Effect of leaf structure and water status on carbon isotope discrimination in field-grown durum wheat

The relationships between leaf and kernel carbon isotope discriminations (Δ) and several leaf structural parameters that are indicators of photosynthetic capacity were studied in durum wheat grown in the field under three water regimens. A set of 144 genotypes were cultivated in two rain-fed trials, and 125 of these were grown under supplementary irrigation before heading. Total chlorophyll and nitrogen (N) contents, the dry mass per unit leaf area (LDM, the reciprocal of specific leaf area) and carbon isotope discrimination (Δ) were measured in penultimate leaves and Δ of mature kernels was also analysed. Both LDM and N per unit area showed significant (P≤ 0.001) negative correlation (r=–0.60 and r=–0.36, respectively) with leaf Δ in the wettest trial. Little or no correlation was found for any structural parameter and leaf Δ in the rain-fed trials. In contrast, in the two rain-fed trials LDM was the parameter with the strongest positive correlation (P≤ 0.001) with kernel Δ (r= 0.47 and 0.30) and grain yield (r= 0.43 and 0.29), whereas no correlation was found in the irrigation trial. These correlations, rather than representing a causal link between the amount of photosynthetic tissue and Δ, were probably indirect associations caused by a parallel effect of water status and phenology on leaf structure, grain Δ and yield. Correlations across trials (i.e. environments) between leaf structure and either Δ and yield were very high, although also spurious. Our results suggest that LDM should be used to cull segregating population differences in leaf Δ based on the internal photosynthetic capacity only in the absence of drought. Selecting for kernel Δ and grain yield on the basis of LDM is worthwhile for rain-fed trials.     

Drought effects on canopy properties and productivity in thinned and unthinned Turkey oak stands

ABSTRACT

Drought responses, leaf area index (LAI), leaf characteristics and light extinction coefficient (k) were analysed in thinned and unthinned Turkey oak (Quercus cerris L.) stands at two sites: Valsavignone, in the Apennines, with a mild climate, and Caselli, near the Tyrrhenian coast, with a longer and more accentuated dry period in the summer. Turkey oak showed a good adaptability to drought due to a series of modifications in leaf characteristics, canopy properties and biomass allocation such as leaf area reduction, increased leaf thickness, smaller number of leaves and, at stand level, lower LAI, leaf biomass and LWR values and higher light extinction coefficients. In spite of the better environmental conditions and the higher LAI values, productivity was lower in the wet site. The differences in Turkey oak canopy properties, light extinction coefficients, LAI and their relations with drought and productivity are discussed.     

Temporal dynamics and spatial variability in the enhancement of canopy leaf area under elevated atmospheric CO2

Increased canopy leaf area (L) may lead to higher forest productivity and alter processes such as species dynamics and ecosystem mass and energy fluxes. Few CO₂ enrichment studies have been conducted in closed canopy forests and none have shown a sustained enhancement of L. We reconstructed 8 years (1996–2003) of L at Duke's Free Air CO₂ Enrichment experiment to determine the effects of elevated atmospheric CO₂ concentration ([CO₂]) on L before and after canopy closure in a pine forest with a hardwood component, focusing on interactions with temporal variation in water availability and spatial variation in nitrogen (N) supply. The dynamics of L were reconstructed using data on leaf litterfall mass and specific leaf area for hardwoods, and needle litterfall mass and specific leaf area combined with needle elongation rates, and fascicle and shoot counts for pines. The dynamics of pine L production and senescence were unaffected by elevated [CO₂], although L senescence for hardwoods was slowed. Elevated [CO₂] enhanced pine L and the total canopy L (combined pine and hardwood species; P<0.050); on average, enhancement following canopy closure was ～16% and 14% respectively. However, variation in pine L and its response to elevated [CO₂] was not random. Each year pine L under ambient and elevated [CO₂] was spatially correlated to the variability in site nitrogen availability (e.g. r²=0.94 and 0.87 in 2001, when L was highest before declining due to droughts and storms), with the [CO₂]‐induced enhancement increasing with N (P=0.061). Incorporating data on N beyond the range of native fertility, achieved through N fertilization, indicated that pine L had reached the site maximum under elevated [CO₂] where native N was highest. Thus closed canopy pine forests may be able to increase leaf area under elevated [CO₂] in moderate fertility sites, but are unable to respond to [CO₂] in both infertile sites (insufficient resources) and sites having high levels of fertility (maximum utilization of resources). The total canopy L, representing the combined L of pine and hardwood species, was constant across the N gradient under both ambient and elevated [CO₂], generating a constant enhancement of canopy L. Thus, in mixed species stands, L of canopy hardwoods which developed on lower fertility sites (～3 g N inputs m^?2 yr^?1) may be sufficiently enhanced under elevated [CO₂] to compensate for the lack of response in pine L, and generate an appreciable response of total canopy L (～14%).     

