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Livestock-poultry-grassland (LPG), a novel land use that couples chicken farming and livestock grazing in the grasslands of northern China, has great potential in improving both ecological and productive functions of degraded grasslands. However, previous studies have mainly focused on the influences of chicken farming on grassland production and herder income while ignoring their influences on species diversity. We carried out two experiments to clarify how chicken farming influences the plant communities in degraded grasslands. First, we selected 10 typical plants for a chicken feeding experiment, and results showed that plants in the Chenopodiaceae family, such as Chenopodium glaucum , were the favorite forage, followed by plants in the Leguminosae family, such as Medicago ruthenica and Astragalus adsurgens , and plants in the Compositae family, such as Taraxacum mongolicum . Plants in Gramineae family were rarely consumed. When chickens were farmed in grasslands, their total intake amount was significantly negatively correlated with plant crude fiber content and was significantly positively correlated with both plant crude fat and crude protein contents. Chickens consumed plants in very low amounts, typically between 3– 9 g dry matter per chicken per day, accounting for 4%–11% of the total food intake. In the second experiment, we compared chicken farming (MJ) with zero grazing (CK) in degraded grasslands over 3 years, and results showed that species richness did not significantly differ between treatments or years. There were around 10 species in the plant communities of both MJ and CK during the 3-year period. The Shannon Wiener diversity and evenness indexes of the plant community were maintained at approximately 1.5 and 0.7, respectively. In MJ, plant height in the community was significantly reduced. In the second and third years, compared to CK, the plant height in MJ decreased by 19.1% and 27.2%, respectively. However, in MJ, the net primary production improved, reaching 464.3 g m−2 yr−1 in the third year, 1.7 times that in CK. Vegetation cover in MJ reached 74.3%, 1.5 times that in CK. Overall, chicken farming had no negative impacts on species diversity. However, if LPG is employed in the future in degraded grasslands, we should pay continuous attention to choosing suitable chicken farming methods and monitoring biodiversity changes and their consequences.

Ecologically relevant low UV-B is reported to alter reactive oxygen species metabolism and anti-oxidative systems through an up-regulation of enzymes of the phenylpropanoid pathway. However, little is known about low UV-B-induced changes in carotenoid profile and their impacts on light harvesting and photoprotection of photosystem II (PSII) in plants. We investigated carotenoids profile, chlorophyll pigments, phenolics, photosynthetic efficiency and growth in Arabidopsis thaliana (Col-0) plants grown under photosynthetically active radiation (PAR), PAR+ ultraviolet (UV)-A and PAR+UV-A+B regimes for 10 days in order to assess plant acclimation to low UV-B radiation. A chlorophyll fluorescence assay was used to examine UV-B tolerance in plants further exposed to acute high UV-B for 4 and 6 h following a 10-day growth under different PAR and UV regimes. We found that both PAR+ UV-A and PAR+UV-A+B regimes had no negative effect on quantum efficiency, electron transport rate, rosette diameter, relative growth rate and shoot dry weight of plants. Chronic PAR+ UV-A regime considerably (P < 0.05) increased violaxanthin (26 %) and neoxanthin (92 %) content in plants. Plant exposure to chronic PAR+UV-A+B significantly (P < 0.05) increased violaxanthin (48 %), neoxanthin (63 %), lutein (33 %), 9-cis s-carotene (28 %), total s-carotene (29 %) and total phenolics (108 %). The maximum photochemical efficiency (Fv/Fm) in leaves was found to be positively correlated with total phenolics (rho = 0.81 and rho = 0.91, P < 0.05 for 4 and 6 h, respectively) and non-photochemical quenching (qN) (rho = 0.81 and rho = 0.84, P < 0.05 for 4 and 6 h, respectively) in plants exposed to acute high UV-B for 4 and 6 h following a 10-day growth under chronic PAR+UV-A+B. There was also a significant positive correlation (rho = 0.93, P < 0.01) between qN and lutein content in the plants exposed to acute high UV-B stress for 4 h following plant exposure to chronic PAR+UV-A+B. The findings from our study indicate that plants grown under chronic PAR+UV-A+B displayed higher photoprotection of PSII against acute high UV-B stress than those grown under PAR and PAR+ UV-A regimes. An induction of phenolics and lutein-mediated development of qN were involved in the photoprotection of PSII against UV-B-induced oxidative stress.

