Effects of soil nitrate：ammonium ratio on plant carbon：nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.     

Effects of N:P ratio of Artemisia ordosica on growth influenced by soil calcium carbonate

Soil calcium carbonate(CaCO_3) has a strong solid phosphorus effect, and high content of CaCO_3 can significantly reduce the effectiveness of soil phosphorus. To reveal the limiting effect of soil CaCO_3 on the growth of plants on sand land and its mechanism of plant physiology, we performed pot experiments with a two-factor randomized block design and a three-factor orthogonal design for different soil CaCO_3 content treatments using Artemisia ordosica seedlings. In the experiments, we surveyed plant height, aboveground biomass, root length and root weight and analyzed N, P concentrations and RNA content of the seedlings, and discussed the relationships between relative growth rate(RGR) of the seedlings and N:P ratio as well as RNA. Results show that, the RGRs of plant height and above-ground biomass of the seedlings decreased significantly with the increase of soil CaCO_3 content, and those for root length and root weight decreased. The RGRs of plant height and above-ground biomass of the seedlings were significantly negatively correlated with leaf N:P ratios, but significantly positively correlated with leaf RNA content and leaf P concentrations. It can be seen that soil CaCO_3 is a stress factor for the growth of A. ordosica seedlings, and the growth response of the seedlings under the influence of soil CaCO_3 is in line with the Growth Rate Hypothesis.     

Spatial relationships among species, above-ground biomass, N, and P in degraded grasslands in Ordos Plateau, northwestern China

We chose five communities, representing a mild to severe gradient of grassland desertification in a semi-arid area of Ordos Plateau, northwestern China, to explore the spatial relationships among plant species, above-ground biomass (AGB), and plant nutrients (N and P). Community 1 (C1) was dominated by Stipa bungeana; Community 2 (C2) by a mix of S. bungeana and the shrub Artemisia ordosica; Community 3 (C3) by A. ordosica; Community 4 (C4) by a mix of Cynanchum komarovii and C. komorovii; and Community 5 (C5) by C. komorovii. Quantitative methods, including geostatistics, were used to compare community composition, structure, and indicators of ecosystem function (i.e. AGB, plant N and P) in five 16-m² plots. The highest AGB, plant nitrogen (N) and plant phosphorus (P) were found in lightly degraded community C2. With increasing desertification effects from C3 to C5, the AGB, N, and P decreased significantly while plant density remained unchanged. The spatial variations of AGB were higher in shrub-dominated communities (C1 and C5) than in grass-dominated communities (C2–C4). Strong spatial relationships were detected within and among the communities, with stronger relationships between AGB and density than between AGB and species richness. Spatial patterns of plant N and P were different from those of AGB, reflecting different N and P contents of individual plants and different species that can redistribute soil resources in these communities. The AGB was positively correlated with soil nutrients (TOC, TN, TP, and IN), except for soil AP. We concluded that several specific aspects of ecosystem properties were directly associated with the conversion of the grass and shrub “functional types” in these degraded grasslands.     

Carbon accumulation, nitrogen and phosphorus use efficiency of Sophora davidii seedlings in response to nitrogen supply and water stress

A greenhouse experiment was conducted to explore whether additional nitrogen (N) supply could enhance carbon (C) accumulation, and phosphorus (P) use efficiency (NUE_P) of Sophora davidii seedlings under dry conditions. Two-month-old seedlings were subjected to a completely randomized design with three water (80, 40 and 20% water field capacity (FC)) and three N supply (N0: 0, Nl: 92 and Nh: 184 mg N kg⁻¹ soil) regimes. Water stress decreased C, N and P accumulation, NUE_P, N and P uptake efficiency (NUtE_N and NUtE_P) regardless of N supply. The S. davidii seedlings exhibited strong responses to N supply, but the responses were not consistent with the various N supply levels. Nl increased C, N and P accumulation, and improved NUE_P, NUtE_N and NUtE_P in the same water treatment. In contrast, Nh did few or even depress effects on C, N and P accumulation, and NUE_P, although NUtE_N and NUtE_P increased with Nh in the same water treatment. Even so, NUE_N decreased with increase of N supply in the same water treatment. The results suggested that appropriate or low N supply should be recommended for S. davidii seedling establishment in dry environment by improving C accumulation and NUE_P.     

