黄土丘陵区不同种植行距下柳枝稷光合生理日变化研究

以引进禾草柳枝稷为材料,在半干旱黄土丘陵区人工梯田设置20cm(L20)、40cm(L40)和60cm(L60)3种种植行距,比较研究了其光合生理参数日变化、地上部分生物量及土壤水分剖面分布特征,探讨其光合生理和水分利用特征与种植行距的关系。结果表明:(1)不同行距下,柳枝稷叶片净光合速率(Pn)日变化均呈双峰曲线,第一峰值均出现在10:00,第二峰值L40出现在14:00,L20和L60出现在16:00,具有明显的光合"午休"现象,且均由非气孔因素限制引起;柳枝稷叶片Pn日均值大小依次为:L60>L40>L20,且两两间差异显著。(2)柳枝稷叶片水分利用效率(WUE)日变化与Pn相似,分别在10:00和14:00达到峰值,日均值大小依次为:L60>L40>L20。(3)不同行距下,土壤体积含水量均随土层深度增加呈先增加后减少再增加的趋势,除0～50cm土层外,其它各土层土壤储水量均存在较大差异,0～380cm土层总土壤储水量表现为:L20>L40>L60。(4)柳枝稷地上生物量大小依次为:L20>L60>L40。研究发现,20cm行距的柳枝稷个体虽光合速率较低,但群体生物量和土壤储水量较高,所以柳枝稷在黄土丘陵区梯田的较优行距为20cm。     

The effect of environmental factors on floating fresh marsh end-of-season biomass

We used both stepwise and quantile regression to determine the sources of environmental variation that explained the observed inter-annual variation in end-of-season freshwater floating marsh aboveground biomass over an 18-year period. The vegetation at our study site had high species diversity with an average of 20 species recorded from 10 0.25 m⁻² plots. However, Panicum hemitomon was clearly the dominant contributing 74% of the total biomass. Only three other species (Solidago sempervirens, Vigna luteola, and Thelypteris palustris) were so common that they were sampled in all years. We expected that the most important factors controlling interannual variation in aboveground biomass are temperature and nitrogen availability. We also expected that nitrogen availability to the plants is affected by water movement through and under the mat driven by precipitation (lower N), evaporation (transportation of higher N waters to roots), and local runoff (higher N). Stepwise regression analysis indicated that P. hemitomon average biomass was negatively related to average water level and positively related to maximum water level and had a curvilinear response with TKN. Using quantile regression the best fit for P. hemitomon maximum-biomass with two parameters was obtained using hot days (positive relationship) and maximum water level (negative relationship). Both analytical methods showed maximum water level (negative relationship) and cold front passage (positive relationship) to be the environmental parameters that best explained interannual variation in S. sempervirens biomass. V. luteola biomass was positively related to temperature. Stepwise regression added chloride concentration as an additional positive parameter explaining V. luteola biomass, while quantile regression identified nitrogen as an important positive parameter. Both analytical methods identified pH, TKN, and water level as environmental parameters that were negatively correlated with T. palustris biomass. The overall negative effect of water level on all species was unexpected in this floating mat system. We initially assumed that higher water levels were due to higher runoff which should have a positive effect on biomass. However, higher water levels may also be related to a higher retention time in this fresh-water tidal system, which decreases water exchange and nutrient replenishment.     

Biomass and leaf‐level gas exchange characteristics of three African savanna C4 grass species under optimum growth conditions