The livestock-poultry-grassland (LPG) system, a novel land use of grassland promoted by chicken farming, is important for controlling locust disaster, fertilizing infertile soils, and providing income to herders. It has great potential to improve both ecological and productive functions of degraded grasslands. The common chicken-farming mode used in agricultural regions (MJ) is simple and easy to learn. The feasibility of introducing MJ in grassland pastoral regions is unclear, because its effects on vegetation have not been studied. We experimented by comparing MJ and zero grazing (CK). The results showed that chickens in MJ plots had a clumped pattern and depended on the stocking rate. The stocking rates of free-range chickens significantly decreased with distance from the chicken house, from 4000 birds per hm2 (at R R ( R >60 m). The plant community was significantly affected by MJ, distance, and MJ×distance. At distances from 0 to 20 m, the vegetation was severely damaged by MJ, with community height, coverage, and aboveground biomass significantly lower than those in CK. At distances from 20 to 60 m, species richness, coverage, and aboveground biomass of MJ were significantly greater than those of CK because of nutrient addition, with an increase of 110.0%, 54.7%, and 43.2%, respectively, in the current year. These values remained nearly the same in the subsequent year. At distances greater than 60 m, MJ had no significant effects on the vegetation. Therefore, considering the uneven distribution of chickens and severe vegetation damage around the chicken house, MJ is not suitable for the LPG system. To promote vegetation growth and grassland restoration, we propose chicken farming with a moderate stocking rate and an evenly distributed mode as well as the maximum possible development of the nutrient addition effect.

Free-range chicken farming (CF) has been demonstrated to be effective in controlling locust plagues and restoring degraded vegetation in rangelands. However, the effects of CF on vegetation growth and soil conditions of rangeland ecosystems are not yet well known. We studied the effects of CF (treated by three stocking rates from low-intensity to high-intensity), livestock grazing (LG) and zero grazing (ZG) on vegetation characteristics and soil nutrient conditions in a degraded rangeland of northern China. CF significantly improved vegetation growth and soil quality compared with LG. The moderate CF2 with 333 birds per hectare enhanced the aboveground net primary production to 204·0 g m−2 yr−1 and vegetation cover to 88·8%, which is significantly higher than LG by 80·7% and 62·9%, respectively. Moreover, CF2 neutralized the pH value and raised soil organic matter, total N content, available N content and available P content to approximately 7·59 g kg−1, 0·34 g kg−1, 83·52 mg kg−1 and 3·4 mg kg−1, respectively. Compared with ZG, the positive impacts of CF on rangelands depended on the stocking rate, and better performance was achieved when lower stocking rates were used. We also analysed the economic benefits of CF through a cost–benefit analysis. A local family could obtain a net present value of at least $252·19 per hectare by engaging in CF, which was two-fold higher than LG. Finally, we proposed a novel land-use model that introduces CF into traditional LG dominated system and can be widely applied to promote socio-ecological sustainable development in degraded rangelands. Copyright © 2017 John Wiley & Sons, Ltd.

A field experiment was carried out to compare the responses to ozone (O 3 ) in two common herbaceous plant species, Plantago major L. and Sonchus oleraceus L., by building open-top growth chambers in situ to simulate O 3 stress (+ O 3 , 85 ± 5 ppb, 9 hr/day for 30 days) in a lowland habitat in Inner Mongolia, Northern China. Responses to O 3 of gas exchange, chlorophyll a fluorescence, leaf pigment content, antioxidant capability, soluble protein content, membrane lipid peroxidation and dark respiration ( R d ) were analyzed. Results showed that elevated O 3 exposure significantly reduced the light-saturated net photosynthesis ( P Nsat ), stomatal conductance ( g s ) and transpiration rate ( E ) in both species. Although non-significant interactive effect between species and O 3 on P Nsat was analyzed, the reduction in P Nsat in S. oleraceus might be due primarily to the higher fraction of close PSII reaction centers and impaired activities of plant mesophyll cells as evidences by decreased maximum efficiency of PSII photochemistry after dark adapted state ( F v / F m ) and unchanged intercellular CO 2 concentration ( C i ). Besides, biochemical analysis showed that S. oleraceus had lower antioxidant ability compared to P. major . As a result, S. oleraceus was damaged to the larger extent in terms of lipid peroxidation and visible O 3 injury, indicating that S. oleraceus was more sensitive to O 3 than P. major . Our results indicated that wild herbaceous plant species growing in a lowland habitat in sandy grassland were sensitive to O 3 stress and S. oleraceus can be considered as one of the bio-indicators for high O 3 concentration in semi-arid grassland of northern China.