霸王根茎叶非结构性碳与C:N:P计量特征对干旱的响应

通过选取阿拉善地区3个典型霸王群落为研究对象,研究霸王器官间(根、茎、叶)生态化学计量比特征及非结构性碳水化合物(Non-structural carbohydrates,NSCs)的变化,以便加深对霸王生存策略的理解,更好的服务于荒漠生态系统的生态恢复.结果 表明:霸王茎和叶中可溶性糖(Solu?ble sugar,...     

Seasonal dynamics of N:P ratio stoichiometry and Ca fraction for four dominant plants in the Alxa Desert

Desert plants take on unique physiologically adaptive mechanisms in response to an adverse environment. In this study, we determined the concentrations of leaf nitrogen(N), phosphorus(P), and calcium(Ca) fraction for dominant species of Artemisia ordosica, A. frigida, Calligonum mongolicum, and Oxytropis aciphylla in the Alxa Desert and discussed seasonal changes of their leaf N:P ratio and Ca fraction. The results showed that, from May to September, the N:P ratios of A. ordosica and C. mongolicum gradually and significantly increased, while those of A. frigida, and O. aciphylla had an increase trend that was not significant; the physiologically active Ca of A. ordosica and A. frigida increased significantly,while that of C. mongolicum and O. aciphylla decreased significantly. The physiologically inert calcium of C. mongolicum increased extremely significantly, while that of others was not significant. There was a significantly positive correlation between the N:P ratio and physiologically active Ca for A. ordosica, and the N:P ratio was significantly and negatively correlated with physiologically active Ca for O. aciphylla. These findings revealed that the physiological regulation mechanism was different for the plants either in earlier stage or later stage of plant-community succession.     

Arbuscular mycorrhizal associations in Solanum centrale (bush tomato), a perennial sub-shrub from the arid zone of Australia

Arbuscular mycorrhizal (AM) fungi convey well documented benefits to plant growth in domesticated species. We investigated AM in Solanum centrale, a desert shrub of central Australia and traditional food for Indigenous Australians. AM were observed in roots of S. centrale from wild and cultivated stands of different ages and management regimes. Greenhouse seedlings grown in sterilised sand were provided with no or minor additions of phosphorus, with or without AM fungi. Inoculated seedlings not fertilised with phosphorus exhibited moderate AM formation. Added phosphorus resulted in an absence of AM. Inoculation did not significantly affect dry weight, root length and plant height of seedlings fertilised with phosphorus but significantly increased the size of unfertilised seedlings. Inoculation significantly increased root phosphorus content, decreased root to shoot ratio and decreased root biomass at all phosphorus additions, despite the absence of observable AM. Thus it appears AM fungi in the root zone influenced certain plant characteristics, regardless of phosphorus nutrition. Overall, S. centrale benefited from the presence of AM through increased phosphorus uptake, but only when the seedlings were growing in soil with extremely low available phosphorus. The response was immediate in our experimental system and is likely to be important in the wild.     

毛乌素沙地油蒿(Artemisia ordosica)灌丛穿透雨量特征及影响因素

于2012年5—9月观测了毛乌素沙地油蒿(Artemisia ordosica)灌丛的穿透雨量,分析了其变化特征及影响因素。结果显示:油蒿灌丛的平均穿透雨量占降雨量百分比(Th%)为72.3%,其中有枯枝灌丛的Th%平均为69.3%,较无枯枝灌丛的75.3%低,这可能是油蒿灌丛老化后土壤水分条件变差的原因之一。油蒿灌丛下穿透雨量及其空间分布受到有无枯枝和距主干辐射距离远近的影响,且受到降雨量和风速风向等气象条件作用明显。     

阿拉善荒漠典型植物功能群氮、磷化学计量特征

氮（N）、磷（P）作为荒漠生态系统重要的养分元素和限制性因子,在维持植物功能群组成及结构稳定、生态系统内养分循环中发挥着重要的作用。本研究沿水热梯度从东至西在阿拉善荒漠设置52个调查样地,通过对优势植物的调查取样,分析了荒漠植物不同功能（类）群N、P元素的生态化学计量特征,并就N、P含量及N：P值对荒漠植物的限制性作用进行了检验和讨论。结果显示：（1）所调查阿拉善荒漠区植物叶片的N、P含量分别为10.65±7.91 mg·g^-1和1.04±0.81 mg·g^-1,N：P值为11.53±5.06,叶片N含量与P含量及N：P值均显著正相关,P含量与N：P值显著负相关;通过对比分析认为该区植物同时受到N、P双重制约,且更易受N限制。（2）从植物生活型比较,认为草本植物叶片N、P含量均高于灌木植物叶片,而灌木植物叶片的N：P值大于草本植物;对光合作用途径分析发现,C₃植物叶片N含量高于C₄植物叶片,而C₄植物叶片P含量高于C₃植物叶片;从系统发育类型方面分析,认为单子叶植物叶片N含量低于双子叶植物叶片N含量,而P含量则高于双子叶植物叶片P含量。     