Improvement of somatic embryogenesis in Medicago arborea

A number of medium constituents were evaluated in an attempt to improve somatic embryo production in Medicago arborea ssp. arborea, using cotyledons, petioles and leaves as explants. Two culture steps were applied: in the first stage (2 months), Murashige–Skoog (MS) medium was used, containing 2,4 dichlorophenoxyacetic acid (9M 2,4-D) and kinetin (9 M KIN) together with different nitrogen sources (alanine, glutamine, proline or tryptophan (2.5 and 5 mM); casein hydrolysate (100, 500 and 1000 mg l^–1; nitrate (4.69 and 9.39 mM) or casein hydrolysate (100 mg l^–1) and nitrate (4.69 mM)), polyalcohols (mannitol at 164 and 328 mM or sorbitol at 219 and 438 mM), sucrose (43.8 and 175.4 mM) or calcium (1.5 and 6 mM). In the second stage (3 months of cultivation), calli were transferred to a kinetin-free MS medium with 2,4-D (2.25 M) only. The inclusion of proline (2.5 mM) was the most effective treatment for the induction of somatic embryos, with the petiole being the best explant. Treatment with casein hydrolysate (100 mg l^–1) also improved the embryonic efficiency. The rest of the treatments neither affect nor inhibit the embryonic response.A special treatment with sorbitol (219 mM) in the second stage of cultivation produced a slight increase in embryogenesis, but less than that obtained with proline.     

紫花苜蓿复合体(Medicago sativa complex)叶片形态特征及数量分类研究

运用比较形态学和比较解剖学方法,使用扫描电镜和光学显微镜对紫花苜蓿复合体(Medicago sativa complex)6个分类群的叶片形态特征和叶片解剖结构进行了观察和比较,并以15个叶片表征形态性状为基础,采用聚类分析法(UPGMA)和主成分分析方法(PCA)对6个分类群进行了数量分类研究.观察结果表明:各分类群叶片的上、下表皮多为不规则形细胞;垂周壁呈深浅不一的波状;气孔器为不规则型,具有蜡质气孔盖,气孔密度有一定差异.6个分类群的叶片均为薄纸质型,厚度130～170 μm,表皮细胞切面近圆形或近长方形;栅栏组织细胞1～2层,厚度41～68 μm,细胞排列紧密;海绵组织厚度32～75 μm,细胞排列疏松;不同分类群叶片的组织疏松度和组织紧缩度有一定的差异,大花苜蓿(M. trautvetterii Sumnev. )叶片的组织疏松度最高,紫花苜蓿叶片的组织紧缩度最高.UPGMA结果显示:在结合线1.53处可将6个分类群划分为2支,其中,黄花苜蓿(M. falcata L. )独立为一支,其余5个分类群聚成另一支;在结合线1.18处,第2支又被分成2个亚支,其中一个亚支包含紫花苜蓿和天山苜蓿(M. tianschanica Vassilcz. ),另一个亚支则包含西锡金苜蓿(M. schischkinii Sumnev. )、座垫苜蓿(M. rivularis Vassilcz. )和大花苜蓿.PCA结果表明:对紫花苜蓿复合体而言,叶片表皮细胞形状、垂周壁式样、轴性分化特征、组织疏松度和气孔密度等特征具有较好的分类价值;基于主成分分析的Q分布图与聚类分析结果也具有较高的一致性.根据本研究结果及前人的研究结果,认为国产的紫花苜蓿复合体应包含3个分类群,即紫花苜蓿、黄花苜蓿及多变苜蓿(M. varia Martyn).此外,西锡金苜蓿、座垫苜蓿、天山苜蓿和大花苜蓿等杂交后代分类群的性状分化不稳定,应属于多变苜蓿的同种异名植物.     

