEPC) and the expression of genes encoding RuBISCO large subunit (RBCL), small subunit (RBCS), D1 protein (psbA), and PEPC in maize seedlings grown in iron-deficient solution. These results indicate that H2S is closely related to iron uptake, transport, and accumulation, and consequently increases chlorophyll biosynthesis, chloroplast development, and photosynthesis in plants.

Land-use conversion and changing soil carbon stocks in China's 'Grain-for-Green' Program: a synthesis.

The establishment of either forest or grassland on degraded cropland has been proposed as an effective method for climate change mitigation because these land use types can increase soil carbon (C) stocks. This paper synthesized 135 recent publications (844 observations at 181 sites) focused on the conversion from cropland to grassland, shrubland or forest in China, better known as the 'Grain-for-Green' Program to determine which factors were driving changes to soil organic carbon (SOC). The results strongly indicate a positive impact of cropland conversion on soil C stocks. The temporal pattern for soil C stock changes in the 0-100 cm soil layer showed an initial decrease in soil C during the early stage (<5 years), and then an increase to net C gains (>5 years) coincident with vegetation restoration. The rates of soil C change were higher in the surface profile (0-20 cm) than in deeper soil (20-100 cm). Cropland converted to forest (arbor) had the additional benefit of a slower but more persistent C sequestration capacity than shrubland or grassland. Tree species played a significant role in determining the rate of change in soil C stocks (conifer < broadleaf, evergreen < deciduous forests). Restoration age was the main factor, not temperature and precipitation, affecting soil C stock change after cropland conversion with higher initial soil C stock sites having a negative effect on soil C accumulation. Soil C sequestration significantly increased with restoration age over the long-term, and therefore, the large scale of land-use change under the 'Grain-for-Green' Program will significantly increase China's C stocks.

[Effects of root exudates C:N on soil physical and chemical characteristics and soil respiration in Robinia pseudoacacia plantation]. / æ ¹ç³»åˆ†æ³Œç‰©C∶N对刺槐林地土壤理化特征和土壤呼吸的影响.

We explored the effects of C:N ratio in root exudates of Robinia pseudoacacia plantations on soil nutrient cycling and microbial activity on the Loess Plateau. We collected in-situ soil from the R. pseudoacacia plantations with essentially identical habitat conditions and growing time of 15, 25, 35, and 45 years. By adding root exudates with different C:N ratios (N only, C:N=10, C:N=50, C:N=100, C only) to the soil and using deionized water as a control, we analyzed the effects of C:N ratio of root exudates on the physicochemical properties of elements such as carbon, nitrogen and phosphorus, soil pH, and soil respiration. The results showed that: 1) Organic carbon content was positively correlated with the C:N ratio of root exudates. Soil organic carbon (SOC) decomposition was faster when root exudates C:N=10. Higher C:N ratio of root exudates (C:N=100) could inhibit SOC decomposition, but only C addition had no significant effect on SOC. 2) Different root exudate C:N produced no significant influence on the total nitrogen. The addition of carbon promoted microbial uptake of ammonium nitrogen, while the addition of nitrogen promoted the nitrification of ammonium nitrogen. As the C:N ratio of root exudates increased, soil ammonium nitrogen content decreased. 3) The addition of nitrogen would reduce soil pH and increase soil total phosphorus content. 4) Soil respiration of R. pseudoacacia plantations was positively correlated with the C:N ratio of root exudates. With the increases of C:N ratio, the promoting effect of root exudates on soil respiration at 25 and 35 years R. pseudoacacia plantations was stronger. In conclusion, higher C:N ratio of root exudates will significantly promote the effect on soil respiration of R. pseudoacacia plantations. Our results improved the understan-ding of the root-soil-microbial interactions in forests.

Changes in soil water holding capacity and water availability following vegetation restoration on the Chinese Loess Plateau.