氮磷添加对黑果枸杞(Lycium ruthenicum)营养器官非结构性碳水化合物特征的影响

非结构性碳水化合物(NSC)在植物生长、繁殖、防御和生存等方面发挥着基础性作用.为探究黑果枸杞(Lyciumruthenicum)NSC积累的器官间规律及其对土壤氮磷供应水平的响应,以3年生黑果枸杞为对象,测定了3个氮磷比例和供应量条件下根茎叶NSC含量.结果表明:(1)黑果枸杞根、茎、叶NSC组成均以可溶性糖为主,淀...     

施氮对高寒草甸草原植物群落和土壤养分的影响

于2013-2014年在青藏高原东缘测定了不同梯度施氮后植物群落特征、牧草营养和土壤质量的变化,并分析了施氮后的经济效益。结果表明:(1)施氮显著增加了各功能群植物的高度和禾本科功能群植物盖度,而对莎草科和豆科植物盖度无显著影响;施氮显著增加了禾本科、莎草科、豆科和植物群落生物量,降低了杂类草盖度和生物量,其中施肥量为30.86～38.58 g·m^-2时效果最为显著。(2)施氮显著增加了0～20 cm土层根系生物量;施氮当年显著增加了根冠比,施氮第2年根冠比无显著变化。(3)施氮不同程度降低了高寒草甸草原植物群落多样性,其中,施肥量在30.86～38.58 g·m^-2时最低。(4)施氮不同程度地提高了禾本科、莎草科和杂类草植物的粗蛋白含量,降低了各功能群植物纤维含量;施氮不同程度提高了高寒草甸草原土壤养分和有机碳含量,其中在施肥量为30.86～38.58 g·m^-2时最高。(5)施氮当年和第二年净收益均在施肥量为30.86 g·m^-2时最大,分别为1 860元·hm^-2和878元·hm^-2。施氮缓解了青藏高原东缘高寒草甸草原植物生长的营养限制,提高了可食牧草产量,30.86～38.58 g·m^-2可作为该区最佳施氮水平。     

Nutrient status of Populus euphratica growing in desert riparian forests of northwestern China

Seasonal and microhabitat variations of chemical constituents of foliar organic carbon (C), total nitrogen (N), total phosphorus (P), and total potassium (K), in Populus euphratica growing in desert riparian forests in northwestern China and their correlations were studied. Results show that ranges of C, N, P and K contents in the leaves of P. euphratica were 39.08%?46.16%, 0.28%?2.81%, 0.05%?0.18% and 0.35%?2.03%, with means of 43.51%, 1.49%, 0.102% and 1.17%, respectively. The ratio of C/N, C/P and N/P changed from 16.26 to 146.61, from 258.08 to 908.67 and from 2.89 to 26.67; the mean was 37.24, 466.27 and 15.14, respectively. The mean N content was significantly lower than of deciduous trees in China, but the mean P content was nearly equivalent. The ratio of C/N was remarkably higher than of global land plants. The ratio of N/P indicated that growth of P. euphratica was jointly limited by N and P nutrient deficiency. During the growth season, total trends of leaf C, N, P and K contents decreased. The maximum appeared in May, and the minimum in September. Among microhabitats, C, N and K contents gradually increased from riparian lowland, flatland, sandpile, Gobi and dune, but C/N ratio was opposite, and P content was not apparent. Foliar C content was extremely, significantly and positively correlated with N and K contents, respectively. The relationships of N-K and P-K were both significantly positive.     