Chlorophyll a fluorescence during flag leaf senescence of field-grown winter wheat plants under drought conditions

Improving wheat grain yield plays a significant role in ensuring global food security. Wheat production could be increased by the genetic improvement of wheat genotypes where delayed senescence with enhanced post-anthesis capacity and staygreen traits could have an important role. In this study, chlorophyll a fluorescence (ChlF) rise kinetics from the early until late senescence of flag leaves, grain yield and other agro-morphological characteristics were compared for three winter wheat advanced lines (Osk.4.312/10-18, Osk.4.330/6-18 and Osk.4.354/12-18) under natural drought conditions. The differences between lines were observed when considering the heading date which was 1 and 4 days earlier for the line Osk.4.354/12-18, than lines Osk.4.312/10-18 and Osk.4.330/6-18, respectively. Furthermore, line Osk.4.354/12-18 had the highest test weight (kg hl⁻¹), while line Osk.4.330/6-18 showed a tendency of decreased grain yield, compared to the other two lines. Analysis of ChlF transients and several JIP-test parameters indicated that all three lines had a generally similar course of changes in the photosynthetic performance of flag leaves during senescence under drought conditions. However, at the point when a decrease in photosynthetic performance was initiated, it was slightly less intensive in line Osk.4.354/12-18 accompanied by longer preservation of functionality and connectivity of PSII units, than in the other two lines, which contributed to its better agronomical performance. These results indicated that even delicate variations in the functioning of the photosynthetic apparatus of the flag leaf during grain filling were agronomically important, especially when plants were exposed to drought stress, and could be used to differentiate otherwise similar wheat genotypes. Even small genotype-specific differences in the photosynthetic performance of senescing flag leaves, along with earlier heading dates, could assist in the selection of genotypes with a better ability to cope with unfavourable environmental conditions.     

Alteration of the phenology of leaf senescence and fall in winter deciduous species by climate change: effects on nutrient proficiency

Leaf senescence in winter deciduous species signals the transition from the active to the dormant stage. The purpose of leaf senescence is the recovery of nutrients before the leaves fall. Photoperiod and temperature are the main cues controlling leaf senescence in winter deciduous species, with water stress imposing an additional influence. Photoperiod exerts a strict control on leaf senescence at latitudes where winters are severe and temperature gains importance in the regulation as winters become less severe. On average, climatic warming will delay and drought will advance leaf senescence, but at varying degrees depending on the species. Warming and drought thus have opposite effects on the phenology of leaf senescence, and the impact of climate change will therefore depend on the relative importance of each factor in specific regions. Warming is not expected to have a strong impact on nutrient proficiency although a slower speed of leaf senescence induced by warming could facilitate a more efficient nutrient resorption. Nutrient resorption is less efficient when the leaves senesce prematurely as a consequence of water stress. The overall effects of climate change on nutrient resorption will depend on the contrasting effects of warming and drought. Changes in nutrient resorption and proficiency will impact production in the following year, at least in early spring, because the construction of new foliage relies almost exclusively on nutrients resorbed from foliage during the preceding leaf fall. Changes in the phenology of leaf senescence will thus impact carbon uptake, but also ecosystem nutrient cycling, especially if the changes are consequence of water stress.     

Differences in invertase activity in embryogenic and non-embryogenic calli from Medicago arborea

The different invertase activities in embryogenic and non-embryogenic calli induced from explants (cotyledons, petioles, hypocotyls and leaves) obtained from Medicago arborea L. subsp. arborea seedlings were evaluated. Total invertase activity was lower in the calli with the greatest embryogenic capacity. The greatest fraction of this activity corresponded to soluble invertase. Wall-bound invertase showed maximum activity during the first two months of culture and the highest activities of this type were found in non-embryogenic calli. Extracellular invertase formed the smallest fraction of the total invertase activity evaluated. Acid and alkaline invertase activities were found in all calli but differences were detected between the embryogenic and non-embryogenic calli. In the former, the activity of both types of invertase exhibited a similar type of behaviour but different from that observed in the non-embryogenic calli. The calli with the greatest embryogenic capacity had very low levels of acid invertase and very high levels of the alkaline form. Soluble invertase – both acid and alkaline – accounted for the highest fraction after the first two months of culture and was present in lower amounts in the embryogenic than in the non-embryogenic calli. Regarding bound invertase, the highest production was seen to correspond to acid invertase. The extracellular invertase evaluated corresponded to the acid form since the alkaline extracellular invertase did not show any physiologically significant activity.     