The role of livestock grazing in regulating woody cover and biomass in grass-dominant systems is well recognized. However, the way in which woody plant populations in respond when livestock are removed from grazing in the absence of other disturbances, such as fire, remains unclear.We conducted a 10-year, replicated fencing experiment in a sandy semiarid rangeland in northern China (which has a mean annual rainfall of 365 mm), where fires have been actively suppressed for decades.Fencing dramatically influenced the growth and age structure of the native tree species, Ulmus pumila, which is the sole dominant tree in the area. After a decade, the density of the U. pumila tree population in the fencing plots increased doubly and canopy cover increased triply. The proportion of both saplings (U 2 ) and young trees (U 3 ) increased in fencing plots but decreased in grazing plots after the 10-year treatment period. The effects of fencing on U. pumila trees varied by age class, with potential implications for the future structure of the U. pumila tree community. Decadal fencing led to approximately 80-fold increase in recruitment and a nearly 2.5-fold decrease in the mortality of both U 2 and U 3 . Further, livestock grazing generated a "browsing trap" to the recruitment of both U 2 and U 3 , and had a small impact on the mortality of old trees. A long-term, fencing-driven shift in woody species composition was mediated via its effects on both recruitment and mortality rates.Synthesis and applications. Our results demonstrate that in the long-term absence of both fire and livestock, native woody plant encroachment tends to occur in sandy rangelands, transforming the woody plant demography in the process. The feasibility of full livestock exclusion in sandy rangelands requires further discussion. A balanced amount of livestock grazing may provide critical ecosystem services by regulating woody cover and mediating woody plant encroachment.

Long-term irrational land uses have fatigued the fragile grasslands globally, causing severe environmental problems and socio-economic losses. This paper addresses the feasibility of a new land use of chicken farming (CF) from natural, economic and social perspectives for devising sustainable development in a semi-arid grassland in northern China. The results of a 4-year controlled field experiment showed that CF could amend the infertile soils through feces inputs as indicated by the improvements in soil properties. Although there were some damage to grass growth in the first year of the experiment, vegetation coverage and aboveground biomass increased greatly in the following years, particularly in the third and fourth years. A quarter of feedstuff could be saved by chickens farmed in grassland compared with cage-raised chickens, accompanied by biological control of pest outbreaks. The 4-year practice at large scales by local household suggested that CF could be a more profitable enterprise compared to the conventional land use of ruminate grazing. Besides, CF could diversify livelihoods, which will lighten the reliance on traditional livestock grazing and thus help improve local social-ecological development. It was concluded that CF could be an integrative ecosystem management to rehabilitate the degraded grassland ecosystems toward a sustainable way. Finally, we highlighted an essential integration of bottom-up mechanism among local households with top-down incentives created by governments for sustainable development of chicken farming in the degraded grassland regions.

Key message Ulmus pumila vary its water use strategy from seedling to maturity in a water-limited sandy land by adopting different photosynthetical capacities, water use efficiencies and morphological traits.

The beneficial effects of elevated CO 2 on plants are expected to be compromised by the negative effects posed by other global changes. However, little is known about ozone (O3)-induced modulation of elevated CO2 response in plants with differential sensitivity to O3. An old (Triticum aestivum cv. Beijing 6, O3 tolerant) and a modern (T. aestivum cv. Zhongmai 9, O3 sensitive) winter wheat cultivar were exposed to elevated CO2 (714 ppm) and/or O3 (72 ppb, for 7 h d –1 ) in open-topped chambers for 21 d. Plant responses to treatments were assessed by visible leaf symptoms, simultaneous measurements of gas exchange and chlorophyll a fluorescence, in vivo biochemical properties, and growth. It was found that elevated CO2 resulted in higher growth stimulation in the modern cultivar attributed to a higher energy capture and electron transport rate compared with the old cultivar. Exposure to O3 caused a greater growth reduction in the modern cultivar due to higher O3 uptake and a greater loss of photosystem II efficiency (mature leaf) and mesophyll cell activity (young leaf) than in the old cultivar. Elevated CO2 completely protected both cultivars against the deleterious effects of O3 under elevated CO2 and O3. The modern cultivar showed a greater relative loss of elevated CO2-induced growth stimulation due to higher O3 uptake and greater O3-induced photoinhibition than the old cultivar at elevated CO2 and O3. Our findings suggest that the elevated CO 2-induced growth stimulation in the modern cultivar attributed to higher energy capture and electron transport rate can be compromised by its higher O3 uptake and greater O3-induced photoinhibition under elevated CO2 and O3 exposure.