Arbuscular mycorrhizal fungi improve reestablishment of Leymus chinensis in bare saline-alkaline soil: Implication on vegetation restoration of extremely degraded land

Salinization and alkalinization are increasing problems in the world. Some land has been degraded to bare saline-alkaline soil where vegetation restoration is difficult because high toxic ionic content and pH are harmful to the survival of introduced plants. We grew Leymus chinensis with and without arbuscular mycorrhizal fungi (Glomus mosseae and G. geosporum) in either pots filled with soil from bare saline-alkaline land, or transplanted seedlings into field plots, to determine the influence of AM fungi on the reestablishment of this dominant grass species in bare degraded land. Association with AM fungi increased the absorption of N, P, K⁺, Ca²⁺, but decreased Mg²⁺, Na⁺ and Cl⁻ uptake under saline-alkaline stress. Therefore, higher K/Na, Ca/Na, P/Na, and P/Cl ratios were found in the inoculated plants. Plants inoculated with AM fungi accumulated significantly higher biomass, root/shoot ratio and tiller number than non-inoculated plants. AM fungi also significantly increased the survival of seedlings when they were transplanted into a bare saline-alkaline land in the field. The improvement of survival, growth and asexual reproduction of inoculated plants indicated that the plant-AM fungi mutualism could improve the reestablishment of vegetation in bare saline-alkaline soil, drive the vegetation restoration to a community dominated by original species.     

毛乌素沙地不同类型生物结皮与下层土壤酶活性及土壤碳氮磷化学计量特征

生物结皮在土壤养分累积和循环中起着重要作用.土壤酶活性能敏感地指示土壤的恢复程度,是衡量沙区生态恢复与健康的重要生物学指标.采用时空互代法,以毛乌素沙地不同演替阶段生物结皮(藻结皮、混生结皮和藓结皮)为研究对象,通过测定生物结皮及下层土壤的物理化学性质和酶活性,探讨不同演替阶段的生物结皮对土壤酶活性和碳氮磷化学计量特征...     

Inter- and intraspecific variations of the chemical properties of high-Arctic mosses along water-regime gradients

We examined and compared the contents of organic chemical components (lignin-like compounds, total carbohydrates and extractives), carbon and nutrients (nitrogen, phosphorus, potassium, calcium, magnesium) among the mosses Calliergon giganteum, Hylocomium splendens, Racomitrium lanuginosum, and among three populations of H. splendens collected from habitats in contrasting water regimes in the Canadian high-arctic tundra. C:N:P ratios were analyzed among and within moss species. Mosses from hydric habitats had lower total carbohydrate and higher nutrients contents than did mosses from drier habitats; however, we found no intraspecific variations in nitrogen and calcium contents in the different populations of H. splendens along water-regime gradients. The contents in lignin-like compounds, extractives and carbon showed no clear trends along water-regime gradients. Mosses from hydric habitats had lower C:N, C:P and N:P ratios than mosses from drier habitats, although we found no intraspecific variations in C:N ratios in H. splendens along water-regime gradients. These results suggest that chemical properties of mosses, especially nutrient contents, are strongly correlated with water availability in high-Arctic tundra.     

Foliar carbohydrate differs between Picea crassifolia and Sabina przewalskii with the altitudinal variation of Qilian Mountains, China

Nonstructural carbohydrates(NSC) and nitrogen metabolism strongly influence growth and development in plants. The biosynthesis of cellulose and lignin(structural carbohydrates, SC) depends largely on the supply of NSC. We desire to examine which hypothesis, carbon limitation or growth limitation, best fits the alpine plant response between NSC, SC, carbon(C), nitrogen(N) and altitude. We compared the foliar concentrations of carbohydrates, C and N between the leaves of Picea crassifolia(lower-elevation tree-line species) and Sabina przewalskii(high-elevation tree-line species) in their response to changing elevation. Our site was located in the mid-northern area of Qilian Mountains, China. We found that foliar soluble sugar(SG) concentrations were significantly higher in P. crassifolia than in S. przewalskii at the 2,700–3,400 m level. Foliar NSC levels in P. crassifolia increased at the 2,700–3,100 m level, indicating that growth was limited gradually resulting in a surplus of NSC(to conform to GLH), subsequently decreasing at the 3,100–3,400 m level, the assimilation declined leading to C deficit(to conform to CLH). SC(SC metabolism disorders at 3,100–3,400 m), C, N and starch were significantly lower in P. crassifolia than in S. przewalskii. Conversely, foliar SG concentration shows a fall-rise trend with increasing elevation for S. przewalskii. SC concentration in S. przewalskii leaves decreased with an increase of elevation and has a significantly positive correlation to N concentration marking the assimilation of plants. Therefore, the high-elevation tree-line species(S. przewalskii) utilize or store more foliar SG leading to a decrease of SG concentration for survival and growth/regrowth in an adverse environment, higher total C, N, SC, starch contents and lower NSC level. Also, their change trends along the elevational gradient in leaves of S. przewalskii indicate better assimilation strategies for SG use under environmental stress compared to P. crassifolia. This indicates that foliar C metabolism along the elevation follows the principle of the growth-limitation hypothesis(GLH) or carbon limitation hypothesis(CLH), which depends on the acclimation of different alpine life-forms to the environment.     

