Interactive responses of old‐field plant growth and composition to warming and precipitation

As Earth's atmosphere accumulates carbon dioxide (CO₂) and other greenhouse gases, Earth's climate is expected to warm and precipitation patterns will likely change. The manner in which terrestrial ecosystems respond to climatic changes will in turn affect the rate of climate change. Here we describe responses of an old‐field herbaceous community to a factorial combination of four levels of warming (up to 4 °C) and three precipitation regimes (drought, ambient and rain addition) over 2 years. Warming suppressed total production, shoot production, and species richness, but only in the drought treatment. Root production did not respond to warming, but drought stimulated the growth of deeper (> 10 cm) roots by 121% in 1 year. Warming and precipitation treatments both affected functional group composition, with C₄ grasses and other annual and biennial species entering the C₃ perennial‐dominated community in ambient rainfall and rain addition treatments as well as in warmed treatments. Our results suggest that, in this mesic system, expected changes in temperature or large changes in precipitation alone can alter functional composition, but they have little effect on total herbaceous plant growth. However, drought limits the capacity of the entire system to withstand warming. The relative insensitivity of our study system to climate suggests that the herbaceous component of old‐field communities will not dramatically increase production in response to warming or precipitation change, and so it is unlikely to provide either substantial increases in forage production or a meaningful negative feedback to climate change later this century.     

Overexpression of Arabidopsis translationally controlled tumor protein gene AtTCTP enhances drought tolerance with rapid ABA-induced stomatal closure

Translationally controlled tumor protein (TCTP), also termed P23 in human, belongs to a family of calcium- and tubulin-binding proteins, and it is generally regarded as a growth-regulating protein. Recently, Arabidopsis TCTP (AtTCTP) has been reported to function as an important growth regulator in plants. On the other hand, plant TCTP has been suggested to be involved in abiotic stress signaling such as aluminum, salt, and water deficit by a number of microarray or proteomic analyses. In this study, the biological functions of AtTCTP were investigated by using transgenic Arabidopsis plants overexpressing AtTCTP. Interestingly, AtTCTP overexpression enhanced drought tolerance in plants. The expression analysis showed that AtTCTP was expressed in guard cells as well as in actively growing tissues. Physiological studies of the overexpression lines showed increased ABA- and calcium-induced stomatal closure ratios and faster stomatal closing responses to ABA. Furthermore, in vitro protein-protein interaction analysis confirmed the interaction between AtTCTP and microtubules, and microtubule cosedimentation assays revealed that the microtubule binding of AtTCTP increased after calcium treatment. These results demonstrate that the overexpression of AtTCTP confers drought tolerance to plants by rapid ABA-mediated stomatal closure via the interaction with microtubules in which calcium binding enhances the interaction. Collectively, the present results suggest that the plant TCTP has molecular properties similar to animal TCTPs, such as tubulin- and calcium-binding, and that it functions in ABA-mediated stomatal movement, in addition to regulating the growth of plants.     

Spatio-temporal heterogeneity in Arabidopsis thaliana leaves under drought stress

Using chlorophyll (chl) fluorescence imaging, we studied the effect of mild (MiDS), moderate (MoDS) and severe (SDS) drought stress on photosystem II (PSII) photochemistry of 4-week-old Arabidopsis thaliana. Spatio-temporal heterogeneity in all chl fluorescence parameters was maintained throughout water stress. After exposure to drought stress, maximum quantum yield of PSII photochemistry (F(v)/F(m)) and quantum efficiency of PSII photochemistry (Φ(PSΙΙ)) decreased less in the proximal (base) than in the distal (tip) leaf. The chl fluorescence parameter F(v) /F(m) decreased less after MoDS than MiDS. Under MoDS, the antioxidant mechanism of A. thaliana leaves seemed to be sufficient in scavenging reactive oxygen species, as evident by the decreased lipid peroxidation, the more excitation energy dissipated by non-photochemical quenching (NPQ) and decreased excitation pressure (1-q(p)). Arabidopsis leaves appear to function normally under MoDS, but do not seem to have particular metabolic tolerance mechanisms under MiDS and SDS, as revealed by the level of lipid peroxidation and decreased quantum yield for dissipation after down-regulation in PSII (Φ(NPQ)), indicating that energy dissipation by down-regulation did not function and electron transport (ETR) was depressed. The simultaneous increased quantum yield of non-regulated energy dissipation (Φ(NO)) indicated that both the photochemical energy conversion and protective regulatory mechanism were insufficient. The non-uniform photosynthetic pattern under drought stress may reflect different zones of leaf anatomy and mesophyll development. The data demonstrate that the effect of different degrees of drought stress on A. thaliana leaves show spatio-temporal heterogeneity, implying that common single time point or single point leaf analyses are inadequate.     

The potential of the satellite derived green chlorophyll index for estimating midday light use efficiency in maize, coniferous forest and grassland

Light use efficiency (LUE) is an important variable in carbon cycle and climate change research. We present an investigation of remotely estimating midday LUE using the green chlorophyll index (CI_green) derived from the cloud-free Moderate Resolution Imaging Spectroradiometer (MODIS) images in maize, coniferous forest and grassland. Similar temporal patterns are observed in both canopy chlorophyll content and midday LUE which indicates that the chlorophyll content in the maize canopy servers as a proxy of midday LUE (R² = 0.736, p < 0.001). Therefore, the CI_green, tested as a good indicator of canopy chlorophyll content (R² = 0.840, p < 0.001), has been demonstrated to be a reliable candidate in providing reasonable estimates of midday LUE with determination coefficient R² equals to 0.820 and a root mean square error (RMSE) of 0.002 mol CO₂ per mol incident photosynthetic photon flux density (PPFD). Further validation of the prediction model derived from the maize site demonstrates that the CI_green has potential to be applied in the coniferous forest and grassland ecosystems with RMSE of 0.005 and 0.004 mol CO₂ mol⁻¹ PPFD, respectively. A comparison analysis between different vegetation types is included and these results could be helpful in the development of future LUE and terrestrial models.     