Changes in land use type can lead to variations in soil water characteristics. The objective of this study was to identify the responses of soil water holding capacity (SWHC) and soil water availability (SWA) to land use type (grassland, shrubland and forestland). The soil water characteristic curve describes the relationship between gravimetric water content and soil suction. We measured the soil water characteristic parameters representing SWHC and SWA, which we derived from soil water characteristic curves, in the 0-50 cm soil layer at sites representing three land use types in the Ziwuling forest region, located in the central part of the Loess Plateau, China. Our results showed that the SWHC was higher at the woodland site than the grassland and shrubland, and there was no significant difference between the latter two sites, the trend of SWA was similar to the SWHC. From grassland to woodland, the soil physical properties in the 0-50 cm soil layer partially improved, BD was significantly higher at the grassland site than at the shrubland and woodland sites, the clay and silt contents decreased significantly from grassland to shrubland to woodland and sand content showed the opposite pattern, the soil porosity was higher in the shrubland and woodland than that in the grassland, the soil physical properties across the 0-50 cm soil layer improved. Soil texture, porosity and bulk density were the key factors affecting SWHC and SWA. The results of this study provide insight into the effects of vegetation restoration on local hydrological resources and can inform soil water management and land use planning on the Chinese Loess Plateau.

[Effects of natural vegetation restoration and afforestation on soil carbon and nitrogen storage in the Loess Plateau, China.] / é»„åœŸé«˜åŽŸæ¤è¢«è‡ªç„¶æ¢å¤å’Œäººå·¥é€ æž—å¯¹åœŸå£¤ç¢³æ°®å‚¨é‡çš„å½±å“.

Changes in land use can have important impacts on soil carbon and nitrogen storage. To explore the effects of different land use types on soil carbon and nitrogen storage, we examined the differences of soil carbon and nitrogen storage, ratio of carbon to nitrogen and root biomass in the 0-100 cm soil layer of the natural grassland and Pinus tabuliformis plantation since the implementation of the project (15 years) of "Returning Farmland to Forest (Grassland)" in the Ziwuling forest region of the Loess Plateau, China. The results showed that soil organic carbon of both natural grassland and P. tabuliformis plantation showed surface polymerization effect. Soil organic carbon storage in the 0-20 cm soil layer of natural grassland was significantly lower than that of P. tabuliformis plantation, while the other soil layers showed no significant difference. The total soil carbon storage of P. tabuliformis plantation in the 0-100 cm soil layer was 117.94 Mg·hm-2, which was 28.4% higher than that of natural grassland. There was no significant difference in total nitrogen storage in different soil layers of the two vegetation types. The soil total nitrogen storage of natural grassland was 7.69 Mg·hm-2 in the 0-100 cm soil layer, which was 17.7% higher than P. tabuliformis plantation. There was significant difference in ammonium storage among different soil layers in natural grassland and P. tabuliformis plantation. The ammonium storage in natural grassland was significantly higher than that in P. tabuliformis plantation, exhibited first increase and then decrease trend with the increases of soil depth. Only in the 0-20 cm soil layer, nitrate storage in natural grassland was significantly higher than the P. tabuliformis plantation. The ratio of carbon to nitrogen of natural grassland and P. tabuliformis plantation showed no significant difference in 0-20 cm soil layer. With the increases of soil layers, the ratio of carbon to nitrogen in P. tabuliformis plantation were higher than in the natural grassland, and the difference increased gradually. In addition, soil carbon and nitrogen storage showed significantly positive correlation with root biomass in natural grassland and P. tabuliformis plantation. Therefore, natural grassland was conductive to the accumulation of soil nitrogen storage, and P. tabuliformis plantation was beneficial to increase soil carbon storage. Root was an important factor affecting the distribution of soil carbon and nitrogen storage.

[Storage of carbon and nitrogen in Quercus and Platycladus orientalis plantations at different ages in the hilly area of western Henan Province, China.] / è±«è¥¿é»„åœŸä¸˜é™µåŒºä¸åŒæž—é¾„æ Žç±»å’Œä¾§æŸäººå·¥æž—ç¢³ã€æ°®å‚¨é‡.