Somatic embryogenesis and plant regeneration in Medicago arborea L.

Summary An efficient plant regeneration system employing cotyledons, hypocotyls, petioles and leaves as explants and characterized by continuous and prolific production of somatic embryos, has been developed with Medicago arborea ssp. arborea. The optimal somatic embryogenic response was obtained using a two-step protocol, where explants were incubated under a 16 h photoperiod for 2 mo. on Murashige and Skoog (MS) medium containing 2,4-dichlorophenoxyacetic acid (2,4-D; 9 μM) and kinetin (9 μM), and followed by transfer to kinetin-free MS medium with 2,4-D (2.25 μM). Removal of the cytokinin and a reduction in the concentration of auxin (2.25 μM) in the second step of culture were critical for enhanced production of somatic embryos. The best explants proved to be cotyledons and petioles (i.e. a mean of 18.0±0.70 somatic embryos at 3 mo. for petiole culture). Somatic embryos were converted into normal plantlets (8.0±0.89%) when cultured on basal MS medium with 5 μM indolebutyric acid. No somatic embryos were obtained when thidiazuron was used in the culture media. Using petioles as explants and N⁶-benzyladenine (BA), embryogenesis was induced in the second step of culture when BA was removed from the medium and the concentration of 2,4-D was decreased to 2.25 μM.     

Influence of initial organic N reserves and residual leaf area on growth, N uptake, N partitioning and N storage in alfalfa (Medicago sativa) during post-cutting regrowth

BACKGROUND AND AIMS: The influence of initial residual leaf area and initial N reserves on N uptake, final N distribution, and yield in alfalfa regrowing after cutting, were studied. METHODS: The effects of two levels of initial residual leaf area (plants cut to 15 cm, with (L+) or without (L-) their leaves) and two initial levels of N status [high N (HN) or low N (LN)] on growth, N uptake and N partitioning, allocation and storage after 29 d of post-cutting regrowth were analysed. KEY RESULTS: During most of the regrowth period (8-29 d after the initial harvest), HN and L+ plants had higher net N uptake rates than LN and L- plants, respectively, resulting in a greater final mineral N uptake for these treatments. However, the final partitioning of exogenous N to the regrowing shoots was the same for all treatments (67 % of total exogenous N on average). Final shoot growth, total plant N content, and N allocation to the different taproot N pools were significantly lower in plants with reduced initial leaf area and initial N reserve status. CONCLUSIONS: Although both initial residual leaf area and initial N reserves influenced alfalfa regrowth, the residual leaf area had a greater effect on final forage production and N composition in the taproot, whereas the N uptake rate and final total N content in plant were more affected by the initial N reserve status than by the residual leaf area. Moreover, N storage as proteins (especially as vegetative storage proteins, rather than nitrate or amino acids) in the taproot allowed nitrate uptake to occur at significant rates. This suggests that protein storage is not only a means of sequestering N in a tissue for further mobilization, utilization for growth or tissue maintenance, but may also indirectly influence both N acquisition and reduction capacities.     

冬小麦旗叶旱促衰老过程中氧化伤害与抗氧化系统的尖

研究了土壤缓慢干旱胁迫下抗旱性不同的２个冬小麦品种旗叶老过程中氧化丰以及酶促与硕果发现,在抗旱性强的品种中,冬泪科叶片旱个衰老与膜脂过氧化程度之间并无直接的联系。超氧化物歧化酶（ＳＯＤ）活性在不同抗旱性品种中均呈现持志下降的趋势,但在生强的品种中下降幅度较小,过氧化氢酶（ＣＡＴ）活性在胁迫初期基本不变,至中后期明显下降,且在抗旱性弱的品种中下降幅度较大,抗坏血酸过氧化物酶（ＡＰ）和谷胱甘肽还原酶（     