C₄ savanna grass species, Digitaria eriantha, Eragrostis lehmanniana and Panicum repens, were grown under optimum growth conditions with the aim of characterizing their above‐ and below‐ground biomass allocation and the response of their gas exchange to changes in light intensity, CO₂ concentration and leaf‐to‐air vapour pressure deficit gradient (D_l). Digitaria eriantha showed the largest above‐ and below‐ground biomass, high efficiency in carbon gain under light‐limiting conditions, high water use efficiency (WUE) and strong stomatal sensitivity to D_l (P = 0.002; r² = 0.5). Panicum repens had a high aboveground biomass and attained high light saturated photosynthetic rates (A_sat, 47 μmol m^?2 s^?1), stomatal conductance, (g_sat, 0.25 mol m^?2 s^?1) at relatively high WUE. Eragrostis lehmanniana had almost half the biomass of other species, and had similar A_sat and g_sat but were attained at lower WUE than the other species. This species also showed the weakest stomatal response to D_l (P = 0.19, r² = 0. 1). The potential ecological significance of the contrasting patterns of biomass allocation and variations in gas exchange parameters among the species are discussed.     

淹水胁迫对铺地黍几种保护酶活性的影响

目的:探讨淹水胁迫对铺地黍几种保护酶活性的影响.方法:通过模拟试验,研究不同淹水时间对铺地黍体内超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)及多酚氧化酶(PPO)活性的影响.结果:在淹水胁迫前期,铺地黍体内SOD、CAT和PPO活性总体表现为升高的变化特征.之后,随着胁迫时间的延长,3种酶活性均逐渐降低,在淹水5w时,SOD、CAT和PPO活性分别为对照的38.7%、50.3%和178.2%.而在整个淹水期间POD活性则一直呈升高的趋势.结论:几种保护酶对淹水胁迫的响应能力有差异,其中SOD、CAT活性的变化可作为铺地黍对淹水反应的生理指标.     

A quantitative review comparing the yield of switchgrass in monocultures and mixtures in relation to climate and management factors

Switchgrass (Panicum virgatum L.), a US Department of Energy model species, is widely considered for US biomass energy production. While previous studies have demonstrated the effect of climate and management factors on biomass yield and chemical characteristics of switchgrass monocultures, information is lacking on the yield of switchgrass grown in combination with other species for biomass energy. Therefore, the objective of this quantitative review is to compare the effect of climate and management factors on the yield of switchgrass monocultures, as well as on mixtures of switchgrass, and other species. We examined all peer‐reviewed articles describing productivity of switchgrass and extracted dry matter yields, stand age, nitrogen fertilization (N), temperature (growing degree days), and precipitation/irrigation. Switchgrass yield was greater when grown in monocultures (10.9 t ha^?1, n=324) than when grown in mixtures (4.4 t ha^?1, n=85); yield in monocultures was also greater than the total yield of all species in the mixtures (6.9 t ha^?1, n=90). The presence of legume species in mixtures increased switchgrass yield from 3.1 t ha^?1 (n=65) to 8.9 t ha^?1 (n=20). Total yield of switchgrass‐dominated mixtures with legumes reached 9.9 t ha^?1 (n=25), which was not significantly different from the monoculture yield. The results demonstrated the potential of switchgrass for use as a biomass energy crop in both monocultures and mixtures across a wide geographic range. Monocultures, but not mixtures, showed a significant positive response to N and precipitation. The response to N for monocultures was consistent for newly established (stand age <3 years) and mature stands (stand age ≥3 years) and for lowland and upland ecotypes. In conclusion, these results suggest that fertilization with N will increase yield in monocultures, but not mixtures. For monocultures, N treatment need not be changed based on ecotype and stand age; and for mixtures, legumes should be included as an alternative N source.     

Regulation and roles of phosphoenolpyruvate carboxykinase in plants

Phosphoenolpyruvate carboxykinase (PCK) is probably ubiquitous in flowering plants, but is confined to certain cells or tissues. It is regulated by phosphorylation, which renders it less active by altering both its substrate affinities and its sensitivity to regulation by adenylates. In the leaves of some C4 plants, such as Panicum maximum, dephosphorylation increases its activity in the light. In other tissues such regulation probably avoids futile cycling between phosphoenolpyruvate and oxaloacetate. Although PCK generally acts as a decarboxylase in plants, its affinity for CO2 measured at physiological concentrations of metal ions is high and would allow it to be freely reversible in vivo. While its function in gluconeogenesis in seeds postgermination and in leaves of C4 and crassulacean acid metabolism plants is clearly established, the possible functions of PCK in other plant cells are discussed, drawing parallels with those in animals, including its integrated function in cataplerosis, nitrogen metabolism, pH regulation, and gluconeogenesis.     

