Photosynthesis and photoinhibition in two xerophytic shrubs during drought

Seasonal changes in water relations, net photosynthetic rate (P _N), and fluorescence of chlorophyll (Chl) a of two perennial C₃ deciduous shrubs, Ipomoea carnea and Jatropha gossypifolia, growing in a thorn scrub in Venezuela were studied in order to establish the possible occurrence of photoinhibition during dry season and determine whether changes in photochemical activity of photosystem 2 (PS2) may explain variations of P _N in these species. Leaf water potential () decreased from –0.2 to –2.1 MPa during drought in both species. The P _N decreased with in I. carnea and J. gossypifolia by 64 and 74 %, respectively. Carboxylation efficiency (CE) decreased by more than 50 and 70 % in I. carnea and J. gossypifolia, respectively. In I. carnea, relative stomatal limitation (L_s) increased by 17 % and mesophyll limitation (L_m) by 65 % during drought, while in J. gossypifolia L_s decreased by 27 % and L_m increased by 51 %. Drought caused a reduction in quantum yield of PS2 (_PS2) in both species. Drought affected the capacity of energy dissipation of leaves, judging from the changes in the photochemical (q_P) and non-photochemical quenching (NPQ) coefficients. Photoinhibition during drought in I. carnea and J. gossypifolia was evidenced in the field by a drop in the maximum quantum yield of PS2 (F_v/F_m) below 0.8 and also by non-coordinated changes in _PS2 and quantum yield of non-photochemical excitation quenching (Y_n). Total soluble protein content on an area basis increased with but the ribulose-1,5-bisphosphate carboxylase/oxygenase content remained unchanged. A reduction of total Chl content with drought was observed. Hence in the species studied photoinhibition occurred, which imposed an important limitation on carbon assimilation during drought.     

从旱生植物叶结构探讨其生态适应的多样性

以西北地区６２种旱生植物的叶器官为研究对象,通过切片显微观察、生物学统计及模糊数学分析,探讨旱生植物生态适应的多样性,获得如下结果：①旱生植物依叶肉组成和细胞排列可划分为正常型、双栅型、环栅型、全栅型、不规则型,折迭和和无叶肉型;②叶肉类型的演化是以正常型与不规则型两条路线呈树枝状发展。深化较原始的偏向于中生,演化层次较高的更具适应旱生环境的能力;③进生植物的叶肉类型与生活型具有相关性,与环境具有     

贺兰山10种不同植物的旱生结构研究

对贺兰山10种不同生活型植物的形态解剖研究表明,长期生长在干旱贫瘠环境中植物,均形成适应生境的一些特殊形态结构．叶器官主要表现在：（1）叶表面积与体积之比缩小,表面覆有厚的角质膜,并被有表皮毛,气孔下陷,具孔下室;（2）栅栏薄壁组织细胞明显增多,海绵薄壁组织细胞减少．有叶肉不分化叶、等而叶和异而叶3种结构形式;（3）叶内贮水组织和机械组织增强。轴器官主要表现在：（1）根普遍形成周皮,且木栓层细胞层数增多;（2）机械组织非常发达,在周皮、皮层和韧皮部中有许多厚壁细胞分布。维管组织中的木薄壁细胞的细胞壁也明显木质化加厚;（3）有些植物的根具有异常维管组织。另外,这些植物根、茎、叶中均有粘液细胞和含晶细胞分布。这些结构具有重要的适应干旱生境的意义。     

A possible optical role of the bundle sheath extensions of the heterobaric leaves of Vitis vinifera and Quercus coccifera