西南干旱对哀牢山常绿阔叶林凋落物及叶面积指数的影响

为探讨2010年初西南干旱对这一地区原生植被林冠和凋落物量的影响,以及这一地区凋落物量和气候条件之间的关系,对比研究了哀牢山亚热带常绿阔叶林2010年和一般年份的凋落物特征以及各层的叶面积指数,并分析了凋落物量和气候因子之间的关系.2010年凋落物总量和往年相比无显著差异,但是叶凋落总量、旱季凋落物总量、旱季叶凋落量为历年来最高,其中旱季叶凋落物量比一般年份平均高35.2％ (0.81 t/hm2).而2010年附生苔蘚年凋落量为历年来最低.2010年最旱月的乔木层和灌木层叶面积指数和2005同期相比无显著差异,但是草本层叶面积指数却极显著低于2005年同期.因此,2010年初西南干旱尽管使哀牢山常绿阔叶林旱季落叶增加,但还没有到显著影响冠层叶面积指数的程度.而草本层和附生苔藓的生长则受到了干旱事件的显著影响.此外,哀牢山常绿阔叶林年总凋落量和年降水量显著正相关,而和年均温却不相关,表明该亚热带森林凋落物量主要由降水而非温度决定.     

Combined effects of girdling and leaf removal on fluorescence characteristic of Alhagi sparsifolia leaf senescence

Plant senescence is largely influenced by carbohydrate content. In order to investigate the impact of carbohydrate content on leaf senescence and photosystem II (PSII) during the senescence process, phloem girdling (PG), leaf removal (LR) and a combination of phloem girdling and leaf removal (GR) were performed on Alhagi sparsifolia (Fabaceae) at the end of the growing season. The results showed that during senescence, leaf soluble sugar content, starch content, the energy absorbed by the unit reaction centre (ABS/RC) increased; whereas, leaf photosynthetic rate, photosynthetic pigment content, maximum photochemical efficiency (φ_Po) and energy used by the acceptor site in electron transfer (ET_o/RC) decreased. The degree of change was PG> GR> CK (control)> LR. The results of the present work implied that phloem girdling (PG) significantly accelerated leaf senescence, and that single leaf removal (LR) slightly delayed leaf senescence; although leaf removal significantly delayed the senescence process on the girdled leaf (GR). Natural or delayed senescence only slightly inhibited the acceptor site of PSII and did not damage the donor site of PSII. On the other hand, induced senescence not only damaged the donor site of PSII (e.g. oxygen‐evolving complex), but also significantly inhibited the acceptor site of PSII. In addition, leaf senescence led to an increase in the energy absorbed by the unit reaction centre (ABS/RC), which subsequently resulted in increasing excitation pressure in the reaction centre (DI_o/RC), as well as additional saved Car for absorbing residual light energy and quenching reactive oxygen species during senescence.     

Satellite detection of cumulative and lagged effects of drought on autumn leaf senescence over the Northern Hemisphere

Climate change has substantial influences on autumn leaf senescence, that is, the end of the growing season (EOS). Relative to the impacts of temperature and precipitation on EOS, the influence of drought is not well understood, especially considering that there are apparent cumulative and lagged effects of drought on plant growth. Here, we investigated the cumulative and lagged effects of drought (in terms of the Standardized Precipitation–Evapotranspiration Index, SPEI) on EOS derived from the normalized difference vegetation index (NDVI3g) data over the Northern Hemisphere extra‐tropical ecosystems (>30°N) during 1982–2015. The cumulative effect was determined by the number of antecedent months at which SPEI showed the maximum correlation with EOS (i.e., R_max‐cml) while the lag effect was determined by a month during which the maximum correlation between 1‐month SPEI and EOS occurred (i.e., R_max‐lag). We found cumulative effect of drought on EOS for 27.2% and lagged effect for 46.2% of the vegetated land area. For the dominant time scales where the R_max‐cml and R_max‐lag occurred, we observed 1–4 accumulated months for the cumulative effect and 2–6 lagged months for the lagged effect. At the biome level, drought had stronger impacts on EOS in grasslands, savannas, and shrubs than in forests, which may be related to the different root functional traits among vegetation types. Considering hydrological conditions, the mean values of both R_max‐cml and R_max‐lag decreased along the gradients of annual SPEI and its slope, suggesting stronger cumulative and lagged effects in drier regions as well as in areas with decreasing water availability. Furthermore, the average accumulated and lagged months tended to decline along the annual SPEI gradient but increase with increasing annual SPEI. Our results revealed that drought has strong cumulative and lagged effects on autumn phenology, and considering these effects could provide valuable information on the vegetation response to a changing climate.     