In vitro differentiation of multiple shoot clumps from intact seedlings of switchgrass

Summary An efficient and reproduciblein vitro culture system has been developed for regeneration of multiple shoot clumps from intact seedlings of both lowland and upland cultivars of switchgrass (Panicum virgatum L.). The multiple shoots were induced on Murashige and Skoog medium supplemented with various combinations of 2,4-dichlorophenoxyacetic acid (2,4-D) and 1-phenyl-3-(1,2,3-thiadiazol-5YL)-urea (thidiazuron or TDZ). Maximum response was obtained with 4.5 μM 2,4-D and 18.2 μM TDZ. These shoots proliferated and rooted efficiently on MS medium without growth regulators. The developmental pattern of the multiple shoots indicated their origin from the enlarged shoot apex via proliferation of axillary buds and subsequent reprogramming of shoot meristems followed by secondary differentiation of adventitious shoots The simplicity of the protocol and direct production of multiple shoots make this a potential system that is highly attractive and amenable for microprojectile-mediated gene transfer.     

Inoculation of forage grasses with N2-fixing Enterobacteriaceae

Summary Previous investigations indicated some forage grass roots in Texas are heavily colonized with N₂-fixing bacteria. The most numerous N₂-fixing bacteria were in the genera Klebsiella and Enterobacter. In the present investigation inoculation experiments were conducted using 18 isolates of these bacteria to determine if a N₂-fixing association could be established between the bacteria and the grassesCynodon dactylon andPanicum coloratum. Plants were grown in soil for approximately 5 months in a greenhouse and were measured periodically for dry matter, nitrogen accumulation, and acetylene reduction activity. Results of the investigation indicated that 25% of the plant-soil systems were active in acetylene reduction and the activity was high enough to indicate agronomically significant quantities of N₂ were being fixed (>8kg N ha⁻¹). However, plant systems extrapolated to fix>8 kg N ha⁻¹ contained less nitrogen and accumulated less dry matter than plants less active in acetylene reduction. Inocula could not be re-isolated from healthy grass roots indicating that the N₂-fixing activity may have not have been closely assiciated with plant roots. Future research is needed to determine factors limiting colonization of grass roots.     

Photosynthesis, immediate export and carbon partitioning in source leaves of C3, C3-C4 intermediate, and C4Panicum and Flaveria species at ambient and elevated CO2 levels

Immediate export in leaves of C₃‐C₄ intermediates were compared with their C₃ and C₄ relatives within the Panicum and Flaveria genera. At 35 Pa CO₂, photosynthesis and export were highest in C₄ species in each genera. Within the Panicum, photosynthesis and export in ‘type I’ C₃‐C₄ intermediates were greater than those in C₃ species. However, ‘type I’ C₃‐C₄ intermediates exported a similar proportion of newly fixed ¹⁴C as did C₄ species. Within the Flaveria, ‘type II’ C₃‐C₄ intermediate species had the lowest export rather than the C₃ species. At ambient CO₂, immediate export was strongly correlated with photosynthesis. However, at 90 Pa CO₂, when photosynthesis and immediate export increased in all C₃ and C₃‐C₄ intermediate species, proportionally less C was exported in all photosynthetic types than that at ambient CO₂. All species accumulated starch and sugars at both CO₂ levels. There was no correlation between immediate export and the pattern of ¹⁴C‐labelling into sugars and starch among the photosynthetic types within each genus. However, during CO₂ enrichment, C₄Panicum species accumulated sugars above the level of sugars and starch normally made at ambient CO₂, whereas the C₄Flaveria species accumulated only additional starch.