白草光合蒸腾日变化及其与气象因子的关系

[目的]探讨气象因子对白草光合生理特性的影响。[方法]以生长良好的白草植株的健康叶片为材料,采用Li-6400便携式光合系统仪对其进行活体测定,研究白草光合速率和蒸腾速率的日变化及其与气象因子的关系。[结果]白草为C4植物,无光合午休现象,其光合速率和蒸腾速率的日变化均为单峰曲线,光合速率最高值出现在12：00,蒸腾速率最高值出现在14：00;白草的净光合速率与光照强度呈极显著正相关,而与相对湿度、气温及叶温的相关性不显著;白草蒸腾速率与气温及叶温呈显著正相关,与光强呈极显著正相关,而与相对湿度呈显著负相关。[结论]白草的最佳浇水时间为1d中的10：00和18：00。     

土壤水分胁迫下油菜光合特性变化和膜伤害研究

对4种不同水分条件下油菜叶片的光合变化和膜伤害进行了研究。结果表明,在轻度干旱条件下,油菜叶片光合速率(Pn)和蒸腾速率(Tr)会增加,而气孔导度(Gs)则缓慢下降。随着胁迫程度加重,三者均出现明显下降。细胞间隙CO2浓度(Ci)在不同的水分胁迫下表现各异,轻度干旱胁迫下先下降再升高,而中度和重度干旱胁迫条件下却呈现明显上升然后趋于平缓趋势。叶片细胞膜透性和丙二醛(MDA)含量随着胁迫程度增加而明显增加。     

强光胁迫对18个冬小麦幼苗叶片光合特性的影响

为了研究强光胁迫对小麦叶片光合作用及某些相关指标的影响,以18个冬小麦品种幼苗为材料,对室外自然光条件下生长的幼苗进行强光(1 500 μmol·m-2·s-1)照射处理3 h(强光处理),对实验室内人工光照下生长的幼苗进行临时强光(1 500 μmol·m-2·s-1)照射处理3 h(临时强光处理).结果表明,强光胁迫对色素含量的影响较为复杂,品种间差异较大.强光处理对叶绿素含量的影响较小,对类胡萝卜素舍量的影响较大;临时强光处理对叶绿素含量的影响较强光处理大,而类胡萝卜素含量与强光处理的差异不显著.强先胁迫抑制了所用供试品种的Fv/Fm比值,其中临时强光胁迫抑制作用更大.说明强光胁迫下PSⅡ的功能较易受到抑制,影响光电转换及电子传递,对光合作用影响较大.强光胁迫使光化学反射指数PRI呈降低的趋势,但是对PRI的影响比对上述指标的影响小.     

Water use efficiency and photosynthesis of glyphosate-resistant soybean as affected by glyphosate

Previous studies comparing cultivars of different maturity groups in different soils demonstrated that early maturity group cultivars were more sensitive to glyphosate injury than those of other maturity groups. In this work, we evaluated the effect of increasing rates of glyphosate on water absorption and photosynthetic parameters in early maturity group cultivar BRS 242 GR soybean. Plants were grown in a complete nutrient solution and subjected to a range of glyphosate rates either as a single or sequential leaf application. Net photosynthesis, transpiration rate, stomatal conductance, sub-stomatal CO₂, carboxylation efficiency, fluorescence, maximal fluorescence and chlorophyll content were monitored right before and at different stages after herbicide application; water absorption was measured daily. All photosynthetic parameters were affected by glyphosate. Total water absorbed and biomass production by plants were also decreased as glyphosate rates increased, with the affect being more intense with a single full rate than half the rate applied in two sequential applications. Water use efficiency (WUE) was significantly reduced with increasing rates of glyphosate.     

Bentazone and bromoxynil induce H and H2O2 accumulation, and inhibit photosynthetic O2 evolution in Synechococcouselongatus PCC7942

Using a unicellular cyanobacterium, Synechococcouselongatus PCC7942, we have shown that cytosolic acidification, O₂⁻; H₂O₂ production and photosystem II-inactivation are the causes of cell death from bentazone/bromoxynil incubations. Butyric acid evoked solely pH lowering response and yet inhibited PS II activity indicating that herbicide-caused acidification is sufficient to kill the cyanobacterial cells, but other factors like excess H₂O₂ production due to an imbalance in the peroxide sequestration machinery might be contributory. While the activities of superoxide dismutase and pyrogallol peroxidase increased consequent to herbicide incubations and displayed oligomeric states with mobility shift, catalase and glutathione peroxidase though present remained insensitive.     

Can glyphosate stimulate photosynthesis?

Gas-exchange and biomass growth was measured on barley plants sprayed with glyphosate in order to investigate what might cause the growth increase observed in low dose glyphosate treated plants. Gas-exchange over 7 days after spraying was measured together with photosynthesis/irradiance and photosynthesis/CO₂ curves. In addition, growth experiments at 100, 200, 400 and 800 ppm CO₂ were conducted. Dark respiration rates increased in response to the glyphosate treatment, but so did photosynthesis at doses of 11-45 g a.e. ha⁻¹. The increase in photosynthetic rates was mainly due to an increased efficiency of CO₂ fixation under irradiance and CO₂ saturated conditions. The photosynthesis measurements were confirmed by the growth experiments, where glyphosate growth stimulations were observed only at 400 and 800 ppm CO₂. It can, hence, be concluded that low glyphosate doses can stimulate photosynthesis, though the causes behind this increase is still not understood.     