Seasonal timing of N pulses influences N capture in a saltbush scrub community

Limiting resources are generally available in brief temporal pulses in arid systems. We compared the abilities of dominant shrubs in a saltbush scrub community to capture N from pulses and evaluated whether N capture and partitioning within this community is influenced by the seasonal timing of pulses. Based on previous research in agronomic systems we predicted that the ability of a species to capture N following a pulse would depend on when the pulse occurred in relation to plant growth rate and N demand. Supporting this hypothesis, Atriplex confertifolia and Sarcobatus vermiculatus, which had greater growth rates early in the growing season compared to Atriplex parryi, captured more N from early spring pulses than A. parryi. Atriplex parryi, which had higher growth rates later in the growing season, captured more N from mid- and late spring pulses than the other species. These temporal differences in N capture among species, however, also depended on the magnitude of the N pulse. These results suggest that temporal variation in N availability may differentially impact competitive abilities of coexisting species and potentially facilitate species coexistence in arid systems.     

The effect of radiation on seedling growth and physiology in four species of Prosopis L. (Mimosaceae)

Domestication of wild plants needs efforts focused particularly on the development of the theoretical basis of plant responses to environmental conditions. The objective of this study was to assess the effect of radiation on seedling growth and physiology of Prosopis alba, P. chilensis, P. flexuosa and P. glandulosa. Seedlings were grown in a greenhouse and randomly assigned to three light environments: full-sun, 52% sun, and 38% sun. No significant differences were found in the rate of leaf appearance and plant height 60 days after the light treatments began. Instantaneous CO₂uptake was not affected by the light environment during leaf development and did not differ among species. Variations in radiation availability resulted in significant differences in biomass accumulation, shoot/root ratio, protein and total non-structural carbohydrates contents. The practice of shading seedlings reduces the chances of survival ofProsopis due to an increase of the shoot/root ratio and a reduction of total biomass, stored carbohydrates, and the C:N balance.     

Selection of plant species for rehabilitation of gypsum mine spoil in arid zone

Ten species were selected based on their economic value in order to study and compare their growth, nutrient uptake pattern, AM-fungal infection etc. in both mine spoil and normal cultivated soil in pot culture. In general, per cent root infection and number of viable AM fungal spores in the rhizosphere of the plant species grown in mine spoil were higher compared to those in normal cultivated soil. Mine spoil had supported significantly higher growth ofProsopis juliflora,Salvadora oleoidesandCenchrus ciliariscompared to normal soil. Concentrations of phosphorus, potassium and calcium in plants growing on gypsum mine spoil were higher than observed in normal soil. In general, micronutrient concentrations (namely Cu, Zn and Fe) were lower in all the plant species growing in normal soil.Salvadora oleoides,Colophospermum mopaneandPithecellobium dulcewere identified as calcium-loving plants. All the species tested can be employed for rehabilitation of gypsum mine spoil.     

Growth and water relation parameters in drought-stressed Coriaria nepalensis seedlings

In the present study, growth and water relation parameters were analysed in drought-stressed Coriaria nepalensis Wall. seedlings. C. nepalensis seedlings were subjected to four drought cycles of 7, 14, 21, and 28-days, and to one control level (watered on alternate days) in a glasshouse. The seedlings failed to survive a 28-days drought during summer. Osmotic adjustment (defined as the decrease in osmotic potential at zero or full turgor in response to water deficit) was measured as the difference between the osmotic potential of seedlings watered on alternate days (control) and those subjected to 21-days drought cycle. Seedlings subjected to 21-days drought had a predawn water potential of −2.60 MPa, and showed an osmotic adjustment of −1.95 MPa at full turgor and −2.17 MPa at zero turgor. The growth of seedlings was positively related to moisture and with water potential. With decline in soil moisture the root:shoot ratio increased while leaf weight ratio decreased. Leaf characteristics, such as leaf number, leaf area, leaf area ratio, specific leaf area and leaf drop, were also affected by moisture stress. This study has indicated that osmotic adjustment is a major adaptive mechanism of C. nepalensis that aids successful regeneration of seedlings in degraded sites with inhospitable soil conditions.