A field experiment was carried out to compare the responses to ozone (O

Attention should be paid to ozone (O3) sensitivity of greening plant since ground-level O3 concentrations are increasing especially in urban and suburban area. We studied the ecophysiological responses to elevated O3 of four shrub species [Euonymus bungeanus Maxim. (EB), Photinia × fraseri (PF), Chionanthus retusus Lindl. & Paxt. (CR) and Cornus alba L. (CA)], which are often used for garden greening in China. Saplings of those species were exposed to high O3 concentration (70 nmol mol−1, 7 h d−1 for 65 d) in open-top growth chambers. Responses to O3 were assessed by gas exchanges, chlorophyll (Chl) fluorescence and dry mass. We found that elevated O3 significantly decreased lightsaturated net photosynthetic rate (PNsat), transpiration rate (E) and stomatal conductance (gs). The ratio of intercellular CO2 to ambient CO2 concentration (Ci/Ca) did not reduce under O3 fumigation which suggested that the O3-induced depressions of PNsat under O3 fumigation were probably due to limitation of mesophyll processes rather than stomatal limitation. High O3 exposure also significantly depressed the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (Fv/Fm) which meant the O3-induced photoinhibition. Both root dry mass and root/shoot ratios were significantly decreased under ozone fumigation, but the total mass was unchanged. The responses of gas exchange such as PNsat in these four shrubs to O3 exposure were species-specific. Highest loss of PNsat was observed in EB (−49.6%), while the CR had the lowest loss (−36.5%). Moreover, the O3-exposed CR showed similar gs as CF, reflecting that its O3 flux might be unchanged under elevated O3 environment. Ozone drastically decreased actual quantum yield of PSII (ΦPSII) and electron transport rate (ETR) in EB while increased ΦPSII and ETR in CR. Furthermore, the relative losses in PNsat positively correlated with the relative decreases in ΦPSII and ETR which indicated that the impairment of photosynthesis was probably affected by the light reaction process. The light reaction of EB was impaired most seriously but that of CR was not damaged. All results indicated that EB was probably the most sensitive shrub species to O3 while CR the most tolerant one. Therefore, CR might be an ideal choice for greening in ozone-polluted areas.

Contrasting winter wheat cultivars, salt-tolerant DK961 and intolerant JN17, which sown in no salinity (-S) and salinity (+S) boxes were exposed to charcoal filtered air (CF) and elevated O(3) (+O(3)) in open top chambers (OTCs) for 30 days. In -S DK961 and JN17 plants, +O(3) DK961 and JN17 plants had significantly lower light-saturated net photosynthetic rates (A(sat), 26% and 24%), stomatal conductance (g(s), 20% and 32%) and chlorophyll contents (10% and 21%), while O(3) considerably increased foliar electrolyte leakage (13% and 39%), malondialdehyde content (9% and 23%), POD activity and ABA content. However, responses of these parameters to O(3) were significant in DK961 but not in JN17 in +S treatment. Correlation coefficient of DK961 reached significance level of 0.01, but it was not significant in JN17 under interaction of O(3) and salinity. O(3)-induced reductions were larger in shoot than in root in both cultivars. Results indicate that the salt-tolerant cultivar sustained less damage from salinity than did the intolerant cultivar but was severely injured by O(3) under +S condition. Therefore, selecting for greater salt tolerance may not lead to the expected gains in yield in areas of moderate (100 mM) salinity when O(3) is present in high concentrations. In contrast, salinity-induced stomatal closure effectively reduced sensitivity to O(3) in the salt-intolerant cultivar. Hence we suggest salt-tolerant winter wheat cultivars might be well adapted to areas of high (100 mM) salinity and O(3) stress, while intolerant cultivars might be adaptable to areas of mild/moderate salinity but high O(3) pollution.

Spatial turnover of species lies at the heart of macroecology and conservation biogeography. However, our knowledge of the causes of species turnover remains poor, particularly for herpetofaunas including amphibians and reptiles. Here, using regression, variance partitioning, and hierarchical partitioning analyses, we examine the relationships of species turnover in herpetofaunas among provinces in eastern China with respect to geographic distance and environmental difference. We found that species turnover in herpetofaunas is moderately to strongly correlated with geographic distance and difference in most environmental variables examined between provinces. Geographic distance and environmental difference together explain 87.1 and 89.9% of the variance of species turnover for amphibians and reptiles, respectively. Variance partitioning analysis indicated that most variance in species turnover is explained by the joint effect of geographic distance and environmental difference. Beyond this shared variance, environmental difference is a stronger predictor of species turnover than geographic distance, particularly for reptiles. Hierarchical partitioning analysis showed that energy-related variables explained more variance in species turnover for both amphibians and reptiles, compared with water-related variables. The independent effects of water-related variables are slightly higher for amphibians than for reptiles whereas the independent effects of energy-related variables are slightly higher for reptiles than amphibians. These patterns are consistent with different ecophysiological requirements of the two taxa. Our results have important implications for predicting changes in biodiversity of herpetofaunas under climate change scenarios. Global warming will affect the immigration and local extinction of both amphibians and reptiles, and precipitation change may affect amphibians more strongly, compared with its effect on reptiles.