In the study, the method of space substituting time was used to investigate the distribution pattern of carbon and nitrogen storages in Quercus and Platycladus orientalis plantation ecosystems at different ages in hilly area of western Henan Province, China. We also analyzed the dynamic changes of soil carbon and nitrogen storages in different soil layers in the two plantation ecosystems. The results showed that the carbon storage in the arbor and litter layers increased with the increasing tree age. The storage of carbon and nitrogen in soil aggregated mainly in the surface layer and showed a trend of decrease-increase-decrease with the increasing tree age in all soil layers. The ranges of carbon and nitrogen storage in the surface soil were 20.31-50.07 and 1.68-2.12 t·hm-2 in Quercus plantation, and 23.99-48.76 and 1.59-2.34 t·hm-2 in P. orientalis plantation, respectively. Carbon storage ranges in Quercus and P. orientalis plantation ecosystems at different ages were 52.04-275.82 and 62.18-279.81 t·hm-2, respectively. The carbon sequestration capacity in P. orientalis plantation was a little higher than that in Quercus plantation. Soil C/N increased with the increase of afforestation age.

The function of hydrogen sulphide in iron availability: Sulfur nutrient or signaling molecule?

Hydrogen sulphide (H2S) has traditionally been considered as a phytotoxin, having deleterious effects on the plant growth and survival. Recently, it was recongnized as a potential signaling molecule involving in physiological regulation similar to nitric oxide (NO) and carbon monoxide (CO) in plants. In a recent study, we mainly focused on the signaling function of H2S in improving adaptation of Zea mays seedlings to iron deficiency. We reported that H2S was closely related to iron uptake, transport, and accumulation, and consequently increased chlorophyll biosynthesis, chloroplast development, and photosynthesis in Z. mays seedlings. Here, we provide more commentary on the signaling roles of H2S in coping with Fe deficiency in plants through increasing sulfur containing metabolites and regulating the expression level of iron homeostasis and sulfur metabolism-related genes in maize seedlings.

Water-use efficiency of dryland wheat in response to mulching and tillage practices on the Loess Plateau.

Mulching and tillage are widely considered to be major practices for improving soil and water conservation where water is scarce. This paper studied the effects of FM (flat mulching), RFM (ridge-furrow mulching), SM (straw mulching), MTMC (mulching with two materials combined), MOM (mulching with other materials), NT (no-tillage) ST (subsoiling tillage) and RT (rotational tillage) on wheat yield based on a synthesis of 85 recent publications (including 2795 observations at 24 sites) in the Loess Plateau, China. This synthesis suggests that wheat yield was in the range of 259-7898 kg ha(-1) for FM and RFM. The sequence of water use efficiency (WUE) effect sizes was similar to that of wheat yield for the practices. Wheat yields were more sensitive to soil water at planting covered by plastic film, wheat straw, liquid film, water-permeable plastic film and sand compared to NT, ST and RT. RFM and RT increased the yields of wheat by 18 and 15%, respectively, and corresponding for WUE by 20.11 and 12.50%. This synthesis demonstrates that RFM was better for avoiding the risk of reduced production due to lack of precipitation; however, under conditions of better soil moisture, RT and MTMC were also economic.

Yield responses of wheat to mulching practices in dryland farming on the Loess Plateau.

Improving farming practices of soil and water conservation has profound effects on the yield of wheat (Triticum aestivum L.) in dryland farming regions of the Loess Plateau in China. Mulching has proven to be an effective practice to increase crop yield, and possibly contribute to replenishing groundwater. This evaluation study collected and analyzed the data of 1849 observations published in 38 papers using meta-analysis to investigate effects of the mulching practices on wheat yield in terms of different rainfall and regions in comparison with conventional tillage. The main results of the study follow. The effects of the mulching practices were ranked in the order of RFM (ridge-furrow mulching) > MTMC (mulching with two materials combined) > MOM (mulching with other materials) > WSM (wheat straw mulching) > FM (flat mulching). The effects of the mulching practices at the different levels of rainfall during the wheat growing season were in the order: (< 150 mm) > (> 250 mm) > (150-250 mm). The effects of the mulching practices in the different regions were in the order of Henan > Shanxi > Shaanxi > Gansu. WSM, MTMC and FM performed better in improving wheat yield for rainfall of < 150, 150-250 and > 250 mm during the growing season, respectively. The wheat yield with FM, MTMC, MOM and MOM was higher than those with the other mulching practices in Shaanxi, Gansu, Henan and Shanxi. The wheat yield with RFM was 27.4% higher than that with FM, indicating that RFM was the most effective practice to improve wheat yield among all the practices. These findings have important implications for choosing appropriate crop field management to improve wheat yield.