Heterobaric leaves are characterized by transparent regions in their lamina, due to the occurrence of bundle sheath extensions. Fused silica fibre‐optic microprobes were used to monitor light gradients and part of the spectral regime along the bundle sheath extensions, as well as along the mesophyll in the heterobaric leaves of two representative plants, one mesomorphic (Vitis vinifera L.) and one xeromorphic (Quercus coccifera L.). It was found that the attenuation of collimated visible light by the bundle sheath extensions of both plants was weaker than the attenuation by the photosynthetic parenchyma layers. However, only a small portion of the amount of light that strikes the leaf surface is transmitted through these structures. The adaxial epidermis covering the bundle sheath extensions, as well as the mesophyll, afforded similar effective protection against UV radiation in both tissues. The relative amount of the forward‐scattered visible light inside the bundle sheath extensions approached that detected by the microprobe at the adaxial illuminated leaf surface. Moreover, light transmitted through the bundle sheath extensions was enriched mainly in the blue and red regions, compared to light transmitted through the photosynthetic tissue. The time course of photosynthetic starch formation in the leaves of V. vinifera detected by iodine staining showed that the accumulation of starch during the first minutes of illumination was high within photosynthetic parenchyma cells adjacent to the bundle sheath extensions. The data showed that bundle sheath extensions act as transparent ‘windows’ which enrich the neighbouring mesophyll areas with high levels of photosynthetically active radiation (400–700 nm). The phenomenon was more pronounced in the thick and compact sclerophyllous leaves of Q. coccifera by virtue of the greater abundance of bundle sheath extensions as compared to that in V. vinifera. The enhancement of the light micro‐environment within the deep internal layers of the mesophyll may affect the photosynthetic performance of such leaves, giving adaptive advantages.     

8种木本旱生植物的木质部解剖学特性研究

从生态学角度对8种旱生植物木材的次生木质部结构进行了对比研究.结果表明,8树种次生木质部结构的共同特点为:生长轮分界明显(霸王和四合木的年轮有时不连续),半环孔材,单穿孔,导管壁间纹孔互列,木纤维无横隔膜,联合傍管轴向薄壁组织丰富,导管壁上呈现螺纹加厚,都具有异型射线;它们主要差异在于射线和导管的数量化指标:四合木异型射线1~2列,霸王、白刺、沙冬青和胡枝子射线2~5列,柽柳、柠条和花棒大型射线4~10列;导管分子长度和纤维长度在树种间和同一树种个体间差异较明显.四合木和沙冬青导管频率较大,导管管孔较小,因此Vulnerability和Mesomorphy值也较小,更能适应干旱环境.     

Adaptive responses to drought of two Retama raetam subspecies from Tunisia

两个突尼斯细枝豆属植物亚种对干旱的适应性响应 干旱生境植物的生存和生态分布主要取决于水的可获得性以及植物抵御干旱的生理适应能力。在 本研究中，我们比较了来自突尼斯的细枝豆属植物Retama raetam的两个亚种对干旱的生理响应，其中一 种生长在沙漠气候下(raetam亚种)，另一种生长于海岸带(bovei亚种)。为了对这两个亚种进行生理表征并揭示它们耐旱性的主要机制，从受干旱胁迫最长达一个月的四月龄植株中获取了多项参数，涉及植株的萌发、生长、光合作用(净光合速率、细胞内CO₂浓度、蒸腾速率、气孔导度和水分利用效率)和渗透物(脯氨酸、甜菜碱和总可溶性糖)积累等。研究结果表明，干旱会显著抑制植株的萌发、生长，对所研究的各项光合参数也都产生很大的负面影响。经过3周的处理后，bovei亚种受到了干旱条件的显著影响，其光合作用速率与对照相比最高下降了7倍。与此同时，该亚种中出现了对脯氨酸和甜菜碱的显著积累(相较于灌溉条件下的对照)，但远低于raetam亚种；在raetam亚种中，脯氨酸和甜菜碱分别增加至相应对照的24和6倍。综上所述，相较于生长在半干旱海岸气候下的细枝豆属植物种群，生长于沙漠地区的种群对干旱胁迫表现出更强的耐性，表明这种耐性在很大程度上取决于渗透物质在体内的累积。     

C3- and C4-Plants of the Xerophilic Vegetation in the Loess Hills of the Yellow River,Gansu-Province,NW-China*

The climate of the loess-hill area near Lanzhou, on the Yellow River, Gansu-Province, NW-China is arid throughout the year. The vegetation is xerophilic and mainly dominated by species of Zygophyllaceae, Chenopodiaceae, Plumbaginaceae, Tamaricaceae, Asclepiadaceae and Asteraceae. Among 11 species sampled of these families, δ¹³C-analyses only indicated C₄-photosynthesis for 2 species. This relatively low frequency of C₄-plants may be due to elevation (1978 m a.s.l.) and the relatively cold temperatures (annual mean 5.9°C).