Early production and high energy efficiency are important in greenhouse vegetable production in cold regions. A dynamic temperature integration strategy with low pre-night temperature (PNT) has been developed to reduce energy consumption and to improve early fruit yield and energy use efficiency. However, the application of this temperature control strategy is feasible only if there is no crop yield and quality loss. To determine the low PNT tolerance threshold and explore the mechanism of this temperature control strategy on plant growth and development, the effects of four PNT temperature integration treatments (PNT9, PNT11, PNT13, and PNT15, with an actual PNT of 9.4, 11.3, 13.3, and 15.1 °C, respectively) on greenhouse tomatoes (Solanum lycopersicum) were investigated. The PNT was applied at the beginning of the night for 3 h, whereas temperatures in other periods during a day (24 h) were adjusted accordingly to ensure the same 24-h average temperature (19.4 °C) for all PNT treatments. Four cultivars (Bigdena, Clarance, Quest, and Conchita), representing all three types (beefsteak, cluster, and cherry) of greenhouse tomatoes, were used in the study. The optimum PNT for fruit yield was 13.8 and 14.9 °C for ‘Bigdena’ and ‘Conchita’, respectively. Low PNT down to 11 °C did not compromise fruit yield and plant development in ‘Clarance’, and thus a PNT lower than 13 °C can be used for ‘Clarance’ if it does not have a negative effect on fruit quality. In ‘Bigdena’ and ‘Conchita’, the above-ground biomass increased with increasing PNT at the low range of PNT, peaked at ≈13 °C PNT (13.7 and 13 °C for ‘Bigdena’ and ‘Conchita’, respectively), then declined at high PNT. Leaf photosynthesis rates were increased by the highest PNT (PNT15), whereas respiration rates were reduced by the lowest PNT (PNT9). Therefore, PNT at ≈13 °C might have allowed for the proper balance between the high photosynthesis for photoassimilate generation and the low respiration for photoassimilate conservation and thus accumulated the highest photoassimilate and the highest fruit yield in ‘Bigdena’. Flower development rate in ‘Conchita’ decreased linearly with low PNT, which might have limited the response of its fruit yield to low PNT and raised the optimum PNT for fruit yield to 14.9 °C. Temperature integration with proper low PNT can be an effective climate control strategy for increasing early fruit yield and energy use efficiency in greenhouse tomato production.

In order to investigate the effect of chromosome doubling on ozone tolerance, we compared the physiological responses of a diploid honeysuckle (Lonicera japonica Thunb.) and its autotetraploid cultivar to elevated ozone (O3) exposure (70 ng g−1, 7 h d−1 for 31 d). Net photosynthetic rate (P N) of both cultivars were drastically (P

Development and use of ozone (O3)-resistant crop cultivars are key measures to avoid agricultural yield reduction in a high O3 environment. However, little is known about the impacts of breeding methods and breeding sites on the development of O3 tolerance in winter wheat cultivars. To explore such impacts, 20 Chinese winter wheat cultivars bred using four breeding methods (viz. introduction, reselection, conventional breeding and hybridization) at four breeding sites having different levels of O3 exposures, were exposed to charcoal-filtered (CF) air or high O3 (82 ppb, 7 h d−1) for 21 days. O3 tolerance of cultivars was assessed by the relative levels of visible injury, growth, gas exchange, dark respiration, antioxidative activities and oxidative modification of proteins and cellular membranes. We found that conventional breeding and hybridization demonstrated higher potential capacity for O3 tolerance as indicated by a higher level of ascorbate and peroxidase activity in cultivars exposed to CF air. Despite the highest potential capacity for O3 tolerance, hybridization displayed the lowest O3 tolerance as represented by antioxidative activities, oxidative stress, photosynthesis and growth. The causes of higher O3 sensitivity in hybrid cultivars included lower O3 exclusion by stomatal closure, higher reduction in antioxidative activities, higher O3-induced modification of proteins and cellular membranes, lower level of repair of O3-induced cellular damage and higher loss of assimilation rate as well as growth in O3 relative to control plants. Cultivars bred at breeding sites experiencing higher ambient O3 exposures demonstrated higher potential capacity for O3 tolerance. The observed O3 tolerance in cultivars bred by different breeding methods was uncorrelated to ambient O3 levels in breeding sites as well as to the potential O3 tolerance capacity as observed in CF air. Results from our experiment, therefore, clearly indicated that potential O3 sensitivity would have little use in predicting actual O3 tolerance of winter wheat cultivars. Our findings also suggested that sensitivity to O3 in winter wheat cultivars was related to breeding methods, but not to O3 concentrations in breeding sites.