Hydrogen sulfide enhances salt tolerance through nitric oxide-mediated maintenance of ion homeostasis in barley seedling roots.

Hydrogen sulfide (H2S) and nitric oxide (NO) are emerging as messenger molecules involved in the modulation of plant physiological processes. Here, we investigated a signalling network involving H2S and NO in salt tolerance pathway of barley. NaHS, a donor of H2S, at a low concentration of either 50 or 100 µM, had significant rescue effects on the 150 mM NaCl-induced inhibition of plant growth and modulated the K(+)/Na(+) balance by decreasing the net K(+) efflux and increasing the gene expression of an inward-rectifying potassium channel (HvAKT1) and a high-affinity K(+) uptake system (HvHAK4). H2S and NO maintained the lower Na(+) content in the cytoplast by increasing the amount of PM H(+)-ATPase, the transcriptional levels of PM H(+)-ATPase (HvHA1) and Na(+)/H(+) antiporter (HvSOS1). H2S and NO modulated Na(+) compartmentation into the vacuoles with up-regulation of the transcriptional levels of vacuolar Na(+)/H(+) antiporter (HvVNHX2) and H(+)-ATPase subunit ß (HvVHA-ß) and increased in the protein expression of vacuolar Na(+)/H(+) antiporter (NHE1). H2S mimicked the effect of sodium nitroprusside (SNP) by increasing NO production, whereas the function was quenched with the addition of NO scavenger. These results indicated that H2S increased salt tolerance by maintaining ion homeostasis, which were mediated by the NO signal.

"Grain for Green" driven land use change and carbon sequestration on the Loess Plateau, China.

Land-use change is widely considered to be a major factor affecting soil carbon (C) sequestration (ΔCs). This paper studied changes to soil C stocks (Cs) following the conversion of farmland to forest, shrub and grassland across the key area for implementing China's "Grain for Green"--the Loess Plateau. The results are based on a synthesis of 44 recent publications (including 424 observations at 70 sites) which has allowed us to further refine our understanding of the mechanisms driving the increase in Cs following farmland conversion. This synthesis suggests that the ΔCs potential of the Loess Plateau could reach 0.59 Tg yr(-1) based on an estimated annual average ΔCs rate of 0.29 Mg ha(-1) yr(-1). In the region's different rainfall zones both the main contributing factors and Cs dynamics varied. Across the entire Loess Plateau, Cs showed first an increasing (<5 yr) then a decreasing (6-10 yr) tendency only to increase (>10 yr) yet again. In addition, the ΔCs rates depended primarily on restoration age. This synthesis demonstrates that both the initial s Cs and the average annual temperature have a significant effect on ΔCs while the effect of land-use conversion type, rainfall zone, and average annual precipitation were minimal.

Changes in soil carbon and nitrogen following land abandonment of farmland on the Loess Plateau, China.

The revegetation of abandoned farmland significantly influences soil organic C (SOC) and total N (TN). However, the dynamics of both soil OC and N storage following the abandonment of farmland are not well understood. To learn more about soil C and N storages dynamics 30 years after the conversion of farmland to grassland, we measured SOC and TN content in paired grassland and farmland sites in the Zhifanggou watershed on the Loess Plateau, China. The grassland sites were established on farmland abandoned for 1, 7, 13, 20, and 30 years. Top soil OC and TN were higher in older grassland, especially in the 0-5 cm soil depths; deeper soil OC and TN was lower in younger grasslands (<20 yr), and higher in older grasslands (30 yr). Soil OC and N storage (0-100 cm) was significantly lower in the younger grasslands (<20 yr), had increased in the older grasslands (30 yr), and at 30 years SOC had increased to pre-abandonment levels. For a thirty year period following abandonment the soil C/N value remained at 10. Our results indicate that soil C and TN were significantly and positively correlated, indicating that studies on the storage of soil OC and TN needs to focus on deeper soil and not be restricted to the uppermost (0-30 cm) soil levels.

[Dynamic changes of photosynthetic characteristics in big-spike wheat yield formation].