华南地区8种常见园林地被植物抗旱性比较研究

以华南地区8种常见园林地被植物为研究对象,在温室内设置盆栽控水试验,分组测定各参试植物的永久萎蔫率,叶片失水率、相对含水量、相对电导率、可溶性糖、脯氨酸以及丙二醛含量等生理生化指标,并用隶属函数法对其抗旱性进行综合评价。结果表明:(1)植物的永久萎蔫率和叶片失水率以鹅掌藤、白蝴蝶相对较低,其植株表现出较强的抗旱性。(2)随着持续干旱时间的延长,8种地被植物的叶片相对含水量呈不同程度下降趋势;叶片相对电导率、MDA含量均有不同程度升高;叶片可溶性糖和脯氨酸含量的变化趋势不一。(3)3种木本植物的抗旱性强弱依次为鹅掌藤>红花龙船花>红背桂,5种草本植物依次为水鬼蕉>蚌兰>白蝴蝶>葱兰>大叶红草。研究表明,植物的永久萎蔫率、叶片失水率、相对含水量、相对电导率、丙二醛含量与其实际抗旱性密切相关,可作为评价园林地被植物抗旱性的有效指标。     

盐芥叶片响应干旱胁迫的蛋白质组学初步分析

盐芥是新兴起的植物非生物逆境研究模式植物,研究盐芥叶片蛋白质组对于干旱胁迫的响应,以推进对植物干旱耐受机制的认识。该研究应用双向电泳技术分析了干旱胁迫对于盐芥叶片蛋白质组的影响,结果共鉴定了63个干旱胁迫差异表达蛋白,包括丰度上调的31个,新出现的蛋白点14个,丰度下调的15个,消失的蛋白点3个。应用生物质谱分析技术确定了包括硫氧还蛋白,铁蛋白-1和凝集素在内的9个干旱胁迫响应蛋白的身份,对这些干旱胁迫响应蛋白的功能分类分析表明,盐芥的耐旱机制可能涉及自由基清除能力的增强、能量代谢的调整以及光合作用的维持。     

二乔玉兰开花过程中花色变化的生理生化机制

以4年生二乔玉兰不同花期外层花瓣为试材,测定其在开花过程中花瓣色度值、花色苷、类黄酮、可溶性糖含量、细胞pH值以及相关酶活性的变化,以探讨二乔玉兰花色呈色机理。结果显示:(1)随着花期的推移,苯丙氨酸解胺酶(PAL)和查尔酮异构酶(CHI)活性逐渐减弱,细胞pH值逐渐变大,可溶性糖、花色苷、类黄酮含量不断降低,而花瓣明亮度增强,红色度以及彩色度减弱,且不同花期各参数值之间差异显著。(2)花瓣可溶性糖含量、PAL和CHI的活性与其花色素苷、类黄酮含量变化之间呈显著正相关关系,花瓣pH值的变化、明亮度L*值与花色素苷、类黄酮含量之间呈显著负相关,色相值a*与花色苷含量的变化呈显著正相关。研究表明,二乔玉兰花瓣花色苷和类黄酮含量的高低可以影响其花色的深浅,可溶性糖含量、PAL和CHI活性、细胞pH通过参与一定的生理代谢来调节花色素的形成,进而引起二乔玉兰花色色调的改变。     

干旱胁迫下红麻和大麻状罗布麻水分生理及光合作用特征研究

以中国红麻和美国大麻状罗布麻为材料,采用防雨棚内盆栽控水法研究了4种土壤水分条件下2种罗布麻的水分生理及光合作用日变化特性,探讨2种罗布麻对干旱胁迫的响应和适应能力,为美国大麻状罗布麻引种栽培提供理论依据。结果显示:(1)随干旱胁迫的加剧,2种罗布麻叶片的组织含水量、相对含水量均逐渐降低,但大麻状罗布麻的降幅较小;同一水分条件下,大麻状罗布麻的组织含水量、相对含水量均高于红麻,而水分饱和亏均低于红麻;不同水分条件下,大麻状罗布麻叶片相对含水量在离体2h后仍维持高位,降幅极显著低于红麻(P<0.01),离体8h后仍能维持较高水平。(2)在饱和供水(CK)、轻度胁迫(LS)和中度胁迫(MS)条件下,2种罗布麻叶片的Pn、Tr、Gs日变化均呈相似的"双峰"型曲线,而重度胁迫(SS)下却呈单峰曲线,各胁迫条件下Pn第二峰值比CK推迟2h左右;各处理Pn和WUE日均值在大麻状罗布麻中表现为LS>CK>MS>SS,而在红麻中则为CK>LS>MS>SS,且2种罗布麻除WUE指标在处理CK与T1间差异不显著外(P>0.05),其余处理间差异均达到显著水平以上(P<0.05);同一水分条件下,大麻状罗布麻的Pn和WUE值均显著高于红麻,如大麻状罗布麻在SS条件下的Pn和WUE日均值分别为2.28μmol·m-2.s-1和1.41μmol·mmol-1,而红麻的仅为0.29μmol·m-2.s-1和0.16μmol·mmol-1。研究表明,在土壤干旱胁迫条件下,大麻状罗布麻叶片在水分生理和光合生理方面均表现出明显优势,比当地红麻具有更强的保水及光合生产能力,耐旱性更强,可在宁夏地区引种栽培。