In order to study the responses of winter wheat cultivars released in different years to short-term high O3 exposure, an old cultivar (‘Nongda 311’, released in 1960s) and a modern one (‘Yannong 19’, released in 1990s) were treated with an O3 exposure (145 ± 12 mm3 m−3, 4 h d−1 for 3 d) shortly after anthesis stage (> 50 % main stems blossomed). During the O3 exposure, light-saturated photosynthetic rate (P N) and stomatal conductance (g s) of both cultivars decreased considerably. Elevated O3 did not decrease dark-adapted maximum photochemical efficiency, but induced significant reduction in actual photochemical efficiency and thereby considerably increase in non-photochemical quenching. P N, g s of the modern cultivar ‘Yannong 19’ decreased more than the older one ‘Nongda 311’, indicating the former exhibited higher sensitivity to O3 than the latter. After O3 exposure, P N, g s and chlorophyll (Chl) content in flag leaf decreased more quickly than control, indicating induction of faster premature leaf senescence. As a result, the short-term O3 exposure caused substantial yield loss, with larger reduction in ‘Yannong 19’ (−19.2 %) than in ‘Nongda 311’ (−8.4 %). Our results indicated that high O3 exposure at grain filling stage would have greater negative impacts on the high yielding modern cultivar relative to the old one with lower yield.

The density of seeds in soil seed banks and the species composition of both seed banks and aboveground vegetation were examined in naturally restored sites (NRS) and aerially seeded sites (ASS) in the Hunshandak sandlands of northern China. Five sites were naturally restored 1, 2, 4, 8, and 15 years ago and four sites were aerially seeded 1, 2, 5, and 7 years ago. In total, 36 species were recorded in the seed bank and 41 species in the aboveground vegetation for all NRS, whereas the numbers were 17 and 19, respectively, for ASS, indicating that the NRS can support higher diversity of species than the ASS. During the initial 2 years of restoration, introduced alien shrubs by aerial seeding dominated the vegetation of ASS, although there were indigenous pioneer species in the seed bank which failed to establish in the community. In contrast, indigenous species were dominant components in both the seed bank and the vegetation at the NRS. These findings suggest that the establishment of introduced species might have restricted the germination of certain indigenous pioneer species. Seed bank density of NRS significantly increased with time from 459 ± 76 seeds m−2 at NRS2 to 3,351 ± 694 seeds m−2 at NRS15, showing that the seed bank in degraded grassland is large enough to allow natural restoration. It is not always necessary to actively introduce seeds to enhance vegetation diversity.

Ozone (O 3 ) concentrations in periurban areas in East Asia are sufficiently high to decrease crop yield. However, little is known about the genotypic differences in O 3 sensitivity in winter wheat in relation to year of cultivar release. This paper reports genotypic variations in O 3 sensitivity in 20 winter wheat cultivars released over the past 60 years in China highlighting 03-induced mechanisms. Wheat plants were exposed to elevated Q3 (82 ppb O 3 , 7h day -1 ) or charcoal-filtered air (

Experiments were conducted to investigate the photosynthetic activity and thermostability of photosystem II (PSII) in elm seedling (Ulmus pumila) leaves from initiation to full expansion. During leaf development, photosynthesis, measured as CO2 fixation, increased gradually and reached a maximum value when leaves were fully developed. In parallel with the increase of carbon assimilation, chlorophyll content increased. The chlorophyll a fluorescence measurements showed that the maximum quantum yield of PSII primary photochemistry (φpo), the efficiency with which the energy of trapped excitons is converted into the electron transport beyond QA (Ψo) and the quantum yield of electron transport beyond QA (φEo) increased gradually. The low light experiments confirmed these results independently. When subjected to heat stress, young leaves exhibited progressively lower φpo and maximal fluorescence (Fm) values with considerably higher minimal fluorescence (Fo) than mature leaves, demonstrating that PSII in newly initiating leaves is more sensitive to heat stress. Further analysis revealed that PSII structure in newly initiating leaves showed a robust alteration under heat stress, which was reflected by the clear K phase in the OJIP curves. Therefore, we suggest that the enhanced thermostability of PSII in the case of leaf growth might be associated with an improvement of the stability of the oxygen-evolving complex (OEC) to heat stress during leaf development.