A field experiment was conducted to investigate the yield traits, leaf photosynthetic rate, chlorophyll fluorescence parameters, chlorophyll content (Chl), and leaf area index (LAI) of eight new big-spike wheat lines, with multiple-spike cultivar Xinong 979 (Triticum aestivum cv. Xinong 979) as the control. The eight new lines had significantly higher kernel numbers per spike, kernel qualities, and 1000-grain mass but lower spike numbers per unit area, and the lines 2036, 2037, 2038, and 2040 had significantly higher yields than the control. The average net photosynthetic rate (P(n)) of the eight new lines had no significant difference with that of the control, but the PS II maximum energy conversion efficiency, PS II actual photochemical efficiency, photochemical quenching coefficient, and PS II reaction center activity of the lines were higher than those of the control. The leaf Chl of the lines 2037, 2040, 2039, 2038 and 2036 were 17.5%, 19.1%, 15.3%, 13.9%, and 7.9% higher than those of the control, and their LAI was significantly higher than that of the control and declined slowly in late growth period.

[Leaf nutrient contents and photosynthetic physiological characteristics of Ulmus pumila-Robinia pseudocacia mixed forests].

A field experiment was conducted to study the leaf N, P, and chlorophyll contents, photosynthetic gas exchange parameters, and chlorophyll fluorescence parameters in pure Ulmus pumila forest, pure Robinia pseudoacacia forest, and U. pumila-R. pseudoacacia mixed forests [1:1 (1B1C), 1:2 (1B2C), and 2:1 (2B1C)] in different growth periods. From May to September, the plant leaf N and P contents in pure and mixed forests all presented a decreasing trend. By the end of growth period, the leaf N content of U. pumila and the P content of R. pseudoacacia in 1B2C were obviously higher than those in pure forests. In the mixed forests, the chlorophyll content of U. pumila was obviously higher than that of R. pseudoacacia, and the chlorophyll content of U. pumila in 1B2C reached the highest in July. The photosynthetic rate (Pn) of U. pumila and R. pseudoacacia in mixed forests was higher than that in pure forests, and the Pn of R. pseudoacacia in 1B2C reached the highest (18.54 micromol x m(-2) x s(-1)) in July. The transpiration rate (Tr) and stomatal conductance (Gs) of R. pseudoacacia in mixed forests were higher than those in pure forests, and the Tr and Gs in mixed forests were in the order of 1B2C>1B1C>2B1C. In September, the quantum yield of PSII electron transport (phi(PS II)) of U. pumila in mixed forests was obviously higher than that in pure forest. The photochemical quenching coefficients (q(P)) of U. pumila and R. pseudoacacia in pure and mixed forests had no significant difference, but the non-photochemical quenching coefficient (NPQ) of the two tree species in 1B2C was significantly lower than that in corresponding pure forests. It was suggested that mixed planting U. pumila and R. pseudoacacia could significantly improve the leaf nutrient contents and photosynthetic capacity of the two tree species, and the optimum mixed ratio of U. pumila and R. pseudoacacia was 1:2.

[Energy and nutrient characteristics of Carex lanceolata in Ziwuling of Loess Plateu].

The study on the energy and nutrient characteristics of Carex lanceolata, a dominant companion species in different plant communities in Ziwuling forest area of Loess Plateau showed that the ash free caloric values of the aboveground and underground parts of the species tended to decline in the communities experienced different successional stages. The aboveground part of C. lanceolata had the highest ash free caloric value in Sophora viciifolia community and the lowest in Hippophae rhamnoides community. The underground part of C. lanceolata had the highest ash free caloric value in S. viciifolia community and the lowest in Quercus liaotungensis community. The aboveground part of C. lanceolata had a remarkably higher caloric value than its underground part, and the underground part appeared to extremely significantly differ in gross and ash-free caloric values among different communities. The caloric value of C. lanceolata varied greatly in the communities going through their early successional stages (S. viciifolia, H. rhamnoides, Populus davidiana and Betula platyphylla communities), and less greatly in the communities experiencing their later successional stages (Pinus tabulaeformis and Q. liaotungensis communities). There was a significant positive correlation between the gross caloric value and the C/N ratio in the underground part of C. lanceolata.

[Characteristics of caloric value and nutrient content of four garden tree species].