紫花苜蓿和菊苣比叶面积和光合特性对不同用量保水剂的响应

为研究紫花苜蓿(Medicago sativa)和菊苣(Cichorium intybus)叶片生长和光合生理对不同用量保水剂的适应能力和生理响应机制,以不施保水剂作为对照(CK),测定了施用不同用量保水剂(15 kg · hm~(-2),30 kg · hm~(-2))条件下大田种植的紫花苜蓿(Medicago sativa)和菊苣(Cichorium intybus)的比叶面积和光合特性.结果表明,保水剂对紫花苜蓿的比叶面积无显著影响(P>0.05),但对菊苣的比叶面积具有显著影响(P<0.05).对紫花苜蓿而言,保水剂施用量为15 kg · hm~(-2)时,其P_n、g_s和WUE均显著高于对照(P<0.01),但施用量为30 kg · hm~(-2)处理时,其P_n、和g_s均显著低于对照处理(P<0.01),但是却维持较高的WUE;对菊苣而言,施用保水剂降低了其P_n和T_r(P<0.01),但WUE与对照无显著差异(P>0.05),这表明紫花苜蓿和菊苣采取两种不同的生理适应策略来适应变化了的水分环境条件.紫花苜蓿P_n与g_s、P_n与T_r的相关性均以保水剂施用量为30 kg · hm~(-2)处理最紧密(P<0.01),而P_n与WUE的相关性则以对照最为紧密,依次为15 kg · hm~(-2)处理和30 kg · hm~(-2)处理;菊苣P_n与g_s、Tr和WUE的相关性强弱均表现为15 kg · hm~(-2)处理<30 kg · hm~(-2)处理<对照,表明保水剂影响叶片气体交换参数之间的关系.研究表明,不同植物叶片参数和光合特性对保水剂的响应并不具有一致性,植物可以根据环境条件的变化调节其形态和生理过程,以维持其正常生长.     

Light inhibition of leaf respiration in field-grown Eucalyptus saligna in whole-tree chambers under elevated atmospheric CO2 and summer drought

We investigated whether the degree of light inhibition of leaf respiration (R) differs among large Eucalyptus saligna grown in whole‐tree chambers and exposed to present and future atmospheric [CO₂] and summer drought. Associated with month‐to‐month changes in temperature were concomitant changes in R in the light (R_light) and darkness (R_dark), with both processes being more temperature dependent in well‐watered trees than under drought. Overall rates of R_light and R_dark were not significantly affected by [CO₂]. By contrast, overall rates of R_dark (averaged across both [CO₂]) were ca. 25% lower under drought than in well‐watered trees. During summer, the degree of light inhibition of leaf R was greater in droughted (ca. 80% inhibition) than well‐watered trees (ca. 50% inhibition). Notwithstanding these treatment differences, an overall positive relationship was observed between R_light and R_dark when data from all months/treatments were combined (R² = 0.8). Variations in R_light were also positively correlated with rates of Rubisco activity and nitrogen concentration. Light inhibition resulted in a marked decrease in the proportion of light‐saturated photosynthesis respired (i.e. reduced R/A_sat). Collectively, these results highlight the need to account for light inhibition when assessing impacts of global change drivers on the carbon economy of tree canopies.     

铜胁迫对紫花苜蓿幼苗叶片抗氧化系统的影响

采用1/4强度Hoagland营养液培养法研究了不同浓度Cu处理(O、10、30、50、100μmol·L-1 CuSO4)对紫花苜蓿幼苗叶片生理生化特性的影响.结果表明:30、50、100μmol·L-1 Cu处理使叶片中过氧化氢(H2O2)、羟基自由基(OH·)和丙二醛(MDA)含量升高;随Cu浓度的增加,愈创木酚过氧化物酶(POD)、谷胱甘肽还原酶(GR)和抗坏血酸过氧化物酶(APX)的活性逐渐上升,过氧化氢酶(CAT)和葡萄糖-6-磷酸脱氢酶(G6PDH)的活性先上升后下降;30、50、100 μmol·L-1Cu处理增强Fe-SOD和酯酶(EST)的活性,使叶片中谷胱甘肽(GSH)和抗坏血酸(AsA)含量显著升高.＞10 μmol·L-1的Cu处理下,叶片中抗氧化系统清除活性氧的能力上升,以防止叶片在Cu诱导的氧化胁迫下受到伤害.