A better understanding of the ecophysiology of sandy plants will facilitate the prediction of the community succession in sandy environment. The photosynthetic characteristics of Hedysarum fruticosumvar. mongolicum, a sand-fixing leguminous C 3 species in Hunshandak Sandland (HS) of northern China, were monitored and compared with those of Salix gordejevii, a typical C3 species co-existing with H. fruticosum in semi-fixed or fixed sand dunes. The maximal photosynthetic rate ( Amax) and instantaneous water use efficiency (WUE i )o fH. fruticosum was approximately two times higher than those of S. gordejevii. Except Ribulose-1.5-bisphosphate carboxylase (RuBPcase), the activities of photosynthetic carbon assimilation enzymes such as phosphoenolpyruvate carboxylase (PEPcase), NAD-malic enzymes (NAD-ME), NADP-malic enzymes (NADP-ME), NAD-malate dehydrogenase (NAD-MDH), NADP-malate dehydrogenase (NADP-MDH) and pyruvate phosphate dikinase (PPDK), were at least five times greater in H. fruticosum than those in S. gordejevii, suggesting H. fruticosum might have aC 4 photosynthetic syndrome. However, stable carbon isotope analysis revealed that H. fruticosum had the 13 C value of −23‰, which was close to that of C3 plants. Therefore, it is likely that H. fruticosum is either a C3–C4 intermediate species, or a C3 species displaying C4 metabolic characteristics in habitat of sand dune. The involvement of C4 metabolism in H. fruticosummight account for its greater efficiencies for photosynthesis and water use, allowing H. fruticosum to colonize the shifting sand dune with high temperature, light intensities and water stress.

About one third of the world's land surface is covered with arid and semi-arid areas. It is predicted that global warming will increase desertification by 17% before 2050. At present, desertification is making approximately 12 million hectares every year useless for cultivation and grazing worldwide. Over 250 million people and one third of the earth's land surface are directly threatened by desertification (Diallo 2003). China is one of several countries severely affected by desertification; almost 90% of natural grassland has been affected to differing degrees (Lu & Yang 2001; State Environmental Protection Administration of the People's Republic of China 2002). The land desertification rate in China was 1560 km2 yr−1 in the 1970s. This rate had increased to 2100 km2 yr−1 by the 1980s, and was 2460 km2 yr−1 by 1995 and 3436 km2 yr−1 in 1999 (Zhu et al. 1999). Areas that have shown increased desertification are derived from degraded grassland or cultivated land (Zhang & Cheng 2001). One very serious direct consequence of grassland degradation is thought to be the frequent occurrence of sandstorms. Whereas China was hit by almost 70 sandstorms over the past century (Qing 2002), with an average frequency of one sandstorm every three years in the 1940s, this had increased to one every two years by the 1960s. By the 1990s, the sandstorms in north China took place several times a year and this increased further to 12 in 2000 and 18 in 2001 (Jiang 2002a). The frequency of sandstorms in north China appears to be a direct consequence of grassland degradation. Taking Hunshandak Sandland in Inner Mongolia as an example (Fig. 1), the proportion of sand dunes that are shifting rose from 2.3% in the 1950s to 50% in the 1990s, while available grasslands declined by some 40% between the 1950s and the 1990s. The economic cost of these sandstorms has prompted the Chinese government to commit substantial funds to meet this loss, but the degradation is ongoing in the area and the living standards of local people are still low (Liu et al. 2003). It is opportune to adjust strategies to reach two objectives simultaneously, namely to restore the degraded grassland, and improve the living conditions of local people. To illustrate this, we focus on Zhenglan Banner (county), which is representative of the whole Hunshandak Sandland in terms of climate (Ma et al. 1998), economy and ecology (Fig. 1). Zhenglan Banner has a total area of 100 600 km2, a human population of 78 730 and stock raising is the dominant industry, the average income per person per year being US$ 225 (Bureau of Stock Raising in Zhenglan Banner 2002).

Sparse-elm grassland is the remarkable landscape of Hunshandak Sandland in Inner Mongolia Autonomic Region of China. Maximum quantum efficiency (Fv/Fm) of 99 native plant species (85 grasses, 11 shrubs, and 3 trees) of different plant functional Types (PFTs) distributed in fixed sand dune, lowland, and wetland was investigated. Deep-rooted plant species (tree, shrub, and perennial grass) had higher Fv/Fm values than the shallow-rooted species (annual grasses), suggesting that soil drought is the major environmental stress. Annual C4 grasses had higher Fv/Fm values than annual C3 or CAM ones, indicating that C4 photosynthesis is more ecologically adaptive than CAM and C3 grasses. According to the habitats with annual C3 grass distribution, Fv/Fm values were in the order of fixed dune>lowland>wetland, suggesting that salt and pH value may enhance irradiance or heat stress for those distributed in pickled and watery habitats. Based on such characteristics, Ulmus pumila, Salix gordejevii, Caragana microphylla, Agriophyllum pungens, and Agropyron cristatum are recommended as ideal species for ecological restoration in degraded sand-land ecosystems.