两种水分条件下夏玉米叶片气孔行为对光质的瞬时响应

在灌水和不灌水(整个生长期不灌溉)两种水分条件下,利用LI-6400便携式光合测定仪,测定3个主要生育期(拔节期、抽雄期和灌浆期选择典型日)夏玉米(郑单958)第一个功能叶片的气孔导度(Gs)、净光合速率(Pn)和蒸腾速率(Tr)指标,据此计算叶片的瞬时水分利用效率(WUE),测定时设定了5种比例的红蓝光组合(即B/(R+B)分别为0、25%、50%、75%和100%),以对比分析不同红蓝光比对玉米叶片气孔行为的瞬时影响。结果表明:与不灌水相比,灌水处理的叶片平均Gs、Pn和Tr在抽雄期明显较高,但在拔节期和灌浆期差异不显著。不论何种水分处理,光合有效辐射为500μmol·m-2·s-1时,叶片Gs、Pn和Tr均表现为单色红光照射时最大,随着蓝光所占比例的增加,各指标均有不同程度的降低。从节水角度来看,高红光比例的光质有利于提高玉米叶片WUE。     

Reduced carbon sequestration in terrestrial ecosystems under overcast skies compared to clear skies

There is still no consensus on the impact of cloud on terrestrial carbon sequestration. Nevertheless, the fraction of sky irradiance which is diffuse (fDIF) is close to half as a global annual average, owing mainly to the presence of clouds. Furthermore, as a consequence of human-induced perturbations, the occurrence and opacity of cloud is changing both regionally (due to deforestation and drainage) and globally (shortwave “solar” dimming). In this study, we quantify the impact of cloud on carbon assimilation at an unprecedented number of FLUXNET sites (38) and for six plant functional types (PFTs). We compare results from previously established empirical and statistical methods with novel land-surface and three-dimensional (3D) radiative-transfer (RT) simulations that take explicit account of diffuse sunlight. We record a much lower enhancement in canopy light-use efficiency (LUE) under diffuse sunlight relative to direct sunlight (factor 1.12–1.80) compared to previous authors (factors 2–3). Increased radiation-sharing, due to varied leaf orientation within the canopy, is the primary cause of LUE-enhancement rather than beam penetration within an open crown structure. Under cloud, we consistently record a decrease in primary productivity (≥10–40%) and an unequivocal decline in daily carbon sequestration (60–80%), owing to the dramatic reduction in total (direct plus diffuse) irradiance that occurs when clouds obscure the solar disk (≥60% attenuation). A cooling-induced reduction in ecosystem respiration offsets the decline in primary productivity by about one third.     

有效微生物群对舒玛栎容器苗生长的影响

以舒玛栎( Quercus shumardii.)容器苗为试验材料,研究施用不同体积分数有效微生物群(EM)对其生长的影响。结果表明:T 1(50倍稀释液)、T 2(100倍稀释液)和T 3(150倍稀释液)对苗高和地径生长均有一定提升效果,T 1和T 2处理后苗木的高径比显著低于清水对照(CK);不同体积分数EM处理后,苗木地下(根系)和地上部分(茎和叶)的鲜质量、干质量均显著大于CK;T 1和T 2显著提高了苗木叶片全氮、全磷和全钾的质量分数,对全钾质量分数的增加效果尤其显著;EM处理后显著提高了苗木叶片叶绿素质量分数、净光合速率( P n)、气孔导度( G s)和蒸腾速率( T r),而胞间CO 2摩尔分数( C i)低于CK。因此,施用EM后对舒玛栎苗木生长有一定的提升效果,特别是高浓度的T 1显著提高了苗木的各项指标。     

ALA叶面肥对春小麦光合特性和灌浆速率的影响

为了解含5-氨基乙酰丙酸(ALA)的叶面肥对春小麦光合特性、灌浆特性及产量的影响,以宁春15号春小麦为试验材料,采用单因素随机区组试验,研究了拔节期喷施稀释2 000倍（T1）、1 500倍（T2）、1 000倍（T3）、500倍（T4）的ALA叶面肥和清水（CK）5个处理对春小麦灌浆期光合特性、灌浆特性和产量的影响。结果表明,拔节期喷施一定浓度的ALA叶面肥能提高小麦灌浆期叶片净光合速率(P_n)、蒸腾速率(T_r)和胞间CO₂浓度(C_i),但以T2处理增幅最大。ALA叶面肥能够提高春小麦灌浆中前期的灌浆速率,以T2处理的效果最佳;可不同程度提高小麦产量及其构成因素,以T3处理成穗数、产量最高,与CK差异显著,较CK增产10.74%。综上所述,一定浓度ALA叶面肥能够改善春小麦的叶片光合特性,提高小麦籽粒产量,以稀释1 000~1 500倍施用效果较佳。