In this study, the caloric value, nutrient content, and ash content in the stem, leaf, and root of four garden tree species Prunus mume Meiren, P. serrulata, Magnolia denudata and M. grandiflora were determined to explore the distribution characteristics of caloric value in different tree organs at different development stages, and related affecting factors. The results showed that the gross caloric value (GCV) and ash free caloric value (AFCV) in different organs of the tree species ranged from 17.02 to 21.93 kJ g(-1) and from 18.42 to 22.57 kJ g(-1), respectively. Leaf and fine root had relatively higher GCV and AFCV than stem, and AFCV had a decreasing trend with the development of stem and root. P. mume Meiren and P. serrulata had higher GCV and AFCV than M. grandiflora and M. denudate. Both GCV and AFCV of fine root were significantly correlated with its nutrient and ash contents (P <0.01). With the development of root, the correlations of GCV and AFCV with organic carbon content declined gradually, while the GCV of different organs had the strongest correlation with total nitrogen content.

[Effects of nitrogen application rate on nitrate reductase activity, nitric oxide content and gas exchange in winter wheat leaves].

In this paper, the effects of different nitrogen application rates on the nitrate reductase (NR) activity, nitric oxide (NO) content and gas exchange parameters in winter wheat (Triticum aestivum L.) leaves from tillering stage to heading stage and on grain yield were studied. The results showed that the photosynthetic rate (P(n)), transpiration rate (T(r)) and instantaneous water use efficiency (IWUE) of leaves as well as the grain yield were increased with increasing nitrogen application rate first but decreased then, with the values of all these parameters reached the highest in treatment N180. The NR activity increased with increasing nitrogen application rate, and there was a significant linear correlation between NR activity and NO content at tillering and jointing stages (R2 > or = 0.68, n = 15). NO content had a quadratic positive correlation with stomatal conductance (G(s)) (R2 > or = 0.43, n = 15). The lower NO content produced by lower NR activity under lower nitrogen application rate promoted the stoma opened, while the higher NO content produced by higher NR activity under higher nitrogen application rate induced the stoma closed. Although the leaf NO content had a quadratic positive correlation with stomatal conductance (R2 > or = 0.36, n = 15), no remarkable correlation was observed between NR activity and NO content at heading stage, suggesting that nitrogen fertilization could not affect leaf NO content through promoting NR activity, and further more, regulate the stomatal action. Under appropriate nitrogen application the leaf NR activity and NO content were lower, G(s), T(r) and IWUE were higher, and thus, the crop had a better drought-resistant ability, higher P(n), and higher grain yield.

[Photosynthetic characteristics of dominant plant species at different succession stages of vegetation on Loess Plateau].

According to the succession sequence of vegetation on Ziwuling of Loess Plateau, the dominant species at different secondary succession stages, i. e., Bothriochloa ischaemum, Artemisia gmelinii, Hippophae rhamnoides, Sophara viciifolia, Populus davidiana and Quercus liaotungensis, were selected to measure the total N contents in their leaves and soil, and the parameters of leaf gas exchange, chlorophyll content and chlorophyll fluorescence. The results showed that with the succession of vegetation, the total N content in 0-20 cm soil layer had an increasing trend, while the leaf total N and chlorophyll contents were increased first but decreased then. The leaf total N content of dominant species at shrub community stage (H. rhamnoides and S. viciifolia) was significantly higher (P < 0.05) than that at other succession stages, and the photosynthetic rate (P(n)) was higher at the stages of herbaceous and shrub communities than at the early and climax stages of forest community. Stomatal conductance (g(s)) and P(n) had the similar variation trends. The dominant species at the stages of herbaceous and shrub communities had a higher transpiration rate (T(r)), while those at the climax stage of forest community had the lowest one. With vegetation succession, the maximum photochemical efficiency (F(v)/F(m)) had a slow increase, while the actual photochemical efficiency of PS II (Phi(PSII)) was increased first but decreased then. Along the succession sequence, photochemical quenching coefficient (q(P)) presented an increasing trend, while non-photochemical quenching coefficient (q(NP)) showed a single-peaked curve. Therefore, the ecophysiological attributes and adaptation to microhabitats of early succession plant are different from the late succession plants.