A sand-culture experiment was conducted in open-top chambers which were constructed in a greenhouse to investigate the responses of salt-stressed wheat (Triticum aestivum L.) to O3. Plant seeding of JN17 (a popular winter wheat cultivar) was grown in saltless (−S) and saline (+S, 100 mM NaCl) conditions combined with charcoal-filtered air (CF, < 5 ppb O3) and elevated O3 (+O3, 80 ± 5 ppb, 8 h day−1) for 30 d. O3 significantly reduced net photosynthetic rate (PN), stomatal conductance, chlorophyll contents and plant biomass in -S treatment, but no considerable differences were noted in those parameters between +O3+S and CF+S treatments. O3-induced loss in cellular membrane integrity was significant in -S plants, but not in +S plants evidenced by significant elevations being measured in electrolyte leakage (EL) and malondialdehyde (MDA) content in -S plants, but not in +S plants. Both O3 and salinity increased proline content and stimulated antioxidant enzymes activities. Soluble protein increased by salinity but decreased by O3. Abscisic acid (ABA) was significantly elevated by O3 in -S plants but not in +S plants. The results of this study suggested that the specificity of different agricultural environments should be considered in order to develop reliable prediction models on O3 damage to wheat plants.

To cope with adverse environments, the majority of indigenous plants in arid regions possess adaptive plasticity after long-term evolution. Leaf-level morphology, anatomy, biochemical properties, diurnal water potential and gas exchange of Salix gordejevii dis- tributed in fixed dunes and lowlands in Hunshandake Sandland, China, were compared. Compared to plants growing in lowlands, individuals of S. gordejevii in fixed dunes displayed much smaller leaf area (0.26 vs 0.70 cm 2 ) and thicker leaves (leaf total thickness 148.59 vs 123.44 lm), together with heavier crust wax, denser hairs, and more compacted epidermal cells. Moreover, those growing in fixed dunes displayed stronger drought-resis- tance properties as evidenced by higher levels of proline (3.68 vs 0.20 mg g -1 DW) and soluble sugar (17.24 vs 14.49%). Furthermore, S. gordejevii in fixed dunes dem- onstrated lower water potential and lower light compen- sation point (28.8 vs 51.9 lmol m -2 s -1 ). Our findings suggest that morphological and/or anatomical plasticity in leaves has had great adaptive value for Salix in responding to deteriorating environments. The evidence provided here may facilitate the prediction of plant adaptation in com- munity succession in sandy habitats.

Modern wheat (Triticum aestivum L.) is one of the most ozone (O(3))-sensitive crops. However, little is known about its genetic background of O(3) sensitivity, which is fundamental for breeding O(3)-resistant cultivars. Wild and cultivated species of winter wheat including donors of the A, B and D genomes of T. aestivum were exposed to 100 ppb O(3) or charcoal-filtered air in open top chambers for 21 d. Responses to O(3) were assessed by visible O(3) injury, gas exchange, chlorophyll fluorescence, relative growth rate, and biomass accumulation. Ozone significantly decreased light-saturated net photosynthetic rate (-37%) and instantaneous transpiration efficiency (-42%), but increased stomatal conductance (+11%) and intercellular CO(2) concentration (+11%). Elevated O(3) depressed ground fluorescence (-8%), maximum fluorescence (-26%), variable fluorescence (-31%), and maximum photochemical efficiency (-7%). Ozone also decreased relative growth rate and the allometric coefficient, which finally reduced total biomass accumulation (-54%), but to a greater extent in roots (-77%) than in the shoot (-44%). Winter wheat exhibited significant interspecies variation in the impacts of elevated O(3) on photosynthesis and growth. Primitive cultivated wheat demonstrated the highest relative O(3) tolerance followed by modern wheat and wild wheat showed the lowest. Among the genome donors of modern wheat, Aegilops tauschii (DD) behaved as the most O(3)-sensitive followed by T. monococcum (AA) and Triticum turgidum ssp. durum (AABB) appeared to be the most O(3)-tolerant. It was concluded that the higher O(3) sensitivity of modern wheat was attributed to the increased O(3) sensitivity of Aegilops tauschii (DD), but not to Triticum turgidum ssp. durum (AABB) during speciation.